Electroreduction of Dioctadecylviologen in a Self-Assembled Phospholipid Monolayer on Mercury and Its Role as an Electron Mediator

The electroreduction mechanism of dioctadecylviologen (V 2+ ) incorporated in a self-assembled dioleoylphosphatidylcholine (DOPC) monolayer supported on a mercury electrode has been investigated in aqueous 0.1 M KCl by chronocoulometry and other electrochemical techniques. V 2+ is reduced in two consecutive charge steps, 2V 2+ + 3e → V 2 + and V 2 + + e → 2V 0, involving 3/2 and 1/2 of a Faraday per mole of reactant, respectively. Both charge steps are exclusively controlled by the rate of the elementary coupling step V + + V 0 → V 2 + . V 2+ acts as an electron transfer mediator from Fe(CN) 6 3- dissolved in the aqueous solution to the mercury surface across the DOPC monolayer, which is impermeable to Fe(CN) 6 3- in the absence of V 2+ . This mediation takes place only along the first charge step, 2V 2+ + 3e → V 2 + and increases with the V 2+ concentration in the lipid monolayer less than proportionally; this behavior points to the radical cation V + as the electron transfer mediator from the mercury surface to the aqueous ferricyanide.