Odd–Even Effect in the Formation and Extraction Performance of Ionic-Liquid-Based Aqueous Biphasic Systems

Abstract

Aqueous biphasic systems constituted by ionic liquids (IL-based ABSs) are a target of investigation in the separation of high-value biomolecules. However, identification of the molecular-level mechanisms ruling the two-phase formation and extraction performance of these systems is crucial to the successful design of effective separation processes. In this work, IL-based ABSs formed by K2HPO4 and cholinium carboxylate ILs ([Ch]­[C n CO2] with n = 1–7, comprising anions with odd and even alkyl chain lengths) were investigated. The corresponding ternary phase diagrams, including binodal curves, tie-lines, tie-line lengths, and critical points, as well as the Setschenow salting-out coefficients (k s), which quantitatively describe the two-phase formation ability, were determined at 298 K. The extraction capability of these systems was then evaluated for four amino acids (l-tryptophan, l-phenylalanine, l-tyrosine, and l-3,4-dihydroxyphenylalanine/l-dopa). It was found that ILs composed of anions with even alkyl chains display slightly higher k s values, meaning that these ILs are more easily salted out or more easily phase-separated to form ABSs, whereas ABSs formed by ILs with anions comprising odd alkyl chains lead to slightly higher partition coefficients of amino acids. Beyond the neat IL odd–even effect resulting from their nanostructuration, being this a well-known phenomenon occurring in a series of their thermophysical properties, the existence of an odd–even effect displayed by the IL anion aliphatic moiety in aqueous solution is shown here, visible in both the two-phase formation ability and extraction performance of ABSs. These findings contribute to elucidate of the molecular-level mechanisms governing ABS formation and partitioning of biomolecules, ultimately contributing to the design of proficient separation platforms.

Liquid–Liquid Equilibrium and Extraction Performance of Aqueous Biphasic Systems Composed of Water, Cholinium Carboxylate Ionic Liquids and K2CO3

“…Accordingly, the ability of cholinium-ILs to form ABS at (298 ± 1) K at 2.0 mol·kg –1 follows the rank: [Ch]­[C 4 CO 2 ] > [Ch]­[C 3 CO 2 ] ≈ [Ch]­[C 5 CO 2 ] ≈ [Ch]­[C 6 CO 2 ] > [Ch]­[C 2 CO 2 ]. Although this order shows that the capability to form ABS (or of the IL to be salted-out) increases with the increase of the alkyl chain length of the IL anion, this is only observed up to cholinium pentanoate; for higher anion alkyl chain lengths the self-aggregation of the ILs occurs, decreasing their ability to create ABS. , This trend in ABS formation is in agreement with what has been recently observed for cholinium-based ILs + K 2 HPO 4 ABS and seems to be independent of the salt used . Moreover, the same trend was previously reported for the IL cation effect in ABS formation …”

“…38,39 This trend in ABS formation is in agreement with what has been recently observed for cholinium-based ILs + K 2 HPO 4 ABS and seems to be independent of the salt used. 40 Moreover, the same trend was previously reported for the IL cation effect in ABS formation. 41 Three mixture compositions at the biphasic region of each ABS were prepared, and eqs 1 to 7 were applied to determine the respective TLs, along with their respective length (TLLs), which are reported in Table 3.…”

Protic Ionic Liquids as Cell-Disrupting Agents for the Recovery of Intracellular Carotenoids from Yeast Rhodotorula glutinis CCT-2186

“…The similar positive slopes obtained for the three types of carotenoids confirm the increase of the recovery yields with the hydrophobicity of the PIL anion, as demonstrated by the good correlation of the linear least-squares regression obtained for all the PILs ( R 2 > 0.92). Although it is not the focus of the work, the slight negative deviation in the linearity observed with [Pro] − -based PILs is probably a result of an odd–even effect previously observed by some authors , where the length of the alkyl chain spacer of the anion caused a reduction of the carotenoid recovery. Figure also depicts the following cation trend for the recovery of the three carotenoids: [DEAPA]­[X] > [DMAPA]­[X] > [PA]­[X].…”

Recovery of Syringic Acid from Industrial Food Waste with Aqueous Solutions of Ionic Liquids

“…In the same figure, additional results for the ILs [Ch]­[Ac], [Ch]­[But], [Ch]­[Hex], [Ch]­[Oct], and [Ch]­[Dec] are given to address the effect of carboxylate-based anions combined with the cholinium cation to improve the syringic acid solubility in water. Among these, [Ch]­[Oct] and [Ch]­[Dec] display surface-active properties. , …”

“…In addition to [C 4 C 1 im]-based ILs, cholinium-based ILs have been investigated. Both short alkyl side-chain cholinium carboxylates (acetate, butanoate, and hexanoate), which could act as hydrotropes, and long alkyl side-chain cholinium carboxylate (octanoate and decanoate), able to form micelles in aqueous solutions and with reported CMCs, , were studied. Contrary to the [C 8 C 1 im]Cl previously discussed that is a cationic surfactant, [Ch]­[Oct] and [Ch]­[Dec] are anionic surfactants.…”