Kinetics and Mechanism of Oxidation of L-Leucine by Alkaline Diperiodatonickelate(IV)-A Free Radical Intervention,Deamination,and Decarboxylation

摘要

The kinetics of oxidation of L-leucine by alkaline diperiodatonickelate(IV)was studied spectrophotometrically using a rapid kinetic accessory.The reaction is first order with respect to [DPN]and apparently less than unit order,each in [L-leucine]and [alkali]iunder the experimental conditions.However,the order in [L-leucine]adn [alkali]changes from first order to zero order as the concentrations change from lower to higher values.Addition of periodate has no effect on the reaction rate.A mechanism involving the deprotonated diperiodatonickelate(IV)(DPN)as the reactive oxidant is proposed.The reaction constants involved in the mechanism were evaluated.There is a good agreement between the observed and calculated rate constants under varying experimental conditions.The isokinetic temperature was determined and the activation parameters with respect to the slow step of the reaction scheme were evaluated and discussed.