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201.
Frank Seela Ping Ding Xiaohua Peng Henning Eickmeier Hans Reuter 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o600-o602
The title compound, 2,4‐diamino‐5‐bromo‐7‐(2‐deoxy‐2‐fluoro‐β‐d ‐arabinofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine, C11H13BrFN5O3, shows two conformations of the exocyclic C4′—C5′ bond, with the torsion angle γ (O5′—C5′—C4′—C3′) being 170.1 (3)° for conformer 1 (occupancy 0.69) and 60.7 (7)° for conformer 2 (occupancy 0.31). The N‐glycosylic bond exhibits an anti conformation, with χ = −114.8 (4)°. The sugar pucker is N‐type (C3′‐endo; 3T4), with P = 23.3 (4)° and τm = 36.5 (2)°. The compound forms a three‐dimensional network that is stabilized by several intermolecular hydrogen bonds (N—H...O, O—H...N and N—H...Br). 相似文献
202.
Huifang Xu Wei Wei Chengliang Zhang Shujiang Ding Xiaozhong Qu Dr. Jiguang Liu Dr. Yunfeng Lu Prof. Zhenzhong Yang Prof. 《化学:亚洲杂志》2007,2(7):828-836
This report presents a facile approach for the low‐temperature synthesis of crystalline inorganic‐oxide composite hollow spheres by employing the bulk controlled synthesis of inorganic‐oxide nanocrystals with polymer spheres as templates. The sulfonated polystyrene gel layer can adsorb the target precursor and induce inorganic nanocrystals to grow on the template in situ. The crystalline phase and morphology of the composite shell is tunable. By simply adjusting the acidity of the titania sol, crystalline titania composite hollow spheres with tunable crystalline phases of anatase, rutile, or a mixture of both were achieved. The approach is general and has been extended to synthesize the representative perovskite oxide (barium and strontium titanate) composite hollow spheres. The traditional thermal treatment for crystallite transformation is not required, thus intact shells can be guaranteed. The combination of oxide properties such as high refractive index, high dielectric constant, and catalytic ability with the cavity of the hollow spheres is promising for applications such as opacifiers, photonic crystals, high‐κ‐gate dielectrics, and photocatalysis. 相似文献
203.
Polycapillary X-ray optics (capillary X-ray lens) are now popular in X-ray fluorescence (XRF) analysis. Such an X-ray lens can collect X-rays emitted from an X-ray source in a large solid angle and form a very intense X-ray microbeam which is very convenient for microbeam X-ray fluorescence (MXRF) analysis giving low minimum detection limits (MDLs) in energy dispersive X-ray fluorescence (EDXRF). A new method called position sensitive X-ray spectrometry (PSXS) which combines an X-ray lens used to form an intense XRF source and a position sensitive detector (PSD) used for wavelength dispersive spectrometry (WDS) measurement was developed recently in the X-ray Optics Laboratory of Institute of Low Energy Nuclear Physics (ILENP) at Beijing Normal University. Such a method can give high energy and spacial resolution and high detection efficiency simultaneously. A short view of development of both the EDXRF using a capillary X-ray lens and the new PSXS is given in this paper. 相似文献
204.
A novel norvancomycin-bonded chiral stationary phase (NVC-CSP) was synthesized by using the chiral selector of norvancomycin. The chiral separation of enantiomers of several dansyl-amino acids by high-performance liquid chromatography (HPLC) in the reversed-phase mode is described. The effects of some parameters, such as organic modifier concentration, column temperature, pH and flow rate of the mobile phase, on the retention and enantioselectivity were investigated. The study showed that ionic, as well as hydrophobic interactions were engaged between the analyte and macrocycle in this chromatographic system. Increasing pH of buffers usually improved the chiral resolution for dansyl--amino-n-butyric acid (Dns-But), dansyl-methionine (Dns-Met) and dansyl-threonine (Dns-Thr), but not for dansyl-glutamic acid (Dns-Glu) which contains two carboxylic groups in its molecular structure. The natural logarithms of selectivity factors (ln ) of all the investigated compounds depended linearly on the reciprocal of temperature (1/T), most processes of enantioseparation were controlled enthalpically. Interestingly, the process of enantioseparaton for dansyl-threonine was enthalpy-controlled at pH of 3.5, while at pH of 7.0, it was entropy-controlled according to thermodynamic parameters ΔR,SΔH° and ΔR,SΔS° afforded by Van’t Hoff plots. In order to get baseline separation for all the solutes researched, norvancomycin was also used as a chiral mobile phase additive. In combination with the NVC-CSP, remarkable increases in enanselectivity were observed for all the compounds, as the result of a “synergistic” effect. 相似文献
205.
本文建立了流动注射二甲酚橙光度法测定镀锌纯化液中Zn ̄2+的自动分析方法。利用区域采样技术和调整管路参数自动完成对样品的上千倍稀释,确定了最佳分析条件并研究了干扰离子的影响及消除办法。所建方法仪器简单,分析速度为84次/小时,变异系数(Zn ̄2+16.0g/L,n=20)为1.O%,用于实际钝化液分析,相对误差小于±10%。 相似文献
206.
This work evaluated derivatization procedures for detecting both natural and synthetic estrogenic chemicals by gas chromatography/mass spectrometry (GC/MS). Different silylating agents, mainly trimethylsilylating (TMS) agents, were compared, and the roles of various content of trimethylchlorosilane (TMCS, as a stimulator) were investigated. The difference in the abundances of the derivatives was caused by the steric hindrance of multiple hydroxyl groups and ethynyl groups in the structures of estrogenic chemicals. The use of TMCS produces an increase in the derivatization yield, especially for the compounds with multiple hydroxyl groups (i.e., 17beta-estradiol (E(2)) and estriol (E(3))). Mass spectra of O-TMS derivatives and tentative fragmentation profiles are proposed. Molecular ions were the base peaks for all the derivatives, and were used as the quantitation ions to obtain maximum detection sensitivity and specificity. Sample enrichment was achieved by Oasis HLB solid-phase extraction cartridges. The quantitation limits of these compounds ranged from 5 to 10 ng/L in 1000-mL water samples. Recovery of the estrogenic chemicals in spiked various water samples ranged from 78 to 102% while relative standard deviation (RSD) ranged from 1 to 15%. 相似文献
207.
An automated method for the rapid determination of microorganisms using a flow-injection system is presented. Electrochemical measurement of a mediator reduced by microbial metabolism allowed the determination of fungi and bacteria in a few minutes. The lowest detection limit was 5 × 106 colony-forming units (cfu) ml?1 for Escherichia coli. Correlation between the flow-injection method and standard microbiological methods was excellent (r = 0.997, n = 4 for Beauveria bassiana; r = 0.997, n = 7 for E. coli). The flow-injection system was applied to the on-line control of an E. coli cultivation. 相似文献
208.
Sheng‐Xiong Huang Xun Liao Quan‐Jiang Nie Li‐Sheng Ding Shu‐Lin Peng 《Helvetica chimica acta》2004,87(3):598-604
Three new phenyl glycosides, scrophenoside A ( 1 ), B ( 2 ), and C ( 3 ), and two new phenylethyl glycosides, scroside D ( 4 ) and scroside E ( 5 ), were isolated from the stem of Picrorhiza scrophulariiflora Pennell (Scrophularlaceae), besides five known compounds. On the basis of spectroscopic evidence, the structures of the new compounds were elucidated as 4‐acetyl‐2‐methoxyphenyl 6‐O‐[4‐(β‐D ‐glucopyranosyloxy)vanilloyl]‐β‐D ‐glucopyranoside ( 1 ), 4‐acetylphenyl 6‐O‐[(E)‐p‐coumaroyl]‐β‐D ‐glucopyranoside ( 2 ), 4‐[(1R)‐ and (1S)‐1‐hydroxyethyl]‐2‐methoxyphenyl β‐D ‐glucopyranoside ( 3a and 3b , resp.), 2‐(3,4‐dihydroxyphenyl)ethyl O‐β‐D ‐glucopyranosyl‐(1→3)‐4‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranoside ( 4 ), and 2‐(3,4‐dihydroxyphenyl)ethyl O‐β‐D ‐glucopyranosyl‐(1→3)‐6‐O‐[(E)‐feruloyl]‐β‐D ‐glucopyranoside ( 5 ). 相似文献
209.
Yueping?Fang Xiaogang?Wen Shihe?YangEmail author Qi?Pang Lu?Ding Jiannong?Wang Weikun?Ge 《Journal of Sol-Gel Science and Technology》2005,36(2):227-234
Uniform ZnO nanorods arrays are grown directly from and on Zn foils in pure water under hydrothermal conditions at a relatively
low temperature. The nanorods are 80–200 nm in diameter and ∼ 1 μm in length, which grow on the Zn foil along the [001] direction.
By changing the pure water to a urea solution, a Zn compound ([Zn5(OH)6(CO3)2], a precursor of ZnO nanoflowers film, is created by self-assembly. The ZnO nanoflowers film can be easily obtained by heating
the [Zn5(OH)6(CO3)2] compound in N2 at 350∘C for 5–6 hours. Possible growth processes of the ZnO nanorods arrays and the [Zn5(OH)6(CO3)2] nanoflowers are discussed. Photoluminescence properties of the as-prepared ZnO nanostructures have been measured. The ZnO
nanorods array synthesized using our method has minimal defects so that only band-gap emission is observed. However, the ZnO
nanoflowers film, obtained by heating the [Zn5(OH)6(CO3)2] nanoflower precursor in N2, is polycrystalline and displays strong defect-related emission. 相似文献
210.
The effects of the pretreatment of copper in benzimidazole solutions on the anodic reactions have been observed. The structures of the chemisorbed benzimidazole on copper were studied by using the infrared reflection-absorption technique and X-ray photoelectron spectroscopy. It was found that a compact film of benzimidazolato copper(I) was formed on the copper surface when copper was immersed in a stirred benzimidazole solution and cyclic voltammetry applied. This compact polymer film inhibited anodic oxidation effectively. 相似文献