Antimicrobial toxicity studies of ionic liquids leading to a ‘hit’ MRSA selective antibacterial imidazolium salt

Abstract

Imidazolium salts can be classed as surfactants, detergents, ionic liquids, reagents, catalysts or solvents. A study of the toxicity and ecotoxicity of these salts yields valuable information for their use as pharmaceuticals as well as impact on the environment. Our approach to screen a series of chiral imidazolium salts for toxicity to bacteria and fungi, including clinical pathogen strains, has led to the identification of a ‘hit’ MRSA selective antimicrobial compound. Preliminary structure–activity-relationship (SAR) information (required position of L-phenylalanine and L-valine group) is also elucidated within this first generation of compounds. Conversely, most of the imidazolium salts were nontoxic (IC₉₅ > 2 mM) to the 12 fungi strains and 8 bacteria strains screened, and we propose that they are suitable candidates for ‘green chemistry’ applications. Ecotoxicity studies (Biodegradation ISO 14593 ‘CO₂ Headspace Test’) of two bromide ionic liquids containing L-phenylalanine residues indicate that these ionic liquids passed the test (>60% in 28 days) and classed as readily biodegradable.