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  Subjects -> CHEMISTRY (Total: 841 journals)
    - ANALYTICAL CHEMISTRY (50 journals)
    - CHEMISTRY (593 journals)
    - CRYSTALLOGRAPHY (21 journals)
    - ELECTROCHEMISTRY (25 journals)
    - INORGANIC CHEMISTRY (41 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: 233)
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: 68)
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: 222)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 213)
Annales UMCS, Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 3)
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: 295)
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: 121)
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: 70)
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: 142)
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: 44)
Chemistry of Materials     Full-text available via subscription   (Followers: 258)
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: 8)
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: 17)

        1 2 3 | Last

Journal Cover Chemistry - A European Journal
  [SJR: 2.323]   [H-I: 188]   [142 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]
  • Energetic 1,2,5-oxadiazolo-pyridazine and its N-oxide
    • Authors: Jean'ne Shreeve; Yongxing Tang, Chunlin He, Gregory H. Imler, Damon Parrish
      Abstract: Achieving an energetic compound which exhibits high performance and insensitivity is important in the field of energetic materials and remains a major challenge. Here we find that oxidation of 4,7-diaminopyridazino[4,5-c]furoxan (5) with hypofluorous acid (HOF) or a mixture of 50% hydrogen peroxide and trifluoroacetic anhydride gives rise to 6-amino-7-nitro-[1,2,5]oxadiazolo[3,4-c]pyridazine (7) and its N-oxide derivative (8). Compound 8 displays an energetic performance compared to TATB and insensitive properties (IS: 36 J and FS:>360 N). Such excellent properties make it attractive for high performance applications where insensitivity is important.
      PubDate: 2017-09-23T01:20:22.262964-05:
      DOI: 10.1002/chem.201703930
       
  • Development of Phenyl Cyclohexylcarboxamides as a Novel Class of Hsp90
           C-terminal Inhibitors
    • Authors: leah forsberg; gaurav garg, huiping zhao, Brian Blagg
      Abstract: Inhibition of the heat shock protein 90 (Hsp90) C-terminus represents a promising therapeutic strategy for the treatment of cancer. Novobiocin, a coumarin antibiotic, was the first Hsp90 C-terminal inhibitor identified, however, it manifested poor anti-proliferative activity (SKBr3, IC50 ~ 700 μM). Subsequent SAR studies on novobiocin led to development of several analogues that exhibited improved anti-proliferative activity against several cancer cell lines. Recently, we demonstrated that the biphenyl core could be used in lieu of the coumarin ring system, which resulted in more efficacious analogues. In continuation of previous efforts, the work described herein has identified the phenyl cyclohexyl core as a novel scaffold for Hsp90 C-terminal inhibition. SAR studies on this scaffold led to the development of compounds that manifest mid-nanomolar activity against SKBr3 and MCF-7 breast cancer cell lines through Hsp90 inhibition.
      PubDate: 2017-09-22T10:20:44.728099-05:
      DOI: 10.1002/chem.201703206
       
  • Spectroscopic observation and molecular dynamics simulation of Ga surface
           segregation in liquid Pd-Ga alloys
    • Authors: Christian Papp; Mathias Grabau, Jannis Erhard, Nicola Taccardi, Sandra Krick Calderon, Peter Wasserscheid, Andreas Görling, Hans-Peter Steinrück
      Abstract: Liquid binary Pd-Ga alloys with low Pd contents of 0.8, 1.8 and 4.7 at.% of Pd were examined as a function of sample temperature in ultra-high vacuum using angle-resolved x-ray photoelectron spectroscopy (XPS). Upon cooling from 750 to 400 K, a pronounced temperature-dependence of the Pd concentration in the liquid phase is observed, which is explained by the transition from the pure liquid phase to a two-phase system, consisting of a solid Ga5Pd phase and a Pd-depleted liquid Pd-Ga alloy. In the liquid Pd-Ga alloy, Pd is always depleted from the topmost interface layer, as deduced from angle-resolved XPS at 0 and 80° emission, independent of temperature and Pd concentration. This observation is interpreted as an inhomogeneous depth distribution function of Pd, that is, the segregation of Ga to the surface of the liquid phase. The results of a DFT-based molecular dynamics simulation (MD) independently show interfacial stratification of Ga and inhomogeneous Pd distribution along the surface normal. The evaluation of the experimental data with a rigid layer model based on the MD calculations leads to excellent agreement with the simulation.
      PubDate: 2017-09-22T08:20:31.487829-05:
      DOI: 10.1002/chem.201703627
       
  • Microwave-assisted rapid one-pot synthesis of fused and non-fused indoles
           and 5-[18F]fluoroindoles from phenylazocarboxylates
    • Authors: Jasmin Krüll; Anja Hubert, Natascha Nebel, Olaf Prante, Markus Rolf Heinrich
      Abstract: Substituted indoles can be prepared from phenylazo-carboxylates through a rapid one-pot sequence featuring a microwave-assisted Fischer indole synthesis as key step. As the phenylazocarboxylates may beforehand be modified by mild nucleophilic aromatic substitution, including the introduction of [18F]fluoride, the overall strategy offers an attractive new access to 5-[18F]fluoroindoles.
      PubDate: 2017-09-22T07:20:25.400095-05:
      DOI: 10.1002/chem.201703890
       
  • C−H Cyanation of 6-Ring N-Containing Heteroaromatics
    • Authors: Bryony L. Elbert; Alistair J. M. Farley, Timothy W. Gorman, Tarn C. Johnson, Christophe Genicot, Bénédicte Lallemand, Patrick Pasau, Jakub Flasz, José L. Castro, Malcolm MacCoss, Robert S. Paton, Christopher J. Schofield, Martin D. Smith, Michael C. Willis, Darren J. Dixon
      Abstract: Heteroaromatic nitriles are important compounds in drug discovery, both for their prevalence in the clinic and due to the diverse range of transformations they can undergo. As such, efficient and reliable methods to access them have the potential for far-reaching impact across synthetic chemistry and the biomedical sciences. Herein, we report an approach to heteroaromatic C−H cyanation through triflic anhydride activation, nucleophilic addition of cyanide, followed by elimination of trifluoromethanesulfinate to regenerate the cyanated heteroaromatic ring. This one-pot protocol is simple to perform, is applicable to a broad range of decorated 6-ring N-containing heterocycles, and has been shown to be suitable for late-stage functionalization of complex drug-like architectures.A direct, reliable and general one-pot N-heteroaromatic C−H cyanation procedure by triflic anhydride N-activation, nucleophilic addition of cyanide, and concomitant elimination of trifluoromethanesulfinate is reported. The protocol is simple to perform, has computationally predictable site selectivity, and is applicable to a broad range of decorated 6-ring N-containing heterocycles, including complex drug-like architectures.
      PubDate: 2017-09-22T06:22:05.735886-05:
      DOI: 10.1002/chem.201703931
       
  • Synthesis and Reactivity of a Scandium Terminal Hydride: H2 Activation
           by a Scandium Terminal Imido Complex
    • Authors: Xianghao Han; Li Xiang, Carlos A. Lamsfus, Weiqing Mao, Erli Lu, Laurent Maron, Xuebing Leng, Yaofeng Chen
      Abstract: Dihydrogen is easily activated by a scandium terminal imido complex containing the weakly coordinated THF. The reaction proceeds through a 1,2-addition mechanism, which is distinct from the σ-bond metathesis mechanism reported to date for rare-earth metal-mediated H2 activation. This reaction yields a scandium terminal hydride, which is structurally well-characterized, being the first one to date. The reactivity of this hydride is reported with unsaturated substrates, further shedding light on the existence of the terminal hydride complex. Interestingly, the H2 activation can be reversible. DFT investigations further eludciate the mechanistic aspects of the reactivity of the scandium anilido-terminal hydride complex with PhNCS but also on the reversible H2 activation process.Reversible activation: Activation of H2 by scandium terminal imido complex through 1,2-addition provided the first structurally characterized scandium terminal hydride. DFT investigations further highlighted the easiness of H−H bond cleavage over the Sc=N double bond. This hydride can also release H2 to regenerate the imido complex, making the H2 activation reversible.
      PubDate: 2017-09-22T06:21:57.091093-05:
      DOI: 10.1002/chem.201703905
       
  • In-Situ Fabrication of MOF-Derived Co−Co Layered Double Hydroxide Hollow
           Nanocages/Graphene Composite: A Novel Electrode Material with Superior
           Electrochemical Performance
    • Authors: Xue Bai; Jingyuan Liu, Qi Liu, Rongrong Chen, Xiaoyan Jing, Bin Li, Jun Wang
      Abstract: Rational design of a transition metal layered double hydroxide (LDH) and graphene composite is vitally important for designing high-performance supercapacitor electrodes. Although various methods are performed, the realization of high-performance is still impeded by the agglomeration of graphene and layered double hydroxide. Here, metal–organic framework derived cobalt–cobalt layered double hydroxide (Co−Co LDH) hollow nanocages, uniformly deposited on graphene nanosheets, are fabricated through facile in situ co-deposition and thermal ion-exchange reaction. Electrochemical investigation reveals that Co−Co LDH/15 mg graphene is rather outstanding, which delivers high specific capacitance of 1205 F g−1, excellent rate capability (60.3 % capacitance retention is obtained after the current density increased 6.67 times), and cycling stability. The excellent performance of electrode is also confirmed by assembling an asymmetric supercapacitor, which delivers high energy density of 49.5 Wh kg−1 as well as the maximum power density of 7000 W kg−1. The Co−Co LDH/graphene composite proves a promising concept for constructing hierarchical structure materials in the future.Layer cake: A metal–organic framework derived Co−Co LDH/graphene composite was successfully synthesized through facile co-precipitation method followed by chemical etching. The special hollow nanocages structure of Co−Co LDH combined with high conductivity of graphene nanosheets endowed the material with superior electrochemical performance. Moreover, an asymmetric supercapacitor based on the composite and active carbon exhibit outstanding electrochemical properties ascribed to the co-effect of graphene and Co−Co LDH.
      PubDate: 2017-09-22T06:21:52.246448-05:
      DOI: 10.1002/chem.201702676
       
  • 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: Association of photoswitch within curcubit[7]- and -[8]uril tunes the kinetics of the thermal isomerization from VHF-to-DHA in the photoswitch. The sun setting through the rolling wave symbolizes the aqueous medium in which the photoswitching processes take place. More information can be found in the Full Paper by M. B. Nielsen, S. R. Beeren, M. Pittelkow et al. (
      DOI : 10.1002/chem.201703196).
      PubDate: 2017-09-22T06:15:55.772585-05:
       
  • Embedded Isoreticular Zeolites: Concept and Beyond
    • Authors: Jung Cho; Hyun June Choi, Peng Guo, Jiho Shin, Xiaodong Zou, Suk Bong Hong
      Abstract: The naming and building rules of body-centered cubic embedded isoreticular zeolites (EIZs) with lta cage as the lattice point are presented. The procedures for the classification, description, and prediction presented herein will serve as a guideline for finding new EIZs and, eventually, for zeolites and related microporous materials with desired properties. More information can be found in the Full Paper by X. Zou, S. B. Hong et al. (
      DOI : 10.1002/chem.201702417).
      PubDate: 2017-09-22T06:15:39.218767-05:
       
  • Embedded Isoreticular Zeolites: Concept and Beyond
    • Authors: Jung Cho; Hyun June Choi, Peng Guo, Jiho Shin, Xiaodong Zou, Suk Bong Hong
      Abstract: Invited for the cover of this issue are the groups of Xiadong Zou at the Stockholm University and Suk Bong Hong at the POSTECH in Pohang. The image depicts a zeolite family with expanding structural complexity and embedded isoreticular structures. Read the full text of the article at 10.1002/chem.201702417.“The prediction and synthesis of new crystal structures enables the targeted preparation of materials with desired properties.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201702417).
      PubDate: 2017-09-22T06:15:33.361859-05:
       
  • Single-Scan 13C Diffusion-Ordered NMR Spectroscopy of DNP-Hyperpolarised
           Substrates
    • Authors: Ludmilla Guduff; Dennis Kurzbach, Carine van Heijenoort, Daniel Abergel, Jean-Nicolas Dumez
      Abstract: Diffusion-ordered NMR spectroscopy (DOSY) is a powerful approach for the analysis of molecular mixtures, yet its application range is limited by the relatively low sensitivity of NMR. We show here that spectrally resolved 13C DOSY data can be collected, in a single scan, for substrates hyperpolarised by dissolution dynamic nuclear polarisation (D-DNP), which provides signal enhancements of several orders of magnitude. For this we use a convection-compensation pulse scheme, which we also analyse by numerical simulation. The proposed method further allows the acquisition of several consecutive DOSY spectra in a single D-DNP experiment.Taken in one shot: 13C DOSY NMR spectra are obtained in a single scan from DNP-hyperpolarised substrates, using a convection-compensated spatial encoding of the diffusion dimension.
      PubDate: 2017-09-22T06:15:25.459941-05:
      DOI: 10.1002/chem.201703300
       
  • Lanthanide Fluorobenzoates as Bio-Probes: a Quest for the Optimal Ligand
           Fluorination Degree
    • Authors: Alena S. Kalyakina; Valentina V. Utochnikova, Ivan S. Bushmarinov, Irina M. Le-Deygen, Daniel Volz, Patrick Weis, Ute Schepers, Natalia P. Kuzmina, Stefan Bräse
      Abstract: The thorough study of fluorinated benzoates of lanthanides (Eu, Tb, Nd, Er, Yb, Gd, La, Lu) is reported. Their composition in single crystal and powder state revealed two predominant structural motifs. An in-depth luminescence study has been performed on the reported fluorobenzoates, showing, that terbium and europium complexes in solid state possess high luminescence intensity with the quantum yield of up to 69 %. High solubility in most organic solvents, as well as in water, combined with the high luminescence intensity in water solution and non-toxicity allowed the testing of europium complexes as bioprobes in cellulo. Among all tested fluorobenzoates, europium 2-fluorobenzoate dihydrate combined the best luminescent properties, thermodynamic stability, aqueous solubility, and non-toxicity, and was shown to be a viable bio-marker.Probe: An in-depth study on the luminescence of fluorinated benzoates of lanthanides was performed, optimizing the fluorination degree of the complexes. This leads to a europium 2-fluorobenzoate dehydrate showing excellent properties, as a viable bio-marker.
      PubDate: 2017-09-22T03:27:18.346209-05:
      DOI: 10.1002/chem.201703543
       
  • An Unsymmetrical Squaraine Dye based Chemical Platform for Multiple
           Analyte Recognition
    • Authors: Ayyappanpillai Ajayaghosh; Divya Susan Philips, Samrat Ghosh, Karivachery V Sudheesh, Cherumuttathu H Suresh
      Abstract: Design of fluorescent molecular platforms capable of responding to multiple analytes is a topic of great interest. Herein, we report the use of a Zn2+-complexed unsymmetrical squaraine dye, Sq-Zn2+ as a chemical platform for recognizing structurally distinct analytes. The squaraine ring is substituted on one side with a dipicolylamine unit which acts as the metal ion receptor while the other part of the molecule carries a dibutyl aniline moiety which is an electron donor. The molecular system is unique as it could respond specifically to different types of analytes viz atmospheric carbon dioxide, cyclic phosphates and picric acid. Moreover, the interaction of these analytes can be monitored colorimetrically and fluorimetrically, favoring both qualitative and quantitative analyses. The distinct response towards the cyclic and linear phosphates as well as the selective response towards picric acid among the various nitroaromatic compounds was achieved with sensitivity at ppm level. The flexible coordination offered by Zn2+ plays a significant role in the discrimination of these analytes with high specificity. Sq-Zn2+, introduced here is a single molecular construct that can be used for the selective and sensitive response towards analytes of environmental and biological relevance.
      PubDate: 2017-09-22T03:20:24.221833-05:
      DOI: 10.1002/chem.201703645
       
  • Silver–Sulfur Hybrid Supertetrahedral Clusters: The Hitherto Missing
           Members in the Metal–Chalcogenide Tetrahedral Clusters
    • Authors: Geng-Geng Luo; Hai-Feng Su, An Xiao, Zhi Wang, Yang Zhao, Qiao-Yu Wu, Ji-Huai Wu, Di Sun, Lan-Sun Zheng
      Abstract: The synthesis of Group 11 metal chalcogenide supertetrahedral clusters (SCs) still remains a great challenge mainly due to the high tendency of metal aggregation through metallophilicity and global charge balance. Demonstrated herein are the preparation, crystallographic characterization, and optical properties of two stable silver–sulfur SCs through ligand-control; one as a discrete zero-dimensional (0D) V3,4-type cluster and the other as a one-dimensional (1D) zigzag chain extended by alternating V3,2-type clusters. The notation Vn,m (where n is the number of metal layers, and m is the number of vacant corners) is used to describe a new series of vacant-corner SCs, which can be derived from the regular Tn clusters. The existence of vacant-corner-type SCs may be ascribed to the low valence and tri-coordinated environment of silver ions. These are the first representatives of structurally determined silver–sulfur tetrahedral clusters thus far. This work enriches the coinage-metal chalcogenide tetrahedral cluster portfolio, discovers vacant-corner SCs present in silver–sulfur hybrid tetrahedral clusters, and provides effective means for further development of Group 11 coinage-metal chalcogenide SCs.Rise of the silver sulfur: Two silver–sulfur supertetrahedral clusters (SCs) with modified geometry were synthesized through ligand control and characterized by single-crystal X-ray diffraction. Their physical properties were also investigated. These are the first representatives of structurally determined silver–sulfur T3 superclusters so far.
      PubDate: 2017-09-22T02:00:58.194556-05:
      DOI: 10.1002/chem.201703468
       
  • A Platinum(II)-based photosensitive tripod as an effective photodynamic
           anticancer agent via DNA damage
    • Authors: Yi-Fang Zhong; Hang Zhang, Wen-Ting Liu, Xiao-Hui Zheng, Yi-Wei Zhou, Qian Cao, Yong Shen, Yong Zhao, Peter Z. Qin, Liang-Nian Ji, Zong-Wan Mao
      Abstract: Herein, two photosensitive platinum(II)-based tripods were designed and synthesized. Notably, complex 1 ({[Pt(dien)]3L}(NO3)6, L = tri(4-pyridylphenyl)amine and dien = diethylenetriamine), which mainly accumulated in cell nucleus, exhibited very low cytotoxicity in the absence of light irradiation, but displayed remarkably increase cytotoxicity upon visible light irradiation. Mechanistic investigations revealed that 1 interacted with DNA in the nucleus, induced ROS generation upon light irradiation, consequently elicited rapid DNA damage response and triggered cancer cell apoptosis.
      PubDate: 2017-09-22T00:20:42.786647-05:
      DOI: 10.1002/chem.201703598
       
  • Mixed Monosilyl Acetals and Catalyst-Dependent Chemoselective Mukaiyama
           Aldol Reactions
    • Authors: Jung Woon Yang; Sun Min Kim, Hye Sung Yang, Heesung Eum, Hyun-Joon Ha
      Abstract: We report a direct, simple, and straightforward approach for the construction of a mixed monosilyl acetal as a new and synthetically valuable functional group by mixing an aldehyde, sodium tert-butoxide and trimethylsilyl azide. We also demonstrate catalyst-dependent chemoselective reaction between mixed monosilyl acetals and silyl ketene acetals through Mukaiyama aldol reactions to give different structures of O-protected β-hydroxy esters in excellent yields with high chemoselectivities. This study provided the existence of an oxonium ion intermediate and of its kinetically controlled reaction with the pre-equilibrated silyl enol ether obtained from (E)- and (Z)-isomerization.
      PubDate: 2017-09-21T22:20:25.690551-05:
      DOI: 10.1002/chem.201704456
       
  • Cooperative Noncovalent Interactions Induce Ion Pair Separation in
           Diphenylsilanides
    • Authors: Eric A. Marro; Eric M. Press, Tapas K. Purkait, Daniel Jimenez, Maxime A. Siegler, Rebekka S. Klausen
      Abstract: This crystallographic and computational study describes an unusual potassium silanide structure. A contact ion pair is expected in the solid state between potassium and silicon, yet the potassium cation binds an aromatic ring and the anionic silanide interacts with CH bonds on neighboring crown ether molecules. These structure-bonding phenomena are attributed to strong soft-soft interactions.
      PubDate: 2017-09-21T21:20:48.185522-05:
      DOI: 10.1002/chem.201704217
       
  • Halogen contacts-induced unusual coloring in Bi(III) bromide complex:
           anion-to-cation charge transfer via Br···Br interactions
    • Authors: Sergey A. Adonin; Igor D. Gorokh, Alexander S. Novikov, Pavel A. Abramov, Maxim N. Sokolov, Vladimir P. Fedin
      Abstract: A yellow bromobismuthate {(2-BrPy)2H}[BiBr4] (1) transforms into unusually deeply colored cherry-red (2-BrPyH)2[BiBr5] (2). Combination of structural studies and theoretical calculations confirms that appearance of short non-covalent Br···Br interactions (≈ 3.3 Å) in 2 is responsible for the anion-to-cation charge transfer (LP(Brligand) σ*(Br-C)), yielding in dramatic changes in optical behavior. This effect opens the way towards novel halogen bonding-templated halometalate-based hybrid materials with enhanced optical properties.
      PubDate: 2017-09-21T12:20:51.573486-05:
      DOI: 10.1002/chem.201703747
       
  • 1-Alkali-metal-2-alkyl-1,2-dihydropyridines: soluble hydride surrogates
           for catalytic dehydrogenative coupling and hydroboration applications
    • Authors: Ross McLellan; Alan R Kennedy, Robert E. Mulvey, Samantha A Orr, Stuart D Robertson
      Abstract: Equipped with excellent hydrocarbon solubility, the lithium hydride surrogate 1-lithium-2-t-butyl-1,2-dihydropyridine (1tLi) functions as a precatalyst to convert Me₂NH·BH₃ to [NMe₂BH₂]₂ (89% conversion) under competitive conditions (2.5 mol%, 60h, 80°C, toluene solvent) to that of previously reported LiN(SiMe₃)₂. Sodium and potassium dihydropyridine congeners produce similar high yields of [NMe₂BH₂]₂ but require longer times. Switching the solvent to pyridine induces a remarkable change in the dehydrocoupling product ratio, with (NMe₂)₂BH favoured over [NMe₂BH₂]₂ (e.g., 94%:2% for 1tLi). Demonstrating its versatility, precatalyst 1tLi was also successful in promoting hydroboration reactions between pinacolborane and a selection of aldehydes and ketones. Most reactions gave near quantitative conversion to the hydroborated products in 15 minutes, though sterically demanding carbonyl substrates require longer times. The mechanisms of these rare examples of group 1 metal catalysed processes are discussed.
      PubDate: 2017-09-21T10:20:27.887297-05:
      DOI: 10.1002/chem.201703609
       
  • Pacman-Compounds: from Energy Transfer to Cooperative Catalysis
    • Authors: Philipp Lang; Matthias Schwalbe
      Abstract: In this concept article we present the syntheses and application of homo and heterodinuclear 'Pacman' compounds. This architecture implies that two metal coordination fragments are brought in close vicinity to each other via a covalent linkage to either support energy transfer between the two units or cooperative transformation of a substrate. Nature has shown that the combination of, in particular two different metal units, can dramatically improve the efficiency of small molecule activation. We exemplify this strategy for the activation of water, dioxygen and carbon dioxide. Furthermore, we present artificial systems in which a positive effect on the catalytic performance because of the combination of two (different) metal centers could be observed. Thus, Pacman-type compounds are very well suited as structural and functional models for their biological counterparts.
      PubDate: 2017-09-21T09:21:04.686839-05:
      DOI: 10.1002/chem.201703675
       
  • Synthesis of Tetranuclear Palladium(II) Complexes and their Catalytic
           Activity for Cross Coupling Reactions
    • Authors: Florian Puls; Nils Richter, Olga Kataeva, Hans-Joachim Knölker
      Abstract: We have developed a short and simple synthesis of tetranuclear palladium(II) complexes which have been structurally confirmed by X-ray analysis. These complexes were formed in about 30 % overall yield by spontaneous metalation of dimethylaminoarene derivatives and exhibit a high stability. We have studied the utility of the tetranuclear palladium(II) complexes as precatalysts for Mizoroki-Heck and Suzuki-Miyaura cross coupling reactions. Our novel complexes show excellent catalytic activities with high turnover numbers and high turnover frequencies (e.g. for the Suzuki-Miyaura reaction: TON up to 538000 and TOF up to 23400 h-1 at room temperature).
      PubDate: 2017-09-21T09:20:34.00188-05:0
      DOI: 10.1002/chem.201703926
       
  • Control of Reversible Activation Dynamics of
           [Ru{η6:κ1-C6H5(C6H4)NH2}(XY)]n+ and the Effect of Chelating-Ligand
           Variation
    • Authors: Francisco Martínez-Peña; Ana M. Pizarro
      Abstract: The design of organometallic pH-dependent switches to control in-tumor drug activation is presented. In this picture, the middle and background show that inactive ruthenium(II) arene complexes are innocuous (represented in blue), locked away inside boxes, unable to interact with their molecular target. It is shown, however, that protons (represented by the keys) can open the boxes and release the active form of the ruthenium drug (in red, with Ru in metallic grey), which can bind to DNA. The potential of a series of ruthenium(II) complexes to become pH-responsive anticancer drugs is thus demonstrated. More information can be found in the Full Paper by A. M. Pizarro and F. Martínez-Peña (
      DOI : 10.1002/chem.201701681).
      PubDate: 2017-09-21T09:02:32.417531-05:
       
  • Auxiliary-Directed C(sp3)−H Arylation by Synergistic Photoredox and
           Palladium Catalysis
    • Authors: Milena L. Czyz; David W. Lupton, Anastasios Polyzos
      Abstract: Herein we describe the auxiliary-directed arylation of unactivated C(sp3)−H bonds with aryldiazonium salts, which proceeds under synergistic photoredox and palladium catalysis. The site-selective arylation of aliphatic amides with α-quaternary centres is achieved with high selectivity for β-methyl C(sp3)−H bonds. This operationally simple method is compatible with carbocyclic amides, a range of aryldiazonium salts and proceeds at ambient conditions.Of earth and light: An auxiliary-directed arylation of unactivated C(sp3)−H bonds with synergistic photoredox and palladium catalysis is reported. This approach enables the site-selective arylation of aliphatic amides with α-quaternary centers and high selectivity for β-methyl C(sp3)−H bonds. The operationally simple method is compatible with a range of amides, aryldiazonium salts and proceeds at room temperature.
      PubDate: 2017-09-21T09:02:21.393308-05:
      DOI: 10.1002/chem.201704045
       
  • Determination of the Absolute Configuration of (−)-Hydroxynitrilaphos
           and Related Biosynthetic Questions
    • Authors: Katharina Pallitsch; Barbara Happl, Christian Stieger
      Abstract: The fascinating enzymology involved in phosphonate metabolism often seems as complex as if it involved some kind of magic. Extraordinary enzymes are identified at a rapid pace and experience has taught us that seemingly simple reactions often involve very complex transformations in phosphonate biochemistry. While the possible substrate (2-amino-1-hydroxyethylphosphonic acid=2-AEP) and cofactors (Fe2+) necessary for hydroxynitrilaphos biosynthesis were already suggested, we have now determined the stereochemical course of this unusual transformation. However, the reaction intermediates and exact mechanism remain elusive. More information can be found in the Full Paper by K. Pallitsch et al. (
      DOI : 10.1002/chem.201702904).
      PubDate: 2017-09-21T09:00:57.105828-05:
       
  • Robust Macroscopic 3D Sponges of Manganese Oxide Molecular Sieve
    • Authors: Zhenxin Liu; Depeng Wu, Xuehui Guo, Shaoming Fang, Lizhen Wang, Yu Xing, Steven L. Suib
      Abstract: Free-standing 3D OMS-2 sponges with controlled densities are presented. The 3D OMS-2 sponges possess a combination of outstanding physical, mechanical, and electrical properties. Moreover, some of these properties have systematic trends with various densities. This study sheds new light on manipulating properties of such sponges through controlling sponge densities. These new materials are promising for various applications such as catalysis, sensing, energy storage, and environmental materials. More information can be found in the Full Paper by Z. Liu, Y. Xing et al. (
      DOI : 10.1002/chem.201702787).
      PubDate: 2017-09-21T09:00:35.12062-05:0
       
  • Dual Visible Light-Triggered Photoswitch of a Diarylethene Supramolecular
           Assembly with Cucurbit[8]uril
    • Authors: Guoxing Liu; Ying-Ming Zhang, Conghui Wang, Yu Liu
      Abstract: Research on photochromic molecules switched by visible light is of particular interest for their application in bioimaging and stimuli-responsive materials. Here, a photoswitchable supramolecular assembly comprised of monocharged bispyridinium-modified diarylethenes (DAEs) and cucurbit[8]uril (CB[8]) has been constructed, which exhibits reversible photochromic behaviour with visible light in both directions. The transformation of CB[8] not only prompts the DAEs to form charge-transfer complexes, but also restricts its intramolecular rotation to enhance fluorescence emission. In this CB[8]-containing supramolecular system, the π-conjugation is extended and its absorption is bathochromically shifted for visible light-driven cyclization of DAEs. Meanwhile, the fluorescence of the supramolecular assembly can also be reversibly modulated by visible light. These findings may furnish a new strategy for the development of visible light-driven fluorescent biomaterials and molecular machines.Switching on the lights: A photoswitchable supramolecular assembly comprised of monocharged bispyridinium-modified diarylethene and cucurbit[8]uril has been constructed, exhibiting reversible photochromic behaviour and tunable fluorescence emission with visible light in both directions.
      PubDate: 2017-09-21T08:56:40.134416-05:
      DOI: 10.1002/chem.201703562
       
  • Photoswitchable Carbohydrate-Based Macrocyclic Azobenzene: Synthesis,
           Chiroptical Switching, and Multistimuli-Responsive Self-Assembly
    • Authors: Chaoqi Lin; Stéphane Maisonneuve, Rémi Métivier, Juan Xie
      Abstract: A one-pot O-alkylation mediated macrocyclization approach has been used for the synthesis of carbohydrate-based macrocyclic azobenzene. The synthesized macrocycle can be reversibly isomerized between E and Z isomers upon UV or visible irradiation with excellent photostability and thermal stability (t1/2=51 days at 20 °C for the Z isomer). A chirality transfer from the chiral sugar unit to azobenzene was observed by circular dichroism (CD). DFT and TD-DFT calculations were performed to calculate the optimal geometry and the theoretical absorption and CD spectra. Comparison of the experimental CD spectra with the theoretical ones suggests that both E- and Z-macrocycles adopt preferentially P-helicity for the azobenzene moiety. Furthermore, the macrocycle showed gelation ability in cyclohexane and ethanol with multistimuli-responsive behavior upon exposure to environmental stimuli including thermal-, photo-, and mechanical responses. Moreover, these organogels display temperature-dependent helical inversion, which can be tuned by a repeated heating–cooling procedure.Switchable carbohydrate-embedded macrocyclic supramolecular gelator: A one-pot O-alkylation mediated macrocyclization approach has been used for the synthesis of a photoswitchable and bistable carbohydrate-based macrocyclic azobenzene, which showed chirality transfer, multistimuli-responsive organogel formation behavior upon exposure to external triggers, and helical inversion during the self-assembly and gel formation.
      PubDate: 2017-09-21T08:56:32.439129-05:
      DOI: 10.1002/chem.201703461
       
  • Chemical Potential of the Solvent: A Crucial Player for Rationalizing
           Host–Guest Affinities
    • Authors: Karine Baudet; Sebastiano Guerra, Claude Piguet
      Abstract: Access to reliable values of the thermodynamic constants β1,1H,G, which control simple host–guest ([HG]) association, is crucial in medicine, biology, pharmacy, and chemistry, since the optimum concentration of an effector (i.e., a drug) acting on a receptor is set to 1β1,1H,G. Intermolecular association between charged species in polar solvents, for which water is the archetype, largely obeys this principle. Any deviation from ideality, which alters the speciation in solution, is mastered by the Debye–Hückel theory of ionic atmosphere. Much less is known for related association reactions involving neutral species in non-polar (lipophilic) media such as membranes, bilayers, or organic polymers. Taking the intermolecular association between [La(hfa)3dig] guest (hfa=hexafluoroacetylacetonate, dig=2-{2-methoxyethoxy}ethane) and tridentate polyaromatic host receptors L1–L3 in dichloromethane as a proof-of-concept, we show that the progress of the association reactions, as measured by the increase in the mole fraction of occupied sites of the receptors, disrupt the chemical potential of the solvent to such an extent that β1,1H,G may seemingly be shifted by two orders of magnitude, thus leading to erroneous dose-response prescriptions. A simple chemical model, which considers a subset of solvent molecules in surface contact with the partners of the association reaction, restores reliable access to true and interpretable thermodynamic constants. The concomitant emergence of a concentration-dependent corrective parameter reestablishes satisfying dose-dependent response under real conditions. This “complement” to the law of mass action offers a simple method for safely taking care of the non-predictable variations of the activity coefficients of the various partners when host–guest reactions are conducted in non-polar media.Forces of attraction: During the straightforward titration of tridentate host-receptors L with the [La(hfa)3dig] guest in dichloromethane, the apparent exchange constants β1,1,exchL,La exponentially increase with the amount of formed complex [La(hfa)3L]. How is it possible'
      PubDate: 2017-09-21T08:56:24.852004-05:
      DOI: 10.1002/chem.201703184
       
  • Transition Metal Catalyzed, Regioselective B(4)-Halogenation and
           B(4,5)-Diiodination of Cage B−H Bonds in o-Carboranes
    • Authors: Hairong Lyu; Yangjian Quan, Zuowei Xie
      Abstract: Transition metal catalyzed, regioselective carborane-cage B(4)−H iodination, bromination, and chlorination as well as B(4,5)−H diiodination were achieved by using NXS (X=I, Br), FeCl3, or IOAc as the halogenating agent, respectively. A series of previously inaccessible B(4)-halogenated o-carboranes were synthesized in a simple one-pot process, and proved to be valuable synthons for the functionalization of carboranes. Mono- and di-selectivity can be controlled by in situ removal of the carboxy directing group. The resultant 4-I-o-C2B10H11 can serve as a versatile feedstock for the construction of cage B−C(sp2), B−C(sp), B−O, and B−N bonds.Access granted: Transition metal catalyzed, regioselective cage B(4)−H iodination, bromination, and chlorination as well as B(4,5)−H diiodination were achieved to grant access to a series of previously inaccessible B(4)-halogenated o-carboranes in a simple one-pot process (see scheme). Mono- and di-selectivity can be controlled by in situ removal of the carboxyl directing group.
      PubDate: 2017-09-21T08:56:15.620249-05:
      DOI: 10.1002/chem.201703006
       
  • Helicity-Dependent Regiodifferentiation in the Excited-State Quenching and
           Chiroptical Properties of Inward/Outward Helical Coumarins
    • Authors: Arindam Mukhopadhyay; Tousif Hossen, Indrajit Ghosh, Apurba Lal Koner, Werner M. Nau, Kalyanasis Sahu, Jarugu Narasimha Moorthy
      Abstract: Influence of helicity on the excited-state as well as chiroptical properties of two sets of regiohelical coumarins that are differentiated by “inward” and “outward” disposition of the pyran-2-one ring has been investigated. A subtle difference in the helicities manifests in divergent excited-state properties and significant differences in the dipole moments. The latter permit heretofore unprecedented regiodifferentiation in the O−H⋅⋅⋅O hydrogen-bond assisted electron-transfer quenching by phenols. Furthermore, the enantiopure hexahelical coumarins exhibit strong Cotton effects and lend themselves to a very high differentiation in the specific rotations and anisotropic dissymmetry factors. The specific rotation observed for 6-in turns out being the highest of the values reported for all hexahelicenes reported so far.So similar, yet so divergent: The inward/outward divergence replicates in the excited-state quenching phenomenon as well as chiroptical properties of regiohelical coumarins. Unprecedented regiodifferentiation is observed in the hydrogen-bond assisted electron-transfer quenching by phenols, as also in anisotropic dissymmetry factors and specific rotations.
      PubDate: 2017-09-21T08:56:07.115268-05:
      DOI: 10.1002/chem.201701787
       
  • β-Acrolein-Substituted Corroles: A Route to the Preparation of
           
    • Authors: Andrea Savoldelli; Gabriele Magna, Corrado Di Natale, Alexandro Catini, Sara Nardis, Frank R. Fronczek, Kevin M. Smith, Roberto Paolesse
      Abstract: An efficient β-functionalization of [5,10,15-tris-(4-methylphenyl)corrolato]cobalt derivatives through a Vilsmeier-type reaction allows the introduction of an acrolein substituent, which is subsequently copolymerized with pure acrolein. The obtained hybrid microspheres are exploited as nanogravimetric chemical sensors. The sensing properties of the developed sensors are tested through exposure to different volatile organic compounds chosen as model analytes. The results show improved sensor sensitivity of the resulting devices for all the tested analytes with respect to sensors functionalized with either corrole or polyacrolein. The enhanced properties are attributed to the accurate and tunable merging of the properties of both exploited materials.Unity is strength: Grafting of a functionalized Co corrole complex on polyacrolein microspheres affords a composite material, which shows improved properties upon application as a sensing material for the development of quartz microbalance sensors (see figure).
      PubDate: 2017-09-21T08:55:55.481517-05:
      DOI: 10.1002/chem.201702380
       
  • Catalytic Asymmetric Formal [3+2] Cycloaddition of 2-Isocyanatomalonate
           Esters and Unsaturated Imines: Synthesis of Highly Substituted Chiral
           γ-Lactams
    • Authors: Miguel Espinosa; Gonzalo Blay, Luz Cardona, M. Carmen Muñoz, José R. Pedro
      Abstract: Unlike their isocyano and isothiocyanato analogues, isocyanato esters remain almost unexplored as formal 1,3-dipoles in asymmetric catalytic reactions. The first asymmetric formal [3+2] cycloaddition involving isocyanato esters and electrophilic alkenes is reported. Diisopropyl 2-isocyanatomalonate reacts with α,β-unsaturated N-(o-anisidyl) imines in the presence of a Mg(OTf)2–BOX complex to give highly substituted chiral pyrrolidinones featuring a conjugate exocyclic double bond with excellent yields and enantiomeric excesses up to 99 %. Several transformations of the resulting heterocycles, including the synthesis of a pyroglutamic acid derivative, have been carried out.Close the ring: The first asymmetric formal [3+2] cycloaddition involving 2-isocyanato esters and electrophilic alkenes is reported. Diisopropyl 2-isocyanatomalonate reacts with α,β-unsaturated N-(o-anisidyl) imines in the presence of a Mg(OTf)2–BOX complex to give highly substituted chiral pyrrolidinones with excellent yields and enantiomeric excesses up to 99 % (see scheme).
      PubDate: 2017-09-21T08:55:49.929546-05:
      DOI: 10.1002/chem.201702777
       
  • Prediction of Reduction Potentials of Copper Proteins with Continuum
           Electrostatics and Density Functional Theory
    • Authors: Nicholas J. Fowler; Christopher F. Blanford, Jim Warwicker, Sam P. de Visser
      Abstract: Blue copper proteins, such as azurin, show dramatic changes in Cu2+/Cu+ reduction potential upon mutation over the full physiological range. Hence, they have important functions in electron transfer and oxidation chemistry and have applications in industrial biotechnology. The details of what determines these reduction potential changes upon mutation are still unclear. Moreover, it has been difficult to model and predict the reduction potential of azurin mutants and currently no unique procedure or workflow pattern exists. Furthermore, high-level computational methods can be accurate but are too time consuming for practical use. In this work, a novel approach for calculating reduction potentials of azurin mutants is shown, based on a combination of continuum electrostatics, density functional theory and empirical hydrophobicity factors. Our method accurately reproduces experimental reduction potential changes of 30 mutants with respect to wildtype within experimental error and highlights the factors contributing to the reduction potential change. Finally, reduction potentials are predicted for a series of 124 new mutants that have not yet been investigated experimentally. Several mutants are identified that are located well over 10 Å from the copper center that change the reduction potential by more than 85 mV. The work shows that secondary coordination sphere mutations mostly lead to long-range electrostatic changes and hence can be modeled accurately with continuum electrostatics.Mutant enzymes: A unique, computationally efficient modeling approach is presented to calculate reduction potentials of copper proteins, which is tested on the mononuclear copper enzyme azurin. We predict a series of unexplored azurin mutants with significant changes in reduction potential that may have significant and biotechnologically relevant changes.
      PubDate: 2017-09-21T08:55:33.606488-05:
      DOI: 10.1002/chem.201702901
       
  • Hybrid Surfactants with N-Heterocyclic Carbene Heads as a Multifunctional
           Platform for Interfacial Catalysis
    • Authors: Sebastian Polarz; Adrian Donner, Kay Hagedorn, Lorenz Mattes, Markus Drechsler
      Abstract: Processing of substrates with different solvent compatibility is a persistent problem in homogeneous catalysis, in particular when one starting compound is water soluble and the other is not. A tempting concept found in literature is micellar catalysis. However, developing catalysts, which are surfactants at the same time, stands at its beginning. We report the synthesis of a new surfactant system with a N-heterocyclic carbene (NHC) moiety as a head group. Characteristic surfactant properties such as the formation of micelles or liquid crystals is documented. The new surfactant ligand forms coordination compounds with various metals, most importantly Pd2+ in square planar geometry. The Pd-NHC compound as well shows surfactant features, and can be used successfully for C-C cross coupling reactions (Suzuki, Heck). The boost in catalytic activity by one order of magnitude compared to analogous, but non-amphiphilic species is reported.
      PubDate: 2017-09-21T08:29:49.522603-05:
      DOI: 10.1002/chem.201703902
       
  • Total Synthesis of Strychnine
    • Authors: David Yu-Kai Chen
      Abstract: Total synthesis of the flagship Strychnos indole alkaloid, strychnine, has been accomplished. The developed synthetic sequence featured a novel vinylogous 1,4-addition, a challenging iodinium salt mediated silyl enol ether arylation, a palladium-catalyzed Heck reaction, and a streamlined late-stage conversion to strychnine. Furthermore, an application of asymmetric counterion-directed catalysis (ACDC) in the context of target-oriented organic synthesis has been demonstrated to render access to optically active material. The synthetic sequence described herein represents the most concise entry to optically active strychnine to date.
      PubDate: 2017-09-21T05:20:48.788163-05:
      DOI: 10.1002/chem.201704455
       
  • Aqueous magnesium ion battery based on carbon-coated FeVO4 as anode and
           Mg-OMS-1 as cathode with high energy density
    • Authors: Hongyu Zhang; Ke Ye, Kai Zhu, Ruibai Cang, Jun Yan, Kui Cheng, Guiling Wang, Dianxue Cao
      Abstract: The porous FeVO4 is prepared by hydrothermal method and further modified by coating carbon to obtain the FeVO4/C with hierarchical pore structure, which are used as anodic electrodes in aqueous rechargeable magnesium ion battery. And the FeVO4/C material can not only improve the electrical conductivity by coating a carbon layer but also increase the specific surface area by hierarchical pore structure, which is more beneficial for magnesium ion insertion/deinsertion. Therefore, the aqueous rechargeable magnesium ion full battery is successfully constructed by FeVO4/C as anode, Mg-OMS-1 as cathode and in 1.0 mol L−1 MgSO4 as electrolyte. The discharge capacity of Mg-OMS-1 // FeVO4/C aqueous battery can be obtained 58.9 mAh g−1 at the current density of 100 mA g−1 by calculating the total mass of two electrodes and the capacity retention rate of this device is 97.7% after 100 cycles with the nearly 100% coulombic efficiency, which indicates that the system owns a good electrochemical reversibility. More than that, this system can achieve a high energy density of 70.4 Wh kg−1, which provides a powerful evidence to make the aqueous magnesium ion battery possible.
      PubDate: 2017-09-21T03:21:18.938484-05:
      DOI: 10.1002/chem.201703806
       
  • Asymmetric reduction of prochiral ketones by using self-sufficient
           heterogeneous biocatalysts based on NADPH-dependent ketoreductases
    • Authors: Ana I Benítez-Mateos; Eneko San Sebastián, Nicolás Ríos Lombardía, Francisco Morís, Javier González-Sabín, Fernando Lopez-Gallego
      Abstract: Development of cell-free and self-sufficient biocatalytic systems represents an emerging approach to address more complex synthetic schemes under non-physiological conditions. Herein, we report the fabrication of a self-sufficient heterogeneous biocatalyst for the synthesis of chiral alcohols without the addition of exogenous cofactor. In this work, a NADPH-dependent ketoreductase was primarily stabilized and further co-immobilized with NADPH to catalyze asymmetric reductions without exogenous cofactor addition. As a result, the immobilized cofactor is accessible and thus recycled inside the porous structure without diffusing out to the bulk as demonstrated by single-particle in operando studies. This self-sufficient heterogeneous biocatalyst was finally used and recycled for the asymmetric reduction of 11 carbonyl compounds in a batch reactor without addition of NADPH, achieving the corresponding alcohols with 100% yield and ee> 99% in 5 consecutive cycles. Likewise, the self-sufficient heterogeneous biocatalyst was integrated into a flow-plug reactor for the continuous synthesis of one model secondary alcohol, giving rise to 97-112 g x L-1 x day-1 space-time yield, additionally the immobilized cofactor accumulated a total turnover number of 1076 for 120 hours. This is one of the few examples of the successful implementation of continuous reactions in aqueous media catalyzed by cell-free and immobilized systems integrating both enzymes and cofactors into the solid phase.
      PubDate: 2017-09-21T03:21:16.054546-05:
      DOI: 10.1002/chem.201703475
       
  • One-dimensional Phosphorus Nanostructures: from Nanorings to Nanohelices
    • Authors: Giuseppe Sansone; Lorenzo Maschio, Antti J. Karttunen
      Abstract: Phosphorus nanorings and nanohelices - which were speculated to exist over 20 years ago - have been systematically derived from one parent structure and studied with quantum chemical methods. The (P8P2)n nanorings have been recently synthetized inside carbon nanotube templates, and our comprehensive analysis of possible structural arrangements strongly supports the possibility to experimentally realize the closely-related (P8P2)n nanohelices. The nanohelices possess very low stiffness, suggesting interesting mechanical properties with nano-spring -like behavior.
      PubDate: 2017-09-21T03:21:12.710251-05:
      DOI: 10.1002/chem.201703876
       
  • Ultrathin Cobalt-Based Metal-Organic Framework Nanosheets with both Metal
           and Ligand Redox Activities for Superior Lithium Storage
    • Authors: Yanqun Ning; Xiaobing Lou, Chao Li, Xiaoshi Hu, Bingwen Hu
      Abstract: The controllable synthesis and structural tailoring of nanostructured metal organic frameworks (MOFs) is of huge significance in boosting their potential for rechargeable batteries. We herein present the facile synthesis of cobalt-based ultrathin metal- organic framework nanosheets (referred as "u-CoTDA") by using 2, 5-thiophenedicarboxylic (H2TDA) as the organic building block through a one-pot ultrasonic method for the first time. The obtained u-CoTDA exhibits high reversible capacity (790 mAh g-1 after 400 cycles at 1 A g-1) and excellent rate capability (694 mAh g-1 at 2 A g-1), which outperforms its bulk counterpart. Moreover, the detailed lithiation/delithiation processes of u-CoTDA were studied by the combination of Co K-edge X-ray absorption near edge structure (XANES), O K-edge soft X-ray spectroscopy (sXAS) and electron paramagnetic resonance (EPR) techniques, which demonstrate that both the Co(Ⅱ) centers and organic ligands of u-CoTDA are involved in the reduction/oxidation processes.
      PubDate: 2017-09-21T01:21:54.557257-05:
      DOI: 10.1002/chem.201703077
       
  • Frontispiece: Transition-Metal Chalcogenide/Graphene Ensembles for
           Light-Induced Energy Applications
    • Authors: Antonia Kagkoura; Theodosis Skaltsas, Nikos Tagmatarchis
      Abstract: Combining transition-metal chalcogenides with graphene sheets yields hybrid materials that exhibit excellent photocatalytic properties suitable for hydrogen evolution, degradation of organic pollutants and redox reactions, as well as with high prospect to be employed in photovoltaic devices, photodetectors and biosensing. In the Review by N. Tagmatarchis et al. on page 12967 ff., the recent developments in this field are discussed.
      PubDate: 2017-09-21T01:17:15.674929-05:
      DOI: 10.1002/chem.201785362
       
  • Frontispiece: A Consecutive C−H Functionalization Triggered by Oxidation
           of Active sp3 C−H Bonds: Construction of 3,4-Dihydroquinoline-3-one
           Derivatives
    • Authors: Xiaodong Jia; Wentao Hou, Yu Shao, Yu Yuan, Qian Chen, Pengfei Li, Xiaofei Liu, Honghe Ji
      Abstract: Construction of 3,4-dihydroquinoline-3-ones is achieved by radical cation-initiated aerobic oxidation. In this transformation, the active sp3 C−H bonds of glycines act as the “Achilles′ heel”, triggering the consecutive oxidation of the inert C−H bonds. Furthermore, one heterocylic ring with a quaternary carbon center is also constructed. More information can be found in the Communication by X. Jia et al. on page 12980 ff.
      PubDate: 2017-09-21T01:17:13.446344-05:
      DOI: 10.1002/chem.201785363
       
  • Frontispiece: Small “Yaw” Angles, Large “Bite” Angles and an
           Electron-Rich Metal: Revealing a Stereoelectronic Synergy To Enhance
           Hydride-Transfer Activity
    • Authors: Shrivats Semwal; Indulekha Mukkatt, Ranjeesh Thenarukandiyil, Joyanta Choudhury
      Abstract: Catalytic hydride delivery from in situ generated metal hydride complexes to substrates represents an important process in a variety of catalysis. Investigations revealed a “multidimensional synergistic control” among the stereoelectronic factors—yaw angle, bite angle, as well as the electronic properties of both the ligand and the metal center within the cyclometalated iridium catalysts—that govern the hydride donor ability (hydricity) of the complexes during catalysis. A frontier molecular orbital analysis provided the rationale of such a correlation. For more details, see the Full Paper by J. Choudhury et al. on page 13051 ff.
      PubDate: 2017-09-21T01:17:07.463772-05:
      DOI: 10.1002/chem.201785364
       
  • Frontispiece: Stereoselective Arene-Forming Aldol Condensation:
           Catalyst-Controlled Synthesis of Axially Chiral Compounds
    • Authors: Reto M. Witzig; Dominik Lotter, Vincent C. Fäseke, Christof Sparr
      Abstract: Stereoselective arene-forming aldol condensation reactions were investigated which lead to the formation of configurationally stable binaphthalenes, axially chiral amides and oligo-1,2-naphthylenes. This versatile strategy provides various rotationally restricted compounds with high enantioselectivity and is thus expected to be useful in many areas. For more details, see the Concepts article by C. Sparr et al. on page 12960 ff.
      PubDate: 2017-09-21T01:17:03.565437-05:
      DOI: 10.1002/chem.201785361
       
  • Hydrogen chemisorption on singly vanadium doped aluminum clusters
    • Authors: Jan Vanbuel; Eva M. Fernández, Piero Ferrari, Sandy Gewinner, Wieland Schöllkopf, Luis C Balbás, André Fielicke, Ewald Janssens
      Abstract: The effect of vanadium doping on the hydrogen adsorption capacity of aluminum clusters (Al_n^+, n = 2-18) is studied experimentally by mass spectrometry and infrared multiple photon dissociation (IRMPD) spectroscopy. We find that vanadium doping enhances the reactivity of the clusters towards hydrogen, albeit in a size-dependent way. IRMPD spectra, which provide a fingerprint of the hydrogen binding geometry, show that H_2 dissociates upon adsorption. Density functional theory (DFT) calculations for the smaller Al_nV^+ (n = 2 - 8,10) clusters are in good agreement with the observed reactivity pattern and underline the importance of activation barriers in the chemisorption process. Orbital analysis shows that the activation barriers are due to an unfavorable overlap between cluster and hydrogen orbitals.
      PubDate: 2017-09-20T12:20:25.589796-05:
      DOI: 10.1002/chem.201704361
       
  • In Situ Integration of Ultrathin PtCu Nanowires with Reduced Graphene
           Oxide Nanosheets for Efficient Electrocatalytic Oxygen Reduction
    • Authors: Xiaoxiao Yan; Yifan Chen, Sihui Deng, Yifan Yang, Zhenna Huang, Cunwang Ge, Lin Xu, Dongmei Sun, Gengtao Fu, Yawen Tang
      Abstract: Ultrathin Pt-based nanowires are considered as promising electrocatalysts due to their high atomic utilization efficiency and structural robustness. Moreover, integration of Pt-based nanowires with graphene oxide (GO) could further increase the electrocatalytic performance, yet remains challenging to date. Herein, we for the first time demonstrate the in situ synthesis of ultrathin PtCu nanowires grown over reduced GO (PtCu-NWs/rGO) via a one-pot hydrothermal approach with the aid of amine-terminated poly (N-isopropyl acrylamide) (PNIPAM-NH2). The judicious selection of PNIPAM-NH2 facilitates the in situ nucleation and anisotropic growth of nanowires on rGO surface and oriented attachment mechanism accounts for the formation of PtCu ultrathin nanowires. Due to the synergy between PtCu NWs and rGO support, the PtCu-NWs/rGO outperforms the rGO supported PtCu nanoparticles (PtCu-NPs/rGO), PtCu-NWs and commercial Pt/C toward the oxygen reduction reaction (ORR) with higher activity and better stability, making it a promising cathodic electrocatalyst for both fuel cells and metal-air cells. Moreover, the present synthetic strategy could inspire the future design of other metal alloy nanowires/carbon hybrid catalysts.
      PubDate: 2017-09-20T09:23:02.721885-05:
      DOI: 10.1002/chem.201703900
       
  • Hybridized 1T/2H MoS2 having controlled 1T concentrations and its use in
           supercapacitor
    • Authors: Jyh-Ming Ting; Thi Xuyen Nguyen
      Abstract: Molybdenum disulfide (MoS2) nanoflowers consisting of hybridized 1T/2H phases have been synthesized using a microwave-assisted hydrothermal (MTH) method. The concentration of the 1T phase, ranging from 40% to 73%, is controlled by simply adjusting the ratio of the Mo and S precursors. Using the hybridized 1T/2H MoS2 as electrode material, we demonstrate that the resulting supercapacitor performance is dominated by the 1T phase concentration. It was found that supercapacitor having 73% 1T phase exhibits excellent capacitance of 259 F/g and great cyclic stability after 1,000 cycles. We also report the formation mechanism of the MHT-synthesized hybridized 1T/2H MoS2. More importantly, the mechanism also explains the observed relation between the 1T phase concentration and the ratio of the Mo and S precursors.
      PubDate: 2017-09-20T09:22:59.445415-05:
      DOI: 10.1002/chem.201703690
       
  • Quadruple Stimuli-Responsive Mechanized Silica Nanoparticles: A Promising
           Multifunctional Nanomaterial for Diverse Applications
    • Authors: Chendi Ding; Ling Tong, JiaJun Fu
      Abstract: Novel quadruple stimuli-responsive mechanized silica nanoparticles were constructed by installation of supramolecular nanovalves onto exterior surface of mesoporous silica nanoparticles. The release of cargo molecules is triggered by acid/Zn2+/alkali/reduction potential stimuli, which offers application prospects of developing the drug delivery systems or construction of smart anticorrosion coatings.
      PubDate: 2017-09-20T09:20:53.856711-05:
      DOI: 10.1002/chem.201704245
       
  • A solid iridium catalyst for diastereoselective hydrogenation
    • Authors: Iuliia Romanenko; Louis Jaffeux, Laurent Veyre, Emmanuel Lacôte, Valérie Meille, Chloé Thieuleux
      Abstract: An Ir(NHC) supported catalyst is used in the selective hydrogenation of terpinen-4-ol to cis p-menthan-4-ol. Its activity, selectivity and stability are compared to those of a homogeneous homologue [IrCl(COD)MesImPr] and to a commercial Pd/C. The solid Ir catalyst is much more selective than the Pd catalyst (92 vs. 42% at 80°C) but also more active, more selective and more stable than the iridium complex in solution. For the first time, a supported catalyst shows an enhanced activity with respect to a complex in a diastereoselective hydrogenation reaction.
      PubDate: 2017-09-20T08:21:11.906017-05:
      DOI: 10.1002/chem.201703872
       
  • Quantitative Analysis of Self-Assembly Process of Hexagonal Pt(II)
           Macrocyclic Complexes: Effect of Solvent and Components
    • Authors: Ayako Baba; Tatsuo Kojima, Shuichi Hiraoka
      Abstract: The self-assembly process of three Pt(II)-linked hexagonal macrocycles consisting of dinuclear Pt(II) complexes and organic ditopic ligands was investigated in polar and less polar solvents by recently developed approach: quantitative analysis of self-assembly process (QASAP). In polar CD₃NO₂, for all the three macrocycles, an ML₂ complex was the dominant intermediate during the self-assembly as a result of high positive allosteric cooperativity for the ligand exchange on the Pt(II) centers of dinuclear Pt(II) complexes. On the other hand, in less polar CD₂Cl₂, the self-assembly process was affected by the components and, as for two of the three macrocycles, the chainlike oligomers that contain fewer metals and ligands than the corresponding macrocycles grew with time and type of the chainlike intermediates correlated with the allostericity of the two binding sites in the organic ditopic ligands. In every case, no long oligomers containing more components than the macrocycles were produced during the self-assembly even though free rotation around single bonds in the chainlike oligomers allows them to adopt various conformations not to facilitate the cyclization. This result suggests hat electrostatic and/or steric factors besides rigidity of the components make the cyclization advantageous not only thermodynamically but also kinetically.
      PubDate: 2017-09-20T08:21:03.973707-05:
      DOI: 10.1002/chem.201702955
       
  • Two New Preyssler-Type Polyoxometalate-Based Coordination Polymers and
           Their Application in Horseradish Peroxidase Immobilization
    • Authors: Jing Du; Mei-Da Cao, Shu-Li Feng, Fang Su, Xiao-Jing Sang, Lan-Cui Zhang, Wan-Sheng You, Mei Yang, Zai-Ming Zhu
      Abstract: Enzyme immobilization is of increasing importance for biocatalysis, for which good supports are critical. Herein, two new Preyssler-type polyoxometalate (POM)-based coordination polymers, namely, {[Cu(H2biim)2][{Cu(H2biim)2(μ-H2O)}2Cu(H2biim)(H2O)2]H[({Cu(H2biim)(H2O)2}0.5)2((μ-C3HN2Cl2){Cu(H2biim)}2){Z(H2O)P5W30O110}]⋅x H2O}n (1: Z=Na, x=9; 2: Z=Ag, x=10; H2biim=2,2′-biimidazole) were designed and synthesized. Compounds 1 and 2 exhibit the same skeletons, which contain multiple CuII complex fragments and penta-supported {ZP5W30} (Z=Na, Ag) clusters. They were first employed to immobilize horseradish peroxidase (HRP). Results show that compounds 1 and 2 are good supports for HRP immobilization, and exhibit higher enzyme loading, lower loading times, and excellent reusability. The immobilized HRP (HRP/1 or HRP/2) was further applied to detect H2O2, and good sensitivity, wide linear range, low detection limit, and fast response were achieved. This work shows that POM-based hybrid materials are a new kind of promising support for enzyme immobilization.Pinning down catalysts: Two new Preyssler-type polyoxometalate-based coordination polymers were synthesized and applied to immobilize horseradish peroxidase (HRP). These polymers exhibited higher enzyme loading, required a shorter loading time, and exhibited excellent reusability (see figure).
      PubDate: 2017-09-20T06:28:09.811145-05:
      DOI: 10.1002/chem.201703158
       
  • Synthesis of electron-rich, planarized silicon(IV) species and the
           theoretical analysis of dimerizing aminosilanes
    • Authors: Nina Kramer; Christoph Jöst, Alexandra Mackenroth, Lutz Greb
      Abstract: Equipping silicon(IV) with electron-rich, geometrically constrained NNN- and ONO-tridentate substituents leads to aminosilanes with increased Lewis acidity - expressed through the formation of Si2N2 rings by head-to-tail dimerization. Depending on the substituents, the dimerization can be controlled for the first time, yielding monomeric, structurally reversible and dimeric states. The monomeric species display substantial distortions from tetrahedral towards planar geometry at silicon. The dimerization and the Lewis acidiy of aminosilanes are rationalized by (conceptual) DFT, NBO, ETS-NOCV and QTAIM methods. The preorganization at silicon, London dispersion between the substituents and resonance phenomena inside the formed Si2N2 tetracycles are identified as driving forces for the dimerization. Comparison with selected aminosilanes permits general conclusions on the Lewis acidity of silicon species and on the aggregation of amphiphilic compounds.
      PubDate: 2017-09-20T05:15:32.658861-05:
      DOI: 10.1002/chem.201703649
       
  • Organocatalytic Asymmetric Synthesis of Spiro−tetrahydrothiophene
           Oxindoles Bearing Four Contiguous Stereocenters by One-Pot
           Michael-Henry-Cascade-Rearrangement Reactions
    • Authors: Shengzheng Wang; Zhongjie Guo, Shuqiang Chen, Yan Jiang, Fan Zhang, Xueying Liu, Weiping Chen, Chunquan Sheng
      Abstract: Asymmetric construction of tetrahydrothiophenes with four contiguous stereocenters remains a formidable challenge. Herein, the bottleneck was addressed by an unprecedented one-pot Michael−Henry−Cascade−Rearrangement reaction which could simultaneously create four consecutive stereogenic centers including two tetrasubstituted carbon stereocenters. The highly functionalized chiral spirotetrahydrothiophene scaffolds were assembled in moderate to good yield (54 ~ 79%), excellent diastereo− (>20: 1 dr) and enantio-selectivities (up to 93% ee).
      PubDate: 2017-09-20T04:20:48.090688-05:
      DOI: 10.1002/chem.201703837
       
  • Pd/C-Catalysed Aminocarbonylation of Aryl Iodides with Anthranils in Water
           Using Mo(CO)6 as the CO Source
    • Authors: Xiao-Feng Wu; Zechao Wang, Zhiping Yin
      Abstract: A convenient procedure for the synthesis of N-(2-carbonylaryl)benzamides has been developed. Through Pd/C−catalysed aminocarbonylation of anthranils with various hindered and functionalized aryl iodides, the desired amides were afforded in moderate to good yields. The protocol is advantageous due to the recyclable Pd/C catalyst, safe Mo(CO)6 as the solid CO source, and environmentally benign water as solvent. No inert atmosphere protection is needed.
      PubDate: 2017-09-20T02:20:22.776399-05:
      DOI: 10.1002/chem.201703994
       
  • Rutile TiO2 mesocrystals as a novel sulfur host for high performance
           lithium-sulfur batteries
    • Authors: Qingqing Sun; Kaixiang Chen, Yubin Liu, Yafeng Li, Mingdeng Wei
      Abstract: Although Lithium-sulfur (Li-S) batteries are one of the most promising rechargeable batteries in energy storage devices, the poor cycling performance of Li-S batteries restricts their potential application. The polar materials can improve the cycling stability due to their inherent strong chemical interaction with polysulfides. Herein, a novel rutile TiO2 mesocrystals (RTMs) was employed as the host of sulfur in Li-S, displaying a stable cycling performance with a capacity retention of 64% and a small average capacity decay rate of 0.12% per cycle over 300 cycles at 1 C rate. The good electrochemical property was attributed to the inside ordered nanopores of RTMs which can effectively limit the dissolution of polysulfides, and the ultrafine nanowires in RTMs shorten the path for lithium-ion transport effectively.
      PubDate: 2017-09-19T20:51:05.585411-05:
      DOI: 10.1002/chem.201703130
       
  • Mixed Phthalocyanine-porphyrin-fused Conjugated Pentameric Nanoarrays
    • Authors: Jianzhuang Jiang; Yuehong Zhang, Zheng Xue, Dongdong Qi, Kang Wang, Huibiao Liu
      Abstract: The largest phthalocyanine-porphyrin-fused pentameric molecular arrays have been synthesized and spectroscopically characterized. The saddled molecular conformation revealed for the pentamer by DFT-D3 calculation in combination with the bulky peripheral substituents precludes effective face-to-face π-π intermolecular interaction. As a consequence, intermolecular C-H…π interactions together with the ubiquitous dispersion force arrays help to self-assemble the representative metal-free pentameric molecules into the three-dimensional supramolecular structures with nanaorod morphology in CHCl3 and n-butanol. Powder X-ray diffraction (XRD) analysis and selected area electron diffraction (SAED) disclose the gradually increased long range of molecular ordering in the nanorods along with the increase in the substrate temperature from 30, 40, 50, to 60C. This in turn results in an increase in the semiconductivity of the single nanorod in the same order from 9.4×10-9 to 3.8×10-8, 7.6×10-7, and 6.3×10-5 S/m.
      PubDate: 2017-09-19T20:50:47.961867-05:
      DOI: 10.1002/chem.201703787
       
  • An Fe(III) Aza-macrocyclic Complex as pH-Tunable Catholyte and Anolyte for
           Redox-Flow Battery Applications
    • Authors: Pavel B Tsitovich; Anjula M Kosswattaarachchi, Matthew R Crawley, Timothy Y Tittiris, Timoth R Cook, Janet Ruth Morrow
      Abstract: A reversible Fe3+/Fe2+ redox couple of an aza-macrocyclic complex is evaluated as an electrolyte with a pH-tunable potential range for aqueous redox-flow batteries (RFBs). The Fe(III) complex is formed by 1,4,7-triazacyclononane (TACN) appended with three 2-methyl-imidazole donors, denoted as Fe(Tim). This complex exhibits pH-sensitive redox couples that span E1/2(Fe3+/Fe2+)=317 to -270 mV vs. NHE at pH 3.3 and pH 12.8, respectively. The 590 mV shift in potential and kinetic inertness are driven by ionization of the imidazoles at various pH values. The Fe3+/Fe2+ redox is proton-coupled at alkaline conditions, and bulk electrolysis is non-destructive. The electrolyte demonstrates high charge/discharge capacities at both acidic and alkaline conditions throughout 15 cycles. Given its tunable redox, fast electrochemical kinetics, exceptional stability/cyclability, this complex is promising for the design of aqueous RFB catholytes and anolytes that utilize the earth-abundant element, iron.
      PubDate: 2017-09-19T20:50:44.173666-05:
      DOI: 10.1002/chem.201704381
       
  • Copper-Catalysed Aminoboration of Vinylarenes with Hydroxylamine Esters -
           A Computational Mechanistic Study
    • Authors: Sven Tobisch
      Abstract: This first comprehensive computational study of the copper-mediated formal aminoboration utilising an electrophilic strategy has identified the most accessible pathway for the productive catalysis. The mechanistic picture derived from smooth energy profiles acquired by employing a reliable computational protocol applied to a realistic catalyst model conforms to all available experimental data. The high degree of chemo- and stereoselectivity achieved in syn-borylcupration and Umpolung electrophilic amination is instrumental to the exclusive generation of the (syn)-beta-aminoalkylborane product. On the one hand, syn-borylcupration furnishes exclusively beta-borylalkylcopper nucleophile upon boryl addition onto the vinylarene beta-carbon. Its subsequent approach by the hydroxylamine electrophile to deliver the product with the release of {P^P}CuI benzoate favours a stepwise stereoretentive SN2-type oxidative addition/N-C bond forming reductive elimination sequence. The benzoatecopper represent the catalyst resting state and its transformation into the catalytically competent borylcopper upon salt metathesis with Li(OtBu) base and transmetalation with B2pin2 is turnover limiting. Electronically modified beta-alkylstyrenes featuring a para-CF3 substituted phenyl ring render the borylcupration faster, whilst more electron-rich hydroxylamine agents decelerate the electrophilic amination.
      PubDate: 2017-09-19T10:46:30.191491-05:
      DOI: 10.1002/chem.201703803
       
  • Synthesis of thiophene based optical ligands that selectively detect tau
           pathology in Alzheimer´s disease
    • Authors: Peter Nilsson; Hamid Shirani, Hanna Appelqvist, Marcus Bäck, Therese Klingstedt, Nigel Cairns
      Abstract: The accumulation of protein aggregates is associated with many devastating neurodegenerative diseases and the development of molecular ligands able to detect these pathological hallmarks is essential. Here, we report the synthesis of thiophene based optical ligands, denoted bi-thiophene-vinyl-benzothiazoles (bTVBTs) that can be utilized for selective assignment of tau aggregates in brain tissue with Alzheimer´s disease (AD) pathology. The ability of the ligands to selectively distinguish tau deposits from the other AD associated pathological hallmark, senile plaques consisting of aggregated amyloid-β (Aβ) peptide, were reduced when the chemical composition of the ligands were altered, verifying that specific molecular interactions between the ligands and the aggregates are necessary for the selective detection of tau deposits. Our findings provide the structural and functional basis for the development of new fluorescent ligands that can distinguish between aggregated proteinaceous species consisting of different proteins. In addition, the bTVBT scaffold might be utilized to create powerful practical research tools for studying the underlying molecular events of tau aggregation and for creating novel agents for clinical imaging of tau pathology in AD.
      PubDate: 2017-09-19T10:46:23.751008-05:
      DOI: 10.1002/chem.201703846
       
  • 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: Doxorubicin (Dox) was conjugated to a zinc(II) phthalocyanine (ZnPc) through an acid-cleavable hydrazone linker. This azido-containing conjugate was then anchored to the nanochannels of an alkyne-modified mesoporous silica nanoparticle (MSN) system via copper(I)-catalyzed azide–alkyne cycloaddition. An analogous nanosystem was also prepared by immobilization of a hydrazine-substituted ZnPc to the MSN followed by coupling with Dox. The release of Dox under acidic conditions was studied in phosphate-buffered saline. After internalization into human hepatocellular carcinoma HepG2 cells, these nanoparticles showed fluorescence not only for ZnPc, but also for Dox, suggesting that release of Dox was triggered by the acidic intracellular environment. The chemocytotoxic Dox together with singlet oxygen generated upon irradiation on the encapsulated ZnPc in these MSNs could kill the cells effectively. A synergistic cytotoxicity was suggested by a less-than-unity combination index. These nanoparticles function as both nanophotosensitizers for photodynamic therapy and as nanoplatforms for pH-controlled drug release.Photodynamic duo: Doxorubicin (Dox) was conjugated to a zinc(II) phthalocyanine (ZnPc) and then anchored to mesoporous silica. The chemocytotoxic Dox released under acidic conditions together with singlet oxygen generated upon irradiation on the encapsulated ZnPc could kill cancer cells effectively. The nanoparticles function as both nanophotosensitizers for photodynamic therapy and as nanoplatforms for pH-controlled drug release.
      PubDate: 2017-09-19T07:21:08.821401-05:
      DOI: 10.1002/chem.201703188
       
  • An Unprecedented Blue Chromophore Found in Nature using a “Chemistry
           First” and Molecular Networking Approach: Discovery of Dactylocyanines
           A–H
    • Authors: Natacha Bonneau; Guanming Chen, David Lachkar, Asmaa Boufridi, Jean-François Gallard, Pascal Retailleau, Sylvain Petek, Cécile Debitus, Laurent Evanno, Mehdi A. Beniddir, Erwan Poupon
      Abstract: Guided by a “chemistry first” approach using molecular networking, eight new bright-blue colored natural compounds, namely dactylocyanines A–H (3–10), were isolated from the Polynesian marine sponge Dactylospongia metachromia. Starting from ilimaquinone (1), an hemisynthetic phishing probe (2) was prepared for annotating and matching structurally related natural substances in D. metachromia crude extract network. This strategy allowed characterizing for the first time in Nature the blue zwitterionic quinonoid chromophore. The solvatochromic properties of the latter are reported.Blue-eyed meroterpenes: Guided by a “chemistry first” approach using molecular networking, eight new bright-blue-colored natural compounds, namely dactylocyanines A–H bearing a zwitterionic quinonoid chromophore, were isolated from the Polynesian marine sponge Dactylospongia metachromia.
      PubDate: 2017-09-19T07:20:59.580315-05:
      DOI: 10.1002/chem.201702336
       
  • Mild N-Alkylation of Amines with Alcohols Catalyzed by the Acetate
           Ru(OAc)2(CO)(DiPPF) Complex
    • Authors: Rosario Figliolia; Salvatore Baldino, Hans G. Nedden, Antonio Zanotti-Gerosa, Walter Baratta
      Abstract: The acetate complex Ru(OAc)2(DiPPF) (2) obtained from Ru(OAc)2(PPh3)2 (1) and 1,1′-bis(diisopropylphosphino)ferrocene (DiPPF) reacts cleanly with formaldehyde affording Ru(OAc)2(CO)(DiPPF) (3) in high yield. The monocarbonyl complex 3 (0.4-2 mol %) efficiently catalyzes the N-alkylation of primary and secondary alkyl and aromatic amines using primary alcohols ROH (R=Et, nPr, nBu, PhCH2) under mild reaction conditions (30–100 °C) with an alcohol/amine molar ratio of 10-100. Formation of the monohydride RuH(OAc)(CO)(DiPPF) (4) has been observed by reaction of 3 with iPrOH in the presence of NEt3 at RT through an equilibrium reaction.Amico rutenio: The complex Ru(OAc)2(CO)(DiPPF), easily prepared by carbonylation of Ru(OAc)2(DiPPF) with H2CO, efficiently catalyzes the alkylation of primary and secondary amines with alcohols under mild reaction conditions. Addition of a suitable amount of trifluoroacetic acid increases the rate of reaction. Evidence of the formation of the monohydride RuH(OAc)(CO)(DiPPF) species is provided.
      PubDate: 2017-09-19T07:20:34.134812-05:
      DOI: 10.1002/chem.201702996
       
  • Gold(I) Metallo-Tweezers for the Recognition of Functionalized Polycyclic
           Aromatic Hydrocarbons by Combined π–π Stacking and H-Bonding
    • Authors: Chiara Biz; Susana Ibáñez, Macarena Poyatos, Dmitry Gusev, Eduardo Peris
      Abstract: Two gold(I)-based metallo-tweezers with bis(Au−NHC) pincers and a carbazole connector have been obtained and used for the recognition of polycyclic aromatic hydrocarbons (PAHs). In the case of the tweezer with pyrene–NHC ligands, the presence of the pyrene fragment and the N−H bond in the carbazole linker enable the receptor to show significant enhanced binding abilities toward PAHs functionalized with H-bonding groups, through combined π–π stacking and H-bonding.Easy-tweezy: The presence of pyrene tags at the NHC ligands and the N−H group of a carbazole linker enables AuI tweezers to bind polyaromatic guests through combined π-stacking and H-bonding.
      PubDate: 2017-09-19T07:15:34.886346-05:
      DOI: 10.1002/chem.201703984
       
  • Chemistry of Peptidoglycan in Mycobacterium tuberculosis life style: an
           off-the-wall balance of synthesis and degradation
    • Authors: Flavia Squeglia; Alessia Ruggiero, Rita Berisio
      Abstract: The cell wall envelope of mycobacteria is structurally distinct from that of both Gram-positive and Gram-negative bacteria. In Mycobacterium tuberculosis, this cell wall has unique structural features and plays a crucial role in drug resistance and macrophage survival under stress conditions. Peptidoglycan is the major constituent of this cell wall, with an important structural role, giving structural strength, and counteracting the osmotic pressure of the cytoplasm. Synthesis of this complex polymer takes place in three stages that occur at three different locations in the cell, from the cytoplasm to the external side of the cell membrane, where polymerization occurs. A fine balance of peptidoglycan synthesis and degradation is responsible for a plethora of molecular mechanisms which are key to the pathogenicity of M. tuberculosis. Enlargement of mycobacterial cells can occur via synthesis of new peptidoglycan, autolysis of old peptidoglycan or a combination of both processes. Here, we discuss the chemical aspects of peptidoglycan synthesis and degradation, in relation to metabolic stages of M. tuberculosis. In a travel from inside the mycobacterial cytoplasm to outside its membrane, we describe the assembly line of peptidoglycan synthesis and polymerization, to continue with its depolymerization events and their consequences on mycobacterial life and resuscitation from dormancy.
      PubDate: 2017-09-19T06:45:40.718427-05:
      DOI: 10.1002/chem.201702973
       
  • Rational design of bifunctional, 2-fold interpenetrated
           Zn(II)-metal-organic framework for selective adsorption of CO2 and
           efficient aqueous phase sensing of 2,4,6-trinitrophenol
    • Authors: C M Nagaraja; Sandeep Dhankhar, Nayuesh Sharma, Sandeep Kumar, Dhilip Kumar
      Abstract: A bifunctional, microporous Zn(II) metal-organic framework, [Zn2(NH2BDC)2(dpNDI)]n (MOF1) (where, NH2BDC =2-aminoterephthalic acid, dpNDI =N,N'-di(4-pyridyl)-1,4,5,8-naphthalenediimide) has been synthesized solvothermally. MOF1 shows a 2-fold interpenetrated, 3D pillar-layered framework structure composed of two types of 1D channels with dimensions of ~3.80 x 16.9 Å2 and 7.49 x 17.01 Å2 decorated with pendent -NH2 group. Owing to the presence of basic functionalized pore surface, MOF1 exhibits selective adsorption of CO2 with high value of heat of adsorption (Qst = 46.5 kJ/mol) which is further supported by theoretically calculated binding energy of 48.4 kJ/mol. Interestingly, the value of Qst observed for MOF1 is about 10 kJ/mol higher than that of analogues MOF with BDC ligand, which establishes the critical role of -NH2 group for CO2 capture. Moreover, MOF1 exhibits highly selective and sensitive sensing of nitroaromatic compound (NAC), 2,4,6-trinitrophenol (TNP) over other competing NACs through luminescence quenching mechanism. The observed selectivity for TNP over other nitro phenols has been correlated to stronger hydrogen bonding interaction of TNP with the basic -NH2 group of MOF1, unveiled from DFT calculations. To the best of our knowledge, MOF1 is the first example of an interpenetrated Zn(II)-MOF exhibiting selective adsorption of CO2 as well as efficient aqueous-phase sensing of TNP investigated through combined experimental and theoretical studies.
      PubDate: 2017-09-19T06:45:37.395976-05:
      DOI: 10.1002/chem.201703384
       
  • A One-Step Germole to Silole Transformation and a Stable Isomer of a
           Disilabenzene
    • Authors: Thomas Müller; Crispin Reinhold, Zhaowen Dong, Jan Winkler, Henning Steinert, Marc Schmidtmann
      Abstract: An unusual germole-to-silole transformation is described. As key intermediates hetero-fulvenes are formed which rearrange to more stable bicyclic carbene analogues. The so-formed germylenes undergo a reductive elimination yielding elemental germanium and siloles. In contrast, the analogous silylenes are stable at ambient conditions and were identified by MS spectrometry and NMR spectroscopy supported by the results of quantum mechanical calculations. These bicyclic silylenes are stable derivatives of the global minimum of the C4Si2H6 potential energy surface.
      PubDate: 2017-09-19T06:45:23.411347-05:
      DOI: 10.1002/chem.201703955
       
  • 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
       
  • 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
       
  • Front Cover: Water-Mediated Structural Transformations of CuII
           5-Halonicotinates Coordination Networks with Distinct Mechanisms (Chem.
           Eur. J. 53/2017)
    • Authors: Cheng-Peng Li; Hang Zhou, Yue Ju, Miao Du
      Pages: 12955 - 12955
      Abstract: Three types of mechanisms regulated by halogen substituent effect, namely single-crystal to single-crystal transformation as well as “core-to-core” and “core-on-shell” processes, have been confirmed for elucidation of the “black box” during structural transformations of dynamic crystalline materials. The combination of time-lapse optical microscopy and X-ray single-crystal diffraction techniques provides a convenient and straightforward approach to reveal the transformation mechanisms. More information can be found in the Communication by M. Du et al. on page 12985.
      PubDate: 2017-07-21T02:25:26.40755-05:0
      DOI: 10.1002/chem.201703245
       
  • Cover Feature: Base-Mediated Generation of Ketenimines from Ynamides:
           Direct Access to Azetidinimines by an Imino-Staudinger Synthesis (Chem.
           Eur. J. 53/2017)
    • Authors: Eugénie Romero; Corinne Minard, Mohamed Benchekroun, Sandrine Ventre, Pascal Retailleau, Robert H. Dodd, Kevin Cariou
      Pages: 12956 - 12956
      Abstract: Ynamides were used as precursors for the in situ generation of highly reactive ketenimines which were trapped with imines in a [2+2] cycloaddition under microwave irradiation. Twenty novel azetidinimines have been prepared in this straightforward and operationally simple manner. Furthermore, the products arising from this imino-Staudinger synthesis were functionalized using a wide range of protocols that leave the four-membered amidine ring intact. (Illustration by E. Menneteau, CNRS-PRC 2017). More information can be found in the Communication by R. H. Dodd, K. Cariou et al. on page 12991.
      PubDate: 2017-07-28T03:40:48.054873-05:
      DOI: 10.1002/chem.201703248
       
  • Cover Feature: An Exceptionally Water Stable Metal–Organic Framework
           with Amide-Functionalized Cages: Selective CO2/CH4 Uptake and Removal of
           Antibiotics and Dyes from Water (Chem. Eur. J. 53/2017)
    • Authors: Wei-Guang Jin; Wei Chen, Pei-Hang Xu, Xin-Wen Lin, Xiao-Chun Huang, Guang-Hui Chen, Fushen Lu, Xiao-Ming Chen
      Pages: 12957 - 12957
      Abstract: A new highly porous MOF platform, namely PCN-124-stu was elegantly designed and prepared. The PCN-124-stu(Cu) displays not only high surface area, but also excellent thermal and chemical stability. The MOFs efficiently adsorbed dyes and fluoroquinolones in water, showing promise for water purification. Based on the work above, the cover depicts a traditional Chinese-style landscape-painting in which PCN-124-stu(Cu) cleanses the water and provides an attractive environment for all creatures. More information can be found in the Full Paper by X.-C. Huang et al. on page 13058.
      PubDate: 2017-07-27T08:00:40.491774-05:
      DOI: 10.1002/chem.201702833
       
  • Cover Feature: Aggregation-Induced Emission (AIE) Fluorophore Exhibits a
           Highly Ratiometric Fluorescent Response to Zn2+ in vitro and in Human
           Liver Cancer Cells (Chem. Eur. J. 53/2017)
    • Authors: Hassan Mehdi; Weitao Gong, Huimin Guo, Michael Watkinson, Hua Ma, Ali Wajahat, Guiling Ning
      Pages: 12958 - 12958
      Abstract: A new AIE-active fluorophore that exhibits a rapid and highly selective ratiometric response to Zn2+ with a limit of detection (LOD) up to 2.6 nm is reported. Furthermore, the fluorophore was successfully applied in ratiometric imaging of intracellular Zn2+ in human hepatoma cancer cells by fluorescent confocal microscopy. More information can be found in the Full Paper by W. Gong, M. Watkinson, G. Ning et al. on page 13067.
      PubDate: 2017-08-01T09:01:00.357616-05:
      DOI: 10.1002/chem.201703192
       
  • Water-Mediated Structural Transformations of CuII 5-Halonicotinates
           Coordination Networks with Distinct Mechanisms
    • Authors: Cheng-Peng Li; Hang Zhou, Yue Ju, Miao Du
      Pages: 12959 - 12959
      Abstract: Invited for the cover of this issue is the group of Miao Du at Tianjin Normal University. The image depicts the structural transformation of a dynamic coordination network. Read the full text of the article at 10.1002/chem.201702405.“The results will offer a convenient strategy to illuminate the mechanisms for solvent-mediated crystal transformations.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 12985 ff. (
      DOI : 10.1002/chem.201702405).
      PubDate: 2017-07-31T10:17:30.227005-05:
       
  • Stereoselective Arene-Forming Aldol Condensation: Catalyst-Controlled
           Synthesis of Axially Chiral Compounds
    • Authors: Reto M. Witzig; Dominik Lotter, Vincent C. Fäseke, Christof Sparr
      Pages: 12960 - 12966
      Abstract: The fundamental role that aldol chemistry adopts in various disciplines, such as stereoselective catalysis or the biosynthesis of aromatic polyketides, illustrates its exceptional versatility. On the one hand, numerous aldol addition reactions reliably transfer the stereochemical information from catalysts into various valuable products. On the other hand, countless aromatic polyketide natural products are produced by an ingenious biosynthetic machinery based on arene-forming aldol condensations. With the aim of complementing aldol methodology that controls stereocenter configuration, we recently combined these two tenets by investigating small-molecule-catalyzed aldol condensation reactions that stereoselectively form diverse axially chiral compounds through the construction of a new aromatic ring.An arena for carbonyl compounds: Intrigued by the biosynthesis of aromatic polyketides, stereoselective arene-forming aldol condensation reactions were investigated that lead to the formation of configurationally stable binaphthalenes, axially chiral amides and oligo-1,2-naphthylenes. As this versatile strategy provides various rotationally restricted compounds with high enantioselectivity, it is expected to be useful in many areas of application.
      PubDate: 2017-09-05T06:41:20.940844-05:
      DOI: 10.1002/chem.201702471
       
  • Transition-Metal Chalcogenide/Graphene Ensembles for Light-Induced Energy
           Applications
    • Authors: Antonia Kagkoura; Theodosis Skaltsas, Nikos Tagmatarchis
      Pages: 12967 - 12979
      Abstract: Recently, nanomaterials that harvest solar energy and convert it to other forms of energy are of great interest. In this context, transition metal chalcogenides (TMCs) have recently been in the spotlight due to their optoelectronic properties that render them potential candidates mainly in energy conversion applications. Integration of TMCs onto a strong electron-accepting material, such as graphene, yielding novel TMC/graphene ensembles is of high significance, since photoinduced charge-transfer phenomena, leading to intra-ensemble charge separation, may occur. In this review, we highlight the utility of TMC/graphene ensembles, with a specific focus on latest trends in applications, while their synthetic routes are also discussed. In fact, TMC/graphene ensembles are photocatalytically active and superior as compared to intact TMCs analogues, when examined toward photocatalytic H2 evolution, dye degradation and redox transformations of organic compounds. Moreover, TMC/graphene ensembles have shown excellent prospect when employed in photovoltaics and biosensing applications. Finally, the future prospects of such materials are outlined.A light ensemble! Transition-metal chalcogenides/graphene ensembles are a novel class of materials for energy applications particularly in photocatalysis, photovoltaics and biosensing (see figure). In this Review, a critical evaluation of the development in the field is presented, with key-examples from the recent literature.
      PubDate: 2017-08-10T10:43:41.73183-05:0
      DOI: 10.1002/chem.201700242
       
  • A Consecutive C−H Functionalization Triggered by Oxidation of Active sp3
           C−H Bonds: Construction of 3,4-Dihydroquinoline-3-one Derivatives
    • Authors: Xiaodong Jia; Wentao Hou, Yu Shao, Yu Yuan, Qian Chen, Pengfei Li, Xiaofei Liu, Honghe Ji
      Pages: 12980 - 12984
      Abstract: We report a consecutive C−H functionalization that constructs 3,4-dihydroquinoline-3-one derivatives in high yields. This reaction is triggered by oxidation of active sp3 C−H bonds of glycines and N-benzylanilines. In this radical mediated transformation, four sp3 C−H bonds are functionalized efficiently, together with construction of one heterocyclic ring with a quaternary carbon center.A consecutive C−H functionalization was achieved by radical cation salt initiated aerobic oxidation, constructing 3,4-dihydroquinoline-3-one derivatives in high yields. In this consecutive process, oxidation of active sp3 C−H bonds of glycines and N-benzylanilines promoted further oxidation of inert C-H bonds, forging one heterocyclic ring with a quaternary carbon center.
      PubDate: 2017-08-10T10:45:23.569264-05:
      DOI: 10.1002/chem.201702497
       
  • Water-Mediated Structural Transformations of CuII 5-Halonicotinates
           Coordination Networks with Distinct Mechanisms
    • Authors: Cheng-Peng Li; Hang Zhou, Yue Ju, Miao Du
      Pages: 12985 - 12990
      Abstract: Currently, no unequivocal evidence is given for elucidation of “black box” during the structural transformations of dynamic crystalline materials. Here, three types of mechanisms are revealed for such transformations through X-ray diffraction and optical microscopy; namely, single-crystal to single-crystal (SC–SC), as well as “core-to-core” and “core-on-shell” processes. As confirmed by time-lapse optical microscopy, the latter two cases can be properly ascribed as partial recrystallization processes, while the former one is a continuous process with two different crystal lattices simultaneously maintained in one single crystal. Interestingly, these three distinct pathways can be exquisitely realized by changing only the halogen substituent (from -F, -Cl, to -Br) of the organic ligands in the coordination supramolecular systems.Lifting the lid: Structural transformations of dynamic crystals are usually seen as a black box process. Here the transformations are followed by crystallography and optical microscopy, and three different mechanisms are revealed.
      PubDate: 2017-07-11T07:53:13.482876-05:
      DOI: 10.1002/chem.201702405
       
  • Base-Mediated Generation of Ketenimines from Ynamides: Direct Access to
           Azetidinimines by an Imino-Staudinger Synthesis
    • Authors: Eugénie Romero; Corinne Minard, Mohamed Benchekroun, Sandrine Ventre, Pascal Retailleau, Robert H. Dodd, Kevin Cariou
      Pages: 12991 - 12994
      Abstract: Ynamides were used as precursors for the in situ generation of highly reactive ketenimines that could be trapped with imines in a [2+2] cycloaddition. This imino-Staudinger synthesis led to a variety of imino-analogs of β-lactams, namely azetidinimines (20 examples), that could be further functionalized through a broad range of transformations.Base Jump: Under strongly basic conditions ynamides gave highly reactive ketenimines that could be trapped with imines in a [2+2] cycloaddition. This imino-Staudinger synthesis led to a variety of imino analogues of β-lactams, namely azetidinimines (20 examples), that could be further functionalized through a broad range of transformations.
      PubDate: 2017-08-03T07:25:28.225925-05:
      DOI: 10.1002/chem.201702545
       
  • Large-Diameter TiO2 Nanotubes Enable Wall Engineering with Conformal
           Hierarchical Decoration and Blocking Layers for Enhanced Efficiency in
           Dye-Sensitized Solar Cells (DSSC)
    • Authors: Abdelhamid Elzarka; Ning Liu, Imgon Hwang, Mustafa Kamal, Patrik Schmuki
      Pages: 12995 - 12999
      Abstract: Herein, we grew anodic TiO2 nanotube layer with a tube diameter>500 nm and an open tube mouth. We use this morphology in dye-sensitized solar cells (DSSCs) and show that these tubes allow the construction of hybrid hierarchical photoanode structures of nanotubes with a defined and wall-conformal TiO2 nanoparticle decoration. At the same time, the large diameter allows the successful establishment of an additional (insulating) blocking layer of SiO2 or Al2O3 on the tube wall. We showed that this combination of hierarchical structure and blocking layer significantly enhances the solar-cell efficiency by suppressing recombination reactions. In such a DSSC structure, the solar-cell efficiency under back side illumination with AM1.5 illumination was enhanced from 3 % for the neat tube to 5 % for the hierarchical structure to 7 % when additionally a blocking layer was attached.Blocking layers: Large diameter>500 nm and open-tube-mouth TiO2 nanotubes can be grown by anodization and applied to DSSCs. These tubes can be layer-by-layer decorated with TiO2 nanoparticles forming a hierarchical, high-surface-area structure. In particular, these tubes allow to additionally establish a thin blocking layers of SiO2 or Al2O3 that were found to significantly affect the DSSC performance (see scheme).
      PubDate: 2017-08-29T04:43:08.025111-05:
      DOI: 10.1002/chem.201702434
       
  • Assessing Guest-Molecule Diffusion in Heterogeneous Powder Samples of
           Metal–Organic Frameworks through Pulsed-Field-Gradient (PFG) NMR
           Spectroscopy
    • Authors: Roland Thoma; Jörg Kärger, Nader de Sousa Amadeu, Sandra Nießing, Christoph Janiak
      Pages: 13000 - 13005
      Abstract: Investigation of guest diffusion in porous metal–organic frameworks (MOFs) is of major importance, because many porosity-related properties of MOFs are influenced by diffusion effects. The diffusion of dimethyl sulfoxide (DMSO) in the MOF MIL-53-NH2(Al) was investigated through pulsed-field-gradient (PFG) NMR spectroscopy. The microporous material was synthesized in small crystallites (under 500 nm), which agglomerated in a large range of particle sizes (from hundreds of nanometers to tens of micrometers), giving a morphologically very heterogeneous sample. No special agglomeration pattern could be observed, which makes a PFG NMR investigation very challenging, yet it represents a realistic situation for the diffusion of guest molecules in porous materials. We were able to distinguish between two diffusion regimes existing in parallel with each other over the total range from 15 to 200 ms of observation times as accessible in the experiments: In the large crystal agglomerates (diameters above 20 μm), guest movement was found to be subdiffusive, with a time exponent κ=0.8 (rather than one as for normal diffusion). Guest diffusion in the remaining, smaller host particles followed the pattern of normal diffusion within a bed of spheres of impenetrable external surfaces, with a size distribution in good agreement with that of the material under study. Diffusion in a rather complex system could thus be referred to a two-region model with new potentials for application to systems of intricate topology.Restricted diffusion: Abundancy-weighted guest diffusivities plotted in matrix form with reference to the different ranges of observation times (Δ) and particle size (R) serve as a new tool for quantifying pulsed-field-gradient (PFG) NMR diffusivities in MOF agglomerates (see figure).
      PubDate: 2017-08-28T12:42:59.155527-05:
      DOI: 10.1002/chem.201702586
       
  • The Chemistry of 1-Acylphosphirane Complexes: A Phosphorus Analogue of the
           Cloke–Wilson Rearrangement
    • Authors: Rongqiang Tian; Chunli Zhang, Yang Xu, Chenguang Liu, Zheng Duan, François Mathey
      Pages: 13006 - 13009
      Abstract: The stabilization of a phosphirane ring by complexation to tungsten pentacarbonyl allows the emergence of the Cloke–Wilson rearrangement in 1-acylphosphirane complexes around 130 °C. Contrary to the cyclopropane case, this transformation of the 1-acylphosphirane to the 1,3-oxaphosphol-3-ene complexes is reversible. It is favored by a 2-phenyl, and even a 2-vinyl substitution. The 1,3-oxaphosphol-3-ene complexes are trapped by conjugated dienes.The stabilization of a phosphirane ring by complexation to tungsten pentacarbonyl allows the emergence of the Cloke–Wilson rearrangement in 1-acylphosphirane complexes around 130 °C. Contrary to the cyclopropane case, this transformation of the 1-acylphosphirane to the 1,3-oxaphosphol-3-ene complexes is reversible. It is favored by a 2-phenyl and, even more, a 2-vinyl substitution. The 1,3-oxaphosphol-3-ene complexes are trapped by conjugated dienes.
      PubDate: 2017-08-23T12:24:54.140759-05:
      DOI: 10.1002/chem.201702722
       
  • Small-Molecule-Induced Soluble Oligomers of α-Synuclein with Helical
           Structure
    • Authors: Luis Fonseca-Ornelas; Carla Schmidt, Aldo R. Camacho-Zarco, Claudio O. Fernandez, Stefan Becker, Markus Zweckstetter
      Pages: 13010 - 13014
      Abstract: Accumulation of α-synuclein (αSyn) aggregates constitutes the hallmark of synucleinopathies including Parkinson's disease. However, many steps from the innocuous, monomeric αSyn toward misfolded oligomers and fibrillar species remain unclear. Here, we show that αSyn can form in solution α-helical oligomers, which are off-pathway to fibrillization, through interaction with the tetrapyrrole phthalocyanine tetrasulfonate. Chemical cross-linking combined with mass spectrometry reveals a large number of intermolecular cross-links along the entire αSyn sequence in the phthalocyanine tetrasulfonate-stabilized αSyn oligomers. Our study suggests that stabilization of structured oligomers by small molecules provides a viable strategy to interfere with αSyn fibrillization.Small and soluble: Interaction of the Parkinson-related protein α-synuclein with the small molecule PcTS generates soluble oligomers that contain helical α-synuclein structure and are off-pathway to amyloid fibril formation.
      PubDate: 2017-08-23T12:21:14.926916-05:
      DOI: 10.1002/chem.201703001
       
  • Approach Matters: The Kinetics of Interfacial Inverse-Electron Demand
           Diels–Alder Reactions
    • Authors: Rickdeb Sen; Digvijay Gahtory, Jorge Escorihuela, Judith Firet, Sidharam P. Pujari, Han Zuilhof
      Pages: 13015 - 13022
      Abstract: Rapid and quantitative click functionalization of surfaces remains an interesting challenge in surface chemistry. In this regard, inverse electron demand Diels–Alder (IEDDA) reactions represent a promising metal-free candidate. Herein, we reveal quantitative surface functionalization within 15 min. Furthermore, we report the comprehensive effects of substrate stereochemistry, surrounding microenvironment and substrate order on the reaction kinetics as obtained by surface-bound mass spectrometry (DART-HRMS).Nailing the landing: For click reactions on a surface, the angle of approach matters greatly. We show for closely monitored inverse electron demand Diels–Alder reactions that fast and quantitative landings are feasible.
      PubDate: 2017-08-23T12:24:36.54966-05:0
      DOI: 10.1002/chem.201703103
       
  • Tailored Band Gaps in Sulfur- and Nitrogen-Containing Porous
           Donor–Acceptor Polymers
    • Authors: Dana Schwarz; Yaroslav S. Kochergin, Amitava Acharjya, Arun Ichangi, Maksym V. Opanasenko, Jiří Čejka, Uwe Lappan, Pal Arki, Junjie He, Johannes Schmidt, Petr Nachtigall, Arne Thomas, Ján Tarábek, Michael J. Bojdys
      Pages: 13023 - 13027
      Abstract: Donor–acceptor dyads hold the key to tuning of electrochemical properties and enhanced mobility of charge carriers, yet their incorporation into a heterogeneous polymer network proves difficulty owing to the fundamentally different chemistry of the donor and acceptor subunits. A family of sulfur- and nitrogen-containing porous polymers (SNPs) are obtained via Sonogashira–Hagihara cross-coupling and combine electron-withdrawing triazine (C3N3) and electron-donating, sulfur-containing linkers. Choice of building blocks and synthetic conditions determines the optical band gap (from 1.67 to 2.58 eV) and nanoscale ordering of these microporous materials with BET surface areas of up to 545 m2 g−1 and CO2 capacities up to 1.56 mmol g−1. Our results highlight the advantages of the modular design of SNPs, and one of the highest photocatalytic hydrogen evolution rates for a cross-linked polymer without Pt co-catalyst is attained (194 μmol h−1 g−1).Catalysis in a SNP: Sulfur- and nitrogen-containing porous polymers (SNPs) combine two key features for heterogeneous photocatalysts, namely an open pore structure and a modular, π-conjugated backbone. The electronic and optical properties of these photoactive materials can be tuned by the choice of building blocks and via post-synthetic doping.
      PubDate: 2017-08-17T06:56:34.906447-05:
      DOI: 10.1002/chem.201703332
       
  • Selective Conversion of P=O-Bridged Rhodamines into P=O-Rhodols:
           Solvatochromic Near-Infrared Fluorophores
    • Authors: Marek Grzybowski; Masayasu Taki, Shigehiro Yamaguchi
      Pages: 13028 - 13032
      Abstract: The substitution of an oxygen atom in rhodols with a phosphine oxide (P=O) moiety affords P=O-bridged rhodols as a new type of near-infrared (NIR) fluorophore. This compound class can be readily accessed upon exposure of the corresponding rhodamines to aqueous basic conditions. The electron-withdrawing effect of the P=O group facilitates the hydrolytic deamination, and, moreover, prolonged exposure to aqueous basic conditions generates P=O-bridged fluoresceins, that is, a series of three P=O-bridged xanthene dyes is available in one simple operation. The P=O-bridged rhodols show significant bathochromic shifts of the longest-wavelength absorption maximum (Δλ=125 nm;>3600 cm−1) upon changing the solvent from toluene to water, whereas the emission is shifted less drastically (Δλ=70 nm; 1600 cm−1). The hydrogen bonding between the P=O and C=O groups with protic solvents results in substantial stabilization of the LUMO level, which is responsible for the solvatochromism.Lock on the target: The hydrolytic deamination of P=O-bridged rhodamines directly and selectively produces the corresponding rhodols and fluoresceins. The P=O substitution of the endocyclic oxygen in rhodols gives significant impact with ≈150 nm redshifted absorption and fluorescence. The P=O-bridged rhodols exhibit a characteristic solvatochromism in the absorption and emit NIR fluorescence in water with pronounced photostability.
      PubDate: 2017-08-22T11:57:25.100204-05:
      DOI: 10.1002/chem.201703456
       
  • Chemical Tagging with tert-Butyl and Trimethylsilyl Groups for Measuring
           Intermolecular Nuclear Overhauser Effects in a Large Protein–Ligand
           Complex
    • Authors: Shereen Jabar; Luke A. Adams, Yao Wang, Luigi Aurelio, Bim Graham, Gottfried Otting
      Pages: 13033 - 13036
      Abstract: Intermolecular 1H-1H nuclear Overhauser effects (NOE) present a powerful tool to assess contacts between proteins and binding partners, but are difficult to identify for complexes of high molecular weight. This report shows that intermolecular NOEs can readily be observed following chemical labeling with tert-butyl or trimethylsilyl (TMS) groups. Proteins can be furnished with tert-butyl or TMS groups site-specifically using genetically encoded unnatural amino acids or by chemical modification of single cysteine residues. No isotope labeling is required. The approach is demonstrated with the 95 kDa complex between tetrameric E. coli single-stranded DNA binding protein (SSB) and single-stranded DNA.Making contact: Intermolecular nuclear Overhauser effects between large proteins and binding partners can be observed selectively and with high sensitivity following site-specific chemical tagging of the proteins with tert-butyl or trimethylsilyl groups.
      PubDate: 2017-08-18T01:25:35.151513-05:
      DOI: 10.1002/chem.201703531
       
  • Copper-Catalyzed Enantioselective Domino Arylation/Semipinacol
           Rearrangement of Allylic Alcohols with Diaryliodonium Salts
    • Authors: Hua Wu; Qian Wang, Jieping Zhu
      Pages: 13037 - 13041
      Abstract: A copper-catalyzed enantioselective arylative semipinacol rearrangement of allylic alcohols was developed. In the presence of a catalytic amount of an in situ generated chiral copper-bisoxazoline complex, reaction of allylic alcohols with diaryliodonium salts afforded spirocycloalkanones in high yields with high diastereo- and enantioselectivities. A two-point binding model engaging the carbon–carbon double bond and the proximal hydroxyl group was proposed to be responsible for the highly efficient chirality transfer.Selective arylation and shift: Copper-catalyzed enantioselective arylative semipinacol rearrangement of allylic alcohols with diaryliodonium salts afforded spirocycloalkanones in good to high yields with high diastereo- and enantioselectivities.
      PubDate: 2017-08-21T07:11:45.044302-05:
      DOI: 10.1002/chem.201703563
       
  • N-Heterocyclic Carbene Catalyzed [3+2] Cycloaddition of Enals with Masked
           Cinnamates for the Asymmetric One-Pot Synthesis of Adipic Acid Derivatives
           
    • Authors: Xiang-Yu Chen; Sun Li, He Sheng, Qiang Liu, Ehsan Jafari, Carolina von Essen, Kari Rissanen, Dieter Enders
      Pages: 13042 - 13045
      Abstract: A novel short entry to 3,4-disubstituted adipic acids has been developed by employing an asymmetric NHC-catalyzed [3+2] cycloaddition of enals with masked cinnammates in moderate to good yields and high stereoselectivities. The synthetic utility of the protocol was demonstrated by the basic conversion of the masked cyclopentanone intermediates to 3S,4S-disubstituted adipic acid precursors of pharmaceutically important gababutins.One-pot to adipic acids: The NHC-catalyzed asymmetric [3+2] cycloaddition of enals with masked cinnamates opens a new short entry to adipic acid derivatives in moderate to good yields and high stereoselectivities. The utility of the protocol is showcased by the one-pot asymmetric synthesis of 3S,4S-disubstituted adipic acids, precursors for the synthesis of 3,4-disubstituted gababutins, which are used for the treatment of various diseases.
      PubDate: 2017-08-22T11:57:00.841869-05:
      DOI: 10.1002/chem.201703579
       
  • Zn-, Mg-, and Li-TMP Bases for the Successive Regioselective Metalations
           of the 1,5-Naphthyridine Scaffold (TMP=2,2,6,6-Tetramethylpiperidyl)
    • Authors: Moritz Balkenhohl; Robert Greiner, Ilya S. Makarov, Benjamin Heinz, Konstantin Karaghiosoff, Hendrik Zipse, Paul Knochel
      Pages: 13046 - 13050
      Abstract: A set of successive regioselective metalations and functionalizations of the 1,5-naphthyridine scaffold are described. A combination of Zn-, Mg-, and Li-TMP (TMP=2,2,6,6-tetramethylpiperidyl) bases and the presence or absence of a Lewis acid (BF3⋅OEt2) allows the introduction of up to three substituents to the 1,5-naphthyridine core. Also, a novel “halogen dance” reaction was discovered upon metalation of an 8-iodo-2,4-trifunctionalized 1,5-naphthyridine allowing a fourth regioselective functionalization. Additionally, reactions leading to key 1,5-naphthyridines for the preparation of OLED materials and a potential antibacterial agent were performed.Step by step: Successive regioselective metalations of the 1,5-naphthyridine scaffold are achieved by using a combination of Zn-, Mg-, and Li-TMP (TMP=2,2,6,6-tetramethylpiperidyl) bases in the presence or absence of BF3⋅OEt2 allowing the introduction of up to three substituents. A novel “halogen dance” rearrangement allows the introduction of a fourth substituent leading to 2,4,7,8-tetrafunctionalized 1,5-naphthyridines. Also, two key 1,5-naphthyridines for the synthesis of OLED materials and an antibacterial agent were prepared.
      PubDate: 2017-08-23T12:20:57.629807-05:
      DOI: 10.1002/chem.201703638
       
  • Small “Yaw” Angles, Large “Bite” Angles and an Electron-Rich
           Metal: Revealing a Stereoelectronic Synergy To Enhance Hydride-Transfer
           Activity
    • Authors: Shrivats Semwal; Indulekha Mukkatt, Ranjeesh Thenarukandiyil, Joyanta Choudhury
      Pages: 13051 - 13057
      Abstract: Cyclometalated complexes are an important class of (pre)catalysts in many reactions including hydride transfer. The ring size of such complexes could therefore be a relevant aspect to consider while modulating their catalytic activity. However, any correlation between the cyclometalating ring size and the catalytic activity should be drawn by careful assessment of the pertinent geometrical parameters, and overall electronic effects thereof. In this study, we investigated the vital role of key stereoelectronic functions of two classes of iridacyclic complexes—five-membered and six-membered cycles—in manupulating the catalytic efficiency in a model hydride-transfer reaction. Our investigation revealed that there exists an interesting multidimensional synergy among all the relevant stereoelectronic factors—yaw angle, bite angle, and the electronic properties of both the ligand and the metal center—that governs the hydride donor ability (hydricity) of the complexes during catalysis. Thus the six-membered chelate complexes with small yaw and large bite angles, strong donor ligand, and electron-rich metal were found to be better catalysts than their five-membered analogues. A frontier molecular orbital analysis supported the significant role of the above stereoelectronic synergistic effect associated with the chelate ring to control the hydride donor ability of the complexes.A multidimensional “stereo-electronic synergy” in metal complexes that controls hydride transfer catalysis is disclosed.
      PubDate: 2017-08-09T02:46:37.643471-05:
      DOI: 10.1002/chem.201702173
       
  • An Exceptionally Water Stable Metal–Organic Framework with
           Amide-Functionalized Cages: Selective CO2/CH4 Uptake and Removal of
           Antibiotics and Dyes from Water
    • Authors: Wei-Guang Jin; Wei Chen, Pei-Hang Xu, Xin-Wen Lin, Xiao-Chun Huang, Guang-Hui Chen, Fushen Lu, Xiao-Ming Chen
      Pages: 13058 - 13066
      Abstract: As the main organic pollutants in wastewater, antibiotics and organic dyes are harmful to the environment and public health, and their removal is important but challenging. In this work, highly porous 3D metal–organic frameworks (MOFs) [M2(PDAD)(H2O)]n (PCN-124-stu; M=Cu, Zn; H4PDAD = 5,5′-(pyridine-3,5-dicarbonyl)bis(azanediyl)diisophthalic acid) were synthesized, and PCN-124-stu(Cu) shows excellent chemical and thermal stability. PCN-124-stu(Cu) was used as a host for efficient extraction of various organic dyes, especially the large-molecule dye Coomassie brilliant blue, and fluoroquinolones from water, in comparison with five common MOFs, zeolite 13X, and activated carbon. PCN-124-stu(Cu) exhibits absolute predominance for fluoroquinolone adsorption among these microporous materials because of the H-bonds between fluoroquinolone molecules and the amide groups in the frameworks, except for MIL-100(Cr), which is a mesoporous MOF. Moreover, PCN-124-stu(Cu) could release fluoroquinolones slowly in physiological saline and retained its framework structure after four adsorption/desorption cycles. In addition, PCN-124-stu(Cu) can be used as a platform for selective adsorption of CO2/CH4.Waterproof MOF: An exceptionally water stable metal–organic framework (MOF) with amide-functionalized cages (see figure), namely, PCN-124-stu(Cu), was synthesized, and its porous structure exhibits selective adsorption CO2/CH4. Furthermore, PCN-124-stu(Cu) can serve as a platform for removal of antibiotic and dye pollutants from water.
      PubDate: 2017-07-27T07:45:40.322505-05:
      DOI: 10.1002/chem.201701884
       
  • Aggregation-Induced Emission (AIE) Fluorophore Exhibits a Highly
           Ratiometric Fluorescent Response to Zn2+ in vitro and in Human Liver
           Cancer Cells
    • Authors: Hassan Mehdi; Weitao Gong, Huimin Guo, Michael Watkinson, Hua Ma, Ali Wajahat, Guiling Ning
      Pages: 13067 - 13075
      Abstract: Two novel organic fluorophores, containing bis-naphthylamide and quinoline motifs, have been designed and synthesized. One of the fluorophores contains an isobutylene unit and exhibits a significant aggregation-induced emission (AIE) and a remarkable highly selective ratiometric fluorescence response towards Zn2+ in solution as well as in human liver cancer cells. The AIE behavior of this fluorophore was fully verified by fluorescence and UV/Vis spectroscopy, quantum yield calculations, and single-crystal X-ray diffraction, which revealed an intricate crystal packing system. Conversely, a fluorophore that lacks the isobutylene moiety did not exhibit any significant fluorescent properties as a result of its more flexible molecular structure that presumably allows free intramolecular rotational processes to occur.Let it shine: A novel fluorophore 8AQ containing an isobutylene unit exhibits a significant AIE feature and remarkable ratiometric response to Zn2+ in solution as well as intracellular bio-imaging behavior in human liver cancer cells. Conversely, fluorophore 8WB, which lacks the isobutylene moiety did not exhibit any significant fluorescent properties as a result of its more flexible molecular structure.
      PubDate: 2017-08-01T09:03:56.311785-05:
      DOI: 10.1002/chem.201701948
       
  • Altering the Coordination of Iron Porphyrins by Ionic Liquid Nanodomains
           in Mixed Solvent Systems
    • Authors: Abderrahman Atifi; Michael D. Ryan
      Pages: 13076 - 13086
      Abstract: The solvent environment around iron porphyrin complexes was examined using mixed molecular/RTIL (room temperature ionic liquid) solutions. The formation of nanodomains in these solutions provides different solvation environments for substrates that could have significant impact on their chemical reactivity. Iron porphyrins (Fe(P)), whose properties are sensitive to solvent and ligation changes, were used to probe the molecular/RTIL environment. The addition of RTILs to molecular solvents shifted the redox potentials to more positive values. When there was no ligation change upon reduction, the shift in the E° values were correlated to the Gutmann acceptor number, as was observed for other porphyrins with similar charge changes. As %RTIL approached 100 %, there was insufficient THF to maintain coordination and the E° values were much more dependent upon the %RTIL. In the case of FeIII(P)(Cl), the shifts in the E° values were driven by the release of the chloride ion and its strong attraction to the ionic liquid environment. The spectroscopic properties and distribution of the FeII and FeI species into the RTIL nanodomains were monitored with visible spectroelectrochemistry, 19F NMR and EPR spectroscopy. This investigation shows that coordination and charge delocalization (metal versus ligand) in the metalloporphyrins redox products can be altered by the RTIL fraction in the solvent system, allowing an easy tuning of their chemical reactivity.Changes in the coordination environment of iron porphyrins in mixed THF/room temperature ionic liquids were probes using cyclic voltammetry, UV/visible, 19F NMR and EPR spectroscopy. The results were consistent with the formation of nanodomains in the mixed solvent system that significantly affected the redox and spectral properties. Without coordination changes, the E° values were correlated with the Gutmann acceptor number, but strong deviations were observed as the iron porphyrin lost THF coordination.
      PubDate: 2017-08-30T11:12:20.563151-05:
      DOI: 10.1002/chem.201701540
       
  • Synthesis and Characterization of Nitro-, Trinitromethyl-, and
           Fluorodinitromethyl-Substituted Triazolyl- and Tetrazolyl-trihydridoborate
           Anions
    • Authors: Guillaume Bélanger-Chabot; S. Max Kaplan, Piyush Deokar, Norbert Szimhardt, Ralf Haiges, Karl O. Christe
      Pages: 13087 - 13099
      Abstract: The problem of preparing energetic, exclusively mono-azolyl substituted hydridoborate anions in high yield and purity from [BH4]− and nitroazoles by hydrogen elimination was overcome by reacting the corresponding nitroazolate anions with the BH3 adducts BH3⋅S(CH3)2 or BH3⋅THF. The highly-energetic, nitro-, trinitromethyl-, and fluorodinitromethyl- substituted triazolyl- and tetrazolyl-trihydridoborate anions were synthesized in this manner and characterized by vibrational and multinuclear NMR spectroscopy and their crystal structures. The use of excess BH3 resulted in some cases in the addition of a second BH3 molecule bound more-weakly to one of the nitrogen atoms of the azole ring. All monoazolyl-trihydridoborates were thermally less stable than the parent azolate anions. A decomposition product of tetraphenylphosphonium (5-(trinitromethyl)-5H-2λ4-tetrazol-2-yl)trihydridoborate, the tetraphenyl-phosphonium (dinitro-1H-tetrazol-5-yl)methanide monohydrate, was also structurally characterized, providing some insight into the decomposition pathways of the nitromethyl-substituted azolyltrihydridoborate anions.Bangin′ boron: Highly-energetic (nitroazolyl)trihydridoborate anions are difficult to prepare in high yield and purity. A simple, one-step method was found to achieve this goal and numerous novel (polynitroazolyl)trihydridoborate anions were isolated and fully characterized. Despite their relatively weak Lewis basicity, these azoles can form stable complexes with boranes. The polynitroazolylborate complex anions were less stable than the parent polynitroazolates.
      PubDate: 2017-08-22T02:15:54.331553-05:
      DOI: 10.1002/chem.201701690
       
  • Dynamic Cooperation of Hydrogen Binding and π Stacking in ssDNA
           Adsorption on Graphene Oxide
    • Authors: Zhen Xu; Xiaoling Lei, Yusong Tu, Zhi-Jie Tan, Bo Song, Haiping Fang
      Pages: 13100 - 13104
      Abstract: Functional nanoscale structures consisting of a DNA molecule coupled to graphene or graphene oxide (GO) have great potential for applications in biosensors, biomedicine, nanotechnology, and materials science. Extensive studies using the most sophisticated experimental techniques and theoretical methods have still not clarified the dynamic process of single-stranded DNA (ssDNA) adsorbed on GO surfaces. Based on a molecular dynamics simulation, this work shows that an ssDNA segment could be stably adsorbed on a GO surface through hydrogen bonding and π–π stacking interactions, with preferential binding to the oxidized rather than to the unoxidized region of the GO surface. The adsorption process shows a dynamic cooperation adsorption behavior; the ssDNA segment first captures the oxidized groups of the GO surface by hydrogen bonding interaction, and then the configuration relaxes to maximize the π–π stacking interactions between the aromatic rings of the nucleobases and those of the GO surface. We attributed this behavior to the faster forming hydrogen bonding interaction compared to π–π stacking; the π–π stacking interaction needs more relaxation time to regulate the configuration of the ssDNA segment to fit the aromatic rings on the GO surface.DNA on graphene: With dynamic cooperation of hydrogen bonding and π stacking, we find that single-stranded DNA (ssDNA) is stepwise adsorbed on graphene oxide (GO) using molecular dynamics simulations; the ssDNA segment first captures the oxidized groups of the GO surface by forming hydrogen bonds, then it forms π–π stacking interactions between the aromatic rings of the nucleobases and the GO surface. We attribute this behavior to the faster forming hydrogen bonding interaction compared to π–π stacking.
      PubDate: 2017-08-23T12:26:20.565308-05:
      DOI: 10.1002/chem.201701733
       
  • Photocaged Competitor Guests: A General Approach Toward Light-Activated
           Cargo Release From Cucurbiturils
    • Authors: Miguel A. Romero; Nuno Basílio, Artur J. Moro, Mara Domingues, José A. González-Delgado, Jesús F. Arteaga, Uwe Pischel
      Pages: 13105 - 13111
      Abstract: A general approach toward the light-induced guest release from cucurbit[7]uril by means of a photoactivatable competitor was devised. An o-nitrobenzyl-caged competitor is photolyzed to generate a competitive guest that can displace cargo from the host macrocycle solely based on considerations of chemical equilibrium. With this method the release of terpene guests from inclusion complexes with cucurbit[7]uril was demonstrated. The binding of the herein investigated terpenes, all being lead fragrant components in essential oils, has been characterized for the first time. They feature binding constants of up to 108 L mol−1 and a high differential binding selectivity (spanning four orders of magnitude for the binding constants for the particular set of terpenes). By fine-tuning the photoactivatable competitor guest, selective and also sequential release of the terpenes was achieved.The competition is on: The phototriggered generation of competitor guests from o-nitrobenzyl-caged precursors can be used to displace functional guests from the cucurbit[7]uril cavity. This general approach was harnessed for the light-triggered release of terpene fragrances from a supramolecule in a selective and also sequential manner.
      PubDate: 2017-08-21T07:11:00.282987-05:
      DOI: 10.1002/chem.201702185
       
  • Synthesis of Ultra-Small Palladium Nanoparticles Deposited on CdS Nanorods
           by Pulsed Laser Ablation in Liquid: Role of Metal Nanocrystal Size in the
           Photocatalytic Hydrogen Production
    • Authors: Hanbit Park; D. Amaranatha Reddy, Yujin Kim, Seunghee Lee, Rory Ma, Tae Kyu Kim
      Pages: 13112 - 13119
      Abstract: It is imperative to suppress the rate of recombination of photogenerated carriers to improve the semiconductor-catalyzed solar-driven production of hydrogen. To this end, photocatalysts comprising active sunlight-harvesting photo-absorbers and stable metal co-catalysts have attracted significant attention. However, the size, clean surface, and highly dispersed nature of the metal co-catalysts are crucial factors affecting catalyst performance and reaction rate. Nevertheless, most of the available metal nanocrystals have been synthesized by complex procedures using harmful organic templates and stabilizers, affording high-purity compounds with difficulty and high cost. To overcome these problems, in this study, the pulsed laser ablation in liquid approach was utilized to generate palladium and bimetallic palladium–platinum nanoparticles with an average size and distribution by adjusting the laser wavelength and fluence. A high rate of evolution of hydrogen of 130.33 mmol g−1 h−1 was obtained by using the optimized CdS-PdPt catalyst under simulated sunlight irradiation. This value is 51.31 times greater than that observed for bare CdS nanostructures. Furthermore, the amount of hydrogen evolved was significantly better than that obtained by using several other noble-metal co-catalysts deposited on CdS. This proposed strategy is thought to open new avenues for the design of advanced photocatalytic materials for efficient solar-driven production of hydrogen.Enhanced activity: This work has demonstrated a novel strategy (see figure) for the production of hydrogen by sunlight-driven photocatalysis using CdS-PdPt nanostructures, prepared by pulsed laser ablation in liquid, as photocatalysts. The rate of hydrogen production in the presence of the CdS-PdPt nanostructures is significantly enhanced compared with the CdS nanorods alone.
      PubDate: 2017-08-23T12:25:50.1063-05:00
      DOI: 10.1002/chem.201702304
       
  • Expanded Indacene–Tetrathiafulvalene Scaffolds: Structural Implications
           for Redox Properties and Association Behavior
    • Authors: Johannes Fabritius Petersen; Conerd K. Frederickson, Jonathan L. Marshall, Gabriel E. Rudebusch, Lev N. Zakharov, Ole Hammerich, Michael M. Haley, Mogens Brøndsted Nielsen
      Pages: 13120 - 13130
      Abstract: Redox-controlled dimerization of tetrathiafulvalene (TTF) derivatives is an important tool for achieving reversible assemblies. Herein, the synthesis and characterization of indacene–TTF hybrids, in which the central core is fused to naphtho or benzothieno units, are reported. The orientation of these units has a strong influence on the redox properties, with regard to the number of electrons involved in the first oxidation event and the ability of the oxidized forms to associate. The formation of mixed-valence and π-dimer complexes is turned off for those systems in which geometrical constraints provide nonplanar π-systems. Introduction of bulky substituents presents another way of preventing association, as revealed by studies of indenofluorene and diindenoanthracene scaffolds with (triisopropylsilyl)ethynyl groups. Horner–Wadsworth–Emmons reactions present a general synthetic protocol to access superextended TTFs, by using diones of polycyclic conjugated hydrocarbons as substrates.Tuning redox properties: The formation of mixed-valence (MV) complexes (cation⋅neutral) and π-dimers (cation⋅ cation) upon oxidation of indacene-extended tetrathiafulvalenes can be finely tuned by elongating the acene core in various ways (see figure). Cyclic voltammetry experiments show that the associations are prevented either by distorting the π-system from planarity or by introducing bulky substituent groups.
      PubDate: 2017-08-23T12:25:37.037965-05:
      DOI: 10.1002/chem.201702347
       
  • Dissociative Ionization and Thermal Decomposition of Cyclopentanone
    • Authors: Johan I. M. Pastoors; Andras Bodi, Patrick Hemberger, Jordy Bouwman
      Pages: 13131 - 13140
      Abstract: Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2H4, and C2H5, leading to daughter ions at m/z 56 and 55. Exploring the C5H8O.+ potential energy surface reveals hydrogen tunneling to play an important role in low-energy decarbonylation and probably also in the ethene-loss processes, yielding 1-butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl-radical loss and a second ethene-loss channel, respectively. A statistical Rice–Ramsperger–Kassel–Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed-shell pyrolysis products, namely 1,3-butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass-selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies.Unravelling the decomposition of cyclopentanone: With the growing use of renewable fuels, there is a strong need to understand their unimolecular dissociation mechanism. Here, we investigate the decomposition of neutral and cationic cyclopentanone initiated by flash pyrolysis and tuneable vacuum ultraviolet radiation, respectively. The decomposition products (see figure) are isomer-specifically identified by mass-selected TPES and detailed reaction mechanisms are discussed.
      PubDate: 2017-08-31T11:08:13.837742-05:
      DOI: 10.1002/chem.201702376
       
  • A Novel Bulky Heteroaromatic-Substituted Methanide Mimicking NacNac:
           
    • Authors: Ingo Koehne; Sebastian Bachmann, Thomas Niklas, Regine Herbst-Irmer, Dietmar Stalke
      Pages: 13141 - 13149
      Abstract: A novel bulky bis(4,6-tBu-benzoxazol-2-yl)methane ligand was synthesized in a straightforward three-step synthesis. The corresponding complexes [Li{(4,6-tBu-NCOC6H2)2CH}THF], [K{η5-(4,6-tBu-NCOC6H2)2CH}]∞, and [MgCl{(4,6-tBu-NCOC6H2)2CH}(THF)2] were obtained upon metalation with alkaline or alkaline-earth-metal reagents. Reduction of [MgCl{(4,6-tBu-NCOC6H2)2CH}(THF)2] with potassium metal or KC8 led to the formation of the homoleptic compound [Mg{(4,6-tBu-NCOC6H2)2CH}2]. All compounds were fully characterized. Their solid-state structures as well as their behavior in solution, which was analyzed with the help of advanced NMR spectroscopic techniques, are discussed in detail.NacNac mimic: Metalation of the methylene bridging moiety in a novel bulky bis(4,6-tBu-benzoxazol-2-yl)methanide ligand with s-block organometallic reagents gave the corresponding N,N-chelated metal salts. Structural features in the solid state (see figure) and in solution were compared to related complexes derived from the ubiquitous NacNac ligand.
      PubDate: 2017-08-22T11:57:53.84493-05:0
      DOI: 10.1002/chem.201702378
       
  • Self-Assembled CoS Nanoflowers Wrapped in Reduced Graphene Oxides as the
           High-Performance Anode Materials for Sodium-Ion Batteries
    • Authors: Yingying Zhao; Qiang Pang, Yuan Meng, Yu Gao, Chunzhong Wang, Bingbing Liu, Yingjin Wei, Fei Du, Gang Chen
      Pages: 13150 - 13157
      Abstract: It remains a big challenge to identify high-performance anode materials to promote practical applications of sodium-ion batteries. Herein, the facile synthesis of CoS nanoflowers wrapped in reduced graphene oxides (RGO) is reported, and their sodium storage properties are systematically studied in comparison with bare CoS. The CoS@RGO nanoflowers deliver a high reversible capacity of 620 mAh g−1 at a current density of 100 mA g−1 and superior rate capability with discharge capacity of 329 mAh g−1 at 4 A g−1, much higher than those of the bare CoS. Evidenced by electrochemical impedance spectra and ex-situ SEM images, the improvement in the sodium storage performance is found to be due to the introduction of RGO which serves as a conducting matrix, to not only increase the kinetic properties of CoS, but also buffer the volume change and maintain the integrity of working electrodes during (de)sodiation processes. More importantly, the pseudocapacitive contribution of more than 89 % is only observed in the CoS@RGO nanocomposites, owing to the enhanced specific area and surface redox behavior.Flower power: Cobalt sulfide nanoflowers, wrapped in reduced graphene oxides have been synthesized as potential anode materials for sodium ion batteries. The graphene oxide not only aids the conductivity, but also buffers the volume expansion–contraction, leading to improved cycle performance.
      PubDate: 2017-08-30T11:11:22.421683-05:
      DOI: 10.1002/chem.201702399
       
  • Synthesis and Applications of Cyclohexenyl Halides Obtained by a Cationic
           Carbocyclisation Reaction
    • Authors: Pedro Alonso; Pilar Pardo, Raquel Fontaneda, Francisco J. Fañanás, Félix Rodríguez
      Pages: 13158 - 13163
      Abstract: The synthesis of cyclic alkenyl halides (mainly fluorides, chlorides and bromides) from alkynol or enyne derivatives by an acid-mediated cationic cyclisation reaction is disclosed. This high-yielding, scalable and technically simple method complements and challenges conventional methodologies. This study includes the development of biomimetic cationic cyclisation reactions of polyenyne derivatives to give interesting halogen-containing polycyclic compounds. The application of this reaction in the key step of the synthesis of two terpenes, namely austrodoral and pallescensin A, and the potent odorant 9-epi-Ambrox demonstrates the potential of the reaction for natural product synthesis.It's all under regio-control! Cyclic alkenyl fluorides, chlorides, bromides and iodides are readily obtained by a cationic cyclisation process. Related biomimetic polycyclisation reactions allow the synthesis of interesting polycyclic core skeletons that may be used in the context of natural product synthesis (see scheme).
      PubDate: 2017-08-23T12:25:19.794159-05:
      DOI: 10.1002/chem.201702490
       
  • Pyrene Molecular Orbital Shuffle—Controlling Excited State and Redox
           Properties by Changing the Nature of the Frontier Orbitals
    • Authors: Julia Merz; Julian Fink, Alexandra Friedrich, Ivo Krummenacher, Hamad H. Al Mamari, Sabine Lorenzen, Martin Haehnel, Antonius Eichhorn, Michael Moos, Marco Holzapfel, Holger Braunschweig, Christoph Lambert, Andreas Steffen, Lei Ji, Todd B. Marder
      Pages: 13164 - 13180
      Abstract: We show that by judicious choice of substituents at the 2- and 7-positions of pyrene, the frontier orbital order of pyrene can be modified, giving enhanced control over the nature and properties of the photoexcited states and the redox potentials. Specifically, we introduced a julolidine-like moiety and Bmes2 (mes=2,4,6-Me3C6H2) as very strong donor (D) and acceptor (A), respectively, giving 2,7-D-π-D- and unsymmetric 2,7-D-π-A-pyrene derivatives, in which the donor destabilizes the HOMO−1 and the acceptor stabilizes the LUMO+1 of the pyrene core. Consequently, for 2,7-substituted pyrene derivatives, unusual properties are obtained. For example, very large bathochromic shifts were observed for all of our compounds, and unprecedented green light emission occurs for the D/D system. In addition, very high radiative rate constants in solution and in the solid state were recorded for the D-π-D- and D-π-A-substituted compounds. All compounds show reversible one-electron oxidations, and Jul2Pyr exhibits a second oxidation, with the largest potential splitting (ΔE=440 mV) thus far reported for 2,7-substituted pyrenes. Spectroelectrochemical measurements confirm an unexpectedly strong coupling between the 2,7-substituents in our pyrene derivatives.Doing the orbital shuffle: 2,7-D-π-D- and unsymmetric 2,7-D-π-A-pyrene derivatives, based on a julolidine-like moiety as very strong donor (D) and Bmes2 (mes=2,4,6-Me3C6H2) as acceptor (A), have been prepared and show unusual photophysics, such as large bathochromic shifts and high radiative rate constants, and unprecedented green light emission for the D/D system. Spectroelectrochemical measurements indicate strong coupling between the 2- and 7-substituents.
      PubDate: 2017-08-21T02:30:54.919419-05:
      DOI: 10.1002/chem.201702594
       
  • Ferrichrome Has Found Its Match: Biomimetic Analogues with Diversified
           Activity Map Discrete Microbial Targets
    • Authors: Jenny Besserglick; Evgenia Olshvang, Agnieszka Szebesczyk, Joseph Englander, Dana Levinson, Yitzhak Hadar, Elzbieta Gumienna-Kontecka, Abraham Shanzer
      Pages: 13181 - 13191
      Abstract: Siderophores provide an established platform for studying molecular recognition principles in biological systems. Herein, the preparation of ferrichrome (FC) biomimetic analogues varying in length and polarity of the amino acid chain separating between the tripodal scaffold and the pendent FeIII chelating hydroxamic acid groups was reported. Spectroscopic and potentiometric titrations determined their iron affinity to be within the range of efficient chelators. Microbial growth promotion and iron uptake studies were conducted on E. coli, P. putida and U. maydis. A wide range of siderophore activity was observed in the current series: from a rare case of a species-specific growth promotor in P. putida to an analogue matching FC in cross-phylum activity and uptake pathway. A fluorescent conjugate of the broad-range analogue visualized siderophore destination in bacteria (periplasmic space) vs. fungi (cytosol) mapping new therapeutic targets. Quantum dots (QDs) decorated with the most potent FC analogue provided a tool for immobilization of FC-recognizing bacteria. Bacterial clusters formed around QDs may provide a platform for their selection and concentration.Ferrying Ferric: A “true” analogue matching ferrichrome (FC) in cross-phylum activity, uptake pathway, and iron affinity is described. This fluorescently labeled analogue sheds light on the fate of siderophores following iron delivery and provides a tool for identifying microbial targets. Quantum dots (QD) decorated with this analogue trigger cluster formation by FC-recognizing bacteria, suggesting a method for microbial concentration and separation (see scheme).
      PubDate: 2017-08-31T11:07:39.158126-05:
      DOI: 10.1002/chem.201702647
       
  • Prediction of EPR Spectra of Lyotropic Liquid Crystals using a Combination
           of Molecular Dynamics Simulations and the Model-Free Approach
    • Authors: Christopher Prior; Vasily S. Oganesyan
      Pages: 13192 - 13204
      Abstract: We report the first application of fully atomistic molecular dynamics (MD) simulations to the prediction of the motional electron paramagnetic resonance (EPR) spectra of lyotropic liquid crystals in different aggregation states doped with a paramagnetic spin probe. The purpose of this study is twofold. First, given that EPR spectra are highly sensitive to the motions and order of the spin probes doped within lyotropic aggregates, simulation of EPR line shapes from the results of MD modelling provides an ultimate test bed for the force fields currently employed to model such systems. Second, the EPR line shapes are simulated using the motional parameters extracted from MD trajectories using the Model-Free (MF) approach. Thus a combined MD-EPR methodology allowed us to test directly the validity of the application of the MF approach to systems with multi-component molecular motions. All-atom MD simulations using the General AMBER Force Field (GAFF) have been performed on sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium chloride (DTAC) liquid crystals. The resulting MD trajectories were used to predict and interpret the EPR spectra of pre-micellar, micellar, rod and lamellar aggregates. The predicted EPR spectra demonstrate good agreement with most of experimental line shapes thus confirming the validity of both the force fields employed and the MF approach for the studied systems. At the same time simulation results confirm that GAFF tends to overestimate the packing and the order of the carbonyl chains of the surfactant molecules.How it fits together: Characterisation of molecular organisation and motions in different aggregate states of lyotropic liquid crystals by a combination of all-atom MD simulations and EPR spectroscopy.
      PubDate: 2017-08-23T12:25:10.569816-05:
      DOI: 10.1002/chem.201702682
       
  • Efficient and Selective N-Methylation of Nitroarenes under Mild Reaction
           Conditions
    • Authors: Elena Pedrajas; Iván Sorribes, Eva Guillamón, Kathrin Junge, Matthias Beller, Rosa Llusar
      Pages: 13205 - 13212
      Abstract: Herein, we report a straightforward protocol for the preparation of N,N-dimethylated amines from readily available nitro starting materials using formic acid as a renewable C1 source and silanes as reducing agents. This tandem process is efficiently accomplished in the presence of a cubane-type Mo3PtS4 catalyst. For the preparation of the novel [Mo3Pt(PPh3)S4Cl3(dmen)3]+ (3+) (dmen: N,N′-dimethylethylenediamine) compound we have followed a [3+1] building block strategy starting from the trinuclear [Mo3S4Cl3(dmen)3]+ (1+) and Pt(PPh3)4 (2) complexes. The heterobimetallic 3+ cation preserves the main structural features of its 1+ cluster precursor. Interestingly, this catalytic protocol operates at room temperature with high chemoselectivity when the 3+ catalyst co-exists with its trinuclear 1+ precursor. N-heterocyclic arenes, double bonds, ketones, cyanides and ester functional groups are well retained after N-methylation of the corresponding functionalized nitroarenes. In addition, benzylic-type as well as aliphatic nitro compounds can also be methylated following this protocol.Direct and mild N-methylation: Nitroarenes have been smoothly methylated using formic acid as a C1 source and phenylsilane as reducing agent. In the presence of cubane-type complexes (see scheme) tertiary amines were obtained under mild conditions with good functional group tolerance.
      PubDate: 2017-09-04T07:50:38.119626-05:
      DOI: 10.1002/chem.201702783
       
  • Protein–Glycan Quinary Interactions in Crowding Environment Unveiled
           by NMR Spectroscopy
    • Authors: Ana Diniz; Jorge S. Dias, Jesús Jiménez-Barbero, Filipa Marcelo, Eurico J. Cabrita
      Pages: 13213 - 13220
      Abstract: Protein–glycan interactions as modulators for quinary structures in crowding environments were explored. The interaction between human galectin 3 (Gal-3) and distinct macromolecular crowders, such as bovine and human serum albumin (BSA and HSA), Ficoll 70 and PEG3350, was scrutinized. The molecular recognition event of the specific ligand, lactose, by Gal-3 in crowding conditions was evaluated. Gal-3 interactions were monitored by NMR analysing chemical shift perturbation (CSP) and line broadening of 1H15N-HSQC signals. The intensity of the Gal-3 1H15N-HSQC signals decreased in the presence of all crowders, due to the increase in the solution viscosity and to the formation of large protein complexes. When glycosylated containing samples of BSA and HSA were used, signal broadening was more severe than that observed in the presence of the more viscous solutions of PEG3350 and Ficoll 70. However, for the samples containing glycoproteins, the signal intensity of 1H15N-HSQC recovered upon addition of lactose. We show that serum proteins interact with Gal-3, through their α2,3-linked sialylgalactose moieties exposed at their surfaces, competing with lactose for the same binding site. The quinary interaction between Gal-3 and serum glycoproteins, could help to co-localize Gal-3 at the cell surface, and may play a role in adhesion and signalling functions of this protein.Glycosylation as key player for quinary structure in crowding environments: Glycan-mediated human galectin 3 (Gal-3) and serum protein interactions strongly affect the dynamics of Gal-3, as proven by the NMR experiments in crowding conditions. Gal-3 binds through α2,3-sialylgalactose chains present in serum glycoproteins competing with lactose binding site. Gal-3/serum protein quinary structure could help to co-localize Gal-3 at the cell surface and may have implications in adhesion and signalling functions of this protein.
      PubDate: 2017-08-17T06:55:58.753948-05:
      DOI: 10.1002/chem.201702800
       
  • Long Straczekite δ-Ca0.24V2O5⋅H2O Nanorods and Derived β-Ca0.24V2O5
           Nanorods as Novel Host Materials for Lithium Storage with Excellent
           Cycling Stability
    • Authors: Yining Ma; Huaijuan Zhou, Shuming Zhang, Sui Gu, Xun Cao, Shanhu Bao, Heliang Yao, Shidong Ji, Ping Jin
      Pages: 13221 - 13232
      Abstract: Nanorods of δ-Ca0.24V2O5⋅H2O, a straczekite group mineral with an open double-layered structure, have been successfully fabricated by a facile hydrothermal method and can be transformed into the tunnel β geometry (β-Ca0.24V2O5) through a vacuum annealing treatment. The generated β-Ca0.24V2O5 still preserves the nanorod construction of δ-Ca0.24V2O5⋅H2O without substantial sintering and degradation of the nanostructure. As cathode materials, both calcium vanadium bronzes exhibit high reversible capacity, good rate capability, as well as superior cyclability. Compared with the hydrated vanadium bronze, the β-Ca0.24V2O5 nanorods show better cycling performance (81.68 and 97.93 % capacity retention after 200 cycles at 100 and 400 mA g−1, respectively) and excellent long-term cyclic stability with an average decay of 0.035 % per cycle over 500 cycles at 500 mA g−1. Note that the double-layered δ-Ca0.24V2O5⋅H2O electrode irreversibly converts into β-CaxV2O5 phase during the initial Li+ insertion/extraction process, while in contrast, the β-phase calcium vanadium bronze electrode shows excellent structural stability during cycling. The excellent electrochemical performance demonstrates that the two calcium vanadium bronzes are potential cathode candidates for rechargeable lithium-ion batteries.Bronze medal: Straczekite δ-Ca0.24V2O5⋅H2O could be converted into the tunnel β geometry through either a vacuum annealing treatment or the lithiation/delithiation process. Both of the calcium vanadium bronzes exhibit excellent cycling stability as cathode materials for lithium ion batteries.
      PubDate: 2017-08-30T11:11:00.9001-05:00
      DOI: 10.1002/chem.201702814
       
  • Is Single Layer MoS2 Stable in the Air'
    • Authors: Jana Martincová; Michal Otyepka, Petr Lazar
      Pages: 13233 - 13239
      Abstract: Molybdenum disulfide (MoS2) is extensively studied because of its potential applications in catalysis, electronic and optoelectronic devices, and composite nanostructures. However, a recent experimental study indicated that, contrary to current beliefs, MoS2 monolayers lack long-term stability in air. Here, a study is presented on the oxidation of MoS2 monolayers based on density functional theory (DFT) calculations. The results suggest that single-layer MoS2 samples with exposed edge sites are indeed unstable to oxidation, which occurs because of the low energetic barrier to dissociation of oxygen molecules at the Mo-edges of MoS2. After an oxygen molecule dissociates, oxygen atoms replace sulfur atoms, and further oxidation causes the formation of a one-dimensional chain-like structure resembling that of bulk MoO3. This MoO3 structure facilitates the spread of oxidation onto the surface, and the stress associated with the misfit between the MoS2 and MoO3 lattices may cause the experimentally observed cracking of MoS2 flakes.Density functional calculations were used to study the stability of MoS2 to oxidation. The results suggest that single-layer MoS2 samples with exposed edge sites are indeed unstable to oxidation, which occurs because of the low energetic barrier to dissociation of oxygen molecules at the Mo-edges of MoS2
      PubDate: 2017-08-30T11:22:15.33205-05:0
      DOI: 10.1002/chem.201702860
       
  • Synthesis and Characterization of Bioinspired [Mo2Fe2]–Hydride Cluster
           Complexes and Their Application in the Catalytic Silylation of N2
    • Authors: Yasuhiro Ohki; Yuna Araki, Mizuki Tada, Yoichi Sakai
      Pages: 13240 - 13248
      Abstract: The hydride-supported [Mo2Fe2] cluster complex {Cp*Mo(PMe3)}2{FeN(SiMe3)2}2(H)8 (2 a; Cp*=η5-C5Me5) and its [Mo2Mn2] congener 2 b were synthesized from the reactions of Cp*Mo(PMe3)(H)5 (1) with M{N(SiMe3)2}2 (M=Fe, Mn). The amide-to-thiolate ligand-exchange reactions of complex 2 a with bulky thiol reagents (HSR; R=2,4,6-iPr3C6H2 (Tip), 2,6-(SiMe3)2C6H3 (Btp)) furnished the corresponding hydride-supported [Mo2Fe2](SR)2 cluster complexes. The [Mo2Fe2] clusters served as catalyst precursors for the reductive silylation of N2 and yielded ≈65–69 equivalents of N(SiMe3)3 relative to the [Mo2Fe2] clusters. Treatment of complexes 2 a and b with an excess of CNtBu resulted in the formation of dinuclear Mo−Fe and Mo−Mn complexes, which indicated that the [Mo2M2] cores (M=Fe, Mn) split into two dinuclear species upon accommodation of substrates.Reduction of N2: Taking inspiration from the biological process, hydride-supported [Mo2Fe2] cluster complexes are synthesized, characterized, and successfully used as catalyst precursors for the reductive silylation of N2 (see scheme).
      PubDate: 2017-08-23T12:24:46.080627-05:
      DOI: 10.1002/chem.201702925
       
  • Competing Pathways in O-Arylations with Diaryliodonium Salts: Mechanistic
           Insights
    • Authors: Elin Stridfeldt; Erik Lindstedt, Marcus Reitti, Jan Blid, Per-Ola Norrby, Berit Olofsson
      Pages: 13249 - 13258
      Abstract: A mechanistic study of arylations of aliphatic alcohols and hydroxide with diaryliodonium salts, to give alkyl aryl ethers and diaryl ethers, has been performed using experimental techniques and DFT calculations. Aryne intermediates have been trapped, and additives to avoid by-product formation originating from arynes have been found. An alcohol oxidation pathway was observed in parallel to arylation; this is suggested to proceed by an intramolecular mechanism. Product formation pathways via ligand coupling and arynes have been compared, and 4-coordinated transition states were found to be favored in reactions with alcohols. Furthermore, a novel, direct nucleophilic substitution pathway has been identified in reactions with electron-deficient diaryliodonium salts.Put a ring on it! The arylation of aliphatic alcohols and hydroxide with diaryliodonium salts, to give alkyl aryl ethers and diaryl ethers, has been studied using experimental techniques and DFT calculations. Aryne formation and alcohol oxidation pathways were observed in parallel to arylation, and additives to avoid by-product formation originating from arynes have been found. A novel, direct nucleophilic substitution pathway has been identified in reactions with electron-deficient diaryliodonium salts.
      PubDate: 2017-09-05T06:36:22.851276-05:
      DOI: 10.1002/chem.201703057
       
 
 
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