DNA binding and cleavage behaviors of copper(II) complexes with amidino-O-methylurea and N-methylphenyl-amidino-O-methylurea,and their antibacterial activities

The two designed copper(II) complexes, Cu(L^1m)₂]Cl₂ (1) (L^1m = amidino-O-methylurea) and Cu(L^2m)₂]Cl₂ (2) (L^2m = N-methylphenyl-amidino-O-methylurea), have been investigated for their interaction with calf thymus DNA by utilizing the absorption titration method, viscometric studies and thermal denaturation. The cleavage reaction on pBR322 DNA has been monitored by agarose gel electrophoresis. The results suggest that the two complexes can bind to DNA by non-intercalative modes and exhibit nuclease activities in which supercoiled plasmid DNA is converted to the linear form. Complex 2, with an intrinsic binding constant (K_b) of 1.16 × 10⁵ M⁻¹, shows a higher binding efficiency and a better nuclease activity than complex 1, with a K_b value of 5.67 × 10⁴ M⁻¹. Their DNA cleavage potential can be significantly enhanced by hydrogen peroxide, indicating an oxidative cleavage process. Further examination of the antibacterial activities against Campylobacter has revealed inhibition zones of 9.0 (for 1) and 14.5 mm (for 2), which are in agreement with their minimum inhibitory concentration (MIC) values of 1.56 and 0.78 mg mL⁻¹, respectively. The substantially better reactivity of 2 results from the aromatic moieties on the side chain of the L^2m ligand which act as an additional binding site.