Synthesis, molecular structure, electronic, spectroscopic, NLO and antimicrobial study of N-benzyl-2-(5-aryl-1,3,4-oxadiazol-2-yl)aniline derivatives

Abstract

The cyclization reaction between two benzohydrazides with 2-(benzylamino)benzoic acid afforded the novel 2,5-disubstituted oxadiazole derivatives; N-benzyl-2-(5-phenyl-1,3,4-oxadiazol-2-yl)aniline (NBPOA) and N-benzyl-2-(5-(4-chlorophenyl)-1,3,4-oxadiazol-2-yl)aniline (NBCPOA). Theoretical investigation of these newly synthesized oxadiazole derivatives was carried out by density functional theory (DFT) method at the B3LYP/6-311++G(d,p) level of theory. TD-DFT computations were performed to have insights into the three singlet electronic states of the electronic absorption spectra and to assign and correlate with the experimental UV-Vis spectra. The electronic absorption measurements were done in DCM and DMSO solvents. The increase in solvent polarity exerted a blue shift on the first singlet electronic excited state and a red shift on the second and the third electronic excited states suggesting different polarities of the excited states. Vibrational band assignments were scaled and compared with the experimental frequencies. Structural parameters and chemical reactivity such as HOMO and LUMO energies, MESP surfaces, Mulliken charges, and global reactivity descriptors were analyzed. It was observed that NBCPOA has a smaller HOMO-LUMO energy gap and larger global softness than NBPOA. The charge transfer that takes place in NBPOA and NBCPOA is supported by the oscillator strength. These compounds were also screened for their in vitro antibacterial activity against two Gram-negative bacterial strains namely Escherichia coli and Salmonella typhi and two Gram-positive bacterial strains namely Bacillus subtilis and Bacillus megaterium and antifungal activity against Aspergillus niger, Rhizopus oryzae, Penicillium chrysogenum, and Candida albicans fungal strains. The synthesized compounds exhibited moderate antibacterial and antifungal properties.