Metal centre in salen-acridine dyad N2O2 ligand-metal complex modulates DNA binding and photocleavage efficiency
Studies on the significance of metal centre on the activity of metal complexes was less reported. Herein, we reported the synthesis and structural characterisation of copper and zinc complexes containing Schiff-base type ligand, N, N’-Bis(salicylidene)-9-(3, 4-diaminophenyl) acridine (H2daasal). The single crystal X-diffraction analysis revealed that the structure of [Zn(daasal)] is monoclinic (space group P 1 21/n 1, unit cell parameters a = 10.6126(3) Å, b = 30.5317(10) Å, c = 11.0273(3) Å, α = 90°, β = 111.0380(10) Å, γ= 90°, V = 3334.90(17) Å3 and Z = 4) with dihedral angle of 74° across the salophen and acridine moiety. Electron spin resonance (ESR) spectroscopy studies suggest that [Zn(daasal)] is diamagnetic and [Cu(daasal)] is paramagnetic. ESR spectral analysis revealed that the monomeric form of [Cu(daasal)] is either square planar or square pyramidal. A detail spectroscopy analysis and viscosity studies indicate that [Cu(daasal)] is an efficient binder to CT DNA (~ 9 times) than that of [Zn(daasal)], with a slight preference on acridine unit rather than salen moiety. Molecular docking studies suggest that [Cu(daasal)] efficiently intercalate into DNA with higher free energy values than [Zn(daasal)] complexes. Photocleavage studies revealed that the [Cu(daasal)] cleaves plasmid pBR322 DNA effectively in the presence of a reducing agent. Mechanistic studies suggest that the superoxide anion radical (O2-•) forms as an intermediate and proceeds to produce hydroxyl radical (OH•) to induce DNA photoclevage. In summary, we demonstrated that changing the metal centre in an effective ligand may offer an attractive method to produce efficient DNA intercalators.