Evaluation of Toxicity and Biodegradability of Cholinium Amino Acids Ionic Liquids

Xue-Dan Hou,Min-Hua Zong,Ning Li,Thomas J Smith,Qiu-Ping Liu,Vipul Bansal

doi:10.1371/journal.pone.0059145

Abstract

Cholinium amino acid ionic liquids ([Ch][AA] ILs), which are wholly composed of renewable biomaterials, have recently been demonstrated to have very promising properties for applications in organic synthesis and biomass pretreatment. In this work, the toxicity of these ILs toward enzymes and bacteria was assessed, and the effect of the anion on these properties is discussed. The inhibitory potentials of this type of ILs to acetylcholinesterase were weaker approximately an order of magnitude than the traditional IL 1-butyl-3-methylimidazolium tetrafluoroborate. Additionally, the [Ch][AA] ILs displayed low toxicity toward the bacteria tested. Furthermore, the biodegradability of the [Ch][AA] ILs was evaluated via the closed bottle and CO2 headspace tests using wastewater microorganisms. All the ILs were classified as ‘readily biodegradable’ based on their high levels of mineralization (62-87%). The presence of extra carboxyl or amide groups on the amino acid side chain rendered the ILs significantly more susceptible to microbial breakdown. In addition, for most of the [Ch][AA] ILs, low toxicity correlated with good biodegradability. The low toxicity and high biodegradability of these novel [Ch][AA] make them promising candidates for use as environmentally friendly solvents in large-scale applications.

Highlights

In the last two decades, ionic liquids (ILs) have attracted growing interest in various areas such as organic synthesis, catalysis, biocatalysis and biomass pretreatment, owing to their excellent thermal and chemical stability, their outstanding ability to dissolve a broad range of compounds and the fact that their properties can be tuned by individual engineering of the anion and cation components [1,2]
It was used as the test enzyme because its active center is highly conserved and well known, and this enzyme has been widely used for toxicity assay of ILs [8,24,27,28]
The inhibitory effects of these [Ch][AA] ILs were approximately an order of magnitude weaker than that of [Bmim][BF4], which is in agreement with previous results where high toxicity of ILs containing imidazolium cations was attributed to the formation of strong p–p interactions between the aromatic imidazolium head group of the cation and the side chain of amino acid Trp 279 present in the peripheral anionic site of AChE [8]

Summary

Introduction

In the last two decades, ionic liquids (ILs) have attracted growing interest in various areas such as organic synthesis, catalysis, biocatalysis and biomass pretreatment, owing to their excellent thermal and chemical stability, their outstanding ability to dissolve a broad range of compounds and the fact that their properties can be tuned by individual engineering of the anion and cation components [1,2] They are widely regarded as ‘green’ solvents primarily based on their negligible vapour pressure and low flammability [3]. Based on current restricted knowledge about the relationships between structures and properties of ILs, a TSAR (Thinking in terms of Structure-Activity Relationships) strategy has been proposed for rational design of novel ‘greener’ ILs [8] According to this strategy, cholinium is a promising candidate as the IL cation, since the quaternary ammonium cation incorporating a polar hydroxyl group is expected to have relatively low toxicity. These cholinium-based ILs have been reported to have low toxicity [13,14,15], and most examples tested are readily biodegradable [14,16]

Objectives

Methods

Results

Conclusion