碱性介质中分光光度法研究二过碲酸合铜(Ⅲ)氧化某些氨基酸的反应动力学及机理

Kinetics and Mechanism of Oxidation of Some Amino Acid Salts by Ditelluratocuprate(Ⅲ) with Spectrophotometry in Alkaline Medium

在碱性介质中,用分光光度法研究了二过碲酸合铜(Ⅲ)(DTC)氧化天冬氨酸(Asp)和谷氨酸(Glu)的反应动力学及其机理.结果表明,反应对DTC为准一级,对氨基酸均为分数级;表观速率常数kobs随[OH-]和[TeO42-]的增大均减小,且有负盐效应.据此提出了包括配离子和氨基酸形成络合物的前期快速平衡的反应机理,由假设反应机理推出的速率方程能解释全部实验现象,进一步求得速控步的速率常数和活化参数.

The kinetics of oxidation of aspartic acid salt （Asp） and glutamic acid salt （Glu） by ditelluratocuprate（ Ⅲ ） （DTC） were studied spectrophotometrically between 293.2 K and 308.2 K in alkaline medium. The reaction rate showed first order dependence in DTC and fractional order in each amino acid. It was found that the pseudo-first order rate constant kobs decreased with an increase in concentration of OH^- and concentration of TeO4^2- respectively. There is a negative salt effect. A plausible mechanism involving a pre-equilibrium of an adduct formation between the complex and amino acid was proposed. The rate equations derived from mechanism can explain all experimental observations. The activation parameters alongwith the rate constants of the rate-determining step were calculated.