Design of Phosphonium-Type Zwitterion as an Additive to Improve Saturated Water Content of Phase-Separated Ionic Liquid from Aqueous Phase toward Reversible Extraction of Proteins

Yoritsugu Ito,Nobuhumi Nakamura,Yuki Kohno,Hiroyuki Ohno

doi:10.3390/ijms140918350

Abstract

We designed phosphonium-type zwitterion (ZI) to control the saturated water content of separated ionic liquid (IL) phase in the hydrophobic IL/water biphasic systems. The saturated water content of separated IL phase, 1-butyl-3-methyimidazolium bis(trifluoromethanesulfonyl)imide, was considerably improved from 0.4 wt% to 62.8 wt% by adding N,N,N-tripentyl-4-sulfonyl-1-butanephosphonium-type ZI (P555C4S). In addition, the maximum water content decreased from 62.8 wt% to 34.1 wt% by increasing KH2PO4/K2HPO4 salt content in upper aqueous phosphate buffer phase. Horse heart cytochrome c (cyt.c) was dissolved selectively in IL phase by improving the water content of IL phase, and spectroscopic analysis revealed that the dissolved cyt.c retained its higher ordered structure. Furthermore, cyt. c dissolved in IL phase was re-extracted again from IL phase to aqueous phase by increasing the concentration of inorganic salts of the buffer solution.

Highlights

Ionic liquids (ILs) are organic molten salts with very low melting temperature [1,2,3]
We studied the effect of concentration of K2HPO4/KH2PO4 salts in buffer solution added to mixture on the saturated water content of hydrophobic IL phase
The saturated water content of the hydrophobic IL phase was considerably improved from 0.4 wt% to 62.8 wt% by adding

Summary

Introduction

Ionic liquids (ILs) are organic molten salts with very low melting temperature [1,2,3]. There are a growing number of articles on aqueous biphasic systems (ABSs) based on ILs [7]. Previous ABSs were mainly composed of two different polymers or a polymer and aqueous salt solution. These ABSs have been used for product recovery and downstream processing in biotechnology. It was shown that polymers like poly(ethylene glycol) and dextran and ILs in combination with a kosmotropic inorganic salt are able to form ABS [8]. Some ILs having hydrophobic ions form liquid/liquid biphases after mixing with water.

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