Solvent Properties of Aqueous Biphasic Systems Composed of Polyethylene Glycol and Salt Characterized by the Free Energy of Transfer of a Methylene Group between the Phases and by a Linear Solvation Energy Relationship (original) (raw)
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Physical Chemistry Chemical Physics, 2002
The effect of the molecular size of components on preferential solvation analysis has been investigated by studying aqueous solutions of the poly(ethylene glycol) (PEG) homologous chemical series. Precise density data are analyzed for some PEG-water systems, for polymers of molecular weight up to 3400 at 25 C, at the highest practicable concentrations. The combination of density, activity, and compressibility data allows the evaluation of Kirkwood-Buff integrals for these systems. Data were discussed in terms of preferential solvation, showing that co-operativity takes part to some extent in the PEG-PEG interaction, depending on PEG concentration and molecular weight. The size mismatch between solvent and solute requires a proper reference state, the Matteoli-Shulgin-Ruckenstein state, which takes into account the excluded volume effect. This correction must be applied when considering macromolecular systems, otherwise physically meaningless analyses are developed. Density data at high concentration have been analyzed in order to evaluate progressive aggregation up to network formation, recently proposed for PEG-water systems. The study provides a new picture of aqueous PEG solutions useful for the interpretation of protein precipitation induced by this uncharged polymer. Comparisons with a preferential solvation analysis of the PEG oligomers and with a recent velocity-correlation analysis of PEG polymers have been also made. This paper provides a new picture of PEG-water media, useful to interpret the colloidal stability in the presence of PEG.
European Polymer Journal, 2007
Solubility of systems involving four different molecular weights of poly(ethylene glycol) (PEG) in tetrahydrofuran (THF), chloroform, dimethylsulfoxide (DMSO), methanol and water have been investigated by different algorithmic approaches as the mathematical application of the ''like dissolves like'' principle. In this study, the solubility parameters and their components for PEG and solvents have been evaluated by using of atomic group contribution methods; Small, van Krevelen-Hoftyzer (VKH), Hoy and Breitkreutz methods, respectively. Then their 2-dimensional graphs (Bagley, Henry and Hoernschemeyer diagrams) and 3-dimensional graph (Hansen diagram) have been drawn by creating the solubility profiles of the polymer in selected solvents. The dissolving capability of these solvents has been discussed. In addition the solubility parameters have been calculated by use of the van der Waals volume in the selected molecule or repeating unit of the polymer instead of the molar volume which is used in atomic group contribution methods (Askadskii approach). Surface tensions of the polymer and solvent systems have been calculated with this method and solubility criteria of PEG have been explained after a serial calculation steps. In addition, influence of molecular weight of PEG on solubility has been also analyzed. As a consequence of algorithmic calculations, THF has been determined as the best solvent whereas water is found to be the weakest solvent for polymer/solvent systems.
Fluid Phase Equilibria, 2012
In this work, liquid-liquid and solid-liquid equilibria (LLE and SLE, respectively), at atmospheric pressure, of the solutions of poly(ethylene glycol) (PEG) with several organic solvents were studied. The studied solvents include benzene, toluene, o-xylene, p-xylene, tetrahydrofuran (THF), pyridine, nicotine, aniline, 1-hexanol, 1-octanol and 1-decanol. Previous and present solubility tests showed that pyridine, nicotine, THF and aniline are completely soluble in liquid PEG200 and PEG400. This study confirmed and extended the previous discoveries that PEG can adjust its polarity and may be soluble with both polar and nonpolar compounds as well as that the addition of a methyl group dramatically reduces the solubility of PEG with arenes. These remarkable features were thoroughly reviewed and discussed. Further on, they were used to explain the new results brought by this work-LLE of the solutions of (liquid) PEG200/or PEG400 with xylene isomers and SLE of the solutions of (solid) PEG2050 with all the aforementioned compounds. Molar excess volumes (V E) of the solutions (PEG200/or PEG400 + benzene/or toluene) were measured at 298.15 K-these results were used to additionally discuss and explain the LLE behavior of these solutions. Finally, the results of this study showed the possibilities for sustainable applications (i) of liquid PEG200/or PEG400 for the separation of of o-xylene from p-xylene and (ii) of (solid) PEG2050 for benzene, toluene, pyridine and aniline treatment.
Solvatochromic studies in polyethylene glycol-salt aqueous biphasic systems
2000
The polarities of the co-existing phases of a polyethylene glycol (PEG)-2000-K PO aqueous biphasic system (ABS) 3 4 have been examined using Reichardt's carboxylated pyridinium-N-phenoxybetaine dye as a probe. Using this probe, the polarities of these phases have been compared to those of conventional solvent extraction systems and micellar systems using values obtained from the literature. In general, these extraction systems are comparable in polarity to rather polar solvents. Data on the free energy of transfer of solvents suggests that this may be due to the failure of the probe to account for the real polarity of the salt-rich phase compared to the polymer-rich phase. Examination of the monophasic region of these systems suggests that the reason for this is that the probe is partitioned to a discreet solvent domain dominated by PEG, even though phase separation of the solution is not observed. The use of linear free energy relationships for the characterization of ABS is briefly discussed.
Effect of ionic liquids as adjuvants on PEG-based ABS formation and the extraction of two probe dyes
Fluid Phase Equilibria, 2014
Aqueous biphasic systems (ABS) are relevant for the development of environmentally friendly and "biocompatible" separation processes. However, the common polyethylene glycol (PEG) polymers present a limited range of applicability, due to the low polarity of the PEG-rich phase. To overcome this limitation, a new approach was recently proposed based on the use of ionic liquids (ILs) as adjuvants in ABS, enlarging the polarity range of these systems. This work addresses the use of imidazolium-based ILs as ionic adjuvant compounds in the formation of ABS, namely potassium salts + water + PEG (1500, 4000, 6000 and 8000). To explore the differences induced by the presence of the IL as adjuvant the partition behavior of two dyes, Chloranilic Acid and Rhodamine 6G, is analyzed and correlated with the phase behavior and the IL distribution on the ABS under study.
ΔG(CH2) as solvent descriptor in polymer/polymer aqueous two-phase systems
Journal of Chromatography A, 2008
Phase diagrams were determined for aqueous two-phase systems (ATPSs) formed by different paired combinations of Dextran (Dex-75), Ficoll-70, polyethylene glycol (PEG-8000), hydroxypropyl starch (PES-100), and Ucon50HB5100 (a random copolymer of ethylene glycol and propylene glycol) all containing 0.15 M NaCl in 0.01 M phosphate buffer, pH 7.4, at 23 • C. Partition coefficients of a series of dinitrophenylated (DNP) amino acids with aliphatic side-chains were studied in all the ATPSs at particular polymer concentrations. Free energies of transfer of a methylene group between the coexisting phases, G(CH 2 ), were determined as measures of the difference between the hydrophobic character of the phases. Furthermore, partition coefficients of tryptophan (Trp) and its di-and tri-peptides and a set of p-nitrophenyl (NP)-monosaccharides were measured in all the two-phase systems, and the data obtained compared with the G(CH 2 ) values obtained in the systems. It was established that for eight out of 10 of two-phase systems of different polymer compositions the partition coefficients for Trp peptides correlate well with the G(CH 2 ) values. Similar correlations for NP-monosaccharides were valid for seven out of 10 two-phase systems. These observations indicate that the difference between the hydrophobic characters of the coexisting phases represented by the G(CH 2 ) value cannot be used as a single universal measure for comparison of the ATPSs of different polymer compositions.
Journal of Solution Chemistry, 2018
Polyethylene glycols have become more popular alternate reaction media due to interesting properties like non-toxicity, bio-degradability, and full miscibility with water and organic solvents. Binary mixtures of polyethylene glycols with common solvents can be useful to tune their physical and chemical properties and to facilitate chemical and physical processes. In this study, solvatochromic parameters were spectrophotometrically determined for binary solvent mixtures of poly(ethylene glycol)-400 (PEG-400) with methanol, 2-propanol, 1-butanol, dimethyl sulfoxide, N,N-Dimethylformamide, and dichloromethane under ambient conditions, over the whole range of mole fractions. The solvatochromic parameters showed different trends in protic and aprotic solvents mixed with PEG-400. Methanol/PEG-400 mixtures showed special properties in polarity and polarizability so that the mixtures are more dipolar/polarizable than their pure components. Positive or negative deviations from ideal behavior confirmed that the indicators were involved in a preferential solvation process in the solvent mixtures. These deviations from ideality can be attributed to strong solvent-solvent interactions in the binary mixtures.
Physical Chemistry Chemical Physics, 2014
The relative ability of cholinium-([Ch] +)-based salts, including ionic liquids (ILs), to form biocompatible aqueous biphasic systems (ABS) with polyethylene glycols (PEGs) was deeply scrutinized in this work. Aqueous solutions of low molecular weight PEG polymers (400, 600, and 1000 g mol À1) and [Ch] + salts of chloride, acetate, bicarbonate, glycolate, lactate, dihydrogenphosphate, dihydrogencitrate, and bitartrate can undergo liquid-liquid demixing at certain concentrations of the phase-forming components and at several temperatures. Cholinium butanoate and propanoate were also studied; however, these long alkyl side chain ILs are not able to promote an immiscibility region with PEG aqueous solutions. The ternary liquid-liquid phase diagrams, binary water activities, PEG-salt and salt-H 2 O solubility data, and binary and ternary excess enthalpies estimated by COSMO-RS (COnductor-like Screening MOdel for Realistic Solvation) were used to obtain new insights into the molecular-level mechanisms responsible for phase separation. Instead of the expected and commonly reported salting-out phenomenon induced by the [Ch] + salts over the polymer, the formation of PEG-[Ch] + salt ABS was revealed to be an end result of a more intricate molecular scenario. The multifaceted approach employed here reveals that the ability to promote an ABS is quite different for the higher melting salts vs. the lower melting or liquid ILs. In the latter systems, the ABS formation seems to be controlled by the interplay of the relative strengths of the ion-ion, ion-water, ion-PEG, and water-PEG interactions, with a significant contribution from specific hydrogen-bonding between the IL anion and the PEG hydroxyl groups.
Journal of Chemical & Engineering Data, 2004
The study of aqueous two-phase systems (ATPSs) formed by ionic liquids based on the choline cation and nonionic surfactants has received attention in recent years because of the biodegradability and nontoxicity of their components. In this work, liquid−liquid equilibrium data were obtained for ATPSs composed of Triton X (Triton X-100, Triton X-165, and Triton X-305), choline chloride, and water, at 298.15, 313.15, and 328.15 K. In general, these systems presented a top phase rich in choline chloride and a bottom phase rich in surfactant, although the phenomenon of phase inversion was observed for a specific thermodynamic condition of the system formed by Triton X-165. It was observed that increase of the temperature led to an increase of the biphasic region, indicating an endothermic phase separation process. In addition, higher hydrophobicity of the surfactant increased its ability to promote phase segregation (the biphasic region increased in the following order: Triton X-100 > Triton X-165 > Triton X-305). The reliability of the equilibrium data was confirmed using the Othmer−Tobias and Bancroft correlations. liquid−liquid systems. 2,3 ATPSs are ternary systems that have water as one of their components and under certain conditions of temperature, pressure, and composition present two immiscible phases coexisting in thermodynamic equilibrium. The two other components forming ATPSs may be two different polymers, 4 two different electrolytes, 5 one polymer and one electrolyte, 6 one surfactant and one electrolyte, 7,8 or a polymer and a surfactant. 9,10 Since many ATPSs offer the advantages of high water content, low toxicity, low cost, and easy scale-up, they are attractive strategies in processes of purification, extraction, and separation of important solutes such as proteins, 7,11,12 nucleic acids, 13 nanomaterials, 14,15 dyes, 16 and metal ions. 17,18 Recently, special attention has been directed toward ATPSs formed by nonionic surfactants. Since they have both hydrophilic and hydrophobic characteristics, the use of surfactants in ATPSs enables modulation of the characteristics of the phases, making these systems more versatile in processes of separation/extraction of strategic analytes. In order to promote the phase segregation, surfactants have been used together with polymers 19,20 or organic 21 and inorganic 22−24 salts. These systems offer lower interfacial tension, lower costs, absence of toxicity or flammability (in most cases), and short phase segregation times. 25,26 Notably, the nonionic surfactants known as Triton X, especially Triton X-100, Triton X-102, and Triton X-114, have been extensively used to obtain ATPSs. 8,23,27−29
Journal of Chemical & Engineering Data, 1999
Activities of water are reported for aqueous solutions of poly(ethylene glycol) (PEG) with number average molecular weights of 300, 400, 4000, and 6000 are measured at 35, 45, 55, and 65 °C and at various concentrations from 0 to 40 wt % of PEG using vapor-pressure osmometery. A cubic equation in terms of PEG concentrations is sufficient for correlation of activities. Using measured activities, the Flory-Huggins interaction parameters have been calculated. The effect of temperature, molecular weight of PEG and its concentration, and volume change upon mixing on interaction parameter have been considered. Ignoring the volume change of mixing can lead to an average error of 2.5% with a maximum error of 5.3%.