Fourier transform infrared spectroscopy has been used to examine the structural dynamics of lipid fatty acyl chains, lipid/water interface and phosphate headgroup of phospholipid mixtures containing dioleoylphosphatidylethanolamine (DOPE) and dioleoylphosphatidylcholine (DOPC) in lamellar liquid crystalline (L,,) and inverted hexagonal (H u) phases. The CH 2 symmetric stretching, C=O stretching and O=P=O symmetric and antisymmetric stretching bands of the lipids were measured at different lipid compositions (0-100% DOPE) and temperatures (0-75ยฐC). For pure DOPE, a significant increase in the C=O and a slight increase in the CH 2 stretching frequencies were found at 5-10ยฐC which corresponds to the known La-HII transition temperature of DOPE. No significant changes were observed for the O=P=Q symmetric and antisymmetric frequencies. Upon increasing the content of DOPC in the DOPE/DOPC binary mixtures, the La-H H transition became broadened and shifted to higher temperatures. This behavior was further quantitated by the use of a contour plot of C=O frequency as a function of temperature and PE%. Ternary mixtures of DOPE/DOPC/tetradecane were also studied at a fixed DOOPE/DOPC ratio (75:25) and at 23ยฐC. The C=O stretching frequency increased as the oil concentration varied from 0ยฐ/, to 6% (oil/lipid weight"/,,) and remain constant as the oil content increased from 6-20%. A slight decline in the CH 2 frequency was also noticed at 6-8% tetradecane. These results agreed with the known HI! promotion effect of tetradecane in the binary DOPE/DOPC mixtures.