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  Subjects -> CHEMISTRY (Total: 841 journals)
    - ANALYTICAL CHEMISTRY (50 journals)
    - CHEMISTRY (593 journals)
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CHEMISTRY (593 journals)                  1 2 3 | Last

Showing 1 - 200 of 735 Journals sorted alphabetically
2D Materials     Hybrid Journal   (Followers: 8)
Accreditation and Quality Assurance: Journal for Quality, Comparability and Reliability in Chemical Measurement     Hybrid Journal   (Followers: 26)
ACS Catalysis     Full-text available via subscription   (Followers: 34)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 18)
ACS Combinatorial Science     Full-text available via subscription   (Followers: 23)
ACS Macro Letters     Full-text available via subscription   (Followers: 23)
ACS Medicinal Chemistry Letters     Full-text available via subscription   (Followers: 39)
ACS Nano     Full-text available via subscription   (Followers: 234)
ACS Photonics     Full-text available via subscription   (Followers: 11)
ACS Synthetic Biology     Full-text available via subscription   (Followers: 21)
Acta Chemica Iasi     Open Access   (Followers: 2)
Acta Chimica Sinica     Full-text available via subscription   (Followers: 1)
Acta Chimica Slovaca     Open Access   (Followers: 1)
Acta Chromatographica     Full-text available via subscription   (Followers: 9)
Acta Facultatis Medicae Naissensis     Open Access  
Acta Metallurgica Sinica (English Letters)     Hybrid Journal   (Followers: 5)
Acta Scientifica Naturalis     Open Access   (Followers: 2)
adhäsion KLEBEN & DICHTEN     Hybrid Journal   (Followers: 5)
Adhesion Adhesives & Sealants     Hybrid Journal   (Followers: 7)
Adsorption Science & Technology     Full-text available via subscription   (Followers: 5)
Advanced Functional Materials     Hybrid Journal   (Followers: 50)
Advanced Science Focus     Free   (Followers: 3)
Advances in Chemical Engineering and Science     Open Access   (Followers: 55)
Advances in Chemical Science     Open Access   (Followers: 13)
Advances in Chemistry     Open Access   (Followers: 14)
Advances in Colloid and Interface Science     Full-text available via subscription   (Followers: 18)
Advances in Drug Research     Full-text available via subscription   (Followers: 22)
Advances in Enzyme Research     Open Access   (Followers: 9)
Advances in Fuel Cells     Full-text available via subscription   (Followers: 15)
Advances in Heterocyclic Chemistry     Full-text available via subscription   (Followers: 8)
Advances in Materials Physics and Chemistry     Open Access   (Followers: 19)
Advances in Nanoparticles     Open Access   (Followers: 15)
Advances in Organometallic Chemistry     Full-text available via subscription   (Followers: 15)
Advances in Polymer Science     Hybrid Journal   (Followers: 41)
Advances in Protein Chemistry     Full-text available via subscription   (Followers: 18)
Advances in Protein Chemistry and Structural Biology     Full-text available via subscription   (Followers: 19)
Advances in Quantum Chemistry     Full-text available via subscription   (Followers: 5)
Advances in Science and Technology     Full-text available via subscription   (Followers: 12)
African Journal of Bacteriology Research     Open Access  
African Journal of Chemical Education     Open Access   (Followers: 2)
African Journal of Pure and Applied Chemistry     Open Access   (Followers: 7)
Agrokémia és Talajtan     Full-text available via subscription   (Followers: 2)
Alkaloids: Chemical and Biological Perspectives     Full-text available via subscription   (Followers: 3)
AMB Express     Open Access   (Followers: 1)
Ambix     Hybrid Journal   (Followers: 3)
American Journal of Biochemistry and Biotechnology     Open Access   (Followers: 69)
American Journal of Biochemistry and Molecular Biology     Open Access   (Followers: 14)
American Journal of Chemistry     Open Access   (Followers: 26)
American Journal of Plant Physiology     Open Access   (Followers: 14)
American Mineralogist     Hybrid Journal   (Followers: 14)
Analyst     Full-text available via subscription   (Followers: 40)
Angewandte Chemie     Hybrid Journal   (Followers: 204)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 214)
Annales UMCS, Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 2)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 3)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 4)
Annual Reports Section B (Organic Chemistry)     Full-text available via subscription   (Followers: 8)
Annual Review of Chemical and Biomolecular Engineering     Full-text available via subscription   (Followers: 12)
Annual Review of Food Science and Technology     Full-text available via subscription   (Followers: 15)
Anti-Infective Agents     Hybrid Journal   (Followers: 3)
Antiviral Chemistry and Chemotherapy     Hybrid Journal  
Applied Organometallic Chemistry     Hybrid Journal   (Followers: 7)
Applied Spectroscopy     Full-text available via subscription   (Followers: 23)
Applied Surface Science     Hybrid Journal   (Followers: 28)
Arabian Journal of Chemistry     Open Access   (Followers: 6)
ARKIVOC     Open Access   (Followers: 2)
Asian Journal of Biochemistry     Open Access   (Followers: 1)
Atomization and Sprays     Full-text available via subscription   (Followers: 4)
Australian Journal of Chemistry     Hybrid Journal   (Followers: 7)
Autophagy     Hybrid Journal   (Followers: 2)
Avances en Quimica     Open Access   (Followers: 1)
Biochemical Pharmacology     Hybrid Journal   (Followers: 10)
Biochemistry     Full-text available via subscription   (Followers: 293)
Biochemistry Insights     Open Access   (Followers: 6)
Biochemistry Research International     Open Access   (Followers: 6)
BioChip Journal     Hybrid Journal  
Bioinorganic Chemistry and Applications     Open Access   (Followers: 9)
Bioinspired Materials     Open Access   (Followers: 5)
Biointerface Research in Applied Chemistry     Open Access   (Followers: 2)
Biointerphases     Open Access   (Followers: 1)
Biology, Medicine, & Natural Product Chemistry     Open Access   (Followers: 1)
Biomacromolecules     Full-text available via subscription   (Followers: 19)
Biomass Conversion and Biorefinery     Partially Free   (Followers: 10)
Biomedical Chromatography     Hybrid Journal   (Followers: 6)
Biomolecular NMR Assignments     Hybrid Journal   (Followers: 3)
BioNanoScience     Partially Free   (Followers: 4)
Bioorganic & Medicinal Chemistry     Hybrid Journal   (Followers: 124)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 98)
Bioorganic Chemistry     Hybrid Journal   (Followers: 10)
Biopolymers     Hybrid Journal   (Followers: 18)
Biosensors     Open Access   (Followers: 2)
Biotechnic and Histochemistry     Hybrid Journal   (Followers: 1)
Bitácora Digital     Open Access  
Boletin de la Sociedad Chilena de Quimica     Open Access  
Bulletin of the Chemical Society of Ethiopia     Open Access   (Followers: 2)
Bulletin of the Chemical Society of Japan     Full-text available via subscription   (Followers: 24)
Bulletin of the Korean Chemical Society     Hybrid Journal   (Followers: 1)
C - Journal of Carbon Research     Open Access   (Followers: 3)
Cakra Kimia (Indonesian E-Journal of Applied Chemistry)     Open Access  
Canadian Association of Radiologists Journal     Full-text available via subscription   (Followers: 3)
Canadian Journal of Chemistry     Hybrid Journal   (Followers: 10)
Canadian Mineralogist     Full-text available via subscription   (Followers: 3)
Carbohydrate Research     Hybrid Journal   (Followers: 26)
Carbon     Hybrid Journal   (Followers: 66)
Catalysis for Sustainable Energy     Open Access   (Followers: 7)
Catalysis Reviews: Science and Engineering     Hybrid Journal   (Followers: 8)
Catalysis Science and Technology     Free   (Followers: 6)
Catalysis Surveys from Asia     Hybrid Journal   (Followers: 3)
Catalysts     Open Access   (Followers: 8)
Cellulose     Hybrid Journal   (Followers: 7)
Cereal Chemistry     Full-text available via subscription   (Followers: 4)
ChemBioEng Reviews     Full-text available via subscription   (Followers: 1)
ChemCatChem     Hybrid Journal   (Followers: 8)
Chemical and Engineering News     Free   (Followers: 13)
Chemical Bulletin of Kazakh National University     Open Access  
Chemical Communications     Full-text available via subscription   (Followers: 71)
Chemical Engineering Research and Design     Hybrid Journal   (Followers: 23)
Chemical Research in Chinese Universities     Hybrid Journal   (Followers: 3)
Chemical Research in Toxicology     Full-text available via subscription   (Followers: 19)
Chemical Reviews     Full-text available via subscription   (Followers: 176)
Chemical Science     Open Access   (Followers: 22)
Chemical Technology     Open Access   (Followers: 16)
Chemical Vapor Deposition     Hybrid Journal   (Followers: 5)
Chemical Week     Full-text available via subscription   (Followers: 8)
Chemie in Unserer Zeit     Hybrid Journal   (Followers: 57)
Chemie-Ingenieur-Technik (Cit)     Hybrid Journal   (Followers: 26)
ChemInform     Hybrid Journal   (Followers: 8)
Chemistry & Biodiversity     Hybrid Journal   (Followers: 6)
Chemistry & Biology     Full-text available via subscription   (Followers: 30)
Chemistry & Industry     Hybrid Journal   (Followers: 5)
Chemistry - A European Journal     Hybrid Journal   (Followers: 143)
Chemistry - An Asian Journal     Hybrid Journal   (Followers: 15)
Chemistry and Materials Research     Open Access   (Followers: 18)
Chemistry Central Journal     Open Access   (Followers: 4)
Chemistry Education Research and Practice     Free   (Followers: 5)
Chemistry in Education     Open Access   (Followers: 9)
Chemistry International     Hybrid Journal   (Followers: 2)
Chemistry Letters     Full-text available via subscription   (Followers: 45)
Chemistry of Materials     Full-text available via subscription   (Followers: 260)
Chemistry of Natural Compounds     Hybrid Journal   (Followers: 9)
Chemistry World     Full-text available via subscription   (Followers: 22)
Chemistry-Didactics-Ecology-Metrology     Open Access   (Followers: 1)
ChemistryOpen     Open Access   (Followers: 2)
Chemkon - Chemie Konkret, Forum Fuer Unterricht Und Didaktik     Hybrid Journal  
Chemoecology     Hybrid Journal   (Followers: 3)
Chemometrics and Intelligent Laboratory Systems     Hybrid Journal   (Followers: 15)
Chemosensors     Open Access  
ChemPhysChem     Hybrid Journal   (Followers: 9)
ChemPlusChem     Hybrid Journal   (Followers: 2)
ChemTexts     Hybrid Journal  
CHIMIA International Journal for Chemistry     Full-text available via subscription   (Followers: 2)
Chinese Journal of Chemistry     Hybrid Journal   (Followers: 6)
Chinese Journal of Polymer Science     Hybrid Journal   (Followers: 10)
Chromatographia     Hybrid Journal   (Followers: 24)
Clay Minerals     Full-text available via subscription   (Followers: 10)
Cogent Chemistry     Open Access  
Colloid and Interface Science Communications     Open Access  
Colloid and Polymer Science     Hybrid Journal   (Followers: 10)
Colloids and Surfaces B: Biointerfaces     Hybrid Journal   (Followers: 7)
Combinatorial Chemistry & High Throughput Screening     Hybrid Journal   (Followers: 4)
Combustion Science and Technology     Hybrid Journal   (Followers: 18)
Comments on Inorganic Chemistry: A Journal of Critical Discussion of the Current Literature     Hybrid Journal   (Followers: 2)
Composite Interfaces     Hybrid Journal   (Followers: 6)
Comprehensive Chemical Kinetics     Full-text available via subscription   (Followers: 2)
Comptes Rendus Chimie     Full-text available via subscription  
Comptes Rendus Physique     Full-text available via subscription   (Followers: 1)
Computational and Theoretical Chemistry     Hybrid Journal   (Followers: 9)
Computational Biology and Chemistry     Hybrid Journal   (Followers: 12)
Computational Chemistry     Open Access   (Followers: 2)
Computers & Chemical Engineering     Hybrid Journal   (Followers: 9)
Coordination Chemistry Reviews     Full-text available via subscription   (Followers: 2)
Copernican Letters     Open Access   (Followers: 1)
Critical Reviews in Biochemistry and Molecular Biology     Hybrid Journal   (Followers: 5)
Crystal Structure Theory and Applications     Open Access   (Followers: 3)
CrystEngComm     Full-text available via subscription   (Followers: 12)
Current Catalysis     Hybrid Journal   (Followers: 2)
Current Metabolomics     Hybrid Journal   (Followers: 5)
Current Opinion in Colloid & Interface Science     Hybrid Journal   (Followers: 9)
Current Research in Chemistry     Open Access   (Followers: 8)
Current Science     Open Access   (Followers: 58)
Dalton Transactions     Full-text available via subscription   (Followers: 22)
Detection     Open Access   (Followers: 2)
Developments in Geochemistry     Full-text available via subscription   (Followers: 2)
Diamond and Related Materials     Hybrid Journal   (Followers: 12)
Dislocations in Solids     Full-text available via subscription  
Doklady Chemistry     Hybrid Journal  
Drying Technology: An International Journal     Hybrid Journal   (Followers: 4)
Eclética Química     Open Access   (Followers: 1)
Ecological Chemistry and Engineering S     Open Access   (Followers: 4)
Ecotoxicology and Environmental Contamination     Open Access  
Educación Química     Open Access   (Followers: 1)
Education for Chemical Engineers     Hybrid Journal   (Followers: 5)
EJNMMI Radiopharmacy and Chemistry     Open Access  
Elements     Full-text available via subscription   (Followers: 2)
Environmental Chemistry     Hybrid Journal   (Followers: 9)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 4)
Environmental Science & Technology Letters     Full-text available via subscription   (Followers: 5)
Environmental Science : Nano     Partially Free   (Followers: 1)
Environmental Toxicology & Chemistry     Hybrid Journal   (Followers: 18)

        1 2 3 | Last

Journal Cover Chemistry - A European Journal
  [SJR: 2.323]   [H-I: 188]   [143 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0947-6539 - ISSN (Online) 1521-3765
   Published by John Wiley and Sons Homepage  [1577 journals]
  • Co3O4 Nanowire Arrays toward Superior Water Oxidation Electrocatalysis in
           Alkaline Media by Surface Amorphization
    • Authors: Xuping Sun
      Abstract: In this communication, we report our recent finding that the generation of amorphous Co-Bi layer on Co3O4 nanowire arrays supported on Ti mesh (Co3O4@Co-Bi NA/TM) leads to significantly boosted OER activity. The as-prepared Co3O4@Co-Bi NA/TM demands overpotential of 304 mV to drive a ge-ometrical current density of 20 mA cm-2 in 1.0 M KOH, which is 109 mV less than that for Co3O4 NA/TM, with its catalytic activity being preserved for at least 20 h. It suggests that the existence of amorphous Co-Bi layer promotes more CoOx(OH)y generation on Co3O4 surface.
      PubDate: 2017-09-19T04:40:45.817437-05:
      DOI: 10.1002/chem.201703565
       
  • Quasi-emulsion Confined Synthesis of Edge-rich Ultrathin MoS2
           Nanosheets/Graphene Hybrid for Enhanced Hydrogen Evolution
    • Authors: Xuying Yin; Ya Yan, Mao Miao, ke Zhan, Pingwei Li, Junhe Yang, Bin Zhao, Bao Yu Xia
      Abstract: Hydrogen with high purity produced by water splitting is considered as one of the most promising technology to replace the traditional fossil fuels. Developing highly efficient electrocatalysts towards hydrogen evolution is vital for the realization of H2 generation in large scale. With assistance of glycerol, we report herein a facile solvothermal process to synthesize edge-rich ultrathin MoS2/RGO composites. The introduction of glycerol plays an important role in the formation of such an interesting structure. Thereafter, the as-obtained MoS2/RGO electrocatalyst exhibits an excellent HER activity and remarkable stability, owing to the rich active edges and improved electrical conductivity of the catalysts composites. This work provides the new insights in the synthesis system to engineer the structures of MoSx based composites and thus achieve more active and efficient electrocatalysts.
      PubDate: 2017-09-19T04:40:32.042805-05:
      DOI: 10.1002/chem.201703493
       
  • The Nature of Hydrated Protons on Platinum Surface
    • Authors: YounJoon Jung; Heon Kang, Youngsoon Kim, Chanwoo Noh
      Abstract: The nature of hydrated protons formed at water/metal interfaces is one of the most intriguing research questions in the field of interfacial chemistry. We prepared coadsorption layers of hydrogen and water on a Pt(111) surface in ultrahigh vacuum and studied the ionization of adsorbed hydrogen atoms to H+ ions by employing a combined experimental and theoretical approach. Spectroscopic evidence obtained by mass spectrometry and reflection absorption infrared spectroscopy as well as corresponding density functional theory calculations consistently show that adsorbed hydrogen atoms ionize into multiply hydrated proton species (H5O2+, H7O3+, and H9O4+) on the surface, rather than H3O+. Then, upon addition of a water overlayer, the metal-bound hydrated protons spontaneously evolve into three-dimensional fully hydrated proton structures via proton transfer along the water overlayer. The stability of hydrated protons on Pt surface and their bulk dissolution behavior suggest the possibility that surface hydrated protons are a key intermediate in electrochemical interconversion between adsorbed H atoms and H+(aq) in water electrolysis and hydrogen evolution reactions.
      PubDate: 2017-09-19T03:41:18.013207-05:
      DOI: 10.1002/chem.201703882
       
  • Size-dependent reactivity of nano-sized neutral manganese oxide clusters
           toward ethylene
    • Authors: Jiao-Jiao Chen; Ting Zhang, Mei-Qi Zhang, Qing-Yu Liu, Xiao-Na Li, Sheng-Gui He
      Abstract: Neutral manganese oxide clusters Mn2NO3N+x (N = 2−22; x = −1, 0, 1) with dimensions up to a nanosize were prepared by laser ablation and reacted with C2H4 in a fast flow reactor. The size-dependent reactivity of C2H4 adsorption on these clusters was experimentally identified and the adsorption reactivity decreases generally with the increase of cluster size. Density functional theory calculations were performed to study the geometrical and electronic structures of Mn2NO3N (N = 1−6) clusters. The calculated results indicated that the coordination number and the charge distribution of the metal centers are responsible for the experimentally observed size-dependent reactivity. The highly charged Mn atoms with low coordination are preferential to adsorb C2H4. In contrast, the neutral manganese oxide clusters are completely inert toward the saturated hydrocarbon molecule C2H6. This work provides new perspectives to design related materials in the separation of hydrocarbon molecules.
      PubDate: 2017-09-19T03:41:07.542151-05:
      DOI: 10.1002/chem.201703745
       
  • Accessing two-coordinate Zn(II) Organocations via NHC coordination:
           synthesis, structure and use as π-Lewis acids in alkene, alkyne, and CO2
           hydrosilylation
    • Authors: Samuel Dagorne; David Specklin, Frédéric Hild, Christophe Fliedel, Christophe Gourlaouen, Luis Veiros
      Abstract: Discrete two-coordinate Zn(II) organocations are first reported, presently of the type (NHC)Zn-R+, thanks to NHC stabilization. In preliminary reactivity studies, such entities, which are direct cationic analogues of long-known ZnR2 species, act as effective and tunable π-Lewis acid catalysts in alkene, alkyne and CO2 hydrosilylation.
      PubDate: 2017-09-19T03:40:43.587329-05:
      DOI: 10.1002/chem.201704382
       
  • Understanding the Catalytic Mechanism and the Nature of Transition State
           of an Attractive Drug-Target Enzyme (Shikimate Kinase) by QM/MM Studies
    • Authors: Jianzhuang Yao; Xia Wang, Haixia Luo, Pengfei Gu
      Abstract: Shikimate kinase (SK), is the fifth bacterial enzyme involved in the shikimate pathway for biosynthesis of life indispensable components, such as aromatic amino acids. Absence of shikimate pathway in human makes SK an attractive target for rational design of drug toward pathogenesis bacteria, such as Mycobacterium tuberculosis and Helicobacter pylori. However, effective inhibitor of SK (e.g., transition state analogue) is still not available in the market due to (at least partly) the lack of knowledge on the catalytic mechanism and the nature of the rate-limiting transition state. In this paper, quantum mechanical/molecular mechanical (QM/MM) reaction coordinate, molecular dynamics (MD), and free-energy simulations were performed to answer these questions. The results given here demonstrate that the phosphoryl-transfer process, which is the rate-limiting step of SK-catalyzed phosphorylation of shikimate acid (SKM), is a concerted one-step reaction proceeding through a loose transition state. The computational results agree well with the experimental studies in terms of NMR results, X-Ray Crystal structure observation, and activation free energy barrier.
      PubDate: 2017-09-18T20:45:44.232932-05:
      DOI: 10.1002/chem.201703867
       
  • Better Organic Ternary Memory Performance through Self-Assembled
           Alkyltrichlorosilane Monolayers on Indium Tin Oxide (ITO) Surfaces
    • Authors: Xiang Hou; Xue-Feng Cheng, Jin Zhou, Jing-Hui He, Qing-Feng Xu, Hua Li, Na-Jun Li, Dong-Yun Chen, Jian-Mei Lu
      Abstract: Recently surface engineering of the indium-tin oxide (ITO) electrode of sandwich-like organic electric memory is found to effectively improve their memory performances. However, there are few methods to modify ITO substrates. In this paper, we have successfully prepared alkyltrichlorosicane self-assembled monolayers (SAMs) on ITO substrates, and resistive random access memory devices are fabricated on these surfaces. Compared to the unmodified ITO substrates, organic molecules SA-Bu grown on these SAM-modified ITO substrates have rougher surface morphologies but smaller mosaicity. The organic layer on SAM-modified ITO further aged to eliminate the crystalline phase diversity. In consequence, the ternary memory yield are effetively improved to 40~47%. Our results suggest that insertion of alkyltrichlorosicanes self-assembled monolayer could be an efficient method to improve the performance of organic memory.
      PubDate: 2017-09-18T20:40:54.441513-05:
      DOI: 10.1002/chem.201704059
       
  • One-pot synthesis of Size-Controllable core-shell CdS and derivative
           CdS@ZnxCd1-xS structures for dramatic Photocatalytic Hydrogen Production
    • Authors: Shuangshuang Kai; Baojuan Xi, Yifeng Wang, Shenglin Xiong
      Abstract: Chalcogenide micro/nano composite structures have been attracting world-wide attention due to the enormous prospect of applications in photocatalytic hydrogen production. Well-defined micro/nanostructures, featured with predominant properties, are of extraordinary importance. Herein, we reported a facile one-pot method on synthesis of monodispersed size-controllable CdS and CdS@ZnxCd1-xS core-shell submicrospheres, which were engineered with respect to the structural conformation and size. CdS core-shell submicrospheres with different size were selectively prepared for the first time. The growth mechanism was investigated in detail by monitoring the time-dependent morphology of intermediates via TEM technique. By introduction of zinc precursor in the synthetic system, CdS@ZnxCd1-xS core-double shell submicrospheres had been obtained by cation exchange of CdS with zinc ions, experiencing the process of diffusion of CdS towards outside and transformation of ZnxCd1-xS crystallites. The H2 evolution rate over CdS@CdxZn1-xS (5.17 mmol h-1 g -1) is 12.3 times that of CdS core-shell (0.42 mmol h- 1 g -1) under visible light, owing to the efficient charge separation demonstrated by the electrochemical impedance and transient-state time-resolved photoluminescence spectra. Furthermore, CdS@ZnxCd1-xS core-double shell structures exhibited excellent stability over 20 h hydrogen production.
      PubDate: 2017-09-18T20:40:48.61836-05:0
      DOI: 10.1002/chem.201703506
       
  • Synergistic Configuration of Diols as Brønsted Bases
    • Authors: Ye-Jin Kim; Surajit Rakshit, Geun Young Jin, Prasun Ghosh, Young Min Lee, Won-Woo Park, Yung Sam Kim, Oh-Hoon Kwon
      Abstract: As viscous hydroxylic organic compounds, diols are of interest for their functional molecular conformation, which is based on inter- and intramolecular hydrogen (H)-bonds. By utilising steady-state electronic and vibrational spectroscopy, time-resolved fluorescence spectroscopy, and computational analyses, we report the association of the hydroxyl groups of diols via intra- or intermolecular H-bonds to enhance their reactivity as a base. Whereas the formation of an intermolecularly H-bonded dimer is requisite for diols of weak intramolecular H-bond to extract a proton from a model strong photoacid, a well-configured single diol molecule having an optimised intramolecular H-bond is revealed to serve as an effective Brønsted base with increased basicity. This observation highlights the collective role of H-bonding in acid-base reactions, and provides mechanistic backgrounds to understand the reactivity of polyols in the acid-catalysed dehydration for the synthesis of cyclic ethers at the molecular level.
      PubDate: 2017-09-18T20:40:44.453039-05:
      DOI: 10.1002/chem.201703668
       
  • The Stepwise Reaction of Rhodium and Iridium Complexes of Formula
           [MCl2(κ4C,N,N′,P−L)] with Silver Cations: A Case of trans-Influence
           and Chiral Self-Recognition
    • Authors: María Carmona; Leyre Tejedor, Ricardo Rodríguez, Vincenzo Passarelli, Fernando J. Lahoz, Pilar García-Orduña, Daniel Carmona
      Abstract: Acetonitrile suspensions of the dichlorido complexes [MCl2(κ4C,N,N′,P−L)] [M=Rh (1), Ir (2)] react with AgSbF6 in a 1:2 molar ratio affording the bis-acetonitrile complexes [M(κ4C,N,N′,P−L)(NCMe)2][SbF6]2 (3 and 4). The reaction takes place in a sequential manner and the intermediates can be isolated varying the M:Ag molar ratio. In a 2:1 molar ratio, it affords the dimetallic monochlorido-bridged compounds [{MCl(κ4C,N,N′,P−L)}2(μ-Cl)][SbF6] (5 and 6). In a 1:1 molar ratio, the monosubstituted solvato-complexes [MCl(κ4C,N,N′,P−L)(Solv)][SbF6] (Solv=H2O, MeCN, 7–10) were obtained. Finally, in a 2:3 molar ratio, it gives complexes 11 and 12 of formula [{M(κ4C,N,N′,P−L)(NCMe)(μ-Cl)}2Ag][SbF6]3 in which a silver cation joints two cationic monosubstituted acetonitrile-complexes [MCl(κ4C,N,N′,P−L)(NCMe)]+ through the remaining chlorido ligands and two Ag⋅⋅⋅C interactions with one of the phenyl rings of each PPh2 group. In all the complexes, the aminic nitrogen and the central metal atom are stereogenic centers. In the trimetallic complexes 11 and 12, the silver atom is also a stereogenic center. The formation of the cation of the dimetallic complexes 5 and 6, as well as that of the trimetallic complexes 11 and 12, takes place with chiral molecular self-recognition. Experimental data and DFT calculations provide plausible explanations for the observed molecular recognition. The new complexes have been characterized by analytical, spectroscopic means and by X-ray diffraction methods.Let's go step by step: The chlorido ligands in complexes [MCl2(κ4C,N,N′,P−L)] (M=Rh, Ir) were sequentially removed to give bis-solvato complexes of formula [M(κ4C,N,N′,P−L)(NCMe)2]2+. The involved mono-, di- and trimetallic intermediates were isolated and characterized. The formation of these intermediates takes place with chiral self-recognition. The stereochemistry determined for the new species is compatible with the retention of the configuration of the metallic fragments throughout the whole process.
      PubDate: 2017-09-18T11:52:56.989615-05:
      DOI: 10.1002/chem.201702711
       
  • Helical Threads: Enantiomerically Pure Carbo[6]Helicene Oligomers
    • Authors: Cédric Schaack; Eric Sidler, Nils Trapp, François Diederich
      Abstract: We report the synthesis of enantiomerically pure carbo[6]helicene oligomers with buta-1,3-diyne-1,4-diyl bridges between the helicene nuclei. The synthesis of monomeric (±)-2,15-bis[(triisopropylsilyl)ethynyl]carbo[6]helicene was achieved in 25 % yield over six steps. Pure (+)-(P)- and (−)-(M)-enantiomers were obtained by HPLC on a chiral stationary phase. The dimeric (+)-(P)2- and (−)-(M)2-configured and the tetrameric (+)-(P)4- and (−)-(M)4-configured oligomers were obtained by sequential oxidative acetylenic coupling. The ECD spectra of the tetrameric oligomers displayed large Cotton effect intensities of Δϵ=−851 m−1 cm−1 at λ=370 nm ((M)4-enantiomer). We transformed the buta-1,3-diyne-1,4-diyl bridge in the dimeric (P)2 and (M)2 oligomer by heteroaromatization into a thiene-2,5-diyl linker. Although the resulting chromophore showed reduced ECD intensities, it exhibited a remarkably strong fluorescence emission at 450–500 nm, with an absolute quantum yield of 25 %.Bigger, better! An efficient route to enantiopure 2,15-dialkynylated carbo[6]helicenes and buta-1,3-diyne-1,4-diyl- and thiene-2,5-diyl-linked dimeric and tetrameric oligomers is described. The chiroptical properties are correlated with the extent of π-electron delocalization. X-ray analysis provided conformational information consistent with DFT-calculated structures. The thiene-2,5-diyl-bridged dimers display intense fluorescence emission, which is a rare property in carbohelicene chemistry (see scheme).
      PubDate: 2017-09-18T11:52:47.031792-05:
      DOI: 10.1002/chem.201703024
       
  • Bonding in Heavier Group 14 Zero-Valent Complexes—A Combined Maximum
           Probability Domain and Valence Bond Theory Approach
    • Authors: Jan Turek; Benoît Braïda, Frank De Proft
      Abstract: The bonding in heavier Group 14 zero-valent complexes of a general formula L2E (E=Si–Pb; L=phosphine, N-heterocyclic and acyclic carbene, cyclic tetrylene and carbon monoxide) is probed by combining valence bond (VB) theory and maximum probability domain (MPD) approaches. All studied complexes are initially evaluated on the basis of the structural parameters and the shape of frontier orbitals revealing a bent structural motif and the presence of two lone pairs at the central E atom. For the VB calculations three resonance structures are suggested, representing the “ylidone”, “ylidene” and “bent allene” structures, respectively. The influence of both ligands and central atoms on the bonding situation is clearly expressed in different weights of the resonance structures for the particular complexes. In general, the bonding in the studied E0 compounds, the tetrylones, is best described as a resonating combination of “ylidone” and “ylidene” structures with a minor contribution of the “bent allene” structure. Moreover, the VB calculations allow for a straightforward assessment of the π-backbonding (EL) stabilization energy. The validity of the suggested resonance model is further confirmed by the complementary MPD calculations focusing on the E lone pair region as well as the E–L bonding region. Likewise, the MPD method reveals a strong influence of the σ-donating and π-accepting properties of the ligand. In particular, either one single domain or two symmetrical domains are found in the lone pair region of the central atom, supporting the predominance of either the “ylidene” or “ylidone” structures having one or two lone pairs at the central atom, respectively. Furthermore, the calculated average populations in the lone pair MPDs correlate very well with the natural bond orbital (NBO) populations, and can be related to the average number of electrons that is backdonated to the ligands.Zero-valent complexes: Heavier Group 14 zero-valent complexes, the “tetrylones”, are investigated by combining valence bond (VB) theory and maximum probability domain (MPD) approaches. As confirmed by both VB and MPB, the bonding in the studied E0 (E=Si, Ge, Sn and Pb) compounds is best described as a resonating combination of “ylidone” and “ylidene” structures with a minor contribution of the “bent allene” structure. Moreover, the VB calculations allow for a straightforward assessment of the π-backbonding stabilization energy.
      PubDate: 2017-09-18T11:52:09.726749-05:
      DOI: 10.1002/chem.201703053
       
  • Germanium-Bridged 2-Phenylbenzoheteroles as Luminophores Exhibiting Highly
           Efficient Solid-State Fluorescence
    • Authors: Masaki Shimizu; Daiki Ryuse, Takumi Kinoshita
      Abstract: [1]Benzogermolo[3,2-b]indoles, [1]benzogermolo[3,2-b]benzofuran, [1]benzogermolo[3,2-b]benzothiophene, and [1]benzogermolo[3,2-b]benzothiophene-S,S-dioxide were synthesized from the corresponding 3-bromo-2-(2-bromophenyl)benzoheteroles and characterized. A comparison of the absorption spectra of the Ph2Ge- and Ph2Si-bridged 2-phenylindoles reveals that the Ge bridge has the effect of slightly widening the HOMO–LUMO energy gap of the bridged 2-phenylindole π-system with regard to the Si-bridged system. Replacement of the indole ring by benzofuran or benzothiophene rings induces blueshifts in the absorption spectrum, whereas the absorption spectrum of the benzothiophene-S,S-dioxide derivative was redshifted with respect to the indole derivative. These results are consistent with the changes in the HOMO–LUMO energy gaps calculated by using density functional theory. The Ph2Ge-bridged indole, benzofuran, and benzothiophene-S,S-dioxide derivatives exhibit brilliant fluorescence in the violet-to-blue region with good-to-excellent quantum yields in toluene (λem=376–439 nm, Φ=0.62–0.99) and powder form (λem=401–451 nm, Φ=0.64–0.80).Germanium bridges: Adding a Ge bridge on 2-phenylbenzoheteroles is found to be effective as a new molecular design principle for organic luminophores that exhibit highly efficient solid-state fluorescence. It is found that [1]benzogermolo[3,2-b]indole, -benzofuran, and -thiophene-S,S-dioxide emit violet-to-blue light with good-to-high quantum yields in powder form, demonstrating the high potential of such bilaterally unsymmetrical germylene-bridged biaryls as solid-state light-emitting materials (see scheme).
      PubDate: 2017-09-18T11:51:25.35843-05:0
      DOI: 10.1002/chem.201703235
       
  • Total Synthesis of the Diglycosidic Tetramic Acid Ancorinoside A
    • Authors: Markus Petermichl; Rainer Schobert
      Abstract: Ancorinoside A, a metabolite of a sponge Ancorina sp., was prepared in 18 steps as the first derivative of this class of glycosylated 3-acyltetramic acids. It features a β-D-glucopyranosyl-(14)-β−D-galacturonic acid linked to a D-aspartic acid derived tetramic acid via a 3-docosanoyl spacer. The diglycoside was built up by connecting the protected monosaccharides D-galactose and D-glucose via a thioglycoside glycosylation. Attachment of the spacer by a subsequent Schmidt glycosylation of this diglycoside, TEMPO oxidation to the uronic acid, functionalisation of the spacer terminus with an N-(β-ketoacyl)aspartate, and a final Dieckmann cyclisation of the latter were the key steps leading to ancorinoside A. This approach should also allow access to ancorinoside D.
      PubDate: 2017-09-18T11:45:07.736323-05:
      DOI: 10.1002/chem.201704379
       
  • Locally Excited State–Charge Transfer State Coupled Dyes as Optically
           Responsive Neuron Firing Probes
    • Authors: Dumitru Sirbu; John B. Butcher, Paul G. Waddell, Peter Andras, Andrew C. Benniston
      Abstract: A selection of NIR-optically responsive neuron probes was produced comprising of a donor julolidyl group connected to a BODIPY core and several different styryl and vinylpyridinyl derived acceptor moieties. The strength of the donor–acceptor interaction was systematically modulated by altering the electron withdrawing nature of the aryl unit. The fluorescence quantum yield was observed to decrease as the electron withdrawing effect of the aryl subunit increased in line with changes of the Hammett parameter. The effectiveness of these fluorophores as optically responsive dyes for neuronal imaging was assessed by measuring the toxicity and signal-to-noise ratio (SNR) of each dye. A great improvement of SNR was obtained when compared to the first-generation BODIPY-based voltage sensitive dyes with concomitant toxicity decrease. The mechanism for the optical response is disparate from conventional cyanine-based dyes, opening up a new way to produce effective voltage sensitive dyes that respond well into the NIR region.Rhythm of the Light: Extended donor–acceptor BODIPY derivatives were examined as new optical neuron probes. The dyes were tested by recording the activity of neurons in the stomatogastric ganglion (STG) of the brown crab Cancer pagurus. A simple structure reactivity relationship was derived.
      PubDate: 2017-09-18T11:29:23.302403-05:
      DOI: 10.1002/chem.201703366
       
  • Titanocene Silylpropyne Complexes: Promising Intermediates en route to a
           Four-Membered 1-Metallacyclobuta-2,3-diene'
    • Authors: Fabian Reiß; Melanie Reiß, Anke Spannenberg, Haijun Jiao, Dirk Hollmann, Perdita Arndt, Uwe Rosenthal, Torsten Beweries
      Abstract: Coordination of the alkyl-substituted alkynes Me3SiC2CH2R (1: R=SiMe3; 2: R=N(SiMe3)2) to titanocene centres [Cp′2Ti] (Cp′=Cp, Cp*) yields stable alkyne complexes of the type Cp′2Ti(η2-Me3SiC2CH2R) (3: Cp′=Cp, R=SiMe3; 5: Cp′=Cp, R=N(SiMe3)2; 6: Cp′=Cp*, R=SiMe3) that are not prone to alkyne/allene isomerisation. When reacting alkyne 2 with Cp*2TiCl2 and Mg formation of the complex Cp*2Ti(III)(η3-Me3SiC2CH2) (7) which displays a propargylic unit coordinated to the TiIII centre takes place. All complexes were fully characterised, the molecular structures for 5, 6, and 7 are discussed.Rings of titan: The reaction of alkyl substituted alkynes Me3SiC2CH2R (1: R=SiMe3; 2: R=N(SiMe3)2) with Cp′2TiCl2 (Cp′=Cp, Cp*) and Mg yields three stable alkyne complexes or the unusual Cp*2Ti(III)(η3-Me3SiC2CH2) η3-propargyl complex.
      PubDate: 2017-09-18T11:29:14.920357-05:
      DOI: 10.1002/chem.201703444
       
  • From an Easily Accessible Pentacarbonylcobalt(I) Salt to Piano Stool
           Cations [(arene)Co(CO)2]+
    • Authors: Stefan C. Meier; Albina Holz, Alexei Schmidt, Daniel Kratzert, Daniel Himmel, Ingo Krossing
      Abstract: The facile synthesis of a pentacarbonyl cobalt(I) salt without the need for a super acid as solvent is presented. This salt, [Co(CO)5]+[Al(ORF)4]− {RF=C(CF3)3}, readily accessible on a multigram scale, undergoes substitution reactions with arenes yielding the hitherto unknown class of two-legged cobalt piano stool complexes [(arene)Co(CO)2]+ with four different arene ligands. Such a substitution chemistry would have been impossible in superacid solution, as the arenes used would have been oxidized and/or protonated. Thus, the general approach described herein may have a wide synthetic use. Additionally, the thermochemistry of the piano-stool complexes is shown to be not easy to describe computationally and most of the established DFT methods overestimate the reaction energies. Only CCSD(T) calculations close to the basis set limit gave energies fully agreeing with the experiment.Metal carbonyl cations go organic: The facile preparation of [Co(CO)5]+, stabilized by the weakly coordinating anion [Al(ORF)4]- {RF=C(CF3)3}, works without superacids in the organic solvent ortho-difluorobenzene (C6H4F2). The salt can be easily isolated on a multigram scale and used for further CoI chemistry, for example, the preparation of the hitherto unknown cationic two-legged piano-stool carbonyl complexes [(arene)Co(CO)2]+ (arene=C6H5CH3, C6H6, C6H5F, and C6H4F2).
      PubDate: 2017-09-18T11:29:09.409804-05:
      DOI: 10.1002/chem.201703589
       
  • Organo-Photoredox Catalyzed Oxidative Dehydrogenation of N-Heterocycles
    • Authors: Manoj K. Sahoo; Garima Jaiswal, Jagannath Rana, Ekambaram Balaraman
      Abstract: We report here for the first time the catalytic oxidative dehydrogenation of N-heterocycles by a visible-light organo-photoredox catalyst with low catalyst loading (0.1–1 mol %). The reaction proceeds efficiently under base- and additive-free conditions with ambient air at room temperature. The utility of this benign approach is demonstrated by the synthesis of various pharmaceutically relevant N-heteroarenes such as quinoline, quinoxaline, quinazoline, acridine, and indole.Promoting hetero-aromaticity: We report a room temperature oxidative dehydrogenation of N-heterocycles to N-hetero-aromatics. This unified strategy has been achieved by a metal-free visible-light photoredox catalyst in air under base and additive-free conditions. The broad substrate scope, high functional group tolerance, and simplicity of the reaction make this process more attractive towards the effective synthesis of a wide range of important N-hetero-aromatic commodities such as quinoline, quinoxaline, quinazoline, acridine, and indole.
      PubDate: 2017-09-18T11:28:58.202645-05:
      DOI: 10.1002/chem.201703642
       
  • On the Electronic Origin of Remarkable Ligand Effects on the Reactivities
           of [NiL]+ Complexes (L=C6H5, C5H4N, CN) towards Methane
    • Authors: Shaodong Zhou; Marjan Firouzbakht, Maria Schlangen, Martin Kaupp, Helmut Schwarz
      Abstract: The gas-phase reactions of [NiL]+ (L=C6H5, C5H4N, CN) with methane have been explored by using electrospray-ionization mass spectrometry (ESI-MS) complemented by quantum chemical calculations. Though the phenyl Ni complex [Ni(C6H5)]+ exclusively abstracts one hydrogen atom from methane at ambient conditions, the cyano Ni complex [Ni(CN)]+ brings about both H-atom abstraction and ligand exchange to generate [Ni(CH3)]+. In contrast, the complex 2-pyridinyl Ni [Ni(C5H4N)]+ is inert towards this substrate. The presence of the empty 4s(Ni) orbital dominates the proton-coupled electron transfer (PCET) processes for the investigated systems.The gas-phase reactions of [Ni(C6H5)]+, [Ni(C5H4N)]+, and [Ni(CN)]+ with methane have been investigated both experimentally and computationally. Whereas [Ni(C6H5)]+ exclusively abstracts one hydrogen atom from methane, [Ni(CN)]+ brings about both H-atom abstraction and the ligand exchange to release HCN; in contrast, [Ni(C5H4N)]+ is inert towards this substrate under the same conditions.
      PubDate: 2017-09-18T11:28:51.143455-05:
      DOI: 10.1002/chem.201703767
       
  • Chemoselective Reduction of Phosphine Oxides by 1,3-Diphenyl-Disiloxane
    • Authors: Joseph A. Buonomo; Carter G. Eiden, Courtney C. Aldrich
      Abstract: Reduction of phosphine oxides to the corresponding phosphines represents the most straightforward method to prepare these valuable reagents. However, existing methods to reduce phosphine oxides suffer from inadequate chemoselectivity due to the strength of the P=O bond and/or poor atom economy. Herein, we report the discovery of the most powerful chemoselective reductant for this transformation to date, 1,3-diphenyl-disiloxane (DPDS). Additive-free DPDS selectively reduces both secondary and tertiary phosphine oxides with retention of configuration even in the presence of aldehyde, nitro, ester, α,β-unsaturated carbonyls, azocarboxylates, and cyano functional groups. Arrhenius analysis indicates that the activation barrier for reduction by DPDS is significantly lower than any previously calculated silane reduction system. Inclusion of a catalytic Brønsted acid further reduced the activation barrier and led to the first silane-mediated reduction of acyclic phosphine oxides at room temperature.Simple and clean: We report the discovery of the most powerful chemoselective reductant for the reduction of phosphine oxides to the corresponding phosphines to date, 1,3-diphenyl-disiloxane (DPDS). DPDS could be deployed alone to afford high yields of phosphines from secondary and tertiary phosphine oxides very rapidly or used in tandem with the Brønsted acid bis-(p-nitrophenyl)phosphoric acid (BNPA) in reductions of acyclic phosphine oxides at ambient temperature.
      PubDate: 2017-09-18T11:28:45.438794-05:
      DOI: 10.1002/chem.201703875
       
  • Photo-Induced Assembly of a Luminescent Tetraruthenium Square
    • Authors: Baptiste Laramée-Milette; Francesco Nastasi, Fausto Puntoriero, Sebastiano Campagna, Garry S. Hanan
      Abstract: Self-assembly is a powerful synthetic tool that has led to the development of one-, two- and three-dimensional architectures. Herein a strategy for the construction and de-construction of a supramolecular structure through light-induced assembly and dis-assembly is described. These results open the way to a new avenue in supramolecular chemistry, leading to the preparation of structurally-organized assemblies by photochemical techniques. More information can be found in the Full Paper by G. S. Hanan et al. (
      DOI : 10.1002/chem.201702714).
      PubDate: 2017-09-18T11:28:39.996363-05:
       
  • Encapsulating pH-Responsive Doxorubicin–Phthalocyanine Conjugates in
           Mesoporous Silica Nanoparticles for Combined Photodynamic Therapy and
           Controlled Chemotherapy
    • Authors: Roy C. H. Wong; Dennis K. P. Ng, Wing-Ping Fong, Pui-Chi Lo
      Abstract: Zinc(II) phthalocyanine (ZnPc) was conjugated with doxorubicin (Dox) through an acid-cleavable hydrazone linker, and the resulting conjugate was encapsulated into mesoporous silica nanoparticles. Upon internalization into cancer cells, Dox was released after acidic cleavage of the hydrazone linker. The synergistic effect of the chemocytotoxic agent and the singlet oxygen generated upon irradiation of the encapsulated ZnPc killed the cells efficiently. These nanoparticles thus exhibit dual functionality as nanophotosensitizers for photodynamic therapy and as nanoplatforms for pH-controlled drug release. More information can be found in the Full Paper by D. K. P. Ng, P.-C. Lo et al. (
      DOI : 10.1002/chem.201703188).
      PubDate: 2017-09-18T11:28:34.227532-05:
       
  • Kinetic Studies on Formic Acid Dehydrogenation Catalyzed by an Iridium
           Complex towards Insights into the Catalytic Mechanism of High-Pressure
           Hydrogen Gas Production
    • Authors: Masayuki Iguchi; Heng Zhong, Yuichiro Himeda, Hajime Kawanami
      Abstract: Kinetic studies of the reaction mechanism of formic acid (FA) dehydrogenation under high-pressure conditions were investigated in the presence of iridium complex with 4,4’-dihydroxy-2,2’-bipyridine ligand. Kinetic isotope effect experiments revealed that the shift of the rate-limiting step at low and high concentrations of FA can be caused by the pH dependence of the reaction steps. The proposed equation corresponds well to the results of the shift phenomena. The results should be useful for designing hydrogen-fuel-filling systems in the near future. More information can be found in the Full Paper by H. Kawanami et al. (
      DOI : 10.1002/chem.201702969).
      PubDate: 2017-09-18T11:28:28.234057-05:
       
  • Coordination Behavior of a Planar Chiral Cyclic (Amino)(Ferrocenyl)Carbene
           Ligand in Iridium Complexes
    • Authors: Yuta Shikata; Risa Yasue, Kazuhiro Yoshida
      Abstract: Owing to their unique electronic properties, N-heterocyclic carbenes (NHCs) have attracted much attention as powerful ligands in transition-metal catalysis. However, the development of effective chiral NHCs remains a challenge, as the flat heterocyclic structures typically used are challenging to design. Herein, coordination behavior of a new chiral NHC, cyclic (amino)(ferrocenyl)carbene (CAFeC), was examined. Full characterization of its iridium complexes revealed that CAFeC has a strong coordination ability, surpassing that of classic NHC ligands, as well as a promising planar chiral environment. These fundamental data are expected to further advance the development of CAFeC ligands. More information can be found in the Full Paper by Y. Shikata, R. Yasue, and K. Yoshida (
      DOI : 10.1002/chem.201703467).
      PubDate: 2017-09-18T11:28:22.73843-05:0
       
  • The 1,6,7,12-Tetraazaperylene Bridging Ligand as an Electron Reservoir and
           Its Disulfonato Derivative as Redox Mediator in an Enzyme–Electrode
           Process
    • Authors: Thomas Brietzke; Thomas Dietz, Alexandra Kelling, Uwe Schilde, Julianae Bois, Harald Kelm, Manuel Reh, Markus Schmitz, Thomas Körzdörfer, Silke Leimkühler, Ulla Wollenberger, Hans-Jörg Krüger, Hans-Jürgen Holdt
      Abstract: Complex dication [{Ru(L-N4Me2)}2{μ-tape-(SO3)2}]2+ ([4]2+) was exploited as a redox mediator between an anaerobic homogenous reaction solution of an enzyme system (sulfite/sulfite oxidase) and the electrode by participation of the low-energy π*-orbital of the disulfonato-substituted bridging ligand tape–(SO3)22−. Tape diruthenium complexes could be a new valuable group of artificial redox mediators. The redox potential of these complexes can be easily modified for the required purpose by different substituents at the bridging tape and the terminal macrocycle. More information can be found in the Communication by H.-J. Krüger, H.-J. Holdt et al. (
      DOI : 10.1002/chem.201703639).
      PubDate: 2017-09-18T11:28:16.772312-05:
       
  • Design and Synthesis of Chiral Diene Ligands for RhI-Catalyzed
           Enantioselective Arylation of N-DPP-protected Aldimines: Synthesis of the
           Antifungal Agent Bifonazole
    • Authors: Jin-Fong Syu; Huang-Ying Lin, Yu-Yi Cheng, Yao-Chu Tsai, Yi-Ching Ting, Ting-Shen Kuo, Damodar Janmanchi, Ping-Yu Wu, Julian P. Henschke, Hsyueh-Liang Wu
      Abstract: Herein we describe the design and synthesis of a novel family of bifunctional, chiral bicyclo[2.2.1]heptadiene ligands bearing aryl and secondary amido groups, and demonstrate their usefulness in the RhI-catalyzed enantioselective addition reaction of arylboronic acids to N-diphenylphosphinyl (N-DPP)-protected aldimines. Unlike the analogous RhI-catalysts comprising diene ligands substituted with aryl and carboxylic ester groups, or only with aryl groups, the addition reaction proceeded with high stereoselectivity. The protocol tolerated a range of N-DPP-aldimines and arylboronic acids, producing the desired optically active N-DPP-protected amines with yields between 31–99 % and with ee values up to 91–99 %. The synthetic utility of the method was demonstrated by the conversion of N-DPP-protected amine 3 ae into the antifungal agent, bifonazole (13).Cyclo-somatic: The design, synthesis and testing of a novel set of chiral diene ligands bearing amido groups for the highly enantioselective 1,2-arylation reactions of N-diphenylphosphinyl-protected aldimines is described. In the presence of 3 mol % of the chiral RhI/L4 ad catalyst at 60 °C in dioxane, the corresponding addition products were isolated in yields between 31–99 % in 91–99 % ee.
      PubDate: 2017-09-18T11:28:12.779188-05:
      DOI: 10.1002/chem.201702509
       
  • Aromatic Micelles as a New Class of Aqueous Molecular Flasks
    • Authors: Kei Kondo; Jeremy K. Klosterman, Michito Yoshizawa
      Abstract: Micelles are a versatile class of molecular assemblies typically composed of aliphatic molecules with hydrophilic groups. Polyaromatic molecules with hydrophilic groups, on the other hand, usually do not assemble into micellar structures in water but rather form columnar, π-stacked architectures. This Minireview article focuses on the recent development of aqueous micellar nanostructures with multiple oligoarylene rods or polyaromatic panels. The new micelles with spherical polyaromatic shells, which we name “aromatic micelles”, serve as functional molecular flasks with superior binding abilities for medium to very large molecules in water.Adaptable nanocontainers: Micelles are the oldest class of supramolecules and are typically composed of amphiphilic molecules with aliphatic subunits. This Minireview focuses on the recent development of micellar nanostructures formed from amphiphiles with oligoarylene or polyaromatic frameworks. The new aromatic micelles providing polyaromatic shells display superior binding capabilities toward medium to large molecules in water.
      PubDate: 2017-09-18T11:28:01.74176-05:0
      DOI: 10.1002/chem.201702519
       
  • Photo-Induced Assembly of a Luminescent Tetraruthenium Square
    • Authors: Baptiste Laramée-Milette; Francesco Nastasi, Fausto Puntoriero, Sebastiano Campagna, Garry S. Hanan
      Abstract: Self-assembly is a powerful synthetic tool that has led to the development of one-, two- and three-dimensional architectures. From MOFs to molecular flasks, self-assembled materials have proven to be of great interest to the scientific community. Here we describe a strategy for the construction and de-construction of a supramolecular structure through unprecedented photo-induced assembly and dis-assembly. The combination of two approaches, a [n×1]-directional bonding strategy and a ligand photo-dissociation strategy, allows the photo-induced assembly of a polypyridyl RuII precursor into a discrete molecular square. Diffusion-ordered NMR spectroscopy confirmed the synthesis of a higher volume species, while the identity of the species was established by high-resolution mass spectrometry and single-crystal X-ray diffraction studies. The self-assembled square is not obtained by classical thermal techniques in similar conditions, but is obtained only by light-irradiation. The tetraruthenium square has an excited-state lifetime (135 ns), 40 times that of its mononuclear precursor and its luminescence quantum yield (1.0 %) is three orders of magnitude higher. These remarkable luminescence properties are closely related to the relatively rigid square structure of the tetraruthenium assembly, as suggested by slow radiationless decay and transient absorption spectroscopy. The results described herein are a rare example of photo-induced assembly and dis-assembly processes, and can open the way to a new avenue in supramolecular chemistry, leading to the preparation of structurally organized supermolecules by photochemical techniques.Lit up like Times Square: The first photo-induced assembly of a metallosupramolecular square exhibits high quantum yield and long excited-state lifetimes.
      PubDate: 2017-09-18T11:27:46.481916-05:
      DOI: 10.1002/chem.201702714
       
  • Rational Design of Rod-Like Liquid Crystals Exhibiting Two Nematic Phases
    • Authors: Richard J. Mandle; Stephen J. Cowling, John W. Goodby
      Abstract: Recently, a polar, rod-like liquid-crystalline material was reported to exhibit two distinct nematic mesophases (termed N and NX) separated by a weakly first-order transition. Herein, we present our initial studies into the structure–property relationships that underpin the occurrence of the lower-temperature nematic phase, and report several new materials that exhibit this same transformation. We have prepared material with significantly enhanced temperature ranges, allowing us to perform a detailed study of both the upper- and lower-temperature nematic phases by using small-angle X-ray scattering. We observed a continuous change in d spacing rather than a sharp change at the phase transition, a result consistent with a transition between two nematic phases, structures of which are presumably degenerate.Soft matter: Structure–property relationship for the recently discovered nematic-to-nematic phase transition exhibited by rod-like liquid crystals, allowing these materials to be accessed by rational design rather than serendipity, is reported (see scheme).
      PubDate: 2017-09-18T11:27:36.567174-05:
      DOI: 10.1002/chem.201702742
       
  • Robust Macroscopic 3D Sponges of Manganese Oxide Molecular Sieves
    • Authors: Zhenxin Liu; Depeng Wu, Xuehui Guo, Shaoming Fang, Lizhen Wang, Yu Xing, Steven L. Suib
      Abstract: The construction of macroscopic 3D sponges is of great technological importance for various applications. An outstanding challenge is the facile fabrication of sponges with the desirable combination of good stability, high electrical conductivity, and absorption ability. Here free-standing 3D OMS-2 sponges are demonstrated, with various densities, which possess a combination of desirable physical properties including high porosity, robustness, permeability, recyclability, high electrical conductivity, and selective water absorption in preference to oil. Some of these properties have systematic trends with various densities. The stress of the OMS-2 sponge, made by nanowire-based freeze-drying process, is four orders of magnitude higher than that made by calcination-related process. These new materials should find practical applications in environmental, catalysis, sensing, absorption, and energy storage, particularly in the removal of water spill cleanup, and beyond.Suck it up: Free-standing 3D OMS-2 sponges with various densities were developed and demonstrated outstanding features, including good mechanical properties, facile preparation, high electrical conductivity, high porosity, permeability, recyclability, as well as selective water absorption in preference to oil. Some of these properties exhibit systematic trends with various densities.
      PubDate: 2017-09-18T11:27:27.55687-05:0
      DOI: 10.1002/chem.201702787
       
  • Anion-Functionalized Pillararenes for Efficient Sulfur Dioxide Capture:
           Significant Effect of the Anion and the Cavity
    • Authors: Wenjun Lin; Xiuyuan Zhou, Jingsong Cai, Kaihong Chen, Xi He, Xueqian Kong, Haoran Li, Congmin Wang
      Abstract: A series of anion-functionalized pillararenes were prepared and applied in the capture of SO2 through incorporating an anion with different basicity into pillararenes. A high SO2 absorption capacity up to 15.9 mmol g−1 and excellent reversibility were achieved by tuning the basicity of the anion and the size of the cavity. Spectroscopic investigations and DFT calculations indicated that high SO2 capacity originated from multiple sites interaction between SO2 and the anion, where SO2 chemical absorption was significant strengthened by the cavity, because the anion was confined in the window of the cavity and the window was electron-deficient. Interestingly, a phase transition occurred during absorption and desorption process. The method proposed in this work provided an efficient strategy for improving gas absorption through a simple functionalization of the supermolecule, which was also very important for some other fields such as polymers and materials.Catch me! A series of anion-functionalized pillararenes were prepared and applied in the capture of SO2, which exhibited high SO2 capacity and excellent reversibility, where SO2 chemical absorption was strenghened significantly by the cavity.
      PubDate: 2017-09-18T11:25:48.836229-05:
      DOI: 10.1002/chem.201703007
       
  • Cyclopalladation in the Periphery of a NHC Ligand as the Crucial Step in
           the Synthesis of Highly Active Suzuki–Miyaura Cross-Coupling Catalysts
    • Authors: Agnes Fizia; Maximilian Gaffga, Johannes Lang, Yu Sun, Gereon Niedner-Schatteburg, Werner R. Thiel
      Abstract: Starting from 2,4-dichloropyrimidine, 4-(2-dialkylamino)pyrimidinyl functionalized mesitylimidazolium chlorides are accessible in a five-step reaction sequence. Two routes leading to palladium NHC complexes derived from these ligands have been worked out: By transmetalation with the corresponding NHC-AgCl complexes, C,N-coordinated palladium(II) complexes can be obtained. Treatment of palladium dichloride with the imidazolium salts in pyridine and in the presence of K2CO3 gives cyclometalated and thus C,C-coordinated compounds. The reactivities of all these compounds were investigated in detail as well as their performance in the catalytic Suzuki–Miyaura cross-coupling reaction. It turned out that the C,C-coordinated derivatives exhibit high catalytic activities in the coupling of arylboronic acids with aryl chlorides, which is consistent with the generally accepted mechanistic ideas on substrate activation.Coordination matters! Two different modes of coordinating an aminopyrimidine to the palladium site of C−C coupling catalysts gives rise to very different reactivities (see figure).
      PubDate: 2017-09-18T11:25:40.865037-05:
      DOI: 10.1002/chem.201702877
       
  • Ligand Influence on Carbonyl Hydroboration Catalysis by Alkali Metal
           Hydridotriphenylborates [(L)M][HBPh3] (M=Li, Na, K)
    • Authors: Hassan Osseili; Debabrata Mukherjee, Thomas P. Spaniol, Jun Okuda
      Abstract: Alkali metal hydridotriphenylborates [(L1)M][HBPh3] (L1=Me6TREN; M=Li, Na, K) chemoselectively catalyze the hydroboration of carbonyls and CO2, with lithium being the most active system. A new series of complexes [(L2)M][HBPh3] [M=Li (1), Na (2), K (3)] featuring the cyclen-derived macrocyclic polyamine Me4TACD (L2) were synthesized in a “one-pot” fashion and fully characterized including X-ray crystallography. In the crystal, 1–3 exhibit wide variation in metal coordination of the [HBPh3]− anion from lithium to potassium. The structures differ from those in [(L1)M][HBPh3]. Effects of coordination of L1, L2, and other N- and O-donor multidentate ligands on [Li(HBPh3)] were used to rationalize the catalytic activity in carbonyl hydroboration.Light metal: Comparison of ligands (L) on the catalytic carbonyl hydroboration by [(L)M][HBPh3] (M=Li, Na, K) confirms the unique combination of Me6TREN and lithium for high activity.
      PubDate: 2017-09-18T11:25:27.548626-05:
      DOI: 10.1002/chem.201702818
       
  • Enhancing the antimicrobial activity of alamethicin F50/5 by incorporating
           N-terminal hydrophobic triazole substituents.
    • Authors: Sanjit Das; Khoubaib Ben Haj Salah, Emmanuel Wenger, Jean Martinez, Jules Kotarba, Vanessa Andreu, Nicolas Ruiz, Filippo Savini, Lorenzo Stella, Claude Didierjean, Baptiste Legrand, Nicolas Inguimbert
      Abstract: We propose a simple and efficient strategy to significantly improve the antibacterial activity of peptaibols and other antimicrobial peptides by N-terminal capping with 1,2,3-triazole bearing various hydrophobic substituents on C-4. We showed, herein, that such N-terminal insertions on alamethicin F50/5 could enhance its antimicrobial activity on gram-positive bacteria without modification of its overall three-dimensional structure. Indeed, while the native peptide and its analogues shared comparable helical contents, the crystal structure of one of the most active derivative showed a local slight distortion of the N-terminal extremity, which was also observed in solution using NMR spectroscopy. Importantly, fluorescence studies showed that the N-capped derivatives had increased affinity for liposomes which may indicate they interacted more strongly with the bacterial membrane than alamethicin F50/5.
      PubDate: 2017-09-18T09:41:49.121122-05:
      DOI: 10.1002/chem.201703569
       
  • Intramolecular SEAr of phosphorus derivatives: computational approach to
           the synthesis of π-extended heterocycles
    • Authors: Olatz Larrañaga; Carlos Romero-Nieto, Abel de Cozar Ruano
      Abstract: The reaction mechanism associated with the synthesis of phosphorus-based heteropolyaromatic architectures by intramolecular SEAr have been investigated by DFT calculations at the B3LYP-D3/6-311+G(D) level of theory. The purpose of this study is to provide essential information for the future development of improved polycyclic organophosphorus materials. To that end, we have studied the impact of the initial reactant and/or the intermediates' structure into the mechanistic features and energetic profiles of the phosphorus cyclization process. Moreover, we have analysed in detail the reactivity parameters within a conceptual DFT framework and extracted underlying reactivity trends. Thus, our findings provide important insights for a rational design of polycyclic phosphorus compounds.
      PubDate: 2017-09-18T09:41:34.132278-05:
      DOI: 10.1002/chem.201703495
       
  • Formation and Structural Diversity of Organo-Functionalized Tin-Silver
           Selenide Clusters
    • Authors: Stefanie Dehnen; Niklas Rinn, Lukas Guggolz, Katharina Gries, Kerstin Volz, Jürgen Senker
      Abstract: When reacting the organic functionalized tin selenide clusters [(SnR1)3Se4Cl] (A, R1 = CMe2CH2C(O)Me) or [(SnR1)4Se6] (B) with (SiMe3)2Se and [Ag(PPh3)3Cl] at −78°C in CH2Cl2, a microcrystalline, intermediate (compound 1) precipitates, which was investigated by magic angle spinning (MAS) NMR spectroscopy, powder X-ray diffraction (PXRD), energy dispersive X-ray (EDX) spectroscopy, and quantum chemistry. From these studies, a suggestion about its identity was derived. Compound 1 re-dissolves under reorganization into the organo-functionalized Ag/Sn/Se cluster compound [Ag6(μ6 Se)(Ag8Se12){(R1Sn)2Se2}6] (2), or the mixed-valence cluster [(AgPPh3)2(SnIICl)2Se2{(R1SnIV)2Se2}2] (3), depending on the presence or the exclusion of daylight, respectively. The addition of N2H4∙H2O to a solution of 1 yields selectively [Ag7(μ7 Se)(Ag7Se12){(R2Sn)2Se2}6] (4, R2 = CMe2CH2C(N2H2)Me), the Ag/Sn/Se core of which is isomeric to that of 2. 2 - 4 were characterized by X-ray diffraction. NMR spectroscopic studies on solutions of 1 indicate the co-existence of different species.
      PubDate: 2017-09-18T09:41:15.495959-05:
      DOI: 10.1002/chem.201703614
       
  • Effect of Carbon Supports on Enhancing Mass Kinetic Current Density of
           Fe-N/C Electrocatalysts
    • Authors: Xinghua Chen; Fei He, Yanfei Shen, Yiran Yang, Hao Mei, Songqin Liu, Toshiyuki Mori, Yuanjian Zhang
      Abstract: The mass kinetic current density (mass JK) of most extensively reported M−N/C catalysts (M represents non-precious metal elements such as Fe, Co, and Cu), a potential alternative to noble metal catalysts in fuel cells, is poorer than that of commercial Pt/C. Thus, deep understanding of the intrinsic roles of carbon supports may contribute to the development of M−N/C catalysts from a practical point of view. Herein, the routinely used carbon supports, i.e. carbon black (CB) and carbon nanotubes (CNT) that have different morphology and crystallinity, were investigated to uncover the factors that affected the mass JK of Fe−N/C in electrocatalytic oxygen reduction. When immobilized on CB, the ionic liquids-derived Fe−N/C exhibited an enhanced mass JK (4.45 A g−1 at 0.80 V vs. RHE) by a factor of 2.14 times, comparable to that of Pt/C (5.79 A g−1) and higher than most reported M−N/C catalysts to our best knowledge. In contrast, the CNT support system showed no improvement. It was revealed that a compatible interface between the Fe−N/C precursors and the carbon supports was vital to ensure in-situ growth of a uniform catalyst layer on the supports during pyrolysis. This subsequently promotes the mass JK by exposing more embedded active sites and introducing favorable slit pores for effective mass-diffusion. This work would be promising to address the long-term overlooked challenge of the low mass JK of M−N/C catalysts in replacing noble-metal catalysts for practical fuel cell applications.Interface effect: A study into the intrinsic role of carbon supports for Fe-N/C alternatives to Pt/C catalysts for oxygen reduction in fuel cells revealed that when immobilized on suitable support, the Fe−N/C demonstrated an improved mass JK that was comparable to that of Pt/C and higher than most reported M−N/C catalysts (see scheme).
      PubDate: 2017-09-18T08:45:40.925292-05:
      DOI: 10.1002/chem.201703020
       
  • Bridging Coordination of Vinylarenes to Pd3- or Pd4 Cluster Sites
    • Authors: Yuki Ishikawa; Seita Kimura, Koji Yamamoto, Tetsuro Murahashi
      Abstract: Though the M3- or M4 face of palladium clusters may serve as the active binding site of substrates, it has been difficult to elucidate their substrate binding modes in solution. Here, it was proved that a soluble Pd3- or Pd4 sheet cluster accommodates vinylarenes at its bridging coordination site in an unusual mode in palladium chemistry; that is, for the former, the coordination of the arene moiety precedes that of olefin moiety; for the latter, vinylarene coordinates to a distorted Pd4 sheet through oxidative π-addition of its styrene moiety.Pd and arene coordination: It was proved that a Pd3- or Pd4 sheet cluster accommodates vinylarenes at its bridging coordination site in an unusual mode in palladium chemistry. The arene coordination precedes olefin coordination at the Pd3 site, and oxidative π-addition takes place at the Pd4 site.
      PubDate: 2017-09-18T08:45:32.195279-05:
      DOI: 10.1002/chem.201703023
       
  • Autonomous and Continuous Stimuli-Responsive Polymer Surface for
           Antibacterial Application through Enzymatic Self-Propagating Reactions
    • Authors: Chao Ding; Zhengqing Yan, Jinsong Ren, Xiaogang Qu
      Abstract: Stimuli-responsive polymer materials inspired by biological materials have invoked increasing research interest; however, they still suffer from limitations such as finite amplified responses and poor sensitivity of the unstimulated parts. Herein, a new strategy for creating H+-responsive polymer surfaces that are capable of transforming specific local fleeting stimuli into global macroscopic changes is described. The introduction of self-propagating reactions into the polymer-surface systems endows them with excellent stimuli-amplifying properties and response of the unstimulated parts. On the basis of this design, a polymer and enzymatic reaction were employed to enable a specific response to a stimulus and then lead to macroscopic changes of the surface. It is further shown that the prepared H+-responsive polymer surfaces can be employed for antibacterial application. This work provides a good example of achieving autonomously reconfigurable materials that respond to local fleeting stimuli.Please respond! pH-Responsive polymer surfaces that are capable of transforming specific local fleeting stimuli into global macroscopic property changes were designed by the introduction of self-propagating reactions into polymer-surface systems (see figure). The H+-responsive polymer surfaces can be employed for antibacterial applications, and this design strategy offers methods for achieving autonomously reconfigurable materials.
      PubDate: 2017-09-18T08:45:27.050045-05:
      DOI: 10.1002/chem.201703067
       
  • Molecular Switching in Confined Spaces: Effects of Encapsulating the
           DHA/VHF Photo-Switch in Cucurbiturils
    • Authors: Michael Å. Petersen; Brian Rasmussen, Nicolaj N. Andersen, Stephan P. A. Sauer, Mogens Brøndsted Nielsen, Sophie R. Beeren, Michael Pittelkow
      Abstract: Confinement of reactive chemical species uniquely affects chemical reactivity by restricting the physical space available and by restricting access to interactions with the solvent. In Nature, for example, confined protein binding pockets govern processes following photoisomerization reactions and the isomerizations themselves. Here we describe the first example of a dihydroazulene/vinylheptafulvene (DHA/VHF) photo-switch functioning in water, and we show how its switching behavior is strongly influenced by supramolecular interactions with a series of cucurbit[n]uril (CB) host molecules. In CB7 inclusion complexes, the kinetics of the thermal VHF-to-DHA back-reaction is accelerated, while in CB8 inclusion complexes, the kinetics is slowed down as compared to the free photo-switch. The effect of the CB encapsulation of the photo-switch can be effectively canceled by introducing a guest that binds the CB more strongly. According to DFT calculations, a stabilization of the reactive s-cis VHF conformer relative to the s-trans VHF appears to be a contributing factor responsible for the accelerated back-reaction when encapsulated in CB7.Switches in water: The dihydroazulene/vinylheptafulvene (DHA/VHF) photo-switching behavior in water is strongly influenced by supramolecular interactions with a series of cucurbit[n]uril (CB) host molecules. In CB7 inclusion complexes, the kinetics of the thermal VHF-to-DHA back-reaction is accelerated, while in CB8 inclusion complexes, the kinetics is slowed down as compared to the free photo-switch.
      PubDate: 2017-09-18T08:41:20.513639-05:
      DOI: 10.1002/chem.201703196
       
  • Magnetic nanotransducers in biomedicine
    • Authors: Agostina Grillone; Gianni Ciofani
      Abstract: Owing to their abilities to identify diseased conditions, to modulate biological process, and to control cellular activities, magnetic nanoparticles have become one of the most popular nanomaterials exploited in the biomedical field. Targeted drug delivery, controlled drug release, hyperthermia treatments, imaging, and stimulation of several biological entities are just some of the several tasks that can be accomplished by taking advantage of magnetic nanoparticles in tandem with magnetic fields. The huge interest towards this class of nanomaterials rises from the possibility to physically drive their spatiotemporal localization inside the body, and to deliver an externally applied stimulation at a target site. They in fact behave as actual nanotransducers, converting energy stemming from the external magnetic field into heat and mechanical forces, which act as signals for therapeutic processes as hyperthermia and controlled drug release. Magnetic nanoparticles result into a non-invasive tool that enables a remote activation of biological processes, besides behaving as formidable tracers for different imaging modalities, thus allowing to simultaneously carry out diagnosis and therapy. In view of all this, owing to their multifunctional and multitasking nature, magnetic nanoparticles are already one of the most important nanotechnological protagonists in medicine and biology, enabling an actual theranostic approach in many pathological conditions. In this Concept, we first provide a brief introduction on some physical properties of magnetic materials and on important features that determine the physical properties of magnetic nanoparticles; thereafter, we will consider some major biomedical applications: hyperthermia, drug delivery / release, and nanoparticle-mediated control of biological processes, even at subcellular level.
      PubDate: 2017-09-18T08:41:09.23872-05:0
      DOI: 10.1002/chem.201703660
       
  • Viologens and Their Application as Functional Materials
    • Authors: Laura Striepe; Thomas Baumgartner
      Abstract: Organic materials have recently gained considerable attention for electronic applications, improving performance and sustainability to current technologies. Commercialized metal-based systems are generally expensive, toxic and difficult to recycle, however organic materials offer promising solutions. Viologens, N,N′ di-quaternized bipyridyl salts, are a well-studied species exhibiting three reversible redox states, possessing valuable electrochromic and electron-accepting properties. These properties can be fine-tuned through synthesis by altering the nitrogen substituents and various counteranions. Currently, viologens have become of great interest as functional materials in a wide array of applications; a few to name include electrochromic devices, molecular machines, and organic batteries. This review highlights representative recent work and advances towards utilizing viologens in practical applications that currently compete with metal-based technologies. Additionally, modified viologens that can be further fine-tuned will be discussed.Organic functional materials: Viologens have recently been rediscovered due to their multifaceted utility for practical applications. This Review focuses on current progress of electrochromic devices, molecular machines and various organic batteries, and how viologens, as an organic material, are an upcoming competitor to conventional metal-based technologies.
      PubDate: 2017-09-18T08:41:02.236087-05:
      DOI: 10.1002/chem.201703348
       
  • C(sp³)-H Bond Activation by Vinylidene Gold(I) Complexes: A Concerted
           Asynchronous or Stepwise Process'
    • Authors: Johannes E. M. N. Klein; Gerald Knizia, Laura Nunes dos Santos Comprido, Johannes Kästner, A. Stephen K. Hashmi
      Abstract: A detailed analysis of the C(sp³)-H activation process by vinylidene Au(I) complexes is described based on an intrinsic bond orbital analysis. Based on our analysis this event can be divided into three phases: (i) hydride transfer, (ii) C-C bond formation, and (iii) σ to π rearrangement of the lone pair coordinated to Au. Small perturbations of the system lead to either a concerted asynchronous reaction, or a stepwise reaction featuring an intermediate with a C-H-C three-centre two-electron (3c-2e) bond. The role of π-donating substituents is highlighted and provides a way of controlling reactions of this type in future experimental studies.
      PubDate: 2017-09-18T08:40:24.996505-05:
      DOI: 10.1002/chem.201703815
       
  • Incorporating an Inert Polymer into the Interlayer Passivates Surface
           Defects in Methylammonium Lead Halide Perovskite Solar Cells
    • Authors: Shiqing Bi; Xuning Zhang, Liang Qin, Rong Wang, Jiyu Zhou, Xuanye Leng, Xiaohui Qiu, Yuan Zhang, Huiqiong Zhou, Zhiyong Tang
      Abstract: The hysteresis effect and instability are important concerns in hybrid perovskite photovoltaic devices that hold great promise in energy conversion applications. In this study, we show that the power conversion efficiency (PCE), hysteresis, and device lifetime can be simultaneously improved for methylammoniumlead halide (CH3NH3PbI3-xClx) solar cells after incorporating poly(methyl methacrylate) (PMMA) into the PC61BM electron extraction layer (EEL). By choosing appropriate molecular weights of PMMA, we obtain a 30 % enhancement of PCE along with effectively lowered hysteresis and device degradation, adopting inverted planar device structure. Through the combinatorial study using Kelvin probe force microscopy, diode mobility measurements, and irradiation-dependent solar cell characterization, we attribute the enhanced device parameters (fill factor and open circuit voltage) to the surface passivation of CH3NH3PbI3-xClx, leading to mitigating charge trapping at the cathode interface and resultant Shockley-Read-Hall charge recombination. Beneficially, modified by inert PMMA, CH3NH3PbI3-xClx solar cells display a pronounced retardation in performance degradation, resulting from improved film quality in the PC61BM layer incorporating PMMA which increases the protection for underneath perovskite films. This work enables a versatile and effective interface approach to deal with essential concerns for solution-processed perovskite solar cells by air-stable and widely accessible materials.Danger danger! High voltage! Incorporating the inert PMMA into the fullerene based electron extraction layer not only suppresses unfavorable hysteresis in perovskite solar cells but also enhances the device stability. The improvements can be primarily ascribed to surface passivation with the functional groups in PMMA and the formation of a more compact and dense layer together with PCBM to improve protection of perovskite films.
      PubDate: 2017-09-18T08:35:37.171629-05:
      DOI: 10.1002/chem.201703382
       
  • Possible Case of Halogen Bond-Driven Self-Disproportionation of
           Enantiomers (SDE) via Achiral Chromatography
    • Authors: Shumpei Terada; Motohiro Hirai, Ayaka Honzawa, Osamu Kitagawa, Angelika Kamizela, Alicja Wzorek, Vadim A. Soloshonok
      Abstract: The major breakthrough reported in this work is the discovery of likely halogen bond-driven self-disproportionation of enantiomers (SDE). Taking into account that the halogen-bonding interactions can be rationally designed and can match, or even exceed, the strength of the more familiar hydrogen bond, this discovery clearly opens an unexpected new direction of research in the areas of molecular chirality and the SDE phenomenon.Enriched by chromatography: The remarkably high magnitude of the self-disproportionation of enantiomers (SDE) phenomenon via achiral chromatography (MPLC, gravity column), observed for axially chiral mebroqualone derivatives, is caused by the formation of intermolecular halogen bonds (C=O−Br). This strong halogen bonding gives a clear preference for heterochiral high-order species, allowing for practical preparation of enantiomerically enriched (up to>99 % ee) and depleted (up to
      PubDate: 2017-09-18T08:35:23.453224-05:
      DOI: 10.1002/chem.201703308
       
  • Polyaspartates as Thermoresponsive Enantiodifferentiating Helically Chiral
           Alignment Media for Anisotropic NMR Spectroscopy
    • Authors: Mira Schwab; Dominik Herold, Christina M. Thiele
      Abstract: Lyotropic liquid crystalline phases of poly-β-phenethylaspartates are presented as new helically chiral enantiodifferentiating alignment media with thermoresponsive properties. In addition to displaying the highest enantiodifferentiation observed for homopolypeptides, the alignment media undergo a temperature induced helix reversal without perturbing the nematic phase. This offers the opportunity to measure residual dipolar couplings (RDCs) in high and low temperature helix conformation (P- and M-helix) in one polymer. Thus different mean orientations of a chiral analyte can be determined within the same sample. Furthermore, we investigated whether the resulting media are diastereomeric and whether we are able to obtain information about the alignment process.Hot and cool RDCs: Herein we present poly-β-phenethylaspartates as new helically chiral enantiodifferentiating alignment media which undergo a temperature induced helix reversal. This allows the measurement of residual dipolar couplings in two different helix conformations (P- and M-helix) within the same sample.
      PubDate: 2017-09-18T08:15:40.71678-05:0
      DOI: 10.1002/chem.201702884
       
  • Novel 3D Semiconducting Open-Frameworks based on Cuprous Bromides with
           Visible Light Driven Photocatalytic Properties
    • Authors: Xiao-Wu Lei; Cheng-Yang Yue, Jun-Chao Wei, Rui-Qing Li, Fu-Qi Mi, Yan Li, Lu Gao, Quan-Xiu Liu
      Abstract: Visible light driven photocatalysts based on crystalline microporous metal halogenides received much less attention compared with dense or composite oxide semiconductors. Using the well-known photosensitive transition metal-complexes [TM(2,2-bipy)3]2+ (TM=Fe, Co, Ni, Ru) as templates, a special three-dimensional (3D) metal halogenide framework of [TM(2,2-bipy)3]Cu4Br6 was designed with [Cu4Br4] cluster as 4-connected node. These microporous materials feature narrow band gaps and stable visible light driven photocatalytic properties including water reduction to provide H2 and photodegradation of organic pollutants. The study of electronic band structure shows that the TM complexes effectively prevent the recombination of photo-induced electron/hole pairs leading to excellent photocatalytic activity and photochemical stability. This work represents the first 3D microporous metal halogenides used as visible light driven photocatalyst to provide hydrogen energy.Using the well-known photosensitive metal-complexes [TM(2,2-bipy)3]2+ as templates, a special three-dimensional metal halogenide framework of [TM(2,2-bipy)3]Cu4Br6 was designed. These microporous materials feature tunable narrow band gaps and stable visible light driven photocatalytic properties including hydrogen evolution from water splitting and photodegradation of organic pollutants, mainly arising from the multi-electronic effects of TM complex templates and host framework. This technique facilitates the integration of crystalline microporous materials and semiconducting photocatalytic properties into one d10 transition metal halogenide for the first time.
      PubDate: 2017-09-18T08:15:31.110771-05:
      DOI: 10.1002/chem.201702736
       
  • Chiral Sulfur Functional Groups as Definers of the Chirality at
           the Metal in Ir and Rh Half-Sandwich Complexes: A Combined CD/X-ray
           Study
    • Authors: Marta G. Avello; María Frutos, María C. de la Torre, Alma Viso, Marina Velado, Roberto Fernández de la Pradilla, Miguel A. Sierra, Heinz Gornitzka, Catherine Hemmert
      Abstract: Mesoionic carbenes (MICs) derived from triazolium salts that contain chiral sulfoxide or sulfoximine functional groups were used to construct enantiopure chiral-at-metal IrIII and RhIII half-sandwich complexes through the synthetic sequence of MIC complexation/C−H aromatic activation. The process was efficient and diastereoselective for the formation of enantiopure five-membered metallacycles. The use of the enantiomers of the chiral sulfur groups allowed us to prepare complexes that had opposite configurations at the metal center. Complete retention of the configuration at the metal center was observed during the formation of cationic IrIII complexes and upon insertion of alkynes into the IrIII−C bond, as demonstrated by a combined circular dichroism/X-ray study. These results point to a vicinal-assisted SN1-like mechanism.La síntesis de complejos “half-sandwich”, conteniendo centros metálicos de IrIII y RhIII enantiomericamente puros, se ha efectuado desde carbenos mesoiónicos (MICs) derivados de sales de triazolio enantiomericamente puras sustituidas por sulfóxidos o sulfoximinas. La preparación de estos complejos se ha efectuado usando una secuencia en la que el MIC se ha complejado al metal y, posteriormente, se ha realizado una activación de un enlace C−H aromático. El proceso de formación de metalaciclos de cinco eslabones enantiomericamente puros es eficiente y completamente diastereoselectivo. Cuando se usan los enantiómeros de los grupos de azufre quirales unidos al MIC se pueden preparar complejos con configuraciones opuestas en el centro metálico. Tanto la formación de complejos de IrIII catiónicos como la inserción de alquinos en el enlace IrIII−C, ocurren con retención completa de la configuración. Esto se demuestra usando una combinación de Dicroísmo Circular y estudios de rayos-X. Los resultados obtenidos sugieren una asistencia vecinal del grupo de azufre quiral en estos procesos similares a la SN1.Enantioenriched metallacycles: Enantiopure chiral-at-metal IrIII and RhIII half-sandwich complexes are produced from mesoionic carbenes (MICs) that contain chiral sulfoxide or sulfoximine functional groups. The synthetic sequence of MIC complexation/C−H aromatic activation efficiently affords enantiopure five-membered metallacycles. The configuration at the metal center remains unaltered during the formation of the cationic IrIII complexes and the insertion of alkynes, as demonstrated by a combined circular dichroism/X-ray study.
      PubDate: 2017-09-18T08:10:29.740249-05:
      DOI: 10.1002/chem.201702662
       
  • Embedded Isoreticular Zeolites: Concept and Beyond
    • Authors: Jung Cho; Hyun June Choi, Peng Guo, Jiho Shin, Xiaodong Zou, Suk Bong Hong
      Abstract: The structure solution, prediction, and targeted synthesis of a family of embedded isoreticular zeolites (EIZs) with expanding structural complexity, denoted the RHO family, were reported recently. Here, the naming and building rules of body-centered cubic EIZs with the lta cage as the lattice point are presented. The rearrangement of a pair of pau and d8r cages between two lta cages and its repetitive insertion, combined with the strong reflections and fragment methods, allows the creation of three other new zeolite families, designated the HPO, RHO(b), and KFI families. Among them, the KFI family is found to be the only EIZ family, on the basis of the similarity of structure factor amplitudes and phases of strong reflections, that is, structural coding, within its family members. The structural credibility of this family is confirmed by both local interatomic distances and T−T−T angle analyses. The existence of tetragonal EIZ families is also demonstrated. The overall results provide useful insights into the prediction of unprecedented EIZ families.Defining embedded isoreticular zeolites: The definition and concept of embedded isoreticular zeolites can uncover a whole series of related structures (see figure) with similar structural properties and provide insight into their rational synthesis.
      PubDate: 2017-09-18T08:06:20.714169-05:
      DOI: 10.1002/chem.201702417
       
  • Organoruthenium Complexes with C^N Ligands Are Highly Potent Cytotoxic
           Agents that Act by a New Mechanism of Action
    • Authors: Vojtech Novohradsky; Jyoti Yellol, Olga Stuchlikova, María Dolores Santana, Hana Kostrhunova, Gorakh Yellol, Jana Kasparkova, Delia Bautista, Jose Ruiz, Viktor Brabec
      Abstract: Our study demonstrates that four novel substitutionally inert C,N-cyclometalated Ru(II) complexes of the type [Ru(C^N)(N^N)2][PF6] containing a handle for functionalization in the C^N ligand are very potent cytotoxic agents against several different human cancer cell lines and are up to 400-fold more potent than clinically used cisplatin. In addition, the investigated ruthenium complexes are less cytotoxic in noncancerous cells, and exhibit higher selectivity for cancer cells than conventional platinum anticancer drugs. The high potency of the investigated ruthenium compounds can be attributed to several factors, including enhanced internalization and their capability to change mitochondrial transmembrane potential in cells. The new ruthenium complexes also interfere with protein synthesis with a markedly higher potency than conventional inhibitors of DNA translation. Notably, the latter mechanism has not been hitherto described for other cytotoxic Ru compounds and cisplatin.
      PubDate: 2017-09-18T07:40:37.962302-05:
      DOI: 10.1002/chem.201703581
       
  • Modulating the structural properties of alpha,gamma-hybrid peptides by
           alpha-amino acid residues: Uniform 12-helix versus "mixed" 12/10-helix
    • Authors: Rajkumar Misra; K. Muruga Poopathi Raja, Hans-Jörg Hofmann, Hosahudya Gopi
      Abstract: Abstract: The most important natural a- and 310-helices are stabilized by unidirectional intramolecular hydrogen bonds along the helical cylinder. In contrast, we are reporting here on 12/10-helical conformations with alternately changing H-bond directionality in sequences of alpha,gamma-hybrid peptides [P1: Boc-Ala-Aic-Ala-Aic-COOH; P2: Boc-Leu-Aic-Leu-Aic-OEt; P3: Boc-Leu-Aic-Leu-Aic-Leu-Aic-Aib-OMe; P4: Boc-Ala-Aic-Ala-Aic-Ala-Aic-Ala-OMe; P5: Boc-Leu-Aic-Leu-Aic-Leu-Aic-Leu-Aic-Aib-OMe] composed of natural a-amino acids and the achiral gamma4,4-dimethyl substituted g-amino acid Aic in solution and in single crystals. The helical conformations are stabilized by alternating I to i+3 and I to i -1 intramolecular H-bonds. The experimental data are supported by ab initio MO calculations. Surprisingly, replacing the natural a-amino acids of the sequence by the achiral dialkyl amino acid Ac6c [P6: Boc-Ac6c-Aic-Ac6c-Aic-Ac6c-Aic-Ac6c-Aic-Ac6c-CONHMe] leads to a 12-helix with unidirectional hydrogen bonds showing an entirely different backbone conformation. The results presented here emphasize the influence of the structure of the alpha-amino acid residues in dictating the helix types in alpha,gamma-hybrid peptide foldamers and demonstrate the consequences for folding by small structure variations in the monomers.
      PubDate: 2017-09-18T06:40:50.175731-05:
      DOI: 10.1002/chem.201703871
       
  • Single oxidative collision events of silver nanoparticles: understanding
           the rate-determining chemistry
    • Authors: Kamonwad Ngamchuea; Richard O. D. Clark, Stanislav V. Sokolov, Neil P. Young, Christopher Batchelor-McAuley, Richard G. Compton
      Abstract: The oxidative dissolution of citrate-capped silver nanoparticles (AgNPs) is investigated herein by two electrochemical techniques: nano-impacts and anodic stripping voltammetry. Nano-impacts or single nanoparticle-electrode collisions allow the detection of individual nanoparticles. The technique offers an advantage over surface-immobilized methods such as anodic stripping voltammetry as it eliminates the effects of particle agglomeration/ aggregation. The electrochemical studies are performed in different electrolytes (KNO3, KCl, KBr and KI) at varied concentrations ( 20 mM). In nano-impact measurements, the AgNP undergoes complete oxidation upon impact at a suitably potentiostated electrode. The frequency of the nanoparticle-electrode collisions observed as current-transient spikes depends on the electrolyte identity, its concentration and the potential applied at the working electrode. The frequencies of the spikes are significantly higher in the presence of halide ions and increase with increasing potentials. From the frequency, the rate of AgNP oxidation as compared with the timescale the AgNP is in electrical contact with the electrode can be inferred, and hence is indicative of the relative kinetics of the oxidation process. Primarily based on these results, we propose the initial formation of the silver (I) nucleus (Ag+, AgCl, AgBr or AgI) as the rate-determining process of silver oxidation on the nanoparticle.
      PubDate: 2017-09-18T06:40:25.707538-05:
      DOI: 10.1002/chem.201703591
       
  • Construction of Condensed Polycyclic Aromatic Frameworks through
           Intramolecular Cycloaddition Reactions Involving Arynes Bearing an
           Internal Alkyne Moiety
    • Authors: Suguru Yoshida; Keita Shimizu, Keisuke Uchida, Yuki Hazama, Kazunobu Igawa, Katsuhiko Tomooka, Takamitsu Hosoya
      Abstract: Facile synthetic methods for condensed polycyclic aromatic compounds via aryne intermediates are reported. The generation of arynes bearing a (3-arylpropargyl)oxy group from the corresponding o-iodoaryl triflate-type precursors efficiently afforded arene-fused oxaacenaphthene derivatives, which were formed through intramolecular [2+4] cycloaddition. Extending the method to the generation of arynes bearing a 1,3-diyne moiety led to a continuous generation of naphthalyne intermediate through the hexadehydro Diels-Alder reaction involving the triple bond of aryne. This novel type of aryne-relay chemistry enabled the synthesis of a unique aminoarylated oxaacenaphthene derivative and highly ring-fused anthracene derivatives.
      PubDate: 2017-09-18T05:40:46.307968-05:
      DOI: 10.1002/chem.201704345
       
  • Frontispiece: Putting Rings around Carbon Nanotubes
    • Authors: Emilio M. Pérez
      Abstract: MINT explorers salute! The synthesis of rotaxane-type mechanically interlocked derivatives of single walled carbon nanotubes (MINTs) is achieved using a templated macrocyclization approach. MINTs combine the advantages of covalent (stability) and noncovalent (structural integrity) derivatives of SWNTs. Characterizing MINTs is harder than making them and requires a combination of spectroscopic, analytical and microscopic techniques. MINTs might find application as polymer fillers, sensors, catalysts…and molecular machines! The MINT ship has nearly just sailed, but we are already finding fascinating new seas and ports. For more information see the Concept article by E. M. Pérez on page 12681 ff. The artwork was created by M. Eugenio Vázquez (CIQUS, Santiago de Compostela).
      PubDate: 2017-09-18T02:43:11.631044-05:
      DOI: 10.1002/chem.201785261
       
  • Frontispiece: Bicyclic Peptides as Next-Generation Therapeutics
    • Authors: Curran A. Rhodes; Dehua Pei
      Abstract: Greater conformational rigidity and metabolic stability than linear and monocyclic peptides can be found in bicyclic peptide which are capable of binding to challenging drug targets with antibody-like affinity and specificity. Powerful combinatorial library technologies have recently been developed to rapidly synthesize and screen large bicyclic peptide libraries for ligands against enzymes, receptors, and protein–protein interaction targets. For more details, see the Minireview by D. Pei and C. A. Rhodes on page 12690 ff.
      PubDate: 2017-09-18T02:43:09.385575-05:
      DOI: 10.1002/chem.201785262
       
  • Frontispiece: Room-Temperature Columnar Nematic and Soft Crystalline
           Columnar Assemblies of a New Series of Perylene-Centred Disc Tetramers
    • Authors: Indu Bala; Santosh Prasad Gupta, Joydip De, Santanu Kumar Pal
      Abstract: An artistic representation of a new series of perylene-centered disc tetramers that self-assemble into room-temperature columnar structures is shown. Although compounds with shorter alkyl spacer chain length self-organize into soft-crystal columnar oblique lattice, the higher one exhibits a columnar nematic phase. The compounds were green-light emissive in solution, as well as in the thin-film state with high quantum yields, and may act as an active component in OLEDs. For more information, see the Full Paper by S. K. Pal et al. on page 12767 ff.
      PubDate: 2017-09-18T02:43:08.809545-05:
      DOI: 10.1002/chem.201785264
       
  • Frontispiece: Control of Helical Chirality of Ferrocene–Dipeptide
           Conjugates by the Secondary Structure of Dipeptide Chains
    • Authors: Toshiyuki Moriuchi; Taiki Nishiyama, Masaki Nobu, Toshikazu Hirao
      Abstract: The helical chirality of a series of ferrocene-dipeptide bioorganometallic conjugates could be controlled by cyclic/acyclic conversion. The suitable regulation of the conformational flexibility allowed a type II β-turn-type second structure to be formed, thus inducing M-helical chirality. Furthermore, the conversion of a type II β-turn-like structure to an antiparallel β-sheet-like structure was achieved through the reductive cleavage of the disulfide bond to thiol groups, leading to the conversion of M-helical chirality into P-helical chirality. For more details, see the Communcation by T. Moriuchi et al. on page 12704 ff.
      PubDate: 2017-09-18T02:43:00.220057-05:
      DOI: 10.1002/chem.201785263
       
  • Dissecting Trichalcogenasumanenes: π-Bowl to Planar, Invertible
           Curvature, and Chiral Polycycles
    • Authors: Xueqing Hou; Xuexiang Li, Chunlin Sun, Lichuan Chen, Yantao Sun, Zhe Liu, Hao-Li Zhang, Xiangfeng Shao
      Abstract: The buckybowl trichalcogenasumanenes show cleavage of flanking benzene ring upon oxidation, which leads their dissection by fusing various amidine moieties onto peripheral region. By gradually increasing the ring size of amidine from five- to six- and seven-membered, the molecule engineering results in the [7-5-6]-, [7-6-6]-, and [7-7-6]-fused polycycles. Three systems are distinct in the molecular geometries, packing motifs, and optoelectronic properties. The [7-5-6]-fused case adopts the flat backbone, displays strong emission with the fluorescence quantum yield up to 52.3 %, and undergoes a two-photon absorption process. The [7-6-6]-fused one is of a curvature with molecular geometry inversion, forms a tight stack of curved π-system, shows broad absorption extended to 700 nm, and exhibits the p-type semiconducting behavior with hole mobility of 4.4×10−3 cm2 V−1 s−1. The [7-7-6]-fused one possesses the highly twisted skeleton to show stable chirality, and exhibits red emission in both solution and solid state. The surgery on trichalcogenasumanene is a promising approach to create polycycles with diverse functionalities.Forceps stat! Performing surgery on hetero-buckybowl trichalcogenasumanene gives the [7-5-6]-fused, [7-6-6]-fused, and [7-7-6]-fused polycycles, and results in the gradual conversion of the molecular geometry from π-bowl to chiral polycycle.
      PubDate: 2017-09-18T01:56:09.839751-05:
      DOI: 10.1002/chem.201703469
       
  • Reduced Graphene Oxide/ Disodium Terephthalate Hybrid as a
           High-performance Anode for Sodium-ion Batteries
    • Authors: Tengfei Cao; Wei Lv, Si-Wei Zhang, Jun Zhang, Qiaowei Lin, Xiangrong Chen, Yanbing He, Fei-Yu Kang, Quan-Hong Yang
      Abstract: As a promising candidate for large scale energy storage systems, sodium-ion batteries (SIBs) are experiencing a rapid development. Organic conjugated carboxylic acids anodes not only have tailorable electrochemical properties but also are easily accessible. However, the low stability and electrical conductivity hamper their practical applications. In this study, disodium terephthalate (Na2TP), the most favorable organic conjugated carboxylic acid anode material for SIB, was proposed to integrate with graphene oxide (GO) by an anti-solvent precipitation process, which ensures the uniform and tight coating of GO on Na2TP surface. GO is electrochemically reduced during the first several cycles of the electrochemical measurement, which buffers the volume change and improves the electrical conductivity of Na2TP, resulting in a better cyclic and rate performance. Only 5 wt% GO incorporating onto Na2TP leads to a reversible capability of 235 mA h g-1 after 100 cycles at a current rate of 0.1 C, which is the best among the state of the art organic anodes for SIBs. The one-step synthesis together with low cost raw materials show a promise for the scalable preparation of anode materials for practical SIBs.
      PubDate: 2017-09-17T21:31:52.247944-05:
      DOI: 10.1002/chem.201703418
       
  • Mechanistic studies on the role of [CuII(CO3)n]2-2n as a water oxidation
           catalyst: Carbonate as a non-innocent ligand
    • Authors: Amir Mizrahi; Dan Meyerstein, Israel Zilbermann, Haya Kornweitz, Eric Maimon, Haim Cohen
      Abstract: Recently it was reported that copper bicarbonate/ carbonate complexes are good electro-catalysts for water oxidation. However, the results did not enable a decision whether the active oxidant is a CuIII or a CuIV complex. Kinetic analysis of pulse radiolysis measurements coupled with DFT calculations point out that CuIII(CO3)n3-2n complexes are the active intermediates in the electrolysis of CuII(CO3)n2-2n solution. The results enable the evaluation of E°((CuIII/II(CO3)n)aq) ~ 1.42 V vs. NHE at pH 8.4. This redox potential is in accord with the electrochemical report. As opposed to literature suggestions for water oxidation, the present results rule out single electron transfer from CuIII(CO3)n3-2n to yield hydroxyl radicals. Significant charge transfer from the coordinated carbonate to Cu(III), results in the formation of C2O62- via a second order reaction of CuIII(CO3)n3-2n. The results point out that carbonate stabilizes transition metal cations at high oxidation states not only as a good sigma donor but also as a non-innocent ligand
      PubDate: 2017-09-16T03:20:36.241523-05:
      DOI: 10.1002/chem.201703742
       
  • Generation of Stable Ruthenium(IV)-Ketimido Complexes via Oxidative
           Addition of Oxime Esters to Ruthenium(II): Reactivity Studies Based on
           Electronic Properties of the Ru-N Bond
    • Authors: Takuya Shimbayashi; Kazuhiro Okamoto, Kouichi Ohe
      Abstract: The reaction of an oxime ester with RuX2(PPh3)3 proceeded smoothly at room temperature to afford a stable Ru(IV)-ketimido complex as an oxidative adduct. The structure of the complex was unambiguously determined by X-ray crystallographic analysis, which showed an almost linear Ru-N-C array. The electronic properties of the nitrogen atom were estimated by density functional theory (DFT) calculations, and results suggested the double-bond character of the Ru-N bond. Kinetic studies combined with consideration of the substituent effect on the oxime ester led to proposing the reaction mechanism involving oxidative addition, which could proceed via N,O-chelate coordination to the Ru center prior to N-O bond cleavage. The obtained Ru-ketimido complex could be transformed into a ruthenacycle by C-H activation via the concerted metalation-deprotonation mechanism in dichloromethane/methanol mixed solvent. The Ru-ketimido complex exhibited another reactivity with a tethered alkyne or alkene moiety to undergo chloroamination of unsaturated C-C bonds, followed by C-H activation, resulting in the formation of an isolated ruthenacycle. Considering the LUMO of an isolated Ru-ketimido complex, the chloroamination should proceed via a synchronous 1,3-dipolar cycloaddition-type mechanism. Insight into the character and reactivity of Ru-ketimido complexes will be helpful for developments in the catalytic transformation of oxime esters.
      PubDate: 2017-09-16T02:22:38.537801-05:
      DOI: 10.1002/chem.201704102
       
  • Metallacrowns as Templates for Diabolo-Like {LnCu8} Complexes with Nearly
           Perfect Square Antiprismatic Geometry
    • Authors: Yan-Zhen Zheng; Guo-Jun Zhou, Tian Han, You-Song Ding, Nicholas F. Chilton
      Abstract: A series of diabolo-like nonanuclear {LnIIICuII8} (Ln = Tb, Dy, Ho, Er, Tm, Yb and Y) clusters in which the LnIII ion is capped by two 8-MC-4 metallacrown ligands to form a nearly ideal square antiprismatic (SAP) coordination geometry with D4d-symmetry have been prepared. Despite the lack of crystallographic symmetry these molecules engender the lanthanide ions with highly axial mJ states. We observe that the axial/equatorial nature of the crystal field in environments close to ideal SAP geometry is very subtle and influenced by the nature of the ligand lone pairs. We find slow magnetic relaxation behaviour for the DyIII, ErIII, TmIII and YbIII analogues, and show that the obtained effective energy barriers are not consistent with excitations on the LnIII ion, suggesting a more nuanced situation.
      PubDate: 2017-09-15T08:20:44.083344-05:
      DOI: 10.1002/chem.201703830
       
  • Co3O4@Co/NCNT Nanostructure Derived from a Dicyanamide Based Metal-Organic
           Framework as Efficient Bi-functional Electrocatalyst for Oxygen Reduction
           and Evolution Reactions
    • Authors: Nivedita Sikdar; Bharathi Konkena, Justus Masa, Wolfgang Schuhmann, Tapas Kumar Maji
      Abstract: There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER) for their potential use in a variety of renewable energy technologies such as regenerative fuel cells and metal-air batteries. Here, we report a bi-functional electrocatalyst derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe)2(N(CN)2)](N(CN)2)(5H2O)}n [Co-MOF-1, bpe = 1,2-bis(4-pyridyl)ethane, N(CN)2− = dicyanamide] under different pyrolysis conditions. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 C) yielded a Co nanoparticles embedded N-doped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H2/Ar atmosphere (at 800 C) and further mild calcination yielded Co3O4@Co core-shell nanoparticles encapsulated N-doped carbon nanotubes (Co3O4@Co/NCNT). Both catalysts show bi-functional activity towards ORR and OER, however, the core-shell Co3O4@Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of -1 mA cm-2 and the OER with a potential of 1.61 V at 10 mA cm-2, which is competitive with the most active bi-functional catalysts reported previously.
      PubDate: 2017-09-15T08:20:38.187831-05:
      DOI: 10.1002/chem.201704211
       
  • Supramolecular Hydro- and Ionogels: a study of their properties and
           antibacterial activity
    • Authors: Carla Rizzo; Rossella Arrigo, Nadka Tz. Dintcheva, Giuseppe Gallo, Francesco Giannici, Renato Noto, Alberto Sutera, Paola Vitale, Francesca D'Anna
      Abstract: Diimidazolium-based organic salts, bearing peptides or aminoacids as anions, have been synthesized and tested for their gelling ability in biocompatible solvents. These low molecular weight salts were successfully used as gelators in phosphate saline buffer and ionic liquids.Then, properties of obtained soft materials were analyzed in terms of melting temperature and gel strength as accounted for by rheological investigation. Gel phase formation was studied using UV-vis and resonance light scattering measurements, whereas morphology of soft materials was analysed using polarized optical microscopy and scanning electron microscopy. To have information about the organization of gelator in the gelatinous matrix, X-ray diffraction measurements were performed both on neat gelators and their gels. Results collected show that properties of gel phases, like thermal stability, self-repairing ability, resistance to flow as well as morphology, are dependent on the anion nature.Furthermore, bioassays revealed that the obtained diimidazolium organic salts possessed antimicrobial activity, against Gram-negative and Gram-positive tester strains. In particular and noteworthy, the diimidazolium organic salts exert a bactericidal capability, which was retained even if they are included in the gel phase. Thus, a novel kind of bioactive soft material was obtained that could be fruitfully employed as a non-covalent coating exerting antibacterial capability.
      PubDate: 2017-09-15T07:27:06.262848-05:
      DOI: 10.1002/chem.201702937
       
  • From Five to Seven - Ring Expansion of Monoazadiene Titanium Complexes by
           Insertion of Aldehydes, Ketones and Nitriles
    • Authors: Manfred Manßen; Christoph Kahrs, Iris Töben, Jens-Henning Bölte, Marc Schmidtmann, Ruediger Beckhaus
      Abstract: Abstract: The ring enlargement reactions at ambient temperatures of non C-terminus substituted monoazabutadiene (η⁴-RN=CHCH=CH₂) titanium complexes 2 are investigated. The insertion of aldehydes/ketones (five examples) and nitriles (four examples) into the Ti-C bonds result in expansion of the five-membered rings to uncommon seven-membered titanacycles 3 and 4 in good yields. These new compounds are fully characterized by NMR spectroscopy and single-crystal X-ray diffraction. In subsequent reactions, the seven-membered ring systems are protolyzed and the released organic fragments are isolated. Whereas the aldehyde/ketone insertion products 3 form substituted δ-amino alcohols 5 after reduction with NaBH₃CN, the nitrile insertion products 4 form substituted pyrroles 6 via cyclisation.
      PubDate: 2017-09-15T06:25:41.792872-05:
      DOI: 10.1002/chem.201703873
       
  • Synthesis of Size-tunable Hollow Polypyrrole Nanostructures and Their
           Assembly into Folate Targeting and pH-responsive Anti-cancer Drug Delivery
           
    • Authors: Jian Chen; Xiufang Li, Yanhua Sun, Yuwei Hu, Yulong Peng, Yimin Li, Gang Yin, Hui Liu, Jiangfeng Xu, Shian Zhong
      Abstract: Chemotherapeutic drugs currently used in clinical settings have a high toxicity, low specificity, and short half-life. Herein, polypyrrole (PPy)-based anticancer drug nanocapsules were prepared by tailoring the nanoparticle size with a template method, controlling drug release by aromatic imine, increasing nanoparticle stability through PEGylation, and improving tumor cell selectivity via folate (FA) mediation. Nanoparticles were characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Flow cytometry and fluorescence imaging were used to verify the cell uptake of the different size nanoparticles. In terms of different size polypyrrole nanoparticles, an optimal functionalized nanoparticle of 180 nm hydrodynamic size was chosen and further used in vitro and in vivo tests. The nanoparticles showed excellent biocompatibility and the drug-loaded nanoparticles exhibited effective tumor cell growth inhibition in vitro. Moreover, the drug-loaded nanoparticles showed a substantially enhanced accumulation in tumor regions and effectively inhibited in vivo tumor growth. Furthermore, the nanoparticles showed reduced doxorubicin (Dox) -induced toxicities and led to no significant side effects in normal organs of tumor bearing mice as measured by body weight shifts and drug distribution evaluation. Overall, the functionalized nanoparticles are a promising nanocarrier candidate for tumor targeting drug delivery.
      PubDate: 2017-09-15T03:20:35.302283-05:
      DOI: 10.1002/chem.201702945
       
  • Contraction of π-Conjugated Rings upon Oxidation from Cyclooctatetraene
           to Benzene via Tropylium Cation
    • Authors: Akira Tamoto; Naoki Aratani, Hiroko Yamada
      Abstract: We have serendipitously discovered the unique transformation of a cyclooctatetraene derivative 1 for the first time in 60 years, to a cycloheptatriene spirolactone 3 upon oxidation. The product 3 could be reversibly interconverted to the aromatic tropylium cation 3H+ by acid/base accompanying drastic spectral changes. The resultant cycloheptatriene could be further converted to benzene upon oxidation. We could characterize all the key structures by X-ray analysis. Eventually, the π-conjugated ring size shrinks from 8 to 7, then finally 6 upon oxidation, directing to the stronger aromatization.
      PubDate: 2017-09-15T02:20:54.633019-05:
      DOI: 10.1002/chem.201704008
       
  • Synergetic Metals on Carbocatalyst Shungite
    • Authors: Martin Pumera
      Abstract: The natural occurring Palaeoproterozoic carbon mineral shungite is a complex raw carbon microporous matrix, loaded with a wide range of elements. Shungite.exhibits disordered and amorphous structure with highly irregular building blocks. Shungite incorporates metals in its structure, typically catalytic elements such Fe and Ni are also present, as well as, the toxic elements Pb and As at mg/g level. We show here that incorporation of the metals in the carbon matrix of shungite leads into synergiustic catalytic effect. We investigate the application of the shungite in energy related electrochemical catalytic reaction, such as the hydrogen evolution reaction (HER), oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). All elements have a synergetic effect, thus contributing for shungite interesting catalytic performance towards a different range of electrochemical reactions, outperforming other tested carbon allotropes, such as carbon black, metal loaded carbon nanotubes, fullerene and glassy carbon. These findings have profound impact on the application of the natural carbon materials for catalysis.
      PubDate: 2017-09-15T01:21:11.039256-05:
      DOI: 10.1002/chem.201703974
       
  • Bimetallic Co-Mn perovskite fluorides as high-stable electrode materials
           for supercapacitors
    • Authors: Wei Shi; Rui Ding, Xudong Li, Qilei Xu, Danfeng Ying, Yongfa Huang, Enhui Liu
      Abstract: Bimetallic Co-Mn perovskite fluorides (KCoxMn1-xF3, denoted as K-Co-Mn-F) with various Co/Mn ratios (1:0, 12:1, 6:1, 3:1, 1:1, 1:3, 0:1) were prepared via one-pot solvothermal strategy and further used as electrode materials for supercapacitors. The optimal K-Co-Mn-F (Co/Mn=6:1) candidate showed size range of 0.1-1 μm and uniform element distribution, exhibiting the light changes in XRD diffraction peaks and XPS binding energy in comparison for the bare K-Co-F and K-Mn-F due to the structural/electronic effects. Owing to the stronger synergistic effect of Co/Mn redox species, the K-Co-Mn-F (Co/Mn=6:1) electrode exhibited superior specific capacity and rate behavior (113-100 C g-1 at 1-16 A g-1) together with excellent cycling stability (118% for 5000 cycles at 8 A g-1), and the AC//K-Co-Mn-F (Co/Mn=6:1) asymmetric capacitor showed superior energy and power densities (8.0-2.4 Wh Kg-1 at 0.14-8.7 KW Kg-1) along with high cycling stability (90% for 10000 cycles at 5 A g-1).
      PubDate: 2017-09-14T22:21:18.186502-05:
      DOI: 10.1002/chem.201703938
       
  • Syntheses and Properties of Tin Containing Conjugated Heterocycles
    • Authors: Sara Urrego-Riveros; Isabel-Maria Ramirez y Medina, Jonas Hoffmann, Anne Heitmann, Anne Staubitz
      Abstract: Heterocycles that contain tin atoms can be aromatic in a similar sense to well-known aromatic compounds such as benzene or thiophene, but such examples are rare. However, due to the low-lying σ*-orbitals of the tin-substituent bond in stannoles, they are capable of σ* - π* conjugation in a way that is exclusive to heavier element containing heterocycles. This makes stannoles very interesting alternatives for purely organic heterocycles in material applications, in which optoelectronic properties are of interest. This concept article will highlight the synthesis, reactivity and physical properties of stannoles and related fluorenostannoles. At first, a brief introduction on different types of tin containing heterocycles is presented, followed by a discussion on different approaches to prepare stannoles, their reactivity and their physical properties. In addition, the first stannole-containing polymer will be reviewed.
      PubDate: 2017-09-14T21:36:50.618172-05:
      DOI: 10.1002/chem.201703533
       
  • Intermolecular C-C Coupling Between 1-Methyl-1,2,3-Triazole and
           2,2'-Bipyridine or 1,10-Phenanthroline at Mo(II) Complexes
    • Authors: Lucia Riera; Julio Pérez, Sergio Fombona, Jesús Díaz
      Abstract: Unsupported 1-methyl-1,2,3-triazole has been coordinated to {Mo(3-methallyl)(CO)2(N-N)} (N-N= 2,2'-bipyridine, bipy; or 1,10-phenanthroline,phen) fragments yielding cationic complexes which can be regarded as metalated triazolium salts. Their reactivity towards a strong base led to the deprotonation of the C5-H group of the triazole moiety, followed by an intermolecular nucleophilic attack to the ortho CH group of a bipy or phen ligand affording cyclic, bimetallic dearomatized C-C coupling products. The reaction of the neutral bipy derivative with an acid led to the formation of dihydropyridyl units by protonation of a CH group of the dearomatized rings, the dimeric nature of complexes being mantained upon protonation.
      PubDate: 2017-09-14T12:15:27.907896-05:
      DOI: 10.1002/chem.201703524
       
  • Bis-Copper(II)/π-Radical Multi-Heterospin System with Non-innocent Doubly
           N-Confused Dioxohexaphyrin(1.1.1.1.1.0) Ligand
    • Authors: Hiroyuki Furuta; Kazuhisa Yamasumi, Keiichi Nishimura, Yutaka Hisamune, Yusuke Nagae, Tomoki Uchiyama, Kazutaka Kamitani, Tomoyasu Hirai, Maiko Nishibori, Shigeki Mori, Satoru Karasawa, Tatsuhisa Kato, Ko Furukawa, Masatoshi Ishida
      Abstract: A contracted doubly N-confused dioxohexaphyrin(1.1.1.1.1.0) complex consisting of two paramagnetic copper metals and open-shell π radical ligand was synthesized as a new multi-heterospin motif. X-ray spectroscopy supported the divalent character of the inner copper centers, and electron paramagnetic resonance and magnetometric studies suggested the presence of unpaired d electrons strongly antiferromagnetically coupled with π-radical delocalized on the macrocycle. The 25π non-innocent dioxohexaphyrin ligand allowed the facile interconversion between antiaromatic 24π and aromatic 26π species, respectively, upon redox reactions.
      PubDate: 2017-09-14T10:20:52.500131-05:
      DOI: 10.1002/chem.201704321
       
  • Synthesis of RNA containing 5-hydroxymethyl-, 5-formyl-, and
           5-carboxycytidine
    • Authors: Iacovos N Michaelides; Nobuhiro Tago, Bastien Viverge, Thomas Carell
      Abstract: 5-Hydroxymethyl-, 5-formyl-, and 5-carboxycytidine are new epigenetic bases (hmdC, fdC, cadC) that were recently discovered in the DNA of higher eukaryotes. The same bases (hmC, fC and caC) have now also been detected in mammalian RNA with a high abundance in mRNA. While for the DNA bases phosphoramidites (PAs) are available that allow the synthesis of xdC-containing oligonucleotides for deeper biological studies, the corresponding RNA PAs for fC and caC have not yet been disclosed. Here we report novel RNA PAs for hmC, fC and caC that can be used in routine RNA synthesis. The new building blocks are compatible with the canonical PAs and also with themselves, which enables even the synthesis of RNA strands containing all three of these bases. The study will pave the way for detailed physical, biochemical and biological studies to unravel the function of these non-canonical modifications in RNA.
      PubDate: 2017-09-14T07:21:47.88104-05:0
      DOI: 10.1002/chem.201704216
       
  • Total Synthesis of Skyllamycins A-C
    • Authors: Richard James Payne; Andrew Giltrap, Jake Haeckl, Kenji Kurita, Roger Linington
      Abstract: The skyllamycins are a family of highly functionalized non-ribosomal cyclic depsipeptide natural products which contain the extremely rare α OH-glycine functionality. Herein we report the first total synthesis of skyllamycins A-C, together with the biofilm inhibitory activity of the natural products. Linear peptide precursors for each natural product were prepared through an efficient solid-phase route incorporating a number of synthetic modified amino acids. A novel macrocyclization step between a C-terminal amide and a N-terminal glyoxylamide moiety served as a key transformation to install the unique α OH-glycine unit and generate the natural products in the final step of the synthesis.
      PubDate: 2017-09-14T07:21:00.37372-05:0
      DOI: 10.1002/chem.201704277
       
  • Gemcitabine, Pyrrologemcitabine and 2'-Fluoro- 2'-Deoxycytidines:
           Synthesis, Physical Properties and Impact of Sugar Fluorination on Silver
           Ion Mediated Base Pairing
    • Authors: Frank Seela; Xiurong Guo, Peter Leonard, Sachin Asaram Ingale
      Abstract: The stability of silver mediated "dC-dC" base pairs relies not only on the structure of the nucleobase but also is sensitive to structural modification on the sugar moiety. 2'-Fluorinated 2'-deoxycytidines with fluorine atoms in the arabino (up) and the ribo (down) configuration, as well as with geminal fluorine substitution (anticancer drug gemcitabine) and the novel fluorescent phenylpyrrolo-gemcitabine (phPyrGem) were synthesized. All nucleosides display the recognition face of naturally occurring 2'-deoxycytidine. Nucleosides were converted into phosphoramidites and incorporated in 12-mer oligonucleotides by solid-phase synthesis. Addition of silver ions to DNA duplexes with a fluorine modified "dC-dC" pair near central position led to significant duplex stabilization. The stability increase was higher for duplexes with fluorinated sugar residues than those with the unchanged 2'-deoxyribose moiety. Similar observations were made on "dC-dT" pairs and to a minor extend on the "dC-dA" pairs. The increase of silver ion mediated base pair stability was reversed by annulation of a pyrrole ring to the cytosine moiety as shown for 2'-fluorinated phPyrGem compared to phenylpyrrolo-dC (phPyrdC). The phenomenon results from stereoelectronic effects induced by fluoro substitution which are transmitted from the sugar moiety to the silver ion mediated base pairs. This depends on the number of fluorine substituents, their configuration and the structure of the nucleobase.
      PubDate: 2017-09-14T05:21:00.064959-05:
      DOI: 10.1002/chem.201703427
       
  • Optical Limiting Properties of 3,5-Dithienylenevinylene BODIPY Dyes at
           532 nm
    • Authors: Jessica Harris; Lizhi Gai, Gugu Kubheka, John Mack, Tebello Nyokong, Zhen Shen
      Abstract: The optical limiting properties of a series of near infrared absorbing 3,5-dithienylenevinylene BODIPY (boron-dipyrromethene) dyes (1–3) that contain donor and acceptor moieties in their π-conjugation systems were studied by using the z-scan technique at 532 nm in the nanosecond pulse range. A strong reverse saturable absorption response was observed when the compounds are embedded into poly(bisphenol carbonate A) polymer thin films, which demonstrates that BODIPY dyes with this type of structure are suitable for use in optical limiting applications.BODIPYs as optical limiters: The optical limiting properties of a series of 3,5-dithienylenevinylene BODIPY dyes with D-π-A type structures were studied by using the z-scan technique at 532 nm in the nanosecond pulse range. An unusually strong reverse saturable absorption response was observed when the compounds are embedded in poly(bisphenol carbonate A) polymer thin films.
      PubDate: 2017-09-14T05:07:48.589473-05:
      DOI: 10.1002/chem.201702503
       
  • Dual-Nuclide Radiopharmaceuticals for Positron Emission Tomography Based
           Dosimetry in Radiotherapy
    • Authors: Alexander Wurzer; Christof Seidl, Alfred Morgenstern, Frank Bruchertseifer, Markus Schwaiger, Hans-Jürgen Wester, Johannes Notni
      Abstract: Improvement of the accuracy of dosimetry in radionuclide therapy has the potential to increase patient safety and therapeutic outcomes. Although positron emission tomography (PET) is ideally suited for acquisition of dosimetric data because PET is inherently quantitative and offers high sensitivity and spatial resolution, it is not directly applicable for this purpose because common therapeutic radionuclides lack the necessary positron emission. This work reports on the synthesis of dual-nuclide labeled radiopharmaceuticals with therapeutic and PET functionality, which are based on common and widely available metal radionuclides. Dual-chelator conjugates, featuring interlinked cyclen- and triazacyclononane-based polyphosphinates DOTPI and TRAP, allow for strictly regioselective complexation of therapeutic (e.g., 177Lu, 90Y, or 213Bi) and PET (e.g., 68Ga) radiometals in the same molecular framework by exploiting the orthogonal metal ion selectivity of these chelators (DOTPI: large cations, such as lanthanide(III) ions; TRAP: small trivalent ions, such as GaIII). Such DOTPI–TRAP conjugates were decorated with 3 Gly-urea-Lys (KuE) motifs for targeting prostate-specific membrane antigen (PSMA), employing Cu-catalyzed (CuAAC) as well as strain-promoted (SPAAC) click chemistry. These were labeled with 177Lu or 213Bi and 68Ga and used for in vivo imaging of LNCaP (human prostate carcinoma) tumor xenografts in SCID mice by PET, thus proving practical applicability of the concept.Take two: Dual-nuclide labeled radiopharmaceuticals with therapeutic and PET functionality, derived from common and widely available metal radionuclides, enable a precise PET-based dosimetry for improvement of individual therapeutic outcome and increased patient safety in molecular radiotherapy.
      PubDate: 2017-09-14T05:07:42.172688-05:
      DOI: 10.1002/chem.201702335
       
  • Synthesis of Ladder Polymers: Developments, Challenges, and Opportunities
    • Authors: Yew Chin Teo; Holden W. H. Lai, Yan Xia
      Abstract: Ladder polymers are unique in that their backbones consist of fused rings with adjacent rings having two or more atoms in common. The restriction of bond rotations in rigid ladder polymers greatly limits their conformational freedom, leading to many intriguing and unique properties. As a non-traditional type of polymers, rigid ladder polymers are of great fundamental interest and technical importance as advanced materials for applications such as membrane gas separation and organic electronics. Ladder polymers can be divided into non-conjugated (with kinked conformations) and conjugated (with planar conformations) structures. Their synthesis can be broadly classified into two general strategies: direct ladder polymerization, and zipping of a linear precursor polymer. This Concept article outlines the historical development of ladder polymers and the chemical strategies used for their synthesis; highlights the challenges associated with their synthesis and characterization, and presents opportunities and outlooks for this unique and intriguing type of polymers.Climbing ladders: Rigid ladder polymers represent an uncommon but intriguing type of polymer architecture consisting of continuously fused rings in their backbones with highly restricted bond rotations. Their unique macromolecular structures lead to unusual and interesting properties. We highlight the synthetic approaches towards non-conjugated and conjugated ladder polymers to elucidate their historical development. We also present challenges and perspectives on the synthesis and understanding of such unconventional rigid polymers.
      PubDate: 2017-09-14T05:07:24.105443-05:
      DOI: 10.1002/chem.201702219
       
  • Selecting Chiral BINOL-Derived Phosphoric Acid Catalysts: General Model To
           Identify Steric Features Essential for Enantioselectivity
    • Authors: Jolene P. Reid; Jonathan M. Goodman
      Abstract: Choosing the optimal catalyst for a new transformation is challenging because the ideal molecular requirements of the catalyst for one reaction do not always simply translate to another. Large groups at the 3,3′ positions of the binaphthol rings are important for efficient stereoinduction but if they are too large this can lead to unusual or poor results. By applying a quantitative steric assessment of the substituents at the 3,3′ positions of the binaphthol ring, we have systematically studied the effect of modulating this group on enantioselectivity for a wide range of reactions involving imines, and verified this analysis using ONIOM calculations. We have shown that in most reactions, the stereochemical outcome depends on both proximal and remote sterics. Summarising detailed calculations into a simple qualitative model identifies and explains the steric features required for high selectivity. This model is consistent with seventy seven papers reporting reactions (over 1000 transformations in total), and provides a straightforward decision tree for selecting the best catalyst.How to choose a cat: A general model to guide the best choice of phosphoric acid catalyst for nucleophilic addition to imines has been developed. These rules are consistent for seventy-seven papers containing over 1000 examples, explaining enantioselectivity trends with varying 3,3′ group and correctively identifying steric features essential for efficient stereoinduction.
      PubDate: 2017-09-14T05:02:57.34432-05:0
      DOI: 10.1002/chem.201702019
       
  • MnAl Layered Double Hydroxide Nanoparticles as a Dual-Functional Platform
           for Magnetic Resonance Imaging and siRNA Delivery
    • Authors: Huali Zuo; Weiyu Chen, Bei Li, Kewei Xu, Helen Cooper, Zi Gu, Zhi Ping Xu
      Abstract: Multifunctional nanoparticles for cancer theranosis have been widely explored for effective cancer detection and therapy. In this work, dually functionalised manganese-based layered double hydroxide nanoparticles (Mn-LDH) were examined as an effective anticancer drug/gene delivery system and for T1-weighted magnetic resonance imaging (MRI) in brain cancer theranostics. Such Mn-LDH have been shown to accommodate dsDNA/siRNAs and efficiently deliver them to Neuro-2a cells (N2a). Mn-LDH have also shown high biocompatibility with low cytotoxicity. Importantly, the cell-death siRNA (CD-siRNA) delivered with Mn-LDH more efficiently kills brain cancer cells than the free CD-siRNA. Moreover, Mn-LDH can act as excellent contrast agents for MRI, with an r1 value of 4.47 mm−1 s−1, which is even higher than that of commercial contrast agents based on Gd complexes (r1=3.4 mm−1 s−1). Altogether, the high delivery efficacy and MRI contrast capability make dual-functional Mn-LDH potential bimodal agents for simultaneous cancer diagnosis and therapy.Multifunctional nanoparticles: Dual-functional manganese-based layered double hydroxide nanoparticles (Mn-LDH) were fabricated by a co-precipitation method. Their pH-sensitive behaviour significantly enhanced T1-weighted magnetic resonance imaging, which is highly beneficial for the detection of tumour cells and tissues. Anticancer therapeutics carried by Mn-LDH more efficiently killed cancer cells than their free counterparts (see figure).
      PubDate: 2017-09-14T04:27:48.202145-05:
      DOI: 10.1002/chem.201702835
       
  • Nitrene Radical Intermediates in Catalytic Synthesis
    • Authors: Petrus F. Kuijpers; Jarl Ivar van der Vlugt, Sven Schneider, Bas de Bruin
      Abstract: Nitrene radical complexes are reactive intermediates with discrete spin density at the nitrogen-atom of the nitrene moiety. These species have become important intermediates for organic synthesis, being invoked in a broad range of C−H functionalization and aziridination reactions. Nitrene radical complexes have intriguing electronic structures, and are best described as one-electron reduced Fischer type nitrenes. They can be generated by intramolecular single electron transfer to the “redox non-innocent” nitrene moiety at the metal. Nitrene radicals generated at open-shell cobalt(II) have thus far received most attention in terms of spectroscopic characterization, reactivity screening, catalytic nitrene-transfer reactions and (computational and experimental) mechanistic studies, but some interesting iron and precious metal catalysts have also been employed in related reactions involving nitrene radicals. In some cases, redox-active ligands are used to facilitate intramolecular single electron transfer from the complex to the nitrene moiety. Organic azides are among the most attractive nitrene precursors in this field, typically requiring pre-activated organic azides (e.g. RSO2N3, (RO)2P(=O)N3, ROC(=O)N3 and alike) to achieve efficient and selective catalysis. Challenging, non-activated aliphatic organic azides were recently added to the palette of reagents useful in synthetically relevant reactions proceeding via nitrene radical intermediates. This concept article describes the electronic structure of nitrene radical complexes, emphasizes on their usefulness in the catalytic synthesis of various organic products, and highlights the important developments in the field.Nitrene radical complexes are reactive intermediates with discrete spin density at the nitrogen atom of the nitrene moiety. They have become important intermediates for organic synthesis. This concept article describes their electronic structure, emphasizes on their usefulness in the catalytic synthesis of various organic products, and highlights the important developments in the field.
      PubDate: 2017-09-14T04:26:10.010329-05:
      DOI: 10.1002/chem.201702537
       
  • One-Pot Self-Assembly of Peptide-Based Cage-Type Nanostructures Using
           Orthogonal Ligations
    • Authors: Eline Bartolami; Jérémie Knoops, Yannick Bessin, Mathieu Fossépré, Joseph Chamieh, Pascal Dumy, Mathieu Surin, Sébastien Ulrich
      Abstract: The designed arrangement of biomolecular entities within monodisperse nanostructures is an important challenge toward functional biomaterials. We report herein a method for the formation of water-soluble peptide-based cages using orthogonal ligation reactions—acylhydrazone condensation and thiol–maleimide addition. The results show that using preorganized cyclic peptides and heterobifunctional spacers as building blocks and a set of orthogonal and chemoselective ligation reactions enable cage formation in one pot from six components and through eight reactions. Molecular modelling simulations reveal the structural dynamics of these structures. Finally, we exploited the reactional dynamics of the acylhydrazone by demonstrating the controlled dissociation of the cage through directed component exchange.All in one pot! The use of orthogonal and chemoselective ligation reactions enables the self-assembly (six components, eight reactions in one-pot) of peptide-based cage nanostructures starting from preorganized cyclic peptides and heterobifunctional spacers.
      PubDate: 2017-09-14T04:23:39.604497-05:
      DOI: 10.1002/chem.201702974
       
  • Targeted Delivery of a Mannose-Conjugated BODIPY Photosensitizer by
           Nanomicelles for Photodynamic Breast Cancer Therapy
    • Authors: Quan Zhang; Ying Cai, Qiu-Yan Li, Lin-Na Hao, Zheng Ma, Xiao-Jun Wang, Jian Yin
      Abstract: The targeted delivery of a photosensitizer (PS) with appropriate carriers represents an attractive means of selectively delivering cargo to target tissues or subcellular compartments for photodynamic therapy (PDT). Herein, a three-arm distyryl BODIPY derivative conjugated with mannose units (denoted by BTM) that can co-assemble with Tween 80 to form nanomicelles (BTM-NMs) for targeted PDT is reported. MDA-MB-231 breast cancer cells recognized and specifically internalized BTM-NMs via mannose-receptor-mediated endocytosis with preferential accumulation in the lysosomes. These NMs could disassemble in cell lysosomes and subsequently induce highly efficient singlet oxygen (1O2) generation upon light irradiation. 1O2 disrupted the lysosomal membrane and promoted the escape of BTM from the lysosome into the cytoplasm, thereby resulting in the efficient and selective killing of cancer cells through PDT. This study may provide a new strategy for designing targeted PDT systems to fight cancer.Therapeutic micelles: Breast cancer cells recognize and internalize nanomicelles co-assembled from a mannose-conjugated BODIPY photosensitizer and Tween 80. These nanomicelles exhibit excellent targeted delivery of the photosensitizer that not only leads to selective cancer cell death but also minimizes damage to normal cells after 665-nm LED light irradiation.
      PubDate: 2017-09-14T04:23:27.175253-05:
      DOI: 10.1002/chem.201702935
       
  • Excitonically Coupled States in Crystalline Coordination Networks
    • Authors: Ritesh Haldar; Antoine Mazel, Reetu Joseph, Michael Adams, Ian A. Howard, Bryce S. Richards, Manuel Tsotsalas, Engelbert Redel, Stéphane Diring, Fabrice Odobel, Christof Wöll
      Abstract: When chromophores are brought into close proximity, noncovalent interactions (π–π/CH–π) can lead to the formation of excitonically coupled states, which bestow new photophysical properties upon the aggregates. Because the properties of the new states not only depend on the strength of intermolecular interactions, but also on the relative orientation, supramolecular assemblies, where these parameters can be varied in a deliberate fashion, provide novel possibilities for the control of photophysical properties. This work reports that core-substituted naphthalene diimides (cNDIs) can be incorporated into surface-mounted metal– organic structures/frameworks (SURMOFs) to yield optical properties strikingly different from conventional aggregates of such molecules, for example, formed in solution or by crystallization. Organic linkers are used, based on cNDIs, well-known organic chromophores with numerous applications in different optoelectronic devices, to fabricate MOF thin films on transparent substrates. A thorough characterization of the properties of these highly ordered chromophoric assemblies reveals the presence of non-emissive excited states in the crystalline material. Structural modulations provide further insights into the nature of the coupling that gives rise to an excited-state energy level in the periodic structure.Periodically arranged core-substituted naphthalene diimides in a Zn-SURMOF-2 structure exhibit excitonically coupled states.
      PubDate: 2017-09-14T04:23:12.076483-05:
      DOI: 10.1002/chem.201702968
       
  • From Anilines to Quinolines: Iodide and Silver-Mediated Aerobic C-H/C-H
           Oxidative Annulation/Aromatization
    • Authors: Jiwei Wu; Zhixiong Liao, Dong Liu, Chien-Wei Chiang, Zheng Li, Zhonghao Zhou, Hong Yi, Xu Zhang, Zixin Deng, Aiwen Lei
      Abstract: Quinolines synthesis from easily accessible raw materials,such as anilines, is valuable and meaningful task. Herein, wecommunicate an iodide and silver-mediated C-H/C-H oxidativeannulation/aromatization between anilines and allyl alcohols. Thisprotocol provides a direct route to the synthesis of quinolinesderivatives f rom inexpensive commodit ies. Various kinds of anilines,even heterocyclic anilines, were shown to be workable substrates,generating the corresponding multi-substituted quinolines in goodyields.
      PubDate: 2017-09-14T04:22:45.48677-05:0
      DOI: 10.1002/chem.201703218
       
  • Magnetic Control of MOF Crystal Orientation and Alignment
    • Authors: Fei Cheng; Ellis S Marshall, Adam J. Young, Peter J. Robinson, Jean-Sebastien G. Bouillard, Ali M. Adawi, Nicolaas A. Vermeulen, Omar K. Farha, Michael R. Reithofer, Jia Min Chin
      Abstract: Most MOFs possess anisotropic properties, the full exploitation of which necessitates a general strategy for the controllable orientation of such MOF crystals. Current methods largely rely upon layer-by-layer MOF epitaxy or tuning of MOF crystal growth on appropriate substrates, yielding MOFs with fixed crystal orientations. Here, the dynamic magnetic alignment of different MOF crystals (NH2-MIL-53(Al) and NU-1000) is shown. The MOFs were magnetized by electrostatic adsorption of iron oxide nanoparticles, dispersed in curable polymer resins (Formlabs 1+ clear resin / Sylgard® 184), magnetically oriented and fixed by resin curing. The importance of crystal orientation on MOF functionality was demonstrated whereby magnetically aligned NU-1000/Sylgard® 184 composite was excited with linearly polarized 405 nm light, affording an anisotropic fluorescence response dependent on the polarization angle of the excitation beam relative to NU-1000 crystal orientation.
      PubDate: 2017-09-14T04:22:34.192837-05:
      DOI: 10.1002/chem.201703812
       
  • Phosphorus and Fluorine Co-doping Induced Enhancement of Oxygen Evolution
           Reaction in Bimetallic Nitride Nanorods Arrays: Ionic Liquid-Driven and
           Mechanism Clarification
    • Authors: Xue Bai; Qin Wang, Feng He, Zhi-jian Wu, Guangran Xu, Keke Huang, Yunkun Ning, Jun Zhang
      Abstract: Electrocatalytic splitting of water is becoming increasingly crucial for renewable energy and device technologies. As one of the most important half-reactions for water splitting reaction, oxygen evolution reaction (OER) is a kinetically sluggish process that will greatly affect the energy conversion efficiency. Therefore, exploring a highly efficient, and durable catalyst to boost the OER is of great urgency. In this work, we develop a facile strategy for synthesis of well-defined phosphorus, fluorine co-doped Ni1.5Co1.5N hybrids nanorods (HNs) by using ionic liquids (1-butyl-3-methylimidazolium hexafluorophosphate, ILs). In comparison to the IrO2 catalyst, the as-obtained PF/Ni1.5Co1.5N HNs manifests a low overpotential of 280 mV at 10 mA cm-2, Tafel slope of 66.1 mV dec-1, and excellent durability in 1.0 M KOH solution. Furthermore, the iR-corrected electrochemical results indicate it could achieve a current density of 100 mA cm-2 at an overpotential of 350 mV. The combination of cobalt and nickel elements, 1D mesoporous nanostructure, heteroatoms incorporation, and ionic liquids assisted nitridation, which result in faster charge transfer capability and more active surface sites, can facilitate the release of oxygen bubbles from the catalyst surface. Our findings confirm that surface heteroatoms doping in bimetallic nitrides could serve as a new class of OER catalyst with excellent catalytic activity.
      PubDate: 2017-09-14T04:22:08.286468-05:
      DOI: 10.1002/chem.201703712
       
  • Proof of Concept Studies Directed Towards Designed Molecular Wires:
           Property-Driven Synthesis of Air and Moisture-Stable Polystannanes
    • Authors: Jeffrey Pau; Alan J. Lough, R. Stephen Wylie, Robert A. Gossage, Daniel A. Foucher
      Abstract: Polystannanes with azobenzene moieties designed to protect the Sn–Sn backbone from light- and moisture-induced degradation are described. The azo-stannyl precursor 3 (70 %) is converted in good yields (88–91 %) to the mono- (4), and dichlorostannanes (5), by sequential chlorination, followed by further reduction of 5 to the dihydride (6) using NaBH4 (78 %). All stannanes were characterised by NMR (1H, 13C, 119Sn) spectroscopy and HRMS; in addition, 3, 4 and 5 were structurally elucidated using X-ray diffraction analysis. Metal-free dehydrocoupling of 6 at RT leads exclusively to homopolymer (7-i) displaying an initial solution 119Sn NMR signal (δ=−196 ppm) that migrates to −235 ppm after 10 days (7-f). In contrast, metal-catalyzed dehydrocoupling of 6 in toluene at RT leads directly 7-f. Random co-polymers formed from 6 and (nBu)2SnH2 at 4:1 (8 a) and 1:1 (8 b) ratios were compared to the alternating polystannane (9) prepared by the reaction of 6 with (nBu)2Sn(NEt2)2. DFT calculations of 3–6 indicate that hypercoordination at Sn is influenced by substituents and by solvation. Homopolymer 7 was found to have unprecedented moisture and light stability in the solid state for>6 months.Stan′s the man! Polystannanes with azobenzene ligands demonstrate improved moisture and light stability.
      PubDate: 2017-09-14T04:19:51.565838-05:
      DOI: 10.1002/chem.201703453
       
  • Tuning the pKa of Fluorescent Rhodamine pH Probes through Substituent
           Effects
    • Authors: Sarah G. Stratton; Grace H. Taumoefolau, Grace E. Purnell, Mona Rasooly, William L. Czaplyski, Elizabeth J. Harbron
      Abstract: Rhodamine spirolactams (RSLs) have recently emerged as popular fluorescent pH probes due to their fluorescence turn-on capability and ease of functionalization at the spirolactam nitrogen. Design of RSLs is often driven by biological targeting or compatibility concerns, rather than the pH sensitivity of the probe, and the relationship between RSL structure and pKa is not well understood. To elucidate the relationship between pKa values and the properties of substituents attached to the spirolactam nitrogen, a series of 19 aniline-derived RSLs is presented. RSLs derived from di-ortho-substituted anilines exhibit pKa tunability across the moderately acidic region (ca. pH 4–6). Evaluation of pKa data using the Fujita–Nishioka model for ortho substituent effects reveals that both steric and electronic substituent properties influence RSL pH responsiveness, with pKa values increasing as substituent size and electron withdrawing character increase. These trends are attributed to changes in the RSL structure induced by large substituents, and to electronic influences on the protonated spirocyclic reaction intermediate. To demonstrate the practical applicability of these probes in completely aqueous environments, RSL-doped conjugated polymer nanoparticles that exhibit a ratiometric fluorescence response to changing pH levels are presented.Deformed dye: The quest for a structure-pKa relationship for fluorescent rhodamine pH probes yields a tale of steric and electronic substituent effects, linear free energy relationships, a crystal structure, and ratiometric fluorescent pH sensing in water with doped conjugated polymer nanoparticles. The pKa values of aniline-derived rhodamine spirolactams can be increased by 2 pH units by employing large substituents to deform the xanthene ring system and electron withdrawing ones to destabilize a key intermediate.
      PubDate: 2017-09-14T04:19:03.190536-05:
      DOI: 10.1002/chem.201703176
       
  • Anti-Electrostatic CH–Ion Bonding in Decorated Graphanes
    • Authors: Martin Novák; Radek Marek, Cina Foroutan-Nejad
      Abstract: State-of-the-art computations combined with Ziegler–Rauk energy decomposition analyses are employed to introduce a new class of anti-electrostatic ion–σ bonds with considerable stability and a substantial contribution from charge transfer and dispersion between ions and finite-size functionalized graphane flakes, G-XYs. G-XYs have diverse electric multipolar moments that are comparable with those of newly synthesized all-cis-hexa-halocyclohexanes. The strong, long-range electrostatic and Pauli repulsions between some G-XYs and certain ions induce a gas-phase energy barrier to the physisorption of ions on the surface of G-XYs. However, the repulsive interactions can be overbalanced by the strong orbital interactions operating in the formation of ion–σ complexes at short range, leading to covalent-type intermolecular bonds as strong as −34 kcal mol−1.Ion–σ interactions: A new class of anti-electrostatic ion–σ bonds between ions and functionalized graphane flakes, G-XYs, is introduced. The strong, long-range electrostatic and Pauli repulsions can be overbalanced by strong orbital interactions (see figure), leading to ion–σ complexes with covalent-type intermolecular bonds as strong as −34 kcal mol−1.
      PubDate: 2017-09-14T04:18:55.450059-05:
      DOI: 10.1002/chem.201703459
       
  • Coordination Behavior of a Planar Chiral Cyclic (Amino)(Ferrocenyl)Carbene
           Ligand in Iridium Complexes
    • Authors: Yuta Shikata; Risa Yasue, Kazuhiro Yoshida
      Abstract: Iridium complexes bearing a new type of chiral carbene ligand, cyclic (amino)(ferrocenyl)carbene (CAFeC), were prepared. The complexes, which are quite stable in air and moisture, were fully characterized by NMR spectroscopy and X-ray diffraction analysis. The NMR spectra of the dicarbonyl complex [IrCl(CO)2(CAFeC)] showed signals for two isomers in solution, which were assigned to diastereomeric rotamers arising from the rotation of the chiral CAFeC ligand around the axes of the Ir−Ccarbene bond. IR spectroscopy of the dicarbonyl complex revealed that the donor strength of CAFeC is much higher than those of classic N-heterocyclic carbenes (NHCs) and comparable to those of cyclic amino alkyl carbenes (CAACs).Cafecaesque carbenes: Air- and moisture-stable iridium complexes bearing a new type of chiral carbene ligand, cyclic (amino)(ferrocenyl)carbene (CAFeC), were prepared and fully characterized by NMR spectroscopy and X-ray diffraction analysis. The NMR spectra of the dicarbonyl complex [IrCl(CO)2(CAFeC)] displayed signals for two isomers in solution, which were assigned to diastereomeric rotamers arising from the rotation of the chiral CAFeC ligand around the axes of the Ir−Ccarbene bond. IR spectroscopy of the dicarbonyl complex revealed that the donor strength of CAFeC is much higher than for classic N-heterocyclic carbenes (NHCs) and comparable to cyclic (amino)(alkyl)carbenes (CAACs).
      PubDate: 2017-09-14T04:15:51.972871-05:
      DOI: 10.1002/chem.201703467
       
  • Rotationally Active Ligands: Dialing-Up Multiple Interlocked
           Co-Conformations for Silver(I) Coordination
    • Authors: Giorgio Baggi; Stephen J. Loeb
      Abstract: A novel [2]rotaxane ligand has been prepared that contains a bidentate N,N′-chelate as part of a rigid, H-shaped axle and a 24-membered crown ether macrocycle containing six ether O-atoms and a trans olefinic group as the wheel. This unique interlocked connectivity allows access to a number of different donor sets, which are shown to be capable of binding AgI metal ions.Rotaxane roulette: Coordination of AgI ions to the flexible and rotationally active MIM (mechanically interlocked molecule) ligand Ltrans can be likened to playing roulette; the silver ball (AgI ion) tossed at a spinning ([2]rotaxane) wheel will eventually settle into a (binding) pocket, but it may not be the one you bet on!
      PubDate: 2017-09-14T04:15:38.113412-05:
      DOI: 10.1002/chem.201703485
       
  • An Efficient Route to Highly Substituted Indoles via
           Tetrahydroindol-4(5H)-one Intermediates Produced by Ring-Opening
           Cyclization of Spirocyclopropanes with Amines
    • Authors: Hisanori Nambu; Wataru Hirota, Masahiro Fukumoto, Takafumi Tamura, Takayuki Yakura
      Abstract: An efficient method for the synthesis of highly substituted indoles via tetrahydroindol-4(5H)-one intermediates, prepared by ring-opening cyclization of spirocyclopropanes with amines, was developed. Syntheses of 4-, 5-, 6- or 7-substituted indoles were accomplished by regioselective functionalizations of the intermediates and subsequent oxidation. Furthermore, 4,5,6,7-tetrasubstituted indoles were synthesized by using these regioselective functionalizations. More information can be found in the Full Paper by H. Nambu, T. Yakura et al. (
      DOI : 10.1002/chem.201702622).
      PubDate: 2017-09-14T04:15:25.783326-05:
       
  • On the Mechanism of Connecting Deltahedral Zintl Clusters via Conjugated
           Buta-1,3-dien-1,4-diyl Functionalities: Synthesis and Structure of
           [Ge9-CH=CH-CH=CH-Ge9]6-
    • Authors: Thomas Friedrich Fässler; Manuel Bentlohner, Sabine Frischhut
      Abstract: We report on the synthesis and structure as well as on the mechanism of formation of the [Ge9-CH=CH-CH=CH-Ge9]6- unit. As shown by in situ NMR spectroscopy (1H, COSY, HSQC, HMBC), both (1Z,3Z)- and (1E,3Z)-[Ge9-CH=CH-CH=CH-Ge9]6- are formed during the reaction of a mixture of 1,4-bis(trimethylsilyl)butadiyne and A4Ge9 (A = K, Rb) with ethylenediamine. However, upon layering of the obtained solution with 222-crypt/toluene (222-crypt = 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo-[8.8.8]hexacosan) only the (1Z,3Z)-isomer crystallizes as {[A(222-crypt)]6[(1Z,3Z)-(Ge9-CH=CH-CH=CH-Ge9)]}·(tol)2·(en)2 (A = K, Rb) salts. Single crystals of these salts were characterized by X-ray structure analysis and Raman spectroscopy, indicating the presence of three superimposed conformers of (1Z,3Z)-[Ge9-CH=CH-CH=CH-Ge9]6-, which show different orientations of the cluster units with respect to the planar (1Z,3Z)-buta-1,3-dien-1,4-diyl linker unit.
      PubDate: 2017-09-14T01:50:16.027929-05:
      DOI: 10.1002/chem.201703494
       
  • The Phosphinoboration of N-Heterocycles
    • Authors: Stephen J. Geier; Christopher M. Vogels, Niall R. Mellonie, Erika N. Daley, Andreas Decken, Simon Doherty, Stephen A. Westcott
      Abstract: The addition of phosphinoboronate ester Ph2PBpin (pin=1,2-O2C2Me4) (1) to a number of different N-heterocycles has been investigated. Reaction of 1 with pyridine resulted in highly selective formation of the corresponding 1,4-addition product, with addition of the electron-deficient Bpin group to the pyridine nitrogen atom and the phosphido group to the para carbon atom. Conversely, reactions of para-substituted pyridine derivatives occurred predominately to afford 1,2-addition products while quinoline reacted to afford the 1,2-adduct which ultimately isomerized to afford the corresponding 1,4-addition product. Preliminary computational studies have been undertaken to explore possible pathways for these transformations including transfer of the PPh2− anion from [B(PPh2)2pin]− to the 4-position of a borenium/boronium activated pyridine and concerted pathways for 1,2-addition via intramolecular nucleophilic attack of PPh2 at C2 of a Ph2PBpin-coordinated pyridine via a four-centered transition state and intramolecular transfer of PPh2 to the 2-position of a boron-activated pyridine in a phosphido-bridged dimer involving a six-centered transition state.Do you like Piña colato' The addition of Ph2PBpin (1, pin=pinacolato, O2C2Me4) to a variety of pyridine derivatives and benzofused N-heterocycles results in 1,2- and/or 1,4-addition depending upon the nature of the substrate. Borenium/boronium cation intermediates are implicated in reactions using polar solvents that afford 1,4-addition products.
      PubDate: 2017-09-13T13:11:54.685736-05:
      DOI: 10.1002/chem.201702203
       
  • Mechanistic Insight into the Binding of Multivalent Pyrrolidines to
           α-Mannosidases
    • Authors: Stefania Mirabella; Giampiero D'Adamio, Camilla Matassini, Andrea Goti, Sandra Delgado, Ana Gimeno, Inmaculada Robina, Antonio J. Moreno-Vargas, Sergej Šesták, Jesús Jiménez-Barbero, Francesca Cardona
      Abstract: Novel pyrrolidine-based multivalent iminosugars, synthesized by a CuAAC approach, have shown remarkable multivalent effects towards jack bean α-mannosidase and a Golgi α-mannosidase from Drosophila melanogaster, as well as a good selectivity with respect to a lysosomal α-mannosidase, which is important for anticancer applications. STD NMR and molecular modeling studies supported a multivalent mechanism with specific interactions of the bioactive iminosugars with Jack bean α-mannosidase. TEM studies suggested a binding mode that involves the formation of aggregates, which result from the intermolecular cross-linked network of interactions between the multivalent inhibitors and two or more dimers of JBMan heterodimeric subunits.Multivalent glycosidase inhibitors: Synthesis, biological evaluation, NMR analysis, and molecular modeling studies underlines, for the first time, the existence of a specific interaction between the jack bean α-mannosidase and pyrrolidine-based multivalent inhibitors. TEM studies suggest the formation of an intermolecular cross-linking network between enzyme and inhibitors.
      PubDate: 2017-09-13T13:10:41.579578-05:
      DOI: 10.1002/chem.201703011
       
  • Kinetic Studies on Formic Acid Dehydrogenation Catalyzed by an Iridium
           Complex towards Insights into the Catalytic Mechanism of High-Pressure
           Hydrogen Gas Production
    • Authors: Masayuki Iguchi; Heng Zhong, Yuichiro Himeda, Hajime Kawanami
      Abstract: Kinetic studies on the catalytic reaction mechanism of formic acid (FA) dehydrogenation were performed in the presence of a water-soluble iridium complex bearing a 4,4′-dihydroxy-2,2′-bipyridine ligand. Determination of kinetic isotope effects revealed that a shift of the rate-limiting step at low and high concentrations of FA can be caused by the pH dependence of the reaction steps. The proposed equation for the reaction rate corresponds well with the experimental results concerning the shift phenomena. Towards industrial application in future hydrogen fueling stations, this will able the design of a dehydrogenation system catalyzed by the iridium complex.Rate-limiting step shift: Kinetic studies on the catalytic reaction mechanism of the dehydrogenation of formic acid catalyzed by a water-soluble iridium complex were performed, and a shift of the rate-limiting step at low and high concentrations of formic acid was observed (see figure).
      PubDate: 2017-09-13T13:10:24.786109-05:
      DOI: 10.1002/chem.201702969
       
  • In-situ and Real-time Monitoring of Mechanochemical Preparation of
           Li2Mg(NH2BH3)4 and Na2Mg(NH2BH3)4 and their Thermal Dehydrogenation
    • Authors: Nikola Biliskov; Andreas Borgschulte, Krunoslav Užarević, Ivan Halasz, Stipe Lukin, Sanja Milošević, Igor Milanović, Jasmina Grbović Novaković
      Abstract: For the first time, in-situ monitoring of uninterrupted mechanochemical synthesis of two bimetallic amidoboranes,M2Mg(NH2BH3)4(M = Li, Na), by means of Raman spectroscopy has been applied. This approach allowed real-time observation of key intermediatephases and a straightforward follow-up of the reaction course. Detailed analysis of time-dependent spectra revealeda two-step mechanism through MNH2BH3.NH3BH3 adducts as key intermediate phases which further reacted with MgH2, giving M2Mg(NH2BH3)4 as final products. The intermediates partially take a competitive pathway toward the oligomeric M(BH3NH2BH2NH2BH3) phases. The crystal structure of the novel bimetallic amidoborane Li2Mg(NH2BH3)4 was solved from high-resolution powder diffraction data and showed an analogous metal coordination as in Na2Mg(NH2BH3)4, but a significantly different crystal packing. Li2Mg(NH2BH3)4 thermally dehydrogenates releasing highly pure H2 in the amount of 7 wt% and at a lower temperature then its sodium analogue making it significantly more viable for practical applications.
      PubDate: 2017-09-13T12:15:47.913761-05:
      DOI: 10.1002/chem.201702665
       
  • Insight into the Activation of In Situ-Generated Chiral Rh(I)-Catalysts
           and their Application in Cyclotrimerizations
    • Authors: Indre Thiel; Moritz Horstmann, Phillip Jungk, Sonja Keller, Fabian Fischer, Hans-Joachim Drexler, Detlef Heller, Marko Hapke
      Abstract: The generation of highly active chiral catalysts at mild temperatures for [2+2+2] cycloaddition reactions is a requirement for high conversions as well as selectivities with selected examples giving up to 96% ee in single cases. We herein report a detailed study on the generation of [Rh(diphosphine)(solvent)]+ complexes as catalysts for cyclotrimerizations, with single examples applying the ((Sc,Rp)-Duanphos) ligand giving up to 96% ee selectivity in single cases. Novel ammonia complexes of the type [Rh(diphosphine)(NH3)2]+ were also successfully tested for the generation of the highly reactive solvent complexes. A valuable alternative approach to generate novel chiral Rh(I)-complexes was found by in situ generation from Wilkinson's catalyst RhCl(PPh3)3 with chiral P,N ligands. The generated catalysts led to moderate to good enantioselectivities and excellent yields in cyclotrimerizations of triynes. The combination of RhCl(PPh3)3/(R,Sa)-O-PINAP proved to be a convenient alternative catalytic system in this context for the synthesis of benzene derivatives possessing axial chirality.
      PubDate: 2017-09-13T11:15:41.947433-05:
      DOI: 10.1002/chem.201703198
       
  • Efficient catalytic microreactors with atomic layer deposited platinum
           nanoparticles on oxide support
    • Authors: Ville Rontu; Anne Selent, Vladimir Zhivonitko, Gianmario Scotti, Igor Koptyug, Ville-Veikko Telkki, Sami Franssila
      Abstract: Microreactors attract a significant interest for chemical synthesis due to benefits of small scales such as high surface to volume ratio, rapid thermal ramping and well-understood laminar flows. The suitability of atomic layer deposition for applying of both the catalyst nanoparticles and the support material on the surfaces of channels of microfabricated silicon microreactors is demonstrated in this research. Continuous flow hydrogenation of propene into propane at low temperatures with TiO₂ supported catalytic Pt nanoparticles was used as a model reaction. Reaction yield and mass transport were monitored by high sensitivity microcoil Nuclear Magnetic Resonance (NMR) spectroscopy as well as time-of-flight remote detection NMR imaging. The microreactors were shown to be very efficient in propene conversion into propane. The yield of 100 % was achieved at 50 °C with a reactor decorated with Pt nanoparticles of average size of ca. 1 nm and surface coverage of 3.2 % in 20 mm long reaction channels with the residence time of 1100 ms. The activity of the Pt catalyst surfaces was on the order of few to tens of mmol s-¹m-².
      PubDate: 2017-09-13T10:15:34.631227-05:
      DOI: 10.1002/chem.201703391
       
  • Formation and Photodynamic Behavior of Transition Metal Dichalcogenide
           Nanosheet-Fullerene Inorganic-Organic Nanohybrids on Semiconducting
           Electrodes
    • Authors: Jinseok Baek; Tomokazu Umeyama, Wookjin Choi, Yusuke Tsutsui, Hiroki Yamada, Shu Seki, Hiroshi Imahori
      Abstract: Composite films consisting of C60 and well-exfoliated nanosheets of transition metal dichalcogenides (TMDs), i.e., MoS2 or WS2, with a bulk heterojunction structure were facilely fabricated onto a semiconducting SnO2 electrode via a two-step methodology; self-assembly into their composite aggregates by injecting poor solvent into good solvent with the dispersion and subsequent electrophoretic deposition. Photoexcitation of the composites on SnO2 exhibited enhanced transient conductivities in comparison with single components of TMDs or C60, demonstrating that the bulk heterojunction nanostructure of TMD and C60 promoted the charge separation (CS). In addition, the decoration of the TMD nanosheets with C60 hindered the undesirable charge recombination (CR) between an electron in SnO2 and a hole in TMD nanosheets. Owing to the accelerated CS and suppressed CR, photoelectrochemical devices based on the MoS2-C60 and WS2-C60 composites achieved remarkably improved incident photon-to-current efficiencies (IPCEs) as compared to the single component films. Despite more suppressed CR in WS2-C60 than MoS2-C60, the IPCE value of the device with WS2-C60 was smaller than that with MoS2-C60 due to its inhomogeneous film structure. These results will provide profound insights into photodynamics of TMD-fullerene nanohybrids and thereby valuable information on the design of TMD-based inorganic-organic hybrid devices.
      PubDate: 2017-09-13T03:27:12.031999-05:
      DOI: 10.1002/chem.201703699
       
  • Self-Assembly of Heterogeneously Shaped Nanoparticles into Plasmonic
           Metamolecules on DNA Origami
    • Authors: Wenyan Liu; Ling Li, Shuo Yang, Jie Gao, Risheng Wang
      Abstract: Fabrication of plasmonic metamolecules (PMs) with rationally designed complexity is one of the major goals of nanotechnology. Most self-assembled PMs, however, have been constructed using single-component systems. The corresponding plasmonic assemblies still suffer from the lack of complexity, which is required to achieve a high degree of functionality. Here, we report a general applicable strategy that can realize a series of high-ordered hetero-PMs using bottom-up DNA self-assembly. DNA-functionalized differently shaped nanoparticles were deliberately arranged in prescribed positions on 3D triangular DNA origami frames to form various hetero-PMs. Importantly, we showed that the optical properties of assembled PMs could be facially tuned by selectively regulating the position of each component. This method provides a promising pathway for manufacturing more complex and advanced materials by integrating diverse nanocomponents with particular properties.Self-assembly of plasmonic metamolecules consisting of heterogeneously shaped metal nanoparticles by using DNA origami as a scaffold is reported. The assembled hetero-PMs exhibit strong interparticle plasmonic coupling in the visible spectra range. This approach provides opportunities to manufacture more complex and advanced materials by integrating diverse nanocomponents with particular properties.
      PubDate: 2017-09-13T01:25:43.808283-05:
      DOI: 10.1002/chem.201703927
       
  • A Reusable N-Carbon coated Mo2C Composite Counter Electrode for
           High-Efficiency Dye-Sensitized Solar Cells
    • Authors: Ting Wang; Jia-Bo Wang, Wei-Lin Chen, Xiao-Tao Zheng, En-Bo Wang
      Abstract: The design and development of efficient and stable nonprecious metal-based catalysts for counter electrode (CE) in Dye-Sensitized Solar Cells (DSSCs) has received great attentions. In this work, the molybdenum carbide nanoparticles homogeneously distributed in the nitrogen rich carbon matrix (Mo2C@NC) are synthesized by using inexpensive raw materials (polyoxometalate and dicyandiamide) via a facile one-step solid phase synthesis method. The Mo2C@NC hybrid was not only firstly used as CEs in DSSCs but also showed superior catalytic activity towards I3-/I- redox electrolyte, the efficiency of the DSSC using Mo2C@NC as a CE is achieved to 6.49% which is comparable to Pt (6.38%). What's more, the CE was prepared by drop-coating method without the addition of other conductive polymer, most importantly, the method prevents the sample falling off the FTO and the CE can be reused with the unchanged efficiency. Therefore, it broadens the way for developing platinum free catalysts with low cost, simple process, good stability and high efficiency.
      PubDate: 2017-09-12T21:28:11.342046-05:
      DOI: 10.1002/chem.201703519
       
  • Mild Decarboxylative C-H Alkylation: Computational Insights for
           Solvent-Robust Ruthenium(II) Domino Manifold
    • Authors: Phani Kumar; Torben Rogge, Santhivardhana Reddy Yetra, Alexander Bechtholdt, Eric Clot, Lutz Ackermann
      Abstract: Computational studies on decarboxylative C-H alkenylations provided key insights into the solvent-independent nature of C-H activation/decarboxylation domino reactions, which was exploited for ruthenium(II)-catalyzed C-H alkylations by decarboxylative ruthenium(II) catalysis with ample scope under copper- and silver-free reaction conditions.
      PubDate: 2017-09-12T21:28:07.465103-05:
      DOI: 10.1002/chem.201703680
       
  • Different and often opposing forces drive the encapsulation and multiple
           exterior binding of charged guests to a M₄L₆ supramolecular vessel in
           water
    • Authors: Carmelo Sgarlata; Jeffrey S. Mugridge, Michael D. Pluth, Valeria Zito, Giuseppe Arena, Kenneth Raymond
      Abstract: The supramolecular assembly [Ga₄L₆]¹²¯ acts as a nanoscale flask to mediate the reactivity of encapsulated reactive guests and also functions as a catalyst to carry out enzyme-like chemical transformations. The guest binding to the interior cavity and exterior of this host is difficult to untangle because multiple equilibria occur in solution, and only when refining simultaneously data obtained from different techniques, such as NMR, UV-vis and calorimetry, can the accurate solution thermodynamics of these host guest-systems be determined. This study reports on the driving forces for the inclusion and stepwise exterior guest binding of different aliphatic quaternary ammonium guests to the [Ga₄L₆]¹²¯assembly. Encapsulation into the host cavity was found to be an entropy driven process whereas exterior ion-association is driven either by enthalpically favorable attractive forces or by the entropy gain due to desolvation, depending on guest size and character. The analysis of the energetics of reaction may help predicting and understanding the intimate role and contribution of the transition state in those rate accelerated reactions involving this supramolecular assembly as an enzyme-like molecular flask.
      PubDate: 2017-09-12T12:15:23.556371-05:
      DOI: 10.1002/chem.201703202
       
  • High pressure chemistry and the mechanochemical polymerization of
           [5]-cyclo-p-phenylene
    • Authors: Lili Qiu; Miriam Peña-Alvarez, Mercedes Taravillo, Paul J Evans, Evan Darzi, Ramesh Jasti, P. Mayorga Burrezo, Juan T López Navarrete, Valentín G. Baonza, Juan Casado, Miklos Kertesz
      Abstract: We find evidence for the surprising formation of polymeric phases under high pressure for conjugated nanohoop molecules. This paper represents one of the unique cases where the molecular-level effects of pressure in crystalline organic solids is addressed and provides a suitable general approach based on vibrational Raman spectroscopy combining experiments and computations. In particular we studied the structural and supramolecular chemistry of the cyclic conjugated nanohoop molecule, [5]cyclo-para-phenylene under high pressures of 0 to 10 GPa. The theoretical modeling for periodic crystals predict good agreements with Raman spectra in the molecular phase. In addition we have discovered two stable polymeric phases that arise in the simulation. The critical pressures in the simulation are too high, but the formation of polymeric phases at high pressures provides a natural explanation for the observed irreversibility of the Raman spectra upon pressure release between 6 and 7 GPa. The geometric parameters show a deformation toward quinonoid structures at high pressures accompanied by other deformations of the nanohoops. The quinonoidization of the benzene rings is linked to the systematic change of the bond length alternation as a function of pressure, providing a qualitative interpretation of the observed spectral shifts in the molecular phase.
      PubDate: 2017-09-12T11:17:31.188611-05:
      DOI: 10.1002/chem.201703435
       
  • Functionalized Ultrasmall Fluorinated Graphene with High NIR Absorbance
           for Controlled Delivery of Mixed Anticancer Drugs
    • Authors: Peiwei Gong; Qiao Zhao, Dujuan Dai, Shumiao Zhang, Zhenzhen Tian, Lu Sun, Jiashuo Ren, Zhe Liu
      Abstract: Fluorinated graphene (FG) possess distinctively novel properties different from graphene and is suitable for many biomedical applications. However, the hydrophobic nature and inert property of FG are limiting its further application as biological materials. Here we show the preparation of nanosized FG (60 nm) that exhibits high NIR absorbance for photothermal therapy. In order to make it stable in physiological solutions, FG is enriched with oxygen and followed by covalent binding with chitosan as a novel pH-responsive nanocarrier. Furthermore, controlled loading of two anticancer drugs, doxorubicin (DOX) and camptothecin (CPT), is realized and the functionalized ultrasmall FG shows remarkably high cytotoxicity toward Hela cancer cells compared to that loading either CPT or DOX only. This work established nanosized FG as a novel photothermal agent due to small size, stimulus-responsive nanocarrier for mixed drug delivery and combined therapy.
      PubDate: 2017-09-12T10:15:37.083239-05:
      DOI: 10.1002/chem.201702917
       
  • Theoretical Evidence for the Utilization of Low-valent Main-Group
           Complexes as Rare-Synthon Equivalents
    • Authors: Zsolt Benedek; Balazs Orban, Tibor Szilvasi
      Abstract: We examine by the means of computational chemistry the ability of two phosphasilenes to transfer the phosphinidene moiety to four double bonded organic functional groups (>C=CC=O, and>C=S) in the presence of different bulky ligands. We show that large bulky groups in the reactants can sterically prohibit the otherwise favored association of reactants and phosphasilenes and instead a new phosphinidene transfer reaction can occur. We find that the transfer reaction mechanism is generally present independent from the functional group and by introducing large enough trimethylsilyl or tert-butyl-dimethylsilyl ligands it can be used to transfer phosphinidene to organic functional groups such as thioformaldehydes or diazenes, respectively. We propose that by exploiting the complex bonding nature of low-valent main group complexes they can act as synthetic equivalents of hitherto unknown very reactive synthons. We encourage experimentalists to explore the reactivity of their main-group complexes by varying the size of the bulky substituents on the reactants that can result in new unexpected chemistry.
      PubDate: 2017-09-12T09:20:56.615771-05:
      DOI: 10.1002/chem.201703636
       
  • Functionalization of 3-iridacyclopentenes
    • Authors: Margarita Paneque; Margarita Gómez, Nuria Rendón, Eleuterio Álvarez, Kurt Mereiter, Manuel L. Poveda
      Abstract: A series of iridacyclopentenes of composition (TpMe2 = hydrotris(3,5-dimethyl-pyrazolyl)borate; R = R' = H, 1; R = Me, R' = H, 2; R = R' = Me, 3) have been subjected to common organic chemistry procedures for hydrogenation, cyclopropanation, epoxidation, water addition through hydroboration, cis-dihydroxylation and ozonolysis. The stability of metallacycles 1-3, provided by the presence of the coligands TpMe2 and CO, directs the reactivity towards the C=C double bonds, and further the stereochemistry of the products formed is strongly dictated by the steric demands of the TpMe2 ligand. While the products obtained in some of the above mentioned reactions are the expected ones from an organic chemistry point of view, in other cases the results differ from the outcomes of similar reactions carried out with the all-carbon counterparts.
      PubDate: 2017-09-12T08:20:47.239348-05:
      DOI: 10.1002/chem.201703535
       
  • Synthesis of Coordination Polymer Nanoparticles using self-assembled Block
           Copolymers as Template
    • Authors: Birgit Weber
      Abstract: Nowadays there is a high demand in specialized functional materials e.g. for applications as sensors in biomedicine. For the realization of such applications, nano-structures and the integration in a composite matrix are indispensable. Coordination polymers and networks, for example with spin crossover properties, are a highly promising family of switchable materials where the switching process can be triggered by various external stimuli. An overview over different strategies for the synthesis of nanoparticles of such systems is given. A special focus is set on the use of block copolymer micelles as template for the synthesis of nano-composites. The block copolymer defines the final size and shape of the nanoparticle core. Additionally it allows a further functionalization of the obtained nanoparticles by variation of the polymer blocks and an easy deposition of the composite material on surfaces.
      PubDate: 2017-09-12T08:20:34.672793-05:
      DOI: 10.1002/chem.201703280
       
  • Electrocatalytic Azide Oxidation Mediated by a Rh(PNP) Pincer Complex
    • Authors: Bas de Bruin; Christophe Rebreyend, Yann Gloaguen, Martin Lutz, Jarl Ivar van der Vlugt, Inke Siewert, Sven Schneider
      Abstract: One-electron oxidation of the rhodium(I) azido complex [Rh(N3)(PNP)] (5), bearing the neutral PNP ligand 2,6-bis(di-tert-butylphosphinomethyl)pyridine leads to instantaneous and selective formation of the mononuclear rhodium(I) dinitrogen complex [Rh(N2)(PNP)]+ (9+). Interestingly, complex 5 also acts as a catalyst for electrochemical N3- oxidation in the presence of excess azide at a substantially lower potential (Ep ~ -0.23 V vs. Fc+/0) than direct oxidation at Pt-electrodes (Ep ~ +0.19 V vs. Fc+/0). Cyclic voltammetry in the presence of an excess of N(nBu)4N3 reveals that electro-catalytic N3-oxidation occurs at roughly the same potential as the first oxidation wave of 5. The mechanism of azide oxidation is not straightforward. Unlike expected direct N2-loss from [MII(N3)(PNP)]+, followed by dinuclear N-N coupling of two nitridyl species as was reported in related earlier work concerning neutral complexes (M = Rh, Ir), the cationic rhodium(II)-azido [Rh(PNP)(N3)]+ complex 6+ seems to react via a different pathway. IR spectro-electrochemistry, CV simulations, EPR and DFT studies all point to a route involving the coupling of two complexes 6+ to produce the mixed-valent dinuclear [(PNP)RhI(N3)RhIII(N3)(PNP)]2+ complex 72+, which fragments via N-N bond splitting to form 0.5 eq. [Rh(N2)(PNP)]+ (9+) and [RhV(N)(N3)(PNP)]+ (8+). Subsequent intramolecular azide attack at the terminal nitrido moiety of the formally rhodium(V) intermediate 8+ then produces a second 0.5 eq. of 9+.
      PubDate: 2017-09-12T06:15:49.56647-05:0
      DOI: 10.1002/chem.201702938
       
  • η1-Arene Complexes as Intermediates in the Preparation of Molecular
           Phosphorescent Iridium(III) Complexes
    • Authors: Miguel A. Esteruelas; Daniel Gómez-Bautista, Ana M. López, Enrique Oñate, Jui-Yi Tsai, Chuanjun Xia
      Abstract: Molecular phosphorescent heteroleptic bis-tridentate iridium(III) emitters have been prepared via η1-arene intermediates. In the presence of 4.0 mol of AgOTf, complex [{IrCl[κ3-N,C,N-(pyC6HMe2py)]}(μ-Cl)]2 (1; pyC6H2Me2py = 1,3-di(2-pyridyl)-4,6-dimethylbenzene) reacts with 9-(6-phenylpyridin-2-yl)-9H-carbazole (PhpyCzH) and 2-phenoxy-6-phenylpyridine (PhpyOPh) to give [Ir{κ3-N,C,N-(pyC6HMe2py)}{κ3-C,N,C'-(C6H4pyCzH)}]OTf (2) and [Ir{κ3-N,C,N-(pyC6HMe2py)}{κ3-C,N,C'-(C6H4pyOPh)}]OTf (3). The X-ray diffraction structures of 2 and 3 reveal that the carbazolyl and phenoxy substituents of the C,N,C' ligand coordinate to the metal center to form an η1-arene π-bond. Treatment of 2 and 3 with KOtBu produces the deprotonation of the coordinated carbon atom of the η1-arene group to afford the molecular phosphorescent [5t+4t']-heteroleptic iridium(III) complexes Ir{κ3-N,C,N-(pyC6HMe2py)}{κ3-C,N,C'-(C6H4pyCz)} (4) and Ir{κ3-N,C,N-(pyC6HMe2py)}{κ3-C,N,C'-(C6H4pyOC6H4)} (5). They are green emitters, which display short lifetimes and high quantum yields of 0.73 (4) and 0.87 (5) in the solid state.
      PubDate: 2017-09-12T05:21:58.35353-05:0
      DOI: 10.1002/chem.201703252
       
  • Dichloro-cycloazatriphosphane — the missing link between N2P2 and P4
           ring systems in the systematic development of NP chemistry
    • Authors: Axel Schulz; Jonas Bresien, Alexander Hinz, Tim Suhrbier, Max Thomas, Alexander Villinger
      Abstract: An unprecedented dichloro-cycloazatriphosphane that incorporates a cyclic NP3 backbone could be synthesized using knowledge gained from the chemistry of N2P2 and P4 ring systems. It fills the gap between the homologous compounds [ClP(µ-NR)]2 and [ClP(µ-PR)]2 (R = sterically demanding substituent), and thus contributes to the systematic development of nitrogen-phosphorus chemistry in general. The title compound was studied with respect to its formation via a labile aminodiphosphene, which readily underwent different rearrangement reactions depending on the solvent. All compounds were fully characterized by experimental and computational methods.
      PubDate: 2017-09-12T05:21:39.714-05:00
      DOI: 10.1002/chem.201704278
       
  • Modulating the physical and electronical properties over positional
           isomerism: the Dispirofluorene-Dihydroindacenodithiophene (DSF-IDT)
           family.
    • Authors: Joëlle Rault-Berthelot; Jean-David Peltier, Cyril Poriel, Benoît Heinrich, Bertrand Donnio, Olivier Jeannin
      Abstract: We report the first studies on the intrinsic properties of a meta-substituted dihydroindacenodithienyl fragment and more generally the strong impact of positional isomerism on dihydroindacenodithiophene derivatives. The influence of the para and meta linkages has notably been highlighted not only on the electronic properties in solution (electrochemical properties, anodic polymerization, HOMO/LUMO energy levels, optical transitions, fluorescence spectra…) but also on the physical properties in the solid state (molecular organization, crystallinity and phase transitions). The positional isomerism hence appears as a very efficient tool to drastically tune the properties of dihydroindacenodithiophene derivatives.
      PubDate: 2017-09-12T04:21:04.405489-05:
      DOI: 10.1002/chem.201703320
       
  • Stereospecific Winding of Polycyclic Aromatic Hydrocarbons into Trinacria
           Propellers
    • Authors: Dario Mosca; Antoine Stopin, Johan Wouters, Nicola Demitri, Davide Bonifazi
      Abstract: Invited for the cover of this issue is the group of Bonifazi at the University of Cardiff and their collaborators from University of Namur (Belgium) and Elettra, Synchrotron Trieste (Italy). The image depicts the propeller-like conformation of their newly synthesized molecular system that thanks to the peculiar aromatic embracing folding resembles the shape of the Sicilian Trinacria symbol, as demonstrated by its X-ray single-crystal structure. Read the full text of the article at 10.1002/chem.201702032.“It was through X-ray crystallography that we could unravel the conformation of this molecule, namely the formation of a propeller-like structure.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201702032).
      PubDate: 2017-09-12T04:16:11.816889-05:
       
  • Crucible-Free Preparation of Transition-Metal Borides: HfB2
    • Authors: Anne Henschel; Michael Binnewies, Marcus Schmidt, Horst Borrmann, Yuri Grin
      Abstract: The manufacture of metal borides, especially without immixtures of oxygen or nitrogen, is a known problem in the preparation of intermetallic phases. The proof-of-principle for the innovative, crucible-free synthesis of single-phase borides at relatively moderate temperatures by reaction of a metal wire heated by an electrical current with a gaseous boron halide was achieved for hafnium diboride, a material with one of the highest decomposition temperatures. More information can be found in the Communication by Yu. Grin et al. (
      DOI : 10.1002/chem.201703181).
      PubDate: 2017-09-12T04:16:06.873086-05:
       
  • Transition-Metal-Controlled Inorganic Ligand-Supported Non-Precious Metal
           Catalysts for the Aerobic Oxidation of Amines to Imines
    • Authors: Han Yu; Yongyan Zhai, Guoyong Dai, Shi Ru, Sheng Han, Yongge Wei
      Abstract: Most state-of-art transition-metal catalysts usually require organic ligands, which are essential for controlling the reactivity and selectivity of reactions catalyzed by transition metals. However, organic ligands often suffer from severe problems including cost, toxicity, air/moisture sensitivity, and being commercially unavailable. Herein, we show a simple, mild, and efficient aerobic oxidation procedure of amines using inorganic ligand-supported non-precious metal catalysts 1, (NH4)n[MMo6O18(OH)6] (M=Cu2+; Fe3+; Co3+; Ni2+; Zn2+, n=3 or 4), synthesized by a simple one-step method in water at 100 °C, demonstrating that the catalytic activity and selectivity can be significantly improved by changing the central metal atom. In the presence of these catalysts, the catalytic oxidation of primary and secondary amines, as well as the coupling of alcohols and amines, can smoothly proceed to afford various imines with O2 (1 atm) as the sole oxidant. In particular, the catalysts 1 have transition-metal ion core, and the planar arrangement of the six MoVI centers at their highest oxidation states around the central heterometal can greatly enhance the Lewis acidity of catalytically active sites, and also enable the electrons in the center to delocalize onto the six edge-sharing MO6 units, in the same way as ligands in traditional organometallic complexes. The versatility of this methodology maybe opens a path to catalytic oxidation through inorganic ligand-coordinated metal catalysis.A breath of fresh air: A mild aerobic oxidative coupling protocol of primary and secondary amines as well as the coupling of alcohols and amines to afford corresponding imines was developed with inorganic ligand-supported metal catalyst (NH4)n[MMo6O18(OH)6] (M=Cu2+, Fe3+, Co3+, Ni2+, Zn2+). This method utilizes mainly an inorganic polymolybdate ligand to support the Cu2+ ion and 1 atm O2 gas as the sole oxidant, which can smoothly proceed to afford various imines in high yields and selectivity, avoiding the use of expensive, toxic, air/moisture sensitive, and commercially unavailable organic ligands.
      PubDate: 2017-09-12T04:06:29.375058-05:
      DOI: 10.1002/chem.201703185
       
  • Potassium (De-)insertion Processes in Prussian Blue Particles: Ensemble
           versus Single Nanoparticle Behaviour
    • Authors: Giorgia Zampardi; Stanislav V. Sokolov, Christopher Batchelor-McAuley, Richard G. Compton
      Abstract: Potassium (de-)insertion from Prussian blue (PB) is investigated at the single and multi-particle scale. The electrochemical behaviour is found to differ between the two measurement types. At the single particle level, oxidation of the PB nanoparticles with concomitant K+ deinsertion occurs more readily than the associated reduction, relating to K+ insertion. In contrast, the cyclic voltammetry of PB in a composite electrode containing conductive additives and polymeric binder suggests the opposite behaviour. Implications for assessing battery materials are discussed.PB&J: Potassium insertion and deinsertion processes were investigated in Prussian blue at the nanoscale through the nanoimpact method. The electrochemical behaviour of the material at the single particle was confronted to the one at the composite level, which is influenced by the presence of conductive additives and polymeric binder.
      PubDate: 2017-09-12T04:06:17.038499-05:
      DOI: 10.1002/chem.201703175
       
  • Understanding Carbon Dioxide Solubility in Ionic Liquids by Exploring the
           Link with Liquid Clathrate Formation
    • Authors: Steven P. Kelley; Luis A. Flores, Matthew S. Shannon, Jason E. Bara, Robin D. Rogers
      Abstract: The solubilities of the quadrupolar molecules benzene and CO2 in various ionic liquids (ILs) are compared in order to determine the connection between aromatic liquid clathrate formation and CO2 dissolution in ILs. It was found that both CO2 Henry's law constants and benzene solubility are remarkably well correlated with each other and with IL molar volume, suggesting both phenomena depend more on the strength of interionic interactions between the ions of an IL rather than the identity of either ion. However, IL ion-quadrupole interactions were found to have an effect for dicyanamide ([N(CN)2]−), where solubility of CO2 and benzene are affected by destabilizing and stabilizing interactions with [N(CN)2]−, respectively. The results suggest both solubility phenomena are related to the incorporation of the solute into an IL host network. Aromatic liquid clathrate formation thus has potential as a facile experimental probe for predicting the relative ability of ILs to physisorb CO2.Benzene and CO2 dissolution in ionic liquids for CO2 capture are related phenomena, and increases in benzene solubility parallel increases in CO2 solubility.
      PubDate: 2017-09-12T04:06:07.585742-05:
      DOI: 10.1002/chem.201703117
       
  • Design, Synthesis, and Characterization of Brequinar Conjugates as Probes
           to Study DHODH Inhibition
    • Authors: Joseph T. Madak; Christine R. Cuthbertson, Wenmin Chen, Hollis D. Showalter, Nouri Neamati
      Abstract: Brequinar, a potent dihydroorotate dehydrogenase (DHODH) inhibitor, has been evaluated in multiple clinical trials as a potential treatment for cancer. To further understand brequinar-based DHODH inhibition and DHODH′s therapeutic relevance in cancer, we have developed novel brequinar-based probes. We disclose a 16-step convergent synthesis of the first brequinar-PROTAC and a four-step approach towards the first mitochondrial-directed brequinar probe. A PROTAC and mitochondria-directed probe of brequinar both possess cytotoxicity that is superior to brequinar in a colony formation assay.Brequin′ news: A novel convergent synthesis of brequinar-based probes to induce protein degradation (16 steps) and improve mitochondria accumulation (four steps) is disclosed.
      PubDate: 2017-09-12T04:06:00.822471-05:
      DOI: 10.1002/chem.201702999
       
  • Anion-Directed Metallocages: A Study on the Tendency of Anion Templation
    • Authors: Jing-Yun Wu; Ming-Shiou Zhong, Ming-Hsi Chiang
      Abstract: Self-assembly of Cu(NO3)2∙3H2O and a di(3-pyridylmethyl)amine (dpma) ligand with addition of different acids (HNO3, HOAc, HCl, HClO4, HOTf, HPF6, HBF4, and H2SO4) afforded a family of anion-templated tetragonal metallocages having a cationic prismatic structure of [(Gn-){Cu2(Hdpma)4}](8-n)+ (Gn- = NO3-, PF6-, SiF62-) with different ligating anions/solvents (NO3-, Cl-, ClO4-, OTf-, H2O) outside the cage. The systematic competitive experiments have significantly rationalized a tendency of anion templation towards the formation of metallocages [(Gn-){Cu2(Hdpma)4}](8-n)+ as SiF62− ~ PF6−> NO3−> SO42− ~ ClO4− ~ BF4−. This sequence is mostly elucidated by shape control over size selectivity and electrostatic attraction between the cationic {Cu2(Hdpma)4}8+ host and the anionic guests. In addition, these results have also roughly ranked the anion coordination ability in the order Cl-, ClO4-, OTf−> NO3-> BF4-, CH3SO4-. Magnetic studies of metallacages 1t and 2-4 suggest that the fitted magnetic interaction, being weakly magnetically coupled overall, is interpreted as a result of the combination of intra-cage ferromagnetic coupling integrals and inter-cage antiferromagnetic exchange; both contributions are very weak and comparable in strength.
      PubDate: 2017-09-12T02:21:41.519563-05:
      DOI: 10.1002/chem.201702848
       
  • Highly K+ selective Fluorescent Probes for Lifetime Sensing of K+ in
           Living Cells
    • Authors: Hans-Jürgen Holdt; thomas schwarze, Monique Mertens, Peter Müller, Janine Riemer, pablo wessig
      Abstract: The new K+ selective fluorescent probes 1 and 2 were obtained by CuAAC reactions of an alkyne substituted DBD ester fluorophore with azido functionalized N-phenylaza-18-crown-6 ether and N-(o-isopropoxy)-phenylaza-18-crown-6 ether, respectively. Probes 1 and 2 allow the detection of K+ in the presence of Na+ in water by fluorescence enhancement (2.2 for 1 at 2000 mM K+ and 2.5 for 2 at 160 mM K+). Fluorescence life time measurements in the absence and presence of K+ revealed bi-exponential decay kinetics with similar life times, however with different proportions changing the averaged fluorescence decay times (τf(av)). For 1 a decrease of τf(av) from 12.4 to 9.3 ns and for 2 an increase from 17.8 to 21.8 ns was observed. 2 was choosen for studying the efflux of K+ from human red blood cells (RBC). Upon addition of the Ca+ ionophor ionomycin to a RBC suspension in a buffer containing Ca2+ a fluorescence increase for 2 was observed.
      PubDate: 2017-09-12T02:21:08.9031-05:00
      DOI: 10.1002/chem.201703799
       
  • Syntheses, Properties, and Catalytic Activities of Metal(II) Complexes and
           Free Bases of Redox-Switchable 20π, 19π, and 18π
           5,10,15,20-Tetraaryl-5,15-diazaporphyrinoids
    • Authors: Keisuke Sudoh; Takaharu Satoh, Toru Amaya, Ko Furukawa, Mao Minoura, Haruyuki Nakano, Yoshihiro Matano
      Abstract: In spite of significant advances in redox-active porphyrin-based materials and catalysts, little attention has been paid to 20π and 19π porphyrins, because of their instability in air. Here we report the meso-modification of 5,10,15,20-tetraarylporphyrin with two nitrogen atoms, which led to redox-switchable 20π, 19π, and 18π 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (TADAPs). Three kinds of metal(II) complexes and free bases of TADAP were prepared by the metal-templated annulation of the corresponding metal-bis(dipyrrin) complexes. The inductive and resonance effects of the meso-nitrogen atoms on the aromatic, optical, electrochemical, and magnetic properties of the entire TADAP π-systems were assessed, using various spectroscopic measurements and density functional theory calculations. The aromaticity and π-π* electronic transition energies of the TADAPs varied considerably, depending on the oxidation states of the π-systems. The 20π and 19π TADAPs were chemically stable under air, in contrast to the isoelectronic 5,10,15,20-tetraarylporphyrin derivatives. In particular, the 19π TADAP radical cations were extremely stable towards dioxygen, moisture, and silica gel. This reflected the low-lying singly occupied molecular orbitals of their π-systems, and the efficient delocalization of their unshared electron spin. The capability of MgTADAP to catalyze aerobic biaryl formation from aryl Grignard reagents was demonstrated, which presumably involved a 19π-20π redox cycle.
      PubDate: 2017-09-12T02:21:00.706905-05:
      DOI: 10.1002/chem.201703664
       
  • Supramolecular Synthon Approach in Developing anti-inflammatory Topical
           Gel for in vivo Self-delivery
    • Authors: Parthasarathi Dastidar; Rajdip Roy
      Abstract: A new series of TBA salt of various non-steroidal-anti-inflammatory-drugs (NSAIDs) was synthesized and characterized. Nearly 90% of the salts displayed remarkable gelation ability with various solvents including methyl salicylate. SXRD revealed the existence of 1D PAM synthon in the gelator salts. Structure-property correlation studies based on SXRD and PXRD data established the presence of the 1D PAM synthon in the bulk salts as well as in the corresponding xerogels. A parallel series of salts derived from TRIS and the same set of NSAIDs displayed poor gelation ability (only 33% of the salts). A few selected gelator salts of both TBA and TRIS were found to be biocompatible and two of the selected salts (FLR.TBA and FLR.TRIS) possessed anti-inflammatory property as good as the parent drug FLR (flurbiprofen). Finally a methyl salicylate topical gel of FLR.TRIS was successfully delivered in a self-delivery fashion to treat inflammated skin conditions in mice model.
      PubDate: 2017-09-12T01:15:52.709871-05:
      DOI: 10.1002/chem.201703850
       
  • Front Cover: Soluble Platinum Nanoparticles Ligated by Long-Chain
           N-Heterocyclic Carbenes as Catalysts (Chem. Eur. J. 52/2017)
    • Authors: Luis M. Martínez-Prieto; Lena Rakers, Angela M. López-Vinasco, Israel Cano, Yannick Coppel, Karine Philippot, Frank Glorius, Bruno Chaudret, Piet W. N. M. van Leeuwen
      Pages: 12676 - 12676
      Abstract: NHC-ligated Pt nanoparticles were studied with regards to steric bulk of the ligands and their influence on NP size and catalytic properties. Bulky aryl groups at the N-atoms gave small NPs of roughly 65 atoms, whereas small methyl groups gave larger NPs of around 260 atoms both with high ligand coverage, 12 and 70 ligands, respectively. Undecyl chains on the NHC ligands make the nanoparticles highly soluble and allowed for their use as catalysts in solution. Hydroboration of alkynes was observed for the first time with soluble NPs, but surprisingly only the bulky-ligand-containing Pt NPs were active. More information can be found in the Full Paper by F. Glorius, B. Chaudret and P. W. N. M. van Leeuwen et al. on page 12779.
      PubDate: 2017-07-27T02:52:06.3488-05:00
      DOI: 10.1002/chem.201703187
       
  • Cover Feature: Synthesis of gem-Dinitromethylated and
           Fluorodinitromethylated Derivatives of 5,5′-Dinitro-bis-1,2,4-triazole
           as Promising High-Energy-Density Materials (Chem. Eur. J. 52/2017)
    • Authors: Shi Huang; Junjun Tian, Xiujuan Qi, Kangcai Wang, Qinghua Zhang
      Pages: 12677 - 12677
      Abstract: A new family of gem-dinitromethylated and fluorodinitromethylated energetic compounds based on 5,5’-dinitro-3,3’-bis-1,2,4-triazole (DNBT) shows high energy density, good thermal stability, and excellent detonation properties. The proposed strategy of introducing gem-dinitromethyl and fluorodinitromethyl groups into DNBT frameworks demonstrates a great promise for developing new-generation high-energy-density materials (HEDMs) with high-performing detonation level and low sensitivity. More information can be found in the Full Paper by Q. Zhang et al. on page 12787.
      PubDate: 2017-08-02T06:06:37.079728-05:
      DOI: 10.1002/chem.201703132
       
  • Cover Feature: Tunable Ligand Effects on Ruthenium Catalyst Activity for
           Selectively Preparing Imines or Amides by Dehydrogenative Coupling
           Reactions of Alcohols and Amines (Chem. Eur. J. 52/2017)
    • Authors: Takafumi Higuchi; Risa Tagawa, Atsuhiro Iimuro, Shoko Akiyama, Haruki Nagae, Kazushi Mashima
      Pages: 12678 - 12678
      Abstract: Ligand-controlled selective dehydrogenative coupling reactions of alcohols and amines were achieved by using ruthenium complexes bearing P−N bidentate ligands with zinc salts. A wide variety of alcohols and amines were used in the present systems to obtain the corresponding imines and amides. In addition, a ruthenium complex as the catalyst precursor was successfully isolated and reaction mechanisms are proposed based on experiments, including a time-course study, Hammett plot, and measurements of the kinetic isotope effect. More information can be found in the Full Paper by K. Mashima et al. on page 12795.
      PubDate: 2017-08-01T09:04:16.457825-05:
      DOI: 10.1002/chem.201702953
       
  • Cover Feature: Competitive Energy and Electron Transfer in
           β-Functionalized Free-Base Porphyrin–Zinc Porphyrin Dimer Axially
           Coordinated to C60: Synthesis, Supramolecular Formation and Excited-State
           Processes (Chem. Eur. J. 52/2017)
    • Authors: Yi Hu; Michael B. Thomas, R. G. Waruna Jinadasa, Hong Wang, Francis D'Souza
      Pages: 12679 - 12679
      Abstract: A new supramolecular triad comprised of β-functionalized conjugated free-base porphyrin–zinc porphyrin and axially coordinated electron acceptor fullerene has been successfully synthesized. Under light illumination, simultaneous energy transfer to free-base porphyrin and electron transfer to fullerene competitively occur. The cover picture highlights these findings and uses a tug of war to demonstrate the competitive events. More information can be found in the Full Paper by H. Wang, F. D'Souza et al. on page 12805.
      PubDate: 2017-08-02T06:05:42.083482-05:
      DOI: 10.1002/chem.201703136
       
  • Soluble Platinum Nanoparticles Ligated by Long-Chain N-Heterocyclic
           Carbenes as Catalysts
    • Authors: Luis M. Martínez-Prieto; Lena Rakers, Angela M. López-Vinasco, Israel Cano, Yannick Coppel, Karine Philippot, Frank Glorius, Bruno Chaudret, Piet W. N. M. van Leeuwen
      Pages: 12680 - 12680
      Abstract: Invited for the cover of this issue are the groups of Frank Glorius, Bruno Chaudret, and Piet W. N. M. van Leeuwen at the University of Münster (Germany) and at the Laboratoire de Physique et Chimie des Nano-objets (LPCNO) of Toulouse (France). The image depicts a soluble Pt nanoparticle ligated by a long-chain N-heterocyclic carbene (represented as a force field) as an efficient catalyst in hydroboration of acetylenes. Read the full text of the article at 10.1002/chem.201702288.“Remarkably, only the Pt NPs ligated by a bulky ligand were active for the hydroboration of alkynes.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 12779 ff. (
      DOI : 10.1002/chem.201702288).
      PubDate: 2017-08-01T06:10:33.381889-05:
       
  • Putting Rings around Carbon Nanotubes
    • Authors: Emilio M. Pérez
      Pages: 12681 - 12689
      Abstract: In the last five years, we have developed synthetic methods towards encapsulation of single-walled carbon nanotubes (SWNTs) into organic macrocycles, to form rotaxane-type molecules. These are the first examples of mechanically interlocked SWNT derivatives (MINTs). In this article, the motivation to continue developing the chemistry of SWNTs at a time well past their hype is discussed and our synthetic strategy and characterization methodology is explained in detail, stressing the general aspects. In particular, special emphasis is placed on the importance of adequate control experiments and bulk spectroscopic and analytical data to determine the structure of SWNT derivatives, as opposed to relying only (or mostly) on microscopy. Also our experimental results are used as pretext to reflect on more general/conceptual issues pertaining to the chemistry of SWNTs and mechanically interlocked molecules.If you liked'em then you should've put a ring on them! In this Concept paper it is discussed why it is interesting to make rotaxane-type derivatives of single-walled carbon nanotubes (SWNTs), how to do it, and what they might be useful for.
      PubDate: 2017-08-29T05:11:56.838424-05:
      DOI: 10.1002/chem.201702992
       
  • Bicyclic Peptides as Next-Generation Therapeutics
    • Authors: Curran A. Rhodes; Dehua Pei
      Pages: 12690 - 12703
      Abstract: Bicyclic peptides have greater conformational rigidity and metabolic stability than linear and monocyclic peptides and are capable of binding to challenging drug targets with antibody-like affinity and specificity. Powerful combinatorial library technologies have recently been developed to rapidly synthesize and screen large bicyclic peptide libraries for ligands against enzymes, receptors, and protein–protein interaction targets. Bicyclic peptides have been developed as potential therapeutics against a wide range of diseases, drug targeting agents, imaging/diagnostic probes, and research tools. In this Minireview, we provide a summary of the recent progresses on the synthesis and applications of bicyclic peptides.Bicyclic peptides, such as depicted, can now be rapidly synthesized and screened to identify potent, specific ligands against enzymes, receptors, and protein–protein interactions, thus providing a new class of drug modalities and powerful research tools.
      PubDate: 2017-07-27T03:00:40.228227-05:
      DOI: 10.1002/chem.201702117
       
  • Control of Helical Chirality of Ferrocene–Dipeptide Conjugates by the
           Secondary Structure of Dipeptide Chains
    • Authors: Toshiyuki Moriuchi; Taiki Nishiyama, Masaki Nobu, Toshikazu Hirao
      Pages: 12704 - 12708
      Abstract: Controlling helical chirality and creating protein secondary structures in cyclic/acyclic ferrocene–dipeptide bioorganometallic conjugates were achieved by adjusting the conformational flexibility of the dipeptide chains. In systems reported to date, the helical chirality of a conjugate was determined by the absolute configuration of the adjacent amino acid reside. In contrast, it was possible to induce both M- and P-helical chirality, even when the configuration of the adjacent amino acid was the same. It is particularly interesting to note that M-helical chirality was produced in a cyclic ferrocene–dipeptide conjugate composed of the l-Ala-d-Pro-cystamine-d-Pro-l-Ala dipeptide sequence (1), in which a type II β-turn-like secondary structure was established.In control: Controlling helical chirality and creating protein secondary structures in cyclic/acyclic ferrocene–dipeptide bioorganometallic conjugates were achieved by adjusting the conformational flexibility of the dipeptide chains. It is particularly interesting to note that M-helical chirality was produced in a cyclic ferrocene–dipeptide conjugate composed of the l-Ala-d-Pro-cystamine-d-Pro-l-Ala dipeptide sequence, in which a type II β-turn-like secondary structure was established (see scheme).
      PubDate: 2017-08-11T04:50:27.82549-05:0
      DOI: 10.1002/chem.201703102
       
  • Metalloradical Reactivity of RuI and Ru0 Stabilized by an Indole-Based
           Tripodal Tetraphosphine Ligand
    • Authors: Fenna F. van de Watering; Jarl Ivar van der Vlugt, Wojciech I. Dzik, Bas de Bruin, Joost N. H. Reek
      Pages: 12709 - 12713
      Abstract: The tripodal, tetradentate tris(1-(diphenylphosphanyl)-3-methyl-1H-indol-2-yl)phosphane PP3-ligand 1 stabilizes Ru in the RuII, RuI, and Ru0 oxidation states. The octahedral [(PP3)RuII(Cl)2] (2), distorted trigonal bipyramidal [(PP3)RuI(Cl)] (3), and trigonal bipyramidal [(PP3)Ru0(N2)] (4) complexes were isolated and characterized by single-crystal X-ray diffraction, NMR, EPR, IR, and ESI-MS. Both open-shell metalloradical RuI complex 3 and the closed-shell Ru0 complex 4 undergo facile (net) abstraction of a Cl atom from dichloromethane, resulting in formation of the corresponding RuII and RuI complexes 2 and 3, respectively.For whom the Ru tripod indoles: The octahedral [(PP3)RuII(Cl)2] (2), distorted trigonal bipyramidal [(PP3)RuI(Cl)] (3) and trigonal bipyramidal [(PP3)Ru0(N2)] (4) complexes were isolated. Both metalloradical RuI complex 3 and closed-shell Ru0 complex 4 undergo (net) Cl-atom abstraction from dichloromethane, resulting in formation of the corresponding RuII and RuI complexes 2 and 3, respectively.
      PubDate: 2017-08-30T11:10:36.5025-05:00
      DOI: 10.1002/chem.201702727
       
  • Total Synthesis of the Marine Natural Product Hemiasterlin by
           Organocatalyzed α-Hydrazination
    • Authors: Jan Hendrik Lang; Peter G. Jones, Thomas Lindel
      Pages: 12714 - 12717
      Abstract: An efficient synthesis of the potently cytotoxic marine peptide hemiasterlin is presented. The tetramethyltryptophan moiety is assembled by tert-prenylation of indole, followed by the high-yielding organocatalyzed α-hydrazination of a sterically congested aldehyde with excellent enantioselectivity. 2-Bromo-N-ethylpyridinium tetrafluoroborate (BEP)-mediated peptide coupling completes the synthesis, being the first approach that does not employ chiral auxiliaries. A novel phenonium-type rearrangement of the indole system occurred when subjecting dihydroxylated 3-tert-prenylindole to Mitsunobu conditions.Enantioselective α-hydrazination was key: An efficient synthesis of the potently cytotoxic marine peptide hemiasterlin is presented. The tetramethyltryptophan moiety is assembled de novo by tert-prenylation of indole, followed by the high-yielding organocatalyzed α-hydrazination of a sterically congested aldehyde with excellent enantioselectivity. A novel phenonium-type rearrangement of the indole system occurred when subjecting dihydroxylated 3-tert-prenylindole to Mitsunobu conditions.
      PubDate: 2017-08-16T02:55:38.122624-05:
      DOI: 10.1002/chem.201702812
       
  • Self-Templating Construction of Hollow Amorphous CoMoS4 Nanotube Array
           towards Efficient Hydrogen Evolution Electrocatalysis at Neutral pH
    • Authors: Weiyi Wang; Xiang Ren, Shuai Hao, Zhiang Liu, Fengyu Xie, Yadong Yao, Abdullah M. Asiri, Liang Chen, Xuping Sun
      Pages: 12718 - 12723
      Abstract: Environmentally friendly electrochemical hydrogen production needs the development of earth-abundant catalyst materials for the hydrogen evolution reaction with high activity and durability at neutral pH. In this work, the self-templating construction of a hollow amorphous CoMoS4 nanotube array on carbon cloth (CoMoS4 NTA/CC) is reported, using hydrothermal treatment of a Co(OH)F nanowire array on CC in (NH4)2MoS4 solution. When used as a 3D electrode for hydrogen evolution electrocatalysis, the resulting CoMoS4 NTA/CC demonstrates superior catalytic activity and strong long-term electrochemical durability in 1.0 M phosphate buffer solution (pH=7). It shows small onset overpotential of 21 mV and requires low overpotentials of 104 and 179 mV to drive geometrical current densities of 10 and 50 mA cm−2, respectively. Density functional theory calculations suggest that CoMoS4 has a more favorable hydrogen adsorption free energy than Co(OH)F.CoMos def: A hollow amorphous CoMoS4 nanotube array on carbon cloth (CoMoS4 NTA/CC), derived from Co(OH)F nanowire array (Co(OH)F NWA/CC) through an anion exchange reaction, behaves as a superior 3D catalyst for electrochemical hydrogen evolution. DFT calculations suggest a more favorable hydrogen adsorption free energy on CoMoS4 surface.
      PubDate: 2017-08-18T01:35:56.718735-05:
      DOI: 10.1002/chem.201702923
       
  • Tuning the Effects of Bacterial Membrane Permeability through
           Photo-Isomerization of Antimicrobial Cationic Amphiphiles
    • Authors: Joana Salta; Raphael I. Benhamou, Ido M. Herzog, Micha Fridman
      Pages: 12724 - 12728
      Abstract: Several important antimicrobial drugs act by permeabilizing cell membranes. In this study, we showed that the intensity of membrane permeability caused by antimicrobial cationic amphiphiles can be modified not only by their concentration but also through light-induced isomerization of their lipid segment. Two types of photo-isomerizable cationic amphiphiles were developed and the effects of photo-isomerization on bacterial growth and membrane permeability were evaluated. One photo-isomer inhibited cell growth and division, whereas the other photo-isomer led to a rapid and lethal bacterial membrane-disrupting effect. The switch from “on” to “off” can be obtained by either the cis- or trans-isomer depending on the bacterial strain and the type of cationic amphiphile. These cationic amphiphiles offer a novel tool for research and industrial applications that require light-controlled bacterial membrane permeabilization.Hole on the wall! Photo-isomerizable cationic amphiphiles for light-controlled bacterial membrane permeabilization.
      PubDate: 2017-08-18T01:30:40.103383-05:
      DOI: 10.1002/chem.201703010
       
  • Bleaching Earths as Powerful Additives for Ru-Catalyzed Self-Metathesis of
           Non-Refined Methyl Oleate at Pilot Scale
    • Authors: Jessica Allard; Idriss Curbet, Guillaume Chollet, Fabien Tripoteau, Sophie Sambou, Frédéric Caijo, Yann Raoul, Christophe Crévisy, Olivier Baslé, Marc Mauduit
      Pages: 12729 - 12734
      Abstract: A practical and cost-effective ruthenium-catalyzed self-metathesis of non-refined methyl oleate (85 %) derived from very high oleic sunflower oils was demonstrated at pilot scale using a robust and kg-scale commercially available SIPr-M71 pre-catalyst. The simple addition of 1 wt % bleaching earths (Tonsil 110FF) to a thermally pretreated oil could efficiently prevent catalyst deactivation. Remarkably, without the need for filtration, the catalytic system was able to achieve a turnover number (TON) of more than 744 000 at a catalyst loading of only 1 ppm. At large scale (up to 200 kg), the equilibrium of the self-metathesis reaction was reached within 1 hour at 50 °C under neat conditions at a very low 5 ppm catalyst loading to produce the expected primary metathesis products (PMP), that is, 9-octadecene and dimethyl-9-octadecenoate, with a productive TON of 94900.An efficient and cost-effective pretreatment was proposed to mediate the Ru-catalyzed self-metathesis of non-refined methyl oleate ((Z)-1; 85 %) derived from very high oleic sunflower oils. The use of bleaching earths (Tonsil 110FF, 1 wt %) combined with a thermic pretreatment enabled metathesis under neat conditions with a catalytic loading as low as 0.0001 mol % (1 ppm) and impressive turnover number (TON) of 744 000. The robust catalytic process has proven to be efficient at pilot scale (200 kg) with a remarkable productive TON (94 900) for expected primary metathesis products 9-octadecene (2) and dimethyl-9-octadecenoate (3).
      PubDate: 2017-08-16T08:56:22.70965-05:0
      DOI: 10.1002/chem.201703049
       
  • Arsenic-Mediated C−C Coupling of Cyanides Leading to Cyanido
           Arsazolide [AsC4N4]−
    • Authors: Sören Arlt; Jörg Harloff, Axel Schulz, Alrik Stoffers, Alexander Villinger
      Pages: 12735 - 12738
      Abstract: The chemistry of arsenic cyanides has been investigated and is found to be completely different to the chemistry of the heavier analogs antimony and bismuth as well as phosphorus. The reaction of As(CN)3 with cyanide salts resulted in the formation of an unknown cyanido arsazolide heterocycle, which represents a structure isomer of the desired [As(CN)4]−. The structure, bonding, and formation of this unusual heterocycle is discussed featuring an arsenic mediated C−C coupling of cyanides. [AsC4N4]− salts with different counterions such as [PPh4]+, [PPN]+=[Ph3P-N-PPh3]+, Ag+, and [BMIm]+ are reported with [BMIm][AsC4N4] being a low-temperature ionic liquid (Tm=−62 °C).Go get some cyanide and…isomerize: A novel [AsC4N4]− heterocycle is formed in an unusual isomerization process from its structural isomer [As(CN)4]−, which is formed as transient species when As(CN)3 is treated with CN− (see scheme). Two arsenic-mediated C−C coupling steps are necessary for the formation of the [AsC4N4]− aromatic ring system.
      PubDate: 2017-08-18T01:30:44.474714-05:
      DOI: 10.1002/chem.201703317
       
  • HBr–DMPU: The First Aprotic Organic Solution of Hydrogen Bromide
    • Authors: Zhou Li; Rene Ebule, Jessica Kostyo, Gerald B. Hammond, Bo Xu
      Pages: 12739 - 12743
      Abstract: HBr and DMPU (1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone) form a room-temperature-stable complex that provides a mild, effective, and selective hydrobrominating reagent toward alkynes, alkenes, and allenes. HBr–DMPU could also replace other halogenating reagents in the halo-Prins reaction, ether cleavage, and deoxy-bromination reactions.HBr–DMPU (1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone) is a room-temperature-stable complex with HBr. It is an effective and selective hydrobrominating reagent for alkynes and alkenes.
      PubDate: 2017-08-16T03:25:39.761055-05:
      DOI: 10.1002/chem.201703457
       
  • α-Oxo-Ketenimines from Isocyanides and α-Haloketones: Synthesis
           and Divergent Reactivity
    • Authors: Mathias Mamboury; Qian Wang, Jieping Zhu
      Pages: 12744 - 12748
      Abstract: The palladium-catalyzed reaction of α-haloketones with isocyanides afforded α-oxo-ketenimines through β-hydride elimination of the β-oxo-imidoyl palladium intermediates. Reaction of these relatively stable α-oxo-ketenimines with nucleophiles such as hydrazines, hydrazoic acid, amines, and Grignard reagent afforded pyrazoles, tetrazole, β-keto amidines, and enaminone, respectively, with high chemoselectivity. Whereas amines attack exclusively on the ketenimine functions, the formal [3+2] cycloaddition between N-monosubstituted hydrazines and α-oxo-ketenimines was initiated by nucleophilic addition to the carbonyl group.β-Hydride elimination at will: Reaction of α-haloketones with isocyanides in the presence of a catalytic amount of Pd(OAc)2 afforded α-oxo-ketenimines that can be further converted to 5-aminopyrazoles, tetrazole, β-keto amidines and enaminone in good to excellent yields.
      PubDate: 2017-08-16T13:10:41.832077-05:
      DOI: 10.1002/chem.201703458
       
  • Organocatalytic Highly Regio- and Enantioselective Umpolung Michael
           Addition Reaction of α-Imino Esters
    • Authors: Yasushi Yoshida; Takashi Mino, Masami Sakamoto
      Pages: 12749 - 12753
      Abstract: The catalytic asymmetric umpolung reaction of ketimines is of great importance, because it can easily provide chiral amines bearing a tetrasubstituted carbon atom on its asymmetric center. Because amino acids with a tetrasubstituted carbon center are useful due to their wide applicability as pharmaceuticals and chiral building blocks, their enantioselective synthesis has great significance in organic synthesis. Herein, we demonstrate a metal-free novel phase-transfer-catalyzed highly regio- and enantioselective umpolung Michael reaction of α-imino esters, which provides amino acid derivatives in high yields with up to 98 % ee. The products are successfully converted into chiral amino acid derivative and δ-lactone with high enantiopurity.Asymmetric synthesis: A metal-free novel phase-transfer-catalyzed highly regio- and enantioselective umpolung Michael reaction of α-imino esters have been achieved, which provides amino acid derivatives in high yields with up to 98 % ee. The products are successfully converted into chiral amino acid derivative and δ-lactone with high enantiopurity (see scheme).
      PubDate: 2017-08-29T05:11:17.553947-05:
      DOI: 10.1002/chem.201703479
       
  • A Microfluidic Device for Rapid Screening of E. coli O157:H7 Based on
           IFAST and ATP Bioluminescence Assay for Water Analysis
    • Authors: Bongkot Ngamsom; Alma Truyts, Louis Fourie, Shavon Kumar, Mark D. Tarn, Alexander Iles, Klariska Moodley, Kevin J. Land, Nicole Pamme
      Pages: 12754 - 12757
      Abstract: We present a simple microfluidic system for rapid screening of Escherichia coli (E. coli) O157:H7 employing the specificity of immunomagnetic separation (IMS) via immiscible filtration assisted by surface tension (IFAST), and the sensitivity of the subsequent adenosine triphosphate (ATP) assay by the bioluminescence luciferin/luciferase reaction. The developed device was capable of detecting E. coli O157:H7 from just 6 colony forming units (CFU) in 1 mL spiked buffer within 20 min. When tested with wastewater discharged effluent samples, without pre-concentration, the device demonstrated the ability to detect 104 CFU per mL seeded; suggesting great potential for point-of-need microbiological water quality monitoring.E. coli O157:H7 is analyzed from contaminated water using a simple and portable microfluidic method, based on immiscible filtration assisted by surface tension (IFAST). The specific isolation of pathogen cells—using magnetic particles decorated with antibodies—is combined with the highly sensitive ATP assay, allowing results to be obtained within 20 minutes.
      PubDate: 2017-08-18T01:30:55.509861-05:
      DOI: 10.1002/chem.201703487
       
  • Enantioselective Synthesis of Quaternary Δ4- and Δ5-Dehydroprolines
           Based on a Two-Step Formal [3+2] Cycloaddition of α-Aryl and α-Alkyl
           Isocyano(thio)acetates with Vinyl Ketones
    • Authors: Amaiur Odriozola; Mikel Oiarbide, Claudio Palomo
      Pages: 12758 - 12762
      Abstract: A divergent synthesis of optically active quaternary Δ4- and Δ5-dehydro prolines is developed based on the first catalytic enantioselective conjugate addition of α-substituted isocyano(thio)acetates to vinyl ketones that is general for both α-aryl and α-alkyl isocyano(thio)acetates. The new tetrasubstituted C−N stereocenter is formed without the need of any metal salt due to a bifunctional tertiary amine/squaramide catalyst, featuring a bulky polyaryl sidearm and an unusually short squaramide diamide H⋅⋅⋅H interatomic distance in the solid state.Double game: A bifunctional Brønsted base catalyst promotes the reaction of both α-aryl and α-alkyl isocyano(thio)acetates with vinyl ketones, opening a divergent access to quaternary either Δ4- or Δ5-dehydroprolines with high enantioselectivity.
      PubDate: 2017-08-16T03:26:40.533973-05:
      DOI: 10.1002/chem.201703526
       
  • A Direct Arylation-Cyclisation Reaction for the Construction of
           Medium-Sized Rings
    • Authors: Daniel Whitaker; María Batuecas, Paolo Ricci, Igor Larrosa
      Pages: 12763 - 12766
      Abstract: A strategy for assembling biaryls linked through a medium-sized ring is herein presented. π-Complexation of fluoroarenes to chromium tricarbonyl activates the molecule towards both C−H activation and nucleophilic aromatic substitution without covalently altering the molecular connectivity of the arene. The construction of bridged biaryl molecules with 6–10-membered core rings is achieved through a one-pot C−H arylation/nucleophilic aromatic substitution sequence. The methodology is applicable to the synthesis of heterocyclic as well as fully carbocyclic rings.One-pot, two-step, three rings: An intermolecular cyclisation reaction has been developed, combining direct C−H arylation with nucleophilic aromatic substitution. π-Complexation of fluoroarenes to Cr(CO)3 greatly enhances the reactivity of both steps. Rings with 6 to 10 members are accessible through cyclisation with O, N and C-centered nucleophiles.
      PubDate: 2017-09-07T06:26:09.425822-05:
      DOI: 10.1002/chem.201703527
       
  • Room-Temperature Columnar Nematic and Soft Crystalline Columnar Assemblies
           of a New Series of Perylene-Centred Disc Tetramers
    • Authors: Indu Bala; Santosh Prasad Gupta, Joydip De, Santanu Kumar Pal
      Pages: 12767 - 12778
      Abstract: Three new oligomeric perylene (PE) tetraester derivatives, consisting of a PE-based core with four pentaalkynylbenzene units attached through flexible alkyl spacers, are reported. These derivatives were investigated for their mesomorphic properties and thermal, photophysical, and electrochemical behaviour. Small- (SAXS) and wide-angle X-ray scattering (WAXS) studies were performed to deduce the exact nature of the phases. To resolve overlapping reflections and facilitate their indexing, grazing-incidence SAXS/WAXS experiments were carried out on oriented thin films on indium tin oxide (ITO)-coated glass substrate. The corresponding electron density maps were derived from the intensities observed in the diffraction pattern. Whereas compounds with shorter alkyl spacers (n=6 and 8) were found to self-organise into soft crystalline columnar assemblies, those with longer spacers (n=10) exhibited a liquid-crystalline columnar nematic mesophase. This is in contrast to previous reports that describe highly symmetric 2D hexagonal and rectangular columnar structures of PE-based mesogens. The morphology of self-assembly was found to transform from soft crystal columnar to nematic columnar phase through simple variation in the number of alkyl spacers. All compounds exhibited excellent fluorescence emission properties with a very good quantum yield and large band gap. Apart from high solubility and good quantum yield, these compounds can serve as standards to measure quantum yields of unknown samples. These compounds also display green luminescence and may find applications for various optoelectronic devices.Stacked columns: New perylene-centred disc tetraester derivatives that show soft crystal columnar behaviour and a nematic columnar mesophase at room temperature over a wide temperature range have been designed and synthesised (see figure; Crcolob=soft crystal columnar oblique, Ncol=columnar nematic). These materials may find applications in optoelectronic and solid-state devices.
      PubDate: 2017-08-11T02:52:09.760073-05:
      DOI: 10.1002/chem.201702181
       
  • Soluble Platinum Nanoparticles Ligated by Long-Chain N-Heterocyclic
           Carbenes as Catalysts
    • Authors: Luis M. Martínez-Prieto; Lena Rakers, Angela M. López-Vinasco, Israel Cano, Yannick Coppel, Karine Philippot, Frank Glorius, Bruno Chaudret, Piet W. N. M. van Leeuwen
      Pages: 12779 - 12786
      Abstract: Soluble platinum nanoparticles (Pt NPs) ligated by two different long-chain N-heterocyclic carbenes (LC-IPr and LC-IMe) were synthesized and fully characterized by TEM, high-resolution TEM, wide-angle X-ray scattering (WAXS), X-ray photoelectron spectroscopy (XPS), and solution NMR. The surface chemistry of these NPs (Pt@LC-IPr and Pt@LC-IMe) was investigated by FT-IR and solid state NMR using CO as a probe molecule. A clear influence of the bulkiness of the N-substituents on the size, surface state, and catalytic activity of these Pt NPs was observed. While Pt@LC-IMe showed no activity in the hydroboration of phenylacetylene, Pt@LC-IPr revealed good selectivity for the trans-isomer, which may be supported by a homogeneous species. This is the first example of hydroboration of acetylenes catalyzed by non-supported Pt NPs.Telling a tall tail: soluble platinum nanoparticles ligated by two different long-chain N-heterocyclic carbenes (Pt@LC-IPr and Pt@LC-IMe) show marked differences in their catalytic activity depending on the bulkiness of the N-substituents. While Pt@LC-IMe behaves similarly to heterogeneous catalysts, the catalytic activity of Pt@LC-IPr parallels that of molecular complexes in the hydroboration of phenylacetylene.
      PubDate: 2017-07-26T01:50:48.893294-05:
      DOI: 10.1002/chem.201702288
       
  • Synthesis of gem-Dinitromethylated and Fluorodinitromethylated Derivatives
           of 5,5′-Dinitro-bis-1,2,4-triazole as Promising High-Energy-Density
           Materials
    • Authors: Shi Huang; Junjun Tian, Xiujuan Qi, Kangcai Wang, Qinghua Zhang
      Pages: 12787 - 12794
      Abstract: gem-Dinitromethylated and fluorodinitromethylated 5,5′-dinitro-3,3′-bis-1,2,4-triazole (DNBT) (2 and 3) along with seven ionic derivatives 4–9, were synthesized and characterized by NMR and IR spectroscopies, elemental analysis, single-crystal X-ray diffraction (XRD), and differential scanning calorimetry (DSC). XRD revealed that compounds 2 and 3 crystallized in the monoclinic P21/n space group and compound 5 crystallized in the monoclinic P21/c space group. The physicochemical properties of the as-synthesized compounds 2–9 were investigated and the results indicated that compounds 3, 6, and 7 exhibited a good balance between high energy and low sensitivity, demonstrating their potential as new high-energy-density materials (HEDMs). The proposed synthetic strategy for introducing gem-dinitromethyl and fluorodinitromethyl groups into the DNBT framework to prepare materials with high energy and low sensitivity suitable for HEDMs looks promising.Energetic materials: A series of gem-dinitromethylated and fluorodinitromethylated energetic compounds based on 5,5′-dinitro-3,3′-bis-1,2,4-triazole (DNBT) was synthesized and structurally characterized (see figure). These new compounds have potential application as high-energy-density materials that could replace RDX.
      PubDate: 2017-07-31T10:16:53.461863-05:
      DOI: 10.1002/chem.201702451
       
  • Tunable Ligand Effects on Ruthenium Catalyst Activity for Selectively
           Preparing Imines or Amides by Dehydrogenative Coupling Reactions of
           Alcohols and Amines
    • Authors: Takafumi Higuchi; Risa Tagawa, Atsuhiro Iimuro, Shoko Akiyama, Haruki Nagae, Kazushi Mashima
      Pages: 12795 - 12804
      Abstract: Selective dehydrogenative synthesis of imines from a variety of alcohols and amines was developed by using the ruthenium complex [RuCl2(dppea)2] (6 a: dppea=2-diphenylphosphino-ethylamine) in the presence of catalytic amounts of Zn(OCOCF3)2 and KOtBu, whereas the selective dehydrogenative formation of amides from the same sources was achieved by using another ruthenium complex, [RuCl2{(S)-dppmp}2] [6 d: (S)-dppmp=(S)-2-((diphenylphosphenyl)methyl)pyrrolidine], in the presence of catalytic amounts of Zn(OCOCF3)2 and potassium bis(trimethylsilyl)amide (KHMDS). Our previously reported ruthenium complex, [Ru(OCOCF3)2(dppea)2] (8 a), was the catalyst precursor for the imine synthesis, whereas [Ru(OCOCF3)2{(S)-dppmp}2] (8 d), which was derived from the treatment of 6 d with Zn(OCOCF3)2 and characterized by single-crystal X-ray analysis, was the pre-catalyst for the amide formation. Control experiments revealed that the zinc salt functioned as a reagent for replacing chloride anions with trifluoroacetate anions. Plausible mechanisms for both selective dehydrogenative coupling reactions are proposed based on a time-course study, Hammett plot, and deuterium-labeling experiments.Time for a tune: Tunable ligand effects on ruthenium catalyst activity for selective synthesis of imines and amides by dehydrogenative coupling reaction is reported. Plausible mechanisms for both selective dehydrogenative coupling reactions are proposed based on a time-course study, Hammett plot, and deuterium-labeling experiments.
      PubDate: 2017-07-31T10:15:59.994945-05:
      DOI: 10.1002/chem.201701342
       
  • Competitive Energy and Electron Transfer in β-Functionalized Free-Base
           Porphyrin–Zinc Porphyrin Dimer Axially Coordinated to C60: Synthesis,
           Supramolecular Formation and Excited-State Processes
    • Authors: Yi Hu; Michael B. Thomas, R. G. Waruna Jinadasa, Hong Wang, Francis D'Souza
      Pages: 12805 - 12814
      Abstract: Simultaneous occurrence of energy and electron transfer events involving different acceptor sites in a newly assembled supramolecular triad comprised of covalently linked free-base porphyrin–zinc porphyrin dyad, H2P−ZnP axially coordinated to electron acceptor fullerene, has been successfully demonstrated. The dyad was connected through the β-pyrrole positions of the porphyrin macrocycle instead of the traditionally used meso-positions for better electronic communication. Interestingly, the β-pyrrole functionalization modulated the optical properties to such an extent that it was possible to almost exclusively excite the zinc porphyrin entity in the supramolecular triad. The measured binding constant for the complex with 1:1 molecular stoichiometry was in the order of 104 m−1 revealing moderately stable complex formation. An energy level diagram constructed using optical, electrochemical and computational results suggested that both the anticipated energy and electron events are thermodynamically feasible in the triad. Consequently, it was possible to demonstrate occurrence of excited state energy transfer to the covalently linked H2P, and electron transfer to the coordinated ImC60 from studies involving steady-state and time-resolved emission, and femto- and nanosecond transient absorption studies. The estimated energy transfer was around 67 % in the dyad with a rate constant of 1.1×109 s−1. In the supramolecular triad, the charge separated state was rather long-lived although it was difficult to arrive the exact lifetime of charge separated state from nanosecond transient spectral studies due to overlap of strong triplet excited signals of porphyrin in the monitoring wavelength window. Nevertheless, simultaneous occurrence of energy and electron transfer in the appropriately positioned energy and electron acceptor entities in a supramolecular triad was possible to demonstrate in the present study, a step forward to unraveling the complex photochemical events occurring in natural photosynthesis and its implications in building light energy harvesting devices.Formation of a supramolecular triad featuring β-pyrrole connected free-base porphyrin–zinc porphyrin self-assembled to C60, and occurrence of competitive energy and electron transfer processes from transient absorption studies is demonstrated.
      PubDate: 2017-07-27T02:00:36.854591-05:
      DOI: 10.1002/chem.201702178
       
  • Terminally Truncated Isopenicillin N Synthase Generates a Dithioester
           Product: Evidence for a Thioaldehyde Intermediate during Catalysis and a
           New Mode of Reaction for Non-Heme Iron Oxidases
    • Authors: Luke A. McNeill; Toby J. N. Brown, Malkit Sami, Ian J. Clifton, Nicolai I. Burzlaff, Timothy D. W. Claridge, Robert M. Adlington, Jack E. Baldwin, Peter J. Rutledge, Christopher J. Schofield
      Pages: 12815 - 12824
      Abstract: Isopenicillin N synthase (IPNS) catalyses the four-electron oxidation of a tripeptide, l-δ-(α-aminoadipoyl)-l-cysteinyl-d-valine (ACV), to give isopenicillin N (IPN), the first-formed β-lactam in penicillin and cephalosporin biosynthesis. IPNS catalysis is dependent upon an iron(II) cofactor and oxygen as a co-substrate. In the absence of substrate, the carbonyl oxygen of the side-chain amide of the penultimate residue, Gln330, co-ordinates to the active-site metal iron. Substrate binding ablates the interaction between Gln330 and the metal, triggering rearrangement of seven C-terminal residues, which move to take up a conformation that extends the final α-helix and encloses ACV in the active site. Mutagenesis studies are reported, which probe the role of the C-terminal and other aspects of the substrate binding pocket in IPNS. The hydrophobic nature of amino acid side-chains around the ACV binding pocket is important in catalysis. Deletion of seven C-terminal residues exposes the active site and leads to formation of a new type of thiol oxidation product. The isolated product is shown by LC-MS and NMR analyses to be the ene-thiol tautomer of a dithioester, made up from two molecules of ACV linked between the thiol sulfur of one tripeptide and the oxidised cysteinyl β-carbon of the other. A mechanism for its formation is proposed, supported by an X-ray crystal structure, which shows the substrate ACV bound at the active site, its cysteinyl β-carbon exposed to attack by a second molecule of substrate, adjacent. Formation of this product constitutes a new mode of reaction for IPNS and non-heme iron oxidases in general.Chasing its tail' The I325* mutant of isopenicillin N synthase (IPNS) is missing seven amino acids from its C-terminus. Truncation exposes the active site to the external environment, and leads to interception of the key thioaldehyde intermediate by a second molecule of substrate. This affords a remarkable side-product: the ene-thiol tautomer of a dithioester, which evinces an entirely new mode of reaction for IPNS and non-heme iron oxidases more generally.
      PubDate: 2017-08-21T07:10:30.862697-05:
      DOI: 10.1002/chem.201701592
       
  • Synthesis, Optical Properties, and DNA Interaction of New Diquats Based on
           Triazolopyridines and Triazoloquinolines
    • Authors: Pedro J. Llabres-Campaner; Lluís Guijarro, Claudia Giarratano, Rafael Ballesteros-Garrido, Ramón J. Zaragozá, M. José Aurell, Enrique García-España, Rafael Ballesteros, Belén Abarca
      Pages: 12825 - 12832
      Abstract: New diquat derivatives based on [1,2,3]triazolo[1,5-a]pyridine and [1,2,3]triazolo[1,5-a]quinoline have been synthesized in excellent yields. To evaluate the effect of the alkyl bridge length, ethane and propane dibromo alkane substrates were used for their synthesis. Theoretical calculations predicted a very small energetic barrier between the two possible enantiomers P (Ra) and M (Sa), which makes them very difficult to resolve. Thermal denaturation studies, UV/Visible spectroscopy, and fluorescence titrations with ct-DNA evidenced the intercalation of the quinoline derivatives in DNA.Electrostatic interactions: New diquat derivatives based on [1,2,3]triazolo[1,5-a]pyridine and [1,2,3]triazolo[1,5-a]quinoline have been synthesized in excellent yields. To evaluate the effect of the alkyl bridge length, ethane and propane dibromo alkane substrates were used for their synthesis (see scheme).
      PubDate: 2017-08-16T03:20:45.613198-05:
      DOI: 10.1002/chem.201701618
       
  • Synthesis, Characterization, and Electrochemistry of Open-Chain
           Pentapyrroles and Sapphyrins with Highly Electron-Withdrawing
           meso-Tetraaryl Substituents
    • Authors: Wenqian Shan; Nicolas Desbois, Virginie Blondeau-Patissier, Mario L. Naitana, Valentin Quesneau, Yoann Rousselin, Claude P. Gros, Zhongping Ou, Karl M. Kadish
      Pages: 12833 - 12844
      Abstract: A series of open-chain pentapyrroles and sapphyrins with highly electron-withdrawing substituents (i.e., CN, CF3, or CO2Me) on the meso-phenyl rings was synthesized and characterized as to the spectral properties, protonation reactions, and electrochemistry in non-aqueous media. The investigated compounds are represented as (Ar)4PPyH3 and (Ar)4SapH3 where PPy and Sap correspond to the tri-anion of the open-chain pentapyrrole and sapphyrin, respectively, and Ar=p-CNPh, p-CF3Ph, or p-CO2MePh. UV/Vis and 1H NMR spectroscopy as well as mass spectrometry data are given for the confirmation of the structures for the newly synthesized compounds. An X-ray structure for one of the pentapyrroles, that is, (p-CF3Ph)4PPyH3 (2), is also presented. The protonation processes were examined by UV/Vis absorption spectroscopy during the titration of the compounds with trifluoroacetic acid (TFA) in CH2Cl2. Equilibrium constants for the protonation reactions were calculated by using both the Hill equation and the mole ratio method. The protonation-initiated conversion of pentapyrroles to sapphyrins upon oxidation was also investigated. Cyclic voltammetry was used to measure the redox potentials in CH2Cl2, PhCN, and/or pyridine (Py). Electrochemical properties, protonation constants, and chemical reactions of the six compounds in the two series were then analyzed as a function of the solvent properties and the type of the electron-withdrawing groups on the meso-phenyl rings.Open and close: Several open-chain pentapyrroles and sapphyrins with highly electron-withdrawing substituents (i.e., CN, CF3, or CO2Me) on the meso-phenyl rings were synthesized and characterized by, for example, X-ray diffraction analysis (see figure). The behavior towards protonation of these compound was also investigated.
      PubDate: 2017-08-21T02:40:36.300424-05:
      DOI: 10.1002/chem.201701968
       
  • Molecular Dynamics Insights into Polyamine–DNA Binding Modes:
           Implications for Cross-Link Selectivity
    • Authors: Emmanuelle Bignon; Chen-Hui Chan, Christophe Morell, Antonio Monari, Jean-Luc Ravanat, Elise Dumont
      Pages: 12845 - 12852
      Abstract: Biogenic polyamines, which play a role in DNA condensation and stabilization, are ubiquitous and are found at millimolar concentration in the nucleus of eukaryotic cells. The interaction modes of three polyamines—putrescine (Put), spermine (Spm), and spermidine (Spd)—with a self-complementary 16 base pair (bp) duplex, are investigated by all-atom explicit-solvent molecular dynamics. The length of the amine aliphatic chain leads to a change of the interaction mode from minor groove binding to major groove binding. Through all-atom dynamics, noncovalent interactions that stabilize the polyamine–DNA complex and prefigure the reactivity, leading to the low-barrier formation of deleterious DNA–polyamine cross-links, after one-electron oxidation of a guanine nucleobase, are unraveled. The binding strength is quantified from the obtained trajectories by molecular mechanics generalized Born surface area post-processing (MM-GBSA). The values of binding free energies provide the same affinity order, Put
      PubDate: 2017-08-16T03:21:10.763684-05:
      DOI: 10.1002/chem.201702065
       
  • Design and Solution-Phase Synthesis of Membrane-Targeting Lipopeptides
           with Selective Antibacterial Activity
    • Authors: Mohini M. Konai; Utsarga Adhikary, Jayanta Haldar
      Pages: 12853 - 12860
      Abstract: Designing selective antibacterial molecules remains an unmet goal in the field of membrane-targeting agents. Herein, we report the rational design and synthesis of a new class of lipopeptides, which possess highly selective bacterial killing over mammalian cells. The selective interaction with bacterial over mammalian membranes was established through various spectroscopic, as well as microscopic experiments, including biophysical studies with the model membranes. A detailed antibacterial structure–activity relationship was delineated after preparing a series of molecules consisting of the peptide moieties with varied sequence of amino acids, such as d-phenylalanine, d-leucine, and d-lysine. Antibacterial activity was found to vary with the nature and positioning of hydrophobicity in the molecules, as well as number of positive charges. Optimized lipopeptide 9 did not show any hemolytic activity even at 1000 μg mL−1 and displayed>200-fold and>100-fold selectivity towards S. aureus and E. coli, respectively. More importantly, compound 9 was found to display good antibacterial activity (MIC 6.3–12.5 μg mL−1) against the five top most critical bacteria according to World Health Organization (WHO) priority pathogens list. Therefore, the results suggested that this new class of lipopeptides bear real promises for the development as future antibacterial agents.The rational design and synthesis of a new class of lipopeptides, which possess highly selective bacterial killing over mammalian cells, is reported. The selective interaction with bacterial over mammalian membranes was established through various spectroscopic, as well as microscopic experiments, including biophysical studies with the model membranes (see scheme).
      PubDate: 2017-08-21T02:36:02.407847-05:
      DOI: 10.1002/chem.201702227
       
  • “Conducted Tour” Migration of Li+ during the cis/trans Stereoinversion
           of α-Arylvinyllithiums
    • Authors: Rudolf Knorr; Claudia Behringer, Jakob Ruhdorfer, Ulrich von Roman, Ernst Lattke, Petra Böhrer
      Pages: 12861 - 12869
      Abstract: A “conducted tour” migration keeps a mobile client on a profitable route even though an occasional side-step may seem attractive. A stereochemical manifestation of such a migration had been suggested by Donald J. Cram (1964), and we present now a different example that concerns the cis/trans stereoinversion of monomeric H2C=C(Li)-aryl compounds: Upon tetrahydrofuran (THF)-assisted heterolysis of the Li−C bond with formation of a solvent-separated ion pair (SSIP), the unchained “mobile client” Li+(THF)4 is proposed to surmount the rim of the electronically fixed aryl group and to disdain the less encumbered pathways across the H2C=C region. This interpretation is based on knowledge from a previously published series of monomeric α-arylalkenyllithiums in combination with two new members: 4-(α-lithiovinyl)-2,2-dimethylbenz[f]indane (1) revealed both a barrier against α-aryl rotation and a route-distinguishing retardation as compared with the corresponding migration-dependent cis/trans stereoinversion rate constant of 1-(α-lithiovinyl)naphthalene (2). Monomeric and dimeric ground states of 1 and 2 and their microsolvation numbers were determined by using the recently developed primary and secondary NMR criteria.Separation and migration—no digressions: Quasibenzyl-anion resonance is stronger in the linear transition state (see scheme) than in the two tri-solvated, angular ground states (CIP and CIP′), because immobilization of the fourth THF ligand at Li increases the charge delocalization from C(α) to C(4). The excess negative charge (∂−) at C(4) appears to favor the migration of Li+(THF)4 across the C(3)/C(4) region of the conformationally fixed α-aryl group.
      PubDate: 2017-08-18T02:20:54.986811-05:
      DOI: 10.1002/chem.201702353
       
  • Fabrication of Redox-Responsive Degradable Capsule Particles by a
           Shell-Selective Photoinduced Cross-Linking Approach from Spherical Polymer
           Particles
    • Authors: Yukiya Kitayama; Toshifumi Takeuchi
      Pages: 12870 - 12875
      Abstract: In this study, a fabrication route towards functional capsule particles was successfully developed by means of a self-templating shell-selective cross-linking strategy that enables us to prepare shell-cross-linked hollow polymer particles directly from homogeneous spherical polymer particles. To prepare redox-responsive degradable capsule particles, a newly designed monomer bearing a photoinduced post-cross-linking group (cinnamoyl group) and a redox-environment-responsive cleavable group (disulfide group), N-cinnamoyl-N′-methyacryloylcystamine (MCC), was synthesized. Redox-responsive degradable capsule particles were successfully prepared from homogeneous spherical poly(MCC)-based particles by a self-templating shell-selective photoinduced cross-linking approach. Moreover, the cargo loading capability of the shell-cross-linked hollow particles was confirmed through a solvent exchange procedure using dyes, polymer precursors and anticancer reagents. Furthermore, redox-responsive degradability of the capsule polymer particles was also confirmed by adding a reducing agent for cleavage of the disulfide linkage. We hope that the efficient fabrication route of functional capsule particles directly from spherical polymer particles opens efficient routes for the fabrication of a wide range of capsule particles; in particular, this technique is robust, productive, and facile because neither additional sacrificial template particles nor toxic solvents are required.Encapsulating! The synthesis of redox-responsive, degradable capsule particles was carried out from homogeneous spherical polymer particles using the self-templating shell-selective cross-linking methodology. By means of a solvent exchange process dye molecules, polymer precursors, and antitumor reagents were successfully encapsulated (see figure).
      PubDate: 2017-08-21T02:35:27.917495-05:
      DOI: 10.1002/chem.201702367
       
  • Traceless Solid-Phase Synthesis of Fused Chiral Macrocycles via
           Conformational Constraint-Assisted Cyclic Iminium Formation
    • Authors: Eva Schütznerová; Allen G. Oliver, Greg A. Slough, Viktor Krchňák
      Pages: 12876 - 12885
      Abstract: Natural products comprising chiral molecular scaffolds containing fused medium-sized cycles and macrocycles represent an important and relevant pharmacological target for the discovery and development of new drugs. Here, we describe traceless solid-phase synthesis of acyclic intermediates amenable to cyclization to medium (11) and large (12) fused rings. The key aspect of the synthetic strategy is incorporation of a specific conformation constraint that facilitates cyclization in favor of 11- and 12-membered rings rather than possible 7-membered ones. The role of constraints in preorganization required for cyclization is supported by computational analysis. The synthesis involves cyclic N-sulfonyliminium-nucleophilic addition chemistry as the key ring-forming reaction and proceeds with complete stereocontrol of the newly formed stereogenic center. We document the scope and limitations of this strategy in the synthesis of 11+5, 11+6, 11+7, and 12+6 fused rings representing molecular scaffolds with 3D architecture that mimic complex natural products.The traceless solid-phase synthesis of acyclic intermediates amenable to cyclization to medium (11) and large (12) fused rings is described. The key aspect of the synthetic strategy is incorporation of a specific conformation constraint that facilitates cyclization in favor of 11- and 12-membered rings rather than possible 7-membered ones.
      PubDate: 2017-08-16T03:01:15.227018-05:
      DOI: 10.1002/chem.201702461
       
  • Synthesis of Benzofurans and Indoles from Terminal Alkynes and
           Iodoaromatics Catalyzed by Recyclable Palladium Nanoparticles Immobilized
           on Siliceous Mesocellular Foam
    • Authors: Alexandre Bruneau; Karl P. J. Gustafson, Ning Yuan, Cheuk-Wai Tai, Ingmar Persson, Xiaodong Zou, Jan-E. Bäckvall
      Pages: 12886 - 12891
      Abstract: Herein, we report on the utilization of a heterogeneous catalyst, consisting of Pd nanoparticles supported on a siliceous mesocellular foam (Pd0-AmP-MCF), for the synthesis of heterocycles. Reaction of o-iodophenols and protected o-iodoanilines with acetylenes in the presence of a Pd nanocatalyst produced 2-substituted benzofurans and indoles, respectively. In general, the catalytic protocol afforded the desired products in good to excellent yields under mild reaction conditions without the addition of ligands. Moreover, the structure of the reported Pd nanocatalyst was further elucidated with extended X-ray absorption fine-structure spectroscopy, and it was proven that the catalyst could be recycled multiple times without significant loss of activity.Pd nanoparticles supported on siliceous mesocellular foam (Pd0-AmP-MCF) were found to efficiently catalyze the reaction of o-iodophenols and protected o-iodoanilines with acetylenes to produce 2-substituted benzofurans and indoles, respectively. In general, the catalytic protocol afforded the desired products in good to excellent yields under mild reaction conditions without the addition of ligands.
      PubDate: 2017-08-21T02:30:35.643161-05:
      DOI: 10.1002/chem.201702614
       
  • Isomer Selectivity in Low-Energy Electron Attachment to Nitroimidazoles
    • Authors: Anita Ribar; Katharina Fink, Michael Probst, Stefan E. Huber, Linda Feketeová, Stephan Denifl
      Pages: 12892 - 12899
      Abstract: Low-energy electrons effectively decompose the isomers 2-nitroimidazole and 4(5)-nitroimidazole by dissociative electron attachment (DEA) into a variety of fragment anions and radicals. The present study shows that a distinct selectivity for the two isomers occurs in the DEA reactions. Several new decay channels are observed for 2-nitroimidazole, including a dominant one leading to the loss of molecular H2O by attachment of a low-energy electron. In contrast, the loss of a single hydrogen atom is a much more efficient reaction in DEA to 4(5)-nitroimidazole. Quantum chemical calculations were carried out to explain the pronounced isomer effect found in the DEA experiment. Although the free energies of the reactions are similar for the different isomers, the very different natures of the dipole-bound states and valence-bound anions lead to preference for or hindrance of a particular dissociation channel. Nitroimidazolic compounds are considered as radiosensitizing compounds in tumor radiation therapy. The enhanced formation of fragments, including the highly reactive hydroxyl radical, in DEA to 2-nitroimidazole suggests that it may be a more efficient radiosensitizing agent than 4(5)-nitroimidazoles.Selective attachment: Low-energy electrons, which play an important role in the induction of radiation damage, decompose 2-nitroimidazole (2NI) by dissociative electron attachment (DEA) into variety of radicals more efficiently than its isomers 4NI and 5NI. Several new decay channels were observed, including a dominant channel leading to the loss of molecular H2O. Enhanced formation of fragments, including the highly reactive hydroxyl radical, in DEA to 2NI suggests that it may be a more efficient radiosensitizing agent than 4(5)-nitroimidazoles (see figure).
      PubDate: 2017-08-16T03:01:27.364675-05:
      DOI: 10.1002/chem.201702644
       
  • Ketone Formation from Carboxylic Acids by Ketonic Decarboxylation: The
           Exceptional Case of the Tertiary Carboxylic Acids
    • Authors: Borja Oliver-Tomas; Michael Renz, Avelino Corma
      Pages: 12900 - 12908
      Abstract: For the reaction mechanism of the ketonic decarboxylation of two carboxylic acids, a β-keto acid is favored as key intermediate in many experimental and theoretical studies. Hydrogen atoms in the α-position are an indispensable requirement for the substrates to react by following this mechanism. However, isolated observations with tertiary carboxylic acids are not consistent with it and these are revisited and discussed herein. The experimental results obtained with pivalic acid indicate that the ketonic decarboxylation does not occur with this substrate. Instead, it is consumed in alternative reactions such as disintegration into isobutene, carbon monoxide, and water (retro-Koch reaction). In addition, the carboxylic acid is isomerized or loses carbon atoms, which converts the tertiary carboxylic acid into carboxylic acids bearing α-proton atoms. Hence, the latter are suitable to react through the β-keto acid pathway. A second substrate, 2,2,5,5-tetramethyladipic acid, reacted by following the same retro-Koch pathway. The primary product was the monocarboxylic acid 2,2,5-trimethyl-4-hexenoic acid (and its double bond isomer), which might be further transformed into a cyclic enone or a lactone. The ketonic decarboxylation product, 2,2,5,5-tetramethylcyclopentanone was observed in traces (
      PubDate: 2017-08-16T09:02:51.201747-05:
      DOI: 10.1002/chem.201702680
       
  • Understanding Noncovalent Interactions of Small Molecules with Carbon
           Nanotubes
    • Authors: Joaquín Calbo; Alejandro López-Moreno, Alberto de Juan, Jeffrey Comer, Enrique Ortí, Emilio M. Pérez
      Pages: 12909 - 12916
      Abstract: We combine experimental methods, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations in the quantitative analysis of noncovalent interactions between (6,5)-enriched single-walled carbon nanotubes (SWNTs), as hosts, and a set of pyrene derivatives with different electronic properties and surface areas, as guests. The experiments and calculations were carried out in two solvents with markedly different polarities, namely 1,1′,2,2′-tetrachloroethane (TCE) and N,N-dimethylformamide (DMF). Our results show that dispersion forces govern the supramolecular association of small molecules with (6,5)-SWNTs, with negligible contributions from ground-state charge-transfer effects. In the nonpolar solvent (TCE), the binding constants are highly correlated with the contact area between the SWNT and the guests. In the polar solvent (DMF), the binding constants show a complex dependence on the chemical nature of the pyrene substituents, as demonstrated by MD simulations with the explicit inclusion of solvent molecules. The solvation of the small molecules is shown to play a leading role in the binding process. Remarkably, the binding constants obtained from the MD simulations for the five guest molecules correlate with those derived from experiment. Furthermore, the MD simulations also reveal the structure of the adsorbed guest from low to high SWNT surface coverage.Discrete interactions: A quantitative multidisciplinary approach to understanding noncovalent interactions between pyrene molecules and single-walled carbon nanotubes involving experimental analyses, DFT, and molecular dynamics calculations is presented (see figure). The results suggest that the pyrene guests interact through π–π forces with additional discrete contacts promoted by the substituents at the periphery of the pyrene core.
      PubDate: 2017-08-16T08:56:38.866987-05:
      DOI: 10.1002/chem.201702756
       
  • Coexistence of Normal and Auxetic Behavior in a Thermally and Chemically
           Stable sp3 Nanothread: Poly[5]asterane
    • Authors: Biswajit Saha; Saied Md. Pratik, Ayan Datta
      Pages: 12917 - 12923
      Abstract: A one-dimensional nanostructure with sp3-hybridized carbon atoms, namely, poly[5]asterane (PA), is predicted by means of electronic structure calculations and reactive molecular dynamics simulations. Thermochemical analysis based on homodesmotic reactions showed that the formation of poly[5]asterane is more favorable than that of polytriangulane and comparable to that of polytwistane. A plane-wave DFT approach gave a computed Young's modulus of about 0.84 TPa, which is quite promising and comparable to those of other sp3-hybridized nanothreads. Simulations of the desorption of hydrogen atoms from PA showed a high activation energy (Ea≈52 kcal mol−1), which again indicates substantial chemical stability. Interestingly, PA was shown to exhibit auxetic behavior (negative Poisson's ratio). Thus, PA is advocated as a new mechanically and chemically stable nanothread with exotic auxetic behavior.Periodic properties: A new 1D nanostructure, namely, poly[5]asterane is proposed which shows periodically varying diameter along the long axis, and exhibits both normal behavior (positive Poisson's ratio) and auxetic behavior (negative Poisson's ratio) on application of axial force along the long axis (see figure).
      PubDate: 2017-08-16T02:55:44.239448-05:
      DOI: 10.1002/chem.201702775
       
  • Construction of Nitrogen-Doped Carbon-Coated MoSe2 Microspheres with
           Enhanced Performance for Lithium Storage
    • Authors: Wangjia Tang; Dong Xie, Tong Shen, Xiuli Wang, Donghuang Wang, Xuqing Zhang, Xinhui Xia, Jianbo Wu, Jiangping Tu
      Pages: 12924 - 12929
      Abstract: Exploring advanced anode materials with highly reversible capacity have gained great interests for large-scale lithium storage. A facile two-step method is developed to synthesize nitrogen-doped carbon coated MoSe2 microspheres via hydrothermal plus thermal polymerization. The MoSe2 microspheres composed of interconnected nanoflakes are homogeneously coated by a thin nitrogen-doped carbon (N-C) layer. As an anode for lithium ion batteries, the MoSe2/N-C composite shows better reversibility, smaller polarization, and higher electrochemical reactivity as compared to the unmodified MoSe2 microspheres. The MoSe2/N-C electrode delivers a high specific capacity of 698 mAh g−1 after 100 cycles at a current density of 100 mA g−1 and good high rate performance (471 mAh g−1 at a high current density of 2000 mA g−1). The improved electrochemical performance is attributed to the conductive N-C coating and hierarchical microsphere structure with fast ion/electron transfer characteristics.Microsphere of influence: Nitrogen-doped carbon-coated MoSe2 microspheres are constructed by a facile two-step process. These microspheres as anode materials exhibit superior Li ion-storage performance.
      PubDate: 2017-08-21T02:30:42.77368-05:0
      DOI: 10.1002/chem.201702840
       
  • Rhodium-Catalyzed Denitrogenative [3+2] Cycloaddition: Access to
           Functionalized Hydroindolones and the Framework of Montanine-Type
           Amaryllidaceae Alkaloids
    • Authors: Hongjian Yang; Shengtai Hou, Cheng Tao, Zhao Liu, Chao Wang, Bin Cheng, Yun Li, Hongbin Zhai
      Pages: 12930 - 12936
      Abstract: Rhodium-catalyzed denitrogenative [3+2] cycloaddition of 1-sulfonyl-1,2,3-triazoles with cyclic silyl dienol ethers has been developed for the synthesis of functionalized hydroindolones or their corresponding silyl ethers. The present method has been employed to construct synthetically valuable bicyclo[3.3.1]alkenone derivatives and pyrrolidine-ring-containing bicyclic indole compounds. As a further synthetic application, a stereoselective synthesis of 5,11-methanomorphanthridin-3-one, which shares a key skeleton with montanine-type Amaryllidaceae alkaloids has been achieved by using this chemistry.Rhodium-catalyzed denitrogenative [3+2] cycloaddition of 1-sulfonyl-1,2,3-triazoles with cyclic silyl dienol ethers has been developed for the synthesis of functionalized hydroindolones or their corresponding silyl ethers. Furthermore, the diastereoselective synthesis of the framework of montanine-type Amaryllidaceae alkaloids has also been explored by using this chemistry.
      PubDate: 2017-08-21T02:25:39.389445-05:
      DOI: 10.1002/chem.201702893
       
  • Isocyanurate Formation During Oxazolidinone Synthesis from Epoxides and
           Isocyanates Catalysed by a Chromium(Salphen) Complex
    • Authors: Xiao Wu; Jess Mason, Michael North
      Pages: 12937 - 12943
      Abstract: Chromium(salphen) complex 10 is found to be a catalyst for the preparation of oxazolidinones from epoxides and isocyanates. Using the optimal reaction conditions (1.5 mol % of chromium(salphen) complex 10 at 80 °C in toluene for 4 hours), six epoxides were reacted with five isocyanates, providing 15 oxazolidinones in up to 90 % yield. With electron-deficient isocyanates, cyclotrimerisation of the isocyanate to the corresponding isocyanurates is a competing reaction, showing the importance of matching catalyst activity to that of the substrates.A tale of two reactions: A chromimium(salphen) complex catalyses the formation of oxazolidinones from epoxides and isocyanates. However, with particularly electron-deficient isocyanates, the complex catalyses cyclotrimerisation of the isocyanate to an isocyanurate instead (see scheme).
      PubDate: 2017-08-18T01:30:25.50067-05:0
      DOI: 10.1002/chem.201702948
       
  • Nanocrystal-Assembled Porous Na3MgTi(PO4)3 Aggregates as Highly Stable
           Anode for Aqueous Sodium-Ion Batteries
    • Authors: Fang Zhang; Wanfeng Li, Xingde Xiang, Molong Sun
      Pages: 12944 - 12948
      Abstract: Aqueous sodium-ion batteries (SIBs) represent a class of green electrochemical technology for large-scale storage of sustainable energies such as wind power and solar radiation, owing to their low cost, environmental friendliness, and reliable safety. However, there is still lack of available anode materials for aqueous SIBs. Herein, nanocrystal-assembled porous Na3MgTi(PO4)3 aggregates are reported as novel anode material for aqueous SIBs. The crystal structure, morphological features, and electrochemical properties have been analyzed with X-ray diffraction, scanning electron microscopy, transition electron microscopy, cyclic voltammetry, and charge/discharge measurements. As revealed, the material possesses a porous nanostructure composed of 5 nm nanocrystals and mesoporous channels. During Na-insertion/extraction, it undergoes a one-step single-phase reaction mechanism through reversible electrochemistry of the Ti4+/Ti3+ redox couple, showing a rechargeable capacity of 54 mAh g−1 and an average working potential of −0.63 V (vs. Ag/AgCl) at 0.2 C. More importantly, good rate capacity (33 mAh g−1 at 4 C) and excellent cycling performance (94.2 % capacity retention after 100 cycles at 0.5 C) are achieved due to the unique porous nanostructure and robust compositional framework. The finding in this work would create new opportunities for design of low-cost, long-cycling aqueous SIBs.Titanic power: Aqueous sodium-ion batteries (SIBs) represent a class of green electrochemical technology for large-scale storage of sustainable energies such as wind power and solar radiation. Nanocrystal-assembled porous Na3MgTi(PO4)3 aggregates can serve as novel anode material for aqueous SIBs, showing a reversible capacity of 54 mAh g−1, a reasonable working potential of −0.63 V (vs. Ag/AgCl) and a high capacity retention of 94.2 % after 100 cycles (0.5 C).
      PubDate: 2017-08-29T05:11:24.043476-05:
      DOI: 10.1002/chem.201703044
       
  • Magnetic Shielding Studies of C2 and C2H2 Support Higher than Triple Bond
           Multiplicity in C2
    • Authors: Peter B. Karadakov; Josh Kirsopp
      Pages: 12949 - 12954
      Abstract: The carbon–carbon bonds in the ground states of C2 and C2H2, at their equilibrium geometries, are compared by analysing the changes in the off-nucleus magnetic shielding tensor within the space surrounding each of these molecules. A wide range of quantum-chemical approaches, including full-valence CASSCF-GIAO, CCSD(T)-GIAO and CCSDT-GIAO, all with the cc-pVQZ basis set, as well as HF-GIAO and MP2-GIAO, with the cc-pVQZ, cc-pV5Z and cc-pV6Z basis sets, show that the surroundings of the carbon–carbon bond in C2 are more shielded than those of the carbon–carbon bond in C2H2. The additional shielding of the carbon–carbon bond in C2 is found to be due to a larger paramagnetic contribution to the component of the shielding tensor which is perpendicular to the molecular axis. The analysis of the off-nucleus shielding data indicates that the carbon–carbon bond in C2 is “bulkier” and, therefore, of a higher multiplicity, but weaker than the corresponding bond in C2H2. According to the results of the shielding calculations, the carbon nuclei in C2 should be much more shielded than those in C2H2, with 13C isotropic magnetic shieldings in the ranges of around 224–227 ppm and around 123–125 ppm for C2 and C2H2, respectively.When three becomes four: Off-nucleus shielding calculations indicate that the carbon–carbon bond in C2 is more shielded than the triple carbon–carbon bond in C2H2 and can, therefore, have higher than triple bond multiplicity (see figure).
      PubDate: 2017-08-18T01:30:32.13164-05:0
      DOI: 10.1002/chem.201703051
       
 
 
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