Photochemistry of water-soluble quinones.: Production of the hydroxyl radical, singlet oxygen and the superoxide ion

Quantum yields for the photosensitized production of singlet oxygen and superoxide ion by the several quinones 1,4-benzoquinone, BQ, 2-methyl-1,4-benzoquinone, MBQ, sodium I,4-naphthoquinone-2-sulfonate, NQ2S, sodium 9, 10-anthraquinone-2-sulfonate, AQ2S, I, 4-naphthoquinone, NQ, 2-hydroxy-1,4-naphthoquinone, LWQ, 5,8-dihydroxy-1,4-naphthoquinone, NZQ, 5-hydroxy-1,4-naphthoquinone, JQ, and disodium 9,10-anthraquinone-1,5-disulfonate, AQDS in aqueous buffer (pH 7), at wavelengths above 310 nm, have been determined. Quantum yields for the production of singlet oxygen were found to be smaller than that for the production of superoxide. The quantum yield for the production of the hydroxyl adduct of 5,5-dimethyl pyrroline-l-oxide, DMPO-OH, by NQ was also determined and was found to be oxygen-concentration-dependent while the photoproduction of this adduct by hydroxynaphthoquinones was not observed. Evidence was obtained which suggests that the observed DMPO-OH adduct is produced by the free hydroxyl radical, at least at low NQ concentration. (C)1999 Elsevier Science S.A, All rights reserved.