Kinetics and Mechanism of Silver(I)-Catalyzed Oxidation of Tryptophan by Platinum(IV) in Perchlorate Solutions

摘要

The kinetics of oxidation of tryptophan by platinum(IV) was investigated in aqueous perchlorate solutions in the presence of silver(I) catalyst at a constant ionic strength of 2.0 mol dmsup-3/sup and at 25°C. The progress of the reaction was followed spectrophotometrically. The reaction did not proceed in the absence of the catalyst. The catalyzed reaction exhibited a first order dependence on both [PtsupIV/sup] and [AgsupI/sup] whereas the order with respect to tryptophan concentration was found to be less than unity. Increasing ionic strength and dielectric constant was found to decrease the oxidation rate. The suggested oxidation mechanism involves formation of a silver(I)-tryptophan intermediate complex in a pre-equilibrium step, which confirmed by both spectral and kinetic evidences. The complex reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. The final oxidation products of tryptophan were identified as the corresponding aldehyde (indole-3-acetaldehyde), ammonium ion and carbon dioxide.