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91.
92.
A traceless synthesis of 3,5-disubstituted 1,2,4-triazoles has been developed on polymeric supports. The synthetic process utilizes immobilized mesoionic 1,3-oxazolium-5-olates (munchnones) as key intermediates in the 1,3-dipolar cycloaddition reaction. The initial step in the synthesis involves reductive alkylation of phenylglycine methyl esters with Ameba resin. The resulting immobilized amino acid esters were subsequently acylated with a variety of carboxylic acid chlorides and subjected to hydrolysis with 15% KOH to yield the polymer-bound carboxylic acids. Finally, the cycloaddition between diethyl diazocarboxylate or 4-phenyl-4H-1,2,4-triazoline-3,5-dione and the polymer-bound munchnones generated from the corresponding carboxylic acids afforded the polymer-bound 3,5-disubstituted 1,2,4-triazoles. Cleavage from the polymeric support using trifluoroacetic acid gave the desired 3,5-disubstituted 1,2,4-triazoles with excellent yield and high purity. 相似文献
93.
For the first time, the dispersion stability of silica nanoparticles has been investigated in high-temperature and high-pressure ethanol by measuring the hydrodynamic diffusion coefficient of the particles by means of dynamic light scattering. The silica nanoparticles remain stable in ethanol within a wide temperature range of 24-304 degrees C at 12.3 MPa, and they start to aggregate at T >or= 305 degrees C. Numerical analysis reveals that the net interparticle repulsive potential barrier decreases dramatically with increasing temperature due to the changes in the properties of the medium. We observed that particles remain highly stable in the nonpolar supercritical ethanol in the temperature regime 241-304 degrees C, where the DLVO potential barrier is only 5-2 k(B)T. The dispersion stability of silica nanoparticles at this low potential barrier in high-temperature and high-pressure ethanol, especially in the supercritical ethanol, is fascinating. The silica-ethanol system might be a unique and special example in the colloidal dispersions. Results suggest that silica nanoparticles may be used as a model colloid to investigate the colloidal transport phenomena in the supercritical ethanol. 相似文献
94.
Krishna C. Majumdar Swapan K. Samanta 《Monatshefte für Chemie / Chemical Monthly》2002,133(9):1187-1192
Summary. 5-(Cyclohex-2-enyl)-1,3-dimethyl-6-hydroxyuracil undergoes regioselective heterocyclization to afford fused tricyclic heterocycles
upon treatment with bromine and m-CPBA. However, the same substrate furnished bridged tricyclic heterocycles when treated with N-iodosuccinimide and conc. H2SO4 and a mixture of bridged tricyclic heterocycles and fused tricyclic heterocycles when treated with hexamine hydrotribromide
or pyridine hydrotribromide.
Corresponding author. E-mail: kcm@klyuniv.ernet.in
Received September 27, 2001. Accepted (revised) December 3, 2001 相似文献
95.
Krishna C. Majumdar Swapan K. Samanta 《Monatshefte für Chemie / Chemical Monthly》2002,36(6):1187-1192
5-(Cyclohex-2-enyl)-1,3-dimethyl-6-hydroxyuracil undergoes regioselective heterocyclization to afford fused tricyclic heterocycles upon treatment with bromine and m-CPBA. However, the same substrate furnished bridged tricyclic heterocycles when treated with N-iodosuccinimide and conc. H2SO4 and a mixture of bridged tricyclic heterocycles and fused tricyclic heterocycles when treated with hexamine hydrotribromide or pyridine hydrotribromide. 相似文献
96.
97.
98.
Tamal Pramanick 《计算数学(英文版)》2021,39(4):493-517
We study spatially semidiscrete and fully discrete two-scale composite finite element method for approximations of the nonlinear parabolic equations with homogeneous Dirich-let boundary conditions in a convex polygonal domain in the plane.This new class of finite elements,which is called composite finite elements,was first introduced by Hackbusch and Sauter[Numer.Math.,75(1997),pp.447-472]for the approximation of partial differential equations on domains with complicated geometry.The aim of this paper is to introduce an efficient numerical method which gives a lower dimensional approach for solving par-tial differential equations by domain discretization method.The composite finite element method introduces two-scale grid for discretization of the domain,the coarse-scale and the fine-scale grid with the degrees of freedom lies on the coarse-scale grid only.While the fine-scale grid is used to resolve the Dirichlet boundary condition,the dimension of the finite element space depends only on the coarse-scale grid.As a consequence,the resulting linear system will have a fewer number of unknowns.A continuous,piecewise linear composite finite element space is employed for the space discretization whereas the time discretization is based on both the backward Euler and the Crank-Nicolson methods.We have derived the error estimates in the L∞(L2)-norm for both semidiscrete and fully discrete schemes.Moreover,numerical simulations show that the proposed method is an efficient method to provide a good approximate solution. 相似文献
99.
So-Yon Lim Adam Bauermeister Richard A Kjonaas Swapan K Ghosh 《Journal of immune based therapies and vaccines》2006,4(1):5-10
Background
Adjuvants are known to significantly enhance vaccine efficacy. However, commercial adjuvants often have limited use because of toxicity in humans. The objective of this study was to determine the comparative effectiveness of a diterpene alcohol, phyto l and its hydrogenated derivative PHIS-01, relative to incomplete Freund's adjuvant (IFA), a commonly used adjuvant in augmenting protective immunity in mice against E. coli and S. aureus, and in terms of inflammatory cytokines. 相似文献100.
Keith R. Burnett M.D. Edward J. Goldstein Ph.D. M.D. Gerald L. Wolf Ph.D. M.D. Swapan Sen B.S. R.T. R.D.M.S. Alex C. Mamourian M.D. 《Magnetic resonance imaging》1984,2(4):307-314
Mn+2 (as MnCl2) was administered to rabbits intravenously and orally (a route of administration which based upon our previous experiments in rats7 promises to give selective hepatobiliary enhancement with less systemic toxicity). Nuclear magnetic relaxation dispersion or T1 (NMRD) was performed on selected tissues (heart, liver, kidney, serum, and bile) in both animal groups to examine possible qualitative and semiquantitative differences in T1 relaxation at equivalent sacrifice times. One animal was given an oral dose of MnCl2 (620 micromoles/kg) and imaged sequentially (T1 weighted sequence, .12T) for 30 minutes. The NMRD curves for organ tissues show an increase in relaxation efficacy in the 10–20MHz range characteristic of Mn-macromolecular complexes and are similar irrespective of the route of administration. The lack of increased relaxation enhancement for bile in this frequency range reflects cleavage of this complex upon excretion. Decreased overall relaxation in the liver is observed when oral Mn+2 is compared to IV Mn+2 due to the small fraction of administered dose that is absorbed. However, the images document a significant increase in the intensity of liver signal after the oral dose. We suspect this dose may ultimately be adjusted downward to give selective hepatobiliary effects. 相似文献