DEGRADATION OF PSORALEN PHOTOOXIDATION PRODUCTS INDUCED BY FERROUS-IONS

Psoralen was irradiated at 366 nm in aerated aqueous or ethanol soluti ons. Fe2+ ions reduced photo-oxidized psoralen (POP) with the formatio n of free radicals and electronically excited states. Free radicals we re 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 des truction of POP by Fe2+ ions. PBN could not scavenge directly free rad icals generated by the reduction of POP with Fe2+ and required the pre sence of ethanol during the reaction. Analysis of ESR spectra indicate d that PBN trapped hydroxyethyl free radicals which were produced as a byproduct in the reaction of POP and Fe2+. The dependence of the yiel d of PBN adducts on the fluence of psoralen irradiation and the concen tration of Fe2+ ions was measured. Although both ESR and ChL estimated the POP products destructible by Fe2+ (POP(Fe)), they gave informatio n about different POP(Fe). products. A kinetic analysis showed that Ch L-estimated POP(Fe). 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 POP(Fe) products were produced with the participation of one molecule of psoralen in the ex cited state. ESR-estimated products were stable in both water and etha nol solutions and could be stored for 20 h without significant decay; pre-incubation of POP solutions with catalase or glutathione-peroxidas e decreased the yield of PBN adducts by 50%. ChL-estimated products we re essentially less stable, about 30% being spontaneously destroyed du ring storage in ethanol solution at room temperature; pre-incubation o f these products with catalase decreased the ChL by 90%. The possible biological role of POP(Fe) products is discussed.