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 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.