Spectroscopic, crystal structure, antimicrobial and antioxidant evaluations of new Schiff base compounds: An experimental and theoretical study

Abstract

The increase in multidrug-resistant pathogens has necessitated continuous research for lead antimicrobial compounds. Herein, the design and synthesis of three Schiff base compounds (SB1–SB3) from aroom temperature reaction of an equimolar amount of 2,4-di-substituted anilines and salicylaldehyde as potential antimicrobial agents is reported. The compounds were validated using elemental analysis (CHN), nuclear magnetic resonance [1H, 13C, DEPT,COSY, NOESY, HSQC and HMBC], Fourier transform infrared, UV–Visible spectroscopies, scanning electron microscope-energy dispersive X-ray (SEM-EDX) analysis and mass spectrometry. Single-crystal X-ray diffraction measurements were used to properly establish the structures of compounds. SB1 and SB2 crystallized in a monoclinic P21/c space group, while SB3 crystallizedin a triclinic space group Pī. The compounds' antibacterial activity was tested in vitro against two gram-positive bacteria (Staphylococcus aureus ATCC-25923 and Streptococcus pyogenes ATCC-19615) and two gram-negative bacteria (Escherichia coli ATCC-25922 and Pseudomonas aeruginosa ATCC-27853). All compounds inhibited the bacteria quite well, with SB3 having the lowest MIC of 0.25 g.mL−1 on some of the species. A similar trend was observed for the DPPH radical scavenging activities of the compounds. To estimate chosen quantum chemical parameters of SB1-SB3, ab initio simulations of the compounds' electronic and structural properties were performed. Molecular docking studies were also used to investigate the compounds' mechanism of action against the bacteria. The theoretical findings are consistent with the experimental findings.