Cyclization of chalcones into N-propionyl pyrazolines for their single crystal X-ray, computational and antibacterial studies

Abstract

The chalcones have been cyclized into the N-propionyl-2-pyrazolines using propionic acid with hydrazine hydrate. The structures of pyrazolines were determined by FT-IR, NMR spectroscopy, and confirmed by single crystal X-ray diffraction (SC-XRD) study. Further, a combined experimental and density functional theory (DFT) based study of these pyrazolines has been reported. A comprehensive DFT investigation was performed with the level of theory as B3LYP/6-311 + G(d,p), investigating the electronic structure characteristics, FMOs and non-linear optical features of said compounds. However, the UV absorption spectra of 2a, 2b and 2c were calculated in acetone by Polarizable Continuum Model (PCM) at TD-B3LYP/6-311+G(d,p), and TD-Cam-B3LYP/6-311+G(d,p), levels. The AIM calculations were performed to explore the non-covalent interactions (NCIs). The calculated bond lengths and bond angles of said compounds are in good agreement with the SC-XRD determined parameters. The computed alignment of the frontier molecular orbitals of the derivatives with smaller energy gap provides additional information into the electronic features which enhancing the nonlinear optical (NLO) efficiency of the derivatives. Besides, synthesized compounds were applied for antibacterial activity and found compound 2c was most significant antibacterial agent. It has an antibacterial efficiency in the form of zone inhibition 20 ± 0.50 and 21 ± 0.25 mm against Gram-positive bacterial strains S. aureus and B. subtilis and 19 ± 0.35 and 18 ± 0.40 mm against Gram-negative bacterial strains E. coli and P. peli. Overall, antibacterial activity of synthesized compounds was significant against bacteria, though variable against Gram-positive and negative bacterial strains.