Synthesis and characterization of novel chelation-free Zn(II)-azole complexes: Evaluation of antibacterial, antioxidant and DNA binding activity

Abstract

Here, we synthesized novel chelation-free Zn(II)-complexes (<strong>1</strong>-<strong>3</strong>) [ZnCl₂L₂] of monodentate ligands with L = 2-isopropylimidazole (<strong>L1</strong>), 2-methylbenzimidazole (<strong>L2</strong>), and 2-methylbenzoxazole (<strong>L3</strong>) and evaluated their antibacterial, antioxidant and DNA binding activities. The chelation-free properties of these coordination complexes were confirmed by UV-visible spectroscopy, ¹H NMR spectroscopy, single X-ray crystallography and elemental analysis. Complexes <strong>1</strong>-<strong>3 </strong>exhibited substantial antibacterial activity against all antibiotic susceptible bacteria within a concentration range of 100-200 µg/ml while free ligands<strong> L1 </strong>and<strong> L2</strong> exhibited weak antibacterial activity considerably concentration above 200 µg/ml. Also, both complexes <strong>2 </strong>and <strong>3</strong> were twice more active against methicillin-resistant <em>Staphylococcus aureus </em>(<em>MRSA</em><em>) </em>than complex <strong>1</strong>. Furthermore, we found that complexes <strong>1</strong>-<strong>3 </strong>showed DNA binding activity with <em>E. coli</em> plasmid DNA and calf thymus DNA, which may be a plausible mechanism for their antibacterial activity. We also investigated the antioxidant activity of complexes <strong>1</strong>-<strong>3</strong> and found that complex <strong>2 </strong>exhibited potential antioxidant activity compared to complexes <strong>1</strong> and <strong>3</strong>. All these results suggest that the chelation-free Zn(II)-complexes can be the future candidates for more advance biological studies.