Self-aggregation and antimicrobial activity of imidazolium and pyridinium based ionic liquids in aqueous solution

Two series of long-chain imidazolium and pyridinium based ionic liquids (1-alkyl-3-methylimidazolium and 1-alkylpyridinium bromides) were synthesised and the effect of the alkyl chain length and the nature of the cationic head group on micellization and antimicrobial activity of the ionic liquids (ILs) were investigated. Tensiometry, conductometry, spectrofluorimetry and PGSE-NMR were applied to study the self-aggregation of the amphiphilic ILs in aqueous solution. The ILs investigated displayed surface activity and the characteristic chain length dependence of the micellization process of surfactants. The antimicrobial activity was evaluated against Gram-negative and Gram-positive bacteria and fungi. ILs containing more than eight carbon atoms in the alkyl chain showed antimicrobial activity. Their efficiency as antimicrobial agents increased with the hydrophobicity of the amphiphilic cation being the C14 homologous the most active compounds.

Long-chain imidazolium and pyridinium ionic liquids show surfactant-like properties in aqueous solution and display antimicrobial activity which increases with the alkyl chain length.Figure optionsDownload high-quality image (61 K)Download as PowerPoint slideResearch highlights
► Long-chain imidazolium and pyridinium ionic liquids show surfactant-like behaviour.
► Similar polarity of methylimidazolium and pyrdidinium headgroups in aqueous solution.
► Long-chain imidazolium and pyridinium ionic liquids display antimicrobial activity.
► Antimicrobial activity increases with the ionic liquid alkyl chain length.