Simulations of the water exchange dynamics of lanthanide ions in 1-ethyl-3-methylimidazolium ethyl sulfate ([EMIm][EtSO4]) and water. Issue 44 (26th August 2016)

• Record Type: Journal Article
• Authors: Tu, Yi-Jung; Allen, Matthew J.; Cisneros, G. Andrés
• Is Part Of: Physical chemistry chemical physics. Volume 18:Issue 44(2016)
• Page Start: 30323
• Page End: 30333
• Publication Date: 2016-08-26
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c6cp04957e
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Molecular dynamics simulations have been carried out to explain the water-exchange rates of lanthanide ions in water and water/[EMIm][EtSO4 ] observed from 17 O-NMR experiments. Our simulations are in agreement with experimental results with respect to water-exchange trends. Abstract : The dynamics of ligand exchange on lanthanide ions is important for catalysis and organic reactions. Recent 17 O-NMR experiments have shown that water-exchange rates of lanthanide ions in water/1-ethyl-3-methylimidazolium ethyl sulfate (water/[EMIm][EtSO4 ]) increase as a function of increasing charge density. The trend of water-exchange rates in this solvent is opposite to that observed in water. Since the lanthanide ions and ionic liquids investigated in that work were highly charged, an advanced polarizable potential is desirable for accurate simulations. To this end, we have developed atomic multipole optimized energetics for biomolecular applications (AMOEBA) parameters for all lanthanides and [EMIm][EtSO4 ], and molecular dynamics simulations with the optimized parameters have been carried out to provide possible explanations for these observed behaviors from the experiments. In water, the association of a water molecule with the first hydration shell can lead to water exchange. Smaller lanthanide ions exhibit slower water-exchange rates than larger ones because they form smaller aqua complexes, preventing the binding of incoming water molecules from the outer hydration shells. By contrast, smaller lanthanide ions undergo faster water exchange in water/[EMIm][EtSO4 ] because the dissociation of a water molecule is a key step for water-exchange events in this solvent. The first shell [EtSO4 ] − anions bind closer to the smaller lanthanide ions, resulting in more steric crowding effects on the surrounding water and facilitating the release of water molecules.