Attenuated total reflection Fourier transform infrared spectroscopic characterization of fluid lipid bilayers tethered to solid supports

Attenuated total reflection Fourier transform infrared spectroscopy has been developed to monitor the tethering of phospholipid bilayers to gold-coated, ZnSe crystals. Bilayer attachment has been accomplished by fusing lipid vesicles onto a self-assembled monolayer comprised of a mixture of 2-mercaptoethanol (EO1) and a hexaethyleneoxythiol derivative of cholesterol (EO6C). The cholesteryl moieties penetrate into the lower leaflet of the bilayer and serve to "anchor" the bilayer to the solid support. For fractional surface area coverage of EO6C < 0.24, no lipid adsorption was detected, while for higher EO6C coverages, bilayers are formed with the outer and inner leaflets comprised, respectively, of pure lipid and the complementary lipid/cholesteryl mixture. From a thermodynamic analysis of this result we conclude that the initial step in bilayer self-assembly onto the surface is adsorption and rupture of a single lipid vesicle. The frequencies of the lipid CH2 stretching vibrations are characteristic of a fluid liquid-crystalline bilayer.