Evidence for acyl chain trans/gauche isomerization during the thermal pretransition of dipalmitoyl phosphatidylcholine bilayer dispersions.

In order to clarify, in dipalmitoyl phosphatidylcholine multilayers, the effect of the 34 degrees C thermal pretransition on the acyl chain intramolecular disordering process, Raman spectra of dipalmitoyl phosphatidylcholine gels at 20 and 34 degrees C were compared in the 1000--1200 cm-1 skeletal C-C stretching region. In addition to an overall intensity decrease associated with a change in chain packing characteristics, the growth of intensity in the 1080--1090 and 1122 cm-1 regions in the 34--20 degrees C) difference spectrum clearly indicates that the thermal pretransition is accompanied by an increase in the population of hydrocarbon chain gauche rotamers toward the center of the bilayer.