Oxidation of copper(II) bis(glycinate) by methyl free radicals in aqueous solutions. A pulse-radiolysis study

Abstract

The reaction of {sm bullet}CH{sub 3} free radicals with Cu{sup II}(NH{sub 2}CH{sub 2}CO{sub 2}{sup {minus}}){sub 2} in aqueous solutions was studied. The formation of the unstable intermediate (NH{sub 2}CH{sub 2}CO{sub 2}{sup {minus}}){sub 2}Cu{sup III}-CH{sub 3}(aq) in this reaction was observed. This intermediate decomposes into Cu{sup III}(NH{sub 2}CH{sub 2}CO{sub 2}{sup {minus}}){sub 2}{sup +}(aq) + CH{sub 4}. The formation of Cu{sup III}(NH{sub 2}CH{sub 2}CO{sub 2}{sup {minus}}){sub 2}{sup +}(aq) is not observed, as this complex is short-lived under these conditions and decomposes via ligand oxidation. The {sm bullet}CH{sub 3} free radicals react with the transient complex (NH{sub 2}CH{sub 2}CO{sub 2}{sup {minus}}){sub 2}Cu{sup III}-CH{sub 3}(aq) to form ethane and Cu{sup II}(NH{sub 2}CH{sub 2}CO{sub 2}{sup {minus}}){sub 2}; the specific rate of this reaction approaches the diffusion-controlled limit. The results thus point out that aliphatic free radicals can oxidize copper(II) complexes to copper(III) complexes. The results suggest that the reactions of aliphatic free radicals with copper complexes might cause the reported radiosensitization by copper compounds. 18 refs., 3 figs., 3 tabs.