Synthesis, structure, DNA binding and photonuclease activity of a nickel(II) complex with a N,N′-Bis(salicylidene)-9-(3,4-diaminophenyl)acridine ligand

A new class of salen functionalized novel ligand N,N′-Bis(salicylidene)-9-(3,4-diaminophenyl)acridine, H2daasal (two potential intercalators, salen and acridine, which are linked together via C–C bond) and its metal complex [Ni(daasal)] have been synthesized and characterized by X-ray diffraction, elemental analysis, UV–Vis, IR, 1H NMR, MALDI-TOF mass spectrometry and cyclic voltammetry methods. From the crystal structure, the salphen moiety is not coplanar with the acridine ring, having a dihedral angle of 68° and 76° in both H2daasal and [Ni(daasal)], respectively. [Ni(daasal)] shows a reversible oxidation cyclic voltammetric response near 1.03 V versus SCE in CH3CN (0.1 M TBAP) assignable to the Ni(II)/Ni(III) couple. The interaction of these compounds with calf-thymus (CT) DNA was examined using spectroscopic and viscosity measurements. These studies reveal that both compounds bind to CT DNA via an intercalative mode. Molecular-modeling studies also support an intercalative mode of binding to the model duplex d(CGCAATTGCG)2 possibly from the major groove with a slight preference for GC rich region. Additionally, [Ni(daasal)] promotes the cleavage of plasmid pBR322 DNA upon irradiation under terminal oxidant Oxone.