Biocompatible Deep Eutectic Solvents Based on Choline Chloride: Characterization and Application to the Extraction of Rutin from Sophora japonica

The development of novel green solvents has been one of the hottest subjects in green chemistry. Deep eutectic solvents (DESs) have logically and naturally emerged in the search for more biocompatible and biodegradable solvents. In this study, some basic physical properties, including viscosity, conductivity, and density, of 20 DESs prepared from choline chloride and various hydrogen-bond donors were investigated systematically. In addition, the biocompatibility of the tested DESs was qualitatively and quantitatively evaluated using two Gram-positive (Staphylococcus aureus and Listeria monocytogenes) and two Gram-negative (Escherichia coli and Salmonella enteritidis) bacteria. A closed bottle test was used to assess the biodegradability of these DESs. The results demonstrated that these choline chloride-based DESs were excellent solvents with extremely low toxicity and favorable biodegradability. Finally, DESs were used to extract a flavonoid (rutin) from the flower buds of Sophora japonica. An extraction efficiency of 194.17 ± 2.31 mg·g–1 was achieved using choline chloride/triethylene glycol containing 20% water. The excellent properties of DESs indicate their potential as promising green solvents for the extraction of rutin with favorable prospects for wide use in the field of green technology.