Collect. Czech. Chem. Commun. 1995, 60, 719-735

Molecular Dynamics of Vesicles of Unsaturated Phosphatidylcholines Studied by 13C NMR Spin-Lattice Relaxation

Jaroslav Zajíčeka, Jeffrey F. Ellenab, Gerald D. Williamsc, Mohammad A. Khadimd and Michael F. Browne

a University NMR Spectroscopy Center, Washington State University, Pullman, WA 99164, U.S.A.
b Department of Chemistry, University of Virginia, Charlottesville, VA 22901, U.S.A.
c Department of Radiology, Pennsylvania State Medical Center, Hershey, PA 17033, U.S.A.
d Hoechst Celanese Corporation, Coventry, RI 02816, U.S.A.
e Department of Chemistry, University of Arizona, Tucson, AZ 85721, U.S.A.


13C spin-lattice relaxation times, T1Z, were measured at four different magnetic field strengths for a vesicles of a series of unsaturated 1,2-diacyl-sn-glycero-3-phosphocholines over the temperature range from 5 to 50 °C. The acyl chains of the phosphatidylcholines varied in length from 14 to 18 carbons and in the degree of unsaturation: myristoleoyl (14 : 1), palmitoleoyl (16 : 1), oleoyl (18 : 1), linoleoyl (18 : 2), linolenoyl (18 : 3). For each of the phosphatidylcholines studied the R1Z = (NT1Z)-1 values of the acyl chain methylene carbons, where N is the number of directly bonded hydrogens, decreased from the C2 position which is situated close to the glycerol backbone towards the acyl terminal methyl group. The effect of the double bond was manifested by an increase in R1Z and was less pronounced if it was located closer to the terminal methyl group than in the middle of the chain. A minimum in the T1Z relaxation times was not observed, even for highest frequency of 125.8 MHz and the lowest temperature of 5 °C. In the case of the phosphocholine headgroup and glycerol backbone carbons the T1Z times showed similar temperature and frequency dependencies as the acyl chain carbons. The results of the measurements indicate substantial differences in the dynamics of these systems in the liquid-crystalline state. Analysis of the data using various dynamical models is consistent with a distribution of motions which is not described by a single Lorentzian spectral density. This dispersion appears to be an inherent feature of the dynamics of phosphatidylcholines in the liquid-crystalline state.