Journal Cover Chemistry - A European Journal
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   ISSN (Print) 0947-6539 - ISSN (Online) 1521-3765
   Published by John Wiley and Sons Homepage  [1592 journals]
  • Synthesis and Reactivity of Donor-Stabilized
           Bis(pentafluoroethyl)stannylene [Sn(C2F5)2(D)n] (D=THF, DMAP, PMe3,
           [Sn(C2F5)3]−)
    • Authors: Johannes Klösener; Markus Wiesemann, Mark Niemann, Beate Neumann, Hans-Georg Stammler, Berthold Hoge
      Abstract: In this contribution we report on the synthesis of bis(pentafluoroethyl)stannane, H2Sn(C2F5)2. In the reaction with donor molecules a ready elimination of hydrogen and the formation of the corresponding donor-stabilized monomeric bis(pentafluoroethyl)stannylene, Sn(C2F5)2, becomes apparent. With dependence on the Lewis basicity and steric demand of the donor, varying coordination numbers are realized. Whereas the reaction with nitrogen bases like 4-(dimethylamino)pyridine (DMAP) leads to the complexation of two donor molecules, [Sn(C2F5)2(dmap)2], treatment with PMe3 or [Sn(C2F5)3]− furnished the corresponding neutral or anionic monoadducts, [Sn(C2F5)2(D)] (D=PMe3, [Sn(C2F5)3]−). In contrast, the utilization of sterically demanding donors, such as iPr2O, as well as the thermal treatment of ether complexes, [Sn(C2F5)2(D)n] (D=Et2O, THF), leads to the formation of oligomeric and cyclic stannylene moieties [Sn(C2F5)2]n. The reactivity of H2Sn(C2F5)2 and the donor-stabilized stannylenes was proven by hydrostannylation and complexation reactions with tetracarbonylnickel and bimetallic compounds. In the latter case, a donor-dependent stannylene or distannylene insertion into the metal–metal bond was observed.Sn(C2F5)2 exists in the complexed monomeric form [Sn(C2F5)2(D)n] (D=THF, 4-(dimethylamino)pyridine (DMAP), PMe3, [Sn(C2F5)3]−), whereas under donor-free conditions the formation of oligomeric and cyclic stannylenes becomes apparent. In reactions with bimetallic compounds, a donor-dependent stannylene or distannylene insertion into metal–metal bonds is observed (see scheme).
      PubDate: 2018-02-23T06:06:15.865704-05:
      DOI: 10.1002/chem.201705770
       
  • N−C Axially Chiral Anilines: Electronic Effect on Barrier to Rotation
           and A Remote Proton Brake
    • Authors: Yumiko Iwasaki; Ryuichi Morisawa, Satoshi Yokojima, Hiroshi Hasegawa, Christian Roussel, Nicolas Vanthuyne, Elsa Caytan, Osamu Kitagawa
      Abstract: N-Aryl-N-methyl-2-tert-butyl-6-methylaniline derivatives exhibit a rotationally stable N−C axially chiral structure and the rotational barriers around an N−C chiral axis increased with the increase in electron-withdrawing character of para-substituent on the aryl group. X-ray crystal structural analysis and the DFT calculation suggested that the considerable change of the rotational barriers by the electron effect of para-substituents is due to the disappearance of resonance stabilization energy caused by the twisting of para-substituted phenyl group in the transition state. This structural property of the N−C axially chiral anilines was employed to reveal a new acid-decelerated molecular rotor caused by the protonation at the remote position (remote proton brake).The barrier of N−C bond rotation in axially chiral N-(para-substituted phenyl)aniline derivatives was considerably influenced by the electronic effect of a remote para-substituent. This structural property was applied to a new acid-decelerated molecular rotor caused by the protonation at the remote position (remote proton brake).
      PubDate: 2018-02-23T05:21:06.340569-05:
      DOI: 10.1002/chem.201706115
       
  • Complexes of Stiboranium Mono-, Di-, and Trications
    • Authors: Christopher Frazee; Neil Burford, Robert McDonald, Michael J. Ferguson, Andreas Decken, Brian O. Patrick
      Abstract: Reaction of Ph2SbCl3 with 2,2′-bipyridine and Me3SiOSO2CF3 releases chlorobenzene, which is interpreted as a reductive (SbV/SbIII) elimination from a complex of a stiboranium cation. Conversely, reactions of Ph2SbCl3 with 4-methylpyridine-N-oxide and AgOSO2CF3 give redox-resistant complexes with the generic formulae [Ph2SbCl3−xLx+1][OTf]x, including a compound containing a pnictogen(V) trication.Diverse redox chemistry: A series of SbV complexes with the generic formula [Ph2SbCl3−xLx+1][OTf]x (L=OPyrMe) has been prepared by chloride-ion abstraction in the presence of a ligand and characterized, including the first structural characterization of a PnV trication.
      PubDate: 2018-02-23T05:20:40.14839-05:0
      DOI: 10.1002/chem.201800196
       
  • Understanding the Unexpected Product Distribution in the Aerial Oxidation
           of Carbene-Stabilized Diphosphorus Complex
    • Authors: Boyli Ghosh; Ambar Banerjee, Ankan Paul
      Abstract: Oxidation of nonmetallic singlet molecules by oxygen has its own share of intricacies. Herein, by means of DFT and ab initio techniques, mechanistic details of the aerial oxidation of an N-heterocyclic carbene (NHC) stabilized diphosphorus complex are revealed. This particular oxidation process is known to produce an unexpected P−P bond containing diphosphorus tetroxide complex, instead of the more thermodynamically stable oxo-bridged (P−O−P) compound. These findings suggest that the P−P bond containing less stabilized species is a kinetically controlled product (KCP) and obtained due to the presence of lower lying transition states (TSs) in the pathway leading to its formation, relative to the higher lying corresponding minimum-energy crossing points (MECPs) present in the pathway involved in the formation of the oxo-bridged species, which is the thermodynamically controlled product (TCP). Thus, an intriguing variant of the well-known KCP/TCP phenomenon is presented here, in which the KCP is formed not by merely traditionally known lower barrier heights of TSs involved in the formation of KCP, but by faster transmission of a system through a low barrier TS relative to a higher lying MECP. Additionally, the faster kinetics of an irreversible unimolecular O−O dissociation step, which avoids the formation of the TCP is a contributing factor in dictating the fate of the reaction. The insights provided herein may help to understand the oxidation of other P−P-containing species, such as black phosphorene.Kinetics versus thermodynamics: A mechanistic investigation into the production of an unusual phosphorus oxide containing a P−P bond reveals interesting involvement of the kinetically controlled product (KCP)/thermodynamically controlled product (TCP) phenomenon (see figure). KCP–TCP is controlled by the rate of transfer of a system through a minimum-energy crossing point (MECP) or transition state (TS), unlike the traditionally known case in which barriers of two TSs are compared.
      PubDate: 2018-02-23T05:16:13.340954-05:
      DOI: 10.1002/chem.201705496
       
  • Spacer Length-Independent Shuttling of the Pillar[5]arene Ring in Neutral
           [2]Rotaxanes
    • Authors: Tomoki Ogoshi; Daisuke Kotera, Shungo Nishida, Takahiro Kakuta, Tada-aki Yamagishi, Albert M Brouwer
      Abstract: For a series of neutral [2]rotaxanes consisting of a pillar[5]arene ring and axles possessing two stations separated by flexible spacers of different lengths, the free energies of activation for the ring shuttling between the stations are found to be independent of the spacer length. The constitution of the spacer affects the activation energies: replacement of CH2 groups by repulsive oxygen atoms in the axle increases the barrier. The explanation for the observed length-independence lies in the presence of a barrier for re-forming the stable co-conformation, which makes the ring travel back and forth along the thread in an intermediate state.
      PubDate: 2018-02-23T01:00:46.610292-05:
      DOI: 10.1002/chem.201800104
       
  • High-Nuclearity Heterometallic tert-Butylethynide Clusters Assembled with
           tert-Butylphosphonate
    • Authors: Yun-Peng Xie; Guang-Xiong Duan, Jun-Ling Jin, Li-Piao Bao, Xing Lu, Thomas C. W. Mak
      Abstract: Tertiarybutyl phosphonic acid and lanthanide precursor have been employed to construct two high-nuclearity hybrid silver(I)-ytterbium(III) phosphonate clusters: compound 1 consists of a Ag16 ethynide cluster fused with a trinuclear hydroxo-ytterbium phosphonate cluster, while compound 2 is composed of two Ag16 ethynide clusters bridged by a hexanuclear oxo/hydroxo-ytterbium phosphonate cluster. Using transition metal-substituted lacunary polyoxotungstates in place of the lanthanide reactant, new phosphonate-functionalized silver(I)-copper(II) ethynide clusters (Ag34Cu6 3 and Ag37Cu6 4) and silver(I) ethynide clusters (Ag51 5 and Ag72 6) were obtained. The structures of complexes 3-6 feature core-shell arrangements, in which silver(I)-copper(II) or silver(I) ethynide cluster shells stabilized by peripheral phosphonate ligands enclose different kinds of tungstate core templates.
      PubDate: 2018-02-22T23:25:31.158271-05:
      DOI: 10.1002/chem.201705906
       
  • Recent Advances in the Synthesis of β-Functionalized Ketones via
           Radical-Mediated 1,2-Rearrangement of Allylic Alcohols
    • Authors: Wei-Zhi Weng; Bo Zhang
      Abstract: β-Functionalized ketones are a highly important and valuable class of compounds, which have gained increasing attention from organic chemists due to their intensive uses as versatile synthetic intermediates and building blocks in complex molecule assembly and natural product synthesis. Accordingly, there is continuing interest in the development of new approaches for the synthesis of β-functionalized ketones. In recent years, radical-mediated 1,2-rearrangement reactions of allylic alcohols, which proceed through cationic (semipinacol) rearrangements or radical (neophyl) rearrangements, have presented an attractive and powerful strategy to access various diversely β-functionalized ketones. Interestingly, this strategy allows directly installing a variety of valuable functional groups into the β-position of cyclic and acyclic ketones by employing different radical precursors. However, a review focusing on the preparation of β-functionalized ketones via radical-mediated 1,2-rearrangement reactions of allylic alcohols has not been summarized to date. This Minireview highlights recent progress made in this highly active and interesting research area, and the corresponding mechanism will be discussed.
      PubDate: 2018-02-22T22:00:38.23264-05:0
      DOI: 10.1002/chem.201800004
       
  • Direct Integration of Red-NIR Emissive Ceramic-like AnM6Xi8Xa6 Metal
           Cluster Salts in Organic Copolymers Using Supramolecular Interactions
    • Authors: Yann Molard; Malo Robin, Noée Dumait, Maria Amela-Cortes, Claire Roiland, Maxime Harnois, Emmanuel Jacques, Hervé Folliot
      Abstract: Hybrid nanomaterials made of inorganic nanocomponents dispersed in an organic host raise an increasing interest as low-cost solution-processable functional materials. However, preventing phase segregation while allowing a high inorganic doping content remains a major challenge, and usual methods require a functionalization step prior integration. Herein, we report a new approach to design such nanocomposite in which lead-free and cadmium-free ceramic-like metallic nanocluster compounds are embedded at 10 wt % in organic copolymers, without any functionalization. Homogeneity and physical stability are ensured by weak interactions occurring between the copolymer lateral chains and the nanocluster compound. Photophysical studies show that the intrinsic properties of the native cluster (absolute quantum yield of around 0.5, phosphorescence lifetime) are fully retained in the nanocomposite. Hybrids could be ink-jet printed and casted on a blue LED. The proof-of-concept device emits in the Red-NIR area and generates singlet oxygen, of particular interest for lightings, display, sensors or photodynamic based therapy applications.
      PubDate: 2018-02-22T15:55:24.671024-05:
      DOI: 10.1002/chem.201800860
       
  • Role of the open-shell character in the pressure-induced conductivity in
           an organic radical D-A dyad
    • Authors: Jaume Veciana; Manuel Souto, Maria Chiara Gullo, Hengbo Cui, Nicola Casati, Fabio Montisci, Harald O. Jeschke, Roser Valentí, Imma Ratera, Concepció Rovira
      Abstract: Single-component conductors based on neutral organic radicals have received a lot of attention due to the possibility that the unpaired electron can serve as a charge carrier without the need of a previous doping process. Although most of these systems are based on delocalised planar radicals, we present here a nonplanar and spin localised radical based on a tetrathiafulvalene (TTF) moiety, linked to a perchlorotriphenylmethyl (PTM) radical by a conjugated brige, which exhibits a semiconducting behavior upon application of high pressure. The synthesis, electronic properties and crystal structure of this neutral radical TTF-Ph-PTM derivative (1) are reported and implications of its crystalline structure on its electrical properties dicussed. On the other hand, the non-radical derivative TTF-Ph-PTM-H (2), which is isostructural with the radical 1, shows an insulating behavior at all measured pressures. The different electronic structures of these two isostructural systems have a direct influence on the conducting properties as demonstrated by band structure DFT calculations.
      PubDate: 2018-02-22T13:25:28.703372-05:
      DOI: 10.1002/chem.201800881
       
  • Styrene polymerization under ambient conditions using a transient
           1,3,2-diazaphospholane-2-oxyl complex
    • Authors: Rainer Streubel; Tobias Heurich, Zheng-Wang Qu, Robert Kunzmann, Gregor Schnakenburg, Zenada Nožinović, Marianne Engeser
      Abstract: A combined theoretical and experimental study on the formation and reactivity of a P-OTEMP substituted 1,3,2-diazaphospholane W(CO)5 complex is presented including DFT-based mechanistic details. The complex possesses a thermally labile O-N bond that cleaves homolytically yielding the transient 1,3,2-diazaphospholane-2-oxyl complex [(CO)5W(R2PO*)] acting as radical initiator for the styrene polymerization under ambient conditions.
      PubDate: 2018-02-22T13:25:23.135732-05:
      DOI: 10.1002/chem.201800413
       
  • Polycarboxyl decorated Fe(III) based xerogel derived multifunctional
           efficient electrode material for oxygen reduction reaction and
           supercapacitor application
    • Authors: Bandhana Devi; M Venkateswarulu, Himmat Kushwaha, Aditi Halder, Rik Koner
      Abstract: Low cost, non-noble metal catalyst with good oxygen reduction reaction (ORR) activity comparable to that of platinum and having good energy storage properties is highly desirable but challenging. Several challenges are associated with the development of such materials. Herein, we demonstrate a new polycarboxyl functionalized Fe (III) based gel material, synthesized following solvothermal method and the development of its composite (Fe3O4/Fe/C) by annealing at optimised temperature. The developed composite displayed excellent electrocatalytic activity for oxygen reduction reaction (ORR) with onset potential of 0.87 V (vs. RHE) and diffusion limited current density value -5.5 mA/cm2 which are comparable with commercial 20 wt% Pt/C. In addition, as one of the most desirable properties, the composite exhibits better methanol tolerance and more durability than Pt/C. The same material was explored as an energy storage material for supercapacitors which showed specific capacitance of 245 F/g at current density of 1 A/g with a remarkably high energy density of 49 W h/kg. It is expected that this Fe3O4/Fe composite with disordered graphitized carbon matrix will pave a horizon for developing energy conversion and energy storage devices.
      PubDate: 2018-02-22T12:55:27.451702-05:
      DOI: 10.1002/chem.201705232
       
  • Elucidating the Nature of the Excited State of a Heteroleptic Copper
           Photosensitizer Using Time-Resolved X-ray Absorption Spectroscopy
    • Authors: Dooshaye Moonshiram; Pablo Garrido-Barros, Carolina Gimbert-Suriñach, Antonio Picon, Cunming Liu, Xiaoyi Zhang, Michael Karnahl, Antoni Llobet
      Abstract: We report the light-induced electronic and geometric changes taking place within a heteroleptic Cu(I) photosensitizer, namely [(xant)Cu(Me2phenPh2)]PF6 (xant = xantphos, Me2phenPh2 = bathocuproine), by time-resolved X-ray absorption spectroscopy in the ps-µs time-regime. Time-resolved X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis enabled the elucidation of the electronic and structural configuration of the copper centre in the excited state as well as its decay dynamics in different solvent conditions with and without triethylamine acting as a sacrificial electron donor. A three-fold decrease in the decay lifetime of the excited state is observed in the presence of triethylamine showing the feasibility of the reductive quenching pathway in the latter case. A prominent pre-edge feature is observed in the XANES spectrum of the excited state upon metal to charge ligand transfer transition showing an increased hybridization of the 3d states with the ligand p orbitals in the tetrahedron around the Cu centre. EXAFS and Density Functional Theory illustrate a significant shortening of the Cu-N and an elongation of the Cu-P bonds together with a decrease in the torsional angle between the xantphos and bathocruproine ligand. This study provides mechanistic time-resolved understanding for the development of improved heteroleptic Cu(I) photosensitizers, which can be used for the light-driven production of hydrogen from water.
      PubDate: 2018-02-22T12:55:23.557687-05:
      DOI: 10.1002/chem.201800330
       
  • Magnetic reduced graphene oxide/nickel/platinum nanoparticles micromotors
           for mycotoxin analysis
    • Authors: Águeda Molinero-Fernández; Adrián Jodra, María Moreno-Guzmán, Miguel Ángel López, Alberto Escarpa
      Abstract: In this work, magnetic reduced graphene oxide/nickel/ platinum nanoparticles micromotors (rGO/Ni/PtNPs) for mycotoxin analysis in food samples are proposed as relevant example in food safety diagnosis. While the utilization of self-propelled micromotors in bioassays has led to a fundamentally new approach, mainly due to the greatly target-receptor contacts enhancements by their continuous movement around the sample and the mixing associated effect, here, the magnetic properties of rGO/Ni/PtNPs micromotors for mycotoxin analysis are additionally explored. The micromotor-based strategy for target mycotoxins biosensing was focused on the accurate control in the micromotor-based properties operations: (i) on-the-move catching of free aptamers exploiting the adsorption (outer rGO layer) and catalytic (inner PtNPs layer) properties and, (ii) micromotor "stopped flow" in just 2 min. exploiting the magnetic properties (intermediate Ni layer). This strategy allowed Fumonisin B1 (FB1) determination with high sensitivity (LOD=0.70 ng mL−1) and excellent accuracy (Er = 0.05% in certified reference material and quantitative recoveries 104 ± 4% in beer) even in presence of concurrent Ochratoxin A (OTA) (105-108 ± 8% in wines). These excellent results confirm the developed approach as an innovative and reliable analytical tool for food safety monitoring, confirming the role of micromotors as new paradigm in analytical chemistry.
      PubDate: 2018-02-22T11:25:53.866407-05:
      DOI: 10.1002/chem.201706095
       
  • Mechanisms in Iodine Catalysis
    • Authors: Martin Breugst; Daniel von der Heiden
      Abstract: Molecular iodine has been used for more than 100 years as a remarkable catalyst for many organic transformations such as cycloadditions, Michael and aldol reactions, or esterifications. Different explanations for the origin of its catalytic effect have been proposed in the last decades including a "hidden" Brønsted-acid catalysis by HI, a Lewis-acid (or halogen-bond) activation, or catalysis by an iodonium (I) species. Recently, iodine catalysis again gained more interest due to the latest developments in halogen-bond catalysis. In this MiniReview, we first summarize the experimental basis for the proposed modes of activation. Subsequently, we analyze typical iodine-catalyzed reactions to gain more insights into the underlying reaction mechanisms.
      PubDate: 2018-02-22T08:26:16.903918-05:
      DOI: 10.1002/chem.201706136
       
  • Reaction Pathway Dependence in Plasmonic Catalysis: Hydrogenation as a
           Model Molecular Transformation
    • Authors: Eduardo C. M. Barbosa; Jhonatan L. Fiorio, Tong Mou, Bin Wang, Liane M. Rossi, Pedro H. C. Camargo
      Abstract: The localized surface plasmon resonance (LSPR) excitation in plasmonic nanoparticles can enhance or mediate chemical transformations. Increased reaction rates for several reactions have been reported due to this phenomenon; however, the fundamental understanding of mechanisms and factors that affect activities remains limited. Here, by investigating hydrogenation reactions as a model transformation and employing different reducing agents, H2 and NaBH4, which led to different hydrogenation reaction pathways, we observed that plasmonic excitation of Au nanoparticle catalysts can lead to negative effects over the activities. The underlying physical reason was explored using density functional theory calculations. We observed that positive versus negative effects on the plasmonic catalytic activity is reaction-pathway dependent. These results shed important insights on our current understanding of plasmonic catalysis, demonstrating reaction pathways must be taken into account for the design of plasmonic nanocatalysts.Lighting the way: By employing hydrogenation as a model transformation, the activity in plasmonic catalysis displayed reaction-pathway-dependent behavior. Both positive (catalytic enhancement) and negative (reaction rate suppression) effects could be detected under visible-light illumination in Au/TiO2 and Au/SiO2 catalysts. The underlying physical principles were explored using density functional theory, which shed important insights on plasmonic catalysis.
      PubDate: 2018-02-22T07:01:18.933716-05:
      DOI: 10.1002/chem.201705749
       
  • Secondary Metabolites from Escovopsis weberi and Their Role in Attacking
           the Garden Fungus of Leaf-Cutting Ants
    • Authors: Basanta Dhodary; Michele Schilg, Rainer Wirth, Dieter Spiteller
      Abstract: The specialized, fungal pathogen Escovopsis weberi threatens the mutualistic symbiosis between leaf-cutting ants and their garden fungus (Leucoagaricus gongylophorus). Because E. weberi can overwhelm L. gongylophorus without direct contact, it was suspected to secrete toxins. Using NMR and mass spectrometry, we identified several secondary metabolites produced by E. weberi. E. weberi produces five shearinine-type indole triterpenoids including two novel derivatives, shearinine L and shearinine M, as well as the polyketides, emodin and cycloarthropsone. Cycloarthropsone and emodin strongly inhibited the growth of the garden fungus L. gongylophorous at 0.8 and 0.7 μmol, respectively. Emodin was also active against Streptomyces microbial symbionts (0.3 μmol) of leaf-cutting ants. Shearinine L instead did not affect the growth of L. gongylophorus in agar diffusion assays. However, in dual choice behavioral assays Acromyrmex octospinosus ants clearly avoided substrate treated with shearinine L for the garden fungus after a 2 d learning period, indicating that the ants quickly learn to avoid shearinine L.Against ants and symbionts: The pathogen Escovopsis weberi produces a variety of compounds, such as shearinines, cycloarthropsone and emodin, to both overwhelm the garden fungus and to interfere with the defense of leaf-cutting ants and their mutualistic Actinomyces symbionts.
      PubDate: 2018-02-22T07:01:08.563573-05:
      DOI: 10.1002/chem.201706071
       
  • Anisotropic Colloids: from Non-Templated Synthesis to Patchy Templated
           Synthesis
    • Authors: Bing Liu; Yuanyuan Wu, Shuping Zhao
      Abstract: Self-assembly of colloidal particles is an important and challenging way to generate novel colloidal superstructures for new materials. Recent progress on syntheses of anisotropic colloids highlights opportunities for such self-assembly, particularly in defining new non-cubic superstructures. Both non-templated synthesis and templated synthesis have played an important role in preparing anisotropic colloidal particles. In this article, we briefly summarize recent progresses in anisotropic colloids by non-templated synthesis and conventional templated synthesis, and introduce a conceptual strategy of "patchy templated synthesis" that differs from the former. We illustrate this strategy with recent example emanating from colloidal rings, and discuss the future opportunities with this strategy for the synthesis of anisotropic colloids.
      PubDate: 2018-02-22T06:26:14.084779-05:
      DOI: 10.1002/chem.201705960
       
  • Bi5+, Bi(3-x)+, and oxygen vacancy induced BiOClxI1-x solid solution
           toward promoting visible-light driven photocatalytic activity
    • Authors: Guoqiang Zhang; Lei Cai, yanfeng zhang, Yu Wei
      Abstract: BiOClxI1-x solid solutions with different bandgaps were synthesized by adjusting the initial Cl to I molar ratios via chemical precipitation method at room temperature. The structures, morphologies, and optical properties of the samples were characterized by XRD, XPS, Raman, SEM, TEM, and UV-vis, respectively. The photocatalytic experiments showed that the BiOCl0.9I0.1 sample totally decomposed a large concentration of 50 mg L-1 aqueous Rhodamine B (RhB) solution within 12 minutes under the visible light irradiation (λ>420nm), which is 11 times higher than that of pure BiOI. Furthermore, the electron band structure and states density of BiOCl, BiOI and BiOClxI1-x have been investigated using the DFT (Density Functional Theory) calculation method and electrochemical method. It was found that there are some multiple crystal defects of Bi5+, Bi(3-x)+ and oxygen vacancy in the BiOClxI1-x samples. The results for Mott-Schottky plots and Valence band XPS spectra showed the position of conduction band (CB) for BiOCl0.9I0.1 was up-shift, which is favorable to the redox capacity for the photocatalysts. It could be elucidated that the synergistic effects of multiple crystal defects and unique band structure are critical to improving solar driven photocatalytic activity. This work provides a new highlight toward the construction of high property photocatalysts by tuning the crystal defect and band structure in a simple and efficient way.
      PubDate: 2018-02-22T03:25:56.285843-05:
      DOI: 10.1002/chem.201706164
       
  • New Control Over Silicone Synthesis Using SiH Chemistry: The Piers
           Rubinsztajn Reaction
    • Authors: Michael A Brook
      Abstract: There is a strong imperative to synthesize polymers with highly controlled structures and narrow property ranges. Silicone polymers do not lend themselves to this paradigm because acids or bases lead to siloxane equilibration and loss of structure. By contrast, elegant levels of control are possible when using the Piers-Rubinsztajn reaction and analogues, in which the hydrophobic, strong Lewis acid B(C6F5)3 activates SiH groups, permitting the synthesis of precise siloxanes under mild conditions in high yield; siloxane decomposition processes are slow under these conditions. A broad range of oxygen nucleophiles including alkoxysilanes, silanols, phenols, and aryl alkyl ethers participate in the reaction to create elastomers, foams and green composites, for example, derived from lignin. In addition, the process permits the synthesis of monofunctional dendrons that can be assembled into larger entities including highly branched silicones and dendrimers either using the Piers Rubinsztajn process alone, or in combination with hydrosilylation or other orthogonal reactions.
      PubDate: 2018-02-21T21:50:43.546114-05:
      DOI: 10.1002/chem.201800123
       
  • (Multi-)Metallic Cluster Growth
    • Authors: Stefanie Dehnen; Bastian Weinert, Stefan Mitzinger
      Abstract: This review article provides a survey of contemporary investigations on main group metal cluster formation, addressing homo- and heterometallic clusters (including small numbers of transition metal atoms) with or without an external ligand shell, thereby excluding clusters with non-metal atoms as bridging ligands. Most of the studies reflected herein represent insights into the formation of intermediates from the starting material, or the final cluster formation from established intermediates. In rare cases, the entire process was suggested as a result of comprehensive, multi-method elucidations. The article is to be understood as a state-of-the-art report, as the subject matter is currently a rising field of research, which is still in its infancy, despite some early activities that date back to the 1980s. At the same time, the article intends to point toward both the importance and the feasibility of according studies, in order to encourage researchers to gain even more knowledge in this field. Only deep understanding of cluster formation will allow for design and ultimately control of their syntheses, with the long-term goal of their optimization and purposeful application in catalysis or novel material synthesis.
      PubDate: 2018-02-21T14:50:25.81153-05:0
      DOI: 10.1002/chem.201704904
       
  • A variety of bond analysis methods, one answer' An investigation of
           the element-oxygen bond of hydroxides HnXOH
    • Authors: Malte Fugel; Jens Beckmann, Dylan Jayatilaka, Gerald V. Gibbs, Simon Grabowsky
      Abstract: There is a great variety of bond analysis tools which aim to extract information on the bonding situation from the molecular wavefunction. Since none of these can fully describe bonding in all of its complexity, it is necessary to regard a balanced selection of complementary analysis methods to obtain a reliable chemical conclusion. This is, however, not a feasible approach in most studies since it is a time consuming procedure. Therefore, here we provide the first comprehensive comparison of modern bonding analysis methods to reveal their informative value. The element-oxygen bond of neutral HnX-OH model compounds (X = Li, Be, B, C, N, O, F, Na, Mg, Al, Si, P, S, Cl) is investigated with a selection of different bond analysis tools which may be assigned into three different categories: (i) Real space bonding indicators (Quantum Theory of Atoms in Molecules (QTAIM), the electron localizability indicator and the Raub-Jansen index), (ii) orbital-based descriptors (natural bond orbitals (NBO), natural resonance theory (NRT) and valence bond calculations) and (iii) energy analysis tools (energy decomposition analysis and the Q-analysis). Besides gaining a deep insight into the nature of the element-oxygen bond across the periodic table, this systematic investigation allows us to get an impression on how well these tools complement each other. Ionic, highly polarized, polarized covalent and charge shift bonds are discerned from each other.
      PubDate: 2018-02-21T11:50:29.668146-05:
      DOI: 10.1002/chem.201800453
       
  • The Dynamic Equilibrium of Hexakis(pentafluoroethyl)distannane Adducts
           [XSn(C2F5)3{Sn(C2F5)3}]− (X=Cl, Br, I, Sn(C2F5)3)
    • Authors: Markus Wiesemann; Johannes Klösener, Beate Neumann, Hans-Georg Stammler, Berthold Hoge
      Abstract: The tin–tin bond cleavage of hexaorganodistannanes by nucleophiles is a long-known reaction and widely used for stannate formation or stannyl group transfer. Herein, we detail our experiments to provide analytical evidence for the existence of the reasonably stable anionic complexes [XSn(C2F5)3{Sn(C2F5)3}]− (X=Cl, Br, I, Sn(C2F5)3) derived from hexakis(pentafluoroethyl)distannane. NMR investigations at low temperature lend further mechanistic insights. Thus, by detection of the imposing ion [Sn(C2F5)3{Sn(C2F5)3}2]−, one can surmise that the chemistry of Sn2(C2F5)6 has more in common with the isolobal iodine than with classical distannanes.Isolobal relationship: The introduction of electron-withdrawing groups facilitates the NMR spectroscopic investigation of the stable complexes [XSn(C2F5)3{Sn(C2F5)3}]− (X=Cl, Br, I, Sn(C2F5)3) derived from hexakis(pentafluoroethyl)distannane. By detection of the trimeric ion [Sn(C2F5)3{Sn(C2F5)3}2]− one can surmise that the chemistry of Sn2(C2F5)6 has more in common with the isolobal iodine than with classical distannanes (see Scheme; R=C2F5).
      PubDate: 2018-02-21T09:51:34.041722-05:
      DOI: 10.1002/chem.201705069
       
  • Enhanced Li Storage Stability Induced by Locating Sn in Metal-Organic
           Frameworks
    • Authors: Na Wu; Wei Wang, Lu-Qing Kou, Xue Zhang, Ya-Ru Shi, Tao-Hai Li, Feng Li, Jin-Ming Zhou, Yu Wei
      Abstract: By locating elemental Sn in an open anionic framework, the particle cracking arising from huge volume expansion of Sn-based anode material during lithiation/delithiation is alleviated and the cycling stability is greatly improved. The Sn-based metal-organic frameworks anode material shows superior cyclic stability with a capacity retention >92% (after 200 cycles) and high lithium storage capacity (610 mAh g-1).
      PubDate: 2018-02-21T09:50:23.330572-05:
      DOI: 10.1002/chem.201800215
       
  • New Water-Soluble Cluster Compound {Zn(en)3}3[V15Sb6O42(H2O)]⋅
           (Ethylenediamine)3⋅10 H2O as a Synthon for the Generation of Two New
           Antimonato Polyoxovanadates
    • Authors: Lisa K. Mahnke; Ulrike Warzok, Mengxi Lin, Christian Näther, Christoph A. Schalley, Wolfgang Bensch
      Abstract: A new antimonato polyoxovanadate {Zn(en)3}3[V15Sb6O42(H2O)]⋅3 en⋅10 H2O (en=ethylenediamine) synthesized under hydrothermal conditions exhibits remarkable solubility in water. Electrospray ionization mass spectrometry (ESI-MS) investigations on an aqueous solution demonstrate that the cluster core remains fully intact for 72 h. At longer times, slow transformation into a {V14Sb8O42} cluster is observed. The conversion reaches 50 % after 14 days and is complete after approximately 20 days. The rate of this {V15Sb6}{V14Sb8} cluster transformation is significantly increased in the presence of ammonium acetate. Applying the new compound as a synthon in the presence of 1,10-phenanthroline (phen) led to crystallization of {Zn(phen)3}2[Zn(en)2V15Sb6O42(H2O)]⋅23 H2O after a short reaction time, whereas addition of Sb2O3 led to fast crystallization of {(Zn(en)2(H2O)2)(Zn(en)2)}[Zn(en)2V15Sb6O42(H2O)] ⋅8.5 H2O. In the crystal structure of {Zn(en)3}3 [V15Sb6O42(H2O)]⋅3 en⋅10 H2O, the en molecules are seen to be attached to the cluster anion through Sb−N bonds. In the structures of the two new compounds obtained, the [V15Sb6O42(H2O)]6− anions are expanded by Zn2+-centered complexes through Zn−O−V bond formation.Cluster synthesis in water: A new water-soluble hetero-polyoxovanadate has been prepared, with zinc complexes as charge-balancing units. Its transformation to two new {V15}-polyoxovanadates in water is reported.
      PubDate: 2018-02-21T09:38:49.968667-05:
      DOI: 10.1002/chem.201705732
       
  • Cyclodextrin-Sandwiched Hexaphyrin Hybrids: Side-to-Side Cavity Coupling
           Switched by a Temperature- and Redox-Responsive Central Device
    • Authors: Mickaël Ménand; Matthieu Sollogoub, Bernard Boitrel, Stéphane Le Gac
      Abstract: Access to allosteric enzyme mimics that ideally associate communicating compartments for catalysis and regulation is still challenging. Whereas a sandwich “cavity–catalyst–cavity” approach, developed mainly with cyclodextrins and porphyrins, appears promising, its counterpart with hexaphyrins featuring rich conformation, aromaticity, and coordination behavior has not been prospected at all. We thus developed sandwich hybrids made of two cyclodextrins triply linked on each side of a hexaphyrin. The latter displays switchable oxidation states with interconvertible conformations (28π antiaromatic and 26π aromatic, each adopting rectangular and dumbbell forms). These four states are connected by two orthogonal switches under redox [aromaticity] and thermal [shape] control. This leads to twin compartmentalized confined spaces either locked or unlocked depending on the conformation of the hexaphyrin, and the reversibility of the lockunlock transition relies on the aromaticity of the hexaphyrin. The sandwiched heteroannulene thus behaves as an unprecedented dual-responsive double-latched device. Such hybrid systems open interesting perspectives in the allosteric regulation of receptors, catalysts, and machineries.Royale with cheese: Sandwich compounds made of a hexaphyrin doubly capped by cyclodextrins are developed. The hexaphyrin behaves as a dual-responsive device, coupling the cavities with different operating modes in a switchable manner depending on its (anti)aromaticity and conformation. The accessibility of two compartmentalized-and-coupled confined spaces is locked/unlocked reversibly, opening perspectives in allosteric regulation.
      PubDate: 2018-02-21T09:38:28.845067-05:
      DOI: 10.1002/chem.201705958
       
  • Circularly Polarized Luminescence from Inorganic Materials: Encapsulating
           Guest Lanthanide Oxides in Chiral Silica Hosts
    • Authors: Masumi Sugimoto; Xin-Ling Liu, Seiji Tsunega, Erika Nakajima, Shunsuke Abe, Takuya Nakashima, Tsuyoshi Kawai, Ren-Hua Jin
      Abstract: Invited for the cover of this issue is the group of Ren-Hua Jin at the Kanagawa University and co-workers at Nara Institute of Science and Technology. The image depicts lanthanide metals encapsulated within temperature-resistant chiral silica emitting polarized light. Read the full text of the article at 10.1002/chem.201705862.“Beauty always comes from simple processes even if the target seems complex.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201705862).
      PubDate: 2018-02-21T09:25:41.061067-05:
       
  • Programming Recognition Arrays through Double Chalcogen-Bonding
           Interactions
    • Authors: Nicolas Biot; Davide Bonifazi
      Abstract: A programmed recognition motif constructed around a chalcogenazolo-pyridine scaffold (CGP) is presented. Exploiting the formation of frontal double chalcogen-bonding interactions, the CGP motif associates into dimeric EX-type complexes with the Te-congener depicting the strongest recognition persistence. The high recognition fidelity, chemical and thermal stability and easy derivatization at the 2-position makes CGP a convenient motif for constructing supramolecular architectures through programmed chalcogen-bonding interactions. More information can be found in the Communication by D. Bonifazi and N. Biot (
      DOI : 10.1002/chem.201705428).
      PubDate: 2018-02-21T09:20:49.577785-05:
       
  • Computational Study of the Aza-Michael Addition of the Flavonoid
           (+)-Taxifolin in the Inhibition of β-Amyloid Fibril Aggregation
    • Authors: Tiziana Ginex; Marta Trius, F. Javier Luque
      Abstract: Inhibition of abnormal protein self- aggregation is a promising strategy against amyloidogenic diseases, but has found limited success. New avenues for therapeutic intervention may arise from the ability of catechol-containing compounds to interfere with the aggregation process through formation of covalent adducts. The mechanism of this process was examined for the anti- aggregation activity of the oxidized form of (+)-taxifolin, a process that would involve the aza-Michael addition of the o-quinone species with Lys16 in early Aβ42 aggregates. More information can be found in the Full Paper by T. Ginex, F. J. Luque, et al. (
      DOI : 10.1002/chem.201706072).
      PubDate: 2018-02-21T09:05:30.443448-05:
       
  • Frontispiece: Photosensitization of Molecular Oxygen on Graphene Oxide for
           Ultrasensitive Signal Amplification
    • Authors: Xinfeng Zhang; Li Deng, Chengpeng Huang, Jinyi Zhang, Xiandeng Hou, Peng Wu, Juewen Liu
      Abstract: By using a photosensitizer as a molecular catalyst, chromogenic 3,3′,5,5′-tetramethylbenzidine (TMB) can be directly oxidized by oxygen with green LED irradiation, avoiding expensive and unstable peroxidase and hydrogen peroxidase. For more information on demonstrating its application for detection of cancer biomarkers, see the Full Paper by P. Wu and J. Liu et al. on page 2602 ff.
      PubDate: 2018-02-21T09:04:32.722142-05:
      DOI: 10.1002/chem.201881164
       
  • Frontispiece: Selective Single-Site Pd−In Hydrogenation Catalyst for
           Production of Enhanced Magnetic Resonance Signals using Parahydrogen
    • Authors: Dudari B. Burueva; Kirill V. Kovtunov, Andrey V. Bukhtiyarov, Danila A. Barskiy, Igor P. Prosvirin, Igor S. Mashkovsky, Galina N. Baeva, Valerii I. Bukhtiyarov, Aleksandr Yu. Stakheev, Igor V. Koptyug
      Abstract: Pd−In/Al2O3 single-site catalyst was able to show high selectivity in the gas phase semihydrogenation of propyne. When parahydrogen was used 3400-fold NMR signal enhancement for reaction product propene was observed, demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd−In catalyst allowed to acquire 1H MR images of hyperpolarized propene. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors. For more information, see the Communication by K. V. Kovtunov et al. on page 2547 ff.
      PubDate: 2018-02-21T09:04:31.813353-05:
      DOI: 10.1002/chem.201881163
       
  • Frontispiece: Chemistry of Peptidoglycan in Mycobacterium tuberculosis
           Life Cycle: An off-the-wall Balance of Synthesis and Degradation
    • Authors: Flavia Squeglia; Alessia Ruggiero, Rita Berisio
      Abstract: Between the inside of the mycobacterial cytoplasm and the periplasmic space, a complex assembly line of peptidoglycan synthesis and polymerization occurs. A fine balance of peptidoglycan synthesis and depolymerization is responsible for a plethora of molecular mechanisms, which are key to mycobacterial pathogenicity. In the process of resuscitation from dormancy, attack of the polymeric peptidoglycan by RipA and Rpf hydrolases produce free muropeptides, which act as molecular sensors of favorable living conditions for mycobacterial revival. More details are available in the Review article by Berisio et al. on page 2533 ff.
      PubDate: 2018-02-21T09:04:31.764299-05:
      DOI: 10.1002/chem.201881162
       
  • Frontispiece: Selection and Screening of DNA Aptamers for Inorganic
           Nanomaterials
    • Authors: Yibo Zhou; Zhicheng Huang, Ronghua Yang, Juewen Liu
      Abstract: Although aptamer selection has been very successful for molecular targets, this process for inorganic surfaces is complicated by strong non-specific DNA binding. Rational screening of a small group of DNA sequences is a useful alternative and poly-C DNA has been found to be a strongly binding sequence for various surfaces. For more details, see the Concept article by J. Liu et al. on page 2525 ff.
      PubDate: 2018-02-21T09:04:30.229827-05:
      DOI: 10.1002/chem.201881161
       
  • Interfacial Generation of a Carbanion: The Key Step of PTC Reaction
           Directly Observed by Second Harmonic Generation
    • Authors: Michal Hamkalo; Piotr Fita, Michal Fedorynski, Mieczyslaw Makosza
      Abstract: We present the first unambiguous evidence of the interfacial mechanism of phase-transfer catalysis (PTC) by direct observation of the formation of carbanions in the interfacial region between the aqueous and the organic phase by using a surface-sensitive spectroscopic method known as second harmonic generation (SHG). Ion exchange of carbanions adsorbed at the surface after addition of lipophilic tetraalkylammonium salts (TAA) to organic phase and transport of the lipophilic ion-pairs to the organic phase is observed. Results allow for the formulation of a more detailed mechanism of PTC.Carbanions are created only at the interface between organic and aqueous phases. A second harmonic (SH) beam is generated only by these carbanions.
      PubDate: 2018-02-21T08:56:38.058348-05:
      DOI: 10.1002/chem.201705597
       
  • Self-Assembled Cofacial Zinc–Porphyrin Supramolecular Nanocapsules as
           Tuneable 1O2 Photosensitizers
    • Authors: Cédric Colomban; Carles Fuertes-Espinosa, Sébastien Goeb, Marc Sallé, Miquel Costas, Lluís Blancafort, Xavi Ribas
      Abstract: We demonstrate the benefits of using cofacial Zn–porphyrins as structural synthons in coordination-driven self-assembled prisms to produce cage-like singlet oxygen (1O2) photosensitizers with tunable properties. In particular, we describe the photosensitizing and emission properties of palladium- and copper-based supramolecular capsules, and demonstrate that the nature of the bridging metal nodes in these discrete self-assembled prisms strongly influences 1O2 generation at the Zn–porphyrin centers. The PdII-based prism is a particularly robust photosensitizer, whereas the CuII self-assembled prism is a dormant photosensitizer that could be switched to a ON state upon disassembly of the suprastructure. Furthermore, the well-defined cavity within the prisms allowed encapsulation of pyridine-based ligands and fullerene derivatives, which led to a remarkable guest tuning of the 1O2 production.Get in tune: The benefits of using self-assembled cofacial Zn–porphyrin prisms as cage-like photosensitizers with tunable photosensitizing properties are reported (see figure).
      PubDate: 2018-02-21T08:56:34.014382-05:
      DOI: 10.1002/chem.201705531
       
  • Recent Advances in the Synthesis of Peptoid Macrocycles
    • Authors: Alexandra M. Webster; Steven L. Cobb
      Abstract: Over the past two decades, developing medical applications for peptides has, and continues to be a highly active area of research. At present there are over 60 peptide-based drugs on the market and more than 140 in various stages of clinical trials. The interest in peptide-based therapeutics arises from their biocompatibility and their ability to form defined secondary and tertiary structures, resulting in a high selectivity for complex targets. However, there are significant challenges associated with the development of peptide-based therapeutics, namely peptides are readily metabolised in vivo. Peptoids are an emerging class of peptidomimetic and they offer an alternative to peptides. Peptoids are comprised of N-substituted glycines where side-chains are located on the nitrogen atom of the amide backbone rather than the α-carbon as is the case in peptides. This change in structure confers a high degree of resistance to proteolytic degradation but the absence of any backbone hydrogen bonding means that peptoids exhibit a high degree of conformational flexibility. Cyclisation has been explored as one possible route to rigidify peptoid structures, making them more selective, and, therefore more desirable as potential therapeutics. This review outlines the various strategies that have been developed over the last decade to access new types of macrocyclic peptoids.Macrocyclic peptoids: Developing medical applications for peptides has, and continues to be a highly active area of research. However, there are significant challenges associated with the development of peptide-based therapeutics. Peptoids offer an alternative to peptides but the absence of any backbone hydrogen bonding means they exhibit a high degree of conformational flexibility. Cyclisation has been explored as one possible route to rigidify peptoid structures. This review outlines the recent strategies that have been developed to access new types of macrocyclic peptoids.
      PubDate: 2018-02-21T08:55:39.062831-05:
      DOI: 10.1002/chem.201705340
       
  • An Adverse Effect of Higher Catalyst Loading and Longer Reaction Time on
           Enantioselectivity in Organocatalytic Multicomponent Reaction
    • Authors: Ramakrishna G. Bhat; Tushar M Khopade, Trimbak B. Mete, Jyotsna S Arora
      Abstract: Enantioselective organocatalytic multicomponent reaction of aldehyde, ketone and Meldrum's acid has been developed for the first time. Cinchona based primary amine (1 mol%) catalyzes the multicomponent reaction via the formation of Knoevenagel product and chiral enamine to form enantiopure δ-keto Meldrum's acids in a tandem catalytic pathway. An adverse effect of higher catalytic loading and longer reaction time on enantioselectivity is studied. This mild protocol provides an easy access to enantiopure carboxylic acids, esters and amides and the method proved to be scalable on a gram scale. DFT calculations were carried out on the proposed reaction mechanism and they were in close agreement with the experimental results.
      PubDate: 2018-02-21T08:50:37.48304-05:0
      DOI: 10.1002/chem.201800278
       
  • The Hydrophobic Effect Applied to Organic Synthesis: Recent Synthetic
           Chemistry “in Water”
    • Authors: Bruce H. Lipshutz; Subir Ghorai, Margery Cortes-Clerget
      Abstract: Recent developments over the past few years in aqueous micellar catalysis are discussed. Applications to problems in synthesis are highlighted, enabled by the use of surfactants that self-aggregate in water into micelles as nanoreactors. These include amphiphiles that have been available for some time, as well as those that have been newly designed. Reactions catalyzed by transition metals, including Pd, Cu, Rh, and Au, are of particular focus.Micellar catalysis is providing valuable tools that enable synthetic chemistry to be performed in an aqueous medium, rather than in traditional organic solvents. This review outlines several of the advances made in just the past few years, most involving organometallics, that showcases newly designed surfactants, ligands, reagents and tandem, one-pot sequences. Taken together, these provide additional compelling evidence that organic chemistry is on the road towards becoming an environmentally responsible and sustainable discipline.
      PubDate: 2018-02-21T07:31:48.823106-05:
      DOI: 10.1002/chem.201705499
       
  • Piecing it Together: An Additivity Scheme for Aromaticity using NICS-XY
           Scans
    • Authors: Renana Gershoni-Poranne
      Abstract: Aromatic compounds are prevalent in both nature and man-made materials, yet their properties are still not fully understood and are therefore hard to predict. Herein, we introduce an additivity scheme for the prediction of the aromatic character of polycyclic aromatic hydrocarbons. Using a small set of building blocks and combination rules, we demonstrate the simple and intuitive construction of complete NICS-XY-scans for several test cases of one- and two-dimensional systems comprising six-membered rings. Partitioning the contribution of discrete building blocks provides insight into the aromatic character of these systems. The results obtained with this methodology provide a new perspective on the distribution of ring currents within polycyclic compounds and the effect of topology on the overall aromatic profile. The concept and strategy presented here are general and highly customizable. The scheme is easily applied to a wide range of interesting systems; it is especially beneficial for the investigation of large systems, as NICS-XY-scans are useful for their predictive utility with respect to optoelectronic and thermochemical properties.Piecing it together: The aromatic profiles of complex systems have been constructed from a small set of building blocks (see figure), thereby enabling rapid and simple prediction of their properties. The dissection to discrete contributions sheds light on the role of each building block and the topology of the system.
      PubDate: 2018-02-21T07:30:55.477873-05:
      DOI: 10.1002/chem.201705407
       
  • Identification of the Minimal Glycotope of Streptococcus pneumoniae 7F
           Capsular Polysaccharide using Synthetic Oligosaccharides
    • Authors: Petra Ménová; Mauro Sella, Katrin Sellrie, Claney L. Pereira, Peter H. Seeberger
      Abstract: Streptococcus pneumoniae causes life-threatening diseases including meningitis, pneumonia and sepsis. Existing glycoconjugate vaccines based on purified capsular polysaccharides are widely used and help to prevent millions of deaths every year. Herein, the total syntheses of oligosaccharides resembling portions of the S. pneumoniae serotype 7F (ST7F) capsular polysaccharide repeating unit are reported. To define minimal glycan epitopes, glycan microarrays containing the synthetic oligosaccharides were used to screen human reference serum and revealed that both side chains of the ST7F play a key role in antigen recognition. The identification of protective minimal epitopes is vital to design efficient semi- and fully-synthetic glycoconjugate vaccines.Fighting pneumonia: Synthetic oligosaccharides resembling the Streptococcus pneumoniae serotype 7F capsular polysaccharide repeating unit were printed onto glycan microarrays. Screening of human reference serum helped to define minimal epitopes where both side chains on the central glycan are essential. Identification of protective minimal epitopes is key to the design of semi- and fully-synthetic glycoconjugate vaccines.
      PubDate: 2018-02-21T07:30:45.224191-05:
      DOI: 10.1002/chem.201705379
       
  • Cp2TiX Complexes for Sustainable Catalysis in Single-Electron Steps
    • Authors: Ruben B. Richrath; Theresa Olyschläger, Sven Hildebrandt, Daniel G. Enny, Godfred D. Fianu, Robert A. Flowers, Andreas Gansäuer
      Abstract: We present a combined electrochemical, kinetic, and synthetic study with a novel and easily accessible class of titanocene catalysts for catalysis in single-electron steps. The tailoring of the electronic properties of our Cp2TiX-catalysts that are prepared in situ from readily available Cp2TiX2 is achieved by varying the anionic ligand X. Of the complexes investigated, Cp2TiOMs proved to be either equal or substantially superior to the best catalysts developed earlier. The kinetic and thermodynamic properties pertinent to catalysis have been determined. They allow a mechanistic understanding of the subtle interplay of properties required for an efficient oxidative addition and reduction. Therefore, our study highlights that efficient catalysts do not require the elaborate covalent modification of the cyclopentadienyl ligands.Modifications not necessary! With the aid of cyclic voltammetry and kinetic investigations Cp2TiX2 complexes with sulfonate ligands were identified as attractive catalysts in radical arylations and tetrahydrofuran synthesis. They do not require additives for catalyst stabilization and render the covalent modification of the cyclopentadienyl ligands superfluous for the tailoring of their performance in catalysis in single-electron steps.
      PubDate: 2018-02-21T07:26:55.433041-05:
      DOI: 10.1002/chem.201705707
       
  • Aggregation Pathways of Native-Like Ubiquitin Promoted by Single-Point
           Mutation, Metal Ion Concentration, and Dielectric Constant of the Medium
    • Authors: Simona Fermani; Matteo Calvaresi, Vincenzo Mangini, Giuseppe Falini, Andrea Bottoni, Giovanni Natile, Fabio Arnesano
      Abstract: Ubiquitin-positive protein aggregates are biomarkers of neurodegeneration, but the molecular mechanism responsible for their formation and accumulation is still unclear. Possible aggregation pathways of human ubiquitin (hUb) promoted by both intrinsic and extrinsic factors, are here investigated. By a computational analysis, two different hUb dimers are indicated as possible precursors of amyloid-like structures, but their formation is disfavored by an electrostatic repulsion involving Glu16 and other carboxylate residues present at the dimer interface. Experimental data on the E16V mutant of hUb shows that this single-point mutation, although not affecting the overall protein conformation, promotes protein aggregation. It is sufficient to shift the same mutation by only two residues (E18V) to regain the behavior of wild-type hUb. The neutralization of Glu16 negative charge by a metal ion and a decrease of the dielectric constant of the medium by addition of trifluoroethanol (TFE), also promote hUb aggregation. The outcomes of this research have important implications for the prediction of physiological parameters that favor aggregate formation.Prefibrillar ubiquitin dimers: Ubiquitin dimers, with parallel (see figure, left) or antiparallel (right) alignment of edge β-strands, are indicated as possible precursors of amyloid structures. A computational analysis, complemented with experimental data, shows that the formation of such prefibrillar dimers is disfavored by electrostatic repulsion involving Glu16 and other carboxylate residues at the dimer interface.
      PubDate: 2018-02-21T07:26:10.894536-05:
      DOI: 10.1002/chem.201705543
       
  • A Three-State System Based on Branched DNA Hybrids
    • Authors: Shiliang He; Clemens Richert
      Abstract: There is a need for materials that respond to chemical or physical stimuli through a change in their structure. While a transition between water-soluble form and solid is not uncommon for DNA-based structures, systems that transition between three different states at room temperature and ambient pressure are rare. Here we report the preparation of branched DNA hybrids with eight oligodeoxycytidylate arms via solution-phase, H-phosphonate-based synthesis. Some hybrids assemble into hydrogels upon lowering the pH, acting as efficient gelators at pH 4–6, but can also transition into a more condensed solid state form upon exposure to divalent cations. Together with the homogeneous solutions that the i-motif-forming compounds give at neutral pH, three-state systems result. Each state has its own color, if chromophores are included in the system. The assembly and gelation properties can be tuned by choosing the chain length of the arms. Their responsive properties make the dC-rich DNA hybrids candidates for smart material applications.Solutions of branched oligonucleotide hybrids form gels or solids, depending on the chemical stimulus, and the transitions can be detected optically.
      PubDate: 2018-02-21T07:26:02.870194-05:
      DOI: 10.1002/chem.201705941
       
  • Further Development of Weakly Coordinating Cations: Fluorinated
           Bis(triarylphosphoranylidene)iminium Salts
    • Authors: Lisa Mann; Elisabeth Hornberger, Simon Steinhauer, Sebastian Riedel
      Abstract: So far unknown bis(triarylphosphoranylidene)iminium cations [PPN]+ with one fluorine atom in para ([PPN-1F]+), two in meta ([PPN-2F]+), or three in para and meta positions of the phenyl rings ([PPN-3F]+) were obtained by a newly developed one-pot reaction. These halogenated [PPN]+ cations were characterized by IR and Raman spectroscopy in comparison with quantum-chemical calculations, ESI+ mass spectrometry, NMR spectroscopy, and single-crystal X-ray diffraction. To assess their quality as weakly coordinating cations and the associated ability to stabilize labile anions, the electrostatic potential and fluoride-ion affinity were calculated and compared with those of the unsubstituted and so far unknown perfluorinated [PPN-5F]+ cations.The weaker the better: Fluorinated bis(triarylphosphoranylidene)iminium cations [{(C6H4F)3P}2N]Cl, [{(C6H3F2)3P}2N]Cl, and [{(C6H2F3)3P}2N]Cl were synthesized by a new one-pot reaction and characterized (see figure). Their performance as weakly coordinating cations was assessed by quantum-chemical calculations.
      PubDate: 2018-02-21T07:21:01.180005-05:
      DOI: 10.1002/chem.201705992
       
  • One-Carbon Oxidative Annulations of 1,3-Enynes by Catalytic C−H
           Functionalization and 1,4-Rhodium(III) Migration
    • Authors: Johnathon D. Dooley; Hon Wai Lam
      Abstract: Rhodium(III)-catalyzed C−H functionalization-oxidative annulations of aromatic substrates with 1,3-enynes that contain allylic hydrogen atoms cis to the alkyne are described. The key step in these reactions is an alkenyl-to-allyl 1,4-rhodium(III) migration to give electrophilic π-allylrhodium(III) species. Nucleophilic trapping of these species gives heterocycles such as benzopyrans, isobenzofuranones, and isoindolinones.Can't wait to migrate: Rhodium(III)-catalyzed C−H functionalization–oxidative annulations of aromatic substrates with 1,3-enynes that contain allylic hydrogen atoms cis to the alkyne are described. The key step in these reactions is an alkenyl-to-allyl 1,4-rhodium(III) migration to give electrophilic π-allylrhodium(III) species, which are trapped to give benzopyrans, isobenzofuranones, and isoindolinones.
      PubDate: 2018-02-21T07:20:55.093704-05:
      DOI: 10.1002/chem.201706043
       
  • Critical Impact of Peptidoglycan Precursor Amidation on the Activity of
           l,d-Transpeptidases from Enterococcus faecium and Mycobacterium
           tuberculosis
    • Authors: Flora Ngadjeua; Emmanuelle Braud, Saidbakhrom Saidjalolov, Laura Iannazzo, Dirk Schnappinger, Sabine Ehrt, Jean-Emmanuel Hugonnet, Dominique Mengin-Lecreulx, Delphine Patin, Mélanie Ethève-Quelquejeu, Matthieu Fonvielle, Michel Arthur
      Abstract: The bacterial cell wall peptidoglycan contains unusual l- and d-amino acids assembled as branched peptides. Insight into the biosynthesis of the polymer has been hampered by limited access to substrates and to suitable polymerization assays. Here we report the full synthesis of the peptide stem of peptidoglycan precursors from two pathogenic bacteria, Enterococcus faecium and Mycobacterium tuberculosis, and the development of a sensitive post-derivatization assay for their cross-linking by l,d-transpeptidases. Access to series of stem peptides showed that amidation of free carboxyl groups is essential for optimal enzyme activity, in particular the amidation of diaminopimelate (DAP) residues for the cross-linking activity of the l,d-transpeptidase LdtMt2 from M. tuberculosis. Accordingly, construction of a conditional mutant established the essential role of AsnB indicating that this DAP amidotransferase is an attractive target for the development of anti-mycobacterial drugs.Synthetic routes to the peptide stem of peptidoglycan precursors and a sensitive fluorescent cross-linking assay were developed to assess the impact of structural variability on peptidoglycan polymerization. In the search for new targets for anti-mycobacterial drug development, this strategy was applied to the evaluation of diaminopimelate amidation in Mycobacterium tuberculosis, revealing the essential role of the AsnB amidotransferase for peptidoglycan transpeptidation both in vitro and in vivo.
      PubDate: 2018-02-21T07:20:47.860084-05:
      DOI: 10.1002/chem.201706082
       
  • Recent advances in the cycloisomerizations of methylenecyclopropanes under
           gold catalysis
    • Authors: Min Shi; Wei Fang
      Abstract: During the past decades, cycloisomerizations of methylenecyclopropanes under gold catalysis have attracted much attention from organic chemists. The different patterns of cycloisomerizations have been developed from gold(I)-catalyzed ring-opening and ring-expansion of methylenecyclopropanes. This synthetic methodology provides a new approach to novel cyclic- or polycyclic compounds and even polycyclic aromatic hydrocarbons, organic light emitting materials and biologically active substances. The corresponding products have great potential for material science, medicinal chemistry and total synthesis. This Concept article will mainly focus on the recent advances in the cycloisomerizations of methylenecyclopropanes in the past four year
      PubDate: 2018-02-21T07:20:41.265498-05:
      DOI: 10.1002/chem.201705788
       
  • Organoactinide Catalyzed Monohydroboration of Carbodiimides
    • Authors: Moris S. Eisen; Heng Liu, Kseniya Kulbitski Kulbitski, Matthias Tamm
      Abstract: The organoactinide catalyzed monohydroboration of carbodiimides is reported herein. The catalytic reactions proceed under very mild conditions in a highly atom-efficient and highly selective fashion to afford the corresponding monohydroborated N-borylformamidine products in high yields. A plausible mechanism is proposed based on stoichiometric and kinetic studies.
      PubDate: 2018-02-21T07:20:38.553355-05:
      DOI: 10.1002/chem.201705987
       
  • Arene-Ligand-Free Ruthenium(II/III) Manifold for meta-C−H Alkylation:
           Remote Purine Diversification
    • Authors: Fernando Fumagalli; Svenja Warratz, Shou-Kun Zhang, Torben Rogge, Cuiju Zhu, A. Claudia Stückl, Lutz Ackermann
      Abstract: meta-Selective C−H alkylations of bioactive purine derivatives were accomplished by versatile ruthenium catalysis. Thus, the arene-ligand-free complex [Ru(OAc)2(PPh3)2] enabled remote C−H functionalizations with ample scope and excellent levels of chemo- and positional selectivities. Detailed experimental and computational mechanistic studies provided strong support for a facile C−H activation within a ruthenium(II/III) manifold.Pur(in)e remote: meta-C−H alkylations were accomplished on sensitive purine nucleosides by an arene-ligand-free ruthenium catalyst with ample scope.
      PubDate: 2018-02-21T07:15:52.711989-05:
      DOI: 10.1002/chem.201800530
       
  • Constrained chemical dynamics of CO dissociation/hydrogenation on Rh
           surfaces
    • Authors: Peter Kraus; Irmgard Frank
      Abstract: Among noble metal catalysts, rhodium (Rh) is unique in its ability to perform one step synthesis of ethanol from syngas. The first steps following adsorption of syngason Rh surfaces are assumed to be responsible for the conversion of CO and selectivity effects between C1, C2 and oxygenated species. In the current work, we have applied constrained ab initio molecular dynamics to investigate the kinetics of CO dissociation and hydrogenation over flat and stepped Rh surfaces. The obtained barriers for the Rh(111) surface are in a good agreement with the literature. On the stepped Rh(211) surface, a large site-dependent variation in barrier height is shown, with the upper terrace exhibiting behaviour comparable to the Rh(111) surface, while the barriers over the lower terrace site are generally significantly lower. We have calculated rate constants using transition state theory for both surfaces, and successfully applied them in a microkinetic model, confirming the predicted impact on CO conversion and CH4 /C1-oxygenate/C2Hn selectivity. In addition to reporting high-accuracy energetics and rate constants for CO dissociation/hydrogenation, and presenting an updated microkinetic mechanism for Rh catalysts, we have confirmed the applicability of constrained molecular dynamics for reaction barrier calculation, and we have also highlighted sensitive pathways affecting the selectivity between formaldehyde/methanol over Rh catalysts.
      PubDate: 2018-02-21T03:55:41.934656-05:
      DOI: 10.1002/chem.201705867
       
  • Carbothermal Reduction Induced Ti3+ Self-Doped TiO2/GQD Nanohybrids for
           High-Performance Visible Light Photocatalysis
    • Authors: Jialin Tang; Yousong Liu, Yingjie Hu, Guoqing Lv, Chengtao Yang, Guangcheng Yang
      Abstract: A facile calcination method is developed for the in situ synthesis of nanohybrids of Ti3+ self-doped TiO2/graphene quantum dot nanosheets (Ti3+-TiO2/GQD NSs). Ti3+ sites are formed on the surface of the TiO2 nanosheets through carbothermal reduction by GQDs, using citric acid as a carbon source. Such heterojunctions exhibit enhanced visible-light absorption properties, large photocurrent current densities, and low recombination of photoinduced carriers. The methylene blue (MB) and rhodamine B (RhB) photodegradation result demonstrates a higher visible-light photocatalysis performance than that of the original TiO2. On one hand, inducing Ti3+ sites is efficient for the separation of photogenerated charge carriers and for reducing electron–hole pair recombination. On the other hand, GQDs are beneficial for generating more photocurrent carriers and facilitating the charge transfer across the TiO2 surface. It is proposed that Ti3+ sites and GQDs induced in TiO2 nanosheets have a synergistic effect, leading to excellent photocatalysis properties. Finally, a theoretical calculation is provided of the carbothermal reduction for the formation mechanism of the Ti3+ defect sites.Heterojunctions for photocatalysis: Ti3+ self-doped TiO2/graphene quantum dot (Ti3+-TiO2/GQDs) heterojunctions are formed at 450 °C under a N2 atmosphere (see figure). The GQDs act as the reduction agents in the nanohybrids and lead directly to the formation of Ti3+ sites. Theoretical calculations and experimental results show the synergistic effect of the Ti3+/Ov defect sites and GQDs for enhanced photocatalytic performance.
      PubDate: 2018-02-21T03:32:28.051938-05:
      DOI: 10.1002/chem.201705637
       
  • Direct Reductive N-Functionalization of Aliphatic Nitro Compounds
    • Authors: Marian Rauser; Christoph Ascheberg, Meike Niggemann
      Abstract: The first general protocol for the direct reductive N-functionalization of aliphatic nitro compounds is presented. The nitro group is partially reduced to a nitrenoid, with a mild and readily available combination of B2pin2 and zinc organyls. Thereby, the formation of an unstable nitroso intermediate is avoided, which has so far severely limited reductive transformations of aliphatic nitro compounds. The reaction is concluded by an electrophilic amination of zinc organyls.No N=O! The first general protocol for a direct reductive N-functionalization of aliphatic nitro compounds is presented. This type of transformation was so far limited to nitro compounds devoid of α-protons, due to the fast nitroso-oxime tautomerization. N-functionalization is enabled by an alternative reaction path via a more stable nitrenoid intermediate.
      PubDate: 2018-02-21T03:31:07.497051-05:
      DOI: 10.1002/chem.201705986
       
  • Dynamic Polymorph Formation during Evaporative Crystallization from
           Solution: The Key Role of Liquid-Like Clusters as “Crucible” at
           Ambient Temperature
    • Authors: Narumi Oka; Fuyuki Ito, Yohei Haketa, Hiromitsu Maeda, Tetsuya Miyano, Norimitsu Tohnai, Syoji Ito, Hiroshi Miyasaka, Sumio Ozeki
      Abstract: Understanding the polymorph phenomenon for organic crystals is essential for the development of organic solid materials. Here, the fluorescence study of the evaporative crystallization of 1,3-dipyrrol-2-yl-1,3-propanedione boron difluoride complex (1), which has three polymorphs showing different emission profiles, is reported. The droplet of 1 in 1,2-dichloroethane showed blue emission just after dropping. Solids with bluish-green emission were observed. As time elapsed, a solid with red or orange emission was observed around the droplet. Time evolution of the fluorescence spectra, observed for the first time, implied that the molten state of 1 was observed by emission of an intermediate, even at ambient temperature. These findings suggested that the liquid-like cluster incidentally forms an ordered array as the crystallites nucleate. The liquid-like cluster can be considered as the “crucible” in the nucleation of polymorphs.Melting pot: The fluorescence study of the evaporative crystallization of 1,3-dipyrrol-2-yl-1,3-propanedione boron difluoride complex, which has three polymorphs, was carried out. The molten state was observed by emission as an intermediate, even at ambient temperature. It is suggested that the liquid-like cluster incidentally forms an ordered array as the crystallites nucleate. The liquid-like cluster can be considered as the “crucible” in the nucleation of polymorphs.
      PubDate: 2018-02-21T03:06:15.394846-05:
      DOI: 10.1002/chem.201705356
       
  • Orthogonal 19F-Labeling for Solid-State NMR Spectroscopy Reveals the
           Conformation and Orientation of Short Peptaibols in Membranes
    • Authors: Stephan L. Grage; Sezgin Kara, Andrea Bordessa, Véronique Doan, Fabio Rizzolo, Marina Putzu, Tomáš Kubař, Anna Maria Papini, Grégory Chaume, Thierry Brigaud, Sergii Afonin, Anne S. Ulrich
      Abstract: Peptaibols are promising drug candidates in view of their interference with cellular membranes. Knowledge of their lipid interactions and membrane-bound structure is needed to understand their activity and should be, in principle, accessible by solid-state NMR spectroscopy. However, their unusual amino acid composition and noncanonical conformations make it very challenging to find suitable labels for NMR spectroscopy. Particularly in the case of short sequences, new strategies are required to maximize the structural information that can be obtained from each label. Herein, l-3-(trifluoromethyl)bicyclopent[1.1.1]-1-ylglycine, (R)- and (S)-trifluoromethylalanine, and 15N-backbone labels, each probing a different direction in the molecule, have been combined to elucidate the conformation and membrane alignment of harzianin HK-VI. For the short sequence of 11 amino acids, 12 orientational constraints have been obtained by using 19F and 15N NMR spectroscopy. This strategy revealed a β-bend ribbon structure, which becomes realigned in the membrane from a surface-parallel state towards a membrane-spanning state, with increasing positive spontaneous curvature of the lipids.Tagging lipids: A set of four orthogonal 19F and 15N labels was developed for structural determination of membrane-bound peptides by means of solid-state NMR spectroscopy (see figure). This approach maximizes the information content by employing a small number of labels. In an application, the secondary structure and orientation of a membrane-active peptaibol bound to lipid bilayers was elucidated, despite its short length and high mobility.
      PubDate: 2018-02-21T03:05:41.152999-05:
      DOI: 10.1002/chem.201704307
       
  • Reactions of Metal-Carbon Bonds within Six-Membered Metallaaromatic Rings
    • Authors: Xiaoxi Zhou; Hong Zhang
      Abstract: Metallaaromatics represent a distinct and attractive class of heterocycles, which have greatly expanded the library of known aromatics. They have garnered extensive research interest on account of their unique properties, organometallic reactivity, and aromaticity. The metal-carbon bonds have been regarded as the most active reaction sites of metallaaromatics and a variety of related reactions have been demonstrated in the literature. This mini review summarized recent findings on the reactivity of the metal-carbon bonds, mainly relevant to the representative metallaaromatics with six-membered ring scaffolds. A series of reactions occurred on the metal-carbon bonds, including the nucleophilic addition reactions, nucleophilic aromatic substitution reactions, electrophilic addition reactions, reactions with unsaturated compounds, and migratory insertion reactions, have been classified. These reactions demonstrate that the metal-carbon bonds of metallaaromatics can undergo typical reactions for both aromatic species and metal carbene/carbyne complexes. Meanwhile, the reactivity trends of the metal-carbon bonds are strongly affected by the metal centers and the effect of the corresponding substituents of metallacycles.
      PubDate: 2018-02-20T23:20:25.261527-05:
      DOI: 10.1002/chem.201705679
       
  • QM/MM calculations Reveal the Role of the
           Methionine−Tyrosine−Tryptophan Radical Adduct in the Catalase Reaction
           of KatGs: O2 release mediated by Proton-Coupled Electron Transfer
    • Authors: Carme Rovira; Binju Wang, Ignacio Fita
      Abstract: Catalase-peroxidases (KatGs) are bifunctional enzymes exhibiting both peroxidase activities and substantial catalase activities as monofunctional catalases. It is widely recognized from experiments that the high catalatic activity of KatGs are correlated with the unique covalent adduct (M-Y-W) formed in the active site, but the exact role of this adduct is elusive up to now. Here, we employed quantum mechanical/molecular mechanical (QM/MM) calculations and QM/MM metadynamics to elucidate the molecular mechanism and the catalytic role of M-Y-W adduct in the catalase reaction. Our study shows that O2 formation proceeds through a mechanism involving proton-coupled electron transfer (PCET). The M-Y-W cation radical adduct, which is close to the heme, His112 and the HOO* radical intermediate, acts as an electron sink during the PCET process. The present study also highlights the structural differences and functional similarities between KatGs and monofunctional catalases.
      PubDate: 2018-02-20T13:50:25.430926-05:
      DOI: 10.1002/chem.201706076
       
  • Ullazine Donor-π bridge-Acceptor Organic Dyes for Dye-Sensitized
           Solar Cells
    • Authors: Yanbing Zhang; Hammad Cheema, Louis McNamara, Leigh Anna Hunt, Nathan Hammer, Jared Heath Delcamp
      Abstract: A series of 4 ullazine-donor based donor-π bridge-acceptor (D-π-A) dyes have been synthesized and compared to a prior ullazine donor-acceptor (D-A) dye as well as a triphenylamine donor with an identical π-bridge and acceptor. The D-π-A ullazine series demonstrates an unusually uniform-in-intensity panchromatic UV-Vis absorption spectrum throughout the visible region. This is in part due to the introduction of strong high-energy bands through incorporation of the ullazine building block as shown by computational analysis. The dyes were characterized on TiO2 films and in DSC devices. Performances of 5.6% power conversion efficiency were obtained with IPCE onsets reaching 800 nm.
      PubDate: 2018-02-20T11:20:39.156502-05:
      DOI: 10.1002/chem.201800030
       
  • Large Negative Differential Resistance and Rectification from a
           Donor-σ-Acceptor Molecule in Presence of Dissimilar Electrodes
    • Authors: Sayantanu Koley; Swapan Chakrabarti
      Abstract: We propose a multifunctional spin quantum device by sandwiching 11-mercaptoundeca-2,4,8,10-tetraenenitrile, a donor-σ-acceptor molecule between gold and iron electrode. The device can act as a spin rectifier at lower bias and also exhibits negative differential resistance (NDR) after attaining the bias 1.3V. The rectification feature is quite prominent in the up spin channel with appreciable rectification ratio of 68 while the NDR indicator, that means, the peak to valley ratio (~10) of the current-voltage characteristics after 1.3V is also quite significant. To understand the origin of this in-silico observation, we have performed non-equilibrium green's function based density functional theory calculation. Our analyses reveal that both the properties are originating from the bias independent energy offset between the frontier orbitals and the electrode Fermi levels, popularly known as Fermi level pinning. More precisely, the rectification comes from the Fermi Level pinning of the HOMO and LUMO with the gold and iron electrode, respectively while the Fermi level pinning forces a HOMO-LUMO cross-over that helps explain the origin of the NDR.
      PubDate: 2018-02-20T03:51:07.326586-05:
      DOI: 10.1002/chem.201705683
       
  • Biradicaloid and Zwitterion Reactivity of Dicarbondiphosphide Stabilized
           with N-Heterocyclic Carbenes
    • Authors: Zhongshu Li; Yuanfeng Hou, Yaqi Li, Alexander Hinz, Xiaodan Chen
      Abstract: Balancing the biradicaloid and zwitterion reactivity within one single molecule is nearly an unexplored field because both characters represent highly reactive species. Here, it is demonstrated that the dicarbondiphsphide (C2P2) stabilized with N-heterocyclic carbenes exhibited both biradicaloid and zwitterion reactivity experimentally, which is further corroborated by theoretical studies. With the feasible tuning of carbene substituents on the central C2P2 heterocycle, a new branch of main group phosphorus chemistry may develop. More information can be found in the Full Paper by Z. Li, A. Hinz, X. Chen et al. (
      DOI : 10.1002/chem.201705403).
      PubDate: 2018-02-20T03:22:20.111121-05:
       
  • Synthesis of Pd Nanoscale Octahedra through a One-Pot, Dual-Reductant
           Route and the Kinetic Analysis
    • Authors: Younan Xia; Legna Figueroa-Cosme, Kyle D. Gilroy, Tung-Han Yang, Madeline Vara, Jinho Park, Shixiong Bao, Anderson G. M. da Silva
      Abstract: Shape-controlled synthesis of colloidal metal nanocrystals has traditionally relied on the use of an approach that involves the reduction of a metal precursor by a single reductant. Once the concentration of the atoms surpasses supersaturation, they will undergo homogeneous nucleation to generate nuclei and then seeds, followed by further growth into nanocrystals. In general, it is a grand challenge to optimize such an approach because the kinetic requirement for nucleation tends to be drastically different from what is needed for guiding the growth process. In this work, we overcome this difficulty by switching to a dual-reductant approach, in which both strong and weak reductants are added into the same reaction solution. By controlling their amounts to program the reduction kinetics, the strong reductant only regulates the homogeneous nucleation process to generate the desired seeds, and once consumed, the weak reductant will take over to control the growth pattern and thereby the shape of the resulting nanocrystals.
      PubDate: 2018-02-19T13:15:29.700473-05:
      DOI: 10.1002/chem.201705720
       
  • Promotion of a Reaction by Cooling - Stereoselective
           1,2-cis-alpha-Thioglycoconjugation by Thiol-Ene Coupling at −80 °C
    • Authors: Dániel Eszenyi; Viktor Kelemen, Fanny Balogh, Miklós Bege, Magdolna Csávás, Pál Herczegh, Anikó Borbás
      Abstract: The photoinitiated thiol-ene coupling reactions of 2-substituted glycals were studied as a generally applicable strategy for the stereoselective 1,2-cis-alpha-thioconjugation. While all glycals reacted with full alpha-selectivity, the efficacy of the reactions varied in a broad range depending on their configuration and glycals bearing axial acetoxy substituents reacted with very low efficacy at room temperature. Our study revealed that the reaction progress could be promoted by cooling and inhibited by heating. At −80 °C, the equilibrium of the rapidly reversible addition of the thiyl radical to alkenes is shifted almost completely toward products, leading to efficient addition reactions. By exploiting this unique temperature effect a series of alpha-thio-L-fucosides, -D-galactosides and D-GlcNAc derivatives were prepared with high efficacy and complete stereoselectivity.
      PubDate: 2018-02-19T11:20:31.126418-05:
      DOI: 10.1002/chem.201800668
       
  • Circularly Polarized Luminescence from Inorganic Materials: Encapsulating
           Guest Lanthanide Oxides in Chiral Silica Hosts
    • Authors: Masumi Sugimoto; Xin-Ling Liu, Seiji Tsunega, Erika Nakajima, Shunsuke Abe, Takuya Nakashima, Tsuyoshi Kawai, Ren-Hua Jin
      Abstract: Excellent ceramic materials emit colorful circularly polarized luminescence (CPL) in spite of their high-temperature syntheses of up to 1000 °C. The process consists of three very simple self-controlled steps: 1) self-generation of a nanofibrous polymeric complex polyethylenemine/tartrate (PEI/tart) in water; 2) self-deposition of silica around the complex to form chiral SiO2@PEI/tart hybrids; 3) self-encapsulation of lanthanide ions into the hybrid to form a precursor of SiO2@PEI/tart/Ln3+. Final sintering of the precursors affords the circularly polarized light (CPL)-active ceramics with chiral silica hosts and emissive lanthanide guests. More information can be found in the Communication by R.-H. Jin et al. (
      DOI : 10.1002/chem.201705862).
      PubDate: 2018-02-19T09:45:34.402047-05:
       
  • Metal Cluster Models for Heterogeneous Catalysts: A Matrix-Isolation
           Perspective
    • Authors: Hans-Jörg Himmel; Olaf Hübner
      Abstract: Metal cluster models are of high relevance for establishing new mechanistic concepts for heterogeneous catalysis. The high reactivity and particular selectivity of metal clusters is caused by the wealth of low-lying electronically excited states that are often thermally populated. Thereby the metal clusters are flexible with regard to its electronic structure and can adjust their states to be appropriate for the reaction with a particular substrate. The matrix isolation technique is ideally suited for studying excited state reactivity. The low matrix temperatures (generally 4-40 K) of the noble gas matrix host guarantee that all clusters are in their electronic ground-state (with only a very few exceptions). Electronically excited states can then be selectively populated and their reactivity probed. Unfortunately, a systematic research in this direction has not been made up to date. The purpose of this review is to provide the grounds for a directed approach to understand cluster reactivity through matrix-isolation studies combined with quantum chemical calculations.
      PubDate: 2018-02-19T09:28:01.799188-05:
      DOI: 10.1002/chem.201706097
       
  • Controlling Photoconductivity in PBI Films by Supramolecular Assembly
    • Authors: Emily R. Draper; Lewis J. Archibald, Michael C. Nolan, Ralf Schweins, Martijn A. Zwijnenburg, Stephen Sproules, Dave J. Adams
      Abstract: Perylene bisimides (PBIs) self-assemble in solution. The solubility of the PBIs is commonly changed through the choice of substituents at the imide positions. It is generally assumed this substitution does not affect the electronic properties of the PBI, and that the properties of the self-assembled aggregate are essentially that of the isolated molecule. However, substituents do affect the self-assembly, resulting in potentially different packing in the formed aggregates. Here, we show that the photoconductivity of films formed from a library of substituted PBIs varies strongly with the substituent and demonstrate that this is due to the different ways in which they pack. Our results open the possibility for tuning the optoelectronic properties of self-assembled PBIs by controlling the aggregate structure through careful choice of substituent, as demonstrated by us here optimising the photoconductivity of PBI films in this way.The photoconductivity of films formed from self-assembled perylene bisimides varies strongly with the amino acid substituent at the imide position. The substituent controls the molecular packing, and this leads to the differences.
      PubDate: 2018-02-19T09:27:31.554252-05:
      DOI: 10.1002/chem.201800201
       
  • Synthesis of α-l-Fucopyranoside-Presenting Glycoclusters and
           Investigation of Their Interaction with Photorhabdus asymbiotica Lectin
           (PHL)
    • Authors: Gita Jančaříková; Mihály Herczeg, Eva Fujdiarová, Josef Houser, Katalin E. Kövér, Anikó Borbás, Michaela Wimmerová, Magdolna Csávás
      Abstract: Photorhabdus asymbiotica is a gram-negative bacterium that is not only as effective an insect pathogen as other members of the genus, but it also causes serious diseases in humans. The recently identified lectin PHL from P. asymbiotica verifiably modulates an immune response of humans and insects, which supports the idea that the lectin might play an important role in the host–pathogen interaction. Dimeric PHL contains up to seven l-fucose-specific binding sites per monomer, and in order to target multiple binding sites of PHL, α-l-fucoside-containing di-, tri- and tetravalent glycoclusters were synthesized. Methyl gallate and pentaerythritol were chosen as multivalent scaffolds, and the fucoclusters were built from the above-mentioned cores by coupling with different oligoethylene bridges and propargyl α-l-fucosides using 1,3-dipolar azide-alkyne cycloaddition. The interaction between fucoside derivates and PHL was investigated by several biophysical and biological methods, ITC and SPR measurements, hemagglutination inhibition assay, and an investigation of bacterial aggregation properties were carried out. Moreover, details of the interaction between PHL and propargyl α-l-fucoside as a monomer unit were revealed using X-ray crystallography. Besides this, the interaction with multivalent compounds was studied by NMR techniques. The newly synthesized multivalent fucoclusters proved to be up to several orders of magnitude better ligands than the natural ligand, l-fucose.Focus on Fucose: A novel class of α-l-fucopyranoside-presenting glycoclusters have been synthesized to target multiple binding sites of PHL lectin from Photorhabdus asymbiotica. The interaction between fucosides and PHL was investigated by biological methods, X-ray crystallography and saturation transfer difference NMR (STD-NMR). The potency of ligands depended on their valency and architecture, but all fucoclusters proved to be up to several orders of magnitude better ligands than its natural ligand, l-fucose.
      PubDate: 2018-02-19T09:27:14.710674-05:
      DOI: 10.1002/chem.201705853
       
  • Synthesis of Multifunctional Spirocyclic Azetidines and their Application
           in Drug Discovery
    • Authors: Alexander A. Kirichok; Irina O. Shton, Irina M. Pishel, Sergey A. Zozulya, Petro O. Borysko, Vladimir Kubyshkin, Olha A. Zaporozhets, Andrei A. Tolmachev, Pavel K. Mykhailiuk
      Abstract: A new spirocyclic amino acid for drug discovery, a surrogate for l-proline/pipecolic acids, is described. The synthesis of multifunctional spirocycles starts from the commonly available cyclic carboxylic acids, for example, cyclobutane carboxylate, cyclopentane carboxylate, and l-proline. The whole sequence includes only two chemical steps: synthesis of azetidinones and reduction into azetidines. The obtained spirocyclic amino acids were incorporated into a structure of the known anesthetic drug bupivacaine. The obtained analogues were more active and less toxic than the original drug. We believe that this discovery will lead to the wide use of spirocyclic building blocks in drug discovery in the nearest future. More information can be found in the Communication by P. K. Mykhailiuk et al. (
      DOI : 10.1002/chem.201800193).
      PubDate: 2018-02-19T09:21:51.308036-05:
       
  • Tuning the Electronic Properties of Prussian Blue Analogues for Efficient
           Water Oxidation Electrocatalysis: Experimental and Computational Studies
    • Authors: Elif Pınar Alsaç; Emine Ülker, Satya Vijaya Kumar Nune, Yavuz Dede, Ferdi Karadas
      Abstract: Electrochemical studies were performed on a series of Prussian blue analogues (PBAs), Cox[M(CN)6]y (M=Fe2+/3+, Cr3+, and Co3+), to study the effect of neighboring metal ions on the electronic properties of catalytically active cobalt sites. The experimental and computational studies indicate that the nucleophilic attack of water to cobalt-oxo species should be the rate-determining step, the rate of which can be tuned by changing the type of M(CN)6 fragment in PBAs. More information can be found in the Full Paper by Y. Dede, F. Karadas et al. (
      DOI : 10.1002/chem.201704933).
      PubDate: 2018-02-19T09:20:35.397917-05:
       
  • New Water-Soluble Cluster Compound
           {Zn(en)3}3[V15Sb6O42(H2O)]⋅(Ethylenediamine)3⋅10 H2O as a Synthon
           for the Generation of Two New Antimonato Polyoxovanadates
    • Authors: Lisa K. Mahnke; Ulrike Warzok, Mengxi Lin, Christian Näther, Christoph A. Schalley, Wolfgang Bensch
      Abstract: A new compound featuring the {V15Sb6O42} core exhibits a remarkable solubility and stability in water. Electrospray ionization mass spectrometry (ESI-MS) provides evidence of the slow transformation into a more vanadium-poor and more antimony-rich compound. Applying the new {V15Sb6O42} compound as a synthon, two additional and new antimonato-polyoxovanadate compounds containing the {V15Sb6O42} cluster could be synthesized within a short reaction time of 24 h. More information can be found in the Full Paper by W. Bensch et al. (
      DOI : 10.1002/chem.201705732).
      PubDate: 2018-02-19T09:20:28.82974-05:0
       
  • Effect of Crystal Packing on the Thermosalient Effect of the Pincer-Type
           Diester Naphthalene-2,3-diyl-bis(4-fluorobenzoate): A New Class II
           Thermosalient Solid
    • Authors: Majid I. Tamboli; Durga Prasad Karothu, Mysore S. Shashidhar, Rajesh G. Gonnade, Panče Naumov
      Abstract: The pincer-like double ester naphthalene-2,3-diyl-bis(4-fluorobenzoate) (2) is pentamorphic. Upon heating crystals of form I to below their melting point (441–443 K), they undergo a phase transition accompanied by a thermosalient effect, that is, rare and visually striking motility whereby the crystals jump or disintegrate. The phase transition and the thermosalient effect are reversible. Analysis of the crystal structure revealed that form I is a class II thermosalient solid. Crystals of form III also underwent a reversible phase transition in the temperature range of 160 to 170 K; however, they were not thermosalient. Comparison of the structures and the mechanical responses of the two polymorphs revealed that the thermosalient effect of form I was due to reversible closing and opening of the arms of the diester molecules in a tweezer-like action.In top form: Form I of pentamorphic naphthalene-2,3-diyl-bis(4-fluorobenzoate) (2) undergoes a reversible phase transition to form IV followed by a thermosalient effect, whereby the crystals jump or burst. The effect is due to reversible closing and opening of the arms of the diester molecules in a tweezer-like action. Form III also undergoes a reversible phase transition; however, it is not thermosalient. Form II is a disappearing polymorph.
      PubDate: 2018-02-19T09:02:39.149743-05:
      DOI: 10.1002/chem.201705586
       
  • Formation of Cyanamide–Glyoxal Oligomers in Aqueous Environments
           Relevant to Primeval and Astrochemical Scenarios: A Spectroscopic and
           Theoretical Study
    • Authors: Nieves Lavado; Juan García de la Concepción, Reyes Babiano, Pedro Cintas
      Abstract: The condensation of cyanamide and glyoxal, two well-known prebiotic monomers, in an aqueous phase has been investigated in great detail, demonstrating the formation of oligomeric species of varied structure, though consistent with generalizable patterns. This chemistry involving structurally simple substances also illustrates the possibility of building molecular complexity under prebiotically plausible conditions, not only on Earth, but also in extraterrestrial scenarios. We show that cyanamide–glyoxal reactions in water lead to mixtures comprising both acyclic and cyclic fragments, largely based on fused five- and six-membered rings, which can be predicted by computation. Remarkably, such a mixture could be identified using high-resolution electrospray ionization (ESI) mass spectrometry and spectroscopic methods. A few mechanistic pathways can be postulated, most involving the intermediacy of glyoxal cyanoimine and further chain growth, thus increasing the diversity of the observed products. This rationale is supported by theoretical analyses with clear-cut identification of all of the stationary points and transition-state structures. The properties and structural differences of oligomers obtained under thermodynamic conditions in water as opposed to those isolated by precipitation from organic media are also discussed.Complex, not messy! Organic matter detected in extraterrestrial bodies might not be as intractable as thought. Prebiotic simulations with simple monomers provide clues to regular structural patterns obtained in aqueous environments (see graphic).
      PubDate: 2018-02-19T09:00:38.630738-05:
      DOI: 10.1002/chem.201705747
       
  • Influence of Flexibility on the Separation of Chiral Isomers in STW-Type
           Zeolite
    • Authors: Rocio Bueno-Perez; Salvador R. G. Balestra, Miguel A. Camblor, Jung Gi Min, Suk Bong Hong, Patrick J. Merkling, Sofia Calero
      Abstract: Molecular simulation, through the computation of adsorption isotherms, is a useful predictive tool for the selective capacity of nanoporous materials. Generally, adsorbents are modelled as rigid frameworks, as opposed to allowing for vibrations of the lattice, and this approximation is assumed to have negligible impact on adsorption. In this work, this approach was tested in an especially challenging system by computing the adsorption of the chiral molecules 2-pentanol, 2-methylbutanol and 3-methyl-2-butanol in the all-silica and germanosilicate chiral zeolites STW and studying their lattice vibrations upon adsorption. The analysis of single- and multicomponent adsorption isotherms showed the suitability of STW-type zeolites as molecular sieves for chiral separation processes, which pose a challenging task in the chemical and pharmaceutical industries. Moreover, new experimental adsorption data validate the force field employed. The results reveal that the lattice vibrations of the all-silica framework are sorbate-independent, while those of germanosilicate STW show host–guest coupling modulated by uptake and sorbate type that disrupts the chiral recognition sites. This study indicates that the effects of intrinsic flexibility on the selective capacity of nanoporous materials may range from low to high impact, and some of them could not have been foreseen even after examination of the structural dynamics of an empty framework.Flexible frameworks: The adsorption of 2-pentanol (2P), 2-methylbutanol (2MB) and 3-methyl-2-butanol (3M2B) was investigated in all-silica and germanosilicate zeolites STW, and their lattice vibrations upon adsorption were studied. Regarding chiral selectivity, right-handed STW-Si is selective towards (R)-2P, whereas right-handed STW-SiGe is selective towards (S)-3M2B (see figure). The lattice vibrations of STW-Si are sorbate-independent, whereas those of STW-SiGe show host–guest coupling modulated by uptake and sorbate type that disrupts the chiral recognition sites.
      PubDate: 2018-02-19T08:55:54.199892-05:
      DOI: 10.1002/chem.201705627
       
  • 9,9′-Bifluorenylidene-Core Perylene Diimide Acceptors for As-Cast
           Non-Fullerene Organic Solar Cells: The Isomeric Effect on Optoelectronic
           Properties
    • Authors: Yuan Zhao; Huan Wang, Shengpeng Xia, Feng Zhou, Zhenghui Luo, Jiajia Luo, Feng He, Chuluo Yang
      Abstract: Two different non-fullerene small-molecule acceptors, m-PIB and p-PIB, based on 9,9′-bifluorenylidene (BF) and perylene diimide (PDI) were designed and synthesized. Four β-substituted PDIs were linked to BF in different positions. Based on DFT analysis, derivative p-PIB exhibited reduced intramolecular twisting between the PDI moieties, more delocalized wave function, and sufficiently wider π-electron delocalization than that of m-PIB. The absorption ability of p-PIB was enhanced due to increased intermolecular interactions. By blending p-PIB with poly{4,8-bis[5-(2ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-b′]dithiophene-co-3-fluorothieno[3,4-b]-thiophene-2-carboxylate} (PTB7-Th), organic solar cells (OSCs) based on p-PIB obtained a maximum power conversion efficiency of 5.95 % without any treatments. Due to the improved and balanced hole and electron mobilities, the short-circuit current and fill factor of OSCs based on PTB7-Th and p-PIB were significantly increased. The AFM and TEM results revealed that the PTB7-Th:p-PIB film had favorable nanoscale phase separation and formed a bicontinuous interpenetrating network.Core configuration: Isomeric effect on the optoelectronic properties of two small-molecule non-fullerene acceptors based on bifluorenylidene and perylene diimide were investigated. Organic solar cells based on these materials achieved the highest power conversion efficiency of 5.95 % without any treatments (see figure).
      PubDate: 2018-02-19T08:46:24.867453-05:
      DOI: 10.1002/chem.201705480
       
  • Water–Tryptophan Interactions: Lone-pair⋅⋅⋅π or
           O−H⋅⋅⋅π' Molecular Dynamics Simulations of β-Galactosidase
           Suggest that Both Modes Can Co-exist
    • Authors: Matúš Durec; Radek Marek, Jiří Kozelka
      Abstract: In proteins, the indole side chain of tryptophan can interact with water molecules either in-plane, forming hydrogen bonds, or out-of-plane, with the water molecule contacting the aromatic π face. The latter interaction can be either of the lone pair⋅⋅⋅π (lp⋅⋅⋅π) type or corresponds to the O−H⋅⋅⋅π binding mode, an ambiguity that X-ray structures usually do not resolve. Here, we report molecular dynamics (MD) simulations of a solvated β-galactosidase monomer, which illustrate how a water molecule located at the π face of an indole side chain of tryptophan can adapt to the position of proximate residues and “select” its binding mode. In one such site, the water molecule is predicted to rapidly oscillate between the O−H⋅⋅⋅π and lp⋅⋅⋅π binding modes, thus gaining entropic advantage. Our MD simulations provide support for the role of lp⋅⋅⋅π interactions in the stabilization of protein structures.Lone-pair⋅⋅⋅π or O-H⋅⋅⋅π' Water molecules contacting π faces of aromatic residues have both options. In the interior of β-galactosidase, a water-filled cavity (see figure) offers an example where two H2O molecules contact the same π face of tryptophan each in a different mode: one forming an O−H⋅⋅⋅π bond and the other dynamically exchanging between lone-pair⋅⋅⋅π and O−H⋅⋅⋅π bonds.
      PubDate: 2018-02-19T08:46:07.985563-05:
      DOI: 10.1002/chem.201705364
       
  • Nucleophilic Substitution in Solution: Activation Strain Analysis of Weak
           and Strong Solvent Effects
    • Authors: Trevor A. Hamlin; Bas van Beek, Lando P. Wolters, F. Matthias Bickelhaupt
      Abstract: We have quantum chemically studied the effect of various polar and apolar solvents on the shape of the potential energy surface (PES) of a diverse collection of archetypal nucleophilic substitution reactions at carbon, silicon, phosphorus, and arsenic using density functional theory at OLYP/TZ2P. In the gas phase, all our model SN2 reactions have single-well PESs, except for SN2@C which has a double-well energy profile. The presence of the solvent can have a significant effect on the shape of the PES and thus on the nature of the SN2 process. Solvation energies, charges on nucleophile or leaving group, and structural features are compared for the various SN2 reactions in a spectrum of solvents. We demonstrate how solvation can change the shape of the PES, depending not only on the polarity of the solvent, but also on how the charge is distributed over the interacting molecular moieties during different stages of the reaction. In the case of nucleophilic substitution at three-coordinate phosphorus, the reaction can be made to proceed via a single-well (no TS), bimodal barrier (two TSs), and then through a unimodal transition state (one TS) by increasing the polarity of the solvent.
      PubDate: 2018-02-19T08:45:27.986504-05:
      DOI: 10.1002/chem.201706075
       
  • Integration of Open Metal Sites and Lewis Basic Sites for Construction of
           a Cu MOF with a Rare Chiral Oh-type cage for high performance in methane
           purification
    • Authors: Lingkun Meng; Ziyuan Niu, Chen Liang, Xinglong Dong, Kang Liu, Guanghua Li, Chunguang Li, Yu Han, Zhan Shi, Shouhua Feng
      Abstract: A Cu metal-organic framework (MOF), [Cu4(PMTD)2(H2O)3]⋅20 H2O, 1, (where PMTD is 1,4-phenylenebis(5-methyl-4H-1,2,4-triazole-3,4-diyl)bis(5-carboxylato-3,1-phenylene)bis(hydroperoxymethanide)), with a rare chiral Oh-type cage, and dual functionalities of open metal sites and Lewis basic sites, based on a designed U-shaped ligand, was synthesized by hydrothermal methods. It exhibits high CO2, C2, and C3 hydrocarbon storage capacity under atmospheric pressure, as well as high H2 (1.96 wt.%) adsorption capacity at 77 K. Methane purification capacity was tested and verified step by step. Isosteric heats (Qst) studies reveal that CH4 has the weakest van der Waals host–guest interactions among the seven gases at 298 K. Ideal adsorbed solution theory (IAST) calculation reveals that compound 1 is more selective toward CO2, C2H6, and C3H8 over CH4 in further calculating its separation capacity, as exemplified for CO2/CH4 (50:50, 5:95), C2H6/CH4 (50:50, 5:95), or C3H8/CH4 (50:50, 5:95) binary gas mixtures. Breakthrough experiments show that 1 has a significantly higher adsorption capacity for CO2, C2H6, and C3H8 than CH4. The selective adsorption properties of 1 make it a promising candidate for methane purification.Gassed up: A Cu MOF, with dual functionalities and rare chiral Oh-type cage has been designed and synthesized for methane purification. The MOF exhibits high adsorption capacity for seven C1, C2, and C3 hydrocarbons and little adsorption for methane. Isosteric heats (Qst) reveals that CH4 has the weakest van der Waals host–guest interactions. Ideal adsorbed solution theory (IAST) calculation and breakthrough experiments testify that the Cu MOF is a promising candidate for methane purification.
      PubDate: 2018-02-19T07:55:29.113078-05:
      DOI: 10.1002/chem.201800010
       
  • 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 indices (defined as (IC50dark)/(IC50irradiation)) are essential for the development of ideal photosensitizing properties for this technology. Herein, we report a series of photocytotoxic copper(II) complexes [Cu(RQYMP)(dppn)] (RQYMP=N,N,O-tridentate Schiff-base derivatives, dppn=benzo[i]dipyrido[3,2-a;2′,3′-c]phenazine), the structures of which have been confirmed by mass spectrometry and FTIR spectroscopy. X-ray crystallography revealed that the CuN4O core of the [Cu(cumylQYMP)(dppn)](ClO4) complex (3) has a distorted square-pyramidal geometry. Phototoxicity indices of 329 against human squamous cell carcinoma (SCC15) and 296 against basal cell carcinoma (BCC) cell lines have been determined with [Cu(3-OMeQYMP)(dppn)](ClO4) (4). This can be attributed to the formation of reactive oxygen species, cell apoptosis, and caspase-3 activation, indicating high potential of complex 4 as a photosensitizer candidate in PDT. Thus, copper complexes bearing suitable Schiff-base ligands with a dppn co-ligand may be considered for the design of efficient metal-based anticancer agents for PDT.Copper complexes for PDT: Photocytotoxic copper(II) complexes [Cu(RQYMP)(dppn)] (RQYMP=N,N,O-tridentate Schiff-base derivatives, dppn=benzo[i]dipyrido[3,2-a;2′,3′-c]phenazine) show high phototoxicity indices against SCC15 and BCC cancer cells owing to the generation of reactive oxygen species and caspase-3-mediated cell apoptosis.
      PubDate: 2018-02-19T07:25:55.755886-05:
      DOI: 10.1002/chem.201705640
       
  • A Synthetic Binder of Breast Cancer Stem Cells
    • Authors: Luxi Chen; Chao Long, Kha Andy Minh Tran, Jiyong Lee
      Abstract: Cancer stem cells (CSCs) are associated with drug resistance, metastasis and recurrence of cancer. A synthetic binder of CSCs can provide a valuable tool to study the biology of CSCs and a lead to develop imaging, diagnostic and therapeutic agents targeting CSCs. Herein, a synthetic ligand (1) that specifically binds to CSCs over non-CSCs of breast cancer cells was identified for the first time via a cell-binding screening of a chemical library. The ligand 1 showed specific binding to CD24−/CD44+/ALDH+ CSC population of MCF-7 and MDA-MB-231. We have demonstrated that 1-immobilized beads can be used as matrices for affinity isolation of 1-binding CSC population from breast cancer cells. The 1-binding population showed significantly increased expressions of stemness-associated transcription factors. Importantly, the 1-binding population demonstrated accelerated tumor growth in vivo, and the resulting tumor displayed an increased migratory activity and high expressions of CSC markers.Cancer stem cells (CSCs) are known to be associated with therapy-resistance, metastasis and recurrence. A synthetic binder of CSCs can provide a valuable tool to study the biology of CSCs as well as a lead to develop imaging, diagnostic and therapeutic agents of CSCs. In this study, a peptoid that specifically binds to CSCs over non-CSCs of breast cancer cells was identified by chemical library screening.
      PubDate: 2018-02-19T07:20:53.63679-05:0
      DOI: 10.1002/chem.201705663
       
  • A Highly Reversible Mechanochromic Difluorobenzothiadiazole Dye with
           Near-Infrared Emission
    • Authors: Jianhua Chen; Dongyang Li, Weijie Chi, Guotao Liu, Sheng Hua Liu, Xiaogang Liu, Chun Zhang, Jun Yin
      Abstract: A difluorobenzothiadiazole-based fluorescent material with a D-π-A-π-D structure exhibits a reversible mechanofluorochromic characteristic in the solid state. Its red fluorescent emission switches to near-infrared fluorescence upon mechanical stimulation, but recover after fuming the ground solid powder with dichloromethane.Near-infrared mechanochromism: A difluorobenzothiadiazole-based fluorescent material exhibits a reversible switch from red emission to near-infrared fluorescence upon mechanical stimulation in the solid state, confirmed by laser confocal fluorescence imaging and Xenogen IVIS spectrum imaging Theoretical calculations suggest that molecular sliding is likely the reason for the redshift.
      PubDate: 2018-02-19T07:20:41.343998-05:
      DOI: 10.1002/chem.201705780
       
  • Chemoselective Glycosylation of Peptides via S-Alkylation Reaction
    • Authors: Stefania De Luca; Enrica Calce, Valeria Manchise, Michele Saviano, Giuseppe Digilio
      Abstract: An efficient and fast procedure in execution for synthesizing S-linked glycopeptides is reported. It uses activated molecular sieves as a base to promote the selective S-alkylation of readily prepared cysteine-containing peptides, upon reaction of appropriate glycosyl halides. Due to the very mild conditions employed, the chemoselective linkage of the electrophilic sugar with a peptide sulfhydryl group occurred in a satisfactory yield, allowing the incorporation of mono and disaccharide moieties. The sugar-peptide conjugates obtained from α-D-glycosyl derivatives adopt a beta-S-conformation, indicating the high stereoselectivity of the substitution reaction.
      PubDate: 2018-02-19T06:45:48.044043-05:
      DOI: 10.1002/chem.201800265
       
  • Tandem Functionalization in One Highly Branched Polymer with Layered
           Structure
    • Authors: Xiaosong Cao; Yi Shi, Weiping Gan, Haifeng Gao
      Abstract: In this report, we developed a hyperbranched polymer with multi-layer structure to demonstrate the possibility of highly efficient tandem functionalization reactions at different domains within one nanostructured platform. The polymer scaffold was constructed using the chain-growth copper-catalyzed azide-alkyne cycloaddition (CuAAC) polymerization of three functional monomers with sequential monomer addition in one pot. Subsequent reactions onto different monomer units exhibited efficient functionalization in each segment, constructing a highly sophisticated polymer structure via a robust procedure. As a proof of concept, we demonstrated the ability of this polymer structure to quantitatively load six species of guest molecules through three different types of conjugation reactions.
      PubDate: 2018-02-19T06:21:11.038549-05:
      DOI: 10.1002/chem.201800683
       
  • Production and structural analysis of membrane-anchored proteins in
           phospholipid nanodiscs
    • Authors: Kolio Raltchev; Joka Pipercevic, Franz Hagn
      Abstract: Structural studies on membrane-anchored proteins containing a transmembrane (TM) helix has been hampered by difficulties in producing these proteins in a natively folded form. Detergents that are required to solubilize the hydrophobic TM helix usually destabilize the soluble domain. Thus, TM helices are removed for structural studies, which neglects the pivotal role of a membrane on protein function. Here, we present a versatile strategy for the production of this protein class attached to phospholipid nanodiscs. By inserting the TM-helix into nanodiscs and a subsequent SortaseA-mediated ligation of the soluble domain, membrane-anchored BclxL could be obtained in a folded conformation. We show that this strategy is suitable for high-resolution structure determination as well as for probing membrane location by NMR. This method will be applicable to a wide range of membrane-anchored proteins and will be useful to decipher their functional role in a native membrane environment.
      PubDate: 2018-02-19T06:20:42.984247-05:
      DOI: 10.1002/chem.201800812
       
  • Efficient Catalytic Enantioselective Hydroxyamination of
           α-Aryl-α-Cyanoacetates with 2-Nitrosopyridines
    • Authors: Xiaoming Feng; Jingchuan Zhang, Kai Fu, Lili Lin, Yan Lu, Xiaohua Liu
      Abstract: The highly enantioselective totally N-selective hydroxyamination reaction of α-aryl-α-cyanoacetates with 2-nitrosopyridines was realized by using a chiral N,N'-dioxide/Mg(OTf)2 complex as catalyst, which enriches the nitroso chemistry. A variety of 2-cyano-2-[hydroxyl(pyrydin-2-yl)amino]acetates with quaternary stereocenters and potential antibacterial activities were obtained in excellent yields with good to excellent ee values under as low as 0.05 mol% catalyst loading. The products could be easily transformed to useful α-amino amides and 1,2-diamines. Besides, a possible transition state model was proposed to elucidate the origin of the chirality induction.
      PubDate: 2018-02-19T05:21:39.779823-05:
      DOI: 10.1002/chem.201800592
       
  • Spin Selectivity in Chiral Linked Systems
    • Authors: Aleksandra A. Ageeva; Ekaterina A. Khramtsova, Ilya M. Magin, Denis A. Rychkov, Peter A. Purtov, Miguel A. Miranda, Tatyana V. Leshina
      Abstract: This work has shown spin selectivity in electron transfer (ET) of diastereomers of (R,S)-naproxen-(S)-N-methylpyrrolidine and (R,S)-naproxen-(S)-tryptophan dyads. Photoinduced ET in these dyads is interesting because of the still unexplained phenomenon of stereoselectivity in the drug activity of enantiomers. The chemically induced dynamic nuclear polarization (CIDNP) enhancement coefficients of (R,S)-diastereomers are double those of the (S,S)-analogue. These facts are also interesting because spin effects are among the most sensitive, even to small changes in spin and molecular dynamics of paramagnetic particles. Therefore, CIDNP reflects the difference in magnetoresonance parameters (hyperfine interaction constants (HFIs), g-factor difference) and lifetimes of the paramagnetic forms of (R,S)- and (S,S)-diastereomers. The difference in HFI values for diastereomers has been confirmed by a comparison of CIDNP experimental enhancement coefficients with those calculated. Additionally, the dependence of the CIDNP enhancement coefficients on diastereomer concentration has been observed for the naproxen-N-methylpyrrolidine dyad. This has been explained by the participation of ET in homo-(R,S-R,S or S,S-S,S) and hetero-(R,S-S,S) dimers of dyads. In this case, the effectivity of ET, and consequently, CIDNP, is supposed to be different for (R,S)- and (S,S)-homodimers, heterodimers, and monomers. The possibility of dyad dimer formation has been demonstrated by using high-resolution X-ray and NMR spectroscopy techniques.Difference of dimer reactivity: A new manifestation of chirality was observed through the difference in chemically induced dynamic nuclear polarization (CIDNP) enhancement coefficients for diastereomers of donor–acceptor dyads. The difference in the CIDNP effects, formed in electron transfer (ET), is interpreted as a result of the difference in hyperfine interaction (HFI) constants in the paramagnetic forms of diastereomers (see figure).
      PubDate: 2018-02-19T03:04:07.105451-05:
      DOI: 10.1002/chem.201705863
       
  • A Capillary Flow Dynamics-Based Sensing Modality for Direct Environmental
           Pathogen Monitoring
    • Authors: Katherine E. Klug; Kelly A. Reynolds, Jeong-Yeol Yoon
      Abstract: Toward ultra-simple and field-ready biosensors, we demonstrate a novel assay transducer mechanism based on interfacial property changes and capillary flow dynamics in antibody-conjugated submicron particle suspensions. Differential capillary flow is tunable, allowing pathogen quantification as a function of flow rate through a paper-based microfluidic device. Flow models based on interfacial and rheological properties indicate a significant relationship between the flow rate and the interfacial effects caused by target-particle aggregation. This mechanism is demonstrated for assays of Escherichia coli K12 in water samples and Zika virus (ZIKV) in blood serum. These assays achieved very low limits of detection compared with other demonstrated methods (1 log CFU/mL E. coli and 20 pg/mL ZIKV whole virus) with an operating time of 30 s, showing promise for environmental and health monitoring.A novel assay transducer mechanism is demonstrated based on interfacial property changes and capillary flow dynamics in antibody-conjugated submicron particle suspensions. Pathogens are quantified as a function of flow rate through a paper microfluidic device. Flow models based on interfacial and rheological properties indicate a significant relationship between the flow rate and the interfacial effects caused by target-particle aggregation.
      PubDate: 2018-02-19T03:04:00.093368-05:
      DOI: 10.1002/chem.201800085
       
  • Streamlined Synthesis and Evaluation of Teichoic Acid Fragments
    • Authors: Daan van der Es; Francesca Berni, Wouter F. J. Hogendorf, Nico Meeuwenoord, Diana Laverde, Angela van Diepen, Herman S. Overkleeft, Dmitri V. Filippov, Cornelis H. Hokke, Johannes Huebner, Gijsbert A. van der Marel, Jeroen D. C. Codée
      Abstract: Teichoic acids (TAs) are key components of the Gram-positive bacterial cell wall that are composed of alditol phosphate repeating units, decorated with alanine or carbohydrate appendages. Because of their microhetereogeneity, pure well-defined TAs for biological or immunological evaluation cannot be obtained from natural sources. We present here a streamlined automated solid-phase synthesis approach for the rapid generation of well-defined glycosylated, glycerol-based TA oligomers. Building on the use of a “universal” linker system and fluorous tag purification strategy, a library of glycerolphosphate pentadecamers, decorated with various carbohydrate appendages, is generated. These are used to create a structurally diverse TA-microarray, which is used to reveal, for the first time, the binding preferences of anti-LTA (lipoteichoic acids) antibodies at the molecular level.Using a streamlined, automated solid-phase synthetic approach, well-defined glycosylated, glycerol-based teichoic acid oligomers were synthesized. These are used to create a structurally diverse teichoic acid microarray, which is used to reveal, for the first time, the binding preferences of anti-LTA antibodies at the molecular level.
      PubDate: 2018-02-19T03:03:54.612122-05:
      DOI: 10.1002/chem.201800153
       
  • AgI-Induced Switching of DNA Binding Modes via Formation of a
           Supramolecular Metallacycle
    • Authors: Shibaji Basak; J. Christian Léon, Annaleizle Ferranco, Renu Sharma, Marian Hebenbrock, Alan Lough, Jens Müller, Heinz-Bernhard Kraatz
      Abstract: The histidine derivative L1 of the DNA intercalator naphthalenediimide (NDI) forms a triangular AgI complex (C2). The interactions of L1 and of C2 with DNA were studied by circular dichroism (CD) and UV/Vis spectroscopy and by viscosity studies. Different binding modes were observed for L1 and for C2, as the AgI complex C2 is too large in size to act as an intercalator. If AgI is added to the NDI molecule that is already intercalated into a duplex, higher order complexes are formed within the DNA duplex and cause disruptions in the helical duplex structure, which leads to a significant decrease in the characteristic CD features of B-DNA. Thus, via addition of a metal we show how a classic and well-known organic intercalator unit can be turned into a partial metallo insertor. We also show how electrochemical impedance spectroscopy (EIS) can be used to probe DNA binding modes on DNA films that are immobilized on gold surfaces.Supra with silver: A histidine-linked NDI ligand formed a triangular metallacycle in presence of AgI. The ligand has been used as a DNA intercalator, which transforms into a metallo-insertor.
      PubDate: 2018-02-19T03:02:58.05123-05:0
      DOI: 10.1002/chem.201800440
       
  • Epitope-Targeted Macrocyclic Peptide Ligand with Picomolar Cooperative
           Binding to Interleukin-17F
    • Authors: Bert T. Lai; Jeré A. Wilson, Jacquie Malette Loredo, Suresh M. Pitram, Nicole A. LaBerge, James R. Heath, Heather D. Agnew
      Abstract: The IL-17 cytokine family is associated with multiple immune and autoimmune diseases and comprises important diagnostic and therapeutic targets. This work reports the development of epitope-targeted ligands designed for differential detection of human IL-17F and its closest homologue IL-17A. Non-overlapping and unique epitopes on IL-17F and IL-17A were identified by comparative sequence analysis of the two proteins. Synthetic variants of these epitopes were utilized as targets for in situ click screens against a comprehensive library of synthetic peptide macrocycles with 5-mer variable regions. Single generation screens yielded selective binders for IL-17F and IL-17A with low cross-reactivity. Macrocyclic peptide binders against two distinct IL-17F epitopes were coupled using variable length chemical linkers to explore the physical chemistry of cooperative binding. The optimized linker length yielded a picomolar affinity binder, while retaining high selectivity. The presented method provides a rational approach towards targeting discontinuous epitopes, similar to what is naturally achieved by many B cell receptors.Cooperative binding: Macrocyclic peptide ligands were developed against distinct and discontinuous epitopes of two interleukin-17 isoforms. These ligands achieved differential detection of the targeted isoform. Knowledge of the targeted epitopes informed a potentially general strategy for conjoining two ligands by a chemical linker to yield a cooperative biligand with picomolar binding affinity.
      PubDate: 2018-02-19T02:57:11.53053-05:0
      DOI: 10.1002/chem.201704752
       
  • Stereoselective Transfer Semi-Hydrogenation of Alkynes to E-Olefins with
           N-Heterocyclic Silylene–Manganese Catalysts
    • Authors: Yu-Peng Zhou; Zhenbo Mo, Marcel-Philip Luecke, Matthias Driess
      Abstract: Invited for the cover of this issue is the group of Matthias Driess at the Technical University in Berlin. The image depicts the “catchy performance” conducted by the efficient silylene crab. Read the full text of the article at 10.1002/chem.201705745.“The term ”chelate“ was first described in 1920: The adjective ”chelate“, derived from the great claw or ”chela“ (”chely“) of the lobster or other crustaceans, is suggested for the caliper-like groups which function as two associating units and fasten to the central atom so as to produce heterocyclic rings.” Read more about the story behind the cover in the Cover Profile and about the research itself on page ▪▪ ff. (
      DOI : 10.1002/chem.201705745).
      PubDate: 2018-02-19T02:56:24.393176-05:
       
  • Ion Selectivity in Nonpolymeric Thermosensitive Systems Induced by
           Water-Attenuated Supramolecular Recognition
    • Authors: Zhenhui Qi; Leonardo Chiappisi, Hanlin Gong, Ren Pan, Ning Cui, Yan Ge, Christoph Böttcher, Shengyi Dong
      Abstract: The chemistry of aqueous salt solutions is rich with ambiguities, especially in stimuli-responsive supramolecular systems. Rational use of ion specificity to design supramolecular responsive materials, however, remains a challenging task. In this work, a low-molecular-weight supramolecular system was developed that was used to reveal the underlying systematic relationship between ions, water, and solutes. By utilizing these water-attenuated supramolecular forces (with Ka only ca. 30 m−1), an alternative concept for fabricating an aqueous responsive system in ionic medium was demonstrated. This work not only provides mechanistic insight into the underdeveloped role of topology in ion specificity upon noncharged polar surfaces, but also demonstrates the feasibility of utilizing weak supramolecular approaches to control the thermoresponsiveness.Little force but large effect: Specialized ion-binding sites with tailored functional groups and geometries have been designed that not only provide mechanistic insight into the underdeveloped role of topology in the Hofmeister effect, which has been long ignored in the previous studies, but also demonstrates the feasibility of utilizing those “water-damaged” supramolecular forces to precisely control the ion specificity in aqueous supramolecular system (see figure).
      PubDate: 2018-02-19T02:56:21.131479-05:
      DOI: 10.1002/chem.201705838
       
  • Hierarchical Nanostructures of Metal-Organic Frameworks Applied in Gas
           Separating ZIF-8-on-ZIF-67 Membranes
    • Authors: Alexander Knebel; Paul Wulfert-Holzmann, Sebastian Friebe, Janet Pavel, Ina Strauß, Alexander Mundstock, Frank Steinbach, Jürgen Caro
      Abstract: Membranes from metal-organic frameworks (MOFs) are highly interesting for industrial gas separation applications. Strongly improved performances for carbon capture and H2 purification tasks in MOF membranes are obtained by using highly reproducable and very accuratly, hierarchically grown ZIF-8-on-ZIF-67 (ZIF-8@ZIF-67) nanostructures. To forgo hardly controllable solvothermal synthesis, particles and layers are prepared by self-assembling methods. It was possible for the first time to confirm ZIF-8-on-ZIF-67 membrane growth on rough and porous ceramic supports using the layer-by-layer deposition. Additionally, hierarchical particles are made in a fast RT synthesis with high monodispersity. Characterization of the hierarchical and epitaxial grown layers and particles is performed by SEM, TEM, EDXM and gas permeation. The system ZIF-8@ZIF-67 shows a nearly doubled H2/CO2 separation factor, regardless of whether neat membrane or mixed-matrix-membrane in comparison to other MOF materials.MOF-on-MOF: Hierarchical nanostructures were fabricated by highly tunable and accurately adjustable self-assembly techniques. The ZIF-8-on-ZIF-67, either applied as mixed-matrix membrane or as neat MOF layer, shows highly increased performance in hydrogen separation tasks. They outperform the single ZIF-8 and ZIF-67 materials and other MOF materials in gas separation membranes, because of their additive adsorption effects originating from stacking of the frameworks.
      PubDate: 2018-02-19T02:56:10.400386-05:
      DOI: 10.1002/chem.201705562
       
  • Hierarchically Porous Multilayered Carbon Barriers for High-Performance
           Li–S Batteries
    • Authors: Zhi Chang; Bing Ding, Hui Dou, Jie Wang, Guiyin Xu, Xiaogang Zhang
      Abstract: As one of the most promising energy storage devices, the practical application of lithium–sulfur batteries is limited by the low electrical conductivity of sulfur and the notable “shuttle effects” of sulfur-based electrodes. In this work, we describe a hierarchically porous N-doped zeolitic imidazolate framework-8 (ZIF-8)-derived carbon nanosphere (N-ZDC) with an outer shell and an inner honeycomb-like interconnected nanosheet network as sulfur host material for high-performance and long-term lithium–sulfur batteries. The N-ZDC serves as multilayered barrier against the dissolution of lithium polysulfides. The porously inner interconnected carbon network of the N-ZDC facilitates the electron and ion transportation, ensures a high sulfur loading, and accommodates a volume expansion of the sulfur species. As a result, the optimized N-ZDC4/S electrodes displayed high initial specific capacities of 1343, 1182, and 698 mAh g−1 at 0.5, 1, and 2 C, respectively, and an ultraslow capacity decay of only 0.048 % per cycle at 2 C over 800 cycles. Even with a high sulfur loading of 3.1 mg cm−2, N-ZDC4/S still delivered a reversible capacity of 956 mAh g−1 and stabilizes at 544 mAh g−1 after 500 cycles at 0.5 C, revealing the great potential of the novel carbon nanospheres for energy storage application.Shuttle break: Hierarchically porous N-doped carbon (N-ZDC) spheres with an outer shell and an inner interconnected carbon network act as multilayered barrier to effectively suppress the dissolution of lithium polysulfides and enhance the active material utilization, thus improving the cycling performance of Li–S batteries.
      PubDate: 2018-02-19T02:55:32.503346-05:
      DOI: 10.1002/chem.201704757
       
  • Asymmetric Catalytic Double Michael Additions for the Synthesis of
           Spirooxindoles
    • Authors: Tengfei Kang; Peng Zhao, Jian Yang, Lili Lin, Xiaoming Feng, Xiaohua Liu
      Abstract: Asymmetric cascade double Michael additions to construct 2′-substituted 3,3′-spirooxindoles by using a chiral guanidine organocatalyst has been developed. A series of spirooxindole derivatives containing dihydrofuran or pyrrolidine subunits were obtained with good to excellent diastereo- and enantioselectivities. The method showed great tolerance of a number of aromatic and aliphatic alkynones. The strategy gave access to the asymmetric synthesis of (−)-salacin for the first time.Michael additions go chiral: The title reaction was realized by using guanidine catalyst. The present working model functions well for a variety of aryl- and alkyl-substituted alkynes as well as substituted oxindoles with good enantioselectivities (up to 97.5:2.5 er). The first catalytic asymmetric synthesis of (−)-salacin is also reported. The desired spirooxindoles are found as core structures in numerous bioactive compounds.
      PubDate: 2018-02-19T02:54:15.029227-05:
      DOI: 10.1002/chem.201800043
       
  • Catalytic Dearomative Spirocyclization via Gold Carbene Species Derived
           from Ynamides: Efficient Synthesis of 2-Azaspiro[4.5]decan-3-ones
    • Authors: Mamoru Ito; Ryosuke Kawasaki, Kyalo Stephen Kanyiva, Takanori Shibata
      Abstract: An intramolecular catalytic dearomatization of phenols via gold carbene species proceeded to provide 2-azaspiro[4.5]decan-3-ones. The use of NHC ligand and water as a co-solvent was critical for achieving high reactivity. This reaction did not require hazardous diazo compounds as carbene sources and proceeded even under air. The obtained spirocyclic product could be readily transformed into a gabapentin derivative by hydrogenation and deprotection.Gold prize for safety: An intramolecular catalytic dearomatization of phenols via gold carbene species proceeded to provide 2-azaspiro[4.5]decan-3-ones. The use of NHC ligand and water as a co-solvent was critical for achieving high reactivity. This reaction did not require hazardous diazo compounds as carbene sources and proceeded even under air.
      PubDate: 2018-02-19T02:51:37.713908-05:
      DOI: 10.1002/chem.201800314
       
  • Intermolecular Desymmetrizing Gold-Catalyzed Yne–Yne Reaction of
           Push–Pull Diarylalkynes
    • Authors: Vanessa Weingand; Thomas Wurm, Vanessa Vethacke, Martin C. Dietl, Daniel Ehjeij, Matthias Rudolph, Frank Rominger, Jin Xie, A. Stephen K. Hashmi
      Abstract: Push–pull diaryl alkynes are dimerized in the presence of a cationic gold catalyst. The polarized structure of the applied starting materials enables the generation of a highly reactive vinyl cation intermediate in an intermolecular reaction. Trapping of the vinyl cation by a nucleophilic attack of the electron-poor aryl unit then leads to the selective formation of highly substituted naphthalenes in a single step and in complete atom economy.Tolan wedding: The intermolecular and selective gold-catalyzed dimerization of polarized tolan derivatives gives highly substituted naphthalenes via reactive vinyl cation intermediates. This methodology is superior to existing unselective strategies catalyzed by other transition metals and offers an entry to naphthalenes with a controlled substitution pattern of electron-rich and electron-poor aryl groups (see scheme).
      PubDate: 2018-02-19T02:51:27.756029-05:
      DOI: 10.1002/chem.201800360
       
  • Plasmid-Templated Control of DNA–Cyclodextrin Nanoparticle Morphology
           through Molecular Vector Design for Effective Gene Delivery
    • Authors: Laura Gallego-Yerga; Juan M. Benito, Laura Blanco-Fernández, María Martínez-Negro, Itziar Vélaz, Emilio Aicart, Elena Junquera, Carmen Ortiz Mellet, Conchita Tros de Ilarduya, Jose M. García Fernández
      Abstract: Engineering self-assembled superstructures through complexation of plasmid DNA (pDNA) and single-isomer nanometric size macromolecules (molecular nanoparticles) is a promising strategy for gene delivery. Notably, the functionality and overall architecture of the vector can be precisely molded at the atomic level by chemical tailoring, thereby enabling unprecedented opportunities for structure/self-assembling/pDNA delivery relationship studies. Beyond this notion, by judiciously preorganizing the functional elements in cyclodextrin (CD)-based molecular nanoparticles through covalent dimerization, here we demonstrate that the morphology of the resulting nanocomplexes (CDplexes) can be tuned, from spherical to ellipsoidal, rod-type, or worm-like nanoparticles, which makes it possible to gain understanding of their shape-dependent transfection properties. The experimental findings are in agreement with a shift from chelate to cross-linking interactions on going from primary-face- to secondary-face-linked CD dimers, the pDNA partner acting as an active payload and as a template. Most interestingly, the transfection efficiency in different cells was shown to be differently impacted by modifications of the CDplex morphology, which has led to the identification of an optimal prototype for tissue-selective DNA delivery to the spleen in vivo.Specific vectors: The morphology and in vivo fate of cyclodextrin (CD)–plasmid DNA (pDNA) superstructures can be controlled by judicious design of the molecular constituents: a shift from chelate to cross-linking interactions takes place. Whereas spherical nanocomplexes exhibit tropism towards the lung and the liver, rod-type nanoparticles afforded selective transfection in the spleen (see figure).
      PubDate: 2018-02-19T02:47:04.681056-05:
      DOI: 10.1002/chem.201705723
       
  • Bioconjugation with Thiols by Benzylic Substitution
    • Authors: Kenji Watanabe; Takashi Ohshima
      Abstract: A benzylic substitution of 3-indolyl(hydroxyl)acetate derivatives with thiols proceeded specifically in the presence of amino, carboxy, and phosphate groups in weakly acidic aqueous solutions under nearly physiological condition, while no reaction occurred at pH over 7. Kinetic studies revealed that the reaction followed second-order kinetics (first-order in the reactant and first-order in thiol) in contrast with the SN1 mechanism of common benzylic substitution of alcohols. The utility of the present method for functionalization of biomacromolecules was demonstrated using several model proteins, such as lysozyme, insulin, trypsin, and serum albumin. The catalytic bioactivity of lysozyme in lysis of Micrococcus lysodeikticus cells was completely retained after the modification.A benzylic substitution of 3-indolyl(hydroxyl)acetate derivatives with thiols proceeded specifically in the presence of amino, carboxy, and phosphate groups in weakly acidic aqueous solutions under physiological conditions. The utility of the present method for functionalization of proteins was demonstrated.
      PubDate: 2018-02-19T02:46:50.107548-05:
      DOI: 10.1002/chem.201706149
       
  • Palladium-Catalyzed Decarboxylative Heck-Type Coupling of Activated
           Aliphatic Carboxylic Acids Enabled by Visible Light
    • Authors: Maximilian Koy; Frederik Sandfort, Adrian Tlahuext-Aca, Linda Quach, Constantin Daniliuc, Frank Glorius
      Abstract: The palladium-catalyzed coupling reaction of N-hydroxyphthalimide esters and styrenes to deliver exclusively (E)-substituted olefins under irradiation with visible light is reported. This method tolerates N-hydroxyphthalimide esters derived from primary, secondary, tertiary as well as benzylic carboxylic acids. Notably, Pd(PPh3)4 is employed as an inexpensive palladium source and no addition of base or classical photocatalyst is required. Mechanistic studies suggest a light-mediated single electron reduction of the activated acid by a photoexcited palladium(0) species to access alkyl radicals via decarboxylation.
      PubDate: 2018-02-16T10:10:32.829461-05:
      DOI: 10.1002/chem.201800813
       
  • Impact of Zeolite Structure on Entropic-Enthalpic Contributions to Alkane
           Monomolecular Cracking, an IR Operando study
    • Authors: Shashikant A. Kadam; Haoguang Li, Richard F. Wormsbecher, Arnaud Travert
      Abstract: The monomolecular cracking rates of propane and n-butane over MFI, CHA, FER and TON zeolites were determined simultaneously with the coverage of active sites at reaction condition using IR operando spectroscopy. This allowed direct determination of adsorption thermodynamics and intrinsic rate parameters. The results show that the zeolite confinement mediates enthalpy-entropy trade-offs only at the adsorbed state, leaving the true activation energy insensitive to the zeolite or alkane structure while the activation entropy was found to increase with the confinement. Hence, relative cracking rates of alkanes within zeolite pores are mostly governed by activation entropy.
      PubDate: 2018-02-16T09:40:28.540846-05:
      DOI: 10.1002/chem.201800793
       
  • Molecular Tectonics with Di- and Trinuclear Organometallic Tin Compounds
    • Authors: Irán Rojas-León; Hazem Alnasr, Klaus Jurkschat, Maria G. Vasquez-Ríos, Irán F. Hernández-Ahuactzi, Herbert Höpfl
      Abstract: Di- and trinuclear organometallic tin (IV) complexes, in which the metal atoms are separated by large aromatic connectors, are useful building blocks for self-assembly. This is demonstrated by the preparation of [1+1], [2+2] and [2+3] macrocyclic and cage-type structures in combination with organic aromatic dicarboxylates. The linkage of the metal atoms by organic binders and the option of varying the number of reactive M-X sites generate versatile building blocks enabling molecular tectonics instead of the node-based strategy generally employed in metallo-supramolecular self-assembly.
      PubDate: 2018-02-16T05:41:11.183524-05:
      DOI: 10.1002/chem.201800791
       
  • Electronically Unsaturated Three Coordinated Aluminum Hydride and
           Organoaluminum Cations
    • Authors: Billa Prashanth; Mamta Bhandari, Satyam Ravi, K. R. Shamasundar, Sanjay Singh
      Abstract: New three coordinated and electronically unsaturated aluminum hydride [LAlH]+[HB(C6F5)3]- and aluminum methyl [LAlMe]+[MeB(C6F5)3]- cations have been prepared. The quantitative estimation of Lewis acidity by Gutmann−Beckett method reveals [LAlH]+[HB(C6F5)3]- to be better Lewis acid than B(C6F5)3 and AlCl3 making these compounds ideal catalysts for Lewis acid mediated reactions. To highlight that the work is of fundamental importance, catalytic hydroboration of aliphatic and aromatic aldehydes and ketones have been demonstrated. Important steps of the catalytic cycle have been probed using multinuclear NMR measurements including successful characterization of the proposed aluminum benzyloxide cationic intermediate, [LAl-O-CH2Ph]+[HB(C6F5)3]-. The catalytic cycle proposed has been found to be consistent with experimental observations and computational studies clearly indicating the migration of hydride from cationic aluminum center to the carbonyl carbon is the rate limiting step of the catalytic cycle. LH = [{(2,6-iPr2C6H3N)P(Ph2)}2N]H.
      PubDate: 2018-02-16T05:41:04.113563-05:
      DOI: 10.1002/chem.201800299
       
  • Anisotropic Thermal and Guest-Induced Responses of an Ultramicroporous
           Framework with Rigid Linkers
    • Authors: Josie E. Auckett; Samuel G. Duyker, Ekaterina I. Izgorodina, Chris S. Hawes, David R. Turner, Stuart R. Batten, Vanessa Kate Peterson
      Abstract: The interdependent effects of temperature and guest uptake on the structure of the ultramicroporous metal-organic framework [Cu3(cdm)4] (cdm = C(CN)2(CONH2)-) are explored in detail using in situ neutron scattering and density functional theory calculations. The tetragonal lattice displays an anisotropic thermal response related to a hinged "lattice-fence" mechanism, unusual for this topology, which is facilitated by pivoting of the rigid cdm anion about the Cu nodes. Calculated pore size metrics clearly illustrate the potential for temperature-mediated adsorption in ultramicroporous frameworks due to thermal fluctuations of the pore diameter near the value of the target guest kinetic diameter, though in [Cu3(cdm)4] this is counteracted by a competing contraction of the pore with increasing temperature as a result of the anisotropic lattice response.
      PubDate: 2018-02-16T02:12:56.731389-05:
      DOI: 10.1002/chem.201800261
       
  • Electron-Catalyzed Coupling of Magnesium Amides with Aryl Iodides
    • Authors: Kazuya Kiriyama; Keisho Okura, Fumiko Tamakuni, Eiji Shirakawa
      Abstract: The coupling reaction of magnesium diarylamides with aryl iodides was found to proceed through single electron transfer mechanism to give triarylamines with no aid of a transition metal catalyst and an additive.
      PubDate: 2018-02-15T21:46:08.97657-05:0
      DOI: 10.1002/chem.201800011
       
  • Dehydration Polymerization for Poly(hetero)arene Conjugated Polymers
    • Authors: Derek Schipper; Rafael Alberto Mirabal, Luke Vanderzwet, Sara Abuadas, Michael Emmett
      Abstract: The lack of scalable and sustainable methods to prepare conjugated polymers belies their importance in many enabling technologies. Accessing high-performance poly(hetero)arene conjugated polymers via dehydration has remained an unsolved problem in synthetic chemistry and has historically required transitional-metal coupling reactions. Here we report a dehydration method that allows access to conjugated heterocyclic materials. Using the technique, we have prepared a series of small molecules and polymers. The reaction avoids using transition metals, proceeds at room temperature, the only required reactant is a simple base and water is the sole by-product. The dehydration reaction is technically simple and provides a sustainable and straightforward method to prepare conjugated heteroarene motifs.
      PubDate: 2018-02-15T21:46:00.031215-05:
      DOI: 10.1002/chem.201800642
       
  • Sulfur Hydrogen Bonding in Isolated Monohydrates: Furfuryl Mercaptan vs.
           Furfuryl Alcohol
    • Authors: Marcos Juanes; Alberto Lesarri, Ruth Pinacho, Elena Charro, José E. Rubio, Lourdes Enriquez, Martín Jaraíz
      Abstract: The hydrogen bonds involving sulfur in the furfuryl mercaptan monohydrate are compared with the interactions originated by the hydroxyl group in furfuryl alcohol. The dimers with water were created in a supersonic jet expansion and characterized using microwave spectroscopy and supporting molecular orbital calculations. In furfuryl alcohol - water a single isomer is observed, in which the water molecule forms an insertion complex with two simultaneous hydrogen bonds to the alcohol (O-H···Ow) and the ring oxygen (Ow-H···Or). When the alcohol is replaced by a thiol group in furfuryl mercaptan - water two isomers are observed, with the thiol group preferentially behaving as proton donor to water. The first isomer is topologically equivalent to the alcohol analog but the stronger hydrogen bond is now established by water and the ring oxygen, assisted by a thiol S-H···Ow hydrogen bond. In the second isomer the sulfur group accepts a proton from water, forming a Ow-H···S hydrogen bond. Binding energies for the mercaptan - water dimer are predicted around 12 kJ mol-1 (B3LYP-D3(BJ)) weaker than in the alcohol hydrate. The non-covalent interactions in the furfuryl dimers are dominantly electrostatic according to a SAPT(0) energy decomposition, but with increasing dispersion components in the mercaptan dimers, larger for the isomer with the weaker Ow-H···S interaction.
      PubDate: 2018-02-15T15:40:26.628211-05:
      DOI: 10.1002/chem.201705727
       
  • A Step into the Future - Applications of Nanoparticle Enzyme Mimics
    • Authors: Wolfgang Tremel; Karsten Korschelt, Muhammad Nawaz Tahir
      Abstract: We describe elementary concepts, up-to-date developments, and per-spectives of the emerging field of nanoparticle enzyme mimics (so-called "nanozymes") at the interface of chemistry, biology, materials, and nanotechnology. The design and synthesis of functional enzyme mimics is a long-standing goal of biomimetic chemistry. Metal com-plexes, polymers and engineered biomolecules capturing the structure of natural enzymes or their active centers have been made to achieve high rates and enhanced selectivities. Still, the design of new "artificial en-zymes" that are not related to proteins but with capacity of production and stability at industrial level, remains a goal. Inorganic nanoparticles bear this potential. Although it seems counterintuitive to compare nanoparti-cles and natural enzymes because they appear very different they have many features in common: nano-size, irregular shape, and rich surface chemistry. These features enable nanomaterials to mimic reactions of natural enzymes. Representative examples with biomedical and envi-ronmental applications are given.
      PubDate: 2018-02-15T13:10:27.887982-05:
      DOI: 10.1002/chem.201800384
       
  • Experimental and Theoretical Identification of the Origin of Magnetic
           Anisotropy in Intermediate Spin Ground State Iron(III) Complexes.
    • Authors: Lianke Wang; Matija Zlatar, Filip Vlahovic, Serhiy Demeshko, Christian Philouze, Florian Molton, Franc Meyer, Carole Duboc, Maja Gruden, Marcello Gennari
      Abstract: The complexes [FeLN2S2X] (where LN2S2 = 2,2'-(2,2'-bipryridine-6,6'-diyl)bis(1,1'-diphenylethanethiolate) and X = Cl, Br and I), characterized crystallographically earlier and here (Fe(L)Br), reveal a square pyramidal coordinated FeIII ion. Unusually, all three complexes have intermediate spin ground states. Susceptibility measurements, powder cw X- and Q-band EPR spectra, zero-field powder Mössbauer spectra and DFT calculations show that all complexes display distinct magnetic anisotropy.
      PubDate: 2018-02-15T12:40:32.716265-05:
      DOI: 10.1002/chem.201705989
       
  • Dicyanamide salts that adopt smectic, columnar or bicontinuous cubic
           liquid-crystalline mesophases
    • Authors: Geonhui Park; Karel Goossens, Tae Joo Shin, Christopher W. Bielawski
      Abstract: While dicyanamide (i.e., [N(CN)2]-) has been commonly used to obtain low-viscosity, halogen-free, room-temperature ionic liquids, liquid-crystalline salts containing such anions have remained virtually unexplored. Here we report a series of amphiphilic dicyanamide salts that, depending on their structures and compositions, adopt smectic, columnar or bicontinuous cubic thermotropic liquid-crystalline mesophases, even at room temperature in some cases. Thermal properties were explored using polarized light optical microscopy, differential scanning calorimetry, thermogravimetric analysis (including evolved gas analysis), and variable-temperature synchrotron X-ray diffraction. A comparison of the thermal phase characteristics of the new liquid-crystalline salts featuring "V-shaped" [N(CN)2]- anions with those of structural analogues containing [SCN]-, [BF4]-, [PF6]- or [CF3SO3]- anions indicated that not only the size of the counterion but also its shape should be considered in the development of mesomorphic salts. Collectively, these discoveries should facilitate the design of thermotropic ionic liquid crystals that form inverted-type bicontinuous cubic and other sophisticated liquid-crystalline phases.
      PubDate: 2018-02-15T11:23:03.086362-05:
      DOI: 10.1002/chem.201705794
       
  • Sensitive and Specific Guest Recognition via Pyridinium-Modification in
           Spindle like Coordination Containers
    • Authors: Nagarajan Bhuvaneswari; Feng-Rong Dai, Zhong-Ning Chen
      Abstract: An elaborately designed pyridinium-functionalized octanuclear zinc(II) coordination container 1-Zn was prepared through the self-assembly of Zn2+, p-tert-butylsulfonylcalix[4]arene, and pyridinium functionalized angular flexible dicarboxylate linker (H2BrL1). The structure was determined by single crystal X-ray diffractometer. 1-Zn displays highly sensitive and specific recognition to 2-picolylamine as revealed by drastic blue-shifts of the absorption and emission spectra, ascribed to the decrease of intramolecular charge transfer (ICT) character of the container and the occurrence of intermolecular charge transfer between the host and guest molecules. The intramolecular charge transfer plays a key role in the modulation of the electronic properties and is tunable through endo-encapsulation of specific guest molecules.
      PubDate: 2018-02-15T11:22:48.443271-05:
      DOI: 10.1002/chem.201705210
       
  • Simultaneous G-quadruplex DNA Logic
    • Authors: Antoine Bader; Scott Lee Cockroft
      Abstract: A fundamental principle of digital computer operation is Boolean logic, where inputs and outputs are described by binary integer voltages. Similarly, inputs and outputs may be processed on the molecular level as exemplified by synthetic circuits that exploit the programmability of DNA base-pairing. Unlike modern computers, which execute large numbers of logic gates in parallel, most implementations of molecular logic have been limited to single computing tasks, or sensing applications. Here we report three G-quadruplex-based logic gates that operate simultaneously in a single reaction vessel. The gates respond to unique Boolean DNA inputs by undergoing topological conversion from duplex to G-quadruplex states that were resolved using a thioflavin T dye and gel electrophoresis. The modular, addressable and label-free approach could be incorporated into DNA-based sensors, or used for resolving and debugging parallel processes in DNA computing applications.
      PubDate: 2018-02-15T07:41:16.090883-05:
      DOI: 10.1002/chem.201800756
       
  • Nanopore Detection of Single-molecule Binding within a
           Metallosupramolecular Cage
    • Authors: Stefan Borsley; James Arthur Cooper, Paul J. Lusby, Scott Lee Cockroft
      Abstract: Guest encapsulation is a fundamental property of coordination cages. However, there is a paucity of methods capable of quantifying the dynamics of guest binding processes. Here, we demonstrate nanopore detection of single-molecule binding within metallosupramolecular cages. Real-time monitoring of the ion current flowing through a transmembrane α-hemolysin nanopore resolved the binding of different guests to both cage enantiomers. This enabled the single-molecule kinetics of guest binding to be quantified, while the ordering and durations of events were consistent with a guest-exchange mechanism that does not involve ligand dissociation. In addition to providing a new approach for single-molecule interrogation of dynamic supramolecular processes, we also established that cage complexes which are too large to enter the nanopore can be exploited for detecting small molecules, thus constituting a new class of molecular adapter.
      PubDate: 2018-02-15T07:40:40.754697-05:
      DOI: 10.1002/chem.201800760
       
  • Specific interaction sites determine differential adsorption of protein
           structural isomers to nanoparticle surfaces
    • Authors: Andrea Bortot; Serena Zanzoni, Mariapina D'Onofrio, Michael Assfalg
      Abstract: In biological milieus, nanoparticles (NPs) elicit bioactivity upon interaction with proteins. As a result of post-translational modification, proteins occur in a variety of alternative covalent forms, including structural isomers, which present unique molecular surfaces. We aimed at a detailed description of the recognition of protein isomeric species by NP surfaces. The transient adsorption of isomeric Ub dimers to NPs was investigated by solution NMR spectroscopy. Lys63-linked Ub2 and Lys48-linked Ub2 adsorbed to large anionic NPs with different affinity, while the binding strength was similar in the case of smaller particles. After incorporation of paramagnetic tags into NPs, the observed site-resolved paramagnetic footprints provided a high-resolution map of the different protein surfaces binding to NPs. The described approach could be extended to further protein isoforms and more specialized NP systems, allowing better control of interactions between NPs and protein targets.
      PubDate: 2018-02-15T06:35:39.966688-05:
      DOI: 10.1002/chem.201705994
       
  • Mechanism for enolate transfer between Si and Cu
    • Authors: Samira BOUAOULI; Kim SPIELMANN, Emmanuel VRANCKEN, Jean-Marc CAMPAGNE, Hélène Gérard
      Abstract: Exchange of X (F, Cl and OMe) and a substituted enolate chain between SiMe3 and various Cu(I) complexes has been examined. Reaction mechanisms go through a cyclic transition state in which the reaction coordinate is associated to the rotation of the SiMe3 moiety. The dependence of the thermodynamic and kinetic features to the nature of the active and ancillary ligand was examined. Formation of copper enolate is shown to be favoured when stabilized enolates are used. Replacement of F by Cl reverses the preference of the reaction. This was associated to the small difference between the Cu-Cl and Si-Cl bond energies, in contrast to other Si-X bonds which are systematically stronger than their Cu-X analogues.
      PubDate: 2018-02-15T06:10:50.413523-05:
      DOI: 10.1002/chem.201800099
       
  • Microwave-assisted, asymmetric synthesis of 3-amino-2,3-dihydrobenzofuran
           flavonoid derivatives from chalcones
    • Authors: Travis R. Helgren; Lianyan L. Xu, Daniel Sotelo, Yash R. Mehta, Melissa A. Korkmaz, Ivan Pavlinov, Leslie Aldrich
      Abstract: A route to access 3-amino-2,3-dihydrobenzofurans that utilizes microwave-assisted organic synthesis to rapidly generate analogues has been developed. The route begins with an acid-catalyzed, microwave-assisted aldol condensation to generate chalcone intermediates, followed by a Corey-Bakshi-Shibata reduction and subsequent Sharpless asymmetric epoxidation to access stereoisomeric epoxyalcohols. The final step is a one-pot, microwave-assisted, regioselective, acid-catalyzed epoxide opening with various amines followed by an intramolecular nucleophilic aromatic substitution reaction to generate the 3-amino-2,3-dihydrobenzofurans. This route provides ready access to stereochemically and structurally diverse analogues of these flavonoid scaffolds. Additionally, a pilot library was synthesized, and the biological activity diversity of the chalcones and dihydrobenzofurans was explored in human carcinoma cell lines.
      PubDate: 2018-02-14T21:46:17.192358-05:
      DOI: 10.1002/chem.201705984
       
  • One-Pot Generation of Bicyclo[3.1.0]hexanols and Cyclohexanones via Double
           Interrupted Nazarov Reaction
    • Authors: Shorena Gelozia; Yonghoon Kwon, Robert McDonald, F. G. West
      Abstract: Organoaluminum mediated double interrupted Nazarov cyclization to access bicyclo[3.1.0]hexanols via nucleophilic methyl attack followed by Simmons-Smith type electrophilic cyclopropanation is reported. These alcohols can undergo ring opening to afford cyclohexanones or cyclohexenones, broadening the range of scaffolds available via interrupted Nazarov reaction beyond the usual cyclopentanoid products. Throughout the sequence, a total of four new C-C bonds are formed, along with four new stereogenic centers.
      PubDate: 2018-02-14T14:05:50.21248-05:0
      DOI: 10.1002/chem.201800758
       
  • Bioorthogonal metabolic cellular DNA labelling using vinyl thioether
           modified thymidine and o-quinolinone quinone methide
    • Authors: Amu Gubu; Long Li, Ning Yan, Xiaoyun Zheng, Seonghyun Lee, Mengke Feng, Qiang Li, Xiaoguang Lei, Kyubong Jo, Xinjing Tang
      Abstract: Bioorthogonal metabolic DNA labelling with fluorochromes is a powerful strategy to visualize DNA molecules and their functions. Herein, we report the development of a new DNA metabolic labelling strategy enabled by the catalyst-free bioorthogonal ligation using vinyl thioether modified thymidine and o-quinolinone quinone methide. With the newly designed vinyl thioether-modified thymidine (VTdT), we added labelling tags on cellular DNA, which could further be linked to fluorochromes in cells. Therefore, we successfully visualized the DNA localization within cells as well as single DNA molecules without other staining reagents. In addition, we further characterized this bioorthogonal DNA metabolic labelling using DNase I digestion, MS characterization of VTdT as well as VTdT-oQQF conjugate in cell nuclei or mitochondria. This technique provides a powerful strategy to study DNA in cells, which paves the way to achieve future spatiotemporal deciphering of DNA synthesis and functions.
      PubDate: 2018-02-14T11:35:25.599977-05:
      DOI: 10.1002/chem.201705917
       
  • Regioselective C-H alkylation via carboxylate-directed hydroarylation in
           Water
    • Authors: Guodong Zhang; Fan Jia, Lukas J Goossen
      Abstract: In the presence of catalytic [Ru(p-cym)Cl2]2 and using Li3PO4 as the base, benzoic acids react with olefins in water to afford the corresponding 2-alkylbenzoic acids in moderate to excellent yields. This C-H alkylation process is generally applicable to diversely substituted electron-rich and electron-deficient benzoic acids, along with a,b-unsaturated olefins including unprotected acrylic acid. The widely available carboxylate directing group can be removed tracelessly or utilized for further derivatization. Mechanistic investigations revealed that the transformation proceeds via a ruthenacycle intermediate.
      PubDate: 2018-02-14T09:06:51.914989-05:
      DOI: 10.1002/chem.201800757
       
  • Organocatalytic C-F Bond Activation with Alanes
    • Authors: Alma Dorothea Jaeger; Christian Ehm, Dieter Lentz
      Abstract: Hydrodefluorination reactions (HDF) of per- and polyfluorinated olefins and arenes by cheap aluminum alkyl hydrides in non-coordinating solvents can be catalyzed by O and N donors. TONs with respect to the organocatalysts of up to 87 have been observed. Depending on substrate and concentration, high selectivities can be achieved. For the prototypical hexafluoropropene, however, low selectivities are observed (E/Z ~ 2). DFT studies show that the preferred HDF mechanism for this substrate in the presence of donor solvents proceeds from the dimer Me4Al2(μ-H)2·THF via nucleophilic vinylic substitution (SNV) like transition states with low selectivity and without formation of an intermediate, not via hydrometallation or σ-bond metathesis. In the absence of donor solvents, hydrometallation is preferred but this is associated with inaccessibly high activation barriers at low temperatures. Donor solvents activate the aluminium hydride bond, lower the barrier for HDF significantly and switch the product preference from Z to E. The exact nature of the donor has only a minimal influence on the selectivity at low concentrations, as the donor is located far away from the active center in the transition states. The mechanism changes at higher donor concentrations and proceeds from Me2AlH·THF via SNV and formation of a stable intermediate from which elimination is unselective, which results in a loss of selectivity.
      PubDate: 2018-02-14T09:06:13.252847-05:
      DOI: 10.1002/chem.201706061
       
  • Cation Triggered Stannate(II)/Stannylenoid/Stannylene Conversion
    • Authors: Xu-Qiong Xiao; Hui Zhao, Junxia Li, Zhifang Li, Mitsuo Kira, Thomas Müller
      Abstract: The reaction of dipotassio-tetrasilan-1,4-diide 4 with anhydrous SnCl2 at low temperature results in the formation of five-membered cyclic potassio chlorostannate(II) ([(18-C-6)K](1)). By careful cation exchange reactions, it was transformed into the sodium chloro stannylenoid 2 (using Na2[B12Cl12]) or into the non-stabilized cyclic bissilylstannylene 3 (applying Li[Al(OC(CF3)3)4]). The increasing Lewis basicity of bissilyl-stannylene 3 was analysed by combined methods of DFT calculations and NMR spectroscopy and substantiuated by the synthesis of the corresponding iron carbonyl complexes (7 and 8) from chlorostannate 1 and stannylene 3.
      PubDate: 2018-02-14T07:12:31.710246-05:
      DOI: 10.1002/chem.201800602
       
  • Optimization of synthetically versatile pyridylideneamide ligands for
           efficient iridium-catalyzed water oxidation
    • Authors: Miquel Navarro; Christene Smith, Mo Li, Stefan Bernhard, Martin Albrecht
      Abstract: The synthetic versatility of PYA ligands has been exploited to prepare and evaluate a diverging series of iridium complexes containing C,N-bidentate chelating aryl-PYA ligands for water oxidation catalysis. The phenyl-PYA lead structure was modified (i) electronically through introduction of one, two, or three electron-donating methoxy substituents on the aryl ring, (ii) by incorporating long aliphatic chains to the pyridyl fragment of the PYA unit, and (iii) by altering the PYA positions from para-PYA to its ortho- and meta-isomers. Electrochemistry indicated no substantial electronic effect of the aliphatic chains, and only minor changes of the electron density at iridium when modifying the aryl ligand site, yet substantial alteration if the PYA ligand is the ortho-, para-, or meta-isomer. In water oxidation catalysis, the long alkyl chains did not induce any rate enhancement compared to the phenyl-PYA lead compound, while MeO groups incorporated in the aryl group enhanced catalytic activity from a TOFmax =1600 h-1 in the original Ph-PYA system gradually as more MeO groups were introduced up to a TOFmax = 3200 h-1 for a tris(MeO)-substituted aryl-PYA system. The variation of the PYA substitution had only a minor impact on catalytic activity and revealed only a weak trend in the sequence ortho> meta> para. The high activity of the tris(MeO) system and the ortho-PYA isomer were attributed to efficient hydrogen bonding that assists O-H bond activation and proton transfer.
      PubDate: 2018-02-14T04:36:13.036023-05:
      DOI: 10.1002/chem.201705619
       
  • Augmenting Photoinduced Transport in a Single Component Gel System through
           Room Temperature Controlled In Situ Gel-Crystal Transformation
    • Authors: Sitakant Satapathy; Palani Prabakaran, Edamana Prasad
      Abstract: Smart single component materials with versatile functions requires pre-programming of a higher order molecular assembly. The contribution here introduces an electroactive supergelator (c = 0.07 wt%), i.e., triphenyl amine core appended poly(aryl ether) dendron (TPAPAE), where the substantial dendritic effect improves the order and crystallinity by switching the local minimum from self-assembled molecular wires to thermodynamically favourable global minimum of ordered crystals, ripened within the fibers. Controlled in situ phase change at room temperature ultimately stabilized the mixed valence states in the single component supramolecular assembly with an amplified photoluminescence and photoinduced charge transport by two orders of magnitude.
      PubDate: 2018-02-14T03:36:25.477992-05:
      DOI: 10.1002/chem.201800218
       
  • Self-assembly of a Guanosine Derivative to Form Nanostructures and
           Transmembrane Channels
    • Authors: Jyotirmayee Dash; Y. Pavan Kumar, S. Arun Kumar, Ole Mathis Schütte, Claudia Steinem, Jyotirmayee Dash
      Abstract: We herein report the self-assembly of a lipophilic bromoguanosine derivative (G1) in homogeneous solution, in the solid state, and in planar bilayer membrane. The self-assembly of G1, driven by H-bonding and - stacking interactions can form different nano-structures depending on incubation time. The G1 nanostructure is able to bind a bioactive dye like Rose Bengal. In crystal state, it shows ribbon type H-bonding pattern and exhibits birefringence in polarized light. And further, the self-assembled nanostructure of G1 can form discrete transmembrane ion channels in the biological membrane, enabling transportation of potassium ions.
      PubDate: 2018-02-14T03:05:35.883889-05:
      DOI: 10.1002/chem.201800205
       
  • Enhanced Drug Photosafety by Interchromophoric Interaction Due to
           Intramolecular Charge Separation
    • Authors: Ming-De Li; Zhiping Yan, Ruixue Zhu, David Lee Phillips, Isabel Aparici-Espert, Virginie Lhiaubet-Vallet, Miguel Angel Miranda
      Abstract: Imatinib is a tyrosinase inhibitor employed for the treatment of some kinds of human cancer. This drug has a low phototoxicity toward DNA but its pyridylpyrimidine (1) fragment by itself exhibits significant phototoxicitiy. The intrinsic mechanism that leads to the enhanced photosafety of Imatinib is not yet known. Here, the properties of the excited state and interchromophoric interactions of Imatinib have been explored using ultrafast laser flash photolysis and agarose electrophoresis studies. An intramolecular charge separation is directly observed upon the illuminated imatinib, which accounts for the relaxation of its excited state. An anion form of pyridyl-pyrimidine is deduced from results of time-resolved resonance Raman spectra and quenching experimental studies on 1 and diaminotoluene. In contrast, 1 efficiently transforms into triplet excited states with a long lifetime, which leads to the phototoxicity associated with 1. Our work provides insight into how to design drugs to have lower phototoxicitiy or improved photostability using interchromophoric interactions.
      PubDate: 2018-02-14T03:05:22.789103-05:
      DOI: 10.1002/chem.201800716
       
  • 12-Vertex Zwitterionic Bis-phosphonium-nido-carborates via Ring-opening
           Reaction of 1,2-Diphosphetanes
    • Authors: Evamarie Hey-Hawkins; Jan Schulz, Anika Kreienbrink, Peter Coburger, Benedikt Schwarze, Toni Grell, Peter Lönnecke
      Abstract: Carborane-substituted 1,2-diphosphetanes (Ia,b) react with lithium in THF with cleavage of the P−P bond to give a deep red solution from which red crystals of a lithiated intermediate, [{1-PtBuLi(THF)-6-PtBu-4,1,6-closo-Li(THF)C2B10H10}{Li(THF)3}]2∙ 2 THF (2), were obtained. The compound is dimeric and contains six Li and four P atoms. Two Li atoms are capping the six-membered C2B4 faces resulting in two 13-vertex closo-clusters with docosahedral geometry. Addition of MeI resulted in formation of the zwitterionic bis-phosphonium-nido-carborates, 7,10-bis(tert-butyl-dimethylphosphonium)-dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1a) and 7,10-bis(N,N-diisopropylamino-dimethylphosphonium)-dodecahydro-7,10-dicarba-nido-dodecaborate(2-) (1b) in moderate to good yields. 1a and 1b exhibit short C-P bonds and large C∙∙∙C distances in the solid state. Further insight into the ring opening and reduction potential of the alkyl halide was obtained from methylation reactions of different 1,2-bis-phosphinocarboranes. Reaction of rac/meso-1,2-bis(tert-butyl-methylphosphino)-1,2-dicarba-closo-dodecaborane(12) (3a) with two equivalents of methyl iodide resulted in formation of 1a as well (as shown by NMR spectroscopy) while the reaction of 1,2-bis(diphenylphosphino)-1,2-dicarba-closo-dodecaborane(12) with methyl triflate afforded the phosphonium salt 1-methyl-diphenylphosphonium-2-diphenylphosphino-1,2-dicarba-closo-dodecaborane(12) triflate (4) without reduction of the cluster.
      PubDate: 2018-02-13T22:06:48.812311-05:
      DOI: 10.1002/chem.201800172
       
  • Aerobic Oxidation Catalysis by a Molecular Barium Vanadium Oxide
    • Authors: Manuel Lechner; Katharina Kastner, Chee Jian Chan, Robert Güttel, Carsten Streb
      Abstract: Aerobic catalytic oxidations are promising routes to use O2 instead of environmentally harmful oxidants in organic syntheses. Here, we report the first example of a molecular barium vanadium oxide, [Ba4(dmso)14V14O38(NO3)] (= {Ba4V14}), as homogeneous aerobic oxidation catalyst. In N,N-dimethyl formamide at 8 bar O2 pressure, {Ba4V14} catalyses the dehydrogenation / aromatization of the model compound 9,10-dihydroanthracene, leading to anthracene formation. Stepwise catalytic oxygen transfer to anthracene subsequently results in the formation of the mono-oxygenated anthrone and the di-oxygenated target product, anthraquinone. Comparative reaction analyses using the Neumann catalyst [PV2Mo10O40]5- as reference show that oxygen diffusion into the reaction mixture is the rate-limiting step, resulting in accumulation of the reduced catalyst species. This understanding therefore allows us to propose improved reactor designs to overcome this fundamental challenge for aerobic oxidation catalysis.
      PubDate: 2018-02-13T13:05:24.762524-05:
      DOI: 10.1002/chem.201706046
       
  • Highly Efficient Photocatalytic System Constructed from CoP/Carbon
           Nanotubes or Graphene for Visible-Light-Driven CO2 Reduction
    • Authors: Wen Gan Fu
      Abstract: Visible-light-driven conversion of CO2 to CO and high- value-added carbon products is a promising strategy for mitigating CO2 emissions and reserving solar energy in chemical form. We report an efficient system for CO2 transformation to CO catalyzed by bare CoP, hybrid CoP/carbon nanotubes (CNTs), and CoP/reduced graphene oxide (rGO) in mixed aqueous solutions containing a Ru-based photosensitizer, under visible-light irradiation. The in situ prepared hybrid catalysts, i.e., CoP/CNT and CoP/rGO, show excellent catalytic activities in CO2 reduction to CO, with a catalytic rates of up to 39,510 and 47,330 μmol h−1 g−1 in the first 2 h of reaction, respectively; a high CO selectivity of 73.1% for the former was achieved in parallel competing reactions in the photoreduction of CO2 and H2O. A combination of experimental and computational studies clearly shows that strong interactions between CoP and carbon-supported materials and partially adsorbed H2O molecules on the catalyst surface significantly improve CO-generating rates.
      PubDate: 2018-02-13T11:35:24.462865-05:
      DOI: 10.1002/chem.201800335
       
  • Cover Feature: Panchromatic Photosensitizers Based on Push–Pull,
           Unsymmetrically Substituted Porphyrazines (Chem. Eur. J. 11/2018)
    • Authors: Javier Fernández-Ariza; Maxence Urbani, M. Salomé Rodríguez-Morgade, Tomás Torres
      Pages: 2522 - 2522
      Abstract: A series of A3B type push–pull porphyrazines, in which unit B is an isoindole 4-carboxylic acid, has been prepared. The A units have been endowed with electron-donor functions, either directly attached to the β-position of the pyrrolic units, or connected to the porphyrazine core through p-substituted phenyl groups. Their attachment to the porphyrazine periphery produces strong perturbation on the electronic properties of the dyes. The effective interaction of peripheral substitution with the macrocycle produces chromophores with panchromatic absorption between 300 and 750–850 nm. More information can be found in the Full Paper by M. S. Rodríguez-Morgade, T. Torres, et al. on page 2618.
      PubDate: 2018-01-29T08:30:38.704138-05:
      DOI: 10.1002/chem.201800113
       
  • Cover Feature: Rh-Catalyzed Denitrogenative Reaction of
           N-Sulfonyl-1,2,3-triazoles with Isatoic Anhydrides and Oxadiazolones
           (Chem. Eur. J. 11/2018)
    • Authors: Kuntal Pal; Abdul Hoque, Chandra M. R. Volla
      Pages: 2523 - 2523
      Abstract: The selective O−H over N−H insertion in the reaction of isatoic anhydrides with highly reactive Rh–azavinyl carbenes (Rh-AVC) is illustrated on the cover. Using this strategy, biologically interesting 2-amino-benzoxazinones and 5-oxadiazoles were obtained under operationally simple conditions from easily available isatoic anhydrides and oxadiazolones, respecively. Furthermore, the potential of the developed protocol was demonstrated by the novel synthesis of imidazo-fused benzoxazinones. More information can be found in the Communication by C. M. R. Volla et al. on page 2558.
      PubDate: 2018-02-05T10:15:10.294097-05:
      DOI: 10.1002/chem.201800388
       
  • Selective Single-Site Pd−In Hydrogenation Catalyst for Production of
           Enhanced Magnetic Resonance Signals using Parahydrogen
    • Authors: Dudari B. Burueva; Kirill V. Kovtunov, Andrey V. Bukhtiyarov, Danila A. Barskiy, Igor P. Prosvirin, Igor S. Mashkovsky, Galina N. Baeva, Valerii I. Bukhtiyarov, Aleksandr Yu. Stakheev, Igor V. Koptyug
      Pages: 2547 - 2553
      Abstract: Pd−In/Al2O3 single-site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd−In compound was studied by XPS during reduction of the catalyst. FTIR−CO spectroscopy confirmed single-site nature of the intermetallic Pd−In phase reduced at high temperature. Utilization of Pd−In/Al2O3 in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400-fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd−In catalyst allowed to acquire 1H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH2 and CH3 groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.Pd-In/Al2O3 single-site catalyst was able to show high selectivity in the both gas phase semihydrogenation of propyne and pairwise hydrogen addition with 3400-fold NMR signal enhancement. Significant signal enhancement as well as the high catalytic performance of the Pd-In catalyst allowed the use of hyperpolarized propene for 1H MRI visualization selectively to the protons of CH3, CH2, and CH groups that is hardly possible in the case of thermal propene.
      PubDate: 2018-01-29T08:26:36.340905-05:
      DOI: 10.1002/chem.201705644
       
  • Ultrafine and Ligand-Free Precious Metal (Ru, Ag, Au, Rh and Pd)
           Nanoclusters Supported on Phosphorus-Doped Carbon
    • Authors: Ben Liu; Lei Jin, Wei Zhong, Aaron Lopes, Steven L. Suib, Jie He
      Pages: 2565 - 2569
      Abstract: We report the use of phosphorus-doped carbon (P-C) as support to grow ultrasmall (1–3 nm) and ligand-free precious metal nanocrystals (PMNCs) via chemical reduction. We show that the valence states of surface phosphorus species are critical in tuning the affinity between the carbon support and metal precursors, which rationally controls the loading size and uniformity of resultant PMNCs. Five kinds of PMNCs, including Ru, Ag, Au, Rh, and Pd, were grown in situ to demonstrate the key role of surface phosphorus sites on the P-C support. As a proof-of-concept application, Ru nanocatalysts with an average diameter of 1.0±0.2 nm supported on P-C were examined for the electrocatalytic hydrogen evolution reaction (HER). Ultrasmall and ligand-free Ru nanocatalysts exhibited superior HER activity and stability compared to its counterparts with surface agents or larger sizes. An overpotential of 27.6 mV (vs. reversible hydrogen electrode) for Ru nanocatalysts was achieved at a current density of 10 mA cm−2. This novel method opens a new avenue to immobilize ligand-free and well-dispersed PMNCs on carbon; and, more importantly, it provides a new library of supported PMNCs with high catalytic activity.Phosphorus-doped carbon is used as the support to grow in situ ultrasmall and ligand-free precious metal nanoclusters (PMNCs). We demonstrate that the content and the oxidation state of surface phosphorus species are vital to control the loading size and distribution of supported PMNCs. The resultant Ru nanoclusters exhibit the excellent activity for hydrogen evolution, comparable to that of commercial Pt/C.
      PubDate: 2018-01-29T04:51:55.30127-05:0
      DOI: 10.1002/chem.201705504
       
  • Phosphine/Sulfoxide-Supported Carbon(0) Complex
    • Authors: Mariana Lozano González; Laura Bousquet, Sophie Hameury, Cecilio Alvarez Toledano, Nathalie Saffon-Merceron, Vicenç Branchadell, Eddy Maerten, Antoine Baceiredo
      Pages: 2570 - 2574
      Abstract: A new carbon(0) complex 2 with two different L ligands, a phosphine and a sulfoxide, was synthesized and fully characterized. This new type of carbone exhibits excellent coordination ability, in contrast to the related phosphine/sulfide-supported carbon(0) complexes. Several organometallic complexes were isolated and, of special interest, the νav(CO) value of RhI-dicarbonyl complex indicates that 2 has a donor capability superior to classical NHCs.A stable phosphine/sulfoxide carbone was isolated and fully characterized by NMR spectroscopy and by X-ray crystallography. This species exhibits excellent coordination ability and the corresponding RhI-dicarbonyl complex indicates a strong nucleophilic character, in clear agreement with theoretical calculations.
      PubDate: 2018-01-31T11:58:14.826988-05:
      DOI: 10.1002/chem.201705557
       
  • Mechanistic Insights into Hydrogen Activation by Frustrated N/Sn Lewis
           Pairs
    • Authors: Shubhajit Das; Sukanta Mondal, Swapan K. Pati
      Pages: 2575 - 2579
      Abstract: The mechanism of H2 activation by recently reported N/Sn Lewis pairs is unravelled using the representative iPr3SnOTf/DABCO combination. Computations provide evidence for weak intermolecular associations between Lewis acid and Lewis base (LA/LB) in which the counteranion to cationic LA fragment plays a critical role. Two frustrated Lewis pairs (FLPs) are observed; an unprecedented counteranion-mediated noncovalent LA/LB association is characterised along with the usual FLP structure. Both the FLPs are shown to be capable of H2 activation through cooperative electron transfer processes involving the LA/LB centres. Overall, computed results are in good agreement with the experimental findings and account for the observed reactivity. Insights obtained in this study are fundamentally important for the rational design of Sn-based alternative FLP LAs. The present findings could also provide a general mechanistic framework for H2 activation by FLPs having an ion pair LA component.The adventures of tin and N: The mechanism of H2 activation by recently reported N/Sn Lewis pairs is unravelled using the representative iPr3SnOTf/DABCO combination. Computations provide evidence for weak intermolecular associations between Lewis acid and Lewis base (LA/LB) in which the counteranion to cationic LA fragment plays a critical role. Two frustrated Lewis pair structures are shown to be capable of H2 activation through cooperative electron transfer processes involving the LA/LB centres.
      PubDate: 2018-01-25T09:30:40.583792-05:
      DOI: 10.1002/chem.201705861
       
  • Metal Complex-Controlled Regio-, Diastero- and Enantioselective
           1,3-Dipolar Cycloaddition of Azomethine Ylides with Benzo[b]thiophene
           Sulfones
    • Authors: Masato Harada; Shuma Kato, Ryosuke Haraguchi, Shin-ichi Fukuzawa
      Pages: 2580 - 2583
      Abstract: The Cu(MeCN)4PF6/DTBM-Segphos complex catalyzed the highly diastereo- and enantioselective 1,3-dipolar cycloaddition of azomethine ylides with benzo[b]thiophene sulfones with the usual regiochemistry to give single isomers of the exo-cycloadducts in good yields. In contrast, the AgOAc/ThioClickFerrophos complex catalyzed the reaction with atypical regiochemistry to give the endo-cycloadducts as major products with excellent enantioselectivities. Thus, the choice of chiral metal complex enabled the regio- and stereoselective synthesis of chiral fused sulfolanes.A chiral copper complex catalyzed the highly diastereo- and enantioselective 1,3-dipolar cycloaddition of azomethine ylides with benzo[b]thiophene sulfones with the usual regiochemistry to give single isomers of the exo-cycloadducts. In contrast, a chiral silver complex catalyzed the reaction with atypical regiochemistry to give the endo-cycloadducts as major products with excellent enantioselectivities.
      PubDate: 2018-01-29T04:47:02.944844-05:
      DOI: 10.1002/chem.201706033
       
  • Fluorescent Polyvinylphosphonate Bioconjugates for Selective Cellular
           Delivery
    • Authors: Christina Schwarzenböck; Andreas Schaffer, Elfriede Nößner, Peter J. Nelson, Ralf Huss, Bernhard Rieger
      Pages: 2584 - 2587
      Abstract: To date, many poly(ethylene glycol) (PEG) and poly(N-isopropylacrylamide) (PNIPAAm) biomolecule conjugates have been described, but they often show long response times, are not bio-inert, or lose function in biological fluids. Herein, we present a modular synthetic approach to generate polyvinylphosphonate biomolecule conjugates. These conjugates exhibit a sharp phase transition temperature even under physiological conditions where few other examples with this property have been described to date. Furthermore, it was feasible to add biological functions to the polymers via the conjugation step. The polyvinylphosphonate cholesterol constructs are attached to the cellular membrane and the folic acid anchored polymers are shuttled into the cells. This is an exceptional finding through a straightforward synthetic approach.Fluorescent polyvinylphosphonates were obtained by post-polymerization transesterification. Thiol-ene click reactions led to fluorescent cholesterol- and folic acid-functionalized polyvinylphosphonates. Turbidity measurements in complex biological fluids could show the retention of the thermoresponsive properties. Concluding the confocal microscopy experiments proved to selective cellular uptake of the bioconjugates into the cells or its anchoring to the plasma membrane.
      PubDate: 2018-01-25T07:40:52.76882-05:0
      DOI: 10.1002/chem.201706034
       
  • Structural and Magnetic Variations in a Family of Isoskeletal,
           Oximate-Bridged {MnIV2MIII} Complexes (MIII=Mn, Gd, Dy)
    • Authors: Alysha A. Alaimo; Anne Worrell, Sayak Das Gupta, Khalil A. Abboud, Christos Lampropoulos, George Christou, Theocharis C. Stamatatos
      Pages: 2588 - 2592
      Abstract: The self-assembly reaction of MnCl2⋅4H2O, acenaphthenequinone dioxime (acndH2) and NEt3 has yielded an unprecedented, linear {MnIV2MnIII} complex with an S=5 spin ground state and non-SMM behavior. The targeted replacement of the central MnIII ion with GdIII and DyIII ions has successfully increased the S and turned on the SMM dynamics without affecting the core structure and the nature of the magnetic exchange interactions.The self-assembly reaction of MnCl2⋅4 H2O, acenaphthenequinone dioxime (acndH2) and NEt3 has yielded an unprecedented, linear {MnIV2MnIII} complex with an S=5 spin ground state and non-SMM behavior. The targeted replacement of the central MnIII ion with GdIII and DyIII ions has successfully increased the S and turned on the SMM dynamics without affecting the core structure and the nature of the magnetic exchange interactions.
      PubDate: 2018-01-25T07:37:00.598109-05:
      DOI: 10.1002/chem.201706098
       
  • Sialyl Tn Unit with TFA-Labile Protection Realizes Efficient Synthesis of
           Sialyl Glycoprotein
    • Authors: Naoki Takeda; Toshiki Takei, Yuya Asahina, Hironobu Hojo
      Pages: 2593 - 2597
      Abstract: Amino acids bearing 4-methylbenzyl (MBn) and 4-methoxybenzyl (MPM)-protected sialic acid were synthesized and used for the 9-fluorenylmethoxycarbonyl (Fmoc) solid-phase synthesis of a glycopeptide. The α-sialyl linkage of the MBn-protected unit was partially cleaved under the final deprotection by trifluoroacetic acid (TFA). In addition, the removal of several MBn groups were incomplete. On the other hand, the MPM-protected unit gave the desired glycopeptide without decomposition of the α-sialyl linkage. Using this unit, peptide thioesters of the tandem repeat unit of MUC1 mucin were synthesized by the N-alkylcysteine (NAC) method and used for the one-pot ligation by the thioester method. As a result, the three tandem repeats of MUC1 carrying sialyl Tn antigens were successfully synthesized.A novel protection strategy for an efficient synthesis of sialylpeptides was developed. Two acid-labile protecting groups, MPM groups for Neu5Ac and MBn groups for GalNAc, realized the one-pot final deprotection using a TFA cocktail, keeping α-sialyl linkage intact. The fully deprotected sialyl glycopeptides were thioesterified by the N-alkylcysteine method and ligated by the thioester method in one-pot to obtain the MUC1 three-tandem repeat domain carrying sialyl Tn antigens.
      PubDate: 2018-01-25T07:40:56.976251-05:
      DOI: 10.1002/chem.201706127
       
  • Direct Catalytic Asymmetric Aldol Reaction of Thioamide with an
           α-Vinyl Appendage
    • Authors: Jin Cui; Akimichi Ohtsuki, Takumi Watanabe, Naoya Kumagai, Masakatsu Shibasaki
      Pages: 2598 - 2601
      Abstract: The direct catalytic asymmetric aldol reaction is an emerging catalytic methodology that provides atom-economical access to functionalized chiral building blocks. Thioamides are useful aldol donors due to their high-fidelity chemoselective enolization and divergent post-aldol transformations. Herein we describe the incorporation of an α-vinyl appendage on a thioamide, which expands the utility of aldol adducts for natural product synthesis. This vinylated thioamide was not accommodated under the previously identified catalyst settings, but the newly developed catalytic conditions furnished aldol products containing the pendant vinyl group.The direct catalytic asymmetric aldol reaction is an emerging catalytic methodology that provides atom-economical access to functionalized chiral building blocks. Thioamides are useful aldol donors due to their high-fidelity chemoselective enolization and divergent post-aldol transformations. Herein we describe the incorporation of an α-vinyl appendage on a thioamide, which expands the utility of aldol adducts for natural product synthesis. This vinylated thioamide was not accommodated under the previously identified catalyst settings, but the newly developed catalytic conditions furnished aldol products containing the pendant vinyl aldol reaction
      PubDate: 2018-01-25T07:35:29.170558-05:
      DOI: 10.1002/chem.201800020
       
  • Photosensitization of Molecular Oxygen on Graphene Oxide for
           Ultrasensitive Signal Amplification
    • Authors: Xinfeng Zhang; Li Deng, Chengpeng Huang, Jinyi Zhang, Xiandeng Hou, Peng Wu, Juewen Liu
      Pages: 2602 - 2608
      Abstract: H2O2 and horseradish peroxidase (HRP) are commonly used together in bioassays. HRP is required to accelerate the reaction between a chromogenic substrate (e.g., 3,3′,5,5′-tetramethylbenzidine, TMB) and H2O2, and thus amplifies the signal. Herein, molecular oxygen for enzyme-free and H2O2-free oxidation is explored, still using the same colorimetric reaction. Restricted by spin selection rules, the ground-state triplet oxygen needs to be converted to the singlet state to oxidize TMB. Phloxine B (PB) is used as the photosensitizer because of its excellent performance and safety. Under green light irradiation, each PB has a turnover of approximately 51 TMB molecules in 20 min, making PB a “molecular enzyme mimic” for signal amplification. With its small size, multiple PB molecules are loaded on a graphene oxide nanosheet to design a modified enzyme-linked immunosorbance (ELISA) assay (termed photosensitization immunosorbent assay, PISA), improving the 1:1 enzyme/target ratio to n:1. PISA is more sensitive for carcinoembryonic antigen than a commercial ELISA kit, and successfully measures the antigen in the serum of multiple cancer patients. This simple and green method of oxidation coupled with the small size of the photosensitizer and graphene oxide may enable many other applications in biosensor development, smart materials, and energy harvesting.Green ELISA: The photosensitizer phloxine B (PB) is explored for the activation of molecular oxygen to allow direct oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB), eliminating the need for the unstable enzymes and H2O2 required for traditional immunoassays. Visual detection of carcinoembryonic antigen (CEA) is possible for concentrations as low as 50 pg mL−1 (see figure).
      PubDate: 2018-01-09T08:37:06.029687-05:
      DOI: 10.1002/chem.201704866
       
  • Dithiocarboxylic Acids: An Old Theme Revisited and Augmented by New
           Preparative, Spectroscopic and Structural Facts
    • Authors: Johanna Grote; Felix Friedrich, Katarína Berthold, Loreen Hericks, Beate Neumann, Hans-Georg Stammler, Norbert W. Mitzel
      Pages: 2626 - 2633
      Abstract: The unstable dithiocarboxylic acids dithioacetic acid, 2-methyl-dithiopropionic acid, 2,2-dimethyl-dithiopropionic acid and dithiobenzoic acid were synthesized and characterized by NMR spectroscopy and GC/MS. The stable dithiocarboxylic acids 2,4,6-trimethyl benzoic acid, 2,4,6-tri-iso-propylbenzoic acid and 2,6-dimesityl benzoic acid were synthesized, isolated and characterized by spectroscopic methods and in parts by mass spectrometry and X-ray crystallography. The new data were used to re-evaluate literature data on the synthesis, spectroscopy and structural data of dithiocarboxylic acids as a fundamental class of organic compounds in general.Acids revisited: Although described since more than 150 years, dithiocarboxylic acids remained a scarcely characterized class of compounds; here we describe synthesis and isolation of true free acids and critically review earlier data.
      PubDate: 2018-01-31T09:30:40.568269-05:
      DOI: 10.1002/chem.201704235
       
  • Asymmetric Total Syntheses and Structure Confirmation of Chlorofucins and
           Bromofucins
    • Authors: Byungsook Kim; Te-ik Sohn, Deukjoon Kim, Robert S. Paton
      Pages: 2634 - 2642
      Abstract: Substrate-controlled asymmetric total syntheses and structure confirmation of (+)-(3E)- and (−)-(3Z)-chlorofucin [(E)-1 a and (Z)-1 a], and (+)-(3E)- and (−)-(3Z)-bromofucin [(E)-1 b and (Z)-1 b] were accomplished. Our syntheses feature as key steps haloetherification (either ‘conventional’ or ‘one-pot organoselenium-mediated’) of α,α′-trans-γ,δ-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 α,α′-trans-γ,δ-unsaturated oxocene alcohol 9 and its α,α′-cis isomer 9′ in the presence of different electrophiles during the intramolecular electrophilic addition reactions.Control is crucial: Substrate-controlled asymmetric total syntheses and structure confirmation of chlorofucins and bromofucins have been achieved through haloetherification, either ‘conventional’ or ‘one-pot organoselenium-mediated’ (see scheme). More importantly, a rationale is provided for the strikingly different pathways followed by α,α′-trans-γ,δ-unsaturated oxocene alcohol 9 and its α,α′-cis isomer in the presence of different electrophiles during the intramolecular electrophilic addition reactions.
      PubDate: 2018-01-25T09:31:46.032309-05:
      DOI: 10.1002/chem.201704564
       
  • Tunable Emission from Fluorescent Organic Nanoparticles in Water: Insight
           into the Nature of Self-Assembly and Photoswitching
    • Authors: Akash Gulyani; Nilanjan Dey, Santanu Bhattacharya
      Pages: 2643 - 2652
      Abstract: Excitation-dependent tuning of the emission behavior of fluorescent organic nanoparticles (FONs) with two simple luminescent pyrenyl–pyridyl conjugates as model systems is demonstrated. In the case of the compound with a flexible bis-picolyl moiety, the simultaneous presence of multiple ground-state species with distinct absorption and emission characteristics can be observed. The relative ratios of these species can easily be modulated, and it is possible to selectively stimulate any one of them individually by choosing an appropriate excitation channel. Moreover, at high concentration, a drastic change in the nature of the self-assembly is observed, which shifts from donor–acceptor-type self-assembly to exciplex-type self-agglomeration. On the contrary, the compound containing a rigid terpyridine unit has only a single ground state and shows no such tunable emission. However, it can exhibit multiple emission bands in water, whereby the positions of their emission maxima depend on the extent of aggregation-induced planarization of the probe molecules. Overall, this work demonstrates multimodal modulation of FON emission and a gives insight into how molecular order can translate into complete switching of nanoparticle self-assembly and photophysics.Excitation-dependent emission tuning of fluorescent organic nanoparticles is demonstrated. In the case of the flexible compound, the simultaneous presence of multiple ground-state species with distinct absorption and emission characteristics can be observed. Their relative ratios can be modulated, and they can be selectively stimulated by choosing an appropriate excitation channel (see figure). The rigid compound shows no such tunable emission, but it can exhibit multiple emission bands in water, the positions of which depend on the extent of aggregation-induced planarization of the molecules.
      PubDate: 2018-01-26T05:00:34.199696-05:
      DOI: 10.1002/chem.201704607
       
  • Sulfoxide-Induced Homochiral Folding of ortho-Phenylene Ethynylenes
           (o-OPEs) by Silver(I) Templating: Structure and Chiroptical Properties
    • Authors: Sandra Resa; Delia Miguel, Santiago Guisán-Ceinos, Giuseppe Mazzeo, Duane Choquesillo-Lazarte, Sergio Abbate, Luis Crovetto, Diego J. Cárdenas, M. Carmen Carreño, María Ribagorda, Giovanna Longhi, Antonio J. Mota, Luis Álvarez de Cienfuegos, Juan M. Cuerva
      Pages: 2653 - 2662
      Abstract: A new family of homochiral silver complexes based on carbophilic interactions with ortho-phenylene ethynylene (o-OPE) scaffolds containing up to two silver atoms are described. These compounds represent a unique class of complexes with chirality at the metal. Chiral induction is based on the inclusion of chiral sulfoxides, which allow efficient transfer of chirality to the helically folded o-OPE, leading to circularly polarized luminescence (CPL)- and vibrational circular dichroism (VCD)-active compounds. In the presence of silver(I) cations, carbophilic interactions dominate, which promote helical structures with a defined helicity. This is one of the very scarce examples of the use of such interactions in the attractive field of abiotic foldamers. The switching event has been extensively studied by using different chiroptical techniques, including circular dichroism, CPL, and VCD, and represents one of the few CPL switches described in the literature.Silver twists: A new family of homochiral silver complexes based on carbophilic interactions with ortho-phenylene ethynylene (o-OPE) scaffolds containing up to two silver atoms are described. In the presence of silver(I) cations, carbophilic interactions dominate, which promote helical structures with a defined helicity (see figure). This is one of the very scarce examples of the use of such interactions in the attractive field of abiotic foldamers.
      PubDate: 2018-01-24T03:26:12.18741-05:0
      DOI: 10.1002/chem.201704897
       
  • Investigations of the Copper-Catalyzed Oxidative Cross-Coupling of
           Tetrahydroisoquinolines with Diethylzinc by a Combination of Mass
           Spectrometric and Electrochemical Methods
    • Authors: J. Alexander Willms; Hermann Gleich, Michael Schrempp, Dirk Menche, Marianne Engeser
      Pages: 2663 - 2668
      Abstract: The aerobic oxidative cross-coupling of tetrahydroisoquinolines (THIQs) with diethylzinc catalyzed by CuCl2 has been examined by means of electrospray mass spectrometry (ESI-MS). Substrates, intermediates, and the product were readily detected. Particular emphasis has been placed on the role of CuCl2. Formation of the intermediate iminium species has been investigated in more detail by ESI-MS, electrochemistry-coupled ESI mass spectrometry (EC-MS), and cyclic voltammetry (CV). Our experiments have consistently revealed strong influences of the N-substituent of the THIQ derivative and its oxidation stability with respect to CuCl2. The results may help to expand the synthetic scope of the reaction, while also further establishing EC-MS as a valuable technique for linking mass spectrometry with cyclic voltammetry in mechanistic studies of organic redox reactions.Substrate screening beyond synthesis: Through a combination of electrospray mass spectrometry (ESI-MS), online electrochemistry mass spectrometry (EC-MS), and cyclic voltammetry (CV), mechanistic insight has been gained into the cross-coupling of tetrahydroisoquinolines (THIQs) with diethylzinc.
      PubDate: 2018-01-26T05:01:17.581299-05:
      DOI: 10.1002/chem.201704914
       
  • Correlation between Ionic Liquid Cytotoxicity and Liposome–Ionic
           Liquid Interactions
    • Authors: Suvi-Katriina Ruokonen; Corinna Sanwald, Alexandra Robciuc, Sami Hietala, Antti H. Rantamäki, Joanna Witos, Alistair W. T. King, Michael Lämmerhofer, Susanne K. Wiedmer
      Pages: 2669 - 2680
      Abstract: This study aims at extending the understanding of the toxicity mechanism of ionic liquids (ILs) using various analytical methods and cytotoxicity assays. The cytotoxicity of eight ILs and one zwitterionic compound was determined using mammalian and bacterial cells. The time dependency of the IL toxicity was assessed using human corneal epithelial cells. Hemolysis was performed using human red blood cells and the results were compared with destabilization data of synthetic liposomes upon addition of ILs. The effect of the ILs on the size and zeta potential of liposomes revealed information on changes in the lipid bilayer. Differential scanning calorimetry was used to study the penetration of the ILs into the lipid bilayer. Pulsed field gradient nuclear magnetic resonance spectroscopy was used to determine whether the ILs occurred as unimers, micelles, or if they were bound to liposomes. The results show that the investigated ILs can be divided into three groups based on the cytotoxicity mechanism: cell wall disrupting ILs, ILs exerting toxicity through both cell wall penetration and metabolic alteration, and ILs affecting solely on cell metabolism.Ionic liquids: The toxicity of ionic liquids is predicted using biomimicking-liposomes instead of living organisms and the results are in a good agreement with the cytotoxicity results obtained using various cell lines.
      PubDate: 2018-01-24T03:45:31.57356-05:0
      DOI: 10.1002/chem.201704924
       
  • Microporous MOFs Engaged in the Formation of Nitrogen-Doped Mesoporous
           Carbon Nanosheets for High-Rate Supercapacitors
    • Authors: Ya-Nan Hou; Zongbin Zhao, Zhengfa Yu, Su Zhang, Shaofeng Li, Juan Yang, Han Zhang, Chang Liu, Zhiyu Wang, Jieshan Qiu
      Pages: 2681 - 2686
      Abstract: Nitrogen-doped mesoporous carbon nanosheets (NMCS) have been fabricated from zinc-based microporous metal–organic frameworks (ZIF-8) by pyrolysis in a molten salt medium. The as-prepared NMCS exhibit significantly improved specific capacitance (NMCS-8: 232 F g−1 at 0.5 A g−1) and capacitance retention ratio (75.9 % at 50 A g−1) compared with the micropore-dominant nitrogen-doped porous carbon polyhedrons (NPCP-5: 178 F g−1 at 0.5 A g−1, 15.9 % at 20 A g−1) obtained by direct pyrolysis of nanocrystalline ZIF-8. The excellent capacitive performance and high rate performance of the NMCS can be attributed to their unique combination of structure and composition, that is, the two-dimensional and hierarchically porous structure provides a short ion-transport pathway and facilitates the supply of electrolyte ions, and the nitrogen-doped polar surface improves the interface wettability when used as an electrode.Converting micropore into mesopore: Nitrogen-doped mesoporous carbon nanosheets (NMCS) have been fabricated from a zinc-based microporous MOF (ZIF-8) by pyrolysis in a molten salt medium for application in high-rate supercapacitors (see figure). The as-prepared NMCS exhibit significantly improved specific capacitance and capacitance retention ratio compared with the micropore-dominant nitrogen-doped porous carbon polyhedrons obtained by direct pyrolysis of nanocrystalline ZIF-8.
      PubDate: 2018-01-31T12:03:03.555605-05:
      DOI: 10.1002/chem.201705006
       
  • Methylsemicarbazide as a Ligand in Late 3d Transition Metal Complexes
    • Authors: Norbert Szimhardt; Jörg Stierstorfer
      Pages: 2687 - 2698
      Abstract: Most ignition and initiation systems nowadays still contain poisonous chemicals such as lead styphnate and lead azide but also chromates and other compounds of high concern. Therefore, methylsemicarbazide (1, MSC), which can be prepared in a one-step reaction and in an extraordinary high yield of 95 %, has been evaluated as ligand in energetic coordination compounds. For the first time 25 new transition metal complexes (Mn2+, Ni2+, Co2+, Cu2+, and Zn2+) using methylsemicarbazide (1) as the ligand were prepared and comprehensively analyzed by, for example, XRD, IR, EA, UV/Vis and DSC/DTA/TGA. Many show a strong energetic character, which can be tuned by using different anions such as Cl−, SO42−, NO3−, ClO4−, picrate or styphnate. Selected compounds were additionally evaluated as lead-free primary explosives in initiation tests (nitropenta filled detonators) and in laser ignition systems. Especially compound 7 showed very promising results during these tests and could be a potential candidate for future applications.Methylsemicarbazide (MSC) was successfully demonstrated as a suitable building block in the formation of 25 new energetic coordination compounds (ECC). The further clever selection of late 3d metals, co-solvents and anions yielded a wide choice of different functional materials partly suitable for laser ignition or as a classical primary explosive.
      PubDate: 2018-01-31T11:57:15.979736-05:
      DOI: 10.1002/chem.201705030
       
  • 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
      Pages: 2699 - 2708
      Abstract: A versatile two-step synthesis of tris(pentafluoroethyl)stannane, HSn(C2F5)3, is presented. Electron-withdrawing C2F5 groups significantly influence the polarity of the tin–hydrogen bond, which allows 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 remarkably high reactivity of HSn(C2F5)3 is demonstrated in fast hydrostannylations, even in the absence of activators, whereby the regioselectivity of this process turns 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 that allow facile separation of the tin-containing byproducts from the reaction mixtures.Volatile separations: A versatile two-step synthesis of tris(pentafluoroethyl)stannane, HSn(C2F5)3, as a rare example of an electron-deficient stannane is presented. The utility of this volatile stannane is illustrated through the hydrostannylations of alkenes and alkynes, and dehalogenation reactions in the absence of activators.
      PubDate: 2018-01-30T02:35:31.863736-05:
      DOI: 10.1002/chem.201705068
       
  • Effects of the Bidentate Ligand on the Photophysical Properties, Cellular
           Uptake, and (Photo)cytotoxicity of Glycoconjugates Based on the
           [Ru(tpy)(NN)(L)]2+ Scaffold
    • Authors: Lucien N. Lameijer; Tobias G. Brevé, Vincent H. S. van Rixel, Sven H. C. Askes, M. A. Siegler, Sylvestre Bonnet
      Pages: 2709 - 2717
      Abstract: Ruthenium polypyridyl complexes have received widespread attention as potential chemotherapeutics in photodynamic therapy (PDT) and in photochemotherapy (PACT). Here, 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. However, the non-toxic complexes are excellent candidates as PACT carriers.Lighting the path: Sixteen different ruthenium polypyridyl complexes based upon the [Ru(tpy)(N−N)(L)]+ scaffold were thoroughly investigated as potential agents for anticancer phototherapy. Photophysical, cytotoxicity, and uptake studies provide a structure–activity relationship for this family of compounds. Photoactivated chemotherapy (PACT) initiated upon photosubstitution, or photodynamic therapy (PDT) through singlet-oxygen generation may occur, depending on the ligand.
      PubDate: 2018-01-30T02:36:17.216804-05:
      DOI: 10.1002/chem.201705388
       
  • A Zwitterionic Ligand-Based Cationic Metal-Organic Framework for Rapidly
           Selective Dye Capture and Highly Efficient Cr2O72− Removal
    • Authors: Chenghui Zhang; Yuchuan Liu, Libo Sun, Huaizhong Shi, Chao Shi, Zhiqiang Liang, Jiyang Li
      Pages: 2718 - 2724
      Abstract: A cationic metal–organic framework (MOF), [Cu2L(H2O)2]⋅(NO3)2⋅5.5 H2O (1) has been successfully synthesized from a zwitterionic ligand 1,1′-bis(3,5-dicarboxyphenyl)-4,4′-bipyridinium chlorine ([H4L]Cl2). The framework of compound 1 contains classical {Cu2(O2C)4} paddlewheels, and possesses typical nbo-type topology and two types of channels with sizes of 5.0 and 15.54 Å. Benefitting from the 3D cationic framework and high pore volume, compound 1 shows interesting selective adsorption ability for anionic dyes. Such material can be successfully employed in a chromatographic column to efficiently separate mixed dyes of Fluorescein Sodium and Methylene Blue. In addition, compound 1 exhibits excellent Cr2O72− removal capacity with maximum adsorption amount of 222.5 mg g−1, which ranks among the higher Cr2O72− adsorption amounts of MOF materials ever reported, based on ion-exchange. The strategy to construct cationic MOFs based on zwitterionic ligands will promote the development of functional porous materials for the capture and removal of anionic pollutant species from contaminated liquid.Capture the imagination: A new multifunctional cationic Cu-MOF based on zwitterionic ligand has been designed and synthesized. It exhibits selective dye capture and highly efficient Cr2O72− removal properties.
      PubDate: 2018-01-31T02:42:52.441651-05:
      DOI: 10.1002/chem.201705399
       
  • Selective Base-free Transfer Hydrogenation of α,β-Unsaturated Carbonyl
           Compounds using iPrOH or EtOH as Hydrogen Source
    • Authors: Ronald A. Farrar-Tobar; Zhihong Wei, Haijun Jiao, Sandra Hinze, Johannes G. de Vries
      Pages: 2725 - 2734
      Abstract: Commercially available Ru-MACHOTM-BH is an active catalyst for the hydrogenation of several functional groups and for the dehydrogenation of alcohols. Herein, we report on the new application of this catalyst to the base-free transfer hydrogenation of carbonyl compounds. Ru-MACHOTM-BH proved to be highly active and selective in this transformation, even with α,β-unsaturated carbonyl compounds as substrates. The corresponding aliphatic, aromatic and allylic alcohols were obtained in excellent yields with catalyst loadings as low as 0.1–0.5 mol % at mild temperatures after very short reaction times. This protocol tolerates iPrOH and EtOH as hydrogen sources. Additionally, scale up to multi-gram amounts was performed without any loss of activity or selectivity. An outer-sphere mechanism has been proposed and the computed kinetics and thermodynamics of crotonaldehyde and 1-phenyl-but-2-en-one are in perfect agreement with the experiment.Without prodding: Transfer hydrogenation of α,β-unsaturated aldehydes and ketones with EtOH or iPrOH can be effected using 0.1 mol % of Ru-MACHO-BH as a catalyst. This catalyst does not need any base activation, thus resulting in very high selectivities.
      PubDate: 2018-01-30T02:30:33.977379-05:
      DOI: 10.1002/chem.201705423
       
  • A Golden Access to Acenopentalenes
    • Authors: Thomas Wurm; Elias C. Rüdiger, Jürgen Schulmeister, Silke Koser, Matthias Rudolph, Frank Rominger, Uwe H. F. Bunz, A. Stephen K. Hashmi
      Pages: 2735 - 2740
      Abstract: By employing gold catalysis, starting from dialkynylated acenes a series of novel un-symmetrical aceno-annulated dibenzopentalenes has been prepared. The achieved yields range from 62–68 %. The fused systems contain naphthalene, anthracene, tetracene, and pentacene units. All new compounds are soluble and stable under standard conditions. The optical properties of the systems are dominated by the dibenzopentalene core for the smaller representatives, while for the anthracene-pentacene-based aceno-benzopentalenes the optical properties of the acene group dominates. Preliminary morphology tests on thin films showed a reverse trend between crystal size and molecule size.Simply gold: A simple access to acenopentalenes was opened by gold catalysis. The optical properties are dominated by the benzopentalene core for the smaller derivatives while the acene core takes the lead for π-extended systems.
      PubDate: 2018-02-05T04:52:06.100903-05:
      DOI: 10.1002/chem.201705456
       
  • 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
      Pages: 2741 - 2749
      Abstract: A randomized library is constructed based on pET30a-CYP119-T214V plasmid. This library of random mutants of CYP119-T214V was screened by means of the reduced CO difference spectra and epoxidation of styrene. By using directed evolution, a new CYP119 quadruple mutant S148P/I161T/K199E/T214V is constructed, expressed, and purified. This quadruple mutant significantly increases the turnover rate and conversion for the asymmetric epoxidation of styrene and its derivatives. The kcat. value of cis-β-methylstyrene epoxidation catalyzed by the quadruple mutant exhibits an approximately 10-fold increase, relative to the previously reported T213M mutant under the same conditions. This is the first engineered CYP119 peroxygenase for the epoxidation of cis-β-methylstyrene with a high turnover rate. The proposed mechanism, on the basis of a 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 CYP119 peroxygenase might result in high efficiency for the formation of compound I, and its subsequent peroxygenation by reconstructing the hydrogen-bonding interaction and increasing the substrate affinity and access.Developing enhanced mutants: A randomized library is constructed based on pET30a-CYP119-T214V plasmid. By using directed evolution, a new CYP119 quadruple mutant, S148P/I161T/K199E/T214V, has been constructed, expressed, and purified. This is the first engineered CYP119 peroxygenase for the epoxidation of cis-β-methylstyrene with a high turnover rate (see figure).
      PubDate: 2018-01-25T07:50:30.392917-05:
      DOI: 10.1002/chem.201705460
       
  • Bonding Insights from Structural and Spectroscopic Comparisons of {SnW5}
           
    • Authors: Balamurugan Kandasamy; Peter G. Bruce, William Clegg, Ross W. Harrington, Antonio Rodríguez-Fortea, Magda Pascual-Borrás, R. John Errington
      Pages: 2750 - 2757
      Abstract: Incorporation of {MX}n+ groups into polyoxometalates (POMs) provides the means not only to introduce reactivity and functionality but also to tune the electronic properties of the oxide framework by varying M, X and n. In order to elucidate the factors responsible for differences in reactivity between {TiW5} and {SnW5} Lindqvist-type hexametalates, a series of alkoxido- and aryloxido-tin substituted POMs (nBu4N)3[(RO)SnW5O18] (R=Me, Et, iPr and tBu) and (nBu4N)3[(ArO)SnW5O18] (Ar=C6H5, 4-MeC6H5, 4-tBuC6H5, 4-HOC6H4, 3-HOC6H4 and 2-CHOC6H4) has been structurally characterised and studied by multinuclear NMR (1H, 13C, 17O, 119Sn and 183W) and FTIR spectroscopy. Spectroscopic and structural parameters were compared with those of titanium-substituted homologues and, when coupled with theoretical studies, indicated that Sn−OR and Sn−OAr bonds are ionic with little π-contribution, whereas Ti−OR and Ti−OAr bonds are more covalent with π-bonding that is more prevalent for Ti−OR than Ti−OAr. This experimental and theoretical analysis of bonding in a homologous series of reactive POMs is the most extensive and detailed to date, and reveals factors which account for significant differences in reactivity between tin and titanium congeners.Sn versus Ti: The effects of metal substitution on the bonding within a homologous series of [(RO)MW5O18]3− polyoxometalates have been studied by combined structural, spectroscopic and theoretical studies of Ti and Sn derivatives, highlighting the influence of M−OR π-bonding on the distributed electronic effects within the oxide framework.
      PubDate: 2018-01-29T08:20:59.822669-05:
      DOI: 10.1002/chem.201705547
       
  • Mechanochemical Preparation of Stable Sub-100 nm
           γ-Cyclodextrin:Buckminsterfullerene (C60) Nanoparticles by Electrostatic
           or Steric Stabilization
    • Authors: Joachim F. R. Van Guyse; Victor R. de la Rosa, Richard Hoogenboom
      Pages: 2758 - 2766
      Abstract: Buckminster fullerene (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.Overcoming attraction: A well-known problem of cyclodextrin inclusion complexes is their aggregation. 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 to inhibit the aggregation found in native-γCD:C60 complexes, via Coulombic repulsion or steric hindrance. This led to partial inhibition of the aggregation, yielding stable sub-100 nm nanostructures.
      PubDate: 2018-01-25T07:40:41.458732-05:
      DOI: 10.1002/chem.201705647
       
  • Global Structural Flexibility of Metalloproteins Regulates Reactivity of
           Transition Metal Ion in the Protein Core: An Experimental Study Using
           Thiol-subtilisin as a Model Protein
    • Authors: Takashi Matsuo; Takamasa Kono, Isamu Shobu, Masaya Ishida, Katsuya Gonda, Shun Hirota
      Pages: 2767 - 2775
      Abstract: The functions of metal-containing proteins (metalloproteins) are determined by the reactivities of transition metal ions at their active sites. Because protein macromolecular structures have several molecular degrees of freedom, global structural flexibility may also regulate the properties of metalloproteins. However, the influence of this factor has not been fully delineated in mechanistic studies of metalloproteins. Accordingly, we have investigated the relationship between global protein flexibility and the characteristics of a transition metal ion in the protein core using thiol-subtilisin (tSTL) with a Cys-coordinated Cu2+ ion as a model system. Although tSTL has two Ca2+-binding sites, the Ca2+-binding status hardly affects its secondary structure. Nevertheless, guanidinium-induced denaturation and amide H/D exchange indicated the increase in the structural flexibility of tSTL by the removal of bound Ca2+ ions. Electron paramagnetic resonance and absorption spectral changes have revealed that the protein flexibility determines the characteristics of a Cu2+ ion in tSTL. Therefore, global protein flexibility should be recognized as an important factor that regulates the properties of metalloproteins.Importance of flexibility: To address the significance of macromolecular structure in metal-containing proteins for intrinsic protein functions, the correlation between global protein flexibility and the characteristics of CuII bound to thiol-subtilisin has been investigated. The CuII reactivity depends on the backbone flexibility of the protein. Thus, the global structural effect is essential to control the reactivity of a metal ion at the active sites of metal-containing proteins (see picture).
      PubDate: 2018-02-06T09:12:19.814782-05:
      DOI: 10.1002/chem.201705920
       
  • Advanced Continuous Flow Platform for On-Demand Pharmaceutical
           Manufacturing
    • Authors: Ping Zhang; Nopphon Weeranoppanant, Dale A. Thomas, Kohei Tahara, Torsten Stelzer, Mary Grace Russell, Marcus O'Mahony, Allan S. Myerson, Hongkun Lin, Liam P. Kelly, Klavs F. Jensen, Timothy F. Jamison, Chunhui Dai, Yuqing Cui, Naomi Briggs, Rachel L. Beingessner, Andrea Adamo
      Pages: 2776 - 2784
      Abstract: As a demonstration of an alternative to the challenges faced with batch pharmaceutical manufacturing including the large production footprint and lengthy time-scale, we previously reported a refrigerator-sized continuous flow system for the on-demand production of essential medicines. Building on this technology, herein we report a second-generation, reconfigurable and 25 % smaller (by volume) continuous flow pharmaceutical manufacturing platform featuring advances in reaction and purification equipment. Consisting of two compact [0.7 (L)×0.5 (D)×1.3 m (H)] stand-alone units for synthesis and purification/formulation processes, the capabilities of this automated system are demonstrated with the synthesis of nicardipine hydrochloride and the production of concentrated liquid doses of ciprofloxacin hydrochloride, neostigmine methylsulfate and rufinamide that meet US Pharmacopeia standards.On-demand pharmaceutical production: The capabilities of a second-generation, compact, continuous flow platform for on-demand pharmaceutical manufacturing are demonstrated with the synthesis of nicardipine hydrochloride and the production of concentrated liquid doses of ciprofloxacin hydrochloride, neostigmine methylsulfate and rufinamide that meet US Pharmacopeia standards.
      PubDate: 2018-01-31T11:58:53.254989-05:
      DOI: 10.1002/chem.201706004
       
  • Versatile Organic Chemistry on Vanadium-Based Multi-Electron Reservoirs
    • Authors: Olaf Nachtigall; Johann Spandl
      Pages: 2785 - 2789
      Abstract: We report the synthesis, post-functionalization, and redox behavior of two organically functionalized aggregates, [V6O7(OMe)9{(OCH2)3C−CH2N3}] and [V6O7(OMe)9{(OCH2)3C−NH2}]. All twelve μ2-oxo groups on the edges of the Lindqvist-type {V6O19} core were replaced by alkoxo ligands. The absence of a negative charge and the closed organic shell make these neutral mixed-valence compounds very stable towards hydrolysis and well soluble in almost all common organic solvents. These are important advantages over classical POMs. By post-functionalization through copper(I)-catalyzed Huisgen cycloaddition or imine formation, various organic moieties could be introduced. Even a well-soluble trimer composed of three hexanuclear vanadium units connected through an aromatic triimino core was synthesized and studied. The diverse redox behavior, the versatile reactivity, the good stability, and the excellent solubility make our vanadium compounds highly interesting for applications as building blocks in macromolecular chemistry as well as redox labels in biochemistry.Reservoir POMs: Strategies are provided for the organic functionalization and post-functionalization of neutral Lindqvist-type vanadium alkoxides with high solubility and redox activity. The functionalized aggregates can be applied as building blocks in macromolecular chemistry, multi-electron reservoirs in functional materials, or redox labels in biochemistry.
      PubDate: 2018-02-06T02:55:41.449478-05:
      DOI: 10.1002/chem.201800041
       
  • Front Cover: Unveiling the Role of Macrodipolar Interactions in the
           Properties of Self-Assembled Supramolecular Materials (Chem. Eur. J.
           11/2018)
    • Authors: Marina Pereira Oliveira; Hans-Werner Schmidt, Rodrigo Queiroz Albuquerque
      Pages: 2520 - 2520
      Abstract: Atomistic molecular dynamics simulations are an excellent tool for understanding the role of macrodipolar interactions on the properties of supramolecular materials. These simulations also complement X-ray structural elucidations of noncovalent materials in general. Neighboring supramolecular columns can exhibit parallel or antiparallel macrodipoles of different magnitudes, which influences the phase-transition disassembly mechanism. More information can be found in the Full Paper by R. Queiroz Albuquerque et al. on page 2609.
      PubDate: 2017-11-30T02:55:27.466319-05:
      DOI: 10.1002/chem.201705334
       
  • Cover Feature: Evidence for Iron-Catalyzed α-Phosphinidene Elimination
           with Phenylphosphine (Chem. Eur. J. 11/2018)
    • Authors: Justin K. Pagano; Brandon J. Ackley, Rory Waterman
      Pages: 2521 - 2521
      Abstract: Phosphinidenes are powerful synthetic reagents used to prepare important organophosphorus compounds, but historically, their generation has been stoichiometric. A simple iron compound, [CpFeMe(CO)2], can catalytically transfer a phosphinidene fragment to unsaturated fragments with loss of hydrogen. This apparent α-phosphinidene elimination reaction may enable more green syntheses of organophosphines. More information can be found in the Communication by R. Waterman et al. on page 2554.
      PubDate: 2017-12-20T09:15:26.565706-05:
      DOI: 10.1002/chem.201705827
       
  • Unveiling the Role of Macrodipolar Interactions in the Properties of
           Self-Assembled Supramolecular Materials
    • Authors: Marina Pereira Oliveira; Hans-Werner Schmidt, Rodrigo Queiroz Albuquerque
      Pages: 2524 - 2524
      Abstract: Invited for the cover of this issue is the group of Rodrigo Queiroz Albuquerque at Liverpool John Moores University. The image depicts an antiparallel interaction among macrodipoles inside the supramolecular material, each arrow representing the macrodipole of a 1D supramolecular column self-assembled from tricarboxamide derivatives. Read the full text of the article at 10.1002/chem.201704548.“We show that molecular modelling tools are of great help to address experimental problem of the structural characterization of supramolecular columnar materials.” Read more about the story behind the cover in the Cover Profile and about the research itself on page 2609 ff. (
      DOI : 10.1002/chem.201704548).
      PubDate: 2017-12-14T08:51:29.654203-05:
       
  • Selection and Screening of DNA Aptamers for Inorganic Nanomaterials
    • Authors: Yibo Zhou; Zhicheng Huang, Ronghua Yang, Juewen Liu
      Pages: 2525 - 2532
      Abstract: Searching for DNA sequences that can strongly and selectively bind to inorganic surfaces is a long-standing topic in bionanotechnology, analytical chemistry and biointerface research. This can be achieved either by aptamer selection starting with a very large library of ≈1014 random DNA sequences, or by careful screening of a much smaller library (usually from a few to a few hundred) with rationally designed sequences. Unlike typical molecular targets, inorganic surfaces often have quite strong DNA adsorption affinities due to polyvalent binding and even chemical interactions. This leads to a very high background binding making aptamer selection difficult. Screening, on the other hand, can be designed to compare relative binding affinities of different DNA sequences and could be more appropriate for inorganic surfaces. The resulting sequences have been used for DNA-directed assembly, sorting of carbon nanotubes, and DNA-controlled growth of inorganic nanomaterials. It was recently discovered that poly-cytosine (C) DNA can strongly bind to a diverse range of nanomaterials including nanocarbons (graphene oxide and carbon nanotubes), various metal oxides and transition-metal dichalcogenides. In this Concept article, we articulate the need for screening and potential artifacts associated with traditional aptamer selection methods for inorganic surfaces. Representative examples of application are discussed, and a few future research opportunities are proposed towards the end of this article.Very apt! A careful screening of a small number of rationally designed DNA oligonucleotide sequences is preferred over the traditional SELEX process to obtain aptamers for inorganic surfaces owing to strong non-specific DNA binding. Poly-cytosine (poly-C) DNA has been discovered to be a general binder for many surfaces including graphene oxide, various metal oxides, and transition-metal dichalcogenides.
      PubDate: 2017-12-27T04:11:04.125095-05:
      DOI: 10.1002/chem.201704600
       
  • Chemistry of Peptidoglycan in Mycobacterium tuberculosis Life Cycle: An
           off-the-wall Balance of Synthesis and Degradation
    • Authors: Flavia Squeglia; Alessia Ruggiero, Rita Berisio
      Pages: 2533 - 2546
      Abstract: The cell wall envelope of mycobacteria is structurally distinct from that of both Gram-positive and Gram-negative bacteria. In Mycobacterium tuberculosis, this cell wall has unique structural features and plays a crucial role in drug resistance and macrophage survival under stress conditions. Peptidoglycan is the major constituent of this cell wall, with an important structural role, giving structural strength, and counteracting the osmotic pressure of the cytoplasm. Synthesis of this complex polymer takes place in three stages that occur at three different locations in the cell, from the cytoplasm to the external side of the cell membrane, where polymerization occurs. A fine balance of peptidoglycan synthesis and degradation is responsible for a plethora of molecular mechanisms which are key to the pathogenicity of M. tuberculosis. Enlargement of mycobacterial cells can occur through the synthesis of new peptidoglycan, autolysis of old peptidoglycan, or a combination of both processes. Here, we discuss the chemical aspects of peptidoglycan synthesis and degradation, in relation to metabolic stages of M. tuberculosis. Going from inside the mycobacterial cytoplasm to outside its membrane, we describe the assembly line of peptidoglycan synthesis and polymerization, and continue with its depolymerization events and their consequences on mycobacterial life and resuscitation from dormancy.Mycobacterial Peptidoglycan Cell Wall Turnover: A complex assembly line is responsible for the Peptidoglycan wall construction, from the synthesis of Park's nucleotide synthesis inside the cytoplasm to Peptidoglycan polymerization in the periplasmic space. In resuscitation from mycobacterial dormancy, the wall is attacked by RipA and Rpf hydrolases, which produce free muropeptide sensors and wake up mycobacteria from a dormant “comfortably numb” state.
      PubDate: 2017-11-27T07:58:47.678383-05:
      DOI: 10.1002/chem.201702973
       
  • Evidence for Iron-Catalyzed α-Phosphinidene Elimination with
           Phenylphosphine
    • Authors: Justin K. Pagano; Brandon J. Ackley, Rory Waterman
      Pages: 2554 - 2557
      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
       
  • Rh-Catalyzed Denitrogenative Reaction of N-Sulfonyl-1,2,3-triazoles with
           Isatoic Anhydrides and Oxadiazolones
    • Authors: Kuntal Pal; Abdul Hoque, Chandra M. R. Volla
      Pages: 2558 - 2564
      Abstract: A convenient and simple, RhII-catalyzed denitrogenative method for the synthesis of biologically interesting 2-amino-benzoxazinones and 5-amino-oxadiazoles from readily available isatoic anhydrides and oxadiazolones has been developed. These reactions proceed via an O−H insertion onto α-imino RhII–carbenoid species followed by a rearrangement. The scope of the reaction can also be extended to benzoxazinones to access amino-substituted benzoxazines.O(N) the (Rh)oad: A novel and highly efficient RhII-catalyzed denitrogenative reaction of triazoles with isatoic anhydrides and oxadiazolones for the synthesis of 2-amino-benzoxazinones and 5-amino-oxadiazoles, respectively is reported.
      PubDate: 2017-12-05T08:07:03.753158-05:
      DOI: 10.1002/chem.201705036
       
  • Unveiling the Role of Macrodipolar Interactions in the Properties of
           Self-Assembled Supramolecular Materials
    • Authors: Marina Pereira Oliveira; Hans-Werner Schmidt, Rodrigo Queiroz Albuquerque
      Pages: 2609 - 2617
      Abstract: Self-assembling of supramolecules composed of benzene and cyclohexane tricarboxamide derivatives can form highly organized 1 D fibers exhibiting macrodipoles. The way fibers pack in the condensed phase governs the final properties of the supramolecular material, in which macrodipoles can be oriented parallel or antiparallel to each other, and their magnitude can be tuned by additional intra-columnar dipole stabilization. X-ray structural elucidation of these materials remains a real challenge due to the difficulty in growing single crystals. This problem can be tackled by using atomistic molecular dynamics to simulate supramolecular materials composed of cyclohexanetricarboxamide derivatives assuming different magnitudes and orientations of macrodipoles in the condensed phase, as we show here. The results provide insight on the isotropization mechanism of the supramolecules and also reveal that the relative orientation between macrodipoles can indeed influence their stability. This work nicely complements X-ray structural characterizations of supramolecular materials, and helps understand structure–property relationships of a range of similar noncovalent materials.The influence of macrodipolar interactions on the properties of self-assembled supramolecular materials is unveiled with the help of atomistic molecular dynamics simulations.
      PubDate: 2017-12-06T07:56:18.824082-05:
      DOI: 10.1002/chem.201704548
       
  • Panchromatic Photosensitizers Based on Push–Pull, Unsymmetrically
           Substituted Porphyrazines
    • Authors: Javier Fernández-Ariza; Maxence Urbani, M. Salomé Rodríguez-Morgade, Tomás Torres
      Pages: 2618 - 2625
      Abstract: A series of five push–pull porphyrazines of A3B type, in which unit B is an isoindole 4-carboxylic acid, has been prepared. The units A have been endowed with thioether, amine, ether and alkyl functions, either directly attached to the β-position of the pyrrolic units, or connected to the porphyrazine core through p-substituted phenyl groups. Attaching the electron-donor functions to the porphyrazine periphery produces strong perturbations in the electronic and redox properties of the dyes. Their HOMO and LUMO energies, estimated from the optical and redox data, as well as with DFT calculations, raise upon functionalization with amines, while the corresponding frontier orbital energetic levels lower upon functionalization with thioethers, p-methoxyphenyl or p-tert-butylphenyl groups. The effective interaction of peripheral substitution with the macrocycle produces chromophores with panchromatic absorption between 300 and 750–850 nm.To me, to you: Attaching six donor thioether, amine, ether and alkyl functions, either directly, or through p-phenyl substituents, to the periphery of A3B-type porphyrazines, which contain an isoindole 4-carboxylic acid as the B unit, produces strong perturbations in the electronic and redox properties of synthesized dye compounds. These push–pull chromophores display panchromatic absorption between 300 and 750–850 nm.
      PubDate: 2017-12-28T03:01:53.387464-05:
      DOI: 10.1002/chem.201705242
       
 
 
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