Potassium ion transport by gramicidin and valinomycin across a Ag(111)-supported tethered bilayer lipid membrane

A tethered bilayer lipid membrane (tBLM)was prepared by anchoring a thiolipid monolayer to a Ag(1 1 1) single crystal froma thiolipid solution in ethanol; a diphytanoylphosphatidylcholine monolayerwas then self-assembled on top of the thiolipid monolayer froma lipid solution in hexane or ethanol. The thickness of the mixed thiolipid|lipid bilayer was estimated at 7.5±0.5nm by scratching holes in the tBLM with an AFM tip and determining their height profile and the frequency distribution of height. The effect of the incorporation of gramicidin A and valinomycin upon K+ ion transport across the tBLM was investigated by electrochemical impedance spectroscopy. The position of the inflection point of the sigmoidal curve of the in-phase component of the electrode admittance against potential allowed the determination of an approximate scale of the absolute potential difference across the whole Ag(1 1 1)|(aqueous solution) interface, on the basis of a model of the electrified interface.