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911.
Yanan Hao Xiaohui Wang Hui Zhang Limin Guo Longtu Li 《Journal of Sol-Gel Science and Technology》2013,67(1):182-187
Ultrafine tetragonal BaTiO3 nanocrystals have been prepared by a sol–gel based method. By adjusting the volume ratio of H2O/DEG (diethylene glycol) in the solutions, hydrolysis rate of tetra-n-butyl titanate was strongly inhibited and the particle size could be controlled as small as 4–8 nm. The powder X-ray diffraction and transmission electron microscopy characterizations exhibit that the nanocrystals are spherical and well crystallized. The Raman spectrum shows the products are composed of the orthorhombic phase and tetragonal phase. The Fourier transform infrared spectrum revealed that a surface modification layer was formed around the BaTiO3 nanocrystals, which can prevent them from aggregation and help to form a stable, high solid content sol. 相似文献
912.
Preparation and characterization of ZrCO/C composite aerogels 总被引:1,自引:0,他引:1
Li Ye Wenfeng Qiu Hao Li Aijun Zhao Tao Cai Tong Zhao 《Journal of Sol-Gel Science and Technology》2013,65(2):150-159
Zr-containing organic aerogels were synthesized by ligand substitution reaction of polyzirconoxone and 2, 4-dihydroxybenzoic acid, followed by polymerization with formaldehyde, and then supercritical drying using CO2. After carbonization and carbothermal reduction under an argon atmosphere, ZrCO/C composite aerogels with controllable zirconium content (47.8–78.6 wt%) were obtained. The carbothermal reduction was substantially completed at 1,500 °C, and the obtained ZrCO/C composite aerogels exhibit low oxygen contents (9.4–6.7 wt%) and high surface areas (589–147 m2/g). Pore morphologies of the ZrCO/C composite aerogels were investigated in detail by nitrogen sorption measurements, scanning electron microscopy and its associated energy-dispersive X-ray microanalysis measurements. The results show that the aerogels are composed of carbon framework and Zr-conglomerations, and the surface area of aerogel is severely affected by its zirconium content. The presence of reductive ZrC crystals can greatly enhance the oxidation resistance ability of amorphous carbon framework and prevent collapse. 相似文献
913.
Microscopic structures of Zn(II) adsorbed on anatase TiO2 surface with different densities were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) calculation. Quantitative analysis of the EXAFS spectra showed that microscopic structures of Zn(II) were fourfold coordinated complexes, and different microscopic structures were present of the solid surface. Three modes of corner–corner/sharing-corner/sharing-edge adsorptions on anatase (101) face cluster were calculated by the DFT method. The results from DFT method were consistent with the EXAFS fittings. The optimized Zn–O average distance of the Zn–O tetrahedron was determined as about 2.00 Å. The Zn–Ti distance was 3.69 Å for the corner–corner adsorption, 3.35 Å for the sharing-corner adsorption, and 3.02 Å for the sharing-edge adsorption. According to the adsorption energies calculated by the DFT method, the microscopic structure of corner–corner adsorption was less stable than those of the other adsorption modes. With the increasing adsorption density, the corner–corner adsorption mode would be enhanced more intensively than the other adsorption modes. 相似文献
914.
Dr. Peng Cui Dr. Thomas P. Spaniol Prof. Dr. Laurent Maron Prof. Dr. Jun Okuda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(40):13437-13444
The rare‐earth‐metal? hydride complexes [{(1,7‐Me2TACD)LnH}4] (Ln=La 1 a , Y 1 b ; (1,7‐Me2TACD)H2=1,7‐dimethyl‐1,4,7,10‐tetraazacyclododecane, 1,7‐Me2[12]aneN4) were synthesized by hydrogenolysis of [{(1,7‐Me2TACD)Ln(η3‐C3H5)}2] with 1 bar H2. The tetrameric structures were confirmed by 1H NMR spectroscopy and single‐crystal X‐ray diffraction of compound 1 a . Both complexes catalyze the dehydrogenation of secondary amine? borane Me2NH ? BH3 to afford the cyclic dimer (Me2NBH2)2 and (Me2N)2BH under mild conditions. Whilst the complete conversion of Me2NH ? BH3 was observed within 2 h with lanthanum? hydride 1 a , the yttrium homologue 1 b required 48 h to reach 95 % conversion. Further reactions of compound 1 a with Me2NH ? BH3 in various stoichiometric ratios gave a series of intermediate products, [{(1,7‐Me2TACD)LaH}4](Me2NBH2)2 ( 2 a ), [(1,7‐Me2TACDH)La(Me2NBH3)2] ( 3 a ), [(1,7‐Me2TACD)(Me2NBH2)La(Me2NBH3)] ( 4 a ), and [(1,7‐Me2TACD)(Me2NBH2)2La(Me2NBH3)] ( 5 a ). Complexes 2 a , 3 a , and 5 a were isolated and characterized by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction studies. These intermediates revealed the activation and coordination modes of “Me2NH ? BH3” fragments that were trapped within the coordination sphere of a rare‐earth‐metal center. 相似文献
915.
Liang Cui Yanling Song Guoliang Ke Zhichao Guan Huimin Zhang Ya Lin Yishun Huang Dr. Zhi Zhu Prof. Chaoyong James Yang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(32):10442-10451
Recently, the binding ability of DNA on GO and resulting nuclease resistance have attracted increasing attention, leading to new applications both in vivo and in vitro. In vivo, nucleic acids absorbed on GO can be effectively protected from enzymatic degradation and biological interference in complicated samples, making it useful for targeted delivery, gene regulation, intracellular detection and imaging with high uptake efficiencies, high intracellular stability, and very low toxicity. In vitro, the adsorption of ssDNA on GO surface and desorption of dsDNA or well‐folded ssDNA from GO surface result in the protection and deprotection of DNA from nucleic digestion, respectively, which has led to target‐triggered cyclic enzymatic amplification methods (CEAM) for amplified detection of analytes with sensitivity 2–3 orders of magnitude higher than that of 1:1 binding strategies. This Concept article explores some of the latest developments in this field. 相似文献
916.
Dr. Kun Cui Dr. Xuemin Lu Junfang Guan Prof. Qinghua Lu Dr. Zhaofu Fei Prof. Paul J. Dyson 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(26):8550-8557
Fluorescent nanoparticles (FNPs) are obtained in water by self‐assembly from a polymeric ionic liquid, fluorescent carboxylate moiety, and a surfactant through two main supramolecular interactions, that is, ionic bonds and hydrophobic/hydrophilic interactions. The hydrophobicity of the surfactant is tunable and a highly hydrophobic surfactant increases the fluorescence intensity and stability of the FNPs. The fluorescence of the FNPs is sensitive to a quenching effect by various ions with high selectivity, and consequently, they may be used as sensors. The self‐assembly approach used to generate the FNPs is considerably simpler than other methods based on more challenging synthetic methods and the flexibility of the approach should allow a wide and diverse range of FNPs to be prepared with specific sensor applications. 相似文献
917.
Dr. Hong‐Dong Hao Dr. Sergio Wittlin Prof. Dr. Yikang Wu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(23):7605-7619
Perhydrolysis of a sterically congested multifunctional epoxide was achieved in ethereal H2O2 with the aid of a recently developed Mo catalyst. The resulting hydroperoxide cyclized to give a 1,2,4‐trioxane, which could be readily elaborated into qinghaosu and a range of novel analogues. Some of the compounds with two such trioxane moieties showed in vitro antimalarial activity comparable to or even better than that of artesunate or chloroquine. 相似文献
918.
Ying‐Lu Cui Ji‐Long Zhang Prof. Qing‐Chuan Zheng Rui‐Juan Niu Yu Xu Prof. Hong‐Xing Zhang Chia‐Chung Sun 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(2):549-557
Cytochrome P450 (CYP) 7B1 is a steroid cytochrome P450 7α‐hydroxylase that has been linked directly with bile salt synthesis and hereditary spastic paraplegia type 5 (SPG5). The enzyme provides the primary metabolic route for neurosteroids dehydroepiandrosterone (DHEA), cholesterol derivatives 25‐hydroxycholesterol (25‐HOChol), and other steroids such as 5α‐androstane‐3β,17β‐diol (anediol), and 5α‐androstene‐3β,17β‐diol (enediol). A series of investigations including homology modeling, molecular dynamics (MD), and automatic docking, combined with the results of previous experimental site‐directed mutagenesis studies and access channels analysis, have identified the structural features relevant to the substrate selectivity of CYP7B1. The results clearly identify the dominant access channels and critical residues responsible for ligand binding. Both binding free energy analysis and total interaction energy analysis are consistent with the experimental conclusion that 25‐HOChol is the best substrate. According to 20 ns MD simulations, the Phe cluster residues that lie above the active site, particularly Phe489, are proposed to merge the active site with the adjacent channel to the surface and accommodate substrate binding in a reasonable orientation. The investigation of CYP7B1–substrate binding modes provides detailed insights into the poorly understood structural features of human CYP7B1 at the atomic level, and will be valuable information for drug development and protein engineering. 相似文献
919.
920.
正癸烷与二甲苯在超临界压力下的热裂解 总被引:1,自引:0,他引:1
采用连续流动装置对正癸烷和二甲苯在超临界压力下的热裂解对比研究. 用气相色谱和色质联用仪对其气相产物和液相产物进行分析, 计算气相产物产率和裂解转化率, 并运用计算化学方法获得正癸烷和二甲苯不同化学键的键能, 从实验和理论上分析其裂解反应的难易程度和裂解规律. 实验结果表明, 在4 MPa和650、700、750 ℃条件下, 正癸烷比二甲苯更容易裂解, 正癸烷裂解产物以C1-C3小分子的烃类和氢气为主, 而二甲苯裂解产物主要为乙苯、甲苯和其它芳香类化合物; 键能计算结果表明, 正癸烷碳链骨架的C-C键能和C-H键能均较小, 裂解反应的诱发步骤应该是C-C键断裂, 而二甲苯苯环上C-C和C-H键能均较大, 裂解诱发步骤应该是侧链甲基脱氢反应. 因此正癸烷裂解反应以C-C键断裂和脱氢反应为主, 二甲苯裂解主要发生侧链甲基C-C键断裂和脱氢反应, 而芳环则比较稳定, 理论计算键能分析与裂解实验结果一致. 相似文献