Green, Aqueous Two-Phase Systems Based on Cholinium Aminoate Ionic Liquids with Tunable Hydrophobicity and Charge Density

Abstract

Cholinium-based ionic liquids made of aminoate anions ([Ch][AA] ILs) have been proven to have low toxicity and to be readily biodegradable. This class of ILs has great potential as a novel phase-forming component for aqueous two-phase system (ATPS) used in protein separation. In this study, environmentally benign ATPSs were prepared by using a series of [Ch][AA] ILs (where [AA] = lysinate, βalaninate, glycinate, serinate) with a thermo-separable polypropylene glycol 400 (PPG 400). These [AA] anion components differ in both hydrophobicity and acid/base behavior, allowing a tunable response to the pH of the ATPS. By using the effective excluded volume theory, the phaseseparation abilities of the different [Ch][AA]-based ATPSs were determined, and the trends showed good agreement with the [AA] anion hydration capacities. The partition behavior of a model protein, i.e., bovine serum albumin (BSA), was investigated by measuring the IL-rich (bottom) phase extraction efficiency and partition coefficient. The results showed that the partition behavior of the protein was governed by the hydrophobicity of the [AA] anion, whereby the BSA showed a greater affinity toward the IL-rich phase comprising a less hydrophobic [AA] anion. Furthermore, the effect of pH on the partition behavior of model proteins (i.e., BSA and trypsin) was investigated. When the pH of the system is greater than the isoelectric point pI of the model proteins and the [AA] anion, the model proteins are found to be mainly partitioned to the bottom phase. However, at a pH below the pI of the model proteins and the pI of the [AA] anion, the partitioning of model proteins favored the polymer-rich top phase. Overall, our findings demonstrate the flexibility possible in directing the target protein to a desired phase in ATPS through a proper selection of the IL's hydrophobicity and [AA] anion.

Cholinium-Based Good’s Buffers Ionic Liquids as Remarkable Stabilizers and Recyclable Preservation Media for Recombinant Small RNAs

“…ILs, commonly described as molten salts at temperatures below 100 °C, and composed of large and unsymmetrical organic cations and organic or inorganic anions, have been reported as appropriate stabilizing media for proteins and enzymes 20–22. During the last years, ILs have also been applied to improve some properties of nucleic acids, mainly of DNA, such as solubility, stability and bioavailability 23–29.…”

Water‐insoluble cosolvent in aqueous two‐phase system improved the extraction of paeonol from cortex moutan

“…However, ATPSs are generally suitable for extraction of hydrophilic components, because both the top phase and bottom phase contain high percentages of water. Researchers have tried to tune the hydrophobicity of ATPSs by addition of ionic liquids (ILs) to achieve a wider hydrophilic–lipophilic range allowing for extensive separations . Despite the fascinating potential of IL‐based ATPSs, the ILs for improving the hydrophobicity of ATPSs generally are required to have long alkyl chains .…”

“…Despite the fascinating potential of IL‐based ATPSs, the ILs for improving the hydrophobicity of ATPSs generally are required to have long alkyl chains . But ILs with long alkyl chains usually exhibit high toxicity and poor biodegradability which lead to environmental pollution . So, due to the toxicity and high cost of ILs, ATPSs with hydrophobic ILs are not suitable for extraction on an industrial scale.…”

“…So we can understand that the hydrophobicity of an ATPS can be tuned using a hydrophobic polymer (or polymer with high molecular weight). PEG‐based ATPSs have been widely investigated in protein separation, separation/extraction of small organic molecules and metal ion separation . However, extraction with PEG‐based ATPSs also has to face the problem of downstream removal of PEG from the target components.…”

Purification of the Recombinant Green Fluorescent Protein Using Aqueous Two-Phase System Composed of Recyclable CO2-Based Alkyl Carbamate Ionic Liquid

“…Moreover, some of the conventionally used ILs (i.e., imidazolium- and pyridinium-based ILs) are reported to be highly toxic (Docherty and Kulpa, 2005 ). With the rising environmental consciousness in public, the application of environmentally benign ILs (e.g., cholinium- and amino acids-based ILs) in forming ATPS has been on the rise (Song et al, 2015 , 2017 , 2018a ).…”