Effect of Ionic Liquid [C4C1im]Br on the Formation of Aqueous Biphasic Systems Composed of PEG and Biodegradable Salts, and on the Partition of L-Tryptophan

Abstract

In this work, the extractive potential, for biomolecules, of several aqueous biphasic systems (ABS) composed of polyethylene glycol (PEG) with varying molecular weight (400 and 4000) and different biodegradable organic salts, sodium citrate (Na3C6H5O7), sodium tartrate (Na2C4H4O6), and sodium succinate (Na2C4H4O4), were evaluated in the presence of the ionic liquid (IL) 1-butyl-3-methylimidazolium bromide ([C4C1im]Br) as adjuvant. For this purpose, firstly, the binodal curves and the liquid-liquid equilibrium (LLE) data of the studied ABS were determined, at T = 298.15 K, by the addition of 5 wt% IL to investigate its effect on the two-phase formation. The tie-line lengths (TLL) were also addressed. To evaluate the extraction capacity of the studied ABS for biomolecules, the essential amino acid L-tryptophan (Trp) was used as a molecular probe. Thus, the partition coefficients of Trp, KTrp, were determined, at T = 298.15 K, in ABS with and without IL. The effects of salt, PEG molecular weight, and ABS composition on the partition coefficients of Trp were also investigated. It was found that the KTrp values are increased with increasing the salting-out strength of salts, PEG molecular weight, and the ABS composition. Moreover, in the studied ABS, by the addition of 5 wt% [C4C1im]Br into the ABS containing PEG 400, the KTrp values are increased, whereas, the opposite is observed for systems with PEG 4000. Finally, the experimental LLE and partition coefficients data are accurately correlated using the NRTL model.