EVALUATION OF N-HYDROXY-2-THIOPYRIDONE AS A NONMETAL DEPENDENT SOURCE OF THE HYDROXYL RADICAL (HO.) IN AQUEOUS SYSTEMS

N-hydroxy-2-thiopyridone (1), an established source of the hydroxyl radical (HO·, Boivin, J., Crepon, E., and Zard, S. Z. (1990), Tetrahedron Lett. 31, 6869-6872), produced HO· under conditions directly applicable to biological studies. Generation of HO· by subjecting 1 to irradiation with visible light was monitored in the following "HO·" assays: deoxyribose degradation, addition to dimethyl sulfoxide, and hydroxylation of salicylate and phenol. All four assays demonstrated the production of HO· from 1 (added as a sodium salt) under mild conditions in aqueous buffer systems. An improved analysis method was developed for the phenol assay. A time course analysis demonstrated that a flux of HO· is generated from 1 throughout the irradiation period, in contrast to the classical Fenton reaction of H2O2 with a transition metal in which a burst of HO· is generated in a short time period. While a thiyl radical is generated from 1 concurrent with HO· generation, this species does not contribute to, or interfere with, any of the HO· assays, suggesting that it is weakly reactive in aqueous buffers. Thus, irradiation of 1 can be used as an alternative, complementary, approach for the un-equivocal generation of the biologically significant and reactive HO·. © 1992.