Solvation dynamics of an ionic probe in choline chloride-based deep eutectic solvents

Abstract

Solvation of the thiocyanate ion in three different deep eutectic solvents (DES) was investigated by linear FTIR spectroscopy, and Two Dimensional IR spectroscopy. Linear infrared spectroscopy reveals that the thiocyanate ion forms a hydrogen bond through its sulphur atom, while its nitrile end remains free. Photon-echo vibrational spectroscopy shows that the thiocyanate has a frequency-frequency correlation function (FFCF) with two distinct dynamics occurring on the picosecond time scale in all of the studied solvents. The observed dynamics is assigned to in-place and diffusional motions of the components within the thiocyanate solvation shell. Molecular dynamics simulations and ab initio calculations confirm the experimental findings and their molecular interpretation. In addition, theoretical modeling of the thiocyanate nitrile stretch lineshape suggests that alcohol-based DES are more structurally disorganized than the amide-based analogue. However, the organization observed in the different DES is not sufficient to explain physical properties, such as density, indicating that the amount of defects (i.e., hole theory) is not sufficient to fully describe the properties of DES.

High seebeck coefficient in middle-temperature thermocell with deep eutectic solvent

“…We chose to utilize one of the DESs known as ethaline, which comprises of a 1:2 mixture of choline chloride (ChCl) and ethylene glycol (EG). Ethaline was chosen due to its disorganized characteristic, which owes to the presence of the hydroxy constituent 20 , 21 . We envisioned that this characteristic corresponds to the low internal order of the ethaline DES, allowing a for large entropy change to arise and thus a high S e to be obtained.…”

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

“…Considering the gradual lowering of viscosity upon increasing water content in the DESs, polarization-selective 2D IR spectroscopy is suitable to identify the transition from a eutectic to an aqueous environment from the solute’s perspective. As thiocyanate is one of the common vibrational probes, − we have performed polarization-selective 2D IR experiments on ammonium thiocyanate dissolved in reline and reline–water mixtures (Figures and S1). We prepared a series of aqueous reline mixtures ( x W) by mixing x (ranging from 0 to 15) moles of water (D 2 O) with one mole of reline.…”

Computer Simulations of Deep Eutectic Solvents: Challenges, Solutions, and Perspectives

“…In a study on ChCl/acetylsalicylic acid (ASA) therapeutic DESs by Saha et al [ 155 ], radial distribution functions obtained from MD simulations demonstrated the presence of several H-bonds between the components and DFT calculations allowed demonstrating that Cl − is acting as a charge transfer bridge between choline and ASA. Finally, a combination of QM and MD methods is often not an independent research method, but an auxiliary way to confirm a hypothesis formulated on the basis of experimental findings, which is no exception in the case of DES studies [ 156 , 157 ].…”