Anodic oxidation of oxidized forms of coenzymes Q10 and Q0 on carbon electrodes in acetic acid solutions

The anodic oxidation of oxidized forms of coenzyme Q10 (ubiquinone, CoQ10) and Q0 (CoQ0) on a glassy carbon macroelectrode (GC) and on a carbon fiber microelectrode (CF) was investigated in acetic acid using voltammetric techniques. Voltammograms recorded on these electrodes show well-defined peaks or waves in the potential range of above 1.5 V (vs. Ag/AgCl). The existence of these signals cannot be connected with the well-known redox couple CoQ/CoQH2 but may be attributed to the irreversible and diffusion-controlled two-electron oxidation of methoxy groups in molecules of coenzymes. The overall number of electrons involved in the anodic oxidation of CoQ10 is higher than for CoQ0. This indicates that oxidation also proceeds in an unsaturated isoprene side chain. Smaller oxidation potentials for CoQ10 in comparison to such unsaturated fatty acids as oleic, linoleic and linolenic ones indicate that this compound can show direct antioxidative properties. The antioxidative power of CoQ10 is much smaller than that of reduced CoQ10 (ubiquinol) and α-tocopherol. The results presented can be useful in the determination of this compound in real samples and in the assessment of biochemical properties of CoQ10 in living cells.

► Coenzymes Q10 and Q0 are oxidized on carbon electrodes in acetic acid solutions.
► Irreversible oxidation of methoxy groups of coenzymes.
► Additional oxidation of isoprene side chain of CoQ10.
► Direct antioxidative properties of ubiquinones.