On the structure and stability of self-assembled zwitterionic peptide amphiphiles: A theoretical study

The structures of self-assembled peptide amphiphiles are studied using empirical force fields and atomistic molecular dynamics calculations. The hydrophilic headgroups of these amphiphiles possess a lower, rigid part and an upper, flexible part. At an appropriate pH large dipoles are found in the flexible part of the headgroups, leading to attractive interactions between them, while the rigid parts participate in the formation of an effective parallel beta sheet due to hydrogen bonding oriented in the same direction as the large dipoles, and stabilizing the self-assembly in that direction. Molecular dynamics simulations on the self-assembled amphiphiles are performed with periodic boundary conditions in two dimensions. The tendency of the nanostructure to curve around an axis parallel to the dipoles and the beta sheet is revealed by removing the periodic boundary conditions, one direction at a time, leading to the conclusion that a cylindrical micelle would be the most stable one.