Schiff bases from chlorine substituted anilines and salicylaldehyde: Synthesis, characterization, fluorescence, thermal features, biological studies and electronic structure investigations

Abstract

Schiff bases have been developed as potent biological agents due to their advanced physical, chemical and biomedical characteristics. Herein, 2 and 4 chloro anilines containing salicylaldehyde Schiff bases (2CAS and 4CAS) were successfully synthesised. Both simulated and experimental FTIR, UV–vis, 1H NMR, 13C NMR spectroscopic techniques were employed to characterise the synthesised compounds and the comparable spectra confirm the formation of products. The obtained fluorescence intensity values 219 (2CAS) and 1369, 2429 (4CAS) strongly suggest the fluorescence nature of the compounds. Using thermogravimetric analysis, thermal stability of the compounds were measured that were found to be 288 and 299 °C respectively. DFT optimised the geometry.Calculated energy gap for both the compounds were found to be 4.01 and 3.98 eV respectively.Molecular electrostatic potential analysis showed that carbon and oxygen atoms for both the compounds are susceptable to electrophillic attack. Mullicken charge analysis identified, for both compounds carbon atoms showed positive and negative charges, hydrogen atoms showed positive charges only,electronegative atoms such as chlorine,oxygen and nitrogen atoms showed negative charges only. NBO analysis explained detailed hyperconjugative interactions present in both the compounds. Wave function studies such as ELF found that delocalised electron density were found on the Cl, N and C atoms of both compounds and its delocalised orbitals positions were present in Cl, N, C and localised orbitals positions in hydrogen atoms of both compounds, which were identified by LOL. RDG maps demonstrates regions where van der waals interactions weak and the steric effects dominates in the prepared compounds. The antimicrobial study of the synthesised compounds showed higher activity than the commercial amoxicillin against gram positive staphylococcus aureus bacteria and moderate activity against candida albicans fungi. Furthermore, the compounds were subjected to molecular docking studies using PDB:4F2T protein of staphylococcus aureus with lowest binding attractions were determined to be- 4.94 (2CAS) and −5.02 (4CAS) kcal/ml respectively and the results were comparable to the experimental data.