A Biomimetic Membrane Consisting of a Polyethyleneoxythiol Monolayer Anchored to Mercury with a Phospholipid Bilayer on Top

A biomimetic membrane was obtained by anchoring a hydrophilic monolayer consisting of a triethyleneoxythiol (EO3) or hexaethyleneoxythiol “spacer” to a hanging mercury drop electrode and by interposing a lipid film previously spread on the surface of an aqueous electrolyte between the spacer-coated electrode and the aqueous solution. The impedance spectrum of this biomimetic membrane and its response to the incorporation of the ion carrier valinomycin and of the physiological quinone ubiquinone-10 indicate that it has a good fluidity and consists of a stable lipid bilayer on top of the hydrophilic spacer acting as an ionic reservoir. Upon incorporation of the channel-forming polypeptide melittin, this model system exhibits a conductance entirely analogous to that reported on black lipid membranes, with the appreciable advantage of a higher stability and resistance to disruption. The surface dipole potential of the EO3 monolayer alone was obtained from the extrathermodynamic “free charge density” q M on EO3-coated mercury, as experienced by the diffuse layer ions. The partial charge transfer from the sulfydryl group of EO3 to mercury was estimated from q M and from the thermodynamic “total charge density” σ M on EO3-coated mercury.