Aqueous biphasic systems: a boost brought about by using ionic liquids

Abstract

During the past decade, ionic-liquid-based Aqueous Biphasic Systems (ABS) have been the focus of a significant amount of research. Based on a compilation and analysis of the data hitherto reported, this critical review provides a judicious assessment of the available literature on the subject. We evaluate the quality of the data and establish the main drawbacks found in the literature. We discuss the main issues which govern the phase behaviour of ionic-liquid-based ABS, and we highlight future challenges to the field. In particular, the effect of the ionic liquid structure and the various types of salting-out agents (inorganic or organic salts, amino acids and carbohydrates) on the phase equilibria of ABS is discussed, as well as the influence of secondary parameters such as temperature and pH. More recent approaches using ionic liquids as additives or as replacements for common salts in polymer-based ABS are also presented and discussed to emphasize the expanding number of aqueous two-phase systems that can actually be obtained. Finally, we address two of the main applications of ionic liquid-based ABS: extraction of biomolecules and other added-value compounds, and their use as alternative approaches for removing and recovering ionic liquids from aqueous media.

Purification of C-phycocyanin from Spirulina platensis in aqueous two-phase systems using an experimental design

“…In the past, traditional protein purification methods have been used, including ion exchange gel filtration chromatography, affinity chromatography, membrane separation, ammonium sulfate precipitation, salting out and electrophoresis, but they are expensive and not suitable for mass production. Furthermore, due to the poor stability, proteins in the conditions of acids, alkali or heating are easily denatured (Gutowski et al 2003;Freire et al 2012;Shahriari et al 2013;Zeng and Wang 2013). Hence, the aqueous two-phase system (ATPS), a simple and economic system, has been studied.…”

Alkaloids as Alternative Probes To Characterize the Relative Hydrophobicity of Aqueous Biphasic Systems

“…7,8 Moreover, several classes of ABS are simpler and cheaper than most of chromatographic techniques used for separation approaches and are highly selective for a wide variety of solutes, enhancing thus their importance in biotechnological, chemical and pharmaceutical industries. [2][3][4] Recently, the use of ILs in the formation of ABS 3,4 increased the number of possible systems and applications for this type of extractions, mainly due to their excellent selectivity for extracting similar or complex solutes. 4 ILs are ionic compounds with low melting points, exhibiting a series of interesting properties, some closely related with their application as phase-forming agents of ABS, in particular their large solvation capability and great tunability.…”

“…4 ILs are ionic compounds with low melting points, exhibiting a series of interesting properties, some closely related with their application as phase-forming agents of ABS, in particular their large solvation capability and great tunability. 4,9 Besides these important solvation characteristics of ILs, some environmental concerns about have been expressed, in particular for IL families based on imidazolium or pyridinium cations, and ILs with fluorinated anions, which present an undesirable level of toxicity and low biodegradability. 10 According to the Green Chemistry principles, to be considered as an environmentally friendly compound an IL should accomplish a set of particular features, for instance, it should have minor accumulation and persistence in the environment (biodegradability), it should be based in renewable raw materials, be obtained by less hazardous and more economic synthesis, among others.…”

“…1,2 ABS are water-based systems formed by combinations of compounds ranging from the most common polymer/polymer 1,2 and polymer/salt 1,2 to the recent ionic liquid (IL)/salt 3,4 , polymer/IL 4,5 and IL/carbohydrate 4,6 pairs of phase-forming components. Due to their low interfacial tension and high water content, ABS preserve the biological activity of biomolecules by the formation of a biocompatible aqueous environment similar to intracellular environments.…”

“…[2][3][4] Recently, the use of ILs in the formation of ABS 3,4 increased the number of possible systems and applications for this type of extractions, mainly due to their excellent selectivity for extracting similar or complex solutes. 4 ILs are ionic compounds with low melting points, exhibiting a series of interesting properties, some closely related with their application as phase-forming agents of ABS, in particular their large solvation capability and great tunability. 4,9 Besides these important solvation characteristics of ILs, some environmental concerns about have been expressed, in particular for IL families based on imidazolium or pyridinium cations, and ILs with fluorinated anions, which present an undesirable level of toxicity and low biodegradability.…”