OXIDATION OF A DIPEPTIDE BY ELECTROLYTICALLY GENERATED MANGANESE(III)IN AQUEOUS SULFURIC-ACID MEDIUM - A KINETIC AND MECHANISTIC STUDY

The kinetics of oxidation of the simplest dipeptide, glycylglycine (GG ) by electrolytically generated manganese-(III)sulfate in aqueous sulf uric acid has been studied. The rate shows first order dependence on [ Mn-III] and a fractional order each on [GG] and [H+]. The reduced prod uct, Mn-II has no significant effect on the rate. An increase in ionic strength or decrease in dielectric constant of the. medium increases the rate, while addition of complexing agents such as Cl-, F-, and P2O 74- decreases the rate. A Michaelis-Menten type mechanism has been sug gested to explain the results. The coefficient of the rate-determining step has been evaluated as a function of temperature, by measuring th e rates at different temperatures. The corresponding activation parame ters have also been computed. Evidence for transient existence of a fr ee radical reaction intermediate has been given. The kinetics of oxida tion of GG have also been compared with those of the monomer amino aci d, glycine.