Estimate of the potential difference across metal/water interfaces and across the lipid bilayer moiety of biomimetic membranes: an approach

Abstract

Mercury is a particularly advantageous support of lipid, thiol and disulfide self-assembled monolayers (SAMs), because it provides them with a perfectly smooth and fluid surface and allows their gradual expansion in aqueous solution with progressive tilt of the adsorbed molecules, without water incorporation. These unique advantageous features permit an estimate of the extrathermodynamic absolute potential difference, ϕ, across the Hg|water interface and of the surface dipole potential of mercury-supported SAMs. Two different models of metal-supported tethered bilayer lipid membranes (tBLMs) incorporating a cation-selective channel predict that the ϕ value at the inflection point of a plot of the in-phase component, Y′, of the electrochemical admittance against the applied potential E is almost coincident with the surface dipole potential, χ_s, of the hydrophilic spacer moiety of the tBLM. This prediction allows an estimate of the absolute potential difference, ϕ, across the interface between any metal capable of supporting tBLMs and the bulk aqueous phase, provided the χ_s value of the tBLM is known. Moreover, the potential difference across the lipid bilayer moiety of the tBLM (i.e., the transmembrane potential) is shown to be practically equal to χ_s at the inflection point of the corresponding Y′ vs.E plot. This approach is applied to polycrystalline Au and Ag(111).