A procedure for estimating the absolute potential difference across metal|water interfaces: A reassessment

Abstract

The estimate of the absolute potential difference across metal|aqueous solution (M|W) interfaces is of paramount importance to compare the behavior of ion channels incorporated in metal-supported biomimetic membranes with that in biomembranes and, most importantly, to obtain further behavioral information by the use of surface sensitive techniques. In 2011 Guidelli and Becucci described a procedure based on the use of a thiolipid called DPTL, consisting of a tetraethyleneoxy (TEO) hydrophilic chain terminated at one end with a lipoic acid residue, for anchoring to the mercury surface, and covalently linked at the other end to two phytanyl chains mimicking the hydrocarbon tails of a phospholipid. DPTL has been widely employed to fabricate metal supported tethered bilayer lipid membranes (tBLMs) by anchoring it to the metal surface of Hg, Au, and Ag. The above procedure relies on an independent estimate of the surface dipole potential χTEO of the TEO chain tethered to Hg and on the reasonable assumption that it remains unaltered when tethered to other metals. The present note corrects an erroneous estimate of the absolute potential difference across a polycrystalline Au|W interface in the 2011 paper, provides a clearer explanation of the procedure using the concept of electrochemical potential of electrons, estimates the absolute potential difference across the Au(111)|W interface, and compares the results of the proposed procedure with Trasatti’s ‘interfacial term’.