Francisca A. e Silva

Ionic-Liquid-Mediated Extraction and Separation Processes for Bioactive Compounds: Past, Present, and Future Trends

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.

Novel biocompatible and self-buffering ionic liquids for biopharmaceutical applications.

Antibodies obtained from egg yolk of immunized hens, immunoglobulin Y (IgY), are an alternative to the most focused mammal antibodies, because they can be obtained in higher titers by less invasive approaches. However, the production cost of high-quality IgY for large-scale applications remains higher than that of other drug therapies due to the lack of efficient purification methods. The search for new purification platforms is thus vital. The solution could be liquid-liquid extraction by using aqueous biphasic systems (ABS). Herein, we report the extraction and attempted purification of IgY from chicken egg yolk by using a new ABS composed of polymers and Goods buffer ionic liquids (GB-ILs). New self-buffering and biocompatible ILs based on the cholinium cation and anions derived from Goods buffers were synthesized and the self-buffering characteristics and toxicity were characterized. Moreover, when these GB-ILs are combined with PPG 400 (poly(propylene) glycol with a molecular weight of 400 g mol(-1)) to form ABS, extraction efficiencies, of the water-soluble fraction of proteins, ranging between 79 and 94% were achieved in a single step. Based on computational investigations, we also demonstrate that the preferential partitioning of IgY for the GB-IL-rich phase is dominated by hydrogen-bonding and van der Waals interactions.

Environmental safety of cholinium-based ionic liquids: assessing structure-ecotoxicity relationships

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.

Good's buffers as a basis for developing self-buffering and biocompatible ionic liquids for biological research

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 (Goods buffers, GB). Five Goods buffers (Tricine, TES, CHES, HEPES, and MES) were neutralized with four suitable hydroxide bases (1-ethyl-3-methylimidazolium, tetramethylammonium, tetraethylammonium, and tetrabutylammonium) producing 20 Goods 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.

Sustainable design for environment-friendly mono and dicationic cholinium-based ionic liquids.

Cholinium-based ionic liquids are receiving crescent interest in diverse areas of application given their biological compatibility and potential for industrial application. In this work, mono and dicationic cholinium ionic liquids as well as cholinium derivatives were synthesized and their toxicity assessed using the luminescent bacteria Vibrio fischeri. A range of cholinium derivatives was synthesized, using different amines and the correspondent brominated derivatives, through the alkylation of the amine with the halide in MeCN. The results indicate that their toxicity is highly dependent on the structural modifications of the cholinium cation, mainly related to the alkyl side or linkage chain length, number of hydroxyethyl groups and insertion of carbon-carbon multiple bonds. The data indicated that it is possible to perform environmentally advantageous structural alterations, namely the addition of double bonds, which would not negatively affect V. fischeri. Moreover, the dicationic compounds revealed a significantly lower toxicity than the monocationic counterparts. The picture emerging from the results supports the idea that cholinium derivatives are promising ionic liquids with a low environmental impact, emphasizing the importance of a careful and directed design of ionic liquid structures.

Ionic liquid-based aqueous biphasic systems as a versatile tool for the recovery of antioxidant compounds

The comparative evaluation of distinct types of ionic liquid‐based aqueous biphasic systems (IL‐ABS) and more conventional polymer/salt‐based ABS to the extraction of two antioxidants, eugenol and propyl gallate, is focused. In a first approach, IL‐ABS composed of ILs and potassium citrate (C6H5K3O7/C6H8O7) buffer at pH 7 were applied to the extraction of two antioxidants, enabling the assessment of the impact of IL cation core on the extraction. The second approach uses ABS composed of polyethylene glycol (PEG) and potassium phosphate (K2HPO4/KH2PO4) buffer at pH 7 with imidazolium‐based ILs as adjuvants. Their application to the extraction of the compounds allowed the investigation of the impact of the presence/absence of IL, the PEG molecular weight, and the alkyl side chain length of the imidazolium cation on the partition. It is possible to maximize the extractive performance of both antioxidants up to 100% using both types of IL‐ABS. The IL enhances the performance of ABS technology. The data puts in evidence the pivotal role of the appropriate selection of the ABS components and design to develop a successful extractive process, from both environmental and performance points of view.

Recovery of an antidepressant from pharmaceutical wastes using ionic liquid-based aqueous biphasic systems

This study is aimed at developing a sustainable process for the recovery of valuable drugs from pharmaceutical wastes using ionic liquid (IL)-based aqueous biphasic systems (ABS). Because in pharmaceutical wastes, excipients represent the major contaminants, the search for selective routes for their elimination is of primordial relevance and for that purpose IL-based ABS were evaluated. The effects of different process parameters, namely the IL nature, pH and mixture composition used in the extraction system, were studied and the process was optimized to maximize the extraction of the antidepressant from pharmaceutical wastes. Moreover, the maximum amount of amitriptyline able to be processed using such systems was assessed. The set of ABS investigated herein revealed a high extraction performance, as indicated by the outstanding logarithmic functions of the amitriptilyne partition coefficients ranging from 2.41 ± 0.05 to >2.5 and extraction efficiencies between 66% ± 1% and 100%. The best ABS and conditions were considered in the development of an integrated multi-step purification process. The process here proposed comprises three main stages as follows: the solid–liquid extraction of the antidepressant from ADT 25 pills, its purification using the optimal IL-based ABS and the antidepressant isolation by precipitation with anti-solvent. After the removal of most water insoluble excipients in the first step, with the selected IL-based ABS, it was possible to further eliminate water soluble contaminants. A high capability of extraction and purification, leading to the selective separation of amitriptyline hydrochloride from the main contaminants contained in solid pharmaceutical wastes was achieved. Finally, the isolation of the amitriptilyne in a pure state was successfully accomplished through precipitation with the anti-solvent.

Recovery of ibuprofen from pharmaceutical wastes using ionic liquids

This work aims at developing a process to valorise pharmaceutical wastes through the recovery of pharmaceutically active compounds. The ibuprofen extraction and isolation from solid pharmaceutical wastes is used here as a case study and an integrated approach comprising the ibuprofen solid–liquid extraction, the removal of the insoluble excipients present in the pills, the target drug recovery and the recycling of the aqueous solutions is proposed. The present work is centred on the optimization of the first (solid–liquid extraction) and third (drug recovery) steps mentioned above. For the solid–liquid extraction step, various ionic liquid aqueous solutions were tested, tetrabutylammonium chloride ([N4444]Cl) being adopted to further optimize the process. A solution composed of 45 wt% of [N4444]Cl + 5 wt% of citrate buffer + 50 wt% of H2O led to the highest ibuprofen extraction efficiency (EEIBU = 97.92 ± 2.65%) while in the absence of citrate the extraction efficiency was somewhat lower (EEIBU = 93.53 ± 0.62%). The polishing task was affected by the type of aqueous solution utilized during the solid–liquid extraction step: in the presence of citrate buffer water was not prone to induce significant ibuprofen precipitation (maximum REIBU of 34.71 ± 4.00%) the aqueous KCl solution being the best option (maximum REIBU of 87.97 ± 1.00%); when no citrate buffer is used water can be used as an anti-solvent with a maximum REIBU of 91.60 ± 0.19% while aqueous KCl solutions lead to an REIBU up to 97.07 ± 0.14%. Based on these results an integrated process is proposed for the ibuprofen recovery and isolation aimed at adding value to pharmaceutical wastes.