Abstract: The temperature dependence of the infrared and Raman spectra of anhydrous dimyristoylphosphatidylethanolamine (DMPE ) was investigated in the temperature range from 290 to 405K. The spectra of the C-H,C=Oand PO₂^- stretching mode regions reflect that a cooperative phase transition occurs at about 365K. During the transition a significant lateral expansion of the lipid bilayer is present and accompanied both by an increased number of gauche rotamers within the hydrocarbon chain region and by muItiple conformers in both the head group and glycerol backbone moieties. When the lipids are rapidly cooled,the acyl chain region reorders without a concomitant reordering of the head group and interface region.

Key words: dimyristoylphsphatidylethanolamine, molecular conformation, infrared spec-troscopy, Raman spectroscopy