Computer simulation of short-range repulsion between supported phospholipid membranes.

The grand canonical Monte Carlo technique is used to calculate the water-mediated pressure between two supported 1,2-dilauroyl-DL-phosphatidylethanolamine (DLPE) membranes in the short separation range. The intra- and intermolecular interactions in the system are described with a combination of a united-atom AMBER-based force field for DLPE and a TIP4P model for water. The total pressure is analyzed in terms of its hydration component and the component due to the direct interaction between the membranes. The latter is, in addition, partitioned into the electrostatic, dispersion, and steric repulsion contributions to give an idea of their relative significance in the water-mediated intermembrane interaction. It is found that the force field used exaggerates the water affinity of the membranes, resulting in an overestimated hydration level and intermembrane pressure. The simulations of the hydrated membranes with damped water-lipid interaction potentials show that both the hydration and pressure are extremely sensitive to the strength of the water-lipid interactions. Moreover, the damping of the mixed interactions by only 10%-20% changes significantly the relative contribution of the individual pressure components to the intermembrane repulsion.