A comprehensive computational and principal component analysis on various choline chloride-based deep eutectic solvents to reveal their structural and spectroscopic properties.

Abstract

In this study, the quantum chemical properties, nonbonding interactions, and spectroscopic insights of a wide variety of choline chloride (ChCl)-based deep eutectic solvents were investigated employing molecular dynamics (MD), density functional theory, and spectroscopic analyses. Nine experimentally reported ChCl-based deep eutectic solvents (DESs) were selected for this study where ChCl was common in all the DESs and the hydrogen bond donors (HBDs) were varied. The most energetically favorable cluster was selected using MD simulation followed by density functional theory calculation. The most stable cluster structures were fully optimized, and their quantum chemical properties and IR spectra were computed at the ωB97XD/6-31G++(d,p) level of theory. Principal component analysis was performed to distinguish their behavioral differences and to find out if any correlation exists among the 1:1 and 1:2 clusters. The atom-atom radial distribution functions based on MD simulations revealed that several hydrogen bonds were formed among the donor and acceptor molecules. However, the most prominent hydrogen bonds were found to be N-HHBD⋯Cl- for ChCl:U, ChCl:TU, and ChCl:Ace and O-HHBD⋯Cl- for ChCl:Glu, ChCl:Ma, ChCl:Ox, ChCl:Gly, and ChCl:Phe. Both N-HHBD⋯Cl- and O-HHBD⋯Cl- were major interactions for ChCl:Pro, where Cl- worked as a bridge between Ch+ and the respective donors. In addition, the -OH of Ch+ showed strong intermolecular interactions with the acceptor groups of the donor molecules, such as C=O and O-H. This study has tried to extract a pattern of the contributions of HBDs by comparing the structural, spectroscopic, and thermodynamic properties of ChCl-based DESs, which have also been successfully correlated with the intermolecular interactions.