Monomeric and Dimeric Oxidomolybdenum(V and VI) Complexes, Cytotoxicity, and DNA Interaction Studies: Molybdenum Assisted C=N Bond Cleavage of Salophen Ligands

Four novel dimeric bis-mu-imido bridged metal-metal bonded oxidomolybdenum(V) complexes [(Mo2O2L2)-O-V'(1-4)] (1-4) (where L'(1-4) are rearranged ligands formed in situ from H2L1-4) and a new mononuclear dioxidomolybdenum(VI) complex [(MoO2L5)-O-VI] (5) synthesized from salen type N2O2, ligands are reported. This rare series of imido-bridged complexes (1-4) have been furnished from rearranged H3L'(1-4) ligands, containing an aromatic diimine (o-phenylenediamine) linker, where Mo assisted hydrolysis followed by -C=N bond cleavage of one of the arms of the ligand H2L1-4 took place. A monomeric molybdenum(V) intermediate species [(MoO)-O-V(HL'(1-4))(OEt)] (I-d(1-4)) was generated in situ. The concomitant deprotonation and dimerization of two molybdenum(V) intermediate species (I-d(1-4)) ultimately resulted in the formation of a bis-mu-imido bridge between the two molybdenum centers of [(Mo2O2L2)-O-V'(1-4)] (1-4). The mechanism of formation of 1-4 has been discussed, and one of the rare intermediate monomeric molybdenum(V) species I-d(4) has been isolated in the solid state and characterized. The monomeric dioxidomolybdenum(VI) complex [(MoO2L5)-O-VI] (5) was prepared from the ligand H2L5 where the aromatic linker was replaced by an aliphatic diimine (1,2-diaminopropane). All the ligands and complexes have been characterized by elemental analysis, IR, UV-vis spectroscopy, NMR, ESI-MS, and cyclic voltammetry, and the structural features of 1, 2, 4, and 5 have been solved by X-ray crystallography. The DNA binding and cleavage activity of 1-5 have been explored. The complexes interact with CT-DNA by the groove binding mode, and the binding constants range between 10(3) and 10(4) M-1. Fairly good photoinduced cleavage of pUC19 supercoiled plasmid DNA was exhibited by all the complexes, with 4 showing the most promising photoinduced DNA cleavage activity of similar to 93%. Moreover, in vitro cytotoxic activity of all the complexes was evaluated by MTT assay, which reveals that the complexes induce cell death in. IMF-7 (human breast adenocarcinoma) and HCT-15 (colon cancer) cell lines.