Reactions of copper(II)-N-polycarboxylate complexes with hydrogen peroxide in the presence of biological reductants: ESR evidence for the formation of hydroxyl radical.

The formation of hydroxyl radicals (.OH) by the reaction of CuII(edta) (edta: ethylenediaminetetraacetic acid) with hydrogen peroxide (H2O2) in the presence of biological reductants, such as L-ascorbic acid and L-cysteine, has been demonstrated for the first time by ESR spectroscopy using water-soluble spin-traps, 5,5-dimethyl-1-pyrroline N-oxide (DMPO, 1), alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone (POBN, 2) and 3,5-dibromo-4-nitrosobenzenesulfonate (DBNBS, 3). Ethylenediaminetetraacetic acid (edta) is one of the polyamine-N-polycarboxylate chelating agents and it is commonly used by chemists and biochemists. Edta can chelate several metal ions. It is known that the CuII(edta) complex is usually less active than free copper ions in radical reactions, whereas complexes of edta with Fe(II) or Fe(III) still react with hydrogen peroxide (H2O2) or superoxide ion (O2-) (1). In our previous papers (2-4), we also have shown that copper(II) complexes with polyamine-N-polycarboxylates, such as edta and dtpa (diethylenetriaminepentaacetic acid), do not react with H2O2, whereas CuII(en)2 (en: ethylenediamine) can easily do so to give hydroxyl radical (.OH) as a reactive intermediate. Further, we assumed that the change of redox potential of Cu(II) ions as a result of ligation with different ligands causes the difference in reactivity of Cu(II) complexes towards H2O2. To verify this assumption, the reactions of CuII(edta), which was chosen as a Cu(II)-polyamine-N-polycarboxylate complex, with H2O2 were investigated in the presence of some biological reductants, using an ESR-spin trapping method.(ABSTRACT TRUNCATED AT 250 WORDS)