Miscibility behavior of ternary lipidphospholipid/water systems

Abstract

Differential-scanning-calorimetry was applied to study the lyotropic and thermotropic properties of the two ternary systems dimyristoylcephaline (di-(C14:0)-PE)/Palmitic acid (C15COOH)/water (H2O) and dimyristoylcephaline (di-(C14:0)-PE)/palmitic acid methyl ester (C15COOMe)/water (H2O) in dispersions with excess water (50 wt.%). The phase diagrams of both systems showed that the two systems differ in their miscibility behavior. The system di-(C14:0)-PE/C15COOH/H2O is completely miscible in its high-temperature phase. In the low-temperature phase the mixing gap was found within the concentration range of C15COOH and was also indicated by a maximum value of the transition enthalpy of the pseudo-binary mixtures. In the pseudo-binary system di-(C14:0)-PC/C15COOMe/H2O, the tendency towards demixing is much more pronounced. It was observed that the incorporated C15COOMe melted above its normal melting point, but below the transition temperature of di(C14:0)-PE/H2O system; therefore, the phase transition started at lower temperature. In the low-temperature phase, both lipids are partially miscible. The demixing range of the phase diagram lies within the concentration region of C15COOMe. Up to the mole fraction ofXC15COOMe=0.43, C15COOMe can be incorporated into theLβ-phase of the system di-(C14:0)-PE/H2O.