Phase equilibrium and insulin partitioning in aqueous two-phase systems containing block copolymers and potassium phosphate

In this work, phase diagrams of aqueous two-phase systems (ATPS) containing PEO–PPO–PEO block copolymers and potassium phosphate as well as the partitioning behavior of insulin in these systems are presented. Experiments aimed at the identification of the effects of copolymer structure (by varying the number of EO units per polymer molecule), temperature (283.15 and 298.15 K) and pH (5.0 and 7.0) on the phase behavior of these systems were carried out. The results indicated the enlargement of the two-phase region upon increasing the temperature, pH and copolymer hydrophobicity (expressed as the PO/EO ratio in the copolymer molecule). Experimental measurements of the partitioning of human insulin in these ATPS also indicated the dependency of the partition coefficients on temperature, pH, and copolymer hydrophobicity, with the latter being the most influential factor. Finally, experimental data on the phase behavior and insulin partitioning were correlated using an excess Gibbs energy virial-type model modified in order to account for coulombic interactions and ionization equilibrium between the various forms of the phosphate ion.     

Measurement and correlation of phase equilibria in aqueous two-phase systems containing polyvinylpyrrolidone and di-potassium tartrate or di-potassium oxalate at different temperatures

Experimental (liquid + liquid) equilibrium (LLE) measurements and the phase diagram have been determined for aqueous two-phase systems containing polyvinylpyrrolidone (PVP) and di-potassium oxalate or di-potassium tartrate at T = (298.15, 308.15, and 318.15) K. Also, the effects of temperature on the binodal curve and tie-lines have been studied. The Merchuk equation was used to correlate the binodal curves of these systems. Furthermore, several suitable equations were used to fit the tie-line data points. The results show that at each temperature, the agreement between the correlated and the experimental values is good with all of these equations. Also, the effects of the type of salt on LLE are discussed.     

Liquid-liquid phase equilibria of aqueous two-phase systems containing salts and polyethylene glycol

Liquid-liquid phase equilibria of the ternary systems: (a) polyethylene glycol - ammonium sulfate- water and (b) polyethylene glycol - sodium carbonate -water have been determined experimentally at 15°, 25°, 35° and 45°C and for two different molecular weights of the polymer (Avg. M.W. 1000 and 2000). Details of the glass cell and of the equilibration and analytical procedures used are described. Equilibrium data along with phase diagrams are presented. Finally the effect of temperature and of the molecular weight of the polymer are also discussed.     

The influence of temperature on the phase behavior of ionic liquid aqueous two-phase systems

In this article, the equilibrium behavior of solutions of 1-ethyl-3-methylimidazolium dimethyl phosphate ([Emim]DMP) and ethyl acetate or acetone in aqueous two-phase system (ATPS) was discussed to understand the liquid–liquid equilibrium (LLE) behavior of these organic solvents. Thus, we determined phase diagrams and LLE data at 303.15, 308.15, 313.15, and 323.15 K for the investigated biphasic systems. Four empirical equations were used to study the tie lines. The results showed that for the [Emim]DMP?+?acetone?+?water biphasic systems within the investigated temperature range, temperature influences the phase behavior, but for the [Emim]DMP?+?ethyl acetate?+?water biphasic systems within the investigated temperature range, there are no notable changes on the phase behavior with rising temperature. The results may have important applications for the separation of antibiotics and for the recovery of ionic liquids (ILs).     

Partitioning behavior of amino acids in aqueous two-phase systems containing polyethylene glycol and phosphate buffer

The partitioning behavior of four amino acids, cysteine, phenylalanine, methionine, and lysine in 15 aqueous two-phase systems (ATPSs) with different polyethylene glycol (PEG) molecular weights and phosphate buffers has been studied in the present paper. The phase diagrams of the systems are investigated together with the effect of the PEG molecular weight and pH of the phosphate solutions. The composition of these systems and some parameters such as density and refractive index are determined. The influences of salts in ATPSs, side chain structure of the amino acids, pH of ATPSs, and the PEG molecular weight on the distribution ratios of the amino acids have been studied. This work is useful for the purification of amino acids and the separation of some proteins whose main surface exposed amino acid residues are these four amino acids, respectively.     

成相无机盐种类对PEG双水相相平衡影响

不同种类无机盐分别与PEG1000、PEG2000、PEG,4000和PEG6000构成双水相体系,在298.15K下,采用浊点滴定法研究双水相体系相平衡,通过Merchuk经验方程拟合实验点确定双水相体系的双节线,进而考察成相无机盐种类对PEG双水相相平衡的影响.结果表明:具有相同阴离子,易于形成双水相的无机盐顺序为...     

(Liquid + liquid) and (liquid + solid) equilibrium of aqueous two-phase systems containing poly ethylene glycol di-methyl ether 2000 and di-sodium hydrogen phosphate

(Liquid + liquid) equilibrium (LLE) for the {poly ethylene glycol di-methyl ether 2000 (PEGDME₂₀₀₀) + Na₂HPO₄ + H₂O} system have been determined experimentally at T = (298.15, 308.15, 313.15, and 318.15) K. The effects of temperature on the binodals and tie-lines for the investigated aqueous two-phase system (ATPS) have been studied. An empirical non-linear expression developed by Merchuk was used for reproducing the experimental binodal data. In this work, the three fitting parameters of the Merchuk equation were obtained with the temperature dependence expressed in the linear form with (T ? T₀) K as a variable. Furthermore, the modified local composition segment-based NRTL and Wilson models and also osmotic virial equation were used to describe the LLE data of the studied system. Also, the effects of the type of salt on LLE are discussed. In addition, the effects of end groups of the polymers PEGDME₂₀₀₀ and poly ethylene glycol 2000 on phase forming ability were studied. The complete phase diagram for the poly ethylene {glycol di-methyl ether 2000 (PEGDME₂₀₀₀) + Na₂HPO₄ + H₂O} system has also been determined at T = 298.15 K.     

Partitioning of l-methionine in aqueous two-phase systems containing poly(propylene glycol) and sodium phosphate salts

The partitioning behavior of l-methionine has been studied in aqueous two-phase systems of (poly(propylene glycol) + sodium phosphate salts + H₂O) at different temperatures. The salts used were sodium di-hydrogen phosphate (NaH₂PO₄), di-sodium hydrogen phosphate (Na₂HPO₄) and tri-sodium phosphate (Na₃PO₄). The effects of tie line length, salt type, and temperature on the partition coefficient of this amino acid have been studied. In addition, thermodynamic parameters (ΔH°, ΔS° and ΔG°) as a function of temperature were calculated. The results showed that increasing tie line length led to decreasing of the partition coefficient. We also showed that the partition coefficients of the amino acid in the systems containing Na₃PO₄ are greater than the other two salts. Moreover, it is verified that increasing temperature led to decreasing the partition coefficient. The experimental partition coefficient data are correlated using a modified virial-type model.     

Equilibrium phase behavior of aqueous two-phase systems containing 17R4/L64 and citrates

The cloud points (CPs) of the copolymers 17R4 and L64 were first measured, and then the effects of salts ((NH₄)₃C₆H₅O₇, K₃C₆H₅O₇) on 17R4 and L64 were researched. After finishing the work described above, the temperature (278.15, 283.15, and 288.15) K of aqueous two-phase systems was determined, which consist of 17R4-(NH₄)₃C₆H₅O₇, 17R4-K₃C₆H₅O₇, L64-(NH₄)₃C₆H₅O₇, and L64-K₃C₆H₅O₇. Finally, the liquid–liquid equilibrium (LLE) data of binodal curve and the tie line for 17R4-(NH₄)₃C₆H₅O₇ aqueous two- phase systems (ATPSs) 17R4-K₃C₆H₅O₇ ATPSs, L64-(NH₄)₃C₆H₅O₇ ATPSs, and L64-K₃C₆H₅O₇ ATPSs were obtained. Nonlinear fitting of the empirical equation was used for making the diagram. The results showed that the change in the size of the two-phase areas increases with the increase of temperature. The capacity of the salts to induce phase segregation follows the Hofmeister series, that is, K₃C₆H₅O₇?>?(NH₄)₃C₆H₅O₇. In addition, the findings also showed that the phase separation ability of 17R4 is better than that of L64.     

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.     

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.     

Effect of polyvinylpyrrolidone and sodium lauroyl isethionate on kaolinite suspension in an aqueous phase

Suspension of concentrated kaolinite (20 g/30 ml-medium) in the presence of polyvinylpyrrolidone (PVP) and sodium lauroyl isethionate (SLI) was allowed to evaluate its degree of dispersion based on their rheological studies. Flow curves at low shear rate, measured by means of cone-plate method, showed a non-Newtonian flow. Plastic viscosity and Bingham yield value were derived from the flow curves. Relative viscosity, effective volume fraction and void fraction of secondary particle were also obtained. Results of dispersity and fluidity of the suspension were explained. PVP acted as a flocculant at a concentration lower than 0.1% but as a dispersant at a higher concentration. The presence of SLI could decrease both the Bingham yield value and suspension viscosity. Cooperative and competitive effects of PVP and SLI were found. Results indicated that SLI enhanced the degree of dispersion of kaolinite when PVP was less than 0.1%. The suspension, however, showed a maximum flocculation (i.e., aggregation) at 4 mM SLI when the concentration of PVP was higher than 0.1%.     

Liquid-liquid equilibrium of novel aqueous two-phase systems and evaluation of salting-out abilities of salts

Binodal data are beneficial to the design of aqueous two-phase extraction and the establishment of thermodynamic models. For the 2-propanol + Li₂SO₄/Na₂SO₄/ (NH₄)₂SO₄/K₃PO₄ + water systems and 1-propanol + K₃PO₄/K₃C₆H₅O₇/(NH₄)₃C₆H₅O₇ + water systems, binodal data were determined at 298.15 K. The binodal data were correlated by a theoretical equation on the basis of statistical geometry. The salting-out abilities of salts and the phase-separation abilities of alcohols were evaluated by the effective excluded volume of salt and the binodal curves plotted in molality. A simple Hofmeister series of cations and anions were obtained. The organic salt, K₃C₆H₅O₇, shows as high a salting-out ability as K₃PO₄.      

Extraction of the antimicrobial peptide cerein 8A by aqueous two-phase systems and aqueous two-phase micellar systems

Cerein 8A is an antimicrobial peptide with potential application against food spoilage and pathogenic bacteria. The partitioning of cerein 8A was investigated in two liquid-liquid extraction systems that are considered promising for bioseparation and purification purposes. Aqueous two-phase systems (ATPSs) were prepared with polyethylene glycol (PEG) and inorganic salts, and the addition of NaCl was investigated in this system. The best results concerning partition coefficients (K (b)) were obtained with PEG?+?ammonium sulphate, and K (b) value significantly increases when NaCl was added. Cerein 8A was effectively extracted into the micelle-rich phase in a 4% Triton X-114 medium. Recovery yield was higher for ATPS compared to micellar systems. Cerein 8A can be isolated from a crude suspension containing the bioactive molecule by ATPSs. Successful implementation of peptide partitioning represents an important step towards developing a low-cost effective separation method for cerein 8A.     

Prediction of vapor-liquid-liquid-hydrate phase equilibrium for multicomponent systems containing tetrahydrofuran

Numbers of hydrate-based new techniques require the algorithm to be able to perform multiphase flash calculation where one phase is a gas hydrate phase.Tetrahydrofuran(THF)is frequently used as a thermodynamic promoter in the development of hydrate-based technique,which can reduce the hydrate formation pressure,especially when methane or hydrogen exists.However,it is a hard work to describe accurately the phase behavior of THF-water system due to their polarities.It has been proved that the water-in-oil(W/O)emulsion can raise the hydrate formation rate and improve the single stage separation efficiency,and furthermore prevent the hydrate from agglomeration to plug the facilities.The goal of this work is to present an extension of our previous work to the prediction of the vapor-liquid-liquid-hydrate equilibrium of such complex systems.These include ternary and quaternary mixtures with W/O emulsion containing THF.The proposed algorithm of four phase equilibrium calculation is very simple due to avoiding the complexity of simultaneous solution of the sophisticated equation group.The calculation results were found to be in satisfactory agreement with the experimental data.     

Thermodynamics of phase equilibrium for systems containing N-isopropyl acrylamide hydrogels

Hydrogels are crosslinked polymers of hydrophilic monomers. Hydrogels can swell and shrink in aqueous solutions. The swelling behavior of hydrogels and the encountered phase behavior are of interest in many areas, e.g., in biotechnology, membrane science and controlled drug release. This contribution presents the criteria for such phase equilibria and a previously developed thermodynamic model for correlating/predicting the swelling and shrinking of hydrogels. The application of the method is demonstrated by describing the swelling equilibrium of some synthetic, non-ionic N-isopropyl acrylamide (N-IPAAm) hydrogels in aqueous solutions of sodium chloride at 298 K. Furthermore, new experimental results are presented for the degree of swelling of synthetic hydrogels that contain – besides the non-ionic monomer N-IPAAm – either a combination of a cationic comonomer (here, N-[3-(dimethylamino)propyl]methacrylamide (DMAPMA)) and an anionic comonomer (here, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS)) or a zwitterionic comonomer (here, [3-(methacryloylamino)propyl]dimethyl(3-sulfopropyl)ammonium hydroxide inner salt (MPSA)). These gels were equilibrated with aqueous solutions of sodium chloride at 298 K.     

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.     

Partitioning behavior of erythrocytes in aqueous two-phase systems containing hydroxypropyl starch and polyethylene glycol

The partitioning behavior of erythrocytes in Reppal PES 200 (a hydroxypropyl starch produced by Reppe Glykos AB, V?xj?, Sweden)-polyethylene glycol (PEG) and in dextran (Dx)-PEG aqueous phase systems made isotonic with phosphate is similar in a number of ways: (i) There is a correlation between the relative electrophoretic mobilities and partition ratios, P, of red blood cells from different species; (ii) The cell P is reduced when, at constant polymer concentrations, phosphate is systematically replaced by sodium chloride (with the total concentration isotonic); (iii) The cell P is increased with reduced polymer concentrations (decreased interfacial tensions); (iv) Treatment of erythrocytes with neuraminidase results in a reduced P value; (v) Rat red cells of different ages can be fractionated by counter-current distribution; and (vi) Differences between red blood cells from genetically distinct rats or between humans can be detected. Aquaphase (a hydroxypropyl starch marketed by Perstorp AB, Lund, Sweden) has been tested as in ii-iv above with analogous results. The partitioning behavior of erythrocytes in PES-PEG and Dx-PEG aqueous phase systems containing sodium chloride differs in a number of ways: (vii) The correlation, apparent in Dx-PEG systems, between the P value of red blood cells from different species and the ratio of their membrane poly- to monounsaturated fatty acids is absent in PES-PEG systems. It is replaced by a correlation as in i; (viii) The increase in P value in Dx-PEG observed from red blood cells after treatment with neuraminidase is replaced by a decrease in P value in PES-PEG or Aquaphase-PEG systems. We conclude that PES (and Aquaphase) can be substitutes for dextran in cell partitioning studies when charge-sensitive phases are used (e.g., those containing phosphate) while separations based on properties reflected by Dx-PEG systems containing sodium chloride are not duplicated by PES-PEG (and probably not by Aquaphase-PEG). The hydroxypropyl starch-PEG systems containing sodium chloride, unlike the analogous Dx-PEG systems, have a significant electrostatic potential difference between the phases.     

Effect of temperature on hydrogen peroxide photolysis in aqueous solutions

The photolysis of hydrogen peroxide in dilute aqueous solution (1 × 10⁻⁴ M) at various temperatures (15–85°C) and pH (ph 2.5–7) was studied by flash photolysis. The rate of oxygen production under continuous photolysis conditions was measured at room temperature. The rate constants and activation parameters are reported. Evidence for the formation of complexes between hydrogen peroxide and intermediate radicals is presented. The liquid phase data are discussed and compared with those available for the gas phase.     

Study of apparent molal volume and viscosity of mutual citric acid and disodium hydrogen orthophosphate aqueous systems

Fundamental properties, density (ρ) and viscosity (η), of citric acid (CA) and disodium hydrogen orthophosphate (DSP) at various strengths were obtained at different temperatures. The ρ and η values were used to determine apparent molal volumes and viscosity of systems. The ρ, V_Φ and η values were regressed against molalitym for ρ⁰, η⁰ and V _Φ ⁰ , the limiting constants at infinite dilution (m → 0) for ionic and molecular interactions. The ρ⁰ and V _Φ ⁰ of aq. acids are higher than those of aq. DSP and the viscosity of DSP is higher than that of aq. CA. Examination of ρ⁰ and V _Φ ⁰ functions indicates that mutual compositions of CA and DSP counterbalance concentration and temperature effects on pH in bioprocesses.