Atomistic molecular dynamics simulations have been performed to investigate the microscopic structure of ethaline deep eutectic solvent (DES), a mixture of choline chloride ([Ch][Cl]) and ethylene glycol (EG) in molar ratio of 1:2, respectively. As much as the structure of a DES is derived by the composition of the species present in it, the chemical nature of the hydrogen bond donor species involved also plays a crucial role in laying down the microscopic structure of DESs. By virtue of its inherent chemical structure, EG renders both intra-and intermolecular hydrogen bonds. Therefore, the molecular level structural landscape of DESs containing EG as hydrogen bond donor is reckoned to be a bit complex. In the present study, we aim to understand the structural morphology of ethaline using optimum force-field parameters for EG recently proposed by our group. After an initial assessment of the refined force-field parameters for ethaline DES, we have presented an in-depth analysis of the arrangement and ordering of its components at the molecular level. Simulated X-ray scattering structure function and its partial components reveal the presence of short-range as well as long-range interactions in ethaline. The role of hydrogen bonding interactions among all the three species [Ch] + , [Cl] − , and EG was predominantly observed through radial and radial−angular distribution functions and substantiated by spatial distribution functions. The observation of the competitive nature of [Ch] + and EG to form a hydrogen bond with the anion is one of the major outcomes of the present study. Also, weaker intra-and intermolecular hydrogen bonding interactions between EG molecules were seen along with their simultaneous involvement with the ammonium group of the choline cation.

Deep eutectic solvents (DESs) are emerging as an alternative media for the sequestration of greenhouse gases such as CO 2 and SO 2 . Herein, we performed ab initio molecular dynamics (AIMD) simulations to elucidate the solvation structure around CO 2 and SO 2 in choline chloride-based DESs, namely, reline and ethaline. We show that in all four systems the structures of the nearest neighbor shells around these molecules are distinct. We observe that because of the electrophilic character, the carbon atom of CO 2 and the sulfur atom of SO 2 are preferentially solvated by the chloride anions. The strength of the correlation between the chloride anions and the sulfur atom is much stronger because of charge transfer, which is more profound in ethaline DES. In both DESs, the choline cations are found to be closer to the oxygen atoms of CO 2 and SO 2 . We observe that upon changing the solute from CO 2 to SO 2 , the nearest neighbor solvation structure changes drastically; while the chloride anions prefer to stay in a circular shell around the carbon atom of CO 2 , they are found to be much more localized near the sulfur atom of SO 2 . The solvation shells formed by the urea molecules in reline and EG molecules in ethaline also overlap with that of the chloride anion around CO 2 . In ethaline, the hydroxyl group of the choline cation is found to be closer to the solute molecules as compared to its ammonium headgroup.

The observation of the prepeak in the simulated total X-ray scattering structure function (S(q)) reveals the presence of intermediate-range structural heterogeneity in hydrophobic deep eutectic solvents.

Because of the rising concentration of harmful greenhouse gases like methane in the atmosphere, researchers are striving for developing novel techniques for capturing these gases. Recently, neoteric liquids such as deep eutectic solvents (DESs) have emerged as an efficient means of sequestration of methane. Herein, we have performed ab initio molecular dynamics (AIMD) simulations to elucidate the solvation structure around a methane molecule dissolved in reline and ethaline DESs. We aim to elicit the structural organization of different constituents of the DESs in the vicinity of methane, particularly highlighting the key interactions that stabilize such gases in DESs. We observe quite different solvation structures of methane in the two DESs. In ethaline, chloride ions play an active role in solvating methane. Instead, in reline, chloride ions do not interact much with the methane molecule in the first solvation shell. In reline, choline cations approach the methane molecule from their hydroxyl group side, whereas urea molecules approach methane from their carbonyl oxygen as well as amide group sides. In ethaline, ethylene glycol and Cl– dominate the nearest neighbor solvation structure around the methane molecule. In both the DESs, we do not observe any significant methane–DES charge transfer interactions, apart from what is present between choline cation and Cl– anion.

Hydrophobic deep eutectic solvents (HDESs) have gained immense popularity because of their promising applications in extraction processes. Herein, we employ atomistic molecular dynamics simulations to unveil the dynamics of DL-menthol (DLM) based HDESs with hexanoic (C6), octanoic (C8), and decanoic (C10) acids as hydrogen bond donors. The particular focus is on understanding the nature of dynamics with changing acid tail length. For all three HDESs, two modes of hydrogen bond relaxations are observed. We observe longer hydrogen bond lifetimes of the inter-molecular hydrogen bonding interactions between the carbonyl oxygen of the acid and hydroxyl oxygen of menthol with hydroxyl hydrogen of both acids and menthol. We infer strong hydrogen bonding between them compared to that between hydroxyl oxygen of acids and hydroxyl hydrogens of menthol and acids, marked by a faster decay rate and shorter hydrogen bond lifetime. The translational dynamics of the species in the HDES becomes slower with increasing tail length of the organic acid. Slightly enhanced caging is also observed for the HDES with a longer tail length of the acids. The evidence of dynamic heterogeneity in the displacements of the component molecules is observed in all the HDESs. From the values of the α-relaxation time scale, we observe that the molecular displacements become random in a shorter time scale for DLM-C6. The analysis of the self-van Hove function reveals that the overall distance covered by DLM and acid molecules in the respective HDES is more than what is expected from ideal diffusion. As marked by the shorter time scale associated with hole filling, the diffusion of the oxygen atom of menthol and the carbonyl oxygen of acid from one site to the other is fastest for hexanoic acid containing HDES.