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41.
42.
8—氮鸟嘌呤的极谱伏安行为 总被引:4,自引:0,他引:4
用循环伏安法(CV)、电流采样极诸法(SCP,即TAST)、常规脉冲极谱法(NPP)、微分脉冲极谱法(DPP)、线性扫描伏安法(LSV)、Osteryoung方波伏安法(OSWV)和计时库仑法(CC)等电化学技术研究了抗癌药物8-氮鸟嘌呤(8-azaguanine,guanazolo,简称8-AG)的极谱伏安行为.在 0. 1mol/L H2SO4底液中,8-AG有一良好的还原峰,峰电位(Ep)在-0. 95V(vs.Ag/AgCl,下同)附近,8-AG浓度在4×10-6~8×10-4mol/L范围内.峰高与浓度有良好的线性关系,线性相关系数r=0.9999~0.9910,检出限为1× 10-6mol/L.实验证明了该峰具有吸附性.本文提出了电极反应机理,它包括:酸性介质中8-AG的质子化、质子化的8-AG在汞电极上吸附以及完全不可逆的两电子还原过程.同时用量子化学计算方法(全略微分重叠法即CNDO/2)对8-AG和鸟嘌呤的各原子的净电荷以及Wiberg键级进行了计算,从理论上解释了8-AG的电化学还原机理。 相似文献
43.
Jianjun ZhangFanzuo Kong 《Tetrahedron letters》2003,44(9):1839-1842
A general method for the synthesis of 2-xylose or glucuronic acid branched (1→3)-linked mannose oligosaccharides has been developed. As a typical example, the synthesis of the methyl glycoside of β-d-GlcpA-(1→2)-α-d-Manp-(1→3)-[β-d-Xylp-(1→2)-]α-d-Manp-(1→3)-[β-d-Xylp-(1→2)-]α-d-Manp, the repeating unit of the exopolysaccharide from Cryptococcus neoformans serovar A, was achieved in a regio- and stereoselective manner. 相似文献
44.
Xu X Zhao J Jiang D Kong J Liu B Deng J 《Analytical and bioanalytical chemistry》2002,374(7-8):1261-1266
A novel hydrogen peroxide biosensor was developed based on the immobilization of horseradish peroxidase (HRP) in a TiO(2) sol-gel matrix on an electropolymerized phenazine methosulfate (PMS) modified electrode surface. Such membranes are of interest due to their high surface area, biological compatibility, and ease of fabrication. HRP entrapped in the TiO(2) matix was stable and retained its activity to a large extent. Cyclic voltammetry and amperometric measurements were employed to demonstrate the feasibility of electron transfer between immobilized HRP and the glassy carbon electrode via electropolymerized PMS. The influence of various experimental parameters such as operating potential, pH, temperature, and stability was investigated for optimum analytical performance. The biosensor provided a wide linear calibration range from 4.0x10(-6) M to 1.0x10(-3) M, with a detection limit of 8.0x10(-7) M at a signal-to-noise ratio of 3. The sensor retained 80% of its original activity after two months of operation. 相似文献
45.
Silicon nitride powders were synthesized in an atmospheric-pressure convection-stabilized arc using silicon and ammonia as reactants. The morphology and particle size distributions of the silicon nitride particles were characterized by SEM, TEM, and electron diffraction analyses. The silicon nitride particles collected in the plasma reactor were formed by either gas-condensed phase reactions or chemical vapor reactions. The morphologies of the particles formed by gas-condensed phase reactions consisted of -Si3N4 prisms, -Si3N4 matte, -Si3N4 needles, and spaghetti-like whiskers. For the homogeneously nucleated particles, the morphologies included dendrites, needles, platelets, and amorphous particles. Most of the particles formed were aggregates with particle size distributions ranging from 500 to 1500 Å depending on the location of injection of the reactants. 相似文献
46.
The syntheses of macrocyclic species composed of carborane derivatives joined via their carbon vertices by electrophilic mercury atoms are described. The reaction of closo-1,2-Li(2)[C(2)B(10)H(10)(-)(x)()R(x)()] with HgI(2) gives Li(2)[(1,2-C(2)B(10)H(10)(-)(x)()R(x)()Hg)(4)I(2)] [R = Et, x = 2 (5.I(2)Li(2)); R = Me, x = 2 (6.I(2)Li(2)); R = Me, x = 4 (7.I(2)Li(2))]. 6.I(2)(K.[18]dibenzocrown-6)(2) crystallizes in the monoclinic space group C2/m [a = 28.99(2) ?, b = 18.19(1) ?, c = 13.61(1) ?, beta = 113.74(2) degrees, V = 6568 ?(3), Z = 4, R = 0.060, R(w) = 0.070]; 7.I(2)(NBu(4))(2) crystallizes in the monoclinic space group P2(1)/c [a = 12.77(1) ?, b = 21.12(2) ?, c = 20.96(2) ?, beta = 97.87(2) degrees, V = 5600 ?(3), Z = 2, R = 0.072, R(w) = 0.082]. The precursor to 7, closo-8,9,10,12-Me(4)-1,2-C(2)B(10)H(8) (4), is made in a single step by reaction of closo-1,2-C(2)B(10)H(12) with MeI in trifluoromethanesulfonic acid. The free hosts 5, 6, and 7 are obtained by reaction of the iodide complexes with stoichiometric quantities of AgOAc. A (199)Hg NMR study indicates that sequential removal of iodide from 5.I(2)Li(2) and 6.I(2)Li(2) with aliquots of AgOAc solution leads to formation of two intermediate host-guest complexes in solution, presumed to be 5(6)ILi and 5(2)(6)(2).ILi. Crystals grown from a solution of 6.I(2)Li(2) to which 1 equiv of AgOAc solution had been added proved to be an unusual stack structure with the formula 6(3).I(4)Li(4) [tetragonal, I4/m, a = 21.589(2) ?, c = 21.666(2) ?, V = 10098 ?(3), Z = 2, R = 0.058, R(w) = 0.084]. Addition of 2 equiv of NBu(4)Br ion to 5 or 6 gives 5.Br(2)(NBu(4))(2) and 6.Br(2)(NBu(4))(2), respectively, while addition of 1 equiv of KBr to 6 forms 6.BrK. 5.Br(2)(NBu(4))(2) crystallizes in the triclinic space group P&onemacr;, [a = 10.433(1) ?, b = 13.013(1) ?, c = 15.867(2) ?, alpha = 91.638(2) degrees, beta = 97.186(3) degrees, gamma = 114.202(2) degrees, V = 1492 ?(3), Z = 1, R = 0.078, R(w) = 0.104]. The hosts 5 and 6 form 1:1 supramolecular adducts with the polyhedral anions B(10)I(10)(2)(-) and B(12)I(12)(2)(-) in solution. 相似文献
47.
S. M. Fields R. C. Kong J. C. Fieldsted M. L. Lee P. A. Peaden 《Journal of separation science》1984,7(6):312-318
Fused silica capillary columns with internal diameters from 100 to 25 μm were coated with SE-54 and evaluated under supercritical fluid chromatographic conditions using carbon dioxide as mobile phase. Experimental results compared well with theoretical predictions. At ten times the optimum mobile phase velocity and for a capacity factor, k of 3, efficiencies of 2300 to 5600 plates m?1 were obtained for column diameters of 100 to 25 μm, respectively. 相似文献
48.
Biofingerprinting chromatogram analysis, which is defined as the comparison of fingerprinting chromatograms of the extract of traditional Chinese medicines (TCMs) before and after the interaction with biological systems (DNA, protein, cell, etc.), was proposed for screening and analysis of the multiple bioactive compounds in TCMs. A method of microdialysis sampling combined with high performance liquid chromatography (HPLC) was applied to the study of DNA-binding property for the extracts of TCMs. Seven compounds were found to bind to calf thymus DNA (ct-DNA) from the TCMs of Coptis chinensis Franch (Coptis), but only three ones from Phellodendron amurense Rupr. (Phellodendron) and none from Sophoraflavescens Ait. (Sophora) to bind to ct-DNA, respectively. Three of them were identified as berberine, palmatine and jatrorrhizine and their association constants (K) to ct-DNA were determined by microdialysis/HPLC. Competitive binding behaviors of them to ct-DNA were also investigated. 相似文献
49.
Modeling of a counterflow plasma reactor 总被引:2,自引:0,他引:2
Modeling of a counterflow plasma reactor is presented, using liquid injection for the synthesis of fine particles. An experimental reactor has been developed in this laboratory, and feasibility has been demonstrated for synthesizing advanced ceramic powders. The flow field calculations show two major recirculating regions which are of importance for increasing the particles' residence time inside of the reactor. In addition, the temperature within these recirculation zones remains relatively uniform. For simulation, water droplet trajectories have been calculated for droplets produced by an injection probe. It is shown that the droplets in a size range below 50 m in diameter will follow the streamlines and evaporate completely within a short traveling distance. This finding suggests that this reactor configuration provides a favorable environment for the synthesis of fine particles using liquid precursors. 相似文献
50.