Regensburg 2013 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 33: Poster: Charged Soft Matter
CPP 33.1: Poster
Mittwoch, 13. März 2013, 16:30–18:30, Poster C
Why is the partition coefficient of some ionic liquids concentration-dependent? — •Axel Arnold1,3, Dirk Reith2,3, and Thorsten Köddermann3 — 1Institute for Computational Physics, University of Stuttgart, Stuttgart, Germany — 2Bonn-Rhein-Sieg University of Applied Studies, Sankt Augustin, Germany — 3Fraunhofer-Institute for Algorithms and Scientific Computing (SCAI), Sankt Augustin, Germany
The partition coefficient of a substance measures its solubility in octanol compared to water, and is frequently used as a rough estimate of toxicity. If a substance is hardly soluble in octanol, it is practically impossible for it to enter (human) cells, and therefore is less likely to be toxic. While for simple substances, the partition coefficient is concentration-independent, this is not true for a few important classes of complex molecules, such as ionic liquids or tensides.
We present a simple model for the partition coefficient of ionic liquids based on the association and dissociation of ion pairs. Using solvation free energies in water and octanol from computer simulations, this model can reproduce the partition coefficient of the commonly used ionic liquid 1-Butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [C4MIM][NTf2] for a wide range of concentrations. Our findings show that the concentration dependence of the partition coefficient is mostly an entropic effect due to the strong tendency of the ionic liquid to associate in water, but dissociate in octanol.