Transition of a Deep Eutectic Solution to Aqueous Solution: A Dynamical Perspective of the Dissolved Solute

Abstract

Disruption of the deep eutectic solvent (DES) nanostructure around the dissolved solute upon addition of water is investigated by polarization-selective two-dimensional infrared spectroscopy and molecular dynamics simulations. The heterogeneous DES nanostructure around the solute is partially retained up to 41 wt % of added water, although water molecules are gradually incorporated in the solute’s solvation shell even at lower hydration levels. Beyond 41 wt %, the solute is observed to be preferentially solvated by water. This composition denotes the upper hydration limit of the deep eutectic solvent above which the solute senses an aqueous solvation environment. Interestingly, our results indicate that the transition from a deep eutectic solvation environment to an aqueous one around the dissolved solute can happen at a hydration level lower than that reported for the “water in DES” to “DES in water” transition.

Structural adaptations in the bovine serum albumin protein in archetypal deep eutectic solvent reline and its aqueous mixtures

“…The observed abnormality is probably because of the structural transition in reline–water from a “DES-in-water” like at 50/50 reline/water composition to a more “water-in-DES” like structural arrangement in 75/25 reline/water composition. 29,30 On comparing the overall effect of reline DES on the BSA structure with the impact of their individual components observed in previous studies, 27,47 we deduce that the presence of urea in an extensive H-bonded network with [Ch][Cl] reduces its efficacy towards protein denaturation.…”

“…This irregular increase at this concentration variation can be a consequence of structure transition of the solvent system from “DES-in-water” to “water-in-DES” like, occurring at ∼59/41 reline/water composition. 29,30…”

“…Further addition of reline to 75/25 reline/water composition increases the viscosity of the medium as well as significantly alters the structure from aqueous solution of DES components (DES-in-water) to more like water-in-DES. 28–30 These changes in the mixture of reline–water structure and viscosity suppress the fluctuations to some extent in 75% reline; however a few of the residues gained more flexibility in this mixture.…”

“…Given the high viscosity of reline DES, the aqueous diluted reline in 50/50 and 75/25 wt % reline/water solvent systems were also considered where the solvent structure varied significantly. 28–30 BSA is a multidomain globular protein homologous to human serum albumin. 31 The BSA protein functions as a fatty acid binder and possesses a great binding affinity for various bioactive molecules and drugs, making it a potent drug delivery agent.…”

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

“…A matter that emerges from a large number of experimental reports is the effect of water on the properties of DES. It has become evident that the effect of water on the physicochemical properties and on the structural features of DES has important practical implications [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24]. Water addition promotes structural changes on DES at the microscopic level and these changes are not yet fully understood.…”