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991.
Systematic Study of Ti‐Distribution in Titanosilicate *BEA Zeolites via Symmetry‐Adapted Enumeration
The high performance of titanosilicate zeolites in various industrial oxidation reactions is highly affected by the distribution of Ti atoms in their frameworks. Because of their structural complexity, previous theoretical studies mainly focus on the preferential location of single Ti atoms within the unit cells of titanosilicate zeolites. When multiple Ti atoms are required, conventional approaches consider only symmetrically related T sites to reduce the computation complexity. Such symmetry‐constrained approaches obviously overlooked many possible configurations. Herein, we conduct a systematic study on the distribution of two Ti atoms in the unit cell of titanosilicate zeolite *BEA . Different from conventional symmetry‐constrained approaches, we introduce two Ti atoms simultaneously without any constraint and adopt a symmetry‐adapted algorithm to enumerate all possible configurations for double‐Ti introduction. We generate a total of 273 distinct configurations and analyze the Ti‐distribution via Boltzmann statistics. We find that many of the configurations overlooked by conventional symmetry‐constrained approaches indeed exhibit more feasible energies, which may lead to different Ti‐distributions. Our study indicates the necessity of unconstrained introduction of Ti atoms when multiple‐Ti atoms are considered for calculations. 相似文献
992.
Wang F Han MY Mya KY Wang Y Lai YH 《Journal of the American Chemical Society》2005,127(29):10350-10355
A novel class of monodisperse conjugated polymer nanoparticles have been readily prepared by the facile reprecipitation of poly{1,3-bis[2-(3-alkylthienyl)]azulene} or poly{1,3-bis[2-(3-alkoxythienyl)]azulene}. The multicomponent poly(bithiophene-alt-azulene) macromolecules were efficiently self-assembled into a wide range of size-tunable nanoparticles from a few tens to five hundred nanometers via the hydrophobic and pi-stacking effects in the mixed chloroform/methanol solutions. Electronically altered polymer structures with different alkyl or alkoxy substitutes exhibited variable self-assembling behaviors to precisely tune the size and the optical/electronic properties of nanoparticles. A strong size dependence of continuous bathochromic absorption and significant enhanced emission were observed with the increase of particle size. A linear relationship between the absorption or fluorescence intensities and the particle size was demonstrated as well, and this is very useful to probe the intermolecular interactions and the size evolutions of conjugated polymer nanoparticles. After the size-dependent optical and electronic properties are created, they can be further optimized to improve the performance of materials prior to the use in novel organic nanodevices in a cost-effective way. 相似文献
993.
994.
3-苯氧甲基-6-(2,4-二氟苯基)-7H-1,2,4-三唑并[3,4-b][1,3,4]噻二嗪的合成与晶体结构研究 总被引:2,自引:0,他引:2
由苯氧乙酸出发,经多步反应,制得3-苯氧甲基-4-氨基-5-巯基-1,2, 4-三唑,它与2-氯-2',4'-二氟苯乙酮进行环化反应,生成3-苯氧甲基-6-( 2,4-二氟苯基)-7H-1,2,4-三唑并[3,4-b][1,3,4]噻二嗪,通过元素分析、红外 光谱、核磁共振氢谱与碳谱、质谱进行表征,并利用单晶X射线衍射法测定其结构 。晶体属单斜晶系、P2_(1/c)空间群,a = 1.339(3) nm, b = 1.4683(4) nm, c = 0.8606(2) nm, β = 108.49(2)°, Z = 4, F(000) = 736, R_1 = 0.0509。还 对均三唑并噻二唑两类稠杂环的晶体结构作了比较。 相似文献
995.
996.
The effects of four factors (different side chains, side-chain disorder, conformational change, and ions and water) on the energy band structures of proteins have been investigated with the aid of the CNDO/2 crystal orbital method. The results indicate that these factors are very important. The consequences of these effects on the semiconductive properties of proteins are discussed. 相似文献
997.
This paper introducesa novel method for packing Capillary Electrochromatography Columns (CEC). Using vacuum packing methodology, silica particles as small as 1 microm were successfully packed into the capillary columns with 75 microm inner diameter. The columns are verystable and show no noticeable loss in efficiency after 200 sample injections. The performance of these vacuum packed capillary columns was evaluated with a mixture of aromatic and non-aromatic compounds. A 24 cm long capillary column can produce peak efficiencies of around 45,000 plates for benzene. 相似文献
998.
A series of novel hemicyanine dye-β-cyclodextrin compounds: mono-6-deoxy-β-cyclodextrin-6-[p-(p-substituted styryl)pyridium] p-totylfulfonates were synthesized by the condensation of mono-6-deoxy-β- cyclodextrin-6-(p-methyl pyridinium) p-toluenesulfonate with (un)substituted benzaldehydes. Their structures were established by 1^H NMR, IR, UV-Vis and elemental analysis. The absorption and fluorescence properties of the novel compounds were measured in solution and the photostability of a selected hemicyanine dye-β-cyclodextrin compound was also investigated. 相似文献
999.
Zhen‐Yu Li Ping Chen Hong‐Gui Xu Shu‐Ying Peng Yi‐Ming Yang Zhong‐Zhen Zhao Yue‐Wei Guo 《Helvetica chimica acta》2007,90(7):1353-1359
Five new polycyclic Daphniphyllum alkaloids, macropodumines F ( 1 ) and G ( 2 ), 17‐oxoyuzurimine ( 3 ), and macropodumines H ( 4 ) and I ( 5 ), were isolated from the leaves of D. macropodum Miq ., collected in Sichuan Province, China. The structures and relative configurations of the new compounds – as well as of four known, related alkaloids – were elucidated on the basis of in‐depth spectroscopic and mass‐spectrometric analyses, by chemical derivatization, and by comparison of spectroscopic data with those of known compounds. 相似文献
1000.
Gao H Petzold CJ Leavell MD Leary JA 《Journal of the American Society for Mass Spectrometry》2003,14(8):916-924
A rapid and accurate method of quantifying positional isomeric mixtures of phosphorylated hexose and N-acetylhexosamine monosacchrides by using gas-phase ion/molecule reactions coupled with FT-ICR mass spectrometry is described. Trimethyl borate, the reagent gas, reacts readily with the singly charged negative ions of phosphorylated monosaccharides to form two stable product ions corresponding to the loss of one or two neutral molecules of methanol from the original adduct. Product distribution in the ion/molecule reaction spectra differs significantly for isomers phosphorylated in either the 1- or the 6-position. As a result, the percents of total ion current of these product ions for a mixture of the two isomers vary with its composition. In order to determine the percentage of each isomer in an unknown mixture, a multicomponent quantification method is utilized in which the percents of total ion current of the two product ions for each pure monosaccharide phosphate and the mixture are used in a two-equation, two-unknown system. The applicability of this method is demonstrated by successfully quantifying mock mixtures of four different isomeric pairs: Glucose-1-phosphate and glucose-6-phosphate; mannose-1-phosphate and mannose-6-phosphate; galactose-1-phosphate and galactose-6-phosphate; N-acetylglucosamine-1-phosphate and N-acetylglucosamine-6-phosphate. The effects of mixture concentrations and ion/molecule reaction conditions on the quantification are also discussed. Our results demonstrate that this assay is a fast, sensitive, and robust method to quantify isomeric mixtures of phosphorylated monosaccharides. 相似文献