Complex conversion of the redox pair CoIII–NO2 to CoII–NO3: Synthesis, crystal structure and DNA-binding of trans,trans,trans-[Co(py)2(H2O)2(NO3)2]

The mononuclear Co(II) complex trans,trans,trans-[Co(py)2(H2O)2(NO3)2], where py is pyridine, has been prepared under atmospheric conditions via a redox reaction of the starting material, Na3[Co(NO2)6]. The product has been characterized by elemental analysis, spectroscopic methods (UV–Vis and IR) and single-crystal X-ray structure analysis. The Co(II) atom is six-coordinated by two pyridine, two nitrato and two aqua ligands, and shows a distorted octahedral coordination environment. The interaction of the complex with FS-DNA has been investigated by electronic absorption, competitive fluorescence titration, circular dichroism and voltammetric techniques. It can be concluded that the Co(II) complex intercalates into the base pairs of DNA as evidenced by a hypochromic effect of the absorption spectra, by displacing ethidium bromide bound to DNA and by induced CD spectral changes. The complex has also the ability to cleave supercoiled plasmid DNA.

Graphical abstractThe mononuclear Co(II) complex trans,trans,trans-[Co(py)2(H2O)2(NO3)2] has been prepared under atmospheric conditions via a redox reaction of the starting material Na3[Co(NO2)6]. The interaction of the complex with FS-DNA has been investigated by electronic absorption, competitive fluorescence titration, circular dichroism and voltammetric techniques.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Synthesis of trans,trans,trans-[Co(py)2(H2O)2(NO3)2] via a redox reaction of Na3[Co(NO2)6]. ► Single-crystal X-ray crystallography for this complex. ► A slightly distorted octahedral for CoN2O4 chromophore. ► The binding investigation of the complex with DNA by spectroscopic and electrochemical methods. ► The complex has the ability to cleave supercoiled plasmid DNA.