Comparison of the dehalogenation of dihalomethanes (CH2XI, where X = Cl, Br, I) following ultraviolet photolysis in aqueous and NaCl saltwater environments

The ultraviolet photolysis of low concentrations of CH(2)XI (X = Cl, Br, I) were investigated in water and saltwater solutions by photochemistry and picosecond time-resolved resonance Raman spectroscopy. Photolysis in both kinds of solutions formed mostly CH(2)(OH)(2) and HI and HX products. However, photolysis of the CH(2)XI molecules in saltwater resulted in production of some CH(2)XCl products not observed in aqueous solutions without salt present. The appearance of these new products in saltwater solutions is accompanied by a decrease in the amount of CH(2)(OH)(2), HI, and HX products compared to photolysis in aqueous solutions without salt present. The possible implications for photolysis of CH(2)XI and other polyhalomethanes in seawater and other salt aqueous environments compared to nonsaltwater solvated environments is briefly discussed.     

Effects of polymer architecture and composition on the adhesion of poly(tetrafluoroethylene).

Poly(glycidyl methacrylate), PGMA, chains in linear and arborescent structures were incorporated onto surfaces of poly(tetrafluoroethylene), PTFE, films by hydrogen plasma and ozone treatment and atom transfer radical polymerization. The epoxide groups of the PGMA chains were further reacted with acetic acid (AAc), oxalic acid (XAc), allyl amine (AA), and ethylenediamine (EDN) to introduce hydroxyl and amine groups to the surfaces of the PTFE films. Surface characterizations performed by Fourier Transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the surface modification and the chemical structure. The PGMA chains in arborescent structures show a high effectiveness for the enhancement of the adhesion of PTFE films. The adhesion of PTFE films was also significantly enhanced by ring-opening reactions of the PGMA epoxide groups with acetic acid and amine compounds. A high value of 9.5 N cm(-1) in the optimum 180 degrees peel strength test was observed with PTFE/copper assemblies.     

关于静电作用对酶活性部位残基pKa影响的定量计算

随着基因技术的发展,人们几乎已经可以任意替换蛋白质序列中的特定残基。由于理论上对蛋白质性能的预测工作还远远跟不上实验的发展,只能花费大量的人力、物力利用实验方法筛选突变体。这就迫切需要建立一套能够正确预测蛋白质性质的方法。静电作用在酶促反应中起到了重要作用。基于表面带电残基对酶活性部位残基pK_α的影响,可利用替换表面残基的方法改变酶促反应随pH的变化趋势,是蛋白质工程研究中的一种有效方法。由于表面极性残基处于高介电常数的溶剂(水)与低介电常数的蛋白质的界面上,对此问题尚未有圆满的理论方法进行解决。我们利用Kirkwood理论定量地表述了表面荷电残基的替换对酶活性部位残基pK_α的影响,为研究酶突变体的性质,如突变体的电化学性质、酶催化反应随pH变化趋势的改变,酶专一性的改变等提供了一种简便的方法。     

少量人发中硫的测定

建立了测定一根长2～3cm人发中硫的间接分光光度法,表观吸光系数为5.1×10~4,络合物组成Ba:CPA-mA为1:2,比耳定律范围为0～20μg硫。硫的检测限为0.025μg/mL,变动系数为2.7%,回收率为91.2～97.2%,且不用掩蔽即可直接进行测定,测定211例人发的结果表明,含硫量范围为(28.5±3.2)×10~3μg/g。     

Excess partial molar enthalpies,entropies, Gibbs energies,and volumes in aqueous dimethylsulfoxide

The excess partial molar enthalpies, the vapor pressures, and the densities of dimethylsulfoxide (DMSO)–H₂O mixtures were measured and the excess partial molar Gibbs energies and the partial molar volumes were calculated for DMSO and for H₂O. The values of the excess partial molar Gibbs energies for both DMSO and H₂O are negative over the entire composition range. The results for the water-rich region indicated that the presence of DMSO enhances the hydrogen bond network of H₂O. Unlike monohydric alcohols, however, the solute-solute interaction is repulsive in terms of the Gibbs energy. This was a result of the fact that the repulsion among solutes in terms of enthalpy surpassed the attraction in terms of entropy. The data in the DMSO-rich region suggest that DMSO molecules form clusters which protect H₂O molecules from exposure to the nonpolar alkyl groups of DMSO.     

The synthesis and fluxional behavior of the first [2.1.2.1] metacyclophane

8,15,23,30-Tetramethyl[2.1.2.1]metacyclophane,4, is synthesised. Variable temperature ¹Hmr and ¹³Cmr spectra indicate that 4e is the most likely conformation and that at temperatures above 50°C the molecule is fluxional (ΔG^≠₃₂₃ = 15.4 kcal/mole).     

贮氢材料电极循环寿命的定量预测定时放电半衰期法的应用

贮氢材料电极循环寿命的定量预测定时放电半衰期法的应用韩剑文，袁满雪，周作祥，赖城明（南开大学化学系天津３０００７１）关键词：贮氢电极，循环寿命，半衰期。前文￣［１］讨论了应用定终点电位放电半衰期法来预测贮氢材料电极循环寿命的问题。本文讨论如何采用定时...     

A Density Functional Study of Substituent Effects on the O-H and O-CH(3) Bond Dissociation Energies in Phenol and Anisole

The substituent effects on O-H and O-CH(3) bond dissociation energies for a series of 18 para-substituted phenols (p-XC(6)H(4)OH) and 11 para-substituted anisoles have been studied using the density functional method in order to understand the origin of these effects. The calculated substituent effects agree well with experimental measurements for phenols but are substantially larger than the reported values for anisoles. Both ground-state effect and radical effect contribute significantly to the overall substituent effect. An electron-donating group causes a destabilization in phenols or anisoles (ground-state effect) but a stabilization in the phenoxy radicals (radical effect), resulting in reduced O-R bond dissociation energy. An electron-withdrawing group has the opposite effect. In most cases, the radical effect is more important than the ground-state effect. There is a good correlation between the calculated radical effects and calculated variations in charge and spin density on the phenoxy oxygen. This supports the concept that both polar and spin delocalization effects influence the stability of the phenoxy radical. While almost every para-substituent causes a stabilization of the phenoxy radical by spin delocalization, electron-donating groups stabilize and electron-withdrawing groups destabilize the phenoxy radical by the polar effect.