EFFECT OF pH ON ONE-ELECTRON OXIDATION OF SELENIUM AMINOACIDS

A b s t r a c t Pulse radiolysis has been employed to study one-electron oxidation of selenomethionine (SeM), selenocystine (SeCys), and methyl selenocysteine (MeSeCys) in aqueous solutions. Hydroxyl radicals (•OH) in the pH range from 1 to 7 and specific one-electron oxidants Cl2 •-(pH 1) and Br2 •- (pH 7) have been used, to carry out the oxidation reactions. Reactions of oxidizing radicals with all these compounds, produced selenium centered radical cations. The structure and stability of the radical cation was found to depend mainly on the substituent and pH. From these studies it is concluded, that formation of monomer and dimer radical cations mainly depend on the substitution, pH and the heteroatom like N, O. Availability of lone pair on N or O atom at or g position, results in monomer radical cations having intra-molecular stabilization. When such lone pair is not available, the monomer radical cation is converted into a dimer radical cation, which acquires intermolecular stabilization by the other selenium atom