No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Mechanisms ruling the partition of solutes in ionic-liquid-based aqueous biphasic systems – the multiple effects of ionic liquids
Abstract
In the past decade it has been demonstrated the remarkable potential of ionic-liquid-based aqueous biphasic systems (IL-based ABS) to extract and purify a large range of valued-added biocompounds. However, the transposal of lab-experiments to an industrial scale has been precluded by a poor understanding of the molecular-level mechanisms ruling the separation or partition of target compounds between the coexisting phases. To overcome this limitation we carried out a systematic evaluation of specific interactions, induced by ILs and several salts used as phase-forming components, and their impact on the partition of several solutes in IL-based ABS. To this end, the physicochemical characterization of ABS composed of imidazolium-based ILs, three salts (Na2SO4, K2CO3 and K3C6H5O7) and water was performed. The ability of the coexisting phases to participate in different solute-solvent interactions (where “solvent” corresponds to each ABS phase), were estimated based on the Gibbs free energy of transfer of a methylene group between the phases in equilibrium,∆G(〖CH〗_2), and on the Kamlet-Taft parameters – dipolarity/polarizability (π^*), hydrogen-bonding donor acidity (α) and hydrogen-bonding acceptor basicity (β) – of the coexisting phases. Relationships between the partition coefficients, the phases properties expressed as Kamlet-Taft parameters and COSMO-RS descriptors were established, highlighting the ability of ILs to establish specific interactions with given solutes. The assembled results clearly support the idea that the partition of solutes in IL-based ABS is due to multiple effects resulting from both global solute-solvent and specific solute-IL interactions. Solute-IL specific interactions are often dominant in IL-based ABS, explaining the higher partition coefficients, extraction efficiencies and selectivities observed with these systems when compared to more traditional ones majorly composed of polymers.
... To obtain the parameter α (hydrogen-bond donating ability), the probe pyridine-N-oxide (PyO) was used, and following standard procedures, determined by 13 C nuclear magnetic resonance (NMR) spectra, using a Bruker Avance 300 equipment operating at 75 MHz, deuterium oxide (D 2 O) as solvent and trimethylsilyl propanoic acid (TSP) as the internal reference. The 13 C NMR chemical shifts δ(Ci) in ppm of the carbon atoms in positions i = 2 and 4 of pyridine-N-oxide were determined, and α was calculated by [31][32][33]: ...
Artemisinin is an antimalarial substance very sparingly soluble in water. In the attempt to identify environmental-friendly and non-toxic aqueous-based solvents to extract it from Artemisia annua L., the solubility of artemisinin in aqueous solutions of different hydrotropes was measured at 303.2 K, for hydrotrope concentrations up to 5 M. The ability of the studied hydrotropes for enhancing the artemisinin solubility increases in the following order: Na[N(CN)2] < Na[SCN] < [Chol][Van] < [Chol][Gal] < [N4,4,4,4]Cl < [Chol][Sal] < [P4,4,4,4]Cl < Na[Sal], with Na[Sal] allowing an increase in the solubility of 750fold compared to pure water.
The COSMO-RS model and experimental Kamlet-Taft solvatochromic parameters were applied to connect the solubility enhancement with solvent properties. At low hydrotrope concentration, the solubility increases with the decreasing of the difference between the Apolar Factors of the hydrotrope and artemisinin, while for higher hydrotrope concentration, the hydrogen-bond acceptor character of the hydrotrope seem to have an impact on the solubility enhancement. Even if some mechanistic understanding is still to unfold, quantitatively the empirical correlations of solubility enhancement with the hydrotrope concentration and the solvatochromic parameters show very high accuracy. In particular, 93% of the change on the artemisinin solubility enhancement could be explained using the hydrotrope concentration and two combined solvatochromic parameters (αβ and π*2) as explaining variables.
... The pH of each phase was also determined. The fitting of the experimental binodal curves and calculation of the TLLs were accomplished according to the literature [44]. Studies on the ferulic acid partition were conducted using biphasic mixtures, and the experimental details can be found in the Supplementary Materials. ...
Bio-based ionic liquids (ILs) are being increasingly sought after, as they are more sustainable and eco-friendly. Purines are the most widely distributed, naturally occurring N-heterocycles, but their low water-solubility limits their application. In this work, four purines (theobromine, theophylline, xanthine, and uric acid) were combined with the cation tetrabutylammonium to synthesize bio-based ILs. The physico–chemical properties of the purine-based ILs were characterized, including their melting and decomposition temperatures and water-solubility. The ecotoxicity against the microalgae Raphidocelis subcapitata was also determined. The ILs show good thermal stability (>457 K) and an aqueous solubility enhancement ranging from 53- to 870-fold, in comparison to their respective purine percursors, unlocking new prospects for their application where aqueous solutions are demanded. The ecotoxicity of these ILs seems to be dominated by the cation, and it is similar to chloride-based IL, emphasizing that the use of natural anions does not necessarily translate to more benign ILs. The application of the novel ILs in the formation of aqueous biphasic systems (ABS), and as solubility enhancers, was also evaluated. The ILs were able to form ABS with sodium sulfate and tripotassium citrate salts. The development of thermoresponsive ABS, using sodium sulfate as a salting-out agent, was accomplished, with the ILs having different thermosensitivities. In addition, the purine-based ILs acted as solubility enhancers of ferulic acid in aqueous solution.
... For GLC, chromatographic retention is a very complex process because there are multiple intermolecular forces, e.g., London forces (or dispersion), dipole-dipole, or Keesom forces (orientation), dipole-induced dipole or Debye forces (induction), and electron donor-acceptor forces. Hydrogen bonding can lead to the partition of the solute between the gas and liquid phases [26][27][28]. Besides these forces, the size and shape of solute including the steric hindrance of substituent groups within its molecule can also affect chromatographic behavior [29][30][31]. ...
A novel approach is introduced for reliable prediction of the retention time of morphine and its derivatives, which have widespread use in medical and pharmaceutical applications. A core correlation is introduced based on the number of carbon and hydrogen atoms as well as the number of ester, noncyclic ether, and ketone functional groups from experimental data of 42 compounds. An improved correlation is developed to increase the reliability of the core correlation by inserting a correcting function. The reliability of two correlations is tested and compared with the best available complex method based on a backpropagation artificial neural network (BP-ANN) for further 15 compounds. The values of root mean squared error (RMSE) of core and improved correlations for the test set are 0.5681 and 0.4832 min, which are lower than those reported by BP-ANN (0.6052 min). Cross-validations of the improved correlation corresponding to the coefficients of determination for leave-one-out (Q²LOO) and the fivefold cross-validation (Q²5CV) are close to its the coefficient of determination (R² = 0.982), which confirms goodness-of-fit, goodness-of-prediction, accuracy, and precision of the novel model.
... This approach consists on the use of a set of solvatochromic probes which allow the assessment of different interactions for the same solvent, such as its dipolarity/polarizability (π*) and hydrogen-bond acceptor abilities (β) [58][59][60]. This approach has been successfully used for the description of solutes partition in ATPS composed of polymers and salts [61][62][63], and salts and ionic liquids [64]. ...
... [18][19][20][21][22][23] By using ILs as phase-forming components of ABS it is possible to tailor the phases' polarities and affinities to specific bioproducts, overcoming the limited polarity difference presented by traditional polymer-based systems. 18,24 Given the designer solvents ability of ILs, they can be foreseen as promising phase-forming components to carry out the purification and recovery of mAbs. To the best of our knowledge, there are no reports in the literature considering the mAbs recovery from CHO cell culture supernatants using ILs as phase-forming components of ABS. ...
Monoclonal antibodies (mAbs) are of crucial interest for therapeutic purposes, particularly in vaccination and immunization, and in the treatment of life-threatening diseases. However, their downstream processing from the complex cell culture media in which they are produced still requires multiple steps, making mAbs extremely high-cost products. Therefore, the development of cost-effective, sustainable and biocompatible purification strategies for mAbs is in high demand to decrease the associated economic, environmental and health burdens. Herein, novel aqueous biphasic systems (ABS) composed of glycine–betaine analogue ionic liquids (AGB-ILs) and K2HPO4/KH2PO4 at pH 7.0, the respective three-phase partitioning (TPP) systems, and hybrid processes combined with ultrafiltration were investigated and compared in terms of performance as alternative strategies for the purification and recovery of anti-human interleukin-8 (anti-IL-8) mAbs, which are specific therapeutics in the treatment of inflammatory diseases, from Chinese Hamster Ovary (CHO) cell culture supernatants. With the studied ABS, mAbs preferentially partition to the IL-rich phase, with recovery yields up to 100% and purification factors up to 1.6. The best systems were optimized in what concerns the IL concentration, allowing to take advantage of IL-based three-phase partitioning approaches where a precipitate enriched in mAbs is obtained at the ABS interface, yielding 41.0% of IgG with a purification factor of 2.7 (purity of 60.9%). Hybrid processes combining the two previous techniques and an ultrafiltration step were finally applied, allowing the recovery of mAbs from the different fractions in an appropriate buffer solution for further biopharmaceutical formulations, while allowing the simultaneous IL removal and reuse. The best results were obtained with the hybrid process combining TPP and ultrafiltration, allowing to obtain mAbs with a purity higher than 60%. The recyclability of the IL was additionally demonstrated, revealing no losses in the purification and recovery performance of these systems for mAbs. The biological activity of anti-IL-8 mAbs is maintained after the several purification and recovery steps, indicating that the novel ABS, three-phase partitioning and hybrid processes comprising AGB-ILs are promising and sustainable strategies in mAbs downstream processing.
... The probes N,N-diethyl-4-nitroaniline, 4-nitroaniline, and pyridine-N-oxide were used to determine the dipolarity/ polarizability, π * , hydrogen-bond (acceptor) basicity, β, and hydrogenbond (donor) acidity, α, of both PEG-and salt-rich phases of the studied ATPS. The experimental procedure followed in this work to determine the Kamlet-Taft parameters using these probes was previously reported by Coutinho and co-workers [24]. ...
Aqueous two-phase systems (ATPS) have been proposed as platforms for the purification of biomolecules, and the application of adjuvants to tune the properties of ATPS phases and their ability to extract and separate biological products investigated. This work addresses, for the first time, the use of acetonitrile (ACN) as adjuvant in ATPS composed of polyethylene glycol (PEG) of different molecular weights (from 400 to 20,000 g·mol ⁻¹ ) and potassium phosphate. The effect of ACN concentration (at 0.25, 2.5, 5 and 7.5 wt%) in the liquid-liquid equilibrium is here studied by measuring the phase diagrams, the composition of the phases in equilibrium and their Kamlet-Taft parameters. The results obtained demonstrate that the ACN presence increases the biphasic region of PEG-K 3 PO 4 ATPS and its distribution between the coexisting phases is dependent on its concentration and ATPS composition. The difference in the dipolarity/polarizability of the coexisting phases is significantly affected by the presence of ACN in the ternary mixture. The partition of two phenolic compounds – protocatechuic acid and gallic acid – was studied, showing that ACN improves the partition of these molecules to the salt-rich phase, and that the system selectivity can be significantly improved by changing the concentration of the phase forming compounds.
Artemisinin is a sesquiterpenoid lactone peroxide, known for its potent antimalarial activity that can be extracted from Artemisia annua L. This compound is only sparingly soluble in water, making its extraction using environmental-friendly and non-toxic aqueous solvents difficult. In the attempt to overcome this limitation, hydrotropes, which are a class of compounds that can assist in increasing the solubility of hydrophobic solutes in water, were investigated in this work. In particular, the hydrotropic capability of ionic liquids (ILs) on the aqueous solubility of artemisinin was studied. The effects of IL concentration and anion nature of 1-butyl-3-methylimidazolium-based ILs on the solubility of artemisinin at 303.2 K in water were evaluated. It is here shown the excellent capacity of ILs containing thiocyanate or dicyanamide anions to enhance the solubility of artemisinin in aqueous media, with a magnitude comparable to that obtained with the best organic solvents. Furthermore, solvatochromic parameters of the ILs aqueous solutions were also measured and combined with COSMO-RS and the cooperative hydrotropy model to establish relations between the artemisinin solubility enhancement and the solvent characteristics. The solubility enhancement of artemisinin is favored by the apolarity of the medium and the lower hydrogen-bond acceptor character of the hydrotrope.
Water-in-water (W/W) emulsion is an interesting template for microentrapment of hydrophilic compounds due to biocompatible nature of its aqueous media. W/W emulsification can be established from a destabilised aqueous two-phase system (ATPS). In this study, binodal data of ATPSs comprising polyethylene glycol (PEG) and gelatin were generated. Binodal curves of PEG + gelatin + water systems were successfully correlated using non-linear empirical Merchuk equation, and the tie lines were constructed using lever-arm rule. The effects of temperature, type of gelatin, and molecular weight of PEG on the binodal curves were evaluated. Notably, a higher molecular weight of PEG decreased the concentration of gelatin required for two-phase formation. ATPSs made of gelatin bovine has a larger biphasic region than that of gelatin porcine. Gelatin microgel was successfully synthesized from the PEG + gelatin emulsion system via rapid cooling of the dispersed phase of gelatin. The size of gelatin microgel was reduced by a higher stirring speed, while a temperature as high as 333.15 K increased the size distribution of gelatin microgel. Lastly, the microentrapment of model protein, green fluorescent protein, was demonstrated. PEG/Gelatin system holds good potential for food engineering and delivery system.
Aqueous biphasic systems (ABS) composed of ionic liquids (ILs) and conventional salts have been largely investigated and successfully used in separation processes, for which the determination of the corresponding ternary phase diagrams is a previous requirement. However, due the large number of ILs that can be prepared and their high structural versatility, it is impossible to experimentally cover and characterize all possible combinations of ILs and salts that may form ABS. The development of tools for the prediction and design of IL-based ABS is thus a crucial requirement. Based on a large compilation of experimental data, a correlation describing the formation of IL-based ABS is here shown, based on the hydrogen-bonding interaction energies of ILs (EHB) obtained by the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) and the molar entropy of hydration of the salt ions. The ability of the proposed model to predict the formation of novel IL-based ABS is further ascertained.
In this work novel solvent, poly(ethylene glycol) diacrylate (PEGDA) of average number molecular weight 700, is proposed for design of aqueous biphasic systems with salting-out agents: K3PO4/Na3C6H5O7/K2CO3/MnSO4/Li2SO4/ZnSO4. Ternary liquid-liquid equilibrium experiments were conducted at constant temperature 298.15 K and 0.1 MPa, where binodal curves and tie-lines were determined. The consistency of equilibrium data were checked and confirmed using Othmer-Tobias and Bancroft equations. Density ρ viscosity η and refractive index nD have been experimentally measured for PEGDA 700 + water system over the temperature range T = (293.15 to 323.15) K with temperature step 5 K and at atmospheric pressure. Excess molar volumes VE, viscosity deviations Δη deviations in refractive index ΔnD, excess Gibbs free energy of activation of viscous flow ∆G⁎E, partial molar volumes V¯i, excess partial molar volumes V¯iE and it's values at infinite dilutions V¯iE,∞ were calculated from experimental data and used to analyze non-ideal behavior of polymer aqueous solution. Fourier-transform infrared analysis (FT-IR) of PEGDA + water mixture and corresponding pure components was performed at T = 298.15 K in order to gain insight into the molecular structure of the mixture. FT-IR analysis indicates the absence of hydrogen bonding between PEGDA 700 and water. This leads to the conclusion that non-ideal behavior of mixture is contributed to geometrical packing or van der Waals forces of different species.
Affinity partitioning refers to the preferential dissolution of solute molecules in a particular liquid phase of an immiscible liquid-liquid mixture, such as an aqueous two-phase system (ATPS). Affinity partitioning in ATPS is widely used to achieve extraction and purification of biomolecules. However, the potential of applying it to direct the self-assembly of solutes into controlled structures has been largely overlooked. Here we introduce the affinity partitioning of polyelectrolytes in ATPS to induce their self-assembly into polyelectrolyte microcapsules. The approach is purely based on the preferential solubility of different polyelectrolytes in different aqueous phases; therefore it has wide applicability and exhibits excellent compatibility with bioactives. The release of encapsulated components can be triggered by changing the pH value or ionic strength of the surrounding environment. The proposed method represents an important advance in fabricating multifunctional materials and inspires new ways to engineer sophisticated structures with hydrophilic macromolecules.
In order to overcome the lack of characterization on the relative hydrophobicity of aqueous biphasic systems (ABS), the partition of three alkaloids as alternative probes, was evaluated in a series of biocompatible ABS composed of cholinium-based salts or ionic liquids (ILs) and polyethylene glycol (PEG). The caffeine partitioning in ABS was firstly addressed to infer on the effect of the phase-forming components composition. In all systems, caffeine preferentially concentrates in the lower water content PEG-rich phase. Additionally, a linear dependence between the logarithmic function of the partition coefficients and the water content ratio was found. To confirm this linear dependency, the partition coefficients of caffeine, theobromine and theophylline were determined in other ABS formed by different cholinium-based salts/ILs. In most systems, it is shown that all alkaloids partition to the most hydrophobic phase. To support the experimental results, COSMO-RS (Conductor-like Screening Model for Real Solvents) was used to compute the screening charge distributions of both phase-forming components of ABS and alkaloids, the excess enthalpy of mixing and the activity coefficients at infinite dilution. It is here demonstrated that the partition trend of alkaloids can be used to address the relative hydrophobicity of the coexisting phases in polymer-salt/-IL ABS.
Partition coefficients of seven low molecular weight compounds were measured in multiple aqueous two-phase systems (ATPSs) formed by pairs of different polymers. The ionic composition of each ATPS was varied to include 0.01M sodium phosphate buffer (NaPB), pH 7.4 and 0.1M Na2SO4, 0.15M NaCl, and 0.15M NaClO4 all in 0.01M NaPB, pH 7.4. The differences between the solvent features of the coexisting phases in all the ATPSs were estimated from partitioning of a homologous series of dinitrophenylated-amino acids and by the solvatochromic method. The solute-specific coefficients for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. It is established that the solute specific coefficients characterizing different types of the solute-water interactions (dipole-dipole, dipole-ion, and H-bonding) for a given solute change in the presence of different salt additives in the solute specific manner. It is also found that these characteristics are linearly interrelated. It is suggested that there is a cooperativity between various types of solute-water interactions governed by the solute structure.
Copyright © 2015 Elsevier B.V. All rights reserved.
One of the main drawbacks comprising an appropriate selection of ionic liquids (ILs) for a target application is related with the lack of an extended and well-established polarity scale for these neoteric fluids. Albeit a considerable progress has been made on identifying chemical structures and factors that influence the polarity of ILs, there still exists a high inconsistency on the experimental values reported by different authors. Furthermore, due to the extremely large number of possible ILs that can be synthesized, the experimental characterization of their polarity is a major limitation when envisaging the choice of an IL with a desired polarity. Therefore, it is of crucial relevance to develop correlation schemes and a priori predictive methods able to forecast the polarity of new (or not yet synthesized) fluids. In this context, and aiming at broadening the experimental polarity scale available for ILs, the solvatochromic Kamlet-Taft parameters of a broad range of bis(trifluoromethylsulfonyl)imide-([NTf2]-)-based fluids were determined. The impact of the IL cation structure on the hydrogen-bond donating ability of the fluid was comprehensively addressed. Based on the large amount of novel experimental values obtained, we then evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond acidity of ILs. A three-parameter model based on the cation-anion interaction energies was found to adequately describe the experimental hydrogen-bond acidity or hydrogen-bond donating ability of ILs. The proposed three-parameter model is also shown to present a predictive capacity and to provide novel molecular-level insights into the chemical structure characteristics that influence the acidity of a given IL. It is shown that although the equimolar cation-anion hydrogen-bonding energies (EHB) play the major role, the electrostatic-misfit interactions (EMF) and van der Waals forces (EvdW) also contribute, admittedly in a lower extent, towards the hydrogen-bonding acidity of ILs. The new extended scale provided for the hydrogen-bonding acidity of ILs is of high value for the design of new ILs for task-specific applications.
Hydrotropes are compounds able to enhance the solubility of hydrophobic substances in aqueous media and therefore are widely used in the formulation of drugs, cleaning and personal care products. In this work, it is shown that ionic liquids are a new class of powerful catan-ionic hydrotropes where both the cation and the anion synergistically contribute to increase the solubility of biomolecules in water. The effects of the ionic liquid chemical structures, their concentration and of the temperature on the solubility of different biomolecules were evaluated and compared with the performance of conventional hydrotropes. The solubility of two selected biomolecules was studied in the whole composition range, from pure water to pure ionic liquids, and an increase in the solubility of up to 40-fold was observed, con-firming the potential of ionic liquids to act as hydrotropes. The underlying molecular phenomena responsible for the enhanced solubility were investigated by Dynamic Light Scattering, NMR and molecular dynamics simulations and result from the formation of ionic-liquid-solute aggregates. Finally, it was demonstrated that hydrotropy induced by ionic liquids can be used to recover solutes from aqueous media by precipitation, simply by using water as anti-solvent. The results here reported have a significant impact in the understanding of the role of ionic liquids aqueous solutions in the extraction of added-value compounds from biomass as well as in the design of novel processes for their recovery from aqueous media.
Abstract Analysis of the macromolecular crowding effects in polymer solutions show that the excluded volume effect is not the only factor affecting the behavior of biomolecules in a crowded environment. The observed inconsistencies are commonly explained by the so-called "soft" interactions, such as electrostatic, hydrophobic, and van der Waals interactions, between the crowding agent and the protein, in addition to the hard non-specific steric interactions. We suggest that the changes in the solvent properties of aqueous media induced by the crowding agents may be the root of these "soft" interactions. To check this hypothesis, the solvatochromic comparison method was used to determine the solvent dipolarity/polarizability, hydrogen-bond donor acidity, and hydrogen-bond acceptor basicity of aqueous solutions of different polymers (Dextran, poly(ethylene glycol), Ficoll, Ucon, and polyvinylpyrrolidone) with the polymer concentration up to 40% typically used as crowding agents. Polymer-induced changes in these features were found to be polymer type and concentration specific, and, in case of polyethylene glycol, molecular mass specific. Similarly sized polymers PEG and Ucon producing different changes in the solvent properties of water in their solutions induced morphologically different α-synuclein aggregates. It is shown that the crowding effects of some polymers on protein refolding and stability reported in the literature can be quantitatively described in terms of the established solvent features of the media in these polymers solutions. These results indicate that the crowding agents do induce changes in solvent properties of aqueous media in crowded environment. Therefore, these changes should be taken into account for crowding effect analysis.
Ionic liquids have earned the reputation of being ‘designer solvents’ due to the wide range of accessible properties and the degree of fine-tuning afforded by varying the constituent ions. Mixtures of ionic liquids offer the opportunity for further fine-tuning of properties. A broad selection of common ionic liquid cations and anions are employed to create a sample of binary and reciprocal binary ionic liquid mixtures, which are analysed and described in this paper. Physical properties such as the conductivity, viscosity, density and phase behaviour (glass transition temperatures) are examined. In addition, thermal stabilities of the mixtures are evaluated. The physical properties examined for these formulations are found to generally adhere remarkably closely to ideal mixing laws, with a few consistent exceptions, allowing for the facile prediction and control of properties of ionic liquid mixtures.
In the past decade, ionic liquids (ILs) have been the focus of intensive research regarding their use as potential and alternative solvents in many chemical applications. Targeting their effectiveness, recent investigations have attempted to establish polarity scales capable of ranking ILs according to their chemical behaviours. However, some major drawbacks have been found since polarity scales only report relative ranks because they depend on the set of probe dyes used, and they are sensitive to measurement conditions, such as purity levels of the ILs and procedures employed. Due to all these difficulties it is of crucial importance to find alternative and/or predictive methods and to evaluate them as a priori approaches capable of providing the chemical properties of ILs. Furthermore, the large number of ILs available makes their experimental characterization, usually achieved by a trial and error methodology, burdensome. In this context, we firstly evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond basicity of ILs. After demonstrating a straight-line correlation between the experimental hydrogen-bond basicity values and the COSMO-RS hydrogen-bonding energies in equimolar cation-anion pairs, an extended scale for the hydrogen-bond accepting ability of IL anions is proposed here. This new ranking of the ILs' chemical properties opens the possibility to pre-screen appropriate ILs (even those not yet synthesized) for a given task or application.
The potential use of ionic liquids (ILs) as adjuvants in typical polymer-salt aqueous systems for the separation and purification of vital biomolecules is investigated. An innovative study involving the addition of various imidazolium-based ILs to conventional PEG/inorganic salt aqueous biphasic systems (ABS), aiming at controlling their phase behaviour and extraction capability for L-tryptophan, is carried out here. For this purpose, phase diagrams and respective tie-lines for PEG 600/Na2SO4 ABS with the addition of small quantities of IL were established. In addition, the partition coefficients of L-tryptophan were determined in those systems. The results obtained indicate that the addition of small amounts of IL to the typical PEG/inorganic salt aqueous systems could largely control the extraction efficiency for L-tryptophan, and that efficiency depends on the IL employed. Salting-in inducing ILs enhance the partition coefficient of L-tryptophan for the PEG-rich phase while salting-out inducing ILs decrease the partitioning of the amino acid. These results are an interesting advance in biotechnological separation processes regarding the extraction of biomolecules that could be used instead of the common approach of PEG functionalization.
The polarities of a wide range of ionic liquids have been determined using the Kamlet-Taft empirical polarity scales α, β and π*, with the dye set Reichardt's Dye, N,N-diethyl-4-nitroaniline and 4-nitroaniline. These have been compared to measurements of these parameters with different dye sets and to different polarity scales. The results emphasise the importance of recognising the role that the nature of the solute plays in determining these scales. It is particularly noted that polarity scales based upon charged solutes can give very different values for the polarity of ionic liquids compared to those based upon neutral probes. Finally, the effects of commonplace impurities in ionic liquids are reported.
Thermodynamic data is the fundament of any process design. While accurately measured experimental data almost always is the most reliable source of information for the thermodynamic data required for process design, there are many situations in which this data is not available. In such situations predictive models are required. Correlative models as NRTL or SAFT, or group contribution methods as UNIFAC are the traditional approaches for property prediction in chemical engineering. Correlative methods require some experimental data for exactly the compounds and mixtures under consideration and only extrapolate to other state points. UNIFAC extrapolates to new compounds, but only if the compounds are well describable by the additive group concept and do not have major intramolecular interactions. For structurally really new and demanding compounds, robust predictions require sound physical concepts for the description of the molecular interactions. The Conductor-like Screening Model for Realistic Solvation, COSMO-RS, is the most fundamental of such models, combining the sound quantum chemical polarity information with the efficient concept of surface segment interactions, also known as quasi-chemical approach. Thus, it provides reliable predictions for pure compound vapor pressures and mixture activity coefficients. COSMO-RS has been initially published more than 20 years ago, and meanwhile it has become a popular method in academia and industry. The talk will cover the basic concepts of the method, its potential and limitations, and outline several extensions and new application areas which have opened up by the various methodological improvements developed during the past 20 years.
Although highly relevant to a priori select adequate solvents for a given application, the determination of the hydrogen-bond acidity or proton donor ability of aqueous solutions of ionic liquids is a difficult task due to the poor solubility of the commonly used probes in aqueous media. In this work, we demonstrate the applicability of the
pyridine-N-oxide probe to determine the hydrogen-bond acidity of both neat ionic liquids and their aqueous solutions, based on 13C NMR chemical shifts, and the suitability of these values to appraise the ability of ionic liquids to form aqueous two-phase systems.
This review covers the fundamentals of protein partitioning in aqueous two-phase systems (ATPS). Included is a review of advancements in the analytical application of solute partitioning in ATPS over the last two decades, with multiple examples of experimental data providing evidence that phase-forming polymers do not interact with solutes partitioned in ATPS. The partitioning of solutes is governed by the differences in solute interactions with aqueous media in the two phases. Solvent properties of the aqueous media in these two phases may be characterized and manipulated. The solvent interaction analysis (SIA) method, based on the solute partitioning in ATPS, may be used for characterization and analysis of individual proteins and their interactions with different partners. The current state of clinical proteomics regarding the discovery and monitoring of new protein biomarkers is discussed, and it is argued that the protein expression level in a biological fluid may be not the optimal focus of clinical proteomic research. Multiple examples of application of the SIA method for discovery of changes in protein structure and protein-partner interactions in biological fluids are described. The SIA method reveals new opportunities for discovery and monitoring structure-based protein biomarkers.
Now in its 4th edition, this book remains the ultimate reference for all questions regarding solvents and solvent effects in organic chemistry. Retaining its proven concept, there is no other book which covers the subject in so much depth, the handbook is completely updated and contains 15% more content, including new chapters on "Solvents and Green chemistry", "Classification of Solvents by their Environmental Impact", and "Ionic Liquids". An essential part of every organic chemist's library.
Measurements of the C-13 nmr chemical shifts delta of pyridine-N-oxide as a probe in 18 solvents, with literature values for others, established that the differences d24 and d34 of the delta of carbons 2 and 3 with respect to that of carbon 4 depend solely on the hydrogen bond donation ability of the solvents, as measured by the Taft-Kamlet alpha parameter. This substance and method can, therefore, be used as an effective probe for alpha, without the need to invoke other solvent properties, such as their polarities/polarizabilities, measured by pi*, required by other probes. The probe was applied also to aqueous mixtures of acetone, acetonitrile, and methanol (values of pi* and beta for acetone, besides those of alpha, being reported here too) with similar results. The two aqueous aprotic solvent mixtures exhibit microheterogeneity, as previously established for aqueous acetonitrile from other results.
Partitioning of a homologous series of dinitrophenylted (DNP-) amino acids with aliphatic side chains was examined in aqueous polyethylene glycol (PEG)-8000-sodium sulfate two-phase systems (ATPS) with the additives NaSCN, NaClO4, and NaH2PO4 at concentrations varied from 0.025 M up to 0.54 M. The differences between the relative hydrophobicities and electrostatic properties of the two phases in all ATPS were estimated. Partitioning of adenine, adenosine mono-, di- and tri-phosphates was also examined in all ATPSs, including those with NaCl additive. Partition coefficients for these compounds and for nonionic organic compounds previously reported [Ferreira et al., J. Chromatogr. A, 1220, 14-20 (2012)] were analyzed in terms of linear solvent regression relationship. The results obtained suggest that the effects of the salts additives are related to their influence on the water structure.
A range of ionic liquids has been investigated using the Kamlet–Taft parameters α, β, and π*. It was found that π* is high for all of the ionic liquids studied and varies with both anion and cation, α is generally moderate and depends mainly on the cation, β is also moderate and depends mainly on the anion. Comparison is made with other polarity measurements in ionic liquids.
A novel and very efficient method for the a priori prediction of thermophysical data of liquids is presented. It is based on unimolecular quantum chemical calculations that provide the necessary information for the evaluation of molecular interactions in liquids. Combined with a very fast and accurate statistical thermodynamics, the new method is an alternative to structure-interpolating group contribution methods (GCMs). The most important advantages are the essentially general applicability, the sound physical basis, and the graphicness of the procedure, which easily allows for chemical interpretation and understanding of thermophysical behaviour. A methodological comparison with GCMs is given. Example applications are presented.
Albeit ionic-liquid-based aqueous biphasic systems (ABS) have been largely explored as liquid–liquid extractive approaches for a large array of (bio)molecules, the application of biodegradable and nontoxic salts as phase constituents of these systems has been seldom investigated. In this work 15 ionic liquids were evaluated toward their ability to form ABS in the presence of a common biodegradable organic salt: potassium citrate. The ternary phase diagrams, tie-lines, and respective tie-line lengths, were determined at 25 °C. The gathered data allowed the evaluation of the effects of the ionic liquid cation core, of the cation side alkyl chain length, and of the anion nature, to form two-phase systems. It is shown that the ionic liquids aptitude to undergo liquid–liquid demixing is mainly controlled by their hydrophobicity. The large differences observed between the phase diagrams behavior suggest the possibility of tailoring the aqueous phases’ polarities for a specific extraction. Therefore, the partitioning of a hydrophobic amino acid produced by bacteria fermentation, l-tryptophan, was also addressed aiming at exploring the applicability of the proposed systems in the biotechnology field. Single-step extraction efficiencies of l-tryptophan for the ionic-liquid-rich phase range between 72% and 99%.
Solvents and solutions are ubiquitous in chemistry. For instance, in synthesis the solvent allows reagents to mix intimately so that reactions between these may occur. Consequently, understanding how solutes behave in solutions has been one of the major themes of chemistry throughout its history. Ionic liquids (liquid salts) are an exciting recent addition to the range of available solvents. Here we show that these solvents interact with dissolved salts to give solutions that are completely different from those of salts in either traditional organic solvents or water. Observations of these ideal salt solutions will require new models of solvation and polarity and have the potential to lead to new chemical processes.
In this work, glycine ionic liquids tetramethylammonium glycine ([N1111][Gly]), tetraethylammonium glycine ([N2222][Gly]), tetra-n-butylammonium glycine ([N4444][Gly]), tetra-n-butylphosphonium glycine ([P4444][Gly]) and tetra-n-pentylammonium glycine ([N5555][Gly]) were synthesized and used to prepare aqueous two-phase systems (ATPSs) in the presence of K2HPO4. Binodal curves of such ATPSs and partition coefficients of a series of dinitrophenylated (DNP) amino acids in these ATPSs were determined at 298.15K to understand the effect of cationic structure of the ionic liquids on the phase-forming ability of glycine ionic liquids, relative hydrophobicity between the phases in the ionic liquids ATPSs, and polarity of the ionic liquids-rich phases. With the attempt to correlate the relative hydrophobicity of the phases in the ATPSs with their extraction capability for proteins, partition coefficients of cytochrome-c in the ATPSs were also determined. It was shown that partition coefficients of cytochrome-c were in the range from 2.83 to 20.7 under the studied pH conditions. Then, hydrophobic interactions between cytochrome-c and the ionic liquid are suggested to be the main driving force for the preferential partition of cytochrome-c in the glycine ionic liquid-rich phases of the ATPSs. Result derived from polarity of the ionic liquids-rich phases supports this mechanism.
A study of salt–salt aqueous biphasic systems (ABS) was conducted to increase our understanding of solutions of kosmotropic vs. chaotropic salts, especially since most ionic liquids (ILs) fall within the latter class. The salting-out strength of the kosmotropic salts follows the well established Hofmeister series, as observed in polymer–salt ABS, and can be directly related to the ions' Gibbs free energies of hydration (ΔGhyd). Most currently studied ILs are designed to have chaotropic cations and are thus salted-out by kosmotropic salts. Here, we describe the phase diagrams for imidazolium-, pyridium-, and quaternary ammonium- and phosphonium-based chloride salts (all chaotropic salts) salted-out by K3PO4, K2HPO4, K2CO3, KOH, and (NH4)2SO4 (all kosmotropic salts). The Gibbs free energy of methylene transfer (ΔGCH2) was also determined for 1-butyl-3-methylimidazolium chloride ([C4mim]Cl)/K3PO4, K2HPO4, and K2CO3 ABS. The latter results are in the range of an ethanol–water to a chloroform–water system, and can be controlled predominately by the system composition.
The solvatochromic properties α, β, and π* have been determined for an aqueous biphasic system (ABS) composed of polyethylene glycol and the salts (NH4)2SO4 or K3PO4 using the probes Reichardt's carboxylated betaine, 4-nitrophenol, and 4-nitroanisole. It was found that the co-existing phases rich in either polymer or salt differed little in their relative polarity or relative basicity and that their basicity and polarity differed little from that of water. On the other hand, the polymer-rich phase was found to be significantly depleted in H-bond donor ability relative to the salt-rich phase and to pure water. The results of this study compared favorably with the results of a solute distribution study encapsulated in a linear free energy relationship. As a result, it seems possible to conclude that the principal molecular determinants of partitioning in
ABS are the solute properties size, basicity, and aromaticity or halogenicity.
We have used linear solvation energy relationships (LSERs) to study the fundamental chemical interactions responsible for solute retention in micellar electrokinetic capillary chromatography (MEKC). We investigated retention in micellar solutions of sodium dodecyl sulfate (SDS), sodium decyl sulfate (SDecS), and sodium octyl sulfate (SOS). The purpose of the study was to elucidate the effect of surfactant chain length on the solute/micelle interactions that ultimately govern retention and selectivity in MEKC. The nature of the solute/micelle interactions were found to be nearly equivalent in all three systems, implying that the chromatographic selectivity in all three systems will be quite similar. Additionally, the LSERs show that solute size and hydrogen bond basicity play the largest roles in determining solute retention and chromatographic selectivity. Finally, from the LSERs and an analysis of the free energy of transfer of methylene units from water to the micellar phase (δ). we conclude that the solutes reside in the polar, hydrated head group region of the micelles, and not in the nonpolar core. Based on the δ, values for five different homologous solute series, the effect of the solutes' functional groups on the location and orientation of the solutes inside the micelles is briefly discussed.
An analysis of published partition coefficients measured in various two-phase systems for homologous series of fatty acids, aliphatic alcohols and amines was performed in order to clarify the physical meaning of the constants in the so-called solvent regression equation: ln Ki = ai ln K0 + bi, where Ki and K0 are the partition coefficients for a given solute determined in the partitioning system in question and in that chosen as the reference, respectively, and ai and bi are constants. The difference in the relative hydrophobicities of two phases of a given partitioning system is expressed in terms of the free energy of transfer of a CH2 group from the non-aqueous to the aqueous phase of the system (ΔgiCH2). It is shown that ai is related to the ΔgiCH2 and Δg0CH2 values by the equation ai = ΔgiCH2/Δg0CH2. The term bi appears to account for the specific solute-water (and/or solute-solvent) interactions characteristic of a polar group contained by the solute molecule.The analysis of literature data indicates that the difference in the relative hydrophobicities between any two groups depends on the choice of partitioning system. The physical meaning of the relative hydrophobicity of a chemical compound is discussed, and it is concluded that an aqueous two-phase system should be used as the reference. The aqueous two-phase polymeric system Ficoll-dextran is proposed for this purpose and its advantages are briefly considered.
Partition coefficients for a homologous series of dinitrophenylated amino acids with aliphatic side-chains have been determined in two aqueous polymeric Ficoll-dextran 70 and dextran 500-polyethylene glycol 6000 biphasic systems and in the systems formed by n-octanol and the aqueous phases of the above systems. The results afford an estimation of the free energy of transfer of a CH2 group from one to the other phase of the systems examined. This parameter (ΔgtrCH2) was taken as a measure of the hydrophobic character of an aqueous phase with respect to n-octanol. It was shown that when the partition of a set of homologues in two biphasic systems is correlated according to the known equation ln Ki = a ln Ko + b, where Ki and Ko are the partition coefficients for a given solute in the ith system and in the system chosen for reference, respectively, the parameter a is related to the Δgtr1CH2 and Δgtr0CH2 by a = Δgtr1CH2/Δgtr0CH2.This equation was used to determine the hydrophobic character of various organic solvents and that of the aqueous polymeric phases of the aqueous biphasic systems studied, and was found to be valid for comparison of the partition values determined in an aqueous polymeric biphasic system and in the water-n-octanol system. This seems to extend the possibilities of structure-activity relationships studies as the Ficoll-dextran aqueous biphasic system provides as promising a means for their study in biological chemistry as the water-n-octanol system in drug research.
Three new phase diagrams for polymer−salt aqueous two-phase systems (ATPS) at 23 °C are presented. Then, partition coefficients for a series of five dinitrophenylated amino acids were obtained experimentally in five polymer−salt ATPS. The ATPS were obtained combining a polymer, polyethylene glycol (PEG) or Ucon (a random copolymer of 50 % ethylene oxide and 50 % propylene oxide), and a salt (Na2SO4, (NH4)2SO4, or Li2SO4). The series of amino acids allowed the calculation of the free energy of transfer of a methylene group, which is used as a measure of the relative hydrophobicity of the equilibrium phases. Ucon-rich phases proved to have a higher affinity for methylene groups than PEG which suggests a more efficient biphasic separation system with lower cross-contamination.
Partition ratios of 10 l-amino acids with non-polar side chains (Gly, Ala, Val, nor-Val, Ile, Leu, nor-Leu, Phe, Trp and Pro) were measured in ten different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15M NaCl in 0.01M phosphate buffer, pH 7.4. The solute-specific coefficients representing the solute dipole-dipole, hydrogen bonding and electrostatic interactions with aqueous environment for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. It is shown that linear combinations of these coefficients are correlated with the amino acid lipophilicity/hydrophobicity scales reported in the literature. The results obtained imply that the solute-specific coefficients may be used as solute descriptors for quantitative structure-property relationship (QSPR) analysis.
Partition ratios of several ionic compounds in 20 different polymer/polymer aqueous two-phase systems (ATPS) containing 0.15M NaCl in 0.01M phosphate buffer, pH 7.4, were determined. The differences between the electrostatic properties of the phases in all the ATPS were estimated from partitioning of the homologous series of dinitrophenylated-amino acids. Also the solvatochromic solvent parameters characterizing the solvent dipolarity/polarizability (π*), solvent hydrogen-bond donor acidity (α), and solvent hydrogen-bond acceptor basicity (β) of aqueous media were measured in the coexisting phases of the ATPS. The solute-specific coefficients for the compounds examined were determined by the multiple linear regression analysis using the modified linear solvation energy relationship equation. The minimal number of ATPS necessary for determination of the coefficients was established and 10 ATPS were selected as a reference ATPS set. The solute-specific coefficients values obtained with this reference set of ATPS were used to predict the partition ratios for the compounds in 10 ATPS not included in the reference set. The predicted partition ratios values were compared to those determined experimentally and found to be in good agreement. It is concluded that the presented model of solute-solvent interactions as the driving force for solute partitioning in polymer/polymer ATPS describes experimental observations with 90-95% accuracy.
Starting from the screening in conductors, an algorithm for the accurate calculation of dielectric screening effects in solvents is presented, which leads to rather simple explicit expressions for the screening energy and its analytic gradient with respect to the solute coordinates. Thus geometry optimization of a solute within a realistic dielectric continuum model becomes practicable for the first time. The algorithm is suited for molecular mechanics as well as for any molecular orbital algorithm. The implementation into MOPAC and some example applications are reported.
Seventy solvents are arranged in a π* scale of solvent polarities, so named because it derives from and best correlates solvatochromic effects on p → π*and π →* electronic spectral transitions. Solvent effects on f max values of seven primary indicator compounds are employed in the initial construction of the π* scale, and correlations with 40 additional spectral indicators are used to expand and refine the data base. Standard deviations in the 47 correlation equations of vmax with solvent π* values average 0.11 kK, which compares well with the 0.10 kK precision limit of the solvatochromic comparison method. A number of stratagems are employed to exclude or minimize hydrogen bonding effects in determining π* values of HBA (hydrogen bond acceptor) and amphiprotic HBA-D (hydrogen bond acceptor-donor) solvents. Values of 5 in the solvatochromic equation, vmax = v0 + π*, show logical variations with indicator structure, lending confidence that this new solvatochromic parameter will come to serve as a convenient and meaningful indicator of the interaction of a chromophore with its cybotactic environment. Poor correlation of vmas values for Dimroth's betaine, 4-(2,4,6-triphenylpyridinium)-2,6-diphenylphenoxide with the π* scale is rationalized in terms of differing polarity and polarizability contributions to overall solvent effects.
The solvatochromic comparison method is used to evaluate hydrogen-bonding contributions in HBD (hydrogen-bond donor) solvents to several commonly used dye indicator solvent polarity scales (Dimroth's Eτ-30, Brooker's χR, Kosower's Z). Hydrogen-bonding effects on other spectral properties, equilibria, and reaction rates are determined, and the results are used to construct an α-scale of solvent HBD acidities.
The solvatochromic comparison method is outlined. Magnitudes of enhanced solvatochromic shifts in HBA (hydrogen-bond acceptor) solvents are determined for 4-nitroaniline (1) relative to N,N-diethyl-4-nitroaniline (2) [-ΔΔν(1-2)B←H2N] and for 4-nitrophenol (3) relative to 4-nitroanisole (4) [-ΔΔν(3-4)B←HO]. The -ΔΔν values for the HBD (hydrogen-bond donor) substrates 1 and 3 in corresponding HBA solvents are shown to be proportional to one another, proportional to limiting 19F NMR shifts of hydrogen-bonded complexes of 4-fluorophenol with the same HBA's, and linear with log association constants of hydrogen-bonded complexes between 4-fluorophenol (pKHB) and phenol and the same HBA molecules. The LFE relationships are used to establish a β-scale of solvent HBA basicities.
Starting from the question of why dielectric continuum models give a fairly good description of molecules in water and some other solvents, a totally new approach for the calculation of solvation phenomena is presented. It is based on the perfect, i.e., conductor-like, screening of the solute molecule and a quantitative calculation of the deviations from ideality appearing in real solvents. Thus, a new point of view to solvation phenomena is presented, which provides an alternative access to many questions of scientific and technical importance. The whole theory is based on the results of molecular orbital continuum solvation models. A few representative solvents are considered, and the use of the theory is demonstrated by the calculation of vapor pressures, surface tensions, and octanol/water partition coefficients.
Aqueous biphasic systems (ABSs) composed of poly(ethylene glycol) (PEG) and dextran have long been proposed as useful liquid/liquid extraction systems for biological macromolecules. More recently, they have been proposed as useful partitioning systems for molecular characterization in quantitative structure activity relationships. In this context, the distribution ratios of a wide range of organic solutes differing in structure and functionality were measured in a PEG/dextran ABS and the results compared to the corresponding 1-octanol/water partition coefficients. The relative hydrophobicity of the phases was quantified from the free energy of transfer of a methylene group measured for a homologous series of alcohols. A linear free energy relationship based on Abraham's generalized solvation equation has been derived from the solute partitioning data, which allows a direct comparison to be made between the solvent properties of a PEG/dextran ABS and those of traditional solvent/water systems used, for example, in the determination of log P. A comparison with similar parameters previously determined for ABSs composed of PEG and a salt is also enabled.
Aqueous biphasic systems (ABSs) composed of poly(ethylene glycol) (PEG) and salt have been examined as potential environmentally benign solvents for liquid/liquid extraction. These systems might also represent an alternative to traditional solvent/water systems used in quantitative structure−activity relationships (QSARs). For the application and design of these systems, it is important to have a thorough understanding of the nature of the solvent and its interactions with the solute, and thus, PEG/salt ABSs have been characterized to this end by a variety of methods. The relative hydrophobicities of several PEG/salt ABSs composed of different molecular weights of PEG (1000, 2000, and 3400) and a variety of inorganic salts [K3PO4, K2CO3, (NH4)2SO4, Li2SO4, MnSO4, ZnSO4, and NaOH] were measured by the free energy of transfer of a methylene group ΔGCH2. These results indicate that the relative hydrophobicity of a PEG/salt ABS is a function of only the degree of phase divergence of the biphasic system as expressed by the difference in polymer concentration between the phases [delta poly(ethylene glycol) (ΔPEG), delta ethylene oxide monomer (ΔEO)] or the tie line length (TLL). The distributions of a wide range of solutes differing in structure and functionality were also measured in PEG/salt ABSs, and the results were compared to the corresponding 1-octanol/water partition coefficients. These data were used to develop a linear free energy relationship (LFER) based on Abraham's generalized solvation equation, enabling a direct comparison to be made between the solvent properties of PEG/salt ABSs and those of traditional solvent/water systems used, for example, in the determination of log P. Similar comparisons are also enabled with the properties of certain aqueous micellar systems.
Ionic liquids are a fascinating class of novel solvents, which are attracting attention as possible ‘green’ alternative to volatile molecular organic solvents to be applied in catalytic and organic reactions and electrochemical and separation processes. Over 200 room temperature ionic liquids are known but for most of them physico-chemical data are incomplete or lacking. Furthermore, despite the incredible number of potential ionic liquids (evaluated as > 1014), generally only a few imidazolium-based salts are used in synthesis. Moreover, most of the data reported to date were focused on the effect that these new solvents have on chemical reaction products; only a few reports evidence the effect on reaction mechanisms or rate or equilibrium constants. In this review, the physico-chemical properties of the most used ionic liquids, that are relevant to synthesis, are discussed and a decided emphasis is placed on those properties that most clearly illuminate the ability of ionic liquids to affect the mechanistic aspects of some organic reactions. Copyright © 2004 John Wiley & Sons, Ltd.
The polyethylene glycol-sodium sulfate aqueous two-phase system has been characterized at 23 °C. Tie-lines for the phase diagram were obtained experimentally. Phases in equilibrium were characterized by means of the solvatochromic parameters π*, R, and , which provide a measurement of the polarity/polarizability and the H-bond donor and acceptor abilities, respectively. The ability of the phases to participate in hydrophobic interactions was characterized by means of the free energy of transfer of a methylene group between the conjugated phases, using the partition of a homologous series of dinitrophenylated amino acids. The results show the effect of the presence of polymer and salt in the aqueous phase, and a comparison of both phases with pure water is made.
During the past decade, ionic-liquid-based Aqueous Biphasic Systems (ABS) have been the focus of a significant amount of research. Based on a compilation and analysis of the data hitherto reported, this critical review provides a judicious assessment of the available literature on the subject. We evaluate the quality of the data and establish the main drawbacks found in the literature. We discuss the main issues which govern the phase behaviour of ionic-liquid-based ABS, and we highlight future challenges to the field. In particular, the effect of the ionic liquid structure and the various types of salting-out agents (inorganic or organic salts, amino acids and carbohydrates) on the phase equilibria of ABS is discussed, as well as the influence of secondary parameters such as temperature and pH. More recent approaches using ionic liquids as additives or as replacements for common salts in polymer-based ABS are also presented and discussed to emphasize the expanding number of aqueous two-phase systems that can actually be obtained. Finally, we address two of the main applications of ionic liquid-based ABS: extraction of biomolecules and other added-value compounds, and their use as alternative approaches for removing and recovering ionic liquids from aqueous media.
Aqueous two-phase systems (ATPS) have been studied and used for product recovery and purification from diverse biological sources. ATPS are characterized by their versatility, easy scale up parameters, process integration capability and relative low cost. This technique is commonly regarded as a primary recovery stage mainly due to its low selectivity. However, the use of strategies involving the modification of ATPS with affinity ligands have resulted in significant increases in recovery yields and purification folds of biological products. The aim of this review is to highlight current applications, trends and challenges regarding affinity partitioning in aqueous two-phase systems for the fractionation, recovery and purification of biological products.
As an effective extraction method, aqueous two-phase extraction systems based on imidazolium ionic liquids have been used, in this work, to extract proteins of bovine serum albumin, trypsin, cytochrome c and γ-globulins. Effects of the ionic liquids concentration, pH value, and temperature of the systems on the extraction efficiencies have been investigated. Experimental results show that 75–100% of the proteins could be extracted into the ionic liquid-rich phase in a single-step extraction. The extraction efficiency of cytochrome c was changed slightly with the increase of pH values. Extraction efficiencies of the proteins were found to increase with increasing temperature and increasing alkyl chain length of cation of the ionic liquids. Thermodynamic studies indicated that hydrophobic interactions were the main driving force, although electrostatic interactions and salting-out effects were also important for the transfer of the proteins. Importantly, conformation of the proteins was not affected after extraction into the upper ionic liquid-rich phase as determined by UV–visible (UV–vis) and Fourier transform infrared (FT-IR) spectroscopy of the proteins. The enzyme activity of native trypsin and the trypsin in ionic liquids was determined using N-α-benzoyl-l-arginine ethyl ester as a substrate. This novel process is suggested to have important applications for the separation of proteins.
The solvatochromic parameters characterizing the solvent dipolarity/polarizability (π*), solvent hydrogen-bond donor acidity (α), and solvent hydrogen-bond acceptor basicity (β) of aqueous media were measured in the coexisting phases of aqueous Dextran-Ficoll, Dextran-Ucon, Dextran-PEG, PEG-Ucon, Ficoll-Ucon, and Ficoll-PEG two-phase systems (ATPS). Ionic composition of each ATPS included 0.15M KCl, 0.15M KBr, 0.15M NaBr, 0.1M Na(2)SO(4), and 0.1M Li(2)SO(4) in 0.01 M sodium phosphate buffer (NaPB), pH 7.4; and 0.01 M and 0.11 M sodium phosphate buffer, pH 7.4. Partition ratios of sodium salts of dinitrophenylated (DNP) amino acids with aliphatic side-chains (glycine, alanine, norvaline, norleucine, and α-amino-n-caprylic acid) were measured in all ATPSs, and the results were evaluated in terms of the differences between the relative hydrophobicity (parameter E) and the electrostatic properties (parameter C) of the aqueous media of the coexisting phases. It was established that parameter E is described by a linear combination of the differences between the solvent dipolarity/polarizability (Δπ*) and between the solvent hydrogen-bond acidity (Δα) of the media in the coexisting phases. Parameter C depends on the phase forming polymer pair and is shown to be described by a linear combination of three parameters: the differences between the solvent hydrogen-bond acidity (Δα) and between the solvent hydrogen-bond basicity (Δβ) of the media in the coexisting phases, and a measure of the effect of a given salt additive on the hydrogen bonds in water. This effect was represented by a parameter (K(b-l)), characterizing the equilibrium between populations of hydrogen bonds with a bent hydrogen bond conformation and with linear hydrogen bond conformation affected by a given salt additive.
Compared with the conventional ionic liquids, amino acid ionic liquids are more biodegradable and biocompatible, and can enhance stability of biomaterials. In this work, amino acid ionic liquids 1-butyl-3-methylimidazolium L-serine ([C(4)mim][Ser]), 1-butyl-3-methylimidazolium glycine ([C(4)mim][Gly]), 1-butyl-3-methylimidazolium L-alanine ([C(4)mim][Ala]) and 1-butyl-3-methylimidazolium L-leucine ([C(4)mim][Leu]) have been synthesized. These ionic liquids are found to form aqueous two-phase systems (ATPSs) by the salted-out of K(3)PO(4) in aqueous solutions. Phase diagram of the ATPSs and the Gibbs energies of transfer of methylene group from the bottom salt-rich phase to the top ionic liquid-rich phase have been determined at 298.15K and pH 14, and the effect of anionic structure of the ionic liquids on phase formation of the ATPSs and the relative hydrophobicity between the top and the bottom phases are then examined. In order to understand the effect of relative hydrophobicity of the phases in equilibrium in the ATPSs on the extraction/separation capability of biomolecules, the partition coefficients of cytochrome-c (as a model biomolecule) in the ATPSs are measured by spectrophotometry. It is suggested that hydrophobic interactions are mainly responsible for the higher partition coefficients of cytochrome-c in aqueous two-phase systems at pH 14, and the extraction and separation capacity of biomolecules can be improved by the modulation of the relative hydrophobicity of the phases and/or the pH of the system.
The polarity of a series of ionic liquids (ILs) arising from the quaternarization of N-methylmorpholine, N-methylpyrrolidine, N-methylpiperidine, N-methylazepane, 4-hydroxy-1-methylpiperidine, 1,2-dimethylimidazole, and 1-methylimidazole with simple alkyl chains and/or hydroxyl (mono- or dihydroxyl) functionalized alkyl chains and having bistriflimide, dicyanamide, or nitrate as counteranions has been investigated using solvatochromic dyes and expressed in terms of E(T)(N) and Kamlet-Taft parameters (dipolarity/polarizability (π*), hydrogen bond donor acidity (α), and hydrogen bond basicity (β)). Significant variations of polarity were observed on changing the anion and cation combination. The resulting E(T)(N) and α values were strongly anion dependent; on going from bistriflimide to dicyanamide, a significant decrease in E(T)(N) and α values was observed. On the other hand, the alkyl chain length has only a moderate effect on these parameters; either an increase or decrease in E(T)(N) and α values was observed on increasing the alkyl chain length, depending on the cation core. In the case of cyclic onium salts, the size of the cation ring affected the α parameter; the ILs based on the seven-membered ring system N-methyl-N-butylazepanium (also named N-methyl-N-butylhexamethyleneiminium, [HME(1,4)](+)) have high polarity values, comparatively to the ILs based on analogous five- and six-membered cyclic cations (pyrrolidinium and piperidinium). The introduction of the OH groups on the cation alkyl chain increases the polarity; the effect is substantial for the first OH group and more moderate for the second. Also, the thermosolvatochromism (changes in solvatochromic properties with the change in temperature) was studied for four dihydroxyl functionalized ILs. Finally, the principal component analysis (PCA) carried out on 67 ILs has shown that there are only two statistically relevant parameters: PC1, a weighted sum of E(T)(N) and α, which is able to discern between the cation core structure, functionalization, and cation-anion association, and PC2, very close to β, which is related principally to the anion nature.
The biotech industry is, nowadays, facing unparalleled challenges due to the enhanced demand for biotechnology-based human therapeutic products, such as monoclonal antibodies (mAbs). This has led companies to improve substantially their upstream processes, with the yield of monoclonals increasing to titers never seen before. The downstream processes have, however, been overlooked, leading to a production bottleneck. Although chromatography remains the workhorse of most purification processes, several limitations, such as low capacity, scale-related packing problems, low chemical and proteolytic stability and resins' high cost, have arisen. Aqueous two-phase extraction (ATPE) has been successfully revisited as a valuable alternative for the capture of antibodies. One of the important remaining questions for this technology to be adopted by the biotech industries is, now, how it compares to the currently established platforms in terms of costs and environmental impact. In this report, the economical and environmental sustainability of the aqueous two-phase extraction process is evaluated and compared to the currently established protein A affinity chromatography. Accordingly, the ATPE process was shown to be considerably advantageous in terms of process economics, especially when processing high titer cell culture supernatants. This alternative process is able to purify continuously the same amount of mAbs reducing the annual operating costs from 14.4 to 8.5 million (US$/kg) when cell culture supernatants with mAb titers higher than 2.5 g/L are processed.