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Molecular Dynamics Simulation of Membrane Free Energy Profiles Using Accurate Force Field for Ionic Liquids

: Köddermann, Thorsten; Schenk, Martin R.; Hülsmann, Marco; Krämer, Andreas; Kirschner, Karl N.; Reith, Dirk


Griebel, Michael; Schüller, Anton; Schweitzer, Marc Alexander:
Scientific Computing and Algorithms in Industrial Simulation : Projects and Products of Fraunhofer SCAI
Cham: Springer International Publishing, 2017
ISBN: 978-3-319-62457-0 (Print)
ISBN: 978-3-319-62458-7 (Online)
Aufsatz in Buch
Fraunhofer SCAI ()

Ionic liquids are highly relevant for industrial applications as they stand out due to their special chemical and physical features, e.g. low vapor pressure, low melting point or extraordinary solution properties. The goal of this work is to study the capability of the three ionic liquids to diffuse through a {POPC} membrane (1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine). To achieve this, we used molecular simulation techniques, which on the one hand give insight into specific domains of the membrane and on the other hand compute partition coefficients and free energy profiles of solutes in lipid membranes, which cannot be measured by labor experiments. To be as accurate as possible we parameterized a new united atom force field for the ionic liquid of type 1-alkyl-3-methylimidazoliumethylsulfate with n = 1,2,4,6,8. The new force field reproduces the experimental data extremely well. Using this force field, the influences of cation and anion exchanges as well as the variation of the chain length on the free energy could be analyzed. We performed umbrella-sampling to characterize the free energy profile of one ion pair, accompanied by a second one, in solution, at the membrane interface, and inside the membrane. In the outlook we present our intention to parameterize force fields in a systematic and user-friendly way. We will use the combination of two optimization toolkits, developed at {SCAI}: The global optimization toolkit {CoSMoS} and the local optimization techniques implemented in the software package {GROW}.