Addition of hydrophilic and lipophilic compounds of biological relevance to the monoolein/water system. I. Phase behavior

The solubilization of hydrophilic and lipophilic molecules, with biological relevance. in the monoolein/water (MO/W) system has been investigated for phase behavior. Small angle X-ray scattering (SAXS). nuclear magnetic reson ance (NMR) and optical microscopy (OM) have been used to characterize the m icrostructure Of the liquid crystalline phases. Partial phase diagrams of t he MO/W system in the presence of sodium decanoate, 1-adamantanamine hydroc hloride. decanoic and dodecanoic acids, acetyl salicilic acid and retinol h ave been determined. The stability of the various phases has been follow ed for at least eight months. The polarity and the molecular structure of the additive determine whether it is located at the polar interface or in the apolar legion of the lipid layer. Therefore, the additive affects the inter facial curvature of the lipid layer differently. which in turn will trigger transition to disparate phases. A cubic-to-reverse hexagonal phase transit ion has been observed with time for most of the ternary systems. with the e xception of 1-adamantanamine hydrochloride and retinol. The release of free glycerol and oleic acid due to MO hydrolysis has been clearly demonstrated by C-13 NMR. This would account for the changes in phase behavior observed with time. The released oleic acid, located in the MO acyl chain region, f avors the inverse interfacial curvature. The average lipid dimensions in th e cubic and in the reverse hexagonal phases have been calculated from SAXS data. (C) 2001 Elsevier Science Ireland Ltd. All rights reserved.