PHOTO-ENHANCED PRODUCTION OF THE SPIN ADDUCT 5,5-DIMETHYL-1-PYRROLINE-N-OXIDE CENTER-DOT-OH IN AQUEOUS MENADIONE SOLUTIONS/

The production of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO)/. OH in aque ous solutions of menadione and DMPO is enhanced by fluorescent room li ght. The formation of DMPO/. OH requires oxygen and water, is enhanced by superoxide dismutase, and occurs to a much smaller extent for benz oquinone than for menadione. This process is assigned as photo-initiat ed redox cycling of the menadione, which causes oxidation of DMPO to D MPO(+.) and reduction of oxygen to superoxide. DMPO(+.) reacts with wa ter to produce DMPO/ . OH. Although DMPO/. OOH was not observed in the menadione solutions, the possibility that some of the DMPO/. OH was p roduced by decomposition of DMPO/. OOH cannot be ruled out. There is n o evidence for participation of hydroxyl radicals. Because benzo-semiq uinone is less readily oxidized than the semiquinone of menadione, red ox cycling is less favorable for benzoquinone than for menadione and s maller quantities of DMPO/. OH are produced by photoexcitation of benz oquinone than of menadione. (C) 1996 Academic Press, Inc.