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 sup eroxide ion by the several quinones 1,4-benzoquinone, BQ, 2-methyl-1,4-benz oquinone, MBQ, sodium I,4-naphthoquinone-2-sulfonate, NQ2S, sodium 9, 10-an thraquinone-2-sulfonate, AQ2S, I, 4-naphthoquinone, NQ, 2-hydroxy-1,4-napht hoquinone, LWQ, 5,8-dihydroxy-1,4-naphthoquinone, NZQ, 5-hydroxy-1,4-naphth oquinone, JQ, and disodium 9,10-anthraquinone-1,5-disulfonate, AQDS in aque ous buffer (pH 7), at wavelengths above 310 nm, have been determined. Quant um yields for the production of singlet oxygen were found to be smaller tha n that for the production of superoxide. The quantum yield for the producti on 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 whi le the photoproduction of this adduct by hydroxynaphthoquinones was not obs erved. Evidence was obtained which suggests that the observed DMPO-OH adduc t is produced by the free hydroxyl radical, at least at low NQ concentratio n. (C)1999 Elsevier Science S.A, All rights reserved.