Deuterium magnetic resonance of selectively deuterated cholesteryl esters in dipalmitoyl phosphatidylcholine dispersions.

Dispersions (50 wt% water) containing 95 mol% dipalmitoyl phosphatidylcholine/5 mol% deuterated cholesteryl palmitate (or stearate) were studied using 2H-NMR. Incorporation of ester into the phospholipid bilayer was found to be 0.5 mol% at 50 degrees C. From the profile of 2H quadrupolar splitting vs. chain position, support for an average conformation resembling a 'horseshoe' within the bilayer is obtained. Quadrupolar relaxation times T2e of approx. 250 microseconds and approx. 850 microseconds are measured for cholesteryl palmitate-2,2-d2 and cholesteryl palmitate-16,16,16-d3, respectively, which are less than one-half those obtained for the corresponding positions in dipalmitoyl-d62 phosphatidylcholine. This is ascribed to a slower rate of motion of the ester chain and/or an extra, slow motion of the molecule.