PHOTOCHEMISTRY OF WATER-SOLUBLE QUINONES - PRODUCTION OF A WATER-DERIVED SPIN ADDUCT

The photolyses of phosphate-buffered (pH 7) air-and nitrogen-saturated solutions containing the water-soluble quinones, 1,4-benzoquinone (BQ ), 2-methyl-1,4-benzoquinone (MBQ), sodium 1,4-naphthoquinone-2-sulfon ate (NQ2S), 9,10-anthraquinone-2-sulfonate (AQ2S) or 9,10-anthraquinon e-1,5-disulfonate (AQDS), and the spin trap 5,5-dimethylpyrroline-1-ox ide (DMPO) produce a DMPO-OH adduct, Electron paramagnetic resonance s pectroscopy of the photolyzed samples in O-17-enriched water demonstra tes that this adduct derives almost exclusively from water, With the e xception of BQ, quantum yields for the formation of DMPO-OH are larger in air than in nitrogen-saturated samples, thus supporting the idea o f the formation of air-oxidized intermediates that enhance the DMPO hy droxylation reaction rate, Evidence has been obtained which suggests t hat BQ and MBQ, but not AQDS, are able to photooxidize water, with the consequent production of the free OH radical.