Functional molecular films at electrode surfaces

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The general objective of this project is to study the structure and reactivity of functional monolayers and bilayers of phospholipids deposited onto a metal electrode at the metal-solution interface. The functionality of these films will be determined by the presence of peptides and proteins. Our goal is to learn how phospholipid molecules aggregate to form monolayer or bilayer films. What is the stability of these films in the presence of electric fields that are comparable in magnitude to the fields acting on biological membranes? How do these fields affect ordering of molecules within the membrane and how they cause a phase transition from the liquid crystalline to the gel state? We are also interested to learn how the electric field affects the stability of mixed bilayers composed of phospholipids and cholesterol, the incorporation of proteins into the bilayer and electron and ion transfer through proteins incorporated into the supported bilayer. To achieve these goals, we will employ electrochemical methods, scanning probe microscopies such as scanning tunneling microscopy (STM) and atomic force microscopy (AFM), in situ photon polarization modulation Fourier transform infrared reflection absorption spectroscopy (PM-IRRAS), circular dichroism in the UV and neutron scattering techniques. The metal electrode surface, covered by a film of surfactants or phospholipids, can be charged and electric fields on the order of 10^7 - 10^8V/m can be applied to these supported films. These fields have comparable magnitude to the fields acting on biological membranes. The field may be conveniently used to manipulate organic molecules within the monolayer and the bilayer membrane. By controlling the field, one can force phase transitions in the film of organic molecules or force them to disperse or to aggregate at the surface. We will use electrochemical techniques to control the physical state of the film and the scanning probe microscopies to image the field-driven transformations of the membranes. In addition, spectroscopic and neutron scattering techniques will be employed to study conformational changes of organic molecules and their ordering within the membrane.