OPLS All-Atom (OPLS/AA) is a generic all-atom force field which was fine-tuned to accurately reproduce condensed phase properties of organic liquids. Its application in modeling of lipid membranes is, however, limited mainly due to the inability to correctly describe phase behavior and organization of the hydrophobic core of the model lipid bilayers. Here we report new OPLS/AA parameters for n-pentadecane, methyl acetate, and dimethyl phosphate anion. For the new force field parameters, we show very good agreement between calculated and numerous reference data, including liquid density, enthalpy of vaporization, free energy of hydration, and selected transport properties. The new OPLS/AA parameters have been used in successful submicrosecond MD simulations of bilayers made of bacterial glycolipids whose results will be published elsewhere shortly.

For over 20 years, the OPLS-All Atom (OPLS-AA) force field has been efficiently used in molecular modelling studies of proteins, carbohydrates and nucleic acids. OPLS-AA is successfully applied in computer modelling of many organic compounds, including decane and shorter alkanes, but it fails when employed for longer linear alkanes, whose chemical structure corresponds to hydrocarbon tails in phospholipids constituting cellular membranes. There have been several attempts to address this problem. In this work we compare the ability to reproduce various condensed phase properties by six distinct sets of force field parameters which can be assigned to phospholipid hydrocarbon chains. In this comparison, we include three alternative sets of the OPLS-AA force field, as well as the commonly used CHARMM C36, Slipids, and Berger lipids’ parameters.

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