Electrochemical Characterization of Biochemically Active Cu(II) Mixed Ligand Complex with Histidine and Cysteine

Copper(II) complexes with cysteine and histidine, amino acids that coordinate copper(II) in human body, were investigated. Cu‐His and Cu‐Cys complexes were detected in pH range from 5.0 to 9.0 using voltammetric techniques. CuHis₂] complex reduces by two‐electron reversible process at ≈−0.40 V, while CuCys] complex by one‐electron quasireversible process at −0.6 V, revealing strong adsorption at the electrode surface. When both amino acids are present in the solution, new peak appeared at −0.5 V, which corresponded to the CuHisCys] complex reduction. Formation and characterization of mixed ligand complex was also supported by UV‐Vis spectra recorded at fixed histidine and various cysteine concentrations. Formation of CuHisCys] complex in the solution was detected and stability constant calculated to amount to log K Cu_HisCys=16.9±0.3. This study was the first attempt to characterize formation of Cu(II) mixed ligand complexation process with biochemically important amino acids in electron transport and oxygenation reactions in human body.