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  Subjects -> CHEMISTRY (Total: 849 journals)
    - ANALYTICAL CHEMISTRY (50 journals)
    - CHEMISTRY (598 journals)
    - CRYSTALLOGRAPHY (22 journals)
    - ELECTROCHEMISTRY (25 journals)
    - INORGANIC CHEMISTRY (42 journals)
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    - PHYSICAL CHEMISTRY (67 journals)

CHEMISTRY (598 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: 32)
ACS Chemical Neuroscience     Full-text available via subscription   (Followers: 17)
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: 227)
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: 53)
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 Fluorine Science     Full-text available via subscription   (Followers: 8)
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: 14)
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: 67)
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: 13)
American Mineralogist     Hybrid Journal   (Followers: 13)
Analyst     Full-text available via subscription   (Followers: 38)
Angewandte Chemie     Hybrid Journal   (Followers: 158)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 208)
Annales UMCS, Chemia     Open Access   (Followers: 1)
Annals of Clinical Chemistry and Laboratory Medicine     Open Access   (Followers: 1)
Annual Reports in Computational Chemistry     Full-text available via subscription   (Followers: 3)
Annual Reports Section A (Inorganic Chemistry)     Full-text available via subscription   (Followers: 3)
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: 14)
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: 3)
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: 283)
Biochemistry Insights     Open Access   (Followers: 5)
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: 108)
Bioorganic & Medicinal Chemistry Letters     Hybrid Journal   (Followers: 93)
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: 2)
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: 67)
Catalysis for Sustainable Energy     Open Access   (Followers: 6)
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: 7)
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: 12)
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: 170)
Chemical Science     Open Access   (Followers: 21)
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: 55)
Chemie-Ingenieur-Technik (Cit)     Hybrid Journal   (Followers: 25)
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: 144)
Chemistry - An Asian Journal     Hybrid Journal   (Followers: 15)
Chemistry and Materials Research     Open Access   (Followers: 18)
Chemistry Central Journal     Open Access   (Followers: 4)
Chemistry Education Research and Practice     Free   (Followers: 5)
Chemistry in Education     Open Access   (Followers: 9)
Chemistry International     Hybrid Journal   (Followers: 2)
Chemistry Letters     Full-text available via subscription   (Followers: 45)
Chemistry of Materials     Full-text available via subscription   (Followers: 226)
Chemistry of Natural Compounds     Hybrid Journal   (Followers: 9)
Chemistry World     Full-text available via subscription   (Followers: 22)
Chemistry-Didactics-Ecology-Metrology     Open Access  
ChemistryOpen     Open Access   (Followers: 2)
Chemkon - Chemie Konkret, Forum Fuer Unterricht Und Didaktik     Hybrid Journal  
Chemoecology     Hybrid Journal   (Followers: 2)
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)
Chromatography Research International     Open Access   (Followers: 7)
Clay Minerals     Full-text available via subscription   (Followers: 9)
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: 8)
Combinatorial Chemistry & High Throughput Screening     Hybrid Journal   (Followers: 3)
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  
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: 11)
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: 56)
Dalton Transactions     Full-text available via subscription   (Followers: 20)
Detection     Open Access   (Followers: 2)
Developments in Geochemistry     Full-text available via subscription   (Followers: 2)
Diamond and Related Materials     Hybrid Journal   (Followers: 12)
Dislocations in Solids     Full-text available via subscription  
Doklady Chemistry     Hybrid Journal  
Drying Technology: An International Journal     Hybrid Journal   (Followers: 4)
Eclética Química     Open Access   (Followers: 1)
Ecological Chemistry and Engineering S     Open Access   (Followers: 4)
Ecotoxicology and Environmental Contamination     Open Access  
Educación Química     Open Access   (Followers: 1)
Education for Chemical Engineers     Hybrid Journal   (Followers: 5)
EJNMMI Radiopharmacy and Chemistry     Open Access  
Elements     Full-text available via subscription   (Followers: 2)
Environmental Chemistry     Hybrid Journal   (Followers: 9)
Environmental Chemistry Letters     Hybrid Journal   (Followers: 4)
Environmental Science & Technology Letters     Full-text available via subscription   (Followers: 5)

        1 2 3 | Last

Journal Cover Chemistry - A European Journal
  [SJR: 2.323]   [H-I: 188]   [144 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  [1576 journals]
  • Selective Conversion of P=O-Bridged Rhodamines into P=O-Rhodols:
           Solvatochromic Near-Infrared Fluorophores
    • Authors: Marek Grzybowski; Masayasu Taki, Shigehiro Yamaguchi
      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) fluorophores. 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, i.e., 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, while 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.
      PubDate: 2017-07-27T03:26:22.62136-05:0
      DOI: 10.1002/chem.201703456
       
  • Bicyclic Peptides as Next-Generation Therapeutics
    • Authors: Curran A. Rhodes; Dehua Pei
      Abstract: Bicyclic peptides have greater conformational rigidity and metabolic stability than linear and monocyclic peptides and are capable of binding to challenging drug targets with antibody-like affinity and specificity. Powerful combinatorial library technologies have recently been developed to rapidly synthesize and screen large bicyclic peptide libraries for ligands against enzymes, receptors, and protein–protein interaction targets. Bicyclic peptides have been developed as potential therapeutics against a wide range of diseases, drug targeting agents, imaging/diagnostic probes, and research tools. In this Minireview, we provide a summary of the recent progresses on the synthesis and applications of bicyclic peptides.Bicyclic peptides, such as depicted, can now be rapidly synthesized and screened to identify potent, specific ligands against enzymes, receptors, and protein–protein interactions, thus providing a new class of drug modalities and powerful research tools.
      PubDate: 2017-07-27T03:00:40.228227-05:
      DOI: 10.1002/chem.201702117
       
  • Structural Phase Transitions and Dielectric Switching in a Series of
           Organic-Inorganic Hybrid Perovskites ABX3 (X=ClO4− or BF4−)
    • Authors: Yu-Ling Sun; Xiang-Bin Han, Wen Zhang
      Abstract: A series of organic-inorganic hybrid perovskites ABX3 (A=diprotonated 1,4-diazabicyclo[2.2.2]octane or piperazine; B=Na+ or K+; X=ClO4− or BF4−) has been synthesized. They feature a cubic cage-like host-guest structures of which A is the cationic guest residing in the anionic cage B8X12, B is the vertex of the cage with variable coordination numbers between six and twelve, and X is the bridging ligand with mono- and/or bidentate coordination modes. The extended Goldschmidt tolerance factor t is used to describe the phase stability of the compounds. Differential scanning calorimetry, variable-temperature structural analyses, and dielectric measurements reveal that order-disorder transitions of the A guest and/or X bridging ligand are supposed to be responsible for structural phase transitions and dielectric switching in the compounds.Transform: A series of organic-inorganic hybrid perovskites ABX3 (A=diprotonated 1,4-diazabicyclo[2.2.2]octane or piperazine; B=Na+ or K+; X=ClO4- or BF4-) has been synthesized, showing structural phase transitions and dielectric switching that are caused by order–disorder transitions of the A guest and/or X bridging ligand.
      PubDate: 2017-07-27T02:56:12.526684-05:
      DOI: 10.1002/chem.201702228
       
  • Vertical-Aligned Li2S–Graphene Encapsulated within a Carbon Shell as a
           Free-Standing Cathode for Lithium–Sulfur Batteries
    • Authors: Donghuang Wang; Xinhui Xia, Yadong Wang, Dong Xie, Yu Zhong, Jianbo Wu, Xiuli Wang, Jiangping Tu
      Abstract: Construction of a novel matrix with both high conductivity and an excellent confinement effect for polysulfides is of great importance for developing high-performance lithium–sulfur (Li-S) batteries. In this work, we have developed a double-modification strategy to integrate lithium sulfide (Li2S) into a conductive composite network consisting of vertical graphene (VG) arrays and an amorphous carbon shell, forming an integrated cathode (VG/Li2S-C). Facile liquid-solution/evaporation methods in combination with chemical vapor deposition were successfully adopted for preparation of the above cathode. Due to the enhanced electrical conductivity and noticeable blocking effect for the shuttle of polysulfides, the binder-free flexible VG/Li2S-C cathode exhibits high rate performance and reinforced cycles (656.2 mAh g−1 after 100 cycles). The pronounced electrochemical performance is ascribed to the unique architecture with a coherent conductive network of VG and the carbon shell, which not only provides a conductive network for fast reaction kinetics, but also forms a durable protective shield to suppress the shuttle of polysulfides. Our research further demonstrates the synergistic effectiveness by means of inner and outer carbon matrixes for electrochemical enhancement of Li-S batteries.Support your local batteries! A facile strategy is demonstrated for fabricating free-standing vertical graphene (VG) supported Li2S encapsulated within carbon shell (VG/Li2S-C) cathode, which exhibits enhanced electrochemical performance with high capacity and noticeable cycles due to the unique architecture coherent conductive network and good blocking layer for polysulfides (see figure).
      PubDate: 2017-07-27T02:56:03.017561-05:
      DOI: 10.1002/chem.201702779
       
  • Dinaphthotetrathiafulvalene Bisimides: A New Member of the Family of
           π-Extended TTF Stable p-Type Semiconductors
    • Authors: Masataka Yamashita; Koki Kawano, Akinobu Matsumoto, Naoki Aratani, Hironobu Hayashi, Mitsuharu Suzuki, Lei Zhang, Alejandro L. Briseno, Hiroko Yamada
      Abstract: Air-stable organic semiconductors based on tetrathiafuluvalene (TTF) were developed by synthesising a series of dinaphthotetrathiafulvalene bisimides (DNTTF-Im) using electron-donating TTF, π-extended naphthalene, and electron-withdrawing imide. Electron-spin-resonance spectroscopy and X-ray single-crystal structure analysis of aryl-substituted DNTTF-Im radical cations confirmed that localisation of the spin resides on the electron-donating TTF moiety. The organic field-effect transistor properties derived from the use of highly crystalline n-butyl (C4) and n-hexyl(C6)-substituted DNTTF-Im were assessed. The hole carrier mobility of C6-DNTTF-Im was improved from 3.7×10−3 cm2 V−1 s−1 to 0.30 cm2 V−1 s−1 in ambient conditions. This is attributed to the raise of the substrate temperature from 25 °C to 200 °C during sublimation. The XRD and microscopy analysis suggested that increasing the substrate temperature accelerates the end-on packing resulting in larger grains suitable for hole charge transport parallel to the substrate.Stable p-type semiconductors: Hole mobility as high as 0.3 cm2 V−1 s−1 in ambient condition was realized by a film of dinaphthotetrathiafulvalene bisimide by raise the substrate temperature to 200 °C during sublimation.
      PubDate: 2017-07-27T02:55:45.855604-05:
      DOI: 10.1002/chem.201702657
       
  • Soluble Platinum Nanoparticles Ligated by Long-Chain N-Heterocyclic
           Carbenes as Catalysts
    • Authors: Luis M. Martínez-Prieto; Lena Rakers, Angela M. López-Vinasco, Israel Cano, Yannick Coppel, Karine Philippot, Frank Glorius, Bruno Chaudret, Piet W. N. M. van Leeuwen
      Abstract: NHC-ligated Pt nanoparticles were studied with regards to steric bulk of the ligands and their influence on NP size and catalytic properties. Bulky aryl groups at the N-atoms gave small NPs of roughly 65 atoms, whereas small methyl groups gave larger NPs of around 260 atoms both with high ligand coverage, 12 and 70 ligands, respectively. Undecyl chains on the NHC ligands make the nanoparticles highly soluble and allowed for their use as catalysts in solution. Hydroboration of alkynes was observed for the first time with soluble NPs, but surprisingly only the bulky-ligand-containing Pt NPs were active. More information can be found in the Full Paper by F. Glorius, B. Chaudret and P. W. N. M. van Leeuwen et al. (
      DOI : 10.1002/chem.201702288).
      PubDate: 2017-07-27T02:52:06.3488-05:00
       
  • Tris(2,4,6-trifluorophenyl)borane: An Efficient Hydroboration Catalyst
    • Authors: James R. Lawson; Lewis C. Wilkins, Rebecca L. Melen
      Abstract: The metal-free catalyst tris(2,4,6-trifluorophenyl)borane has demonstrated its extensive applications in the 1,2-hydroboration of numerous unsaturated reagents, namely alkynes, aldehydes and imines, consisting of a wide array of electron-withdrawing and donating functionalities. A range of over 50 borylated products are reported, with many reactions proceeding with low catalyst loading under ambient conditions. These pinacol boronate esters, in the case of aldehydes and imines, can be readily hydrolyzed to leave the respective alcohol and amine, whereas alkynyl substrates result in vinyl boranes. This is of great synthetic use to the organic chemist.What a boron discovery: The use of tris(2,4,6-trifluorophenyl)borane in the metal-free 1,2-syn-hydroboration of various unsaturated moieties such as alkynes, aldehydes and imines generates a plethora of over 50 borylated products with many reactions proceeding with low catalyst loading under ambient conditions.
      PubDate: 2017-07-27T02:51:42.197344-05:
      DOI: 10.1002/chem.201703109
       
  • pH-Responsive Fluorescence Enhancement in Graphene Oxide–Naphthalimide
           Nanoconjugates: A Fluorescence Turn-On Sensor for Acetylcholine
    • Authors: Sreejith Mangalath; Silja Abraham, Joshy Joseph
      Abstract: A pH-sensitive, fluorescence “turn-on” sensor based on a graphene oxide–naphthalimide (GO–NI) nanoconjugate for the detection of acetylcholine (ACh) by monitoring the enzymatic activity of acetylcholinesterase (AChE) in aqueous solution is reported. These nanoconjugates were synthesized by covalently anchoring picolyl-substituted NI derivatives on the GO/reduced GO surface through a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide/N-hydroxysuccinimide coupling strategy, and the morphological and photophysical properties were studied in detail. Synergistic effects of π–π interactions between GO and the NI chromophore, and efficient photoinduced electron- and energy-transfer processes, were responsible for the strong quenching of fluorescence of these nanoconjugates, which were perturbed under acidic pH conditions, leading to significant enhancement of fluorescence emission. This nanoconjugate was successfully employed for the efficient sensing of pH changes caused by the enzymatic activity of AChE, thereby demonstrating its utility as a fluorescence turn-on sensor for ACh in the neurophysiological range.Activating surfaces: A pH-sensitive, fluorescence “turn-on” sensor based on a graphene oxide–naphthalimide nanoconjugate for the detection of acetylcholine (ACh) by monitoring the enzymatic activity of acetylcholinesterase (AChE) in aqueous solution is reported (see figure). Synergistic effects of π–π interactions and efficient photoinduced electron- and energy-transfer processes are responsible for the strong quenching of fluorescence of these nanoconjugates.
      PubDate: 2017-07-27T02:01:27.043651-05:
      DOI: 10.1002/chem.201702198
       
  • Competitive Energy and Electron Transfer in β-Functionalized Free-Base
           Porphyrin–Zinc Porphyrin Dimer Axially Coordinated to C60: Synthesis,
           Supramolecular Formation and Excited-State Processes
    • Authors: Yi Hu; Michael B. Thomas, R. G. Waruna Jinadasa, Hong Wang, Francis D'Souza
      Abstract: Simultaneous occurrence of energy and electron transfer events involving different acceptor sites in a newly assembled supramolecular triad comprised of covalently linked free-base porphyrin–zinc porphyrin dyad, H2P−ZnP axially coordinated to electron acceptor fullerene, has been successfully demonstrated. The dyad was connected through the β-pyrrole positions of the porphyrin macrocycle instead of the traditionally used meso-positions for better electronic communication. Interestingly, the β-pyrrole functionalization modulated the optical properties to such an extent that it was possible to almost exclusively excite the zinc porphyrin entity in the supramolecular triad. The measured binding constant for the complex with 1:1 molecular stoichiometry was in the order of 104 m−1 revealing moderately stable complex formation. An energy level diagram constructed using optical, electrochemical and computational results suggested that both the anticipated energy and electron events are thermodynamically feasible in the triad. Consequently, it was possible to demonstrate occurrence of excited state energy transfer to the covalently linked H2P, and electron transfer to the coordinated ImC60 from studies involving steady-state and time-resolved emission, and femto- and nanosecond transient absorption studies. The estimated energy transfer was around 67 % in the dyad with a rate constant of 1.1×109 s−1. In the supramolecular triad, the charge separated state was rather long-lived although it was difficult to arrive the exact lifetime of charge separated state from nanosecond transient spectral studies due to overlap of strong triplet excited signals of porphyrin in the monitoring wavelength window. Nevertheless, simultaneous occurrence of energy and electron transfer in the appropriately positioned energy and electron acceptor entities in a supramolecular triad was possible to demonstrate in the present study, a step forward to unraveling the complex photochemical events occurring in natural photosynthesis and its implications in building light energy harvesting devices.Formation of a supramolecular triad featuring β-pyrrole connected free-base porphyrin–zinc porphyrin self-assembled to C60, and occurrence of competitive energy and electron transfer processes from transient absorption studies is demonstrated.
      PubDate: 2017-07-27T02:00:36.854591-05:
      DOI: 10.1002/chem.201702178
       
  • Selective Catalytic Performances of Noble Metal Nanoparticle@MOF
           Composites: The Concomitant Effect of Aperture Size and Structural
           Flexibility of MOF Matrices
    • Authors: Luning Chen; Wenwen Zhan, Huihuang Fang, Zhenmin Cao, Chaofan Yuan, Zhaoxiong Xie, Qin Kuang, Lansun Zheng
      Abstract: Noble metal nanoparticles embedded in metal–organic frameworks (MOFs) are composite catalysts with enhanced or novel properties compared to the pristine counterparts. In recent years, to determine the role of MOFs during catalytic process, most studies have focussed on the confinement effect of MOFs, but ignored the structural flexibility of MOFs. In this study, we use two composite catalysts, Pt@ZIF-8 [Zn(mIM)2, mIM=2-methyl imidazole] with flexible structure and Pt@ZIF-71 [Zn(DClIM)2, DClIM=4,5-dichloroimidazole] with rigid structure, and hydrogenation of cinnamaldehyde as model reaction, to show the confinement effect and the structure flexibility of MOF matrices on the catalytic performance of composite catalysts. Both catalysts showed high selectivity for cinnamic alcohol with the confinement effect of the aperture. But, compared to Pt@ZIF-71, Pt@ZIF-8 exhibited higher conversion but lower selectivity owing to the flexible structure. The above results remind us that we will have to consider both the aperture size of MOFs and structure flexibility to select the proper MOF matrices for the composite materials to achieve the optimized performance.Going through the motions: Two composite catalysts (Pt@ZIF-8 and Pt@ZIF-71) were designed and synthesized to investigate the concomitant effect of aperture size and structural flexibility of metal–organic framework matrices in catalysis. Compared to the Pt NPs sheathed with the rigid MOFs (Pt@ZIF-71), the Pt@ZIF-8 composite catalyst exhibited higher conversion but lower selectivity owing to the flexible structure of ZIF-8 matrices.
      PubDate: 2017-07-27T01:55:55.218649-05:
      DOI: 10.1002/chem.201702103
       
  • Triggered and Tunable Hydrogen Sulfide Release from Photogenerated
           Thiobenzaldehydes
    • Authors: Zeyun Xiao; Thomas Bonnard, Aida Shakouri-Motlagh, Ross A. L. Wylie, Joe Collins, Jonathan White, Daniel E. Heath, Christoph E. Hagemeyer, Luke A. Connal
      Abstract: Hydrogen sulfide (H2S) has been identified as an important cell-signaling mediator and has a number of biological functions, such as vascular smooth muscle relaxation, neurotransmission, and regulation of inflammation. A facile and versatile approach for H2S production initiated by light irradiation and controlled by reaction with an amine or an amino acid was developed. The donor was synthesized in a one-pot reaction, and simple crystallization led to a yield of approximately 90 %. The synthetic strategy is scalable and versatile, and the H2S donors can be expressed ina number of different molecular and macromolecular forms, including crystalline small-molecule compounds, water-soluble polymers, polystyrene films, and hydrogels. The H2S donors based on polystyrene film and hydrogel were used as cell-culture scaffolds. The H2S donor based on water-soluble polymer was applied in photocontrolled inhibition of P-selectin expression on human platelets and subsequent regulation of platelet aggregation. This study provides the simplest controllable H2S source to study its biological functions. The developed materials are also new therapeutic platforms to deliver H2S, as there is no accumulation of toxic byproducts, and the donor materials from polystyrene films and hydrogels can be readily removed after releasing H2S.Dual-trigger H2S donors: A facile and versatile approach to H2S release has been developed by trapping photogenerated thiobenzaldehydes with amines. The H2S release process can be controlled with light and an amine. In addition to a crystalline small-molecule H2S donor, water-soluble polymer, polystyrene film, and hydrogel H2S donors were easily obtained. The new materials showed excellent biocompatibility and were used for controlled delivery of H2S to cells and antiplatelet applications (see scheme).
      PubDate: 2017-07-27T01:55:29.240324-05:
      DOI: 10.1002/chem.201701206
       
  • Highly Diastereo- and Enantioselective Synthesis of
           Tetrahydro-5H-Indolo[2,3-b]quinolines via Copper-Catalyzed Propargylic
           Dearomatization of Indoles
    • Authors: Shuli You; Wen Shao
      Abstract: The first copper-catalyzed intermolecular asymmetric propargylic dearomatization/annulation cascade sequence of indoles via copper-allenylidene amphiphilic intermediate has been realized. This protocol provides a direct asymmetric synthetic method for the preparation of tetrahydro-5H-indolo[2,3-b]quinolones, the core structure of indole alkaloids communesins A-H and perophoramidine. This method features excellent yields, high diastereoselectivity (up to>19/1 dr) and enantioselectivity (up to 94% ee), mild conditions and wide substrate scope.
      PubDate: 2017-07-26T21:26:02.147534-05:
      DOI: 10.1002/chem.201703443
       
  • Towards improved oligonucleotide therapeutics through faster target
           binding kinetics
    • Authors: Mirjam Menzi; Bettina Wild, Ugo Pradère, Andreas Brunschweiger, Anna L Malinowska, Helen Louise Lightfoot, Jonathan Hall
      Abstract: When used as inhibitors of gene expression in vivo, oligonucleotides require modification of their structures to boost their binding affinity for complementary target RNAs. To date, hundreds of modifications have been designed and tested but few have proven to be useful. Among those investigated are mono- and polyamino-groups. These are positively charged at physiological pH and have been appended to oligonucleotides in an effort to reduce electrostatic repulsion during hybridization to RNAs, but have generally shown relatively minor benefits to binding. We conjugated spermine to uracils in oligonucleotides via a triazole linker so that the polyamine fits in the major groove of a subsequently formed RNA-duplex. The modifications produced large increases in target-binding affinity of the oligonucleotides. Using surface plasmon resonance-based assays, we showed that the increases derived mainly from faster annealing (kon). We propose that the spermine fragments play a similar role to that of natural polyamines during oligonucleotide-target interactions in cells, and may be advantageous for oligonucleotides that operate catalytic mechanisms.
      PubDate: 2017-07-26T14:25:25.381944-05:
      DOI: 10.1002/chem.201701670
       
  • α,β-Unsaturated Amides as Dipolarophiles: Catalytic Asymmetric
           exo-Selective 1,3-Dipolar Cycloaddition with Nitrones
    • Authors: Ming Zhang; Naoya Kumagai, Masakatsu Shibasaki
      Abstract: Invited for the cover of this issue are Ming Zhang, Naoya Kumagai, and Masakatsu Shibasaki at the Institute of Microbial Chemistry (IMC) in Tokyo. The image depicts a hypothetical molecular architecture composed of five-membered heterocycles. Read the full text of the article at 10.1002/chem.201702330.“Manifestation of both endo-selectivity and broad substrate generality has been long awaited in the 1,3-dipolar cycloaddition of nitrones and electron-deficient olefins.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201702330).
      PubDate: 2017-07-26T07:00:40.403928-05:
       
  • Coordination-Driven Folding in Multi-ZnII-Porphyrin Arrays Constructed on
           a Pillar[5]arene Scaffold
    • Authors: Thi Minh Nguyet Trinh; Iwona Nierengarten, Haifa Ben Aziza, Eric Meichsner, Michel Holler, Matthieu Chessé, Rym Abidi, Christian Bijani, Yannick Coppel, Emmanuel Maisonhaute, Béatrice Delavaux-Nicot, Jean-François Nierengarten
      Abstract: Invited for the cover of this issue are the groups of Emmanuel Maisonhaute at Sorbonne Universités, Béatrice Delavaux-Nicot at the Laboratoire de Chimie de Coordination (LCC) du CNRS (Université de Toulouse), and Jean-François Nierengarten at the Université de Strasbourg. The image depicts an artistic view of the open molecular flower upon treatment with an imidazole ligand. Read the full text of the article at 10.1002/chem.201701622.“…the ten peripheral porphyrins of these molecules should be arranged in a ring-like fashion as observed for the bacteriochlorophylls in the light-harvesting antenna of photosynthetic purple bacteria.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201701622).
      PubDate: 2017-07-26T06:55:53.81224-05:0
       
  • Target Identification of Kinase Inhibitor Alisertib (MLN8237) by Using
           DNA-Programmed Affinity Labeling
    • Authors: Dong-Yao Wang; Yan Cao, Le-Yi Zheng, Lang-Dong Chen, Xiao-Fei Chen, Zhan-Ying Hong, Zhen-Yu Zhu, Xiaoyu Li, Yi-Feng Chai
      Abstract: Accurate identification of the molecular targets of bioactive small molecules is a highly important yet challenging task in biomedical research. Previously, a method named DPAL (DNA-programmed affinity labeling) for labeling and identifying the cellular targets of small molecules and nucleic acids was developed. Herein, DPAL is applied for the target identification of Alisertib (MLN8237), which is a highly specific aurora kinase A (AKA) inhibitor and a drug candidate being tested in clinical trials for cancer treatment. Apart from the well-established target of AKA, several potential new targets of MLN8237 were identified. Among them, p38 mitogen-activated protein kinase (p38) and laminin receptor (LAMR) were validated to be implicated in the anticancer activities of MLN8237. Interestingly, these new targets were not identified with non-DNA-based affinity probes. This work may facilitate an understanding of the molecular basis of the efficacy and side effects of MLN8237 as a clinical drug candidate. On the other hand, this work has also demonstrated that the method of DPAL could be a useful tool for target identification of bioactive small molecules.Lighting-up targets: New molecular targets have been identified for Alisertib (MLN8237), which is an aurora kinase A (AKA) inhibitor and an anticancer drug candidate, through the application of DPAL (DNA-programmed affinity labeling; see figure). The DPAL method could be a useful tool for target identification of bioactive small molecules.
      PubDate: 2017-07-26T06:55:50.131077-05:
      DOI: 10.1002/chem.201702033
       
  • A Flexible, Fused, Azomethine–Boron Complex: Thermochromic Luminescence
           and Thermosalient Behavior in Structural Transitions between Crystalline
           Polymorphs
    • Authors: Shunsuke Ohtani; Masayuki Gon, Kazuo Tanaka, Yoshiki Chujo
      Abstract: A new boron complex for obtaining aggregation-induced emission properties was designed based on the strategy to improve the flexibility of a molecular skeleton. From the computer calculation and synthesis, the desired complex with environment-sensitive solid-state emission was obtained. Furthermore, the complex showed thermosalient effects in the heating and cooling processes with luminescent chromism. More information can be found in the Full Paper by K. Tanaka, Y. Chujo et al. (
      DOI : 10.1002/chem.201702309).
      PubDate: 2017-07-26T06:55:27.34688-05:0
       
  • Green Synthesis of A2SiF6 (A=Li–Cs) Nanoparticles using Ionic Liquids as
           Solvents and as Fluorine Sources: A Simple Approach without HF
    • Authors: Jacob Olchowka; Markus Suta, Claudia Wickleder
      Abstract: In this Communication, nanoparticles of the fluoridosilicates A2SiF6 (A=Li, Na, K, Rb, Cs), which are extremely promising host lattices for future LEDs, are presented for the first time. The preparation method we introduce here is a very simple and energy and time saving one, moreover the usage of toxic HF or elemental fluorine is avoided. In detail, the ionic liquid [Bmim]PF6 was used both as solvent and fluoride source in an ionothermally assisted microwave synthesis. The small size of the so-obtained nanoparticles is of huge relevance for their applications as thin films or for the coverage of surfaces, for example in next-generation white LEDs upon doping with Mn4+.Nanoparticles of the fluoridosilicates A2SiF6 (A=Li, Na, K, Rb, Cs), which are extremely promising host lattices for future LEDs, are presented for the first time. The preparation method described using the ionic liquid BmimPF6 as solvent, reactant and surfactant is a very simple and energy and time saving one; moreover the usage of toxic HF or elemental fluorine is avoided.
      PubDate: 2017-07-26T06:55:22.629068-05:
      DOI: 10.1002/chem.201702375
       
  • Solvent-Directed Helical Stereomutation Discloses Pathway Complexity on
           N-Heterotriangulene-Based Organogelators
    • Authors: Jorge S. Valera; Roberto Sánchez-Naya, Francisco J. Ramírez, José L. Zafra, Rafael Gómez, Juan Casado, Luis Sánchez
      Abstract: The chiroptical features of supramolecular polymers formed from N-heterotriangulenes 1–3 have been investigated by circular dichroism (ECD) and vibrational circular dichroism (VCD) techniques. In solution, the CD spectra demonstrate that the helicity of the aggregates depends on only the stereogenic centres located at the peripheral chains. In the gel state, the chiroptical features are conditioned by the point chirality of the stereogenic centres and by the achiral solvent utilised. Sonication of the gels formed in CCl4 reveals both kinetic and thermodynamic phases. These findings reveal the presence of pathway complexity in the gel state triggered by sonication. The described solvent-induced helical stereomutation demonstrates that the gel state can be utilised as an outstanding benchmark for investigating uncommon chiroptical effects and to explore the rules of chirality transmission.Twists and turns: The chiroptical features of supramolecular polymers formed from N-heterotriangulenes 1–3 have been investigated by circular dichroism and vibrational circular dichroism techniques. Solvent-directed pathway complexity, yielding kinetic or thermodynamic aggregates, is observed for N-heterotriangulenes 1–3 in the gel state (see figure).
      PubDate: 2017-07-26T06:51:03.98966-05:0
      DOI: 10.1002/chem.201702391
       
  • Hydrogen-Bonded Open-Framework with Pyridyl-Decorated Channels:
           Straightforward Preparation and Insight into Its Affinity for Acidic
           Molecules in Solution
    • Authors: Georges Mouchaham; Nans Roques, Walid Khodja, Carine Duhayon, Yannick Coppel, Stéphane Brandès, Tamás Fodor, Michel Meyer, Jean-Pascal Sutter
      Abstract: Off-charge-stoichiometry assemblage of ionic H-bond donors and acceptors was found to be a straightforward approach to a hydrogen-bonded open framework with pores decorated by basic sites. The supramolecular architecture exhibits 1-nm-wide channels functionalized by pyridyl groups and high accessible voids (53 %).Remarkable affinity was achieved for acidic organic molecules, including larger drug molecules. Notably, good selectivity of the porous material for the halogenated acids was also observed. More information can be found in the Full Paper by N. Roques, J.-P. Sutter et al. (
      DOI : 10.1002/chem.201701732).
      PubDate: 2017-07-26T06:50:57.056746-05:
       
  • Asymmetric Synthesis of Pyrrolidine-Containing Chemical Scaffolds via
           Tsuji–Trost Allylation of N-tert-Butanesulfinyl Imines
    • Authors: Rafid S. Dawood; Irene Georgiou, Ross P. Wilkie, William Lewis, Robert A. Stockman
      Abstract: A simple and efficient asymmetric synthesis of novel sp3-rich pyrrolidine chemical scaffolds over five steps starting from simple ketones is described. Key steps involve the use of tert-butanesulfinamide as a chiral auxiliary to perform an asymmetric Tsuji–Trost allylation, with subsequent cross-metathesis with an acrylate ester and reduction of the sulfinimine/cyclisation of the resulting amine giving the pyrrolidine scaffolds in high yields and diastereoselectivites. By removing the chiral auxiliary and functionalising the ester group, the resulting scaffold core can be further derivatised.Three is the magic number: Use of the chiral tert-butane sulfinyl directing group allows installation of three stereogenic centres in three separate reactions with control of chirality, and a rapid entry into highly sp3-rich three-dimensional bicyclic pyrrolidine chemical scaffolds.
      PubDate: 2017-07-26T06:50:51.197059-05:
      DOI: 10.1002/chem.201702616
       
  • Nitrato-Functionalized Task-Specific Ionic Liquids as Attractive
           Hypergolic Rocket Fuels
    • Authors: Yi Wang; Shi Huang, Wenquan Zhang, Tianlin Liu, Xiujuan Qi, Qinghua Zhang
      Abstract: Hypergolic ionic liquids (HILs) are a family of promising green fuels among the liquid propellants. As compared to previous studies and mainly focusing on structural innovations and ignition improvement of anions, here a new strategy of introducing energetic nitrato group into the cationic framework is proposed and is aimed at providing additional oxygen in the fuel molecule to enhance the combustion performance of HILs. These newly developed nitrato-functionalized HILs exhibit improved physical properties and combustion behavior including higher density, larger combustion flames, and longer combustion duration. More information can be found in the Full Paper by Q. Zhang et al. (
      DOI : 10.1002/chem.201701804).
      PubDate: 2017-07-26T06:50:26.233684-05:
       
  • AuI⋅⋅⋅AuI Interaction Assisted Host–Guest Interactions and
           Stimuli-Responsive Self-Assembly in Tetranuclear Alkynylgold(I)
           Calix[4]arene-Based Isocyanide Complexes
    • Authors: Anlea Chu; Franky Ka-Wah Hau, Vivian Wing-Wah Yam
      Abstract: Multi-stimuli-responsive tetranuclear gold(I) complexes were prepared based on a tetra(alkynyl)calix[4]arene framework, with incorporation of a series of isocyanide ligands of tunable hydrophilicity. This class of complex was found to exhibit high sensitivity towards group IIIA metal ions especially In3+. Drastic electronic absorption and emission changes were observed, which could be attributed to the formation of AuI⋅⋅⋅AuI interactions during the binding event. Solvent-induced self-aggregation was also observed upon changing the solvent environment to a more polar medium, with the formation of nanoaggregates and the turning-on of the aurophilic interactions, leading to interesting luminescence and morphological changes. The aggregation process was monitored by UV/Vis absorption, emission and 1H NMR spectroscopy and dynamic light scattering (DLS) studies, and the morphological changes were studied by electron microscopy. This new class of complex has shown high sensitivity towards external stimuli and demonstrated the feasibility of employing the on–off switching of aurophilicity as an effective design strategy for the construction of functional supramolecular systems.By the love of gold: Multi-stimuli-responsive tetranuclear gold(I) complexes based on a tetra(alkynyl)calix[4]arene framework demonstrate high selectivity towards binding of In3+ ions with turning-on of AuI⋅⋅⋅AuI interactions. Modulation of aurophilic interactions could also be achieved through solvent-induced self-aggregation with interesting luminescence and morphological changes.
      PubDate: 2017-07-26T06:45:38.57007-05:0
      DOI: 10.1002/chem.201701631
       
  • A Highly Fluorinated Chiral Aldehyde for Enantioselective Fluorescent
           Recognition in a Biphasic System
    • Authors: Chao Wang; Xuedan Wu, Lin Pu
      Abstract: A 1,1′-bi-2-naphthol (BINOL)-based aldehyde containing four perfluoroalkyl groups has been designed and synthesized. It shows enantioselective fluorescence enhancement at 420 nm when treated with the enantiomers of trans-1,2-diaminocyclohexane in an organic/fluorous biphasic system. The enantiomeric excess of the diamine in methanol can be linearly correlated with the emission intensity of of the aldehyde in perfluorohexane (FC-72). This is the first example to determine the enantiomeric composition of a chiral molecule by using a fluorescent sensor in a fluorous/organic biphasic system. The mechanism of the reaction was investigated by NMR spectroscopy and mass spectrometry.A highly fluorinated molecular probe can selectively extract one enantiomer of a chiral diamine from a methanol solution into a fluorous phase to show enantioselective fluorescent enhancement.
      PubDate: 2017-07-26T06:45:30.870197-05:
      DOI: 10.1002/chem.201702354
       
  • β-Hydroxy-tetrahydroquinolines from Quinolines Using Chloroborane:
           Synthesis of the Peptidomimetic FISLE-412
    • Authors: Ahmad S. Altiti; Kai Fan Cheng, Mingzhu He, Yousef Al-Abed
      Abstract: A new synthetic protocol provides a simple and direct method to generate functionalized β-hydroxy-tetrahydroquinolines (THQs). Hydroboration of quinolines using chloroboranes followed by oxidation with NaBO3⋅H2O led to the formation of functionalized β-hydroxy THQs. High regio- and diastereoselectivities were observed in α and γ substituted quinolines and the trans diastereomer of the β-hydroxy-THQ was the major isostere. This new protocol was utilized to build the novel antibody-targeted lupus peptidomimetic, FISLE-412.Special effects: The synthetic protocol presented provides a simple and direct method to generate functionalized β-hydroxy-tetrahydroquinolines (THQs). Hydroboration of quinolines using chloroboranes followed by oxidation with NaBO3⋅H2O led to the formation of functionalized β-hydroxy THQs. This protocol was used to build the novel antibody-targeted lupus peptidomimetic FISLE-412.
      PubDate: 2017-07-26T06:45:24.490617-05:
      DOI: 10.1002/chem.201701944
       
  • [2.2]Paracyclophane-Bis(triazole) Systems: Synthesis and Photochemical
           Behavior
    • Authors: Lucian G. Bahrin; Laura G. Sarbu, Peter G. Jones, Lucian M. Birsa, Henning Hopf
      Abstract: Mono-, pseudo-gem, and pseudo-para ethynylcyclophanes and bis(azides) have been employed as addition partners in CuAAC reactions to design and build complex extended molecular scaffolds. The reactivity of the resulting triazoles was investigated under photochemical conditions. A variety of newly substituted [2.2]paracyclophanes were identified; deazotization of pseudo-gem and pseudo-para adducts provided indolophane derivatives. An intramolecular stabilization effect was observed in the case of pseudo-gem derivatives. A photochemical rearrangement from a pseudo-para adduct to a pseudo-ortho product was identified.Click reactions: Mono- and disubstituted ethynylcyclophanes and azides have been employed as addition partners in CuAAC reactions to build designed complex extended molecular scaffolds. The resulting triazoles were investigated under photochemical conditions. A variety of newly substituted [2.2]paracyclophanes were identified; deazotation of pseudo-gem and pseudo-para adducts provided indolophane derivatives.
      PubDate: 2017-07-26T06:41:00.543126-05:
      DOI: 10.1002/chem.201701593
       
  • Electrochemical Graphitization: An Efficient Conversion of Amorphous
           Carbons to Nanostructured Graphites
    • Authors: Xianbo Jin; Rui He, Sheng Dai
      Abstract: This concept paper describes a new electrochemical method for the graphitization of amorphous carbons. The graphitization is achieved by a simple cathodic polarization of the carbons at merely ≈1100 K in molten CaCl2. This electrochemical process is applicable to both graphitizable and non-graphitizable carbons, generating porous graphitic structures of high-crystallinity nanosheets. The transformation of carbon blacks, microspheres, and fibers to porous graphites, hollow graphite spheres, and pipes with porous shells have been demonstrated and the potential graphitization mechanism discussed.A cathodic polarization in molten calcium chloride facilitates the conversion of various amorphous carbons to nanostructured graphite (see scheme) with high crystallinity at merely about 1100 K.
      PubDate: 2017-07-26T06:40:31.303607-05:
      DOI: 10.1002/chem.201701620
       
  • Soluble Two-Dimensional Covalent Organometallic Polymers by
           (Arene)Ruthenium-Sulfur Chemistry
    • Authors: Johann Coraux; Wael Hourani, Valentin L. Müller, Simon Lamare, Danial Aiman Kamaruddin, Laurence Magaud, Nedjma Bendiab, Martien Den Hertog, Olivier Leynaud, Frank Palmino, Roland Salut, Frédéric Chérioux
      Abstract: A class of two-dimensional (2D) covalent organometallic polymers, with nanometer-scale crosslinking, was obtained by arene(ruthenium) sulfur chemistry. Their ambivalent nature, with positively charged crosslinks and lypophylic branches is the key to the often sought-for and usually hard-to-achieve solubility of 2D polymers in various kinds of solvents. Solubility is here controlled by the planarity of the polymer, which in turn controls Coulomb interactions between the polymer layers. High planarity is achieved for high symmetry crosslinks and short, rigid branches. Owing to their solubility, the polymers are easily processable, and can be handled as powder, deposited on surfaces by mere spin-coating, or suspended across membranes by drop-casting. The novel 2D materials are potential candidates as flexible membranes for catalysis, cancer therapy, and electronics.Powder up: A two-dimensional material, consisting of (arene)ruthenium-sulfur crosslinks and polyphenylic branches, was synthesized in solution. Its ambivalent nature provides affinity with a variety of solvents, while its flatness and rigidity minimize interlayer interactions. As a result, the polymer is easily soluble and processable in a versatile way.
      PubDate: 2017-07-26T06:35:54.368064-05:
      DOI: 10.1002/chem.201700054
       
  • Catalytic Dehydrogenative Coupling of Hydrosilanes with Alcohols for the
           Production of Hydrogen On-demand: Application of a Silane/Alcohol Pair as
           a Liquid Organic Hydrogen Carrier
    • Authors: David Ventura-Espinosa; Alba Carretero-Cerdán, Miguel Baya, Hermenegildo García, Jose A. Mata
      Abstract: The compound [Ru(p-cym)(Cl)2(NHC)] is an effective catalyst for the room-temperature coupling of silanes and alcohols with the concomitant formation of molecular hydrogen. High catalyst activity is observed for a variety of substrates affording quantitative yields in minutes at room temperature and with a catalyst loading as low as 0.1 mol %. The coupling reaction is thermodynamically and, in the presence of a Ru complex, kinetically favourable and allows rapid molecular hydrogen generation on-demand at room temperature, under air, and without any additive. The pair silane/alcohol is a potential liquid organic hydrogen carrier (LOHC) for energy storage over long periods in a safe and secure way. Silanes and alcohols are non-toxic compounds and do not require special handling precautions such as high pressure or an inert atmosphere. These properties enhance the practical applications of the pair silane/alcohol as a good LOHC in the automotive industry. The variety and availability of silanes and alcohols permits a pair combination that fulfils the requirements for developing an efficient LOHC.On demand! An effective supported ruthenium catalyst on the surface of rGO controls the hydrogen production from hydrosilanes. The hydrogen storage properties show the potential application of the silane/alcohol pair as an efficient liquid organic hydrogen carrier.
      PubDate: 2017-07-26T06:35:27.218915-05:
      DOI: 10.1002/chem.201700243
       
  • A Simple Optoelectronic Tongue Discriminates Amino Acids
    • Authors: Uwe Heiko Bunz; Benhua Wang, Jinsong Han, Chao Ma, Markus Bender, Kai Seehafer, andreas Herrmann
      Abstract: A self-assembled nine-element optoelectronic tongue consisting of a po¬sitively charged water soluble poly(para-phenyleneethynylene) and three metal ions (Fe2+, Co2+ and Cu2+) at three different pH-values (pH 7, 10 and 13) discriminates all of the 20 natural amino acids in water. Unknown identification was not ideal. Addition of a highly positively charged green fluorescent protein in the presence of Fe2+, Co2+ and Cu2+ increased the unknown identification to above 86%. Li¬near discriminant analysis (LDA) orders the responses ac¬cording to the amino acid type, i.e. hydrophobic, polar, anionic or cationic.
      PubDate: 2017-07-26T05:27:07.831492-05:
      DOI: 10.1002/chem.201702826
       
  • Dioxygen binding to protonated heme in the gas phase, an intermediate
           between ferric and ferrous heme.
    • Authors: Niloufar Shafizadeh; Satchin Soorkia, Gilles Gregoire, Michel Broquier, Maria-Elisa Crestoni, Benoit Soep
      Abstract: In view of characterizing the influence of the electronic structure of the Fe atom on the nature of its bond with dioxygen in heme compounds, a study of the UV-Vis action spectra and binding energy of heme-O2 molecules has been undertaken in the gas phase. The binding reaction of protonated ferrous heme [FeII-hemeH]+ to dioxygen (O2) has been studied in the gas phase, by determining the equilibrium of complexed, [FeII-hemeH(O2)]+, to uncomplexed protonated heme in an ion trap at controlled temperatures. The binding energy of O2 to the Fe atom of protonated ferrous heme was obtained from a van't Hoff plot. Surprisingly, this energy (1540 ±170 cm-1, 18.4±2 kJ.mol- 1) is median between that of ferric heme and of ferrous heme. This result is interpreted in terms of a delocalization of the positive charge over the porphyrin cycle, where the Fe atom bears a fractional positive charge. The resulting electronic distribution on the Fe atom differs notably from that of a purely low spin ferrous heme [FeII-heme(O2)] complex as deduced from its absorption spectrum. It also differs from that of ferric heme [FeIII-heme(O2)]+ as seen in the absorption spectra. Protonated heme creates a specific bond that however cannot accomodate a strong sigma donation .
      PubDate: 2017-07-26T03:25:37.298071-05:
      DOI: 10.1002/chem.201702615
       
  • Frontispiece: Responsive, Water-Soluble Europium(III) Luminescent Probes
    • Authors: Sergey Shuvaev; Matthieu Starck, David Parker
      Abstract: Perturbation of the bright, red emission of europium coordination complexes is being used to signal real-time chemical changes in vitro and in cellulo. The design principles, mechanism of action and performance of europium(III) complexes that serve as strongly emissive and responsive molecular probes are critically discussed by S. Shuvaev, M. Starck and D. Parker in their Minireview on page 9974 ff. By understanding their key design principles and their mode of action, new probes for cations, anions, pH and for the local chiral chemical environment can be created. In this Minireview, selected examples are highlighted emphasising the need to take care in establishing reversibility of action and in calibration.
      PubDate: 2017-07-26T02:44:17.893138-05:
      DOI: 10.1002/chem.201784261
       
  • Frontispiece: Sulfur–Fluoride Exchange (SuFEx)-Mediated Synthesis of
           Sterically Hindered and Electron-Deficient Secondary and Tertiary Amides
           via Acyl Fluoride Intermediates
    • Authors: Christopher J. Smedley; Andrew S. Barrow, Christian Spiteri, Marie-Claire Giel, Pallavi Sharma, John E. Moses
      Abstract: The development of “SuFExAmide”: A new sulfur–fluoride exchange (SuFEx) click chemistry based protocol for the efficient amidation of carboxylic acids via acyl fluoride intermediates is described. Benzene-1,3-disulfonyl fluoride has been synthesized as a cost effective, powerful and versatile coupling agent, which delivers challenging secondary and tertiary amides in excellent yields from sterically hindered and electron-deficient amines. For more details, see the Communication by J. E. Moses et al on page 9990 ff.
      PubDate: 2017-07-26T02:44:16.419759-05:
      DOI: 10.1002/chem.201784262
       
  • Frontispiece: Rigidly Tethered Bis-phosphoric Acids: Generation of Tunable
           Chiral Fluorescent Frameworks and Unexpected Selectivity for the Detection
           of Ferric Ions
    • Authors: Frescilia Octa-Smolin; Raja Mitra, Maike Thiele, Constantin G. Daniliuc, Linda Stegemann, Cristian Strassert, Jochen Niemeyer
      Abstract: Rigidly tethered bis-phosphoric acids can be applied for the chemoselective detection of ferric ions (Fe3+). The fluorescent and chiral nature of the 1,1′-binaphthyl-based sensors allows for a detection of ferric ions by both fluorescence- and CD-spectroscopy. In the Frontispiece artwork, the “Zeche Zollverein” as a symbol for the formerly strong coal and iron industry in Essen (Germany) connects the local setting of this work with its focus on iron-sensing. Copyright for the background-picture: © Thomas Wolf, www.foto-tw.de (CC BY-SA 3.0 DE). For more details see the Full Paper by J. Niemeyer et al. on page 10058 ff.
      PubDate: 2017-07-26T02:44:10.52543-05:0
      DOI: 10.1002/chem.201784263
       
  • Green Energetic Nitrogen-Rich Salts of
           1,1′-Dinitramino-5,5′-bistetrazolate
    • Authors: Piao He; Le Wu, Jinting Wu, Qianyou Wang, Zhimin Li, Michael Gozin, Jianguo Zhang
      Abstract: A series of nitrogen-rich energetic salts of 1,1′-dinitramino-5,5′-bistetrazolate (DNABT) guanidinium (1), aminoguanidinium (2), diaminoguanidinium (3), triaminoguanidinium (4), diaminouronium (5), 3,4-diamino-1,2,4-triazolium (6), and ethylenediammonium (7) was synthesized by a metathesis strategy and characterized by elemental analysis, mass spectrometry, and IR spectroscopy as well as single-crystal X-ray diffraction and differential scanning calorimetry (DSC). The natural bond orbitals (NBOs) and electrostatic potentials (ESPs) were further computed for a better understanding of the structures of the DNABT molecule. The heats of formation were calculated based on the Born–Haber energy cycle. The detonation parameters were evaluated by using the EXPLO5 program, and the sensitivities were measured according to BAM standers. These new salts exhibit highly positive heats of formation (407.0–1377.9 kJ mol−1) and good thermal stabilities (180–211 °C). Most of these compounds possess detonation velocities comparable to RDX and acceptable detonation pressures. The high volumes of explosion gases of the salts 3 and 4 (921 and 933 L kg−1, respectively) further support their power as explosives. The enhancing performances, the fact of being free of metals, and the more moderate sensitivities than K2DNABT, suggest that the salts 4 (D=8851 m s−1, P=29.0 GPa), 5 (D=9053 m s−1, P=32.3 GPa), and 6 (D=8835 m s−1, P=30.2 GPa) might be potential environmentally friendly energetic materials.Big bang: Several new nitrogen-rich salts based on the 1,1′-dinitramino-5,5′-bistetrazolate ion have been synthesized and were characterized by using mass spectrometry, IR spectroscopy, and X-ray diffraction analysis. The salts were also investigated with regard to their thermal and energetic properties.
      PubDate: 2017-07-26T02:21:28.167492-05:
      DOI: 10.1002/chem.201702759
       
  • Biphasic Liquid Crystal and the Simultaneous Measurement of Isotropic and
           Anisotropic Parameters by Spatially Resolved NMR Spectroscopy
    • Authors: Malin Reller; Svenja Wesp, Martin R. M. Koos, Michael Reggelin, Burkhard Luy
      Abstract: Residual dipolar couplings and other anisotropic NMR parameters are powerful tools for molecular structure elucidation when conventional techniques do not suffice. With current liquid crystalline preparations it is necessary to prepare two samples to extract isotropic and anisotropic data from spectra and to derive the residual dipolar couplings. Here, we present the preparation, measurement, and interpretation of a novel biphasic liquid crystalline phase where a single sample can be used to generate both isotropic and anisotropic data. First, we introduce the synthesis of the chiral polymer leading to the biphasic liquid crystal. Second, we present two approaches to measure spatially selective CLIP-HSQC spectra. From these spectra, we extracted the couplings, performed an assignment of diastereotopic protons, and achieved the enantiomeric discrimination of isopinocampheol as a well-studied test molecule.Two for One! A chiral polymer forming a biphasic lyotropic liquid crystalline sample is introduced, which allows measurement of both isotropic and anisotropic NMR data in a single sample. A characterization of the biphasic system, spatially discriminative NMR pulse sequences, and an example for prochiral assignment as well as enantiodiscrimination is provided.
      PubDate: 2017-07-26T01:55:50.224008-05:
      DOI: 10.1002/chem.201702126
       
  • Reversible and Efficient Sequestration of Cesium from Water by the Layered
           Metal Thiophosphate K0.48Mn0.76PS3⋅H2O
    • Authors: Ekashmi Rathore; Provas Pal, Kanishka Biswas
      Abstract: Water body contamination with radioactive species is an important issue due to significant developments in nuclear energy. Cesium (137Cs) radioisotope is a non-actinide fission product of uranium and plutonium that is long-lived. Hence, selective removal/capture of cesium is essential for managing radioactive waste. Herein, a detailed Cs+ ion-exchange study on a potassium intercalated layered metal thiophosphate, K0.48Mn0.76PS3⋅H2O (K-MPS-1), is reported. The sorption of Cs+ by K-MPS-1 follows the Langmuir model with a high capacity of 337.5 mg g−1 and high distribution coefficients in the order of about 104 mL g−1. K-MPS-1 can sequester Cs+ efficiently, even from very low concentrations (ppb level). K-MPS-1 exhibits high cesium uptake over a broad pH range of 2–12 and the ion-exchange process reaches equilibrium within a short time (≈15 min), following pseudo-second-order kinetics. Moreover, K-MPS-1 demonstrates selectivity towards Cs+ capture in the presence of complex solutions containing excess Na+, Ca2+, and Mg2+ ions; this is due to favorable interactions between Cs (soft Lewis acid) and S (soft Lewis base). K-MPS-1 reversibly captures Cs+ and it can be regenerated by treating Cs-MPS-1 with a solution of KCl.Radioactive clean up: A potassium intercalated layered metal chalcophosphate, K0.48Mn0.76PS3⋅H2O, rapidly and reversibly captures Cs+ with a high capacity of 337.5 mg g−1 and high distribution coefficients in the order of about 104 mL g−1, even when the concentration of Cs+ is very low (5–100 ppb), through utilizing the concept of hard/soft acid–base interactions (see figure).
      PubDate: 2017-07-26T01:55:38.185093-05:
      DOI: 10.1002/chem.201701883
       
  • Addressing Chirality in the Structure and Synthesis of
           [18F]5-Fluoroaminosuberic Acid ([18F]FASu)
    • Authors: Hua Yang; Brian Tam, Milena Čolović, Lily Southcott, Helen Merkens, François Bénard, Paul Schaffer
      Abstract: An increasing number of positron emission tomography (PET) radiotracers are being developed that are modelled on various amino acids to better understand disease in a manner that is complementary to traditional glycolysis-targeting [18F]-fluorodeoxyglucose. Since chiral centers are ubiquitous in amino acids, generating an optically pure radiolabeled amino acid is important for patient dose, image quality and understanding the physiology behaviour. Past studies on the radiosynthesis of amino acid radiotracers seldom address the impact of reaction conditions on their chirality. The amino acid PET tracer, [18F]5-fluoroaminosuberic acid ([18F]FASu), has two chiral centers at the 2- and 5-positions and is being developed as a specific tracer for the cystine transporter (system xC−), a biomarker for oxidative stress. Herein we report a method for synthesizing pure 2S,5R/S-FASu. We have resolved the 5-position configuration by applying Mosher's method combined with 2D NMR, which has enabled the synthesis of 18FASu with fully known configuration. Our study serves as an example of a systematic method to identify and characterize amino acid tracers with chiral centers.Heard it on the radio: Generating an optically pure radiolabeled amino acid is important for patient dose, image quality and understanding the physiology behaviour. A method for synthesizing optically pure FASu, an oxidative stress PET imaging tracer with 2- and 5-position chiral centers, was developed. Cell uptake study showed only the 2S-FASu was uptaken by the tumor cells.
      PubDate: 2017-07-26T01:55:31.696319-05:
      DOI: 10.1002/chem.201702007
       
  • Kinetic Selectivity and Thermodynamic Features of Competitive Imine
           Formation in Dynamic Covalent Chemistry
    • Authors: Sirinan Kulchat; Manuel N. Chaur, Jean-Marie Lehn
      Abstract: The kinetic and thermodynamic selectivities of imine formation have been investigated for several dynamic covalent libraries of aldehydes and amines. Two systems were examined, involving the reaction of different types of primary amino groups (aliphatic amines, alkoxy-amines, hydrazides and hydrazines) with two types of aldehydes, sulfobenzaldehyde and pyridoxal phosphate in aqueous solution at different pD (5.0, 8.5, 11.4) on one hand, 2-pyridinecarboxaldehyde and salicylaldehyde in organic solvents on the other hand. The reactions were performed separately for given amine/aldehyde pairs as well as in competitive conditions between an aldehyde and a mixture of amines. In the latter case, the time evolution of the dynamic covalent libraries generated was followed, taking into consideration the operation of both kinetic and thermodynamic selectivities. The results showed that, in aqueous solution, the imine of the aliphatic amine was not stable, but oxime and hydrazone formed well in a pH dependent way. On the other hand, in organic solvents, the kinetic product was the imine derived from an aliphatic amine and the thermodynamic products were oxime and hydrazone. The insights gained from these experiments provide a basis for the implementation of imine formation in selective derivatization of mono-amines in mixtures as well as of polyfunctional compounds presenting different types of amino groups. They may in principle be extended to other dynamic covalent chemistry systems.Several dynamic covalent libraries of aldehydes and amines have been investigated with the focus on the kinetic and thermodynamic selectivities of imine formation. Two systems were examined, involving the reaction of different types of primary amino groups (aliphatic amines, alkoxy-amines, hydrazides and hydrazines) with two types of aldehydes, sulfobenzaldehyde and pyridoxal phosphate in aqueous solution at different pD on one hand, 2-pyridinecarboxaldehyde and salicylaldehyde in organic solvents on the other hand.
      PubDate: 2017-07-26T01:55:25.23372-05:0
      DOI: 10.1002/chem.201702088
       
  • Soluble Platinum Nanoparticles Ligated by Long-Chain N-Heterocyclic
           Carbenes as Catalysts
    • Authors: Luis M. Martínez-Prieto; Lena Rakers, Angela M. López-Vinasco, Israel Cano, Yannick Coppel, Karine Philippot, Frank Glorius, Bruno Chaudret, Piet W. N. M. van Leeuwen
      Abstract: Soluble platinum nanoparticles (Pt NPs) ligated by two different long-chain N-heterocyclic carbenes (LC-IPr and LC-IMe) were synthesized and fully characterized by TEM, high-resolution TEM, wide-angle X-ray scattering (WAXS), X-ray photoelectron spectroscopy (XPS), and solution NMR. The surface chemistry of these NPs (Pt@LC-IPr and Pt@LC-IMe) was investigated by FT-IR and solid state NMR using CO as a probe molecule. A clear influence of the bulkiness of the N-substituents on the size, surface state, and catalytic activity of these Pt NPs was observed. While Pt@LC-IMe showed no activity in the hydroboration of phenylacetylene, Pt@LC-IPr revealed good selectivity for the trans-isomer, which may be supported by a homogeneous species. This is the first example of hydroboration of acetylenes catalyzed by non-supported Pt NPs.Telling a tall tail: soluble platinum nanoparticles ligated by two different long-chain N-heterocyclic carbenes (Pt@LC-IPr and Pt@LC-IMe) show marked differences in their catalytic activity depending on the bulkiness of the N-substituents. While Pt@LC-IMe behaves similarly to heterogeneous catalysts, the catalytic activity of Pt@LC-IPr parallels that of molecular complexes in the hydroboration of phenylacetylene.
      PubDate: 2017-07-26T01:50:48.893294-05:
      DOI: 10.1002/chem.201702288
       
  • Buttressing effect as key design principle towards highly efficient
           palladium/N-heterocyclic carbene Buchwald-Hartwig amination catalysts
    • Authors: Yin Zhang; Guy Lavigne, Noël Lugan, Vincent César
      Abstract: A thorough structure/activity study aiming at rationalizing the beneficial effect of the substitution of the 4 and 5 positions of the standard 1,3-bis(2,6-diisopropylphenyl)-2H-imidazol-2-ylidene (IPr) ligand has on the catalytic activity of the corresponding Pd-PEPPSI pre-catalysts in N-arylation reaction is described. In addition to the previously reported IPrNMe2 and IPr(NMe2)2 ligands, the new IPrNiPr2 and IPr(NMe2,Cl) ligands bearing, respectively, one bulkier diisopropylamino group and a combination of dimethylamino and chloro substituents have been designed and included in the study. It is shown that the influence of the backbone-substitution is actually steric in origin and is related to the well-known buttressing effect encountered in arene chemistry. The usefulness and versatility of this approach are demonstrated through the development of a highly efficient catalytic system for the challenging arylation of bulky α,α,α-trisubstituted primary amines. The optimized system based on the [PdCl(η3-cinnamyl)(IPr(NMe2)2)] or [PdCl(η3-cinnamyl)(IPrNiPr2)] pre-catalysts operates under unprecedented mild conditions (catalyst loadings: 0.5-2 mol%, reaction temperatures: 40-60°C) and over a large substrate scope
      PubDate: 2017-07-25T21:26:02.980119-05:
      DOI: 10.1002/chem.201702859
       
  • A structurally characterized Cu(III) complex supported by a bis(anilido)
           ligand and its oxidative catalytic activity
    • Authors: Fabrice Thomas; Amelie Kochem, Jennifer K Molloy, Gisèle Gellon, Nicolas Leconte, Christian Philouze, Olivier Jarjayes, Florian Berthiol
      Abstract: Three copper(II) complexes of the (R,R)-N,N'-Bis(3,5-di-tert-butyl-2-aminobenzylidene)-1,2-diaminocyclohexane, namely [Cu(NL)], [Cu(NLH)]+ and [Cu(NLH2)]2+, were prepared and structurally characterized. In [Cu(NLH2)]2+ the copper ion lies in an octahedral geometry with the aniline groups coordinated in equatorial positions. In [Cu(NL)] the anilines are deprotonated (anilido moieties) and coordinated to an almost square metal ion. Complex [Cu(NL)] displays two oxidation waves at E1/2ox,1 = -0.14 V and E1/2ox,2 = 0.36 V vs Fc+/Fc in CH2Cl2. Complex [Cu(NLH2)]2+ displays an irreversible oxidation wave at high potential (1.22 V), but shows a readily accessible and reversible metal-centered reduction at E1/2red = -0.67 V (CuII/CuI redox couple). Oxidation of [Cu(NL)] by AgSbF6 produces [Cu(NL)](SbF6), which was isolated as single crystals. X-ray structure analysis discloses a contraction of the coordination sphere by 0.05 Ǻ upon oxidation, supporting a metal-centered process. Complex [Cu(NL)](SbF6) displays an intense NIR band at 1260 nm corresponding to an anilido-to-copper(III) charge transfer transition. This compound slowly evolves in CH2Cl2 solution towards [Cu(NLH)](SbF6), which is a copper(II) complex comprised of both anilido and aniline groups coordinated to the metal center. The copper(III) complex [Cu(NL)](SbF6) is an efficient catalyst for benzyl alcohol oxidation, with 236 TON in 24 h at 298 K, without additives other than oxygen and a base.
      PubDate: 2017-07-25T13:20:29.813824-05:
      DOI: 10.1002/chem.201702010
       
  • Altering the Coordination of Iron Porphyrins by Ionic Liquid Nanodomains
           in Mixed Solvent Systems
    • Authors: Abderrahman Atifi; Michael Ryan
      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 the strong attraction within the ionic liquid environment. The spectroscopic properties and distribution of the Fe(II) and Fe(I) 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.
      PubDate: 2017-07-25T08:25:37.087122-05:
      DOI: 10.1002/chem.201701540
       
  • Confinement of Reactive Oxygen Species in Artificial Enzyme-based Hollow
           Structure for Eliminating Photocatalytic Adverse Effect of UV Filters
    • Authors: Enguo Ju; Kai Dong, Zhenzhen Wang, Yan Zhang, Fangfang Cao, Zhaowei Chen, Fang Pu, Jinsong Ren, Xiaogang Qu
      Abstract: Skin cancers caused by UV irradiation have been a major public health problem. One simple and effective way to avoid the above detrimental effects is the use of UV-protective sunscreens. However, there has been considerable concern with the issue of production of reactive oxygen species by the photo-degradation of commercial UV filters. Herein, we reported for the first time that the integration of ZnO nanoparticles and CeOx nanoparticles into hollow microspheres (ZnO/CeOx HMS) could provide broad UV spectrum protection and scavenge generated ROS under UV irradiation. Benefiting from cooperation effect of the hollow structure and the anti-oxidative activity of CeOx, the generated ROS under UV irradiation could be effectively catalyzed into nontoxic molecules as a consequence of proximity and increased collision frequency. Therefore, both the primary direct UV-induced damage and the secondary ROS toxicity could be greatly reduced.
      PubDate: 2017-07-25T04:20:35.27912-05:0
      DOI: 10.1002/chem.201703005
       
  • A Series of Linear {FeIII2FeII} Complexes with Paramagnetic Building
           Block-Modified Spin Crossover Behaviors
    • Authors: Ji-Xiang Hu; Yin-Shan Meng, Liang Zhao, Hai-Lang Zhu, Lei Liu, Qiang Liu, Cheng-Qi Jiao, Tao Liu
      Abstract: Tuning the spin crossover (SCO) behavior through paramagnetic building blocks with different steric hindrance is of great interest for the synergy between SCO and magnetic interactions. Here we modified the steric effect of specified FeIII building blocks from large steric hindrance Tp* (hydridotris(3,5-dimethylpyrazol-1-yl)borate) analogue to small steric hindrance Tp (hydrotris(pyrazolyl)borate) derivative, the FeII SCO unit and FeIII paramagnetic ions were incorporated into three well-isolated trinuclear complexes featuring thermally- and light-induced SCO properties. Reanalyzing the structures uncovered that π-π-stacking interactions played a key role in the thermal hysteresis and anomalous octahedral distortion parameter Σ around FeII ion; the Tp* ligand showing the largest steric hindrance induced the elongated FeII-N bond lengths and bending of C≡N-FeII angle in 1, as well as its relatively large electron donor effect, leading to the lowest thermal transition temperature among three compounds.
      PubDate: 2017-07-25T03:37:37.906133-05:
      DOI: 10.1002/chem.201703110
       
  • Stepwise Growth of Fullerene Nanoparticles through Guest Exchange of
           γ-Cyclodextrin Complexes in Water
    • Authors: Kouta Sugikawa; Kentaro Kozawa, Masafumi Ueda, Atsushi Ikeda
      Abstract: Stepwise growth of fullerene nanoparticles (nCx; x=60 or 70) was performed through guest exchange of a γ-cyclodextrin (γ-CD) complex. Fullerenes bicapped by γ-CD were mixed with presynthesized nCx in the presence of polyethylene glycol (PEG) in water. Fullerenes expelled from the γ-CD hosts by PEG were piled on the original nCx, resulting in the growth of nCx. This process could be repeated and the size of nCx increased according to the number of growth steps. The growth of fullerene nanoparticles was confirmed by UV/Vis absorption spectroscopy, dynamic light scattering measurements, and transmission electron microscopy observations. Furthermore, the stepwise growth method also enabled the preparation of C60/C70 core/shell fullerene nanoparticles, showing the ability to photogenerate active oxygen, 1O2.
      PubDate: 2017-07-25T03:37:28.417779-05:
      DOI: 10.1002/chem.201701717
       
  • Advances in stereoselective 1,2-cis glycosylation using C-2 auxiliaries
    • Authors: Rens Mensink; Thomas Jan Boltje
      Abstract: The control of stereoselectivity in a glycosylation reaction remains one of the most challenging aspects of oligosaccharide synthesis. Especially the synthesis of 1,2-cis-glycosides is challenging and generally applicable methodology to prepare this linkage is needed to standardize oligosaccharide synthesis. This review highlights the recent development of an elegant strategy employing a C-2 auxiliary to control the anomeric stereoselectivity in glycosylations. The various auxiliaries developed to date, their compatibility with protecting groups and monosaccharide types as well as mechanistic aspects are summarized. Furthermore, the application, advantages and limitations of C-2 auxiliaries in oligosaccharide synthesis is discussed.
      PubDate: 2017-07-25T03:00:30.166734-05:
      DOI: 10.1002/chem.201700908
       
  • Diastereoselective Self-Assembly of a Neutral Dinuclear Double-Stranded
           Zinc(II) Helicate via Narcissistic Self-Sorting
    • Authors: Andreas Jarzebski; Christina Tenten, Christoph Bannwarth, Gregor Schnakenburg, Stefan Grimme, Arne Lützen
      Abstract: A new bis(salicylimine) ligand based on the Tröger's base scaffold was synthesized in racemic and enantiomerically pure form. Upon coordination to zinc(II) ions this ligand undergoes highly diastereoselective self-assembly into neutral dinuclear double-stranded helicates as proven by XRD analysis and via comparison of experimental ECD spectra with those simulated with quantum-chemical methods. When the racemic ligand was used, self-assembly occurs under narcissistic self-sorting resulting in the formation of a racemic pair of helicates as revealed by NMR spectroscopy and XRD analysis.A new bis(salicylimine) ligand based on Tröger's base scaffold was synthesized in racemic and enantiomerically pure form. Upon coordination to zinc(II) ions this ligand undergoes highly diastereoselective self-assembly into neutral dinuclear double-stranded helicates. Self-assembly of the racemic ligand occurs under narcissistic self-sorting, resulting in the formation of a racemic pair of helicates as revealed by NMR spectroscopy and XRD analysis.
      PubDate: 2017-07-25T01:50:37.741183-05:
      DOI: 10.1002/chem.201702125
       
  • Exploiting the MeDbz Linker to Generate Protected or Unprotected
           C-Terminally Modified Peptides
    • Authors: Christine A Arbour; Hasina Y Saraha, Timothy F McMillan, Jennifer Stockdill
      Abstract: C-terminally modified peptides are important targets for pharmaceutical and biochemical applications. Known methods for C-terminal diversification are limited mainly in terms of the scope of accessible modifications or by epimerization of the C-terminal amino acid. In this work, we present a broadly applicable approach that enables access to a variety of C-terminally functionalized peptides in either protected or unprotected form. This chemistry proceeds without epimerization of C-terminal Ala and tolerates nucleophiles of varying nucleophilicity. Finally, unprotected peptides bearing nucleophilic side chain groups can be selectively functionalized by strong nucleophiles, while macrocyclization is observed for weaker nucleophiles. The potential utility of this method is demonstrated through the divergent synthesis of the conotoxin conopressin G and GLP-1(7-36) and analogs.
      PubDate: 2017-07-24T18:09:53.767478-05:
      DOI: 10.1002/chem.201703380
       
  • Prediction of EPR Spectra of Lyotropic Liquid Crystals using a combination
           of Molecular Dynamics simulations and the Model Free Approach
    • Authors: Vasily S. Oganesyan; Christopher Prior
      Abstract: We report the first application of fully atomistic molecular dynamics (MD) simulations to the prediction of the motional EPR spectra of lyotropic liquid crystals in different aggregation states. 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.
      PubDate: 2017-07-24T17:09:32.233437-05:
      DOI: 10.1002/chem.201702682
       
  • Significantly Enhanced Hydrogen Evolution Activity of Freestanding Pd-Ru
           Distorted Icosahedral Clusters with less than 600 Atoms
    • Authors: Zhihui Dai; Suli Liu, Qinghua Zhang, Jianchun Bao, Yafei Li, Lin Gu
      Abstract: Freestanding metal nanoclusters can tune, precisely and effectively, the Gibbs free energy (ΔGH) of atomic hydrogen on the surface of materials. This enables the enhancement of hydrogen evolution activity. In this paper, we report a study of freestanding Pd-Ru distorted icosahedral clusters (ico-clusters) with less than 600 atoms using a simple one-pot synthesis method. This Pd-Ru ico-cluster can be used as an efficient electrocatalyst for the hydrogen evolution reaction (HER) in acidic water, which is a promising alternative to Pt. The experimental and theoretical results suggest that the fcc freestanding Pd-Ru distorted ico-clusters with less than 600 atoms ensure increased active edges and distorted defect sites that reduce the coordination number for the atoms on the catalyst surface. Furthermore, Ru is a more effective hydrogen dissociation source, while Pd has a better hydrogen storage function. Pd-Ru can tune the ΔGH of atomic hydrogen adsorbed on a catalyst and reach an optimal equilibrium state that improves the HER performance. Our studies represent a robust approach towards the development of freestanding Pd-Ru distorted ico-clusters and advanced catalysts with non-Pt content for HER and many other heterogeneous reactions.
      PubDate: 2017-07-24T15:40:34.980765-05:
      DOI: 10.1002/chem.201702913
       
  • Gold Redox Catalysis through Base-Initiated Diazonium Decomposition toward
           Alkene, Alkyne, and Allene Activation
    • Authors: Boliang Dong; Haihui Peng, Stephen E. Motika, Xiaodong Shi
      Abstract: The discovery of photoassisted diazonium activation toward gold(I) oxidation greatly extended the scope of gold redox catalysis by avoiding the use of a strong oxidant. Some practical issues that limit the application of this new type of chemistry are the relative low efficiency (long reaction time and low conversion) and the strict reaction condition control that is necessary (degassing and inert reaction environment). Herein, an alternative photofree condition has been developed through Lewis base induced diazonium activation. With this method, an unreactive AuI catalyst was used in combination with Na2CO3 and diazonium salts to produce a AuIII intermediate. The efficient activation of various substrates, including alkyne, alkene and allene was achieved, followed by rapid AuIII reductive elimination, which yielded the C−C coupling products with good to excellent yields. Relative to the previously reported photoactivation method, our approach offered greater efficiency and versatility through faster reaction rates and broader reaction scope. Challenging substrates such as electron rich/neutral allenes, which could not be activated under the photoinitiation conditions (
      PubDate: 2017-07-24T15:18:17.579007-05:
      DOI: 10.1002/chem.201701970
       
  • α,β-Unsaturated Amides as Dipolarophiles: Catalytic Asymmetric
           exo-Selective 1,3-Dipolar Cycloaddition with Nitrones
    • Authors: Ming Zhang; Naoya Kumagai, Masakatsu Shibasaki
      Abstract: A highly endo-selective and enantioselective 1,3-dipolar cycloaddition of nitrones and α,β-unsaturated amides was manifested by indium catalyst decorated with chiral bishydroxamic acid ligands. The five-membered ring system of the product isooxazolines featuring the neighboring nitrogen and oxygen atoms are versatile chiral building blocks in synthetic organic chemistry, and the cover art represents the hypothetical molecular architecture composed of the five-membered heterocycles. More information can be found in the Communication by M. Zhang, N. Kumagai, and M. Shibasaki (
      DOI : 10.1002/chem.201702330).
      PubDate: 2017-07-24T14:26:46.364163-05:
       
  • Unearthing [3-(Dimethylamino)propyl]aluminium(III) Complexes as Novel
           Atomic Layer Deposition (ALD) Precursors for Al2O3: Synthesis,
           Characterization and ALD Process Development
    • Authors: Lukas Mai; Maximilian Gebhard, Teresa de los Arcos, Ignacio Giner, Felix Mitschker, Manuela Winter, Harish Parala, Peter Awakowicz, Guido Grundmeier, Anjana Devi
      Abstract: Identification and synthesis of intramolecularly donor-stabilized aluminium(III) complexes, which contain a 3-(dimethylamino)propyl (DMP) ligand, as novel atomic layer deposition (ALD) precursors has enabled the development of new and promising ALD processes for Al2O3 thin films at low temperatures. Key for this promising outcome is the nature of the ligand combination that leads to heteroleptic Al complexes encompassing optimal volatility, thermal stability and reactivity. The first ever example of the application of this family of Al precursors for ALD is reported here. The process shows typical ALD like growth characteristics yielding homogeneous, smooth and high purity Al2O3 thin films that are comparable to Al2O3 layers grown by well-established, but highly pyrophoric, trimethylaluminium (TMA)-based ALD processes. This is a significant development based on the fact that these compounds are non-pyrophoric in nature and therefore should be considered as an alternative to the industrial TMA-based Al2O3 ALD process used in many technological fields of application.Easy to handle Al precursors: A new class of [3-(dimethylamino)propyl]aluminium(III) complexes were developed as novel atomic layer deposition (ALD) precursors, which were successfully applied for low-temperature thermal and plasma ALD of Al2O3 thin films. The non-pyrophoric nature of these compounds, as well as the outstanding process characteristics, render them as a real alternative to the industrially used trimethylaluminium process for Al2O3.
      PubDate: 2017-07-24T14:25:27.239279-05:
      DOI: 10.1002/chem.201702939
       
  • Selectivity of C−H versus C−F Bond Oxygenation by Homo- and
           Heterometallic Fe4, Fe3Mn, and Mn4 Clusters
    • Authors: Graham de Ruiter; Kurtis M. Carsch, Michael K. Takase, Theodor Agapie
      Abstract: A series of tetranuclear [LM3(HFArPz)3OM′][OTf]2 (M, M′=Fe or Mn) clusters that displays 3-(2-fluorophenyl)pyrazolate (HFArPz) as bridging ligand is reported. With these complexes, manganese was demonstrated to facilitate C(sp2)−F bond oxygenation via a putative terminal metal-oxo species. Moreover, the presence of both ortho C(sp2)−H and C(sp2)−F bonds in proximity of the apical metal center provided an opportunity to investigate the selectivity of intramolecular C(sp2)−X bond oxygenation (X=H or F) in these isostructural compounds. With iron as the apical metal center, (M′=Fe) C(sp2)−F bond oxygenation occur almost exclusively, whereas with manganese (M′=Mn), the opposite reactivity is preferred.Oxygen atom transfer: The selectivity of intramolecular C(sp2)−H versus C(sp2)−F bond oxygenation was examined with a new series of [LM3(PhPz)3OM′][OTf]2 (M, M′=Fe or Mn) clusters. The distribution of metal centers within these clusters provided insight into how a single metal center (Fe vs. Mn) can control the selectivity of oxygenation chemistry. Although for iron (M=Fe, M′=Fe) essentially exclusive C(sp2)−F bond oxygenation was observed, with manganese (M=Fe or Mn, M′=Mn), C(sp2)−H oxygenation was preferred (see scheme).
      PubDate: 2017-07-24T14:24:40.38701-05:0
      DOI: 10.1002/chem.201702302
       
  • Decoding Nucleation and Growth of Zeolitic Imidazolate Framework Thin
           Films with Atomic Force Microscopy and Vibrational Spectroscopy
    • Authors: Zafer Öztürk; Matthias Filez, Bert M. Weckhuysen
      Abstract: The synthesis of metal-organic framework (MOF) thin films has garnered significant attention during the past decade. By better understanding the parameters governing the nucleation and growth of such thin films, their properties can be rationally tuned, empowering their application as (reactive) membranes. Here, a combined AFM-vibrational spectroscopy research strategy is employed to detail the chemistries governing the nucleation and growth of zeolitic imidazolate framework (ZIF) thin films, in particular isostructural Co-ZIF-67 and Zn-ZIF-8. First, a single step direct synthesis approach is used to investigate the influence of different synthesis parameters –metal/linker ratio, temperature, and metal type– on the thin film nucleation and growth behaviour. While the metal/linker ratio has a pronounced effect on the thin film nucleation rate, the temperature mainly influences the growth kinetics of nuclei forming the thin film. In addition, the nucleation and growth of ZIF thin films is shown to be highly dependent on the electronegativity of the metal type. Thin-film thickness control can be achieved by using a multistep synthesis strategy, implying repetitive applications of single step deposition under identical synthesis conditions, for which a growth mechanism is proposed. This study provides insight into the influence of synthesis parameters on the ZIF thin film properties, using tools at hand to rationally tune MOF thin film properties.Probing film growth: A combined AFM-vibrational spectroscopy research strategy is presented to investigate the chemistries governing the nucleation and growth of Zn-ZIF-8 and Co-ZIF-67 thin films. The influence of synthesis parameters is discussed, leading to a nucleation and growth mechanism for these materials.
      PubDate: 2017-07-24T14:24:25.703506-05:
      DOI: 10.1002/chem.201702130
       
  • Interactions between Ketones and Alcohols: Rotational Spectrum and
           Internal Dynamics of the Acetone–Ethanol Complex
    • Authors: Qian Gou; Laura B. Favero, Gang Feng, Luca Evangelisti, Cristóbal Pérez, Walther Caminati
      Abstract: The rotational spectra of two isotopologues of the 1:1 complex formed between acetone and ethanol have been recorded and analyzed by using Fourier-transform microwave spectroscopy. One rotamer was detected, in which ethanol adopts the gauche form. The two subunits are linked by a conventional O−H⋅⋅⋅O and a weak C−H⋅⋅⋅O hydrogen bond, forming a six-membered ring. Each rotational transition is split into five component lines due to the internal rotations of two nonequivalent acetone methyl groups. The V3 barriers to internal rotation of the two CH3 tops of acetone were determined to be 252(4) and 220(1) cm−1, which are noticeably lower than the value for the monomer (266 cm−1).Going for a spin: The rotational transitions of the hydrogen bonded acetone–ethanol complex are split into five components due to the nonequivalent nature of the methyl tops of acetone in the complex. The hydrogen bonding between acetone and ethanol leads to a noticeable decrease in the V3 barriers to internal rotation of the methyl groups in the acetone–ethanol complex compared with in acetone itself (see figure).
      PubDate: 2017-07-24T14:23:11.037496-05:
      DOI: 10.1002/chem.201702090
       
  • A Flexible, Fused, Azomethine–Boron Complex: Thermochromic Luminescence
           and Thermosalient Behavior in Structural Transitions between Crystalline
           Polymorphs
    • Authors: Shunsuke Ohtani; Masayuki Gon, Kazuo Tanaka, Yoshiki Chujo
      Abstract: This manuscript reports the multi-functional boron complex presenting aggregation-induced emission (AIE), crystallization-induced emission enhancement (CIEE), and thermosalient behavior accompanying thermochromic luminescence during crystal–crystal transitions by employing the fused azomethine ligand. In particular, we propose that these properties can be explained by molecular “flexibility” toward external stimuli, including temperature changes and photo-excitation, and two types of crystal polymorphs with different absorption and luminescent properties were obtained. Optical measurements indicated that both polymorphs showed individual AIE and strong CIEE properties. From the investigations, the boron complex showed large structural relaxation and formed the bent structure in the excited state, followed by emission annihilation in the absence of structural restriction. In addition, it was shown that interconversion between these polymorphs could be reversibly induced by heating and cooling. The data from the single-crystal X-ray analyses suggested that alteration of crystal packing and intermolecular interaction should influence the luminescent chromism. Moreover, we also found that the crystals showed unusual mechanical behavior, such as hopping and fragmentation by heating and cooling, respectively, which is called thermosalient behavior. It was suggested that the loosely-fused structure could be responsible for expressing unique optical and mechanical properties.A new boron complex with aggregation-induced emission property was designed and synthesized based on the strategy to improve the flexibility of a molecular skeleton. The complex showed environment-sensitive solid-state emission and unexpectedly thermosalient effects with luminescent chromism.
      PubDate: 2017-07-24T14:22:52.302814-05:
      DOI: 10.1002/chem.201702309
       
  • Xenon Recovery at Room Temperature using Metal–Organic Frameworks
    • Authors: Sameh K. Elsaidi; Daniele Ongari, Wenqian Xu, Mona H. Mohamed, Maciej Haranczyk, Praveen K. Thallapally
      Abstract: Xenon is known to be a very efficient anesthetic gas, but its cost prohibits the wider use in medical industry and other potential applications. It has been shown that Xe recovery and recycling from anesthetic gas mixtures can significantly reduce its cost as anesthetic. The current technology uses series of adsorbent columns followed by low-temperature distillation to recover Xe; this method is expensive to use in medical facilities. Herein, we propose a much simpler and more efficient system to recover and recycle Xe from exhaled anesthetic gas mixtures at room temperature using metal–organic frameworks (MOFs). Among the MOFs tested, PCN-12 exhibits unprecedented performance with high Xe capacity and Xe/O2, Xe/N2 and Xe/CO2 selectivity at room temperature. The in situ synchrotron measurements suggest that Xe is occupies the small pockets of PCN-12 compared to unsaturated metal centers (UMCs). Computational modeling of adsorption further supports our experimental observation of Xe binding sites in PCN-12.Xenon is known to be a very efficient anesthetic gas, but its cost prohibits the wider use in medical industry and other potential applications. The current technology uses a series of adsorbent columns followed by low-temperature distillation to recover Xe; this method is expensive to use in medical facilities. A much more efficient and simpler system is proposed to recover and recycle Xe from simulant exhaled anesthetic gas mixtures at room temperature using metal–organic frameworks (see scheme).
      PubDate: 2017-07-24T14:21:16.160155-05:
      DOI: 10.1002/chem.201702668
       
  • Densification of Silica Spheres: A New Pathway to Nano-Dimensioned
           Zeolite-Based Catalysts
    • Authors: Albert Gonche Fortunatus Machoke; Benjamin Apeleo Zubiri, Rainer Leonhardt, Venkata Ramana Reddy Marthala, Martin Schmiele, Tobias Unruh, Martin Hartmann, Erdman Spiecker, Wilhelm Schwieger
      Abstract: Nanosized materials are expected to play a unique role in the development of future catalytic processes. Herein, pre-prepared and geometrically well-defined amorphous silica spheres are densified into silica-rich zeolites with nanosized dimensions. After the densification, the obtained nanosized zeolites exhibit the same spherical morphology like the starting precursor but characterized by a drastically reduced size, higher density, and high crystallinity. The phase transformation into crystalline zeolite material and the densification effect are achieved through a well-controlled steam-assisted treatment of the larger precursor particles so that the transformation process proceeds always towards the center of the spheres, just like a shrinking process. Furthermore, this procedure is applicable also to commercially available silica particles, as well as aluminum-containing systems (precursors) leading to acidic nano-catalysts with improved catalytic performance.Silica-rich nanosized zeolites were crystallized by the densification of amorphous, mesoporous silica particles acting as the precursor. Interestingly, during this transformation, the morphology of the precursor was maintained and just the size, phase and porosity changed.
      PubDate: 2017-07-24T14:21:07.997954-05:
      DOI: 10.1002/chem.201702768
       
  • A Truncated Molecular Star
    • Authors: Soumyakanta Prusty; Kohei Yazaki, Michito Yoshizawa, Dillip Kumar Chand
      Abstract: A pentanuclear palladium(II) complex has been prepared by incorporating non-chelating ligands in a supramolecular framework by using a self-assembly method. The unprecedented title complex is heteroleptic, planar, and polycyclic and resembles the shape of a pentagram. Interim paths leading to the star were probed to decipher related dynamics of the system. The molecular shape resembles a starfish as shown in the cover artwork. More information can be found in the Communication by D. K. Chand et al. (
      DOI : 10.1002/chem.201702264).
      PubDate: 2017-07-24T14:20:23.611475-05:
       
  • Energy Efficient Synthesis of Ordered Mesoporous Carbon Nitrides with a
           High Nitrogen Content and Enhanced CO2 Capture Capacity
    • Authors: Dae-Hwan Park; Kripal S. Lakhi, Kavitha Ramadass, Min-Kyu Kim, Siddulu N. Talapaneni, Stalin Joseph, Ugo Ravon, Khalid Al-Bahily, Ajayan Vinu
      Abstract: Highly ordered mesoporous carbon nitrides (MCN) with 3D structure and a high nitrogen content are successfully prepared for the first time using “uncalcined” mesoporous silica template, KIT-6 and 3-amino-1,2,4-triazole as a single molecular carbon and nitrogen precursor. The prepared MCN with C and N stoichiometry of C3N5 shows unique CN framework and exhibits the CO2 capture capacity of 5.63 mmol g−1 at 273 K and 30 bar, which is higher than that of MCN with 2D structure and C3N4 stoichiometry.Catch and don′t release: Mesoporous carbon nitrides (MCN) with highly ordered 3D structure and a high nitrogen content show a unique CN framework with C and N stoichiometry of C3N5 and the CO2 capture capacity up to 5.63 mmol g−1 at 273 K and 30 bar.
      PubDate: 2017-07-24T14:20:12.046825-05:
      DOI: 10.1002/chem.201702566
       
  • Distinguishing Two Ammonium and Triazolium Sites of Interaction in a
           Three-Station [2]Rotaxane Molecular Shuttle
    • Authors: Philip Waelès; Karine Fournel-Marotte, Frédéric Coutrot
      Abstract: This paper reports on the synthesis of a tri-stable [2]rotaxane molecular shuttle, in which the motion of the macrocycle is triggered by either selective protonation/deprotonation or specific carbamoylation/decarbamoylation of an alkylbenzylamine. The threaded axle is surrounded by a dibenzo[24]crown[8] (DB24C8) macrocycle and contains three sites of different binding affinities towards the macrocycle. An N-methyltriazolium moiety acts as a molecular station that has weak affinity for the DB24C8 macrocycle and is located in the centre of the molecular axle. Two other molecular stations, arylammonium and alkylbenzylammonium moieties, sit on either side of the triazolium moiety along the molecular axle and have stronger affinities for the DB24C8 macrocycle. These two ammonium moieties are covalently linked to two different stopper groups at each extremity of the thread: a tert-butylphenyl group and a substituted DB24C8 unit. Owing to steric hindrance, the former does not allow any π–π stacking interactions with the encircling DB24C8 macrocycle, whereas the latter residue does; therefore, this allows the discrimination of the two ammonium stations by the surrounding DB24C8 macrocycle in the fully protonated state. In the deprotonated state, the contrasting reactivity of the amine functional groups, as either a base or a nucleophile, allows for selective reactions that trigger the controlled shuttling of the macrocycle around the three molecular stations.Station to station: Three distinct co-conformational states are obtained through the selective deprotonation of either one or two ammonium stations and/or the protection of one out of the two ammonium stations through carbamoylation. The relative affinity of the DB24C8 macrocycle for the stations is N-methyltriazolium
      PubDate: 2017-07-24T07:55:54.743631-05:
      DOI: 10.1002/chem.201701912
       
  • Unexpected Importance of Aromatic–Aliphatic and Aliphatic Side
           Chain–Backbone Interactions in the Stability of Amyloids
    • Authors: Dragan B. Ninković; Dušan P. Malenov, Predrag V. Petrović, Edward N. Brothers, Shuqiang Niu, Michael B. Hall, Milivoj R. Belić, Snežana D. Zarić
      Abstract: The role of aromatic and nonaromatic amino acids in amyloid formation has been elucidated by calculating interaction energies between β-sheets in amyloid model systems using density functional theory (B3LYP-D3/6-31G*). The model systems were based on experimental crystal structures of two types of amyloids: (1) with aromatic amino acids, and (2) without aromatic amino acids. Data show that these two types of amyloids have similar interaction energies, supporting experimental findings that aromatic amino acids are not essential for amyloid formation. However, different factors contribute to the stability of these two types of amyloids. In the former, the presence of aromatic amino acids significantly contributes to the strength of interactions between side chains; interactions between aromatic and aliphatic side chains are the strongest, followed by aromatic–aromatic interactions, while aliphatic–aliphatic interactions are the weakest. In the latter, that is, the amyloids without aromatic residues, stability is provided by interactions of aliphatic side chains with the backbone and, in some cases, by hydrogen bonds.Why they stick: Aggregation of amyloid polypeptides containing aromatic and nonaromatic amino acids has been studied through DFT calculations (see graphic). Interactions between side chains and their interactions with the backbone, all play a role in the formation of amyloid plaques.
      PubDate: 2017-07-24T07:51:20.850708-05:
      DOI: 10.1002/chem.201701351
       
  • Catalyst Optimisation for Asymmetric Synthesis by Ligand Chirality Element
           Addition: A Perspective on Stereochemical Cooperativity
    • Authors: Christopher J. Richards; Ross A. Arthurs
      Abstract: The concept of matched and mismatched stereochemical pairings has been utilised extensively in organic synthesis, with the cooperativity resulting from the former enabling many reactions to proceed with high stereoselectivity. This approach was first developed to improve the diastereoselectivity of a reaction by matching the configuration of an enantiopure reagent or catalyst with the configuration of an enantiopure substrate. It has been extended to the asymmetric transformation of prochiral substrates controlled by reagents and catalysts containing two or more stereogenic centres. Matched and mismatched pairings may again be identified, with the former resulting in higher product enantioselectivity. This Minireview examines stereochemical pairings within catalysts generated from the combination of a metal with an enantiopure ligand; specifically examples in which the ligand diastereoisomers examined for cooperativity are formally the result of the addition of a chiral element to an existing enantiopure ligand. Comparison of all three ligands in each of the fifty-six examples examined reveals that, in the majority of cases, the added element of chirality increases and decreases the enantioselectivity with respect to the parent ligand. The iterative application of this effect offers a potentially powerful method for catalyst optimisation for use in asymmetric synthesis.Matched and mismatched: Examination of the results of asymmetric catalysis with metal/ligand complexes reveals that, in the majority of cases, the diastereoisomers arising from chirality element addition to an existing enantiopure ligand result in an increase and decrease in the enantiomeric excess of the product.
      PubDate: 2017-07-24T07:51:14.55325-05:0
      DOI: 10.1002/chem.201700926
       
  • Hydrogen-Bonded Open-Framework with Pyridyl-Decorated Channels:
           Straightforward Preparation and Insight into Its Affinity for Acidic
           Molecules in Solution
    • Authors: Georges Mouchaham; Nans Roques, Walid Khodja, Carine Duhayon, Yannick Coppel, Stéphane Brandès, Tamás Fodor, Michel Meyer, Jean-Pascal Sutter
      Abstract: A hydrogen-bonded open framework with pores decorated by pyridyl groups was constructed by off-charge-stoichiometry assembly of protonated tetrakis(4-pyridyloxymethyl)methane and [Al(oxalate)3]3−, which are the H-bond donor and acceptor of ionic H-bond interactions, respectively. This supramolecular porous architecture (SPA-2) has 1 nm-large pores interconnected in 3D with large solvent-accessible void (53 %). It demonstrated remarkable affinity for acidic organic molecules in solution, which was investigated by means of various carboxylic acids including larger drug molecules. Competing sorption between acetic acid and its halogenated homologues evidenced good selectivity of the porous material for the halogenated acids. The gathered results, including a series of guest@SPA-2 crystal structures and HRMAS-NMR spectra, suggest that the efficient sorption exhibited by the material relies not only on an acid–base interaction. The facile release of these guest molecules under neutral conditions makes this SPA a carrier of acidic molecules.Pore decoration: A hydrogen-bonded open framework (53 % of accessible void) with pores decorated by pyridyl groups, constructed by off-charge-stoichiometry assembly of protonated tetrakis(4-pyridyloxymethyl)methane and [Al(oxalate)3]3−, shows remarkable affinity for acidic organic molecules in solution (see figure).
      PubDate: 2017-07-24T07:51:01.621674-05:
      DOI: 10.1002/chem.201701732
       
  • Nitrato-Functionalized Task-Specific Ionic Liquids as Attractive
           Hypergolic Rocket Fuels
    • Authors: Yi Wang; Shi Huang, Wenquan Zhang, Tianlin Liu, Xiujuan Qi, Qinghua Zhang
      Abstract: Hypergolic ionic liquids (HILs) as potential replacements for hydrazine derivatives have attracted increasing interest over the last decade. Previous studies on HILs have mostly concentrated on the anionic innovations of ionic liquids to shorten the ignition delay (ID) time, but little attention has been paid to cationic modifications and their structure–property relationships. In this work, we present a new strategy of cationic functionalization by introducing the energetic nitrato group into the cationic units of HILs. Interestingly, the introduction of oxygen-rich nitrato groups into the cationic structure significantly improved the combustion performance of HILs with larger flame diameters and duration times. The density-specific impulse (ρIsp) of these novel HILs are all above 279.0 s g cm−3, much higher than that of UDMH (215.7 s g cm−3). In addition, the densities of these HILs are in the range of 1.22–1.39 g cm−3, which is much higher than that of UDMH (0.79 g cm−3), showing their higher loading capacity than hydrazine-derived fuels in a propellant tank. This promising strategy of introducing nitrato groups into the cationic structures has provided a new platform for developing high-performing HILs with improved combustion properties.Fly me to the moon: A series of nitrato-functionalized hypergolic ionic liquids were synthesized, which exhibited improved comprehensive performances including higher densities, higher density-specific impulse, larger combustion flames and longer violent combustion durations upon contact with the oxidizer white fuming nitric acid.
      PubDate: 2017-07-24T07:50:49.781042-05:
      DOI: 10.1002/chem.201701804
       
  • Photocontrol over Molecular Shape: Synthesis and Photochemical Evaluation
           of Glycoazobenzene Macrocycles
    • Authors: Guillaume Despras; Julia Hain, Sven Ole Jaeschke
      Abstract: Reversible shape switching due to external stimuli is an attractive property for the control of molecular features. Hence, we aimed at macrocycles to investigate photoswitching of molecular shape. We prepared the first carbohydrate-based macrocycles comprising a photoresponsive azobenzene hinge. These macrocycles were readily obtained by cyclization of isothiocyanate-armed bis-azobenzene glycosides with piperazine. The unprotected macrocycles exhibit favorable photochromic properties in water and DMSO. Notably, the efficient transcis isomerization results in a remarkable shape transformation of the molecule. Additionally, the structure is characterized by restricted conformational freedom of the backbone, resulting in a single main conformer in each geometrical state (trans or cis). Measurement of optical rotation values and circular dichroism spectra revealed a tremendous change in chirality upon photoisomerization, with a strong helical induction in the cis state. These findings highlight the applicability of the new macrocycles as chiroptical molecular switches.Light switch: The first photoswitchable glycomacrocycles were described and they undergo remarkable molecular shape and chirality changes upon photoisomerization of an azobenzene hinge (see figure).
      PubDate: 2017-07-24T07:50:42.338132-05:
      DOI: 10.1002/chem.201701232
       
  • The Synthesis and Evaluation of Fluoro-, Trifluoromethyl-, and
           Iodomuscimols as GABA Agonists
    • Authors: Mohd Abdul Fatah Abdul Manan; David B. Cordes, Alexandra M. Z. Slawin, Michael Bühl, Vivian W. Y. Liao, Han. C. Chua, Mary Chebib, David O'Hagan
      Abstract: Halogenated analogues of the neurotoxic alkaloid muscimol were prepared with fluorine, iodine or trifluoromethyl at the 4 position of the isoxazole ring system. These compounds were investigated as agonists for GABAA receptors. Only the C-4 fluorine-containing analogue proved to be an active compound in these assays. The fluoro analogue was less active than muscimol, however it showed differential activity between synaptic (α1β2γ2) and extrasynaptic (α4β2γ) GABAA receptors, having a similar potency to the neurotransmitter GABA for the extrasynaptic (α4β2γ) receptor.Magical Mushroom Muscimol! Muscimol is a neurotoxin and potent GABA receptor agonist from the mushroom Amanita muscaria. The first halogenated analogues (F-, I-, CF3-) of muscimol have been prepared, locating the halogen at the C-4 position. Only the mono fluoro analogue showed activity at GABA receptors, displaying a greater maximum response in comparison to GABA at the extrasynaptic GABAA receptors, but lower overall potency. Background photo by Onderwijsgekk is licensed under CC BY-SA 3.0 NL
      PubDate: 2017-07-24T07:46:10.256093-05:
      DOI: 10.1002/chem.201701443
       
  • Complexity in Acid–Base Titrations: Multimer Formation Between
           Phosphoric Acids and Imines
    • Authors: Christian Malm; Heejae Kim, Manfred Wagner, Johannes Hunger
      Abstract: Solutions of Brønsted acids with bases in aprotic solvents are not only common model systems to study the fundamentals of proton transfer pathways but are also highly relevant to Brønsted acid catalysis. Despite their importance the light nature of the proton makes characterization of acid–base aggregates challenging. Here, we track such acid–base interactions over a broad range of relative compositions between diphenyl phosphoric acid and the base quinaldine in dichloromethane, by using a combination of dielectric relaxation and NMR spectroscopy. In contrast to what one would expect for an acid–base titration, we find strong deviations from quantitative proton transfer from the acid to the base. Even for an excess of the base, multimers consisting of one base and at least two acid molecules are formed, in addition to the occurrence of proton transfer from the acid to the base and simultaneous formation of ion pairs. For equimolar mixtures such multimers constitute about one third of all intermolecular aggregates. Quantitative analysis of our results shows that the acid-base association constant is only around six times larger than that for the acid binding to an acid-base dimer, that is, to an already protonated base. Our findings have implications for the interpretation of previous studies of reactive intermediates in organocatalysis and provide a rationale for previously observed nonlinear effects in phosphoric acid catalysis.One and one is greater than two: Diphenyl phosphoric acid and quinaldine do not obey a stoichiometric acid–base reaction but form multimers. These multimers consist of more than one acid molecule and are even formed for an excess of base.
      PubDate: 2017-07-24T07:45:47.607219-05:
      DOI: 10.1002/chem.201701576
       
  • Thermally Activated Delayed Fluorescence in Cu(I) Complexes Originating
           from Restricted Molecular Vibrations
    • Authors: Guangfu Li; Roberto Nobuyasu, Bao-Hua Zhang, Yun Geng, Bing Yao, Zhi-Yuan Xie, Dong-Xia Zhu, Guo-Gang Shan, Wei-Long Che, Li-Kai Yan, Zhong-Min Su, Fernando Dias, Martin Robert Bryce
      Abstract: The mechanism of thermally activated delayed fluorescence (TADF) in molecules in aggregated or condensed solid states has been rarely studied and is not well understood. Nevertheless, many applications of TADF emitters are strongly affected by their luminescence properties in the aggregated state. In this study, two new isomeric tetradentate Cu(I) complexes which simultaneously show aggregation induced emission (AIE) and TADF characteristics are reported for the first time. We provide direct evidence that effectively restricting the vibrations of individual molecules is a key requisite for TADF in these two Cu(I) complexes through in-depth photophysical measurements combined with kinetic methods, single crystal analysis and theoretical calculations. These findings should stimulate new molecular engineering endeavours in the design of AIE-TADF active materials with highly emissive aggregated states.
      PubDate: 2017-07-24T05:20:49.43655-05:0
      DOI: 10.1002/chem.201701862
       
  • Coordination-Driven Folding in Multi-ZnII-Porphyrin Arrays Constructed on
           a Pillar[5]arene Scaffold
    • Authors: Thi Minh Nguyet Trinh; Iwona Nierengarten, Haifa Ben Aziza, Eric Meichsner, Michel Holler, Matthieu Chessé, Rym Abidi, Christian Bijani, Yannick Coppel, Emmanuel Maisonhaute, Béatrice Delavaux-Nicot, Jean-François Nierengarten
      Abstract: Pillar[5]arene derivatives bearing peripheral porphyrin subunits have been efficiently prepared from a deca-azide pillar[5]arene building block (17) and ZnII-porphyrin derivatives bearing a terminal alkyne function (9 and 16). For the resulting deca-ZnII-porphyrin arrays (18 and 20), variable temperature NMR studies revealed an intramolecular complexation of the peripheral ZnII-porphyrin moieties by 1,2,3-triazole subunits. As a result, the molecules adopt a folded conformation. This was further confirmed by UV/Vis spectroscopy and cyclic voltammetry. In addition, we have also demonstrated that the coordination-driven unfolding of 18 and 20 can be controlled by an external chemical stimulus. Specifically, addition of an imidazole derivative (22) to solution of 18 or 20 breaks the intramolecular coordination at the origin of the folding. The resulting molecular motions triggered by the addition of the imidazole ligand mimic the blooming of a flower.Molecular flowers: Deca-ZnII-porphyrin arrays constructed on a pillar[5]arene scaffold adopt a folded conformation due to intramolecular complexation of the ZnII-porphyrin moieties by 1,2,3-triazole subunits. An external chemical stimulus can trigger the unfolding of these compounds thus mimicking the blooming of a flower.
      PubDate: 2017-07-24T02:56:53.273221-05:
      DOI: 10.1002/chem.201701622
       
  • Crystallization caught in the act with terahertz spectroscopy:
           non-classical pathway for L-(+)-tartaric acid
    • Authors: Amin Soltani; Denis Gebauer, Lennart Duschek, Bernd Fischer, Helmut Cölfen, Martin Koch
      Abstract: Crystal formation is a highly debated problem. We show that the crystallization of L-(+)-tartaric acid from water follows a non-classical path involving intermediate hydrated states. Analytical ultracentrifugation indicates solution clusters of the initial stages aggregate to form an early intermediate. Terahertz spectroscopy performed during water evaporation highlights a transient increase in the absorption during nucleation. This indicates the recurrence of water molecules which are expelled from the intermediate phase. Besides, a transient resonance at 750 GHz that can be assigned to a natural vibration of large hydrated aggregates vanishes after the final crystal has formed. Furthermore, THz data reveal the vibration of nanosized clusters in the dilute solution indicated by analytical ultracentrifugation. Infrared spectroscopy and wide-angle X-ray scattering highlight that the intermediate is not a crystalline hydrate. Our results demonstrate that nanoscopic intermediate units assemble to form the first solvent-free crystalline nuclei upon dehydration.
      PubDate: 2017-07-23T21:31:19.46519-05:0
      DOI: 10.1002/chem.201702218
       
  • Non-Covalent Assembly Method that Simultaneously Endows a Liposome Surface
           with Targeting Ligands, Protective PEG Chains, and Deep-Red Fluorescence
           Reporter Groups
    • Authors: Scott K Shaw; Wenqi Liu, Seamus Brennan, Maria Betancourt-Mendiola, Bradley D. Smith
      Abstract: A new self-assembly method is used to rapidly functionalize the surface of liposomes without perturbing the membrane integrity or causing leakage of the aqueous contents. The key molecule is a cholesterol-squaraine-PEG conjugate with three important structural elements: a cholesterol membrane anchor, a fluorescent squaraine docking station that allows rapid and high-affinity macrocycle threading, and a long PEG-2000 chain to provide steric shielding of the decorated liposome. The two-step method involves spontaneous insertion of the conjugate into the outer leaflet of pre-formed liposomes followed by squaraine threading with a tetralactam macrocycle that has appended targeting ligands. A macrocycle with six carboxylates permitted immobilization of intact fluorescent liposomes on the surface of cationic polymer beads, whereas a macrocycle with six zinc(II)-dipicolylamine units enabled selective targeting of anionic membranes, including agglutination of bacteria in the presence of human cells.
      PubDate: 2017-07-23T21:31:15.849476-05:
      DOI: 10.1002/chem.201702649
       
  • Synthesis of Benzofurans and Indoles from Terminal Alkynes and
           Iodoaromatics Catalyzed by Recyclable Palladium Nanoparticles Immobilized
           on Siliceous Mesocellular Foam
    • Authors: Jan-E. Bäckvall; Alexandre Bruneau, Karl Gustafson, Ning Yuan, Ingmar Persson, Xiaodong Zou, Cheuk-Wai Tai
      Abstract: Herein, we report on the utilization of a heterogeneous catalyst, consisting of Pd nanoparticles supported on a siliceous mesocellular foam (Pd0-AmP-MCF), for the synthesis of heterocycles. Reaction of o-iodophenols and protected o-iodoanilines with acetylenes in the presence of a Pd nanocatalyst produced 2-subsituted benzofurans and indoles, respectively. In general, the catalytic protocol afforded the desired products in good to excellent yields under mild reaction conditions without the addition of ligands. Moreover, the structure of the reported Pd nanocatalyst was further elucidated with Extended X-Ray Absorption Fine Structure spectroscopy and it was proven that the catalyst can be recycled multiple times without significant loss of activity.
      PubDate: 2017-07-23T21:31:10.453493-05:
      DOI: 10.1002/chem.201702614
       
  • Divergent Regio- and Stereoselective Gold-catalyzed Synthesis of
           α-Fluorosulfones and β-Fluorovinylsulfones from Alkynylsulfones
    • Authors: Gerald Hammond; bo xu, xiaojun zeng, shiwen liu
      Abstract: We developed a widely applicable, highly efficient synthesis of α-fluorosulfone and β-fluorovinylsulfone catalyzed by gold. Starting with alkynyl sulfone 1, an [Au]/HF/N-oxide system gives α-fluorosulfone 3 via a gold carbene intermediate, and, if no N-oxide is used, direct addition of HF to 1 gives vinyl sulfone 4 via a vinylfluoro gold intermediate. Both methods have good functional group tolerance and the reactions can be conducted in ambient atmosphere.
      PubDate: 2017-07-23T21:30:59.373504-05:
      DOI: 10.1002/chem.201703179
       
  • Component-Customizable Porous Rare Earth-based Colloidal Spheres towards
           Highly Effective Catalysts and Bioimaging Applications
    • Authors: Cheng Chao Li; xianhong rui, Weifeng Wei, libao Chen
      Abstract: Multicomponent porous colloidal spheres are of interest because they not only show a combination of the properties associated with all different components, but also usually present synergy effect. However, combination of different components in a single porous sphere is still greatly challenged due to different precipitation behaviors of each component. In this work, we have developed a general synthetic route to prepare several categories of porous monodisperse RE-based colloidal spheres with customizable elemental compositions and uniform element distribution. The two-step synthetic strategy is based on the integration of coordination chemistry precipitation of RE ions and subsequent ion-exchange process, which steers clear of obstacle from differences in solubility product constant in traditional co-precipitation methods. Our approach provides a new mixing mechanism to realize homogeneous distribution of each element within porous spheres. An array of binary, ternary, and even senary RE colloidal porous spheres with diameters of 500 nm to 700 nm has been successfully synthesized. Taking advantage of their good dispersibility, porosity and customizable component, these porous RE oxide spheres show excellent catalytic activity for the reduction of 4-nitrophenol, and promising application in single-phase multifunctional bioprobes.
      PubDate: 2017-07-23T21:30:47.570585-05:
      DOI: 10.1002/chem.201702161
       
  • Control of Reversible Activation Dynamics of
           [Ru(η⁶:κ¹-C₆H₅(C₆H₄)NH₂)(XY)]n+ and the Effect of Chelate
           Ligand Variation
    • Authors: Francisco Martínez-Peña; Ana M Pizarro
      Abstract: The potential use of organometallic ruthenium complexes as anticancer drugs is well known. Here we show a family of activatable tethered ruthenium(II) arene complexes of general formula [Ru(η⁶:κ¹-C₆H₅(C₆H₄)NH₂)(XY)]n+ (closed tether-ring) bearing different chelating XY ligands (XY = aliphatic diamine, phenylenediamine, oxalato, bis(phosphino)ethane). The activation of these complexes (closed-to-open tether conversion) occurs in methanol and dimethylsulfoxide at different rates, and to different reaction extents at equilibrium. Most importantly, Ru complex activation (cleavage of the Ru-N-tether bond) occurs in aqueous solution when the proton concentration is high (upon N-tether protonation). The activation dynamics can be modulated by rational variation of the XY chelating ligand. The electron-donating capability and steric hindrance of XY have a direct impact on the Ru-N bond reactivity, with XY = N,N'-dimethyl, N,N'-diethyl, and N,N,N',N'-tetramethylethylenediamine affording complexes more prone to activation. Such activation in acidic media is fully reversible, and proton concentration also governs the deactivation rate; i.e., tether ring closure slows down as the pH decreases. Interaction of a closed-tether complex and its open-tether counterpart with 5'-GMP indicates selectivity of the active (open) complex towards nucleobase interaction. This work presents ruthenium tether complexes as exceptional pH-dependent switches with potential exploitation in cancer research.
      PubDate: 2017-07-22T02:10:22.47425-05:0
      DOI: 10.1002/chem.201701681
       
  • Non-Planar [n]Cyclo-1,8-carbazolylenes (n = 3,4,6) and
           [3]Cyclo-1,8-carbazolylenyl B, P, PO, SiPh Complexes
    • Authors: Koji Yamamoto; Palash Pandit, Shuhei Higashibayashi
      Abstract: A new family of non-planar heterocyclic molecules consisting of carbazoles was created. A bowl-shaped cyclodimer, a flake-shaped cyclotrimer, a double-decker-ring-shaped cyclotetramer and a cyclohexamer were synthesized by Ni(0)-mediated one-shot cyclo-oligomerization of 1,8-dibromocarbazole, and were named [n]cyclo-1,8-carbazolylenes (n = 3,4,6). [3]Cyclo-1,8-carbazolylene was found to act as a trivalent tridentate ligand for heteroatoms (B, P, Si), giving flake-shaped complexes. The boron derivative acted as a Lewis acid, and the tetra-coordinated complexes showed an unprecedented red-shift of absorption and emission spectra by the coordination. The synthetic method, the distorted C2 or C1 symmetric shape, the trivalent tridentate coordination ability and the kinds of introduced heteroatoms of [3]cyclo-1,8-carbazolylenes, the electronic structure, the photophysical property, and the Lewis acidity were distinct from those of related subporphyrins/subphthalocyanines.
      PubDate: 2017-07-21T23:10:59.547481-05:
      DOI: 10.1002/chem.201702853
       
  • Solvent-Free Off-On Detection of the Improvised Explosive Triacetone
           Triperoxide TATP with Fluorogenic Materials
    • Authors: Tomas Torroba; Patricia Calvo-Gredilla, Jose Garcia-Calvo, Jose V. Cuevas, Jesus-Luis Pablos, Felix C Garcia, Jose-Miguel Garcia, Nathalie Zink-Lorre, Enrique Font-Sanchis, Angela Sastre-Santos, Fernando Fernandez-Lazaro
      Abstract: We have developed a fluorogenic perylenediimide functionalized polyacrylate capable to generate color and fluorescence changes in the presence of triacetone triperoxide, TATP, an improvised explosive used in terrorist attacks, under solvent-free, solid state conditions. The material works by accumulating the volatile TATP until it reaches a threshold, therefore triggering colorimetric and fluorescent responses.
      PubDate: 2017-07-21T10:10:37.132192-05:
      DOI: 10.1002/chem.201702412
       
  • Reversible pressure-controlled depolymerization of a copper(II)-containing
           coordination polymer
    • Authors: Jack Kay Clegg; Aidan Brock, Katrina Jolliffe, Simon Parsons, Leonard Lindoy, Peter Tasker, Fraser White
      Abstract: A unique pressure-induced Cu-N bond breaking/bond forming reaction is reported. The variation of pressure on a single crystal of a one-dimensional copper(II)-containing coordination polymer (Cu2L2(1-methylpiperazine)2]n, where H2L is 1,1'-(1,3-phenylene)-bis(4,4-dimethylpentane-1,3-dione)), was monitored using single crystal X-ray diffraction with the aid of a diamond anvil cell. At a very low elevated pressure (~0.05 GPa) a remarkable reversible phase change was observed. The phase change results in the depolymerization of the material through the cleavage and formation of axial Cu-N bonds as well as "ring flips" of individual axially coordinated 1-methylpiperazine ligands. Overall, the pressure-induced phase change is associated with a surprising (and non-intuitive) shift in structure - from a 1-dimensional coordination polymer to a discrete dinuclear complex.
      PubDate: 2017-07-21T09:10:47.36964-05:0
      DOI: 10.1002/chem.201703115
       
  • Synthesis, characterization, and efficient catalytic activities of a
           nickel(II) porphyrin: remarkable solvent and substrate effects on
           participation of multiple active oxidants
    • Authors: Cheal Kim; Hye Ahn, Jeong Bae, Min Kim, Kwon Bok, Ha Jeong, Suk Lee
      Abstract: A new nickel(II) porphyrin complex, [NiII(porp)] (1) has been synthesized and characterized by 1H NMR, 13C NMR and mass spectrometry analysis. This NiII porphyrin complex 1 catalyzed quantitatively the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (MCPBA) under mild conditions. Reactivity and Hammett studies, H218O-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants NiII-OOC(O)R 2, NiIV-Oxo 3, and NiIII-Oxo 4 in olefin epoxidation reactions by nickel porphyrin complex is markedly affected by solvent polarity and concentration and type of substrate. In aprotic solvent systems, such as toluene, CH2Cl2, and CH3CN, multiple oxidants, NiII-OOC(O)R 2, NiIV-Oxo 3, and NiIII-Oxo 4, operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy-to-oxidize substrate cyclohexene, whereas NiIV-Oxo 3 and NiIII-Oxo 4 species become the common reactive oxidant for difficult-to-oxidize substrate 1-octene. In protic solvent system, a mixture of CH3CN and H2O (95/5), the NiII-OOC(O)R 2 undergoes heterolytic or homolytic O-O bond cleavage to afford NiIV-Oxo 3 and NiIII-Oxo 4 species by general-acid catalysis prior to direct interaction between 2 and olefin regardless of the type of substrate. In such case, only NiIV-Oxo 3 and NiIII-Oxo 4 species were the common reactive oxidant responsible for olefin epoxidation reactions.
      PubDate: 2017-07-21T08:10:27.382516-05:
      DOI: 10.1002/chem.201702750
       
  • Structural Insights for the Borates with Anion-templated Open-Framework
           Configuration: Asymmetric K2BaB16O26 vs Centrosymmetric K3CsB20O32 and
           Na2M2NB18O30 (M = Rb, Cs; N = Ba, Pb)
    • Authors: Miriding Mutailipu; Min Zhang, Xin Su, Zhihua Yang, Yanna Chen, Shilie Pan
      Abstract: Five new mixed-metal borates, namely, K2BaB16O26, K3CsB20O32, Na2Cs2BaB18O30, Na2Rb2PbB18O30, and Na2Cs2PbB18O30 were synthesized using the high-temperature solution method. Those structures were characterized by single-crystal X-ray diffraction, and the B-O configurations of them are shown to feature complicated three-dimensional (3D) open-framework structures with different types of channels. For all the five compounds, the frameworks can be reduced into four-connected (4-c) uninodal net with sra-, dia- and nbo-type topology by assigning the [B5O10]5- and [B3O7]5- clusters as basic nodes. The first-principles calculations show that the multiple cations in mixed-metal borates influence the ground-state electronic structures and associate optical absorptions. What's more, the theoretical calculations, synthesis, crystal structures, thermal stabilities, and infrared spectra of title compounds have also been performed.
      PubDate: 2017-07-21T07:10:29.592283-05:
      DOI: 10.1002/chem.201702891
       
  • Reactivity of NHC Alane Adducts towards N-Heterocyclic Carbenes and Cyclic
           (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al−H Bond
           Activation
    • Authors: Heidi Schneider; Andreas Hock, Rüdiger Bertermann, Udo Radius
      Abstract: The synthesis of mono-NHC alane adducts of the type (NHC)⋅AlH3 (NHC=Me2Im (1), Me2ImMe (2), iPr2Im (3 and [D3]-3), iPr2ImMe (4), Dipp2Im (10); Im=imidazolin-2-ylidene, Dipp=2,6-diisopropylphenyl) and (NHC)⋅AliBu2H (NHC=iPr2Im (11), Dipp2Im (12)) as well as their reactivity towards different types of carbenes is presented. Although the mono-NHC adducts remained stable at elevated temperatures, ring expansion occurred when (iPr2Im)⋅AlH3 (3) was treated with a second equivalent of the carbene iPr2Im to give (iPr2Im)⋅AlH(RER-iPr2ImH2) (6). In 6, {(iPr2Im}AlH} is inserted into the NHC ring. In contrast, ring opening was observed with the sterically more demanding Dipp2Im with the formation of (iPr2Im)⋅AlH2(ROR-Dipp2ImH2)H2Al⋅(iPr2Im) (9). In 9, two {(iPr2Im)⋅AlH2} moieties stabilize the ring-opened Dipp2Im. If two hydridic sites are blocked, the adducts are stable with respect to further ring expansion or ring opening, as exemplified by the adducts (iPr2Im)⋅AliBu2H (11) and (Dipp2Im)⋅AliBu2H (12). The adducts (NHC)⋅AlH3 and (iPr2Im)⋅AliBu2H reacted with cAACMe by insertion of the carbene carbon atom into the Al−H bond to give (NHC)⋅AlH2/iBu2(cAACMeH) (13–18) instead of ligand substitution, ring-expansion, or ring-opened products.Versatile alanes: (NHC)⋅AlH3 and (NHC)⋅AliBu2H have been synthesized and treated with N-heterocyclic carbenes and cyclic (alkyl)(amino)carbenes (cAACs). The reactions were found to proceed by NHC ring expansion, NHC ring opening, or cAAC-mediated Al−H bond cleavage (see Scheme). Mechanistic considerations are presented.
      PubDate: 2017-07-21T04:32:03.541045-05:
      DOI: 10.1002/chem.201702166
       
  • Rhodium-Catalyzed Silylative and Germylative Cyclization with
           Dehydrogenation Leading to 9-Sila- and 9-Germafluorenes: A Combined
           Experimental and Computational Mechanistic Study
    • Authors: Masahito Murai; Ryo Okada, Sobi Asako, Kazuhiko Takai
      Abstract: Stoichiometric amounts of oxidants are widely used as promoters (hydrogen acceptors) in dehydrogenative silylation of C−H bonds. However, the present study demonstrates that silylative and germylative cyclization with dehydrogenation can proceed efficiently, even without hydrogen acceptors. The combination of [RhCl(cod)]2 and PPh3 was effective for both transformations, and allowed a reduction in reaction temperature compared with our previous report. Monitoring of the reactions revealed that both transformations had an induction period for the early stage, and that the rate constant of dehydrogenative germylation was greater than that of dehydrogenative silylation. Competitive reactions in the presence of 3,3-dimethyl-1-butene indicated that the ratio of dehydrogenative metalation and hydrometalation was affected by reaction temperature when a hydrosilane or hydrogermane precursor was used. Further mechanistic insights of oxidant-free dehydrogenative silylation, including the origin of these unique reactivities, were obtained by density functional theory studies.Activating the unactivated: The combination of [RhCl(cod)]2 and PPh3 is used to catalyze the oxidant-free dehydrogenative silylation and germylation of unactivated C(sp2)−H bonds under neutral conditions (see scheme). The experimentally obtained unique reactivity is supported by the results of theoretical calculations, and a plausible reaction mechanism, including insights into why the current transformation does not require hydrogen acceptors and heteroatom-containing directing groups, is proposed.
      PubDate: 2017-07-21T04:30:43.989756-05:
      DOI: 10.1002/chem.201701579
       
  • Synthesis and Characterization of
           2,2′-Dinitramino-5,5′-bi(1-oxa-3,4-diazole) and Derivatives as
           Economic and Highly Dense Energetic Materials
    • Authors: Tobias S. Hermann; Konstantin Karaghiosoff, Thomas M. Klapötke, Jörg Stierstorfer
      Abstract: 2,2′-Dinitramino-5,5′-bi(1-oxa-3,4-diazole) (2) is a new highly energetic material with superior calculated detonation performance in comparison to cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX) and penta-erythritoltetranitrate (PETN) and can be prepared by an economical and practical two-step synthesis. The starting material 2,2′-diamino-5,5′-bi(1-oxa-3,4-diazole) (1) is synthesized by the reaction of oxalyl dihydrazide with cyanogen bromide. Nitration of 1 yields the title compound in perfect yield and purity. The combination of its high density of 1.986 g cm−3, the positive heat of formation (+190 kJ mol−1), and a slightly positive oxygen balance (+6.2 %) results in ideal calculated detonation parameters (e.g. detonation velocity 9296 m s−1). The sensitivities toward impact and friction can be adjusted by deprotonation and formation of corresponding nitrogen-rich salts, for example, ammonium (3), hydroxylammonium (4), and guanidinium (5) salts.A new highly energetic material, 2,2′-dinitramino-5,5′-bi(1-oxa-3,4-diazole), was prepared by an economical and practical two-step synthesis. The combination of its high density of 1.986 g cm−3, the positive heat of formation (+190 kJ mol−1), and a slightly positive oxygen balance (+6.2 %) resulted in ideal calculated detonation parameters (e.g. detonation velocity 9296 m s−1).
      PubDate: 2017-07-21T04:25:51.230494-05:
      DOI: 10.1002/chem.201702191
       
  • Smart construction of nitrogen-doped carbon coated MoSe2 microspheres with
           enhanced performance for lithium storage
    • Authors: Wangjia Tang; Dong Xie, Tong Shen, Xiuli Wang, Donghuang Wang, Xuqing Zhang, Xinhui Xia, Jianbo Wu, Jiangping Tu
      Abstract: Exploring advanced anode materials with highly reversible capacity have gained great interests for large-scale lithium storage. Herein, a facile two-step method is developed to synthesize nitrogen-doped carbon coated MoSe2 microspheres via hydrothermal plus thermal polymerization. The MoSe2 microspheres composed of interconnected nanoflakes are homogeneously coated by thin nitrogen-doped carbon (N-C) layer. As an anode for lithium ion batteries, the MoSe2/N-C composite shows better reversibility, smaller polarization and higher electrochemical reactivity as compared to the unmodified MoSe2 microspheres. The MoSe2/N-C electrode delivers a high specific capacity of 698 mAh g1 after 100 cycles at a current density of 100 mA g1 and good high rate performance (471 mAh g1 at a high current density of 2000 mA g1). The improved electrochemical performance is attributed to the conductive N-C coating and hierarchical microsphere structure with fast ion/electron transfer characteristics.
      PubDate: 2017-07-21T04:10:28.236756-05:
      DOI: 10.1002/chem.201702840
       
  • The Unusual Role of the Aromatic Solvent in Single Site Al(I) Chemistry:
           Insights from Theory
    • Authors: Shailja Jain; Kumar Vanka
      Abstract: The single site activation of strong σ bonds (such as that of H-H, P-H and N-H) remains a significant challenge in main group chemistry, with only a few cases reported to date. In this regard, recent exciting experiments done with Al(I) complexes hold significance, because they, too, have been seen to activate a variety of strong σ bonds. Such chemistry is generally seen to occur in aromatic solvents. The current computational studies with density functional theory (DFT) reveal the interesting reason for this: it is seen that an explicit aromatic solvent molecule acts as a catalyst by converting the Al(I) complex to Al(III) during the process. Different cases of σ bond activation by Al(I) complexes have been investigated and the efficiency for the H-X (X=H, NHtBu, PPh2) bond activation in the presence of an explicit benzene solvent molecule has been seen to be orders of magnitude higher than in its absence. The current work therefore reveals the chemistry of Al(I) complexes to be richer and more complex than realized to date, and shows it to be dependent on metal-solvent cooperativity, the first known example of its kind in main group chemistry.
      PubDate: 2017-07-21T03:10:55.485874-05:
      DOI: 10.1002/chem.201701642
       
  • Two Structurally Characterized Conformational Isomers with Different
           C−P Bonds
    • Authors: Sudipta Roy; Kartik Chandra Mondal, Subrata Kundu, Bin Li, Christian J. Schürmann, Sayan Dutta, Debasis Koley, Regine Herbst-Irmer, Dietmar Stalke, Herbert W. Roesky
      Abstract: The cyclic alkyl(amino) carbene (cAAC) bonded chlorophosphinidene (cAAC)P−Cl (2/2') was isolated from the direct reaction between cAAC and phosphorus trichloride (PCl3). Compound 2/2' has been characterized by NMR spectroscopy and mass spectrometry. 31P NMR investigations [δ≈160 ppm (major) and δ≈130 ppm (minor)] reveal that there are two different P environments of the P−Cl unit. X-ray single-crystal determination suggests a co-crystallization of two conformational isomers of (cAAC)P−Cl (2/2'); the major compound possessing a cAAC−PCl unit with CcAAC−P 1.75 Å. This C−P bond length is very close to that of (NHC)2P2 [NHC=N-heterocyclic carbene]. The residual density can be interpreted as a conformational isomer with a shorter CcAAC−P bond similar to a non-conjugated phosphaalkene [R−P=CR2]. Our study shows an unprecedented example of two conformational isomers with different Ccarbene−element bonds. Additionally, Br (3c/3c'), I (4c/4c'), and H (5c/5c') analogues [(Me2-cAAC)P−X; X=Br (3), I (4), H (5)] of 2c/2c'[(Me2-cAAC)P−Cl] were also synthesized and characterized by NMR spectroscopy suggesting similar equilibrium in solution. The unique property of cAAC and the required electronegativity of the X (X=Cl, Br, I, and H) atom play a crucial role for the existence of the two isomers which were further studied by theoretical calculations.An unprecedented dual bonding situation is demonstrated by the cyclic alkyl(amino) carbene (cAAC) bound chlorophosphinidene (cAAC)P-Cl (2/2'). The conformational form with a C−P bond length of 1.75 Å is the major conformer (2) possessing a donor–acceptor coordinate (CcAACP−Cl) bond. The minor conformer (2') with a C−P bond length of 1.61 Å contains a double bond (CcAAC=P−Cl). The presence of two resonance forms has been confirmed by NMR studies. The bonding situation and stability of 2/2' have been studied by theoretical calculations.
      PubDate: 2017-07-21T02:31:41.7126-05:00
      DOI: 10.1002/chem.201702870
       
  • 2,6-Bis(diazaboryl)pyridine: A Superbasic Sterically Demanding Pyridine
           Ligand.
    • Authors: Jan Schröder; Daniel Himmel, Tobias Böttcher
      Abstract: Herein a convenient one-pot route to a sterically demanding superbasic pyridine is presented. Functionalization of the 2- and 6-positions with the strongly σ-donating boryl-groups shifts the calculated gas phase basicity of the pyridine nitrogen atom to 1012 kJ mol−1, which outperforms the “proton sponge” 1,8-bis(dimethylamino)naphthalene (996 kJ mol−1). The diazaboryl groups are oriented orthogonally to the pyridine ring and do not block the N-position, which resembles the geometry of commonly used N-heterocyclic carbenes. This allows the substituted pyridine to be used as a neutral N-donor ligand in coordination chemistry that is demonstrated herein with the Lewis adducts of haloboranes. Contrary to NHCs, which can form extraordinarily stable adducts, the pyridine ligand is intended to act as a weaker-coordinating alternative and could allow for alternative ligand chemistry.A superbasic pyridine ligand: A pyridine substituted with diazaboryl groups at the 2- and 6-positions is presented. The strongly σ-donating diazaboryl groups increase the energy of the pyridine nitrogen lone pair and make it become more basic than the “proton sponge” 1,8-bis(dimethylamino)naphthalene. The N-position is not blocked, but is sterically protected, which renders this pyridine a promising ligand for coordination chemistry.
      PubDate: 2017-07-21T02:25:46.447347-05:
      DOI: 10.1002/chem.201702890
       
  • N-Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic
           Activity in Ammonia Borane Dehydrogenation
    • Authors: Micheal Gediga; Christoph M. Feil, Simon H. Schlindwein, Johannes Bender, Martin Nieger, Dietrich Gudat
      Abstract: A neutral N-heterocyclic phosphenium complex of manganese was synthesised by a metathesis approach and characterised by IR, NMR, and XRD studies. The short P−Mn distance suggests a substantial metal–ligand double bond character. Reaction with a hydride produced an anionic phosphine complex, which was also characterised by IR and NMR spectroscopy and, after anion exchange, a single-crystal XRD study. Protonation of the anion occurs at the metal to yield a neutral phosphine metal carbonyl hydride, which releases dihydrogen upon irradiation with UV light. These reactions confirm the electrophilic nature of the phosphenium ligand and suggest that the title complex might undergo reactions displaying metal–ligand cooperativity. Surprisingly, reaction with ammonia borane (AB) did not proceed under transfer hydrogenation of the Mn=P double bond but through the catalytic dehydrogenation of AB. The phosphenium complex behaves here as a class II catalyst, which dehydrogenates AB to NH2BH2 that was trapped with cyclohexene. Computational model studies led to the identification of two possible catalytic cycles, which differ in the regioselectivity of the initial AB activation step. In one case, the activation proceeds as cooperative transfer hydrogenation of the Mn=P bond, whereas in the other case a H+/H− pair is transferred to the phosphorus atom and a nitrogen atom of the phosphenium unit, resulting in a ligand-centred reaction in which the metal fragment acts merely as stabilising substituent. Unexpectedly, this pathway, which constitutes a new reaction mode for phosphenium complexes, seems to be better in accord with experimental findings on the course of the catalysis.Better than ever: A neutral N-heterocyclic phosphenium complex of manganese reacts upon sequential transfer of a H−/H+ pair under formal hydrogenation of the Mn=P double bond and may accomplish the catalytic dehydrogenation of ammonia borane. Computational studies indicate that this reaction illustrates a new scheme of metal–ligand cooperativity in which the ligand adopts the role of the Lewis acidic reaction centre (see scheme).
      PubDate: 2017-07-21T02:25:40.403267-05:
      DOI: 10.1002/chem.201701442
       
  • Vanadium Hydroxide Cluster Ions in the Gas Phase: Bond-Forming Reactions
           of Doubly-Charged Negative Ions by SO2-Promoted V−O Activation
    • Authors: Anna Troiani; Marzio Rosi, Stefania Garzoli, Chiara Salvitti, Giulia de Petris
      Abstract: Doubly-charged vanadium cluster anions undergo fast and efficient bond-forming reactions, producing singly-charged products. The charge separation process does not occur by exothermic electron transfer or fragmentation, but by reaction with sulfur dioxide, which promotes the breakage of strong V−O bonds and formation of new V−O and S−O bonds. More information can be found in the Communication by A. Troiani, G. de Petris et al. (
      DOI : 10.1002/chem.201702165).
      PubDate: 2017-07-21T02:25:30.480848-05:
       
  • Hierarchical Hybrids Integrated by Dual Polypyrrole-Based Porous Carbons
           for Enhanced Capacitive Performance
    • Authors: Zhiwei Li; Nannan Chen, Hongyu Mi, Junhong Ma, Yahong Xie, Jieshan Qiu
      Abstract: Architectural design of nitrogenous polymer-based carbons represents a facile and efficient strategy in performance improvement because of their morphological diversity, tailorability, and N-containing structure. In this research, polypyrrole-derived porous carbons (A-PCS and A-PCT) in zero- and one-dimensional (0D and 1D) forms are first integrated to nitrogen-doped hierarchically porous A-PCS/PCT hybrids through an easy multi-step method. This integration, along with chemical activation, prevents serious agglomeration of carbon particles or tubes and creates a through-connected porous network structure, leading to the improved textural properties (high surface area of 1684 m2 g-1, high pore volume of 1.57 cm3 g-1, and hierarchical porosity). Thus, A-PCS/PCT hybrids in a three-electrode setup reach high specific capacitances of 224 and 206 F g-1 at 1 and 20 A g-1 with high rate capability (92% capacitance retention). Symmetrical supercapacitor with A-PCS/PCT electrodes presents the highest power and energy densities of 12.6 kW kg-1 and 8.58 Wh kg-1, and exceptional cyclic life and stability with 92.4% retention up to 20000 cycles. The study on conductive polymer-based hybrid material may guide many designs of architectures with new structures for the applications of energy storage and conversion technologies.
      PubDate: 2017-07-21T01:11:42.405615-05:
      DOI: 10.1002/chem.201702544
       
  • Discrepancy between experiment and theoretical predictions of the
           adiabaticity of Ti+ + CH3OH
    • Authors: Brendan Sweeney, Shaun Gerald Ard, David McDonald II, Oscar Martinez Jr; Albert Viggiano, Nicholas Shuman
      Abstract: The reaction between Ti+ and methanol (CH3OH) is a model system for competition between activation of C-O, C-H, and O-H bonds and of the role of excited electronic pathways in catalytic processes. Herein, we use experimental kinetics, quantum chemical calculations, and statistical modeling to identify the critical features of the reaction's potential energy surface. Experimental kinetics data between 300 and 600 K shows the reaction largely proceeds through C-O bond activation, yielding TiOH+ and TiO+. Products of the O-H activation pathway, TiOCH2+ and TiOCH3+ are minor, while C-H bond activation is not observed at thermal energies. Statistical modeling well-reproduces the experimental results and offers insight into the reaction mechanism. Notably, efficient spin-crossing along the C-O activation pathway is required to produce the observed product distribution, in contrast to a previous estimate of inefficient crossing based on calculation of a small spin-orbit coupling constant. This discrepancy highlights a potential limitation of simple models within the Landau-Zener framework, which are commonly used to calculate surface-crossing probabilities in reactive systems.
      PubDate: 2017-07-20T21:16:47.135344-05:
      DOI: 10.1002/chem.201703002
       
  • Tuning the Effects of Bacterial Membrane Permeability through
           Photo-Isomerization of Antimicrobial Cationic Amphiphiles
    • Authors: Micha Fridman; Joana Salta, Raphael I. Benhamou, Ido M. Herzog
      Abstract: Several last resort classes of antimicrobial drugs act by permeabilizing cell membranes. Here we demonstrate that insertion of a photo-isomerizable lipid into antimicrobial cationic amphiphiles can modify the intensity of their membrane-permeabilizing activity not only by their concentration but also through light-irradiation. We characterized the photo-isomerization effects of two types of cationic amphiphiles on their bacterial membrane permeabilizing activity and showed that while one photo-isomer inhibited cell growth and division, the other photo-isomer led to a rapid and lethal bacterial membrane-disrupting effect. We demonstrated that the switch from "on" to "off" can be obtained by either the cis- or trans-isomer depending on the bacterial strain and the type of cationic head-group of these membrane disruptors. These photo-isomerizable cationic amphiphiles offer a novel tool for research and industrial applications that require light-controlled membrane permeabilization.
      PubDate: 2017-07-20T09:11:47.768434-05:
      DOI: 10.1002/chem.201703010
       
  • Tailored band gaps in sulphur and nitrogen containing porous
           donor-acceptor polymers (SNPs)
    • Authors: Dana Schwarz; Yaroslav S. Kochergin, Amitava Acharja, Arun Ichangi, Maksym V. Opanasenko, Jiří Čejka, Uwe Lappan, Pal Arki, Junjie He, Johannes Schmidt, Petr Nachtigall, Arne Thomas, Michael Janus Bojdys
      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 due to the fundamentally different chemistry of the donor- and acceptor-subunits. We present a family of sulphur and nitrogen containing porous polymers (SNPs) that are obtained via Sonogashira-Hagihara cross-coupling and that combine electron-withdrawing triazine (C3N3) and electron donating, sulphur-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 we report one of the highest photocatalytic hydrogen evolution rates for a cross-linked polymer without Pt co-catalyst (194 µmol h-1 g-1).
      PubDate: 2017-07-20T08:10:53.319928-05:
      DOI: 10.1002/chem.201703332
       
  • Total synthesis of the marine natural product hemiasterlin via
           organocatalyzed α-hydrazination
    • Authors: Thomas Lindel; Jan Hendrik Lang, Peter G. Jones
      Abstract: An efficient synthesis of the potently cytotoxic marine peptide hemiasterlin is presented. The tetramethyltryptophan moiety is assembled via tert.-prenylation of indole, followed by the high-yielding, organocatalyzed α-hydrazination of a sterically congested aldehyde with excellent enantioselectivity. BEP-mediated peptide coupling completes the synthesis, being the first approach that does not employ chiral auxiliaries. A novel phenonium-type rearrangement of the indole system occurred when subjecting dihydroxylated 3-tert.-prenylindole to Mitsunobu conditions.
      PubDate: 2017-07-20T06:11:43.743848-05:
      DOI: 10.1002/chem.201702812
       
  • A Computational Study of the Intermolecular [2+2+2] Cycloaddition of
           Acetylene and C60 Catalyzed by Wilkinson's Catalyst
    • Authors: Albert Artigas; Agustí Lledó, Anna Pla-Quintana, Anna Roglans, Miquel Solà
      Abstract: The functionalization of fullerenes helps modulating their electronic and physicochemical properties, generating fullerene derivatives with promising features for practical applications. In this work, we use the density functional theory to explore the attachment of a cyclohexadiene ring to C60 via a Rh-catalyzed intermolecular [2+2+2] cycloaddition of C60 and acetylene. We analyze all potential reaction paths to conclude that the [2+2+2] cycloaddition of C60 and two acetylene molecules catalyzed by RhCl(PPh3)3 yielding a cyclohexadiene ring fused to a [6,6] bond of C60 is energetically feasible.
      PubDate: 2017-07-20T06:11:17.369894-05:
      DOI: 10.1002/chem.201702494
       
  • Inversion of cpADH5 Enantiopreference and Altered Chain Length Specificity
           for methyl 3-hydroxyalkanoates
    • Authors: Yunus Ensari; Gaurao V. Dhoke, Mehdi D. Davari, Marco Bocola, Anna Joelle Ruff, Ulrich Schwaneberg
      Abstract: Expanding the substrate scope of enzymes opens up new routes for synthesis of valuable chemicals. Ketone-functionalized fatty acid derivatives and corresponding chiral alcohols are valuable building blocks for the synthesis of a variety of chemicals including pharmaceuticals. The alcohol dehydrogenase from Candida parapsilosis (cpADH5) catalyzes the reversible oxidations of chiral alcohols and has a broad substrate range; a challenge for cpADH5 is to convert alcohols with small substituents (methyl or ethyl) next to the oxidized alcohol moiety.Molecular docking studies revealed that W286 is located in the small binding pocket and limits the access to substrates that contain aliphatic chains longer than ethyl substituent. In the current manuscript, we report that positions L119 and W286 are key residues to boost oxidation of medium chain methyl 3-hydroxy fatty acids; interestingly the enantiopreference toward methyl 3-hydroxybutyrate was inverted. Kinetic characterization of W286A showed a 5.5 fold increase of Vmax and a 9.6 fold decrease of Km values toward methyl 3-hydroxyhexanoate (Vmax: 2.48 U/mg and Km: 4.76 mM). Simultaneous saturation at positions 119 and 286 library yielded a double mutant (L119M/W286S) with more than 30 fold improved activity toward methyl 3-hydroxyoctanoate (WT: no conversion; L119M/W286S: 30 % ) and inverted enantiopreference (S-enantiomer ≥ 99 % activity decrease and R-enantiomer> 20 fold activity improvement) toward methyl 3-hydroxybutyrate.
      PubDate: 2017-07-20T05:11:34.97381-05:0
      DOI: 10.1002/chem.201702581
       
  • Iodine-promoted Semmler-Wolff reactions: step economic access to
           meta-substituted primary anilines via aromatization
    • Authors: Shi-Ke Wang; Xia You, Da-Yuan Zhao, Neng-Jie Mou, Qun-Li Luo
      Abstract: An atom and step economic access to unprotected meta-substituted primary anilines was disclosed via the Semmler-Wolff reaction promoted by molecular iodine, in which noble metal catalysts and inert atmosphere are unnecessary while the forcing reaction conditions and the lengthy synthesis can be avoided. The synthetic utility of this approach is evident in the de novo syntheses of three bioactive molecules with good total yields.
      PubDate: 2017-07-20T00:20:39.298325-05:
      DOI: 10.1002/chem.201701712
       
  • Synthetic Analogs of Nitrogenase Metallocofactors: Challenges and
           Developments
    • Authors: Nathaniel Sickerman; Kazuki Tanifuji, Yilin Hu, Markus Walter Ribbe
      Abstract: Nitrogenase is the only known biological system capable of reducing N2 to NH3, which is a critical component of bioavailable nitrogen fixation. Since the discovery of discrete iron-sulfur metalloclusters within the nitrogenase MoFe protein, synthetic inorganic chemists have sought to reproduce the structural features of these clusters in order to understand how they facilitate the binding, activation and hydrogenation of N2. Through the decades following the initial identification of these clusters, significant progress has been made to synthetically replicate certain compositional and functional aspects of the biogenic clusters. Although much work remains to generate synthetic iron-sulfur clusters that can reduce N2 to NH3, the insights borne from past and recent developments are discussed in this concept article.
      PubDate: 2017-07-20T00:10:43.445214-05:
      DOI: 10.1002/chem.201702496
       
  • N/S co-doped 3D porous carbon nanosheet networks enhancing anode
           performance of sodium ion batteries
    • Authors: Lei Zou; Yanqing Lai, Hongxing Hu, Mengran Wang, Kai Zhang, Peng Zhang, Jing Fang, Jie Li
      Abstract: A facile and scalable method has been realized for the in-situ synthesis of N/S co-doping 3D porous carbon nanosheet networks (NSPCNN) as sodium-ion battery anode material. During the synthesis, NaCl is used for a template to prepare porous carbon nanosheet networks. In the resultant architecture, the unique 3D porous architecture ensures large specific surface area and fast diffusion path of both electrons and ions. Meanwhile, the import of N/S produces abundant defects, increased interlayer space, more active sites and high electronic conductivity. Finally, the obtained products deliver a high specific capacity and excellent long-term cycling performance. Specially, it manifests a capacity of 336.2 mAh g-1 at 0.05A g-1 and as large as 214.9 mA h g-1 after 2000 charge/discharge cycles at 0.5 A g-1. This material has great prospect in future application of scalable, low cost and environmentally friendly sodium ion batteries.
      PubDate: 2017-07-19T13:10:35.999909-05:
      DOI: 10.1002/chem.201702182
       
  • Testing limits of BOPHY platform: preparation, characterization, and
           theoretical modeling of BOPHYs BOPHYs with electron-withdrawing groups at
           b-pyrrolic and bridging positions
    • Authors: Victor N. Nemykin; Yuriy V. Zatsikha, Dion B. Nemez, Rebecca L. Davis, Simarpreet Singh, David E. Herbert, Alex J. King, Christopher J. Ziegler
      Abstract: Several BOPHY derivatives with and without ferrocene fragments and with electron-withdrawing carbethoxy groups appended to the -pyrrolic positions have been prepared and characterized by NMR, UV-Vis-NIR, APCI MS, and fluorescence spectroscopy as well as X-ray crystallography. The redox properties of new BOPHYs were probed by electrochemical (CV and DPV) and spectroelectrochemical methods. In attempt for the preparation of the BOPHY derivatives with cyano group at bridging position using similar to recently communicated BODIPY cyanation approach (Chem. Commun. 2016, 52, 11563-11566 and ChemistrySelect, 2016, 1, 1462-1466), adducts of the nucleophilic attack of the cyanide anion on the bridging position in BOPHY have been isolated and characterized by spectroscopic methods. Oxidation of such adducts, however, resulted in formation of either starting BOPHYs or partial extrusion of the BF2 fragment from the BOPHY core, which was confirmed by spectroscopy and X-ray crystallography. DFT and TDDFT calculations on all target materials correlate well with the experimental data and are suggestive of the dramatic reduction of the nitrogen atom basicity at the hydrazine bridge of BOPHY upon introduction of the cyano group at the bridging carbon atom.
      PubDate: 2017-07-19T12:10:45.89021-05:0
      DOI: 10.1002/chem.201702597
       
  • Construction of all-solid-state batteries based on sulfur-graphene
           composite and Li9.54Si1.74P1.44S11.7Cl0.3 solid electrolyte
    • Authors: Ruochen Xu; Zhang Wu, Shenzhao Zhang, Xiuli Wang, Yan Xia, Xinhui Xia, Xiaohua Huang, Jiangping Tu
      Abstract: Herein we report an effective way for construction of all-solid-state lithium-sulfur batteries (LSBs) with sulfur/reduced graphene oxide (rGO) and Li9.54Si1.74P1.44S11.7Cl0.3 solid electrolyte. In the composite cathode, the Li9.54Si1.74P1.44S11.7Cl0.3 powder is homogeneously mixed with the S/rGO composite to enhance the ionic conductivity. Coupled with metallic Li anode and solid electrolyte, the designed S/rGO-Li9.54Si1.74P1.44S11.7Cl0.3 composite cathode exhibits a high specific capacity and good cyclic stability. A high initial discharge capacity of 969 mAh g−1 is achieved at a current density of 80 mA g−1 at room temperature and the cell retains a reversible capacity over 827 mAh g−1 after 60 cycles. The enhanced performance is attributed to the intimate contact between the S/rGO and Li9.54Si1.74P1.44S11.7Cl0.3 electrolyte, and high electrical conductivity of rGO and high ionic conductivity of the solid electrolyte.
      PubDate: 2017-07-19T09:10:42.286623-05:
      DOI: 10.1002/chem.201703116
       
  • Assessing Guest Molecule Diffusion in Heterogeneous Powder Samples of
           Metal-Organic Frameworks through PFG-NMR
    • Authors: Roland Thoma; Jörg Kärger, Nader de Sousa Amadeu, Sandra Nießing, Christoph Janiak
      Abstract: Investigation of guest diffusion in porous metal-organic frameworks (MOFs) is of major importance since many porosity-related properties of MOFs are influenced by diffusion effects. The diffusion of dimethylsulfoxide (DMSO) in the metal-organic framework (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, 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 ms up 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 sub¬diffusive, with a time exponent κ = 0.8 (rather than 1 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 novel potentials for application to systems of intricate topology.
      PubDate: 2017-07-19T07:11:46.837765-05:
      DOI: 10.1002/chem.201702586
       
  • Alkoxides of Trivacant Lacunary Polyoxometalates
    • Authors: Takuo Minato; Kosuke Suzuki, Kazuya Yamaguchi, Noritaka Mizuno
      Abstract: Lacunary polyoxometalates (POMs) are useful rigid multidentate inorganic ligands to construct multinuclear metal oxo clusters and inorganic-organic hybrid materials. However, the use of multivacant lacunary POMs often suffers from their undesired condensation reactions at the highly reactive vacant sites. Herein, we report the introduction of alkoxy protecting groups into the vacant sites of lacunary POMs in organic media for the first time. By reacting organic solvent-soluble trivacant lacunary Keggin-type POMs with methanol, six methoxy groups were successfully introduced into the vacant sites, resulting in the formation of the alkoxides (Ix-OMe; X = Si, Ge). These methoxy groups could protect the reactive vacant sites and suppress the undesired dimerization reaction into the corresponding α-Dawson-type POMs. Since the introduced monodentate methoxy groups could easily be dissociated by hydrolysis, ISi-OMe could be utilized as the precursor for the synthesis of metal-substituted POMs. In addition, by using pentaerythritol as the multidentate alkoxy ligand, the monomeric alkoxide (ISi-PE) was successfully synthesized. In particular, these multidentate alkoxy groups showed high resistance against hydrolysis. Moreover, by reacting ISi-PE with trivacant lacunary Keggin-type POMs, we successfully synthesized the dimeric inorganic-organic-inorganic hybrid structures (IISiX-PE; X = Si, Ge) with the same or different heteroatoms (Si and Ge).
      PubDate: 2017-07-19T06:12:20.372729-05:
      DOI: 10.1002/chem.201702883
       
  • Synthesis of cyclic peptide mimetics via the successive ring expansion of
           lactams
    • Authors: Thomas C Stephens; Mahendar Lodi, Andrew M Steer, Yun Lin, Matthew T Gill, William Paul Unsworth
      Abstract: A successive ring expansion protocol is reported that enables the controlled insertion of natural and non-natural amino acid fragments into lactams. Amino acids can be installed into macrocycles via an operationally simple and scalable iterative procedure, without the need for high dilution. This method is expected to be of broad utility, especially for the synthesis of medicinally important cyclic peptide mimetics.
      PubDate: 2017-07-19T05:10:41.546679-05:
      DOI: 10.1002/chem.201703316
       
  • Functionalized acupuncture needle as Surface-enhanced Resonance Raman
           Spectroscopy sensor for rapid and sensitive detection of dopamine in serum
           and cerebrospinal fluid
    • Authors: Liangbao Yang; pan li, binbin zhou, xiaomin cao, xianghu tang, ling hu, jinhuai liu
      Abstract: It is challenging to develop a robust sensor for simple and rapid operation and sensitive detection of neurotransmitter in complex specimen. In the present work, the ferric-citrate-functionalized Au nanoparticles [Au NPs/CA-Fe(III)] is utilized to develop a facile sensor based on Surface-enhanced Resonance Raman spectroscopy (SERRS) for sensitive detection of dopamine (DA). The sensor is prepared by decorating acupuncture needle with Au NPs, which enables the sufficient SERS enhancement. CA-Fe(III) structure was highly sensitive and selective to DA with formation of CA-Fe(III)-DA resonant structure, indicating the advantages of capturing, carrying and separating DA molecules from complicated samples with simple operation. Furthermore, the practical application of fabricated sensor is validated by detection of analyte DA in the pretreated serum and acupuncture-mice cerebrospinal fluid (CSF) sample with 0.1 nM and 2.5 nM levels of detection limits, respectively. The developed sensing strategy on acupuncture needle has potential benefits for sensitive detection and qualitative identification of biological basis involving DA molecule.
      PubDate: 2017-07-19T04:16:02.214914-05:
      DOI: 10.1002/chem.201702607
       
  • Mesoporous Tin-based Oxide Nanospheres and Graphene Composites as Advanced
           Anodes for Lithium Ion Half/Full and Sodium Ion Batteries
    • Authors: Yanyan He; Aihua Li, Caifu Dong, Chuanchuan Li, Liqiang Xu
      Abstract: The large volume variations of tin-based oxides hinder their extensive applications in the field of lithium ion batteries (LIBs). In this study, structure design, hybrid fabrication and carbon coating approaches have been simultaneously adopted to relieve these weaknesses. Therefore, uniform mesoporous NiO/SnO2@rGO, Ni-Sn oxide@rGO and SnO2@rGO nanosphere composites have been selectively fabricated. Among them, the obtained NiO/SnO2@rGO composite exhibits high capacity 800 mAh g-1 at 1000 mA g−1 after 400 cycles. The preliminary electrochemical mechanism of NiO/SnO2 as an anode for LIBs has been investigated by ex-situ XRD pattern analysis. Furthermore, the NiO/SnO2@rGO-LiCoO2 lithium ion full cells shows high capacity of 467.8 mA g-1 at 500 mA g-1 after 100 cycles. It is worth noting that the NiO/SnO2@rGO composite also demonstrates good performance when investigated as anode for sodium ion batteries (SIBs). It is believed that the unique mesoporous nanospherical framework, synergistic effects of different components and uniform rGO wrapping of NiO/SnO2 shorten the Li+ ion diffusion pathways, maintain sufficient contact between active material and electrolyte, mitigate volume changes and finally improve the electrical conductivity of the electrode.
      PubDate: 2017-07-19T02:35:40.738927-05:
      DOI: 10.1002/chem.201702225
       
  • Manipulation of inorganic atomic-layer networks by solution phase
           co-assembly
    • Authors: Yajiao Hao; Lin Yu, Chuying Dai, Song Li, Yang Yu, Bo Ju, Minjie Li, Sean Xiao-An Zhang
      Abstract: Homogeneous two-dimensional (2D) lamellar assemblies of Au(I)-thiolate coordination polymer (ATCP) have been achieved with double-ligand co-assembly. The orbital levels and the bandgap of the 2D Au(I)-S network in the centre of the lamellae can be continuously tuned by the capping ligands on both sides, demonstrating a new type of inorganic-organic composite semiconductor, whose band structure can be easily tuned by low-temperature solution-phase co-assembly. What's more, the chemical reactivity of these ATCP co-assemblies is also proved to be largely dependent on the organic substituents, showing well-tunable transforming rates to gold nanoparticles. As far as we know, it is the first work to demonstrate how organic substituent can continuously tune the electron band structure and chemical reactivity of inorganic atomic-layers of semiconductor with co-assembly.
      PubDate: 2017-07-18T22:30:38.050672-05:
      DOI: 10.1002/chem.201703200
       
  • Tunable biogenic manganese oxides
    • Authors: Alexandr Nikolaevich Simonov; Rosalie K. Hocking, Lizhi Tao, Thomas Gengenbach, Timothy Williams, Xi-Ya Fang, Hannah J. King, Shannon A. Bonke, Dijon A. Hoogeveen, Christine A. Romano, Bradley M. Tebo, Lisandra L. Martin, William H. Casey, Leone Spiccia
      Abstract: Influence of the conditions for aerobic oxidation of Mn2+(aq) catalysed by the MnxEFG protein complex on the morphology, structure and reactivity of the resulting biogenic manganese oxides (MnOx) is explored. Physical characterisation of MnOx includes scanning and transmission electron microscopies, X-ray photoelectron and K-edge Mn, Fe X-ray absorption spectroscopies. This characterisation reveals that the MnOx materials share the structural features of birnessite, yet differ in the degree of structural disorder. Importantly, these biogenic products exhibit strikingly different morphologies that can be easily controlled. Changing the substrate-to-protein ratio produces MnOx either as nm-thin sheets, or rods with diameters below 20 nm, or a combination of the two. Mineralisation in solutions that contain Fe2+(aq) makes solids with significant disorder in the structure, while the presence of Ca2+(aq) facilitates formation of more ordered materials. The (photo)oxidation and (photo)electrocatalytic capacity of the MnOx minerals is examined and correlated with their structural properties.
      PubDate: 2017-07-18T21:35:45.120312-05:
      DOI: 10.1002/chem.201702579
       
  • Dynamic Covalent Chemistry of Aldehyde Enamines: Bi(III)- and
           Sc(III)-Catalysis of Amine-Enamine Exchange
    • Authors: Yang Zhang; Sheng Xie, Mingdi Yan, Olof Ramström
      Abstract: The dynamic exchange of enamines from secondary amines and enolizable aldehydes has been demonstrated in organic solvents. The enamine exchange with amines was efficiently catalyzed by Bi(OTf)3 and Sc(OTf)3 (2 mol%) and the equilibria (60 mM) could be attained within hours at room temperature. The formed dynamic covalent systems displayed high stabilities in basic environment with
      PubDate: 2017-07-18T21:35:29.319482-05:
      DOI: 10.1002/chem.201702363
       
  • Synthesis and Properties of New N-Heteroheptacenes for Solution-Based
           Organic Field Effect Transistors
    • Authors: Fei Zhou; Sheng Liu, Bernard D. Santarsiero, Donald J. Wink, Damien Boudinet, Antonio Facchetti, Tom G Driver
      Abstract: A series of N-heteroheptacenes was synthesized from ortho-thiophene-substituted aryl azides using a Rh2(II)-catalyzed C-H bond amination reaction to construct the thienoindole moieties. This reaction tolerated the presence of electron-donating or withdrawing groups on the aryl azide without adversely affecting the yield of the amination reaction. The central thiophene ring was created from two thienoindole pieces through a Pd-catalyzed Stille reaction to install the thioether followed by a Cu-mediated Ullman reaction to trigger the cyclization. The photophysical and electrochemical properties of the resulting focused library of N-heteroheptacenes revealed that the electronic nature is controlled by the arene substituent while single crystals grown reveal that the packing motif is influenced by the N-substituent. Solution-processed thin-film OFET devices were fabricated with the N-heteroheptacenes, and one exhibited a hole-mobility of 0.02 cm2·V-1·s-1.
      PubDate: 2017-07-18T13:30:37.816506-05:
      DOI: 10.1002/chem.201701966
       
  • Putting rings around carbon nanotubes
    • Authors: Emilio M. Pérez
      Abstract: In the last five years, we have developed synthetic methods towards encapsulation of single walled carbon nanotubes (SWNTs) into organic macrocycles, to form rotaxane-type molecules. These are the first examples of mechanically interlocked SWNTs derivatives (MINTs). In this article, I discuss our motivation to continue developing chemistry of SWNTs at a time well past their hype. We explain our synthetic strategy and characterization methodology in detail, stressing the general aspects. In particular, we emphasize the importance of adequate control experiments and bulk spectroscopic and analytical data to determine the structure of SWNT derivatives, as opposed to relying only (or mostly) on microscopy. I also use our experimental results as pretext to reflect on more general/conceptual issues pertaining the chemistry of SWNTs and mechanically interlocked molecules.
      PubDate: 2017-07-18T08:30:54.822589-05:
      DOI: 10.1002/chem.201702992
       
  • Pyrene MO 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 Al Mamari, Sabine Lorenzen, Martin Hähnel, Antonius Eichhorn, Michael Moos, Marco Holzapfel, Holger Braunschweig, Christoph Lambert, Andreas Steffen, Lei Ji, Todd B. Marder
      Abstract: We show that by judicious choice of substituents at the 2,7-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-substitutents in our pyrene derivatives.
      PubDate: 2017-07-18T05:15:40.026251-05:
      DOI: 10.1002/chem.201702594
       
  • Design and Solution Phase Synthesis of Membrane Targeting Lipopeptides
           with Selective Antibacterial Activity
    • Authors: Mohini Mohan Konai; Utsarga Adhikary, Jayanta Haldar
      Abstract: Designing selective antibacterial molecules remains an unmet goal in the field of membrane targeting agents. To this aim, herein we report the rational design and synthesis of a new class of lipopeptides which possess highly selective bacterial killing over mammalian cells. The selective interaction with bacterial over mammalian membranes was established through various spectroscopic as well as microscopic experiments including biophysical studies with the model membranes. A detailed antibacterial structure-activity relationship was delineated after preparing a series of molecules consisting of the peptide moieties with varied sequence of amino acids such as D-phenylalanine, D-leucine and D-lysine. Antibacterial activity was found to vary with the nature and positioning of hydrophobicity in the molecules as well as number of positive charges. Optimized lipopeptide, 9 did not show any hemolytic activity even at 1000 µg/mL and displayed>200-fold and>100-fold selectivity towards S. aureus and E. coli respectively. More importantly, compound 9 was found to display good antibacterial activity (MIC = 6.3-12.5 µg/mL) against the five top most critical bacteria according to WHO (World Health Organization) priority list. Therefore, altogether the results suggested that this new class of lipopeptides bear real promises for the development as future antibacterial agents.
      PubDate: 2017-07-18T01:15:40.383187-05:
      DOI: 10.1002/chem.201702227
       
  • MacroEvoLution - A New Method for the Rapid Generation of Novel Scaffold
           Diverse Macrocyclic Libraries
    • Authors: Kunz Oliver; Jörn Saupe, Haustedt Ole Lars, Sven Jakupovic, Christian Mang
      Abstract: Macrocycles are a structural class bearing great promise for future challenges in medicinal chemistry. Nevertheless there are few flexible approaches for the rapid generation of structurally diverse macrocyclic compound collections. We have developed an efficient method for the generation of novel macrocyclic peptide-based scaffolds. The process, called MacroEvoLution is based on a cyclization screening approach which gives reliable access to novel macrocyclic architectures. Classification of building blocks into specific pools ensures that scaffolds with orthogonally addressable functionalities are generated which can easily be used for the generation of structurally diverse compound libraries. The method grants rapid access to novel scaffolds with scalable synthesis (gram scale) and the introduction of further diversity on a late stage. Despite being developed for peptidic systems the approach can easily be extended for the synthesis of systems with a decreased peptidic character.
      PubDate: 2017-07-17T10:16:54.410473-05:
      DOI: 10.1002/chem.201703209
       
  • Asymmetric Alkynylation of β-Ketoesters and Naphthols Promoted by New
           Chiral Biphenylic Iodanes
    • Authors: Simon Companys; Philippe Peixoto, Cyril Bosset, Stefan Chassaing, Karinne Miqueu, Jean-Marc Sotiropoulos, Laurent Pouységu, Stephane Quideau
      Abstract: The preparation of new chiral biphenylic λ3-iodane reagents bearing transferable alkynyl ligands is described. These reagents transfer their carbon-based ligands onto β-ketoesters with an enantiomeric excess (ee) up to 68%, and most remarkably, enable the dearomative alkynylation of naphthols in good to high yields up to 84% ee.
      PubDate: 2017-07-17T10:15:56.11585-05:0
      DOI: 10.1002/chem.201703238
       
  • Magnetic Shielding Studies of C2 and C2H2 Support Higher than Triple Bond
           Multiplicity in C2
    • Authors: Peter B. Karadakov; Josh Kirsopp
      Abstract: The carbon-carbon bonds in the ground states of C2 and C2H2, at their equilibrium geometries, are compared by analysing the changes in the off-nucleus magnetic shielding tensor within the space surrounding each of these molecules. A wide range of quantum-chemical approaches, including full-valence CASSCF-GIAO, CCSD(T)-GIAO and CCSDT-GIAO, all with the cc-pVQZ basis set, as well as HF-GIAO and MP2-GIAO, with the cc-pVQZ, cc-pV5Z and cc-pV6Z basis sets, show that the surroundings of the carbon-carbon bond in C2 are more shielded than those of the carbon-carbon bond in C2H2. The additional shielding of the carbon-carbon bond in C2 is found to be due to a larger paramagnetic contribution to component of the shielding tensor which is perpendicularto the molecular axis. The analysis of the off-nucleus shielding data indicates that the carbon-carbon bond in C2 is "bulkier" and, therefore, of a higher multiplicity, but weaker than the corresponding bond in C2H2. According to the results of the shielding calculations, the carbon nucleiin C2 should be much more shielded than those in C2H2, with 13C isotropic magnetic shieldings in the ca. 224-227 ppm and ca. 123-125 ppm ranges for C2 and C2H2, respectively.
      PubDate: 2017-07-17T09:15:36.309915-05:
      DOI: 10.1002/chem.201703051
       
  • Silver-Catalyzed Dehydrogenative Synthesis of Carboxylic Acids from
           Primary Alcohols
    • Authors: Robert Madsen; Hajar Golshadi Ghalehshahi
      Abstract: A simple silver-catalyzed protocol has been developed for the acceptorless dehydrogenation of primary alcohols into carboxylic acids and hydrogen gas. The procedure uses 2.5% Ag2CO3 and 2.5 - 3 equiv. of KOH in refluxing mesitylene to afford the potassium carboxylate which is then converted into the acid with HCl. The reaction can be applied to a variety of benzylic and aliphatic primary alcohols with alkyl and ether substituents, and in some cases halide, olefin and ester functionalities are also compatible with the reaction conditions. The dehydrogenation is believed to be catalyzed by silver nanoparticles that are formed in situ under the reaction conditions.
      PubDate: 2017-07-17T07:15:52.278198-05:
      DOI: 10.1002/chem.201702420
       
  • Two Enabling Strategies for the Stereoselective Conversion of Internal
           Alkynes into Trisubstituted Alkenes
    • Authors: Alois Fürstner; Nikolas Huwyler, Karin Radkowski, Stephan M. Rummelt
      Abstract: An expedient method for the C-methylation of alkenylstannanes with formation of trisubstituted alkenes is described, which relies on the use of MeI in combination with copper thiophene-2-carboxylate (CuTC) as promotor and tetra-n-butylammonium diphenylphosphinate as an effective tin scavenger; in some cases, it proved beneficial to further supplement the mixture with catalytic amounts of Pd(PPh3)4. Under these conditions, the reaction proved robust, high yielding and compatible with many functional groups that might not subsist under more traditional conditions used to C-alkylate organotin derivatives. A qualitative analysis of the reaction profile suggested that the in situ formation of a reactive organocopper intermediate and its interception by MeI is only barely faster than O-methylation of the phosphinate additive by the same alkylating agent. To guarantee high yields and prevent net protodestannation from occuring, the reaction protocol had to be optimized such that these competing processes are properly decoupled. The new method is particularly well suited for the stereoselective preparation of the (E)-2-methylbut-2-en-1-ol motif that is present in numerous natural products. Alternatively, this particular target structure can be accessed starting from -hydroxy alkenylsiloxane precursors, which get C-methylated upon exposure to CuI/LiOtBu and MeI by what is thought to be a Brook rearrangement / alkylation sequence.
      PubDate: 2017-07-17T05:15:51.093199-05:
      DOI: 10.1002/chem.201702470
       
  • 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
      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 a GO surface. 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 a π-π stacking interaction, with preferential binding to an oxidized region rather than to an unoxidized region of the GO surface. The adsorption process shows dynamic cooperation adsorption behavior; that is, usually the ssDNA segment first captures the oxidized group of the GO surface by the formation of the 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 these behaviors to that the hydrogen bonding interaction is faster to be formed than the π-π stacking interaction. The π-π stacking interaction needs more relaxation time to regulate the configuration of the ssDNA segment to fit the aromatic rings on GO surface.
      PubDate: 2017-07-16T22:15:26.895465-05:
      DOI: 10.1002/chem.201701733
       
  • Controlled gelation of graphene towards unprecedented superstructures
    • Authors: ling Qiu; Soren Vermehren Petersen, Dan Li
      Abstract: Graphene exhibits a range of exceptional physical properties and holds great promise for development of novel bulk materials for widespread applications. Properly engineering of assembled structures of graphene at multiple length scales is essential to realize its full potential in bulk forms. In this Concept article, we highlight the unique colloidal and gelation behavior of a commonly used precursor for graphene, graphene oxide (GO), and discuss how the colloidal chemistry of GO and reduced GO can enable new scalable and cost-effective approaches to construct graphene-based soft superstructures with excellent properties.
      PubDate: 2017-07-16T21:20:20.401889-05:
      DOI: 10.1002/chem.201703121
       
  • Cover Picture: Silyl Chalconium Ions: Synthesis, Structure and Application
           in Hydrodefluorination Reactions (Chem. Eur. J. 42/2017)
    • Authors: Natalie Kordts; Sandra Künzler, Saskia Rathjen, Thorben Sieling, Henning Großekappenberg, Marc Schmidtmann, Thomas Müller
      Pages: 9971 - 9971
      Abstract: Silylated chalconium ions based on peri-naphthalene and acenaphthene scaffolds are synthesized and introduced as versatile amphiphilic reagents. The investigation of their spectroscopic, structural and bonding properties revealed that their silyl Lewis acidity is controlled by the nature of the chalcogen donor and by the carbon backbone. This opens the perspective for an effective fine tuning and control of their reactivity. Their use as amphiphilic CATalyst was exemplarily demonstrated in hydrodefluorination reactions. More information can be found in the Full Paper by T. Müller et al. on page 10068.
      PubDate: 2017-06-07T09:20:49.552578-05:
      DOI: 10.1002/chem.201702049
       
  • Inside Cover: Induction of Axial Chirality in 8-Arylquinolines through
           Halogenation Reactions Using Bifunctional Organocatalysts (Chem. Eur. J.
           42/2017)
    • Authors: Ryota Miyaji; Keisuke Asano, Seijiro Matsubara
      Pages: 9972 - 9972
      Abstract: Bifunctional catalysis to control the molecular conformations realizes the enantioselective syntheses of axially chiral quinoline derivatives, which have rarely been synthesized in an enantioselective catalytic manner, through the aromatic electrophilic halogenation of 3-(quinolin-8-yl)phenols. This protocol, which controls the reaction enantioselectivity through the use of mono-ortho-substituted substrates, also enables the synthesis of 8-arylquinolines bearing two different halogen groups in high enantioselectivity. More information can be found in the Communication by R. Miyaji, K. Asano, and S. Matsubara on page 9996.
      PubDate: 2017-06-01T13:10:50.106326-05:
      DOI: 10.1002/chem.201702325
       
  • Silyl Chalconium Ions: Synthesis, Structure and Application in
           Hydrodefluorination Reactions
    • Authors: Natalie Kordts; Sandra Künzler, Saskia Rathjen, Thorben Sieling, Henning Großekappenberg, Marc Schmidtmann, Thomas Müller
      Pages: 9973 - 9973
      Abstract: Invited for the cover of this issue is the group of Thomas Müller at the University of Oldenburg. The image depicts the allegorism of the studied reactions. Read the full text of the article at 10.1002/chem.201700995.“…chalconium ions may be used in bond activation reactions” Read more about the story behind the cover in the Cover Profile and about the research itself on page 10068 ff. (
      DOI : 10.1002/chem.201700995).
      PubDate: 2017-06-07T09:20:53.008879-05:
       
  • Responsive, Water-Soluble Europium(III) Luminescent Probes
    • Authors: Sergey Shuvaev; Matthieu Starck, David Parker
      Pages: 9974 - 9989
      Abstract: The design principles, mechanism of action and performance of europium(III) complexes that serve as strongly emissive and responsive molecular probes in water are critically discussed. Examples of systems designed to assess pH, selected metal ions and anions, including chiral species, as well as selected small molecules and biopolymers are considered, and prospects evaluated for improved performance in more complex biological media such as in bio-fluids and within living cells. Modulation of the emission spectral form, lifetime and degree of circular polarisation can be used to quantify the spectral response and permit calibration.Perturbation of the bright, red emission of europium coordination complexes is being used to signal real-time chemical changes in vitro and in cellulo. By understanding their key design principles and their mode of action, new probes for cations, anions, pH and for the local chiral chemical environment can be created. In this critical Minireview, selected examples are highlighted emphasising the need to take care in establishing reversibility of action and in calibration.
      PubDate: 2017-06-22T08:06:20.816699-05:
      DOI: 10.1002/chem.201700567
       
  • Sulfur–Fluoride Exchange (SuFEx)-Mediated Synthesis of Sterically
           Hindered and Electron-Deficient Secondary and Tertiary Amides via Acyl
           Fluoride Intermediates
    • Authors: Christopher J. Smedley; Andrew S. Barrow, Christian Spiteri, Marie-Claire Giel, Pallavi Sharma, John E. Moses
      Pages: 9990 - 9995
      Abstract: Amide bond formation is one of the most executed reactions in chemistry and biology. This is largely due to the ubiquity of the amide functional group in biological molecules, natural products and pharmaceutically important drugs. We report here the development of “SuFExAmide”: a new sulfur–fluoride exchange (SuFEx) click chemistry based protocol for the efficient amidation of carboxylic acids via acyl fluoride intermediates. We have developed benzene-1,3-disulfonyl fluoride as a cost effective, powerful and versatile coupling agent, which delivers challenging secondary and tertiary amides in excellent yields from sterically hindered and electron-deficient amines. The straightforward method offers significant benefits over existing protocols in terms of substrate scope, efficiency and ease of operation and is demonstrated by the synthesis of 44 amides, including GNF6702, an antiprotozoal drug candidate. In the majority of cases, the amide products are obtained in high yield without the need for excess reagents or chromatographic purification.The perfect couple: A new SuFEx (sulfur–fluoride exchange) click chemistry based protocol for the efficient amidation of carboxylic acids via acyl fluoride intermediates, using benzene-1,3-disulfonyl fluoride as a condensing reagent. SuFExAmide has broad substrate scope and is well suited for the synthesis of challenging, sterically hindered and electron-deficient secondary and tertiary amides. The majority of the 44 examples of amide products described here were obtained in high yield without the need for excess reagents or chromatographic purification.
      PubDate: 2017-07-26T02:44:15.480879-05:
      DOI: 10.1002/chem.201701552
       
  • Induction of Axial Chirality in 8-Arylquinolines through Halogenation
           Reactions Using Bifunctional Organocatalysts
    • Authors: Ryota Miyaji; Keisuke Asano, Seijiro Matsubara
      Pages: 9996 - 10000
      Abstract: The enantioselective syntheses of axially chiral heterobiaryls were accomplished through the aromatic electrophilic halogenation of 3-(quinolin-8-yl)phenols with bifunctional organocatalysts that control the molecular conformations during successive halogenations. Axially chiral quinoline derivatives, which have rarely been synthesized in an enantioselective catalytic manner, were afforded in moderate-to-good enantioselectivities through bromination, and an analogous protocol also enabled enantioselective iodination. In addition, this catalytic reaction, which allows enantioselective control through the use of mono-ortho-substituted substrates, allowed the asymmetric synthesis of 8-arylquinoline derivatives bearing two different halogen groups in high enantioselectivities.Bifunctional catalysis: The enantioselective syntheses of axially chiral heterobiaryl compounds are accomplished through the aromatic electrophilic halogenation of 3-(quinolin-8-yl)phenols with bifunctional organocatalysts to control the molecular conformations during successive halogenation reactions. Axially chiral quinoline derivatives, which have rarely been synthesized in an enantioselective catalytic manner, are afforded through bromination and iodination reactions. In addition, this protocol, which controls the reaction enantioselectivity through the use of mono-ortho-substituted substrates, also enables the synthesis of 8-arylquinolines bearing two different halogen groups in high enantioselectivity.
      PubDate: 2017-05-15T08:06:07.756928-05:
      DOI: 10.1002/chem.201701707
       
  • Precise Control of the Lateral and Vertical Growth of Two-Dimensional Ag
           Nanoplates
    • Authors: Taixing Tan; Lili Yao, Huiling Liu, Chengyu Li, Cheng Wang
      Pages: 10001 - 10006
      Abstract: Tuning localized surface plasmon resonance (LSPR) is crucial for practical applications of two-dimensional Ag nanoplates (AgNPs) and relies on the precise control of their lateral length or/and thickness. In the present seed-mediated synthetic method, by taking advantage of underpotential deposition (UPD) of Cu on the (111) surfaces of AgNPs, a solely lateral growth of AgNPs was achieved when Cu(NO3)2 was employed, while a vertical growth of AgNPs could be attained by introducing CuCl2 into our growth solutions. The lateral length and the vertical thickness of the AgNPs could be tuned in the ranges of 115 to nearly 300 nm and 13.4 to around 200 nm, respectively. Along with control of the dimensional size of AgNPs, LSPR could also be tuned in the visible to near infrared range. Plausible growth mechanisms for the precise control of the lateral and vertical growth of AgNPs were proposed.Direction-controlled growth: The growth direction of Ag nanoplates can be precisely controlled along the lateral or vertical direction exclusively by introduction of Cu(NO3)2 or CuCl2, respectively. The lateral growth was favored by Cu underpotential deposition (UDP) formed on (111) faces, while the vertical growth was dominated in the coexistence of Cl− and Cu2+.
      PubDate: 2017-07-03T06:50:46.838409-05:
      DOI: 10.1002/chem.201701146
       
  • Metal-free Hydroalkoxylation-Formal [4+2] Cycloaddition Cascade for the
           Synthesis of Ketals
    • Authors: Santosh J. Gharpure; Santosh K. Nanda, Padmaja, Yogesh G. Shelke
      Pages: 10007 - 10012
      Abstract: A transition metal free, acid promoted cascade hydroalkoxylation–formal [4+2] cycloaddition of various alkynols with salicylaldehyde is demonstrated for the synthesis of tetrahydrofurano/pyrano-chromenes and spiroketals. In general, alkynols underwent hydroalkoxylations in an endo-dig manner when internal alkynes were used to furnish the heteroannular ketals, whereas terminal alkynes proceeded in an exo-dig fashion leading to spiroketals. The study revealed that intramolecular hydroalkoxylation of alkynols is a preferred path over a generation of oxonium ions when coupling partner is salicylaldehyde. This metal-free transformation provides a new avenue for the stereoselective synthesis of tetrahydrofurano- and pyrano-chromenes in an expeditious manner.Cascading chromenes: Lewis/Brønsted acid mediated stereoselective synthesis of chromene ketals is demonstrated. The cascade reaction involved transition-metal-free hydroalkoxylation of alkyne and formal [4+2] cycloaddition with salicylaldehyde. Complex scaffolds like bis-chromene, quinoline-fused chromene, core of xyloketal and paecilospirone natural products could be assembled using this method. The study suggested that substituents on alkyne govern exo versus endo mode of hydroalkoxylation of alkynols to furnish polycyclic heteroannular or spirocyclic chromene ketals.
      PubDate: 2017-07-05T07:41:00.346247-05:
      DOI: 10.1002/chem.201701659
       
  • Trifluoromethyl- and Fluoroalkylselenolations of Alkynyl Copper(I)
           Compounds
    • Authors: Clément Ghiazza; Thierry Billard, Anis Tlili
      Pages: 10013 - 10016
      Abstract: The successful perfluoroalkylselenolation of alkynyl copper(I) compounds is described herein. The reaction occurs under oxidant free conditions at room temperature. This convenient one-pot procedure is based on the in situ generation of trifluoromethylselenyl chlorides. The developed system shows high functional group tolerance and also promotes the employment of fluoroalkyl derivatives.The successful fluoroalkylselenolation of alkynyl copper(I) is described herein. The system shows high functional group tolerance and the applicability of the procedure is extended to various fluoroalkyl derivatives. This convenient one-pot procedure occurs under oxidant-free conditions at room temperature.
      PubDate: 2017-07-05T12:33:39.346373-05:
      DOI: 10.1002/chem.201702028
       
  • Bistable Solid-State Fluorescence Switching in Photoluminescent, Infinite
           Coordination Polymers
    • Authors: Jincheol Kim; Youngmin You, Seong-Jun Yoon, Jong H. Kim, Boseok Kang, Sang Kyu Park, Dong Ryeol Whang, Jangwon Seo, Kilwon Cho, Soo Young Park
      Pages: 10017 - 10022
      Abstract: Photo-functional infinite coordinated polymers (ICPs) were synthesized that consist of the photochromic dithienylethene (DTE) and a luminescent bridging unit to give enhanced fluorescence in the solid state. We could fabricate well-ordered micropatterns of these ICPs by a soft-lithographic method, which repeatedly showed high contrast on–off fluorescence switching.Fluorescent photochromic ICP: Patterned films of highly luminescent infinite coordination polymers (ICPs) showing high contrast on–off fluorescence switching were synthesized and chracterized for the first time.
      PubDate: 2017-07-10T10:58:59.107705-05:
      DOI: 10.1002/chem.201701656
       
  • Pd-Catalyzed Hydroxylation of Aryl Boronic Acids Using In Situ Generated
           Hydrogen Peroxide
    • Authors: Hong Yi; Aiwen Lei
      Pages: 10023 - 10027
      Abstract: Herein, we describe a benign and efficient palladium-catalyzed hydroxylation of aryl boronic acids under mild conditions, with in situ generated hydrogen peroxide from carbon monoxide, water, and oxygen. This novel procedure combines catalytic production of hydrogen peroxide with an aerobic oxidation process in a sole reaction system. This system shows good functional group tolerance and provides a benign and efficient access to a variety of functionalized phenols. Furthermore, the in situ generated hydroperoxide can be well used for triphenylphosphine oxidation, in which the TON is up to 194. Isotope labelling studies provide important mechanistic insights for this process.In situ magic: A benign and efficient palladium-catalyzed hydroxylation of aryl boronic acids under mild conditions, with in situ generated hydrogen peroxide from carbon monoxide, water, and oxygen, is developed in this work. This system shows good functional group tolerance and provides a new route to a variety of functionalized phenols.
      PubDate: 2017-07-05T12:33:53.144985-05:
      DOI: 10.1002/chem.201702045
       
  • Slow Magnetic Relaxation in a Mononuclear Ruthenium(III) Complex
    • Authors: Shu-Qi Wu; Yuji Miyazaki, Motohiro Nakano, Sheng-Qun Su, Zi-Shuo Yao, Hui-Zhong Kou, Osamu Sato
      Pages: 10028 - 10033
      Abstract: The development of magnetic molecules with long spin reversal/decoherence times highly depends on the understanding of relaxation behavior under different external conditions. Herein, a magnetic study on a RuIII complex (1) is presented. Detailed analysis of the relaxation time and the magneto-heat capacity data suggests that the resonant phonon trapping process dominates the magnetic relaxation in the crystalline sample of 1, slowing down the spin relaxation rate, as further confirmed by the measurements on a ground sample and frozen solution. Thus, it provides a rare example showing that 4d metal-centered mononuclear compounds without second-order anisotropy can display slow magnetic relaxation.Relax! The magnetic relaxation behavior of a ruthenium(III) complex (1) has been characterized in detail. The analysis suggests that resonant phonon trapping dominates the relaxation process in the low temperature region, slowing down the relaxation rate.
      PubDate: 2017-07-03T07:01:33.941495-05:
      DOI: 10.1002/chem.201702047
       
  • Two-Step Spin-Crossover with Three Inequivalent FeII Sites in a
           Two-Dimensional Hofmann-Type Coordination Polymer
    • Authors: Yan Meng; Qing-Qing Sheng, Md. Najbul Hoque, Yan-Cong Chen, Si-Guo Wu, Jiri Tucek, Radek Zboril, Tao Liu, Zhao-Ping Ni, Ming-Liang Tong
      Pages: 10034 - 10037
      Abstract: An unprecedented two-step spin-crossover behavior with the sequence of γHS=1γHS=3/4γHS=1/4 was observed in two-dimensional Hofmann type coordination polymer [Fe(isoq)2{Ag(CN)2}2] (isoq=isoquinoline), which resulted from three crystallographically inequivalent FeII sites with distinct transition temperatures.Dancing the tango: An unprecedented two-step spin-crossover behavior with the sequence of γHS=1γHS=3/4 γHS=1/4 was observed in two-dimensional Hofmann type coordination polymer [Fe(isoq)2{Ag(CN)2}2] (isoq=isoquinoline) with three crystallographically inequivalent FeII sites.
      PubDate: 2017-07-05T07:41:23.762987-05:
      DOI: 10.1002/chem.201702356
       
  • Coordination-Supported Imidazolate Networks: Water- and Heat-Stable
           Mesoporous Polymers for Catalysis
    • Authors: Pengfei Zhang; Shize Yang, Matthew F. Chisholm, Xueguang Jiang, Caili Huang, Sheng Dai
      Pages: 10038 - 10042
      Abstract: The poor water stability of most porous coordination polymers (PCPs) or metal-organic frameworks (MOFs) is widely recognized as a barrier hampering their practical applications. Here, a facile and scalable route to prepare metal-containing polymers with a good stability in boiling water (100 °C, 24 h) and air (up to 390 °C) is presented. The bifunctional 1-vinylimidazole (VIm) with a coordinating site and a polymerizable organic group is introduced as the building block. This core strategy includes the synthesis of a rigid monomer with four VIm branches through a coordination process at room temperature, followed by a radical polymerization. We refer to this material as coordination-supported imidazolate networks (CINs). Interestingly, CINs are composed of rich mesopores from 2–15 nm, as characterized by low-energy (60 kV) STEM-HAADF images. In particular, the stable CINs illustrate a high turnover frequency (TOF) of 779 h−1 in the catalytic oxidation of phenol with H2O as the green solvent.Omni-stable polymers: Stable metal-containing polymers are designed from versatile 1-vinyl-imidazole (VIm) with both coordinating sites and reactive organic groups. The synthetic strategy includes the coordination between VIm and metal ions (Zn2+, Co2+, Ni2+), followed by a radical polymerization. This concept enables porous metal-based polymers with exceptional stability in water (100 °C, 24 h) and air (up to 390 °C).
      PubDate: 2017-06-30T04:38:02.150131-05:
      DOI: 10.1002/chem.201702430
       
  • Cobalt-Catalyzed Esterification of Amides
    • Authors: Yann Bourne-Branchu; Corinne Gosmini, Grégory Danoun
      Pages: 10043 - 10047
      Abstract: The first cobalt-catalyzed amide activation of N-Boc-amides, and their conversion into esters, is reported here. This new methodology presents a very practical process that does not require an inert atmosphere, uses an inexpensive cobalt catalyst, and proceeds under mild reaction conditions. This catalytic system has a broad substrate scope and has been shown to be highly efficient, with catalyst loadings as low as 1 mol %.Of gentler, milder mold: A practical mild and efficient cobalt-catalytic system is described that converts amides into esters. This methodology is complementary to previous nickel-catalyzed systems, affording new selectivity and a more diverse range of amide substrates, including common C−H bond activation directing groups. This new reaction requires neither inert atmosphere nor distilled solvents and even proceeds at low catalyst loading such as 1 mol % catalyst.
      PubDate: 2017-07-05T12:34:17.914124-05:
      DOI: 10.1002/chem.201702608
       
  • Integrative Pericyclic Cascade: An Atom Economic, Multi C−C Bond-Forming
           Strategy for the Construction of Molecular Complexity
    • Authors: David Tejedor; Samuel Delgado-Hernández, Jesús Peyrac, Javier González-Platas, Fernando García-Tellado
      Pages: 10048 - 10052
      Abstract: An all-pericyclic manifold is developed for the construction of topologically diverse, structurally complex and natural product-like polycyclic chemotypes. The manifold uses readily accessible tertiary propargyl vinyl ethers as substrates and imidazole as a catalyst to form up to two new rings, three new C−C bonds, six stereogenic centers and one transannular oxo-bridge. The manifold is efficient, scalable and instrumentally simple to perform and entails a propargyl Claisen rearrangement–[1,3]H shift, an oxa-6π-electrocyclization, and an intramolecular Diels–Alder reaction.Playing with dominos: An all-pericyclic cascade process transforms propargyl vinyl ethers into eight different polycyclic ring-fused chemotypes incorporating different topologies. The pericyclic manifold creates up to three fused cycles, one transannular-oxo-bridge and six steroigenic centers via the formation of three new C−C bonds.
      PubDate: 2017-07-11T01:20:32.608667-05:
      DOI: 10.1002/chem.201702667
       
  • Mechanistic Characterization of Two Chimeric Sesterterpene Synthases from
           Penicillium
    • Authors: Takaaki Mitsuhashi; Jan Rinkel, Masahiro Okada, Ikuro Abe, Jeroen S. Dickschat
      Pages: 10053 - 10057
      Abstract: The products of two bifunctional fungal sesterterpene synthases (StTPS), with prenyl transferase (PT) and terpene synthase (TPS) domains from Penicillium, were structurally characterized and their mechanisms studied in detail by labeling experiments. A phylogenetic analysis of the TPS domains of the new and previously characterized enzymes revealed six distinct clades. Enzymes from the same clade catalyze a common initial cyclization step, which suggests the potential for structural predictions from amino acid sequences.The products and cyclization mechanisms of two bifunctional sesterterpene synthases from Penicillium were investigated. A phylogenetic analysis of the new and known fungal terpene synthases reveals clades of enzymes that reflect the initial cyclization step.
      PubDate: 2017-07-03T07:16:42.562896-05:
      DOI: 10.1002/chem.201702766
       
  • Rigidly Tethered Bis-phosphoric Acids: Generation of Tunable Chiral
           Fluorescent Frameworks and Unexpected Selectivity for the Detection of
           Ferric Ions
    • Authors: Frescilia Octa-Smolin; Raja Mitra, Maike Thiele, Constantin G. Daniliuc, Linda Stegemann, Cristian Strassert, Jochen Niemeyer
      Pages: 10058 - 10067
      Abstract: We describe the straightforward synthesis of a series of bis-phosphoric acids (R,R)-1 a–d, featuring two chiral 1,1′-binaphthyl-phosphoric acid units that are tethered by rigid, π-conjugated linkers. The nature of the linker has a profound influence on the properties of the bis-phosphoric acids, such as their self-association behavior and their interaction with metal ions. This led to the identification of one preferred bis-phosphoric acid (R,R)-1 d, which shows selective fluorescence quenching in the presence of ferric ions (Fe3+). Thus, (R,R)-1 d could be applied for the detection of Fe3+, even in the presence of a variety of other metal ions. The chiral nature of the bis-phosphoric acid enables the interaction with Fe3+ to be followed by CD spectroscopy, providing a complementary detection mode with the same probe.Iron turns me off: The preparation and analysis of a series of rigidly tethered 1,1′-binaphthyl-phosphoric acids led to the identification of a novel probe for ferric ions (see figure). The presence of Fe3+ can be detected by means of CD or fluorescence spectroscopy with high chemoselectivity.
      PubDate: 2017-05-24T07:10:39.282616-05:
      DOI: 10.1002/chem.201700954
       
  • Silyl Chalconium Ions: Synthesis, Structure and Application in
           Hydrodefluorination Reactions
    • Authors: Natalie Kordts; Sandra Künzler, Saskia Rathjen, Thorben Sieling, Henning Großekappenberg, Marc Schmidtmann, Thomas Müller
      Pages: 10068 - 10079
      Abstract: The synthesis of two series of silylated chalconium borates, 9 and 10, which are based on the peri-naphthyl and peri-acenaphthyl framework, is reported (chalcogen (Ch): O, S, Se, Te). NMR investigations of the selenium- and tellurium-containing precursor silanes 3 d–f and 8 d, f revealed a significant through-space J-coupling between the chalcogen nuclei and the Me2SiH group. Experimental and computational results typify the synthesized cations 9 and 10 as chalconium ions. The imposed ring strain weakens the Si−Ch linkage compared to acyclic chalconium ions. This attenuation of the Si−Ch bond strength is more pronounced in the acenaphthene series. Surprisingly, the Si−O bonds in oxonium ions 9 a and 10 a are the weakest Si−Ch linkage in both series. The synthesized silyl chalconium borates are active in hydrodefluorination reactions of alkyl fluorides with silanes. A cooperative activation of the silane by the Lewis acidic (silicon) and by the Lewis basic side (chalcogen) is suggested.Oxygen breaks ranks: The structural, spectroscopic and computer–chemical characterization of two series of silylated chalconium ions (Ch=O, S, Se, Te) revealed significant differences between the second row element oxygen and its higher congeners.
      PubDate: 2017-05-31T08:51:35.739214-05:
      DOI: 10.1002/chem.201700995
       
  • Arene-Inserted Extended Germa[n]pericyclynes: Synthesis, Structure, and
           Phosphorescence Properties
    • Authors: Hiroki Tanimoto; Junta Mori, Shunichiro Ito, Yasuhiro Nishiyama, Tsumoru Morimoto, Kazuo Tanaka, Yoshiki Chujo, Kiyomi Kakiuchi
      Pages: 10080 - 10086
      Abstract: This report describes the synthesis and characterization of arene-inserted extended (ArEx) germa[n]pericyclynes composed of germanium and 1,4-diethynylbenzene units. These novel cyclic germanium-π unit materials were synthesized with diethynylbenzene and germanium dichloride. X-ray crystallographic analysis revealed their structures, and the planar conformation of ArEx germa[4]pericyclyne along with the regular aromatic rings. UV/Vis absorption spectra and fluorescence emission spectra showed considerably unique and highly improved character compared to previously reported germa[n]pericyclynes. Even in the absence of transition metal components, phosphorescence emissions were observed, and the emission lifetimes were dramatically improved. ArEx germa[n]pericyclynes showed high photoluminescence quantum yields, whereas low photoluminescence quantum yields were observed for acyclic compounds. Density functional theory calculations show delocalized orbitals between skipped alkyne units through a germanium tether, and an increase in the HOMO energy level, leading to a small HOMO–LUMO energy gap.A link to the future: This report describes the syntheses of arene-inserted type extended (ArEx) germa[n]pericyclynes composed of germanium-1,4-diethynylbenzene units, and their characterization. These novel cyclic germanium-π unit materials were characterized by X-ray crystallography, UV/Vis spectroscopy, fluorescence, and phosphorescence emission spectroscopy, which showed characteristic optical properties and large emission lifetimes compared to previous derivatives.
      PubDate: 2017-06-12T14:05:34.741932-05:
      DOI: 10.1002/chem.201701359
       
  • CuI/Oxalic Diamide-Catalyzed Cross-Coupling of Thiols with Aryl Bromides
           and Chlorides
    • Authors: Chia-Wei Chen; Yi-Ling Chen, Daggula Mallikarjuna Reddy, Kai Du, Chao-En Li, Bo-Hao Shih, Yung-Jing Xue, Chin-Fa Lee
      Pages: 10087 - 10091
      Abstract: We report a general copper-catalyzed cross-coupling of thiols with aryl halides by using N-aryl-N′-alkyl oxalic diamide (L3) or N,N′-dialkyl oxalic diamide (L5) as the ligand. Both aryl and alkyl thiols can be coupled with unactivated aryl bromides and chlorides to give the desired products in good yields. Furthermore, this system features a broad substrate scope and good tolerance of functional groups. Importantly, the oxalic diamides are stable and can be prepared easily from commercially available and cheap starting materials.A practical synthetic method for diversified thioethers using oxalic diamides as highly air-stable ligands through copper catalysis is demonstrated. A variety of aryl- and alkyl thiols can be coupled with aryl bromides and chlorides to afford the corresponding thioethers in good yields. This work is the first general method for copper-catalyzed thioetherification of unactivated aryl chlorides.
      PubDate: 2017-06-16T03:15:33.201609-05:
      DOI: 10.1002/chem.201701671
       
  • Supramolecular Assembly Mediated by Metal Ions in Aqueous Solution and Its
           Application in Their Analysis
    • Authors: Jing Zhang; Qing Tang, Zhong-Zheng Gao, Sheng-Chao Qiu, Ying Huang, Zhu Tao
      Pages: 10092 - 10099
      Abstract: A water-soluble fluorescent sensor based on the interaction of twisted cucurbit[14]uril (tQ[14]) and thiazole orange (TO) in aqueous solution was developed. Formation of the tQ[14]/TO complex gives rise to stronger fluorescence in both neutral and acidic aqueous solutions compared with that of free TO. Further experiments on the interaction of the tQ[14]/TO complex with metal ions revealed that, from a series of nineteen selected common metal ions, 1) only Hg2+ can lead to fluorescence enhancement and then quenching of the tQ[14]/TO (2:1) complex in neutral aqueous solution; 2) only Ba2+ can induce fluorescence quenching of the tQ[14]/TO (2:1) complex in aqueous HCl solution (pH 2); furthermore, the tQ[14]/TO/Ba2+ systems exhibit reversible changes in fluorescent intensity on successively adding SO42− and Ba2+; and 3) only Ba2+ or Pb2+ can induce fluorescence quenching of the tQ[14]/TO (15:1) complex in aqueous HCl solution (pH 2). Thus, the tQ[14]/TO complex can act as a supramolecular fluorescence-based sensor for the determination of Hg2+, Ba2+, and Pb2+ ions.Uniquely responsive: The interaction of thiazole orange (TO) with twisted cucurbit[14]uril (tQ[14]) was investigated, and formation of a stable fluorescent tQ[14]/TO complex was observed. The tQ[14]/TO complex exhibited unique fluorescence responses to Hg2+, Ba2+, and Pb2+ cations in different aqueous media (see figure). Thus, a fluorescent sensor for three heavy-metal ions was developed.
      PubDate: 2017-07-04T06:16:50.48298-05:0
      DOI: 10.1002/chem.201700478
       
  • Photoisomerization of Bis(tridentate) 2,6-Bis(1H-pyrazol-1-yl)pyridine
           Ligands Exhibiting a Multi-anthracene Skeleton
    • Authors: Ivan Šalitroš; Olaf Fuhr, Miroslav Gál, Michal Valášek, Mario Ruben
      Pages: 10100 - 10109
      Abstract: A novel molecular design is described where two peripheral moieties made of 2,6-bis(1H-pyrazol-1-yl)pyridine are linked through multi-1,8-diethynylanthracene moieties. The optimized synthesis of the three isostructural analogues 1 a, 1 b, and 1 c, containing the anthraquinone, anthracene, and 10-methoxyanthracene units, respectively, is reported. The resulting spatial face-to-face arrangement of the peripheral anthracene rings enables to trigger the intramolecular [4+4] photocycloaddition affording the isomers P1 b and P1 c, which can be thermally cleaved back to the original anthracene derivatives 1 b and 1 c, respectively. Single-crystal X-ray diffraction studies confirm the expected molecular structures of compounds 1 a–1 c as well as of their corresponding isomers P1 b and P1 c. The spectral, optical, and electrochemical properties of all synthesized compounds are investigated and discussed.Switch it: Novel 2,6-bis(1H-pyrazol-1-yl)pyridine ligands exhibiting a photoisomerizable multi-anthracene skeleton were prepared (see figure). All synthesized ligands and the corresponding photoisomers were structurally characterized and their spectral, optical, and electrochemical properties were studied in detail.
      PubDate: 2017-07-04T06:16:17.252101-05:
      DOI: 10.1002/chem.201700825
       
  • Interplay of Electronic Cooperativity and Exchange Coupling in Regulating
           the Reactivity of Diiron(IV)-oxo Complexes towards C−H and O−H Bond
           Activation
    • Authors: Azaj Ansari; Mursaleem Ansari, Asmita Singha, Gopalan Rajaraman
      Pages: 10110 - 10125
      Abstract: Activation of inert C−H bonds such as those of methane are extremely challenging for chemists but in nature, the soluble methane monooxygenase (sMMO) enzyme readily oxidizes methane to methanol by using a diiron(IV) species. This has prompted chemists to look for similar model systems. Recently, a (μ-oxo)bis(μ-carboxamido)diiron(IV) ([FeIV2O(L)2]2+ L=N,N-bis-(3′,5′-dimethyl-4′-methoxypyridyl-2′-methyl)-N′-acetyl-1,2-diaminoethane) complex has been generated by bulk electrolysis and this species activates inert C−H bonds almost 1000 times faster than mononuclear FeIV=O species and at the same time selectively activates O−H bonds of alcohols. The very high reactivity and selectivity of this species is puzzling and herein we use extensive DFT calculations to shed light on this aspect. We have studied the electronic and spectral features of diiron {FeIII-μ(O)-FeIII}+2 (complex I), {FeIII-μ(O)-FeIV}+3 (II), and {FeIV-μ(O)-FeIV}+4 (III) complexes. Strong antiferromagnetic coupling between the Fe centers leads to spin-coupled S=0, S=3/2, and S=0 ground state for species I–III respectively. The mechanistic study of the C−H and O−H bond activation reveals a multistate reactivity scenario where C−H bond activation is found to occur through the S=4 spin-coupled state corresponding to the high-spin state of individual FeIV centers. The O−H bond activation on the other hand, occurs through the S=2 spin-coupled state corresponding to an intermediate state of individual FeIV centers. Molecular orbital analysis reveals σ–π/π–π channels for the reactivity. The nature of the magnetic exchange interaction is found to be switched during the course of the reaction and this offers lower energy pathways. Significant electronic cooperativity between two metal centers during the course of the reaction has been witnessed and this uncovers the reason behind the efficiency and selectivity observed. The catalyst is found to prudently choose the desired spin states based on the nature of the substrate to effect the catalytic transformations. These findings suggest that the presence of such factors play a role in the reactivity of dinuclear metalloenzymes such as sMMO.It can be helped: An electrolysis-generated (μ-oxo)bis(μ-carboxamido)diiron(IV) complex has recently been shown to activate inert C−H bonds almost 1000 times faster than mononuclear FeIV=O species and at the same time selectively activates O−H bonds of alcohols. DFT calculations reveal that electronic cooperativity steers the reaction in diiron(IV)-oxo species leading to preferential cleavage of O−H bonds against weaker C−H bonds.
      PubDate: 2017-07-05T07:43:21.190426-05:
      DOI: 10.1002/chem.201701059
       
  • Lanthanum-Based Compounds: Electronic Band-Gap-Dependent Electrocatalytic
           Materials for Oxygen Reduction Reaction
    • Authors: Weiwei Gu; Ye Song, Jingjun Liu, Feng Wang
      Pages: 10126 - 10132
      Abstract: The electronic energy level of lanthanum compounds plays an important role in the oxygen reduction reaction (ORR) electrocatalytic process. In this work, three lanthanum compounds, LaOHCO3, La2O2CO3, and La2O3, have been synthesized through an in situ urea hydrolysis method, followed by annealing at different temperatures. Among these lanthanum compounds, the layer-structured La2O2CO3 has the smallest band gap and moderate values of the conduction band (CB) and valence band (VB). Electrochemical measurements in 0.1 m KOH solution have shown that, compared with the other catalysts, La2O2CO3 exhibits the best electrocatalytic activity with the lowest H2O2 production and highest durability for ORR, which proves the close correlation between electronic energy level and electrocatalytic ORR activity. During the ORR process over La2O2CO3, some covalent electrons from the VB are first excited to the CB and then transfer to the unoccupied π*2p orbitals of an active oxygen molecule, leading to strengthened oxygen adsorption and promotion of the reduction of oxygen. Moreover, La2O2CO3 has an ability to chemically disproportionate hydrogen peroxide (to give HO2−), and the produced HO2− at the energy level of O2/HO2− can undergo prompt chemical disproportionation into O2 and OH−. The O2 generated at this stage is adsorbed on the catalyst surface, which can be utilized for further oxygen reduction.La La La land: Three lanthanum compounds, LaOHCO3, La2O2CO3, and La2O3, have been synthesized on a carbon support as potential catalysts for oxygen reduction. The energy level diagram of La2O2CO3 (see graphic) confirms its eminent suitability for electrocatalytic oxygen reduction with the generation of HO2−.
      PubDate: 2017-07-06T05:40:27.809536-05:
      DOI: 10.1002/chem.201701136
       
  • Ni–Co Binary Hydroxide Nanotubes with Three-Dimensionally Structured
           Nanoflakes: Synthesis and Application as Cathode Materials for Hybrid
           Supercapacitors
    • Authors: Ziyang Dai; Jianjian Lin, Qiuchun Dong, Zhihui Yin, Xiaoxian Zang, Lei Shen, Jung Ho Kim, Wei Huang, Saad M. Alshehri, Christine Young, Yusuke Yamauchi, Xiaochen Dong
      Pages: 10133 - 10138
      Abstract: Nickel–cobalt binary hydroxide nanotubes were fabricated by a facile synthetic approach by using Cu2O nanowires as sacrificial templates. The surface morphology of the binary hydroxide nanotubes can be easily controlled by adjusting the molar ratio of Ni to Co. With increasing Co content, the surfaces of the nanotubes tend to form hierarchical nanoflakes. The obtained nanotubes with high specific surface area exhibit typical battery-like electrochemical behavior. Among them, Ni–Co hydroxide nanotubes with Ni:Co=48:52 showed outstanding electrochemical characteristics, with a specific capacity of 209.9 mAh g−1 at 1 Ag−1 and remarkable cycling stability with 84.4 % capacity retention after 10 000 cycles at 20 A g−1. With the advantages of their unique nanostructure and the synergistic effect of the two elements, the Ni–Co binary hydroxide nanotubes are expected to be effective potential cathode materials for hybrid supercapacitors.Hierarchical nanotubes: Ni–Co binary hydroxides with hierarchical tubular structure were synthesized by employing Cu2O nanowires as sacrificial template in a facile synthetic process. Owing to their unique nanostructure and the synergistic effect of the two elements, the as-prepared Ni–Co hydroxide nanotubes deliver impressive electrochemical performance as electrodes for hybrid supercapacitors (see scheme).
      PubDate: 2017-07-05T12:33:15.486258-05:
      DOI: 10.1002/chem.201701251
       
  • AcetylacetonateBODIPY-Biscyclometalated Iridium(III) Complexes: Effective
           Strategy towards Smarter Fluorescent Photosensitizer Agents
    • Authors: Eduardo Palao; Rebeca Sola-Llano, Andrea Tabero, Hegoi Manzano, Antonia R. Agarrabeitia, Angeles Villanueva, Iñigo López-Arbeloa, Virginia Martínez-Martínez, Maria J. Ortiz
      Pages: 10139 - 10147
      Abstract: Biscyclometalated IrIII complexes involving boron-dipyrromethene (BODIPY)-based ancillary ligands, where the BODIPY unit is grafted to different chelating cores (acetylacetonate for Ir-1 and Ir-2, and bipyridine for Ir-3) by the BODIPY meso position, have been synthesized and characterized. Complexes with the BODIPY moiety directly grafted to acetylacetonate (Ir-1 and Ir-2) exhibit higher absorption coefficients (ϵ≈4.46×104 m−1 cm−1 and 3.38×104 m−1 cm−1 at 517 nm and 594 nm, respectively), higher moderate fluorescence emission (φfl≈0.08 and 0.22 at 528 nm and 652 nm, respectively) and, in particular, more efficient singlet oxygen generation upon visible-light irradiation (φΔ≈0.86 and 0.59, respectively) than that exhibited by Ir-3 (φΔ≈0.51, but only under UV light). Phosphorescence emission, nanosecond time-resolved transient absorption, and DFT calculations suggest that BODIPY-localized long-lived 3IL states are populated for Ir-1 and Ir-2. In vitro photodynamic therapy (PDT) activity studied for Ir-1 and Ir-2 in HeLa cells shows that such complexes are efficiently internalized into the cells, exhibiting low dark- and high photocytoxicity, even at significantly low complex concentration, making them potentially suitable as theranostic agents.Kill and cure: New boron-dipyrromethene (BODIPY)–iridium(III) complexes, synthesized by a straightforward synthetic approach, exhibit efficient singlet oxygen generation, low dark and high photocytoxicity under visible radiation even at low photosensitizer concentrations.
      PubDate: 2017-07-06T05:45:47.762555-05:
      DOI: 10.1002/chem.201701347
       
  • Application of Surface Click Reactions to Localized Surface Plasmon
           Resonance (LSPR) Biosensing
    • Authors: Noga Yaakov; Yulia Chaikin, Ezequiel Wexselblatt, Yitzhak Tor, Alexander Vaskevich, Israel Rubinstein
      Pages: 10148 - 10155
      Abstract: Localized surface plasmon resonance (LSPR) spectroscopy is an effective tool for sensitive, affordable, and label-free biosensing. LSPR transducers based on nanoparticulate Au films have been applied to biosensing of receptor–analyte interactions, employing primarily thiolated receptors for constructing biorecognition interfaces on nanostructured Au surfaces. This popular method suffers from a major drawback, that is, the need to prepare a thiolated receptor for each system used, which is typically synthetically complex and time-consuming. Herein, we present an alternative approach based on the click reaction between azide and terminal alkyne, which avoids the need to synthesize thiol-derivatized receptors and is applicable to the heterogeneous morphology of LSPR transducers. The receptors are tethered with an alkyne group, which is considerably simpler than thiolation, while producing a stable product. The transducer surface is modified with a layer of a commercial long-chain thiol–azide molecule, then clicked with an alkyne-dertivatized receptor to produce the biorecognition interface. This method is employed for immobilization of four different alkyne-bearing receptor molecules on Au nano-island film based LSPR transducers, followed by testing of their performance in biorecognition of specific analytes using LSPR and FTIR spectroscopies. The results establish the usefulness of click chemistry for the preparation of biorecognition interfaces on nanostructured LSPR transducers.Click to make it happen: Use of click chemistry for immobilization of alkyne-tethered receptor molecules on Au nano-island based localized surface plasmon resonance (LSPR) transducers is demonstrated. The method avoids the complexity involved in the synthesis of thiol-derivatized receptors, and is applicable to the heterogeneous morphology of LSPR transducers. The results establish the usefulness of click chemistry for the preparation of biorecognition interfaces on nanostructured LSPR transducers.
      PubDate: 2017-07-10T10:46:14.297456-05:
      DOI: 10.1002/chem.201701511
       
  • αRep A3: A Versatile Artificial Scaffold for Metalloenzyme Design
    • Authors: Thibault Di Meo; Wadih Ghattas, Christian Herrero, Christophe Velours, Philippe Minard, Jean-Pierre Mahy, Rémy Ricoux, Agathe Urvoas
      Pages: 10156 - 10166
      Abstract: αRep refers to a new family of artificial proteins based on a thermostable α-helical repeated motif. One of its members, αRep A3, forms a stable homo-dimer with a wide cleft that is able to accommodate metal complexes and thus appears to be suitable for generating new artificial biocatalysts. Based on the crystal structure of αRep A3, two positions (F119 and Y26) were chosen, and independently changed into cysteine residues. A phenanthroline ligand was covalently attached to the unique cysteine residue of each protein variant, and the corresponding biohybrids were purified and characterized. Once mutated and coupled to phenanthroline, the protein remained folded and dimeric. Copper(II) was specifically bound by the two biohybrids with two different binding modes. Furthermore, the holo-biohybrid A3F119NPH was found to be capable of enantioselectively catalyzing Diels–Alder (D-A) cycloadditions with up to 62 % ee. This study validates the choice of the αRep A3 dimer as a protein scaffold and provides a promising new route for the design and production of new enantioselective biohybrids based on entirely artificial proteins obtained from a highly diverse library.Come again: An artificial repeat protein scaffold (αRep; see figure) has been engineered into novel enantioselective biohybrid catalysts by covalent coupling of a metal cofactor (see graphic).
      PubDate: 2017-07-10T10:46:21.76942-05:0
      DOI: 10.1002/chem.201701518
       
  • The Role of Co-Activation and Ligand Functionalization in Neutral
           Methallyl Nickel(II) Catalysts for Ethylene Oligomerization and
           Polymerization
    • Authors: Daniela E. Ortega; Diego Cortés-Arriagada, Oleksandra S. Trofymchuk, Diana Yepes, Soledad Gutiérrez-Oliva, René S. Rojas, Alejandro Toro-Labbé
      Pages: 10167 - 10176
      Abstract: A detailed quantum chemical study that analyzed the mechanism of ethylene oligomerization and polymerization by means of a family of four neutral methallyl NiII catalysts is presented. The role of the boron co-activators, BF3 and B(C6F5)3, and the position of ligand functionalization (ortho or para position of the N-arylcyano moiety of the catalysts) were investigated to explain the chain length of the obtained polymers. The chain initialization proceeded with higher activation barriers for the ortho-functionalized complexes (≈19 kcal mol−1) than the para-substituted isomers (17–18 kcal mol−1). Two main pathways were revealed for the chain propagation: The first pathway was favored when using the B(C6F5)3 co-activated catalyst, and it produced long-chain polymers. A second pathway led to the β-hydrogen complexes, which resulted in chain oligomerization; this pathway was preferred when the BF3 co-activated catalysts were used. Otherwise, the termination of longer chains occurred via a stable hydride intermediate, which was formed with an energy barrier of about 14 kcal mol−1 for the B(C6F5)3 co-activated catalysts. Significant new insights were made into the reaction mechanism, whereby neutral methallyl NiII catalysts act in oligomerization and polymerization processes. Specifically, the role of co-activation and ligand functionalization, which are key information for the further design of related catalysts, were revealed.The co-catalytic role of boron co-activators in neutral methallyl NiII catalysts is elucidated for its use in the polymerization and oligomerization of ethylene, which results in key information for the further design of catalysts (see figure).
      PubDate: 2017-07-05T07:22:35.155563-05:
      DOI: 10.1002/chem.201701571
       
  • Universal Method for Large-Scale Synthesis of Layered Transition Metal
           Dichalcogenides
    • Authors: Zdeněk Sofer; David Sedmidubský, Jan Luxa, Daniel Bouša, Štěpán Huber, Petr Lazar, Martin Veselý, Martin Pumera
      Pages: 10177 - 10186
      Abstract: The layered transition metal dichalcogenides are currently amongst the most intensively investigated materials. These compounds constitute a broad family of materials, with characteristic layered structures, covering both semiconductors and metallic materials. The great attention arises from the possibility to exfoliate these materials down to single layers with many unique properties, such as thickness dependent band-gap energy, and the possibility of tuning transport properties by phase transitions. The research in the field of transition metal dichalcogenides is also motivated by their high electrocatalytic activity towards several industrially important reactions, such as the hydrogen evolution reaction, as well as many other applications in nano- and optoelectronics. Although these materials are studied intensively, their availability is extremely limited and only disulfides of molybdenum and tungsten are broadly commercially available. Here an optimized procedure for simple direct synthesis of transition metal dichalcogenides using powder metals and elemental chalcogens is reported. The optimized thermal treatment allowed the synthesis scaling of the sulfides, selenides and tellurides of 4th, 5th, 6th, and 7th group of layered-structure dichalcogenides. The synthesized transition metal dichalcogenides were single phase. The phase purity, structure, and morphology were investigated in detail by electron microscopy and EDS, X-ray diffraction, and Raman spectroscopy.Scale it up: A universal method is presented whereby transition metal dichalcogenides can be synthesized, in large scale, from metal powders and chalcogen in sealed quartz ampoules. A large number of materials were prepared and structurally characterized.
      PubDate: 2017-07-05T07:37:55.014521-05:
      DOI: 10.1002/chem.201701628
       
  • Highly Stable Three-Dimensional Porous Nickel-Iron Nitride Nanosheets for
           Full Water Splitting at High Current Densities
    • Authors: Feng Yan; Yue Wang, Kaiyue Li, Chunling Zhu, Peng Gao, Chunyan Li, Xitian Zhang, Yujin Chen
      Pages: 10187 - 10194
      Abstract: A noble-metal-free and highly efficient bifunctional catalyst for overall water splitting is greatly desirable to generate clean and sustainable energy carriers such as hydrogen, but enormous challenges remain. Herein, porous interconnected iron-nickel nitride nanosheets are designed and grown on carbon fiber cloth (FeNi-N/CFC); combining a facile electrodeposition method and in situ nitriding process. The as-synthesized FeNi-N/CFC, with a low mass loading of 0.25 mg cm−2, exhibits excellent catalytic activities for both the oxygen evolution reaction (OER) with 20 mA cm−2 at an overpotential (η) of 232 mV and also the hydrogen evolution reaction (HER) with 10 mA cm−2 at η=106 mV. As a bifunctional electrocatalyst for overall water splitting FeNi-N/CFC only requires a cell voltage of 1.55 V to drive a current density (j) of 10 mA cm−2 and shows robust long-term durability at j>360 mA cm−2 with a negligible change in current density over 60 h; revealing its promising application in commercial electrolyzers.Cut from the same cloth: Porous interconnected iron-nickel nitride nanosheets were designed and grown on carbon fiber cloth (FeNi-N/CFC) combining a facile electrodeposition method and in situ nitriding process. The FeNi-N/CFC serves as bifunctional electrocatalyst, requiring a cell voltage of only 1.55 V at j=10 mA cm−2 and exhibits robust long-term durability at j>360 mA cm−2 over 60 h.
      PubDate: 2017-07-04T06:36:04.515343-05:
      DOI: 10.1002/chem.201701662
       
  • Hydrogen Bonds Involving Cavity NH Protons Drives Supramolecular
           Oligomerization of Amido-Corroles
    • Authors: Rafał Orłowski; Mariusz Tasior, Olga Staszewska-Krajewska, Łukasz Dobrzycki, Wojciech Schilf, Barbara Ventura, Michał K. Cyrański, Daniel T. Gryko
      Pages: 10195 - 10204
      Abstract: trans-A2B-Corroles with amide substituents at different positions versus the macrocyclic core have been synthesized. Their self-organizing properties have been comprehensively evaluated both in solid-state and in solution. The rigid arrangement of the amide functionality with the corrole ring led to the formation of strong intramolecular interactions and precluded intermolecular interactions. Replacement of sterically hindered C6F5 substituents at positions 5 and 15 with smaller electron-withdrawing CO2Me groups resulted in significant changes in the self-assembly pattern. With these substituents, tetramers formed in a crystalline state, in which one of the H-pyrrole subunits is out of the corrole plane. This allows the N-H group to form a hydrogen bond with a neighboring carbonyl group of the n-butyl amide fragment. DOSY NMR studies showed that amido-corroles bearing the OCH2CONHnBu motif formed dimers in millimolar solutions in nonpolar solvents and the dimers existed in equilibrium with monomers. However, the corroles possessing meso-ester groups did not form dimers in polar tetrahydrofuran. Comprehensive optical studies allowed the absorption and emission features of the monomer corroles to be characterized in dilute solutions.Organizing corroles: For trans-A2B-corroles possessing amide substituents, a short tether between the amide moiety and the core facilitates hydrogen-bond formation, but only in the intramolecular mode, whereas a flexible linker drives supramolecular oligomerization in the solid state and a dimerization in nonpolar solvents (see figure). The presence of two CO2Me groups at positions 5 and 15 results in formation of tetramers in the crystalline state.
      PubDate: 2017-07-06T05:30:43.83616-05:0
      DOI: 10.1002/chem.201701674
       
  • Dual-Responsive Molecular Switches Based on Dithienylethene–RuII
           Organometallics in Self-Assembled Monolayers Operating at Low Voltage
    • Authors: Andrea Mulas; Xiaoyan He, Yves-Marie Hervault, Lucie Norel, Stéphane Rigaut, Corinne Lagrost
      Pages: 10205 - 10214
      Abstract: Two carbon-rich ruthenium complexes bearing a dithienylethene (DTE) unit and a hexylthiol spacer were designed to be attached on gold surfaces. Both compounds display photochemically driven switching properties, allowing reversible conversion from open to closed forms of the DTE units upon irradiation in solution. In contrast, only the bimetallic complex undergoes an efficient electrochemical ring closure at low potential, (0.5 V vs. SCE), whereas the monometallic complex shows a simple one-electron reversible redox event. These appealing switching properties could be successfully transferred within diluted self-assembled monolayers (SAMs). Furthermore, the two immobilized organometallics exhibit fast electron-transfer kinetics. Therefore, this organometallic strategy allows us to obtain multifunctional surfaces with the possibility of combining switching events triggered by an electrochemical oxidation at low potential and by light at distinct wavelengths for a write-and-erase function, along with an access to different oxidation states. Importantly, a non-destructive electrochemical read-out is achieved at a sufficiently high scan rate that prevents any electrochemical closing. On the whole, the two surface-confined organometallic compounds exhibit appealing properties for application in molecular electronics.Self-assembled monolayers (SAMs) of RuII–DTE organometallic compounds afford multifunctional surfaces combining electro- or photoswitching at remarkably low voltage and fast nondestructive electrochemical read-out.
      PubDate: 2017-07-07T04:27:09.263979-05:
      DOI: 10.1002/chem.201701903
       
  • Thermal Stimuli-Triggered Drug Release from a Biocompatible Porous
           Metal–Organic Framework
    • Authors: Ke Jiang; Ling Zhang, Quan Hu, Qi Zhang, Wenxin Lin, Yuanjing Cui, Yu Yang, Guodong Qian
      Pages: 10215 - 10221
      Abstract: Drug delivery carriers with a high drug loading capacity and biocompatibility, especially for controlled drug release, are urgently needed due to the side effects and frequently dose in the traditional therapeutic method. In our work, a Zr-based metal–organic framework named ZJU-801, which is isoreticular with NU-801, has been designed and further demonstrated as an excellent drug delivery system (DDS) with a high drug loading of 41.7 %. Such a high drug loading capacity may be ascribed to the appropriate match of the size and the large pore volume of this kind of Zr MOF material. Compared with DS@NU-801, this DDS has successfully achieved on-command heating-activated drug release, which was probably attributed to the bulkier ligand, the better stability, and the intense π–π interaction between ZJU-801 and diclofenac sodium (DS) demonstrated comprehensively by SEM, powder X-ray diffraction (PXRD), FTIR and 13C solid-state NMR spectroscopy as well as computer simulations. It is worth noting that premature drug release was avoided effectively without any complicated post-modifications. The low cytotoxicity and good biocompatibility of our DDS were certificated by the in vitro favorable results from an MTT assay, a WST-1 assay, and confocal microscopy imaging.The heat is on: The isoreticular Zr-cluster-based metal–organic framework (MOF) ZJU-801 was synthesized with high drug loading capacity for thermal stimuli-triggered drug release (see figure, DS=diclofenac sodium), thus it could be used as a local heating method for treatment of disease including cancer.
      PubDate: 2017-07-06T05:56:01.191144-05:
      DOI: 10.1002/chem.201701904
       
  • High-Throughput Assay for Enantiomeric Excess Determination in 1,2- and
           1,3-Diols and Direct Asymmetric Reaction Screening
    • Authors: Elena G. Shcherbakova; Valentina Brega, Vincent M. Lynch, Tony D. James, Pavel Anzenbacher
      Pages: 10222 - 10229
      Abstract: A simple and efficient method for determination of the yield, enantiomeric/diasteriomeric excess (ee/de), and absolute configuration of crude chiral diols without the need of work-up and product isolation in a high throughput setting is described. This approach utilizes a self-assembled iminoboronate ester formed as a product by dynamic covalent self-assembly of a chiral diol with an enantiopure fluorescent amine such as tryptophan methyl ester or tryptophanol and 2-formylphenylboronic acid. The resulting diastereomeric boronates display different photophysical properties and allow for fluorescence-based ee determination of molecules containing a 1,2- or 1,3-diol moiety. This method has been utilized for the screening of ee in a number of chiral diols including atorvastatin, a statin used for the treatment of hypercholesterolemia. Noyori asymmetric hydrogenation of benzil was performed in a highly parallel fashion with errors
      PubDate: 2017-07-06T05:31:19.39293-05:0
      DOI: 10.1002/chem.201701923
       
  • Inside Back Cover: Arene-Inserted Extended Germa[n]pericyclynes:
           Synthesis, Structure, and Phosphorescence Properties (Chem. Eur. J.
           42/2017)
    • Authors: Hiroki Tanimoto; Junta Mori, Shunichiro Ito, Yasuhiro Nishiyama, Tsumoru Morimoto, Kazuo Tanaka, Yoshiki Chujo, Kiyomi Kakiuchi
      Pages: 10230 - 10230
      Abstract: New cyclic germanium element-block materials have been synthesized. Arene-inserted extended (ArEx) germa[n]pericyclynes composed of germylene, diyne, and phenylene units showed unique and highly improved UV absorption and fluorescence emission characteristics compared to previous germapericyclynes. Even in the absence of transition metal components, phosphorescence emissions with long lifetimes were observed. Moreover, ArEx germapericyclynes showed high photoluminescence quantum yields, whereas those of acyclic compounds were low. More information can be found in the Full Paper by H. Tanimoto, K. Kakiuchi et al. on page 10080.
      PubDate: 2017-06-13T06:00:48.142731-05:
      DOI: 10.1002/chem.201702134
       
  • Back Cover: CuI/Oxalic Diamide-Catalyzed Cross-Coupling of Thiols with
           Aryl Bromides and Chlorides (Chem. Eur. J. 42/2017)
    • Authors: Chia-Wei Chen; Yi-Ling Chen, Daggula Mallikarjuna Reddy, Kai Du, Chao-En Li, Bo-Hao Shih, Yung-Jing Xue, Chin-Fa Lee
      Pages: 10231 - 10231
      Abstract: A practical synthetic method for the synthesis of diversified thioethers using oxalic diamides as highly air-stable ligands through copper catalysis is demonstrated. A variety of aryl and alkyl thiols were successfully coupled with aryl bromides and aryl chlorides to afford the corresponding thioethers in good yields. This work is the first copper-catalyzed thioetherification of unactivated aryl chlorides. More information can be found in the Full Paper by C.-F. Lee et al. on page 10087.
      PubDate: 2017-06-13T08:20:32.141173-05:
      DOI: 10.1002/chem.201702327
       
 
 
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