Photodynamic action of some naturally occurring quinones: formation of reactive oxygen species

Four naturally occurring quinones, thespone (TP), thespesone (TPE), mansono ne-D (MD) and mansonone-H (MH), extracted from the heartwood of Thespesia p opulnea, are studied for their ability to generate superoxide anion radical (O-2(-.)) and singlet oxygen (O-1(2)) upon photoirradiation. The generatio n of O-1(2) is followed by N,N-dimethyl-4-nitrosoaniline (RNO) bleaching as say. Relative to rose bengal, singlet oxygen generating efficiencies of TP, MD, MH and TPE are found to be 0.30, 0.13, 0.03 and 0.01, respectively. Th e formation of O-2(-.) is monitored by optical spectroscopy using SOD inhib itable cytochrome c reduction assay. Generation of O-2(-.) radical is effec tively enhanced by the presence of electron donors such as EDTA and DETAPAC . Photolysis of TP, MD, TPE and MH in DMSO, in the presence of 5,5-dimethyl -1-pyrroline-N-oxide (DMPO) generates 12-line EPR spectra characteristic of O-2(-.) EPR spectral studies show the formation of both light dependent an d 'dark' radicals. Our results indicate that both TP and MD possess high ab ility to generate reactive oxygen species. (C) 1999 Elsevier Science S.A. A ll rights reserved.