SYNTHESIS, CHARACTERIZATION, ANTIBACTERIAL ACTIVITY OF 2-HYDROXY BENZYLIDENEAMINO BENZENESULFONAMIDE SCHIFF BASE AND ITS Co (II) AND Ni (II) COMPLEXES.

Abstract

Schiff base ligands are an important class of pharmacologically active compounds with diverse biological properties. In this study, a novel Schiff base ligand, 2-hydroxybenzylideneamino benzenesulfonamide (HBABS), was synthesized via a 1:1 condensation reaction between 2-hydroxybenzaldehyde (2 mmol, 2.12 cm³) and sulfamethoxazole (2 mmol, 5.06 g) in ethanol, achieving a yield of 82.1%. The Co(II) and Ni(II) complexes, [Co(HBABS)·2H2O] and [Ni(HBABS)·2H2O], were prepared by reacting the ligand (2 mmol, 7.14 g) with CoCl2·6H2O and NiCl2·6H2O (2 mmol, 4.76 g) in ethanol, with yields of 78.7% and 85.9%, respectively. Characterization by elemental analysis, melting point, molar conductance, FTIR, UV-Vis, ¹H NMR, and ¹³C NMR confirmed tetradentate coordination through azomethine nitrogen, sulfonamide nitrogen and oxygen, and phenolic oxygen. The complexes exhibited octahedral geometry with coordinated water molecules. Molar conductances of 25.66 and 22.75 S·cm²·mol⁻¹ confirmed their non-electrolytic nature. The ligand and complexes were evaluated for antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. The HBABS ligand showed inhibition zones of 17 mm, 16 mm, and 12 mm, respectively, while the Co(II) complex exhibited enhanced activity with inhibition zones of 23 mm, 18 mm, and 13 mm. The Ni(II) complex showed zones of 20 mm, 19 mm, and 9 mm. Minimum inhibitory concentrations ranged from 2.5 to 10 mg/mL, with the Co(II) complex demonstrating the lowest MIC of 2.5 mg/mL against S. aureus. The enhanced activity of the metal complexes is attributed to chelation, which increases lipophilicity and facilitates microbial cell membrane penetration. These findings suggest that HBABS and its Co(II) and Ni(II) complexes are promising candidates for the development of antibacterial and antifungal agents.