Deep eutectic–water binary solvent associations investigated by vibrational spectroscopy and chemometrics

Abstract

Investigation of the behaviour of deep eutectic solvents (DESs) as novel green solvents in the presence of other solvents is of great interest. In this study the behaviour of a common natural DES, namely choline chloride-glycerol deep eutectic solvent (GDES), was studied in the presence of water. A detailed study of the association of the two solvents was performed by integration of two vibrational spectroscopic methods (FTIR and Raman spectroscopy) followed by multivariate analysis. Moreover, a binary mixture of glycerol (Gly) as one of the liquid constituents of GDES and water was explored under the same conditions. A quintuplet and ternary systems were resolved for GDES-water and Gly-water probes, respectively, using multivariate analysis of global data (multi-technique and multi-experiment data arrangements). The results confirmed that in the presence of water the GDES showed different behaviour from its components. Therefore, a DES can be introduced as an independent solvent with its unique properties. Also, different H-bond interaction energies of GDES and its pure components in the presence of water were shown by theoretical calculations based on a density functional theory framework. To investigate the effects of water on the structure of GDES, molecular dynamics (MD) simulations of GDES-water liquid mixtures were performed at 0.9 mole fraction of water.

The peculiar effect of water on ionic liquids and deep eutectic solvents

“…x water = 0.833, the DES component will be fully solvated by water, and the system changes to an aqueous solution. For a DES-H 2 O binary mixture, Ahmadi et al 216 investigated the character of the ChCl/Gly (1 : 2) system in the presence of water by combining FTIR and Raman spectroscopy. They found that for this DES, the association of water with DES reaches a maximum at x water E 0.9, proposing that the DES-H 2 O interaction is dominant and over the DES-DES interaction.…”

“…ion-pairing and ions hydration) results in a non-ideal behaviour of properties observed from macroscale. For ChCl/Gly (1 : 2)-H 2 O binary mixture, Ahmadi et al 216 performed MD simulations at x H 2 O = 0.9, three typical distributions for the DES constituents were observed, and ChCl prefers to form H-bonds with water instead of glycerol.…”

Phase behavior of aqueous solutions of ethaline deep eutectic solvent

“…The integrity of DES could be destroyed in biphasic aqueous systems, while its local arrangement could be preserved in single-phase aqueous DES mixtures up to a moderate degree of hydration [1,11]. The physical properties of water-ionic liquids and water-DES mixtures, including excess properties, viscosity, acoustic, structural and optical properties have been studied around ambient temperature and above [1,[12][13][14][15][16][17][18][19].…”

Influence of Hydration on the Structure and Interactions of Ethaline Deep‐Eutectic Solvent: A Spectroscopic and Computational Study

“…So, making appropriate solutions from the desired DESs and less viscous cosolvents is an easy way out. In this regard, the aqueous solutions of DESs as hybrid green systems have garnered increased attention …”

“…It has been shown that the hydrogen bonding (H‐bonding) interactions within the studied DESs are strengthened when low amounts of water are added. But when water content increases, the mixtures change from a hydrated DES into an aqueous solution of DES components . Hammond et al .…”