Some new details of the copper-hydrogen peroxide interaction

The addition of neocuproine (NC) or bathocuproinedisulphonate at the end of the autooxidation of Cu(I) in phosphate buffer, pH 7.4, regenerates almost entirely the O2 consumed. Other chelating agents assayed, including o-phenanthroline, cannot replace NC in promoting the O2 formation. O2 is also produced by adding NC to a mixture of Cu(II) and H2O2. Concomitant with the O2 evolution, the typical absorbance of the (NC)2Cu(I) complex appears to account for the complete reduction of Cu(II) to Cu(I). It is concluded that the addition of H2O2 with Cu(II) produces the equilibrium Cu(II)(O2H)(-)<--> Cu(I.)O2H. Addition of NC shifts the equilibrium to the right side by binding Cu(I). The released O2.- then reacts with the remaining Cu(II) yielding, in the presence of NC, the net reaction of 4 NC + 2 Cu(II) + H2O2 --> 2 (NC)2Cu(I) + O2 + 2 H+. O2 is also released in the absence of added NC provided the H2O2 concentration is increased. In these conditions the Cu(II)(O2H) complex undergoes other reactions leading to the copper-catalysed decomposition of H2O2.