Synthesis, Structural Characterization, and DFT Studies of Fe(III), Co(II), and Ni(II) Mixed-Ligand Complexes With Albendazole and Nifuroxazide With Molecular Docking Against Respiratory Pathogen Targets.

In this study, the structural, electronic, and biological characteristics of newly synthesized transition metal complexes FeABNF, CoABNF, and NiABNF, resulting from the chelation compounds albendazole (AB) and nifuroxazide (NF), were studied. The synthesized compounds were found to have excellent yields with high percentage yields (∼80%). Thermal analysis showed that these complexes were highly stable with decomposition temperatures above 300°C. Molar conductivity tests revealed that FeABNF is a 1:1 electrolyte with a value of 38.95 Ω-1·cm2·mol-1, NiABNF is a 1:2 electrolyte with a value of 88.17 Ω-1·cm2·mol-1, while CoABNF is a nonelectrolyte with a value of 9.86 Ω-1·cm2·mol-1. FT-IR analysis proved that these complexes are bidentate due to their N and O donor atoms. The electronic spectra and magnetic moments confirmed that these compounds had octahedral geometry. The DFT calculation and biological assays showed that the complexes exhibited enhanced antimicrobial activity compared to the free ligands. The investigated compounds exhibited variable antibacterial and antifungal activities, with the metal complexes generally showing enhanced activity compared to the free ligands. However, the degree of activity was found to depend on the nature of the metal ion and the tested microbial strain. The most potent antibacterial action was exhibited by NiABNF and CoABNF complexes, which exhibited 28-30-mm inhibition zones and 91%-94% activity index, and good antifungal activity against Candida albicans, 20 mm. Anti-inflammatory activity order was determined as the NiABNF complex with IC50: 56.97 μM and 93% inhibition. These findings were supported at the molecular docking level, as the NiABNF complex had the highest binding affinity to DNA gyrase B (PDB: 4DUH, -8.90 kcal/mol) and SARS-CoV-2 main protease (6LU7, -9.40 kcal/mol) via hydrogen bonding and hydrophobic interactions, which make it a promising therapeutic agent. Both experimental and computational studies reported the same order of bioactivity: NiABNF > CoABNF > FeABNF > free ligands.