Trace element-based Co(II) and Fe(III) mixed-ligand complexes of phenanthroline and sulfasalazine: Structural, DFT, molecular docking, and antimicrobial studies.

New mixed ligand compounds FeSUPT and CoSUPT were successfully prepared using sulfasalazine (SU) and phenanthroline (PT). The compounds were recovered as solid, non-electrolyte substances with good thermal stability (above 300°C) and low molar conductivities (11.85 and 10.63 Ω-1cm2mol-1). Elemental and spectroscopic analyses confirmed the proposed formulations and a 1:1:1 metal-to-ligand ratio. FT-IR data indicated coordination through phenolic oxygen, and carboxylate oxygen from SU, and nitrogen atoms from PT. Electronic spectra and magnetic moments (1.85 and 1.80 B.M.) supported octahedral geometries. TGA results confirmed coordinated water molecules and high structural stability. DFT calculations revealed reduced energy gaps for FeSUPT (2.27 eV)and CoSUPT (2.11 eV), indicating higher reactivity compared to SU (3.37 eV) and PT (4.65 eV). The complexes also showed higher softness (0.44-0.47) and electrophilicity (up to 8.98 eV). Biological evaluation showed a strong enhancement after complexation. Antibacterial activity reached 24-27 mm for the complexes, compared to 5-8 mm for ligands. Activity indices approached 96%, close to amoxicillin. Antifungal activity displayed inhibition zones up to 18 mm, with activity indications reaching 90%. MIC values decreased significantly to 40-50 μM for the complexes, compared to 90-100 μM for ligands. Molecular docking studies against DNA gyrase B (PDB ID: 1KZN) revealed favorable binding affinities, particularly for CoSUPT (-8.40 kcal/mol). These results provide preliminary computational support for the observed antibacterial activity, although they do not constitute direct evidence of enzyme inhibition.