Design of Novel Biocompatible and Green Aqueous two-Phase Systems containing Cholinium L-alaninate ionic liquid and polyethylene glycol di-methyl ether 250 or polypropylene glycol 400 for separation of bovine serum albumin (BSA)

Recently, cholinium aminoate ionic liquids (Ch[AA] ILs) are gaining more attention due to their low toxicity and high biodegradability and this makes them a good candidate when we consider the formation of their aqueous two-phase systems (ATPSs) with suitable polymers that can be used for protein separation. In this work, the phase diagram of novel ATPSs composed of cholinium L-alaninate (Ch[L-Ala]) and polyethylene glycol dimethyl ether 250 at different temperatures or polypropylene glycol 400 at 298.15 K were experimentally determined. The effect of temperature and type of polymer on the binodal curve and tie-lines were investigated systematically. The phase separation abilities in these ATPSs were evaluated using Setschenow-type equation on the basis of a salting-out coefficient obtained from fitting the tie-lines to this equation and the trends showed that two-phase area was expanded by increasing temperature. These results were also confirmed by the trend observed with the effective exclude volume values. Two empirical equations including Merchuk were used for representing binodal data. Reliability of tie-lines was verified by Othmer-Tobias and Bancraft equations. Different versions of NRTL models were used to correlate the obtained tie-line data. In addition, the partition behavior of a model protein, i.e. bovine serum albumin (BSA), was studied by measuring of partition coefficient and extraction efficiency in mentioned systems. The results show that BSA could be enriched effectively into the IL- rich phase with a single step extraction efficiency of about 80% under the optimized conditions.