PHOTOSENSITIZED GENERATION OF SUPEROXIDE RADICAL IN APROTIC-SOLVENTS - AN EPR AND SPIN-TRAPPING STUDY

The UV or visible irradiation of pigments such as curcumin, anthralin, benzanthrone, 1,8-dihydroxyanthraquinone, and rose bengal- or eosine- complexes with cationic surfactants in aerated aprotic solvents, such as benzene, toluene, acetone, n-heptane, cyclohexane, in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) generates EPR spectra with hyperfine splitting constants (hfsc's) a(N) = 12.75 G, a(H)beta = 10.5 0 G, a(H)gamma = 1.26 G in toluene, 12.83 G, 10.64 G, 1.24 G in benzen e, 12.75 G, 10. 19 G, 1.35 G in acetone and 12.54 G, 10.46 G, 1.38 G i n n-heptane and cyclohexane. These spectra are similar to those observ ed when DMPO reacts with 18-crown-6 ether-solubilized KO2 in the respe ctive solvents and suggests that the photoinduced EPR spectra can be s afely assigned to the DMPO/superoxide radical adduct (1). A correlatio n between the hfsc's of 1 and solvent parameters, the solvent acceptor number AN and the Kosower Z value, has been evaluated in terms of its usefulness for the identification of the DMPO/superoxide adduct in or ganic media.