Chiral Interaction in Enantiomeric and Racemic Dipalmitoyl Phosphatidylcholine Langmuir Monolayer

An Effective Pair Potential (EPP) theory is used to study relation between the molecular chiral structure of a phospholipid (Dipalmitoyl phosphatidyl choline; DPPC) and the shape of the mesoscopic domain composed of DPPC. It is experimentally known that the monolayers of DPPC in the condensed phase exhibit the formation of triskellion shaped domains. The curvature of the arms of the triskellions has specific handedness depending on the chirality of the constituent molecule. The study uses an equivalent description of the groups attached to the chiral center and calculates the mutual orientation of a pair of molecules (enantiomeric and racemic pairs). The pair potential is calculated using Lennard Jones potential. Also, the electrial interaction is computed using semi-empirical approach. Based on the minimum energy arrangement, the handedness of the aggregates and their pair potential are predicted. Theoretically obtained results are compared with the experimental results and also with the previously obtained coarse-grained description of the molecule. The study uses no adjustable parameter and uses the microscopic information obtained from X-ray diffraction data. It shows that the equivalent sphere description of the molecule can fairly describe the mesoscopic features of the domains such as the handedness based on the pair potential calculation.