Electrochemical studies of the permeation of FAD and UQ₀ into the self-assembled n-alkanethiol monolayer formed on a gold electrode

The effect of the self-assembled n-alkanethiol monolayer formed onto a gold surface on the voltammetric responses of flavin adenine dinucleotide (FAD), ubiqainone-0 (2,3-dimethoxy-5-methy1-1,4-benzoquinone, UQ₀), and Fe(CN)³⁻₆ has been investigated in relation to the permeability of these species. In contrast to the Fe(CN)^3-₆ ion that was practically unable to permeate into the alkanethiol monolayer assembly, FAD and UQ₀ molecules were found to permeate more easily into the monolayer assembly. The apparent heterogeneous rate constant, k⁰, of Fe(CN)³⁻₆ decreased exponemially with the chain length of the modified alkanethiols. The dependence of the k⁰ value of FAD on the chain length showed the deviation from exponential decay. In contrast, the k⁰ value of UQ₀ was found to be scarcely affected by the chain length of the modified alkanethiols. The differences in the dependence of the k° values on the chain length were attributed to the differences in the permeability of these redox species into the hydrophobic monolayer assembly of the alkanethiols.