Buffered aqueous two-phase systems are effective extraction systems for separating amphoteric hydrocarbons like, for example, polypeptides from aqueous phases. The design and basic engineering of such processes require the knowledge of the liquid-liquid equilibrium. Methods to calculate and predict the liquid-liquid phase equilibrium in those systems can only be developed when a large data base is available. The present contribution is aimed at that goal by presenting experimental results for the partitioning of small amounts (≈0.001 g/g solution) of model substancessamino acids glycine, L-glutamic acid, L-phenylalanine, and L-lysine as well as dipeptides and some higher, but still low, molecular peptides of those single amino acidssin aqueous two-phase systems of dextran and poly(ethylene glycol) in the presence of small amounts (about 0.05 mol/kg) of K 2 HPO 4 /KH 2 PO 4 -buffer at about 293 K. A group contribution model for the excess Gibbs energy is used to correlate/predict that liquid-liquid phase equilibrium.
Experimental results for thermodynamic properties of aqueous two-phase systems of poly(ethy1ene glycol) and di-potassium hydrogen phosphate with and without partitioning biomolecules (glycine, phenylalanine and lysozyme) are reported for temperatures between 277 and 333 K. The results are used to develop a semiempirical group-contribution expression for the excess Gibbs energy of dilute aqueous solutions containing polymeric as well as ionic solutes. The model is applied to correlate some of the new experimental data, while other experimental results are used to test its ability for predicting the electrical potential difference between the coexisting phases, the partition coefficient of lysozyme and the influence of polymer molecular weight on the phase behaviour of aqueous two-phase systems -a field where most previously known methods are often inadequate.
--Ber . Bunsenges. Phys. Chem. 99, 700-712 (199s) No. 5 0 VCH Verlagsgesellschaft mbH, 0-69451 Weinheim, 199s 000S-9021/9S/050S-0700 $ 10.00+.25/0
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