Aqueous choline amino acid deep eutectic solvents

Abstract

We have investigated the structure and phase behavior of biocompatible, aqueous deep eutectic solvents by combining choline acetate, hydrogen aspartate, and aspartate amino acid salts with water as the sole molecular hydrogen bond donor. Using contrast-variation neutron diffraction, interpreted via computational modeling, we show how the interplay between anion structure and water content affects the hydrogen bond network structure in the liquid, which, in turn, influences the eutectic composition and temperature. These mixtures expand the current range choline amino acid ionic liquids under investigation for biomass processing applications to include higher melting point salts and also explain how the ionic liquids retain their desirable properties in aqueous solution.

Vapor pressures and vapor phase compositions of choline chloride urea and choline chloride ethylene glycol deep eutectic solvents from molecular simulation

“…9 Recently, a special issue of the Journal of Chemical Physics titled "Chemical Physics of Deep Eutectic Solvents" was launched, to which the reader is referred for more information on DESs. [10][11][12][13][14][15][16][17][18][19] DESs and ionic liquids (ILs) are often regarded as superior solvents compared to volatile organic compounds (VOCs) due to a negligible vapor pressure at room temperature. 2,5,6,20 Such a low vapor pressure would limit the emission and loss of the DESs into the atmosphere and may facilitate the removal of solutes from DESs by distillation.…”

Design and applications of biocompatible choline amino acid ionic liquids

“…Between the two comprehensive studies, 23,27 values reported by De Santis et al are significantly higher than those of Liu et al The former is more widely supported by other studies such as ChAsp, Ch 2 Asp and ChArg being room temperature solids. 28,29 Despite the differences in reported values, it is generally agreed that most ChAAILs are highly viscous, making them difficult to handle under room conditions. The presence of additional hydrogen bonding sites on the amino acid side chains, such as Asp − , Arg − , Glu − , His − , etc ., seems to further increase viscosity.…”

“…100 Studies have shown that water forms short, linear hydrogen bonds with amino acid anions. 29,101 Therefore, water is likely to compete with hydrogen bonds among ions and weaken the lubricant film at the interface, ultimately leading to the dissolution of amino acid, and cleavage of the lubricant film. This is supported by the observation that the effectiveness of ChPro as a lubricant correlates with water content.…”

“…However, X-ray scattering patterns and simulations provide insufficient detail across all relevant length scales for the optimisation and rational design of these solvents; Highresolution experimental structural studies of ChAAILs with desired functionality and properties are critical. The bulk structure of some ChAAILs has recently been examined using neutron diffraction, 28,29,90,101,174 as well as by simulation (employing >500 ions). 175,176 This has revealed that ChAAILs may have individual origins of nanostructure primarily governed by anion sidechains.…”

“…The ChAAIL-water mixtures can be divided into three categories, in order of increasing water content: water-in-IL, aqueous-IL hybrid solvent and concentrate electrolytes. 29 The first two can be differentiated based on the continuity of the water network or the presence of water in a tetrahedral arrangement. 28,29,148 In these mixtures, the structure of the IL remains the governing factor of the bulk properties of the solution, and the desirable, designer features of ILs are sustained.…”