Synthesis, characterizations, and DFT studies of some vanillin Schiff base derivatives

Abstract

The increase in bacterial infections has necessitated the need for the design of new drugs that can fight against multidrug-resistant bacteria. Schiff bases, especially those of vanillin, have shown promising activity against some bacterial infections. In this article, six new vanillin Schiff bases (L1–L6) were prepared by condensation of vanillin with various substituted anilines for possible medicinal applications. The compounds were characterized by infrared spectra, UV/visible spectra, and melting point measurements. Infrared spectra confirmed the formation of the compounds by the newly emerged azomethine (C=N) bands observed at 1676–1620 cm⁻¹ for the synthesized compounds. The UV/visible spectra showed the expected π–π* transition of the azomethine group at 38000–34000 cm⁻¹ and the n–π* transition at 32000–25000 cm⁻¹, which are characteristics of the molecules. The Schiff bases, L5 and L6, were obtained as thick viscous liquids, while L1–L4 came out as crystals of different colors characterized by sharp melting points. The molecules were modeled and optimized using DFT at the 6-31G(d) level of theory. The computational study shows that the compounds could effectively accept and donate protons, which is a remarkable characteristic for medicinal and other applications. The characterization results reveal that the compounds were successfully prepared. Spectroscopic and computational studies suggested that the compounds may have some medicinal and electronic applications.