Antibacterial properties of surface-active synthesized 1-allyl-3-methylimidazolium based ionic liquids: experimental, molecular docking and DFT calculations

Abstract

Ionic liquids are continuously being synthesized and metathesized with their properties being evaluated, particularly the degradation of these compounds for possible industrial applications. Herein, a series of 1-allyl-3-methylimidazolium based ionic liquids were synthesized, characterized and evaluated for antibacterial potencies including degradation using photocatalytic approach. The obtained thermograms from both TGA and DSC illustrated [1-allyl-3-mim] [OTf] as the most thermally stable among the examined ionic liquids with a glass transition phase at 36.6 °C. The acidity levels of the ionic liquids estimated by using Hammett's acidity function revealed H₀ values in the range of 3.9861 to 4.2857. As a result of the commonly known non-biodegradability of ILs, the photocatalytic degradation process was conducted and proven to be ineffective against 1-allyl-3-methylimidazolium salicylate [1-allyl-3-mim][SaL] which was still present after 72 h. The antibacterial activity of the synthesized compounds was evaluated using the microbial susceptibility testing against selected gram-positive and gram-negative bacteria using an agar well diffusion method and revealed diverse degrees of susceptibility of the tested organisms, with Pseudomonas aeruginosa ATCC BAA 1744 and Escherichia coli ATCC 11775 being the least and most sensitive to all the treatments, respectively. Molecular docking was done by iGEMDOCK software to predict the binding affinities of the ionic liquids and selected bacterial protein targets. This revealed negative binding energies with values of −89.31 kcal/mol for E. coli, −91.83 kcal/mol for P. aeruginosa, −89.91 kcal/mol for S. aureus and − 73.26 kcal/mol for S. pneumoniae. In addition, the electronic properties of the synthesized ionic liquids were calculated using Density Functional Theory (DFT).