Microwave-assisted synthesis, characterizations, antimicrobial activities, and DFT studies on some pyridine derived Schiff bases

This study reports a joint experimental, theoretical and microbiological investigation on the (E)-N,N-dimethyl-4-((pyridine-2-ylmethylene)amino)aniline (5), (E)-N,N-dimethyl-4-((pyridine-4ylmethylene)amino)aniline (6) and (E)-N,N-dimethyl-4-((pyridine-3-ylmethylene)amino)aniline (7). These compounds were synthesized with microwave method and their structures characterized by FT-IR, 1H-NMR, 13 C-NMR, and elemental analysis tecniques. In the theoretical studies, torsional barriers analysis, ground state structure, Fourier Transform Infrared spectra (FT-IR), and Nuclear Magnetic Resonance spectra (NMR) of 5, 6, and, 7 were calculated by Density Functional Theory (DFT) computations. The conformers obtained from the torsional barrier scanning were optimized by B3LYP/6-31G(d,p) level. The harmonic vibrational frequencies, potential energy distribution (PED), infrared intensities, and NMR chemical shifts of the most stable conformers were determined using the B3LYP/6-311++ G(d,p). Theoretically, predicted spectral data were compared with experimental results. Antimicrobial studies of the synthesized compounds were performed against various microbial strains. Antimicrobial activities of 5, 6, and, 7 were tested against selected bacteria and yeast through minimum inhibitory concentration (MIC) and diffusion method. Compound 7 was found to be the most active against bacteria and yeast, while compound 5 was found to be moderately active. Compounds 6 (against S. aureus and C. albicans) and, 7 were found to have a very high minimum inhibitory concentration, ranging between 1.95 and 7.81 g/mL (against P. aeruginosa and E. coli). Compounds (6 and 7) showed zone of inhibition values in the range of 10-20 mm against other bacteria except L. monocytogenes and S. thyphimurium. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigates the synthesis, characterization, and antimicrobial activities of three compounds (5, 6, and 7) through experimental, theoretical, and microbiological approaches. The structures of these compounds were characterized using various techniques, and their theoretical properties were calculated using Density Functional Theory. The antimicrobial activities of the synthesized compounds were tested against different bacterial and yeast strains.