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AKB: Biologische Physik

AKB 4: Membranes: Phase Behavior and Dynamics

AKB 4.2: Vortrag

Montag, 27. März 2006, 12:15–12:30, ZEU 260

Coarse-grained simulations of internal phases in lipid membranes — •Friederike Schmid and Olaf Lenz — Universität Bielefeld

We study internal membrane phase transitions by Monte Carlo simulation of a simple coarse-grained model system. Lipids are modeled as single spring-bead chains. They are forced to self-assemble by a surrounding fluid of “phantom” solvents, which only interact with the lipids, but not with one another. The solvent is thus very cheap from a computational point of view, and the model can be simulated very efficiently. Depending on the model parameters, it exhibits a fluid state, tilted and untilted gel states, and an interdigitated state. In the “pretransition” region between the tilted gel state and the fluid state, two types of undulated rippled structures are observed: an asymmetric structure with a sawtooth profile and a period of roughly 15-20 lipid diameters, and a symmetric structure with a period twice as long. Both structures have been reported in experiments, and their molecular structure is still under debate. The structure of our asymmetric ripple state agrees with that found recently by de Vries et al (PNAS 102, 5392, 2005) in an atomistic simulation of a Lecithin bilayer. Moreover, our simulations suggest a structural model for the structure of the symmetric ripple state.