Spectral, structural, solvatochromism, biological and computational investigation of some new azo–azomethines containing N-alkylpyridinium salts

Abstract

The 4-((4-hydroxy-3-(pyridin-3-ylimino)methyl)phenyl)diazenyl)-1-alkylpyridinium (2a-e) were prepared by reaction of 3-aminopyridine with 4-amino-1-alkyl pyridinium salts (1a-e) in absolute ethanol and identified by NMR, IR, UV–Vis, mass spectroscopy and elemental analysis. The UV–Vis spectra in some organic solvents showed the presence of enol-keto tautomerism in solution for compounds 2a-e. The geometries for 2a tautomers were fully optimized in the gas phase. The vibrational frequencies of the compound were calculated using the density functional theory method. Considering UV–Vis data and the quantum chemical results, exhibited positive solvatochromism for compounds 2a-e that may be for enol-keto tautomerism which occurred between azo-enol-imine (I) and azo-ketone-enamine (II) tautomers. Antibacterial properties of 2a-e were evaluated by paper disk method. Diphenylpicrylhydrazyl (DPPH) assay was chosen to prove the antioxidant activity. The activity of 2b against B. cereus and S. aureus (Gram positive bacteria) was better than the rest of the compounds. These compounds did not show effective activity against E coli and K. pneumonia (Gram negative bacteria). The DPPH test showed a moderate antioxidant activity for these products.