Pressure effect on reversed micelles in water: An infrared spectroscopic study of aqueous dioleoyl phosphatidylethanolamine

摘要

Infrared spectra of aqueous dispersions of reversed micelles of dioleoyl phosphatidylethanolamine have been obtained at constant temperature (i.e. 28deg;C) as a function of pressure up to 55 kbar. The changes detected in different infrared spectral parameters indicate that a major structural phase transition occurs at 9 kbar. From a comparison of the barotropic and thermotropic phase behavior of the reversed micelles in water it is concluded that the pressure event at 9 kbar corresponds to a micellarndash;lamellar transition that encompasses the two thermal events that occur at 5 and minus;4thinsp;deg;C. It is shown that water (D2O) molecules are unable to penetrate the micelles and form hydrogen bonds with the C=O ester groups of the interface region even at pressures as high as 55 kbar. The absence of correlation field splitting bands in the gel phase at high pressures (up to 55 kbar) suggests that the bent oleoyl acyl chains are closely packed with all chains oriented parallel to each other.