Mesoscopic simulations of phase transitions in lipid bilayers

The formation of the rippled phase in biological membranes and its relation with anomalous swelling are still lacking a molecularexplanation. Starting from all-atom simulations we use a mapping to create a mesoscopic model of the lipid dimyristoylphosphatidylcholine(DMPC) in water. We use this model to study the phase behaviour of lipid bilayers. Depending on the lipid structure and head group, our simulations reproduce the experimental phase diagrams. The anomalous swelling is caused by conformational changes of the lipid tails but is not directly related to the rippled phase. A key factor for the rippled phase is a frustration between the surface area of the heads and the lateral density of the tails.