Monolayer and Bilayer Structures of Mixtures of Ceramide IIIb and c16-Alkyl Glucosides

Abstract

Ceramides, one of the major lipid components in the stratum corneum, have been increasingly used in several topical applications of cosmetic and medical products, and the balanced use of ceramides has been shown to be critical to their stability. In this work, we performed molecular dynamics simulations of monolayer and bilayer structures composed of varying compositions of ceramide IIIb and a surfactant (c16-alkyl glucosides). The monolayer was simulated in the interface between water and an oily phase composed of capric triglycerides and the bilayer was in explicit water. We investigated the effect of ceramide IIIb composition on the structural stability of monolayers and bilayers by calculating the area per lipid and the equilibrium structures by observing simulation snapshots and analyzing density profiles along the direction perpendicular to the layers. The results showed that the monolayers in the interface and the bilayers in water reached equilibrium within simulation duration of 100 ns and the layer structures were more ordered at higher ceramide contents. The composition-dependent difference in the order of lipid molecules was interpreted in terms of the difference in the numbers of lipid tails in ceramides and surfactants and, hence, the difference in the spatial volume occupied by head and tail groups of both lipids. The differential volume occupation also resulted in different vertical arrangements of both lipid molecules.