Bioelectrochemistry of Cytochrome c in a closed bipolar electrochemical cell

[Display omitted] •Bioelectrochemistry with a 4-electrode closed bipolar electrochemical cell is shown.•A biphasic configuration permits bioelectrochemistry with lipophilic redox species.•Electron transfer is observed between Cyt c and lipophilic decamethylferrocene.•This heterogeneous electron transfer is reversible using ITO bipolar electrodes. The reversible oxidation and reduction of Cytochrome c (Cyt c) is demonstrated with a closed bipolar electrochemical cell (CBPEC). Herein, a 4-electrode configuration was studied with the opposite poles of the bipolar electrode resting in separate aqueous and organic electrolyte solutions, respectively. Using biocompatible indium tin oxide (ITO) slides as the bipolar electrode poles, we investigated the influence of the redox potential of the reductant (decamethyferrocene or dimethylferrocene) in an α,α,α-trifluorotoluene organic phase on the observed voltammetry. Reversible electron transfer was only observed between Cyt c and decamethylferrocene. Use of the weaker dimethylferrocene as the reductant required a larger external bias of the driving electrodes to initiate the electron transfer reaction between the two poles of the bipolar electrode. Consequently, the surface of the ITO slide at the aqueous pole experienced a significant negative cathodic potential and underwent irreversible reduction. The biphasic setup using the 4-electrode CBPEC provides insights into electron transfer processes at an interface between two immiscible electrolyte solutions (ITIES), highlighting the strong probability of observing interfacial electron transfer between decamethylferrocene (but not dimethylferrocene) and Cyt c within the short ~1 V polarisable potential window available at an ITIES.