Molecular Dynamics Simulations, Solvatochromic Parameters, and Preferential Solvation in Aqueous Solutions of Ethaline, Ethylene Glycol, and Choline Chloride

Abstract

Deep eutectic solvents (DESs) are recent solvents that have the basic characteristics close to ionic liquids, and they have been applied in several reactions. Adding molecular solvents especially water to DESs is beneficial in some cases such as biophysics and biochemistry. Therefore, understanding the effect of different solvents and preferred solvent is critical in binary mixtures. This work describes the principles to investigate the preferential solvation of probe dyes (4-nitroaniline, 4-nitroanisole, and Reichardt’s dye 30) in complex mixed solvents in detail. Experimental and theoretical studies were used to seek the preferential solvation of probes in aqueous solution of ethylene glycol–choline chloride (ethaline) and its components (aqueous solutions of ethylene glycol and choline chloride). Results confirmed that probes prefer to be solvated by ethaline and ethylene glycol. In detail, the microsphere solvation of probe dyes was analyzed, which confirmed fundamental roles of choline and ethylene glycol for synergism effects from ideal mixtures. In most of the mole fractions, probes prefer to be solvated in the order of components, namely, ethylene glycol and choline > water > chloride. Moreover, aggregation of solvents components around probes was calculated profoundly. Molecular dynamics simulations made it possible to understand which combinations of components in mixed solvents display preferential solvation. Also, as a minor goal, solvatochromic parameters in mentioned mixtures were discussed in the related section. Finally, density functional theory (DFT) calculations showed either bathochromic or hypsochromic shifts coming from changes in microsphere solvation and hydrogen bonding of probes with solvents.

Microscopic structural features of water in aqueous–reline mixtures of varying compositions

“…The important role of choline mediated hydrogen bonds in reline and other deep eutectic mixtures has been shown by Minofar and group. [104][105][106] However we focused to elucidate the structure of water in the presence of reline with varying concentrations. We strengthen our study by calculating the fraction of water molecules that could effectively accommodate different numbers of hydrogen bonds.…”

Interfacial Properties of Hydrophobic Deep Eutectic Solvents with Water

“…Molecular dynamics (MD) is a powerful tool that has been widely used to study the thermodynamic and structural properties of aqueous solutions of hydrophilic DESs. 23 − 31 Several MD studies investigating the interfacial properties of biphasic systems of hydrophobic ionic liquids (ILs) and water are also available. 32 − 39 In sharp contrast to this, very limited studies are available exploring the properties of mixtures of hydrophobic DESs with water using MD simulations.…”

Microscopic Structural Features of Water in Aqueous-Reline Mixture of Varying Composition

“…It reveals the substitution of water-water hydrogen bonds substantially by the water-urea hydrogen bonds and to some extent by the water-choline hydrogen and group. [104][105][106] However we focused to elucidate the structure of water in the presence of reline with varying concentrations. We strengthen our study by calculating the fraction of water molecules that could effectively accommodate different numbers of hydrogen bonds.…”