Electric Field-Driven Transformations of a Supported Model Biological Membrane—An Electrochemical and Neutron Reflectivity Study

Abstract

A mixed bilayer of cholesterol and dimyristoylphosphatidylcholine has been formed on a gold-coated block of quartz by fusion of small unilamellar vesicles. The formation of this bilayer lipid membrane on a conductive surface allowed us to study the influence of the support's surface charge on the structure and hydration of the bilayer lipid membrane. We have employed electrochemical measurements and the specular reflection of neutrons to measure the thickness and water content in the bilayer lipid membrane as a function of the charge on the support's surface. When the surface charge density is close to zero, the lipid vesicles fuse directly on the surface to form a bilayer with a small number of defects and hence small water content. When the support's surface is negatively charged the film swells and incorporates water. When the charge density is more negative than -8 micro C cm(-2), the bilayer starts to detach from the metal surface. However, it remains in a close proximity to the metal electrode, being suspended on a thin cushion of the electrolyte. The field-driven transformations of the bilayer lead to significant changes in the film thicknesses. At charge densities more negative than -20 micro C cm(-2), the bilayer is approximately 37 A thick and this number is comparable to the thickness determined for hydrated multilayers of dimyristoylphosphatidylcholine from x-ray diffraction experiments. The thickness of the bilayer decreases at smaller charge densities to become equal to approximately 26 A at zero charge. This result indicates that the tilt of the acyl chains with respect to the bilayer normal changes from approximately 35 degrees to 59 degrees by moving from high negative charges (and potentials) to zero charge on the metal.

Ubiquinone-10 in gold-immobilized lipid membrane structures acts as a sensor for acetylcholine and other tetraalkylammonium cations

“…By performing slow potential scans when the electroactive liposome suspension is added to the electrochemical cell, it is possible to monitor the formation of the sensing layer. It has been reported that the structure of a lipid bilayer on a gold support changes according to the applied potential [31]. Slow scan rates allow the system to reach the equilibrium structure of the immobilized lipid layers at each potential.…”

“…It has been shown by Burgess et al [31] that changes in potential cause changes in the structure of the lipid membrane close to the surface and in the water layer usually found in between the lipids and the gold surface. Therefore, the water content, thickness, density and viscosity of the bilayer in contact with the sensor vary constantly upon potential scanning.…”

Application of Polarization Modulation Infrared Reflection Absorption Spectrosocpy Under Electrochemical Control for Structural Studies of Biomimetic Assemblies

“…Defects are present in these bilayers and the hydrocarbon chains at phospholipid molecules adapt a large tilt with respect to the electrode surface [8,120]. In order to increase the molecular-scale order in phospholipid bilayers obtained by vesicles spreading addition of cholesterol is necessary [9,11,32,88,126]. Phospholipid molecules in bilayers prepared by LB-LS transfer are closer packed, uniformly oriented, and show a higher degree molecular-scale order than lipid molecules in bilayers prepared by vesicles spreading [9,31,33,120,127,128].…”

Label-Free Characterization of Peptide–Lipid Interactions Using Immobilized Lipodisks

“…These systems can be used, e.g., as tools for the study of the properties of lipid membranes and how they are affected by the surrounding conditions (e.g., electric potential 1,2 , composition of the bulk solution 3 etc.). They are also of great interest as systems to study membrane-analyte interactions, including the study of peptide-and protein-membrane interactions 4,5 .…”