Catalytic Role of Cu(II) on the Oxidation of Biologically Active 3‐Mercapto‐ <scp>l</scp> ‐Alanine in Borate Buffer

Oxidation of biologically active 3-mercapto-L-alanine for the formation of disulphide bond (cystine) catalyzed by Copper(II) in alkaline borate buffer and oxygenated condition has been carried out. The progress of the reaction was monitored using an optical spectrophotometer at 355 nm. Kinetic observations and initial rate data reveal a second-order dependence of rate of the oxidation process on 3-mercapto-L-alanine concentrations with k₂ value of 7.52×10^-4 mol^-1 dm^-1 s^-1. In the range of concentration of the metal ion, Copper(II), the finding is unit order dependence of rate on copper catalyst. Over the range of acidity conditions maintained using borate buffer in the present work, the reaction order exhibits a complex dependence on acid concentration. The influence of ionic strength on the initial rate of reaction is conclusive of the fact that there was formation of intermediate complex possibly involving ions of opposite charge. Based on all the kinetic observations and the derived data, the reactive species of 3-mercapto-L-alanine under our reaction conditions are predicted and a suitable mechanism for the occurrence of electron transfer process is suggested. The good agreement of the computed dissociation constant (pK₂ = 8.23) of the substrate leading to its formation of different forms when compared with the literature value validates our proposal of the mechanism of the 3-mercapto-L-alanine to cystine conversion.