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991.
Xu Zhao Sarah E. Cleary Ceren Zor Nicole Grobert Holly A. Reeve Kylie A. Vincent 《Chemical science》2021,12(23):8105
Heterogeneous biocatalytic hydrogenation is an attractive strategy for clean, enantioselective C X reduction. This approach relies on enzymes powered by H2-driven NADH recycling. Commercially available carbon-supported metal (metal/C) catalysts are investigated here for direct H2-driven NAD+ reduction. Selected metal/C catalysts are then used for H2 oxidation with electrons transferred via the conductive carbon support material to an adsorbed enzyme for NAD+ reduction. These chemo-bio catalysts show improved activity and selectivity for generating bioactive NADH under ambient reaction conditions compared to metal/C catalysts. The metal/C catalysts and carbon support materials (all activated carbon or carbon black) are characterised to probe which properties potentially influence catalyst activity. The optimised chemo-bio catalysts are then used to supply NADH to an alcohol dehydrogenase for enantioselective (>99% ee) ketone reductions, leading to high cofactor turnover numbers and Pd and NAD+ reductase activities of 441 h−1 and 2347 h−1, respectively. This method demonstrates a new way of combining chemo- and biocatalysis on carbon supports, highlighted here for selective hydrogenation reactions.Heterogeneous chemo-bio catalytic hydrogenation is an attractive strategy for clean, enantioselective C X reduction. 相似文献
992.
在受阻路易斯酸碱对(FLPs)催化的2,3-二取代2H-1,4-苯并噁嗪氢化反应中,3号位取代基不同会导致反应效率极大改变,因此我们选取反应活性具有较大差别的三种底物作为模型化合物对其反应机理进行了研究,建立了氢化反应势能面.发现当B(C6F5)3与2,3-二苯基2H-1,4-苯并噁嗪或2-甲基-3-苯基2H-1,4-苯并噁嗪混合后,会形成FLPs与路易斯酸碱加合物的混合物.而将B(C6F5)3与2,3-二甲基2H-1,4-苯并噁嗪混合后主要形成没有催化活性的路易斯酸碱加合物,因其能量低于FLPs,在催化体系中不容易转化为FLPs,这导致三种模型化合物在FLPs催化的氢化反应中效率不同.进一步的取代基电子效应及位阻效应计算表明:B(C6F5)3与2-甲基-3-取代2H-1,4-苯并噁嗪混合后形成的路易斯酸碱加合物和FLPs化合物之间稳定性差别源于3位取代基空间位阻不同. 相似文献
993.
994.
铁铝复合柱撑粘土的制备、柱结构和稳定性(I) 总被引:8,自引:0,他引:8
用两种方法合成了一系列不同Fe/Al比的铁铝复合柱撑牯土(FeAl-PlLC). 用~(27)Al-NMR、UV、ESR等手段考察了柱溶液的结构和状态, 用XRD、DTA、UV-DRS 等技术对其结构、稳定性进行了研究. 结果表明, 铁铝柱撑粘土的底面间距为1.98~1.55 nm, Fe/Al比对其柱结构、比表面积、热稳定性均有较大影响. Fe/Al<0.5时, 层间柱主要呈现Keggin结构, Fe/Al≥0.5时, 可能为三聚结构. 随Fc/Al比的增加, d(001)值, 比表面面、热稳定性逐渐下降. 相似文献
995.
We show that the electronic and atomic structures of silicon carbide nanotubes (SiCNTs) undergo dramatic changes with hydrogenation from first-principles calculations based on density-functional theory. The exo-hydrogenation of a single C atom results in acceptor states close to the highest occupied valence band of pristine SiCNT, whereas donor states close to the lowest unoccupied conduction band appear as a Si atom being hydrogenated. Upon fully hydrogenating Si atoms, (8,0) and (6,6) SiCNTs become metallic with very high density of states at the Fermi level. The full hydrogenation of C atoms, on the other hand, increases the band gap to 2.6 eV for (8,0) SiCNT and decreases the band gap to 1.47 eV for (6,6) SiCNT, respectively. The band gap of SiCNTs can also be greatly increased through the hydrogenation of all the atoms. 相似文献
996.
997.
Zhao B 《Langmuir : the ACS journal of surfaces and colloids》2004,20(26):11748-11755
This article reports the study of the effect of relative grafting densities of two polymer chains on solvent-induced self-assembly of mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes through a combinatorial approach. Gradient-mixed PMMA/PS brushes were synthesized from a gradient-mixed initiator-terminated monolayer by combining atom transfer radical polymerization (ATRP) and nitroxide mediated radical polymerization (NMRP) in a two-step process. The gradient-mixed initiator-terminated monolayer was fabricated by first formation of a gradient in density of an ATRP initiator through vapor diffusion followed by backfilling of an NMRP-initiator-terminated trichlorosilane. After treatment of a gradient-mixed brush whose PS Mn was slightly lower than that of PMMA with glacial acetic acid, a selective solvent for PMMA, relatively ordered nanodomains were observed in the region where the ratio of PS to PMMA grafting density (number of polymer chains/nm2) was in the range from 0.67 to 2.17 and the overall grafting density was approximately 0.85 polymer chains/nm2. Contact angle hysteresis were high (> or =40 degrees ) in this region and XPS studies confirmed that the PMMA chains were enriched at the outermost layer. The nanodomains are speculated to be of a micellar structure with PS chains forming the core shielded by PMMA chains. 相似文献
998.
沙林酸印迹聚邻苯二胺纳米膜制备及结构表征 总被引:9,自引:0,他引:9
采用电化学聚合法合成了对有机磷毒剂沙林具有特异识别的聚邻苯二胺(PPD)分子印迹纳米膜(iPPD).利用石英晶体微天平(QCM)证实了印迹效应的存在,并用循环伏安法(CV)、AFM、XPS进行了系统的结构表征.结果表明,分子印迹膜的膜厚约20 nm,膜的表面呈“石林”状,疏松多孔,具有良好的吸附性能.分子印迹主要影响聚合物的三维排列,而聚合物的化学组成没有发生改变.该种分子印迹纳米膜在选择性检测军用毒剂沙林中具有良好的应用前景. 相似文献
999.
J.G. Zhao 《Journal of solid state chemistry》2007,180(10):2816-2823
The single-phase 6H BaRuO3 with the hexagonal BaTiO3 structure was synthesized at 5 GPa and 1000 °C. Rietveld refinement of the powder X-ray data for the 6H phase resulted in the lattice parameters to be a=5.7127(1) Å and c=14.0499(2) Å; the average Ru-O distance and direct Ru-Ru distance in the Ru2O9 dioctahedron being 1.992(6) and 2.5658(14) Å, respectively. The electrical resistivity of the 6H BaRuO3 follows a relationship of ρ versus T3/2 below 60.0 K, a signature deviation from the Fermi-liquid behavior. Both magnetic susceptibility and specific heat data indicate that the 6H BaRuO3 is an exchange-enhanced Pauli paramagnet due to the electron correlation effect with large Wilson ratio RW and Stoner enhancement factor. The comprehensive evolution of transport and magnetic properties from 9R across 4H to 6H BaRuO3 was discussed. 相似文献
1000.
有限群极大子群的θ-子群偶 总被引:21,自引:0,他引:21
N.P.Mukherjee和 P.Bhattacharya在“On theta pairs for a maximal sub-group”(Proc.Amer.Math.Soc,Vl09N3(1990))一文中定义了有限群的极大子群的θ-子群偶概念,研究了极大子群的极大θ-子群偶对群结构的影响,得到了一系列结果.本文在进一步探究θ-子群偶性质的基础上,对该文中一系列主要结果作出了本质性的改进,并给出了可解性、幂零性的一些新刻划. 相似文献