Production of Hydroxyl Radicals from the Reactions of Some Copper(II) Complexes with Hydrogen Peroxide: Ligand Exchange Effects of Copper(II) Complexes on the Activation of Hydrogen Peroxide.

Abstract

The reactions of CuII(en)2 (en : ethylenediamine) with hydrogen peroxide (H2O2) during the successive addition of a polyamine-N-polycarboxylate such as ida (iminodiacetic acid) and edta (ethylenediaminetetraacetic acid) were investigated by the thiobarbituric acid (TBA) method and by the electron spin resonance (ESR) titration method. A relatively good relation between TBA method and ESR titration method was observed.The ligand, en, in CuII(en)2 was easily replaced by ida and edta. In the case of edta, which is a tetradentate ligand, CuII(edta) was formed when the concentration ratio of edta to CuII(en)2 was 1. On the other hand, in the case of ida which is a bidentate ligand, the reactions between CuII(en)2 and ida proceeded stepwise. That is, one is the formation of a mixed ligand complex of Cu(II), CuII(en)(ida), when the concentration ratio of ida to CuII(en)2 was 1. The other is the formation of CuII(ida)2 when the concentration ratio of ida to CuII(en)2 was 2.A mixed ligand complex, CuII(en)(ida), exhibited activity towards H2O2, whereas CuII(ida)2 and CuII(edta) did not show any activity towards H2O2. The different reactivities of these Cu(II) complexes toward H2O2 were discussed.