Anodic oxidation of oxidized forms of coenzymes Q(10) and Q(0) on carbon electrodes in acetic acid solutions.

The anodic oxidation of oxidized forms of coenzyme Q(10) (ubiquinone, CoQ(10)) and Q(0) (CoQ(0)) 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/CoQH(2) 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 CoQ(10) is higher than for CoQ(0). This indicates that oxidation also proceeds in an unsaturated isoprene side chain. Smaller oxidation potentials for CoQ(10) 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 CoQ(10) is much smaller than that of reduced CoQ(10) (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 CoQ(10) in living cells.