Electrochemistry of (Protoporphyrinato IX) Iron(III) and its Imidazole Complexes in Liposomes of L-α-Phosphatidylcholine

The electrochemical behaviour of hemin [(3,7,12,17-tetramethyl-8,13-divinylporphyrin- 2,18-dipropanoate)iron(III)] and its complexes with imidazole and 1-methyl imidazole in aqueous liposomes of L-α-phosphatidylcholine (L-α-Lecithin) was studied by cyclic voltammetry (CV) and Square Wave Voltammetry (SWV) techniques. The redox potential versus Ag-AgCl reference electrode was found to be -339 mV, -390 mV and -355 mV for hemin complexes with ligand -OH, imidazole (ImH) and 1-methyl imidazole (1-MelmH), respectively. Compared to aqueous solutions where hemin exists as aggregated species, hemin encapsulated in liposomes shows a large positive shift of the redox potential of ca. 100 mV. The apolar nature of the local heme environment stabilizes the Fe(II) oxidation state relative to the Fe(III) state. Electron transfer at the heme is influenced by the uptake/release of protons with ca. -59 mV shift of potential per unit change of pH (ΔE/ΔpH).