Molecular simulation study of phospholipid bilayers and insights of the interactions with disaccharides.

Molecular simulations of hydrated dipalmitoylphosphatidylcholine lipid bilayers have been performed for temperatures in the range of 250-450 K. The area per headgroup increases with temperature from 58 to 77 A(2). Other properties such as hydration number, alkyl tail order parameter, diffusion coefficients, and radial distribution functions exhibit a clear dependence on temperature. Simulations of bilayers have also been performed in the presence of two disaccharides, namely trehalose and sucrose, at concentrations of up to 18 wt % (lipid-free basis). The simulated area per headgroup of the bilayer is not affected by the presence of the disaccharides, suggesting that the overall structure of the bilayer remains undisturbed. The results of simulations reveal that the interaction of disaccharide molecules with the bilayer occurs at the surface of the bilayer, and it is governed by the formation of multiple hydrogen bonds to specific groups of the lipid. Disaccharide molecules are observed to adopt specific conformations to fit onto the surface topology of the bilayer, often interacting with up to three different lipids simultaneously. At high disaccharide concentrations, the results of simulations indicate that disaccharides can serve as an effective replacement for water under anhydrous conditions, which helps explain their effectiveness as lyophilization agents for liposomes and cells.