Redox behavior of biologically important Fe-catechol complexes at different pH

The redox behavior of Fe(III) in presence of Catechol (Cc) has been carried out in buffer solution of different pH, scan rate, variation of Fe(III) concentration and Cc concentration. Uncoordinated Fe(III) or Cc has been found to undergo reversible electrode reaction whereas coordinated Fe-Cc is irreversible. The peak positions of the voltammogram of Fe- Cc shifted with respect to that of free Fe(III) or Cc and also developed a new peak at 0.12 V. The peak current of Fe-Cc decreases significantly compared with that of free Fe(III) or Cc in the same experimental conditions. These behaviors ascribed the formation of complex of Fe with Cc. The complex was formed either by the addition of Cc into Fe(III) or by the addition of Fe(III) into Cc. The effect of pH of Fe-Cc complex was studied by varying pH from 2 to 8.5. The electrochemical oxidation of Fe-Cc is facilitated in lower pH media. The slope of the plots of anodic peak current, E_p against pH of Fe-Cc complex is 30 mV, indicates that the oxidation of Fe-Cc complexes proceeded via the 2e^-/2H⁺ processes. The current functions (1/v^-1/2) of the anodic peak of Fe-Cc decreased with the increasing of scan rate demonstrated that the behavior of electrode reaction of Fe-Cc is of ECE type.