Synthesis, Characterization, Antibacterial Activity of 2-hydroxy Benzylideneamino Benzenesulfonamide (HBABS) Schiff Base and its Fe (II) and Cu (II) Complexes

Abstract

This study reports the synthesis, comprehensive characterization, and antimicrobial evaluation of a novel Schiff base ligand, 2-hydroxybenzylideneamino benzenesulfonamide (HBABS), obtained from the condensation of sulfamethoxazole and 2-hydroxybenzaldehyde, along with its Fe(II) and Cu(II) complexes. The ligand was obtained in 82.10% yield with a melting point of 188.24 °C, while the Fe(II) and Cu(II) complexes were obtained in 76.91% and 75.88% yields with decomposition temperatures of 212.35 °C, respectively. Molar conductance values of 16.40–20.47 Ω⁻¹ cm² mol⁻¹ in DMSO indicated non-electrolytic behavior. Magnetic moment values of 1.77 B.M. for both metal complexes suggested paramagnetic octahedral environments. Elemental analysis showed good agreement between calculated and experimental values, confirming purity and proposed stoichiometry. FT-IR spectra revealed azomethine (C=N) stretching bands and a shift in the phenolic (O–H) band upon coordination, while UV-Vis and NMR data further supported bidentate coordination through the deprotonated phenolic oxygen and azomethine nitrogen atoms, consistent with the proposed formula [M(HBABS)(H₂O)₂]. In vitro antimicrobial screening against Gram-positive bacteria (Staphylococcus aureus, Bacillus cereus, Streptococcus pyogenes, Mycobacterium tuberculosis), Gram-negative bacteria (Escherichia coli, Salmonella typhi, Klebsiella pneumoniae, Neisseria gonorrhoeae), and fungal strains (Aspergillus flavus, Candida albicans, Trichophyton rubrum, Aspergillus niger) demonstrated enhanced antibacterial activity upon metal coordination. The Cu(II) complex exhibited the highest activity, producing larger inhibition zones and lower minimum inhibitory concentration (MIC) values compared to the free ligand, and in some cases showing activity comparable to or greater than that of amoxicillin under identical conditions. Antifungal activity was comparatively weak for all compounds. These findings highlight the role of metal complexation in enhancing the biological performance of sulfonamide-derived Schiff bases and identify the Cu(II) complex as a promising candidate for further pharmacological investigation.