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Photosensitization by Harmine: An ESR Spin Trapping Study on the Generation of the Superoxide Anion Radical

Volume 50, Number 11 (Nov. 1996) Page 1446-1451

Calle, Paloma; Fernández-Arizpe, Almudena; Sieiro, Carlos


Harmine was in situ UV-irradiated in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), α-phenyl-N-tert-butyl nitrone (PBN), or α-(4-pyridyl-1-oxide) N-tert-butyl nitrone (4-POBN) as spin traps and observed by electron spin resonance (ESR) spectroscopy. The superoxide radical (O2-) was detected as the corresponding DMPO, PBN, or 4-POBN spin adduct in dimethylsulfoxide (DMSO) or acetonitrile solution. The detection of these spin adducts was prevented by the addition of superoxide dismutase (SOD) to the solution. Also, the O2- adduct formation was inhibited by the addition of antioxidants as cysteine methyl ester or ascorbic acid, in a dose-dependent manner. The studies carried out in aqueous buffered solution did not allow superoxide radical adduct detection. In the presence of DMPO as a spin trap, the DMPO-OH spin adduct was detected. On the other hand, classical scavengers of the hydroxyl radical such as mannitol or glycerol abolished DMPO-OH spin adduct detection. Other scavengers such as ethanol, DMSO, or sodium azide inhibited the trapping of hydroxyl radicals and resulted in the formation of new radical adducts. No PBN or 4-POBN spin adducts were detected in aqueous solution. The origin of the hydroxyl radical is discussed.