Cholesterol rotation in phospholipid vesicles as observed by 13C-NMR.

13C-NMR spectra of cholesterol 90% enriched at C-4 with 13C have been obtained in CHCl3 and in sonicated egg phosphatidylcholine vesicles. 13C spin-lattice relaxation times, nuclear Overhauser effects and spin-spin relaxation times have been measured for the C-4 carbon of cholesterol in phosphatidylcholine bilayers as a function of cholesterol content and temperature. All the data are consistent with a correlation time for axial rotation of about 10(-10) s. This rotation is one or two orders of magnitude faster than axial rotation of the phospholipid molecule.