Pressure effects on the Raman spectra of phospholipid membranes: Pressure induced phase transitions and structural changes in 1,2-dimyristoyl 3-s n-phosphatidylcholine water dispersions

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Abstract
In a study of the pressure dependence of the Raman spectrum of an aqueous dispersion of dimyristoyl phosophatidylcholine from ambient pressure up to 5 kbar, three phase transitions have been observed at 150 bar and at 1 and 2.6 kbar. From the behavior of the spectrum, a correlation may be made between these phase transitions and temperature‐induced changes observed at 24, 14, and −60 °C, respectively. The major cause of the pressure‐induced frequency shift of all the Raman bands is the pressure‐enhanced interchain anharmonic interaction rather than the pressure‐induced compression of intramolecular bonds. It is further shown that the large angle reorientational fluctuations about the long axes of the acyl chains decrease with increasing pressure.