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 N 2 O 2 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 UO 2 (II) complexes. The ligand and complexes were fully characterized by elemental analysis, FT-IR, UV–Vis, 1 H/ 13 C 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 UO 2 (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 × 10 5 M −1 ). The results demonstrate a clear correlation between metal coordination, structural features, DNA affinity, and biological activity. These findings highlight the potential of N 2 O 2 Schiff base metal complexes as promising multifunctional antimicrobial agents with structure-dependent biological properties.