Eur. Phys. J. D (2014) 68: 364
https://doi.org/10.1140/epjd/e2014-50579-2

Regular Article

Potassium ion surrounded by aromatic rings: molecular dynamics of the first solvation shell

¹ IQTCUB, Departament de Química Física, Universitat de Barcelona, 08028 Barcelona, Spain
² Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal

^a e-mail: qtmarque@ci.uc.pt

Received: 6 August 2014
Received in final form: 6 October 2014
Published online: 2 December 2014

Abstract

We study the potassium ion in non-polar environments due to the interaction with aromatic rings, which is relevant to get insight on the selectivity of several biochemical processes. In concrete, we performed molecular dynamics simulations of the first solvation shell of K⁺ surrounded by either benzene (Bz) or hexafluorobenzene (HFBz) molecules. The global intermolecular interaction for these clusters has been decomposed in Bz-Bz (or HFBz-HFBz) and in K⁺-Bz (or K⁺-HFBz) contributions, using a potential model based on different decompositions of the molecular polarizability of the solvent molecule (Bz or HFBz). For the molecular dynamics simulations, we used as starting geometries the low-energy structures of the K⁺-(Bz)_n (n = 3,4) and K⁺-(HFBz)_n (n = 8,9) clusters that were obtained in our previous global optimization studies [J.M.C. Marques, J.L. Llanio-Trujillo, M. Albertí, A. Aguilar, F. Pirani, J. Phys. Chem. A 116, 4947 (2012); J.M.C. Marques, J.L. Llanio-Trujillo, M. Albertí, A. Aguilar, F. Pirani, J. Phys. Chem. A 117, 8043 (2013)]; a total of 11 starting geometries were employed (including the 4 global minima): 4 (4) for K⁺-(Bz)₃ (K⁺-(Bz)₄) and 2 (1) for K⁺-(HFBz)₈ (K⁺-(HFBz)₉). We have found that all the K⁺-(Bz)₃ local minimum structures isomerise to form the lowest-energy aggregate at T< 20 K. As for K⁺-(Bz)₄, such kind of isomerisation is only observed at T> 90 K for two of the local minima; the highest-energy minimum, that corresponds to a K⁺-(Bz)₄ structure with a Bz molecule placed in the second solvation shell, tends to dissociate before it can isomerise. In the case of K⁺-(HFBz)₈ (or K⁺-(HFBz)₉), the dissociation only occurs at higher temperatures, i.e., T = 260 K (or T = 210 K). By lowering the temperature of the simulation after the dissociation of K⁺-(HFBz)₉, one observes the formation of the global minimum structure of K⁺-(HFBz)₈.