Synthesis, Characterization, Biological Evaluation, and In Silico Studies of Imidazolium-, Pyridinium-, and Ammonium-Based Ionic Liquids Containing n-Butyl Side Chains

Ionic liquids (ILs) have emerged as active pharmaceutical ingredients because of their excellent antibacterial and biological activities. Herein, we used the green-chemistry-synthesis procedure, also known as the metathesis method, to develop three series of ionic liquids using 1-methyl-3-butyl imidazolium, butyl pyridinium, and diethyldibutylammonium as cations, and bromide (Br-), methanesulfonate (CH3SO3-), bis(trifluoromethanesulfonyl)imide (NTf2-), dichloroacetate (CHCl2CO2-), tetrafluoroborate (BF4-), and hydrogen sulfate (HSO4-) as anions. Spectroscopic methods were used to validate the structures of the lab-synthesized ILs. We performed an agar well diffusion assay by using pathogenic bacteria that cause various infections (Escherichia coli; Enterobacter aerogenes; Klebsiella pneumoniae; Proteus vulgaris; Pseudomonas aeruginosa; Streptococcus pneumoniae; Streptococcus pyogenes) to scrutinize the in vitro antibacterial activity of the ILs. It was established that the nature and unique combination of the cations and anions were responsible for the antibacterial activity of the ILs. Among the tested ionic liquids, the imidazolium cation and NTf2- and HSO4- anions exhibited the highest antibacterial activity. The antibacterial potential was further investigated by in silico studies, and it was observed that bis(trifluoromethanesulfonyl)imide (NTf2-) containing imidazolium and pyridinium ionic liquids showed the maximum inhibition against the targeted bacterial strains and could be utilized in antibiotics. These antibacterial activities float the ILs as a promising alternative to the existing antibiotics and antiseptics.

Automated summary

Ionic liquids (ILs) have emerged as promising alternatives to existing antibiotics and antiseptics due to their excellent antibacterial activity. In this study, three series of ILs were synthesized using a green-chemistry-synthesis method, and their structures were confirmed through spectroscopic analysis. The ILs exhibited significant antibacterial activity against various pathogenic bacteria, with imidazolium cations and NTf2- and HSO4- anions showing the highest efficacy. In silico studies further demonstrated that these ILs can potentially be used as antibiotics.