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Chemistry: a European Journal

Xingwen Liu, Guangren Qian, Zheng Jiao, Minghong Wu, Haijiao Zhang
Here, a facile self-templating approach has been presented for synthesis of hollow and yolk-shell mesoporous silica nanoparticles (HMSNs and YMSNs) through a selective etching of hybrid silica nanoparticles. The hybrid silica nanoparticles are from the co-condensation of tetraethylorthosilicate (TEOS) and N-[3-(trimethoxysilyl)propyl]ethylenediamine (TSD) by a simple one-step process. Two kinds of products including HMSNs and YMSNs can be easily prepared only by tuning the TSD amounts in the precursor. Significantly, the transformation of hollow structure does not use any sacrificial template and surface protective agent...
April 22, 2017: Chemistry: a European Journal
Brendan Francis Abrahams, David Dharma, Paul Stephen Donnelly, Timothy Adam Hudson, Cameron J Kepert, Richard Robson, Peter D Southon, Keith Forrest White
The uptake of inhalation anesthetics by three topologically identical frameworks is described. The 3D network materials, which possess square channels of different dimensions, are formed from the relatively simple combination of Zn(II) centres and dianionic ligands that contain a phenolate and a carboxylate group at opposite ends. All three framework materials are able to adsorb N2O, Xe and isoflurane. Whilst the framework with the widest channels is able to adsorb large quantities of the various guests from the gas phase, the frameworks with the narrower channels have superior binding enthalpies and exhibit higher levels of retention...
April 22, 2017: Chemistry: a European Journal
Arni Vaughn, Jeremy Ball, Tobias Heil, David Morgan, Giulio Lampronti, Gabija Maršalkaitė, Colin L Raston, Nicholas P Power, Suela Kellici
Fully exploiting the electronic and mechanical properties of 2D laminar materials not only requires efficient and effective means of their exfoliation into low dimensional layers, but also necessitates a means of changing their morphology so as to explore any enhancement that this may offer. MXenes are a rapidly emerging new class of such laminar materials with unique properties. However, access to other morphologies of MXenes has not yet been fully realised. To this end we have developed the synthesis of MXenes (Ti2C) as plates, crumpled sheets, spheres and scrolls, which involves selective intercalation of p-phosphonic calix[n]arenes, with control in morphology arising from the choice of the size of the macrocycle, n = 4, 5, 6 or 8...
April 21, 2017: Chemistry: a European Journal
Venkata R Sabbasani, Hyunjin Lee, Peipei Xie, Yuanzhi Xia, Daesung Lee
A facile thermal cyclization of ynamide-tethered 1,3,8-triynes to form 3,5,6,7-tetrahydro-1H-pyrano[3,4-c]pyridine skeleton is described. Although the mechanism of this unusual reaction is yet to be defined the formation of either a strained keteniminium or a biradical intermediate followed a 1,5-hydride or -hydrogen shift is tentatively proposed as the key elementary steps in the reaction sequence. Appropriate electronic activation at the carbon center donating a hydride or hydrogen is crucial for successful cyclization...
April 21, 2017: Chemistry: a European Journal
Sven Otto, Norman Scholz, Thomas Behnke, Ute Resch-Genger, Katja Heinze
The unparalleled excited state potential energy landscape of the chromium(III)-based dye [1]3+ ([Cr(ddpd)2]3+; ddpd = N,N'-dimethyl-N,N'-dipyridin-2-yl-pyridin-2,6-diamine) enables a strong dual emission in the near infrared. The temperature dependence of this dual emission allows for the use of [1]3+ as an unprecedented molecular ratiometric thermometer in the 210 - 358 K temperature range in organic and in aqueous media. Incorporation of [1]3+ in biocompatible nanocarriers like 100 nm-sized polystyrene nanoparticles and solutol micelles provides nanodimensional thermometers operating under physiological conditions...
April 21, 2017: Chemistry: a European Journal
Samar Kumar Das, Suranjana Bose, Joyashish Debgupta, Rani Ramsundar
The design and synthesis of an efficient and robust water oxidation catalyst (WOC) with inexpensive materials remain an important challenge in the context of 'artificial photosynthesis'. Herein, we report a simple but unique technique to generate in situ a thin-film of α-Co(OH)2 on the surface of zeolite-Y [hereafter named as Y-α-Co(OH)2] that acts as an efficient and stable catalyst for electrochemical water oxidation in an alkaline pH. Catalyst Y-α-Co(OH)2 is so stable that it retains its catalytic activity even after 2000 cyclic voltammetric cycles of water oxidation...
April 21, 2017: Chemistry: a European Journal
Holger Braunschweig, Mehmet Celik, Theresa Dellermann, Gernot Frenking, Kai Hammond, Florian Hupp, Hauke Kelch, Ivo Krummenacher, Felix Lindl, Lisa Mailänder, Jonas Müssig, Annika Ruppert
Electronic and steric factors have been investigated in the thermal ring expansion of boroles with organic azides, a reaction that provides access to highly arylated 1,2-azaborinines, BN analogs of benzene. The reactions with a variety of boroles and organic azides demonstrate that the synthetic method is quite general to furnish 1,2-azaborinines, while the respective reaction rates reveal a strong dependence on the substituents of the two reagents. The products were characterized by UV/vis, electrochemical, NMR, and X-ray diffraction methods, clarifying their constitution and highlighting substituent effects on the electronic structure of the 1,2-azaborinines...
April 21, 2017: Chemistry: a European Journal
Ryota Miyaji, Keisuke Asano, Seijiro Matsubara
The enantioselective syntheses of axially chiral heterobiaryls were accomplished via the aromatic electrophilic halogenation of 3-(quinolin-8-yl)phenols using bifunctional organocatalysts, which control the molecular conformations during successive halogenations. Axially chiral quinoline derivatives, which have rarely been synthesized in an enantioselective catalytic manner, were afforded in moderate-to-good enantioselectivities via bromination, and an analogous protocol also enabled enantioselective iodination...
April 21, 2017: Chemistry: a European Journal
Dehua Xiong, Qingqing Zhang, Sitaramanjaneya Mouli Thalluri, Junyuan Xu, Wei Li, Xiuli Fu, Lifeng Liu
We report a very easy and cost-effective approach to the fabrication of monolithic Co9S8 water oxidation electrodes (Co@Co9S8), which is fabricated by one-step hydrothermal treatment of commercially available cobalt foam in the presence of thiourea. The morphology, crystal structure, microstructure, and composition of as-fabricated Co@Co9S8 electrodes are examined using scanning electron microscopy (SEM), powder X-ray diffraction (XRD), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS), and their electrochemical properties are investigated by cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS)...
April 21, 2017: Chemistry: a European Journal
Andreas Meyer, Tomas Slanina, Alexander Heckel, Burkhard König
Metal ions can have beneficial effects on photoinduced electron transfer. Merging such metal-ion coupled electron transfer (MCET) with consecutive photoinduced electron transfer (conPET) enables the one-electron reduction of chlorobenzene with blue light in the presence of diisopropylethylamine as electron donor. The presence of the metal ions extends the substrate scope of the photoredox catalysis to extreme reduction potentials (beyond -3 V vs SCE).
April 21, 2017: Chemistry: a European Journal
Itaru Nakamura, Keisuke Takeda, Yoshinori Sato, Masahiro Terada
We have disclosed that N-alkynylnitrones are efficiently converted to nitrogenous heterobicyclic compounds having a nitrogen atom at the bridgehead position by using a Rh(III)-catalyst. Our mechanistic studies suggest that the reaction proceeds via an allene intermediate, which is generated in situ through Rh(III)-catalyzed isomerization of the alkyne group.
April 21, 2017: Chemistry: a European Journal
Nils-Alexander Lakomek, Susanne Penzel, Alons Lends, Riccardo Cadalbert, Matthias Ernst, Beat H Meier
15N R1ρ relaxation experiments in solid-state NMR are sensitive to timescales and amplitudes of internal protein motions in the hundreds of ns to µs time window, difficult to probe with solution-state NMR. Using 15N R1ρ relaxation experiments with variable MAS frequency (60-110 kHz) and a model-free analysis, we describe an approach to detect hundreds of ns to low µs protein dynamics and determine residue-specific correlation times from the ratio of 15N R1ρ rate constants at different MAS frequencies. We find that microcrystalline ubiquitin exhibits small-amplitude dynamics on a timescale of about 1 µs across the entire protein, and larger amplitude motions, also on the 1 µs timescale, for several sites, including the β1-β2 turn and the N-terminus of the α-helix...
April 20, 2017: Chemistry: a European Journal
Jonas Häusler, Saskia Schimmel, Peter Wellmann, Wolfgang Schnick
In this contribution, first synthesis of semiconducting ZnSiN2 and ZnGeN2 from solution is presented with supercritical ammonia as solvent and KNH2 as ammonobasic mineralizer. The reactions were conducted in custom-built high-pressure autoclaves made of nickel-based superalloy. The nitrides were characterized by powder X-ray diffraction and their crystal structures were refined by the Rietveld method. ZnSiN2 (a = 5.24637(4), b = 6.28025(5), c = 5.02228(4) Å, Z = 4, Rwp = 0.0556) and isotypic ZnGeN2 (a = 5...
April 20, 2017: Chemistry: a European Journal
Xiang-Yi Chen, Ning-Ning Zhang, Li-Zhen Cai, Pei-Xin Li, Ming-Sheng Wang, Guo-Cong Guo
N,N'-disubstituted bipyridinium (viologen) and N-monosubstituted bipyridinium compounds are well known for their electron-transfer (ET) photochromic behavior. The modification of them was exclusively focused on the N-substituents. For the first time, we studied the photochromic behavior when one pyridyl ring of the bipyridinium was substituted with a multi-functional azole group, and revealed that two new coordination compounds based on N-methyl-4-pyridinium tetrazolate (mptz) zwitterion, [Zn(mptz)2Br2] (1) and [Cd3(mptz)2Cl6]n∙4nH2O (2), exhibit typical ET photochromic behavior owing to photoinduced ET from halogen anion to the mptz ligand...
April 20, 2017: Chemistry: a European Journal
Xiaoyu Wu, Xuehe Lu, Luo Ge, Cang Cheng, Jie Chen, Weiguo Cao
In contrast to the well-studied asymmetric catalyzed synthesis of tetrahydroquinolines, the asymmetric methodologies toward 3,4-dihydroquinolin-2-ones are quite rare. Herein, we report the first asymmetric cascade reaction between ethynyl benzoxazinanones and mixed-anhydride generated from aryl acetic acid and pivaloyl chloride, based on synergistic catalysis. This methodology allows the formation of attractive 3,4-dihydroquinolin-2-ones bearing two vicinal chiral centers at C3 and C4 in high yields with excellent diastereo- and enantioselectivities...
April 19, 2017: Chemistry: a European Journal
Sonja Herres-Pawlis, Patricia Liebhäuser, Kristina Keisers, Alexander Hoffmann, Thomas Schnappinger, Isabella Sommer, Anne Thoma, Claudia Wilfer, Roland Schoch, Kai Stührenberg, Matthias Bauer, Maximilian Dürr, Ivana Ivanovic-Burmazovic
Tyrosinase model systems pinpoint pathways to translate nature´s synthetic abilities into useful synthetic catalysts. Mostly, they use N-donor ligands which mimic the histidine residues coordinating the two copper centres. Copper complexes with bis(pyrazolyl)methanes with pyridinyl or imidazolyl moieties are already reported as excellent tyrosinase models. Substitution of the pyridinyl donor results now in the new ligand HC(3 tBuPz)2(4 CO2MePy) which stabilises a room-temperature stable -2:2-peroxide dicopper(II) species upon oxygenation...
April 19, 2017: Chemistry: a European Journal
Baillie A DeHaven, John T Tokarski, Arthur A Korous, Frederic Mentink-Vigier, Thomas M Makris, Alexander M Brugh, Malcolm D E Forbes, Johan van Tol, Clifford Russ Bowers, Linda S Shimizu
UV-irradiation of a self-assembled benzophenone bis-urea macrocycle generates μM amounts of radicals that persist for weeks under ambient conditions. High-Field EPR and variable temperature X-band EPR studies suggest a resonance stabilized radical pair through H-abstraction. These endogenous radicals were applied as a polarizing agent for magic angle spinning (MAS) dynamic nuclear polarization (DNP) NMR enhancement. The field-stepped DNP enhancement profile exhibits a sharp peak with a maximum enhancement of εon/off = 4 superimposed on a nearly constant DNP enhancement of εon/off = 2 over a broad field range...
April 19, 2017: Chemistry: a European Journal
Marcus Brauns, Marvin Mantel, Julie Schmauck, Marian Guder, Martin Breugst, Joerg Pietruszka
Optimized protecting group for allylboronates allows the use of ketones to synthesize all isomers of quaternary homoallylic alcohols with high enantioselectivities. All symmetric isomers of the allylboronate can be prepared in high yields and diastereoselectivities using SN2' reactions. The improved reactivity of the novel protecting group is verified via 1H-NMR kinetics. Mechanistic studies using DFT calculations are conducted to investigate the new findings. Thus, the stereochemical outcome and enhanced reactivity can be rationalized...
April 19, 2017: Chemistry: a European Journal
Marco Mende, Martin Nieger, Stefan Bräse
Herein a chemical synthesis towards new modified hyaluronic acid oligomers for structure-related biological activity tests using only commercially available D-glucose and D-glucosamine hydrochloride is reported. The syntheses of various protected hyaluronic acid disaccharides bearing new functional groups at the C-6-position of the former β-D-glucuronic acid moiety are described. The orthogonal protecting group pattern creates a readily access to the appropriate higher oligomers. Also 1H NMR studies of the new derivatives are displayed, showing the effect of the group replacement on the intramolecular electronic environment...
April 19, 2017: Chemistry: a European Journal
Helen Moylan, Joseph McDouall
The theory and computation of EPR parameters from first principles has seen a great deal of development over the past two decades. In particular, various techniques for the computation of the electronic g tensor have been implemented in many quantum chemistry packages. These methods have been successfully applied to paramagnetic organic species and transition metal systems. The situation is less well-understood and established in the case of actinide containing molecules and there is a dearth of experimental data available for validation of computations...
April 19, 2017: Chemistry: a European Journal
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