Understanding the physical properties, toxicities and anti-microbial activities of choline-amino acid-based salts: Low-toxic variants of ionic liquids

Abstract

Ionic liquids (ILs) are often touted as potential ‘green’ substitutes for volatile organic compounds in process chemistry. However, their often high solubility in water limits their applications since discharge of spent ILs into natural water bodies may have significant detrimental eco-toxicological consequences for aquatic organisms. This is especially true for most imidazolium and pyrdinium based ILs which have been proven as toxic to aquatic life organisms. The challenge is therefore to synthesize ILs which exhibit inherently low aquatic toxicity. In the present work, five choline based ILs pairing five different amino acid anions [Cho][AA] have been synthesized and characterized. Their thermal stability, density, viscosity and thermal expansion coefficient were reported. The toxicity behavior of a synthesized ILs were investigated on guppy fish (Poecilia reticulate) and three microbial species. Fish acute toxicity test reveal that the studied ILs could be classified as non-toxic while their 50% effective concentrations (EC50) were found to be comparable to the least toxic imidazolium-based ILs.