Nuclear magnetic resonance description of molecular motion and phase separations of cholesterol in lecithin dispersions.

Abstract
Proton-enhanced 13C NMR is used to obtain signals from labeled cholesterols in lecithin dispersions. The [26-13C]cholesterol resonance indicates that the aliphatic tail of the molecule undergoes reorientation fast enough to average completely the chemical shift anisotropy. In contrast, [4,13C]cholesterol signals are characteristic of limited anisotropic reorientation. The resonances from the 4 position are sensitive to the temperature-concentration phase diagram. A phase boundary is observed at about 20 mol % cholesterol.