Kinetic studies on oxidation of Gly-Val-Gly, Gly-Phe-Gly and Ala-Val-Gly using Mn (III)

摘要

The fragments of elastin sequences, glycyl-valyl-glycine (GVG), glycyl-phenylalanyl-glycine (GFG) and alanyl-valyl-glycine (AVG) have been synthesized by classical solution phase method and characterized. Kinetics of oxidation of these tripeptides (TP) by Mn (III) has been studied in the presence of sulphate ions in acidic medium at 25 deg C. The reaction follows spectrophotometrically at #gamma#_(max) 500 nm. A first order dependence of rate on both [Mn (III)] and [TP] has been observed. The rate is independent of concentrations of reduction product, Mn (II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulphate, chloride and perchlorate have been studied. Activation parameters have been evaulated using Arrhenius and Erying plots. The oxidation products are isolated and characterized. A tentative mechanism involving the reaction of TP with Mn (III) in the rate-limiting step is suggested. The effect of hydrophobicity of amino acids on the rate of oxidation is discussed.