ESR spin trapping studies on the reactions of hydroperoxides with Cu (II) complex

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The generation of free radicals from the reaction of lipid hydroperoxide model compounds such as tert-butyl hydroperoxide and cumene hydroperoxide with a copper(Cu)(II) complex was investigated by the electron spin resonance (ESR) spin trapping method. Spin traps used here were 5,5-dimethyl-1-pyrroline N-oxide (DMPO), α-phenyl-N- tert-butylnitrone (PBN), α-(pyridyl-4- N-oxide)-N- tert-butylnitrone (POBN), and 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS). The formation of peroxyl (ROO·) and alkoxyl (RO·) radicals from the reaction of tert-butyl hydroperoxide or cumene hydroperoxide with Cu(CyHH) 2 {CyHH: cyclo(L-histidyl-L-histidyl)} was confirmed by the occurrence of respective DMPO adducts. On the other hand, neither ROO · nor RO · was observed when PBN, POBN, or DBNBS in place of DMPO was used as a spin trap during the reactions of Cu(CyHH)2 with both hydroperoxides. A carbon-centered radical, being generated by β-scissions of RO · radicals, was trapped by these spin traps.