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.

We propose an innovative approach to address the pressing need for efficient and transparent evaluation techniques to assess extraction processes’ sustainability. In response to society's growing demand for natural products and the consequent surge in biomass exploration, a critical imperative arises to ensure that these processes are genuinely environmentally friendly. Extracting natural compounds has traditionally been regarded as a benign activity rooted in ancient practices. However, contemporary extraction methods can also significantly harm the environment if not carefully managed. Recognizing this, we developed a novel metric, Path2Green, tailored specifically and rooted in 12 new principles of a green extraction process. Path2Green seeks to provide a comprehensive framework beyond conventional metrics, offering a nuanced understanding of the environmental impact of extraction activities from biomass collection/production until the end of the process. By integrating factors such as resource depletion, energy consumption, waste generation, and biodiversity preservation, Path2Green aims to offer a holistic assessment of sustainability of an extraction approach. The significance of Path2Green lies in its ability to distill complex environmental data into a simple, accessible metric. This facilitates informed decision-making for stakeholders across industries, enabling them to prioritize greener extraction practices. Moreover, by setting clear benchmarks and standards, Path2Green incentivizes innovation and drives continuous improvement in sustainability efforts, being a new user-friendly methodology.

Ionic liquids (ILs) are innovative solvents that can be tuned for their specific application through the selection, or functionalization, of the cation and the anion. Although the cation has been assumed as the main driver of toxicity, the importance of the anion must not be underestimated. This study considers a series of cholinium based ILs aiming at assessing the effects of the functionalization of the cation and the anion on their ecotoxicity. These effects were assessed using three biological models, the microalgae Raphidocelis subcapitata, the macrophyte Lemna minor and the cladoceran Daphnia magna, representing aquatic ecosystems, a major putative recipient of ILs due to their high water solubility. Since the toxicity trends fluctuated depending on the biological model, the results were integrated with previous data through a species sensitivity distribution approach in an attempt to provide a useful safety variable for the design of eco-friendlier ILs. The results reported here challenge some heuristic rules previously proposed for the design of ILs, in particular in what concerns the side-chain effect for the cholinium ILs, and the notion that cholinium-based ILs are inherently safe and less environmentally hazardous than most conventional solvents. Moreover, it was confirmed that structural changes in the ILs promote differences in toxicity highlighting the importance of the role of the anion in their toxicity. Different biological systems yielded different toxicity trends across the IL series tested, also distinct from previous data retrieved with the bacteria V. fischeri; such a novel integration effort challenges the suitability of establishing structure–ecotoxicity relationships for cholinium-based IL design. Overall, this study reinforces the need to perform complete ecotoxicological characterisation before assuming ILs as suitable, environmentally compatible, alternative solvents.

This work reports a promising approach to the development of novel self-buffering and biocompatible ionic liquids for biological research in which the anions are derived from biological buffers (Good's buffers, GB). Five Good's buffers (Tricine, TES, CHES, HEPES, and MES) were neutralized with four suitable hydroxide bases (1-ethyl-3-methylimidazolium, tetramethylammonium, tetraethylammonium, and tetrabutylammonium) producing 20 Good's buffer ionic liquids (GB-ILs). The presence of the buffering action of the synthesized GB-ILs was ascertained by measuring their pH-profiles in water. Moreover, a series of mixed GB-ILs with wide buffering ranges were formulated as universal buffers. The impact of GB-ILs on bovine serum albumin (BSA), here used as a model protein, is discussed and compared with more conventional ILs using spectroscopic techniques, such as infrared and dynamic light scattering. They appear to display, in general, a greater stabilizing effect on the protein secondary structure than conventional ILs. A molecular docking study was also carried out to investigate on the binding sites of GB-IL ions to BSA. We further used the QSAR-human serum albumin binding model, log K(HSA), to calculate the binding affinity of some conventional ILs/GB-ILs to HSA. The toxicity of the GB and GB-ILs was additionally evaluated revealing that they are non-toxic against Vitro fischeri. Finally, the GB-ILs were also shown to be able to form aqueous biphasic systems when combined with aqueous solutions of inorganic or organic salts, and we tested their extraction capability for BSA. These systems were able to extract BSA with an outstanding extraction efficiency of 100% in a single step for the GB-IL-rich phase, and, as a result, the use of GB-IL-based ABS for the separation and extraction of other added-value biomolecules is highly encouraging and worthy of further investigation.