Utilization of Chromatographic and spectroscopic techniques to study the oxidation kinetics of selenomethionine

Ion-exchange LC and spectroscopic supporting techniques have been successfully used to study the kinetics and mechanism of oxidation reactions of selenomethionine (SeMet). Oxidation of selenomethionine with both cyanogen bromide (CNBr) and hydrogen peroxide (H₂O₂) proceeds through a stable intermediate which undergoes cyclization and C-Se bond cleavage to form 2-amino-4-butyrolactone. This stable intermediate was identified by IR spectroscopy as methionine dihydroxy selenide. The CH₃-Se moiety of SeMet formed methyl selenic acid upon reaction with H₂O₂ and methyl selenocyanate (CH₃SeCN), characterized by GC-MS, for the reaction with CNBr. Both reactions were of apparent first order with respect to the concentration of SeMet. A rate constant (k₁)of 4.0×10^–3 s^–1 for the reaction of SeMet with HO and 4.0×10^–3 s^–1 for the reaction with CNBr were determined at a temperature of 22°C. Oxidation of methionine (Met) gives disparate kinetics and oxidation products from SeMet. Thus the differential rate method can be utilized to quantitatively separate SeMet in biological samples in the presence of much higher concentrations of Met.