Abstract
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.
Highlights
RESULTSEach incubation solution sample was aspirated into a quartz flat cell centered in an ER-4103 TM cavity and recorded as soon as possible after mixing
Alyzed by chloroperoxidase was investigated wiethlec- Oxygen evolution was explained by the formation of comtron spin resonance (ESR) spectroscopy
The g value of the singlet (g = 2.014) is higher thanthat of typical organic radicals and identifies the free radical as a peroxyl radical (13).The signal showed a characteristic broad line width known to be due to the large spin rotation
Summary
Each incubation solution sample was aspirated into a quartz flat cell centered in an ER-4103 TM cavity and recorded as soon as possible after mixing The calibration of both hyperfine coupling constants and g values was done by using potassium peroxylamine disulfonate (g = 2.0055) (11)with an estimated error of g value measurements of &0.0003. Spectrometecronditions were: gain, 2.0 X lo; modulation amplitude, 0.18 G; power, 20 milliwatts; time constant, 0.64 s; scan time, 500 s; scan range, 100 G
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