Deuterium magnetic resonance study of cholesteryl esters in membranes

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Abstract
The ternary systems EYL(egg yolk lecithin):H2O (50:50 wt %) containing 1 and 5 mol % cholesteryl palmitate-d31 or 1 and 5 mol % cholesteryl palmitate-16,16,16-d3 were studied. Cholesteryl palmitate-d31 gave a unique 2H NMR corresponding to a homogeneous and a solid phase. From the characteristic spectra and spin-lattice relaxation times, a procedure for calculating the amount of each phase present in the ternary mixture is given resulting in a maximum value of homogeneously dissolved cholesteryl palmitate of 0.2 .+-. 0.1 mol % and a solid fraction above 0.2 mol %. The most probable order parameter for the (-CD2)n portion of the homogeneous fraction of cholesteryl palmitate-d31 was determined from the quadrupolar splittings to be S = 0.1 which is less than 1/2 that of the order parameter found for the lecithin chains. Possible explanations for the diminution of the order parameter for cholesteryl ester in bilayers are discussed.