Synthesis, structural elucidation, antimicrobial performance, and DNA-binding behavior of a new N2O2 tetradentate schiff base and its transition metal and uranyl complexes

Abstract

A new tetradentate N2O2 Schiff base ligand derived from 2,6-diaminopyridine and 2,4-dihydroxybenzaldehyde was synthesized and used to prepare its Cu(II), Co(II), Ni(II), Mn(II), and UO2 (II) complexes. The ligand and complexes were fully characterized by elemental analysis, FT-IR, UV–Vis, 1H/13C NMR, ESR, mass spectrometry, powder X-ray diffraction, magnetic measurements, and thermal (TGA/DTA) analyses. Spectroscopic data confirm coordination through azomethine nitrogen and phenolic oxygen atoms, leading to predominantly octahedral geometries for the transition metal complexes, while the uranyl complex retains a hexagonal-planar O=U=O environment. Thermal studies reveal enhanced stability of the metal complexes compared to the free ligand. The antimicrobial activity was evaluated against Bacillus subtilis, Enterobacter aerogenes, Aspergillus niger, and Candida albicans using inhibition zone, minimum inhibitory concentration, and minimum microbicidal concentration assays. The Co(II) and Mn(II) complexes exhibit superior antibacterial performance, whereas the UO2 (II) complex shows remarkable antifungal activity. DNA-binding studies with calf thymus DNA indicate intercalative binding, with the Mn(II) complex displaying the highest intrinsic binding constant (Kb = 7.28 × 105 M−1). The results demonstrate a clear correlation between metal coordination, structural features, DNA affinity, and biological activity. These findings highlight the potential of N2O2 Schiff base metal complexes as promising multifunctional antimicrobial agents with structure-dependent biological properties.