ATTENUATED TOTAL-REFLECTION FOURIER-TRANSFORM INFRARED SPECTROSCOPIC CHARACTERIZATION OF FLUID LIPID BILAYERS TETHERED TO SOLID SUPPORTS

Attenuated total reflection Fourier transform infrared spectroscopy ha s been developed to monitor the tethering of phospholipid bilayers to gold-coated, ZnSe crystals. Bilayer attachment has been accomplished b y fusing lipid vesicles onto a self-assembled monolayer comprised of a mixture of 2-mercaptoethanol (EO1) and a hexaethyleneoxythiol derivat ive of cholesterol (EO6C). The cholesteryl moieties penetrate into the lower leaflet of the bilayer and serve to ''anchor'' the bilayer to t he solid support. For fractional surface area coverage of EO6C < 0.24, no lipid adsorption was detected, while for higher EO6C coverages, bi layers are formed with the outer and inner leaflets comprised, respect ively, of pure lipid and the complementary lipid/cholesteryl mixture. From a thermodynamic analysis of this result we conclude that the init ial step in bilayer self-assembly onto the surface is adsorption and r upture of a single lipid vesicle. The frequencies of the lipid CH2 str etching vibrations are characteristic of a fluid liquid-crystalline bi layer.