Design, synthesis, and biological evaluation of Au(III) and Ag(I) complexes of a 4,4′-oxydianiline-derived Bis-Azo Ligand

A novel bis-azo dye ligand (DOBB) was synthesized by diazo-coupling reaction of 4,4′-oxydianiline with methyl 4-hydroxybenzoate, and then the coordination complexes of Au(III) and Ag(I) with DOBB were prepared in a 2:1 metal-to-ligand molar ratio, resulting in dinuclear complexes with the formulas [Au₂(DOBB)Cl₄]·2H₂O and [Ag₂(DOBB)(H₂O)₄]·2H₂O. The ligand and its metal complexes were well characterized by UV–Vis, FT-IR spectroscopy, Elemental (CHN) analysis, 1 H NMR spectrum, Mass spectrometry, Molar conductivity, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The successful complexation was confirmed by the significant changes in the characteristic ligand bands in the infrared spectral data, as well as the appearance of new bands corresponding to the vibrations of the M–N and M–O bonds. Biological screening showed that both the free ligand and its metal complexes have significant inhibitory activity against Streptococcus and Escherichia coli bacterial strains and Penicillium and Aspergillus niger fungal strains. In addition, Au(III) complex showed cytotoxicity in assays against MCF-7 breast cancer cells, showing a concentration-dependent decrease in cell viability up to 35.23% at 400 μg·mL⁻¹, while normal WRI-68 cells exhibited 87.22% viability under the same conditions, suggesting selective anticancer activity with an IC₅₀ of 146.8 µg/mL against MCF-7 cells and a selectivity index (SI) of >2.72, indicating significant selective anticancer activity. The results indicate that the synthesized complexes are promising bioactive compounds with strong antimicrobial activity and selective cytotoxicity against cancer cells. Further mechanistic, toxicity, stability, and in vivo studies are required to assess their full therapeutic potential.