Synthesis, DNA-binding and photocleavage studies of cobalt(III) complexes [Co(bpy)2(dpta)]3+ and [Co(bpy)2(amtp)]3+

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Two novel cobalt(III) mixed-polypyridyl complexes [Co(bpy)2(dpta)]3+ and [Co(bpy)2(amtp)]3+ (bpy = 2,2′-bipyridine, dpta = dipyrido-[3,2-a;2′,3′-c]-thien-[3,4-c]azine, amtp = 3-amino-1,2,4-triazino[5,6-f]-1,10-phenanthroline) have been synthesized and characterized. The interaction of CoIII complexes with calf thymus DNA was investigated by spectroscopic and viscosity measurements. Results suggest that the two complexes bind to DNA via an intercalative mode. Moreover, CoIII complexes have been found to promote the photocleavage of plasmid DNA pBR322 under irradiation at 365 nm. The mechanism studies reveal that hydroxyl radical (OH•) is likely to be the reactive species responsible for the cleavage of plasmid DNA by [Co(bpy)2(dpta)]3+ and superoxide anion radical (O2•−) acts as the key role in the cleavage reaction of plasmid DNA by [Co(bpy)2(amtp)]3+.