Molecular dynamics simulation of n-dodecyl phosphate aggregate structures

Aggregates of n-dodecyl phosphate present an attractive model system of sim ple phospholipid amphiphile supramolecular structures for study by molecula r dynamics simulation, since these systems have previously been studied exp erimentally under various conditions. A detailed molecular dynamics descrip tion of the properties of planar bilayer membranes (as a model for unilamel lar vesicular membranes) and spherical micelles under various simulated con ditions is presented. It is shown that the united-atom model of GROMOS96 ap plying the force-field parameter set 43A2 for biomolecular systems yields p roperties in agreement with experimental ones in most cases. Hydrogen bondi ng plays a role in stabilizing the bilayer aggregates at low pH, but not fo r the micelles, which are energetically favoured at high pH. NMR-S-CD order parameters for a lipid bilayer system, the diffusion of amphiphiles within aggregates and of counterions, and lifetimes of hydrogen bonds between amp hiphiles and to water are estimated from the MD simulations.