Photodynamic effects of two hydroxyanthraquinones

The aim of this work was to investigate the photodynamic action of electron-rich anthraquinones, viz., cynodontin (CYN) and cynodontin-5,8-dimethylether (CYNM). Both optical and EPR methods are used to detect the generation of singlet oxygen. Based on RNO bleaching, relative to rose bengal (RB), singlet oxygen generating efficiencies of CYN and CYNM are derived to be 0.055 and 0.254, respectively. The formation of superoxide anion via electron transfer to O-2 was monitored by optical spectroscopy, using SOD-inhibitable cytochrome c reduction assay. The production of O-2(-.) is enhanced in the presence of electron donors such as EDTA and NADH. Photolysis of CYN and CYNM in DMSO, in the presence of 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), generates a multi-line EPR spectrum, characteristic of spin adduct mixture of O-2(-.) and (OH)-O-.. Both optical and ESR measurements indicate that O-2(-.) (Type I) and O-1(2) (Type II) paths are involved in CYN and CYNM photodynamic action. (C) 2003 Elsevier B.V. All rights reserved.