13 C NMR measurements of unsonicated phosphatidylcholine bilayers of different fatty acid and sterol composition.

(1) 13C NMR linewidths were measured for various 13 C resonances in unsonicated dispersions of synthetic and natural phosphatidylcholines both in the absence and presence of cholesterol at temperatures where the acyl chains are in the liquid-crystalline state. (2) In the absence of cholesterol the linewidths of the various resolved chain resonances were decreased with increasing unsaturation and decreasing chain length. The motion of the delta9-cis olefinic carbon atoms in dioleoylphosphatidylcholine was more restricted than the motion of the delts9-cis olefinic carbon atoms in 1-stearoyl-2-oleoyl-phosphatidylcholine despite the higher overall fluidity of dioleoylphosphatidylcholine. The polar head-group motion was not dependent upon the fatty acid composition. (3) Incorporation of cholesterol broadens all observed chain resonances of all phosphatidylcholines, thus demonstrating a reduction in chain motion by cholesterol. For both the saturated and unsaturated phosphatidylcholines the reduction of the chain motion is decreased with increasing chain length. (4) The chemical shift of the carbonyl resonances of sonicated dipalmitoylphosphatidylcholine vesicle labelled with 13C in both chains in the 1-position was slightly decreased by the incorporation of 50 mol% of cholesterol. In contrast, 50 mol% of epicholesterol, the 3alpha0OH isomer, produced a large downfield shift and a splitting of the carbonyl resonance.