Deuterium nuclear magnetic resonance of phospholipids at high pressure

The effect of hydrostatic pressure on saturated diacyl phospholipids was studied using deuterium NMR. A probe for deuterium NMR studies of soil materials was constructed to operate at pressures up to 2.7 kbar. The response of the bilayer to hydrostatic pressure was found to be highly anisotropic in that the bilayer thickness was observed to increase as the pressure was raised. From the temperature and pressure dependence of the first spectral moments in perdeuterated DMPC, it was concluded that the effect of temperature on area, per lipid decreased with pressure. The main transition in DMPC-d54, was analyzed in terms of a Landau-type free energy model. In another series of experiments lipid headgroups were found to tilt toward the bilayer normal, in response to a pressure-induced reduction in the area per lipid molecule in the bilayer. Experiments where temperature was varied at, high and low pressure led to the conclusion that the headgroup response to temperature consists of two effects - a hcadgroup tilt and a temperature-induced methylene disorder. In a study of perdeuterated DLPC high pressure was found to remove the overlap between the main and the subtransition and to result in the appearance of a true gel phase below the liquid crystalline phase. The low temperature end of the liquid crystalline phase was found to be dominated by an intermolecular ordering process which substantially slowed the motions. In perdeuterated DPPC, high pressure was seen to promote the formation of a number of low temperature phases. When temperature was lowered, the system was observed to pass through the liquid crystalline phase, a possibly interdigitated phase, a phase that might reflect domination by intermolecular correlations, rather than chain order, and a highly ordered crystalline phase. Cholesterol in a DPPC membrane was found to reduce the effects of hydrostatic pressure on the membrane in (lie sense that aside from the pressure-induced temperature shift the ambient pressure phase behaviour was retained even at 2.2 kbar. No evidence was found to suggest that the positioning of the cholesterol molecule in the bilayer might be affected by pressure