Substitution of aqua ligands from ds-[Pt(en)(H2O)2](ClO4)2 and cis-[Pt(dmen)(H2O)2](ClO4)2 (en = ethylenediamine, dmen = Ν,Ν′-dimethylethylenediamine) by glutathione (reduced) (GSH) in aqueous medium - A Kinetic And Mechanistic Study.

Abstract

The kinetics of the interaction of glutathione (reduced) (GSH) with [Pt(en)(H2O)2](ClO4)2and [Pt(dmen)(H2O)2](ClO4)2 (en = ethylenediamine, dmen = N,N'-dimethylethylenediamine) have been studied spectrophotometrically as a function of [substrate complex], [glutathione] and temperature at a particular pH (4.0). The reaction was found to proceed via rapid outersphere association complex formation followed by two slow consecutive steps. The first step involves the transformation of the outersphere complex into the innersphere complex containing Pt-S bond, while the second step involves chelation when the second aqua ligand is displaced. The association equlibrium constant (KE) and the two rate constants k1 and k2 have been evaluated. Activation parameters for both the steps have been calculated using Eyring equation. The low enthalpy of activation and large negative values of entropy of activation indicate an associative mode of activation for both steps.