MANGANESE(III) OXIDATION OF L-LYSINE AND L-HISTIDINE IN PYROPHOSPHATESOLUTION - A KINETIC AND MECHANISTIC STUDY

Kinetic studies on the oxidation of two basic amino acids (AA), L-lysi ne and L-histidine, by manganese(III) ions have been performed in pyro phosphate solution at 328 K and pH 1.3. Manganese(III) pyrophosphate s olution was prepared by a known chemical method and the nature of the oxidizing species present in the solution was determined by spectropho tometric and redox potential measurements. The reaction follows the ra te law: rate = k [Mn(III)] [AA] [H+](x)/{[Mn(II)](y) [P2O74-](z)} wher e x, y, and z are all fractional. The effects of added anions, fluorid e, chloride, and perchlorate, and of varying solvent composition were studied. A solvent isotope effect in D2O medium was investigated. The dependence of the rate on temperature was studied and activation param eters were evaluated from the Arrhenius and Eyring plots. A mechanism, which is consistent with the kinetic data, has been discussed.