Imidazolium-Based Ionic Liquid-Assisted Silver Nanoparticles and Their Antibacterial Activity: Experimental and Density Functional Theory Studies

The exclusive properties of ionic liquids (ILs) offer various opportunities to develop advanced materials with appreciable therapeutic applications. Imidazolium-based ILs have been frequently used as reaction media and stabilizers for the development and surface functionalization of noble metal nanoparticles (NPs). This study reports the citrate-mediated reduction of silver ions in three different ILs, that is, 1-ethyl-3-methylimidazolium methyl sulfate ([EMIM]-[MS]), 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIM]-[OTf]), and 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)-imide ([BMIM]-[TFSI]). The resulting Ag-ILs NPs were characterized using many analytical techniques, including UV-visible spectroscopy, dynamic light scattering (DLS), scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction (XRD). DLS and XRD characterization revealed the negatively charged Ag-[EMIM]-[MS] NPs, Ag-[BMIM]-[OTf] NPs, and Ag-[BMIM]-[TFSI] NPs with mean hydrodynamic sizes of 278, 316, and 279 nm, respectively, and a face-centered cubic structure. These hybrid nanomaterials were subjected to in vitro antibacterial screening against three bacterial strains. The Ag-[BMIM]-[OTf] NPs exhibited significant activities against Escherichia coli, Staphylococcus aureus, and Enterobacter cloacae. The lowest inhibition concentration of 62.5 mu g/mL was recorded against E. coli using Ag-[EMIM]-[MS] and Ag-[BMIM]-[OTf] NPs. Further, the density functional theory calculations carried out on the computed Ag-ILs in the gas phase and water showed relatively stable systems. Ag-[BMIM]-[TFSI] exhibited the lowest Gibbs free energy change of -34.41 kcal/mol. The value of the global electrophilicity index (omega = 0.1865 eV) for the Ag-[BMIM]-[OTf] correlated with its good antibacterial activity.

Automated summary

This study reports the experimental research of citrate-mediated reduction of silver ions in three different ionic liquids, resulting in Ag-ILs nanoparticles with significant antibacterial activity. The nanoparticles were characterized using various analytical techniques and computational calculations.