Current Status of AMOEBA-IL: A Multipolar/Polarizable Force Field for Ionic Liquids

Abstract

Computational simulations of ionic liquid solutions have become a useful tool to investigate various physical, chemical and catalytic properties of systems involving these solvents. Classical molecular dynamics and hybrid quantum mechanical/molecular mechanical (QM/MM) calculations of IL systems have provided significant insights at the atomic level. Here, we present a review of the development and application of the multipolar and polarizable force field AMOEBA for ionic liquid systems, termed AMOEBA-IL. The parametrization approach for AMOEBA-IL relies on the reproduction of total quantum mechanical (QM) intermolecular interaction energies and QM energy decomposition analysis. This approach has been used to develop parameters for imidazolium- and pyrrolidinium-based ILs coupled with various inorganic anions. AMOEBA-IL has been used to investigate and predict the properties of a variety of systems including neat ILs and IL mixtures, water exchange reactions on lanthanide ions in IL mixtures, IL-based liquid-liquid extraction, and effects of ILs on an aniline protection reaction.

Keywords: Computational property prediction; Ionic Liquids, Multipolar/polarizable force field, QM/MM; Molecular Dynamics.

Figure 1

(a) polarization, (b) Coulomb, (c) Van der Waals and (d) Total inter–molecular interacion energies for 77 randomly oriented [sPyr${}^{+}$][BF${}_4$] dimers computed with AMOEBA–IL (MM) compared with QM EDA (SAPT) with (black), or without (red) inter–molecular polarization. Reproduced from Torabifard, H.; Reed, L.; Berry, M.T.; Hein, J.E.; Menke, E.; Cisneros, G.A. Computational and Experimental Characterization of a Pyrrolidinium-Based Ionic Liquid for Electrolyte Applications. J. Chem. Phys. 2017, 147, 161731. [105].

Figure 2

Spyrocyclic pyrrolidinium [SPyr] molecular structure, red circles roughly denote the intra–molecular polarization groups for the 3G set, from Torabifard, H.; Reed, L.; Berry, M.T.; Hein, J.E.; Menke, E.; Cisneros, G.A. Computational and Experimental Characterization of a Pyrrolidinium-Based Ionic Liquid for Electrolyte Applications. J. Chem. Phys. 2017, 147, 161731. [105].

Figure 3

Radial distribution functions and integration curves of water (left) [EtSO${}_4$] (center) and [OTf] (right) around the lanthanide cations. Reproduced from Tu, Y.-J.; Allen, M.J.; Cisneros, G.A. Simulations of Water Exchange Dynamics on Lanthanide Ions in 1-Ethyl-3-Methylimidazolium Ethyl Sulfate ([EMIm][EtSO${}_4$]) and Water. Phys. Chem. Chem. Phys 2016, 18, 30323–30333. With permission from the PCCP Owner Societies [103], and Tu, Y.-J.; Lin, Z.; Allen, M.J.; Cisneros, G.A. Molecular Dynamics Investigation of Solvent-Exchange Reactions on Lanthanide Ions in Water/1-Ethyl-3-Methylimidazolium Trifluoromethylsulfate ([EMIm][OTf]). J. Chem. Phys. 2018, 148, 024503. Copyright 2018 American Physical Society.

Figure 4

(a) Selected snapshots for a water exchange event on Gd${}^{3+}$ in water and (b) corresponding cation—water distance along the MD trajectory. A similar behavior is observed for Dy${}^{3+}$ and Ho${}^{3+}$ in water. Reproduced from Tu, Y.-J., Allen, M.J., Cisneros, G.A., (2016) “Simulations of Water Exchange Dynamics on Lanthanide Ions in 1-Ethyl-3-Methylimidazolium Ethyl Sulfate ([EMIm][EtSO${}_4$]) and Water”, Phys. Chem. Chem. Phys., 18, 30323–30333. With permission from the PCCP Owner Societies. [103].

Figure 5

Selected snapshots for a water exchange event on Ho${}^{3+}$ in water/[EMIm][EtSO${}_4$] and corresponding cation–water distance along the MD trajectory. Similar behaviors were observed for Gd${}^{3+}$ and Dy${}^{3+}$. Reproduced from Tu, Y.-J., Allen, M.J., Cisneros, G.A., (2016) “Simulations of Water Exchange Dynamics on Lanthanide Ions in 1-Ethyl-3-Methylimidazolium Ethyl Sulfate ([EMIm][EtSO${}_4$]) and Water”, Phys. Chem. Chem. Phys., 18, 30323–30333. with permission from the PCCP Owner Societies [103].

Figure 6

MD snapshots for a water-exchange event on Ho${}^{3+}$ during the simulation time, and the distance trajectories of the water O atoms with (a) Gd${}^{3+}$, (b) Dy${}^{3+}$, and (c) Ho${}^{3+}$ in water/[EMIm][OTf]. Reproduced from Tu, Y.-J.; Lin, Z.; Allen, M.J.; Cisneros, G.A. Molecular Dynamics Investigation of Solvent-Exchange Reactions on Lanthanide Ions in Water/1-Ethyl-3-Methylimidazolium Trifluoromethylsulfate ([EMIm][OTf]). J. Chem. Phys. 2018, 148, 024503. Copyright 2018 American Physical Society.

Figure 7

Average total interaction energies of lanthanide ions with a [OTf]${}^{-}$ anion and a first shell (a) and second shell (b) water. Reproduced from Tu, Y.-J.; Lin, Z.; Allen, M.J.; Cisneros, G.A. Molecular Dynamics Investigation of Solvent-Exchange Reactions on Lanthanide Ions in Water/1-Ethyl-3-Methylimidazolium Trifluoromethylsulfate ([EMIm][OTf]). J. Chem. Phys. 2018, 148, 024503. Copyright 2018 American Physical Society.

Figure 8

Schematic representation of molecules used for the simulation of benzene extraction from gasoline with ILs. (a) Benzene (PhH) and dodecane (NC12), (b) [DMIM][BF${}_4$], and (c) [EMIM][BF${}_4$] Reproduced from Vazquez-Montelongo, E.A.; Cisneros, G.A.; Flores–Ruiz, H.M. Multipolar/Polarizable Molecular Dynamics Simulations of Liquid-Liquid Extraction of Benzene from Hydrocarbons Using Ionic Liquids. J. Mol. Liq. 2019, doi:10.1016/j.molliq.2019.111846, [106].

Figure 9

Density profile along the z direction for the (a) ternary mixture [DMIM][BF${}_4$]/benzene/dodecane and (b) ternary mixture [EMIM][BF${}_4$]/benzene/dodecane. Reproduced from Vazquez-Montelongo, E.A.; Cisneros, G.A.; Flores–Ruiz, H.M. Multipolar/ Polarizable Molecular Dynamics Simulations of Liquid-Liquid Extraction of Benzene from Hydrocarbons Using Ionic Liquids. J. Mol. Liq. 2019, doi:10.1016/j.molliq.2019.111846, [106].

Figure 10

(a) SDF of PhH and one nitrogen atom in the ring of [DMIM] in a binary mixture (PhH-[DMIM][BF4]), (b) difference between the SDF of PhH-[DMIM] in the binary mixture and the SDF of PhH and one nitrogen atom in the ring of [DMIM] in the ternary mixture (PhH-NC12-[DMIM][BF4]). (c) SDF of PhH and one nitrogen atom in the ring of [EMIM] in a binary mixture (PhH-[EMIM][BF4]), (d) difference between the SDF of PhH-[EMIM] in the binary mixture and the SDF of PhH and one nitrogen atom in the ring of [EMIM] in the ternary mixture (PhH-NC12-[EMIM][BF4]). Reproduced from. Reproduced from Vazquez-Montelongo, E.A.; Cisneros, G.A.; Flores–Ruiz, H.M. Multipolar/Polarizable Molecular Dynamics Simulations of Liquid-Liquid Extraction of Benzene from Hydrocarbons Using Ionic Liquids. J. Mol. Liq. 2019, doi:10.1016/j.molliq.2019.111846, [106].

Figure 11

(a) SDF of PhH and the boron atom in [BF4], in a binary mixture (PhH-[DMIM][BF4]), (b) difference between the SDF of PhH and [BF4] in the binary mixture and the SDF of PhH and boron atom in [BF4] in the ternary mixture (PhH-NC12-[DMIM][BF4]). (c) SDF of PhH and the boron atom in [BF4], in a binary mixture (PhH-[EMIM][BF4]), (d) difference between the SDF of PhH and [BF4] in the binary mixture, and the SDF of PhH and boron atom in [BF4] in the ternary system (PhH-NC12-[EMIM][BF4]). Reproduced from Vazquez-Montelongo, E.A.; Cisneros, G.A.; Flores–Ruiz, H.M. Multipolar/Polarizable Molecular Dynamics Simulations of Liquid-Liquid Extraction of Benzene from Hydrocarbons Using Ionic Liquids. J. Mol. Liq. 2019, doi:10.1016/j.molliq.2019.111846, [106].

Figure 12

Calculated density at different temperatures for [sPyr${}^{+}$][BF${}_4^{-}$] using one and three polarizable groups for 300–500 K. Reproduced from Torabifard, H.; Reed, L.; Berry, M.T.; Hein, J.E.; Menke, E.; Cisneros, G.A. Computational and Experimental Characterization of a Pyrrolidinium-Based Ionic Liquid for Electrolyte Applications. J. Chem. Phys. 2017, 147, 161731 [105].

Figure 13

Radial distribution functions for [sPyr${}^{+}$][BF${{}_4}^{-}$] with three polarizable groups (3G) at different temperatures. Reproduced from Torabifard, H.; Reed, L.; Berry, M.T.; Hein, J.E.; Menke, E.; Cisneros, G.A. Computational and Experimental Characterization of a Pyrrolidinium-Based Ionic Liquid for Electrolyte Applications. J. Chem. Phys. 2017, 147, 161731, [105].

Figure 14

Calculated diffusion coefficients at different temperatures for [sPyr${}^{+}$][BF${}_4^{-}$] using one (1G) and three (3G) polarizable groups with and without 10% Li${}^{+}$. Reproduced from Torabifard, H.; Reed, L.; Berry, M.T.; Hein, J.E.; Menke, E.; Cisneros, G.A. Computational and Experimental Characterization of a Pyrrolidinium-Based Ionic Liquid for Electrolyte Applications. J. Chem. Phys. 2017, 147, 161731 [105].

Figure 15

Reaction scheme for the N-tert-butoxycarbonylation of aniline. Panel (1) describes the step–wise mechanism and panel (2) describes the concerted mechanism mentioned above.

Figure 16

Minimum energy path for configuration 1, mechanism 1. Reproduced from Vazquez-Montelongo, E.A.; Vazquez-Cervantes, J.E.; Cisneros, G.A. Polarizable ab initio QM/MM Study of the Reaction Mechanism of N-tert-Butyloxycarbonylation of Aniline in [EMIm][BF${}_4$]. Molecules 2018, 23, 2830, doi:10.3390/molecules23112830 [140].

Figure 17

Minimum energy path for configuration 2, mechanism 1. Reproduced from Vazquez-Montelongo, E.A.; Vazquez-Cervantes, J.E.; Cisneros, G.A. Polarizable ab initio QM/MM Study of the Reaction Mechanism of N-tert-Butyloxycarbonylation of Aniline in [EMIm][BF${}_4$]. Molecules 2018, 23, 2830, doi:10.3390/molecules23112830.

Figure 18

Minimum energy path for configuration 2, mechanism 2. Reproduced from Vazquez-Montelongo, E.A.; Vazquez-Cervantes, J.E.; Cisneros, G.A. Polarizable ab initio QM/MM Study of the Reaction Mechanism of N-tert-Butyloxycarbonylation of Aniline in [EMIm][BF${}_4$]. Molecules 2018, 23, 2830, doi:10.3390/molecules23112830 [140].

Figure 19

Combined ELF/NCI surfaces for the TS structures for the rate limiting step in Scheme c. (a) gas–phase, (b) di–chloromethane (implicit solvent), (c) configuration C1, (d) configuration C2. The isovalues for ELF is 0.83 and for NCI is 0.5 with a color scale of −0.05 au < sign($\lambda$2)$\rho$ < 0.05 au. Reproduced from Vazquez-Montelongo, E.A.; Vazquez-Cervantes, J.E.; Cisneros, G.A. Polarizable ab initio QM/MM Study of the Reaction Mechanism of N-tert-Butyloxycarbonylation of Aniline in [EMIm][BF${}_4$]. Molecules 2018, 23, 2830, doi:10.3390/molecules23112830 [140].

Figure 20

Combined ELF/NCI surfaces of the critical structures for configuration C2 for mechanism 2. Panels (a–e) show the reactants, TS1, MI, TS2 and products structures, respectively. The isovalues for ELF is 0.83 and for NCI is 0.5 with a color scale of −0.05 au < sign($\lambda$2)$\rho$ < 0.05 au. Reproduced from Vazquez-Montelongo, E.A.; Vazquez-Cervantes, J.E.; Cisneros, G.A. Polarizable ab initio QM/MM Study of the Reaction Mechanism of N-tert-Butyloxycarbonylation of Aniline in [EMIm][BF${}_4$]. Molecules 2018, 23, 2830, doi:10.3390/molecules23112830 [140].

Figure 21

Minimum energy path for Scheme c (right) and d (left) for configuration C2 without the AMOEBA polarization term. Reproduced from Vazquez-Montelongo, E.A.; Vazquez-Cervantes, J.E.; Cisneros, G.A. Polarizable ab initio QM/MM Study of the Reaction Mechanism of N-tert-Butyloxycarbonylation of Aniline in [EMIm][BF${}_4$]. Molecules 2018, 23, 2830, doi:10.3390/molecules23112830 [140].