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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 KCuHisCys=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. [ABSTRACT FROM AUTHOR]

Speciation of iron(III) ( c Fe = (0.5 - 40) × 10 −5 mol dm −3 ) and indirectly of iron(II), in aqueous solution of L-aspartic acid and aspartic acid - glycine mixture was investigated by square-wave voltammetry on a static mercury drop electrode. A reversible, one-electron reduction process of iron(III)-aspartate complexes with peak potential between +0.04 and -0.17 V was recorded, depending on the solution pH (4.5–8.6) and concentration of aspartic acid ( c Asp = 0.01 - 0.4 mol dm −3 ). Cumulative stability constants of iron(III)-aspartate complexes: FeAsp + (log K = 13.16 ± 0.01), FeAspOH 0 (log β = 20.76 ± 0.02), FeAsp(OH) 2 − (log β = 27.77 ± 0.12) and Fe(Asp) 2 − (log β = 17.62 ± 0.10); and iron(II)-aspartate complexes: FeAsp 0 (log K = 4.17 ± 0.11) and Fe(Asp) 2 2− (log β = 6.53 ± 0.11), were determined at I c = 0.5 mol dm −3 and 25 ± 1 °C. In the solution with mixture of amino acids, aspartic acid and glycine, a formation of mixed (Fe(III)-aspartate-glycine) complexes occurred. The reduction process was also shown to be reversible, so stability constants of mixed complexes (iron(III): FeAspGly 0 (log β = 17.35 ± 0.02), FeAspGly(OH) − (log β = 23.87 ± 0.33), and iron(II): FeAspGly − (log β = 6.83 ± 0.23)) were calculated, as well. [ABSTRACT FROM AUTHOR]