Photogeneration of reactive oxygen species by 3-arylcoumarin and flavanocoumarin derivatives

The photodynamic properties of six 3-arylcoumarins, viz., 3-phenyl-4-hydroxycoumarin (AC1), 3-phenyl-4-methoxycoumarin (AC2), 3-(4-methoxyphenyl)-4-hydroxycoumarin (AC3), 3-(4-methoxyphenyl)-4-methoxycoumarin (AC4), 3-(3′,4′-methylenedioxyphenyl)-4-hydroxycoumarin (AC5), 3-(3′,4′-methylenedioxyphenyl)-4-methoxycoumarin (AC6) and four flavanocoumarins viz., 2-(3-coumaryl)-7-methoxy-3-phenylchromone (FC I), 2-(3-coumaryl)-7-methoxy-3-(4-methoxy)phenylchromone (FC II), 2-(3-coumaryl)-5,7-dimethoxy-3-phenylchromone (FC III) and 2-(3-coumaryl)-5,7-dimethoxy-3-(4-methoxy)phenyl chromone (FC IV) are studied. The photogeneration of 1O2 is followed by N,N-dimethyl-4-nitrosoaniline (RNO) bleaching and EPR–TEMPL (2,2,6,6-tetramethyl piperidinol) methods. Relative to rose bengal, singlet oxygen generating efficiencies of AC1, AC2, AC3, AC4, AC5 and AC6 are found to be 0.113, 0.079, 0.043, 0.028, 0.045 and 0.083, respectively. Similarly of FC I, FC II, FC III and FC IV are found to be 0.04, 0.03, 0.10 and 0.06 respectively. The photogeneration of O2− is monitored by optical spectroscopy using SOD-inhibitable cytochrome c reduction assay and by EPR spin trapping method using the spin trap, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). Photogeneration of O2− radical is effectively enhanced by electron donors. Our results indicate that 3-arylcoumarin and flavanocoumarin derivatives possesses only moderate ability to generate 1O2 and O2−. Both Type I and Type II paths are involved in the photodynamic action of 3-arylcoumarins as well as of flavanocoumarins.