Deuterium nuclear magnetic resonance investigation of dimyristoyllecithin--dipalmitoyllecithin and dimyristoyllecithin--cholesterol mixtures.

Deuterium nuclear magnetic resonance (NMR) spectra of 1,2-dimyristoyl-3-sn-phosphatidylcholines (DMPCs) specifically deuterated in the 2-chain at one of positions 2', 3', 6', or 14' have been obtained by the quadrupole-echo Fourier transform method at 34.1 MHz (corresponding to a magnetic field strength of 5.2 T) or the pure material as a function of temperature, and in the presence of either 1,2-dipalmitoyl-3-sn-phosphatidylcholine (DPPC) or cholesterol as a function of temperature and composition. The results with pure DMPC and DMPC--DPPC mixtures indicate that a sharp, intense deuterium resonance is characteristic of fluid-phase lipids, whereas a broad resonance is characteristic of solid-phase lipids. There is shown to be good agreement between the deuterium NMR derived DMPC--DPPC phase diagram and that derived by using other techniques. The deuterium NMR results obtained with the DMPC--cholesterol system are not interpreted in terms of a phase diagram. They do indicate, however, that the transition breadth is increased considerably and the temperature at which the lipid chains "solidify" is depressed by the addition of cholesterol to the DMPC bilayer. The particular nature of the increase and the depression is found to be dependent on where the label is located on the lipid.