The mechanism of flip-flops in a AOT lamella: A molecular dynamics study

A long 5000 ns run was conducted on sodium dioctyl sulfosuccinate (AOT)/water lamellar system to understand the unusual behavior. During the simulation run, we track up to 24 AOT molecules translocated from upper leaflet (UL) to lower leaflet (LL) and vice-verse. AOT molecule takes ~2-17 ns in average to move from one leaflet to other. The potential energy barrier of AOT interlayer translocation calculated as sum of Lennard-Jones and electrostatic energies is estimated to be around ~100-120 kJ/mol and the free energy barrier about 90 kJ/mol. A long-scale simulation is accompanied with undulations and large curvation of bilayer. We argue that the transbilayer flip-flop process is a pore-mediated, i.e. the events are accompanied with water pores (defects) formation. On the other side, the size of water tunnels is also important, although the successful transbilayer flip-flop events are not depends on the size and lifetime of the water pores.

Automated summary

Through a long simulation experiment, we discovered unusual behavior in the AOT/water lamellar system, where AOT molecules can translocate between leaflets and the potential energy barrier for this process has been estimated. The structure and dynamics of the bilayer are influenced by the formation of water pores.