Kinetics and Mechanism of the Ligand Substitution Reaction of Di-μ-Hydroxobis(Bipyridyl)Dipalladium(Ii)Ion with Dipeptides in Aqueous Solution

Abstract

The interaction of the title complex with dipeptides such as glycylglycine (Gly - Gly) and glycylglutamine (Gly-Gin) has been studied spectrophotometrically in aqueous medium as a function of [substrate complex], [ligand] and temperature at a particular pH (7.4), where the substrate complex exists predominantly as the dimeric dihydroxo-bridged species and the dipeptides are in zwitterionic form, at constant ionic strength. The reactions have been studied under pseudo-first order conditions. The reaction proceeds in a two-step-consecutive manner (A ->B ->C); where the first step is ligand-dependent and second step is ligand-independent, and is assigned to ring closure. Based on the kinetic and activation parameters, an associative interchange mechanism is proposed for the interaction processes.