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排序方式: 共有1310条查询结果,搜索用时 31 毫秒
31.
3-Dimethylarsino-propylamine, (CH3)2As? (CH2)3? NH2, and Bis-[3-aminopropyl]-methylarsane, CH3As[(CH2)3? NH2]2 The reduction of the nitriles Me2As(CH2)2? CN (Me?CH3) and MeAs(CH2CH2? CN)2 results in the formation of the arsines Me2As(CH2)3? NH2 and MeAs[(CH2)3? NH2]2, respectively. The reactivity of these compounds, especially the formation of carbonyl complexes and heterocyclic compounds are described. 相似文献
32.
The chlorination of branched high-pressure polyethylenes, promoted by u.v. at various temperatures in carbon tetrachloride and 1,1–2,2 tetrachloroethane, has been studied. It has been possible to elucidate the influence of the temperature and the nature of the solvent on the characteristics of the chlorinated polymers.The chlorination is more efficient in carbon tetrachloride, where the efficiency of the u.v. is not affected by the medium.At the same degree of chlorination, the chain-breaking mechanisms are more important in carbon tetrachloride than in tetrachloroethane; they increase when the temperature of the medium increases. The chlorine-saturated polyethylene obtained in carbon tetrachloride is richer in 1,2 dichloroethylene sequences.Below 60°, the yield of chlorinated polymer is the same in the two solvents. Chlorination at higher temperature in tetrachloroethane does not improve the structural regularity or the yield of the chlorine-saturated polyethylenes. 相似文献
33.
M. Palumbo F. Baccichetti C. Antonello O. Gia A. Capozzi S. Marciani Magno 《Photochemistry and photobiology》1990,52(3):533-540
The furocoumarin derivative 3,4'-dimethyl-8-methoxypsoralen (DMe-8-MOP) exhibits remarkable antiproliferative activity, but is devoid of skin phototoxicity. To gain insight into this peculiar behaviour we investigated non-covalent and covalent binding of DMe-8-MOP to calf thymus DNA, along with DNA-synthesis inhibition and mutagenic activity. The non-covalent interaction of DMe-8-MOP with the nucleic acid is quite poor as shown by equilibrium dialysis, spectroscopic, chiroptical and hydrodynamic techniques. However, it exhibits relevant photobinding ability to DNA using both isolated nucleic acid samples and cellular systems. Unlike the large majority of congeners, DMe-8-MOP undergoes predominantly photochemical monoaddition to the double helical polynucleotide. Upon examination of the products obtained by enzymatic hydrolysis of DMe-8-MOP photomodified DNA, the formation of an unusual furan side adduct is proposed, which could account for the peculiar photochemical and photobiological properties of the 3,4'-dimethyl furocoumarin derivative. 相似文献
34.
G. Zagotto O. Gia F. Baccichetti E. Uriarte M. Palumbo 《Photochemistry and photobiology》1993,58(4):486-491
The synthesis and the photobiological activity of two new hydroxymethyl derivatives of psoralen namely 4-hydroxymethyl-4'-methyl- and 4-hydroxymethyl-4'-methyl-8-rnethoxypsoralen are described. Both compounds exhibited efficient photobinding to DNA and RNA. The DNA-photobinding process was investigated using different nucleic acid structures such as double-helical DNA, ribosomal RNA, bacterial DNA and DNA organized in the nucleosomal arrangement. The test derivatives were able to induce cross-links to a similar extent as 8-methoxypsoralen (8-MOP), used as a reference photochemotherapeutic drug. In contrast to 8-MOP, they produced relatively high levels of l O2 . Most photobiological effects (DNA synthesis inhibition, T2 phage sensitization, inhibition of tumor transmitting capacity) showed a good correlation with the extent of covalent photoaddition. On the other hand, the new 4-hydroxymethylpsoralens were unable to induce skin erythema, in striking contrast with 8-MOP. Thus, neither cross-linking of the nucleic acid nor 1 O2 production were coupled with skin phototoxicity in this class of compounds. The new derivatives appear to represent an important beginning to development of new active photochemotherapeutic agents devoid of undesired phototoxic side effects. 相似文献
35.
Hai Pham Tuan Hans-Gerd Janssen Ellen M. Kuiper-van Loo Harm Vlap 《Journal of separation science》1995,18(9):525-534
Determination of trace concentrations of sulfur components in natural gas is a true analytical challenge. Only analytical procedures based on gas chromatography can meet the sensitivity and accuracy requirements dictated by environmental regulation institutions and modern chemical industry. In the present contribution the sample pretreatment and chromatographic separation steps have been evaluated and optimized based on the use of a flamebased sulfur chemiluminescence detector (SCD) for target compound detection. The proposed instrument consists of a programmed temperature vaporizing (PTV) injector employing a liner packed with Chromosorb 104, a 4 μm thick film apolar column and a flame-based SCD. Using a 13 mL sample loop the detection limit achievable with the new method is 3 μg S/m3. The precision of replicate measure. ments is generally in the range of 5–15% relative standard deviation. Lower detection limits can be achieved by preconcentrating larger sample volumes, e.g. 100 mL. 相似文献
36.
Feng Xian Liu-Cai Charlotte Pham Farida Bey Gilbert Hervé 《Reaction Kinetics and Catalysis Letters》2002,75(2):305-314
Effects of Cs+, H+ and Cu2+ counterions in the vanadium containing heteropoly compounds CsxH1-xVO[PMo12O40] and CsyH0.5-yCu0.25VO[PMo12O40] on the catalytic oxidation of isobutane and characterization by TGA, IR and ESR spectroscopies are reported. A high selectivity of 76% for methacrylic acid and methacrolein together has been obtained with Cs0.75H0.25VO[PMo12O40] catalysts at a reactivity of 5.3x10-1 mmol/h cm3. 相似文献
37.
Brigitte Florin-Michel Marie-France Llauro R. Spitz Q.-T. Pham 《European Polymer Journal》1979,15(3):277-283
Ethylene 1-hexene copolymers obtained by catalytic polymerization have been examined by 1H and 13C NMR. Copolymer compositions have been determined by 1H NMR and i.r. and the sequence distributions for 1-hexene by 13C NMR. Variations of the copolymer microstructure have been related to the experimental conditions for copolymerization. 相似文献
38.
Christian Pichot Marie-France Llauro Quang-Tho Pham 《Journal of polymer science. Part A, Polymer chemistry》1981,19(10):2619-2633
The compositions and sequence distributions of vinyl acetate–butyl acrylate copolymers obtained with batch and semicontinuous emulsion polymerizations have been studied by 1H and 13C NMR. The batch process gives heterogeneous copolymers while with the semicontinuous one the sequence distribution is statistical. These differences in sequence distributions have been related to the physical properties of the copolymers. 相似文献
39.
The kinetics of the reaction NH2 + NO → N2 + H2O were studied, using a conventional flash photolysis system. A value of k1 = (1.1 ± 0.2) × 1010 & mole?1 s?1 was obtained at room temperature and in the pressure range 2–700 torr in the presence of nitrogen. A slight negative temperature coefficient was observed between 300 and 500 K, equivalent to a negative activation energy of 1.05 ± 0.2 kcal mole?1. 相似文献
40.
Pham TN 《Physical review D: Particles and fields》1992,46(7):2976-2981