Fatty acid-derived ionic liquids as soft and sustainable antimicrobial agents

Abstract

In this study, two sustainability goals are addressed: 1) developing new soft antimicrobial agents (to control antimicrobial resistance) and 2) using natural bio-derived components for this purpose. Fatty acids of bio-renewable origin (stearin, palm kernel and coconut oils) were found to be excellent starting materials for obtaining ester-functionalized ionic liquids (ILs) and mixtures. A series of soft antimicrobial agents based on imidazolium, pyridinium and cholinium ILs with long alkyl ester chains were synthesized, and their properties were examined. The length of the alkyl chain had a notable effect on the physicochemical and biological properties of the synthesized materials. The introduction of a butyl linker and an ester bond lowered the melting point, increased the antimicrobial effectiveness and reduced the cytotoxicity compared to those of non-functionalized ILs with the same hydrocarbon chain. ILs and mixtures with medium chain lengths (C12, C13 and C15) were recognized as promising substitutes for demanding cationic antimicrobial agents. The presence of an ester bond connecting the polar head and hydrophobic tail can promote the breakdown of amphiphilic molecules into less toxic initial compounds. These findings make an important contribution to the development of new, effective amphiphiles with broad-spectrum antimicrobial activity and lower environmental impact.