Peroxyl, alkoxyl, and carbon-centered radical formation from organic hydroperoxides by chloroperoxidase

The decomposition of organic hydroperoxides as catalyzed by chloroperoxidase was investigated with electron spin resonance (ESR) spectroscopy. Tertiary peroxyl radicals were directly detected by ESR from incubations of tert-butyl hydroperoxide or cumene hydroperoxide with chloroperoxidase at pH 6.4. Peroxyl, alkoxyl, and carbon-centered free radicals from tertiary hydroperoxide/chloroperoxidase systems were successfully trapped by the spin trap 5,5-dimethyl-1-pyrroline N-oxide, whereas alkoxyl radicals were not detected in the ethyl hydroperoxide/chloroperoxidase system. The carbon-centered free radicals were further characterized by spin-trapping studies with tert-nitrosobutane. Oxygen evolution measured by a Clark oxygen electrode was detected for all the hydroperoxide/chloroperoxidase systems. The classical peroxidase mechanism is proposed to describe the formation of peroxyl radicals. In the case of tertiary peroxyl radicals, their subsequent self-reactions result in the formation of alkoxyl free radicals and molecular oxygen. beta-Scission and internal hydrogen atom transfer reactions of the alkoxyl free radicals lead to the formation of various carbon-centered free radicals. In the case of the primary ethyl peroxyl radicals, decay through the Russell pathway forms molecular oxygen.