STRUCTURE OF AQUEOUS MIXTURES OF LECITHIN AND CHOLESTEROL

Mixtures containing varying proportions of lecithin, cholesterol and water have been systematically examined by X-ray diffraction in connexion with the established phase diagram of this ternary system. The dimensions of the mixed lipidic layers and that of the intercalated layers of water have thus been determined as a function of the percentage of the different components. The maximum quantity of cholesterol which can be associated with lecithin in the presence of water is 33% (about 1 mole to 1 mole). Before reaching this maximum, the properties of the mixed system undergo a change when a proportion of about 20% of cholesterol is reached (about 1 mole to 2 moles of lecithin). The mean molecular areas of the lipidic molecules in this liquid crystalline structure have been compared to the mean molecular areas of the same mixtures spread as monolayers on the surface of water. Although in the fluid state, the hydrocarbon chains of the lecithin in this aqueous phase have a limited degree of freedom, corresponding to that of a condensed layer. © 1969.