Phosphate radical induced oxidation of thiols in aqueous solution

Abstract

Photolysis ofthiols, viz., cysteine, cysteamine and dithiothreitol in aqueous solution at natural <i>p</i>H in the presence of peroxydiphosphate (POP) has been carried out in a quantum yield reactor using a medium pressure mercury lamp. The respective disulphides, viz., cysteine, cysteamine and oxidised dithiothreitol are found as the products of oxidation. The rates offormation of disulphides have been followed spectrophotometrically by measuring the absorbance at 280 nm. The intensity of light has been measured using peroxydisulphate solution as a standard chemical actinometer. The quantum yields of disulphide formation are found to depend on [POP] as well as on [thiol] and are independent of the intensity of incident light. A mechanism involving photolysis of peroxydiphosphate giving phosphate radical anion followed by a chain propagation step involving disulphide radical anion has been proposed.