Modified Binodal Model Describes Phase Separation in Aqueous Two-phase Systems in Terms of the Effects of Phase-forming Components on the Solvent Features of Water

The binodal model pioneered by Guan et al. [Y. Guan, T. H. Lilley, T. E. Treffry, J. Chem. Soc. Faraday Trans., 89 (1993) 4283–4298] remains the most successful in regard to the quantitative description of phase diagrams among various theoretical models proposed to describe phase separation in aqueous mixtures of polymers. This is a semi-empirical model based on the assumption that any point on the binodal line may be viewed as a saturated solution of the phase-forming compound-1 in the solution of the phase-forming compound-2. Although this model is originally based on the excluded volume concept, we suggest that the solubility of the compound-1 in solutions of compound-2 may depend on the solvent properties of water in solutions of compound-2. The binodal model described in these terms was very successfully applied to the phase diagrams of aqueous two-phase systems formed by different pairs of polymers (dextran, Ficoll, poly(ethylene glycol)-8000, and Ucon). Phase diagram of a new aqueous two-phase system formed by trimethylamine N-oxide (TMAO) and polypopylene glycol-400 and previously reported phase diagram for system formed by TMAO and poly(ethylene glycol)-600 were also described by this model quite well. It was found that the modified binodal model is also applicable to single polymer-salt and polymer-ionic liquid aqueous two-phase systems. The most important conclusion of our study is that the effects of different compounds (polymers, salts, ionic liquids) on the solvent features of water in their aqueous solutions cause changes in the water structure, resulting in phase separation in the mixtures of these compounds

Liquid-liquid extraction of biomolecules in downstream processing - A review paper

Economic analysis shows that protein separation and purification are a very important aspect of biomolecules production and processing. This is particularly true for protein processing which, because of the complexity of the starting material, often requires many steps to reach the levels of purity required for medical and food applications. The separation specialists' task is to develop safe and simple processes to achieve products with a high level of purity. On a large scale, chromatography of proteins is not an easily applied method, although on a laboratory scale it is very effective and relatively simple. When it is scaled up, shortcomings such as discontinuity in the process, slow protein diffusion and large pressure drops in the system are seen. For these reasons a substantial research effort has been directed toward the use of aqueous two-phase systems (ATPSs) to replace the initial steps in protein purification and chromatography. This article reviews the chronology and main ATPS fundamentals and discuss the broader applications of this type of system in the extraction and separation of biomolecules

Liquid-liquid equilibrium of water + PEG 8000 + magnesium sulfate or sodium sulfate aqueous two-phase systems at 35°C: experimental determination and thermodynamic modeling

Liquid-liquid extraction using aqueous two-phase systems is a highly efficient technique for separation and purification of biomolecules due to the mild properties of both liquid phases. Reliable data on the phase behavior of these systems are essential for the design and operation of new separation processes; several authors reported phase diagrams for polymer-polymer systems, but data on polymer-salt systems are still relatively scarce. In this work, experimental liquid-liquid equilibrium data on water + polyethylene glycol 8000 + magnesium sulfate and water + polyethylene glycol 8000 + sodium sulfate aqueous two-phase systems were obtained at 35°C. Both equilibrium phases were analyzed by lyophilization and ashing. Experimental results were correlated with a mass-fraction-based NRTL activity coefficient model. New interaction parameters were estimated with the Simplex method. The mean deviations between the experimental and calculated compositions in both equilibrium phases is about 2%