RESUMO
Psoralen was irradiated at 366 nm in aerated aqueous or ethanol solutions. Fe2+ ions reduced photo-oxidized psoralen (POP) with the formation of free radicals and electronically excited states. Free radicals were detected by the electron spin resonance (ESR) method using the spin trap C-phenyl-N-tert-butyl-nitrone (PBN), and electronically excited states were registered by chemiluminescence (ChL) accompanying the destruction of POP by Fe2+ ions. PBN could not scavenge directly free radicals generated by the reduction of POP with Fe2+ and required the presence of ethanol during the reaction. Analysis of ESR spectra indicated that PBN trapped hydroxyethyl free radicals which were produced as a byproduct in the reaction of POP and Fe2+. The dependence of the yield of PBN adducts on the fluence of psoralen irradiation and the concentration of Fe2+ ions was measured. Although both ESR and ChL estimated the POP products destructible by Fe2+ (POPFe), they gave information about different POPFe products. A kinetic analysis showed that ChL-estimated POPFe products were produced with the participation of two molecules of psoralen (one in the electronically excited state and one in the ground state), whereas ESR-estimated POPFe products were produced with the participation of one molecule of psoralen in the excited state. ESR-estimated products were stable in both water and ethanol solutions and could be stored for 20 h without significant decay; pre-incubation of POP solutions with catalase or glutathione-peroxidase decreased the yield of PBN adducts by 50%. ChL-estimated products were essentially less stable, about 30% being spontaneously destroyed during storage in ethanol solution at room temperature; pre-incubation of these products with catalase decreased the ChL by 90%. The possible biological role of POPFe products is discussed.