Glycine-betaine ionic liquid analogues as novel phase-forming components of aqueous biphasic systems

Abstract

Given the biotechnology advances observed in recent years in terms of upstream, the development of effective downstream processes becomes mandatory to decrease the associated costs of biotechnological-based products. Although a large interest has been devoted to ionic-liquid-based aqueous biphasic systems (IL-based ABS) as tailored separation platforms, imidazolium-based ILs have been the preferred choice as phase-forming agents. To overcome some toxicity and biodegradability issues associated to imidazolium-based ILs, novel ABS composed of ILs analogues of glycine-betaine (AGB-ILs) are here proposed and investigated. Five AGB-ILs were synthesized, characterized in terms of ecotoxicity, and applied toward the development of novel ABS formed with Na₂ SO₄ . Three commercial ILs were also investigated for comparison purposes. The respective ABS ternary phase diagrams, as well as the tie-lines and tie-line lengths, were determined at 25°C. Finally, their performance as extraction strategies was evaluated with five amino acids (L-tryptophan, L-phenylalanine, D-phenylalanine, L-tyrosine and L-3,4-dihydroxyphenylalanine/L-dopa). In all studied systems amino acids preferentially migrate to the IL-rich phase, and with AGB-ILs, the amino acid extraction efficiencies to the IL-rich phase range between 65% and 100%, obtained in a single-step. Furthermore, the studied AGB-ILs display a higher ability to form ABS and to extract amino acids than ABS composed of more traditional and commercial ILs. In summary, novel ABS composed of AGB-ILs can be formed and used as separation routes of value-added compounds of biotechnological interest. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 2018 © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1205-1212, 2018.

Keywords: amino acids; aqueous two-phase systems; extraction; glycine-betaine; ionic liquid.

Figure 1

Chemical structures and abbreviations of the AGB-ILs and amino acids studied.

Figure 2

EC₅₀ values, in mg.L⁻¹, for 15 min of exposure of the marine bacteria Vibrio fischeri to IL aqueous solutions: (■) measured in this work; and (■) values obtained from Ventura et al..

Figure 3

Phase diagrams for the systems composed of AGB-IL + Na₂SO₄ + H₂O at 25 ºC: [MepyrNC₂]Br (◆); [Et₃NC₂]Br (▲); [Pr₃NC₂]Br (●); [Bu₃NC₂]Br (■); [Bu₃PC₂]Br (▲). The lines correspond to the fitting by Equation 1.

Figure 4

Extraction efficiency (EE%) of the studied ABS (composed of 40 wt% of AGB-IL + 7.5 wt% Na₂SO₄ at 25 ºC) for L-tryptophan (■), L-phenylalanine (■)), D-phenylalanine (■)), L-tyrosine (■)), and L-dopa (■)).