The influence of thioether-substituted ligands in dicopper(II) complexes: Enhancing oxidation and biological activities

This paper describes the synthesis, structural analysis, as well as the magnetic and spectroscopic characterizations of three new dicopper(II) complexes with dinucleating phenol-based ligands containing different thioether donor substituents: aromatic (1), aliphatic (2) or thiophene (3). Temperature-dependent magnetometry reveals the presence of antiferromagnetic coupling for 1 and 3 (J = −2.27 cm⁻¹ and -5.01 cm⁻¹, respectively, H = -2JS₁S₂) and ferromagnetic coupling for 2 (J = 5.72 cm⁻¹). Broken symmetry DFT calculations attribute this behavior to a major contribution from the d_z2 orbitals for 1 and 3, and from the d_x2-y2 orbitals for 2, along with the p orbitals of the oxygens. The bioinspired catalytic activities of these complexes related to catechol oxidase were studied using 3,5-di-tert-butylcatechol as substrate. The order of catalytic rates for the substrate oxidation follows the trend 1 > 2 > 3 with k_cat of (90.79 ± 2.90) × 10⁻³ for 1, (64.21 ± 0.99) × 10⁻³ for 2 and (14.20 ± 0.32) × 10⁻³ s⁻¹ for 3. The complexes also cleave DNA through an oxidative mechanism with minor-groove preference, as indicated by experimental and molecular docking assays. Antimicrobial potential of these highly active complexes has shown that 3 inhibits both Staphylococcus aureus bacterium and Epidermophyton floccosum fungus. Notably, the complexes were found to be nontoxic to normal cells but exhibited cytotoxicity against epidermoid carcinoma cells, surpassing the activity of the metallodrug cisplatin. This research shows the multifaceted properties of these complexes, making them promising candidates for various applications in catalysis, nucleic acids research, and antimicrobial activities.