The thermotropic behavior of dipalmitoyl phosphatidylcholine bilayers. A Fourier transform infrared study of specifically labeled lipids.

Fourier transform infrared spectroscopy has been used to study the thermotropic behavior of hydrated multibilayers of specifically deuterated derivatives of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. It is shown that throughout the gel phase there is little or no conformational disorder introduced into the acyl chains. The pretransition effect is greatest in the central segments of the acyl chains, demonstrating that the interchain interactions are more pronounced in this region than in the center of the bilayer and suggesting the presence, in the gel phase, of a "plateau" in the strength of the interchain interactions. As the temperature is reduced, the rate of rotation of the terminal methyl group decreases steadily; below 0 degree C the conformation is rigid on the infrared time scale.