We performed molecular dynamics computer simulations to study the interaction between hydrophilic phospholipid bilayers immersed in water, the interaction known as a 'hydration' force.  Our simulations are performed on model bilayers, and in case when the bilayer surfaces contain zwitterionic lipid headgroups, the water-mediated part of the interaction, measured by the potential of mean force (PMF), is repulsive, as observed in the experiment.  This PMF is dominated by an enthalpic contribution, due to the water-headgroup electrostatic interaction. When the headgroups of the bilayers are discharged the hydrophilic surfaces become hydrophobic and the water-mediated interaction between them turns into attractive. Finally, when one of the bilayers carries a total non-zero charge, and the other is zwitterionic, the water mediated interaction PMF displays attraction at larger distances and repulsion at shorter. The attraction is dominated by an entropic contribution due to water ordering between the surfaces and the repulsion is dominated by an enthalpic contribution.

Computer simulation studies of the water-mediated interaction between model lipid membrane surfaces: Origin of the hydration force

243rd National Meeting (2012)

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