Quantum chemical investigation of choline chloride-based deep eutectic solvents

Abstract

The current quantum-based research focuses on the eutectic mixtures formulated by combining hydrogen bond donors (malic acid, tartaric acid, oxalic acid, ethylene glycol, and glycerol) and acceptor (choline chloride) molecules. Choline chloride (ChCl) is used as a hydrogen bond acceptor (HBA) having specified mole ratios with hydrogen bond donors (HBDs) to develop five deep eutectic solvents (DESs). Density functional theory (DFT) is used to examine the molecular dynamics (MD) of DESs to interpret the method's validity and quantum chemical aspects. The resemblance of the experimental Fourier-transform-infrared (FT-IR) vibrational frequencies with the calculated vibrational frequencies validates the Becke, 3-parameter, Lee–Yang–Parr (B3LYP) functional with basis set 6-31G. The frontier molecular orbitals (FMOs) and quantum chemical investigation reveal that among five solvents, DES1 (ChCl: EG) is the best solvent with the lowest energy gap (0.02 eV), highest chemical potential (0.19 eV), chemical softness (42.73 eV), and electrophilicity index (1.55 eV) and with least chemical hardness (0.01 eV) and electronegativity (−0.19 eV). This quantum acumen provides an effective revelation to design the required conductive solvents based on the DFT study. The density of states (DOS) provides insight that how many states were occupied in the unit of energy and can be used to evaluate the electronic structure. DFT-B3LYP/6-31G is used to simulate vibrational and quantum features of the experimentally prepared DESs.