Pulse Radiolysis of Cycloserine in Aqueous Solutions. One-Electron Oxidation by OH Radicals

Article abstract of DOI:10.1246/bcsj.57.3403

The reaction of (R)-4-amino-3-isoxazolidinone (cycloserine) with OH radicals was studied in aqueous solutions by optical pulse radiolysis at pHs 6.5-12.It was concluded, from a comparison of the transient spectra with those obtained in a reaction with N₃ radicals, that OH radicals attacked at the dissociated peptide group, -N^-CO-, and an oxidized radical, -N^.CO-, was produced through one-electron oxidation.From a kinetic analysis, the reaction was considered to have proceeded by two steps: The first step was the formation of OH adducts, where the rate constant, k(OH+cycloserine), was 8X10⁹ mol^-1dm³s^-1 for the zwitterion form of cycloserine at pH 6.5 and 1.2X10¹⁰mol^-1dm³s^-1 for anion form at pHs 8-10.The second step was the formation of oxidized radicals at a rate of 3-4X10⁶s^-1.These radicals decayed with a second-order rate, suggesting a radical-radical recombination.D-Serine was detected as the major product.