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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  [1589 journals]
  • Ethylene Epoxidation catalyzed by Ag Nanoparticles located on Ag-LSX
           Zeolites formed by Pressure and Temperature Induced Auto-Reduction
    • Authors: Donghoon Kim; Yongmoon Lee, Yonghwi Kim, Kathleen Mingle, Jochen Lauterbach, Douglas Blom, Thomas Vogt, Yongjae Lee
      Abstract: Ag-exchanged LSX, a large pore low silica analogue of faujasite, was prepared and post-synthetically modified using pressure and temperature in the presence of various pore-penetrating fluids. Using high-resolution synchrotron X-ray powder and single crystal diffraction we derive structural models of the as-prepared and post-synthetically modified Ag-LSX materials. In the as-prepared Ag-LSX model we located 96 Ag+ and 245 H2O molecules distributed over seven and five distinctive sites, respectively. At 1.4(1) GPa pressure and 150ºC in ethanol the number of Ag cations within the pores of Ag-LSX are reduced by ca. 47.4%, whereas the number of H2O molecules are increases by ca. 40.8%. The formation of zero-valent Ag nanoparticles deposited on Ag-LSX crystallites depends on the fluid present during pressurization. Ag-nanoparticle-Ag-zeolite hybrid materials are recovered after pressure release and shown to have different chemical reactivity when used as catalysts for ethylene epoxidation.
      PubDate: 2017-12-14T06:05:39.6509-05:00
      DOI: 10.1002/chem.201704923
       
  • Revisiting the Ullman's Radical Chemistry for Phthalocyanine Derivatives
    • Authors: catherine Hirel; Ismail Fidan, Dominique Luneau, Vefa Ahsen
      Abstract: Phthalocyanines derivatives does not cease to aroused attention due to their numerous properties and applications (e.g.,sensor, PDT). This makes them unique scaffold for the design of new material. In this expectative, we were interested to develop the synthesis of an imino nitroxyde-substituted phthalocyanine via the Ullman's procedure; a challenge due to intrinsic low solubility of most phthalocyanine derivative in much solvents. To overcome this solubility problem we designed phthalocyanine with bulky neopentyl substituents in peripheral position as counterpart to the imino nitroxyde moieties. The imino nitroxyde-substituted phthalocyanine was obtained by condensation of a monoformyl-substituted phtahocyanine with 2,3-bis(hydroxylamino)-2,3-dimethylbutane in refluxing THF-MeOH (2:1) mixture in the presence of p-toluenesulfonic acid monohydrate, follow by oxidation with PbO2. Characterization was performed by electrochemistry, UV-Vis and EPR spectroscopy in solution as well as SQUID in solid state.
      PubDate: 2017-12-14T05:35:43.181183-05:
      DOI: 10.1002/chem.201704903
       
  • Frontispiece: C−H Insertions by Iron Porphyrin Carbene: Basic Mechanism
           and Origin of Substrate Selectivity
    • Authors: Rahul L. Khade; Yong Zhang
      Abstract: Despite structural similarity and isoelectronic nature between heme carbene and FeIV=O intermediate, our quantum chemical studies for the first time revealed an FeII-based, concerted, hydride-transfer mechanism, different from the FeIV-based stepwise hydrogen-atom-transfer mechanism for C−H functionalization by native heme enzymes. A trend of broad range experimental C−H insertion yields and kinetic isotope effects were well reproduced. Origin of substrate selectivity was elucidated. For more information, see the Communication by R. L. Khade and Y. Zhang on page 17654 ff.
      PubDate: 2017-12-14T05:28:32.550873-05:
      DOI: 10.1002/chem.201787063
       
  • Frontispiece: Advances in Stereoselective 1,2-cis Glycosylation using C-2
           Auxiliaries
    • Authors: Rens A. Mensink; Thomas J. Boltje
      Abstract: This review summarizes the recent emergence of a new strategy for stereoselective glycosylation using a C-2 chiral auxiliary. The operating principle of this methodology is neighboring group participation of the auxiliary to form a sulfonium ion intermediate. The structure of the auxiliary, the type of protecting groups and stereochemistry of the monosaccharide are important factors that determine the mechanism and selectivity of such reactions. Finally, the application of chiral auxiliaries to oligosaccharide synthesis is discussed. For more information see the Review article by R. A. Mensink and T. J. Boltje on page 17637 ff.
      PubDate: 2017-12-14T05:28:29.389253-05:
      DOI: 10.1002/chem.201787062
       
  • Frontispiece: Metal-Containing Polymers as Light-Emitting and
           Light-Responsive Materials and Beyond
    • Authors: Matteo Mauro; Stéphane Bellemin-Laponnaz, Cristina Cebrián
      Abstract: The rational combination of suitable metal ions and organic multi-topic ligands allows the engineering of multi-functional metal-containing polymers with great structural diversity. The Concept article by M. Mauro, S. Bellemin-Laponnaz, and C. Cebrián on page 17626 ff. provides an overview and future directions in the field of metallopolymers and metallo-supramolecular polymers as luminescent, stimuli-responsive, adaptive and smart materials.
      PubDate: 2017-12-14T05:28:24.908011-05:
      DOI: 10.1002/chem.201787061
       
  • Frontispiece: Spectroscopic Observation and Molecular Dynamics Simulation
           of Ga Surface Segregation in Liquid Pd–Ga Alloys
    • Authors: Mathias Grabau; Jannis Erhard, Nicola Taccardi, Sandra Krick Calderon, Peter Wasserscheid, Andreas Görling, Hans-Peter Steinrück, Christian Papp
      Abstract: An inhomogeneous distribution of Palladium atoms in liquid Gallium is shown by means of a combination of angle resolved X-ray photoelectron spectroscopy and molecular dynamics simulations based on density-functional theory in a temperature range between room temperature and 750 K. This effect is expected to be of high relevance for a novel liquid metal catalyst consisting of a bimetallic Pd/Ga catalyst supported on porous SiO2. For more information see the Full Paper by C. Papp et al. on page 17701 ff.
      PubDate: 2017-12-14T05:28:21.94841-05:0
      DOI: 10.1002/chem.201787064
       
  • Photophysical and Photoacoustic Properties of Quadrupolar Borondifluoride
           Curcuminoid Dyes
    • Authors: Stephanie Bellinger; Maryam Hatamimoslehabadi, Seema Bag, Farha Mithila, Jeffrey La, Mathieu Frenette, Samir Laoui, David J. Szalda, Chandra Yelleswarapu, Jonathan Rochford
      Abstract: The synthesis and characterization of a series of donor-π-acceptor-π-donor (D-A-D) curcuminoid molecules is presented herein that incorporates π-extended aryl and electron-donating amino terminal functionalization. Computational evaluation shows these molecules possess quadrupolar character with the lowest energy transitions displaying high molar extinction coefficients with broad tunability through manipulation of terminal donating groups. Consistent with their quadrupolar nature, these molecules show varying degrees of solvatochromic behavior in both their absorption and emission spectra, which has been analyzed by Lippert–Mataga and Kamlet–Taft analysis. Photophysical and photoacoustic (PA) properties of these molecules have been investigated by the optical photoacoustic z-scan (OPAZ) method. Selected curcuminoid molecules display nonlinear behavior at a high laser fluence through excited state absorption that translates to the production of an enhanced photoacoustic emission. A relative comparison of “molar PA emission” is also presented with the crystal violet linear optical absorbing/linear PA emitting system being utilized as a standard reference material for OPAZ experiments. Furthermore, PA tomography experiments are presented to illustrate the enhanced PA contrast obtainable via an excited state absorption.A series of donor-π-acceptor-π-donor (D-A-D) curcuminoid molecules is presented that incorporates π-extended aryl and electron-donating amino terminal functionalization.
      PubDate: 2017-12-14T04:16:28.963774-05:
      DOI: 10.1002/chem.201704423
       
  • Au-Coated Honeycomb Structure as an Efficient TCO-Free Counter-Electrode
           for Quantum-Dot-Sensitized Solar Cells
    • Authors: Van-Duong Dao; Van-Tien Bui, Minki Baek, The-Long Phan, Kijung Yong, Ho-Suk Choi
      Abstract: This study reports the fabrication of a Petri dish patterned with cylindrical micro-cavities that are produced using a one-step solvent-immersion phase-separation process. The developed 3D honeycomb Petri dish is coated with a Au film through a sputtering method to be an efficient Au-coated FTO-free electrode for quantum-dot-sensitized solar cells. Due to the high specific active surface area of the electrode with the Au-coated honeycomb structure, the energy conversion efficiency of devices that use this electrode is 5.2 % compared to 4.4 and 4.7 % by devices using an Au-coated flat Petri dish and an Au-coated FTO electrode, respectively. This design strategy offers excellent potential for the fabrication of highly efficient counter electrodes with FTO-free substrates of flexible photovoltaic devices.The power of honeycomb: A Petri dish patterned with cylindrical micro-cavity is produced using a one-step solvent-immersion phase-separation process as an efficient template for fabricating Au-coated FTO-free electrode in quantum-dot-sensitized solar cells.
      PubDate: 2017-12-14T04:16:04.300469-05:
      DOI: 10.1002/chem.201704374
       
  • Mutagenesis of Sequence Determinants of Truncated Porcine ALOX15 Induces
           Changes in the Reaction Specificity by Altering the Catalytic Mechanism of
           Initial Hydrogen Abstraction
    • Authors: Patricia Saura; Ilya Kaganer, Dagmar Heydeck, José M. Lluch, Hartmut Kühn, Àngels González-Lafont
      Abstract: The reaction specificity of lipoxygenases is of physiological relevance since the various oxygenation products exhibit different biological activities. Among mammalian ALOX15 orthologs there are arachidonic acid 12- and 15-lipoxygenating enzymes and recent studies suggested an evolutionary switch in that reaction specificity during late primate development. Previous reports showed that 12-lipoxygenating ALOX15 orthologs can be converted to 15-lipoxygenating enzymes by site-directed mutagenesis of some sequence determinants. Unfortunately, the molecular basis for those alterations are not well understood. Here, the arachidonic acid 12-lipoxygenating N-terminal truncation variant of pig ALOX15, for which a crystal structure is available, was used to explore the catalytic mechanism of the specificity switch induced by mutagenesis of Val418 and Val419 sequence determinants. We found that Val418Ile+Val419Met double mutant is dominantly 15-lipoxygenating. Docking and MD simulations, and quantum mechanics/molecular mechanics calculations indicated that the wildtype energy barrier for arachidonic acid 15-lipoxygenation is 3.4 kcal mol−1 higher than for 12-lipoxygenation. In contrast, for the Val418Ile+Val419Met double mutant the energy barrier for 12-lipoxygenation is 6.0 kcal mol−1 higher than for 15-lipoxygenation. Our data suggest that enzyme–substrate complex geometries determine the value of these energy barriers and, as a consequence, the reaction specificity of ALOX15 orthologs.In vitro studies and in silico simulations indicate a strong preference of wildtype pig miniALOX15 for 12-lipoxygenation of arachidonic acid, but selective 15-lipoxygenation for the Val418Ile+Val419Met double mutant. These results provide a suitable explanation for the observed evolutionary switch in ALOX15 specificity, which has taken place during late primate development.
      PubDate: 2017-12-14T03:20:43.28868-05:0
      DOI: 10.1002/chem.201704672
       
  • Rapid Iododeboronation with and without Gold Catalysis: Application to
           Radiolabelling of Arenes
    • Authors: Stacey Webster; Kerry M. O'Rourke, Conor Fletcher, Sally L. Pimlott, Andrew Sutherland, Ai-Lan Lee
      Abstract: Radiopharmaceuticals that incorporate radioactive iodine in combination with single-photon emission computed tomography imaging play a key role in nuclear medicine, with applications in drug development and disease diagnosis. Despite this importance, there are relatively few general methods for the incorporation of radioiodine into small molecules. This work reports a rapid air- and moisture-stable ipso-iododeboronation procedure that uses NIS in the non-toxic, green solvent dimethyl carbonate. The fast reaction and mild conditions of the gold-catalysed method led to the development of a highly efficient process for the radiolabelling of arenes, which constitutes the first example of an application of homogenous gold catalysis to selective radiosynthesis. This was exemplified by the efficient synthesis of radiolabelled meta-[125I]iodobenzylguanidine, a radiopharmaceutical that is used for the imaging and therapy of human norepinephrine transporter-expressing tumours.To catalyse or not to catalyse: A rapid air- and moisture-stable ipso-iododeboronation procedure using NIS has been developed in the non-toxic, green solvent dimethyl carbonate (see scheme). The procedure was utilised for the rapid and highly efficient gold-catalysed radioiododeboronation of arenes.
      PubDate: 2017-12-14T03:20:36.971067-05:
      DOI: 10.1002/chem.201704534
       
  • Electrochemical Conversion of Phthaldianilides to Phthalazin-1,4-diones by
           Dehydrogenative N−N Bond Formation
    • Authors: Anton Kehl; Tile Gieshoff, Dieter Schollmeyer, Siegfried R. Waldvogel
      Abstract: The electrochemical synthesis of 6-membered rings via anodic dianilide N−N coupling is challenging due to concurring benzoxazole co-formation. The rigidity of the a phthalic acid backbone allows a novel access to phthalazin-1,4-diones by N−N bond formation using anodically generated amidyl radicals. Since conventional synthetic routes to phthalazin-1,4-diones require the use of toxic N,N′-diarylhydrazines and generate reagent waste, a safer and more sustainable approach is required. Easy accessible starting materials, a broad scope of applicable functional groups, promising yields, and a very simple set-up elevate this sustainable method.Direct electrochemical synthesis of phthalazin-1,4-diones was realized by anodic N−N bond generation. Easy accessible phthalic dianilides and a simple electrolysis set-up ensure a straightforward access to 6-membered ring systems avoiding the use of highly carcinogenic N,N′-diarylhydrazines as building blocks.
      PubDate: 2017-12-14T03:16:11.734808-05:
      DOI: 10.1002/chem.201705578
       
  • Chiral Discrimination through 1H NMR and Luminescence Spectroscopy:
           Dynamic Processes and Solid Strip for Chiral Recognition
    • Authors: Monalisa Gangopadhyay; Arunava Maity, Ananta Dey, P. R. Rajamohanan, Sapna Ravindranathan, Amitava Das
      Abstract: The appropriate choice of the host molecules with well-defined optical activity (S-H/R-H) helps in the differentiation between two secondary ammonium ion-derivative guest molecules with different optical activities (R-G/S-G) based on the fluorescence resonance energy transfer (FRET)-based luminescence responses. Crown ether-based host molecules with opposite chiral configurations (R-H, S-H) have been derived from 1,1′-bi-2-naphthol (BINOL) derivatives that have axially chiral biaryl centers. These chiral crown ethers form host–guest complexes (i.e., [2]pseudorotaxanes) with chiral secondary ammonium ion derivatives (R-G, S-G). NMR spectroscopic studies show that the complexes are in a dynamic equilibrium in solution. Results of the 1H NMR and fluorescence spectroscopic studies indicate a head-on orientation of the host and guest in the [2]pseudorotaxanes. The difference in the efficiency in the FRET-based responses between anthracene and the BINOL derivatives allow efficient chiral discrimination of the guests. Isothermal titration calorimetry and NMR investigations reveal that inclusion complexes between hosts and guests of the same chirality (R-H⋅R-G, S-H⋅S-G) are more stable relative to those of opposite chirality (R-H⋅S-G, S-H⋅R-G). However, FRET-based energy-transfer efficiency is higher for R-H⋅S-G and S-H⋅R-G complexes. NMR spectroscopic studies show that the relative orientation of the guest in the host cavity is significantly different when the host binds a guest of the same or opposite chirality; furthermore, the latter is more favorable for FRET, thus enabling discrimination between enantiomers. Interestingly, chiral discrimination of guest ions could also be achieved by using silica surfaces modified with chiral host molecules.Positive discrimination: Crown ether-based host molecules with well-defined optical activities (S-H/R-H) help to differentiate between guest molecules with different optical activities (R-G/S-G) based on fluorescence resonance energy transfer (FRET)-based luminescence responses. The physicochemical and thermodynamic parameters for the host–guest adduct are influenced by the relative orientation of the optically pure guest inside the cavity of the enantiomerically pure host during the self-assembly process.
      PubDate: 2017-12-14T03:16:03.919937-05:
      DOI: 10.1002/chem.201704837
       
  • A 3D Covalent Organic Framework with Exceptionally High Iodine Capture
           Capability
    • Authors: Chang Wang; Yu Wang, Rile Ge, Xuedan Song, Xueqing Xing, Qike Jiang, Hui Lu, Ce Hao, Xinwen Guo, Yanan Gao, Donglin Jiang
      Abstract: Using porous materials to cope with environmental issues is promising but remains a challenge especially for removing the radioactive vapor wastes in fission because of harsh adsorption conditions. Here we report a new, stable covalent organic framework (COF) as a porous platform for removing iodine vapor—a major radioactive fission waste. The three-dimensional COF consists of a diamond topology knotted by adamantane units, creates ordered one-dimensional pores and are highly porous. The COF enables the removal of iodine vapor via charge transfer complex formation with the pore walls to achieve exceptional capacity. Moreover, the 3D COF is “soft” to trigger structural fitting to iodine while retaining connectivity and enables cycle use for many times while retaining high uptake capacity. These results set a new benchmark for fission waste removal and suggest the great potential of COFs as a designable porous material for challenging world-threatening pollution issues.A new 3D covalent organic framework is designed to constitute an eightfold interwoven diamond net structure and 1D open channels with π-conjugated pore walls. Merging the structural hardness and softness renders the framework with ultrahigh iodine-uptake capacity, high retention, quick release, and robust reusability, setting a new benchmark porous material for radioactive iodine removal.
      PubDate: 2017-12-14T03:15:50.815991-05:
      DOI: 10.1002/chem.201705405
       
  • Anionic Hosts for the Incorporation of Cationic Guests
    • Authors: Eugenia Peresypkina; Claudia Heindl, Eric Mädl, Helena Brake, Alexander Virovets, Manfred Scheer
      Abstract: Pentaphosphaferrocene [Cp*Fe(η5-P5)] (1a) represents an excellent building block for the template-directed synthesis of spherical supramolecules. Herein, the self-assembly of 1a with Cu(I) and Cu(II) halides in the presence of the template complexes [FeCp2][PF6], [CoCp2][PF6] and [CoCp2] is reported testifying the redox behavior of the formed supramolecules. The oxidation or reduction capacity of these labile complexes does not inhibit their template impact and, for the first time, the cationic metallocene [CoCp2]+ is enclosed in unprecedented anionic organometallic hosts. Furthermore, the large variety of structural motifs, as vacant icosahedral, trigonal antiprismatic, cuboidal and tetragonal antiprismatic arrangements of 1a units are realized in the supramolecules [FeCp2]@[{1a}12(CuBr)17.3] (3), [CoCp2]+3{[CoCp2]+@[{1a}8Cu24.25Br28.25(CH3CN)6]4-} (4), {[Cp2Co]+@[{1a}8(CuI)28(CH3CN)9.8]}{[Cp2Co]+@[{1a)}8Cu24.4I26.4(CH3CN)8]2-} (5), and [{1a}3{(1a)2NH}3Cu16I10(CH3CN)7] (6).
      PubDate: 2017-12-13T11:43:14.70501-05:0
      DOI: 10.1002/chem.201705883
       
  • Ferrocene-Alkynyl Conjugated Molecular Wires: Synthesis, Characterization
           and Conductance Properties
    • Authors: Ye Yuan; Jian-Feng Yan, Da-Qiang Lin, Bing-Wei Mao, Yao-Feng Yuan
      Abstract: A novel series of 1, 2, 3-substituted ferrocene-based wires 1a-2a and 4b-5b have been synthesized using iterative Pd-mediated Sonogashira cross-coupling methodology.The molecular structures of 2a and 3b were determined by single-crystal X-ray analysis.Electrochemical data showed that there was a strong electronic communication among the ferrocenyl moieties in 1b-5b. The UV absorption spectra indicated that replacing 1, 1'-substituted ferrocene unit with 1, 2, 3-substituted ferrocene moiety causes delocalization of electrons in the extended π orbitals. The self-assembled monolayers of wire 1a and 2a on Au surfaces had been comprehensively characterized by electrochemistry and scanning tunneling microscopy break junction. The data demonstrated that 1,2,3- substituted ferrocene-based wires reduced the intermolecular π-π stacking, and furthermore solved the rotation problem in the 1,1'-substituted ferrocene-based wires.
      PubDate: 2017-12-13T10:05:41.492837-05:
      DOI: 10.1002/chem.201705176
       
  • Recent Advances in Metallaaromatic Chemistry
    • Authors: Benjamin J. Frogley; L. James Wright
      Abstract: Metallaaromatics can be broadly defined as aromatic compounds in which one of the ring atoms is a transition metal. The metallabenzenes are one important class of these compounds that has undergone extensive study recently. Closely related species such as fused-ring metallabenzenes, heterometallabenzenes, π-coordinated metallabenzenes and metallabenzynes have also attracted considerable attention. Although many metallaaromatics can be considered as metalla-analogues of classic organic aromatic compounds, this is not always the case. Recent seminal studies have shown that metallapentalenes and metallapentalynes, which are metalla-analogues of the anti-aromatic compounds pentalene and pentalyne, are in fact aromatic and highly stable. Very unusual spiro-metallaaromatic compounds have also recently been isolated. In this concepts article, key features of all these intriguing metallaaromatic compounds are discussed with reference to the structural, spectroscopic, reactivity and theoretical studies that have been undertaken. These compounds continue to generate much interest, not only because of the contributions they make to fundamental chemical understanding, but also because of the promise of possible practical applications.New aromatics with a metallic ring: Aromatic compounds in which one of the ring atoms is a transition metal are attracting growing interest. Recent developments in this field of metallaaromatic chemistry include the isolation and study of metalla-pentalenes, metallapentalynes, metallaanthracenes and spiro-metallaaromatic compounds. These and other recent advances are discussed within the context of established metallaaromatics.
      PubDate: 2017-12-13T09:10:33.664465-05:
      DOI: 10.1002/chem.201704888
       
  • Rational Design and Synthesis of Unsaturated Se-Containing Osmacycles with
           σ-Aromaticity
    • Authors: Xiaoxi Zhou; Jingjing Wu, Yulei Hao, Congqing Zhu, Qingde Zhuo, Haiping Xia, Jun Zhu
      Abstract: Invited for the cover of this issue are the groups of Haiping Xia and Jun Zhu at the University of Xiamen. The image depicts their discovery of metallacyles with σ-aromaticity dominating in an unsaturated Se-containing ring. Read the full text of the article at 10.1002/chem.201703870.“we compare a steel cage broken by osmapentaloselenirene to a breakthrough in σ-aromaticity” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201703870).
      PubDate: 2017-12-13T08:36:22.97304-05:0
       
  • Direct and Enantioselective Synthesis of N-H-Free 1,5-Benzodiazepin-2-ones
           via NHC-Catalyzed [3+4] Annulation Reaction
    • Authors: Ding Du; Jing Cao, Chao Fang, Kewen Sun, Jindong Zhu, Tao Lu
      Abstract: An NHC-catalyzed formal [3+4] annulation of alfa,beta-unsaturated acylazoliums with protecting group-free aryl 1,2-diamines was developed for a direct and highly enantioselective synthesis of 4-aryl N-H-free 1,5-benzodiazepin-2-ones. This methodology offers an efficient and rapid access to a wide range of enantioenriched target compounds from easily accessible starting materials. The protocol is also scalable and the desired products can easily undergo subsequent N-functionalization to afford diverse N-substituted derivatives. Additionally, a mechanism was proposed to explain the high enantioselectivity in this process.
      PubDate: 2017-12-13T08:35:36.602874-05:
      DOI: 10.1002/chem.201705050
       
  • The Development of Functional Mesocrystals for Energy Harvesting, Storage,
           and Conversion
    • Authors: Peng Zhang; Takashi Tachikawa, Mamoru Fujitsuka, Tetsuro Majima
      Abstract: Higher-ordered semiconductors have attracted extensive research interest as an adopted engineering for active solar energy harvesting, storage, and conversion. It is well-known that the effective separation and anisotropic migration of photogenerated charges are the basic driven force required for superior efficiency. However, the morphology and stoichiometric variation of these semiconductors play essential roles in their physicochemical properties of bulk and surface, especially for efficient interparticle or interfacial charge transfer. To this point, the strategy of controlling the topotactic transformation toward superstructures with optimized functionality is preferable for a wide range of optoelectronic and catalytic engineering applications. In this Minireview, we provide an overview of the crystal orientation, synthetic engineering, functional applications, and spatial and temporal charge dynamics in TiO2 mesocrystals and others. The viewpoint of in-depth understanding of the structure-related kinetics would offer an opportunity for design of versatile mesocrystal semiconductors sought-after for potential applications.The (w)hole picture: Mesocrystals are materials with internal pores and anisotropic interfaces, developed for tuning of superior properties in broad areas of application relating to the fields of energy harvesting, storage, and conversion. Herein, an overview is provided of such materials, discussing crystal orientation, synthetic engineering, functional applications, and spatial and temporal charge dynamics in TiO2 mesocrystals as well as others.
      PubDate: 2017-12-13T08:30:44.382051-05:
      DOI: 10.1002/chem.201704680
       
  • On Pentakis(pentafluoroethyl)stannate, [Sn(C2F5)5]−, and the Gas-Free
           Generation of Pentafluoroethyllithium, LiC2F5
    • Authors: Markus Wiesemann; Johannes Klösener, Beate Neumann, Hans-Georg Stammler, Berthold Hoge
      Abstract: Gas-free generation of pentafluoroethyllithium: Perfluoroalkylation reactions are often characterized by the tedious handling of gases which lead to the development of numerous easy-to-handle perfluoroalkylation reagents. In the course of this the hypervalent [PPh4][Sn(C2F5)5] represents an easily accessible, storable and solid precursor for the generation of the highly reactive LiC2F5. Its reactivity and the separation of tin-containing byproducts were proven in pentafluoroethylation reactions. More information can be found in the Full Paper by B. Hoge et al. (
      DOI : 10.1002/chem.201704807).
      PubDate: 2017-12-13T08:25:51.572336-05:
       
  • Protein Recognition by Functionalized Sulfonatocalix[4]arenes
    • Authors: Aishling M. Doolan; Martin L. Rennie, Peter B. Crowley
      Abstract: The interactions of two mono-functionalized sulfonatocalix[4]arenes with cytochrome c were investigated by structural and thermodynamic methods. The replacement of a single sulfonate with either a bromo or a phenyl substituent resulted in altered recognition of cytochrome c as evidenced by X-ray crystallography. The bromo-substituted ligand yielded a new binding mode in which a self-encapsulated calixarene dimer contributed to crystal packing. This ligand also formed a weak halogen bond with the protein. The phenyl-substituted ligand was bound to Lys4 of cytochrome c, in a 1.7 Å resolution crystal structure. A dimeric packing arrangement mediated by ligand–ligand contacts in the crystal suggested a possible assembly mechanism. The different protein recognition properties of these calixarenes are discussed.Calixarene capped cytochrome c: Altered binding sites and assemblies with mono-functionalized sulfonatocalix[4]arenes reveal altered binding sites and assemblies. The different protein recognition properties of these calixarenes are discussed.
      PubDate: 2017-12-13T08:25:47.855922-05:
      DOI: 10.1002/chem.201704931
       
  • Macrocyclic Triruthenium Complexes Having Electronically Coupled
           Mixed-Valent States
    • Authors: Daniel Fink; Michael Bodensteiner, Michael Linseis, Rainer F. Winter
      Abstract: 5-Ethynyl-2-furancarboxylic acid and 3-ethynylbenzoic acid self-assemble with [HRu(CO)Cl(PiPr3)2] to form macrocyclic C3-symmetric triangular triruthenium alkenyl complexes [{Ru(CO)(PiPr3)2(CH=CHArCOO)}3] (Ar=C6H4: 1-B, Ar=C4H2O: 1-F), which were characterized by multinuclear NMR spectroscopy, high-resolution ESI mass spectrometry, and, in the case of 1-B, by X-ray crystallography. Electrochemical studies indicate that the macrocycles are oxidized in three consecutive one-electron steps. The mixed-valent states obtained by electrochemical or chemical oxidation show signs of valence delocalization, which makes these complexes rare examples of molecule-based conductive loops with through-bond charge delocalization.Merry-go-round: Macrocyclic triruthenium complexes formed from 3-ethynyl benzoic acid or 5-ethynylfuran-2-carboxylic acid and the hydride complex [HRu(CO)Cl(PiPr3)2] are oxidized in three individually resolved one-electron steps (see figure). Their associated mixed-valent radical cations and dications show clear signs of through-bond charge delocalization, which makes these macrocycles conductive loops.
      PubDate: 2017-12-13T08:25:38.163481-05:
      DOI: 10.1002/chem.201705143
       
  • One-Step Synthesis of B/N Co-doped Graphene as Highly Efficient
           Electrocatalyst for the Oxygen Reduction Reaction: Synergistic Effect of
           Impurities
    • Authors: Vlastimil Mazánek; Stanislava Matějková, David Sedmidubský, Martin Pumera, Zdeněk Sofer
      Abstract: In the last decade, numerous studies of graphene doping by various metal and nonmetal elements have been done in order to obtain tailored properties, such as non-zero band gap, electrocatalytic activity, or controlled optical properties. From nonmetal elements, boron and nitrogen were the most studied dopants. Recently, it has been shown that in some cases the enhanced electrocatalytic activity of graphene and its derivatives can be attributed to metal impurities rather than to nonmetal elements. In this paper, we investigated the electrocatalytical properties of B/N co-doped graphene with respect to the content of metallic impurities introduced by the synthesis procedures. For this purpose, a permanganate (Hummers) and a chlorate (Hofmann) route were used for the preparation of the starting graphene oxides (GO). The GO used for the synthesis of B/N co-doped graphene had significantly difference compositions of oxygen functionalities as well as metallic impurities introduced by the different synthetic procedures. We performed a detailed structural and chemical analysis of the doped graphene samples to correlate their electrocatalytic activity with the concentration of incorporated boron and nitrogen as well as metallic impurities.Permitted doping: B/N co-doped graphene samples were synthesized by using differently generated graphene oxide and various B/N precursors. The final composition highly depends on both factors. The electrochemical behavior of all samples with respect to the oxygen reduction reaction was also investigated and correlated with the presence of metallic impurities.
      PubDate: 2017-12-13T08:16:15.090009-05:
      DOI: 10.1002/chem.201704515
       
  • Readily Exfoliated TiSe2 Nanosheets for High-Performance Sodium Storage
    • Authors: Dan Zhang; Guoqiang Zhao, Peng Li, Yu Zhang, Wenbin Qiu, Jie Shu, Yinzhu Jiang, Shi Xue Dou, Wenping Sun
      Abstract: Materials with sheet-like morphologies are highly desirable candidates for energy storage and conversion applications, due to the confined atomic thickness and high surface area, which would largely improve the electrochemical reaction kinetics. In this work, the sodium storage performance of TiSe2 nanosheets and corresponding sodiation/desodiation reaction mechanism are studied for the first time. TiSe2 nanosheets are readily exfoliated from bulk TiSe2 after quick ultrasonication or grinding. The TiSe2 nanosheets exhibit a reversible capacity of 147 mAh g−1 at 0.1 A g−1, and show excellent rate capability with a capacity of 103 mAh g−1 at an ultra-high current density of 10.0 A g−1. The combined in situ XRD and ex-situ HRTEM results suggest that sodium storage in TiSe2 is achieved through a multi-step intercalation/deintercalation mechanism. Besides, TiSe2 might be a promising 2D nanomaterial platform for other energy and electronic applications due to its easy exfoliation and unique physicochemical properties.The sodium storage capability of TiSe2 is studied for the first time. The combined in situ XRD and ex-situ HRTEM results suggest that sodium storage is achieved through a multi-step intercalation/deintercalation mechanism. Besides, bulk TiSe2 is easily exfoliated into nanosheets, and might be a promising 2D material platform for energy and electronic applications.
      PubDate: 2017-12-13T08:15:44.55863-05:0
      DOI: 10.1002/chem.201704661
       
  • An Uncommon Carboxyl-Decorated Metal–Organic Framework with Selective
           Gas Adsorption and Catalytic Conversion of CO2
    • Authors: Yong-Zhi Li; Hai-Hua Wang, Hong-Yun Yang, Lei Hou, Yao-Yu Wang, Zhonghua Zhu
      Abstract: A new three-dimensional (3D) framework, [Ni(btzip)(H2btzip)]⋅2 DMF⋅2 H2O (1) (H2btzip=4,6-bis(triazol-1-yl)isophthalic acid) as an acidic heterogeneous catalyst was constructed by the reaction of nickel wire and a triazolyl-carboxyl linker. Framework 1 possesses intersected 2D channels decorated by free COOH groups and uncoordinated triazolyl N atoms, leading to not only high CO2 and C2H6 adsorption capacity but also significant selective capture for CO2 and C2H6 over CH4 and CO in 273–333 K. Moreover, 1 reveals chemical stability toward water. Grand Canonical Monte Carlo simulations confirmed the multiple CO2- and C2H6-philic sites. As a result of the presence of accessible Brønsted acidic COOH groups in the channels, the activated framework demonstrates highly efficient catalytic activity in the cycloaddition reaction of CO2 with propylene oxide/4-chloromethyl-1,3-dioxolan-2-one/3-butoxy-1,2-epoxypropane into cyclic carbonates.Through employing a triazolyl-carboxyl linker, a stable porous Ni metal–organic framework (MOF) was constructed, which contains free carboxyl groups in channels and reveals not only high CO2 and C2H6 loadings but also significant selective capture for CO2 and C2H6 over CH4 and CO, as well as highly efficient catalytic activity in the cycloaddition reaction of CO2 with epoxides. The multi-point framework–CO2/C2H6 interactions were confirmed by Grand Canonical Monte Carlo simulations (see scheme).
      PubDate: 2017-12-13T08:10:32.86788-05:0
      DOI: 10.1002/chem.201704027
       
  • Synthesis, Characterisation and Reactions of Truly Cationic
           NiI–Phosphine Complexes
    • Authors: Miriam Mareen Schwab; Daniel Himmel, Sylwia Kacprzak, Valentin Radtke, Daniel Kratzert, Philippe Weis, Melanie Wernet, Andreas Peter, Zeinab Yassine, Dominik Schmitz, Ernst-Wilhelm Scheidt, Wolfgang Scherer, Stefan Weber, Wolfram Feuerstein, Frank Breher, Alexander Higelin, Ingo Krossing
      Abstract: The recently published purely metallo-organic NiI salt [Ni(cod)2][Al(ORF)4] (1, cod=1,5-cyclooctadiene, RF=C(CF3)3) provides a starting point for a new synthesis strategy leading to NiI phosphine complexes, replacing cod ligands by phosphines. Clearly visible colour changes indicate reactions within minutes, while quantum chemical calculations (PBE0-D3(BJ)/def2-TZVPP) approve exergonic reaction enthalpies in all performed ligand exchange reactions. Hence, [Ni(dppp)2][Al(ORF)4] (2, dppp=1,3-bis(diphenylphosphino)propane), [Ni(dppe)2][Al(ORF)4] (3, dppe=1,3-bis(diphenyl-phosphino)ethane), three-coordinate [Ni(PPh3)3][Al(ORF)4] (4) and a remarkable two-coordinate NiI phosphine complex [Ni(PtBu3)2][Al(ORF)4] (5) were characterised by single crystal X-ray structure analysis. EPR studies were performed, confirming a nickel d9-configuration in complexes 2, 4 and 5. This result is supported by additional magnetization measurements of 4 and 5. Further investigations by cyclic voltammetry indicate relatively high oxidation potentials for these NiI compounds between 0.7 and 1.7 V versus Fc/Fc+. Screening reactions with O2 and CO gave first insights on the reaction behaviour of the NiI phosphine complexes towards small molecules with formation of mixed phosphine-CO-NiI complexes and oxidation processes yielding new NiI and/or NiII derivatives. Moreover, 4 reacted with CH2Cl2 at RT to give a dimeric NiII ylide complex (4 c). As CH2Cl2 is a rather stable alkyl halide with relatively high C−Cl bond energies, 4 appears to be a suitable reagent for more general C−Cl bond activation reactions.Looking for NiI complexes…' A facile route to cationic NiI phosphine complexes starting from recently reported [Ni(cod)2][Al(ORF)4] (1, with RF=C(CF3)3) is described. [Ni(dppp)2][Al(ORF)4] (2), [Ni(dppe)2][Al(ORF)4] (3), three-coordinate [Ni(PPh3)3][Al(ORF)4] (4) and a remarkable two-coordinate NiI phosphine complex [Ni(PtBu3)2][Al(ORF)4] (5) were investigated.
      PubDate: 2017-12-13T08:00:50.991638-05:
      DOI: 10.1002/chem.201704436
       
  • Activating Inert Alkali-Metal Ions by Electron Transfer from Manganese
           Oxide for Formaldehyde Abatement
    • Authors: Jiayi Gao; Zhiwei Huang, Yaxin Chen, Jing Wan, Xiao Gu, Zhen Ma, Jianmin Chen, Xingfu Tang
      Abstract: Alkali-metal ions often act as promoters rather than active components due to their stable outermost electronic configurations and their inert properties in heterogeneous catalysis. Herein, inert alkali-metal ions, such as K+ and Rb+, are activated by electron transfer from a Hollandite-type manganese oxide (HMO) support for HCHO oxidation. Results from synchrotron X-ray diffraction, absorption, and photoelectron spectroscopies demonstrate that the electronic density of states of single alkali-metal adatoms is much higher than that of K+ or Rb+, because electrons transfer from manganese to the alkali-metal adatoms through bridging lattice oxygen atoms. Electron transfer originates from the interactions of alkali metal d–sp frontier orbitals with lattice oxygen sp3 orbitals occupied by lone-pair electrons. Reaction kinetics data of HCHO oxidation reveal that the high electronic density of states of single alkali-metal adatoms is favorable for the activation of molecular oxygen. Mn L3-edge and O K-edge soft-X-ray absorption spectra demonstrate that lattice oxygen partially gains electrons from the Mn eg orbitals, which leads to the upshift in energy of lattice oxygen orbitals. Therefore, the facile activation of molecular oxygen by the electron-abundant alkali-metal adatoms and active lattice oxygen are responsible for the high catalytic activity in complete oxidation of HCHO. This work could assist the design of efficient and cheap catalysts by tuning the electronic states of active components.Reactivity through anchoring: Inert alkali-metal ions were successfully activated for the complete oxidation of HCHO at low temperatures through electron transfer from manganese to potassium through the bridging oxygen of K−O−Mn upon anchoring onto hollandite manganese oxide surfaces (see figure).
      PubDate: 2017-12-13T08:00:41.789332-05:
      DOI: 10.1002/chem.201704398
       
  • A General Asymmetric Formal Synthesis of Aza-Baylis–Hillman Type
           Products under Bifunctional Catalysis
    • Authors: María Frías; Ana Cristina Carrasco, Alberto Fraile, José Alemán
      Abstract: A new organocatalytic strategy for the synthesis of enantioenriched aza-Baylis–Hillman type products via a frustrated vinylogous reaction is presented. This process proceeds under mild conditions with good yields, completed Z/E selectivity and excellent enantioselectivities. Moreover, easy derivatizations of the final products led to important building blocks of organic synthesis such as 1,3-aminoalcohols and Lewis base catalysts.With frustration to success: A new organocatalytic strategy for the synthesis of enantioenriched aza-Baylis–Hillman type products via a frustrated vinylogous reaction is presented.
      PubDate: 2017-12-13T07:56:31.583753-05:
      DOI: 10.1002/chem.201705218
       
  • 1,5-Disubstituted 1,2,3-Triazole-Containing Peptidotriazolamers: Design
           Principles for a Class of Versatile Peptidomimetics
    • Authors: Oliver Kracker; Jerzy Góra, Joanna Krzciuk-Gula, Antoine Marion, Beate Neumann, Hans-Georg Stammler, Anke Nieß, Iris Antes, Rafał Latajka, Norbert Sewald
      Abstract: Peptidotriazolamers are hybrid foldamers combining features of peptides and triazolamers—repetitive peptidomimetic structures with triazoles replacing peptide bonds. We report on the synthesis of a new class of peptidomimetics, containing 1,5-disubstituted 1,2,3-triazoles in an alternating fashion with amide bonds and the analysis of their conformation in solid state and solution. Homo- or heterochiral peptidotriazolamers were obtained from enantiomerically pure propargylamines with stereogenic centers in the propargylic position and α-azido esters by ruthenium-catalyzed azide–alkyne cycloaddition (RuAAC) under microwave conditions in high yields. With such building blocks the peptidotriazolamers are readily available by solution phase synthesis. While the conformation of the homochiral peptidotriazolamer Boc-Ala[5Tz]Phe-Val[5Tz]Ala-Leu[5Tz]Val-OBzl resembles that of a β VIa1 turn, the heterochiral peptidotriazolamer Boc-d-Ala[5Tz]Phe-d-Val[5Tz]Ala-d-Leu[5Tz]Val-OBzl adopts a polyproline-like repetitive structure.Stereochemistry matters: While the conformation of the homochiral peptidotriazolamer Boc-Ala[5Tz]Phe-Val[5Tz]Ala-Leu[5Tz]Val-OBzl resembles that of a βVIa1 turn, the heterochiral peptidotriazolamer Boc-d-Ala[5Tz]Phe-d-Val[5Tz]Ala-d-Leu[5Tz]Val-OBzl adopts a polyproline-like repetitive structure.
      PubDate: 2017-12-13T07:56:22.796556-05:
      DOI: 10.1002/chem.201704583
       
  • Firefly Luciferin-Inspired Biocompatible Chemistry for Protein Labeling
           and In Vivo Imaging
    • Authors: Yuqi Wang; Ruibing An, Zhiliang Luo, Deju Ye
      Abstract: Biocompatible reactions have emerged as versatile tools to build various molecular imaging probes that hold great promise for the detection of biological processes in vitro and/or in vivo. In this Minireview, we describe the recent advances in the development of a firefly luciferin-inspired biocompatible reaction between cyanobenzothiazole (CBT) and cysteine (Cys), and highlight its versatility to label proteins and build multimodality molecular imaging probes. The review starts from the general introduction of biocompatible reactions, which is followed by briefly describing the development of the firefly luciferin-inspired biocompatible chemistry. We then discuss its applications for the specific protein labeling and for the development of multimodality imaging probes (fluorescence, bioluminescence, MRI, PET, photoacoustic, etc.) that enable high sensitivity and spatial resolution imaging of redox environment, furin and caspase-3/7 activity in living cells and mice. Finally, we offer the conclusions and our perspective on the various and potential applications of this reaction. We hope that this review will contribute to the research of biocompatible reactions for their versatile applications in protein labeling and molecular imaging.Biocompatible reactions have emerged as versatile tools to label protein and build molecular imaging probes capable of non-invasive detection of biological processes both in intro and in vivo. In this Minireview, a summary of firefly luciferin-inspired biocompatible reaction between cyanobenzothiazole (CBT) and cysteine is provided, highlighting its applications for site-specific protein labeling and for the development of multimodality imaging probes.
      PubDate: 2017-12-13T07:46:14.49877-05:0
      DOI: 10.1002/chem.201704349
       
  • Achieving Amphibious Superprotonic Conductivity in a CuI Metal–Organic
           Framework by Strategic Pyrazinium Salt Impregnation
    • Authors: Sajal Khatua; Arun Kumar Bar, Javeed Ahmad Sheikh, Abraham Clearfield, Sanjit Konar
      Abstract: Treatment of a pyrazine (pz)-impregnated CuI metal–organic framework (MOF) ([1⊃pz]) with HCl vapor renders an interstitial pyrazinium chloride salt-hybridized MOF ([1⊃pz⋅6 HCl]) that exhibits proton conductivity over 10−2 S cm−1 both in anhydrous and under humid conditions. Framework [1⊃pz⋅6 HCl] features the highest anhydrous proton conductivity among the lesser-known examples of MOF-based materials exhibiting proton conductivity under both anhydrous and humid conditions. Moreover, [1⊃pz] and corresponding pyrazinium sulfate- and pyrazinium phosphate-hybridized MOFs also exhibit superprotonic conductivity over 10−2 S cm−1 under humid conditions. The impregnated pyrazinium ions play a crucial role in protonic conductivity, which occurs through a Grotthuss mechanism.Strategic single crystal to single crystal (SC–SC) transformation of a porous CuI metal–organic framework (MOF) resulted in a pyrazinium salt-impregnated hybridized MOF featuring the first example of superprotonic conductivity both in anhydrous and under humid conditions.
      PubDate: 2017-12-13T07:41:52.121692-05:
      DOI: 10.1002/chem.201704088
       
  • Electrochemical and Reactivity Studies of NSn Coordinated Distannynes
    • Authors: Miroslav Novák; Tomáš Mikysek, Aleš Růžička, Libor Dostál, Roman Jambor
      Abstract: Studies are focused on the redox potentials of NSn coordinated distannnynes {L1–3Sn}2 (L1=1, L2=2 and L3=3, in which L1 is [C6H3-2,6-(Me2NCH2)2]−, L2 is [C6H2-2,4-tBu2-6-(Et2NCH2)]− and L3 is [C6H2-2,4-tBu2-6-(DippN=CH)]−; Dipp=2,6-diisopropylphenyl), containing the tin atom in oxidation state +I. Distannynes 1–3 were used as ligands for transition metals, and complexes [{L1Sn}2⋅Fe(CO)4] (4) and [{L2Sn}2⋅Fe(CO)4] (5) were prepared. The set of NSn coordinated distannynes 1–5 was studied by cyclic voltammetry measurements and the oxidation potentials of tin atoms in 1–5 were determined. The redox potentials are influenced by either ligands L1–3 or SnIFe coordination. Oxidation reactions of 1–3 were also studied. The reaction of 2 with (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) provided mixed organotin oxide {(L2SnO)(L2)Sn(μ-O)}2 (6) as a consequence of the instability of the expected {L2Sn⋅TEMPO} complex. To support this proposed mechanism, the NGe coordinated digermyne {L2Ge}2 (7) was prepared. The reaction of 7 with TEMPO provided the expected complex {L2Ge⋅TEMPO} (8).Focus on tin: Different NSn coordinated distannnynes, {L1–3Sn}2, containing tin atoms in oxidation state +I were prepared and used as ligands for transition metals to provide complexes, [{L1−2Sn}2⋅Fe(CO)4] (see figure). Cyclic voltammetry measurements revealed the oxidation potentials of tin atoms and the influence of NSnI and SnIFe coordination.
      PubDate: 2017-12-13T07:40:52.778165-05:
      DOI: 10.1002/chem.201703960
       
  • Industry–Academia Partnership: The Synthesis and Solid-State
           Pharmaceutical Centre (SSPC) as a Collaborative Approach from Molecule to
           Medicine
    • Authors: Gerard P. McGlacken; Sarah Hayes, Anita R. Maguire, Jon O'Halloran, Kieran Hodnett
      Abstract: A marriage made in Ireland! The Synthesis and Solid-State Pharmaceutical Centre (SSPC) transcends company and academic boundaries and is one of the largest research collaborations of its type globally. Trust, a culture of inclusivity and commitment to mutual benefit are just some of the factors that have led to the success of the SSPC. Fostering these ideals within its industry–academia, and inter-company collaborations remains crucial to further development.
      PubDate: 2017-12-13T07:35:56.820343-05:
      DOI: 10.1002/chem.201704326
       
  • Facile synthesis of ultrahigh-surface-area hollow carbon nanospheres and
           their application in lithium-sulfur batteries
    • Authors: Yuechao Yao; Shaozhong Zeng, Lin Huang, Hongliang Wu, Biaolin Peng, Qi Zhang, Xiaohua Li, Liang Yu, Shiyu Liu, Wenxuan Tu, Tongbin Lan, Xierong Zeng, Jizhao Zou
      Abstract: Hollow carbon nanospheres (HCNs) with specific surface areas up to 2949 m2 g-1 and pore volume up to 2.9 cm3 g-1 were successfully synthesized from polyaniline-co-polypyrrole hollow nanospheres by carbonization and CO2 activation. The cavity diameter and wall thickness of HCNs can be easily controlled by activation time. Owing to their large inner cavity and enclosed structure, HCNs are desirable carriers for encapsulating sulfur. To better understand the effects of pore characteristics and sulfur contents on the performances of lithium-sulfur batteries, three composites of HCNs and sulfur are prepared and studied in detail. The composites of HCNs with moderate specific surface areas and suitable sulfur content present a better performance. The first discharge capacity of this composite reaches 1401 mAh g-1 at 0.2 C. Even after 200 cycles, the discharge capacity remains at 626 mAh g-1.
      PubDate: 2017-12-13T06:35:33.30962-05:0
      DOI: 10.1002/chem.201705211
       
  • Beyond Hydrofunctionalization: A Well-Defined Calcium Compound Catalyzed
           Mild and Efficient Carbonyl Cyanosilylation
    • Authors: Sandeep Yadav; Ruchi Dixit, Kumar Vanka, Sakya S. Sen
      Abstract: Organocalcium compounds have been reported as efficient catalysts for various transformations, for cases where one of the substrates contained a E-H (E=B, N, Si, P) bond. Here, we look at the possibility of employing an organocalcium compound for a transformation in which none of the precursors has a polar E-H bond. This study demonstrates the utilization of a well-defined amidinatocalcium iodide, [PhC(NiPr)2CaI] (1) for cyanosilylation of a variety of aldehydes and ketones with Me3SiCN under ambient conditions without the need of any co-catalyst. The reaction mechanism involves a weak adduct formation between 1 and Me3SiCN leading to the activation of the Si-C bond, which subsequently undergoes σ-bond metathesis with a C=O moiety. Such a mechanistic pathway is unprecedented in alkaline earth metal chemistry. Experimental and computational studies support the mechanism.
      PubDate: 2017-12-13T05:12:23.365446-05:
      DOI: 10.1002/chem.201705795
       
  • Electron-Proton Transfer Mechanism of Excited-State Hydrogen Transfer in
           Phenol-(NH3)n (n=3 and 5)
    • Authors: Mitsuhiko Miyazaki; Ryuhei Ohara, Claude Dedonder, Christophe Jouvet, Masaaki Fujii
      Abstract: Excited-state hydrogen transfer (ESHT) is responsible for various photochemical processes of aromatics, including photoprotection of nuclear basis. Its mechanism is explained by internal conversion from the aromatic ππ* to πσ* states via conical intersection. This means that the electron is transferred to a diffuse Rydberg-like σ* orbital apart from proton migration. This picture means the electron and the proton do not move together and the dynamics are different in principle. Here, we have applied picosecond time-resolved near-infrared (NIR) and infrared (IR) spectroscopy to the phenol-(NH3)5 cluster, the benchmark system of ESHT, and monitored the electron transfer and proton motion independently. The electron transfer monitored by the NIR transition rises within 3 ps, while the overall H transfer detected by the IR absorption of NH vibration appears with a lifetime of about 20 ps. This clearly proves that the electron motion and proton migration are decoupled. Such a difference of the time-evolutions between the NIR absorption and the IR transition has not been detected in a cluster with three ammonia molecules. We will report our full observation together with theoretical calculations of the potential energy surfaces of the ππ* and πσ* states, and will discuss the ESHT mechanism and its cluster size-dependence between n=3 and 5. It is suggested that the presence and absence of a barrier in the proton transfer coordinate cause the different dynamics.Going different ways: Time-resolved NIR and IR spectroscopy coupled with ab initio calculations on solvated clusters of phenol by ammonia established that the initial ultrafast delocalization of an electron over the solvents by photoexcitation next eliminates the proton from phenol to retrieve the hydrogen atom in the solvents moiety (see graphic). The results support the conclusion that decoupling of the electron and proton of a hydrogen atom occurs in the excited state hydrogen transfer (ESHT).
      PubDate: 2017-12-13T04:41:24.219676-05:
      DOI: 10.1002/chem.201704129
       
  • Three-Component Synthesis and Photophysical Properties of Novel
           Coumarin-Based Merocyanines
    • Authors: Julian Papadopoulos; Kay Merkens, Thomas J. J. Müller
      Abstract: Novel E-configured coumarin-based merocyanines were efficiently synthesized by a one-pot, three-component Sonogashira coupling–Michael addition starting from triflyl coumarins, terminal alkynes and secondary amines. The photophysical properties of the synthesized yellow to orange merocyanines were studied by UV/Vis and fluorescence spectroscopy and rationalized by Hammett–Taft correlations and DFT and TD-DFT calculations. Most compounds were only weakly fluorescent in solution; however, two compounds were investigated in more detail with respect to their aggregation behavior. The system for R2=H and NR23=pyrrolidinyl shows aggregation induced emission at a water content of 40–60 % in methanol, while the chromophore with R2=p-Me2NC6H4 and NR23=morpholinyl displays considerable aggregation induced emission enhancement with a concomitant redshift at increasing water contents in THF.Coloring in sequence: A Sonogashira coupling–Michael addition sequence furnishes coumaryl merocyanines in moderate to excellent yield in a consecutive three-component fashion. Besides tunable electronic properties (UV/Vis and fluorescence spectroscopy, and TD-DFT calculations) selected chromophores display aggregation induced emission (enhancement).
      PubDate: 2017-12-13T04:35:57.443208-05:
      DOI: 10.1002/chem.201704912
       
  • Pillar[5]arene-Based Supramolecular Organic Framework with Multi-Guest
           Detection and Recyclable Separation Properties
    • Authors: Qi Lin; Yan-Qing Fan, Peng-Peng Mao, Lu Liu, Juan Liu, You-Ming Zhang, Hong Yao, Tai-Bao Wei
      Abstract: The selective detection and separation of target ions or molecules is an intriguing issue. Herein, a novel supramolecular organic framework (SOF-THBP) was constructed by bis-thioacetylhydrazine functionalized pillar[5]arenes. The SOF-THBP shows a fluorescent response for Fe3+, Cr3+, Hg2+ and Cu2+ ions. The xerogel of SOF-THBP shows excellent recyclable separation properties for these metal ions and the absorption rates were up to 99.29 %. More interestingly, by rationally introducing these metal ions into the SOF-THBP, a series of metal-ion-coordinated SOFs (MSOFs) such as MSOF-Fe, MSOF-Hg and MSOF-Cu were constructed. These metal ions coordinated MSOFs could selectively sense F−, Br−, and l-Cys, respectively. The detection limits of these MSOFs for F−, Br− and l-Cys were about 10−8 m.Multi-Functional SOFs: A novel supramolecular organic framework (SOF-THBP) was constructed by functionalized pillar[5]arenes. By rationally introducing metal ions into the SOF-THBP, a series of metal-ion-coordinated SOFs (MSOFs) were constructed. The SOF-THBP shows excellent recyclable separation properties for Cr3+, Hg2+, etc. The MSOFs could selectively and sensitively sense F−, Br−, and l-Cys, respectively.
      PubDate: 2017-12-13T04:35:46.038235-05:
      DOI: 10.1002/chem.201705107
       
  • Customizing photoredox properties of PXX-based dyes through energy level
           rigid shifts of frontier molecular orbitals
    • Authors: Andrea Sciutto; Andrea Fermi, Andrea Folli, Tommaso Battisti, Joseph Beames, Damien Murphy, Davide Bonifazi
      Abstract: Here we describe the synthesis of electron-rich PXX derivatives in which the energy levels of the excited states have been tailored through the insertion of imide groups. This has allowed the development of a new series of oxygen-doped photoredox-active chromophores with improved oxidizing and reducing properties. Capitalizing on the dehalogenation of organic halides as a model reaction, we could investigate the photooxidative and photoreductive potential of these molecules in model chemical transformations. This prompted us to consider the first chemoselective transformation protocol, in which two different C-Br bonds could be chemoselectively reacted through the sequential photoactivation of two different colorants.
      PubDate: 2017-12-12T12:36:26.056721-05:
      DOI: 10.1002/chem.201705620
       
  • Mechanochemical preparation of stable sub-100 nm
           γ-cyclodextrin:Buckminsterfullerene (C60) nanoparticles by electrostatic
           or steric stabilization
    • Authors: Joachim Van Guyse; Victor R. De la Rosa, Richard Hoogenboom
      Abstract: Buckminsterfullerene (C60)'s main hurdle to enter the field of biomedicine is its low bioavailability, which results from its extremely low water solubility. A well-known approach to increase the water solubility of C60 is by complexation with γ-cyclodextrins. However, the formed complexes are not stable in time as they rapidly aggregate and eventually precipitate due to attractive intermolecular forces, a common problem in inclusion complexes of cyclodextrins. In this study we attempt to overcome the attractive intermolecular forces between the complexes by designing custom γ-cyclodextrin (γCD)-based supramolecular hosts for C60 that inhibit the aggregation found in native γCD-C60 complexes. The approach entails the introduction of either repulsive electrostatic forces or increased steric hindrance to prevent aggregation, thus enhancing the biomedical application potential of C60. These modifications have led to new sub-100 nm nanostructures that show long-term stability in solution.
      PubDate: 2017-12-12T11:35:50.0886-05:00
      DOI: 10.1002/chem.201705647
       
  • Conformational Bias by a Removable Silyl Group: Construction of
           Bicyclo[n.3.1]alkenes by Ring Closing Metathesis
    • Authors: Minggui Lin; Pei-Jun Cai, Zhixiong Zeng, Na Lin, Yang Shen, Bin Tang, Fan Li, Chen Chen, Zhi-Xiang Yu, Yandong Zhang
      Abstract: Herein, we report a novel strategy based on a conformationally controlled RCM by a removable silyl group, which allows the facile synthesis of various bicyclo[n.3.1]alkenes, especially a set of highly strained bicyclo[5.3.1]alkenes. Further derivatizations of the silyl group and the resultant double bond of bicyclo[5.3.1]undecene 2 f enabled a concise synthesis of A-B-C ring skeleton of taxol. Density functional theory (DFT) calculations suggest that the introduction of a bulky silyl group at C-5 position of the 1,3-dialkenylcyclohexanol substrates dramatically lowers the energy bias gap between diaxial conformers (to RCM) and diequatorial conformers (to cross metathesis), thereby favoring the expected RCM reaction to give the challenging bridged molecules.Conformation decides: we report a novel strategy based on a conformationally controlled RCM by a removable silyl group, which allows the facile synthesis of various bicyclo[n.3.1]alkenes, especially a set of highly strained bicyclo[5.3.1]alkenes. Further derivatizations of the silyl group and the resultant double bond enabled a concise synthesis of A-B-C ring skeleton of taxol.
      PubDate: 2017-12-12T09:12:27.725779-05:
      DOI: 10.1002/chem.201705275
       
  • Controllable Syntheses for MOF-derived Materials
    • Authors: Zuo Xi Li; Kang-Yu Zou
      Abstract: Metal-Organic Frameworks (MOFs), as an important kind of porous inorganic-organic hybrid materials with inherent outstanding physicochemistry characteristics, can be widely applied as versatile precursors for the facile preparation of functional MOF-derived materials. However, there is a plenty of sophisticated factors during the synthetic process, and it is far from reaching the goal of effectively controlling over the nature of MOF-derived materials (such as the composition, morphology and surface area). Therefore, it is urgently necessary to develop regular protocols and concepts for controllable syntheses of MOF-derived materials. In this minireview, we mainly summarize and analyze complicated factors in the fabrication of MOF-derived materials according to recently reported literatures, which provides a new insight into the rational design and syntheses of MOF-derived materials.
      PubDate: 2017-12-12T09:01:28.615059-05:
      DOI: 10.1002/chem.201705415
       
  • A Single Mutation is Sufficient to Modify the Metal Selectivity and
           Specificity of a Eukaryotic Manganese Superoxide Dismutase to Encompass
           Iron
    • Authors: Thérèse Hunter; Rosalin Bonetta, Anthony Sacco, Marita Vella, Paul-Michael Sultana, Chi H. Trinh, Hava B. R. Fadia, Tomasz Borowski, Rebeca Garcia-Fandiño, Thomas Stockner, Gary J. Hunter
      Abstract: We have generated a site-directed mutant of the manganese superoxide dismutase SOD-3 of C.elegans (MnSOD-3) which modifies the metal specificity of the enzyme. While wild-type MnSOD-3 functions with manganese in the active site (3600 U mg−1 of protein) it has little or no activity when iron is incorporated. However, when histidine replaces glutamine 142 in the active site, the enzyme retains 50 % of its activity and becomes cambialistic for its metal cofactor exhibiting very similar specific activity with either manganese or iron.Iron manganese and cambialistic mutants: A site-directed mutant of the manganese superoxide dismutase SOD-3 of C.elegans (MnSOD-3) has been generated that modifies the metal specificity of the enzyme. While wild-type MnSOD-3 functions with manganese in the active site (3600 U mg−1 of protein) it has little or no activity when iron is incorporated. However, when histidine replaces glutamine 142 in the active site, the enzyme retains 50 % of its activity and becomes cambialistic for its metal cofactor exhibiting very similar specific activity with either manganese or iron.
      PubDate: 2017-12-12T08:11:19.310766-05:
      DOI: 10.1002/chem.201704655
       
  • Controlled Pyrolysis of Ni-MOF-74 as a Promising Precursor for the
           Creation of Highly Active Ni Nanocatalysts in Size-Selective Hydrogenation
           
    • Authors: Kazuki Nakatsuka; Takeharu Yoshii, Yasutaka Kuwahara, Kohsuke Mori, Hiromi Yamashita
      Abstract: Metal organic frameworks (MOFs) are a class of porous organic-inorganic crystalline materials that have attracted much attention as H2 storage devices and catalytic supports. In this paper, the synthesis of highly-dispersed Ni nanoparticles (NPs) for the hydrogenation of olefins was achieved by employing Ni-MOF-74 as a precursor. Investigations of the structural transformation of Ni species derived from Ni-MOF-74 during heat treatment were conducted. The transformation was monitored in detail by a combination of XRD, in situ XAFS, and XPS measurements. Ni NPs prepared from Ni-MOF-74 were easily reduced by the generation of reducing gases accompanied by the decomposition of Ni-MOF-74 structures during heat treatment at over 300 °C under N2 flow. Ni-MOF-74-300 exhibited the highest activity for the hydrogenation of 1-octene due to efficient suppression of excess agglomerated Ni species during heat treatment. Moreover, Ni-MOF-74-300 showed not only high activity for the hydrogenation of olefins but also high size-selectivity because of the selective formation of Ni NPs covered by MOFs and the MOF-derived carbonaceous layer.The knights who say Ni: Ni-MOF-74 heat-treated at 300 °C showed high activity and size-selectivity, due to selective formation of Ni NPs covered by MOFs and a MOF-derived carbonaceous layer.
      PubDate: 2017-12-12T08:01:39.122351-05:
      DOI: 10.1002/chem.201704341
       
  • Synthetic Approaches to Trifluoromethylselenolated Compounds
    • Authors: Anis Tlili; Ermal Ismalaj, Quentin Glenadel, Clément Ghiazza, Thierry Billard
      Abstract: The association of trifluoromethyl group to chalcogens gives new fluorinated substituents with specific properties, mainly in term of lipophilicity. The trifluoromethylselenyl group is the last of the series that has been studied and despite pioneering approaches in the late 1960s, CF3Se chemistry has been scarcely developed over the last decades. Some modern and efficient methods to obtain trifluoromethylselenolated molecules have recently emerged. This Review describes the advancements that have been reported.From sporadic to emergent chemistry: After “intermittent” developments these last decades, the introductions of CF3Se group into organic molecules are recently showing promising progress.
      PubDate: 2017-12-12T07:56:05.403386-05:
      DOI: 10.1002/chem.201704637
       
  • Potential Therapeutic Applications of MnSODs and SOD-Mimetics
    • Authors: Rosalin Bonetta
      Abstract: Natural as well as synthetic antioxidants are constantly being investigated for their efficiency in combatting the effects of oxidative stress, which appears to be the responsible cause of several diseases, including cancer, central nervous system disorders, ischaemia-reperfusion disorders, cardiovascular conditions, and diabetes. Superoxide dismutases (SODs) constitute the ubiquitous antioxidant defences against oxidative stress that underlies numerous pathological conditions. Therefore, the development of therapeutics aimed at either delivering MnSOD more effectively to target tissues in the body in the form of MnSOD gene therapy, or the synthesis of molecules that mimic the activity of superoxide dismutase is constantly being explored. Classes that have been developed as SOD mimetics include the Mn-metalloporphyrins, Mn-cyclic polyamines, Mn-salen complexes, MnPLED derivatives as well as the nitroxides. Thus far, SOD mimetics have shown remarkable efficacy in several animal models suffering from oxidative stress injuries. A promising approach for the future of SOD and SOD mimic therapeutics appears to involve combination treatment of the antioxidants with radiotherapy or chemotherapy.Mimicking SOD: Methods that use native MnSODs or molecules that mimic the activity of SOD to treat oxidative stress injuries are in constant development.
      PubDate: 2017-12-12T07:55:56.566937-05:
      DOI: 10.1002/chem.201704561
       
  • Porphyrin-Based Air-Stable Helical Radicals
    • Authors: Kenichi Kato; Ko Furukawa, Tadashi Mori, Atsuhiro Osuka
      Abstract: Stable helical radicals are promising multi-functional molecules in light of intriguing magnetic and chiroptical properties. Attempts were made to extend diphenylmethyl-fused NiII porphyrin radical to helical system as the first air-stable organic neutral helical radicals. Intramolecular Pd-catalyzed twofold C−H arylation of methyl- or methoxy-introduced meso-diphenylmethyl NiII porphyrins gave a mixture of the target and rearranged radicals. Oxidative fusion reaction of meso-(bis(1-naphthyl)methyl) NiII porphyrins provided doubly fused NiII porphyrin radicals. One of the helical radicals was separated into enantiomers that showed mirror-image circular dichroism (CD) spectra up to 1300 nm. The helical dinaphthylmethyl-fused NiII porphyrin radical displayed solid-state magnetic property mostly arising from monomeric radicals, different from the parent diphenylmethyl-fused NiII porphyrin radical that showed antiferromagnetic coupling due to π-stacked pairing.Radical behavior: Diarylmethyl-fused NiII porphyrin radicals have been extended to a helical system as the first air-stable organic neutral helical radicals. Di(1-naphthyl)methyl-fused NiII porphyrin radicals thus synthesized were separated into enantiomers that showed mirror-image CD spectra up to 1300 nm, indicating the effective desymmetrization of the frontier molecular orbitals.
      PubDate: 2017-12-12T07:51:37.326939-05:
      DOI: 10.1002/chem.201705291
       
  • In Situ Generated Ruthenium–Arene Catalyst for Photoactivated
           Ring-Opening Metathesis Polymerization through Photolatent N-Heterocyclic
           Carbene Ligand
    • Authors: Julien Pinaud; Thi Kim Hoang Trinh, David Sauvanier, Emeline Placet, Sriprapai Songsee, Patrick Lacroix-Desmazes, Jean-Michel Becht, Bassam Tarablsi, Jacques Lalevée, Loïc Pichavant, Valérie Héroguez, Abraham Chemtob
      Abstract: 1,3-Bis(mesityl)imidazolium tetraphenylborate (IMesH+ BPh4−) can be synthesized in one step by anion metathesis between the corresponding imidazolium chloride and sodium tetraphenylborate. In the presence of 2-isopropylthioxanthone (sensitizer), an IMes N-heterocyclic carbene (NHC) ligand can be photogenerated under irradiation at 365 nm through coupled electron/proton transfer reactions. By combining this tandem NHC photogenerator system with metathesis inactive [RuCl2(p-cymene)]2 precatalyst, the highly active RuCl2(p-cymene)(IMes) complex can be formed in situ, enabling a complete ring-opening metathesis polymerization (ROMP) of norbornene in the matter of minutes at room temperature. To the best of our knowledge, this is the first example of a photogenerated NHC. Its exploitation in photoROMP has resulted in a simplified process compared to current photocatalysts, because only stable commercial or easily synthesized reagents are required.The first N-heterocyclic carbene (NHC) photogenerator consisting of an air-stable imidazolium tetraphenylborate salt as protected form of NHCs and isopropylthioxanthone (ITX) as sensitizer is described. A NHC-coordinated complex effective at photoROMP can be made in situ by subsequent reaction with the conventional ruthenium precatalyst [RuCl2(p-cymene)]2.
      PubDate: 2017-12-12T07:51:15.78873-05:0
      DOI: 10.1002/chem.201705145
       
  • Valence Localization at a Bio-inspired Mixed-Valent {Cu2S}2+ Motif upon
           Solvation in Acetonitrile: Effect on Nitrous Oxide Reductase (N2Or)
           Activity
    • Authors: Charlène Esmieu; Maylis Orio, Jordan Mangue, Jacques Pécaut, Stéphane Ménage, Stéphane Torelli
      Abstract: We demonstrate, based on experimental and theoretical evidence, that the isolated [2(CH3CN)2]2+ complex prepared in CH3CN and containing a mixed-valent {Cu2II,IS} core evolves towards a new [2(CH3CN)3]2+ species upon solvation in CH3CN. Unlike its type III structural analogue [2(H2O)(OTf)]+ active toward N2O reduction, this new type I compound is inactive. This outcome opens new perspectives for a rational for N2O activation using bio-inspired Cu/S complexes, especially on the role of the valence localization/delocalization and the Cu−Cu bond on the reactivity.Delocalized or not delocalized' The mixed valent bis-copper complex [2(CH3CN)2]2+ was isolated as a powder and has spectroscopic properties of a fully delocalized class III mixed-valent system. Solvation in acetonitrile results in its total conversion to [2(CH3CN)3]2+ with this time a fully localized valence (class I). The effect on nitrous oxide reductase (N2Or) activity is discussed.
      PubDate: 2017-12-12T07:50:55.055357-05:
      DOI: 10.1002/chem.201704737
       
  • Kirmse-Doyle- and Stevens-type Rearrangements of Glutarate-derived Oxonium
           Ylides
    • Authors: Benedikt Skrobo; Nils E Schlörer, Jörg-M. Neudörfl, Jan Deska
      Abstract: A novel chemoenzymatic synthetic cascade enables the preparation of densely decorated tetrahydrofuran building blocks. Here, the lipase-catalyzed desymmetrization of 3-alkoxyglutarates renders highly enantioenriched carboxylic acid intermediates, whose subsequent activation and oxonium ylide rearrangement by means of rhodium or copper complexes furnishes functionalized O-heterocycles with excellent diastereoselectivity. The two-step protocol offers a streamlined and flexible synthesis of tetrahydrofuranones bearing different benzylic, allylic or allenylic side chains with full control over up to three stereogenic centers.
      PubDate: 2017-12-12T06:20:43.124442-05:
      DOI: 10.1002/chem.201704624
       
  • A Precisely Assembled Carbon Source to Synthesize Fluorescent Carbon
           Quantum Dots for Sensing Probes and Bioimaging Agents
    • Authors: Yan Liu; Yiqiang Qiao, Dan Luo, Min Yu, Ting Zhang, Xuanping Cao, Yanheng Zhou
      Abstract: A broad range of carbon sources have been used to fabricate varieties of carbon quantum dots (CQDs). However, majority of these studies concern on the influence of primary structures and chemical compositions of precursors on the CQDs; it is still unclear that whether the superstructures of carbon sources have effects on the physiochemical properties of the synthetic CQDs. In this work, the concept of molecular assembly is first introduced into design of a new carbon source. Compared with the tropocollagen molecules, the hierarchically assembled collagen scaffolds, as a new carbon source, immobilizes functional groups of the precursors through hydrogen bonds, electrostatic attraction and hydrophobic forces. Moreover, the accumulation of functional groups in collagen self-assembly further promotes the covalent bond formation in the obtained CQDs through a hydrothermal process. Both of these two chemical superiorities give rise to high-quality CQDs with enhanced emission. The assembled collagen scaffold-based CQDs with heteroatom doping exhibit superior stability, and could be further applied as effective fluorescent probes for Fe3+ detection and cellular cytosol imaging. These findings open a wealth of possibilities to explore more nanocarbons from precursors with assembled superstructures.
      PubDate: 2017-12-12T06:03:03.92423-05:0
      DOI: 10.1002/chem.201705310
       
  • Stable Zn(I)-Containing MOFs with Large [Zn70] Nanocages from Assembly of
           Zn(II) ions and Aromatic [ZnI8] Clusters
    • Authors: Bin Zhao; Huan-Cheng Hu, Ping Cui, Han-Shi Hu, Peng Cheng, Jun Li
      Abstract: Two unique Zn(I)-containing MOFs {[ZnI8ZnII3(H2O)x(HL)12](OH)2∙13H2O}n (x=6, 1; x=2, 2) (HL = tetrazole monoanion) with highnuclear Zn-cages were prepared successfully. These Zn-cages constructed from [ZnI8] clusters with multicentered Zn(I)-Zn(I) bonds and Zn(II) ions. [ZnI8] clusters in 1 and 2 display Oh and D4h symmetry, respectively. Importantly, eight [ZnI8] clusters and six Zn(II) ions form a large [Zn70] nanocage in 1. To our knowledge, this is the first MOFs based on polynuclear Zn-cage consisted of Zn(I) and Zn(II) ions. Compared with reported Zn(I)-species, 1 and 2 display high thermal and solvent stabilities. Theoretical investigations based on DFT calculations uncover that effective 4s-4s orbital overlap and electron delocalization through these a1g + t1u MOs on [ZnI8] cluster lead to considerable aromatic stabilization, which can well explain the intrinsic stability of 1 and 2. Interestingly, 1 can behave as a luminescent probe to detect the toxic Cr(VI) ions in aqueous.
      PubDate: 2017-12-12T04:50:37.90397-05:0
      DOI: 10.1002/chem.201705173
       
  • Photomodulation of DNA-Templated Supramolecular Assemblies
    • Authors: Jenifer Rubio-Magnieto; Tuan-Anh Phan, Mathieu Fossépré, Valérie Matot, Jérémie Knoops, Thibaut Jarrosson, Pascal Dumy, Françoise Serein-Spirau, Claude Niebel, Sébastien Ulrich, Mathieu Surin
      Abstract: A new type of DNA ligand that contains a phosphate-binding group and a photoresponsive azobenzene moiety is reported. When the azobenzene is in trans configuration, the ligand binds to the minor groove of a double-stranded DNA, whereas it partially desorbs upon trans–cis isomerisation with light. The ability to photoswitch the ligand upon interaction with DNA is evidenced by (chir)optical signatures, and deciphered by the differences of binding geometry, stability, and dynamics of the DNA/ligand complexes for the two isomers. We exploit these properties to photomodulate DNA-templated self-assembly, through the incorporation of another π-stacking DNA ligand, which together with the photoresponsive ligand form mixed supramolecular complexes along DNA. Our study demonstrates that well-designed photoresponsive DNA binders can be used to modulate multicomponent supramolecular DNA assemblies.Light makes it fit: A photoresponsive DNA ligand is designed that can reversibly undergo trans–cis photoisomerisation upon interaction with DNA (see scheme). This is exploited to photomodulate DNA-templated self-assembly, through the incorporation of another π-stacking DNA ligand, which, together with the photoresponsive ligand, form mixed supramolecular complexes along DNA.
      PubDate: 2017-12-12T04:33:21.110128-05:
      DOI: 10.1002/chem.201704538
       
  • Stereoselective Ring-Opening of gem-Difluorocyclopropanes: An Entry to
           Stereo-defined (E,E)- and (E,Z)-Conjugated Fluorodienes
    • Authors: Simon Specklin; Johan Fenneteau, Parthasarathi Subramanian, Janine Cossy
      Abstract: The ring-opening of gem-difluorocyclopropyl acetaldehydes producing selectively (E,E)- and (E,Z)-conjugated fluorodienals is described. Two stereo-divergent methods are presented to access both stereoisomers from a common precursor, in high yield and selectivity. The mechanistic aspect of these transformations is discussed.The cyclopropane ring-opening of gem-difluorocyclopropyl acetaldehydes producing selectively (E,E)- and (E,Z)-conjugated fluorodienals is described. Two stereodivergent methods are presented to access both stereoisomers in high yield and selectivity. The mechanistic aspect of these transformations is discussed.
      PubDate: 2017-12-12T04:25:57.544445-05:
      DOI: 10.1002/chem.201704956
       
  • Isolation of Cp*CoIII–Alkenyl Intermediate in Efficient Cobalt-Catalyzed
           C−H Alkenylation with Alkynes
    • Authors: Malay Sen; Nimmakuri Rajesh, Balakumar Emayavaramban, J. Richard Premkumar, Basker Sundararaju
      Abstract: A general and efficient procedure for C−H alkenylation of arenes with a broad substrate scope catalyzed by Cp*CoIII was demonstrated with alkynes. A highly selective mono-alkenylation and sequential bis-C−H bond functionalization was displayed to exemplify the versatility of the cobalt catalyst. Isolation of cationic Cp*CoIII–alkenyl intermediate was achieved under identical catalytic conditions to further establish the proposed pathway.An efficient cobalt-catalyzed C−H alkenylation of arenes with alkyne under mild conditions was developed, with isolated Cp*CoIII–alkenyl intermediate being the catalytically active species. Additionally, the reaction has a broad substrate scope with excellent functional group tolerance and moderate-to-good regioselectivity.
      PubDate: 2017-12-12T04:21:20.470513-05:
      DOI: 10.1002/chem.201705183
       
  • Model Macrocyclic Ligands for Proof-of-Concept Mechanistic Studies in
           Transition-Metal Catalysis
    • Authors: Xavi Ribas; Marc Devillard
      Abstract: In this Concept article, we will scrutinize different approaches devoted to the mechanistic understanding of catalytic processes, paying special attention to the successful use of triazamacrocyclic aryl-halide or arene-containing substrates used for Cu-, Ag-, Au-, Co- and Ni-catalysis. The importance of designing model substrate platforms to unravel mechanistic details at a molecular level of C−C or C-heteroatom bond-forming processes catalyzed by transition metals will be highlighted. This fundamental mechanistic knowledge will serve as a foundation for the catalyst design for a desired transformation.How does it work' The design of model macrocyclic substrate platforms to unravel mechanistic details at a molecular level of C−C or C−heteroatom bond-forming processes catalyzed by transition metals are highlighted.
      PubDate: 2017-12-12T04:17:05.002961-05:
      DOI: 10.1002/chem.201704408
       
  • Chemistry and Biology of Teixobactin
    • Authors: Chuchu Guo; Dhanaraju Mandalapu, Xinjian Ji, Jiangtao Gao, Qi Zhang
      Abstract: Bacterial resistance to existing drugs is becoming a serious public health issue, urging extensive search for new antibiotics. Teixobactin, a cyclic depsipeptide discovered in a screen of uncultured bacteria, shows potent activity against all the tested Gram-positive bacteria. Remarkably, no teixobactin-resistant bacterial strain has been obtained despite extensive efforts, highlighting the great potential of teixobactin as a lead compound in the fight against antimicrobial resistance (AMR). This review summarizes recent progresses in the understanding of many aspects of teixobactin, including chemical structure, biological activity, biosynthetic pathway, and mode of action. We also discuss the different synthetic strategies in producing teixobactin and its analogues, and the structure–activity relationship (SAR) studies.Teixobactin is a cyclic depsipeptide exhibiting potent activity against all the tested Gram-positive bacteria. Remarkably, thus far no teixobactin-resistant bacterial strain has been obtained despite extensive efforts. This Review discusses recent progress in the understanding of many aspects of teixobactin, including biological activity, biosynthetic pathway, mode of action, and the structure–activity relationship studies.
      PubDate: 2017-12-12T04:12:21.609815-05:
      DOI: 10.1002/chem.201704167
       
  • Well-Defined Chiral Copper NHC Complex in the Asymmetric Conjugated
           β-Borylation and One-Pot Metathesis-Asymmetric β-Borylation Reactions
    • Authors: Anupam Jana; Damian Trzybiński, Krzysztof Woźniak, Karol Grela
      Abstract: Highly stereoselective conjugate β-borylation, using a new chiral NHC-based copper catalyst, has been achieved. The chiral NHC copper complex was prepared in gram scale and showed high enantioselectivity and activity (up to 10 000 turnovers at 100 ppm of catalyst loading). This method was employed in the synthesis of a chiral β-borylated ester from simple unconjugated alkenes though an unprecedented one-pot cross metathesis-asymmetric borylation sequence.Proper copper: Gram scale synthesis of a new chiral copper complex is described. This NHC-copper complex showed excellent activity (up to 1000 TON) and was stereoselective towards conjugate β-borylation. Unprecedented one-pot cross metathesis-asymmetric borylation is also demonstrated.
      PubDate: 2017-12-12T04:11:52.728006-05:
      DOI: 10.1002/chem.201704335
       
  • Preparation and Characterization of P2BCh Ring Systems (Ch=S, Se) and
           Their Reactivity with N-Heterocyclic Carbenes
    • Authors: Cameron M. E. Graham; Clément R. P. Millet, Amy N. Price, Juuso Valjus, Michael J. Cowley, Heikki M. Tuononen, Paul J. Ragogna
      Abstract: Four-membered rings with a P2BCh core (Ch=S, Se) have been synthesized by the reaction of phosphinidene chalcogenide (Ar*P=Ch) and phosphaborene (Mes*P=BNR2). The mechanistic pathways towards these rings are explained by detailed computational work that confirmed the preference for the formation of P−P, not P−B, bonded systems, which seems counterintuitive given that both phosphorus atoms contain bulky ligands. The reactivity of the newly synthesized heterocycles, as well as that of the known (RPCh)n rings (n=2, 3), was probed by the addition of N-heterocyclic carbenes, which revealed that all investigated compounds can act as sources of low-coordinate phosphorus species.Some serious (P2)BS: The combination of a phosphinidene chalcogenide and phosphaborene has created a unique heterocycle containing Group 13, 15, and 16 elements. Detailed theoretical work describes the likely pathway in generating P2BCh heterocycles. The reactivity of these, and other (RPCh)n rings, with N-heterocyclic carbenes is reported.
      PubDate: 2017-12-12T04:11:21.308376-05:
      DOI: 10.1002/chem.201704337
       
  • Carbothermal Reduction induced Ti3+ self-doped TiO2/GQDs Nanohybrids for
           High-performance Visible light Photocatalysis
    • Authors: Jialin Tang; Yousong Liu, Yingjie Hu, Guoqing Lv, Chengtao Yang, Guangcheng Yang
      Abstract: A facile method of calcination was developed to in situ synthesize nanohybrids of Ti3+ self-doped TiO2/graphene quantum dot nanosheets (Ti3+-TiO2/GQDs NSs). Ti3+ sites were formed on the surface of TiO2 nanosheets through carbothermal reduction reaction by GQDs using citric acid as carbon source. Such heterojunctions exhibited enhanced visible-light absorption properties, large photocurrent current density and low recombination of photo-induced carriers. The methylene blue (MB) and rhodamine B (RhB) photodegradation result demonstrated higher visible-light photocatalysis performance than that of original TiO2. On one hand, inducing Ti3+ sites is efficient for photogenerated charge carries separation and reducing electron-hole pairs recombination. On the other hand, GQDs is benefit to generate more photocurrent carriers and facilitate the charge transfer across the surface of TiO2. We propose that Ti3+ sites and GQDs induced in TiO2 nanosheets make a synergistic effect for the excellent photocatalysis properties. Finally, we provide a theoretical calculation of carbothermal reduction for the formation mechanism of Ti3+ defect sites.
      PubDate: 2017-12-12T03:51:02.976551-05:
      DOI: 10.1002/chem.201705637
       
  • Stereoselective Transfer Semi-Hydrogenation of Alkynes to (E)-Olefins with
           N-Heterocyclic Silylene-Manganese Catalysts
    • Authors: Matthias Driess; Yupeng Zhou, Zhenbo Mo, Marcel Philip Lücke
      Abstract: The synthesis and structures of the first SiII-donor supported manganese(II) complexes [L1]MnCl2, [L2]MnCl2, and [L3]2MnCl2 are reported, bearing a pincer-type bis(NHSi)-pyridine ligand L1, bidentate bis(NHSi)-ferrocene ligand L2, and two monodentate NHSi ligands L3 (NHSi = N-heterocyclic silylene), respectively. They act as unprecedented very active and stereoselective Mn-based precatalysts (1 mol% loading) in transfer semi-hydrogenations of alkynes to give the corresponding (E)-olefins using ammonia-borane as a convenient hydrogen source under mild reaction conditions. The best catalytic performance shows [L1]MnCl2 with quantitative conversion rates and excellent E-stereoselectivities (up to 97%) for different alkyne substrates. Different types of functional groups can be tolerated, except CN, NH2, NO2, and OH groups at the phenyl group of 1-phenyl substituted alkynes.
      PubDate: 2017-12-11T15:50:32.830316-05:
      DOI: 10.1002/chem.201705745
       
  • Enhancing Van der Waals interactions of non-polar adsorbates with
           functionalized UiO-66: the unique effect of para hydroxyl groups
    • Authors: Trenton Tovar; Ivan Iordanov, Dorina Sava Gallis, Jared Bernard DeCoste
      Abstract: For small, nonpolar adsorbates, physisorption is dominated by weak Van der Waals interactions limiting the adsorption capacity. A common strategy to enhance the adsorption properties of isoreticular metal-organic framework (MOFs), such as UiO-66, is to add functional groups to the organic linker. Low and high pressure O2 isotherms were measured on UiO-66 MOFs functionalized with electron donating and withdrawing groups. It was found that the electron donating effects of -NH2, -OH, and -OCF3 groups enhance the uptake of O2. Interestingly, a significant enhancement in both the binding energy and adsorption capacity of O2 was observed for UiO-66-(OH)2-p, which has two -OH groups para from one another. Density functional theory (DFT) simulations were used to calculate the binding energy of oxygen to each MOF, which trended with the adsorption capacity and agreed well with the heats of adsorption calculated from the Toth model fit to multi-temperature isotherms. DFT simulations also determined the highest energy binding site to be on top of the electron π-cloud of the aromatic ring of the ligand, with a direct trend of the binding energy with low pressure adsorption capacity. Uniquely, DFT found that oxygen molecules adsorbed to UiO-66-(OH)2-p prefer to align parallel to the -OH groups on the aromatic ring. Similar effects for the electron donation of the functional groups were observed for the low pressure adsorption of N2, CH4, and CO2.
      PubDate: 2017-12-11T10:21:23.78404-05:0
      DOI: 10.1002/chem.201704779
       
  • Green synthesis of a new Al-MOF based on the aliphatic linker mesaconic
           acid: structure, properties and in-situ crystallisation studies of
           Al-MIL-68-Mes
    • Authors: Helge Reinsch; Thomas Homburg, Niclas Heidenreich, Dominik Froehlich, Stefan Henninger, Michael Wark, Norbert Stock
      Abstract: : A new aluminium MOF based on the short aliphatic linker molecule mesaconic acid (H2Mes; methylfumaric acid) is reported. Al-MIL-68-Mes with composition [Al(OH)(O2C-C3H4-CO2)]·nH2O is obtained after short reaction times of 45 minutes under mild, aqueous synthesis conditions (95 °C). It exhibits a kagome-like framework structure with large hexagonal and small trigonal channels (diameters of ~ 6 and ~2 Å, respectively) and a specific surface area of SBET ≈ 1040 m2/g (VMIC = 0.42 cm3/g). A sigmoidal vapour sorption isotherm for water and uptakes of water and methanol above 30 wt% were observed. Al-MIL-68-Mes is stable against water ad-/desorption and its thermal stability is 350 °C in air. The proton conductivity for the hydrated MOF showed values up to 1.1*10-5 S/cm at 130°C and 100 % relative humidity, which exceeds the values observed for the non-hydrated compound by up to four orders of magnitude. Using synchrotron radiation we also studied the crystallisation of the MOF by in-situ PXRD at temperatures from 80 to 100 °C. Kinetic evaluation revealed that the induction periods and crystallization times vary depending on the synthesis batch but the rate limiting steps are consistently observed.
      PubDate: 2017-12-11T10:20:30.070894-05:
      DOI: 10.1002/chem.201704771
       
  • MoS2@HKUST-1 Flower-Like Nanohybrids for Efficient Hydrogen Evolution
           Reactions
    • Authors: Chengli Wang; Yingchun Su, Xiaole Zhao, Shanshan Tong, Xiaojun Han
      Abstract: A novel MoS2-based flower-like nanohybrid for hydrogen evolution was fabricated through coating the Cu-containing metal-organic framework (HKUST-1) onto MoS2 nanosheets. It is the first time that MoS2@HKUST-1 nanohybrids have been reported for the enhanced electrochemical performance of HER. The morphologies and components of the MoS2@HKUST-1 flower-like nanohybrids were characterized by scanning electron microscopy, X-ray diffraction analysis and Fourier transform infrared spectroscopy. Compared with pure MoS2, the MoS2@HKUST-1 hybrids exhibit enhanced performance on hydrogen evolution reaction with an onset potential of −99 mV, a smaller Tafel slope of 69 mV dec−1, and a Faradaic efficiency of nearly 100 %. The MoS2@HKUST-1 flower-like nanohybrids exhibit excellent stability in acidic media. This design opens new possibilities to effectively synthesize non-noble metal catalysts with high performance for the hydrogen evolution reaction (HER).Surprise HER with flowers: A novel MoS2-based flower-like nanohybrid for hydrogen evolution was fabricated through coating the Cu-containing metal-organic framework (HKUST-1) onto MoS2 nanosheets (see figure). This design opens new possibilities to effectively synthesize non-noble metal catalysts with high performance for the hydrogen evolution reaction (HER).
      PubDate: 2017-12-11T09:41:36.143145-05:
      DOI: 10.1002/chem.201704080
       
  • A novel reconfigurable logic unit based on the DNA-templated
           potassium-concentration-dependent supramolecular assembly
    • Authors: Chunrong Yang; Dan Zou, Jianchi Chen, Linyan Zhang, Jiarong Miao, Dan Huang, Yuanyuan Du, Shu Yang, Qianfan Yang, Yalin Tang
      Abstract: A plenty of molecular circuits with specific functions have been developed, however, logic units with reconfigurability which could simplify the circuits and speed up the information process are rarely reported. In this work, we designed a novel reconfigurable logic unit based on DNA-templated potassium-concentration-dependent supramolecular assembly, which could response to the input stimuli of H+ and K+. By inputting different concentrations of K+, the logic unit could implement three significant functions respectively, including half adder, half subtractor, and 2-to-4 decoder. Considering its reconfigurable ability and good performance, the novel prototypes developed here may serve as a promising proof of principle in molecular computers.
      PubDate: 2017-12-11T08:21:38.767037-05:
      DOI: 10.1002/chem.201704824
       
  • Oligonucleotides Incorporating Palladacyclic Nucleobase Surrogates
    • Authors: Sajal Kumar Maity; Tuomas Lönnberg
      Abstract: An oligonucleotide incorporating a palladacyclic nucleobase has been prepared by ligand-directed metalation of a phenylpyridine moiety. This oligonucleotide hybridized with natural counterparts placing any of the canonical nucleobases opposite to the palladacyclic residue. The palladated duplexes had B-type conformation and melting temperatures comparable to those of respective unmodified duplexes with a single mismatch. In the duplexes placing C, G or T (but not A) opposite to the palladacyclic residue, greatly increased absorptivity suggested formation of a PdII-mediated base pair. Absorptivity and ellipticity of these duplexes persisted even at the highest temperatures applicable in Tm and CD experiments (90 °C). Evidently the PdII-mediated base pairs do not dissociate under the experimental conditions.
      PubDate: 2017-12-11T06:20:41.237823-05:
      DOI: 10.1002/chem.201705797
       
  • Steric Interaction between Neighboring Components Favors the Formation of
           Large Intermediates in the Self-Assembly Process of a Pd2L4 Capsule
    • Authors: Shumpei Kai; Masanori Nakagawa, Tatsuo Kojima, Xin Li, Masahiro Yamashina, Michito Yoshizawa, Shuichi Hiraoka
      Abstract: The effect of the molecular interaction between the components on the self-assembly process of Pd2L4 structures was investigated by QASAP. While the self-assembly of the Pd2L4 cage without interaction between the bent ligands took place, mainly producing small intermediates, the self-assembly of the Pd2L4 capsule composed of bent ligands with anthracene panels tends to produce large intermediates containing more components than the capsule because of the steric interaction between the panels.
      PubDate: 2017-12-11T05:50:37.377834-05:
      DOI: 10.1002/chem.201705253
       
  • A Redox-Active Bis(ferrocenyl)germylene and Its Reactivity
    • Authors: Yuko Suzuki; Takahiro Sasamori, Jing-Dong Guo, Norihiro Tokitoh
      Abstract: Bis(ferrocenyl)germylene Fc*2Ge: [2; Fc*=2,5-bis(3,5-di-tert-butylphenyl)-1-ferrocenyl] was isolated in the form of red crystals from the reaction of the sterically demanding ferrocenyl lithium dimer (Fc*Li)2 and GeI2. Bis(ferrocenyl)germylene 2 exhibits extraordinary thermal stability in hydrocarbon solution and the solid state, as well as stable redox behavior. Moreover, it undergoes a ligand-redistribution reaction with GeCl2⋅(dioxane) to afford the corresponding chlorogermylene, which was isolated upon coordination with PBu3.A bis(ferrocenyl)germylene compound was obtained from the reaction of a sterically demanding ferrocenyl lithium dimer with GeI2. The compound exhibits exceptionally high thermal stability in solution and the solid state, as well as stable redox properties. Moreover, it undergoes a ligand-redistribution reaction with GeCl2⋅(dioxane) to afford the corresponding chlorogermylene, which was isolated upon coordination with PBu3.
      PubDate: 2017-12-11T05:06:22.617432-05:
      DOI: 10.1002/chem.201705598
       
  • On Pentakis(pentafluoroethyl)stannate, [Sn(C2F5)5]−, and the Gas-Free
           Generation of Pentafluoroethyllithium, LiC2F5
    • Authors: Markus Wiesemann; Johannes Klösener, Beate Neumann, Hans-Georg Stammler, Berthold Hoge
      Abstract: Pentafluoroethyllithium, LiC2F5, has been established as an efficient and versatile reagent for the transfer of the pentafluoroethyl unit to a number of electrophiles. Here, the stability of this species up to −40 °C is of advantage, particularly in comparison to its smaller congener LiCF3. The usual production of LiC2F5, however, from gaseous HC2F5 or IC2F5 and strong bases requires specially designed apparatuses, which severely impeded its value as a laboratory reagent. In this contribution we communicate an alternative gas-free and highly efficient protocol for the synthesis of LiC2F5 from the already commercialized stannate salt [PPh4][Sn(C2F5)5]. The [Sn(C2F5)5]− anion represents not only the first example of a structurally characterized hypervalent pentaalkylstannate but also serves as a precursor for the synthesis of the homoleptic tetrakis(pentafluoroethyl)stannane, Sn(C2F5)4. The reaction of the latter with n-butyllithium provides an insight into the mechanism of LiC2F5 generation.Gas-free pentafluoroethylation: Perfluoroalkylation reactions are often characterized by the tedious handling of gases, which lead to the development of numerous easy-to-handle perfluoroalkylation reagents. In the course of this the hypervalent [PPh4][Sn(C2F5)5] represents an easily accessible, storable and solid precursor for the generation of the highly reactive LiC2F5. Its reactivity and the separation of tin-containing by-products were shown in several pentafluoroethylation reactions.
      PubDate: 2017-12-11T04:54:54.563558-05:
      DOI: 10.1002/chem.201704807
       
  • Stereocontrolled Synthesis of Polypropionate Fragments based on a Building
           Block Assembly Strategy using Lithiation-Borylation Methodologies
    • Authors: Alba Millán; Pablo D. Grigol Martinez, Varinder K. Aggarwal
      Abstract: Polypropionates are important structural motifs in nature and are commonly made by iterative aldol or crotylation methodologies. Herein, an alternative strategy is presented in which stereochemically predefined building blocks, bearing appropriate functionality, are coupled together using a lithiation-borylation methodology with complete stereocontrol. The building blocks comprise lithiated carbamates acting as donors, and boronic esters acting as acceptors. The acceptor building blocks contain β-hydroxyl groups masked as silyl groups to avoid elimination of the boronate intermediates. Subsequent oxidation of both the boron and silyl moieties can then deliver an array of polypropionate fragments with full stereochemical control, including the synthetically challenging anti-anti isomers.Any stereochemical outcome for short chain polypropionate fragments has been achieved by assembly of carbamates and β-silaboronic esters through lithiation-borylation reactions. Stereotriads, tetrads, and pentads are obtained in good yields and excellent diastereoselectivity under reagent-control conditions.
      PubDate: 2017-12-11T04:54:39.698988-05:
      DOI: 10.1002/chem.201704946
       
  • Evidence for Iron-Catalyzed α-Phosphinidene Elimination with
           Phenylphosphine
    • Authors: Justin K. Pagano; Brandon J. Ackley, Rory Waterman
      Abstract: The ubiquitous half-sandwich iron complex [CpFe(CO)2Me] (Cp=η5-C5H5) appears to be a catalyst for α-phosphinidene elimination from primary phosphines. Dehydrocoupling reactions provided initial insight into this unusual reaction mechanism, and trapping reactions with organic substrates gave products consistent with an α elimination mechanism, including a rare example of a three-component reaction. The substrate scope of this reaction is consistent with generation of a triplet phosphinidene. In all, this study presents catalytic phosphinidene transfer to unsaturated organic substrates.A simple iron compound can catalytically transfer a phosphinidene equivalent to a 2,3-dimethyl-1,3-butadiene, alkynes, and diethyl disulfide with loss of hydrogen. These phosphinidene transfer reactions and dehydrocoupling catalysis indicate α-phosphinidene elimination (see scheme).
      PubDate: 2017-12-11T04:54:27.977443-05:
      DOI: 10.1002/chem.201704954
       
  • N-Doped Carbon Nanofibrous Network Derived from Bacterial Cellulose for
           the Loading of Pt Nanoparticles for Methanol Oxidation Reaction
    • Authors: Fanshu Yuan; Yang Huang, Mengmeng Fan, Chuntao Chen, Jieshu Qian, Qingli Hao, Jiazhi Yang, Dongping Sun
      Abstract: The large-scale, low-cost preparation of Pt-based catalysts with high activity and durability for the methanol oxidation reaction is still challenging. The key to achieving this aim is finding suitable supporting materials. In this paper, N-doped carbon nanofibrous networks are prepared by annealing a gel containing two inexpensive and ecofriendly precursors, that is, bacterial cellulose and urea, for the loading of Pt nanoparticles. An undoped analogue is also prepared for comparison. Meanwhile, the effect of the annealing temperature on the performance of the catalysts is evaluated. The results show that the N doping and higher annealing temperature can improve the electron conductivity of the catalyst and provide more active sites for the loading of ultrafine Pt nanoparticles with a narrow size distribution. The best catalyst exhibits a remarkably high electrocatalytic activity (627 mA mg−1), excellent poison tolerance, and high durability. This work demonstrates an ideal Pt supporting material for the methanol oxidation reaction.Supporting cast: A 3 D N-doped nanofibrous carbon network was prepared, which was derived from two inexpensive and ecofriendly precursors (bacterial cellulose and urea). The carbon nanofibrous network was applied as a supporting material for ultrafine Pt nanoparticles in the methanol oxidation reaction.
      PubDate: 2017-12-11T04:45:18.461565-05:
      DOI: 10.1002/chem.201704266
       
  • 2-(Trimethylsilyl)-λ3-Phosphinine: Synthesis, Coordination Chemistry,
           and Reactivity
    • Authors: Marija H. Habicht; Friedrich Wossidlo, Tobias Bens, Evgeny A. Pidko, Christian Müller
      Abstract: The [4+2] cycloaddition reaction between 2-pyrone and Me3Si−C≡P gives the corresponding 2-(trimethylsilyl)-λ3-phosphinine in good yields as a rather air and moisture stable, colorless oil. Insight into the regioselectivity of the pericyclic reaction was obtained with the help of deuterium-labeling experiments. The silyl-phosphinine acts as a ligand for the preparation of a Cu(I) and the first crystallographically characterized phosphinine-Ag(I) complex. The title compound was further used as a starting material for an alternative preparation of the parent phosphinine C5H5P by means of protodesilylation with HCl. C5H5P reacts with CuBr⋅S(CH3)2 to give an infinite Cu(I)Br coordination polymer. DFT calculations shed light on the influence of the -Si(CH3)3 group on the electronic properties of the aromatic phosphorus heterocycle.Phospha-benzene analogues: 2-(Trimethylsilyl)-λ3-phosphinine can easily be prepared by a [4+2] cycloaddition between 2-pyrone and (CH3)3Si−C≡P. Protodesilylation yields the parent phosphine C5H5P. The coordination chemistry was investigated, and DFT calculations give insight into the electronic properties of the phosphorus heterocycles.
      PubDate: 2017-12-11T04:44:52.222609-05:
      DOI: 10.1002/chem.201704539
       
  • Aggregation-Induced Singlet Oxygen Generation: Functional Fluorophore and
           Anthrylphenylene Dyad Self-Assemblies
    • Authors: Sooyeon Kim; Yang Zhou, Norimitsu Tohnai, Hirotaka Nakatsuji, Michiya Matsusaki, Mamoru Fujitsuka, Mikiji Miyata, Tetsuro Majima
      Abstract: The assembly of monomeric building blocks can manifest the display of new properties, including optical, mechanical, and electrochemical functionalities. In this study, we sought to develop a functional fluorophore self-assembly that can generate reactive oxygen species only when aggregated. With an anthrylphenylene (AP) group, negatively charged and neutral fluorescein units form non-fluorescent H-aggregates in aqueous solution because of the weak intermolecular interaction between the anthracene and fluorescein moieties. In stark contrast, a boron dipyrromethene (BODIPY) and AP dyad produces two-color-emissive aggregates through the formation of an intermolecular charge-transfer (CT) complex between the electron-rich anthracene and electron-deficient BODIPY moieties. Furthermore, to our surprise, the BODIPY and AP dyad aggregates generate singlet oxygen (1O2) and photocytotoxicity upon excitation, indicating that the BODIPY–anthracene CT state favors an intersystem crossing process. Based on X-ray crystallographic analysis, the lattice-like molecular packing between the BODIPY and AP moieties was determined to bring about the unprecedented aggregation-induced 1O2 generation (AISG).In aqueous solution, a boron-dipyrromethene (BODIPY) and anthrylphenylene (AP) dyad forms a self-assembly composed of an intermolecular charge-transfer (CT) complex between BODIPY and AP moieties. Surprisingly, the BODIPY and AP dyad generates singlet oxygen (1O2) upon excitation only when aggregated. Based on X-ray crystallographic analysis, the lattice-like molecular packing between the BODIPY and AP moieties was determined to bring about the unprecedented aggregation-induced 1O2 generation.
      PubDate: 2017-12-11T04:43:44.270705-05:
      DOI: 10.1002/chem.201703686
       
  • Ab Initio Ligand Field Molecular Mechanics and the Nature of Metal-Ligand
           π-Bonding in Fe(II) 2,6-di(pyrazol-1-yl)pyridine Spin Crossover Complexes
           
    • Authors: Robert J. Deeth; Malcolm A. Halcrow, Laurence J. Kershaw Cook, Paul R. Raithby
      Abstract: A ligand field molecular mechanics (LFMM) force field has been constructed for the spin states of [Fe(bpp)2]2+ (bpp=2,6-di(pyrazol-1-yl)pyridine) and related complexes. A new charge scheme is employed which interpolates between partial charges for neutral bpp and protonated [H3bpp]3+ to achieve a target metal charge. The LFMM angular overlap model (AOM) parameters are fitted to fully ab initio d orbital energies. However, several AOM parameter sets are possible. The ambiguity is resolved by calculating the Jahn–Teller distortion mode for high spin, which indicates that in [Fe(bpp)2]2+pyridine is a π-acceptor and pyrazole a weak π-donor. The alternative fit, assumed previously, where both ligands act as π-donors leads to an inconsistent distortion. LFMM optimisations in the presence of [BF4]− or [PF6]− anions are in good agreement with experiment and the model also correctly predicts the spin state energetics for 3-pyrazolyl substituents where the interactions are mainly steric. However, for 4-pyridyl or 4-pyrazolyl substituents, LFMM only treats the electrostatic contribution which, for the pyridyl substituents, generates a fair correlation with the spin crossover transition temperatures, T1/2, but in the reverse sense to the dominant electronic effect. Thus, LFMM generates its smallest spin state energy difference for the substituent with the highest T1/2. One parameter set for all substituted bpp ligands is insufficient and further LFMM development will be required.Ligand field molecular mechanics distinguishes the nature of the Fe−N π-bonding in [Fe(bpp)2]2+ complexes on the basis of the Jahn–Teller distortion of the high spin systems. It is also able to predict the correct spin state for complexes with substituents at the 3 position of pyrazole but does not capture the electronic effects for substituents at the 4 position of pyridine or pyrazole.
      PubDate: 2017-12-11T04:42:42.574529-05:
      DOI: 10.1002/chem.201704558
       
  • Inherently Chiral Calixarenes: Synthesis and Applications
    • Authors: Gareth E. Arnott
      Abstract: This article looks at the chemistry surrounding the concept of inherently chiral calixarenes (ICCs), whose synthesis and application have only recently being realised. One challenge in the area of ICC chemistry is the sheer breadth and scope for installing different aspects of inherent chirality. The aim of this article is not to cover every known method, but rather to give the reader an overview of the main themes that have emerged in this area, including more recent additions to the literature. This overview will also touch on the very limited reports on the applications of ICCs which give a glimpse into the potential these compounds may have in future studies.Going chiral: This concept article looks at the chemistry surrounding inherently chiral calixarenes (ICCs), the synthesis and applications of which have only recently been realised.
      PubDate: 2017-12-11T04:36:37.049878-05:
      DOI: 10.1002/chem.201703367
       
  • Spin-State Energetics of Fe Complexes from an Optimally Tuned
           Range-Separated Hybrid Functional
    • Authors: Georgia Prokopiou; Leeor Kronik
      Abstract: We assess the performance of the optimally tuned range-separated hybrid (OT-RSH) functional approach in predicting the ground-state electronic configuration and spin-state energetics of complexes that can potentially exhibit multiple spin configurations. To that end, we investigate eight iron complexes: four spin-crossover complexes, for which reference data from other approximate density functionals are available, and four smaller complexes, for which reference ab initio data are available. We show that the spin-state energetics are mostly governed by the percentage of short-range exact exchange and are only weakly influenced by the choice of the range-separation parameter. However, the electronic structure, especially the fundamental gap, is much more sensitive to the range-separation parameter. We further find that correct prediction of the ground state in spin-crossover compounds requires a reduction in the amount of short-range exact exchange, likely owing to a larger role of static correlation.Range-separated hybrid functionals: The optimally tuned range-separated hybrid functional approach is investigated for eight iron complexes: four spin-crossover complexes, for which reference data from other approximate density functionals are available, and four smaller complexes, for which reference ab initio data are available (see scheme).
      PubDate: 2017-12-11T04:35:20.33047-05:0
      DOI: 10.1002/chem.201704014
       
  • Oxidation of Polynuclear Aromatic Hydrocarbons using
           Ruthenium-Ion-Catalyzed Oxidation: The Role of Aromatic Ring Number in
           Reaction Kinetics and Product Distribution
    • Authors: Ewa Nowicka; Tomos J. Clarke, Meenakshisundaram Sankar, Robert L. Jenkins, David W. Knight, Stanislaw Golunski, Graham J. Hutchings, David J. Willock, Manuel Francisco, Stuart H. Taylor
      Abstract: Oxidation of aromatic hydrocarbons with differing numbers of fused aromatic rings (2–5), have been studied in two solvent environments (monophasic and biphasic) using ruthenium-ion-catalyzed oxidation (RICO). RICO reduces the aromaticity of the polyaromatic core of the molecule in a controlled manner by selective oxidative ring opening. Moreover, the nature of the solvent system determines the product type and distribution, for molecules with more than two aromatic rings. Competitive oxidation between substrates with different numbers of aromatic rings has been studied in detail. It was found that the rate of polyaromatic hydrocarbon oxidation increases with the number of fused aromatic rings. A similar trend was also identified for alkylated aromatic hydrocarbons. The proof-of-concept investigation provides new insight into selective oxidation chemistry for upgrading of polyaromatic molecules.Faster when heavier: Higher molecular weight polyaromatic molecules with more fused aromatic cores are oxidized faster than those with lower molecular weight when using ruthenium-ion-catalyzed oxidation. The same trend was also observed for alkyl-substituted polyaromatics. The degree of oxidation can be controlled towards ring opening, and the catalytic chemistry has potential for upgrading of heavy polyaromatics.
      PubDate: 2017-12-11T04:32:51.55501-05:0
      DOI: 10.1002/chem.201704133
       
  • Exponential Activation of Carbonic Anhydrase by Encapsulation in Dynameric
           Host Matrices with Chiral Discrimination
    • Authors: Yan Zhang; Claudiu T. Supuran, Mihail Barboiu
      Abstract: Herein an unexpected exponential activation of bovine carbonic anhydrase (bCA) in aqueous solutions in the presence of dynameric host matrices is reported. Successive experiments confirmed the important role of dynamic imine exchange within the dynameric host structures for direct enzyme activation. This allows for optimal encapsulation of the guest enzyme, whereas the presence of external proton-sponge amino groups is less important. Non-exchanging polymeric sec-amine congeners formed from imine reduction of dynameric structures show no obvious activation on bCA. Although the dynamers synthesized from diamino chiral-pair precursors displayed similar activation constants toward bCA, different activation delay times were observed from these two dynamers of opposite optical activity. The circular dichroism (CD) spectra demonstrate selective structural changes in the secondary structure of bCA upon dynameric encapsulation in aqueous solution. The different interaction molds observed in CD spectra for the dynamers with opposite chirality explain the longer activation time required for one of the dynamers.Let it go: Dynameric host matrices with opposite optical activities demonstrated differential exponential activation behavior of carbonic anhydrase resulting from dynamic adaptive encapsulation of the host dynamers.
      PubDate: 2017-12-11T04:32:14.520534-05:
      DOI: 10.1002/chem.201704605
       
  • Z−H Bond Activation in (Di)hydrogen Bonding as a Way to Proton/Hydride
           Transfer and H2 Evolution
    • Authors: Natalia V. Belkova; Oleg A. Filippov, Elena S. Shubina
      Abstract: The ability of neutral transition-metal hydrides to serve as a source of hydride ion H− or proton H+ is well appreciated. The hydride ligands possessing a partly negative charge are proton accepting sites, forming a dihydrogen bond, M−Hδ−⋅⋅⋅δ+HX (M=transition metal or metalloid). On the other hand, some metal hydrides are able to serve as a proton source and give hydrogen bond of M−Hδ+⋅⋅⋅X type (X=organic base). In this paper we analyse recent works on transition-metal and boron hydrides showing i) how formation of an intermolecular complex between the reactants changes the Z−H (M−H and X−H) bond polarity and ii) what is the implication of such activation in the mechanisms of hydrides reactions.It takes two: formation of a dihydrogen bond, M−Hδ−⋅⋅⋅δ+HX (MH=transition metal or metalloid hydride; HX=common acid or acidic transition-metal hydride), activates both interacting Z−H bonds (M−H and X−H) changing their polarity. This analysis revealed that the formation of [M(η2-H2)]+ and H2 liberation involve concerted proton and hydride transfer. The more balanced (comparable) are protic and hydridic ZH activations in DHB intermediates the lower is the barrier.
      PubDate: 2017-12-11T04:31:20.813687-05:
      DOI: 10.1002/chem.201704203
       
  • Boron Nanowheel with an Axle Containing Noble Gas Atoms: Viable Noble Gas
           bound MB10- Clusters (M = Nb, Ta)
    • Authors: Sudip Pan; Susmita Kar, Ranajit Saha, Edison Osorio, Ximena Zarate, Lili Zhao, Gabriel Merino, Pratim K. Chattaraj
      Abstract: The viability of noble gas axled boron nanowheel, NgnMB10- (Ng = Ar-Rn, M = Nb, Ta; n = 1, 2), is explored via ab initio computations. In the resulting Ng2-M complexes, the Ng-M-Ng nanorod passes through the center of B10- ring, providing them with an inverse sandwich like structure. While in single Ng bound analogue, the Ng binding enthalpy (Hb) at 298 K ranges from 2.5 to 10.6 kcal/mol, in two Ng bound cases it becomes very low for Ng2MB10- -> Ng + NgMB10- dissociation channel, except for Rn case. For a given Ng, Ta has slightly higher Ng binding ability than Nb. The corresponding free energy changes indicate that these systems, particularly Xe and Rn complexes, are good candidates for experimental realization in the low temperature matrix. The Ng-M bonds are found to be covalent in nature as reflected in their high Wiberg bond indices, formation of 2c-2e sigma-orbital between Ng and M centers in natural bond orbital and adaptive natural density partitioning analyses, and the short Ng-M bond distances. The energy decomposition analysis and the study of the natural orbital for chemical valence show that the Ng-M contact is supported mainly by the orbital and electrostatic interactions, almost with equal contributions. Although both the Ng to M sigma-donation and M to Ng pi-back-donation play roles in the origin of orbital interaction, the former is significantly dominant over the latter. Further, they show doubly aromatic character (both sigma and pi).
      PubDate: 2017-12-11T03:23:34.188788-05:
      DOI: 10.1002/chem.201705790
       
  • Interlocked Photo-Degradable Macrocycles Allow One-Off Photo-Triggerable
           Gelation of Organo- and Hydrogelators
    • Authors: Sheng-Hsien Chiu; Shun-Te Tung, Hung-Te Cheng, Alex Inthasot, Fang-Che Hsueh, Pei-Cong Yan, Ting-Jia Gu, Chien-Chen Lai
      Abstract: [2]Rotaxanes displaying one-off photo-triggerable gelation properties have been synthesized through the "clipping" of photo-degradable macrocycles around the amide or urea functionalities of organo- and hydrogelators. Irradiation with UV light cleaved the photo-labile macrocyclic components from the [2]rotaxanes, resulting in the free gelators being released into solution and, thereafter, forming gels. When the rate of gelation was sufficiently rapid, selective gelation of specific regions of the solution—and, indeed, photo-patterning of the solution—was possible.
      PubDate: 2017-12-10T23:50:53.904091-05:
      DOI: 10.1002/chem.201705753
       
  • A P2-type layered superionic conductor Ga-doped Na2Zn2TeO6 for
           all-solid-state sodium-ion batteries
    • Authors: Yuyu Li; Zhi Deng, Jian Peng, Enyi Chen, Yao Yu, Xiang Li, Jiahuan Luo, Yangyang Huang, Jinlong Zhu, Chun Fang, Qing Li, Jiantao Han, Yunhui Huang
      Abstract: Here, we report a P2-type layered Na2Zn2TeO6 (NZTO) with a high Na+ ion conductivity ~0.6 × 10-3 S cm-1 at room temperature (RT), which is comparable to the currently best Na1+nZr2SinP3−nO12 NASICON structure. As little as the Ga3+ substitution for Zn2+, more Na+ vacancies are introduced in the interlayer gaps, which greatly reduced strong Na+−Na+ coulomb interactions. Ga-substituted NZTO exhibits a superionic conductivity of ~1.1 × 10-3 S cm-1 at RT, and excellent phase and electrochemical stability. All solid-state batteries have been successfully assembled with a capacity of ~70 mAh g−1 over 10 cycles with a rate of 0.2 C at 80 oC. 23Na nuclear magnetic resonance (NMR) studies on powder samples show intragrain (bulk) diffusion coefficients DNMR on the order of 12.35 × 10-12 m2 s-1 at 65 oC that corresponds to a conductivity σNMR of 8.16 × 10-3 S cm-1 assuming the Nernst-Einstein equation, thus which suggests a new perspective of fast Na+ ion conductor for advanced SIBs.
      PubDate: 2017-12-10T21:51:58.426318-05:
      DOI: 10.1002/chem.201705466
       
  • Silver(I)-mediated base pairs in DNA sequences containing
           7-Deazaguanine/Cytosine Base Pairs: Towards DNA with entirely metallated
           Watson-Crick base pairs
    • Authors: José M. Méndez-Arriaga; Carmen R. Maldonado, José A. Dobado, Miguel A Galindo
      Abstract: DNA sequences comprising non-canonical 7-deazaguanine (7CG) and canonical cytosine (C) are capable of forming Watson-Crick base pairs via hydrogen bonds as well as silver(I)-mediated base pairs by coordination to central silver(I) ions. Duplex I and II containing 7CG and C have been synthesized and characterized. The incorporation of silver(I) ions into these duplexes has been studied by means of temperature-dependent UV-spectroscopy, circular dichroism and DFT calculations. The results suggest the formation of DNA molecules comprising contiguous metallated 7CG-AgI-C Watson-Crick base pairs that preserve the original B-type conformation. Furthermore, additional studies performed on duplex III indicated that, in presence of AgI ions, 7CG-C and 7CA-T Watson-Crick base pairs (7CA, 7-deazadenine; T, thymine) can be converted to metallated 7CG-AgI-C and 7CA-AgI-T base pairs inside the same DNA molecule whilst maintaining its initial double helix conformation. These finding are very important for the development of customized silver-DNA nanostructures based on Watson-Crick complementarity pattern.
      PubDate: 2017-12-10T21:51:29.579962-05:
      DOI: 10.1002/chem.201705131
       
  • Multi-functional Peptide-MicroRNA Nanocomplex for Targeted MicroRNA
           Delivery and Function Imaging
    • Authors: Xiao Xiao; Xingxing Wang, Yuqi Wang, Tianren Yu, Lei Huang, Lei Chen, Jinbo Li, Chenyu Zhang, Yan Zhang
      Abstract: Targeted delivery of microRNA (miRNA) mimics into specific cells/tissues and real-time monitoring on the biological function of delivered miRNA mimics at molecular level represent two major challenges in the development of miRNA-based therapeutics. Here we report a highly efficient method to address these two challenges simultaneously by using the self-assembled nanocomplex formed by miRNA mimics with a multi-functional peptide conjugate. Using the nanocomplex formed by tumor-suppressive miR-34a and the multi-functional peptide conjugate FA-R9-FPcas3, we demonstrated the highly efficient and target-selective delivery of miR-34a into HeLa cells and tumors. With the activatable fluorescence probe integrated in the peptide conjugate FA-R9-FPcas3, the intracellular function of miR-34a delivered by the nanocomplex to upregulate active Caspase-3 was imaged in real-time. Meanwhile, the nanocomplex also showed significant therapeutic effects to induce apoptosis in HeLa cells and to suppress tumor growth upon tail vein injection into living mice bearing subcutaneous HeLa tumors.
      PubDate: 2017-12-10T21:51:13.498899-05:
      DOI: 10.1002/chem.201705695
       
  • Asymmetric Total Syntheses and Structure Confirmation of Chlorofucins and
           Bromofucins
    • Authors: Deukjoon Kim; Byungsook Kim, Te-ik Sohn, Robert S. Paton
      Abstract: Substrate-controlled asymmetric total syntheses and structure confirmation of (+)-(3E)- and (-)-(3Z)-chlorofucin [(E)-1a and (Z)-1a], and (+)-(3E)- and (-)-(3Z)-bromofucin [(E)-1b and (Z)-1b] were accomplished. Our syntheses feature as key steps haloetherification (either 'conventional' or 'one-pot organoselenium-mediated') of alpha,alpha'-trans-gamma, delta-unsaturated oxocene alcohol 9 and our (E)- and (Z)-selective cross-metathesis (CM) protocols. More importantly, a rationale is provided for the strikingly different pathways followed by alpha,alpha'-trans-gamma, delta -unsaturated oxocene alcohol 9 and its ,'-cis isomer 9' in the presence of different electrophiles during the intramolecular electrophilic addition reactions.
      PubDate: 2017-12-09T06:01:45.0887-05:00
      DOI: 10.1002/chem.201704564
       
  • A Route to Base Coordinate Silicon Difluoride and the Silicon Trifluoride
           Radical
    • Authors: Herbert W. Roesky; Soumen Sinhababu, Subrata Kundu, Alexander Paesch, Regine Herbst-Irmer, Dietmar Stalke, Israel Fernández, Gernot Frenking, Claudia Stückl, Brigitte Schwederski, Wolfgang Kaim
      Abstract: Silicon difluoride (SiF2) is highly unstable at room temperature and condenses at this temperature rapidly to a polymeric material of unknown structure. Therefore the isolation of a stable monomeric silicon difluoride species is a challenging task. The cyclic alkyl(amino) carbene (cAAC) coordinated silicon difluoride was isolated as (cAAC)2SiF2 (2), synthesized from the reduction of cAAC-SiF4 (1) using two equivalents of KC8 in the presence of one equivalent of cAAC. In the solid state compound 2 is stable at room temperature for a long time under inert conditions. The reduction of compound 1 in the presence of one equivalent KC8 resulted in the first stable silicon trifluoride monoradical (cAAC)SiF3 (3).
      PubDate: 2017-12-09T06:01:41.73495-05:0
      DOI: 10.1002/chem.201705773
       
  • Synthesis of a New Microporous Zincosilicate with CHA Zeolite Topology as
           Efficient Platforms for Ion-Exchange of Divalent Cations
    • Authors: Natsume Koike; Kenta Iyoki, Sye Hoe Keoh, Watcharop Chaikittisilp, Tatsuya Okubo
      Abstract: There is growing interest to develop zeolite materials capable of stabilizing divalent cations such as Cu(II), Fe(II), and Ni(II) for catalytic applications. Herein, we describe for the first time the synthesis of a new microporous zincosilicate with CHA zeolite topology by particularly focusing on the mixing procedures of the raw materials to prevent the precipitation of zinc oxides/hydroxides and the formation of impure phases. The obtained zincosilicate CHA products possess remarkably higher ion-exchange ability for catalytically useful, divalent cations, demonstrated here using Ni(II) as an example, compared to that of aluminosilicate and zincoaluminosilicate analogs. We anticipate that these zincosilicate CHA materials can be an efficient platform for several important catalytic reactions. In addition, the present finding would provide a general guideline for effective substitution of other heteroatoms into the zeolite frameworks.
      PubDate: 2017-12-09T06:01:23.660888-05:
      DOI: 10.1002/chem.201705277
       
  • Photocytotoxic Copper (II) Complexes with Schiff Base Scaffolds for
           Photodynamic Therapy
    • Authors: Rong-Kai Lin; Chin-I Chiu, Cho-Han Hsu, Ying-Ju Lai, Parthiban Venkatesan, Po-Han Huang, Ping-Shan Lai, Chu-Chieh Lin
      Abstract: Photodynamic therapy (PDT) is a promising and minimally invasive method for the treatment of superficial diseases, and photosensitizers with high phototoxicity indexes (defined as (IC50Dark)/(IC50Irridation)) are essential for the development of ideal photosensitizing properties for this technology. In this study, a series of photocytotoxic copper(II) complexes [Cu(RQYMP)(dppn)] (QYMP = NNO-tridentate Schiff base derivatives, dppn = benzo[i]dipyrido[3,2-a;2´,3´-c]-phenazine) were reported, with their respective structural confirmations by mass spectrometry and FTIR spectroscopy. X-ray crystallography revealed that the CuN4O core of the [Cu(cumyQYMP)(dppn)](ClO4) complex (3) has a distorted square pyramidal geometry. From our results, the phototoxicity index of [Cu(3-OMeQYMP)(dppn)](ClO4) (4) was shown to reach 329 in human squamous cell carcinoma (SCC15) and 296 in basal cell carcinoma (BCC) cell lines, involving the formation of reactive oxygen species, cell apoptosis and caspase-3 activation and, hence, indicating the high potential of complex 4 as a photosensitizer candidate in PDT. Thus, copper complexes bearing suitable Schiff base ligands with a dppn co-ligand can be considered for the design of efficient metal-based anticancer agents for PDT.
      PubDate: 2017-12-09T06:01:19.601011-05:
      DOI: 10.1002/chem.201705640
       
  • Isomeric Column-Forming Esters and Imides with Varying Curvatures of the
           Aromatic Plane
    • Authors: Marli Ferreira; Thamires S. Moreira, Rodrigo Cristiano, Hugo Gallardo, Ahmed Bentaleb, Pierre Dechambenoit, Elizabeth A. Hillard, Fabien Durola, Harald Reinhart Bock
      Abstract: Dibenzo[a,j]coronene-tetracarboxylic alkyl esters and imides with either a centrosymmetric bis-peri substitution pattern or a polar bis-ortho substitution pattern form hexagonal columnar mesophases, which in the case of the imides persist at room temperature. The bis-peri isomers are obtained via a two-fold oxidative photocyclization; the bis-ortho isomers are accessed via a glyoxylic Perkin reaction of triphenylene and naphthalene building blocks. Steric congestion between the substituents and the adjacent benzo protrusion in the bis-ortho esters and imides leads to bending of the aromatic plane, which thus avoids twisting. These isomers surprisingly show a more pronounced liquid crystalline behaviour than their non-bent bis-peri homologs, accommodating non-planarity with columnar order by slipped stacking. Whereas both types of ester and the bis-peri imide show an optical behaviour typical for perylene chromophores, the strongly bent bis-ortho imide distinguishes itself notably from them by its absorption spectrum. The electron acceptor strength of the isomeric diimides is found to differ, the hexagonal (peri) diimide having a 0.20 eV lower LUMO energy than the pentagonal (ortho) isomer.
      PubDate: 2017-12-08T14:27:42.76192-05:0
      DOI: 10.1002/chem.201705084
       
  • Effects of the bidentate ligand on the photophysical properties, cellular
           uptake, and phototoxicity of glycoconjugates based upon the
           [Ru(tpy)(NN)(L)]2+ scaffold
    • Authors: Lucien N Lameijer; Tobias G Brevé, Vincent H S van Rixel, Sven H C Askes, Maxime A Siegler, Sylvestre Bonnet
      Abstract: Ruthenium polypyridyl complexes have received widespread attention as potential chemotherapeutics in photodynamic therapy (PDT) and in photochemotherapy (PACT). Herein we investigate a series of sixteen ruthenium polypyridyl complexes with general formula [Ru(tpy)(N-N)(L)]+/2+ (tpy = 2,2':6',2''-terpyridine, N-N = bpy (2,2'-bipyridine), phen (1,10-phenanthroline), dpq (pyrazino[2,3-f][1,10]phenanthroline), dppz (dipyrido[3,2-a:2',3'-c]phenazine, dppn (benzo[i]dipyrido[3,2-a:2',3'-c]phenazine), pmip (2-(4-methyl­phen­yl)-1H-imidazo[4,5-f][1,10]phenanthroline), pymi ((E)-N-phenyl-1-(pyridin-2-yl)methanimine), or azpy (2-(phenylazo)pyridine), L = Cl or 2-(2-(2-(methylthio)ethoxy)ethoxy)ethyl-β-d-glucopyranoside) and their potential for either PDT or PACT. We demonstrate that although increased lipophilicity is generally related to increased uptake of these complexes, it does not necessarily lead to increased (photo)cytotoxicity. Thus, non-toxic and photoactive ruthenium complexes are excellent candidates as PACT carriers.
      PubDate: 2017-12-08T12:25:25.2976-05:00
      DOI: 10.1002/chem.201705388
       
  • Benzothiazole Based Cycloplatinated Chromophores: Synthesis, Optical and
           Biological Studies
    • Authors: Elena Lalinde; M. Teresa Moreno, Rebeca Lara, Icíar P. López, Elvira Alfaro-Arnedo, José G. Pichel, Sergio Piñeiro-Hermida
      Abstract: Complexes based on 2-(4-substituted)benzothiazole ligands of type [Pt(R-pbt-C,N)Cl(L)] (R = Br 1, Me2N 2; L = DMSO a, PTA b, TPPTS c) and [Pt(Br-pbt-C)Cl(PTA)2] 3 are presented. On the basis of the photophysical data and TD-DFT calculations (1a, 2a) the low lying transitions (absorption and emission) were associated to ligand center (LC) with minor MLCT character and to intraligand ILCT charge transfer [Me2N-pbtpbt] excited states, respectively. The study of the effect of the concentration on emissive behavior of 2a,b indicated the occurrence of aggregation induced luminescence properties (Pt···Pt/·· interactions).The behavior of 2a towards p-toluenesulfonic acid (PTSA) in aerated acetonitrile solution and to HCl(gas) in the solid state has been evaluated, showing a clear reversible change between 1ILCT and 3LC/3MLCT states due to protonation of NMe2 group (TD-DFT on 2a-H+). Solid 2a undergoes a surprising oxidation of PtII to PtIV with concomitant deoxygenation of DMSO, under prolonged reaction with HCl(gas), to afford the PtIV dimethyl sulfide mer-[Pt(Me2N-pbt-C,N)Cl3(SMe2)] mer-4, which evolves in solution to fac-4, as confirmed by X-ray. Cytotoxic activity studies towards A549 and HeLa cell lines indicated cytotoxicity activity of 1b,2a,b. Fluorescent cell microscopy revealed cytoplasmatic staining, more visible in perinuclear areas. Inhibition of tubulin polymerization by 1b in both type of cells is presented as a preliminary mechanism of its cytotoxic action.
      PubDate: 2017-12-08T07:25:52.377112-05:
      DOI: 10.1002/chem.201705267
       
  • Self-Assembly through Noncovalent Preorganization of Reactants: Explaining
           the Formation of a Polyfluoroxometalate
    • Authors: Roy E. Schreiber; Liat Avram, Ronny Neumann
      Abstract: High-order elementary reactions in homogeneous solutions involving more than two molecules are statistically improbable and very slow to proceed. They are not generally considered in classical transition-state or collision theories. Yet, rather selective, high-yield product formation is common in self-assembly processes that require many reaction steps. On the basis of recent observations of crystallization as well as reactions in dense phases, it is shown that self-assembly can occur by preorganization of reactants in a noncovalent supramolecular assembly, whereby directing forces can lead to an apparent one-step transformation of multiple reactants. A simple and general kinetic model for multiple reactant transformation in a dense phase that can account for many-bodied transformations was developed. Furthermore, the self-assembly of polyfluoroxometalate anion [H2F6NaW18O56]7− from simple tungstate Na2WO2F4 was demonstrated by using 2D 19F–19F NOESY, 2D 19F–19F COSY NMR spectroscopy, a new 2D 19F{183W} NMR technique, as well as ESI-MS and diffusion NMR spectroscopy, and the crucial involvement of a supramolecular assembly was found. The deterministic kinetic reaction model explains the reaction in a dense phase and supports the suggested self-assembly mechanism. Reactions in dense phases may be of general importance in understanding other self-assembly reactions.Six of two: Self-assembly processes from simple compounds to complicated but thermodynamically stable products are hard to predict and difficult to explain by classical kinetic theory. By monitoring the self-assembly formation process of a polyfluoroxometalate by NMR spectroscopy and mass spectrometry, product formation is explained by preorganization of the reactants in a dense phase in which reactivity can be fitted to a deterministic kinetic model (see figure).
      PubDate: 2017-12-08T07:10:56.153257-05:
      DOI: 10.1002/chem.201704287
       
  • Enantioselective Hydrogenation of Imidazo[1,2-a]pyridines
    • Authors: Christoph Schlepphorst; Mario P. Wiesenfeldt, Frank Glorius
      Abstract: The enantioselective synthesis of tetrahydroimidazo[1,2-a]pyridines by direct hydrogenation was achieved using a ruthenium/N-heterocyclic carbene (NHC) catalyst. The reaction forgoes the need for protecting or activating groups, proceeds with complete regioselectivity, good to excellent yields, enantiomeric ratios of up to 98:2, and tolerates a broad range of functional groups. 5,6,7,8-Tetrahydroimidazo[1,2-a]pyridines, which are found in numerous bioactive molecules, were directly obtained by this method, and its applicability was demonstrated by the (formal) synthesis of several functional molecules.Very heterocyclic: The enantioselective hydrogenation of imidazopyridines was achieved by using a ruthenium(II)–NHC catalyst. Excellent yields and enantioselectivity values were obtained, and a variety of functional groups was tolerated. This method provides straightforward access to valuable enantio-enriched tetrahydroimidazopyridines from readily available aromatic precursors, and its applicability was demonstrated by the synthesis of direct precursors to bioactive molecules and a new chiral NHC ligand.
      PubDate: 2017-12-08T07:06:20.037675-05:
      DOI: 10.1002/chem.201705370
       
  • Evidence for a Cooperative Mechanism Involving two Palladium(0) Centers in
           the Oxidative Addition of Iodoarenes
    • Authors: Laurence Grimaud; Ilaria Ciofini, Luca Alessandro Perego, Pierre-Adrien Payard, Baptiste Haddou
      Abstract: Oxidative addition of iodoarenes (ArI) to Pd(0) ligated by 1¬ methyl-1H-imidazole (mim) in polar solvents leads to cationic arylpalladium(II) complexes [ArPd(mim)3]+. Kinetic analyses evidence that this reaction is second order with respect to the concentration of Pd(0) itself, and a mechanism involving the cooperative intervention of two Pd(0) centers has been postulated to explain this finding. This unusual behavior is also observed with other nitrogen-containing ligands and it is general for iodobenzenes substituted with electron-donating or weak electron-withdrawing groups. By contrast, bromoarenes and electron-poor iodoarenes display first order kinetics with respect to Pd(0). Theoretical calculations performed at the density functional theory (DFT) level suggest the existence of mim-ligated ArI-Pd(0) complexes in which the iodoarene is bound to the metal in a halogen bond-like fashion. Coordination weakens the C-I bond and facilitates the oxidative insertion of another Pd(0) center across the C-I bond itself. This conceptually novel mechanism, involving the cooperative participation of two distinct metal centers, allows to fully explain the experimentally observed kinetics.
      PubDate: 2017-12-08T05:41:53.830636-05:
      DOI: 10.1002/chem.201704899
       
  • Highly Efficient Synthesis of a Staphylococcus aureus Targeting Payload to
           Enable the First Antibody–Antibiotic Conjugate
    • Authors: Xin Linghu; Nathaniel L. Segraves, Ifat Abramovich, Nicholas Wong, Barbara Müller, Nadja Neubauer, Serena Fantasia, Sebastian Rieth, Stephan Bachmann, Michael Jansen, C. Gregory Sowell, David Askin, Stefan G. Koenig, Francis Gosselin
      Abstract: A practical synthesis of the complex payload for an anti-Staphylococcus aureus THIOMABTM antibody–antibiotic conjugate (TAC) is described. The route takes advantage of a delicate oxidative condensation, achieved using a semi-continuous flow procedure. It allows for the generation of kilogram quantities of a key intermediate to enable a mild nucleophilic aromatic substitution to the tertiary amine free drug. The linker component is introduced as a benzylic chloride, which allows formation of the quaternary ammonium salt linker-drug. This chemical process surmounts numerous synthetic challenges and navigates deeply colored and unstable compounds to support clinical studies to counter S. aureus bacterial infections.Enemy in sight: As a sophisticated therapeutic construct, an antibody–antibiotic conjugate (AAC) requires a robust chemical process to furnish the linker-drug for conjugation. Continuous flow processing allows for a sensitive oxidative condensation reaction to proceed by means of a recycle loop method. Further streamlined chemistry allows the deeply colored, quaternary ammonium salt linker-drug to be reproducibly accessed in good yield and purity, and enable the first AAC in the clinic.
      PubDate: 2017-12-08T05:33:26.171931-05:
      DOI: 10.1002/chem.201705392
       
  • Corrigendum: Randomizing the Unfolded State of Peptides (and Proteins) by
           Nearest Neighbor Interactions between Unlike Residues
    • Authors: Siobhan E. Toal; Nina Kubatova, Christian Richter, Verena Linhard, Harald Schwalbe, Reinhard Schweitzer-Stenner
      PubDate: 2017-12-08T05:25:55.996521-05:
      DOI: 10.1002/chem.201705353
       
  • Hybrid silicon-based organic/inorganic block copolymers with sol-gel
           active moieties: Synthetic advances, self-assembly and applications in
           biomedicine and material science
    • Authors: Annabelle Bertin; Sebastian Czarnecki
      Abstract: Hybrid silicon-based organic/inorganic (multi)block copolymers are promising polymeric precursors to create robust nanoobjects and nanomaterials due to their sol-gel active moieties via self-assembly in solution or in bulk. Such nanoobjects and nanomaterials have great potential in biomedicine as nanocarriers or scaffolds for bone regeneration as well as in material science as Pickering emulsifiers, photonic crystals or coatings/films with antibiofouling, antibacterial or water- and oil-repellent properties. Thus, this mini-review outlines recent synthetic efforts in the preparation of these hybrid inorganic/organic block copolymers, gives an overview of their self-assembled structures and finally presents recent examples of their use in the biomedical field and material science.
      PubDate: 2017-12-08T02:41:43.311807-05:
      DOI: 10.1002/chem.201705286
       
  • Gold-Catalyzed Divergent Ring-Closing Modes of Indole-Tethered Amino
           Allenynes
    • Authors: Pedro Almendros; Benito Alcaide, Israel Fernández, Fernando Herrera, Amparo Luna
      Abstract: Indole-tethered amino allenynes were chemodivergently cyclized for the controlled preparation of fused polycyclic indoles using gold catalysis. Double cyclization of terminal allenynes afforded hexacyclic 15H-indolo[1,2,3-de]quinolino[3,2,1-ij]quinoxalines, where allenynes bearing a substituted alkyne at the terminal end generated 12,13-dihydro-7H-indolo[3,2-c]acridines, which are 5-membered cyclized adducts. Density Functional Theory calculations were performed to shed light on this difference in reactivity.
      PubDate: 2017-12-08T02:41:33.126087-05:
      DOI: 10.1002/chem.201705294
       
  • BODIPY-based Antiaromatic Macrocycles: Facile Synthesis by Knoevenagel
           Condensation and Unusual Aggregation-Enhanced Two-Photon Absorption
           Properties
    • Authors: Jishan Wu; Minghui Chua, Taeyeon Kim, Zheng Long Lim, Tullimilli Y. Gopalakrishna, Yong Ni, Jian Wei Xu, Dongho Kim
      Abstract: Two stable BODIPY-based antiaromatic macrocycles, Mc -Fur and Mc-Th, were synthesized via a one-pot Knoevenagel condensation reaction between a BODIPY precursor and furan-2,5-dicarboxaldehyde or thiophene-2,5-dicarboxaldehyde, respectively. 1H NMR characterization of the two macrocycles supported their large antiaromatic character. The oxidation properties of the two macrocycles were studied via electron spin resonance spectroscopy and UV-Vis absorption spectrophotometry, which suggested the formation of a stable mono-radical cation species on first oxidation followed by an aromatic dication species on the subsequent oxidation. Both molecules have a nearly planar π-conjugated backbone and showed strong tendency to aggregate in solution due to efficient stacking of the antiaromatic macrocycles. Transient absorption and two-photon absorption (TPA) measurements in both solution and aggregated states of the macrocycles revealed that aggregation resulted in large enhancement of TPA cross sections and increase of excited lifetimes, in accordance with the decrease of antiaromatic character in the aggregated state.
      PubDate: 2017-12-07T21:39:08.309267-05:
      DOI: 10.1002/chem.201705271
       
  • Enhanced turnover for the P450 119 peroxygenase-catalyzed asymmetric
           epoxidation of styrenes by random mutagenesis
    • Authors: Li Wang; Siping Wei, Xianchao Pan, Pingxian Liu, Xi Du, Chun Zhang, Lin Pu, Qin Wang
      Abstract: A randomized library is constructed based on pET30a-CYP119-T214V plasmid. This library of random mutants of P450 119 T214V was screened by the reduced CO-difference spectra and the epoxidation of styrene. By using the directed evolution, a new P450119 quadruple mutant S148P/I161T/K199E/T214V is constructed, expressed and purified. This quadruple mutant is found to significantly increase the turnover rate and conversion for the asymmetric epoxidation of styrene and its derivatives. The kcat value of cis-beta-methylstyrene epoxidation catalysed by the quadruple mutant exhibits approximately 10-fold increase relative to the previously reported T213M mutant under the same conditions. This is the first engineered P450 119 peroxygenase for the epoxidation of cis-beta-methylstyrene with high turnover rate. The proposed mechanism on the basis of the molecular docking study for the asymmetric epoxidation suggests that the introduction of an acidic amino acid side chain into the active site and a hydrophobic amino acid into the substrate channels of P450 119 peroxygenase might result in high efficiency for the formation of Compound I and the subsequent peroxygenation by reconstructing the hydrogen-bonding interaction and increasing the substrate affinity and access.
      PubDate: 2017-12-07T12:07:07.202307-05:
      DOI: 10.1002/chem.201705460
       
  • From a Metastable Layer to a Stable Ring: A Kinetic Study for
           Transformation Reactions of Li2Mo3TeO12 to Polyoxometalates
    • Authors: Seung-Jin Oh; Seong-Ji Lim, Tae-Soo You, Kang Min Ok
      Abstract: A metastable tellurite, Li2Mo3TeO12, revealing a corrugated layered structure in an extremely strained coordination environment was hydrothermally synthesized in high yield. Li2Mo3TeO12 undergoes Li+-exchange-driven facile structural transformation reactions to polyoxometalates. The kinetic data for the transformation reactions at various conditions were successfully obtained by simple lab-source powder X-ray diffraction. The investigation suggests that the solid-state transformation reactions may occur through the substitution, decomposition, recombination, and precipitation steps in order. This new finding could be utilized in discovering functional metastable materials as well as understanding their phase transition mechanisms.
      PubDate: 2017-12-07T10:35:52.457567-05:
      DOI: 10.1002/chem.201704755
       
  • Highly Electrophilic, Catalytically Active and Redox-Responsive
           Cobaltoceniumyl and Ferrocenyl Triazolylidene Coinage Metal Complexes
    • Authors: Stefan Vanicek; Maren Podewitz, Jessica Stubbe, Dennis Schulze, Holger Kopacka, Klaus Wurst, Thomas Müller, Petra Lippmann, Simone Haslinger, Herwig Schottenberger, Klaus R. Liedl, Ingo Ott, Biprajit Sarkar, Benno Bildstein
      Abstract: A convenient access to a triad of triazoles with ferrocenyl and cobaltoceniumyl substituents are reported. N-Alkylation, deprotonation and metalation with CuI/AgI/AuI synthons affords the heteroleptic triazolylidene complexes. Due to the combination of neutral, electron-donating ferrocenyl substituents and cationic, strongly electron-withdrawing cobaltocenium substituents, the mesoionic carbene (MIC) ligands of these complexes are electronically interesting "push-pull", "pull-push" and "pull-pull" metalloligands with further switchable redox states based on their fully reversible FeII/FeIII, (ferrocene/ferrocenium) and CoIII/CoII, (cobaltocenium/cobaltocene) redox couples. These are the first examples of metal complexes of (di)cationic NHC ligands based on cobaltoceniumyl substituents. DFT calculated Tolman electronic parameter (TEP) of the new MIC ligands, show these metalloligands to be extremely electron-poor NHCs with properties unmatched in other carbene chemistry. Utilization of these multimetallic electronically tunable compounds in catalytic oxazoline synthesis and in antitumor studies are presented. Remarkably, 1 mol% of the AuI complex with the dicationic MIC ligand displays full catalytic conversion, without the need for any other additives, in less than 2 hours at ambient temperatures. These results thus firmly establish these new classes of cobaltoceniumyl based (di)cationic MIC ligands as prominent players in several branches of chemistry.
      PubDate: 2017-12-07T00:06:15.862664-05:
      DOI: 10.1002/chem.201705051
       
  • Multilayer Cucurbit[6]uril-Based Magnetic Nanoparticles Prepared via
           Host-guest Interaction: Remarkable Adsorbent for the Removal of Low
           Density Lipoprotein from Plasma
    • Authors: Dandan Jiang; Xiqian Li, Qiong Jia
      Abstract: Efficient removal of low density lipoprotein (LDL) is a key challenge since its high level in plasma is a primary risk factor in the pathogenesis of atherosclerotic cardiovascular disease. In this work, a facile synthesis strategy based on host-guest interactions was developed to prepare multilayer cucurbit[6]uril-based magnetic nanoparticles, MNPs-(HA-DAH5/HA-CB[6]5). The compound was employed as a blood purification material for the removal of LDL from plasma because it had good blood compatibilitiy and could be easily separated with an external magnet. The efficient removal of LDL was attributed to the electrostatic interactions between the positive charged apoB-100 domain of LDL and the negative charged adsorbent. Moreover, the prepared material exhibited high recyclability and could release LDL in physiological saline for recyclable use. MNPs-(HA-DAH5/HA-CB[6]5) offered promising perspectives and broad applications in extracorporeal treatment for the removal of LDL.
      PubDate: 2017-12-06T22:36:36.070345-05:
      DOI: 10.1002/chem.201705280
       
  • Tris(pentafluoroethyl)stannane: Tin Hydride Chemistry with an
           Electron-deficient Stannane
    • Authors: Markus Wiesemann; Mark Niemann, Johannes Klösener, Beate Neumann, Hans-Georg Stammler, Berthold Hoge
      Abstract: A versatile two-step synthesis for tris(pentafluoroethyl)stannane, HSn(C2F5)3, is presented. Electron withdrawing C2F5 groups significantly influence the polarity of the tin-hydrogen bond allowing facile deprotonation of the compound even in water. The utility of this electron-deficient stannane was illustrated in hydrostannylations of alkenes and alkynes as well as in dehalogenation reactions. The remarkable, high reactivity of HSn(C2F5)3 is demonstrated in fast hydrostannylations, even in the absence of activators, whereby the regioselectivity of this process turned out to be solvent dependent. It is of great advantage that in dehalogenation reactions volatile halogenotris(pentafluoroethyl)-stannanes, XSn(C2F5)3 (X = I, Br), are formed which allows a facile separation of the tin containing by-products from the reaction mixtures.
      PubDate: 2017-12-06T11:36:23.624631-05:
      DOI: 10.1002/chem.201705068
       
  • Biologically Inspired Ligand Design for Asymmetric Dia-stereodivergent
           1,3-Dipolar Cycloaddition
    • Authors: Wen-Jing Xiao; Bin Feng, Jia-Rong Chen, Yun-Fang Yang, Bin Lu
      Abstract: In contrast to the plethora of catalytic systems that enable access to any enantiomers of the chiral products by simply choosing between a pair of enantiomeric or pseudoenantiomeric chiral catalysts, few analogously effective protocols exist for the synthesis of compounds with multiple stereogenic centers with full control of the absolute and relative stereochemical configurations. Inspired by the functional diversification in proteins and enzymes that are resulted from conformational change, here, we report the development of a novel type of modular phosphoramidite-thioether ligands for the diastereodivergent asymmetric catalysis. Our catalytic system enables wider substrate scope, greater stereochemical control, and better reaction efficiency than previously reported approaches for asymmetric diastereoselective 1,3-dipolar cycloaddition of azomethine ylides and nitroalkenes.
      PubDate: 2017-12-06T10:05:32.963049-05:
      DOI: 10.1002/chem.201705301
       
  • Fluorine-Directed Glycosylation Enables the Stereocontrolled Synthesis of
           Selective SGLT2 Inhibitors for Type II Diabetes
    • Authors: Anna Sadurní; Gerald Kehr, Marie Ahlqvist, Helena Peilot Sjögren, Cecilia Kankkonen, Laurent Knerr, Ryan Gilmour
      Abstract: Inhibition of the sodium-glucose co-transporters (SGLT1 and SGLT2) is a validated strategy to address the increasing prevalence of type II diabetes mellitus. However, achieving selective inhibition of human SGLT1 or SGLT2 remains challenging. Orally available small molecule drugs based on the D-glucose core of the natural product Gliflozin have proven to be clinically effective in this regard, effectively impeding glucose reabsorption. Herein, we disclose the influence of molecular editing with fluorine at the C2 position of the pyranose ring of Phlorizin analogues Remogliflozin Etabonate and Dapagliflozin (Farxiga®) to concurrently direct β-selective glycosylation, as is required for biological efficacy, and enhance aspects of the physicochemical profile. Given the abundance of glycosylated pharmaceuticals in diabetes therapy that contain a β-configured D-glucose nucleus, it is envisaged that this strategy may prove to be expansive.
      PubDate: 2017-12-06T09:35:42.222842-05:
      DOI: 10.1002/chem.201705373
       
  • The Role of Terminal Functionality in the Membrane and Antibacterial
           Activity of Peptaibol-Mimetic Aib Foldamers
    • Authors: Catherine Adam; Anna D. Peters, Maria Giovanna Lizio, George F.S. Whitehead, Vincent Diemer, James A. Cooper, Scott L. Cockroft, Jonathan Clayden, Simon John Webb
      Abstract: Peptaibols are peptide antibiotics that typically feature an N-terminal acetyl cap, a C-terminal aminoalcohol, and a high proportion of α-aminoisobutyric acid (Aib) residues. To establish how each feature might affect the membrane-activity of peptaibols, biomimetic Aib foldamers with different lengths and terminal groups were synthesised. Vesicle assays showed that long foldamers (eleven Aib residues) with hydrophobic termini had the highest ionophoric activity. C-terminal acids or primary amides inhibited activity, while replacement of an N-terminal acetyl with an azide group made little difference. Crystallography showed that N3Aib11CH2OTIPS folded into a 3 helix 2.91 nm long, which is close to the bilayer hydrophobic width. Planar bilayer conductance assays showed discrete ion channels only for N-acetylated foldamers. However long foldamers with hydrophobic termini had the highest antibacterial activity, indicating that ionophoric activity in vesicles was a better indicator of antibacterial activity than the observation of discrete ion channels.
      PubDate: 2017-12-06T07:06:12.66669-05:0
      DOI: 10.1002/chem.201705299
       
  • A Rational Approach to Metal Loading of Organic Multi-Site Polymers:
           Illusion or Reality'
    • Authors: Claude Piguet; Lucille Babel, Karine Baudet, Thi Nu Y Hoang, Homayoun Nozary
      Abstract: Since its identification as an independent topic after the first world war, the chemistry of (bio)polymers and macromolecules rapidly benefited from intense synthetic activities driven by contributors focussing on formulation and structural aspects. Satisfying rationalization and predictions concerning polymer organization, stability and reactivity were however delayed until the late fifties, when physical chemists set the basis of an adapted thermodynamic modelling. The recent emergence of metal-containing (bio)organic polymers (i.e. metallopolymers) thus corresponds to a logical extension of this field with the ultimate goal of combining the rich magnetic and optical properties of open-shell transition metals with the processability and structural variety of polymeric organic scaffolds. Since applications as energy storage materials, drug delivery vectors, shape-memory materials and photonic devices can be easily envisioned for these materials, the development of metallopolymers is faced to some urgency in producing novel exploitable structures, while the rational control of their formation, organization and transformation remains elusive. Caught between the sometimes antagonistic requirements of economic efficiency on one side and of scientific pertinence on the other side, the ongoing achievements in the control of the metal loadings of multi-site polymers are highlighted here with some tutorial discussions of luminescent lanthanidopolymers as proof-of-concept.
      PubDate: 2017-12-06T06:36:43.571093-05:
      DOI: 10.1002/chem.201705043
       
  • Dehydrogenation of N-Heterocycles by Superoxide Ion Generated via
           Single-Electron Transfer
    • Authors: Qingmin Wang; Yuan-Qiong Huang, Hong-Jian Song, Yu-Xiu Liu
      Abstract: Nitrogen-containing heteroarene motifs are found in a numerous pharmaceuticals, natural products, and synthetic materials.Although several elegant methods for synthesisof these compounds via dehydrogenation of the corresponding saturated heterocycles have been reported, some of the methods are hampered by long reaction times, harsh conditions, and the need for catalysts that are not readily available. Herein, we report a novel method for dehydrogenation of N-heterocycles. Specifically, O2*− generated in situ acts as the oxidant for N-heterocycle substrates thatare susceptible to oxidation via a hydrogen atom transfermechanism. This method provides a general, green route to N-heteroarenes.
      PubDate: 2017-12-06T04:05:31.280085-05:
      DOI: 10.1002/chem.201705202
       
  • A Water-Stable Luminescent Zn(II) Metal-Organic Framework as Chemosensor
           for High-Efficiency Detection of CrVI-Anions (Cr2O72- and CrO42-) in
           Aqueous Solution
    • Authors: Tong-Liang Hu; Zhao-Quan Yao, Guang-Yu Li, Jian Xu, Xian-He Bu
      Abstract: A new luminescent Zn(II)-MOF with 1D triangular channels along the b axis, namely NUM-5, has been successfully assembled and well characterized, which features good stability, especially in aqueous solution. Interestingly, this compound exhibits a fast, sensitive and selective luminescence quenching response towards CrVI (Cr2O72-/CrO42-) in aqueous solution. The detection limits towards Cr2O72- and CrO42- ions are estimated to be 0.7 and 0.3 ppm, respectively, which are among the lowest detection limits reported for the MOF-based fluorescent probes that can simultaneously detect Cr2O72- and CrO42- in aqueous environment. The possible detection mechanism has been discussed in detail. Moreover, it can be easily regenerated after detection experiments, indicative of excellent recyclability. All these results suggest NUM-5 to be a highly selective and recyclable luminescent sensing material for the quantitative detection of CrVI-anions in aqueous solution.
      PubDate: 2017-12-06T02:06:15.696079-05:
      DOI: 10.1002/chem.201705328
       
  • Differential Modulating Effect of MoS2 on the Assemblies of Amyloid
           Peptides
    • Authors: Jie Wang; Lei Liu, Hongxing Zhang, Yibang Zhang, Yonghai Feng, Menglin Chen, Mingdong Dong, Daohan Ge
      Abstract: : The abnormal fibrillogenesis of amyloid peptides such as amyloid fibril and senior amyloid plaques, is associated with the pathogenesis of many amyloid diseases. Hence, how to modulate amyloid assemblies is considered as an important field related to possible pathogenesis of some diseases. Some two-dimentional nanomaterials, i.e. grapheme oxide, tungsten disulphide, exhibit strong modulation effect on the amyloid fibrillogenesis. Herein, we investigated the modulation effect of Molybdenum Disulfide (MoS2, a kind of 2D nanomaterials) on two amyloid peptide assemblies based on the label-free techniques, including quartz crystal microbalance (QCM), AFM and CD. MoS2 presents different modulating effects on the assembly of Aβ(33-42) and Amylin(20-29), mainly ascribing to the distinct affinity between amyloid peptides and MoS2. So far as we know, it is the first report of MoS2 as a modulator for amyloid aggregation. It enriches the variety of 2D nano-modulators of amyloid fibrillogenesis and the mechanism for self-assembly of amyloid peptides, meanwhile expands the applications of MoS2 in biology.
      PubDate: 2017-12-06T01:35:24.582662-05:
      DOI: 10.1002/chem.201704593
       
  • Highly Luminescent CsPbX3 (X = Cl, Br, I) Nanocrystals Achieved by a Novel
           Rapid Anion Exchange at Room Temperature
    • Authors: Shaofan Fang; Guangshe Li, Yantong Lu, Liping Li
      Abstract: Cesium lead halide perovskite (CsPbX3) nanocrystals (NCs) exhibit excellent photoelectric performance, which is directly governed by composition fine-tuning and preparation of materials with special phase structure and morphology. However, it is still facing challenges to achieve highly stable and luminescent CsPbX3 NCs at room temperature. Herein, we report on a novel exchange reaction, in which metal halides MX2 (M = Zn, Mg, Cu, Ca; X = Cl, Br, I) solids act as anion source to directly prepare CsPbX3 NCs at room temperature without any pretreatment. Introducing small amount of oleic acid and oleylamine speed up the exchange reaction through different promotion mechanisms. Oleic acid coordinates on the NCs surface that increases the reaction activity, and oleylamine greatly enhances the dissolution of ZnCl2. XRD and TEM tests demonstrate that cubic phase structure and morphology of the parent CsPbX3 were well preserved. Moreover, the bandgap energies and photoluminescence (PL) spectra were readily tunable over the entire visible spectral region of 406−685 nm. Our findings would open up the possibilities of using metal halide solids as new anion sources to prepare high-quality CsPbX3 NCs at room temperature.
      PubDate: 2017-12-05T22:30:55.855233-05:
      DOI: 10.1002/chem.201704495
       
  • Synthesis of Functionalized Nitriles via Microwave-Promoted Fragmentations
           of Cyclic Iminyl Radicals
    • Authors: Mary M Jackman; Siyeon Im, Seth R Bohman, Concordia C L Lo, Amanda L Garrity, Steven L. Castle
      Abstract: The synthesis of functionalized nitriles via microwave-promoted radical fragmentations of cyclic O-phenyl oxime ethers is reported. A variety of radical traps can be employed, permitting the generation of diverse adducts via C-O, C-C, C-N, or C-X bond formation. Other salient features include a simple and practical protocol, very short reaction times, and the avoidance of metal catalysts and toxic cyanide reagents. The utility of this method is demonstrated by the ring-distortion of a steroid-derived substrate.
      PubDate: 2017-12-05T13:31:06.823996-05:
      DOI: 10.1002/chem.201705728
       
  • A Rotaxane Scaffold Bearing Multiple Redox Centers: Synthesis, Surface
           Modification and Electrochemical Properties
    • Authors: Jean-Francois Nierengarten; Marie Steffenhagen, Alina Latus, Thi Minh Nguyet Trinh, Iwona Nierengarten, Ivan T. Lucas, Suzanne Joiret, Jessem Landoulsi, Béatrice Delavaux-Nicot, Emmanuel Maisonhaute
      Abstract: A rotaxane scaffold incorporating two dithiolane anchoring units for the modification of gold surfaces has been functionalized with multiple copies of a redox unit, namely ferrocene. Surface modification has been first assessed at the single molecule level by atomic force microscopy (AFM) and scanning tunneling microscopy (STM) imaging, while tip enhanced Raman spectroscopy (TERS) provided the local vibrational signature of the ferrocenyl subunits of the rotaxanes grafted onto the gold surface. Finally, oxidation of the redox moieties within a rotaxane scaffold grafted onto gold microelectrodes has been investigated by ultrafast cyclic voltammetry. Intramolecular electron hopping is indeed extremely fast in this system. Moreover, the kinetics of charge injection depends on the molecular coverage due to the influence of intermolecular contacts on molecular motions.
      PubDate: 2017-12-05T13:31:01.243121-05:
      DOI: 10.1002/chem.201705245
       
  • Synthesis, structure and acidity constants of ligated α-boryl acetic
           acids
    • Authors: Dennis P. Curran; Thomas Allen, steven geib, Stephen Weber, Anthony Robert Horner
      Abstract: Basic hydrolyses of various ligated α-boryl acetic acid esters provided the first ligated derivatives of the unknown compound boroacetic acid (BH2CH2CO2H). Four monoacids (L-BH2CH2CO2H) and one diacid (L-BH(CH2CO2H)2) were prepared with N-heterocyclic carbene, amine and pyridine ligands (L). The stable acids were characterized by X-ray crystallography and acidity constant (pKa) measurements. They rank among the least acidic of all known carboxylic acids. In turn, their conjugate bases are among the strongest of all carboxylates.
      PubDate: 2017-12-05T11:30:22.199755-05:
      DOI: 10.1002/chem.201705754
       
  • A Direct Proof of the Resonance-Impaired Hydrogen Bond (RIHB) Concept
    • Authors: Xuhui Lin; Wei Wu, Yirong Mo
      Abstract: The concept of resonance-enhanced hydrogen bond (RAHB) has been widely accepted and applied as it highlights the positive impact of π conjugation on intramolecular H-bonds. However, electron delocalization is directional and there is a possibility that π resonance goes from the H-bond acceptor to the H-bond donor, leading to a negative impact on H-bonds. Here we used the block-localized wavefunction (BLW) method which is a variant of ab initio valence bond (VB) theory and able to derive strictly electron-localized structures self-consistently, to quantify the interplay between H-bond and π resonance in the terms of geometry, energetics and spectral properties. The comparison of geometrical optimizations with and without π resonance shows that indeed conjugation can either enhance or weaken intramolecular H-bonds. We further experimented with various substituents attached to either the H-bond acceptor and/or H-bond donor side(s) to tune the H-bonding strength in both directions.
      PubDate: 2017-12-05T10:35:57.338715-05:
      DOI: 10.1002/chem.201705424
       
  • Modulation of nickel pyridinedicarboxamidate complexes to explore the
           properties of high-valent oxidants
    • Authors: Paolo Pirovano; Brendan Twamley, Aidan Richard McDonald
      Abstract: High-valent Ni oxidants have been implicated in hydrocarbon oxidation catalysis, however, little is understood about the properties of these oxidant. Herein, a family of NiII complexes supported by a pyridinedicarboxamidate ligand and different ancillary ligands was synthesized. The series spans coordination numbers 4, 5, and 6, and contains neutral, mono- and di-anionic donor types. X-ray crystallography and magnetic measurements showed that the 4-coordinate complexes were square planar and low spin (S = 0) and the 5- and 6-coordinate were high spin (S = 1). The NiII complexes could be oxidized by one electron to form a series of metastable NiIII species. EPR analysis confirmed their description as S = ½ NiIII compounds with signal shape and hyperfine coupling dependent on the coordination environment. The oxidation of phenols by the NiIII species was probed, providing evidence for a correlation between oxidizing power and electron-donating properties of the supporting ligands. Critically, we found that the pyridinedicarboxamidate ligand maybe a non-innocent proton acceptor in the oxidation reactions.
      PubDate: 2017-12-05T09:37:46.188433-05:
      DOI: 10.1002/chem.201704618
       
  • Analytical Understanding of the Materials Design with Well-Described
           Shrinkages in Multiscale
    • Authors: Qiang Ma; Saikat Dutta, Kevin C.-W. Wu, Tatsuo Kimura
      Abstract: Shrinkages derived with condensation of frameworks are one of significant steps for fabricating demanded materials having unique morphologies and properties. Enormous efforts have been paid for understanding their mechanisms that are quite useful for the materials design. In this context, diversified measuring and observing tools have been facilitated in order to evaluate structural contractions and corresponding driving forces. All of the investigations are crucial to encourage the utilization of such shrinkages for the precise design of nanomaterials. In this review, we summarize significant works how to analyze shrinkages in multiscale during the synthesis of materials, which will be useful as a follow-up review of our latest contribution.[1] Well-defined porous materials are also selected as a good candidate for understanding well-described shrinkages. This review aims to provide a detailed glimpse of the development of analyses on shrinking behaviors in multiscale for the materials design. Shrinking degree and direction in multiscale, which are driven by condensation of frameworks, are predominant for undersanding and/or predinting final nanostructures of materials after shrinkages.
      PubDate: 2017-12-05T06:00:28.995711-05:
      DOI: 10.1002/chem.201704198
       
  • Designing the Macrocyclic Dimension in Main Group Chemistry
    • Authors: Hao-Che Niu; Alex J Plajer, Raul Garcia-Rodriguez, Sanjay Singh, Dominic Wright
      Abstract: Outside the confines and well-established domain of organic chemistry, the systematic building of large macromolecular arrangements based on non-carbon elements represents a significant and exciting challenge. Our aim in the past two decades has been to develop robust synthetic methods to construct new types of main group architectures in a methodical way, principles of design that parallel those used in the organic arena. This concept article addresses the fundamental thermodynamic and kinetic problems involved in the design and synthesis of main group macrocycles and looks to future developments of macromolecules in this area, as well as new applications in coordination chemistry.
      PubDate: 2017-12-05T05:32:17.024171-05:
      DOI: 10.1002/chem.201705230
       
  • Superconducting Hydrogen Sulfide
    • Authors: John Sak Tse; Yansun Yao
      Abstract: Recent discovery of superconductivity above 200 K in hydrogen sulfide under high pressure marks a milestone in superconductor research. Not only does its critical temperature Tc exceed the previous record in cuprates by more than 50 K, the superconductivity in hydrogen sulfide also exhibits convincing evidence that it is of conventional phonon-mediated type. Moreover, this is the first time that a previously unknown high-Tc superconductor is predicted by theory and afterwards verified by experiment. In this Minireview, we survey the progress made in the last three years in understanding this novel material, and discuss unsolved problems and possible developments to encourage future investigations.
      PubDate: 2017-12-04T22:01:19.052415-05:
      DOI: 10.1002/chem.201705321
       
  • Investigation of (Me4N)SCF3 as a Stable, Solid & Safe Reservoir for S=CF2
           as a Surrogate for Thiophosgene
    • Authors: Thomas Scattolin; Maoping Pu, Franziska Schoenebeck
      Abstract: While thiophosgene finds widespread usage on a multi-ton scale, its fluorinated counterpart S=CF2 is essentially unexplored in synthesis. Using experimental reactivity tests, ReactIR and computational techniques, we herein showcase that the solid (Me4N)SCF3 functions as a safe reservoir for S=CF2. A key feature is that the reactive electrophile is not simply released over time, but instead is liberated under activation with a protic nucleophile. The reactivity of S=CF2 is mild, allowing large-scale and late-stage synthetic applications without special reaction control. The mechanism was fully elucidated herein, including a rationalization of the role of the Me4N-cation and the origins of selectivity.
      PubDate: 2017-12-04T12:30:27.468576-05:
      DOI: 10.1002/chem.201705240
       
  • Bandgap Optimization of Perovskite Semiconductors for Photovoltaic
           Applications
    • Authors: Zewen Xiao; Yuanyuan Zhou, Hideo Hosono, Toshio Kamiya, Nitin P Padture
      Abstract: Bandgap is the most important physical property for determining the potential of any semiconductors for photovoltaic (PV) applications. This minireview discusses the parameters affecting the bandgap of perovskite semiconductors that are being widely studied for PV applications, and the recent progress in the optimization of the bandgap of these materials. Perspectives are also provided for guiding future research in this area.
      PubDate: 2017-12-04T12:00:42.416475-05:
      DOI: 10.1002/chem.201705031
       
  • Front Cover: Facet-Specific Ligand Interactions on Ternary AgSbS2
           Colloidal Quantum Dots (Chem. Eur. J. 70/2017)
    • Authors: Hyekyoung Choi; Sungwoo Kim, Joseph M. Luther, Sang-Wook Kim, Dongwoon Shin, Matthew C. Beard, Sohee Jeong
      Pages: 17621 - 17621
      Abstract: Pb-free, ternary AgSbS2 colloidal quantum dots have attracted significant attention in solar cell applications. A detailed surface chemistry study suggests a passivation model of cation-rich (1 1 1) surfaces, stabilized by anionic thiolate ligands, and non-polar (1 0 0) surfaces passivated with lattice-associated thiolate ligands in the AgSbS2 quantum dots. More information can be found in the Full Paper by M. C. Beard, S. Jeong et al. on page 17707.
      PubDate: 2017-11-30T03:00:27.107285-05:
      DOI: 10.1002/chem.201704970
       
  • Cover Feature: Ag1Pd1 Nanoparticles–Reduced Graphene Oxide as a Highly
           Efficient and Recyclable Catalyst for Direct Aryl C−H Olefination (Chem.
           Eur. J. 70/2017)
    • Authors: Qiyan Hu; Xiaowang Liu, Guoliang Wang, Feifan Wang, Qian Li, Wu Zhang
      Pages: 17622 - 17622
      Abstract: Ag1Pd1 nanoparticles–reduced graphene oxide (Ag1Pd1-rGO) was used as highly efficient and recyclable catalyst for the chelation-assisted ortho C−H bond olefination of amides with acrylates in good yields with a broad substrate scope. The catalyst can be recovered and reused at least 5 times without losing its activity. A synergistic effect between the Ag and Pd atoms on the catalytic activity was found, and a plausible mechanism for the AgPd-rGO catalyzed C−H olefination was proposed. More information can be found in the Communication by X. Liu, W. Zhang et al. on page 17659.
      PubDate: 2017-10-16T06:40:50.647507-05:
      DOI: 10.1002/chem.201704731
       
  • Cover Feature: Cooperative Adsorption by Porous Frameworks: Diffraction
           Experiment and Phenomenological Theory (Chem. Eur. J. 70/2017)
    • Authors: Iurii Dovgaliuk; Farid Nouar, Christian Serre, Yaroslav Filinchuk, Dmitry Chernyshov
      Pages: 17623 - 17623
      Abstract: Two nanoporous frameworks, γ-Mg(BH4)2 and MIL-91(Ti), with different levels of structural flexibility upon guest adsorption-desorption, were examined with in situ X-ray diffraction. Both frameworks exhibit a cooperative guest adsorption correlated with a lattice deformation. The observed experimental scenarios are rationalized with a mean field Gorsky–Bragg–Williams (GBW) approach for the lattice-gas Ising model, which enables the characterization of the thermodynamics of adsorption not only for the total uptake, but also for every specific guest site. More information can be found in the Full Paper by I.  Dovgaliuk, D. Chernyshov et al. on page 17714.
      PubDate: 2017-10-13T02:00:33.717562-05:
      DOI: 10.1002/chem.201704701
       
  • Cover Feature: A pH-sensitive Macromolecular Prodrug as TLR7/8 Targeting
           Immune Response Modifier (Chem. Eur. J. 70/2017)
    • Authors: Stefan Aichhorn; Anne Linhardt, Angela Halfmann, Markus Nadlinger, Stefanie Kirchberger, Manuela Stadler, Barbara Dillinger, Martin Distel, Alexander Dohnal, Ian Teasdale, Wolfgang Schöfberger
      Pages: 17624 - 17624
      Abstract: The chemical synthesis and biological activity of new functionalized imidazoquinoline derivatives (ImQ) to generate Toll-like receptor (TLR) 7/8 specific prodrugs are presented. In vivo activity of ImQs to induce inflammation was confirmed in zebrafish larvae. After covalent ligation to fully biodegradable polyphosphazenes (ImQ-polymer), the macromolecular prodrugs were designed to undergo intracellular pH-sensitive release of ImQs to induce inflammation through binding to endosomal TLR7/8. More information can be found in the Full Paper by M. Distel, A. Dohnal, I. Teasdale, W.  Schöfberger et al. on page 17721.
      PubDate: 2017-10-16T06:41:05.813553-05:
      DOI: 10.1002/chem.201704767
       
  • Facet-Specific Ligand Interactions on Ternary AgSbS2 Colloidal Quantum
           Dots.
    • Authors: Hyekyoung Choi; Sungwoo Kim, Joseph M. Luther, Sang-Wook Kim, Dongwoon Shin, Matthew C. Beard, Sohee Jeong
      Pages: 17625 - 17625
      Abstract: Invited for the cover of this issue are the groups of Matthew C. Beard at the National Renewable Energy Laboratory (U.S.A) and Sohee Jeong at KIMM and UST, Daejeon (Republic of Korea). The image depicts solar light shining onto a quantum dot. Read the full text of the article at 10.1002/chem.201703681.“We believe that our results provide a basis for further developments in the field of lead-free quantum dot thin-film solar cells” Read more about the story behind the cover in the Cover Profile and about the research itself on page 17707 ff. (
      DOI : 10.1002/chem.201703681).
      PubDate: 2017-11-08T05:00:25.105229-05:
       
  • Metal-Containing Polymers as Light-Emitting and Light-Responsive Materials
           and Beyond
    • Authors: Matteo Mauro; Stéphane Bellemin-Laponnaz, Cristina Cebrián
      Pages: 17626 - 17636
      Abstract: Functional materials that respond to external stimuli are of major current interest. In particular, supramolecular systems that can interact with their surroundings, adapt to environmental changes and evolve with are even more fascinating, yet challenging. Combining the rich physico-chemical properties featured by metal centres with characteristics typical of classical organic polymers, metallopolymers or metallo-supramolecular polymers can be prepared, depending on their static versus dynamic structural features. Additionally, multiple and orthogonal functionalities can be encoded in their chemical structure affording materials with widespread potential applications to be employed as “smart” materials for advanced technologies. In this Concept article, selected examples of metal-containing polymers will be described demonstrating large potentialities of such systems for creating stimuli-responsive materials with special emphasis for those showing optical applications.Functional materials that respond to external stimuli are of major current interest. Supramolecular systems that can interact with their surroundings, adapt to the environmental changes and evolve with are even more fascinating, yet challenging. A judicious combination of multi-topic organic ligands with metal centres affords functional and light-responsive metal-containing polymers that possess widespread potential application.
      PubDate: 2017-11-14T03:05:44.678734-05:
      DOI: 10.1002/chem.201702936
       
  • Advances in Stereoselective 1,2-cis Glycosylation using C-2 Auxiliaries
    • Authors: Rens A. Mensink; Thomas J. Boltje
      Pages: 17637 - 17653
      Abstract: The control of stereoselectivity in a glycosylation reaction remains one of the most challenging aspects of oligosaccharide synthesis. Especially the synthesis of 1,2-cis-glycosides is challenging and generally applicable methodology to prepare this linkage is needed to standardize oligosaccharide synthesis. This review highlights the recent development of an elegant strategy employing a C-2 auxiliary to control the anomeric stereoselectivity in glycosylations. The various auxiliaries developed to date, their compatibility with protecting groups and monosaccharide types as well as mechanistic aspects are summarized. Furthermore, the application, advantages and limitations of C-2 auxiliaries in oligosaccharide synthesis are discussed.Love thy neighbor: A new strategy for stereoselective glycosylation using a C-2 chiral auxiliary is discussed. Neighboring groups of the auxiliary participate in the reaction to form a sulfonium ion intermediate. The structure of the auxiliary, the type of protecting groups and stereochemistry of the monosaccharide all influence the mechanism and selectivity of these reactions. The application of these chiral auxiliaries within oligosaccharide synthesis is also discussed.
      PubDate: 2017-10-04T11:52:13.689958-05:
      DOI: 10.1002/chem.201700908
       
  • C−H Insertions by Iron Porphyrin Carbene: Basic Mechanism and Origin
           of Substrate Selectivity
    • Authors: Rahul L. Khade; Yong Zhang
      Pages: 17654 - 17658
      Abstract: Recent experimental reports of heme carbene C−H insertions show promising results for sustainable chemistry due to good yield and selectivity, low cost of iron, and low/no toxicity of hemes. But mechanistic details are mostly unknown. Despite structural similarity and isoelectronic nature between heme carbene and the FeIV=O intermediate, our quantum chemical studies with detailed geometric and electronic information for the first time reveal an FeII-based, concerted, hydride-transfer mechanism, which is different from the FeIV-based stepwise hydrogen atom transfer mechanism for C−H functionalization by native heme enzymes. A trend of broad range experimental C−H insertion yields (0–88 %) of five different C−H bonds, including mostly non-functionalized moieties, was well reproduced. Results suggest that the substrate selectivity originates from the hydride formation capability. The predicted kinetic isotope effects were also in excellent agreement with experiment. Useful geometry, charge, and energy parameters well correlated with barriers were reported. These results provide the first theoretical evidence that carbene formation is the overall rate-limiting step, and suggest a key role of the formation of strong electrophilic heme carbene in developing heme-based C−H insertion catalysts and biocatalysts.Dank hemes: Heme carbene C−H insertion is good for sustainable chemistry. Our results for the first time show: 1) the FeII-based hydride transfer, early TS; 2) the conformation and spin-state effects on TS; 3) the useful geometry, charge, and energy parameters to well correlate with ΔG≠; 4) the theoretical explanation of a broad range experimental C−H insertion yields; and 5) the significance of strong electrophilic heme carbene with low formation barrier for catalyst development.
      PubDate: 2017-11-15T03:22:21.977032-05:
      DOI: 10.1002/chem.201704631
       
  • Ag1Pd1 Nanoparticles–Reduced Graphene Oxide as a Highly Efficient and
           Recyclable Catalyst for Direct Aryl C−H Olefination
    • Authors: Qiyan Hu; Xiaowang Liu, Guoliang Wang, Feifan Wang, Qian Li, Wu Zhang
      Pages: 17659 - 17662
      Abstract: The efficient and selective palladium-catalyzed activation of C−H bonds is of great importance for the construction of diverse bioactive molecules. Despite significant progress, the inability to recycle palladium catalysts and the need for additives impedes the practical applications of these reactions. Ag1Pd1 nanoparticles–reduced graphene oxide (Ag1Pd1-rGO) was used as highly efficient and recyclable catalyst for the chelation-assisted ortho C−H bond olefination of amides with acrylates in good yields with a broad substrate scope. The catalyst can be recovered and reused at least 5 times without losing activity. A synergistic effect between the Ag and Pd atoms on the catalytic activity was found, and a plausible mechanism for the AgPd-rGO catalyzed C−H olefination is proposed. These findings suggest that the search for such Pd-based bimetallic alloy nanoparticles is a new method towards the development of superior recyclable catalysts for direct aryl C−H functionalization under mild conditions.Direct aryl C−H activation catalyzed by supported bimetallic alloy nanoparticles is described. Ag1Pd1-rGO can be used as a highly efficient and recyclable catalyst for ortho C−H olefination of amides with acrylates in good yields under base-free and additive-free conditions in air.
      PubDate: 2017-10-10T06:10:30.137571-05:
      DOI: 10.1002/chem.201704056
       
  • Design of a Hypersensitive pH-Sensory System Created by a Combination of
           Charge Neutralization and Aggregation-Induced Emission (AIE)
    • Authors: Daisuke Yoshihara; Takao Noguchi, Bappaditya Roy, Junji Sakamoto, Tatsuhiro Yamamoto, Seiji Shinkai
      Pages: 17663 - 17666
      Abstract: In our bodies, a slight pH change causes remarkable activation or serious damage in the biological processes and continuously keeps biological homeostasis. Detection of such a slight pH change has been a constant demand in searching for unusual biological events. In this paper, we demonstrate a novel pH sensory system that has been achieved through a combination of charge neutralization by a slight pH change with aggregation-induced emission (AIE). We selected a cyano-functionalized oligo(phenylene-vinylene) (cyanoOPV) backbone for AIE and introduced ammonium-tethered boronic acid groups as a pH-dependent function. The self-assembling of these dyes (OPV-Cn) was readily achieved by pH-dependent charge neutralization at the neutral pH region. This sensory system showed unusually sensitive pH responsiveness in a narrow pH range. Moreover, this pH change was observed in a biologically important neutral pH region. We therefore believe that this system is broadly applicable to detect the slight pH change occurring in the biological events.A novel pH sensory system can be designed through a unique combination of charge neutralization by a slight pH change with aggregation-induced emission (AIE). This sensory system showed unusually sensitive pH responsiveness in a narrow pH range. Moreover, this pH change was observed in a biologically important neutral pH region.
      PubDate: 2017-11-30T04:55:42.902247-05:
      DOI: 10.1002/chem.201703560
       
  • Cyclic Hydroxamic Acid Analogues of Bacterial Siderophores as
           Iron-Complexing Agents prepared through the Castagnoli–Cushman Reaction
           of Unprotected Oximes
    • Authors: Olga Bakulina; Anton Bannykh, Dmitry Dar'in, Mikhail Krasavin
      Pages: 17667 - 17673
      Abstract: The first application of multicomponent chemistry (the Castagnoli–Cushman reaction) toward the convenient one-step preparation of cyclic hydroxamic acids is described. Cyclic hydroxamic acids are close analogues of bacterial siderophores (iron-binding compounds) and form stable complexes with Fe3+ ions as confirmed by spectrophotometric measurements. These compounds are potential components for the design of chelating agents for iron overload disease therapy, as well as siderophore-based carrier systems for antibiotic delivery across the bacterial cell wall.Homophthalic remedies for iron overdose: The first application of the multicomponent Castagnoli–Cushman reaction toward the convenient one-step preparation of cyclic hydroxamic acids is described. These compounds form stable complexes with Fe3+ ions as confirmed by spectrophotometric measurements and are potential components for the design of chelating agents for iron overload disease therapy, as well as siderophore-based carrier systems for antibiotic delivery across the bacterial cell wall.
      PubDate: 2017-11-29T04:05:47.644701-05:
      DOI: 10.1002/chem.201704389
       
  • Regio- and Stereoselective Iron-Catalyzed Oxyazidation of Enamides Using a
           Hypervalent Iodine Reagent
    • Authors: Sylvain Bertho; Romain Rey-Rodriguez, Cyril Colas, Pascal Retailleau, Isabelle Gillaizeau
      Pages: 17674 - 17677
      Abstract: A novel regio- and diastereoselective iron-catalyzed intermolecular oxyazidation of enamides using various azidobenziodoxolone (ABX) derivatives is presented. A variety of α-N3 amino derivatives and of α-N3 piperidines were synthesized in good yields and under mild reaction conditions. The reaction involves a radical process using cheap FeCl2 as the initiator.Iron catalysis: An iron-catalyzed oxyazidation of enamides was developed. This provided an efficient route to α-N3 amino derivatives and more specifically α-N3 piperidine derivatives in good yields with high regio- and diastereoselectivity.
      PubDate: 2017-11-30T04:45:57.72331-05:0
      DOI: 10.1002/chem.201704499
       
  • Polymer Amplified Enantioselectivity in the Fluorescent Recognition of
           Prolinol
    • Authors: Yachen Wang; Lingling Hu, Feng Zhao, Shanshan Yu, Jun Tian, Dan Shi, Xinjing Wang, Xiaoqi Yu, Lin Pu
      Pages: 17678 - 17681
      Abstract: A 1,1′-bi-2-naphthol (BINOL)-aldehyde-based polymer has been synthesized that exhibits enantioselective fluorescent enhancement toward prolinol. It is found that the polymer shows greatly amplified enantioselectivity over the parent small-molecule sensor under the same conditions. This is attributed to the photoinduced electron transfer processes between the BINOL units in the polymer chain as well as the different steric environment provided by the polymer.Polymer (S)-6 has weaker fluorescence than its corresponding monomeric compound probably because of a fluorescence quenching photoinduced electron transfer process between the adjacent monomer units. The fluorescence of the polymer can be enhanced when treated with prolinol due to the condensation of its aldehyde groups with the amino alcohol to form oxazolidine rings. This fluorescence enhancement is found to have greatly amplified enantioselectivity (ef=3.7) over the monomeric compound.
      PubDate: 2017-11-29T09:06:20.857764-05:
      DOI: 10.1002/chem.201704640
       
  • Nitromethane Bridged Bis(1,3,4-oxadiazoles): Trianionic Energetic Salts
           with Low Sensitivities
    • Authors: Qiong Yu; Gregory H. Imler, Damon A. Parrish, Jean'ne M. Shreeve
      Pages: 17682 - 17686
      Abstract: Trianionic energetic salts based on one nitromethylene and two dinitromethyl anions were designed and synthesized. Interestingly, the unstable dinitromethylene group of diethyl 2,2′-((dinitromethylene)bis(1,3,4-oxadiazole-5,2-diyl))bis(2,2-dinitroacetate) (2) was changed to a mononitromethylene group by an aminolysis reaction to form triammonium ((nitromethanidylene)bis(1,3,4-oxadiazole-5,2-diyl))bis(dinitromethanide) (3), whereas in (dinitrobis(5-(trinitromethyl)-1,3,4-oxadiazol-2-yl)methan) 8 it was hydrolyzed to a carbonyl group resulting in (bis(5-(trinitromethyl)-1,3,4-oxadiazol-2-yl)methanone) 9. All the new compounds were fully characterized by infrared, multinuclear NMR spectra, and elemental analysis. The structures of triammonium ((nitromethanidylene)bis(1,3,4-oxadiazole-5,2-diyl))bis(dinitromethanide) dihydrate (3⋅2 H2O) and bis(2-dinitromethyl-1,3,4-oxadiazole-5-yl)methanone (9) were further confirmed by single-crystal X-ray diffraction analysis. Based on their different physical and detonation properties, some of the energetic salts were found to exhibit good energetic performance and low sensitivity.Feel the energy: A series of new trianionic salts were synthesized and fully characterized. They have large lattice potential energies, which correspond to good thermal stabilities, and they also exhibit low sensitivities towards impact and friction (see scheme).
      PubDate: 2017-11-28T07:40:38.845116-05:
      DOI: 10.1002/chem.201704939
       
  • Inserting Porphyrin Quantum Dots in Bottom-Up Synthesized Graphene
           Nanoribbons
    • Authors: Wade Perkins; Felix R. Fischer
      Pages: 17687 - 17691
      Abstract: Diels–Alder copolymerization of tetraphenylcyclopentadienone, a precursor for cove graphene nanoribbons (cGNRs), with bifunctional porphyrins yields defined nanostructures comprised of a single cGNR-porphyrin-cGNR heterojunction within each ribbon. 13C NMR labeling and high-resolution mass spectrometry of solubilized polymer intermediates indicates that every porphyrin is covalently linked to two extended segments of cGNRs. UV/Vis absorption and fluorescence emission spectroscopy reveal a strong electronic correlation between the porphyrin and the adjacent cGNR segments that can be attenuated through reversible metalation of the porphyrin core. This versatile bottom-up synthetic strategy provides access to structurally well-defined, functional GNR-quantum dot-GNR heterostructures within a single graphene nanoribbon.The bottom-up solution-based synthesis and selective fractionation of graphene nanoribbon-porphyrin-graphene nanoribbon heterostructures is reported. Absorption and fluorescence spectroscopy reveal a strong coupling between the graphene nanoribbon and the central porphyrin quantum dot.
      PubDate: 2017-11-30T03:01:18.427362-05:
      DOI: 10.1002/chem.201705252
       
  • C−F Bond Activation by Silylium Cation/Phosphine Frustrated Lewis Pairs:
           Mono-Hydrodefluorination of PhCF3, PhCF2H and Ph2CF2
    • Authors: Ian Mallov; Adam J. Ruddy, Hui Zhu, Stefan Grimme, Douglas W. Stephan
      Pages: 17692 - 17696
      Abstract: Single defluorination of aryl polyfluoromethyl functionalities is achieved by both intra- and intermolecular silylium cation/phosphine Lewis pairs. Phosphine-captured aryl fluoromethyl cations are then treated with Brønsted base to complete the first mono-hydrodefluorinations of PhCF3, Ph2CF2, and PhCF2.Reactions of CF3: Silylium/phosphine- based frustrated Lewis pairs are shown to effect the selective abstraction of fluoride ion from aryl-CF3 and CF2 groups, ultimate converting CF3 to CF2H to CFH2 fragments.
      PubDate: 2017-11-30T03:01:02.256518-05:
      DOI: 10.1002/chem.201705276
       
  • Pd-Catalyzed β-C(sp3)−H Arylation of Propionic Acid and Related
           Aliphatic Acids
    • Authors: Kiron K. Ghosh; Manuel van Gemmeren
      Pages: 17697 - 17700
      Abstract: A generally applicable Pd-catalyzed protocol for the β-C(sp3)−H arylation of propionic acid and related α-branched aliphatic acids is reported. Enabled by the use of N-acetyl-β-alanine as ligand our protocol delivers a broad range of arylation products. Notably, the highly challenging substrate, propionic acid, which lacks any acceleration through the Thorpe–Ingold effect, can be employed as substrate with synthetically useful yields. Furthermore, the scalability and synthetic applicability of the protocol are demonstrated.No Thorpe–Ingold effect required: A generally applicable Pd-catalyzed protocol for the β-C(sp3)−H arylation of propionic acid and its α-substituted derivatives was developed. The use of N-acetyl-β-alanine as ligand enabled a broad scope and synthetically useful yields with unsubstituted propionic acid as substrate for the first time.
      PubDate: 2017-11-30T02:56:27.526811-05:
      DOI: 10.1002/chem.201705449
       
  • Spectroscopic Observation and Molecular Dynamics Simulation of Ga Surface
           Segregation in Liquid Pd–Ga Alloys
    • Authors: Mathias Grabau; Jannis Erhard, Nicola Taccardi, Sandra Krick Calderon, Peter Wasserscheid, Andreas Görling, Hans-Peter Steinrück, Christian Papp
      Pages: 17701 - 17706
      Abstract: Liquid binary Pd–Ga alloys with low Pd contents of 0.8, 1.8, and 4.7 at % of Pd were examined as a function of sample temperature in ultra-high vacuum by using angle-resolved XPS. Upon cooling from 750 to 400 K, a pronounced temperature-dependence of the Pd concentration in the liquid phase was observed, which was explained by the transition from the pure liquid phase to a two-phase system, consisting of a solid Ga5Pd phase and a Pd-depleted liquid Pd–Ga alloy. In the liquid Pd–Ga alloy, Pd is always depleted from the topmost interface layer, as deduced from angle-resolved XPS at 0 and 80° emission, independent of temperature and Pd concentration. This observation is interpreted as an inhomogeneous depth distribution function of Pd, that is, the segregation of Ga to the surface of the liquid phase. The results of a DFT-based molecular dynamics simulation (MD) independently show interfacial stratification of Ga and an inhomogeneous Pd distribution along the surface normal. The evaluation of the experimental data with a rigid layer model based on the MD calculations leads to excellent agreement with the simulation.X-ray photoelectron spectroscopy and DFT-based molecular dynamics simulations determined an inhomogeneous depth distribution of the liquid metal catalyst Pd/Ga. Additionally, the Pd surface concentration in the examined liquid Pd–Ga alloys was was temperature dependent, which is ascribed to the formation of Pd-rich Ga5Pd particles in the liquid bulk. With increasing temperature, the Pd concentration in the surface near region of the liquid probed by XPS increases (see figure).
      PubDate: 2017-11-06T09:30:48.073725-05:
      DOI: 10.1002/chem.201703627
       
  • Facet-Specific Ligand Interactions on Ternary AgSbS2 Colloidal Quantum
           Dots
    • Authors: Hyekyoung Choi; Sungwoo Kim, Joseph M. Luther, Sang-Wook Kim, Dongwoon Shin, Matthew C. Beard, Sohee Jeong
      Pages: 17707 - 17713
      Abstract: Silver dimetal chalcogenide (Ag-V-VI2) ternary quantum dots (QDs) are emerging lead-free materials for optoelectronic devices due to their NIR band gaps, large absorption coefficients, and superior electronic properties. However, thin film-based devices of the ternary QDs still lag behind due to the lack of understanding of the surface chemistry, compared to that of lead chalcogenide QDs even with the same crystal structure. Herein the surface ligand interactions of AgSbS2 QDs, synthesized with 1-dodecanethiol used as a stabilizer, are studied. For nonpolar (1 0 0) surfaces, it is suggested that the thiolate ligands are associated with the crystal lattices, thus preventing surface oxidation by protecting sulfur after air-exposure, as confirmed through optical and surface chemical analysis. Otherwise, silver rich (1 1 1) surfaces are passivated by thiolate ligands, allowing ligand exchange processes for the conductive films. This in-depth investigation of the surface chemistry of ternary QDs will prompt the performance enhancement of their optoelectronic devices.Ternary AgSbS2 colloidal quantum dots show that the lattice-associated thiolates on (1 0 0) surfaces prevent the surface oxidation and the anionic thiolates on Ag-rich (1 1 1) surfaces allow for the preparation of conductive films through effective ligand exchange processes.
      PubDate: 2017-11-07T05:10:27.731857-05:
      DOI: 10.1002/chem.201703681
       
  • Cooperative Adsorption by Porous Frameworks: Diffraction Experiment and
           Phenomenological Theory
    • Authors: Iurii Dovgaliuk; Farid Nouar, Christian Serre, Yaroslav Filinchuk, Dmitry Chernyshov
      Pages: 17714 - 17720
      Abstract: Materials science of metal open frameworks is a state-of-the-art field for numerous applications, such as gas storage, sensors, and medicine. Two nanoporous frameworks, γ-Mg(BH4)2 and MIL-91(Ti), with different levels of structural flexibility, were examined with in situ X-ray diffraction guest adsorption–desorption experiments. Both frameworks exhibit a cooperative guest adsorption correlated with a lattice deformation. This cooperativity originates from the long-range interactions between guest molecules, mediated by elastic response of the host porous structure. The observed experimental scenarios are rationalized with a mean field Gorsky–Bragg–Williams (GBW) approach for the lattice-gas Ising model. The adjusted GBW model, in combination with in situ synchrotron powder diffraction, demonstrates an efficient experimental and phenomenological approach to characterize thermodynamics of the adsorption in MOFs not only for the total uptake but also for every specific guest site.Cooperate! The elastic response of guest adsorption into γ-Mg(BH4)2 and MIL-91(Ti) nanoporous frameworks were examined with in situ synchrotron X-ray diffraction and analyzed with an adjusted mean field Gorsky–Bragg–Williams (GBW) approach for the lattice-gas Ising model. The applied methods allow the determination of the thermodynamics of the guest adsorption in MOFs, not only for the total uptake but also for every specific guest site.
      PubDate: 2017-10-13T03:55:33.405528-05:
      DOI: 10.1002/chem.201702707
       
  • A pH-sensitive Macromolecular Prodrug as TLR7/8 Targeting Immune Response
           Modifier
    • Authors: Stefan Aichhorn; Anne Linhardt, Angela Halfmann, Markus Nadlinger, Stefanie Kirchberger, Manuela Stadler, Barbara Dillinger, Martin Distel, Alexander Dohnal, Ian Teasdale, Wolfgang Schöfberger
      Pages: 17721 - 17726
      Abstract: The chemical synthesis and biological activity of novel functionalized imidazoquinoline derivatives (ImQ) to generate Toll-like receptor (TLR) 7/8 specific prodrugs are presented. In vivo activity of ImQs to induce inflammation was confirmed in zebrafish larvae. After covalent ligation to fully biodegradable polyphosphazenes (ImQ-polymer), the macromolecular prodrugs were designed to undergo intracellular pH-sensitive release of ImQs to induce inflammation through binding to endosomal TLR7/8 (danger signal). We showed ImQ dissociation from prodrugs at a pH 5 pointing towards endosomal prodrug degradability. ImQ-polymers strongly activated ovalbumin-specific T cells in murine splenocytes as shown by increased proliferation and expression of the IL-2 receptor (CD25) on CD8+ T cells accompanied by strong IFN-γ release. ImQ prodrugs presented here are suggested to form the basis of novel nanovaccines, for example, for intravenous or intratumoral cancer immunotherapeutic applications to trigger physiological antitumor immune responses.GoPro for T cells: A novel pH-sensitive polyphosphazene–imidazoquinoline conjugate serves as a TLR7/8 targeting macromolecular prodrug for T cell activation.
      PubDate: 2017-09-04T08:41:16.838153-05:
      DOI: 10.1002/chem.201702942
       
  • Versatile Tailoring of NH2-Containing Metal–Organic Frameworks with
           Paddle-Wheel Units
    • Authors: Xiang-Guang Guo; Zai-Yong Zhang, Sen Qiu, Xiang Su, Ya-Bing Wang, Xiaoqi Sun
      Pages: 17727 - 17733
      Abstract: An amine-containing non-interpenetrating pillar-layer framework, [Zn2(dbtcb)(L1)]⋅x solvent (1), has been synthesized from Zn(NO3)2 and the ligands 1,4-dibromo-2,3,5,6-tetrakis(4-carboxyphenyl)benzene (H4DBTCB) and 2,5-bis(4-pyridyl)aniline (L1). The [Zn2(COO)4] secondary building units (SBUs) are bridged by DBTCB to form two-dimensional layers that are linked by L1 ligands acting as pillars to form a three-dimensional network. This NH2-containing framework can undergo versatile tailoring through post-synthetic covalent modification, solvent-assisted linker exchange (SALE), and single-crystal-to-single-crystal (SC-SC) transmetalation reactions. Acetamide-functionalized [Zn2(L2)(dbtcb)]⋅xsolvent (2) could be obtained by direct synthesis from Zn(NO3)2, N-acetyl-2,5-bis(4-pyridyl)aniline (L2) and H4DBTCB. Importantly, compound 1 with pure NH2 ligands as pillars could be obtained by SALE of 2 with L1 in DMSO solution. The transmetalation reactions of 1 with CuII, NiII, and CoII were studied; inductively coupled plasma-atomic emission (ICP) analysis revealed that 1 underwent almost complete SC-SC transmetalation with CuII within 30 h, whereas with NiII and CoII only 70 and 80 % substitutions were achieved. Photoluminescence studies revealed that 1 and 2 display yellow-green and UV emission, respectively, under a UV lamp. Furthermore, the photoluminescent properties could be tuned by introducing mixed pillar amino ligands L1 and L2 into the MOF to produce multivariate (MTV) MOF 3 displaying overall orange emission.A pillar of strength! An amine-containing pillar-layered metal–organic framework (MOF) with paddle-wheel subunits has been constructed that could undergo modifications in three ways. This MOF could be obtained with pure NH2-containing ligands as pillars by solvent-assisted linker exchange (SALE) of the corresponding acetamide-containing framework with the NH2-substituted ligands in DMSO solution. Interestingly, the photoluminescent properties could be tuned by introducing mixed pillars into the framework (see figure).
      PubDate: 2017-11-28T07:21:11.051228-05:
      DOI: 10.1002/chem.201703126
       
  • Solvent Effect on the Photoinduced Structural Change of a Phosphorescent
           Molecular Butterfly
    • Authors: Ying-Zhong Ma; Chenkun Zhou, Benjamin Doughty, Davis C. Easley, Justin Deterding, Biwu Ma
      Pages: 17734 - 17739
      Abstract: Photoinduced structural changes (PSC) is one of the fundamental excited-state dynamic processes, and yet often very challenging to distinguish from competing electronic excited-state relaxation channels having similar or even comparable timescales. Here, we report a detailed study on the PSC of a pyrazolate bridged platinum(II) binuclear complex, BFPtPZ (C^NPt(μ-pz′)2PtC^N, C^N=2-(2,4-difluorophenyl)pyridine, pz′=pyrazolate), a molecular butterfly, using time-correlated single photon counting measurements at different wavelengths and sample temperatures. Analysis of the results obtained using dichloromethane (DCM) and ethylene carbonate (EC) as solvents enabled us to reveal an unexpected, strong solvent effect on the PSC processes. We show that a rapid PSC process with a characteristic timescale of 323 ps is observed in DCM, which leads to an excitation equilibrium between the ligand center/metal-to-ligand charge transfer (3LC/MLCT) and metal-metal-to-ligand charge transfer (3MMLCT) triplet states. The subsequent relaxation from these electronic states to the ground state takes place in several nanoseconds. In contrast, the corresponding PSC process in EC appears slow at all temperatures studied in our experiments and showed no sign of such excitation equilibrium. The observed solvent effect is found to arise from distinct solvent properties including their viscosities and polarities as well as the peculiar electronic excited-states of the butterfly-like molecules with charge transfer character.A butterfly-like phosphorescent platinum(II) binuclear complex that can undergo a molecular structure change is probed in real time using time-resolved photoluminescence spectroscopy. Analysis of the kinetics acquired at different wavelengths and temperatures enable us to reveal a pronounced solvent effect.
      PubDate: 2017-11-17T05:35:30.564311-05:
      DOI: 10.1002/chem.201703259
       
  • Gemcitabine, Pyrrologemcitabine, and 2′-Fluoro-2′-Deoxycytidines:
           Synthesis, Physical Properties, and Impact of Sugar Fluorination on Silver
           Ion Mediated Base Pairing
    • Authors: Xiurong Guo; Peter Leonard, Sachin A. Ingale, Frank Seela
      Pages: 17740 - 17754
      Abstract: The stability of silver-mediated “dC-dC” base pairs relies not only on the structure of the nucleobase, but is also sensitive to structural modification of the sugar moiety. 2′-Fluorinated 2′-deoxycytidines with fluorine atoms in the arabino (up) and ribo (down) configuration as well as with geminal fluorine substitution (anticancer drug gemcitabine) and the novel fluorescent phenylpyrrolo-gemcitabine (phPyrGem) have been synthesized. All the nucleosides display the recognition face of naturally occurring 2′-deoxycytidine. The nucleosides were converted into phosphoramidites and incorporated into 12-mer oligonucleotides by solid-phase synthesis. The addition of silver ions to DNA duplexes with a fluorine-modified “dC-dC” pair near the central position led to significant duplex stabilization. The increase in stability was higher for duplexes with fluorinated sugar residues than for those with an unchanged 2′-deoxyribose moiety. Similar observations were made for “dC-dT” pairs and to a minor extent for “dC-dA” pairs. The increase in silver ion mediated base-pair stability was reversed by annulation of a pyrrole ring to the cytosine moiety, as shown for 2′-fluorinated phPyrGem in comparison with phenylpyrrolo-dC (phPyrdC). This phenomenon results from stereoelectronic effects induced by fluoro substitution, which are transmitted from the sugar moiety to the silver ion mediated base pairs. The extent of the effect depends on the number of fluorine substituents, their configuration, and the structure of the nucleobase.Time to talk! Talking between sugar residues and silver ion mediated cytosine–cytosine base pairs: Stereoelectronic effects induced by DNA ribose fluorination lead to changes in the stability of metal–DNA (see figure).
      PubDate: 2017-11-22T03:52:57.159951-05:
      DOI: 10.1002/chem.201703427
       
  • Hemin-Graphene Derivatives with Increased Peroxidase Activities Restrain
           Protein Tyrosine Nitration
    • Authors: Huan Xu; Zhen Yang, Hailing Li, Zhonghong Gao
      Pages: 17755 - 17763
      Abstract: Protein tyrosine nitration is implicated in the occurrence and progression of pathological conditions involving free radical reactions. It is well recognized that hemin can catalyze protein tyrosine nitration in the presence of nitrite and hydrogen peroxide. Generally, the catalytic efficiency is positively correlated to its peroxidase activity. In this study, however, it is found that the efficiency of hemin in catalyzing protein tyrosine nitration is largely suppressed after functionalization with graphene derivatives, even though its peroxidase-like activity is more than quadrupled. Further studies show that the oxidation of tyrosine is still observed for these composites; dityrosine formation, however, is greatly inhibited. Furthermore, these composites also exhibit strong effects on the oxidation of nitrite into nitrate. Therefore, we propose a mechanism in which hemin-graphene derivatives facilitate the oxidation of tyrosine and nitrite to produce tyrosyl radicals and nitrogen dioxide radicals in the presence of hydrogen peroxide, but graphene interlayers serve as barriers that hinder radical–radical coupling reactions; consequently, protein tyrosine nitration is restrained. This property of hemin-graphene derivatives, by which they catalyze substrate oxidation but suppress radical–radical coupling reactions, shows their great potential in selective oxidation procedures for byproduct removal.Selective oxidation: Hemin-graphene derivatives are synthesized. They show a pronounced effect on weakening protein tyrosine nitration. In addition, it is demonstrated that the hemin-graphene derivatives accelerate tyrosine (Tyr) and nitrite oxidation, but suppress the free-radical coupling reaction (see figure).
      PubDate: 2017-11-22T03:53:08.781134-05:
      DOI: 10.1002/chem.201703455
       
  • Synthesis of Electron-Rich, Planarized Silicon(IV) Species and a
           Theoretical Analysis of Dimerizing Aminosilanes
    • Authors: Nina Kramer; Christoph Jöst, Alexandra Mackenroth, Lutz Greb
      Pages: 17764 - 17774
      Abstract: Equipping silicon(IV) with electron-rich, geometrically constrained NNN- and ONO-tridentate substituents leads to aminosilanes with increased Lewis acidity—expressed through the formation of Si2N2 rings by head-to-tail dimerization. Depending on the substituents, the dimerization can be controlled for the first time, yielding monomeric, structurally reversible and dimeric states. The monomeric species display substantial distortions from tetrahedral towards planar geometry at silicon. The dimerization and the Lewis acidity of aminosilanes are rationalized by (conceptual) DFT, NBO, ETS-NOCV and QTAIM methods. The preorganization at silicon, London dispersion between the substituents and resonance phenomena inside the formed Si2N2 tetracycles are identified as driving forces for the dimerization. Comparison with selected aminosilanes permits general conclusions to be reached on the Lewis acidity of silicon species and on the aggregation of amphiphilic compounds.Shape up! Geometrically constrained, electron-rich aminosilanes have been synthesized that can impart control over a unique dimerization process (see figure). Quantum theoretical analyses of the process permit general conclusions to be drawn on the Lewis acidity of silicon compounds and on dimerizing amphiphilic species.
      PubDate: 2017-11-17T05:36:24.3076-05:00
      DOI: 10.1002/chem.201703649
       
  • Experimental and Theoretical Interpretation on the Magnetic Behavior in a
           Series of Pentagonal-Bipyramidal DyIII Single-Ion Magnets
    • Authors: Min Li; Haipeng Wu, Qi Yang, Hongshan Ke, Bing Yin, Quan Shi, Wenyuan Wang, Qing Wei, Gang Xie, Sanping Chen
      Pages: 17775 - 17787
      Abstract: Taking advantage of the steric hindrance and charge-driving effects, four air-stable pentagonal bipyramidal mononuclear DyIII compounds were hydrothermally synthesized. With a tetradentate ligand, N,N′-bis(2-methylenepyridinyl)ethylenediamine (Bpen), invariably coordinates to DyIII in an equatorial plan, 1–3 achieve an orderly transformation of the ligand field by sequentially replacing the remaining sites of the DyIII ion. Compound 4 possesses the same coordination atoms but a different peripheral coordination sphere with 3. Magnetic characterizations display that the compounds are field-induced single-ion magnets (SIM) with actually low barriers, even though 2 has both the same atoms and a similar geometry of the first sphere compared with [Dy(bbpen)Cl] (2′, H2bbpen=N,N′-bis(2-hydroxybenzyl)-N,N′-bis(2-methylpyridyl)ethylenediamin), a high-performance SIM previously reported. Detailed ab initio calculations have been employed to further elucidate the electronic and magnetic structure of the low-lying energy levels of compounds 1–4 and 2′. The theoretical results indicate there is an apparent difference in the electronic structure for these compounds. The analysis on the electrostatic potential further demonstrates that although the pentagonal bipyramidal D5h is one of the ideal configurations expected, the electron density of the donor atoms from the different hybridizations and other functional groups, outside the first sphere, should also be considered in the rational design of promising molecular magnets.A detailed comparison of the structural and magnetic properties in a series of D5h symmetry DyIII SIMs suggests that the electron density affected by different hybridization of donor atoms and other functional groups outside the first sphere remarkably influence the axiality of the KDs and the magnetic relaxation behaviors (see figure)
      PubDate: 2017-11-08T09:36:27.262966-05:
      DOI: 10.1002/chem.201703755
       
  • Effect of the ortho-Hydroxyl Groups on a Bipyridine Ligand of Iridium
           Complexes for the High-Pressure Gas Generation from the Catalytic
           Decomposition of Formic Acid
    • Authors: Masayuki Iguchi; Heng Zhong, Yuichiro Himeda, Hajime Kawanami
      Pages: 17788 - 17793
      Abstract: The hydroxyl groups of a 2,2′-bipyridine (bpy) ligand near the metal center activated the catalytic performance of the Ir complex for the dehydrogenation of formic acid at high pressure. The position of the hydroxyl groups on the ligand affected the catalytic durability for the high-pressure H2 generation through the decomposition of formic acid. The Ir complex with a bipyridine ligand functionalized with para-hydroxyl groups shows a good durability with a constant catalytic activity during the reaction even under high-pressure conditions, whereas deactivation was observed for an Ir complex with a bipyridine ligand with ortho-hydroxyl groups (2). In the presence of high-pressure H2, complex 2 decomposed into the ligand and an Ir trihydride complex through the isomerization of the bpy ligand. This work provides the development of a durable catalyst for the high-pressure H2 production from formic acid.Limited activity: The position-dependent role of the hydroxyl groups at the bipyridine ligand of Ir complexes for the catalytic performance in the decomposition of formic acid is presented. The ortho-hydroxyl ligand enhanced the catalytic activity of the iridium complex, however, it decreased the catalytic durability compared to the complex with a para-hydroxyl ligand. H2 is involved in the catalytic deactivation of the complex (see figure).
      PubDate: 2017-11-22T03:54:26.517979-05:
      DOI: 10.1002/chem.201703766
       
  • Nanosegregated Chiral Materials with Self-Assembled Hierarchical
           Mesophases: Effect of Thermotropic and Photoinduced Polymorphism in
           Rodlike Molecules
    • Authors: Sung-Wook Jeon; Dae-Yoon Kim, Fumito Araoka, Kwang-Un Jeong, Suk-Won Choi
      Pages: 17794 - 17799
      Abstract: Supramolecular chirality in a binary mixture of achiral bent-core (BC) and achiral rodlike mesogens was observed. Three different nanosegregated mesophases were determined in the binary system, and meaningful changes in circular dichroism (CD) were detected near the phase-transition temperatures of the rodlike mesogens. The highest CD intensity in the binary system was noted in the nanosegregated mesophase, in which the BC mesogens were in the helical nanofilament (HNF) phase and the rodlike mesogens were in the smectic A phase. The supramolecular chirality in the binary mixture was attributed to the self-assembled hierarchical chiral superstructures. Based on the experimental results, plausible scenarios for the chiral superstructures of the rodlike molecules embedded in the HNF networks are suggested. In addition, a system comprising BC and rodlike molecules doped with a photoresponsive compound exhibited remarkable photoswitching of CD intensity. According to the isothermal photoinduced phase transition of the embedded molecules in BC molecular HNFs, the observed CD intensities can be dynamically and reversibly modulated. Such a material with easily controllable functionality is of considerable interest in the field of materials science.Going through a phase: A binary mixture of achiral bent-core and rodlike mesogens shows chiroptical responses. Three nanosegregated phases that are closely dependent on the thermotropic polymorphism of the blended rodlike mesogens are observed (see figure), and a plausible scenario is proposed for the chiral superstructures of the rodlike molecules embedded in the helical nanofilament networks in the binary system.
      PubDate: 2017-11-22T03:45:33.106741-05:
      DOI: 10.1002/chem.201703778
       
  • Copper-Catalysed Aminoboration of Vinylarenes with Hydroxylamine
           Esters—A Computational Mechanistic Study
    • Authors: Sven Tobisch
      Pages: 17800 - 17809
      Abstract: An in-depth computational probe of the copper-mediated formal aminoboration of β-alkylstyrenes with bis(pinacolato)diboron B2pin2 and an archetype hydroxylamine ester by a dppbz-ligated {P^P}CuI boryl catalyst (dppbz≡{P^P}≡1,2-bis(diphenylphosphino)benzene) is presented. This first comprehensive computational study of the copper-mediated formal aminoboration utilising an electrophilic strategy has identified the most accessible pathway for productive catalysis. The mechanistic picture derived from smooth energy profiles acquired by employing a reliable computational protocol applied to a realistic catalyst model conforms to all available experimental data. The high degree of regio- and stereoselectivity achieved in syn-borylcupration and Umpolung electrophilic amination is instrumental to the exclusive generation of the (syn)-β-aminoalkylborane product. On the one hand, syn-borylcupration furnishes exclusively β-borylalkylcopper nucleophile upon boryl addition onto the vinylarene β-carbon. Its subsequent approach by the hydroxylamine electrophile to deliver the product with the release of {P^P}CuI benzoate favours a stepwise stereoretentive SN2-type oxidative addition/N−C bond-forming reductive elimination sequence. The copper benzoate species represents the catalyst resting state, and its transformation into the catalytically active borylcopper species upon salt metathesis with Li(OtBu) base and transmetallation with B2pin2 is turnover limiting. Electronically modified β-alkylstyrenes featuring a para-CF3 substituted phenyl ring render the borylcupration faster, and more electron-rich hydroxylamine agents decelerate the electrophilic amination.Computational exploration of the Cu(Bpin)-mediated formal aminoboration of vinylarenes with hydroxylamine esters delineates the precise details of the operative mechanism, and unveils structure-performance relationships.
      PubDate: 2017-11-20T07:55:32.773803-05:
      DOI: 10.1002/chem.201703803
       
  • Near-Infrared-Absorbing Organometallic Diruthenium Complex Intermediates:
           Evidence for Bridging Anthrasemiquinone Formation and against Mixed
           Valency
    • Authors: Thangavel Sathiya Kamatchi; Sudipta Mondal, Thomas Scherer, Martina Bubrin, Karuppannan Natarajan, Wolfgang Kaim
      Pages: 17810 - 17816
      Abstract: The new redox-active complexes [RuH(CO)(EPh3)2(μ-Q2−)RuH(CO)(EPh3)2], E=P (1) and E=As (2) with the bis-chelate bridging ligand Q2−=1,4-dioxido-9,10-anthraquinone were prepared and characterised. The related compound [RuCl(CO)(PPh3)2(μ-Qx2−)RuCl(CO)(PPh3)2] (4) with E=P and Qx2−=5,8-dioxido-1,4-naphthoquinone 4 revealed trans-positioned PPh3 groups. The electrogenerated one-electron oxidised states 1+ and 2+ were examined using spectroelectrochemical techniques (EPR, IR and UV/Vis/NIR). In situ EPR studies gave spectra with 31P or 75As hyperfine splitting of about 16 Gauss, small 99, 101Ru coupling and small g-anisotropy in the frozen solution state. The 31P and 75As hyperfine values reflect axial positioning of the four Ru−E bonds relative to the plane of an anthrasemiquinone bridge. Single CO stretching bands around 1910 cm−1 of the precursors 1 and 2 shift by about 25 cm−1 to higher energies on oxidation. The direction, uniformity and the extent of the shifts confirm ligand bridge-based oxidation. Absorbance by the cations in the near infrared region is thus assigned to intra-ligand transitions of ruthenium(II)-bonded anthrasemiquinones and not to intervalence charge transfer of mixed-valent species. Ruthenium(II) stabilisation by CO and EPh3 is made responsible for the anthrasemiquinone formation instead of metal-centered oxidation.Stable with bulk: Carbonyl ligands and triphenylphosphane or -arsane stabilise the hydridoruthenium(II) states in dinuclear complexes, leaving the 1,4-dioxido-9,10-anthraquinone bridge as the site of electron transfer, which is shown using EPR, UV/Vis and IR spectroelectrochemistry.
      PubDate: 2017-11-20T07:56:19.220318-05:
      DOI: 10.1002/chem.201703888
       
  • K-Region-Extended [c]-Heteroannulated Pyrenes
    • Authors: Kevin Baumgärtner; Tobias Kirschbaum, Fabian Krutzek, Andreas Dreuw, Frank Rominger, Michael Mastalerz
      Pages: 17817 - 17822
      Abstract: Extended fused aromatic compounds are promising materials for organic electronics. Among them, structures with five-membered annulated rings differ from those consisting only of six-membered carbocyclic rings. To date, fusion of five-membered rings has been realized mainly via the [b]-edge, and systems fused via the [c]-edge are of low stability. Whereas linearly double [b]-fused systems are stable, analogous [c]-fused systems have not been described to date. Comparable to the stabilization of longer acenes by peri-fusion, herein the synthesis of doubly [c]-annulated systems stabilized by double peri-fusion is described. The compounds were analyzed by X-ray crystallography, photophysical methods, and DFT calculations to gain deeper insight into the nature of conjugation in these new systems.[c]-Annulation stabilized by Clar's sextets: Pyrene-based extended π-systems with [c]-annulated five-membered heterocycles (see figure) have been synthesized and studied by X-ray structure analysis as well as photophysical investigations, which revealed significant stabilization by benzenoid substructures.
      PubDate: 2017-11-16T08:36:20.610651-05:
      DOI: 10.1002/chem.201703988
       
  • Nitrite-Enhanced Charge Transfer to and from Single Polyaniline Nanotubes
    • Authors: Jianyun Liu; Xiuting Li, Christopher Batchelor-McAuley, Guodong Zhu, Richard G. Compton
      Pages: 17823 - 17828
      Abstract: As Liu et al. reported previously (Appl. Mater. Today 2017, 7, 239–245), the charge transfer to partially oxidized polyaniline (PANI) nanotubes in electrochemical reactions is heavily limited due to the non-conductivity of the reduction/oxidation products. In this paper, the doping level of individual PANI nanotubes was substantially enhanced using nitrite as an electron acceptor in sulfuric acid aqueous solution as recorded by the nano-impact method. The charge transferred to one single tube during reduction process is close to the theoretical value of 170±112 pC per tube (assuming 2-electron reduction for the PANI tubes studied), while the charge during PANI oxidation is dramatically decreased. Reaction processes are proposed based on the oxidative properties of nitrite in acid solution. UV–visible spectroscopy analysis further confirms an oxidation–reduction reaction between PANI and nitrite. In contrast the electrochemical reaction of ensembles (21 μg cm−1) of PANI tubes on glassy carbon electrodes simply show limited electrocatalytic activity.The doping level of individual polyaniline (PANI) nanotubes was substantially enhanced by using nitrite as an electron acceptor in sulfuric acid aqueous solution as recorded by the nano-impact method.
      PubDate: 2017-11-16T08:11:27.543835-05:
      DOI: 10.1002/chem.201704055
       
  • Acenequinocumulenes: Lateral and Vertical π-Extended Analogues of
           Tetracyanoquinodimethane (TCNQ)
    • Authors: Marco Gruber; Kevin Padberg, Jie Min, Andreas R. Waterloo, Frank Hampel, Harald Maid, Tayebeh Ameri, Christoph J. Brabec, Rik R. Tykwinski
      Pages: 17829 - 17835
      Abstract: We have designed a series of molecules and developed synthetic methodology that allows for the inclusion of structural diversity along both the lateral and vertical axes of the basic TCNQ skeleton. In the lateral direction, benzoannulation extends the π-system through (hetero)acene formation, whereas incorporation of a [3]cumulene increases delocalization vertically. The potential of these new molecules as semiconductors is explored through UV/Vis spectroscopy, cyclic voltammetry, X-ray crystallography, thin-film formation, and mobility measurements (using space charge limited current measurements).Wings of a butterfly: New synthetic methodology extends the basic skeleton of tetracyanoquinodimethane (TCNQ) along both the lateral and vertical axes, through benzoannulation and incorporation of a [3]cumulene, respectively. Terminal functionalization of the cumulenic core allows attachment of electron donor and acceptor functional groups.
      PubDate: 2017-11-20T07:56:58.792189-05:
      DOI: 10.1002/chem.201704314
       
 
 
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