Kinetics and mechanism of gold dissolution in thiourea solutions: Effect of sulfide ions

Chronoamperograms for gold in solutions containing 0.1 M thiourea, 0.5 M H₂SO₄, and catalytically active sulfide ions at the concentration c ₁ from 1 × 10^?5 to 4 × 10^?5 M are obtained at different potentials with the aid of an automated setup intended for renewing the electrode surface directly in the solution by cutting off a thin surface layer of the metal. It is shown that the results of measurements of the current practically coincide at a constant value of the product c ₁ t, where t is the time period elapsed after the renewal of the electrode surface. Such a coincidence testifies to a diffusion nature of processes that hamper accumulation of sulfide ions at the gold surface. This fact permitted the use of a procedure developed previously for the calculation of polarization curves at constant values of surface coverage θ by catalytically active ions. At θ = const, the voltammetric curves for gold in sulfide-containing thiourea solutions are shown to correspond to the Tafel equation. With the surface coverage increasing, the effective values of the exchange current i ₀, transfer coefficient α, and anodic reaction order with respect to thiourea P _a increase from the values i }~ 10^?5 A cm^?2, α }~ 0.12, and P _a = 0.2, which are characteristic of pure solutions, to 2 × 10^?4 A cm^?2, α }~ 0.5, and P _a = 1.1 (at θ }~ 0.5). An interpretation to the established regularities is given.     

薄层扫描法测定冬眠过程中刺猬活性组织酶的周期变化

薄层扫描法测定冬眠过程中刺猬活性组织酶的周期变化冯金城（天津师范大学天津３０００７４）孙金生（天津水产研究所天津３００２２１）１前言为了跟踪观察刺猬在冬眠过程中体内乳酸脱氢酶的周期性变化，利用薄层扫描仪测定了其相关的组织同工酶的差异。实践证明，此法简...     

旋光性高分子的合成（下）

旋光性高分子的合成（下）刘引烽，华家栋（上海科技大学化学系，上海，２０１８００）４不对称聚合由外消旋手性单体制备旋光性高分子必须通过选择性聚合才能实现。选择性聚合是指外消旋的两个对映异构单体进行聚合时，由于体系中存在着某种不对称的诱导因素，其中之一比...     

Synthesis and polymerization of N-[N′-(α-methylbenzyl)aminocarbonyl-n-alkyl]maleimide

Two types of optically active N-[N′-(α-methylbenzyl)amino/carbonyl-n-alkyl]maleimides (MBAC) were synthesized from maleic anhydride, 6-amino-n-caproic acid (or 12-amino-n-dodecanoic acid), and (R)-(+)-α-methylbenzylamine. Radical homopolymerizations of MBAC were performed in several solvents at 60 and 110°C for 24 h to give optically active polymers. Radical copolymerizations of MBAC were performed with styrene (ST) and methyl methacrylate (MMA) in dioxane at 60°C. The monomer reactivity ratios and the Alfrey-Price Q-e values were determined. Chiroptical properties of the polymers and copolymers were investigated. © 1995 John Wiley & Sons, Inc.     

On the choice of active space orbitals in MCSCF calculations

We describe a procedure which may be used to aid selection of the active space in multiconfigurational self-consistent field (MCSCF) calculations for general chemical systems. Starting from a restricted Hartree-Fock calculation, we define a hierarchy of interacting virtual orbitals for every occupied orbital. The most strongly interacting orbitals are then taken to constitute the active space in a configuration interaction (CI) calculation. The natural orbital occupation numbers obtained from the CI calculation are then used to choose the active space to be used in a subsequent MCSCF calculation. We illustrate our method on a number of systems (Li₂, B₂, C₂, carbonyl oxide and the transition state for oxidation of H₂S by dioxirane). In all these cases, ‘intuitive’ active spaces are inadequate, as are active spaces derived from the natural orbitals of unrestricted Hartree-Fock calculations.     

Active nickel-based reduction of organic compounds

The reducing system NiCl₂·2H₂O—Li—arene_cat (cat is catalyst) was proposed for use to reduce a wide range of organic compounds, including alkenes, alkynes, carbonyl compounds, imines, halogenated derivatives, sulfonates, aromatic compounds, hydrazines, azo and azoxy compounds, N-oxides, and nitrones. The degree of reduction can be controlled for some substrates. Deuterium can be incorporated in the reaction products using nickel chloride deuteriohydrate. Nitrones, N-alkoxyamides, and acyl azides are also reduced with the Li—arene_cat system containing no nickel salt.     

镉与植物活性氧代谢

镉是毒性最强的重金属之一，对人体健康具有潜在危害。研究证实，镉影响植物活性氧代谢，进而导致植物生理功能紊乱。     

Steam-carbon gasification catalyzed by calcium: Assessment of the porous structure of active carbons from plum stones and synthetic active carbons

A need for an elaboration of the methods for synthesis and characterization of activated carbons with a requisite porous structure has existed for a long time. One of the methods giving possibility for creating controlled mesopore and micropore structures deals with the steam gasification of various carbon materials. In this work the effects of calcium catalyst on the catalytic steam gasification of active carbons from plum stones and porous polymers are presented. Determination of micropores capacity and specific adsorption in mesopores have been performed by means of the _s method, but adsorption on the heterogeneous solids was described by the integral equation with various local isotherms. This equation has been solved by the regularization method. Based on this method the changes in structural parameters of active carbons depending on the amount of calcium catalyst were estimated.Nomenclature d width of slit-like micropore - F(x) distribution function of the half-width - p vapor pressure of sorbate - p/p _N relative pressure - PSAC Plum Stone Active Carbon - average pore radius, nm - S ₁ relative limit of the validity of experimental point on the adsorption isotherm in the computations by means of regularization method - SAC Synthetic Active Carbon - S _BET specific surface area calculated by means of BET method, m²/g - S _mes mesopore surface area, m²/g - S _mic micropore surface area, m²/g - T absolute temperature, K - V _mes sorption capacity of mesopores, cm³/g - V _mic sorption capacity of micropores, cm³/g - V _p sorption capacity of pores, cm³/g - w/w weight in weight concentration - x half-width of slit-like micropore, nm - x ₁ maximum of half-width of micropore slit, nm - average half-width of slit-like micropore, nm - X _min-X _max integration limits of thex Greek Letters Greek Letters variance of average half-width of slit-like micropore, nm² - local relative filling of micropores - total relative filling of micropores     

煤自燃初期的反应机理研究

从实验得到的可能引起煤自燃的8个活性基团入手，提出了一系列简单煤分子模型，利用密度泛函DFT/6-31G对其完成了几何优化，计算了包括反应焓变、吉布斯自由能和活化能等，从热力学和动力学角度分析了计算结果。基于理论计算获得了煤活性基团的活泼性次序，得出了煤自燃初期的反应机理主要是氧分子先进攻煤分子中的活性基团，产生活泼性很高的中间体，然后中间体进一步反应得到水或二氧化碳及其他反应产物，计算结果与实验基本符合。     

常压气相氧化羰基化合成碳酸二乙酯

碳酸二乙酯是一种重要的有机化工原料,可广泛用于合成农药如脱叶灵,医药如喹啉酮衍生物,中间体3-氧硫代羧酸酯,还可用于电子管阴极的镀层[1-3]。生产碳酸二乙酯的传统方法为:无水乙醇与光气反应生成氯甲酸乙酯,氯甲酸乙酯继续与乙醇反应生成碳酸二乙酯后经水洗蒸馏制成。使用光气为原料对设备的要求较高。我们在常压下气相羰基化合成碳酸二乙酯[4]:2ＮＯ+Ｃ2Ｈ5ＯＨ+0.5Ｏ2→2Ｃ2Ｈ5ＯＮＯ+Ｈ2Ｏ(1)ＣＯ+2Ｃ2Ｈ5ＯＮＯ→(Ｃ2Ｈ5Ｏ)2ＣＯ+2ＮＯ(2)产生的一氧化氮可与氧气和乙醇进行反应再生为亚硝酸乙酯,符合原子经济反应且几乎不放出对…