Extension of the LOPLS-AA Force Field for Alcohols, Esters, and Monoolein Bilayers and its Validation by Neutron Scattering Experiments

Abstract

The recently presented LOPLS-AA all-atom force field for long hydrocarbon chains, based on the OPLS-AA force field, was extended to alcohols, esters, and glyceryl monooleate (GMO) lipids as a model lipid. Dihedral angles were fitted against high level ab initio calculations, and ester charges were increased to improve their hydration properties. Additionally, the ester Lennard-Jones parameters were readjusted to reproduce experimental liquid bulk properties, densities, and heats of vaporization. This extension enabled the setup of LOPLS-AA parameters for GMO molecules. The properties of the lipid force field were tested for the liquid-crystalline phase of a GMO bilayer. The obtained area per lipid for GMO is in good agreement with experiment. Additionally, the lipid dynamics on the subpicosecond to the nanosecond time scale is in excellent agreement with results from time-of-flight (TOF) quasielastic neutron scattering (QENS) experiments on a multilamellar monoolein system, enabling here for the first time the critical evaluation of the short-time dynamics obtained from a molecular dynamics simulation of a membrane system.

Viscosity and Interfacial Tension of Binary Mixtures of n-Hexadecane with Dissolved Gases Using Surface Light Scattering and Equilibrium Molecular Dynamics Simulations

“…For a detailed description of the underlying theory of EMD simulations, the reader is referred to the respective literature. − The accuracy of the predicted properties, however, relies strongly on the underlying FF. In our previous publication, the L-OPLS FF , was used and modified by incorporating a temperature dependency of the Lennard–Jones (LJ) parameters, which allowed the overall good prediction of the density, viscosity, surface tension, and self-diffusion coefficients of 12 pure substances for T between 298.15 and 573.15 K . In the present work, the same FF was applied for n -hexadecane.…”

“…In the present work, the same FF was applied for n -hexadecane. The FFs for the gases He, H 2 , N 2 , CO, and CO 2 were the same as those in our previous publications. ,,− For CH 4 , OPLS FF was chosen due to its close relation to L-OPLS FF. , For H 2 O, the three-body SPC/E FF was applied, neglecting the polarization term.…”

“…35−37 The accuracy of the predicted properties, however, relies strongly on the underlying FF. In our previous publication, the L-OPLS FF 38,39 was used and modified by incorporating a temperature dependency of the Lennard− Jones (LJ) parameters, which allowed the overall good prediction of the density, viscosity, surface tension, and selfdiffusion coefficients of 12 pure substances for T between 298.15 and 573.15 K. 34 In the present work, the same FF was applied for n-hexadecane. The FFs for the gases He, H 2 , N 2 , CO, and CO 2 were the same as those in our previous publications.…”

Viscosity, Interfacial Tension, and Density of Binary-Liquid Mixtures of n-Hexadecane with n-Octacosane, 2,2,4,4,6,8,8-Heptamethylnonane, or 1-Hexadecanol at Temperatures between 298.15 and 573.15 K by Surface Light Scattering and Equilibrium Molecular Dynamics Simulations

“…The all-atom class of FF used in EMD simulations has shown to be reliable in the prediction of both equilibrium and dynamic properties. ,,, The optimized potentials for liquid simulations (OPLS) FF , and its extensions to long-chain alkanes and alcohols, L-OPLS, , and highly branched alkanes has been extensively employed by the working group of Fröba for simulations of hydrocarbon-based liquids and liquid mixtures. ,,,, While quite robust around 298 K, the OPLS-based FFs have shown increasing deviations of both equilibrium and dynamic thermophysical properties for increasing temperatures. A recent in-group development to the L-OPLS FF extends the temperature range over which reliable predictions can be made .…”

On the effect of confined fluid molecular structure on nonequilibrium phase behaviour and friction

“…56 In L-OPLS-AA, both bonded and non-bonded parameters have been updated for several atom types to provide a more realistic description of long-chain alkanes 56 and, more recently, alcohols and esters. 57 More details of the molecular dynamics force-field used, as well as validation for the molecules used here, are shown in the ESI. † Fast-moving bonds involving hydrogen atoms were constrained with the SHAKE algorithm.…”