Water in Deep Eutectic Solvents: New Insights From Inelastic Neutron Scattering Spectroscopy

Abstract

The effect of water on the physicochemical properties of deep eutectic solvents (DES) is a trending research topic. In this work, inelastic neutron scattering (INS) spectroscopy, was used to probe intermolecular interactions in the water-deep eutectic solvent mixtures for the cases of choline chloride (the hydrogen bond acceptor) and three different hydrogen bond donors, with different degrees of acidity: urea, glycerol and lactic acid. It was found that quenching samples in liquid nitrogen is a procedure that may retain the liquid phase morphology of DES at the low temperatures required by INS spectroscopy. The three studied systems share the preference of water molecules to bind to chloride anion, as predicted by numerous molecular dynamics simulations. Despite this similarity, the three systems present several distinct INS features upon water addition that are related to their unique properties and structure at the molecular level. In the choline chloride:urea system, water molecules promote a strengthening of hydrogen bonds with the NH and OH donors, while for the choline chloride:lactic acid system INS probed the existence of solvated DES clusters instead of specifically interfering water molecules. This study takes advantage from the unique capabilities of INS and paves the way for future studies in these systems.

Does Viscosity Decoupling Guarantee Dynamic Heterogeneity? A Clue through an Excitation and Emission Wavelength-Dependent Time-Resolved Fluorescence Anisotropy Study

“…For freshly prepared (from overnight vacuum-dried constituents) DES, the water content is measured to be 0.6% (w/w) and in IL, it is 0.7% (w/w). It was reported that highly hygroscopic choline chloride-based binary DES contains ∼0.2–0.8% water (w/w) depending on the second constituent (diol, triol or urea). For squalane, the water content is measured to be 0.3% (w/w).…”

Differences in the Effect of Water on Deep Eutectic Solvents Based on Choline Chloride/Lauric Acid and Choline Chloride/Myristic Acid: Molecular Dynamics Simulations at Three Different Temperatures

“…As can be seen from Table S2, the electrostatic attraction energies in water-containing systems for interaction pairs Cl À -TIP3 (H1 atom) (MD simulations on systems containing DES + water displayed that water molecules tend to preferentially bond to the chloride anion and subsequently, the amount of choline cation and chloride anion interactions is reduced. [37] ) and OA of choline-TIP3 (H1 atom) at a temperature of 343 K are larger and stronger. This quantity has a downward trend with increasing temperature in the presence of LUA, so that, at the temperature of 343 K, we see electrostatic repulsion interactions for LUA (HA atom -Cl À and LUA (O2 atom)-TIP3 (H1 atom).…”

Untapped Potential of Deep Eutectic Solvents for the Synthesis of Bioinspired Inorganic–Organic Materials

“…DESs maintain the identities of their components, which interact via hydrogen bonding, as opposed to covalent bonding. Further, DESs remain in a liquid state: molecular dynamics simulations and inelastic neutron scattering studies , revealed that the strength of hydrogen bonds between DES-forming components is weak enough to prevent them settling into a cocrystal . So far, depending on the chemical composition, five different categories of DESs are distinguished (Figure b).…”