Influence of cation (imidazolium based ionic liquids) as “smart” stabilizers for silver nanoparticles and their evaluation as antibacterial activity on Escherichia coli, Staphylococcus aureus and Enterobacter cloacae

Ionic liquids (ILs) represent versatile solvents and green milieu for the growth and stabilisation of metal nanoparticles. The current study reports the synthesis of silver nanoparticles in ILs based on two different cations, namely 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]). The prepared nanoparticles were characterised by dynamic light scattering, SEM imaging, UV–vis, FTIR, and zeta potential spectral data. The in vitro antibacterial activity of the as-developed nanomaterials was assessed against three bacterial pathogens, including Escherichia coli, Staphylococcus aureus, and Enterobacter cloacae. The results obtained indicate negatively charged and stable nanoparticles with average sizes of 132 nm for Ag NPs-[EMIM][BF4] and 360 nm for Ag NPs-[BMIM][BF4]. The nanoparticles Ag NPs-[BMIM][BF4] and Ag NPs-[EMIM][BF4] exhibited moderate antibacterial activity against E. coli (MIC: 62.5 and 125 µg/ml, respectively) and E. cloacae (MIC: 125 and 250 µg/ml, respectively). Against S. aureus, Ag NPs-[BMIM][BF4] afforded MIC value of 125 µg/ml, suggesting that these particles also possess moderate anti-staphylococcal activity. Further, molecular docking of [BMIM][BF4]) and [EMIM][BF4] with and without Ag against PDB ID: 1C21 and 1JIJ was performed. This computer-aided technique was complemented with DFT calculations to check the thermodynamic properties of ILs with and without Ag. The nature of the alkyl sidechains (1-butyl vs 1-ethyl groups) on the cation might play a crucial role in elevating the antibacterial activity of these nanoparticles.