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Deep eutectic solvents (DES) are eutectic mixtures of hydrogen bond acceptors and hydrogen bond donors. The stability of DES depends on the nature of interatomic interactions during their structural formation. This study focuses on the structural analysis of choline chloride (ChCl)-urea DES system (molar ratio 1:2) at the atomic level using density functional theory. Both gauche- and trans- conformers of choline were considered for geometric optimization with chloride anion at various orientations. The most stable structure of each conformer was further considered with urea to optimize the DES structure. Energy Decomposition Analysis (EDA) study showed that the binding energy (Δ E b i n d) for gauche- DES was more negative (−82.59 kJ/mol) than trans- DES (−7.60 kJ/mol). This indicated lower bond strength in trans- DES, hence higher stability in gauche- DES. It also agrees with calculation by dispersion energy, the Bader's atoms-in-molecules theory for electrostatic interactions, the frontier molecular orbital analysis and Non-Covalent Interactions (NCI) analysis. [Display omitted] • The hydrogen bond and dihydrogen bond play major role in the formation of DES. • HOMO-LUMO energy gap confirmed that gauche- DES is less reactive than trans- DES. • Electrostatic interactions are higher for the gauche- DES as per QTAIM theory. • The stability of the gauche- DES structure was mainly affected by the steric energy. [ABSTRACT FROM AUTHOR]

The interaction of CO 2 with different deep eutectic solvents (DES) has been studied at the molecular level using density functional theory. Choline chloride and choline bromide were selected as the hydrogen bond acceptors (HBA); urea, ethylene glycol and glycerol were selected as the hydrogen bond donors (HBD). The type and intensity of interactions in DES and that between DES and CO 2 molecules at various interaction sites as well as the quantification of short-range interactions has been studied using Bader's quantum theory of atoms in molecules (QTAIM). The distribution of electrostatic potential (ESP) charges during these interactions has been detailed using the Charges from ESP using a grid (CHELPG) scheme. The non-covalent interactions have been identified using the reduced density gradient (RDG) analysis. Strong van der Waals forces were observed to contribute in the formation of DES. The highest interaction energy of −10.65 kcal/mol was found between the DES2 that comprised of choline chloride and ethylene glycol in the molar ratio of 1:2 and the CO 2. The results of this study show that both HBA and HBD affect the interaction between CO 2 and DES. This study can contribute in designing more specific DES for CO 2 capture and utilization. [Display omitted] [ABSTRACT FROM AUTHOR]