INTERACTIONS AND STRUCTURE-ORGANIZATIONS OF MENAQUINONE-4 AND EGG-YOLK PHOSPHATIDYLCHOLINE MIXTURES - FORMATION OF BILAYER AND NONBILAYER STRUCTURES IN AN AQUEOUS-MEDIUM

Structure-organizations of menaquinone-4 and egg yolk phosphatidylcholine mixtures in an aqueous medium were investigated on the basis of electron microscopic, small-angle X-ray scattering, spreading pressure, and trapped volume measurements. The electron microscopic and trapped volume results showed a bilayer formation of the mixture in the MQ4 mole fraction range 0 to 0.8. Intrabilayer-reversed micelles and small unilamellar vesicles in a larger bilayer vesicle were observed as irregular structures in the electron microscopic pictures. The small-angle X-ray scattering profiles indicated coexistence of a nonbilayer phase with bilayers in the hydrated lipid mixture. The nonbilayer phase was tentatively assigned as a cubic phase of reversed micellar aggregates. The spreading pressure measurements showed that the compositions of the bilayers and cubic phase in terms of the MQ4/PC mole ratio were 2 8 and 9 1, respectively. An incomplete hydration of the mixture led to the concomitant formation of reversed hexagonal phases. The irregular structures in bilayers, especially reversed micelles, are expected to give rise to fusion and aggregation of dispersed particles of the lipid mixture in an aqueous medium. © 1992.