Interactions of Thiyl Free Radicals with Oxygen: A Pulse Radiolysis Study

Abstract

A pulse radiolysis study of glutathione in aqueous solution at pH 5·5 containing N₂O/O₂ mixtures at various ratios indicates that oxygen rapidly adds to the thiyl glutathione radical yielding a transient absorption, with a maximum at 540 nm, whose characteristics appear to be compatible with assignment to the GSOO^· radical. The reaction appears to be an equilibrium whose kinetic constants have been estimated (k_f = 2·0 × 10⁹ dm³ mol⁻¹ s⁻¹, k_b = 6·2 × 10⁵ s⁻¹). Evidence for electron transfer from ascorbate to the GSOO^· radical has been obtained and the respective rate constant has been determined to be 1·75 ± 0·15 × 10⁸ dm³ mol⁻¹ s⁻¹.