Synthesis of three new binuclear Mn complexes: characterization and DNA binding and cleavage properties

A series of novel binuclear Mn complexes, [Mn2(L1)2]·2DMF (1), [Mn2O(L2)2](ClO4)2·CH3OH (2), and [Mn2(L3)2Cl2]·2DMF (3), were synthesized and structurally characterized by single-crystal X-ray diffraction. Moreover, their DNA-binding and cleavage properties were investigated. Characterization of the complexes by electron absorption and fluorescence spectroscopy confirmed the binding to calf-thymus DNA (CT-DNA). The apparent binding constants (Kapp) for 1, 2, and 3 were determined as 7.06 × 105, 1.10 × 105, and 3.77 × 105 M−1, respectively, indicating intermediate-strength binding between the complexes and CT-DNA. Moreover, 2 exhibited static fluorescence quenching, while 1 and 3 displayed dynamic fluorescence quenching. Agarose gel electrophoresis studies of the complexes revealed that only 2 exhibits chemical nuclease activity in the absence of a redox agent. When H2O2 was added as the redox agent, 3 was still unable to cleave DNA; however, 1 showed chemical nuclease activity and the activity of 2 was enhanced. The cleavage mechanism exerted by the complexes on plasmid DNA is likely to involve oxidative cleavage processes with hydroxyl radicals (·OH) and singlet oxygen (1O2) as the active species.