Metal complexes of sulfamethazine/benzoin-based Schiff base ligand: synthesis, characterization, DFT calculations, and antimicrobial activities.

Background/aim: The global rise in bacterial resistance poses a significant challenge, exacerbated by the overuse of antibacterial agents. Schiff base-metal complexes have gained attention for their potential antimicrobial properties, attributed to their unique three-dimensional structures and modes of action, such as cell wall inhibition and membrane disruption. The aim of this study was to synthesize and characterize a novel Schiff base (L) derived from sulfamethazine and benzoin, and to develop metal complexes of it with Cu²⁺, Co²⁺, Ni²⁺, and Cd²⁺. This research sought to evaluate the antibacterial and antifungal activities of the synthesized Schiff base and its metal complexes to explore their potential as effective antimicrobial agents.

Materials and methods: The compound L and its metal complexes were synthesized. The compounds were characterized with ¹H NMR, ¹³C NMR, mass spectrometry, UV-vis spectroscopy, and FTIR. Antimicrobial activities were tested on E. coli ATCC 8739, S. aureus ATCC 6538, P. aeruginosa ATCC 9027, and C. albicans ATCC 10231. To investigate the molecular properties of compound L, density functional theory calculations were also performed.

Results: The synthesized compounds (L, 1, 2, 3, 4) were tested for antibacterial and antifungal activities. Copper-based compound 1 showed the best overall antifungal activity, while zinc-based compound 3 demonstrated notable antibacterial efficacy against P. aeruginosa. Although all compounds outperformed L in antifungal tests, none surpassed ciprofloxacin, the reference drug, in antibacterial assays. These results highlight the potential of Schiff base-metal complexes as promising antimicrobial agents.

Conclusion: This study highlights the potential of Schiff base-metal complexes as effective antimicrobial agents in response to the growing challenge of bacterial resistance. The synthesized Schiff base (L) and metal complexes of it with Cu²⁺, Co²⁺, Ni²⁺, and Cd²⁺ exhibited promising antibacterial and antifungal activities, with copper-based compound 1 showing the most potent antifungal action and zinc-based compound 3 demonstrating significant antibacterial efficacy against P. aeruginosa. Although none of the compounds outperformed ciprofloxacin in antibacterial assays, all were more effective than the parent Schiff base in antifungal tests. These findings suggest that Schiff base-metal complexes, particularly copper and zinc derivatives, hold considerable promise for developing new antimicrobial agents. Further optimization and testing could enhance their clinical application in combating resistant infections.