Influence of water on the conformations and interactions within two choline chloride-based deep eutectic solvents: a density functional theory investigation

This work presents the study of the conformations of {[Choline][Chloride]: Phenol} ratio [ 1:2] and {[ Choline] [Chloride]:Glycolic acid} ratio [1:1] deep eutectic solvents in their isolated state and with the presence of water. The optimization of the geometries was carried out using density functional theory with the B3LYP functional and the 6-311(+ +) G(d,p) basis set. Through the study of the geometry optimization and the charge distribution, the most stable conformations of choline, choline chloride, the two aforementioned deep eutectic solvents and their cluster with water are detailed. The main hydrogen bonds are identified using the values of stabilizing energies between interacting orbitals. The results highlight the OH...Cl type of hydrogen bonds as one of the key interactions. It is found that the chloride ion acts as a hydrogen bond acceptor while the choline ion acts primarily as a hydrogen bond donor. Glycolic acid and phenol can play both roles. The molecule of water is able to form various hydrogen bonds. The strongest hydrogen bonds are observed between the chloride ion and a hydroxyl group. Finally, an increasing total number of hydrogen bonds in a system decreases the strength of the overall interactions.