Membrane models assembled on electrodes are widely used tools to study potential-dependent molecular processes at or in membranes. Examples are tethered bilayer lipid membranes (tBLM) or protein-tethered membranes. However, the relationship between the electrode potential and the potential across the membrane is not known. In this project, we first focused on study tBLMs, which consist of lipid bilayers immobilized on mixed self-assembled monolayers (SAMs) on Au electrodes. The mixed SAM is composed of thiol derivatives of different chain lengths such that between the islands of the short one and the tethered lipid bilayer an aqueous compartment is formed. For the present study, mercaptobenzonitrile (MBN) was used as the short SAM component. The nitrile function of MBN which serves as a reporter group for the vibrational Stark effect (VSE), is probed by surface enhanced infrared absorption spectroscopy to determine the local electric field as a function of the electrode potential for pure MBN, mixed SAM, and the bilayer system. In parallel, we calculate electric fields at the VSE probe by molecular dynamics (MD) simulations for different charge densities on the metal, thereby mimicking electrode potential changes. The expected results of the present combined experimental-theoretical approach promise to promote the description of potential-dependent processes at biomimetic interfaces. The project is funded by the Cluster of Excellence UniSysCat.
Collaborations: HU Berlin: J. Kozuch; FMP Berlin: T. Utesch.