Insight into the interactions that control the phase behaviour of new aqueous biphasic systems composed of polyethylene glycol polymers and ionic liquids

Aqueous Two-Phase Systems Based on Ionic Liquids and Deep Eutectic Solvents as a Tool for the Recovery of Non-Protein Bioactive Compounds—A Review

Aqueous two-phase systems (ATPS) based on ionic liquids (IL) and deep eutectic solvents (DES) are ecofriendly choices and can be used to selectively separate compounds of interest, such as bioactive compounds. Bioactive compounds are nutrients and nonnutrients of animal, plant, and microbial origin that benefit the human body in addition to their classic nutritional properties. They can also be used for technical purposes in food and as active components in the chemical and pharmaceutical industries. Because they are usually present in complex matrices and low concentrations, it is necessary to separate them in order to increase their availability and stability, and ATPS is a highlighted technique for this purpose. This review demonstrates the application of ATPS based on IL and DES as a tool for recovering nonprotein bioactive compounds, considering critical factors, results and the most recent advances in this field. In addition, the review emphasizes the perspectives for expanding the use of nonconventional ATPS in purification systems, which consider the use of molecular modelling to predict experimental conditions, the investigation of diverse compounds in phase-forming systems, the establishment of optimal operational parameters, and the verification of bioactivities after the purification process.

Phase Behavior of Ionic Liquid-Based Aqueous Two-Phase Systems

As an environmentally friendly separation medium, the ionic liquid (IL)-based aqueous two-phase system (ATPS) is attracting long-term attention from a growing number of scientists and engineers. Phase equilibrium data of IL-based ATPSs are an important basis for the design and optimization of chemical reactions and separation processes involving ILs. This article provides the recent significant progress that has been made in the field and highlights the possible directions of future developments. The effects of each component (such as salting-out agents and ILs) on the phase behavior of IL-based ATPSs are summarized and discussed in detail. We mainly focus on the phase behavior of ATPSs by using ILs, expecting to provide meaningful and valuable information that may promote further research and application.

Opposite Effects Induced by Cholinium-Based Ionic Liquid Electrolytes in the Formation of Aqueous Biphasic Systems Comprising Polyethylene Glycol and Sodium Polyacrylate

Cholinium-based ionic liquids ([Ch]-based ILs) were investigated as electrolytes in the formation of aqueous biphasic systems (ABS) composed of polyethylene glycol (PEG) and sodium polyacrylate (NaPA) polymers. Both enhancement and decrease in the liquid-liquid demixing ability induced by electrolytes in PEG-NaPA aqueous biphasic systems were observed. It is shown that the ILs that most extensively partition to the PEG-rich phase tend to act as inorganic salts enhancing the two-phase formation ability, while those that display a more significant partition to the NaPA-rich phase decrease the ABS formation capacity. The gathered results allowed us to confirm the tailoring ability of ILs and to identify, for the first time, opposite effects induced by electrolytes on the PEG-NaPA ABS formation ability. The distribution of the electrolyte ions between the coexisting phases and the polyelectrolyte ion compartmentalization are key factors behind the formation of PEG-NaPA-based ABS.

Nucleophilic degradation of diazinon in thermoreversible polymer-polymer aqueous biphasic systems

Although aqueous biphasic systems have been largely investigated in the separation and/or purification of biocompounds, their potential as reaction media to design integrated reaction-separation processes has been less explored. In this work aqueous biphasic systems (ABSs) composed of polypropylene glycol of molecular weight 400 g mol-1 (PPG 400) and different polyethylene glycols (PEGs) were characterized, and investigated for integrated reaction-separation processes, i.e. in the nucleophilic degradation of diazinon and further separation of reaction products by taking advantage of the lower-critical solution temperature (LCST) behaviour of these ABSs. The nucleophilic degradation of diazinon was carried out in the monophasic regime at 298 K, after which an increase in temperature (up to 313 K) allowed the product separation by two-phase formation (thermoreversible systems). The reaction kinetics and reaction pathways have been determined. The reaction kinetic increases as the PEG molecular weight decreases, with the half-life values obtained being competitive to those previously reported using volatile organic solvents as solvent media and significantly higher than under alkaline hydrolysis. One reaction pathway occurs in ABSs comprising PEGs of higher molecular weights, whereas in the ABS composed of PEG 600 two reaction pathways have been identified, meaning that the reaction pathways can be tailored by changing the PEG nature. ABSs formed by PEGs of lower molecular weights were identified as the most promising option to separate the pesticide degradation products by simply applying changes in temperature.

Efficient Purification of R-phycoerythrin from Marine Algae (Porphyra yezoensis) Based on a Deep Eutectic Solvents Aqueous Two-Phase System

R-phycoerythrin (R-PE), a marine bioactive protein, is abundant in Porphyra yezoensis with high protein content. In this study, R-PE was purified using a deep eutectic solvents aqueous two-phase system (DES-ATPS), combined with ammonium sulphate precipitation, and characterized by certain techniques. Firstly, choline chloride-urea (ChCl-U) was selected as the suitable DES to form ATPS for R-PE extraction. Then, single-factor experiments were conducted: the purity (A₅₆₅/A₂₈₀) of R-PE was 3.825, and the yield was 69.99% (w/w) under optimal conditions (adding 0.040 mg R-PE to ChCl-U (0.35 g)/K₂HPO₄ (0.8 g/mL, 0.5 mL) and extracting for 20 min). The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) results revealed that the purified R-PE contained three main bands. One band was presented after purification in native-PAGE. The UV-vis spectra showed characteristic absorption peaks at 495, 540, and 565 nm. R-PE displayed an emission wavelength at 570 nm when excited at 495 nm. All spectra results illustrated that the structure of R-PE remained unchanged throughout the process, proving the effectiveness of this method. Transmission electron microscope (TEM) showed that aggregation and surrounding phenomena were the driving forces for R-PE extraction. This study could provide a green and simple purification method of R-PE in drug development.

Aqueous Biphasic Systems Containing Customizable Poly(Ionic Liquid)s for Highly Efficient Extractions

Ionic liquid (IL)-based aqueous biphasic systems (ABSs) provide a sustainable and efficient alternative to conventional liquid-liquid extraction techniques and can be used for the extraction, recovery, and purification of diverse solutes. However, the construction of a high-performance ABS that has both excellent phase separation ability and extraction performance remains challenging. This study concerns the preparation of a family of novel ABSs based on poly(ionic liquid)s (PILs) with customized structure and controllable molecular weight for the extraction of bioactive compounds. Several tailor-made PILs consisting of a hydrophobic backbone, hydrophilic imidazolium pendant groups and strong hydrogen bonding basic counteranions are prepared by reversible addition fragmentation chain-transfer polymerization. The PILs have a perfect balance of hydrophobicity/hydrophilicity and functionality, affording outstanding phase separation, which was better than with either the IL monomer poly(1-butyl-3-vinylimidazolium bromide ([BVIm]Br) or the normal free-radical polymer P[BVIm]Br*. More importantly, PIL-based ABSs exhibited unprecedented high partition coefficients for six bioactive compounds including tryptophan, phenylalanine, and caffeine, as well as high extraction yields. The performance of the PIL-based ABSs could also be tuned by changing the molecular weight and anionic character of the PILs. This work shows that tailor-made PIL-based ABSs are a promising platform for bioactive compound extraction and provides significant clues for the design of new ABSs for various applications.

Green chemical engineering in China

In China, the rapid development greatly promotes the national economic power and living standard but also inevitably brings a series of environmental problems. In order to resolve these problems fundamentally, Chinese scientists have been undertaking research in the area of green chemical engineering (GCE) for many years and achieved great progresses. In this paper, we reviewed the research progresses related to GCE in China and screened four typical topics related to the Chinese resources characteristics and environmental requirements, i.e. ionic liquids and their applications, biomass utilization and bio-based materials/products, green solvent-mediated extraction technologies, and cold plasmas for coal conversion. Afterwards, the perspectives and development tendencies of GCE were proposed, and the challenges which will be faced while developing available industrial technologies in China were mentioned.

Understanding the Effect of Ionic Liquids as Adjuvants in the Partition of Biomolecules in Aqueous Two-Phase Systems Formed by Polymers and Weak Salting-Out Agents

Ionic liquids (ILs) as adjuvants in polymer-salt aqueous two-phase systems (ATPS) have been used to improve the extraction of biomolecules. However, the impact of ILs as adjuvants on the partition of biomolecules is still poorly understood. Previous works mostly focused on ATPS based on strong salting-out agents, which may mask the IL effect. In this work, ATPS formed by polyethylene glycol (PEG 400) and a weak salting-out salt ((NH₄)₂SO₄) with a wide number of ILs as adjuvants (chloride-based combined with cholinium, imidazolium, pyrrolidinium, piperidinium, tetralkylammonium and tetralkylphosphonium cations) were investigated. The respective phase diagrams were determined, and the systems extraction performance for a wide range of biomolecules (phenolic compounds, alkaloids and amino acids) was investigated. The results obtained show that ILs as adjuvants in polymer-salt ATPS modulate the partition of biomolecules. In particular, more hydrophobic ILs significantly enhance the partition of more hydrophobic biomolecules to the PEG-rich phase (where the IL is enriched). Furthermore, the intensity of the IL effect is more pronounced when using weak salting-out agents. A linear correlation between the biomolecules and the ILs partition coefficients, and with the biomolecules octanol-water partition coefficients, was found. In most ATPS formed by polymers and salts using ILs as adjuvants, the biomolecules partition is driven by the ILs partition and by the difference in hydrophobicity between the coexisting phases.

PVDF based ionogels: applications towards electrochemical devices and membrane separation processes

Ionogels have emerged as one of the most interesting and captivating form of composites which credits to the outstanding characteristics. One of the most important constituent of ionogels is ionic liquid, which show many attractive properties notably non-volatility, in-flammability, negligible vapor pressure, tunability, thermal stability and solvating ability. A large variety of matrix materials have been under consideration for ionogels, presently, polymer/ionic liquid based ionogels have attracted much attention. Numerous polymeric materials such as have been utilized for these polymer/ionic liquids based ionogels. Polyvinylidene fluoride (PVDF) has been on top of the line as a matrix material for polymer based ionogels owing to its stability, aging and chemical resistance and mechanical strength. This review is primarily concerned with the properties of polyvinylidene fluoride based ionogels with an emphasis on their applications in various domains electrochemical devices, gas separation and liquid/liquid separations.

Separation of immunoglobulin G using aqueous biphasic systems composed of cholinium-based ionic liquids and poly(propylene glycol)

BACKGROUND

The use of antibodies, such as immunoglobulin G (IgG), has faced a significant growth in the past decades for biomedical and research purposes. However, antibodies are high cost biopharmaceuticals, for which the development of alternative and cost-effective purification strategies is still in high demand.

RESULTS

Aqueous biphasic systems (ABS) composed of poly(propylene glycol) (PPG) and cholinium-based ionic liquids (ILs) were investigated for the separation of IgG. The ABS phase diagrams were determined and characterized whenever required. Initial optimization studies with commercial IgG were carried out, followed by the extraction of IgG from rabbit serum. In all ABS, IgG preferentially partitions to the IL-rich phase, unveiling preferential interactions between IgG and ILs. Good results were obtained with commercial IgG, with extraction efficiencies ranging between 93% and 100%, and recovery yields ranging between 20% and 100%. Two of the best and two of the worst identified ABS were then evaluated in what concerns their performance to separate and recover IgG from rabbit serum. With these ABS, extraction efficiencies of 100% and recovery yields > 80% were obtained, indicating an increase in the recovery yield and extraction efficiencies when using real matrices. Under the best conditions studied, IgG with a purity level of 49% was obtained in a single-step. This purity level of IgG is higher than those previously reported using other IL-polymer ABS.

CONCLUSION

IgG preferentially migrates to the IL-rich phase in ABS formed by ILs and polymers, allowing the design of effective separation systems for its recovery from serum samples.

Odd-even effect on the formation of aqueous biphasic systems formed by 1-alkyl-3-methylimidazolium chloride ionic liquids and salts

This work provides a comprehensive evaluation of the effect of the cation alkyl side chain length of the 1-alkyl-3-methylimidazolium chloride series ([C _n C₁im]Cl, n = 2-14) of ionic liquids (ILs) on their capability to form aqueous biphasic systems (ABSs) with salts and self-aggregation derived properties. The liquid-liquid phase behavior of ternary systems composed of [C _n C₁im]Cl, water, and K₃PO₄ or K₂CO₃ and the respective Setschenow salting-out coefficients (k_s ), a quantitative measure of the two-phase formation ability, were determined. An odd-even effect in the k_s values along the number of methylene groups of the longest IL cation alkyl side chain was identified for the ABS formed by K₂CO₃, a weaker salting-out agent where the phenomenon is clearly identified. In general, cations with even alkyl side chains, being likely to display higher molar volumes, are more easily salted-out and thus more prone to undergo phase separation. The odd-even effect in the k_s values is, however, more significant in ILs up to n = 6, where the nanostructuration/nanosegregation of ILs plays a less relevant role. Still, with the [C _n C₁im]Cl (n = 7-14) series of ILs, an odd-even effect was also identified in the ILs' ionization degree, molar conductivity, and conductivity at infinite dilution. In summary, it is shown here that the ILs' odd-even effect occurs in IL aqueous solutions and not just in neat ILs, an already well-established phenomenon occurring in a series of ILs' properties described as a result of the orientation of the terminal methyl groups to the imidazolium ring cation and consequent effect in the ILs' cohesive energy.

An integrated process for enzymatic catalysis allowing product recovery and enzyme reuse by applying thermoreversible aqueous biphasic systems

Thermoreversible aqueous biphasic systems (ABS) composed of ammonium-based zwitterions (ZIs) and polymers are here disclosed to act as integrated bioreaction-separation processes. The biocatalytic reaction involving laccase occurs in homogeneous media, after which small changes in temperature induce the formation of two phases and the complete separation of the enzyme from the products in a single-step. These systems also allow the recover and reuse of the enzyme, along with the ZI-rich phase, contributing towards the development of sustainable biocatalytic processes.

Aqueous biphasic systems composed of ionic liquids and polypropylene glycol: insights into their liquid-liquid demixing mechanisms

Novel ternary phase diagrams of aqueous biphasic systems (ABSs) composed of polypropylene glycol with an average molecular weight of 400 g mol(-1) (PPG-400) and a vast number of ionic liquids (ILs) were determined. The large array of selected ILs allowed us to evaluate their tuneable structural features, namely the effect of the anion nature, cation core and cation alkyl side chain length on the phase behaviour. Additional evidence on the molecular-level mechanisms which rule the phase splitting was obtained by (1)H NMR (Nuclear Magnetic Resonance) spectroscopy and by COSMO-RS (Conductor-like Screening Model for Real Solvents). Some systems, for which the IL-PPG-400 pairs are completely miscible, revealed to be of type "0". All data collected suggest that the formation of PPG-IL-based ABSs is controlled by the interactions established between the IL and PPG, contrarily to previous reports where a "salting-out" phenomenon exerted by the IL over the polymer in aqueous media was proposed as the dominant effect in ABS formation. The influence of temperature on the liquid-liquid demixing was also evaluated. In general, an increase in temperature favours the formation of an ABS in agreement with the lower critical solution temperature (LCST) phase behaviour usually observed in polymer-IL binary mixtures. Partition results of a dye (chloroanilic acid, in its neutral form) further confirm the possibility of tailoring the phases' polarities of IL-PPG-based ABSs.

Evaluation of the effect of ionic liquids as adjuvants in polymer-based aqueous biphasic systems using biomolecules as molecular probes

Aqueous biphasic systems (ABS) have been largely investigated for the extraction, separation and/or purification of biomolecules. Recently, the use of ionic liquids (ILs) as additives in conventional polymer-based ABS was proposed to overcome the limited range of polarities of the coexisting phases. However, the impact of ILs on the partitioning of biomolecules on IL additivated ABS is not universal and is still poorly understood. Aiming at obtaining additional insights on this matter, the effects of the chemical structure of the IL, tie-line length (TLL) and biomolecule nature upon the partition of a series of model biomolecules were investigated. For this purpose, ternary ABS (composed of polyethylene glycol (PEG) 400, citrate buffer at pH 7.0, and water), and several quaternary ABS (composed of PEG 400, citrate buffer at pH 7.0, water and ILs at 5 wt%), were prepared using different chloride-based ILs ([C₄mim]Cl, [C₄mpyr]Cl, [C₄mpip]Cl, [P₄₄₄₄]Cl and [N₄₄₄₄]Cl). The partition of a wide range of biomolecules in these systems (gallic acid, vanillic acid, eugenol, nicotine, caffeine, l-tryptophan, l-phenylalanine and l-tyrosine), used here as molecular probes, was studied. These solutes were chosen due to their wide range of polarities. The results obtained support the concept that ILs, when used as adjuvants in polymer-based ABS, change the coexisting phases' characteristics and modify the partition behavior of biomolecules. In general, a positive effect derived from the use of ILs as adjuvants in PEG-salt systems is observed, particularly when dealing with more hydrophobic biomolecules, whereas IL + salt ABS perform better in the extraction of more hydrophilic biomolecules. The favourable partition of more hydrophilic biomolecules in IL + salt ABS seems to be ruled by specific interactions with the IL, while the favourable partition of more hydrophobic biomolecules in PEG + salt and PEG + salt + IL seems to be governed by the differences in the phases hydrophobicities. It is shown that ILs preferentially migrate to the PEG-rich phase, and that there is a correlation between the partition coefficients of the biomolecules and ILs and the biomolecules octanol-water partition coefficients.

Temperature dependency of aqueous biphasic systems: an alternative approach for exploring the differences between Coulombic-dominated salts and ionic liquids

Herein we propose an alternative way to distinguish ionic liquids from Coulombic-dominated salts, based not on their upper limit melting temperature (100 °C), but on the trend of their phase-forming abilities to create aqueous biphasic systems as a function of temperature, in which a wider plethora of interactions can be appraised.

Scaling-up and ionic liquid-based extraction of pectinases from Aspergillus flavipes cultures

The viability of the scaling-up of pectinases production by Aspergillus flavipes at 5L-bioreactor scale has been demonstrated by keeping constant the power input, and a drastic increase in the endo- and exopectinolytic enzyme production was recorded (7- and 40-fold, respectively). The main process variables were modelled by means of logistic and Gompertz equations. In order to overcome the limitations of the conventional downstream strategies, a novel extraction strategy was proposed on the basis of the adequate salting-out potential of two biocompatible cholinium-based ionic liquids (N_1112OHCl and N_1112OHH₂PO₄) in aqueous solutions of Tergitol, reaching more than 90% of extraction.

Suitability of bio-based ionic liquids for the extraction and purification of IgG antibodies

In the past decade, remarkable advances in the production and use of antibodies as therapeutic drugs and in research/diagnostic fields have led to their recognition as value-added proteins. These biopharmaceuticals have become increasingly important, reinforcing the current demand for the development of more benign, scalable and cost-effective techniques for their purification. Typical polymer-polymer and polymer-salt aqueous biphasic systems (ABS) have been studied for such a goal; yet, the limited polarity range of the coexisting phases and their low selective nature still are their major drawbacks. To overcome this limitation, in this work, ABS formed by bio-based ionic liquids (ILs) and biocompatible polymers were investigated. Bio-based ILs composed of ions derived from natural sources, namely composed of the cholinium cation and anions derived from plants natural acids, have been designed, synthesized, characterized and used for the creation of ABS with polypropyleneglycol (PPG 400). The respective ternary phase diagrams were initially determined at 25 °C to infer on mixture compositions required to form aqueous systems of two phases, further applied in the extraction of pure immunoglobulin G (IgG) to identify the most promising bio-based ILs, and finally employed in the purification of IgG from complex and real matrices of rabbit serum. Remarkably, the complete extraction of IgG to the IL-rich phase was achieved in a single-step. With pure IgG a recovery yield of 100% was obtained, while with rabbit serum this value slightly decreased to ca. 85%. Nevertheless, a 58% enhancement in the IgG purity was achieved when compared with its purity in serum samples. The stability of IgG before and after extraction was also evaluated by size exclusion high-performance liquid chromatography (SE-HPLC), sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared spectroscopy (FTIR). In most ABS formed by bio-based ILs, IgG retained its native structure, without degradation or denaturation effects, supporting thus their potential as remarkable platforms for the purification of high-cost biopharmaceuticals.

A critical assessment of the mechanisms governing the formation of aqueous biphasic systems composed of protic ionic liquids and polyethylene glycol

An extensive study on the formation of aqueous biphasic systems (ABS) using aqueous solutions of protic ionic liquids (PILs) and polyethylene glycol (PEG) was performed in order to understand the mechanisms underlying the phase separation. Aqueous solutions of PEG polymers with different molecular weights (600, 1000, 2000, and 3400 g mol^-1) and several N-alkyl-, dialkyl-, and trialkyl-ammonium salts of acetate, propanoate, butanoate, hexanoate and octanoate were prepared and their ability to form ABS at several temperatures assessed. The ternary liquid-liquid phase diagrams were determined at several temperatures, as well as binary PIL (or salt)-PEG-1000 and salt-water solubility data to better clarify the mechanisms responsible for the phase separation. All data gathered indicate that the formation of PEG-PIL-based ABS is mainly governed by the PIL-PEG mutual interactions, where PILs with a higher solubility in the polymer exhibit a lower aptitude to form ABS displaying thus a smaller biphasic region, for which a direct correlation was identified. The effects of the molecular weight and temperature of the polymer were also addressed. The increase of the PEG hydrophobicity or molecular weight favours the phase separation, whereas the effect of temperature was found to be more complex and dependent on the nature of the PIL, with an increase or decrease of the biphasic regime with an increase in temperature.