Silver(I)-CataIyzed Oxidation of L-Tyrosine and N-Acetyl L-Tyrosine by Cerium(IV) in Sulfuric Acid Medium (Stopped Flow Fluorimetric Technique)-A Kinetic and Mechanistic Study

摘要

The kinetics of the oxidation of silver(I) catalyzed oxidation of L-tyrosine, N-acetyl L-tyrosine (L-tyr & N-A-tyr) by Ce(IV) in sulfuric acid medium at a constant ionic strength of 0.1 mol dm~(-3) was studied spectrophotometrically (stopped flow fluorimetry). The reaction between L-tyrosine, N-acetyl L-tyrosine and Ce(IV) in sulfuric acid medium in presence of [Ag(I)] exhibits 1:2 stoichiometry. The reaction was first order with respect to L-tyrosine, N-acetyl L-tyrosine, inverse order with respect to Ce(IV) and a positive fractional order with respect to Ag(I). Intervention of free radicals was observed in the reaction. The oxidation reaction in sulfuric acid medium has been shown to proceed via a Ag(I)-L-tyr and N-A-tyr complex, which reacts with Ce(IV) to decompose in a rate determining step followed by other fast steps to give the products. The main products were identified by LC-ESI-MS and IR spectra. Probable mechanism is proposed and discussed. The activation parameters with respect to the slow step of the mechanism were computed and discussed and thermodynamic quantities were also calculated. The active species of oxidant has been identified as Ce(SO4)2.