Detection of free radicals produced from reactions of lipid hydroperoxide model compounds with Cu(II) complexes by ESR spectroscopy.

Using 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin trap, alkoxyl radicals and peroxyl radicals produced from the reactions of tert-butyl hydroperoxide(tBuOOH) and cumene hydroperoxide (PhC(CH3)2OOH) with some copper(Cu)(II) complexes such as Cu(II) complexes of cimetidine (Cim), cyclo(L-histidyl-L-histidyl) (CyHH), L-histidylglycine (HG), and L-histidylglycylglycine (HGG) were detected by electron spin resonance (ESR) spectroscopy. However, Cu(II) complexes of glycyl-L-histidine (GH), glycyl-L-histidylglycine (GHG),glycylglycyl-L-histidine (GGH), and glycylglycyl-L-histidyl-glycine (GGHG) did not cause the generation of free radicals during the reaction with tert-butyl or cumene hydroperoxide. Addition of a biological reductant such as cysteine or glutathione to the system including these Cu(II) complexes and hydroperoxides gave tert-butoxyl and cumyl alkoxyl (RO.) radicals, respectively. These alkoxyl radicals underwent subsequent beta-scission reaction and generated the carbon-centered radical (R.). Although cysteine and glutathione are considered to be cellular antioxidants, our results suggest that these biological reductants facilitate Cu(II) complexes-dependent free radical generation.