Free radical intervention, deamination and decarboxylation in the ruthenium(III)-catalysed oxidation of L-arginine by alkaline permanganate - a kinetic study

The kinetics of the Ru-III catalysed oxidation of L-arginine by alkaline pe rmanganate was studied spectrophotometrically using a rapid kinetic accesso ry. The reaction follows a two stage process. In both the stages the reacti on is first order with respect to [oxidant] and [catalyst] with an apparent less than unit order in [substrate] and [alkali]. The data suggest that ox idation proceeds via formation of a complex between the active (RuII)-I-I s pecies and L-arginine, which then reacts with one mole of permanganate in a slow step to yield a L-arginine free radical, followed by a fast step to f orm the products. The reaction constants involved in the mechanism were eva luated. There is a good agreement between observed and calculated rate cons tants under different experimental conditions for both stages of reaction. The activation parameters for the slow step were calculated and are discuss ed.