Insights toward the Electrochemical Behavior of Hematin Using a Hematin Modified Glassy Carbon Electrode

Abstract

© 2016 The Electrochemical Society.The electrochemical behavior of heme-phorphyrin iron (III) centered hematin (Htin) was investigated at a Htin modified glassy carbon electrode with cyclic, differential pulse, square wave voltammetry in different pH values. For all pH values, the electrochemical process attributed to the reduction of hematin follows an EE mechanism, in which the ligand suffers mediated electrochemical reduction by the iron metallic center. At the backward scan, the same mechanism is observed for the oxidation of hematin in pH > 5.5. However, the electrochemical oxidation at backward scan in pH < 5.5 occurs firstly and directly at the ligand with the formation of IS (intermediate specie) that is further oxidized at the metallic center and forms Fe(Htin)3+. In acid and neutral media, the oxidation of hematin at the positive potential range is an irreversible and pH-dependent process that follows an ECE mechanism. In the first step, the electrochemical oxidation of hematin involves the transfer of one electron from the pyrrolic nitrogen heteroatom with the formation of a cationic radical that loses its iron (III) center in a subsequent chemical step. The resulting cationic radical suffers further oxidation to produce a structure similar to the protoporphyrin IX.