Effect of salt additives on partition of nonionic solutes in aqueous PEG-sodium sulfate two-phase system

Partition of 12 nonionic organic compounds in aqueous PEG-8000-Na(2)SO(4) two-phase system was examined. Effects of four salt additives (NaCl, NaSCN, NaClO(4), and NaH(2)PO(4)) in the concentration range from 0.027 up to ca. 1.9 M on binodal curve of PEG-sulfate two-phase system and solute partitioning were explored. It was found that different salt additives at the relatively high concentrations display different effects on both phase separation and partition of various nonionic solutes. Analysis of the results indicates that the PEG-Na(2)SO(4) ATPS with the up to 0.215 M NaCl concentration may be viewed as similar to the ATPS without NaCl in terms of the Collander equation's predictive ability of the partitioning behavior of nonionic compounds. All ATPS with each of the salt additive used at the concentration of 0.027 M may be viewed as similar to each other as the Collander equation holds for partition coefficients of nonionic solutes in these ATPS. Collander equation is valid also for the compounds examined in the ATPS with additives of NaSCN and NaClO(4) at the concentrations up to 0.215 M. The observed similarity between these ATPS might be explained by the similar effects of these two salts on the water structure. At concentrations of the salt additives exceeding the aforementioned values, different effects of salt additives on partitioning of various nonionic solutes are displayed. In order to explain these effects of salt additives it is necessary to examine the intensities of different solute-solvent interactions in these ATPS within the framework of the so-called Linear Solvation Energy Relationship (LSER) model.     

Correlations between distribution coefficients of various biomolecules in different polymer/polymer aqueous two-phase systems

Distribution coefficients for a variety of proteins and certain other biomolecules (peptides, amino acids, and carbohydrates) (overall 27 different solutes) were measured in aqueous two-phase systems (ATPSs) dextran (Dex)–polyethylene glycol (PEG) and Dex–Ucon 50-HB-5100 (Ucon—a random copolymer of ethylene glycol and propylene glycol) both containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4, at 23 °C. Distribution coefficients of some selected solutes were also measured in the above two-phase systems at three different polymer concentrations for each system. It was established that the distribution coefficients for all the proteins examined in the ATPSs are correlated according to the so-called Collander linear equation.     

离子液体双水相萃取分离苋菜红的研究

建立了由亲水性离子液体四氟硼酸1-丁基-3-甲基咪唑([Bmim]BF4)和NaH2PO4形成的双水相体系萃取分离苋菜红的新方法.研究了盐的浓度、离子液体浓度、溶液酸度、其它共存物质对苋菜红萃取率的影响.结果表明,NaH2PO4加入量在2～2.5 g,离子液量在1.0～2.0 mL,苋菜红溶液量在1.5 mL,溶液酸度在pH 4～6范围,离子液体双水相体系对苋菜红有较高的萃取率(E%＞90).用加入无机离子、不同类型表面活性剂和吸收光谱探讨了离子液体与苋菜红之间的作用.     

Extraction of testosterone and epitestosterone in human urine using aqueous two-phase systems of ionic liquid and salt

Based on aqueous two-phase systems (ATPS) consisting of 1-butyl-3-methylimidazolium chloride, a hydrophilic ionic liquid (IL), and K2HPO4, a new and simple extraction technique, coupled with a reversed-phase high performance liquid chromatography (RP-HPLC), was developed for the simultaneous concentration and analysis of testosterone (T) and epitestosterone (ET) in human urine. Under the optimal conditions, the extraction efficiencies for both analytes were 80-90% in a one-step extraction. The method required only 3.0 mL of urine and a single hydrolysis/deproteinization/extraction step followed by direct injection of the IL-rich upper phase into HPLC system for analysis. The method has been satisfactorily applied to the analysis of T and ET in human urine with detection limits of 1 ng/mL and linear ranges of 10-500 ng/mL for both compounds. Compared with conventional liquid-liquid extraction or solid phase extraction, this new method is much "greener" due to no use of volatile organic solvent and low consumption of IL. The proposed extraction technique opens up new possibilities in the separation of other drugs.     

Drop formation in aqueous two-phase systems

Extraction using aqueous two-phase systems (ATPSs) is a versatile technique for the downstream processing of various proteins/enzymes. The study of drop formation deals with the fundamental understanding of the behavior of liquid drops under the influence of various external body as well as surface forces. These studies provide a basis for designing of the extractions in column contactors in which liquid drops play a major role. Most of the drop formation studies reported so far is restricted to aqueous-organic systems. ATPSs, differ from aqueous-organic systems in their physical properties. In view of this, an attempt was made to develop a model for drop formation in ATPSs adopting the information available on aqueous-organic systems. In order to validate the model, experiments were performed by using polyethylene glycol (PEG)/salt systems of different phase compositions at various flow rates. At low flow rates the single stage model and at high flow rates the two stage model are able to predict the drop volume during its formation from tip of capillary. The experimental results were found to agree reasonably well with those predicted by the model.     

Solvent properties governing protein partitioning in polymer/polymer aqueous two-phase systems

Distribution coefficients of various proteins were measured in aqueous Dextran-Ficoll, Dextran-PES, and Ficoll-PES two-phase systems, containing 0.15M NaCl in 0.01 M phosphate buffer, pH 7.4. The acquired data were combined with data for the same proteins in different systems reported previously and known solvatochromic solvent properties of the systems to characterize the protein-solvent interactions. The relative susceptibilities of proteins to solvent dipolarity/polarizability, solvent hydrogen bond acidity, solvent hydrogen bond basicity, and solvent ability to participate in ion-ion and ion-dipole interactions were characterized. These parameters, which are representative of solute-solvent interactions, adequately described the partitioning of the proteins in each system. It was found that the relative susceptibilities of proteins to solvent dipolarity/polarizability are interrelated with their relative susceptibilities to solvent hydrogen bond acidity and solvent hydrogen bond basicity similarly to those established previously for small nonionic organic compounds.     

Partitioning of biomaterials in aqueous two-phase systems of mixed cationic-anionic surfactants

In a previous paper, we have showed that, when aqueous solutions of cationicand anionic surfactants at certain concentrations were mixed, the solution separatedspontaneously into two immiscible phases (aqueous two-phases), one phase was rich,and the other was poor in the mixed surfactants. A clear interfacial boundary existsbetween two phases.     

Solvatochromic parameters for binary mixtures of an ionic liquid with various protic molecular solvents

Abstract  Solvatochromic parameters (E _T ^N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) have been determined for binary mixtures of propan-2-ol, propan-1-ol, ethanol, methanol and water with recently synthesized ionic liquid (IL; 2-hydroxyethylammonium formate) at 25 °C. In all solutions except aqueous solution, E _T ^N values of the media increase abruptly with the ILs mole fraction and then increase gradually to the value of pure IL. A synergistic behavior is observed for the α parameter in all solutions. The behavior of π* and β are nearly ideal for all solutions except for solutions of methanol with the IL. The applicability of nearly ideal combined binary solvent/Redlich–Kister equation was proved for the correlation of various solvatochromic parameters with solvent composition. The correlation between the calculated and the experimental values of various parameters was in accordance with this model. Solute–solvent and solvent–solvent interactions were applied to interpret the results. Graphical Abstract  Predicted values of solvatochromic parameters (SP) (E _T ^N, normalized polarity parameter; π*, dipolarity/polarizability; β, hydrogen-bond acceptor basicity; α, hydrogen-bond donor acidity) from the correlation equations versus its experimental values for binary mixtures of 2-hydroxyethylammonium formate with water, methanol, ethanol, propan-1-ol and propan-2-ol.      

Dual affinity method for plasmid DNA purification in aqueous two-phase systems

The DNA binding fusion protein, LacI–His₆–GFP, together with the conjugate PEG–IDA–Cu(II) (10 kDa) was evaluated as a dual affinity system for the pUC19 plasmid extraction from an alkaline bacterial cell lysate in poly(ethylene glycol) (PEG)/dextran (DEX) aqueous two-phase systems (ATPS). In a PEG 600–DEX 40 ATPS containing 0.273 nmol of LacI fusion protein and 0.14% (w/w) of the functionalised PEG–IDA–Cu(II), more than 72% of the plasmid DNA partitioned to the PEG phase, without RNA or genomic DNA contamination as evaluated by agarose gel electrophoresis. In a second extraction stage, the elution of pDNA from the LacI binding complex proved difficult using either dextran or phosphate buffer as second phase, though more than 75% of the overall protein was removed in both systems. A maximum recovery of approximately 27% of the pCU19 plasmid was achieved using the PEG–dextran system as a second extraction system, with 80–90% of pDNA partitioning to the bottom phase. This represents about 7.4 μg of pDNA extracted per 1 mL of pUC19 desalted lysate.     

Modeling continuous aqueous two-phase systems for control purposes

A mathematical model was proposed to allow the analysis of steady-state and transient behaviors of single-stage continuous aqueous two-phase systems. Since the complete system of simultaneous equations contains more equations than unknown variables, a program based on the method of least squares was developed to solve the problem. The methodology was tested using a system composed of thaumatin, sodium chloride, and a contaminant protein. A poly(ethylene-glycol)/phosphate salt/water system was selected to isolate the thaumatin. For the steady-state and transient operations, a constrained optimization procedure--from the Matlab Optimization Toolbox (MathWork, Inc.)--was implemented after recasting the system of equations as a minimization problem. Euler's method was used in the transient case to discretize the differential equations. The steady-state concentrations agreed with published data. An input-output model based on a 4% step change decrease in the inlet stream flow rate showed that output variables such as concentrations of sodium chloride and phosphate salt settled to their final values in different time periods. The proposed analysis may be helpful in the dynamic control of large-scale commercial extractor units using advanced control schemes.     

Prediction of phase diagrams for new pH-thermo sensitive recycling aqueous two-phase systems

The recyclable aqueous two-phase systems formed by thermo-sensitive polymer (P_NB) and pH-sensitive polymer (P_ADB) have been prepared by our laboratory. In this study, the Flory–Huggins model derived from the lattice theories and the COVE model based on the McMillan–Mayer solution theory were used for correlations and predictions of phase diagrams. The interaction parameters between the solvent and the polymers of the Flory–Huggins model were calculated from solubility parameters. The interaction parameters between the polymers and the COVE coefficients were determined by fitting experimental data. Simulation of Flory–Huggins model and COVE model indicates that the deviation between prediction values and experimental data is less than 0.50%. The COVE model was more effective than the Flory–Huggins model to this system.     

Interfacial tension of the aqueous two-phase systems of cationic-anionic surfactant mixtures

Interfacial tensions of the aqueous two-phase systems formed by cationic-anionic surfactant mixtures were measured using spinning drop method. The effects of surfactant structure, molar ratio of cationic to anionic surfactants, surfactant concentration, salt, and temperature on the interfacial tensions were investigated. It was shown that the values of the interfacial tensions of the aqueous two-phase were in the scale of ultra-low interfacial tensions at certain molar ratios of cationic to anionic surfactants. Three types of interfacial tension curves were observed. The first curve comprised two curves that were located on either side of 1:1 molar ratio, and the interfacial tension decreased with the increase of excessive surfactant components. The second one was a saddle-shaped curve that strode over the 1:1 molar ratio. The third type was a saddle-shaped curve that was located beside the 1:1 molar ratio. The types of interfacial tensions depended on the molecular structure of the surfactants such as the hydrophilic groups and the lengths and symmetry of hydrophobic chains.     

Cosolutes effects on aqueous two-phase systems equilibrium formation studied by physical approaches

The effect of urea and sodium salts of monovalent halides on the aqueous polyethyleneglycol solution and binodal diagrams of polyethyleneglycol–potassium phosphate (polyethyleneglycol of molecular mass 1500, 4000, 6000 and 8000) were studied using different physical approaches. The effect of these solutes on the binodal diagram for polyethyleneglycol–potassium phosphate was also investigated. The cosolutes affected in a significant manner the water structured around the ethylene chain of polyethyleneglycol inducing a lost of this. The equilibrium curves for the aqueous two-phase systems were fitting very well by a sigmoidal function with two parameters, which are closely related with the cosolute structure making or breaking capacity on the water ordered.     

Separation, concentration and determination of chloramphenicol in environment and food using an ionic liquid/salt aqueous two-phase flotation system coupled with high-performance liquid chromatography

Ionic liquid–salt aqueous two-phase flotation (ILATPF) is a novel, green, non-toxic and sensitive samples pretreatment technique. ILATPF coupled with high-performance liquid chromatography (HPLC) was developed for the analysis of chloramphenicol, which combines ionic liquid aqueous two-phase system (ILATPS) based on imidazolium ionic liquid (1-butyl-3-methylimidazolium chloride, [C₄mim]Cl) and inorganic salt (K₂HPO₄) with solvent sublation. In ILATPF systems, phase behaviors of the ILATPF were studied for different types of ionic liquids and salts. The sublation efficiency of chloramphenicol in [C₄mim]Cl–K₂HPO₄ ILATPF was influenced by the types of salts, concentration of K₂HPO₄ in aqueous solution, solution pH, nitrogen flow rate, sublation time and the amount of [C₄mim]Cl. Under the optimum conditions, the average sublation efficiency is up to 98.5%. The mechanism of ILATPF contains two principal processes. One is the mechanism of IL–salt ILATPS formation, the other is solvent sublation. This method was practical when applied to the analysis of chloramphenicol in lake water, feed water, milk, and honey samples with the linear range of 0.5–500 ng mL⁻¹. The method yielded limit of detection (LOD) of 0.1 ng mL⁻¹ and limit of quantification (LOQ) of 0.3 ng mL⁻¹. The recovery of CAP was 97.1–101.9% from aqueous samples of environmental and food samples by the proposed method. Compared with liquid–liquid extraction, solvent sublation and ionic liquid aqueous two-phase extraction, ILATPF can not only separate and concentrate chloramphenicol with high sublation efficiency, but also efficiently reduce the wastage of IL. This novel technique is much simpler and more environmentally friendly and is suggested to have important applications for the concentration and separation of other small biomolecules.     

Effect of anionic structure on the phase formation and hydrophobicity of amino acid ionic liquids aqueous two-phase systems

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.     

Droplet-based microextraction in the aqueous two-phase system

This report is about microfluidic extraction systems based on droplets of aqueous two-phase system. Mass transfer between continuous phase and dispersed droplet is demonstrated by microextraction of ruthenium red in a microfluidic device. Droplets are generated with electrohydrodynamic method in the same device. By comparing brightness in the digital image of a solution with known concentrations of ruthenium red and those of a droplet in the microextraction, ruthenium red concentration was measured along the microextraction channel, resulting in good agreement with a simple diffusion model. The maximum partition coefficient was 9.58 in the experiment with the 70-mm-long-channel microextractor. The method is usable for terminating microextraction by electrohydrodynamic manipulation of droplet movement direction. Droplets of different ruthenium red concentration, 0.12 and 0.24% (w/w) in this experiment, can be moved to desired place of microfluidic system for further reaction through respectively branched outlets. In this study droplet-based microextraction is demonstrated and the mass transport is numerically analyzed by solving the diffusion–dissolution model.     

Phase diagrams of ionic liquids-based aqueous biphasic systems as a platform for extraction processes

In the past few years, ionic liquid-based aqueous biphasic systems have become the subject of considerable interest as a promising technique for the extraction and purification of several macro/biomolecules. Aiming at developing guidelines for more benign and efficient extraction processes, phase diagrams for aqueous biphasic systems composed of ionic liquids and inorganic/organic salts are here reported. Several combinations of ionic liquid families (imidazolium, pyridinium, phosphonium, quaternary ammonium and cholinium) and salts [potassium phosphate buffer (KH₂PO₄/K₂HPO₄ at pH 7), potassium citrate buffer (C₆H₅K₃O₇/C₆H₈O₇ at pH 5, 6, 7 and 8) and potassium carbonate (K₂CO₃ at pH ∼13)] were evaluated to highlight the influence of the ionic liquid structure (cation core, anion and alkyl chain length), the pH and the salt nature on the formation of aqueous biphasic systems. The binodal curves and respective tie-lines reported for these systems were experimentally determined at (298 ± 1) K. In general, the ability to promote the aqueous biphasic systems formation increases with the pH and alkyl chain length. While the influence of the cation core and anion nature of the ionic liquids on their ability to form aqueous biphasic systems closely correlates with ionic liquids capacity to be hydrated by water, the effect of the different salts depends of the ionic liquid nature and salt valency.     

利用双水相分离回收离子液体的研究进展

研究离子液体的分离与回收对于减少离子液体对环境的影响、提高离子液体的利用效率、降低离子液体的应用成本、促进离子液体的工业应用具有重要的意义.本文重点综述了利用无机盐-离子液体双水相、糖-离子液体双水相、聚合物-离子液体双水相和CO2诱导的离子液体双水相技术分离回收离子液体的研究进展,分析了影响离子液体分离回收的关键因素,评价了不同离子液体双水相体系的优缺点,展望了该领域的发展方向及面临的挑战.     

Aqueous two-phase systems for protein separation: a perspective

Aqueous two-phase systems (ATPS) that are formed by mixing a polymer (usually polyethylene glycol, PEG) and a salt (e.g. phosphate, sulphate or citrate) or two polymers and water can be effectively used for the separation and purification of proteins. The partitioning between both phases is dependent on the surface properties of the proteins and on the properties of the two phase system. The mechanism of partitioning is complex and not very easy to predict but, as this review paper shows, some very clear trends can be established. Hydrophobicity is the main determinant in the partitioning of proteins and can be measured in many different ways. The two methods that are more attractive, depending on the ATPS used (PEG/salt, PEG/polymer), are those that consider the 3-D structure and the hydrophobicity of AA on the surface and the one based on precipitation with ammonium sulphate (parameter 1/m*). The effect of charge has a relatively small effect on the partitioning of proteins in PEG/salt systems but is more important in PEG/dextran systems. Protein concentration has an important effect on the partitioning of proteins in ATPS. This depends on the higher levels of solubility of the protein in each of the phases and hence the partitioning observed at low protein concentrations can be very different to that observed at high concentrations. In virtually all cases the partition coefficient is constant at low protein concentration (true partitioning) and changes to a different constant value at a high overall protein concentration. Furthermore, true partitioning behavior, which is independent of the protein concentration, only occurs at relatively low protein concentration. As the concentration of a protein exceeds relatively low values, precipitation at the interface and in suspension can be observed. This protein precipitate is in equilibrium with the protein solubilized in each of the phases. Regarding the effect of protein molecular weight, no clear trend of the effect on partitioning has been found, apart from PEG/dextran systems where proteins with higher molecular weights partitioned more readily to the bottom phase. Bioaffinity has been shown in many cases to have an important effect on the partitioning of proteins. The practical application of ATPS has been demonstrated in many cases including a number of industrial applications with excellent levels of purity and yield. This separation and purification has also been successfully used for the separation of virus and virus-like particles.