Studying the structure of single-component ceramide bilayers with molecular dynamics simulations using different force fields

Molecular dynamics simulations are performed on a lipid bilayer that consists of ceramide NS 24:0 in an attempt to examine several structural and physicochemical properties of the specific system. The simulations are carried out with five different force fields (OPLS, GROMOS, BERGER, CHARMM and GAFF) in order to evaluate and compare their performance in modelling lipid systems that contain ceramides. The examined properties include bilayer thickness, chain tilt, density profiles, order parameters, chain conformation, area per lipid and (intermolecular or intramolecular) hydrogen bonding between the head groups. Special focus is given to the lateral lipid arrangement. To this purpose, a method is proposed that utilises the radial distribution functions of the alkyl chains to derive quantitative information about the lateral lipid packing. In most cases, all force fields lead to similar results. For a few properties (e.g. intramolecular hydrogen bonding), there is some discrepancy between the force fields but the lack of respective experimental data does not allow an unambiguous conclusion on which force field is the most reliable.