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  Subjects -> CHEMISTRY (Total: 849 journals)
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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: 164)
Angewandte Chemie International Edition     Hybrid Journal   (Followers: 212)
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: 284)
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: 110)
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: 174)
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: 150)
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: 243)
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: 19)
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]   [150 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]
  • 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:
       
  • Abstract starts in bold Water-Mediated Structural Transformations of CuII
           5-Halonicotinates Coordination Networks with Distinct Mechanisms
    • Authors: Cheng-Peng Li; Hang Zhou, Yue Ju, Miao Du
      Abstract: Three types of mechanisms regulated by halogen substituent effect, namely single-crystal to single-crystal transformation as well as “core-to-core” and “core-on-shell” processes, have been confirmed for elucidation of the “black box” during structural transformations of dynamic crystalline materials. The combination of time-lapse optical microscopy and X-ray single-crystal diffraction techniques provides a convenient and straightforward approach to reveal the transformation mechanisms. More information can be found in the Communication by M. Du et al. (
      DOI : 10.1002/chem.201702405).
      PubDate: 2017-07-21T02:25:26.40755-05:0
       
  • Frontispiece: Amphoteric Borylketenimines: Versatile Intermediates in the
           Synthesis of Borylated Heterocycles
    • Authors: Sherif J. Kaldas; Kowan T. V. O'Keefe, Rodrigo Mendoza-Sanchez, Andrei K. Yudin
      Abstract: Organoboranes have been widely used in synthetic chemistry. The Lewis acidity of boron is responsible for the challenges frequently encountered in this field. Accordingly, there has been a continuing push to develop new borylation strategies that address the key chemoselectivity problems. The cover art represents the diversity of scaffolds synthesized by A. K. Yudin and his colleagues from novel borylketinimines. These intermediates provide access to azetidimines, iminocoumarins, amides, iminooxetanes and amidines. The artwork was created by Sergey and Daria Karmanny. For more details see page 9711 ff.
      PubDate: 2017-07-21T01:32:58.608923-05:
      DOI: 10.1002/chem.201784162
       
  • Frontispiece: Fluorescence-Lifetime Imaging and Super-Resolution
           Microscopies Shed Light on the Directed- and Self-Assembly of Functional
           Porphyrins onto Carbon Nanotubes and Flat Surfaces
    • Authors: Boyang Mao; David G. Calatayud, Vincenzo Mirabello, Navaratnarajah Kuganathan, Haobo Ge, Robert M. J. Jacobs, Ashley M. Shepherd, José A. Ribeiro Martins, Jorge Bernardino De La Serna, Benjamin J. Hodges, Stanley W. Botchway, Sofia I. Pascu
      Abstract: Stimulated emission depletion (STED) super-resolution imaging and multiphoton fluorescence lifetime imaging techniques are used to image the aggregation of ZnII porphyrin arrays onto flat and conductive, as well as insulating, surfaces. New synthetic routes using directed- as well as self-assembling methods of new, luminescent hybrids incorporating these functional porphyrins and pristine single-walled carbon nanotubes (SWNTs) are reported. Multi-domain imaging and spectroscopy techniques shed light on the potential implications of the covalent and supramolecular functionalization approaches in solution, dispersion, on surfaces and in the solid state. For more information, see the Full Paper by S. I. Pascu et al. on page 9772 ff.
      PubDate: 2017-07-21T01:32:54.866427-05:
      DOI: 10.1002/chem.201784163
       
  • Frontispiece: High-Throughput Optical Imaging and Spectroscopy of
           One-Dimensional Materials
    • Authors: Fengrui Yao; Cheng Chen, Can Liu, Jin Zhang, Feng Wang, Kaihui Liu
      Abstract: Conventionally, the optical signal of individual carbon nanotubes (CNTs) is usually too weak to be probed under optical microscopes. By using a homodyne detection method, scattered light wave from the individual CNTs (ENT) interferes with the reference light (Eref), the intensity of carbon nanotube optical signal can be enhanced by two orders of magnitude, which makes it possible to acquire high-throughput optical images and wide-range spectra of individual nanotubes or horizontal arrays. For more information see the Concept article on by K. Liu et al. on page 9703 ff.
      PubDate: 2017-07-21T01:32:52.229966-05:
      DOI: 10.1002/chem.201784161
       
  • 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
       
  • Investigations on Gold-Catalyzed Thioalkyne Activation Toward Facile
           Synthesis of Ketene Dithioacetals
    • Authors: Xiaohan Ye; Jin Wang, Shengtao Ding, Seyedmorteza Hosseyni, Lukasz Wojtas, Novruz G. Akhmedov, Xiaodong Shi
      Abstract: Nucleophilic addition to thioalkynes was investigated under various catalytic conditions with gold(I) complexes being identified as the optimal catalysts. Structural evaluation of the product revealed an unexpected cis-addition, arising from a gold-associated thioketene intermediate. Based on this interesting mechanistic insight, a gold(I)-catalyzed thioether addition to thioalkynes was developed as a novel approach to prepare ketene dithioacetals with good yields and high efficiency.The golden days: Nucleophilic addition to thioalkynes was investigated under various catalytic conditions with gold(I) complexes being identified as the optimal catalysts. Structural evaluation of the product revealed an unexpected cis-addition, arising from a gold-associated thioketene intermediate. Based on this interesting mechanistic insight, a gold(I)-catalyzed thioether addition to thioalkynes was developed as a novel approach to prepare ketene dithioacetals with good yields and high efficiency.
      PubDate: 2017-07-20T08:45:48.995496-05:
      DOI: 10.1002/chem.201702710
       
  • 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
       
  • Constructing a Robust Fluorescent DNA-Stabilized Silver Nanocluster Probe
           Module by Attaching a Duplex Moiety
    • Authors: Ruoyun Lin; Guangyu Tao, Yang Chen, Mingxing Chen, Feng Liu, Na Li
      Abstract: Fluorescent DNA-templated silver nanoclusters (DNA-Ag NCs) have served as excellent luminescent probes and operation units in various applications. However, the fluorescence property of DNA-Ag NCs is very sensitive to elongation or modification of the DNA template, limiting the breadth of applications. In this work, we propose a strategy for constructing a robust fluorescent DNA-Ag NCs probe module by attaching a duplex moiety to the nanocluster-bearing sequence. The fluorescence intensity of the DNA-Ag NCs can be enhanced 90-fold upon hybridization of the elongated moiety. Adenine in the linker sequence has a further enhancing effect on the fluorescence intensity, whereas thymine has a quenching effect. The transformation from a non-fluorescent species to fluorescent nanoclusters is responsible for the fluorescence enhancement with duplex formation of the elongated moiety. We hope that this design will aid future diversification of experimental designs to facilitate more applications that are currently limited by the aforementioned problems.Duplex-enhanced fluorescence: A robust fluorescent DNA-stabilized silver nanocluster probe module has been constructed by attaching an elongated moiety to the nanocluster-bearing moiety. Both the fluorescence intensity and the spectral purity of the nanocluster are remarkably improved upon duplex formation of the elongated moiety (see figure). The simplicity and versatility of this probe module make it promising for various applications.
      PubDate: 2017-07-20T05:05:51.500819-05:
      DOI: 10.1002/chem.201701879
       
  • Direct C2-Functionalization of Indoles Triggered by the Generation of
           Iminium Species from Indole and Sulfonium Salt
    • Authors: Masanori Tayu; Kazuya Nomura, Koki Kawachi, Kazuhiro Higuchi, Nozomi Saito, Tomomi Kawasaki
      Abstract: An indole core bearing a functional group on the C2 position is often found as a key structure in biologically active natural products and pharmaceuticals. Here, we report direct C2-functionalization of indoles triggered by the formation of an iminium species generated from indole and a sulfonium reagent. The reaction proceeded under very mild conditions to give the corresponding C2-substituted indole derivatives in good to high yields.Pulling the trigger: Direct C2-functionalization of indoles triggered by the formation of an iminium species generated from indole and a sulfonium salt is demonstrated. The reaction proceeded under very mild conditions to give the C2-substituted indole derivatives in good to high yields.
      PubDate: 2017-07-20T05:05:33.68714-05:0
      DOI: 10.1002/chem.201702338
       
  • Photo-Controlled Waves and Active Locomotion
    • Authors: Irving R. Epstein; Qingyu Gao
      Abstract: Waves of chemical concentration, created by the interaction between reaction and diffusion, occur in a number of chemical systems far from equilibrium. In appropriately chosen polymer gels, these waves generate mechanical forces, which can result in locomotion. When a component of the system is photosensitive, light can be used to modulate and control these waves. In this Concept article, we examine various forms of photo-control of such systems, focusing particularly on the Belousov–Zhabotinsky oscillating chemical reaction. The phenomena we consider include image storage and image processing, feedback-control and feedback-induced clustering of waves, and phototropic and photophobic locomotion. Several of these phenomena have analogues in or potential applications to biological systems.Making waves: This article addresses how light can be used to control reaction–diffusion waves and wave-driven active locomotion. Inhomogeneous illumination of a gel containing the constituents of an oscillating chemical reaction can be used to generate unidirectional and reciprocating locomotion of the gel, phenomena analogous to biological crawling motion and round-trip migration.
      PubDate: 2017-07-20T05:01:19.666801-05:
      DOI: 10.1002/chem.201700725
       
  • Exploiting Pincer Ligands to Perturb the Geometry at Boron
    • Authors: Kexuan Huang; Jason L. Dutton, Caleb D. Martin
      Abstract: Boranes are ubiquitous in synthesis and materials but advancements in their development have been primarily restricted to the geometric energetic minima, trigonal planar complexes. This report discloses a class of boranes with expanded bond angles achieved by taking advantage of the structural rigidity of tridentate pincer ligands. The bonding of these novel boranes is investigated by X-ray crystallography and computationally.Boron Pinces One Out: Boranes are ubiquitous in synthesis and materials, but advancements in their development have been primarily restricted to the geometric energetic minima, trigonal planar complexes. This report discloses a new class of boranes with distorted geometries that are achieved by taking advantage of the structural rigidity of tridentate pincer ligands.
      PubDate: 2017-07-20T05:01:08.391157-05:
      DOI: 10.1002/chem.201703045
       
  • N-Heterocyclic Phosphenium Complex of Manganese: Synthesis and Catalytic
           Activity in Ammonia Borane Dehydrogenation
    • Authors: M. Gediga; C. M. Feil, S. H. Schlindwein, J. Bender, M. Nieger, D. Gudat
      Abstract: Subsequent reactions of a neutral phosphenium complex of Mn with H− and H+ sources resulted in a stoichiometric H2 addition to the Mn=P double bond, which can be reversed upon thermal or photochemical excitation. In contrast, in the reaction with NH3BH3, the same complex acted as dehydrogenation catalyst. DFT studies suggested to explain this transformation as a ligand-centred process, in which the H+/H− pair is picked up by the phosphenium ligand and the metal is mainly a spectator. Apart from being the first application of a phosphenium complex in catalysis, this discovery adds a new twist to the further development of ligand-centred reactivity and the use of metal complexes in catalysis. More information can be found in the Full Paper by D. Gudat et al. (
      DOI : 10.1002/chem.201701442).
      PubDate: 2017-07-20T05:00:38.643958-05:
       
  • Multiple Magnetic Relaxation Pathways and Dual-Emission Modulated by a
           Heterometallic Tb-Pt Bonding Environment
    • Authors: Takefumi Yoshida; David Chukwuma Izougu, Daichi Iwasawa, Shuhei Ogata, Miki Hasegawa, Brian K. Breedlove, Goulven Cosquer, Wolfgang Wernsdorfer, Masahiro Yamashita
      Abstract: A heterometallic Tb-Pt complex, [Tb2Pt3(SAc)12(H2O)2] (SAc=thioacetate), was synthesized. Dual emission was modulated by the presence of a heterometallic Tb–Pt bonding environment. The heterometallic Tb–Pt bond lowers the symmetry of the Tb ion and enhanced the emission efficiency. In addition, the Tb–Pt complex shows field-induced multiple magnetic relaxation pathways. Furthermore, it served as an antenna for the observed dual emission. In other words, the heterometallic Tb–Pt bond has a significant effect on the luminescence and magnetic properties of the complex.Let it shine: A heterometallic Tb-Pt bonding environment lowered the symmetry around the Tb ion, and caused an enhancement in the observed luminescence and magnetic properties of the complex. Furthermore, it served as an antenna for the observed dual emission.
      PubDate: 2017-07-20T05:00:31.16388-05:0
      DOI: 10.1002/chem.201702989
       
  • 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
       
  • Photoactivation of Anticancer Ru Complexes in Deep Tissue: How Deep Can We
           Go'
    • Authors: Wen Sun; Raweewan Thiramanas, Leonardo D. Slep, Xiaolong Zeng, Volker Mailänder, Si Wu
      Abstract: Activation of anticancer therapeutics such as ruthenium (Ru) complexes is currently a topic of intense investigation. The success of phototherapy relies on photoactivation of therapeutics after the light passes through skin and tissue. In this paper, the photoactivation of anticancer Ru complexes with 671-nm red light through tissue of different thicknesses was studied. Four photoactivatable Ru complexes with different absorption wavelengths were synthesized. Two of them (Ru3 and Ru4) were responsive to wavelengths in the “therapeutic window” (650–900 nm) and could be activated using 671-nm red light after passing through tissue up to 16-mm-thick. The other two (Ru1 and Ru2) could not be activated using red light. Additionally, activated Ru4 caused inhibition of cancer cells. These results suggest that photoactivatable Ru complexes are promising for applications in deep-tissue phototherapy.Anticancer ruthenium (Ru) complexes can be photoactivated by 671-nm light after passing through a 16-mm-thick tissue. The photoactivated Ru complexes can inhibit the growth of cancer cells. These results suggest that Ru complexes are promising anticancer agents for deep-tissue phototherapy.
      PubDate: 2017-07-19T08:25:36.865982-05:
      DOI: 10.1002/chem.201701224
       
  • Programmed Synthesis of Molecular Wires with Fixed Insulation and Defined
           Length Based on Oligo(phenylene ethynylene) and Permethylated
           α-Cyclodextrins
    • Authors: Hiroshi Masai; Tetsuaki Fujihara, Yasushi Tsuji, Jun Terao
      Abstract: The development of new tuning methods for π-conjugated insulated molecular wires with strictly defined axle lengths as well as positions and degrees of macrocycle coverage would provide unprecedented insight into insulation effects in functionalized materials. Herein, iterative reactions of oligo(phenylene ethynylene) (OPE) linked with permethylated α-cyclodextrins were carried out to fabricate insulated molecular wires with a defined length and insulation in desired areas. Insulated OPEs were elongated in a stepwise manner by performing sequential coupling/deprotection reactions. The insulated areas on the OPE units in each expansion step were selectively controlled by means of programmed solvent conditions (high/low polarity). Moreover, a completely insulated OPE (up to a linked [11]rotaxane) with high structural regularity and high covering ratio was synthesized by appropriate tuning of the Pd catalyst and an extension unit bearing a traceless capping unit based on a tert-butyldimethylsilyl group. This strategy may guide the development of the selective synthesis of fully insulated, partially insulated, and uninsulated molecular wires with well-defined lengths and covered/uncovered areas.Word on the wire: A strategy for the synthesis of insulated molecular wires (IMWs) based on oligo(phenylene ethynylene) and permethylated α-cyclodextrins was developed by applying an iterative reaction to rotaxane synthesis, which could strictly control the axle lengths and positions/degrees of coverage with multiple macrocycles (see figure). The precise engineering of IMWs would provide unprecedented materials with highly adjustable properties.
      PubDate: 2017-07-19T08:21:28.752619-05:
      DOI: 10.1002/chem.201701428
       
  • On the Accessible Reaction Channels of Vinyl Gold(I) Species: π- and
           σ-Pathways
    • Authors: Laura Nunes dos Santos Comprido; Johannes E. M. N. Klein, Gerald Knizia, Johannes Kästner, A. Stephen K. Hashmi
      Abstract: The potential of vinyl Au species to react either through a controlled π- or σ-pathway is demonstrated. This nomenclature is directly derived from the orbitals of the vinyl Au species leading to the newly formed bonds. When the π-bond of the vinyl Au intermediate is transformed into a σ-bond, we name it π-pathway, and a σ- to σ- transformation is named σ-pathway. Examples of reactions following these pathways are a Au-catalysed [3,3]-sigmatropic rearrangement and a protodeauration reaction. These reactions have been studied using intrinsic bond orbitals (IBOs) and allow for the clear identification of these pathways. Energies for the reaction path of the Au-catalysed [3,3]-sigmatropic rearrangement were in addition computed using CCSD(T)-F12. Analysis of the intrinsic reaction coordinate (IRC) of the [3,3]-sigmatropic rearrangement using IBOs further allows us to refine the previous mechanistic proposal and identifies a hidden intermediate along the reaction path.One intermediate, two reaction channels: Following the intrinsic reaction coordinates of a Au-catalysed sigmatropic rearrangement and a protodeauration reaction, two different reaction pathways were found aided by intrinsic bond orbital analysis, showing the versatility of vinyl gold species in the context of catalysis.
      PubDate: 2017-07-19T08:20:51.425343-05:
      DOI: 10.1002/chem.201702023
       
  • 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
       
  • Visible Light Induced Organic Transformations Using
           Metal-Organic-Frameworks (MOFs)
    • Authors: Xiaoyu Deng; Zhaohui Li, Hermenegildo García
      Abstract: With the aim of developing renewable energy based processes, researchers are paying increasing interest to light induced organic transformations. Metal-organic frameworks (MOFs), a class of micro-/mesoporous hybrid materials, are recently emerging as a new type of photoactive materials for organic syntheses due to their unique structural characteristics. In this Review, we summarized the recent applications of MOFs as photocatalysts for light induced organic transformations, including (1) oxidation of alcohols, amines, alkene, alkanes and sulfides; (2) hydroxylation of aromatic compounds like benzene; (3) activation of the C−H bonds to construct new C−C or C−X bonds; (4) atom-transfer radical polymerization (ATRP). This Review starts with general background information of using MOFs in photocatalysis, followed by a description of light induced organic transformations promoted by photoactive inorganic nodes and photocatalytic active ligands in MOFs, respectively. Thereafter, the use of MOFs as multifunctional catalysts for light induced organic transformations via an efficient merge of the metal/ligand/guest based catalysis where the photocatalytic activity of MOFs plays a key role are discussed. Finally, the limitations, challenges and the future perspective of the application of MOFs for light induced organic transformations were addressed. The objective of this Review is to serve as a starting point for other researchers to get into this largely unexplored field. It is also our goal to stimulate intensive research in this field for rational designing of MOF materials to overcome their current limitations in photocatalysis, which can lead to more creative visible-light-induced organic transformations.Let there be light: Due to their peculiar structural characteristics, metal-organic frameworks (MOFs), a class of micro-/mesoporous hybrid materials, are recently emerging as a new type of photoactive materials for light-induced organic syntheses.
      PubDate: 2017-07-19T06:58:11.839177-05:
      DOI: 10.1002/chem.201701460
       
  • Nonheme Iron-Oxo-Catalyzed Methane Formation from Methyl Thioethers:
           Scope, Mechanism, and Relevance for Natural Systems
    • Authors: Kathrin Benzing; Peter Comba, Bodo Martin, Bianca Pokrandt, Frank Keppler
      Abstract: A range of nonheme oxo-iron(IV) model systems with tetra- or pentadentate ligands is shown to produce methane from methionine and other thioethers. This model reaction for the natural aerobic production of methane is shown to proceed via two sulfoxidation steps involving the oxo-iron(IV) complexes, with a bifurcation in the second step that either produces the sulfone or leads to demethylation with similar probabilities. In the presence of O2, the resulting methyl radicals produce methanol and formate or, in an O2-depleted environment, lead to formation of methane.Methionine and other methyl thioether natural products might be responsible for the formation of substantial amounts of the greenhouse gas methane.
      PubDate: 2017-07-19T06:36:15.895903-05:
      DOI: 10.1002/chem.201701986
       
  • SERS and SERRS Detection of the DNA Lesion 8-Nitroguanine: A Self-Labeling
           Modification
    • Authors: Susan Dick; Steven E. J. Bell, Katie J. Alexander, Ian A. O'Neil, Richard Cosstick
      Abstract: Rapid and sensitive methods to detect DNA lesions are essential in order to understand their role in carcinogenesis and for potential diagnosis of cancers. The 8-nitroguanine DNA lesion, which is closely associated with inflammation-induced cancers, has been characterized for the first time by surface-enhanced Raman spectroscopy (SERS). This lesion has been studied as the free base, as well as part of a dinucleotide and oligodeoxynucleotides (ODNs) at 5 different excitation wavelengths in the range 785–488 nm. All nitrated samples produced distinctly different spectra from their control guanine counterparts, with nitro bands being assigned by DFT calculations. Additional resonance enhancement was observed at the shorter excitation wavelengths, these SERRS measurements allowed the detection of one nitrated guanine in over 1,300 bases. In addition, SER(R)S can be used to detect whether the unstable lesion is covalently attached to the ODN or has been released by hydrolytic depurination.Inflamed DNA gets found out: The 8-nitroguanine DNA lesion, which is closely associated with chronic inflammation, has been characterized by surface-enhanced Raman (SERS) and resonance Raman (SERRS) spectroscopy. SERRS is exquisitely sensitive for this lesion and allows the detection of one 8-nitroguanine in over 1,300 bases (see scheme).
      PubDate: 2017-07-19T06:35:49.91605-05:0
      DOI: 10.1002/chem.201701791
       
  • Room-Temperature Oligomeric Discotic Nematic Liquid Crystals over a Wide
           Temperature Range: Structure–Property Relationships
    • Authors: Monika Gupta; Santosh Prasad Gupta, Subhransu Sekhar Mohapatra, Surajit Dhara, Santanu Kumar Pal
      Abstract: The design and synthesis of three room-temperature discotic nematic (ND) liquid crystals (LCs) is presented. The LC consists of an azobenzene core attached to which are four pentaalkynylbenzene (PA) units through flexible alkyl spacers. The presence of a short azo linking group provides more disorder in the system, thereby reducing the packing efficiency among the PA units and resulting into the formation of a room-temperature ND phase over a wide temperature range. Dielectric constant and birefringence studies were performed to gain further insights into the physical properties of the mesophase.Oligomeric guys: A new approach is reported for the design of a room-temperature discotic nematic liquid crystal derived from azobenzene and pentaalkynylbenzene units (see scheme). Dielectric constant and birefringence studies were performed to gain further insights into the physical properties of the mesophase.
      PubDate: 2017-07-19T06:35:30.94226-05:0
      DOI: 10.1002/chem.201701578
       
  • Synthesis and Antigenic Evaluation of Oligosaccharide Mimics of Vi Antigen
           from Salmonella typhi
    • Authors: Gao-Lan Zhang; Lin Yang, Jingjing Zhu, Mengman Wei, Wanjun Yan, De-Cai Xiong, Xin-Shan Ye
      Abstract: Salmonella typhi is responsible for typhoid fever, which is a serious health threat in developing countries. As a virulent factor of Salmonella typhi, the purified Vi polysaccharide (Vi PS) has become an effective vaccine to combat typhoid fever. The chemical synthesis can provide homogeneous and well-defined molecules for the development of Vi-based vaccines. However, the synthesis of Vi oligosaccharides in high yields and with exclusive α-stereoselectivities remains very challenging. In this paper, a series of Vi pseudooligosaccharides, including pseudo tetra-, hexa-, and octa-saccharides were efficiently synthesized. These oligosaccharide analogues were conjugated by carbon chain tether through olefin cross metathesis or by the 1,2,3-triazole moiety through copper (I)-catalyzed alkyne–azide cycloaddition reaction (CuAAC). The binding affinities of these oligosaccharide mimics to anti-Vi antibodies were investigated. These results will be beneficial to the further development of Vi-based oligosaccharide vaccines.Three series of new Vi oligosaccharide mimics were efficiently synthesized. These pseudooligosaccharides were linked by the carbon chain tether through olefin cross metathesis or by the 1,2,3-triazole moiety through copper (I)-catalyzed alkyne–azide cycloaddition reaction. The binding affinities of these pseudooligosaccharides to anti-Vi antibodies were investigated.
      PubDate: 2017-07-19T06:30:50.741218-05:
      DOI: 10.1002/chem.201702114
       
  • Achieving High Levels of NMR-Hyperpolarization in Aqueous Media With
           Minimal Catalyst Contamination Using SABRE
    • Authors: Wissam Iali; Alexandra M. Olaru, Gary G. R. Green, Simon B. Duckett
      Abstract: Signal amplification by reversible exchange (SABRE) is shown to allow access to strongly enhanced 1H NMR signals in a range of substrates in aqueous media. To achieve this outcome, phase-transfer catalysis is exploited, which leads to less than 1.5×10−6 mol dm−3 of the iridium catalyst in the aqueous phase. These observations reflect a compelling route to produce a saline-based hyperpolarized bolus in just a few seconds for subsequent in vivo MRI monitoring. The new process has been called catalyst separated hyperpolarization through signal amplification by reversible exchange or CASH-SABRE. We illustrate this method for the substrates pyrazine, 5-methylpyrimidine, 4,6-d2-methyl nicotinate, 4,6-d2-nicotinamide and pyridazine achieving 1H signal gains of approximately 790-, 340-, 3000-, 260- and 380-fold per proton at 9.4 T at the time point at which phase separation is complete.Show me the money: Catalyst separated hyperpolarization through signal amplification by reversible exchange or CASH-SABRE allows access to strongly enhanced 1H, 13C and 15N NMR signals for a range of substrates in aqueous media through phase-transfer catalysis. Very limited catalyst contamination is observed and hence a biocompatible bolus is readily achieved.
      PubDate: 2017-07-19T06:23:24.060654-05:
      DOI: 10.1002/chem.201702716
       
  • Tuning the Reactivity of Functionalized Diallylic Alcohols: Brønsted
           versus Lewis Acid Catalysis
    • Authors: Luisa Lempenauer; Elisabet Duñach, Gilles Lemière
      Abstract: The chemodivergent reactivity of bifunctional, enol thioether-containing diallylic alcohols in acidic medium is disclosed, highlighting the difference between strong Lewis acid and mild Brønsted acid catalysis. In the presence of bismuth(III) triflate, allylic alcohol activation affords diversely substituted cyclopentenones in a Nazarov-type electrocyclization, whereas activation of the thioenol ether by p-toluenesulfonic acid provides an entry to α-sulfenylated β,γ-unsaturated ketones. Both methods represent a facile access to the corresponding products under mild conditions, using inexpensive and non-toxic catalytic systems.Let the acid decide: The chemodivergent reactivity of bifunctional enol thioether-containing diallylic alcohols is described, hereby highlighting the difference between mild Brønsted acid and strong Lewis acid catalysis.
      PubDate: 2017-07-19T06:23:14.496848-05:
      DOI: 10.1002/chem.201702601
       
  • Self-Assembly of Cyclohelicate [M3L3] Triangles Over [M4L4] Squares,
           Despite Near-Linear Bis-terdentate L and Octahedral M
    • Authors: Ross W. Hogue; Sébastien Dhers, Ryan M. Hellyer, Jingwei Luo, Garry S. Hanan, David S. Larsen, Anna L. Garden, Sally Brooker
      Abstract: Self-assembly of 1:1:2 MII(BF4)2 (M=Zn or Fe), pyrazine-2,5-dicarbaldehyde (1) and 2-(2-aminoethyl)pyridine gave trimetallic triangle architectures rather than the anticipated tetrametallic [2×2] squares. Options for the nontrivial synthesis of 1 are considered, and synthetic details provided for both preferred routes. Rare cyclohelicate triangle architectures are observed for the pair of structurally characterized yellow-brown [Zn3L3](BF4)6 and dark green [Fe3L3](BF4)6 complexes of the neutral bis-terdentate Schiff base L. In order to form these pyrazine-edged triangles, the octahedral metal ions—with all 6 N-donors provided by the terdentate binding pockets of two L—are located 0.4–0.5 Å out of the plane of the bridging pyrazines, towards the center of the triangle. Density functional theory calculations confirm that simple particle counting entropic arguments, which predict triangles over squares, are correct here, with the triangles shown to be energetically favored over the corresponding squares. However, importantly, DFT analysis of these and related triangle versus square systems also show that vibrational contributions to entropy dominate and may significantly influence the preferred architecture, such that simple particle counting cannot in general be reliably employed to predict the observed architecture.Rare cyclohelicate triangle architectures, not squares as seen for the bis-terdentate di-amide ligand, self-assemble when the di-imine analogue is employed. In the triangles, the octahedral metal ions are located 0.4–0.5 Å out of the plane of the bridging pyrazine rings, towards the center of the triangle. DFT calculations correctly predict the observed triangle architectures to be energetically favored (see scheme).
      PubDate: 2017-07-19T06:23:01.907321-05:
      DOI: 10.1002/chem.201702153
       
  • A Simple Route to Strong Carbon-13 NMR Signals Detectable for Several
           Minutes
    • Authors: Soumya S. Roy; Philip Norcott, Peter J. Rayner, Gary G. R. Green, Simon B. Duckett
      Abstract: Nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) suffer from low sensitivity and limited nuclear spin memory lifetimes. Although hyperpolarization techniques increase sensitivity, there is also a desire to increase relaxation times to expand the range of applications addressable by these methods. Here, we demonstrate a route to create hyperpolarized magnetization in 13C nuclear spin pairs that last much longer than normal lifetimes by storage in a singlet state. By combining molecular design and low-field storage with para-hydrogen derived hyperpolarization, we achieve more than three orders of signal amplification relative to equilibrium Zeeman polarization and an order of magnitude extension in state lifetime. These studies use a range of specifically synthesized pyridazine derivatives and dimethyl p-tolyl phenyl pyridazine is the most successful, achieving a lifetime of about 190 s in low-field, which leads to a 13C-signal that is visible for 10 minutes.Only time will tell: A fast and cost-effective method to increase carbon-13 NMR sensitivity by three orders of magnitude is detailed for a series of pyridazine derivatives. When the resulting polarization is stored as long-lived singlet order, the resulting hyperpolarized 13C NMR signals remain detectable for up to 10 minutes.
      PubDate: 2017-07-19T06:22:21.155263-05:
      DOI: 10.1002/chem.201702767
       
  • 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
       
  • Simultaneous Visualization and Quantitation of Multiple Steroid Hormones
           Based on Signal-Amplified Biosensing with Duplex Molecular Recognition
    • Authors: Yaning Tan; Xiaoxia Hu, Meng Liu, Xinwen Liu, Xiaobo Lv, Zhihao Li, Jie Wang, Quan Yuan
      Abstract: The simultaneous quantitation of multiple steroid hormones in real time is of great importance in medical diagnosis. In this study, a portable hormone biosensor based on duplex molecular recognition coupled with a signal-amplified substrate was successfully developed for the simultaneous visualization and quantitation of multiple steroid hormones. Aptamer-functionalized upconversion nanoparticles (UCNPs) with different emission peaks are immobilized on the photonic crystal (PC) substrate as the nanoprobes, leading to the specific and simultaneous assay of multiple steroid hormones. Coupled with the luminescence-enhanced effect of the PC substrate, nanomolar quantification limits of multiple hormones are achieved. This well-designed biosensor is also promising in the quantification of multiple hormones in serum samples. The amplified luminescence signals can be visualized with the naked eye and captured by an unmodified phone camera. This hormone quantitation biosensor exhibits the advantages of multi-detection, visualization, high sensitivity, and selectivity for potential applications in clinical disease diagnosis.Simultaneous quantitation of multiple steroid hormones: A portable hormone biosensor based on duplex molecular recognition coupled with a signal-amplified substrate was successfully developed for the simultaneous visualization and quantitation of multiple steroid hormones. This biosensor exhibits the advantages of multi-detection, visualization, high sensitivity, and selectivity for potential applications in clinical disease diagnosis.
      PubDate: 2017-07-19T01:37:24.865361-05:
      DOI: 10.1002/chem.201702220
       
  • Photoelectrochemical H2 Generation from Suboxide TiO2 Nanotubes:
           Visible-Light Absorption versus Conductivity
    • Authors: Shiva Mohajernia; Seyedsina Hejazi, Anca Mazare, Nhat Truong Nguyen, Patrik Schmuki
      Abstract: In the present work we report on the key factors dictating the photoelectrochemical (PEC) performance of suboxide titania (TiOx) nanotubes. TiOx nanotubes were produced by a systematic variation of reduction heat treatments of TiO2 in Ar/H2. The properties of the TiOx tubes were investigated by electron paramagnetic resonance (EPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), solid-state conductivity, reflectivity measurements, photocurrent spectroscopy, and photoelectrochemical hydrogen evolution. In line with earlier literature, these suboxide tubes show a drastically improved photoelectrochemical water-splitting performance compared to non-reduced anatase TiO2 tubes. In this work we show that the key improvement in water-splitting performance is due to the strongly improved conductivity of TiOx semimetalic tubes, reaching 13.5 KΩ per tube compared to 70 MΩ (for non-reduced anatase), and is not due to the enhanced visible-light absorbance.Ar/H2 treatment of anodic titania nanotube layers leads to drastically enhanced electron transport. Reduced TiOx nanotubes were obtained by a systematic variation of the reduction heat treatment. Such nanotubes show a significant enhancement in conductivity and photoelectrochemical performance, with a significantly enhanced photoresponse in the visible range compared to the pristine anatase TiO2 nanotubes (see scheme).
      PubDate: 2017-07-19T01:25:35.814241-05:
      DOI: 10.1002/chem.201702245
       
  • Excess Electron Transfer through DNA Duplexes Comprising a Metal-Mediated
           Base Pair
    • Authors: Susanne Hensel; Kevin Eckey, Philipp Scharf, Nicole Megger, Uwe Karst, Jens Müller
      Abstract: Excess electron transfer through one set of DNA duplexes comprising either one or two metal-mediated thymine–HgII–thymine base pairs was studied. Towards this end, the metal-mediated base pair(s) were introduced between an artificial nucleoside bearing a N,N,N′,N′-tetramethyl-1,5-diaminonaphthalene derivative (dN, acting as a photoinducible electron donor) and 5-bromo-2′-deoxyuridine (dB, acting as an electron acceptor). Upon one-electron reduction, dB loses a bromide ion. The amount of unreacted dB remaining after irradiation—determined by LC/ICP-MS—was used to evaluate the charge-transfer efficiency across the metal-mediated base pair(s). Reference measurements with canonical adenine:thymine base pairs prove the applicability of this approach for the detection of charge transfer in DNA. The data indicate that, for the set of DNA duplexes under investigation, excess electron transfer across a thymine–HgII–thymine base pair proceeds with low efficiency, comparable to the transfer across a thymine:thymine mispair. Two contiguous thymine–HgII–thymine base pairs effectively shut down excess electron transfer.A new method for an evaluation of the efficiency of excess electron transfer through DNA duplexes is introduced. Its application to the study of charge transfer across a thymine–HgII–thymine base pair indicates a significant decline compared with a canonical base pair (see scheme).
      PubDate: 2017-07-19T01:25:27.161624-05:
      DOI: 10.1002/chem.201702241
       
  • 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
       
  • Tandem Tetrahydroisoquinoline-4-carboxylic Acid/β-Alanine as a New
           Construct Able To Induce a Flexible Turn
    • Authors: Raffaella Bucci; Andrea Bonetti, Francesca Clerici, Alessandro Contini, Donatella Nava, Sara Pellegrino, Davide Tessaro, Maria Luisa Gelmi
      Abstract: Tetrahydroisoquinoline-4-carboxylic acid, a constrained β2-amino acid named β-TIC, was synthesised for the first time in enantiopure form. The biocatalytic route applied herein represents one of the few successful examples of enzymatic resolution of β2-amino acids. Model tetrapeptides, namely, Fmoc-l-Ala-β-TIC-β-Ala-l-Val-OBn (Fmoc=fluorenylmethyloxycarbonyl, Bn=benzyl), containing both isomers of β-TIC, were prepared. Both computational and NMR spectroscopy studies were performed. A reverse-turn conformation was observed in the case of (R)-β-TIC enantiomer that was obtained in 99 % enantiomeric excess by enzymatic resolution. The β-TIC/β-Ala construct represents the first example of a flexible turn mimetic containing a cyclic and an acyclic β-amino acid. Furthermore, the presence of an aromatic ring of β-TIC could facilitate non-covalent interactions to increase the potential of this scaffold for the preparation of protein–protein interaction modulators.Flexibility and adaptability: Tetrahydroisoquinoline-4-carboxylic acid, a constrained β2-amino acid named β-TIC, was prepared in enantiopure form, for the first time, and used for the synthesis of model tetrapeptides. The (R)-β-TIC/β-Ala construct represents the first example of a flexible turn mimetic, containing cyclic and acyclic β-amino acids, which could promote hairpin formation (see scheme).
      PubDate: 2017-07-18T06:15:46.947033-05:
      DOI: 10.1002/chem.201701045
       
  • PCR Incorporation of Polyoxometalate Modified Deoxynucleotide
           Triphosphates and Their Application in Molecular Electrochemical Sensing
           of Yersinia pestis
    • Authors: Mayreli Ortiz; Ahmed M. Debela, Marketa Svobodova, Serge Thorimbert, Denis Lesage, Richard B. Cole, Bernold Hasenknopf, Ciara K. O'Sullivan
      Abstract: Redox-labeled nucleotides are of increasing interest for the fabrication of next generation molecular tools and should meet requirements of being thermally stable, sensitive, and compatible with polymerase-mediated incorporation while also being electrochemically discriminable. The synthesis and characterization of Keggin and Dawson polyoxometalate–deoxynucleotide (POM–dNTP) bioconjugates linked through 7-deaza-modified purines is described. The modified POM–dNTPs were used for polymerase-based amplification of a DNA sequence specific for Yersinia pestis and the amplified DNA detected using an electrochemical DNA sensor. This highlights the potential of polyoxometalates as thermally stable, sensitive and polymerase-compatible redox labels for exploitation in bioanalytical applications.Decorating DNA: Keggin and Dawson polyoxometalate–deoxynucleotide (POM–dNTP) bioconjugates were used for decorating a DNA sequence through a polymerase-based amplification. This amplified DNA product was detected using differential pulse voltammetry.
      PubDate: 2017-07-18T06:15:37.170545-05:
      DOI: 10.1002/chem.201701295
       
  • Alternating Copolymer of Double Four Ring Silicate and Dimethyl Silicone
           Monomer–PSS-1
    • Authors: Sam Smet; Steven Vandenbrande, Pieter Verlooy, Stef Kerkhofs, Eric Breynaert, Christine E. A. Kirschhock, Charlotte Martineau-Corcos, Francis Taulelle, Veronique van Speybroeck, Johan A. Martens
      Abstract: Systematic linking of double four-ring (D4R) silicate units through their corners with dimethylsilicone monomers creates a new silicate–silicone copolymer named PSS-1 (polyoligosiloxysilicone number one). PSS-1, which consists of twisted columns of D4R units bridged by dimethylsilicone, shows exceptional thermal stability and mechanical strength. This new polymer is the first member of a new class of materials termed Posisils synthesized from pre-shaped silicate units and silicone linkers. More information can be found in the Full Paper by J. A. Martens et al. (
      DOI : 10.1002/chem.201701237).
      PubDate: 2017-07-18T06:12:44.024195-05:
       
  • Enhancing Catalytic Activity of Bioanode for Glucose Biofuel Cell by
           Compressing Enzyme, Mediator and Carbon Support through Centrifugation
    • Authors: Desmond Chun Long Tan; Hirotaka Sato
      Abstract: Through centrifugation, glucose oxidase, ferrocenemethanol (mediator), and graphene-support mixed in solution can be compressed. The respective components are able to interact with higher mobility. Improved immobilization of glucose oxidase and ferrocenemethanol can also be achieved in the graphene layers, where enhanced electron transfer can be observed via mediators. These results open opportunities for the fabrication of electrodes for diverse enzyme–mediator conjugates in biofuel cells. More information can be found in the Communication by D. C. L. Tan and H. Sato (
      DOI : 10.1002/chem.201702100).
      PubDate: 2017-07-18T06:12:39.329511-05:
       
  • Temporal Control over Transient Chemical Systems using Structurally
           Diverse Chemical Fuels
    • Authors: Jack L.-Y. Chen; Subhabrata Maiti, Ilaria Fortunati, Camilla Ferrante, Leonard J. Prins
      Abstract: Small molecules with multiple negative charges template the formation of vesicular aggregates by stabilizing multivalent interactions with the cationic head group of the surfactants. An enzyme slowly cleaves the molecules leading to a loss of these interactions and, consequently, spontaneous dissociation of the aggregates takes place. The lifetime of the aggregates is determined by the stability of the molecules against enzymatic cleavage. More information can be found in the Full Paper by L. J. Prins et al. (
      DOI : 10.1002/chem.201701533).
      PubDate: 2017-07-18T06:12:36.360204-05:
       
  • α-Unsubstituted Pyrroles by NHC-Catalyzed Three-Component Coupling:
           Direct Synthesis of a Versatile Atorvastatin Derivative
    • Authors: Mirco Fleige; Frank Glorius
      Abstract: A practical one-pot cascade reaction protocol provides direct access to valuable 1,2,4-trisubstituted pyrroles. The process involves an N-heterocyclic carbene (NHC)-catalyzed Stetter-type hydroformylation using glycolaldehyde dimer as a novel C1 building-block, followed by a Paal-Knorr condensation with primary amines. The reaction makes use of simple and commercially available starting-materials and catalyst, an important feature regarding applicability and utility. Low catalyst loading under mild reaction conditions afforded a variety of 1,2,4-substituted pyrroles in a transition-metal-free reaction with high step economy and good yields. This methodology is applied in the synthesis of a versatile Atorvastatin precursor, in which a variety of modifications at the pyrrole core structure are possible.Three at a stroke: Herein, we report a metal-free one-pot three-component coupling using readily available starting materials and catalyst to generate valuable pyrroles. The process involves an N-heterocyclic carbene (NHC)-catalyzed Stetter-type hydroformylation using a glycolaldehyde dimer as a novel C1 building-block, followed by a Paal-Knorr condensation. Furthermore, this methodology is applied in the synthesis of a versatile Atorvastatin precursor and derivatives of it.
      PubDate: 2017-07-18T06:12:31.721242-05:
      DOI: 10.1002/chem.201703008
       
  • Deep Eutectic Solvents as Reaction Media for the Palladium-Catalysed C−S
           Bond Formation: Scope and Mechanistic Studies
    • Authors: Xavier Marset; Gabriela Guillena, Diego J. Ramón
      Abstract: A unique jigsaw catalytic system based on deep eutectic solvents and palladium nanoparticles where C−S bonds are formed from aryl boronic acids and sodium metabisulfite, is introduced. The functionalization step is compatible with a broad spectrum of reagents such as nucleophiles, electrophiles or radical scavengers. This versatile approach allows the formation of different types of products in an environmentally friendly medium by selecting the components of the reaction, which engage one with another as pieces in a jigsaw. This simple procedure avoids the use of toxic volatile organic solvents allowing the formation of complex molecules in a one-pot reaction under mild conditions. Despite the fact that only 1 mol % of metal loading is used, the recyclability of the catalytic system is possible. Kinetic experiments were performed and the reaction order for all reagents, catalyst and ligand was determined. The obtained results were compared to palladium nanocrystals of different known shapes in order to shed some light on the properties of the catalyst.Piecing the puzzle: A unique catalytic system, where C−S bonds are formed from aryl boronic acids and sodium metabisulfite, is introduced. The functionalization step is compatible with nucleophiles, electrophiles or radical scavengers and principles of green chemistry, as in a jigsaw. Kinetic experiments were performed, and the results were compared to palladium nanocrystals of different known shapes in order to shed some light on the properties of the catalyst.
      PubDate: 2017-07-18T06:12:21.599027-05:
      DOI: 10.1002/chem.201702892
       
  • Chlorophyll-Based Organic–Inorganic Heterojunction Solar Cells
    • Authors: Yue Li; Wenjie Zhao, Mengzhen Li, Gang Chen, Xiao-Feng Wang, Xueqi Fu, Osamu Kitao, Hitoshi Tamiaki, Kotowa Sakai, Toshitaka Ikeuchi, Shin-ichi Sasaki
      Abstract: Solid-state chlorophyll solar cells (CSCs) employing a carboxylated chlorophyll derivative, methyl trans-32-carboxypyropheophorbide a, as a light-harvesting dye sensitizer chlorophyll (DSC) deposited on mesoporous TiO2, on which four zinc hydroxylated chlorophyll derivatives were spin-coated for hole transporter chlorophylls (HTCs), are described. Key parameters, including the effective carrier mobility of the HTC films, as determined by the space charge-limited current method, and the frontier molecular orbitals of these DSCs and HTCs, as estimated from cyclic voltammetry and electronic absorption spectra, suggest that both charge separation and carrier transport are favorable. The power conversion efficiencies (PCEs) of the present CSCs with fluorine-doped tin oxide (FTO)/TiO2/DSC/HTCs/Ag were determined to follow the order of HTC-1>HTC-2>HTC-3>HTC-4, which coincided perfectly with the order of their hole mobilities. The maximum PCE achieved was 0.86 % with HTC-1. The photovoltaic devices studied herein with two types of chlorophyll derivatives as dye sensitizers and hole transporters provide a unique solution for the utilization of solar energy with a view to truly realizing “green energy”.Naturally sensitive: Solid-state chlorophyll solar cells can be used that employ a carboxylated chlorophyll derivative, methyl trans-32-carboxypyropheophorbide a, as a light-harvesting dye sensitizer chlorophyll (DSC) deposited on mesoporous TiO2, upon which four zinc hydroxylated chlorophyll derivatives are spin-coated as hole transporter chlorophylls (HTCs; see figure).
      PubDate: 2017-07-18T06:11:31.260532-05:
      DOI: 10.1002/chem.201701858
       
  • Suzuki Cross-Coupling for Post-Complexation Derivatization of Non-Racemic
           Bis-Cyclometalated Iridium(III) Complexes
    • Authors: Thomas Mietke; Thomas Cruchter, Erik Winterling, Matthias Tripp, Klaus Harms, Eric Meggers
      Abstract: A straightforward method for post-complexation derivatizations of diastereo- and enantiomerically pure bis-cyclometalated benzoxazole and benzothiazole iridium(III) complexes is reported. Triflate- and bromine-functionalized iridium(III) complex dimers, represented as [Ir(μ-Cl)(C^N)2]2, were converted to the corresponding diastereomeric complexes, represented as Ir(C^N)2(N^O), using readily available chiral salicyloxazolines and salicylthiazolines as ancillary ligands, which are represented as N^O. The Ir(C^N)2(N^O) complexes, formed as mixtures of diastereomers, were then resolved by flash chromatography and the diastereomerically pure complexes Ir(C^N)2(N^O) subjected to Suzuki cross-couplings. The post-complexation cross-couplings proceed without affecting the metal-located stereocenter and hence provide post-complexation derivatized non-racemic iridium(III) complexes, which were not easily accessible with previous methods. This strategy expands the toolbox to access functionalized non-racemic iridium(III) complexes for diverse applications in the life sciences, materials sciences, and catalysis.Last-minute changes: Suzuki cross- couplings within the ligand sphere of stereochemically defined triflate and bromide bearing iridium complexes expand the toolbox of functionalized non-racemic bis-cyclometalated iridium(III) complexes, useful for diverse applications in the life sciences, materials science, and asymmetric catalysis.
      PubDate: 2017-07-18T06:10:56.296243-05:
      DOI: 10.1002/chem.201701758
       
  • Polar Intermetallics Pr5Co2Ge3 and Pr7Co2Ge4 with Planar Hydrocarbon-Like
           Metal Clusters
    • Authors: Qisheng Lin; Kaiser Aguirre, Scott M. Saunders, Timothy A. Hackett, Yong Liu, Valentin Taufour, Durga Paudyal, Sergey Budko, Paul C. Canfield, Gordon J. Miller
      Abstract: Planar hydrocarbon-like metal clusters may foster new insights linking organic molecules with conjugated π–π bonding interactions and inorganic structures in terms of their bonding characteristics. However, such clusters are uncommon in polar intermetallics. Herein, we report two polar intermetallic phases, Pr5Co2Ge3 and Pr7Co2Ge4, both of which feature such planar metal clusters, namely, ethylene-like [Co2Ge4] clusters plus the concatenated forms and polyacene-like [Co2Ge2]n ribbons in Pr5Co2Ge3, and 1,2,4,5-tetramethylbenzene-like [Co4Ge6] cluster in Pr7Co2Ge4. Just as in the related planar organic structures, these metal–metalloid species are dominated by covalent bonding interactions. Both compounds magnetically order at low temperature with net ferromagnetic components: Pr5Co2Ge3 through a series of transitions below 150 K and Pr7Co2Ge4 through a single ferromagnetic transition at 19 K. Spin-polarized electronic structure calculations for Pr7Co2Ge4 reveal strong spin-orbit coupling within Pr and considerable magnetic contributions from Co atoms. This work suggests that similar structural chemistry can emerge for other rare-earth/late-transition-metal/main-group systems.Polyatomic and valence-electron-rich Co–Ge clusters with planar hydrocarbon-like geometries are identified in Pr5Co2Ge3 and Pr7Co2Ge4 (see scheme). Complex magnetic properties arise from interactions between Pr and these Co–Ge species.
      PubDate: 2017-07-18T06:10:39.635156-05:
      DOI: 10.1002/chem.201702798
       
  • 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
       
  • Sustainable, Oxidative, and Metal-Free Annulation
    • Authors: Luis Bering; Srimanta Manna, Andrey P. Antonchick
      Abstract: Annulation has received steadily growing interest in the interplay with the increasing emphasis towards selective C−H bond functionalization reactions. Metal-free oxidative annulation through functionalization of inert and abundant C−H bonds offers great improvements in terms of atom- and step-economics as well as reduced waste production under mild reaction conditions. Annulation is considered to be a highly efficient strategy for the construction of cyclic molecules because at least two new bonds are formed within a single reaction step. The combination of annulation and direct C−H bond functionalization allows the efficient and straightforward synthesis of carbo- and heterocyclic molecules using simple and non-prefunctionalized precursors. This Concept highlights novel strategies and recent breakthroughs for metal-free annulation through C−H bond functionalization giving access to a variety of important structural motifs.Annulating the competition: The combination of annulation strategies and direct C−H bond functionalization reactions allow the efficient synthesis of cyclic molecules using readily available and non-prefunctionalized precursors. Metal-free oxidative coupling through C−H bond functionalization is a green and sustainable approach because it is environmentally benign as well as both atom- and step-economical. This Concept highlights novel strategies and recent breakthroughs for metal-free annulation through C−H bond functionalization giving access to a variety of important structural motifs.
      PubDate: 2017-07-17T06:46:09.523993-05:
      DOI: 10.1002/chem.201702063
       
  • Alternating Copolymer of Double Four Ring Silicate and Dimethyl Silicone
           Monomer–PSS-1
    • Authors: Sam Smet; Steven Vandenbrande, Pieter Verlooy, Stef Kerkhofs, Eric Breynaert, Christine E. A. Kirschhock, Charlotte Martineau-Corcos, Francis Taulelle, Veronique Van Speybroeck, Johan A. Martens
      Abstract: A new copolymer consisting of double four ring (D4R) silicate units linked by dimethylsilicone monomer referred to as polyoligosiloxysilicone number one (PSS-1) was synthesized. The D4R building unit is provided by hexamethyleneimine cyclosilicate hydrate crystals, which were dehydrated and reacted with dichlorodimethylsilane. The local structure of D4R silicate units and dimethyl silicone monomers was revealed by multidimensional solid-state NMR, FTIR and modeling. On average, D4R silicate units have 6.8 silicone linkages. Evidence for preferential unidirectional growth and chain ordering within the PSS-1 copolymer was provided by STEM and TEM. The structure of PSS-1 copolymer consists of twisted columns of D4R silicate units with or without cross-linking. Both models are consistent with the spectroscopic, microscopic and physical properties. PSS-1 chains are predicted to be mechanically strong compared to silicones such as PDMS, yet more flexible than rigid silica materials such as zeolites.Linking up: Systematic linking of D4R double four ring silicate with dimethylsilicone monomers generates silicone copolymer with enhanced mechanical and thermal stability. The synthesis of the new PSS-1 material (polyoligosiloxysilicone) proceeds by contacting anhydrous [C6H14N]4[Si8O16(OH)4] crystals with dichlorodimethylsilane in organic solvent. The identification of PSS-1 was done using multidimensional solid-state NMR spectroscopy, FTIR, STEM, TEM, and modeling.
      PubDate: 2017-07-17T06:46:01.626177-05:
      DOI: 10.1002/chem.201701237
       
  • Barbier Continuous Flow Preparation and Reactions of Carbamoyllithiums for
           Nucleophilic Amidation
    • Authors: Maximilian A. Ganiek; Matthias R. Becker, Guillaume Berionni, Hendrik Zipse, Paul Knochel
      Abstract: An ambient temperature continuous flow method for nucleophilic amidation and thioamidation is described. Deprotonation of formamides by lithium diisopropylamine (LDA) affords carbamoyllithium intermediates that are quenched in situ with various electrophiles such as ketones, allyl bromides, Weinreb and morpholino amides. The nature of the reactive lithium intermediates and the thermodynamics of the metalation were further investigated by ab initio calculations and kinetic experiments.Hot chemistry at room temperature: An ambient temperature continuous flow method for nucleophilic amidation and thioamidation is described. Deprotonation of formamides in the presence of various electrophiles by lithium diisopropylamine (LDA) affords carbamoyllithium intermediates that are quenched in situ with various electrophiles. Insight into the thermodynamics of their metalation was gained by kinetic experiments an ab initio calculations.
      PubDate: 2017-07-17T06:45:30.773374-05:
      DOI: 10.1002/chem.201702593
       
  • Preparation, Single-Molecule Manipulation, and Energy Transfer
           Investigation of a Polyfluorene-graft-DNA polymer
    • Authors: Mikael Madsen; Rasmus S. Christensen, Abhichart Krissanaprasit, Mette R. Bakke, Camilla F. Riber, Karina S. Nielsen, Alexander N. Zelikin, Kurt V. Gothelf
      Abstract: Conjugated polymers have been intensively studied due to their unique optical and electronic properties combined with their physical flexibility and scalable bottom up synthesis. Although the bulk qualities of conjugated polymers have been extensively utilized in research and industry, the ability to handle and manipulate conjugated polymers at the nanoscale lacks significantly behind. Here, the toolbox for controlled manipulation of conjugated polymers was expanded through the synthesis of a polyfluorene-DNA graft-type polymer (poly(F-DNA)). The polymer possesses the characteristics associated with the conjugated polyfluorene backbone, but the protruding single-stranded DNA provides the material with an exceptional addressability. This study demonstrates controlled single-molecule patterning of poly(F-DNA), as well as energy transfer between two different polymer–DNA conjugates. Finally, highly efficient DNA-directed quenching of polyfluorene fluorescence was shown.Behave polymer! A graft-type polyfluorene-DNA conjugate (poly(F-DNA)) has been developed. The conjugate shows interesting features such as efficient DNA-directed quenching, controlled inter-polymer energy transfer, and efficient single-molecule nanoscale positioning.
      PubDate: 2017-07-17T06:16:29.649014-05:
      DOI: 10.1002/chem.201702780
       
  • A Truncated Molecular Star
    • Authors: Soumyakanta Prusty; Kohei Yazaki, Michito Yoshizawa, Dillip Kumar Chand
      Abstract: A pentanuclear coordination complex assembled from any palladium(II) component and non-chelating ligands is hitherto unreported. The pentanuclear complex [Pd5(L1)5(L2)5](BF4)10, 1 reported here was prepared by the spontaneous complexation of [Pd(DMSO)4](BF4)2 with the non-chelating bidentate ligands 1,4-phenylenebis(methylene) diisonicotinate, L1 and 4,4′-bipyridine, L2 in a one-pot method at room temperature. The planar polycyclic complex 1 with outer diameters of ≈3 nm is termed as a “molecular star” owing to its resemblance with a pentagram shape. Interim paths leading to the star were also probed to decipher related dynamics of the system.High five! A star-shaped heteroleptic pentanuclear complex [Pd5(L1)5(L2)5] (BF4)10 was synthesized in a one-pot method, by combining [Pd(DMSO)4](BF4)2 with the non-chelating bidentate ligands 1,4-phenylenebis(methylene) diisonicotinate, L1 and 4,4′-bipyridine, L2 in an equal ratio. The complex is characterized by NMR spectroscopy, MS and single-crystal X-ray diffraction techniques. Interim paths leading to the star were probed to decipher related dynamics of the system.
      PubDate: 2017-07-17T06:16:21.998445-05:
      DOI: 10.1002/chem.201702264
       
  • Shape-Controlled Hollow Mesoporous Silica Nanoparticles with
           Multifunctional Capping for In Vitro Cancer Treatment
    • Authors: Hongya Geng; Weiyu Chen, Zhi Ping Xu, Guangren Qian, Jing An, Haijiao Zhang
      Abstract: A series of multifunctional shape-controlled nonspherical hollow mesoporous silica nanoparticles (HMSNs) drug carriers have been prepared by employing Fe2O3 with four morphologies (capsule, cube, rice, and rhombus) as a sacrificial template and a multifunctional cap as the encapsulating shell. The resulting shape-controlled nonspherical HMSNs perfectly replicate the original morphology of the Fe2O3 templates, which possess a high specific surface area, good monodispersity, perpendicular mesoporous channels, and excellent biocompatibility. After modification of polyethylene glycol (PEG) and folic acid (FA), the shape-controlled HMSN core and functional shell can then be integrated into a single device (HMSNs-PEG-FA) to provide an efficient and tumor-cell-selective drug-delivery system. The shape-controlled HMSNs and HMSNs-PEG-FA all show controlled pH-responsive release behavior for the anticancer drug doxorubicin hydrochloride (DOX). The in vitro results indicate that HMSNs-PEG-FA is biocompatible and selectively targets HeLa cells (overexpressed folate receptors). Fluorescence images show that desirable surface modification and the nonspherical shape effectively facilitate cellular internalization of HMSNs. It is expected that the construction of these unique nanomaterials with controlled morphology through the hard-templating technique may also provide useful information for the design of nanoscale multifunctional systems.Get in shape: A series of multifunctional shape-controlled hollow mesoporous silica nanoparticle (HMSN) drug carriers have been prepared by employing Fe2O3, with four morphologies (capsule, cube, rice, and rhombus), as a sacrificial template and multifunctional cap as the encapsulating shell (see figure).
      PubDate: 2017-07-17T06:15:57.226406-05:
      DOI: 10.1002/chem.201701806
       
  • 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
       
  • Ion Pairing and Co-facial Stacking Drive High-Fidelity Bisulfate Assembly
           with Cyanostar Macrocyclic Hosts
    • Authors: Elisabeth M. Fatila; Eric B. Twum, Jonathan A. Karty, Amar H. Flood
      Abstract: Hydroxyanions pair up inside CH H-bonding cyanostar macrocycles against Coulombic repulsions and solvation forces acting to separate them. The driving forces responsible for assembly of bisulfate (HSO4−) dimers are unclear. We investigated them using solvent quality to tune the contributing forces and we take advantage of characteristic NMR signatures to follow the species distributions. We show that apolar solvents enhance ion pairing to stabilize formation of a 2:2:2 complex composed of π-stacked cyanostars encapsulating the [HSO4⋅⋅⋅HSO4]2− dimer and endcapped by tetrabutylammonium cations. Without cations engaged, a third macrocycle can be recruited with the aid of solvophobic forces in more polar solvents. The third macrocycle generates a more potent electropositive pocket in which to stabilize the anti-electrostatic anion dimer as a 3:2 assembly. We also see unprecedented evidence for a water molecule bound to the complex in the acetonitrile solution. In methanol, OH H-bonding leads to formation of 2:1 complexes by bisulfate solvation inside the macrocycles inhibiting anion dimers. Knowledge of the driving forces for stabilization (strong OH⋅⋅⋅O H-bonding, CH H-bonding, ion pairs, π-stacking) competing with destabilization (Coulomb repulsion, solvation) allows high-fidelity selection of the assemblies. Thermodynamic stabilization of hydroxyanion dimers also demonstrates the ability to use macrocycles to control ion speciation and stoichiometry of the overall assemblies.A gathering of stars: Stabilization of an anion–anion dimer results in the formation of higher order assemblies with cyanostar. We discovered that intermolecular forces such as ion pairing, solvophobic effects, and ion solvation control the speciation in solution. We demonstrate the ability to control ion speciation and stoichiometry by simple solvent variation.
      PubDate: 2017-07-17T05:05:55.70895-05:0
      DOI: 10.1002/chem.201701763
       
  • Merging Photoredox with Brønsted Acid Catalysis: The
           Cross-Dehydrogenative C−O Coupling for sp3 C−H Bond Peroxidation
    • Authors: Qing Xia; Qiang Wang, Changcun Yan, Jianyang Dong, Hongjian Song, Ling Li, Yuxiu Liu, Qingmin Wang, Xiangming Liu, Haibin Song
      Abstract: A photoredox and Brønsted acid synergistically catalyzed cross-dehydrogenative C−O coupling reaction is developed in which isochroman peroxyacetals are formed through sp3 C−H bond peroxidation. The reported method is characterized by its extremely mild reaction conditions, excellent yields, and broad substrate scope. An oxocarbenium ion p-chlorobenzenesulfonate was speculated to be the reactive intermediate. The role of hemiacetals and oxygenated dimers on the effective stabilization of the oxocarbenium ion was investigated; the presence of acid appeared to establish equilibrium between hemiacetals and oxygenated dimers with the oxocarbenium ion pairs. The broad applicability of the method highlights the potential of the protocol for molecule synthesis.Synergistic catalysis: Isochroman peroxyacetals can be formed by photoredox and Brønsted acid synergistically catalyzed cross-dehydrogenative C−O coupling reaction (see scheme). The role of hemiacetals and oxygenated dimers on the effective stabilization of the oxocarbenium ion was investigated; the presence of acid appeared to establish an equilibrium between hemiacetal and oxygenated dimers with the oxocarbenium ion pairs.
      PubDate: 2017-07-17T05:02:08.218903-05:
      DOI: 10.1002/chem.201701755
       
  • 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
       
  • Aromatic Micelles as a New Class of Aqueous Molecular Flasks
    • Authors: Kei Kondo; Jeremy K. Klosterman, Michito Yoshizawa
      Abstract: Micelles are a versatile class of molecular assemblies typically composed of aliphatic molecules with hydrophilic groups. Polyaromatic molecules with hydrophilic groups, on the other hand, usually do not assemble into micellar structures in water but rather form columnar, π-stacked architectures. This Minireview article focuses on the recent development of aqueous micellar nanostructures with multiple oligoarylene rods or polyaromatic panels. The new micelles with spherical polyaromatic shells, which we name "aromatic micelles", serve as functional molecular flasks with superior binding abilities for medium to very large molecules in water.
      PubDate: 2017-07-15T00:25:24.838687-05:
      DOI: 10.1002/chem.201702519
       
  • Orotidine Containing RNA: Implications for the Hierarchical Selection
           (Systems Chemistry Emergence) of RNA
    • Authors: Eun-Kyong Kim; Vincent Martin, Ramanarayanan Krishnamurthy
      Abstract: The prebiotic synthesis of canonical nucleobases from HCN is a cornerstone for the RNA world hypothesis. However, their role in the primordial pathways to RNA is still debated. The very same process starting from HCN also gives rise to orotic acid, which (via orotidine) plays a crucial role in extant biology in the de novo synthesis of uridine and cytidine, the informational base-pairs in RNA. However, orotidine itself is absent in RNA. Given the prebiotic and biological relevance of orotic acid vis-à-vis uracil, we investigated orotidine containing RNA oligonucleotides and show that they have severely compromised base-pairing properties. While not unexpected, these results suggest that the emergence of extant RNA cannot just be a consequence of the plausible prebiotic formation of its chemical constituents/building blocks. In combination with other investigations on alternative prebiotic nucleobases, sugars and linkers, these findings imply that the selection of the components of extant RNA occurred at a higher hierarchical level of an oligomer/polymer based on its functional properties - pointing to a systems chemistry emergence of RNA from a library of precursors.
      PubDate: 2017-07-14T13:25:22.938936-05:
      DOI: 10.1002/chem.201702912
       
  • A toolbox of chromones and quinolones for measuring a wide range of ATP
           concentrations
    • Authors: Vasyl Georgievich Pivovarenko; Oleksandra Bugera, Nicolas Humbert, Andrey Sergeevich Klymchenko, Yves Mély
      Abstract: A series of 26 3-hydroxychromones, three bis-flavonols and four 3-hydroxyquinolones were studied to evaluate their fluorescence response to interaction with ATP in buffer. The dyes differ by the total charge, the size and number of their aromatic units, as well as the position or electron donating ability of their substituents. All of them were suggested to form complexes with ATP of 1:1 and 1:2 stoichiometry, which can be evidenced by their bright fluorescence and their 3000-6000 cm-1 red-shifted excitation band. These fluorescent complexes allow detection of ATP concentrations over 3 orders of magnitude, while most other known probes cover no more than two orders. In total, the dyes allow ATP detection from 0.001 to 57 mM. In addition, most of the dye-ATP complexes can be excited in the visible and monitored in the red region of the spectrum. The response amplitude of the described dyes to ATP is as high as for the best known probes. Since complexation takes place at neutral pH, the studied dyes form a toolbox of fluorescent probes for intensiometric and ratiometric measurements of ATP concentration in a broad concentration range. Finally, the obtained results stimulate the idea that most of natural 3-hydroxyflavones in living cells may form complexes with ATP.
      PubDate: 2017-07-14T10:25:25.239822-05:
      DOI: 10.1002/chem.201702484
       
  • Ferrichrome has found its match: biomimetic analogs with diversified
           activity map discrete microbial targets
    • Authors: Jenny Besserglick; Evgenia Olshvang, Agnieszka Szebesczyk, Joseph Englander, Dana Levinson, Yitzhak Hadar, Elzbieta Gumienna-Kontecka, Abraham Shanzer
      Abstract: Siderophores provide an established platform for studying molecular recognition principles in biological systems. Herein we describe the preparation of ferrichrome biomimetic analogs varying in length and polarity of the amino acid chain separating between the tripodal scaffold and the pendent FeIII chelating hydroxamic acid groups. Spectroscopic and potentiometric titrations determined their iron affinity to be within the range of efficient chelators. Microbial growth promotion and iron uptake studies were conducted on E. coli, P. putida and U. maydis. A wide range of siderophore activity was observed in the current series: from a rare case of a species-specific growth promotor in P. putida to an analog matching ferrichrome in cross-phylum activity and uptake pathway. A fluorescent conjugate of the broad-range analog visualized siderophore destination in bacteria (periplasmic space) vs fungi (cytosol) mapping new therapeutic targets. Quantum Dots (QD) decorated with the most potent FC analog provided a tool for immobilization of ferrichrome-recognizing bacteria. Bacterial clusters formed around QDs may provide a platform for their selection and concentration.
      PubDate: 2017-07-14T08:25:40.526883-05:
      DOI: 10.1002/chem.201702647
       
  • Fe-containing zeolites for NH3-SCR of NOx: effect of structure, synthesis
           
    • Authors: Avelino Corma; NURIA MARTIN GARCIA, PETER VENNESTROM, JOAKIM REIMER, MANUEL MOLINER
      Abstract: The direct preparation of different Fe-containing Beta and CHA zeolites has been attempted under diverse synthesis conditions, including alkaline and fluoride media, to evaluate the influence of their physico-chemical properties on the selective catalytic reduction (SCR) of NOx using NH3 as a reductant. From the different Fe-Beta zeolites, the sample prepared in absence of alkali-cations with a Si/Al~13, shows high NO conversion values (> 90%). However, this catalyst suffers from severe deactivation when aged at high temperatures in the presence of steam. The preparation of more hydrophobic Fe-Beta zeolites does not allow improving the catalyst resistance against steaming. In contrast, the Fe-CHA material prepared by one-pot methods under alkaline conditions with a Si/Al~13 using trimethyladamantammonium as template, not only shows excellent catalytic activity but also high hydrothermal stability, especially when sodium cations are selectively removed. Moreover, a Fe-CHA synthesized using the less expensive template tetraethylammonium also results in an active and hydrothermally stable catalyst.
      PubDate: 2017-07-14T05:26:17.030362-05:
      DOI: 10.1002/chem.201701742
       
  • Selective Adsorption and Separation of Organic Dyes with Spherical
           Polyelectrolyte Brushes and Compressed CO2
    • Authors: Rui Zhang; Zhenchuan Yu, Yuan Yao, Xiaoyan Hou, Qizhe Shen, Lei Wang, Xuhong Guo, Junwei Wang, Xuedong Zhu
      Abstract: Direct discharge of industry organic dyes has caused serious environmental pollution. Herein, we proposed a rational designed spherical polyelectrolyte brushes (SPB) with cationic charges, polystyrene-poly(2-aminoethylmethacrylate hydrochloride) (PS-PAEMH), as the absorbent and compressed carbon dioxide as the anti-solvent to separate the anionic dye, eosin Y (EY) from a solution of mixed dyes. The adsorption behavior of EY onto PS-PAEMH was highly dependent on CO2 pressure, contact time and initial concentration, and the maximum adsorption capacity of PS-PAEMH was 335.20 mg/g. FTIR and UV-vis measurements proved that the electrostatic interaction played an important role in the absorbance process. The adsorption process fitted the pseudo-second-order kinetic model and Freundlich isotherm model very well. Due to the Donnan effect of polymer brush, the dye and the polymer brush could be easily separated by adding NaCl aqueous solution through ion exchange to regenerate the polymer brush. The recovered PS-PAEMH still kept high adsorption capacity even after five times of regeneration. It provides a simple and effective way to separate ionic materials for environmental engineering.
      PubDate: 2017-07-14T05:26:14.282127-05:
      DOI: 10.1002/chem.201701700
       
  • Structural Features of Eu(II)-Containing Cryptates That Influence
           Relaxivity
    • Authors: Chamika U Lenora; Fabio Carniato, Yimin Shen, Zahid Latif, E. Mark Haacke, Philip D Martin, Mauro Botta, Matthew John Allen
      Abstract: EuII-containing complexes were studied with respect to properties relevant to their use as contrast agents for magnetic resonance imaging. The influences of molecular parameters and field strength on relaxivity were studied for a series of EuII-containing cryptates and their adducts with β-cyclodextrins, poly-β-cyclodextrins, and human serum albumin. Solid- and solution-phase characterization of EuII-containing complexes is presented that demonstrates the presence of inner-sphere molecules of water. Additionally, relaxivity, water-exchange rate, rotational correlation time, and electronic relaxation time were determined using variable-temperature 17O-NMR, nuclear magnetic relaxation dispersion, and electron paramagnetic resonance spectroscopic techniques. We expect that our results will be instrumental in the design of future EuII-based contrast agents.
      PubDate: 2017-07-14T05:26:04.846188-05:
      DOI: 10.1002/chem.201702158
       
  • Lithium Ion Highway by Surface Coordination Polymerization: In Situ Growth
           of Metal-Organic Framework Thin Layers on Metal Oxides for Exceptional
           Rate and Cycling Performances
    • Authors: Yuzhen Han; Danni Yu, Junwen Zhou, Peiyu Xu, Pengfei Qi, Qianyou Wang, Siwu Li, Xiaotao Fu, Xing Gao, Chenghao Jiang, Xiao Feng, Bo Wang
      Abstract: A thin layer of a highly porous metal-organic framework material, ZIF-8, is fabricated uniformly on the surface of nanostructured TMOs (ZnO nanoflakes and MnO2 nanorods) to boost the transfer of lithium ions. The novel design and uniform microstructure of the MOF-coated TMOs (ZIF-8@TMOs) exhibit dramatically enhanced rate and cycling performance comparing to their pristine counterparts. The capacities of ZIF-8@ZnO (nanoflakes) and ZIF-8@MnO2 (nanorods) are 28% and 31% higher that of the pristine ones at the same current density. The nanorods of ZIF-8@MnO2 show a capacity of 1067 mAh g‒1 after 500 cycles at 1 A g‒1 and without any fading. To further improve the conductivity and capacity, the ZIF-8-coated materials are pyrolyzed at 700 °C in N2 atmosphere (ZIF-8@TMO-700N). After pyrolysis, a much higher capacity improvment is achieved, ZIF-8@ZnO-700N and ZIF-8@MnO2-700N have 54% and 69% capacity increases compared with the pristine TMOs, and at 1 A g‒1, the capacity of ZIF-8@MnO2-700N is 1060 mAh g‒1 after cycling for 300 cycles.
      PubDate: 2017-07-14T03:25:51.528671-05:
      DOI: 10.1002/chem.201703016
       
  • Engaging the terminal: promoting halogen bonding interactions with uranyl
           oxo atoms
    • Authors: Korey P. Carter; Mark Kalaj, Robert Gian Surbella III, Lucas C. Ducati, Jochen Autschbach, Christopher L. Cahill
      Abstract: Engaging the nominally terminal oxo atoms of the linear uranyl (UO22+) cation in non-covalent interactions represents both a significant challenge and opportunity within the field of actinide hybrid materials. We have developed an approach for promoting oxo atom participation in a range of non-covalent interactions through judicious choice of electron donating equatorial ligands and appropriately polarizable halogen-donor atoms. As such, we have generated a family of uranyl hybrid materials based on a combination of 2,5-dihalobenzoic acid and aromatic, chelating N-donor ligands. Delineation of criteria for oxo participation in halogen bonding interactions has been achieved by preparing materials containing 2,5-dichloro- (25diClBA) and 2,5-dibromobenzoic acid (25diBrBA) coupled with 2,2'-bipyridine (bipy) (1 and 2), 1,10-phenanthroline (phen) (3-5), 2,2':6',2''-terpyridine (terpy) (6-8), or 4'-chloro-2,2':6',2''-terpyridine (Cl-terpy) (9-10), which have been characterized via single crystal X-ray diffraction, Raman, Infrared (IR), and luminescence spectroscopy, as well as via density functional calculations of electrostatic potentials. Looking comprehensively, these results are compared with recently published 2,5-diiodobenzoic acid analogues indicating that while inclusion of a capping ligand in the uranyl first coordination sphere is important, it is the polarizability of the selected halogen atom that ultimately drives halogen bonding interactions with the uranyl oxo atoms.
      PubDate: 2017-07-13T23:26:24.354493-05:
      DOI: 10.1002/chem.201702744
       
  • On the Dimensional Control of 2D Hybrid Nanomaterials
    • Authors: Alessandro Longo; Dirk-Jan Mulder, Huub P. C. van Kuringen, Daniel Hermida-Merino, Dipanjan Banerjee, Debarshi Dasgupta, Ivelina K. Shishmanova, Anne B. Spoelstra, Dirk J. Broer, Albert P. H. J. Schenning, Giuseppe Portale
      Abstract: Thermotropic smectic liquid crystalline polymers were used as a scaffold to create organic/inorganic hybrid layered nanomaterials. Different polymers were prepared by photopolymerizing blends of a hydrogen bonded carboxylic acid derivative and a 10% cross-linker of variable length in their liquid crystalline phase. Nanopores with dimensions close to 1 nm were generated by breaking the hydrogen bonded dimers in a high pH solution. The pores were filled with positively charged silver (Ag) ions, resulting in a layered silver(I)-polymeric hybrid material. Subsequent exposure to a NaBH4 reducing solution allowed for the formation of supported hybrid metal/organic films. In the bulk of the film the dimension of the Ag nanoparticles was regulated with subnanometer precision by the cross-linker length. Ag nanoparticles with an average size of 0.9, 1.3 and 1.8 nm were produced inside the nanopores thanks to the combined effect of spatially confined reduction and stabilization of the nanoparticles by the polymer carboxylic groups. At the same time, strong Ag migration occurred in the surface region, resulting in the formation of a nanostructured metallic top layer composed of large (10-20 nm) NPs.
      PubDate: 2017-07-13T21:26:05.333129-05:
      DOI: 10.1002/chem.201701493
       
  • ¹⁸F-Labeling of Sensitive Biomolecules for Positron Emission
           Tomography
    • Authors: Hema Krishnan; Longle Ma, Neil Vasdev, Steven Liang
      Abstract: Positron emission tomography (PET) imaging study of 18F-labeled biomolecules is an emerging and rapidly growing area for preclinical and clinical research. The present review focuses on recent advances in radiochemical methods for incorporating 18F into biomolecules via 'direct' or 'indirect' bioconjugation. Recently developed prosthetic groups and pre-targeting strategies, as well as representative examples in 18F-labeling of biomolecules in PET imaging research studies are highlighted.
      PubDate: 2017-07-13T14:25:29.068437-05:
      DOI: 10.1002/chem.201701581
       
  • Large diameter TiO2 nanotubes enable wall engineering with conformal
           hierarchical decoration and blocking layers for enhanced efficiency in
           dye-sensitized solar cells
    • Authors: Patrik Schmuki; A. H. El-Zarka, Ning Liu, Imgon Hwang, Mustafa Kamal
      Abstract: In the present work we grow anodic TiO2 nanotube layer with a tube diameter> 500 nm and an open tube mouth. We use this morphology in dye-sensitized solar cells (DSSCs) and show that these tubes allow the construction of hybrid hierarchical photoanode structures of nanotubes with a defined and wall-conformal TiO2 nanoparticle decoration. At the same time, the large diameter allows the successful establishment of an additional (insulating) blocking layer of SiO2 or Al2O3 on the tube wall. We show that this combination of hierarchical structure and blocking layer significantly enhances the solar cell efficiency by suppressing recombination reactions. In such a DSSC structure, the solar cell efficiency under back side illumination with AM1.5 illumination is enhanced from 3% for the neat tube to 5 % for the hierarchical structure, to 7 % when additionally a blocking layer is attached.
      PubDate: 2017-07-13T11:25:42.212969-05:
      DOI: 10.1002/chem.201702434
       
  • MnCl2-Catalyzed C-H Alkylations with Alkyl Halides
    • Authors: Weiping Liu; Gianpiero Cera, João C. A. Oliveira, Zhigao Shen, Lutz Ackermann
      Abstract: C-H alkylations with challenging β-hydrogen-containing alkyl halides were accomplished with sustainable MnCl2 as the catalyst under phosphine-ligand free conditions. The proximity-induced benzamide C-H activation occurred with ample substrate scope through rate-determining C-H metalation, also setting the stage for manganese-catalyzed oxidative C-H methylations.
      PubDate: 2017-07-13T11:25:39.660718-05:
      DOI: 10.1002/chem.201703191
       
  • Determination of the absolute configuration of (-)-hydroxynitrilaphos and
           related biosynthetic questions
    • Authors: Katharina Pallitsch; Barbara Happl, Christian Stieger
      Abstract: The ongoing search for bioactive natural products led to the development of new genome-based screening approaches to identify possible phosphonate producing microorganisms. From the identified phosphonate producers, several until now unknown phosphonic acid natural products were isolated, including (hydroxy)nitrilaphos (4 and 5) and (hydroxy)phosphonocystoximate (7 and 6). We present the synthesis of phosphonocystoximate via an aldoxime intermediate. Chlorination and coupling with methyl N-acetylcysteinate furnished 6 after global deprotection. The obtained experimental data confirmed the previously assigned structure of the natural product. We were also able to determine the absolute configuration of (-)-hydroxynitrilaphos. Chiral resolution of diethyl cyanohydroxymethylphosphonate (24) with Noe's lactol furnished both enantiomers of 4. Conversion of (+)-24 to (R)-2-amino-1-hydroxyethylphosphonic acid by reduction of the cyano-group showed (-)-hydroxynitrilaphos ultimately to be (S)-configured. Further we present an 13C-isotope labeling strategy for 4 and 5 that will possibly solve the question of whether hydroxynitrilaphos is a biosynthetic intermediate or a downstream product of hydroxyphosphonocystoximate biosynthesis.
      PubDate: 2017-07-13T08:25:25.613808-05:
      DOI: 10.1002/chem.201702904
       
  • The Solvent Induced Inter-Dimensional Phase Transformations of Cobalt
           Zeolitic-Imidazolate Frameworks
    • Authors: Xu Li; Zhenhu Li, Li Lu, Limin Huang, Lu Xiang, Jun Shen, Shuangyi Liu, Dong-Rong Xiao
      Abstract: Studying inter-dimensional phase transitions of zeolitic-imidazolate frameworks (ZIFs) is essential for developing strategies in controlling morphology and properties. Herein, the inter-dimensional topotactic phase transformations of 3D ZIF-67 to 2D ZIF-L are investigated in detail by employing a simple and efficient solvent-induced growth method. In addition to ZIF-67 and ZIF-L, a series of novel core–shell composites of ZIF-67@ZIF-L, with unprecedented morphologies, are also obtained and well-defined. The different behaviors of the amine hydrogen of 2-MIM in the solvents play a pivotal role for inter-dimensional phase transformations, and in combination with the concentration of 2-MIM, the 2D to 3D phase transformations are also revealed. The findings are very beneficial for morphological design of the ZIFs, along with exploration of the corresponding properties. Impressively, Co-ZIFs exhibit interesting tunable CO2 adsorption behaviors with the phase evolution, which might bring broader understanding for designing CO2 detection and adsorption devices.Yin and Yang: A “Tai-Chi” style cycle of inter-dimensional phase transitions of Co-ZIFs is achieved by employing a simple and efficient solvent-induced growth method. Besides obtaining a phase control strategy for a series of novel composites, the interesting selective gas adsorption behaviors of them are investigated, bringing about a broader space for designing CO2 detection and adsorption devices.
      PubDate: 2017-07-13T07:56:01.801411-05:
      DOI: 10.1002/chem.201701721
       
  • Coexistence of Strong Second Harmonic Generation Response and Wide Band
           Gap in AZn4Ga5S12 (A=K, Rb, Cs) with 3D Diamond-like Frameworks
    • Authors: Hua Lin; Hong Chen, Yu-Jun Zheng, Ju-Song Yu, Xin-Tao Wu, Li-Ming Wu
      Abstract: Mid-infrared (MIR, 2–20 μm) second-order nonlinear optical (NLO) materials with outstanding performances are of great importance in laser science and technology. However, the enormous challenge to design and synthesize an excellent MIR NLO material lies in achieving simultaneously a strong second harmonic generation (SHG) response [dij>0.6 × AgGaS2 (AGS)] and wide band gap (Eg>3.5 eV). Herein three new MIR NLO materials, AZn4Ga5S12 (A=K, Rb, Cs) are reported, which crystallize in the KCd4Ga5S12-type structure and adopt a 3D diamond-like framework (DLF) consisting of MS4 (M=Zn/Ga) tetrahedra; achieving the desired balance with strong powder SHG response (1.2–1.4 × AGS) and wide band gap (Eg≈3.65 eV). Moreover, they also show large laser induced damage thresholds (LIDTs, 36 × AGS), a wide range of optical transparency (0.4–25 μm) and ultrahigh thermal stability (up to 1400 K). Upon analyzing the structure-property relationship of AXII4XIII5Q12 family, these 3D DLF structures can be used as a highly versatile and tunable platform for designing excellent MIR NLO materials.Trick of the light: Three new mid-infrared nonlinear optical sulfides, AZn4Ga5S12 (A=K, Rb, Cs), adopt a 3D diamond-like framework (DLF) structure, and achieve the desired balance with strong powder second harmonic generation response (1.2–1.4 × AgGaS2) and wide band gap (Eg≈3.65 eV).
      PubDate: 2017-07-13T07:55:26.760533-05:
      DOI: 10.1002/chem.201701679
       
  • Double Activation Catalysis for α′-Alkylidene Cyclic Enones
           with Chiral Amines and Thiols
    • Authors: Zhou-Xiang Wang; Zhi Zhou, Wei Xiao, Qin Ouyang, Wei Du, Ying-Chun Chen
      Abstract: Cooperative catalysis has contributed greatly to the progress of asymmetric synthesis. However, double-activation catalysis has been less explored, especially for covalently tethered species. Here, we present a double-activation strategy for α′-alkylidene cyclic enone substrates that uses a chiral primary amine and 2-mercaptobenzoic acid to promote regio- and chemoselective addition to generate the complex interrupted iminium ion species. Significantly enhanced reactivity and enantioselectivity were observed for β-regioselective Michael addition and Friedel–Crafts alkylation with malononitriles and indoles, respectively, which produced a spectrum of chiral cyclic adducts with an exo-alkylidene group. Moreover, a HRMS study detected a few key covalently tethered intermediates among the substrates and catalysts, which helped elucidate the catalytic mechanism.Double activation: Complex iminium ion species were generated regio- and chemoselectively from α′-alkylidene cyclic enones, a chiral primary amine, and 2-mercaptobenzoic acid, which led to significantly enhanced reactivity and enantioselectivity in subsequent β-regioselective Michael addition with malononitriles and Friedel–Crafts alkylations with indoles (see scheme).
      PubDate: 2017-07-13T07:50:58.695252-05:
      DOI: 10.1002/chem.201702183
       
  • A Highly Sensitive Enzymatic Catalysis System for Trace Detection of
           Arsenic in Water
    • Authors: Yuanli Liu; Chuanbai Yu, Zhixin Cao, Daniel Shvarts, William C. Trogler
      Abstract: Arsenic (As) is an extremely toxic element that exists in the environment in different chemical forms. The detection of arsenic in potable water remains a challenging task. This study presents a highly sensitive enzymatic catalysis system for trace sensing of inorganic arsenic in water. This is the first enzyme-catalyzed fluorescence assay capable of detecting arsenic at concentrations below the allowable level adopted by the World Health Organization (10 ppb in drinking water). The enzyme catalytically produces fluorescent NADH in the presence of arsenate, which enables facile detection of arsenate at concentrations in the 0–200 ppb range. Calibration curves made at a set time interval allow accurate determination of unknown arsenic samples. This method holds potential for interfacing with automated analytical sampling systems to allow arsenic determinations in environmental health applications.A toxic glow: An enzyme catalytically produces fluorescent NADH in the presence of arsenate and enables facile detection of arsenic with concentrations in the 0–200 ppb range. This method holds potential for a convenient benchtop arsenic assay with concentrations near and below the allowable level adopted by the World Health Organization (10 ppb in potable water).
      PubDate: 2017-07-13T07:50:43.408043-05:
      DOI: 10.1002/chem.201702769
       
  • Visible-Light-Mediated Dual Decarboxylative Coupling of Redox-Active
           Esters with α,β-Unsaturated Carboxylic Acids
    • Authors: Jin-Jiang Zhang; Jun-Cheng Yang, Li-Na Guo, Xin-Hua Duan
      Abstract: An efficient visible-light-induced decarboxylative coupling between α,β-unsaturated carboxylic acids and alkyl N-hydroxyphthalimide esters has been developed. A wide range of redox-active esters derived from aliphatic carboxylic acids (1°, 2° and 3°) proved viable in this dual decarboxylation process, affording a broad scope of substituted alkenes in moderate to excellent yields with good E/Z selectivities. This redox-neutral procedure was highlighted by its mild conditions, operational simplicity, easy accessibility of carboxylic acids, and excellent functional-group tolerance.Light is the key: An efficient, redox-neutral visible-light-induced decarboxylative coupling between α,β-unsaturated carboxylic acids and alkyl N-hydroxyphthalimide esters has been developed. This operationally simple sequential decarboxylation procedure afforded a broad scope of structurally diverse alkenes in moderate to excellent yields with good E/Z selectivities under mild conditions.
      PubDate: 2017-07-13T07:50:28.916527-05:
      DOI: 10.1002/chem.201702200
       
  • Self-Assembly of Di-N-Heterocyclic Carbene-Gold-Adorned Corannulenes on
           C60
    • Authors: Carmen Mejuto; Luis Escobar, Gregorio Guisado-Barrios, Pablo Ballester, Dmitry Gusev, Eduardo Peris
      Abstract: The deprotonation of a corannulene-based bisazolium salt allowed the preparation of a corannulene-based NHC di-AuI complex. The prepared di-AuI-complex was tested in the recognition of fullerene-C60, demonstrating good binding affinity in toluene solution, and producing a host–guest complex with 3:1 stoichiometry, as evidenced by a combination of NMR spectroscopy and ITC titrations. The experimental results are fully supported by DFT calculations. The binding of C60 with the di-AuI complex in toluene solution is enthalpically and entropically favoured. Remarkably, the entropic term is the dominant parameter in the binding process. The good complementarity that exists between the concave shape of the corannulene-di-gold complex and the convex surface of the fullerene, together with the presence of tBu groups and the AuCl fragment are key factors for the measured high affinity between host and guest. The obtained results indicate that fullerene may be acting as a template for the formation of a self-assembled aggregate involving up to three molecules of the di-AuI complex.The super bowl: Excellent binding affinity is found between a corannulene-based di-N-heterocyclic carbene (NHC) gold complex and fullerene-C60, producing guest–host complexes of 1:3 stoichiometry.
      PubDate: 2017-07-13T07:38:12.837902-05:
      DOI: 10.1002/chem.201701728
       
  • A New Polyoxometalate (POM)-Based Composite: Fabrication through
           POM-Assisted Polymerization of Dopamine and Properties as Anode Materials
           for High-Performance Lithium-Ion Batteries
    • Authors: Yan-Hong Ding; Jun Peng, Shifa-Ullah Khan, Yue Yuan
      Abstract: Organic substrates are indispensable in the fabrication of multifunctional polyoxometalate (POM)-based composites for various applications. A new molybdovanadophosphoric heteropolyacid (PMo10V2)-based polydopamine (PDA) composite (PMo10V2/PDA) is first synthesized through a facile, in situ polymerization method under hydrothermal conditions, without the addition of extra buffer solution. The obtained PMo10V2/PDA composite shows homogeneous microsphere morphology. Through utilization of the adhesive ability of PDA, the composite can be used as an anode material without additional binder for rechargeable lithium-ion batteries. Excellent electrochemical performances are obtained, with a high, stable specific capacity of 915.3 mA h g−1 at a current density of 100 mA g−1, remarkable rate capability, and good cycling stability (≈93 % capacity retention after 300 cycles at a high current density of 1000 mA g−1).Polyoxometalate composite anode: Polyoxometalate (POM)-assisted in situ polymerization of dopamine is an effective method for the fabrication of POM and polydopamine (PDA) composite materials. The obtained PMo10V2/PDA composite (see figure) can be exploited as a binder-free anode material for high-performance lithium-ion batteries, with remarkable rate capability and good cycling stability.
      PubDate: 2017-07-13T07:37:09.903282-05:
      DOI: 10.1002/chem.201700773
       
  • Lipophilic N-Hydroxyphthalimide Catalysts for the Aerobic Oxidation of
           Cumene: Towards Solvent-Free Conditions and Back
    • Authors: Manuel Petroselli; Lucio Melone, Massimo Cametti, Carlo Punta
      Abstract: A new class of lipophilic N-hydroxyphthalimide (NHPI) catalysts designed for the aerobic oxidation of cumene in solvent-free conditions was synthesized and tested. The specific strategy proposed for the introduction of lipophilic tails on the NHPI moiety leads to lipophilic catalysts that—while completely preserving the activity of the precursor—allow the catalytic oxidation to be conducted in neat cumene, for the first time. The corresponding cumyl hydroperoxide is obtained in good yields (28–52 %) and with high selectivity (95–97 %), under mild conditions. Importantly, the presence of a polar solvent is no longer required to guarantee complete solubilization of the catalyst. On the other hand, the oxidation conducted in neat cumene reveals the unexpected necessity of using small amounts of acetonitrile to fully promote the hydrogen atom transfer process and prevent the catalyst from detrimental hydrogen-bond (HB) driven aggregation.The degrees of freedom: Novel lipophilic N-hydroxyphthalimide catalysts allowed the catalytic oxidation of neat cumene to be conducted for the first time, and revealed the limits of solvent-free conditions, wherein hydrogen-bond (HB) driven aggregation of the catalyst occurs.
      PubDate: 2017-07-13T07:36:52.364214-05:
      DOI: 10.1002/chem.201701573
       
  • Catalytic Asymmetric Total Synthesis and Stereochemical Revision of
           Leucinostatin A, a Modulator of Tumor-Stroma Interaction
    • Authors: Masakatsu Shibasaki; Hikaru Abe, Hitoshi Ouchi, Chiharu Sakashita, Manabu Kawada, Takumi Watanabe
      Abstract: Total synthesis of leucinostatin A, a modulator of tumor-stroma interactions, using an asymmetric catalysis, a nitroaldol reaction, thioamide-aldol reaction, Strecker-type reaction, and alcoholysis of 3-methylglutaric anhydride, is described. We demonstrated the applicability of the established catalytic asymmetric process to the synthesis of molecules with a complex structure. Careful analysis of the NMR data, HPLC profiles, and biological activity revealed that the correct structure of leucinostatin A is the epimeric form of the reported structure; the secondary alcohol within the AHMOD residue has an R-configuration.
      PubDate: 2017-07-13T07:25:50.791917-05:
      DOI: 10.1002/chem.201703239
       
  • Accessing Low-Valent Inorganic Cations using an Extremely Bulky
           N-Heterocyclic Carbene
    • Authors: Matthey Roy; Paul Lummis, Michael Ferguson, Robert McDonald, Eric Rivard
      Abstract: The extremely bulky N-heterocyclic carbene (NHC), ITr, (ITr = [(HCNCPh3)2C:]) featuring sterically shielding umbrella-shaped trityl (-CPh3) substituents was prepared. This NHC features the highest percent buried volume (%Vbur) to date, and was used to form a thermally-stable quasi one-coordinate thallium(I) cation [ITr-Tl]+. This Tl(I) adduct and the corresponding lithium complex [ITr*Li(OEt2)]+ are versatile "all-in-one" transmetalation/ligation reagents for preparing low-coordinate inorganic species inaccessible via pre-existing routes.
      PubDate: 2017-07-13T05:31:51.279652-05:
      DOI: 10.1002/chem.201703215
       
  • A Combined 1H/6Li NMR DOSY Strategy Finally Uncovers the Structure of
           i-Propyllithium in THF
    • Authors: Anne Harrison-Marchand; Gabriella Barozzino-Consiglio, Ghanem Hamdoun, Catherine Fressigné, Jacques Maddaluno, Hassan Oulyadi
      Abstract: Despite its common use in synthesis, the structure of isopropylliyhium in THF has never been determined, a dimer being generally proposed but not supported. This paper fills this data gap through a sophisticated NMR study that shows that, in THF at low-temperature, isopropyllithium is in the form of a 1:2 mixture of a trisolvated monomer and a disolvated dimer in equilibrium. The presence of the monomer, never evoked before, together with a hypo-solvation of the dimer hinted by DFT calculations, provides a rational explanation to the remarkable reactivity of this organolithium reagent in ethereal solvents.
      PubDate: 2017-07-13T05:31:46.816831-05:
      DOI: 10.1002/chem.201702990
       
  • Approach Matters: The Kinetics of Interfacial Inverse-Electron Demand
           Diels-Alder Reactions
    • Authors: Han Zuilhof; Rickdeb Sen, Digvijay Gahtory, Jorge Escorihuela, Sidharam P. Pujari, 1 P. Pujari, 1 Pujari, Judith Firet
      Abstract: Rapid and quantitative click functionalization of surfaces remains an interesting challenge in surface chemistry. In this regard, inverse electron demand Diels Alder (IEDDA) reactions represent a promising metal-free candidate. Herein, we reveal quantitative surface functionalization within 15 min. Furthermore, we report the comprehensive effects of substrate stereochemistry, surrounding microenvironment and substrate order on the reaction kinetics as obtained via a combination of XPS and surface-bound mass spectrometry (DART-MS).
      PubDate: 2017-07-13T05:31:23.018233-05:
      DOI: 10.1002/chem.201703103
       
  • The synthesis and photophysical analysis of a series of
           4-nitrobenzochalcogenadiazoles for super-resolution microscopy
    • Authors: Daniel Ray Jenkinson; Ashley Cadby, Simon Jones
      Abstract: A series of 4-nitrobenzodiazoles with atomic substitution through the chalcogen group were synthesised and their photophysical properties analysed with a view for use in single-molecule localisation microscopy. Sub-diffraction resolution imaging was achieved for silica nanoparticles coated with each dye. Those containing larger atoms were favoured for super-resolution microscopy due to a reduced blink rate (required for stochastic events to be localised). The sulfur containing molecule was deemed most amenable for widespread use due to the ease of synthetic manipulation compared to the selenium containing derivative.
      PubDate: 2017-07-13T03:25:29.222472-05:
      DOI: 10.1002/chem.201702289
       
  • Efficient Long-Range Charge Transport Through G-quadruplex
    • Authors: Jingyuan Wu; Zhenyu Meng, Yunpeng Lu, Fangwei Shao
      Abstract: DNA offers a means of long range charge transport for biology and electric nanodevices. Here a series of tetra-stranded G-quadruplexes were assembled within a dendritic DNA architecture to explore oxidative charge transport (hole transport) via G-quadruplex. Efficient charge transport was achieved over 28 Å upon UV irradiation. Over a longer G-quadruplex bridge, hole transport was escalated to a higher efficiency, which reflected in a higher yield than that of the optimal duplex DNA for charge transport, adenine tract. Efficient long-range hole transport suggests tetra-stranded G-quadruplex, instead of an oxidation hotspot, holds better potentials as an electron conduit than duplex DNA.
      PubDate: 2017-07-13T01:28:34.60305-05:0
      DOI: 10.1002/chem.201702478
       
  • Control of Helical Chirality of Ferrocene-Dipeptide Conjugates by the
           Secondary Structure of Dipeptide Chains
    • Authors: Toshiyuki Moriuchi; Taiki Nishiyama, Masaki Nobu, Toshikazu Hirao
      Abstract: Controlling helical chirality and creating protein secondary structures in ferrocene-dipeptide bioorganometallic conjugates were achieved by adjusting the conformational flexibility of the dipeptide chains. In systems reported thus far, the helical chirality of a conjugate was determined by the absolute configuration of the adjacent amino acid reside. In contrast, it was possible to induce both M- and P-helical chirality, even when the configuration of the adjacent amino acid was the same. It is particularly interesting to note that M-helical chirality was produced in a cyclic ferrocene-dipeptide conjugate composed of the L-Ala-D-Pro-cystamine-D-Pro-L-Ala dipeptide sequence (1), in which a type II β-turn-like secondary structure was established.
      PubDate: 2017-07-13T00:46:04.636662-05:
      DOI: 10.1002/chem.201703102
       
  • Temporal Control over Transient Chemical Systems using Structurally
           Diverse Chemical Fuels
    • Authors: Jack L.-Y. Chen; Subhabrata Maiti, Ilaria Fortunati, Camilla Ferrante, Leonard J. Prins
      Abstract: The next generation of adaptive, intelligent chemical systems will rely on a continuous supply of energy to maintain the functional state. Such systems will require chemical methodology that provides precise control over the energy dissipation process, and thus, the lifetime of the transiently activated function. This manuscript reports on the use of structurally diverse chemical fuels to control the lifetime of two different systems under dissipative conditions: transient signal generation and the transient formation of self-assembled aggregates. The energy stored in the fuels is dissipated at different rates by an enzyme, which installs a dependence of the lifetime of the active system on the chemical structure of the fuel. In the case of transient signal generation, it is shown that different chemical fuels can be used to generate a vast range of signal profiles, allowing temporal control over two orders of magnitude. Regarding self-assembly under dissipative conditions, the ability to control the lifetime using different fuels turns out to be particularly important as stable aggregates are formed only at well-defined surfactant/fuel ratios, meaning that temporal control cannot be achieved by simply changing the fuel concentration.Chemical fuels to control lifetime: The next generation of adaptive, intelligent materials will require precise control over energy dissipation processes. Towards this goal, structurally diverse chemical fuels are used to control the lifetime of two such processes: transient signal generation and transient self-assembly.
      PubDate: 2017-07-12T06:51:21.817747-05:
      DOI: 10.1002/chem.201701533
       
  • Catalytic Oxygenative Allylic Transposition of Alkenes into Enones with an
           Azaadamantane-Type Oxoammonium Salt Catalyst
    • Authors: Shota Nagasawa; Yusuke Sasano, Yoshiharu Iwabuchi
      Abstract: The first catalytic oxygenative allylic transposition of unactivated alkenes into enones has been developed using an oxoammonium salt as the catalyst. This reaction converts various tri- and trans-disubstituted alkenes into their corresponding enones with transposition of their double bonds at ambient temperature in good yields. The use of a less-hindered azaadamantane-type oxoammonium salt as the catalyst and a combination of two distinct stoichiometric oxidants, namely, iodobenzene diacetate and magnesium monoperoxyphthalate hexahydrate (MMPP⋅6 H2O) are essential to facilitate the enone formation efficiently.It takes two: The first catalytic oxygenative allylic transposition of unactivated alkenes into enones has been developed using an oxoammonium salt as the catalyst. This reaction converts various alkenes into their corresponding enones with transposition of their double bonds at ambient temperature in good yields. The use of a less-hindered azaadamantane-type oxoammonium salt as the catalyst and a combination of two distinct stoichiometric oxidants are essential.
      PubDate: 2017-07-12T06:51:13.759671-05:
      DOI: 10.1002/chem.201702512
       
  • Inosine Can Increase DNA′s Susceptibility to Photo-oxidation by a RuII
           Complex due to Structural Change in the Minor Groove
    • Authors: Páraic M. Keane; James P. Hall, Fergus E. Poynton, Bjørn C. Poulsen, Sarah P. Gurung, Ian P. Clark, Igor V. Sazanovich, Michael Towrie, Thorfinnur Gunnlaugsson, Susan J. Quinn, Christine J. Cardin, John M. Kelly
      Abstract: Key to the development of DNA-targeting phototherapeutic drugs is determining the interplay between the photoactivity of the drug and its binding preference for a target sequence. For the photo-oxidising lambda-[Ru(TAP)2(dppz)]2+ (Λ-1) (dppz=dipyridophenazine) complex bound to either d{T1C2G3G4C5G6C7C8G9A10}2 (G9) or d{TCGGCGCCIA}2 (I9), the X-ray crystal structures show the dppz intercalated at the terminal T1C2;G9A10 step or T1C2;I9A10 step. Thus substitution of the G9 nucleobase by inosine does not affect intercalation in the solid state although with I9 the dppz is more deeply inserted. In solution it is found that the extent of guanine photo-oxidation, and the rate of back electron-transfer, as determined by pico- and nanosecond time-resolved infrared and transient visible absorption spectroscopy, is enhanced in I9, despite it containing the less oxidisable inosine. This is attributed to the nature of the binding in the minor groove due to the absence of an NH2 group. Similar behaviour and the same binding site in the crystal are found for d{TTGGCGCCAA}2 (A9). In solution, we propose that intercalation occurs at the C2G3;C8I9 or T2G3;C8A9 steps, respectively, with G3 the likely target for photo-oxidation. This demonstrates how changes in the minor groove (in this case removal of an NH2 group) can facilitate binding of RuIIdppz complexes and hence influence any sensitised reactions occurring at these sites. No similar enhancement of photooxidation on binding to I9 is found for the delta enantiomer.Feel the groove: Replacement of guanine by inosine in a sequence of DNA results in an unexpected increase in electron transfer by a bound RuII complex. The effect is explained by a change in the binding of the complex due to the removal of an amino group from the minor groove of the DNA.
      PubDate: 2017-07-12T06:41:36.446719-05:
      DOI: 10.1002/chem.201701447
       
  • Equilibrium, Kinetic and Structural Properties of Gallium(III) and Some
           Divalent Metal Complexes Formed with the New DATAm and DATA5m Ligands
    • Authors: Edit Farkas; Johannes Nagel, Bradley P. Waldron, David Parker, Imre Tóth, Ernő Brücher, Frank Rösch, Zsolt Baranyai
      Abstract: The development of 68Ge/68Ga generators has made the positron-emitting 68Ga isotope widely accessible and raised interest in new chelate complexes of Ga3+. The hexadentate 1,4-di(acetate)-6-methyl[amino(methyl)acetate]perhydro-1,4-diazepane (DATAm) ligand and its bifunctional analogue, 1,4-di(acetate)-6-pentanoic acid[amino(methyl)acetate]perhydro-1,4-diazepane (DATA5m), rapidly form complexes with 68Ga in high radiochemical yield. The stability constants of DATAm and DATA5m complexes formed with Ga3+, Zn2+, Cu2+, Mn2+ and Ca2+ have been determined by using pH potentiometry, spectrophotometry (Cu2+) and 1H and 71Ga NMR spectroscopy (Ga3+). The stability constants of Ga(DATAm) and Ga(DATA5m) complexes are slightly higher than those of Ga(AAZTA). The species distribution calculations indicated the predominance of Ga(L)OH mixed-hydroxo complexes at physiological pH. The 1H and 71Ga NMR spectroscopy studies provided information about the coordinated functional groups of ligands and on the kinetics of exchange between the Ga(L) and Ga(L)OH complexes. The transmetalation reactions between the Ga(L) complexes and Cu2+ citrate (6
      PubDate: 2017-07-12T06:41:06.824746-05:
      DOI: 10.1002/chem.201701508
       
  • Cover Picture: Insights into trans-Ligand and Spin-Orbit Effects on
           Electronic Structure and Ligand NMR Shifts in Transition-Metal Complexes
           (Chem. Eur. J. 41/2017)
    • Authors: Anja H. Greif; Peter Hrobárik, Martin Kaupp
      Pages: 9700 - 9700
      Abstract: The nature of the trans ligand influences the ligand NMR shifts in 5d transition-metal complexes, dominated by spin-orbit (SO) effects. As analyzed for various Au(I) and Pt(II) hydride complexes, an increase in trans ligand influence may even change the sign of these SO shifts from shielding to deshielding for d10 or d8 complexes, due to the destabilization of a σ(H-M-L)-type MO by stronger trans ligands and thus modified σ-/π-spinor mixing. This allows general shift predictions. More information can be found in the Full Paper by M. Kaupp et al. on page 9790.
      PubDate: 2017-05-19T06:25:29.860312-05:
      DOI: 10.1002/chem.201701557
       
  • Inside Cover: An Aminocatalyzed Stereoselective Strategy for the Formal
           α-Propargylation of Ketones (Chem. Eur. J. 41/2017)
    • Authors: Igor D. Jurberg
      Pages: 9701 - 9701
      Abstract: A two-step strategy has been developed for the stereoselective preparation of alpha-propargyl ketones using isoxazol-5-ones as key building blocks. The first step is an aminocatalyzed addition of ketones to alkylidene isoxazol-5-ones, whereas the second step is a controlled nitrosative degradation event that transforms the isoxazol-5-one ring into a triple bond. In this regard, the isoxazol-5-one ring can be seen as a masked alkyne. By removing the mask, a new universe is revealed. This metaphor is represented in the artwork. More information can be found in the Communication by I. D. Jurberg on page 9716.
      PubDate: 2017-05-30T05:15:46.751653-05:
      DOI: 10.1002/chem.201702050
       
  • Insights into trans-Ligand and Spin-Orbit Effects on Electronic Structure
           and Ligand NMR Shifts in Transition-Metal Complexes
    • Authors: Anja H. Greif; Peter Hrobárik, Martin Kaupp
      Pages: 9702 - 9702
      Abstract: Invited for the cover of this issue is the group of Martin Kaupp at the Technical University Berlin. The image depicts remarkably general and large trans ligand effects on NMR shifts in 5d transition-metal complexes, and their main MO origins. Read the full text of the article at 10.1002/chem.201700884.“We decided that the cover design should be based on the confrontation of weak vs. strong.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 9790 ff. (
      DOI : 10.1002/chem.201700844).
      PubDate: 2017-05-19T06:10:39.406946-05:
       
  • High-Throughput Optical Imaging and Spectroscopy of One-Dimensional
           Materials
    • Authors: Fengrui Yao; Cheng Chen, Can Liu, Jin Zhang, Feng Wang, Kaihui Liu
      Pages: 9703 - 9710
      Abstract: Direct visualization of one-dimensional (1D) materials under an optical microscope in ambient conditions is of great significance for their characterizations and applications. However, it is full of challenges to achieve such goal due to their relative small size (ca. 1 nm in diameter) in the optical-diffraction-limited laser spot (ca. 1 μm in diameter). In this Concept article, we introduce a polarization-based optical homodyne detection method that can be used as a general strategy to obtain high-throughput, real-time, optical imaging and in situ spectroscopy of polarization-inhomogeneous 1D materials. We will use carbon nanotubes (CNTs) as an example to demonstrate the applications of such characterization with respect to the absorption signal of individual nanotubes, real-time imaging of individual nanotubes in devices, and statistical structure information of nanotube arrays.How to detect a single nanotube! In this concept article, the theory of homodyne optical signal detection is introduced, the construction of polarization-based homodyne microscope is described, and its applications for measurements on carbon nanotubes will be also discussed.
      PubDate: 2017-06-13T07:05:35.919448-05:
      DOI: 10.1002/chem.201700731
       
  • Amphoteric Borylketenimines: Versatile Intermediates in the Synthesis of
           Borylated Heterocycles
    • Authors: Sherif J. Kaldas; Kowan T. V. O'Keefe, Rodrigo Mendoza-Sanchez, Andrei K. Yudin
      Pages: 9711 - 9715
      Abstract: We report the first synthesis of amphoteric borylketenimines from ethynyl N-methyliminodiacetic acid (MIDA) boronate and sulfonyl azides via copper catalysis. In situ trapping of these intermediates with various nucleophiles provided access to novel borylated azetidimines, iminocoumarins, amides, iminooxetanes, and amidines. The described strategy based on borylketenimines offers high levels of chemo- and regioselectivity, enabling the synthesis of unprecedented borylated molecules. This work highlights the unexplored utility of borylketenimines in the synthesis of potentially bioactive molecules.Access to novel borylated azetidimines, iminocoumarins, amides, iminooxetanes, and amidines is provided by in situ trapping of amphoteric borylketenimine intermediates with various nucleophiles. The described strategy offers high levels of chemo- and regioselectivity. This work highlights the unexplored utility of borylketenimines in the synthesis of potentially bioactive molecules.
      PubDate: 2017-07-06T05:30:54.363736-05:
      DOI: 10.1002/chem.201702008
       
  • An Aminocatalyzed Stereoselective Strategy for the Formal
           α-Propargylation of Ketones
    • Authors: Igor D. Jurberg
      Pages: 9716 - 9720
      Abstract: A two-step reaction sequence is described for the asymmetric formal α-propargylation of ketones. This approach takes advantage of an aminocatalyzed conjugate addition of ketones to alkylidene isoxazol-5-ones, followed by a controlled nitrosative degradation event. The target compounds can be accessed in broad scope, in moderate to good yields, perfect diastereocontrol and good to excellent enantioselectivity.Add and unmask! Alkylidene isoxazol-5-ones can be used as key building blocks in a stereoselective aminocatalyzed Michael addition/nitrosative alkynylation sequence to produce an overall process of α-propargylation of ketones. This reaction sequence produces moderate to good yields, perfect diastereocontrol and good to excellent enantioselectivity, therefore making this synthetic route a viable strategy for the construction of densely substituted α-propargyl ketones.
      PubDate: 2017-05-30T05:16:32.552262-05:
      DOI: 10.1002/chem.201701433
       
  • Reductive Coupling of CO2, Primary Amine, and Aldehyde at Room
           Temperature: A Versatile Approach to Unsymmetrically N,N-Disubstituted
           Formamides
    • Authors: Zhengang Ke; Leiduan Hao, Xiang Gao, Hongye Zhang, Yanfei Zhao, Bo Yu, Zhenzhen Yang, Yu Chen, Zhimin Liu
      Pages: 9721 - 9725
      Abstract: We present a simple, metal-free, and versatile route to synthesize unsymmetrically N,N-disubstituted formamides (NNFAs) from CO2, primary amine, and aldehyde promoted by an ionic liquid (1-butyl-3-methylimidazolium chloride) at room temperature. This approach features wide scopes of amines and aldehydes, and various unsymmetrical NNFAs could be obtained in good to excellent yields. The ionic liquid can be reused for at least five runs without obvious activity loss.A simple and versatile route is presented for the synthesis of unsymmetrically N,N-disubstituted formamides (NNFAs) through a three-component reductive coupling of CO2, amine, and aldehyde under mild conditions. This method affords various unsymmetric NNFAs in good to excellent yields.
      PubDate: 2017-06-28T06:30:37.145415-05:
      DOI: 10.1002/chem.201701420
       
  • Alpha- and Beta-Diastereoisomers of Phenylcobalamin from Cobalt-Arylation
           with Diphenyliodonium Chloride
    • Authors: Christopher Brenig; Markus Ruetz, Christoph Kieninger, Klaus Wurst, Bernhard Kräutler
      Pages: 9726 - 9731
      Abstract: Organometallic aryl-cobalamins are B12-derivatives featuring properties of potential ‘B12 antivitamins’. Herein, we describe a new method for the preparation of aryl-cobalamins using versatile diaryliodonium salts as arylation agents. Formate or sodium borohydride reduction of aquocobalamin in presence of diphenyliodonium chloride furnished Coβ-phenyl-cobalamin PhCbl in a roughly 3:1 to 1:1 ratio with its coordination isomer αPhCbl, a first representative ‘base-off’ Coα-aryl-cobalamin. The new structures were secured by detailed spectroscopic analysis, supplemented by an X-ray crystal structure analysis of PhCbl. Both types of coordination isomers of the aryl-cobalamins promise to be useful molecular tools in biomedical and biological studies.Up or down' That is the question: A new method of cobalt-arylation of vitamin B12-derivatives produces βPhCbl and αPhCbl, both possible coordination isomers of phenylcobalamin. Such arylcobalamins may function as ‘B12 antivitamins’ and help decipher new pathways and mechanisms of B12-dependent metabolism.
      PubDate: 2017-06-28T06:30:22.053748-05:
      DOI: 10.1002/chem.201701514
       
  • Fluidic Manufacture of Star-Shaped Gold Nanoparticles
    • Authors: Alessandro Silvestri; Luigi Lay, Rinaldo Psaro, Laura Polito, Claudio Evangelisti
      Pages: 9732 - 9735
      Abstract: Star-shaped gold nanoparticles (StarAuNPs) are extremely attractive nanomaterials, characterized by localized surface plasmon resonance which could be potentially employed in a large number of applications. However, the lack of a reliable and reproducible synthetic protocols for the production of StarAuNPs is the major limitation to their spreading. For the first time, here we present a robust protocol to manufacture reproducible StarAuNPs by exploiting a fluidic approach. Star-shaped AuNPs have been synthesized by means of a seed-less protocol, employing ascorbic acid as reducing agent at room temperature. Moreover, the versatility of the bench-top microfluidic protocol has been exploited to afford hydrophilic, hydrophobic and solid-supported engineered StarAuNPs, by avoiding intermediate NP purifications.Stars in-flow: Anisotropic star-shaped gold nanoparticles are synthesized by exploiting a microfluidic process. The seed-less and user-friendly protocol afforded highly reproducible and morphologically controlled nanoparticles. Moreover, different surface-engineered nanoparticles can be obtained while avoiding time-consuming purification steps.
      PubDate: 2017-07-03T06:56:51.52551-05:0
      DOI: 10.1002/chem.201701617
       
  • The Effect of Solution Conditions on the Driving Forces for Self-Assembly
           of a Pyrene Molecule
    • Authors: Shaowei Shi; Dapeng Liu, Xiaosong Wang
      Pages: 9736 - 9740
      Abstract: Fe(CO){CO(CH2)5CH2-pyrene}(Cp)(PPh3) (Fp-pyrene) is soluble in DMSO and THF, but insoluble in water, methanol, and ethanol. The hydrophobic force drives the molecules′ assembly into vesicles in THF/water. The π–π interaction of the pyrene groups subsequently occurred within the vesicular membrane. The assembly, however, is driven by the π–π interaction in DMSO/water (water content: 40–80 vol %) into membranes, which is attributed to the relatively higher degree of de-solvation (δ) of pyrene in DMSO. Further increase in δ (DMSO/90 vol % water) suppresses the π–π interaction and spherical particles are formed. On the other hand, the supersaturated solutions were prepared via a cycle of heating and cooling of Fp-pyrene in methanol or ethanol. Fp-pyrene aggregates into particles without the π–π interaction in the solutions with a lower degree of supersaturation (σ). In contrast, a higher σ induces the π–π interaction, which drives the assembly into nanotapes. The π–π interaction is a conditional effect depending on the solution conditions, which can be adjusted for the synthesis of nanostructures assembled from the same aromatic molecule.Getting stacked: The driving forces for self-assembly of a pyrene molecule are adjustable depending on the solution conditions.
      PubDate: 2017-06-28T06:30:48.389997-05:
      DOI: 10.1002/chem.201702281
       
  • Amorphous Nickel-Cobalt-Borate Nanosheet Arrays for Efficient and Durable
           Water Oxidation Electrocatalysis under Near-Neutral Conditions
    • Authors: Lanlan Chen; Xiang Ren, Wanqing Teng, Pengfei Shi
      Pages: 9741 - 9745
      Abstract: Electrolytic hydrogen generation needs earth-abundant oxygen evolution reaction electrocatalysts that perform efficiently at mild pH. Here, the development of amorphous nickel-cobalt-borate nanosheet arrays on macroporous nickel foam (NiCo-Bi/NF) as a 3D catalyst electrode for high-performance water oxidation in near-neutral media is reported. To drive a current density of 10 mA cm−2, the resulting NiCo-Bi/NF demands an overpotential of only 430 mV in 0.1 m potassium borate (K-Bi, pH 9.2). Moreover, it also shows long-term electrochemical durability with maintenance of catalytic activity for 20 h, achieving a high turnover frequency of 0.21 s−1 at an overpotential of 550 mV.NiCo-Bi nanosheet arrays on nickel foam support behaves as 3D catalyst electrode for water oxidation at near-neutral pH. This electrode achieves a catalytic current density of 10 mA cm−2 at an overpotential of 430 mV with strong electrochemical stability in 0.1 m K-Bi.
      PubDate: 2017-07-03T07:00:47.197653-05:
      DOI: 10.1002/chem.201702314
       
  • A DFT Study on the Stabilization of the B≡B Triple Bond in a
           Metallaborocycle: Contrasting Electronic Structures of Boron and Carbon
           Analogues
    • Authors: Sagar Ghorai; Eluvathingal D. Jemmis
      Pages: 9746 - 9751
      Abstract: The electronic structure of (η5-Cp)2Zr(NH2-BB-NH2) (3 b) suggests that it could be a candidate for having a boron–boron triple bond in the cyclic system; however, computational studies shows that 3 b is a very high energy isomer on its potential energy surface. Replacement of amines with tricoordinate nucleophilic boron groups (η5-Cp)2Zr[B(PH3)2-BB-B(PH3)2] (3 c) reduces the relative energy dramatically. The B≡B triple bond arises through the donation of two electrons from the metal fragment, ZrCp2, to the in-plane π-bonding orbital of the central B–B unit. Strong σ-donating and chelating bis-phosphine ligands (Me2P(CH2)nPMe2), which stabilize donor–acceptor bonding interaction in gem-diborene L2B-BBr2 (10), would be a good choice along the synthetic path towards 3 d, (η5-Cp)2Zr[B4(Me2P(CH2)3PMe2)2]. A comparison of the energetics of the reaction leading to a cyclic boryne system (3 d), with the linear boryne isomer [(B2NHCPh)2] shows that the angle strain from cyclization is compensated by stabilization from the metal.BB king: Incorporation of a group IV metal fragment ZrCp2 into a borocycle is an effective strategy to stabilize a B≡B triple bond in a cyclic system by donating two electrons to the central BB unit. Additionally, stabilization of the metal center comes from the donation of electrons from terminal tricoordinate nucleophilic boron center. This donor–acceptor bonding feature in metallacycloboryne contrasts with the carbon analogues.
      PubDate: 2017-06-30T04:37:32.487804-05:
      DOI: 10.1002/chem.201702422
       
  • α-Quaternary Mannich Bases through Copper-Catalyzed Amination-Induced
           1,2-Rearrangement of Allylic Alcohols
    • Authors: Wei-Zhi Weng; Jian-Guo Sun, Ping Li, Bo Zhang
      Pages: 9752 - 9755
      Abstract: A novel copper-catalyzed amination-induced 1,2-rearrangement reaction of allylic alcohols has been developed under simple and mild conditions. The commercially available N-fluorobenzenesulfonimide (NFSI) is employed as an amination reagent. In this transformation, not only alkyl, but also aryl substituents can efficiently undergo 1,2-carbon atom migration, thereby providing an efficient and powerful route to prepare a wide range of α-quaternary Mannich bases. The reaction features a broad substrate scope, operational simplicity, and excellent practicality.A novel copper-catalyzed amination-induced 1,2-rearrangement reaction of allylic alcohols has been achieved under simple and mild conditions. This transformation exhibits a broad substrate scope and good functional group tolerance. A variety of Mannich bases containing an α-quaternary center are readily prepared in moderate to excellent yields using the title reaction.
      PubDate: 2017-07-03T07:00:30.139766-05:
      DOI: 10.1002/chem.201702428
       
  • Na+ Ions Induce the Pirouetting Motion and Catalytic Activity of
           [2]Rotaxanes
    • Authors: Yong-Jay Lee; Kuang-Shun Liu, Chien-Chen Lai, Yi-Hung Liu, Shie-Ming Peng, Richard P. Cheng, Sheng-Hsien Chiu
      Pages: 9756 - 9760
      Abstract: We have prepared [2]rotaxanes, the behavior of which as switchable catalysts depends on their pirouetting motion, which can be controlled through the addition and removal of Na+ ions. At least three sequential on/off cycles of a Michael reaction can be performed in situ when using the NaTFPB/[2.2.2]cryptand reagent pair to switch “on” and “off” the catalytic ability of the [2]rotaxanes.Two-way street: The catalytic activity of the [2]rotaxane catalysts can be switched between “on” and “off” states over at least three different cycles through in situ addition and removal of Na+ ions.
      PubDate: 2017-07-03T07:16:29.633539-05:
      DOI: 10.1002/chem.201702525
       
  • Total Synthesis of 7-epi-Pukalide and 7-Acetylsinumaximol B
    • Authors: Kirsten McAulay; J. Stephen Clark
      Pages: 9761 - 9765
      Abstract: Convergent total syntheses of the furanocembranoids 7-epi-pukalide and 7-acetylsinumaximol B have been achieved using a one-pot Knoevenagel condensation and thioether-mediated furan-forming reaction. Furan formation proceeds via a sulfur ylide and results in rapid introduction of structural complexity during the coupling of two highly functionalised fragments. The targets have been prepared in 16 steps from (R)-perillyl alcohol.Inspired by nature: The furanocembranoids 7-epi-pukalide and 7-acetyl-sinumaximol B have been synthesised by a convergent route in which a one-pot Knoevenagel condensation and tetrahydrothiophene-mediated furan-forming reaction is used to couple two fragments to give the complete carbon framework.
      PubDate: 2017-06-28T06:31:03.270465-05:
      DOI: 10.1002/chem.201702591
       
  • Transition and Alkali Metal Complex Ternary Amides for Ammonia Synthesis
           and Decomposition
    • Authors: Hujun Cao; Jianping Guo, Fei Chang, Claudio Pistidda, Wei Zhou, Xilun Zhang, Antonio Santoru, Hui Wu, Norbert Schell, Rainer Niewa, Ping Chen, Thomas Klassen, Martin Dornheim
      Pages: 9766 - 9771
      Abstract: A new complex ternary amide, Rb2[Mn(NH2)4], which simultaneously contains both transition and alkali metal catalytic sites, is developed. This is in line with the recently reported TM-LiH composite catalysts, which have been shown to effectively break the scaling relations and achieve ammonia synthesis under mild conditions. Rb2[Mn(NH2)4] can be facilely synthesized by mechanochemical reaction at room temperature. It exhibits two temperature-dependent polymorphs, that is, a low-temperature orthorhombic and a high-temperature monoclinic structure. Rb2[Mn(NH2)4] decomposes to N2, H2, NH3, Mn3N2, and RbNH2 under inert atmosphere; whereas it releases NH3 at a temperature as low as 80 °C under H2 atmosphere. Those unique behaviors enable Rb2[Mn(NH2)4], and its analogue K2[Mn(NH2)4], to be excellent catalytic materials for ammonia decomposition and synthesis. Experimental results show both ammonia decomposition onset temperatures and conversion rates over Rb2[Mn(NH2)4] and K2[Mn(NH2)4] are similar to those of noble metal Ru-based catalysts. More importantly, these ternary amides exhibit superior capabilities in catalyzing NH3 synthesis, which are more than 3 orders of magnitude higher than that of Mn nitride and twice of that of Ru/MgO. The in situ SR-PXD measurement shows that manganese nitride, synergistic with Rb/KH or Rb/K(NH2)xH1−x, are likely the active sites. The chemistry of Rb2/K2[Mn(NH2)x] and Rb/K(NH2)xH1−x with H2/N2 and NH3 correlates closely with the catalytic performance.Ammonia: The first case of using A2[Mn(NH2)4] (A=Rb and K) for low temperature NH3 synthesis and decomposition is presented. The ternary amides were synthesized through ball-milling under NH3, before thorough structural characterization and evaluation of their ammonia synthesis properties.
      PubDate: 2017-06-29T08:40:27.909783-05:
      DOI: 10.1002/chem.201702728
       
  • Fluorescence-Lifetime Imaging and Super-Resolution Microscopies Shed Light
           on the Directed- and Self-Assembly of Functional Porphyrins onto Carbon
           Nanotubes and Flat Surfaces
    • Authors: Boyang Mao; David G. Calatayud, Vincenzo Mirabello, Navaratnarajah Kuganathan, Haobo Ge, Robert M. J. Jacobs, Ashley M. Shepherd, José A. Ribeiro Martins, Jorge Bernardino De La Serna, Benjamin J. Hodges, Stanley W. Botchway, Sofia I. Pascu
      Pages: 9772 - 9789
      Abstract: Functional porphyrins have attracted intense attention due to their remarkably high extinction coefficients in the visible region and potential for optical and energy-related applications. Two new routes to functionalised SWNTs have been established using a bulky ZnII-porphyrin featuring thiolate groups at the periphery. We probed the optical properties of this zinc(II)-substituted, bulky aryl porphyrin and those of the corresponding new nano-composites with single walled carbon nanotube (SWNTs) and coronene, as a model for graphene. We report hereby on: i) the supramolecular interactions between the pristine SWNTs and ZnII-porphyrin by virtue of π–π stacking, and ii) a novel covalent binding strategy based on the Bingel reaction. The functional porphyrins used acted as dispersing agent for the SWNTs and the resulting nanohybrids showed improved dispersibility in common organic solvents. The synthesized hybrid materials were probed by various characterisation techniques, leading to the prediction that supramolecular polymerisation and host–guest functionalities control the fluorescence emission intensity and fluorescence lifetime properties. For the first time, XPS studies highlighted the differences in covalent versus non-covalent attachments of functional metalloporphyrins to SWNTs. Gas-phase DFT calculations indicated that the ZnII-porphyrin interacts non-covalently with SWNTs to form a donor–acceptor complex. The covalent attachment of the porphyrin chromophore to the surface of SWNTs affects the absorption and emission properties of the hybrid system to a greater extent than in the case of the supramolecular functionalisation of the SWNTs. This represents a synthetic challenge as well as an opportunity in the design of functional nanohybrids for future sensing and optoelectronic applications.Supramolecular and covalent assemblies can influence the morphology and optical properties of porphyrin arrays onto flat, conductive as well as insulating surfaces, and lead to the control of SWNTs (single walled carbon nanotubes) functionalisation at the nanoscale. The synthesis of new functionalised luminescent SWNTs is reported. STED super-resolution microscopy, fluorescence-lifetime imaging as well as XPS, TCSPC (time-correlated single photon counting), UV/Vis, NMR spectroscopy, XRD, TEM and AFM probe the complexity of the emerging covalent and supramolecular aggregates.
      PubDate: 2017-05-19T02:20:42.938327-05:
      DOI: 10.1002/chem.201605232
       
  • Insights into trans-Ligand and Spin-Orbit Effects on Electronic Structure
           and Ligand NMR Shifts in Transition-Metal Complexes
    • Authors: Anja H. Greif; Peter Hrobárik, Martin Kaupp
      Pages: 9790 - 9803
      Abstract: Surprisingly general effects of trans ligands L on the ligand NMR shifts in third-row transition-metal complexes have been found by quasi-relativistic computations, encompassing 5d10, 5d8, and to some extent even 5d6 situations. Closer analysis, with emphasis on 1H shieldings in a series of linear HAuILq complexes, reveals a dominance of spin-orbit (SO) effects, which can change sign from appreciably shielding for weak trans ligands to appreciably deshielding for ligands with strong trans influence. This may be traced back to increasing destabilization of a σ-type MO at scalar relativistic level, which translates into very different σ-/π-mixing if SO coupling is included. For the strongest trans ligands, the σ-MO may move above the highest occupied π-type MOs, thereby dramatically reducing strongly shielding contributions from predominantly π-type spinors. The effects of SO-mixing are in turn related to angular momentum admixture from atomic spinors at the metal center. These SO-induced trends hold for other nuclei and may also be used to qualitatively predict shifts in unknown complexes.σ-Antibonding is the key! Surprisingly general trans ligand effects on NMR shifts in transition metal complexes are revealed by relativistic quantum-chemical analyses of ligand shifts, notably 1H shifts, in 5d10, 5d8, and 5d6 complexes. They are traced back to changes in σ-/π-spinor mixing by spin-orbit coupling due to a destabilization of a σ-type MO by strong trans ligands (see graphic). The insights allow qualitative and quantitative predictions of a wide range of ligand effects.
      PubDate: 2017-05-19T02:15:43.658994-05:
      DOI: 10.1002/chem.201700844
       
  • The Construction of Homochiral Lanthanide Quadruple-Stranded Helicates
           with Multiresponsive Sensing Properties toward Fluoride Anions
    • Authors: Wanmin Chen; Xiaoliang Tang, Wei Dou, Bei Wang, Lirong Guo, Zhenghua Ju, Weisheng Liu
      Pages: 9804 - 9811
      Abstract: A series of unique homochiral lanthanide tetranuclear quadruple-stranded helicates have been self-assembled controllably by using the intrinsic advantages of chiral bridging ligands, (S)-H2L and (R)-H2L, and lanthanide ions with high coordination numbers. The self-assembly process of these chiral helicates not only ensures the structural stability and quadruple-stranded feature of lanthanide cluster in the solid state and solution, but also achieves effective transfer and amplification of the chirality code from the ligand to a higher supramolecular level. Moreover, through using optical rotation, circular dichroism spectra analysis, and luminescence measurements, we demonstrate that these chiral lanthanide helicates could serve as sensitive and multi-responsive sensors to recognize and detect F− anions based on the change of chiral signal and NIR luminescence simultaneously, which represents a meaningful exploration for developing functional lanthanide-based polynuclear clusters.Homochiral lanthanide helicates: Homochiral lanthanide tetranuclear quadruple-stranded helicates were synthesized by using chiral bridging ligands, which exhibit stable structures and achieve the effective transfer and amplification of chirality code. In addition, the chiral lanthanide helicate could be applied to F− anions detection with multimodel responses both in chiral signal and NIR luminescence.
      PubDate: 2017-06-07T08:11:45.149371-05:
      DOI: 10.1002/chem.201700827
       
  • Design, Synthesis, and Chemistry of Bis(σ)borate and Agostic
           Complexes of Group 7 Metals
    • Authors: Koushik Saha; Rongala Ramalakshmi, Suman Gomosta, Kriti Pathak, Vincent Dorcet, Thierry Roisnel, Jean-François Halet, Sundargopal Ghosh
      Pages: 9812 - 9820
      Abstract: A series of new bis(σ)borate and agostic complexes of group 7 metals have been synthesized and structurally characterized from various borate ligands, such as trihydrobis(benzothiazol-2-yl)amideborate (Na[(H3B)bbza]), trihydro(2-aminobenzothiazolyl)borate (Na[(H3B)abz]), and dihydrobis(2-mercaptopyridyl)borate (Na[(H2B)mp2]) (bbza=bis(benzothiazol-2-yl)amine, abz=2-aminobenzothiazolyl, and mp=2-mercaptopyridyl). Photolysis of [Mn2(CO)10] with Na[(H3B)bbza] formed bis(σ)borate complex [Mn(CO)3(μ-H)2BHNCSC6H4(NR)] (1; R=NCSC6H4). Octahedral complex [Re(CO)2(N3C2S2C12H8)2] (2) was generated under similar reaction conditions with [Re2(CO)10]. Similarly, when [Mn2(CO)10] was treated with Na[(H3B)abz], bis(σ)borate complex [Mn(CO)3(μ-H)2BH(HN2CSC6H4)] (3) and the agostic complex [Mn(CO)3(μ-H)BH(HN2CSC6H4)2] (4) were formed. To probe the potential formation of agostic complexes of the heavier group 7 metals, we carried out the photolysis of [M2(CO)10] with Na[(H2B)mp2] and found that [M(CO)3(μ-H)BH(C5H4NS)2] (5: M=Re; 6: M=Mn) was formed in moderate yield. Complexes 1 and 3 feature a (κ3-H,H,N) coordination mode, whereas 4, 5, and 6 display both (κ3-H,N,N) and (κ3-H,S,S) modes of the corresponding ligands. To investigate the lability of the CO ligands of 1 and 3, we treated the complexes with phosphine ligands that generated novel bis(σ)borate complexes [Mn(μ-H)2(BHNCSC6H4)(NR)(CO)2PL2L’] (R=NCSC6H4; 7 a: L=L’=Ph; 7 b: L=Ph, L’=Me) and [Mn(μ-H)2BHN(NCSC6H4)R(CO)2PL2L’] (R=NCSC6H4; 8 a: L=L’=Ph; 8 b: L=Ph, L’=Me). Complexes 7 and 8 are structural isomers with different coordination modes of the bbza ligand. In addition, DFT calculations were performed to shed some light on the bonding and electronic structures of these complexes.Let it B: Several borate ligands with group 7 metals that show novel structures, bonding, and reactivities were synthesized. In addition, some bis(σ)borate complexes reacted with phosphines and led to the isolation of isomeric borate complexes (see scheme).
      PubDate: 2017-06-09T04:55:51.838892-05:
      DOI: 10.1002/chem.201701423
       
  • Synthesis and Characterization of Bromoaluminate Ionic Liquids
    • Authors: Michael Hog; Marius Schneider, Ingo Krossing
      Pages: 9821 - 9830
      Abstract: Twelve bromoaluminate based ionic liquids (ILs) were synthesized and characterized by IR, Raman, and NMR spectroscopy, as well as single crystal X-ray diffraction in part. Their principal physicochemical properties including melting points, conductivities, viscosities, and densities were determined and compared with related ILs. The influence of the cation and anion on the physicochemical properties are discussed. The [AlBr4]−based salts are—with one exception—solid at room temperature, while the compounds based on the anion [Al2Br7]− are liquid at room temperature. The liquid salts show low viscosities (49–139 mPa s), medium to high conductivities (0.76–3.53 mS cm−1) and high densities (1.82–2.04 g cm−3) at 28 °C. Furthermore, we showed aluminum electrodeposition from Lewis acidic ILs based on AlBr3 and 1-hexyl-3-methylimidazolium bromide and investigated the stability range of various formulations.A series of twelve bromoaluminate ionic liquids were synthesized by mixing aluminum bromide with different bromides (see figure). The key features of the seven at RT liquid salts are low viscosities (49–139 mPa s), mid to good conductivities (0.76–3.53 mS cm−1) and high densities (1.82–2.04 g cm−3) at 28 °C. Aluminum can be electrodeposited from Lewis acidic mixtures based on AlBr3 and 1-hexyl-3-methylimidazolium bromide.
      PubDate: 2017-06-29T08:31:19.022111-05:
      DOI: 10.1002/chem.201700105
       
  • Fluorinated Porous Conjugated Polyporphyrins through Direct C−H
           Arylation Polycondensation: Preparation, Porosity, and Use as
           Heterogeneous Catalysts for Baeyer–Villiger Oxidation
    • Authors: Qiang Cao; Qing Yin, Qi Chen, Zhi-Bing Dong, Bao-Hang Han
      Pages: 9831 - 9837
      Abstract: By considering the high reactivity of fluorinated iron–porphyrin and good stability of porphyrin-based porous polymers, fluorinated iron–porphyrin conjugated porous polymers (FPOP-3–6) were synthesized through direct C−H arylation polymerization. The obtained materials are chemically and thermally stable, of which FPOP-3 exhibits the highest Brunauer–Emmett–Teller specific surface area (about 840 m2 g−1). For functional studies of the obtained polymers as heterogeneous catalysts, catalytic transformation of cycloketones into lactones by oxygen through Baeyer–Villiger oxidation was used as a model reaction. Fluorinated phenyl substituents of the iron–porphyrin not only are beneficial to the conversion, but also can stabilize the porphyrin to resist catalyst breakdown. The polymer FPOP-3, with high porosity, exhibits the best catalytic efficiency and recycling effect. The recovered catalyst also shows good catalytic activities after recycling three times with a small loss in yield.Removed from the mix: The synthesis of fluorinated iron–porphyrin conjugated porous polymers through direct C−H arylation polymerization is described (see scheme). The application of these polymers as heterogeneous catalysts for Baeyer–Villiger oxidation is also discussed.
      PubDate: 2017-06-27T07:23:28.385367-05:
      DOI: 10.1002/chem.201700916
       
  • Organic CO Prodrugs: Structure–CO-Release Rate Relationship Studies
    • Authors: Zhixiang Pan; Vayou Chittavong, Wei Li, Jun Zhang, Kaili Ji, Mengyuan Zhu, Xingyue Ji, Binghe Wang
      Pages: 9838 - 9845
      Abstract: Carbon monoxide (CO) is an endogenously produced gasotransmitter in mammals, and may have signaling roles in bacteria as well. It has many recognized therapeutic effects. A significant challenge in this field is the development of pharmaceutically acceptable forms of CO delivery with controllable and tunable release rates. Herein, the structure–release rate studies of the first class of organic CO prodrugs that release CO in aqueous solution at neutral pH is described.Structure–CO-release rate relationship studies of organic CO prodrugs reveal that CO releasing rate can be tuned by modifying the nature of the linker, substituents on dienone ring or linker, and the length of the linker.
      PubDate: 2017-07-04T04:56:14.342086-05:
      DOI: 10.1002/chem.201700936
       
  • Structure-Induced Switching of the Band Gap, Charge Order, and Correlation
           Strength in Ternary Vanadium Oxide Bronzes
    • Authors: Thomas M. Tolhurst; Justin L. Andrews, Brett Leedahl, Peter M. Marley, Sarbajit Banerjee, Alexander Moewes
      Pages: 9846 - 9856
      Abstract: Recently, V2O5 nanowires have been synthesized as several different polymorphs, and as correlated bronzes with cations intercalated between the layers of edge- and corner- sharing VO6 octahedra. Unlike extended crystals, which tend to be plagued by substantial local variations in stoichiometry, nanowires of correlated bronzes exhibit precise charge ordering, thereby giving rise to pronounced electron correlation effects. These developments have greatly broadened the scope of research, and promise applications in several frontier electronic devices that make use of novel computing vectors. Here a study is presented of δ-SrxV2O5, expanded δ-SrxV2O5, exfoliated δ-SrxV2O5 and δ-KxV2O5 using a combination of synchrotron soft X-ray spectroscopy and density functional theory calculations. The band gaps of each system are experimentally determined, and their calculated electronic structures are discussed from the perspective of the measured spectra. Band gaps ranging from 0.66 ± 0.20 to 2.32 ± 0.20 eV are found, and linked to the underlying structure of each material. This demonstrates that the band gap of V2O5 can be tuned across a large portion of the range of greatest interest for device applications. The potential for metal–insulator transitions, tuneable electron correlations and charge ordering in these systems is discussed within the framework of our measurements and calculations, while highlighting the structure-property relationships that underpin them.Bronze medal: A series of vanadium oxide bronzes were studies with X-ray absorptoion and emission spectroscopy. Experimental band gaps were determined and linked with the composition, demonstrating the ability to fine tune the V2O5 band gap.
      PubDate: 2017-06-27T07:23:48.274962-05:
      DOI: 10.1002/chem.201700962
       
  • A Series of Bimetallic Ammonium AlNa Formates
    • Authors: Yao Yu; Ran Shang, Sa Chen, Bing-Wu Wang, Zhe-Ming Wang, Song Gao
      Pages: 9857 - 9871
      Abstract: A series of AlNa bimetallic ammonium metal formate frameworks (AlNa AMFFs) have been prepared by employing various ammoniums from NH4+ to large linear polyammoniums. The series consists of six perovskites of (412⋅63) topology for mono-ammoniums, two chiral (49⋅66) frameworks incorporating polyethylene ammoniums, two niccolites with (412⋅63)(49⋅66) topology containing diammoniums, and two layered compounds made of 2D (4,4) AlNa formate sheets intercalated by small diammoniums. The first ten compounds present the structural hierarchy of (412⋅63)m(49⋅66)n framework topologies for (m, n)=(1, 0), (0, 1), and (1, 1), respectively, in parallel to the homometallic AMFFs for divalent metals. The symmetry lowering, asymmetric formate bridges, and different hydrogen-bonding strengths appeared in the bimetallic structures owing to the different charge and size of Al3+ and Na+ seemingly inhibits the occurrence of phase transitions for more than half the AlNa AMFFs within the series, and the bimetallic members undergoing phase transitions show different transition behaviors and dielectric properties compared with the homometallic analogs. Anisotropic/negative/zero thermal expansions of the materials could be rationally attributed to the librational motion, or flip movement between different sites, of the ammonium cations, and the coupled change of AlNa formate frameworks. The thermal and IR spectroscopic properties have also been investigated.All in the family: A series of ammonium AlNa formates consisting of (412⋅63) perovskites, (49⋅66) chiral frameworks, (412⋅63)(49⋅66) niccolites, and (4,4) layers, and the lower structural symmetries lead to different phase transition behaviors, thermal expansions, and dielectric properties, compared with the homometallic analogs.
      PubDate: 2017-06-29T03:41:58.535759-05:
      DOI: 10.1002/chem.201701099
       
  • A Highly Selective Fluorescent Probe for Detection of Hydrogen Sulfide in
           Living Systems: In Vitro and in Vivo Applications
    • Authors: Shahi Imam Reja; Neetu Sharma, Muskan Gupta, Payal Bajaj, Vandana Bhalla, Ripu D. Parihar, Puja Ohri, Gurcharan Kaur, Manoj Kumar
      Pages: 9872 - 9878
      Abstract: A fluorescein-based fluorescent probe has been designed and synthesised that selectively detects H2S in aqueous medium, among various analytes tested. This fluorescein-based fluorescent probe has also been successfully utilised for real-time imaging of exo- and endogenously produced H2S in cancer cells and normal cells. Moreover, the probe can also detect H2S in the rat brain hippocampus at variable depths and in living nematodes.Revealing images: A fluorescein-based fluorescent probe has been designed and synthesized to detect H2S selectively in aqueous medium containing various analytes (see figure). The probe was also successfully utilized for real-time imaging of exo- and endogenously produced H2S in cancer and normal cells. Moreover, the probe can also detect H2S in the rat brain hippocampus at variable depths and in living nematodes.
      PubDate: 2017-06-29T08:32:03.891552-05:
      DOI: 10.1002/chem.201701124
       
  • Unsaturated Long-Chain Fatty Acids Are Preferred Ferritin Ligands That
           Enhance Iron Biomineralization
    • Authors: Serena Zanzoni; Katiuscia Pagano, Mariapina D'Onofrio, Michael Assfalg, Silvia Ciambellotti, Caterina Bernacchioni, Paola Turano, Silvio Aime, Laura Ragona, Henriette Molinari
      Pages: 9879 - 9887
      Abstract: Ferritin is a ubiquitous nanocage protein, which can accommodate up to thousands of iron atoms inside its cavity. Aside from its iron storage function, a new role as a fatty acid binder has been proposed for this protein. The interaction of apo horse spleen ferritin (HoSF) with a variety of lipids has been here investigated through NMR spectroscopic ligand-based experiments, to provide new insights into the mechanism of ferritin–lipid interactions, and the link with iron mineralization. 1D 1H, diffusion (DOSY) and saturation-transfer difference (STD) NMR experiments provided evidence for a stronger interaction of ferritin with unsaturated fatty acids compared to saturated fatty acids, detergents, and bile acids. Mineralization assays showed that oleate c aused the most efficient increase in the initial rate of iron oxidation, and the highest formation of ferric species in HoSF. The comprehension of the factors inducing a faster biomineralization is an issue of the utmost importance, given the association of ferritin levels with metabolic syndromes, such as insulin resistance and diabetes, characterized by fatty acid concentration dysregulation. The human ferritin H-chain homopolymer (HuHF), featuring ferroxidase activity, was also tested for its fatty acid binding capabilities. Assays show that oleate can bind with high affinity to HuHF, without altering the reaction rates at the ferroxidase site.Chewing the fat: The role of lipids in iron homeostasis is investigated. Oleate is seen to bind to ferritin and increase the iron biomineralization rate.
      PubDate: 2017-06-27T04:08:02.015982-05:
      DOI: 10.1002/chem.201701164
       
  • Evaluation of the Medicinal Potential of Two Ruthenium(II) Polypyridine
           Complexes as One- and Two-Photon Photodynamic Therapy Photosensitizers
    • Authors: Jeannine Hess; Huaiyi Huang, Adrian Kaiser, Vanessa Pierroz, Olivier Blacque, Hui Chao, Gilles Gasser
      Pages: 9888 - 9896
      Abstract: Two [Ru(phen)2dppz]2+ derivatives (phen=1,10-phenantroline, dppz=dipyrido[3,2-a:2′,3′-c]phenazine) with different functional groups on the dppz ligand [dppz-7,8-(OMe)2 (1), dppz-7,8-(OH)2 (2)] have been synthesized, characterized and investigated as photosensitizers (PSs) for photodynamic therapy (PDT) against cancer. Both complexes showed intense red phosphorescence and promising singlet oxygen (1O2) quantum yields of 75 % (1) and 54 % (2) in acetonitrile. Complex 1 (logPo/w=−0.52, 2.4 nmol Ru per mg protein) was found to be more lipophilic, having also a higher cellular uptake efficiency compared to 2 (logPo/w=−0.20, 0.9 nmol Ru per mg protein). Complex 1 localized evenly in HeLa cells whereas 2, was mainly visualized in the cell membrane by confocal microscopy. In the dark, complex 1 (IC50=36.5 μm) was found to be more toxic than complex 2 (IC50>100 μm) on a HeLa cells monolayer. Importantly, in view of PDT applications, both complexes were found to be non-toxic in the dark towards multicellular HeLa spheroids (IC50>100 μm). Upon one-photon irradiation (420 nm, 9.27 J cm−2), 1 exhibited higher phototoxicity (IC50=3.1 μm) than 2 (IC50=16.7 μm) on HeLa cell monolayers. When two-photon irradiation (800 nm, 9.90 J cm−2) was applied, only 1 (IC50=9.5 μm) was found to be active toward HeLa spheroids. This study demonstrates that the functional group on the intercalative ligand has a strong influence on the cellular localization and anticancer activity of RuII polypyridyl complexes.The structure influences the activity! Two RuII polypyridyl complexes have been synthesized, characterized and investigated as photosensitizers (PSs) for photodynamic therapy (PDT) against cancer.
      PubDate: 2017-06-29T03:36:38.583473-05:
      DOI: 10.1002/chem.201701392
       
  • (E)-1,1,4,4-Tetramethyl-2-tetrazene (TMTZ): A Prospective Alternative to
           Hydrazines in Rocket Propulsion
    • Authors: Anne Dhenain; Chaza Darwich, Carlos Miró Sabaté, Duc-Minh Le, Anne-Julie Bougrine, Henri Delalu, Emmanuel Lacôte, Léa Payen, Jérôme Guitton, Emilie Labarthe, Guy Jacob
      Pages: 9897 - 9907
      Abstract: 1,1,4,4-Tetramethyl-2-tetrazene (TMTZ) is considered as a prospective replacement for toxic hydrazines used in liquid rocket propulsion. The heat of formation of TMTZ was computed and measured, giving values well above those of the hydrazines commonly used in propulsion. This led to a predicted maximum Isp of 337 s for TMTZ/N2O4 mixtures, which is a value comparable to that of monomethylhydrazine. We found that TMTZ has a vapor pressure well below that of liquid hydrazines, and it is far less toxic. Finally, an improved synthesis is proposed, which is compatible with existing industrial production facilities after minor changes. TMTZ is thus an attractive liquid propellant candidate, with a performance comparable to hydrazines but a lower vapor pressure and toxicity.Rocket man: The oxidation 1,1′-dimethylhydrazine (UDMH) with monochloramine yields 1,1,4,4-tetramethyl-2-tetrazene (TMTZ). The new process has great potential to be used for the large scale continuous synthesis of the compound, which is a promising candidate to replace liquid hydrazines in rocket propulsion.
      PubDate: 2017-07-03T06:51:04.589401-05:
      DOI: 10.1002/chem.201701468
       
  • Synthesis and Properties of Functional Twisted Tolanes
    • Authors: Yury Kozhemyakin; Andreas Kretzschmar, Maximilian Krämer, Frank Rominger, Andreas Dreuw, Uwe H. F. Bunz
      Pages: 9908 - 9918
      Abstract: The synthesis and optical properties of several novel fluorescent and/or phosphorescent bridged tolanes (tolanophanes) are reported and their optical and structural properties are investigated. Specifically, diiodinated and bisalkynylated tolanophanes were obtained, and characterized by spectroscopy and computational methods. They represent attractive building blocks for novel polymers and emissive solid-state materials.Let's twist again: We access a family of twisted tolanes carrying iodine and alkynyl substituents. The functionalized twisted tolanes show optical and electronic properties that are surprisingly different from those of the unsubstituted twisted tolane.
      PubDate: 2017-06-30T04:25:41.242-05:00
      DOI: 10.1002/chem.201701519
       
  • A Coordination Network with Ligand-Centered Redox Activity Based on
           facial-[CrIII(2-mercaptophenolato)3]3− Metalloligands
    • Authors: Masanori Wakizaka; Takeshi Matsumoto, Atsushi Kobayashi, Masako Kato, Ho-Chol Chang
      Pages: 9919 - 9925
      Abstract: The design of redox-active metal–organic frameworks and coordination networks (CNs), which exhibit metal- and/or ligand-centered redox activity, has recently received increased attention. In this study, the redox-active metalloligand (RML) [Me4N]3fac-[CrIII(mp)3] (1) (mp=2-mercaptophenolato) was synthesized and characterized by single-crystal X-ray diffraction analysis, and its reversible ligand-centered one-electron oxidation was examined by cyclic voltammetry and spectroelectrochemical measurements. Since complex 1 contains O/S coordination sites in three directions, complexation with K+ ions led to the formation of the two-dimensional honeycomb sheet-structured [K3fac-{CrIII(mp)3}(H2O)6]n (2⋅6 H2O), which is the first example of a redox-active CN constructed from a RML with o-disubstituted benzene ligands. Herein, we unambiguously demonstrate the ligand-centered redox activity of the RML within the CN 2⋅6 H2O in the solid state.The facbook network: This study shows that the redox-active metalloligand fac-[CrIII(2-mercaptophenolato)3]3− coordinates to K+ ions through its three-directional O/S sites to form a 2D honeycomb-like coordination network, which exhibits ligand-centered redox properties in the solid state.
      PubDate: 2017-06-29T03:30:54.75882-05:0
      DOI: 10.1002/chem.201701613
       
  • Electronic and Ligand Properties of Skeletally Substituted Cyclic
           (Alkyl)(Amino)Carbenes (CAACs) and Their Reactivity towards Small Molecule
           Activation: A Theoretical Study
    • Authors: Priyam Bharadwaz; Pubali Chetia, Ashwini K. Phukan
      Pages: 9926 - 9936
      Abstract: Quantum chemical calculations have been carried out to understand the ligand properties of skeletally modified cyclic alkyl amino carbenes. The stability of these carbenes has been assessed from an evaluation of their singlet–triplet and stabilization energy values. Ylide substituted carbenes are found to be more stable than non-ylidic ones in their optimized singlet state. Nucleophilicity and electrophilicity indices values were evaluated in order to further investigate the reactivity of these carbenes. The calculated values of proton affinities and the degree of gallium pyramidalization in the carbene-GaCl3 adducts correlate well with the σ-basicity of these carbenes. The reactivity of non-ylidic carbenes toward the activation of both H2 and NH3 are calculated to be more favourable compared to that of parent CAAC. On the other hand, ylide anchored carbenes are found to be unsuccessful toward the activation of both H2 and NH3.Works both ways: Quantum chemical calculations have been carried out to understand the changes in electronic and ligand properties of skeletally modified cyclic alkyl amino carbenes (CAACs). While some of the molecules are found to be stronger donors, others are found to be more ambiphilic than CAAC.
      PubDate: 2017-07-03T06:57:00.844716-05:
      DOI: 10.1002/chem.201701645
       
  • Uniform Yolk–Shell MoS2@Carbon Microsphere Anodes for
           High-Performance Lithium-Ion Batteries
    • Authors: Yunmei Pan; Jiajia Zhang, Hongbin Lu
      Pages: 9937 - 9945
      Abstract: As an electrode material for lithium-ion batteries (LIBs), MoS2 has attracted much attention because of its high capacity and low cost. However, the rational design of a novel electrode structure with a high capacity, fast charge/discharge rate, and long cycling lifetime remains a great challenge. Herein, a environmentally friendly etching strategy is reported for the construction of monodisperse, inner void-controlled yolk–shell MoS2@carbon microspheres. The resulting anode reveals an initial discharge capacity up to 1813 mAh g−1, a high reversible capacity (1016 mAh g−1), excellent cycling stability (200 cycles), and superior rate performance. Such microspheres consist of nanosized MoS2 yolks (≈280 nm), porous carbon shells (≈25 nm) and well-controlled internal voids in between, opening a new pathway for the optimization of the electrochemical properties of MoS2-based anodes without sacrificing their capacity. In addition, this etching strategy offers a new method for the development of functional, hollow MoS2-based composites.A good egg: Highly uniform yolk–shell MoS2@C microspheres were synthesized as lithium-ion battery (LIB) anodes, with the inner cavity between the carbon shell and MoS2 core easily tailored through a novel etching technique (see scheme). The rationally designed microsphere anode exhibits high reversible capacity, and excellent cycling stability and rate performance. The etching strategy developed may provide a new approach for the preparation of other carbon-based hollow nanostructures
      PubDate: 2017-06-29T08:31:05.218625-05:
      DOI: 10.1002/chem.201701691
       
  • Competition versus Cooperation in Catalytic Hydrogelators for
           anti-Selective Mannich Reaction
    • Authors: Nishant Singh; Beatriu Escuder
      Pages: 9946 - 9951
      Abstract: Chemical systems find similarities in different sociological and biological processes, in which the entities compete or cooperate for a favorable outcome. The structural and functional adaptations leading to emergent properties, especially in catalysis, are based on factors such as abundance of substrates, stability of the transition state, and structural/functional attributes of catalysts. Proline and acid groups appended to catalytic fibers of two self-sorting hydrogelators compete for the Mannich reaction between aniline, benzaldehyde, and cyclohexanone to give low overall selectivity (anti/syn 77:23). In a sol–gel system of the same molecules, on the other hand, the soluble acid appended molecules tend to cooperate with the fibers of proline-appended catalyst to give improved selectivity (anti/syn 95:5). The available options for the catalytic molecules are to carry out the reaction independently or in cooperation. However, these options are chosen based on the efficiency, selectivity, and mobility of catalysts as a result of their abilities to self-assemble.Team players: A bottom-up approach can be used to construct functional architectures through noncovalent interactions between self-assembling molecules. Such self-sorted, co-assembled, and sol–gel systems constructed from the same building blocks can have different emergent properties that depend on the relative positioning of the molecules and the final self-assembled structures.
      PubDate: 2017-07-03T07:01:16.287147-05:
      DOI: 10.1002/chem.201701724
       
  • Mesoporous Silica Scaffolds as Precursor to Drive the Formation of
           Hierarchical SAPO-34 with Tunable Acid Properties
    • Authors: Ivana Miletto; Geo Paul, Stephanie Chapman, Giorgio Gatti, Leonardo Marchese, Robert Raja, Enrica Gianotti
      Pages: 9952 - 9961
      Abstract: Using a distinctive bottom-up approach, a hierarchical silicoaluminophosphate, SAPO-34, has been synthesized using cetyl trimethylammonium bromide (CTAB) encapsulated within ordered mesoporous silica (MCM-41) that serves as both the silicon source and mesoporogen. The structural and textural properties of the hierarchical SAPO-34 were contrasted against its microporous analogue, and the nature, strength, and accessibility of the Brønsted acid sites were studied using a range of physicochemical characterization tools; notably probe-based FTIR and solid-state magic angle spinning (SS MAS) NMR spectroscopies. Whilst CO was used to study the acid properties of hierarchical SAPO-34, bulkier molecular probes (including pyridine, 2,4,6-trimethylpyridine and 2,6-di-tert-butylpyridine) allowed particular insight into the enhanced accessibility of the acid sites. The activity of the hierarchical SAPO-34 catalyst was evaluated in the industrially-relevant, acid-catalyzed Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam, under vapor-phase conditions. These catalytic investigations revealed a significant enhancement in the yield of ϵ-caprolactam using our hierarchical SAPO-34 catalyst compared to SAPO-34, MCM-41, or a mechanical mixture of these two phases. The results highlight the merits of our design strategy for facilitating enhanced mass transfer, whilst retaining favorable acid site characteristics.Precursor driven formation: Hierarchical SAPO-34 has been synthesized with a distinctive bottom-up approach, using CTAB encapsulated within ordered mesoporous silica that serves as both the silicon source and mesoporogen.
      PubDate: 2017-06-28T06:30:56.995326-05:
      DOI: 10.1002/chem.201701978
       
  • A Novel Open-Framework Copper Borovanadate with Enhanced Catalytic
           Performance for Oxidation of Benzylic C−H Bond
    • Authors: Yuquan Feng; Zhiguo Zhong, Hongwei Wang, Huitao Fan, Dongqin Bi, Lu Wang, Zhengzheng Xing, Dongfang Qiu
      Pages: 9962 - 9967
      Abstract: A novel open-framework copper borovanadate, with a 6-connected topological net and 1D 8-membered ring channels, has been obtained for the first time. The compound not only exhibits a unique -B3O7(OH)-Cu-B(OH)3 linkage and features the largest ratio between TM2+(Cu2+) and the borovanadate anion, but also possesses enhanced catalytic performance, high recyclability, and stability during the oxidation of benzylic C−H bonds.Oxidation catalyst: An open-framework copper borovanadate with 6-connected topological net and 1D 8-MR channels has been obtained for the first time. The compound not only exhibits a unique -B3O7(OH)-Cu-B(OH)3 linkage and features the largest ratio between TM2+ (Cu2+) and the borovanadate anion, but also possesses enhanced catalytic performance, high recyclability and stability during the oxidations of benzylic C−H bond.
      PubDate: 2017-06-30T04:31:34.362173-05:
      DOI: 10.1002/chem.201702207
       
  • Corrigendum: Synthesis of α-Dawson-Type Silicotungstate
           [α-Si2W18O62]8− and Protonation and Deprotonation Inside the Aperture
           through Intramolecular Hydrogen Bonds
    • Authors: Takuo Minato; Kosuke Suzuki, Keigo Kamata, Noritaka Mizuno
      Pages: 9968 - 9968
      PubDate: 2017-07-06T05:30:23.498856-05:
      DOI: 10.1002/chem.201702856
       
  • Inside Back Cover: The Construction of Homochiral Lanthanide
           Quadruple-Stranded Helicates with Multiresponsive Sensing Properties
           toward Fluoride Anions (Chem. Eur. J. 41/2017)
    • Authors: Wanmin Chen; Xiaoliang Tang, Wei Dou, Bei Wang, Lirong Guo, Zhenghua Ju, Weisheng Liu
      Pages: 9969 - 9969
      Abstract: Chirality, as a signature of life, plays a vital role in the universe. Here a unique homochiral lanthanide tetranuclear quadruple-stranded helicate is presented, which was self-assembled successfully with the aid of a nitrate template to achieve the effective transfer and amplification of chirality code. The homochiral Nd helicate, could serve as a multiresponsive sensor for the recognition and detection of F− anions based on the change of chiral signal and near-infrared luminescence simultaneously, which represents a meaningful exploration for developing functional lanthanide-based polynuclear clusters. More information can be found in the Full Paper by X. Tang, W. Liu et al. on page 9804.
      PubDate: 2017-06-07T07:50:56.244602-05:
      DOI: 10.1002/chem.201702292
       
  • Back Cover: Design, Synthesis, and Chemistry of Bis(σ)borate and Agostic
           Complexes of Group 7 Metals (Chem. Eur. J. 41/2017)
    • Authors: Koushik Saha; Rongala Ramalakshmi, Suman Gomosta, Kriti Pathak, Vincent Dorcet, Thierry Roisnel, Jean-François Halet, Sundargopal Ghosh
      Pages: 9970 - 9970
      Abstract: The lability of the CO ligands of manganese bis(σ)borate complex, [Mn(CO)3(μ-H)2HB(NCSC6H4)NR] (R=NCSC6H4) was studied with different phosphine ligands. Treatment of this Mn-bis(σ)borate complex with PPh3 led to the formation of two manganese bis(σ)borate complexes, [(PPh3)(CO)2Mn(μ-H)2HB(NCSC6H4)NR] and [(PPh3)(CO)2Mn(μ-H)2HBNR(NCSC6H4)] (R=NCSC6H4), as structural isomers having two different arrangements of the bis(benzothiazol-2-yl)amine ligand around the central metal atom. More information can be found in the Full Paper by S. Ghosh et al. on page 9812.
      PubDate: 2017-06-09T04:57:00.001511-05:
      DOI: 10.1002/chem.201702439
       
 
 
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