Aqueous two-phase systems extraction

For modeling of aqueous two-phase extractions systems, see Abbott (1990,1992a-c, 1993). 

Assays of enzymatic activity of polymer degrading enzymes are often difficult to perform using traditionally immobilized systems. Using a liquid-liquid phase system makes it easier to establish contact between the catalyst and the substrate. Products may then partition differendy as compared to the substrate. This forms the basis for the assay of dextranase using a dye substrate, blue dex-tran. The liberated color is preferentially extracted into the more hydrophobic top phase (103). Adding a ferrofluid that is a submicron magnetic preparation to an aqueous two-phase extraction system makes it possible to substantially facilitate phase separation by magnetic force (104). 

Platis, D. and Lebrou, N.E. (2006). Development of an aqueous two-phase partitioning system for fractionating therapeutic proteins from tobacco extract. J. Chromatogr.A 1128(1-2) 114-124. 

The last talk in this session, by Andrew Lyddiatt (University of Birmingham, United Kingdom), showed how liquid-liquid extraction can address some of the problems associated with the purification of nanoparticulates (e.g., viral and nonviral gene delivery vehicles). Nanoparticles (particle size range 20-150 nm) with low diffusivity and low molalities in culture feedstocks pose unique process engineering problems in the design and implementation of selective recovery and formulation operations. This paper demonstrated how aqueous two-phase partition systems (polymer-polymer and polymer-salt) can circumvent the process bottlenecks posed by the use of... 

A theoretical treatment of aqueous two-phase extraction at the isoelectric point is presented. We extend the constant pressure solution theory of Hill to the prediction of the chemical potential of a species in a system containing soivent, two polymers and protein. The theory leads to an osmotic virial-type expansion and gives a fundamentai interpretation of the osmotic viriai coefficients in terms of forces between species. The expansion is identical to the Edmunds-Ogston-type expression oniy when certain assumptions are made — one of which is that the solvent is non-interacting. The coefficients are calculated using simple excluded volume models for polymer-protein interactions and are then inserted into the expansion to predict isoelectric partition coefficients. The results are compared with trends observed experimentally for protein partition coefficients as functions of protein and polymer molecular weights. 

Low-cost maltodextrins (Mavg = 1200,1800,3600) can be combined with polyethylene glycol (PEG) to form aqueous two-phase systems which are useful for protein separations. The physical characteristics of these maltodextrin/FEG systems are similar in many respects to dextran/FEG systems. Maltodextrins are currently available for a hundredth of the cost of fractionated dextran making the large scale application of polymer-polymer aqueous two-phase extractions more likely. The physical characteristics of the maltodextrin/FEG two-phase systems are described in this paper along with their application towards the purification of yeast alcohol dehydrogenase. 

The main drawback to the widespread use of polymer-polymer aqueous two-phase extraction has been the high cost of fractionated dextran. Crude dextran has been used with some success for the purification of enzymes but is much too viscous for many applications. Conversely, polymer-salt systems have relatively low viscosities, separate rapidly, and are inexpensive. Unfortunately, they lack selectivity and cannot be used for affinity partitioning in most cases since the high salt concentrations interfere with the protein-ligand interaction. The starch derivatives are reasonable alternatives for bottom phase polymers but have been hampered by low solubilities and the tendency for gel formation. Tjemeld has reported that chemically modified starches i.e. hydroxypropyl starch... 

F. Generalize. Although the problem statement involved a new type of system—aqueous two-phase extraction of proteins— we could apply the basic principles without difficulty. Since many of the details are often not necessary to solve the problem, it sometimes sinplifies the problem to rewrite it as solute A being removed from diluent into solvent. Then see if you can solve the sinplified version of the problem... 

Aqueous two-phase extraction is an alternative recovery technology that has been investigated for many years in the industry and at universities. The standard two-phase system consists... 

Countercurrent chromatography is based on the distribution of substances in two liquid phases [128,129]. The liquid is fed into a coiled tube that is moved along an orbital trajectory. Due to centrifugal power, the liquids move in a counter-current. For proteins and many other biomolecules, this method is not practical because of denaturation in a nonaqueous phase. In aqueous two-phase systems, at least one phase exhibits high viscosity and, therefore, mass transfer between the two phases is limited. Similar problems occur with reversed micelle extraction as were observed with the aqueous two-phase extraction [130]. CCC has not been used for large-scale purification of proteins and other biopolymers. 

HA2 Haynes, C.A., Blanch, H.W., and Praunsitz, J.M., Separation of protein mixtures by extraction thermodynamic properties of aqueous two-phase polymer systems containing salts and proteins, Fluid Phase Equil, 53, 463, 1989. 

Pereira, M., Wu, Y.-T., Venancio, A., Teixeira, J. (2003). Aqueous two-phase extraction using thermoseparating polymer a new system for the separation of endo-polygalacturonase. Biochemical Engineering Journal, 15, 131-138. 

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