Directional Electron Transfer from Ubiquinone-10 to Cytochrome <i>c</i> at a Biomimetic Self-Assembled Monolayer Modified Electrode

Abstract

The redox behavior of cytochrome c (Cyt c) at a ubiquinone-10 (UQ) incorporated self-assembled monolayer (SAM)-modified electrode was studied by cyclic voltammetry. A well-defined catalytic wave due to the reduction of Cyt c by UQ was observed at around −0.4 V vs. Ag/AgCl (saturated KCl). However, the re-oxidation peak of UQ at around +0.3 V was small, suggesting no significant catalytic ability of UQ for the re-oxidation of Cyt c. These voltammetric behaviors could be well simulated by digital simulation with a simple reaction model in which UQ and Cyt c coexist homogeneously in a reaction layer on the base gold electrode. The parameters obtained by curve fitting of cyclic voltammograms showed that the re-oxidation of Cyt c by UQ is somewhat thermodynamically unfavorable and, importantly, kinetically slow. This slow process is probably originated from spatial separation between the redox species. Such a directional or one-way electron transfer may be occurring in the mitochondrial respiratory chain system to achieve efficient energy production.

Water Interface the Simplest and Best Suited Model for Understanding Biomembranes?

“…The formation of the DM-SAM on a gold disk electrode and the incorporation of UQ therein were performed in a similar manner as reported previously. [8][9][10] As seen in the figure, a pair of well-defined cathodic and anodic peaks were observed for the electrode reaction of UQ (UQ + 2e -+ 2H +  H2UQ). These peaks were much widely separated by more than 0.8 V; this suggests a very strong inhibition effect of the SAM on the electrode reaction.…”

“…We would like to add that in the absence of UQ, Cyt c gave a weak and ill-defined voltammetric signal at around -0.4 V vs. Ag/AgCl (saturated KCl). 10 Here, it should be stressed that the anodic peak for the re-oxidation of UQ was almost unchanged in amplitude, though the peak potential was somewhat shifted to a more negative value (this is probably because of the facilitation of proton transfer induced by a structural disorder of the SAM due to the hydrophobic adsorption of Cyt c). This result suggested no significant catalytic activity of UQ for the re-oxidation of Cyt c. In order to fathom the cause of such directional or one-way ET, we performed a theoretical analysis using digital simulation with a simple reaction model.…”

“…Thus, the O | W interface provides a reaction field for understanding ET behaviors of biological species in a biomembrane-like two-phase system, however its characteristics as the reaction field of ET appear to be rather different from those of biomembranes. This view has come from our recent voltammetric study 10 on the ET between ubiquinone-10 (UQ) and Cyt c at a SAM modified electrode, the surface of which seems to have more "biomembrane-like" characteristics than the O | W interface.…”

“…Biologically significant processes including respiratory and photosynthetic energy production and neural transmission occur in biomembranes. 1 To understand electron transfer (ET) and ion transfer (IT) processes occurring in such biological systems, various biomembrane models have been proposed, which include oil-in-water emulsion, 2 planar or supported bilayer lipid membrane, [3][4][5][6] self-assembled monolayer (SAM) modified electrode, [7][8][9][10] and the interface between two immiscible electrolyte solutions (ITIES), the so-called oil | water (O | W) interface. [11][12][13] A voltammetric technique with the polarized O | W interface, which we call ion-transfer voltammetry (ITV), is very promising for understanding the membrane potential-dependent ET/IT processes in biological systems.…”

Tailoring the electrochemical interface of mesoporous carbon with ubiquinone for detection of parabens in cosmetics

“…From the graph, MPC/Q10 shows enhanced electrocatalytic activity than MPC and Q10 itself in determining paraben and its derivatives. This may be due to the combination of MPC which gives higher electron transfer property and Q10 which enhances the current response because of its redox activity …”