HIGH-PRESSURE H-2 NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE GEL PHASES OF DIPALMITOYLPHOSPHATIDYLCHOLINE

The H-2-NMR lineshapes of dipalmitoylphosphatidylcholine perdeuterated in the acyl chains were studied in a 15% dispersion in water as a function of pressure from 1 bar to 5 kbar over the temperature range from 7-degrees-C to 75-degrees-C. Increasing pressure in the gel state had the same effect as lowering the temperature: the lineshape gradually changed from a motionally averaged to a rigid lattice type spectrum with much of the intensity in the shoulders at +/- 63 kHz. At very high pressures and low temperatures (7-degrees-C, 2.5 kbar; 25-degrees-C, 5 kbar) even the methyl portion of the spectrum became a rigid lattice type spectrum at +/- 21 kHz. In addition to the liquid crystalline phase, five gel phases were detected. Using different techniques to determine the phase transitions, a general pressure-temperature phase diagram was constructed.