Influence of sodium dodecyl sulfate on the kinetics of complex formation between [PdCl(dien)](+) and sulfur containing ligands L-cysteine and glutathione

Abstract

The effect of sodium dodecyl sulfate (SDS) micelles on the kinetics of the complex formation between [PdCl(dien)](+) and sulfur containing ligands L-cysteine and glutathione (GSH) was investigated by using the stopped-flow technique under pseudo-first order conditions (ligand in excess) in the acidity range from pH 1 to 6. The presence of anionic micelles induced the acceleration of the complex formation in the entire acidity range with the maxima corresponding to the first protolytic constant of the ligands. This effect was interpreted in terms of the attractive electrostatic interaction between reacting species and the micellar surface and their effective concentration in the vicinity of micelles. An increase of the ionic strength leads to a decrease of the rate of complex formation in the presence of anionic micelles due to competition of reactive species with cations originating from inert salt for the micellar surface. The calculation of activation parameters revealed that the entropy of activation is strongly negative in the presence and in the absence of micelles, which is compatible with an associative reaction mechanism.