ELECTROREDUCTION OF DIOCTADECYLVIOLOGEN IN A SELF-ASSEMBLED PHOSPHOLIPID MONOLAYER ON MERCURY AND ITS ROLE AS AN ELECTRON MEDIATOR

The electroreduction mechanism of dioctadecylviologen (V2+) incorporat ed in a self-assembled dioleoylphosphatidylcholine (DOPC) monolayer su pported on a mercury electrode has been investigated in aqueous 0.1 M KCl by chronocoulometry and other electrochemical techniques. V2+ is r educed 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 reac tant, respectively. Both charge steps are exclusively controlled by th e rate of the elementary coupling step Vf + V-0 --> V-2(+). V2+ acts a s an electron transfer mediator from Fe(CN)(6)(3-) dissolved in the aq ueous solution to the mercury surface across the DOPC monolayer, which is impermeable to Fe(CN)(6)(3-) in the absence of V2+. This mediation takes place only along the first charge step, 2V(2+) + 3e --> V-2(+) and increases with the V2+ concentration in the lipid monolayer less t han proportionally; this behavior points to the radical cation V+ as t he electron transfer mediator from the mercury surface to the aqueous ferricyanide.