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排序方式: 共有208条查询结果,搜索用时 15 毫秒
91.
The insertion reaction of isocyanide into a C-S bond of dithioacetals is catalyzed by GaCl3 or TiCl4 to afford thioimidates containing an alpha-alkylthio group. Balanced thiophilicity of these Lewis acids is critical for efficient catalysis. 相似文献
92.
A novel silica hydride-based stationary phase was used to evaluate the retention behavior in the aqueous normal-phase (ANP) mode of standards representing three classes of metabolites. The effects on retention behavior of amino acids, carbohydrates and small organic acids were examined by altering the column temperature, and by adding different additives to both the mobile phase and sample solvent. Gradient mode results revealed the repeatability of retention times to be very stable for these compound classes. At both 15 and 30 degrees C, excellent RSD values were obtained with less than 1% variation for over 50 injections of an amino acid mixture. The ability to separate the 19 nonderivatized amino acid standards, organic acids and carbohydrates was demonstrated as well as the potential for this material to separate polar metabolites in complex fluids such as urine. 相似文献
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Michel Sana 《Theoretical chemistry accounts》1982,60(6):543-559
In the present work we propose a numerical approach to estimate the harmonic and anharmonic force constant matrices, supposing we are able to compute analytically the first order derivative vector of the potential energy surface with respect to the internal coordinates. We use a polynomial least square fit to interpolate this gradient in the stationary point region. The structure of the regression matrix shows that the harmonic force constant matrix may be obtained even for large molecules; the evaluation of the anharmonic contributions request slightly more labor but is possible for 5 to 7 atoms. The present work is applicable even at the CI level and the number of computations remains small. We use the experimental planification to select the geometries to be computed in order to improve the estimation of the regression coefficients i.e. this means to lower their variance.chercheur qualifié du Fonds National Belge de la Recherche Scientifique. 相似文献
95.
Rama Moorthy Appa Jangam Lakshmidevi Sana Siva Prasad Baitinti Muralidhar Bandameeda Ramesh Naidu Manchala Narasimhulu 《合成通讯》2019,49(1):56-64
A solvent-free, versatile procedure has been developed for the effective synthesis of tert-butanesulfinylimines of a variety of aldehydes using chiral tert-butanesulfinamides under green, sonochemical conditions. This method utilizes silica supported p-toluenesulfonic acid (pTSA·SiO2) as an efficient, safer and inexpensive catalyst under aerobic conditions. The practicable simplicity, easy preparation of the catalyst from readily available substances, high substrate scope, excellent yields of products in short reaction times and environmentally benign (solvent-free sonochemical) conditions are the exceptional assets of this finding. 相似文献
96.
AbstractAmong heterocyclic compounds, pyridopyrazines are the scaffolds that have gained considerable attention on academic and industrial level due to their widespread applications as intermediates in the preparation of advanced and biologically potent pharmaceutical materials. Many pyridopyrazine derivatives are available in market to cure various pharmacological disorders. These candidates can be synthesized via a number of synthetic routes using various reagents like cyclocondensation of diaminopyridines with carbonyl compounds or their derivatives etc. In the present review, we have elaborated all these protocols along with different factors and reaction conditions such as use of metal catalyst, solvent-free and microwave irradiation, one-pot synthesis etc. that have resulted in high regioselectivity and yields. The review focuses on the synthetic methodologies developed in the last decade for different pyridopyrazine derivatives. 相似文献
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Determination of organic compounds in water using dispersive liquid-liquid microextraction 总被引:15,自引:0,他引:15
Rezaee M Assadi Y Milani Hosseini MR Aghaee E Ahmadi F Berijani S 《Journal of chromatography. A》2006,1116(1-2):1-9
A new microextraction technique termed dispersive liquid-liquid microextraction (DLLME) was developed. DLLME is a very simple and rapid method for extraction and preconcentration of organic compounds from water samples. In this method, the appropriate mixture of extraction solvent (8.0 microL C2Cl4) and disperser solvent (1.00 mL acetone) are injected into the aqueous sample (5.00 mL) by syringe, rapidly. Therefore, cloudy solution is formed. In fact, it is consisted of fine particles of extraction solvent which is dispersed entirely into aqueous phase. After centrifuging, the fine particles of extraction solvent are sedimented in the bottom of the conical test tube (5.0 +/- 0.2 microL). The performance of DLLME is illustrated with the determination of polycyclic aromatic hydrocarbons (PAHs) in water samples by using gas chromatography-flame ionization detection (GC-FID). Some important parameters, such as kind of extraction and disperser solvent and volume of them, and extraction time were investigated. Under the optimum conditions the enrichment factor ranged from 603 to 1113 and the recovery ranged from 60.3 to 111.3%. The linear range was 0.02-200 microg/L (four orders of magnitude) and limit of detection was 0.007-0.030 microg/L for most of analytes. The relative standard deviations (RSDs) for 2 microg/L of PAHs in water by using internal standard were in the range 1.4-10.2% (n = 5). The recoveries of PAHs from surface water at spiking level of 5.0 microg/L were 82.0-111.0%. The ability of DLLME technique in the extraction of other organic compounds such as organochlorine pesticides, organophosphorus pesticides and substituted benzene compounds (benzene, toluene, ethyl benzene, and xylenes) from water samples were studied. The advantages of DLLME method are simplicity of operation, rapidity, low cost, high recovery, and enrichment factor. 相似文献
100.
Projective synchronization of time‒delayed chaotic systems with unknown parameters using adaptive control method 下载免费PDF全文
The present article aims to study the projective synchronization between two identical and non?identical time?delayed chaotic systems with fully unknown parameters. Here the asymptotical and global synchronization are achieved by means of adaptive control approach based on Lyapunov–Krasovskii functional theory. The proposed technique is successfully applied to investigate the projective synchronization for the pairs of time?delayed chaotic systems amongst advanced Lorenz system as drive system with multiple delay Rössler system and time?delayed Chua's oscillator as response system. An adaptive controller and parameter update laws for unknown parameters are designed so that the drive system is controlled to be the response system. Numerical simulation results, depicted graphically, are carried out using Runge–Kutta Method for delay?differential equations, showing that the design of controller and the adaptive parameter laws are very effective and reliable and can be applied for synchronization of time?delayed chaotic systems. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献