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

Abstract

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-4-ylmethylene)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, 13C-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.