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排序方式: 共有151条查询结果,搜索用时 15 毫秒
1.
Agnihotri S Mota JP Rostam-Abadi M Rood MJ 《Langmuir : the ACS journal of surfaces and colloids》2005,21(3):896-904
A procedure, combining molecular simulation, Raman spectroscopy, and standard nitrogen adsorption, is developed for structural characterization of single-walled carbon nanotube (SWNT) samples. Grand canonical Monte Carlo simulations of nitrogen adsorption are performed on the external and internal adsorption sites of homogeneous arrays of SWNTs of diameters previously determined by Raman spectroscopy of the sample. The results show the importance of the peripheral grooves of a nanotube bundle at low relative pressure and the insensitivity of nanotube diameter toward adsorption on the external surface of the bundle at higher pressures. Simulations also reveal that samples containing thin nanotubes have less internal adsorption capacity that saturates at lower pressure than those comprising large diameter nanotubes. The fraction of open-ended nanotubes in a sample can be estimated by scaling the simulated internal adsorption inside nanotubes to obtain a near perfect fit between simulated and experimental isotherms. This procedure allows extrapolation of adsorption properties to conditions in which all nanotubes in the sample are open-ended. 相似文献
2.
Dakoji S Li D Agnihotri G Zhou HQ Liu HW 《Journal of the American Chemical Society》2001,123(40):9749-9759
The inhibitory properties of (methylenecyclopropyl)formyl-CoA (MCPF-CoA), a metabolite derived from a natural amino acid, (methylenecyclopropyl)glycine, against bovine liver enoyl-CoA hydratase (ECH) were characterized. We have previously demonstrated that MCPF-CoA specifically targets ECHs, which catalyze the reversible hydration of alpha,beta-unsaturated enoyl-CoA substrates to the corresponding beta-hydroxyacyl-CoA products. Here, we synthesized (R)- and (S)-diastereomers of MCPF-CoA to examine the stereoselectivity of this inactivation. Both compounds were shown to be competent inhibitors for bovine liver ECH with nearly identical second-order inactivation rate constants (k(inact)/K(I)) and partition ratios (k(cat)/k(inact)), indicating that the inactivation is nonstereospecific with respect to ring cleavage. The inhibitor, upon incubation with bovine liver ECH, labels a tryptic peptide, ALGGGXEL, near the active site of the protein, where X is the amino acid that is covalently modified. Cloning and sequence analysis of bovine liver ECH gene revealed the identity of the amino acid residue entrapped by MCPF-CoA as Cys-114 (mature sequence numbering). On the basis of gHMQC (gradient heteronuclear multiple quantum coherence) analysis with [3-(13)C]-labeled MCPF-CoA, the ring cleavage is most likely induced by the nucleophilic attack at the terminal carbon of the exomethylene group (C(2)'). We propose a plausible inactivation mechanism that involves relief of ring strain and is consistent with examples found in the literature. In addition, these studies provide important clues for future design of more efficient and selective inhibitors to control and/or regulate fatty acid metabolism. 相似文献
3.
Summary An efficient and economical GC method for rapid determination of FAMEs in rapeseed-mustard is described. The seeds were transmethylated
with acetylchloride, using microwave heating and separation achieved on a 3 m column packed with a mixture of 2% SP-2300 and
3% SP-2310 on Chromosorb ‘W’. The method is compared with the conventional heating method and extended efficiently for half-seed
analysis. The fatty acid composition of the FAMEs mixtures prepared by both methods was similar with highly significant correlation
coefficients (P<0.001). 相似文献
4.
Agnihotri S Mota JP Rostam-Abadi M Rood MJ 《The journal of physical chemistry. B》2006,110(15):7640-7647
Hexane adsorption on single-walled carbon nanotube (SWNT) bundles is studied by both simulation and experimentally using a previously developed computer-aided methodology, which employed a smaller physisorbed probe molecule, nitrogen, to explore the porosity of nanotube samples. Configurational-bias grand canonical Monte Carlo simulation of hexane adsorption on localized sites of the bundles is carried out to predict adsorption on their external surface and in their internal sites. These localized isotherms are then combined into a global isotherm for a given sample by using knowledge of its tube-diameter distribution and structural parameters, such as the fraction of open-ended nanotubes and the external surface area of bundles in samples, which have been independently determined from the standard nitrogen adsorption isotherm. The near-perfect replication of experimental isotherms demonstrates the validity of our method for structural characterization of SWNT samples. The effect of temperature on adsorption is also studied and the simulation results are extrapolated to predict the limiting hexane adsorption capacity of the samples. The similarity between the hexane adsorption isotherms and those of other organic molecules demonstrates that the adsorption mechanisms explored here are not specific to hexane, and that the proposed methodology can be potentially applicable to other sorbates with equal success. 相似文献
5.
JPC – Journal of Planar Chromatography – Modern TLC - Gemcitabine belongs to a class of drugs known as antimetabolites (pyrimidine analog) used in various carcinomas, such as pancreatic... 相似文献
6.
Spectrophotometric Determination of Rhenium(IV) with Thiocyanate,TX-100 and N,N′-Diphenylbenzamidine
A spectrophotometric method to determine rhenium(IV) at trace level is based on the extraction of Re(IV)-SCN? complex in sulphuric acid media with N,N′-diphenylbenzamidine(DPBA) in presence of a non-ionic surfactant triton X-100 (TX-100) in chloroform. The complex shows maximum absorbance at 435 nm with amolar absorptivity value of 4.24 × 104 L mol?1 cm?1 at an acidity range 3.5-6.5 M H2SO4. The method followed Beer's Law for the system Re(IV)-SCN?(TX-100)-DPBA upto 4.0 μg Re(IV) mL?1. The detection limit of the method is 5 ppb. None of the tested foreign ions, except molybdenum(VI), interfere with the determination of rhenium. The interference due to molybdenum could effectively be removed by prior precipitation with oxine. The effect of various analytical parameters on the extraction of the metal are discussed. 相似文献
7.
A simple, precise, and accurate isocratic RP-HPLC method was developed and validated for determination of eprosartan in bulk drug and tablets. Isocratic RP-HPLC separation was achieved on a Phenomenex C18 column (250 x 4.6 mm id, 5 microm particle size) using the mobile phase 0.5% formic acid-methanol-acetonitrile (80 + 25 + 20, v/v/v, pH 2.80) at a flow rate of 1.0 mL/min. The retention time of eprosartan was 7.64 +/- 0.05 min. The detection was performed at 232 nm. The method was validated for linearity, precision, accuracy, robustness, solution stability, and specificity. The method was linear in the concentration range of 10-400 microg/mL with a correlation coefficient of 0.9999. The repeatability for six samples was 0.253% RSD; the intraday and interday precision were 0.21-0.57 and 0.33-0.71% RSD, respectively. The accuracy (recovery) was found to be in the range of 99.86-100.92%. The drug was subjected to the stress conditions hydrolysis, oxidation, photolysis, and heat. Degradation products produced as a result of the stress conditions did not interfere with detection of eprosartan; therefore, the proposed method can be considered stability-indicating. 相似文献
8.
Dighe Vidya V. Sane Ramesh T. Menon Shashikumar N. Tambe Harsha N. Pillai Sreedevi 《平面色谱法杂志一现代薄层色谱法》2006,19(4):319-323
JPC – Journal of Planar Chromatography – Modern TLC - A normal-phase high-performance thin-layer chromatographic (HPTLC) method has been established for quantitative estimation of... 相似文献
9.
Various nitroarenes and 2,1,3-benznooxadiazole-1-oxides were selectively and rapidly reduces to their corresponding amino and diamino compounds respectively in high yields using (NH4SO4-Mg/A1/Bi, a new reduction system. 相似文献
10.
G. Satish K. Harsha Vardhan ReddyK. Ramesh B.S.P. Anil KumarY.V.D. Nageswar 《Tetrahedron letters》2014
A simple and efficient, ligand-free C–N cross-coupling of aryl halides/benzyl bromides with trans-4-hydroxy-l-proline has been developed to produce aromatized N-substituted pyrroles, using a catalytic amount of magnetically separable and recyclable CuFe2O4 nanoparticles, in the presence of Cs2CO3 in DMSO at 100 °C. 相似文献