The reduction of Cu(II) in solutions containing histidine (L) has been studied at platinum electrodes by means of cyclic voltammetry. The electrodes employed were either of conventional and microscopic size. The experimental evidences indicated that the copper(II)-histidine complexes undergo a two-electron reduction process to metallic copper in solution containing SO2-4 and ClO-4. A more complex pathway is involved in solutions containing Cl- in that competitive reductions between the Cu(II)L and CuCl-2 occur depending on the ratio between concentrations of histidine and Cl-. It has also been shown that at the microelectrode the enhanced mass transport associated with its smaller surface area allowed the electrochemical process to be simplified to some extent. The formation of stable Cu(I)-histidine complexes in aqueous solutions has also been shown, while no evidence has been obtained supporting their formation during the electrode process starting from the CuII-histidine complexes. This because the reduction potentials of the former species occur at potentials similar to or less negative than the latter parent complexes. The concentration of copper ions has been varied in the range 0.1-1 mM and the measurements have been performed at constant pH = 6. © 1992.
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