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排序方式: 共有106条查询结果,搜索用时 15 毫秒
21.
A series of 1‐alkoxy‐3‐phospholene 1‐oxides available from the microwave‐assisted direct esterification of 1‐hydroxy‐3‐phospholene oxide was converted to the two diastereomers of 6,6‐dichloro‐3‐phosphabicyclo[3.1.0]hexane 3‐oxides by the addition of dichlorocarbene to the double bond. Thermolysis of the 3‐phospholene oxide–dichlorocarbene adducts afforded the corresponding 1,2‐dihydrophosphinine 1‐oxides as a ca. 3:1 mixture of two double bond isomers. Relative stability of the isomers of the intermediates and the products and their stereostructures were evaluated by B3LYP/6‐31G(d,p) calculations. 相似文献
22.
A method based on gas chromatography-mass spectrometry analysis of acetylated methyl glycosides was developed in order to analyze monosaccharides obtained from various hemicelluloses. The derivatives of monosaccharide standards, arabinose, glucose, and xylose were studied in detail and (13)C-labeled analogues were used for identification and quantitative analysis. Excellent chromatographic separation of the monosaccharide derivatives was found and identification of the anomeric configuration was feasible through a prepared and identified pure methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside. The electron ionization mass spectrum and fragmentation path was studied for each monosaccharide derivative. Fragment ion pairs of labeled and unlabeled monosaccharides were used for quantification; m/z 243/248 for glucose, 128/132 for xylose, and 217/218 for arabinose. Using the intensity ratios obtained from the extracted ion chromatograms, accurate quantification of monosaccharide constituents of selected hemicelluloses was demonstrated. 相似文献
23.
László Guczi Györgyi Stefler Zsuzsa Koppány László Borkó 《Reaction Kinetics and Catalysis Letters》2001,74(2):259-269
The promotion of rhenium on the reduction of Co2+ ions in cobalt based samples prepared by various methods, such as, sol/gel technique, incipient wetness impregnationof Al2O3 and NaY, has been investigated in the CO hydrogenation. Among the samples the reducibility of the sol/gel, Re-Co/Al2O3 and Re-Co/NaY(IM) were the highest compared to Re-Co/NaY (IE) [8]. In addition to facilitating reduction of Co2+ ions, the rhenium increased the rate of reaction and the formation ofC5+ hydrocarbons at 10 bar pressures. The samples pretreated in various manner, revealed an about five fold increase in activity and an increase in the chain length in the NaYsupported sample while the activity and selectivity changed in various way in the sol/gel prepared samples. Simultaneously, rhenium increased the amount of olefins of low carbon numbers.In the mechanism the rhenium provides an action preventing fast deactivation of cobalt. 相似文献
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25.
Norbert Szoboszlai Andrea Réti Barna Budai Zsuzsa Szabó Judit Kralovánszky Gyula Záray 《Spectrochimica Acta Part B: Atomic Spectroscopy》2008
The elemental content of Cu, Fe and Zn in two human adenocarcinoma cell lines was investigated by total reflection X-ray fluorescence (TXRF) spectrometry. Cancer cells were sedimented directly to the quartz plates using a modified cytospin slide holder setup. Special glass stands and caps were also constructed to hold the quartz plates with the cells during the vapour-phase microwave assisted digestion. The method was validated by analysis of certified reference materials. The signal-to-noise ratio was optimized by washing the cells with different solutions. The technique was applied to the determination of Cu, Fe and Zn content of HT-29 and HCA-7 colorectal adenocarcinoma cell lines. Dry mass of the centrifuged cells were determined and the elemental analysis data reported for the two cell lines were referred either to cell numbers, to the total protein content or to the dry mass. 相似文献
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27.
Anomeric carbon-sulfur bonds in 1-thioglycosides and glycosyl sulfones can be cleaved by chromium(II) complexes in water-DMF medium. Anomeric radicals as well as sugar-chromium(III) complex intermediates can be generated in these reactions, leading in some cases, to the exclusive formation of the corresponding glycals. 相似文献
28.
Saara Riuttamäki Gergely Laczkó Dr. Ádám Madarász Dr. Tamás Földes Dr. Imre Pápai Anton Bannykh Prof. Dr. Petri M. Pihko 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(45):e202201030
We demonstrate herein the capacity of simple carboxylate salts – tetrametylammonium and tetramethylguanidinium pivalate – to act as catalysts in the isomerization of β,γ-unsaturated thioesters to α,β-unsaturated thioesters. The carboxylate catalysts gave reaction rates comparable to those obtained with DBU, but with fewer side reactions. The reaction exhibits a normal secondary kinetic isotope effect (k1H/k1D=1.065±0.026) with a β,γ-deuterated substrate. Computational analysis of the mechanism provides a similar value (k1H/k1D=1.05) with a mechanism where γ-reprotonation of the enolate intermediate is rate determining. 相似文献
29.
Truong Son Pham László Balázs Imre Petneházy Zsuzsa Jászay 《Tetrahedron: Asymmetry》2010,21(3):346-351
An enantioselective Michael addition of diethyl cyanomethyl phosphonate to chalcones catalysed by bifunctional catalysts based on cinchona alkaloids has been developed, producing enantiomerically enriched cyanophosphonate precursors of α-substituted β-aminophosphonates. 相似文献
30.
Surface modification of mechanochemically activated kaolinites by selective leaching 总被引:2,自引:0,他引:2
Low- and high-defect kaolinites mechanochemically activated for different periods of time have been treated with sulfuric acid solution. These modified materials were analyzed using a combination of X-ray diffraction, thermogravimetry, chemical analysis, diffuse reflectance Fourier transform infrared spectroscopy, as well as specific surface area and pore size distribution measurements. In addition to the mechanochemically amorphized part, the disordered and the adequately distorted phases also reacted with sulfuric acid. The specific surface areas of the leached samples of the partially or the completely amorphized materials were found to be greater than those of the thermally amorphized ones. The acid treatment results in a greater total pore volume for the partially amorphized materials than for the totally amorphized mineral. The partially amorphized high-defect kaolinite was proved to be more soluble than the low-defect kaolinite under similar conditions. 相似文献