Synthesis, Hydration, Antibacterial, Antifungal, and Antiviral Properties of New Surface-Active Nicotine-Based Ionic Liquids

Nicotine is a pyridine alkaloid naturally produced by plants of the Solanaceae family. In this study, four nicotine-based ionic liquids (ILs) with different alkyl side-chain lengths were synthesized by alkylation with alkyl bromides: N-octylnicotinium bromide, N-decylnicotinium bromide, N-dodecylnicotinium bromide, and N-tetradecylnicotinium bromide; of these, only the octyl derivative was previously reported. Their structures were confirmed by NMR spectroscopy. All ILs were water-soluble within the investigated concentration range and exhibited surfactant properties. Critical micelle concentrations (CMC) were determined by conductometry, while density, sound velocity, and viscosity measurements were used to investigate hydration behavior. CMC values decreased with increasing alkyl chain length, indicating enhanced aggregation, while all ILs exhibited structure-making effects in water. Antimicrobial activity was evaluated against three Gram-positive and three Gram-negative bacterial species, four mold species, two yeast species, and five bacteriophage species. The ILs showed substantially greater antimicrobial activity than nicotine. Antibacterial activity increased with alkyl chain length, and longer-chain ILs outperformed a commercial disinfectant, benzalkonium chloride, in selected antibacterial and antiviral assays. Antifungal activity was comparable to or slightly lower than that of benzalkonium chloride, depending on the species. N-tetradecylnicotinium bromide exhibited the strongest antiviral activity. These results demonstrate a clear relationship between IL structure, aggregation behavior, hydration properties, and antimicrobial activity.