Electrochemistry of coupled electron-ion transfer of a heme-like complex in an artificial organic membrane

The electrochemistry of a heme-like complex 5,10,15,20-tetraphenylporphyriniron(III) chloride (Fe(III)–TPP–Cl) embedded in a lipophilic artificial membrane is studied by means of voltammetric techniques. The experimental system used comprises of a thin organic membrane hosting the redox probe, sandwiched between edge plane pyrolytic graphite electrode and an aqueous electrolyte solution. In the course of the voltammetric experiment the redox transformation of Fe(III)–TPP–Cl at the electrode|membrane interface is accompanied by concomitant ion transfer reactions across the membrane|water interface. The overall electrochemical process proceeds as a coupled electron–ion transfer reaction providing insight into energetic and kinetic aspects of the complex membrane charge-transfer reactions. The membrane electrochemistry of Fe(III)–TPP–Cl involves two quasireversible redox transformations typical for the Fe(III)/Fe(II) couple. Both redox processes are coupled with a chemical reactions proceeding inside the membrane as well as by complex ion transfer reactions across the membrane|water interface comprising chloride expulsion from the membrane and cation ingress from the aqueous phase.