Prediction of the handedness of the domains of monolayers of d-N-palmitoyl aspartic acid: Integrated molecular orbital and molecular mechanics based calculation

The condensed phase monolayer domain forms interesting curvature due to chirality of the molecule. The handedness of d-N-palmitoyl aspartic acid is studied using the three-layered ONIOM (MO:MO:MM) model. Optimized structures of a pair of molecules are used to calculate the azimuthal projection of the molecular pairs. The pair of molecules shows a distinct minimum at the mutual azimuthal orientation corresponding to the left-handedness at the optimized separation. The other handedness is completely unfavorable. This is in nice agreement with the experimental data that d-enantiomer gives rise to left-handedness of the domains. Mutual large tilt between the molecules is also unfavored which is in agreement with the concept that molecules should not have large mutual tilt at the condensed phase. The energy surface gradually becomes flattened with increasing intermolecular separation. This is in agreement with the common wisdom that chirality induced effects decreases with increasing intermolecular separation. Present hybrid method based study reveals that the molecular chirality of the amphiphile can dictate the domain morphology in the condensed phase and is in agreement with experimental data and previous theoretical results based on effective pair potential theory and mechanics calculations.