Refined OPLS All-Atom Force Field for Saturated Phosphatidylcholine Bilayers at Full Hydration

We
report parametrization of dipalmitoyl-phosphatidylcholine (DPPC)
in the framework of the Optimized Parameters for Liquid Simulations
all-atom (OPLS-AA) force field. We chose DPPC as it is one of the
most studied phospholipid species and thus has plenty of experimental
data necessary for model validation, and it is also one of the highly important and abundant
lipid types, e.g., in lung surfactant. Overall, PCs have not been
previously parametrized in the OPLS-AA force field; thus, there is
a need to derive its bonding and nonbonding parameters for both the
polar and nonpolar parts of the molecule. In the present study, we
determined the parameters for torsion angles in the phosphatidylcholine
and glycerol moieties and in the acyl chains, as well the partial
atomic charges. In these calculations, we used three methods: (1)
Hartree–Fock (HF), (2) second order Møller–Plesset
perturbation theory (MP2), and (3) density functional theory (DFT).
We also tested the effect of the polar environment by using the polarizable
continuum model (PCM), and for acyl chains the van der Waals parameters
were also adjusted. In effect, six parameter sets were generated and
tested on a DPPC bilayer. Out of these six sets, only one was found
to be able to satisfactorily reproduce experimental data for the lipid
bilayer. The successful DPPC model was obtained from MP2 calculations
in an implicit polar environment (PCM).