Odd-even effect on the formation of aqueous biphasic systems formed by 1-alkyl-3-methylimidazolium chloride ionic liquids and salts.

This work provides a comprehensive evaluation of the effect of the cation alkyl side chain length of the 1-alkyl-3-methylimidazolium chloride series ([C n C1im]Cl, n = 2-14) of ionic liquids (ILs) on their capability to form aqueous biphasic systems (ABSs) with salts and self-aggregation derived properties. The liquid-liquid phase behavior of ternary systems composed of [C n C1im]Cl, water, and K3PO4 or K2CO3 and the respective Setschenow salting-out coefficients (ks ), a quantitative measure of the two-phase formation ability, were determined. An odd-even effect in the ks values along the number of methylene groups of the longest IL cation alkyl side chain was identified for the ABS formed by K2CO3, a weaker salting-out agent where the phenomenon is clearly identified. In general, cations with even alkyl side chains, being likely to display higher molar volumes, are more easily salted-out and thus more prone to undergo phase separation. The odd-even effect in the ks values is, however, more significant in ILs up to n = 6, where the nanostructuration/nanosegregation of ILs plays a less relevant role. Still, with the [C n C1im]Cl (n = 7-14) series of ILs, an odd-even effect was also identified in the ILs' ionization degree, molar conductivity, and conductivity at infinite dilution. In summary, it is shown here that the ILs' odd-even effect occurs in IL aqueous solutions and not just in neat ILs, an already well-established phenomenon occurring in a series of ILs' properties described as a result of the orientation of the terminal methyl groups to the imidazolium ring cation and consequent effect in the ILs' cohesive energy.

Ionic Liquids in Bioseparation Processes.

Bioseparation processes are a relevant part of modern biotechnology, particularly regarding the development of efficient and biocompatible methods for the separation and purification of added-value biologically active compounds. In this field, ionic liquids (ILs) have been proposed, either in liquid-liquid extractions, in which non-water miscible ILs or aqueous biphasic systems (ABS) formed by ILs can be used, or in solid-liquid extractions, in which they are covalently attached to create supported IL phases (SILPs). Aprotic ILs possess unique properties, such as non-volatility and designability, which are valuable in their use in bioseparation processes. In this chapter, we summarize and discuss bioseparation processes based on ILs, including both liquid-liquid and solid-liquid extractions, applied to amino acids and proteins. The most recent and remarkable advances in this area are emphasized, and improvements brought by the use of ILs properly discussed. New insights and envisaged directions with IL-based bioseparation processes are suggested. Graphical Abstract.