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231.
Chiral derivatives of trans-1,2-diaminocyclohexane with different N,N-dialkyl groups in well-defined orientations have been synthesized, and applied as catalysts for the asymmetric aldol reaction between a variety of aldehydes and ketones. Enantiomeric catalyst 1j catalyzed the reaction in ethanol and provided excellent diastereoselectivity and enantioselectivity. Significantly, simple replacement of organic solvents with water switched the products of the aldol reactions from anti to syn configuration. Such catalytic reactions led to the products with anti to syn diastereoselectivity up to 99:1 in ethanol, while in water gave the products with syn to anti diastereoselectivity up to 99:1. 相似文献
232.
233.
Quinoline bridged imidazolium precursors 5,8‐bis(N‐R‐imidazolylidenylmethylene)quinoline PF6– salts [H2L](PF6)2 [R = Me ( 1a ), R = naphthylmethyl ( 1b )] were prepared by quaternization of N‐methylimidazole and N‐naphthylmethylimidazole with 5,8‐bis(bromomethyl)quinoline, respectively. Reaction of the imidazolium ligands 1a and 1b with Hg(OAc)2 and Ag2O in acetonitrile gave the macrocyclic transition metal carbene complexes [Hg2L2](PF6)4 ( 2a and 2b ) and [Ag2L2](PF6)2 ( 3a and 3b ), respectively. All the N‐heterocyclic carbene complexes were characterized in detail by NMR, ESI‐MS, and elemental analysis. Structures of complexes 2a and 3a were determined by X‐ray diffraction studies. Structural studies revealed that the coordination arrangement of the central mercury atom in complex 2a displays a tricoordinate mode and the molecular conformation results in a“closed” form with the bridging quinoline functionality in the macrocycle, whereas the silver complex 3a does not show an coordiantion between the bridging quinoline and the AgI ion, which results in an “open” conformation of the macrocycle. The HgII and AgI NHC complexes showed similar UV absorption and luminescence in acetonitrile solutions. 相似文献
234.
Yao Huang Long‐Jiang Liu Ming‐Shan Zhou Xiao‐Jun Zhou Chao Zhu Fei‐E Fu Yong‐Ming Zhang 《无机化学与普通化学杂志》2013,639(10):1884-1887
Two metal‐organic frameworks, [Zn(dmtrz)(btrc)1/3]n ( 1 ) and [Zn2(dmtrz)2(btec)(H2O)2]n ( 2 ) (dmtrz = 3, 5‐dimethyl‐1‐H‐1, 2,4‐triazole, btrc = 1, 3,5‐benzenetricarboxylate, btec = 1, 2,4, 5‐benzenetetracarboxylate), were synthesized by hydrothermal reaction. The crystal structure analysis reveals that compound 1 is a dense 3D framework with Schläfli symbols of {43}2{46 · 66 · 83}3, which is a loh1 structure. Compound 2 is a 2D network. In addition, the photoluminescence of two compounds were studied in solid state at room temperature, together with their thermal analysis. 相似文献
235.
Ge‐Fei Hao Sheng‐Gang Yang Guang‐Fu Yang Chang‐Guo Zhan 《Journal of computational chemistry》2013,34(24):2055-2064
Gibberellins (GAs) are phytohormones essential for many developmental processes in plants. In this work, fundamental mechanism of hormone perception by receptor GID1 has been studied by performing computational simulations, revealing a new GA‐binding channel of GID1 and a novel hormone perception mechanism involving only one conformational state of GID1. The novel hormone perception mechanism demonstrated here is remarkably different from the previously proposed/speculated mechanism [Murase et al., Nature 2008 , 456, 459] involving two conformational states (“OPEN” and “CLOSED”) of GID1. According to the new perception mechanism, GA acts as a “conformational stabilizer,” rather than the previously speculated “allosteric inducer,” to induce the recognition of protein DELLA by GID1. The novel mechanistic insights obtained in this study provide a new starting point for further studies on the detailed molecular mechanisms of GID1 interacting with DELLA and various hormones and for mechanism‐based rational design of novel, potent growth regulators that target crops and ornamental plants. © 2013 Wiley Periodicals, Inc. 相似文献
236.
Fei Geng Ting Lu Zhen Li Liqiang Zheng Ganzuo Li 《Journal of Dispersion Science and Technology》2013,34(9):1209-1213
The effects of Tris-HCl buffer solution on the cmc of cetyltrimethylammonium bromide (CTAB) were studied by surface tension measurement. The result shows that the effect of the buffer solution depends on the interaction between CTAB and NaCl and the structure accelerants of water, Tris. A series of parameters, including the critical micelle concentration (cmc), the surface tension at cmc (γcmc), the adsorption efficiency (pC20), and the effectiveness of surface tension reduction (∏cmc) were obtained from the surface tension measurements in the presence of glycine with different concentration in the Tris-HCl buffer solution at 27°C. In addition, maximum surface excess concentration (Γ max) and minimum surface area per molecule (Amin) at the air-water interface were estimated according to the Gibbs adsorption isotherm. The thermodynamic parameters (Δ C p,m , Δ H m,tr , Δ C p,m,tr ) of micellization for CTAB in the absence and presence of glycine at different temperature were also been obtained. 相似文献
237.
Zhen Li Bin Dong Fei Geng Ganzuo Li 《Journal of Dispersion Science and Technology》2013,34(8):1066-1071
This article reports a novel preparation of mesoporous silica with series of 1-alky-3-methylimidazolium bromide (CnMIM)Br (n = 12, 14, 16), a kind of amphiphilic room-temperature ionic liquids (RTILs), as a template via a sol-gel nanocasting technique. The pore morphology and structures of these mesoporous silica were characterized by Transmission electron microscopy (TEM). The results show that the RTIL bearing longer alkyl chain is preferred to form the mesoporous silica material with bigger pores. (C16MIM)Br has been chosen to study how the various influencing factors affect the synthesis and structure of the mesoporous silica material, such as the acid concentration, the solling time, the gelling time and the calcination time. N2 adsorption-desorption isotherms measurement was used to characterize the pore size distribution and BET surface area. The results indicate that all of the factors can make an influence on the preparation of the mesoporous silica, which is more sensitive to the concentration of the acid. 相似文献
238.
Fei Han Guang-Hui Zhang Ping Gu 《Journal of Radioanalytical and Nuclear Chemistry》2013,295(1):369-377
The copper ferrocyanide (CuFC) prepared in this study was characterized using X-ray diffraction and scanning election microscopy. The distribution of particle sizes of the CuFC suspension was determined. The adsorption kinetics data were evaluated for an intraparticle diffusion model, a pseudo-first order model and a pseudo-second order model at temperatures of 288, 298 and 308 K, respectively. It was found that the adsorption process of Cs+ on CuFC was best described by a pseudo-second order kinetic model, with a correlation coefficient (R 2) equal to 1.000, and the adsorption rate constant increased with increasing temperature. This result indicated that chemisorptions took place during the adsorption process. The adsorption equilibrium data fit well to the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) isotherm models. The mean adsorption energy (E) between 11 and 13 kJ/mol at different temperatures indicated that ion exchange was the main mechanism during the adsorption process. Thermodynamic parameters were also evaluated during the adsorption. The values of the standard Gibbs free energy change (ΔG o) and standard enthalpy change (ΔH o) suggested that the adsorption was a spontaneous and endothermic process. The distribution coefficient (K d) was more than 2.94 × 106 mL/g when the pH of solution was between 2.6 and 10.9, and the initial Cs+ concentration was 100 μg/L. The existence of K+ and Na+ did not affect the adsorption of Cs+ on CuFC when the concentration of K+ and Na+ in the solution was below 20 and 1,000 mg/L, respectively. 相似文献
239.
以麦秆和稻壳生物质为研究对象,在不同的热解温度、热解速率以及蒸汽活化温度条件下制备了生物质焦,采用比表面积与孔隙度分析仪测定生物质焦的比表面积和孔隙结构参数。利用固定床吸附装置,研究了热解温度、热解速率、活化温度和模拟烟气中SO2和NO浓度等因素对生物质焦吸附SO2和NO性能的影响。结果表明,蒸汽活化可以显著提高生物质焦的BET比表面积、D-R比表面积、D-R微孔容积和总孔容,降低其平均孔径,并显著增加蒸汽活化生物质焦对SO2与NO吸附的起始穿透时间和吸附量。快速热解下制得的蒸汽活化焦对SO2和NO的吸附效果优于慢速热解,热解温度为873 K的蒸汽活化焦的吸附性能明显好于热解温度为673与1 073 K的蒸汽活化焦。在973~1 173 K下,随着蒸汽活化温度的提高,蒸汽活化生物质焦对SO2和NO的吸附量呈现先上升后下降的趋势。随着模拟烟气中SO2与NO浓度的降低,蒸汽活化生物质焦对SO2与NO吸附的起始穿透时间延长,但相应的SO2和NO吸附量下降。在873 K、快速热解和1 073 K条件下制得的蒸汽活化麦秆焦对SO2和NO吸附量最大,其值分别为109.02和21.77 mg/g。 相似文献
240.
仿生制备有机-无机复合微囊固定化葡萄糖氧化酶 总被引:1,自引:0,他引:1
将层层自组装技术与仿生矿化技术相结合,由聚苯乙烯磺酸钠、聚二甲基二烯丙基氯化铵和二氧化硅成功制备(聚苯乙烯磺酸钠-聚二甲基二烯丙基氯化铵)2-二氧化硅复合微囊.采用扫描电子显微镜、红外光谱和热重对微囊的形貌和化学结构进行了表征.以该复合微囊作为理想载体固定化葡萄糖氧化酶.结果表明,固定于复合微囊中的葡萄糖氧化酶的热稳定性、pH稳定性、操作稳定性得到了提高;在最适条件下,复合微囊固定化葡萄糖氧化酶的酶活回收率为72.85%,米氏常数是游离葡萄糖氧化酶的2.21倍.复合微囊在化学/生物催化、药物/基因传递系统和生物传感器应用方面具有一定的潜能. 相似文献