Photogeneration of reactive oxygen species from ketocoumarins

Photosensitising properties of three ketocoumarins, viz., 3-benzoyl-7-methoxycoumarin (BMC), 5,7-dimethoxy-3-(1-naphthoyl)coumarin (DMNC) and 7-diethylamino-3-thenoylcoumarin (DETC) are studied. Photogeneration of singlet oxygen is monitored by both optical (RNO bleaching) and EPR (TEMPL spin trapping) methods. Relative to rose bengal (RB), singlet oxygen generating efficiencies of BMC, DMNC and DETC are derived to be 0.69, 0.07 and 0.06, respectively. These ketocoumarins are also found to photogenerate superoxide anion radical (O2-.) as probed by EPR-spin trapping method using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap and also by optical spectroscopy using SOD-inhibitable cytochrome c reduction assay. The production of O2-. is enhanced in the presence of electron donors such as EDTA, DETAPAC and NADH. Our results indicate that BMC possesses high ability to generate reactive oxygen species. Both O2-. (Type I) and 1O2 (Type II) paths are involved in BMC photosensitisation. © 1998 Elsevier Science S.A. All rights reserved.