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941.
Mechanistic Insights into the Interface‐Directed Transformation of Thiols into Disulfides and Molecular Hydrogen by Visible‐Light Irradiation of Quantum Dots
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Xu‐Bing Li Zhi‐Jun Li Yu‐Ji Gao Qing‐Yuan Meng Shan Yu Prof. Dr. Richard G. Weiss Prof. Dr. Chen‐Ho Tung Prof. Dr. Li‐Zhu Wu 《Angewandte Chemie (International ed. in English)》2014,53(8):2085-2089
Quantum dots (QDs) offer new and versatile ways to harvest light energy. However, there are few examples involving the utilization of QDs in organic synthesis. Visible‐light irradiation of CdSe QDs was found to result in virtually quantitative coupling of a variety of thiols to give disulfides and H2 without the need for sacrificial reagents or external oxidants. The addition of small amounts of nickel(II) salts dramatically improved the efficiency and conversion through facilitating the formation of hydrogen atoms, thereby leading to faster regeneration of the ground‐state QDs. Mechanistic studies reveal that the coupling reaction occurs on the QD surfaces rather than in solution and offer a blueprint for how these QDs may be used in other photocatalytic applications. Because no sacrificial agent or oxidant is necessary and the catalyst is reusable, this method may be useful for the formation of disulfide bonds in proteins as well as in other systems sensitive to the presence of oxidants. 相似文献
942.
Balancing the Rate of Cluster Growth and Etching for Gram‐Scale Synthesis of Thiolate‐Protected Au25 Nanoclusters with Atomic Precision
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Xun Yuan Bin Zhang Zhentao Luo Qiaofeng Yao Prof. David Tai Leong Prof. Ning Yan Prof. Jianping Xie 《Angewandte Chemie (International ed. in English)》2014,53(18):4623-4627
We report a NaOH‐mediated NaBH4 reduction method for the synthesis of mono‐, bi‐, and tri‐thiolate‐protected Au25 nanoclusters (NCs) with precise control of both the Au core and thiolate ligand surface. The key strategy is to use NaOH to tune the formation kinetics of Au NCs, i.e., reduce the reduction ability of NaBH4 and accelerate the etching ability of free thiolate ligands, leading to a well‐balanced reversible reaction for rapid formation of thermodynamically favorable Au25 NCs. This protocol is facile, rapid (≤3 h), versatile (applicable for various thiolate ligands), and highly scalable (>1 g Au NCs). In addition, bi‐ and tri‐thiolate‐protected Au25 NCs with adjustable ratios of hetero‐thiolate ligands were easily obtained. Such ligand precision in molecular ratios, spatial distribution and uniformity resulted in richly diverse surface landscapes on the Au NCs consisting of multiple functional groups such as carboxyl, amine, and hydroxy. Analysis based on NMR spectroscopy revealed that the hetero‐ligands on the NCs are well distributed with no ligand segregation. The unprecedented synthesis of multi‐thiolate‐protected Au25 NCs may further promote the practical applications of functional metal NCs. 相似文献
943.
Self‐Assembly of Pyridinium‐Functionalized Anthracenes: Molecular‐Skeleton‐Directed Formation of Microsheets and Microtubes
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Dr. Jun Hu Peiyi Wang Prof. Yuan Lin Prof. Jidong Zhang Dr. Mark Smith Dr. Perry J. Pellechia Prof. Song Yang Prof. Baoan Song Prof. Qian Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(25):7603-7607
Two amphiphilic regioisomers, 9‐AP (1‐[11‐(9‐anthracenylmethoxy)‐11‐oxoundecyl]pyridinium bromide), and 2‐AP (1‐[11‐(2‐anthracenyl methoxy)‐11‐oxoundecyl]pyridinium bromide), were synthesized and their assembly behaviors were studied. Due to the anisotropic features of the anthracene structure, different substituted positions on the anthracene ring lead 9‐AP and 2‐AP to adapt “shaver” and “spatula”‐like molecular shapes, respectively, which consequently dictate the structure of their final assemblies. While “shaver”‐shaped 9‐AP assembled into microsheets, driven by π–π interactions, “spatula”‐shaped 2‐AP assembled into microtubular structures, promoted primarily by charge‐transfer interactions. 相似文献
944.
JPC – Journal of Planar Chromatography – Modern TLC - 相似文献
945.
Enzymatic Desymmetrising Redox Reactions for the Asymmetric Synthesis of Biaryl Atropisomers
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Samantha Staniland Bo Yuan Nelson Giménez‐Agulló Dr. Tommaso Marcelli Dr. Simon C. Willies Dr. Damian M. Grainger Prof. Nicholas J. Turner Prof. Jonathan Clayden 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13084-13088
Atropisomeric biaryls carrying ortho‐hydroxymethyl and formyl groups were made enantioselectively by desymmetrisation of dialdehyde or diol substrates. The oxidation of the symmetrical diol substrates was achieved using a variant of galactose oxidase (GOase), and the reduction of the dialdehydes using a panel of ketoreductases. Either M or P enantiomers of the products could be formed, with absolute configurations assigned by time‐dependent DFT calculations of circular dichroism spectra. The differing selectivities observed with different biaryl structures offer an insight into the detailed structure of the active site of the GOase enzyme. 相似文献
946.
Control of Chiral Nanostructures by Self‐Assembly of Designed Amphiphilic Peptides and Silica Biomineralization
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Zhehao Huang Dr. Yuan Yao Dr. Lu Han Prof. Shunai Che 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(51):17068-17076
Peptides, the fundamental building units of biological systems, are chiral in molecular scale as well as in spatial conformation. Shells are exquisite examples of well‐defined chiral structures produced by natural biomineralization. However, the fundamental mechanism of chirality expressed in biological organisms remains unclear. Here, we present a system that mimics natural biomineralization and produces enantiopure chiral inorganic materials with controllable helicity. By tuning the hydrophilicity of the amphiphilic peptides, the chiral morphologies and mesostructures can be changed. With decreasing hydrophilicity of the amphiphilic peptides, we observed that the nanostructures changed from twisted nanofibers with a hexagonal mesostructure to twisted nanoribbons with a lamellar mesostructure, and the extent of the helicity decreased. Defining the mechanism of chiral inorganic materials formed from peptides by noncovalent interactions can improve strategies toward the bottom‐up synthesis of nanomaterials as well as in the field of bioengineering. 相似文献
947.
Direct Anisotropic Growth of CdS Nanocrystals in Thermotropic Liquid Crystal Templates for Heterojunction Optoelectronics
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Kai Yuan Prof. Dr. Lie Chen Prof. Dr. Yiwang Chen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(36):11488-11495
The direct growth of CdS nanocrystals in functional solid‐state thermotropic liquid crystal (LC) small molecules and a conjugated LC polymer by in situ thermal decomposition of a single‐source cadmium xanthate precursor to fabricate LC/CdS hybrid nanocomposites is described. The influence of thermal annealing temperature of the LC/CdS precursors upon the nanomorphology, photophysics, and optoelectronic properties of the LC/CdS nanocomposites is systematically studied. Steady‐state PL and ultrafast emission dynamics studies show that the charge‐transfer rates are strongly dependent on the thermal annealing temperature. Notably, annealing at liquid‐crystal state temperature promotes a more organized nanomorphology of the LC/CdS nanocomposites with improved photophysics and optoelectronic properties. The results confirm that thermotropic LCs can be ideal candidates as organization templates for the control of organic/inorganic hybrid nanocomposites at the nanoscale level. The results also demonstrate that in situ growth of semiconducting nanocrystals in thermotropic LCs is a versatile route to hybrid organic/inorganic nanocomposites and optoelectronic devices. 相似文献
948.
Kinetic Resolution of Racemic Mandelic Acid Esters by N,N′‐Dioxide–Scandium‐Complex‐Catalyzed Enantiomer‐Selective Acylation
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Yuheng Zhang Prof. Dr. Xiaohua Liu Lin Zhou Wangbin Wu Tianyu Huang Yuting Liao Lili Lin Prof. Dr. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(48):15884-15890
A simple and efficient acylative kinetic resolution of racemic mandelic acid esters was accomplished with a chiral N,N’‐dioxide–scandium(III) complex under mild and base‐free reaction conditions. A variety of mandelic acid esters performed well in the reaction, obtaining both acylated products (up to 49% yield, 97% ee) and recovered substrates (up to 49% yield, 95% ee) in high enantioselectivities with perfect selectivity factors (up to 247). The enantioselective recognition and catalytic models were also proposed for the catalytic KR reaction. 相似文献
949.
Synthesis of Site‐Specifically Phosphate‐Caged siRNAs and Evaluation of Their RNAi Activity and Stability
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Dr. Li Wu Fen Pei Jinhao Zhang Junzhou Wu Mengke Feng Yuan Wang Dr. Hongwei Jin Prof. Liangren Zhang Prof. Xinjing Tang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12114-12122
A complete set of new photolabile nucleoside phosphoramidites were synthesized, then site‐specifically incorporated into sense or antisense strands of siRNA for phosphate caging. Single caging modification was made along siRNA strands and their photomodulation of gene silencing were examined by using the firefly luciferase reporter gene. Several key phosphate positions were then identified. Furthermore, multiple caging modifications at these key positions led to significantly enhanced photomodulation of gene silencing activity, suggesting a synergistic effect. The caging group on both the terminally phosphate‐caged siRNA and the single‐stranded caged RNA has comparatively high stability, whereas hydrolysis of the caged group from the internally caged siRNA was observed, irrespective of the presence of Mg2+. Molecular dynamic simulations demonstrated that enhanced hydrolysis of the caging group on internally phosphate‐caged siRNAs was due to easy fragmentation of the caging group upon formation of the pentavalent intermediate of the phosphotriester with attack by water. The caging group in the terminally phosphate‐caged siRNA or single‐stranded caged RNA prefers to form π–π stacks with nearby nucleobases. In addition to providing explanations for previous observations, this study sheds further light on the design of caged oligonucleotides and indicates the direction of future development of nucleic acid drugs with phosphate modifications. 相似文献
950.
Zi‐Yu Li Zhen Yuan Dr. Yan‐Xia Zhao Prof. Dr. Sheng‐Gui He 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):4163-4169
Metal carbide species have been proposed as a new type of chemical entity to activate methane in both gas‐phase and condensed‐phase studies. Herein, methane activation by the diatomic cation MoC+ is presented. MoC+ ions have been prepared and mass‐selected by a quadrupole mass filter and then allowed to interact with methane in a hexapole reaction cell. The reactant and product ions have been detected by a reflectron time‐of‐flight mass spectrometer. Bare metal Mo+ and MoC2H2+ ions have been observed as products, suggesting the occurrence of ethylene elimination and dehydrogenation reactions. The branching ratio of the C2H4 elimination channel is much larger than that of the dehydrogenation channel. Density functional theory calculations have been performed to explore in detail the mechanism of the reaction of MoC+ with CH4. The computed results indicate that the ethylene elimination process involves the occurrence of spin conversions in the C?C coupling (doublet→quartet) and hydrogen atom transfer (quartet→sextet) steps. The carbon atom in MoC+ plays a key role in methane activation because it becomes sp3 hybridized in the initial stages of the ethylene elimination reaction, which leads to much lower energy barriers and more stable intermediates. This study provides insights into the C?H bond activation and C?C coupling involved in methane transformation over molybdenum carbide‐based catalysts. 相似文献