Phospholipid/cholesterol membranes containing n-alkanols: a 2H-NMR study

The influences of 1-octanol and 1-decanol on aqueous multilamellar dispersions of 1-hexadecanoyl(octadecanoyl)-2-[2H31]hexadecanoyl-sn-glycero -3-phosphorylcholine (PC-d31)/cholesterol (3:1) have been examined using 2H-NMR. The gel to liquid crystalline phase transition of the PC-d31/cholesterol dispersion is modulated by the addition of 1-alkanol, which reduces the onset temperature and increases the width of the transition. 1-Octanol has a greater effect on the transition onset and completion temperatures than does 1-decanol, as determined from analysis of the temperature-dependent 2H-NMR spectra. 2H-NMR C-2H bond order parameters as a function of phospholipid acyl chain position at 60 degrees C, where all dispersions are fully liquid crystalline, have been calculated from the depaked spectra. 1-Decanol reduces the phospholipid order by only 2%. This can be attributed to the lower effective cholesterol concentration in the 1-alkanol/PC-d31/cholesterol dispersions. 1-Octanol, however, reduces the phospholipid order by 10% at 60 degrees C. Correlations between the effects of 1-octanol and 1-decanol on phospholipid order parameters and phospholipid/cholesterol phase transitions are discussed.