Phospholipid and gramicidin–phospholipid-coated mercury electrodes as model systems of partially blocked electrodes

Impedance measurements in a wide frequency range concerning Tl+ reduction on dioleoylphosphatidylcholine (DOPC)-coated mercury electrodes and on gramicidin-modified DOPC-coated mercury electrodes have been analysed according to the equations for reductions on partially blocked electrodes. In both cases the frequency dispersion of the impedance data fit well the impedance equations and from the analysis the fraction of active area, (1 − θ) and the radius of pinholes, Ra, have been obtained. In the case of the reduction on the gramicidin-modified DOPC-coated mercury electrode, the Warburg coefficient, σ and the forwards rate constant, kf, for the reduction have been obtained at different potentials. The potential dependence of σ fit well the equation for simple one-electron transfer under dc-reversible conditions, thus proving the internal consistence of the model. The potential dependence of kf provides the standard rate constant, ks, and the charge transfer coefficient, α for the electron transfer.