Iron(III)-complexes engaged in the biochemical processes in seawater. II. Voltammetry of Fe(III)-malate complexes in model aqueous solution

Abstract

Characteristics of iron(III) complexes with malic acid in 0.55 mol L-1 NaCl were investigated by voltammetric techniques. Three iron(III)-malate redox processes were detected in the pH range from 4.5 to 11: first one at -0.11 V, second at -0.35 V and third at -0.60 V. First process was reversible, so stability constants of iron(III) and iron(II) complexes were calculated: log K1(FeIII(mal))=12.66±0.33, log β2(FeIII(mal)2)=15.21±0.25, log K1(FeII(mal))=2.25±0.36, and log β2(FeII(mal)2)=3.18±0.32. In the case of second and third reduction process, conditional cumulative stability constants of the involved complexes were determined using the competition method: log β(Fe(mal)2(OH)x)=15.28±0.10 and log b(Fe(mal)2(OH)y)=27.20±0.09. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.