Oxidative DNA cleavage by Cu(II) complexes of 1,10-phenanthroline-5,6-dione

A dimeric dichloro-bridged copper(II) complex [Cu2(pdon)2Cl4] · 2DMF (1) and two mononuclear copper(II) complexes [Cu(pdon)(DMSO)Cl2] · DMSO · H2O (2) and [Cu(pdon)3] · (ClO4)2 · 2.25CH3CN · 6H2O (3) (pdon = 1,10-phenanthroline-5,6-dione) have been synthesized and characterized. Variable-temperature magnetic susceptibility studies indicate the existence of weak anti-ferromagnetic coupling in the binuclear complex. The interaction of these complexes with CT-DNA (calf thymus DNA) has been studied using absorption and emission spectral methods. The apparent binding constants (K app) for 1, 2 and 3 are 5.20 × 105, 2.68 × 105 and 7.05 × 105 M−1, respectively, showing moderate intercalative binding modes. All of these complexes cleave plasmid DNA to nicked DNA in a sequential manner as the concentration or reaction time is increased. The cleavage mechanism between the complex and plasmid DNA is likely to involve singlet oxygen 1O2 and •OH as reactive oxygen species.