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排序方式: 共有474条查询结果,搜索用时 31 毫秒
21.
A. B. Deshpande R. V. Subramanian S. L. Kapur 《Journal of polymer science. Part A, Polymer chemistry》1966,4(7):1799-1811
Kinetics of the polymerization of styrene in the presence of benzene at 30°C., with chromium acetylacetonate in combination with triethylaluminum and also in combination with diethylaluminum bromide as catalyst, have been studied. Chromium acetylacetonate forms a homogeneous system with triethylaluminum, and chromium acetylacetonate with diethylaluminum bromide behaves as a heterogeneous system. This homogeneous catalyst system, though reported inactive in the polymerization of α-olefins, has been found effective with styrene. Depending on the homogeneity and heterogeneity of the system, the rate of polymerization is proportional to half order and first order of catalyst concentration. A probable reason for the effect of homogeneity on the order of reaction has been discussed. A study of the effect of diethylzinc as a chain-transfer agent has helped to confirm the mechanism of polymerization. 相似文献
22.
Copolymerizations of methyl methacrylate (MMA) and butyl methacrylate (BMA) with vinyltriacetoxysilane (VTAS) have been carried out in bulk at 70°. The compositions of the copolymers were determined from their silicon contents; the reactivity ratios were calculated by the Kelen-Tüdős method. For MMA/VTAS, r1 = 7.75 ± 0.31 and for BMA/VTAS, r1 = 4.62 ± 0.15; in both systems, r2 is zero, indicating that VTAS does not homopolymerize under the experimental conditions. The influence of the silicon comonomer on properties of the copolymers, such as solubility annd thermal behaviour, was studied. 相似文献
23.
Microwave-assisted acyl chloride-isonitrile condensation and CaCO3-mediated hydrolysis constitute a one-pot, 2-minute process to prepare α-ketoamides. 相似文献
24.
Heat capacities C
p
and volumes V have been obtained at 25°C for the transfer of cholesteryl oleyl carbonate (ChOC) from a reference solvent, the highly-branched alkane 2,2,4,4,6,8,8-heptamethylnonane into various solvents. These include normal, branched, and cyclic alkanes as well as the pure cholesteric ChOC. V and most C
p
are associated with the change of environmental free volume during the transfer process and are predicted by the Prigogine-Flory theory. However, for n-alkane solvents with more than twelve carbons, C
p
is large, positive, and unattributable to free volume changes. It is consistent with a restriction of alkane segmental motion by the ChOC. The same mechanism has been proposed to explain an antiplasticization effect of ChOC on transitions in polymers. 相似文献
25.
A sensitive, simple, and accurate high-performance liquid chromatographic method has been developed for determination of valdecoxib and the internal standard rofecoxib in human plasma. Protein was precipitated from plasma samples by addition of perchloric acid (HClO4); the drug was then extracted with diethyl ether. Separation was performed on a Cosmosil C18 column (150 mm × 4.6 mm i.d., 5 m particles) with ammonium acetate buffer-acetonitrile, 60:40 (v/v), containing 0.1% TEA, pH 6.5, as mobile phase. Detection and quantification were performed by UV-visible detection at 239 nm. Detection and quantification limits were 3 and 5 ng mL–1, respectively. The linear concentration range for valdecoxib was 5–400 ng mL–1. The validated RP HPLC method was used for determination of the pharmacokinetic data for the drug in humans. 相似文献
26.
Purification and reversible immobilization of d-amino acid oxidase from Trigonopsis variabilis could be simultaneously accomplished by hydrophobic interaction on Phenyl Sepharose CL-4B in the presence of 50 mM pyrophosphate buffer (pH 8.5). The presence of a high salt concentration of 2M, which is generally required for the hydrophobic interactions, was not essential for the hydrophobic immobilization. The
enzyme in free as well as immobilized form was optimally active between pH 7.0 and 9.0. The immobilized preparation could
be reused in a batch process for the conversion of d-amino acids to α-keto acids. When the activity of the preparation dropped below practical limits, the gel could be regenerated
by water wash and recharged with fresh crude extract from yeast. 相似文献
27.
Mukund V. Deshpande 《Applied biochemistry and biotechnology》1991,31(1):75-82
Enzyme stability studies in case of Sclerotium rolfsii UV-8 mutant have been investigated under the conditions used for saccharification of cellulose (50 degrees C, pH 4.5, 48 h). Avicelase (measure of exoenzymes) and xylanase were found to be less stable than CMCase (endoglucanase) and beta-glucosidase. Merthiolate (and other Hg compounds) added as a biocide, inactivated avicelase and xylanase about 60-70%. Of the antibiotics tested, tetracycline, chloramphenicol, and streptomycin sulfate were found suitable as an additive in cellulose hydrolysis system. The optimum hydrolysis of alkali-treated (AT)-rice straw, AT-bagasse, Solka Floc SW40, and Avicel P.H.101 was observed under shaking conditions at pH 4.5, 50 degrees C in CO2 atmosphere. It is suggested, all the studied parameters could be used for the evaluation of mutant strains. 相似文献
28.
29.
Parag Deshpande Zhang Jie Ramesh Subbarayan Vijay Kumar Mamidi Raja Haranadha Babu Chunduri Tapas Das Sathyavageeswaran Shreeram 《Biomedical chromatography : BMC》2013,27(2):142-147
A simple, sensitive and specific high‐performance liquid chromatography mass spectrometry (LC‐MS/MS) method was developed and validated for the quantification of β‐hydroxy‐β‐methyl butyrate (HMB) in small volumes of rat plasma using warfarin as an internal standard (IS). The API‐4000 LC‐MS/MS was operated under the multiple reaction‐monitoring mode using the electrospray ionization technique. A simple liquid–liquid extraction process was used to extract HMB and IS from rat plasma. The total run time was 3 min and the elution of HMB and IS occurred at 1.48 and 1.75 min respectively; this was achieved with a mobile phase consisting of 0.1% formic acid in a water–acetonitrile mixture (15:85, v/v) at a flow rate of 1.0 mL/min on a Agilent Eclipse XDB C8 (150 × 4.6, 5 µm) column. The developed method was validated in rat plasma with a lower limit of quantitation of 30.0 ng/mL for HMB. A linear response function was established for the range of concentrations 30–4600 ng/mL (r > 0.998) for HMB. The intra‐ and inter‐day precision values for HMB were acceptable as per Food and Drug Administration guidelines. HMB was stable in the battery of stability studies, viz. bench‐top, autosampler freeze–thaw cycles and long‐term stability for 30 days in plasma. The developed assay method was applied to a bioavailability study in rats. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
30.
Dynamic mechanical studies of cholesteric liquid crystalline substances in the solid state have been reported using Du Pont's Dynamic Mechanical Analyser, DMA-981. All the substances showed multiple transitions. There is no common transition though the parent structure was similar in the compounds. These weak transitions are not detectable by DSC and hence appear to be second order transitions possibly arising due to rotation of the molecules around the long axis. Alternatively the lattice defects may also be responsible for such transitions. 相似文献