Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
The Raman spectrum of aqueous palmitoyl lysolecithin was monitored as a function of pressure between 1 bar and 26.1 kbar. The changes observed in these Raman spectra are discussed in terms of the effect of hydrostatic pressure on the phase state and the molecular structure of lysolecithins. At pressures between 1 and 1900 bar aqueous palmitoyl lysolecithin exists in a micellar state and at pressures above 1.9 kbar it converts into a series of three coagel phases. The critical pressures at 28°C are 1.9 kbar for the micellar to coagel I transition, 4 kbar for the coagel I to coagel II transition and 15 kbar for the coagel II to coagel III transition. The transition from the micellar phase to the coagel I phase has a high pressure hysteresis of 1.1 kbar, while the transitions between the three coagel phases show only negligible pressure hysteresis. The major change in structure occurs at 1.9 kbar where the cylindrical micellar phase converts to an interdigitated lamellar coagel phase; the structural changes at 4 kbar (coagel I/II transition) and at 15 kbar (coagel II/III transition) involve only a modification of the interchain packing.
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