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971.
Dr. Yashapal Singh Prof. Dr. Alexei V. Demchenko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(6):1461-1465
The discovery that traditional silver(I)-oxide-promoted glycosidations of glycosyl bromides (Koenigs–Knorr reaction) can be greatly accelerated in the presence of catalytic trimethylsilyl trifluoromethanesulfonate (TMSOTf) is reported. The reaction conditions are very mild that allowed for maintaining a practically neutral pH and, at the same time, providing high rates and excellent glycosylation yields. In addition, unusual reactivity trends among a series of differentially protected glycosyl bromides were documented. In particular, benzoylated α-bromides were much more reactive than their benzylated counterparts under these conditions. 相似文献
972.
Xin-Yue Lou Dr. Nan Song Prof. Ying-Wei Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(51):11975-11982
Organic luminescent materials with high quantum yields and/or white-light-emitting properties in particular play a crucial role in labeling and optoelectronic devices. In this work we have synthesized a new 2,3,6,7-tetramethoxy-9,10-di-p-tolylanthracene-bridged pillar[5]arene dimer with persistent mazarine blue fluorescent emission and much higher quantum yields in both solution and the solid state in comparison with its corresponding emissive linker without pillarene units, which exhibits typical aggregation-caused quenching. According to the fluorescence data and single-crystal analyses, their contrasting fluorescent performances can be rationally ascribed to their different stacking structures and intermolecular interactions. Three fluorescent guests containing different chromophores and/or terminal binding sites have also been synthesized to interact with the pillar[5]arene dimer to construct supramolecular ensembles with highly controllable luminescence, taking advantage of the stimuli-responsive properties of the supramolecular host–guest interactions. Intriguingly, multicolor fluorescence, including white-light emission (0.31, 0.35), which is in high demand, has been achieved by tuning the molar ratio of the host and guest and/or by changing the solvent system. This strategy holds great potential for the design and development of fluorescent materials with high quantum yields, controllable emission wavelength, and good stimuli-responsiveness. 相似文献
973.
Meng Liu Dr. Hao Fan Dr. Ou Zhuo Xiao Du Longqi Yang Prof. Peng Wang Lijun Yang Prof. Qiang Wu Prof. Xizhang Wang Prof. Zheng Hu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3843-3848
Molybdenum disulfide (MoS2) is an intensively studied anode material for lithium-ion batteries (LIBs) owing to its high theoretical capacity, but it is still confronted by severe challenges of unsatisfactory rate capability and cycle life. Herein, few-layer MoS2 nanosheets, vertically grown on hierarchical carbon nanocages (hCNC) by a facile hydrothermal method, introduce pseudocapacitive lithium storage owing to the highly exposed MoS2 basal planes, enhanced conductivity, and facilitated electrolyte access arising from good hybridization with hCNC. Thus, the optimized MoS2/hCNC exhibits reversible capacities of 1670 mAh g−1 at 0.1 A g−1 after 50 cycles, 621 mAh g−1 at 5.0 A g−1 after 500 cycles, and 196 mAh g−1 at 50 A g−1 after 2500 cycles, which are among the best for MoS2-based anode materials. The specific power and specific energy, which can reach 16.1 kW and 252.8 Wh after 3000 cycles, respectively, indicate great potential in high-power and long-life LIBs. These findings suggest a promising strategy for exploring advanced anode materials with high reversible capacity, high-rate capability, and long-term recyclability. 相似文献
974.
Dr. He Zhao Xiu Li Rongqing Guan Prof. Huanfeng Jiang Prof. Min Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(69):15858-15862
The tandem dual C−H amination of tetrahydroquinoxalines with free amines under aerobic copper catalysis conditions has been demonstrated. The synthetic protocol proceeds with good substrate and functional group compatibility, mild reaction conditions, short reaction time, the use of the naturally abundant [Cu]/O2 catalyst system, excellent chemoselectivity and synthetic efficiency, and with no need for the pre-installation of specific aminating agents, which offers a practical platform for the rapid and diverse synthesis of diaminoquinoxalines. Moreover, this work has shown the potential of single-electron-oxidation-induced C−H functionalization of N-heterocycles, and its application in the development of optoelectronic materials. 相似文献
975.
Dr. Longyu Li Qianming Lin Miao Tang Dr. Andrew J. E. Duncan Prof. Dr. Chenfeng Ke 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(46):10768-10781
The rapid development of additive manufacturing techniques, also known as three-dimensional (3D) printing, is driving innovations in polymer chemistry, materials science, and engineering. Among current 3D printing techniques, direct ink writing (DIW) employs viscoelastic materials as inks, which are capable of constructing sophisticated 3D architectures at ambient conditions. In this perspective, polymer designs that meet the rheological requirements for direct ink writing are outlined and successful examples are summarized, which include the development of polymer micelles, co-assembled hydrogels, supramolecularly cross-linked systems, polymer liquids with microcrystalline domains, and hydrogels with dynamic covalent cross-links. Furthermore, advanced polymer designs that reinforce the mechanical properties of these 3D printing materials, as well as the integration of functional moieties to these materials are discussed to inspire new polymer designs for direct ink writing and broadly 3D printing. 相似文献
976.
Friedrich Kreyenschmidt Selim E. Meurer Prof. Dr. Konrad Koszinowski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(23):5912-5921
>The combination of CoCl2 with bidentate phosphines is known to catalyze challenging cross-coupling and Heck-type reactions, but the mechanisms of these valuable transformations have not been established. Here, we use electrospray-ionization mass spectrometry to intercept the species formed in these reactions. Our results indicate that a sequence of transmetalation, reductive elimination, and redox disproportionation convert the cobalt(II) precatalyst into low-valent cobalt complexes. These species readily transfer single electrons to alkyl bromides, which thereupon dissociate into alkyl radicals and Br−. In cross-coupling reactions, the alkyl radicals add to the cobalt catalyst to form observable heteroleptic complexes, which release the coupling products through reductive eliminations. In the Heck-type reactions, the low abundance of newly formed ionic species renders the analysis more difficult. Nonetheless, our results also point to the occurrence of single-electron transfer processes and the involvement of radicals in these transformations. 相似文献
977.
Dmitry I. Bugaenko Alexey A. Volkov Dr. Mikhail V. Livantsov Prof. Dr. Marina A. Yurovskaya Dr. Alexander V. Karchava 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12502-12506
The visible-light-induced arylation of tertiary phosphines with aryl(mesityl)iodonium triflates to produce the quaternary phosphonium salts occurs under mild, metal, and catalyst-free conditions. Photo-excited EDA complexes between diaryliodonium salts and phosphines supposedly enable this transformation, which is difficult to achieve through the traditional ground-state reactions. Demonstrating high functional group tolerance, broad scope, and complete selectivity of the aryl group transfer, the method is particularly compatible with sterically congested phosphines, which are challenging under metal-based catalytic methods. 相似文献
978.
Akhil Kumar Singh Dr. Mohammad Usman Dr. Giuseppe Sciortino Prof. Dr. Eugenio Garribba Prof. Dr. Sankar Prasad Rath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(43):10098-10110
Metallophilic interactions between closed-shell metal ions are becoming a popular tool for a variety of applications related to high-end materials. Heavier d8 transition-metal ions are also considered to have a closed shell and can be involved in such interactions. There is no systematic investigation so far to estimate the structure and energy characteristics of metallophilic interactions in AgII/AgII (d9/d9), AgIII/AgIII (d8/d8), and mixed-valent AgII/AgIII (d9/d8) complexes, which have been demonstrated in the present study. Both interporphyrinic and intermetallic interactions were investigated on stepwise oxidation by using a rigid ethene-bridged cis silver(II) porphyrin dimer and the results compared with those for highly flexible ethane-bridged analogues. By controlling the nature of chemical oxidants and their stoichiometry, both 1e and 2e oxidations were done stepwise to generate AgII/AgIII mixed-valent and AgIII/AgIII porphyrin dimers, respectively. Unlike all other ethene-bridged metalloporphyrin dimers reported earlier, in which 2e oxidation stabilizes only the trans form, such an oxidation of silver(II) porphyrin dimer stabilizes only the cis form because of the metallophilic interaction. Besides silver(II) ⋅⋅⋅ silver(II) interactions in cis silver(II) porphyrin dimer, stepwise oxidations also enabled us to achieve various hitherto-unknown silver(II) ⋅⋅⋅ silver(III) and silver(III) ⋅⋅⋅ silver(III) interactions, which thereby allow significant modulation of their structure and properties. The strength of Ag ⋅⋅⋅ Ag interaction follows the order AgII/AgII (d9/d9)<AgII/AgIII (d9/d8)<AgIII/AgIII (d8/d8). Single-crystal XRD, X-ray photoelectron spectroscopy (XPS), 1H NMR and EPR spectroscopy, and variable-temperature magnetic investigations revealed various oxidation states of silver and metallophilic interactions, which are also well supported by computational analysis. 相似文献
979.
Hang Yin Qian Cheng Roselyne Rosas Prof. Stéphane Viel Dr. Valérie Monnier Prof. Laurence Charles Prof. Didier Siri Dr. Didier Gigmes Dr. Olivier Ouari Prof. Ruibing Wang Dr. Anthony Kermagoret Dr. David Bardelang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(54):12552-12559
A viologen derivative carrying a benzimidazole group ( V-P-I 2+; viologen–phenylene–imidazole V-P-I ) can be dimerized in water using cucurbit[8]uril (CB[8]) in the form of a 2:2 complex resulting in a negative shift of the guest pKa, by more than 1 pH unit, contrasting with the positive pKa shift usually observed for CB-based complexes. Whereas 2:2 complex protonation is unclear by NMR, silver cations have been used for probing the accessibility of the imidazole groups of the 2:2 complexes. The protonation capacity of the buried imidazole groups is reduced, suggesting that CB[8] could trigger proton release upon 2:2 complex formation. The addition of CB[8] to a solution containing V-P- I 3+ indeed released protons as monitored by pH-metry and visualized by a coloured indicator. This property was used to induce a host/guest swapping, accompanied by a proton transfer, between V-P-I 3+ ⋅ CB[7] and a CB[8] complex of 1-methyl-4-(4-pyridyl)pyridinium. The origin of this negative pKa shift is proposed to stand in an ideal charge state, and in the position of the two pH-responsive fragments inside the two CB[8] which, alike residues engulfed in proteins, favour the deprotonated form of the guest molecules. Such proton release triggered by a recognition event is reminiscent of several biological processes and may open new avenues toward bioinspired enzyme mimics catalyzing proton transfer or chemical reactions. 相似文献
980.
Qianyu Yu Xiaoteng Ma Yingze Liu Prof. Dr. Hanying Zhao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(72):16712-16717
Protein nanogels have found a wide variety of applications, ranging from biocatalysis to drug/protein delivery. However, in practical applications, proteins in nanogels may suffer from enzymic hydrolysis and denaturation. Inspired by the structure and functionalities of the fowl eggshells, biomimetic mineralization of protein nanogels was studied in this research. Protein nanogels with embedded porcine pancreas lipase (PPL) in the cross-linked nanostructures were synthesized through the thiol–disulfide reaction between thiol-functionalized PPL and poly(N-isopropylacrylamide) with pendant pyridyl disulfide groups. The nanogels were further reacted with reduced bovine serum albumin (BSA) and BSA molecules were coated on the nanogels. Mineralization of BSA leads to the synthesis of biomineralized shells on the nanogels. With the growth of CaCO3 on the shells, the nanogels aggregate into suprastructures. Thermogravimetric analysis, XRD, dynamic light scattering, and TEM were employed to study the mechanism of the biomineralization process and analyze the structures of the mineralized nanogels. The biomineralized shells can effectively protect the PPL molecules from hydrolysis by trypsin; meanwhile, the nanosized channels on the mineralized shells allow the transport of small-molecule substrates across the shells. Bioactivity measurements indicate that PPL in the nanogels maintains more than 80 % bioactivity after biomineralization. 相似文献