Distribution of lipids in non-lamellar phases of their mixtures

TL;DR

This paper models lipid phase behavior using self-consistent field theory, revealing how lipid architecture influences phase formation and distribution in mixtures, with implications for understanding membrane structures.

Contribution

It introduces a theoretical model predicting lipid phase diagrams and distribution patterns in mixtures, highlighting the role of lipid architecture and curvature effects.

Findings

Phase diagram includes body-centered cubic, hexagonal, gyroid, and lamellar phases.

Non-lamellar lipids are found in regions difficult for tails to reach.

Volume fraction variations correlate with mean curvature changes.

Abstract

We consider a model of lipids in which a head group, characterized by its volume, is attached to two flexible tails of equal length. The phase diagram of the anhydrous lipid is obtained within self-consistent field theory, and displays, as a function of lipid architecture, a progression of phases: body-centered cubic, hexagonal, gyroid, and lamellar. We then examine mixtures of an inverted hexagonal forming lipid and a lamellar forming lipid. As the volume fractions of the two lipids vary, we find that inverted hexagonal, gyroid, or lamellar phases are formed. We demonstrate that the non-lamellar forming lipid is found preferentially at locations which are difficult for the lipid tails to reach. Variations in the volume fraction of each type of lipid tail are on the order of one to ten per cent within regions dominated by the tails. We also show that the variation in volume fraction is correlated qualitatively with the variation in mean curvature of the head-tail interface.