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91.
The complex species of UO2(HA)(H2A)+ and UO2(HA)2 were identified in the ascorbic acid solution of uranyl ion at pH<2.1 and pH>2.1, respectively. Polarographic wave was proved to be the simultaneous reduction of UO2+2 and UO2(HA)(H2A)+ at pH <2.1. However, at pH>2.1, the wave is due to the reduction of U02(HA)2 The stability constants of the two complex species were found to be 5.1×10+ and 1.0×105, respectively. The hydrolysis constant of uranyl ion in the solution of ascorbic acid was determined. 相似文献
92.
Xiang-Hua Lai 《Tetrahedron letters》2004,45(23):4469-4472
Mono(6-(p-toluenesulfonyl))permethylated β-cyclodextrin, a versatile precursor for a wide variety of mono-functionalized permethyl β-cyclodextrins, has been generated successfully by the direct methylation of monotosylated cyclodextrin. This afforded a convenient synthesis of mono(6A-N-allylamino-6A-deoxy)permethylated β-cyclodextrin. Hydrosilylation of the chiral selector with (EtO)3SiH and reaction of the resultant reactive siloxane with pristine silica gel afforded a facile entry into a structurally well-defined chiral HPLC stationary phase. 相似文献
93.
The isolation and identification of eleven crystalline components from the aerial part of Cynanchum taiwanianum Yamazaki (Asclepiadaceae) are described. Their structures were determined on the basis of spectral evidence and chemical transformation. Besides caffeic acid, β-amyrin, and methyl phaeophorbide a, the isolated flavonoid components are classified into two groups, i.e. kaempferol derivatives (kaempferol, astragalin, afzelin, trifolin) and quercetin derivatives (quercetin, isoquercitrin, quercitrin, hyperin). 相似文献
94.
Li-Wen Lai Jonathan M. Ducore Barry S. Rosenstein † 《Photochemistry and photobiology》1987,46(1):143-146
Three normal human skin fibroblast cell lines were exposed to the simulated solar UV radiation produced by a fluorescent sunlamp under conditions in which the wavelength components shorter than either 295, 305 or 315 nm were excluded. The level of DNA-protein crosslinks (DPC) was then measured in those cells using the alkaline elution technique either immediately after irradiation or following a 24 h incubation. In each case, cells were exposed to fluences that induce similar levels of DPC. For cells exposed to 10 kJ m(-2) of sunlamp UV > 295 nm, the level of DPC exhibited a 2-5-fold increase following incubation. In contrast, 40-100% of the DPC were removed upon incubation of cells irradiated with either 100 kJ m(-2) of sunlamp UV > 305 nm or 150 kJ m(-2) of sunlamp UV > 315 nm. A major difference between the effects induced by these wavelength regions is that, in addition to DPC, a very high level of pyrimidine dimers is also produced by sunlamp UV > 295 nm, whereas much lower dimer yields result from treatment with either sunlamp UV > 305 nm or sunlamp UV > 315 nm. A potential role for type II DNA topoisomerase in the formation of these DPC resulting from either the change in conformational structure caused by the presence of a high level of dimers or an involvement of this enzyme in dimer excision repair is discussed. 相似文献
95.
Wen-Feng Liaw Chia-Huei Lai Ming-Hsi Chiang Cheng-Kang Hsieh Gcne-Hsiang Lee Shie-Ming Peng 《中国化学会会志》1993,40(5):437-444
Diphenyldichalcogenides (PhE)2 (E = Te, Se) react with Fe(0)-phenylchalcogenolate [PPN] [PhEFe(CO)4] to yield the products of oxidative addition, Fe(II)-mixed-phenylchalcogenolate fac- [PPN][Fe(CO)3(TePh)n(ScPh)3-n] (n = 1, 2). Reactions of [PPN][REFe(CO)4] (E=Se, R=Me; E=S, R=Et) and diphenyldichalcogenides yielded ligand-exchange products [PPN][PhEFe(CO)4] (E=Te, Se, S). The compounds [Fe(CO)3(TePh)(ScPh)2]? (l) and [Fe(CO)3(TePh)2 (2) crystallize in the isomorphous monoclinic space group C2/e, with a = 32.035(8), b = 11.708(6), c = 28.909(6) Å, Z = 8, R = 0.048, and Rw = 0.044 (1); with a = 32.089(5), b= 11.745(2), c = 28.990(8) Å, Z = 8, R = 0.048, and Rw = 0.048 (2). The complexes 1 and 2 crystallize as discrete cations of PPN+ and anions of [Fe(CO)3(TcPh)u(ScPh)3-n] (n=1, 2), and one half solvent molecule THF. The geometry around Fe(II) is a distorted octahedron with three carbonyl groups and three phenylchalcogenolate ligands occupying facial positions. 相似文献
96.
Highly reactive 4-substituted-1,2,4-triazoline-3,5-diones (TDs) have been studied extensively as dienophiles, but little work has been done on their role as enophiles and particularly on their use as propagating species in polymerization studies. The copolymerization between bis-4-substituted-1,2,4-triazoline-3,5-diones (bis-TDs) and styrene has been reported. The purpose of the present work was to synthesize new copolymers derived from a variety of substituted styrenes and bis-TDs and to study the mechanism and kinetics of this novel polymerization. Three bis-TDs were prepared: 3,3′-dimethyl-4,4′-bis[3,5-dioxo-1,2,4-triazoline-4-yl] biphenyl (8), t-1,4-bis[3,5-dioxo-1,2,4-triazoline-4-yl] methyl cyclohexane (9), and 4,4′-bis[3,5-dioxo-1,2,4-triazoline-4-yl] phenyl ether (10). Their structures were fully established by spectroscopic studies, elemental analyses, and indirectly, their quantitative ene reactions with 2,3-dimethyl-2-butene. Copolymerization between bis-TDs and substituted styrenes was carried out in dimethylformamide (DMF), tetrahydrofuran (THF), or dichloroethane (DCE). Polymers formed were characterized by infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and viscometry. Molecular weights of polymers range from 5000 to 16,000 in most cases. They were stable up to 250°C and higher. Polymers derived from bis-TDs and p-t-butylstyrene, α-methylstyrene, p-nitrostyrene, and p-acetoxystyrene contained only Diels-Alder-ene (DAe) repeating units, whereas those derived from styrene, p-chlorostyrene, p-bromostyrene, p-methylstyrene, p-methoxystyrene, and 4-vinylbiphenyl contained both DAe and double Diels-Alder (dDA) repeating units. A kinetic study of the copolymerization of 4,4′-bis-(3,5-dioxo-1,2,4-triazoline-4-yl) phenyl ether with α-methylstyrene, p-t-butylstyrene, styrene, p-chlorostyrene, and p-nitrostyrene in DCE was carried out; the copolymerization rate constants were 60.9, 49.8, 8.4, 5.5, and 0.8 (1 mol?1s), respectively. 相似文献
97.
[formula: see text] The preparation of the first library of imidazo[1,2-a]pyridine derivatives on a solid support is described. A sulfone linker strategy was applied in the synthesis. Key steps involved in the solid-phase synthetic procedure include (i) alpha-haloketone resin formation by sulfinate-->sulfone alkylation, (ii) imidazo[1,2-a]pyridine ring formation by treatment with 2-aminopyridine, (iii) sulfone anion alkylation, and (iv) traceless product release by oxidation-elimination. A library of 12 imidazo[1,2-a]pyridines was synthesized. 相似文献
98.
The pervaporation and vapor permeation performance of symmetrical and asymmetrical polycarbonate membranes, prepared via a dry-phase inversion and wet-phase inversion methods, respectively, were studied by measuring the permeation rate and separation factor. It was found that the polymer concentration effect on the pervaporation performance for the symmetrical polycarbonate membrane was lower than that for the asymmetrical polycarbonate membrane. Compared with pervaporation, vapor permeation has a significantly increased separation factor with a decreased permeation rate for the symmetrical polycarbonate membrane. Water molecules preferentially dissolve into the symmetrical polycarbonate membrane and diffuse easily through the membrane. 相似文献
99.
The starting electrophoretic motion of a porous, uniformly charged, spherical particle, which models a solvent-permeable and ion-penetrable polyelectrolyte coil or floc of nanoparticles, in an arbitrary electrolyte solution due to the sudden application of an electric field is studied for the first time. The unsteady Stokes/Brinkman equations with the electric force term governing the fluid velocity fields are solved by means of the Laplace transform. An analytical formula for the electrophoretic mobility of the porous sphere is obtained as a function of the dimensionless parameters , , , and , where a is the radius of the particle, κ is the Debye screening parameter, λ is the reciprocal of the square root of the fluid permeability in the particle, ρp and ρ are the mass densities of the particle and fluid, respectively, ν is the kinematic viscosity of the fluid, and t is the time. The electrophoretic mobility normalized by its steady-state value increases monotonically with increases in and , but decreases monotonically with an increase in , keeping the other parameters unchanged. In general, a porous particle with a high fluid permeability trails behind an identical porous particle with a lower permeability and a corresponding hard particle in the growth of the normalized electrophoretic mobility The normalized electrophoretic acceleration of the porous sphere decreases monotonically with an increase in the time and increases with an increase in from zero at . 相似文献
100.