Structural Features of Cholinium Based Protic Ionic Liquids through Molecular Dynamics

Abstract

An analysis of the complex proton transfer processes in certain protic ionic liquids, based on amino acid anions, has been carried out through ab initio molecular dynamics in the view of finding naturally conductive and pure mediums. The systems analyzed here might serve as chemical prototypes for pure and dry ionic liquids where mobile protons can act as fast charge carriers. We have exploited the natural tendency of these liquids to form a complex network of hydrogen bonds. The presence of such a network allows the naturally repulsive interaction between like charge ions to be weakened to the point that a proton migration process inside the anionic component of the fluid becomes possible. We have also seen that the extent of these proton migrations is sizable for carboxylic based amino acid anions, while it is very limited for sulfur containing ones.

Cholinium amino acid-based ionic liquids

“…Even in the simplest AA anions with aliphatic side chains, the computational data do suggest the presence of conspicuous anion-anion pairing through H-bonding of their amino and carboxylate groups (Fedotova et al 2019). Le Donne et al ( , 2019 using AIMD have found a rough but evident correlation between the association energies of the dimeric anion-anion structures and the measured viscosities of the corresponding ChAAILs. A recent work by Khorrami and Kowsari (2020) based on classical MD has further extended the study of these like-charge interactions to the mixtures of ChAAILs with water.…”

Modelling biocompatible ionic liquids based on organic acids and amino acids: challenges for computational models and future perspectives

“…In other words, if the position of equilibrium ( 1) is not known or uncertain, the possibilities of obtaining a clear-cut answer from simulations are rather limited. Useful indications can certainly be had from the accurate computations of proton transfer energy profiles in isolated pairs, 126,127 and from AIMD simulations, [128][129][130] but the reliable prediction of equilibrium (1) in condensed system still defies a straightforward computational approach.…”

“…For example, the presence of low-Q scattering peaks in the X-ray diffraction patterns indicated that there existed some form of structural aggregation at the nanoscale that calculations on isolated dimers were unable to grasp. 68,69 From some of our recent studies, 129,131 it was clear that the structure of these fluids was determined, not only by the interactions between molecular components of opposite charges, but also by those between likely charged ones. Modeling such balance requires necessarily a great accuracy in the calculation of the interatomic potentials because of the need to properly account for polarization phenomena.…”

“…The extent to which like-charge interactions exist and influence the frictional properties of AAILs has been explored by us and we have found that, even with the simplest aliphatic amino acids, the results of AIMD simulations suggest conspicuous anion-anion pairing through H-bonding between the aminoand carboxylate groups 43,129,136 . Interestingly, the anion-anion binding energies show an evident correlation with the measured viscosities of the corresponding liquids.…”

Structural Features of Triethylammonium Acetate through Molecular Dynamics

“…Despite their apparent simplicity [6], PILs can sometimes show complex structural patterns and unexpected chemical activity owing to a series of inter-related phenomena such as nano-segregation [7,8], hydrogen bonding [9][10][11][12][13], and tautomerization reactions involving secondary protic functions on the molecular structure [14,15]. The latter, in turn, may spawn proton mobility [16,17].…”