Synthesis, spectroscopic study, antioxidant, DNA-cleavage and enzyme-mimicking activities for metal(II/III) complexes with azo ligand–eugenol scaffold

Abstract A newly synthesized azo ligand, 1-((5-allyl-2-hydroxy-3-methoxyphenyl)diazenyl)anthracene-9,10-dione (H-MND), derived from an anthraquinone nucleus coupled with the natural phenol (eugenol), was employed to prepare Co(II), Ni(II), Cu(II), Rh(III) and Pd(II) complexes, with the ligand proposed to adopt a tridentate coordination mode. Anthraquinone derivatives and natural phenols are recognized for diverse pharmacological activities, making them valuable scaffolds for the design of bioactive ligands. The synthesized compounds were characterized by FT-IR, UV–vis, NMR spectroscopy, mass spectrometry, elemental analysis, thermal analysis thermogravimetric-differential scanning calorimetry (TGA-DSC), assessment of chlorine content, magnetic susceptibility and molar conductance measurements, which collectively suggested predominantly non-electrolytic behaviour. In the 1,1-diphenyl-2-picrylhydrazyl (DPPH) assay, the Ni(II) complex exhibited the highest antioxidant activity among the synthesized compounds, with an IC50 value significantly different from that of gallic acid (t = 4.31, p ˂ 0.01). Only the Pd(II) complex displayed activity towards plasmid DNA consistent with partial cleavage in the absence of externally added redox agents. Furthermore, activity mimicking phenoxazinone synthase was evaluated for the Cu(II) and Co(II) complexes, revealing system-specific catalytic behaviour. These results support further investigation into the biomedical and catalytic potential of these metal complexes.