Ionic liquids (ILs) have been proposed as promising media for the extraction and separation of bioactive compounds from the most diverse origins. This critical review offers a compilation on the main results achieved by the use of ionic-liquid-based processes in the extraction and separation/purification of a large range of bioactive compounds (including small organic extractable compounds from biomass, lipids, and other hydrophobic compounds, proteins, amino acids, nucleic acids, and pharmaceuticals). ILs have been studied as solvents, cosolvents, cosurfactants, electrolytes, and adjuvants, as well as used in the creation of IL-supported materials for separation purposes. The IL-based processes hitherto reported, such as IL-based solid–liquid extractions, IL-based liquid–liquid extractions, IL-modified materials, and IL-based crystallization approaches, are here reviewed and compared in terms of extraction and separation performance. The key accomplishments and future challenges to the field are discussed, with particular emphasis on the major lacunas found within the IL community dedicated to separation processes and by suggesting some steps to overcome the current limitations.

Deep eutectic solvents (DESs) consisting of mixtures of choline halide (chloride/bromide)–urea, choline chloride–thiourea, chlorocholine chloride–urea and betaine hydrochloride–urea were demonstrated to be effective solvent systems for α-chitin. The dissolution of the biopolymer in the DESs was carried out by conventional heating, heating under microwave irradiation and heating assisted by ultrasonication under an inert atmosphere. Microwave and ultrasonication helped to reduce the time and temperature required for dissolution. Maximum dissolution of the biopolymer (9% w/w) was observed in the DES consisting of choline chloride–thiourea. The absence of insoluble particles in the solutions was confirmed by optical light microscope. No remarkable degradation of chitin during the dissolution process was observed upon investigations using FT-IR, XRD, ¹H NMR, TGA, viscometry and rheology.

Plant extract is a complex concoction of several phytochemicals, for instance, phenolics, sugars, flavonoids, xanthones, and several others. In general, it is said that hydroxyl-rich phenolics act as reducing agents for metal ions, but little is discussed about the stabilizing ligands of metal nanoparticles (NPs). Thus, despite the popularity of plant extract-mediated synthesis of NPs, the phytochemical basis of the process and the exact mechanism are still unclear. Herein, a systematic study was carried out to unveil the mechanism of St. John’s wort (Hypericum perforatum (H. perforatum) L.) extract-mediated synthesis of silver (Ag) NPs. Among the phytochemicals present in the extract, phenolic acids and flavonoids are shown to be involved in the reduction of Ag⁺ ions, while xanthones and phloroglucinols act as capping agents, and naphthodianthrones were involved in both steps. Analysis of the postreaction residues by ultra-performance liquid chromatography coupled with a photodiode array and high-resolution mass spectrometry showed a sharp decrease in the concentration of various secondary metabolites present in the extract, of which large amounts of xanthones and phloroglucinols were recovered from the NPs. Consequently, the low polar fraction of H. perforatum extract, rich in xanthones and phloroglucinols, and the pure compounds of these classes (mangiferin and hyperforin) did not reduce Ag⁺ ions. In contrast, the polar fraction of the extract, rich in flavonoids and naphthodianthrones, and the pure compounds of these classes (kaempferol-3-glucoside, quercetin, quercetin-3-glucoside, hypericin, pseudohypericin, and protohypericin) were able to reduce Ag⁺ ions. Overall, the present study contributes significantly to the understanding of green synthesis of NPs by plant extracts.

The solubility of DNA in bio-based deep eutectic solvents (DESs) consisting of mixtures of choline chloride with levulinic acid, glycerol, ethylene glycol, sorbitol and resorcinol was investigated. The macromolecule was found to be soluble and chemically and structurally stable in DESs consisting of mixtures containing glycerol and ethylene glycol. Furthermore recyclability of the DESs was demonstrated over three consecutive reuses in DNA dissolution.