Kinetics and mechanism of oxidation of α-amino acids by Fremy's radical in aqueous borate buffer medium

Abstract

Oxidation of α-amino acids viz., glycine, alanine, phenylalanine, valine, aspartic acid, serine and threonine by Fremy's radical (potassium nitrosodisulphonate, PNDS) in aqueous-borate buffer medium at <i>p</i>H 10.0 shows first order dependence each on [PNDS] and [α-amino acid]. Under the experimental conditions PNDS has been found to be quite stable. However, the little self decomposition of PNDS found on standing for longer period has been prevented by the addition of sulphamate ion. Increase in ionic strength of the medium has no effect on the rate of oxidation. The mechanism proposed involves direct attack of PNDS on α-amino acid to give an α-amino acid radical. PNDS being a very good radical trap, efficiently reacts with α-amino acid radicals to give α-keto acid via easily hydrolysable α-imino acid. The order of reactivity has been found to be phenylalanine > alanine > serine > glycine > valine > threonine > aspartic acid.