Nanosecond field alignment of head group and water dipoles in electroporating phospholipid bilayers.

To investigate the mechanism of biological cell membrane electroporation at the nanosecond and nanometer scale, we tracked pore-forming lipids and water in molecular dynamics simulations of a palmitoyloleoylphosphatidylcholine bilayer in a minimum porating electric field. Although the field-generated torque tilts the mean head group dipole a few degrees away from its equilibrium, zero-field position relative to the bilayer plane, this change in conformation does not appear to contribute directly to the development of the pore-initiating aggregation of lipid head groups and water that leads to the formation of a membrane-spanning hydrophilic pore. Field-directed rotation of the head group dipoles in the plane of the incipient pore wall, in combination with water dipole and solvation interactions at the aqueous-lipid interface, is one component in the coordinated ensemble of electroporation events.