Study of the chlorogenic acid extraction with choline chloride-based deep eutectic solvents and its non-covalent interactions analysis

The microwave-assisted extraction of the main phenolic component of green coffee beans, chlorogenic acid (CGA), was carried out employing deep eutectic solvents based on choline chloride and five different hydrogen bond donors (HBD) in a 1:2 ratio. The best performance for the extraction process of CGA was reached by the mixtures of choline chloride/ethylene glycol and choline chloride/urea. To understand the various interactions between the phenolic compound and the two most efficient deep eutectic solvents, computational calculations were carried out at the density functional theory (DFT) level, as well as Atoms in Molecules (AIM) and Non-Covalent Interactions (NCIs) analyses. In that way, a variety of hydrogen bond types were found in every structure. Nevertheless, the CGA does not disrupt the hydrogen bond network established between ChCl and the HBD. Among the strongest interactions are those hydrogen bonds between the quinic acid moiety and the ethylene glycol or the urea. In addition, the thermochemistry of the formation of the two main deep eutectic solvents and their corresponding complexes with CGA was calculated, where the formation of urea-based structures was slightly more effective by ~3 kcal/mol.