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

Ahmed Fawzy

doi:10.11648/j.ajche.20160401.14

Abstract

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 dm-3 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 [PtIV] and [AgI] 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.

Highlights

Study of amino acids is one of the most exciting fields of organic chemistry
Kinetic investigations on the oxidation reactions of amino acids catalyzed by different metal ions are an important field of chemistry due to the role played by metals in biological systems
Different reaction mixtures with different sets of reactants containing various amounts of PtIV and tryptophan at fixed acidity, ionic strength, and temperature were allowed to react for 24 h in an inert atmosphere

Summary

Introduction

Study of amino acids is one of the most exciting fields of organic chemistry They play a significant role in a number of metabolic reactions like biosynthesis of polypeptide, protein and nucleotides. The mechanism of analogous nonenzymatic chemical processes in the oxidation of amino acids is a potential area for intensive investigation [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18] in order to understand some aspects of enzyme kinetics. Tryptophan (Trp) is an essential amino acid in the human diet It finds extensive application as a reducing agent in chemical and biochemical systems. Kinetic investigations on the oxidation reactions of amino acids catalyzed by different metal ions are an important field of chemistry due to the role played by metals in biological systems.

Materials

Kinetic Measurements

Stoichiometry and Product Identification

Effect of Ionic Strength and Dielectric Constant

Discussion

Conclusion