FOURIER-TRANSFORM INFRARED SPECTROSCOPIC ANALYSIS OF THE ESTER AND AMIDE BANDS OF THE HYDRATED DISPERSIONS OF N-ACYLETHANOLAMINE PHOSPHOLIPIDS

Fourier transform infrared spectroscopy was used to characterize the s tretching vibrations of the ester carbonyl groups and the amide I vibr ation of the amide group of N-acylphosphatidylethanolamine (N-acyIPE) bilayers. To obtain quantitative information about changes in hydratio n, band profiles were simulated with Gaussian-Lorentzian functions. Th e results are particularly significant since they probably reflect dif ferent changes in the hydrogen-bonding interactions in the polar/apola r interfacial region at the gel-liquid-crystalline phase transition of the N-acyIPE bilayers related to the N-acyl chain length. In the same way, the carbonyl eater interfacial region of N-acyIPEs is spectrosco pically similar to those of phosphatidylethanolamine bilayers, in whic h two populations of hydrogen-bonded ester carbonyl groups were observ ed. Moreover, our study provides additional data pertinent to the phys ical basis of the thermotropic phase behaviour of aqueous dispersions of N-acyIPEs and the basis of the differences between these bilayers a nd the more intensively studied phosphatidylcholine and phosphatidylet hanolamine bilayers. Copyright (C) 1996 Elsevier Science Ireland Ltd