Whereas the complex 2 shows an irreversible peak at 0.44 V at a scan rate

of 100 mVs−1. The redox process is assigned to CuII/CuI couple. 30 and 31 The characterization of DNA recognition by transition metal complex has been aided by the DNA cleavage chemistry that is associated with redox-active or photo-activated metal complexes.32 Many copper complexes have been shown to cleave DNA in the presence of H2O2 due to their ability to behave like a Fenton catalyst.33 The ability of present complexes to effect DNA cleavage Selleckchem BAY 73-4506 was monitored by gel electrophoresis using supercoiled pUC19 DNA in Tris–HCl buffer. Fig. 1 shows the nuclease activity of the complexes in the presence and absence of hydrogen peroxide. Lane 1 indicates the control DNA without any additives. Lane 2 shows the activity of DNA in the presence of peroxide. As seen in lanes 3–5, incubation of the complexes 1–3 alone with DNA could not bring about any apparent

cleavage. This confirms that the present copper(II) complexes are not capable of bringing about any hydrolytic cleavage of DNA. The reason behind is that the hydrolytic cleavage requires selleck screening library coordinative binding of the copper(II) complex to the phosphate moiety of the nucleic acid.34 Interestingly all the three complexes show DNA cleavage activity at a concentration of 48 μM. But the cleavage efficiency of complex 2 was found to be significantly lower than that of the other two complexes. It is believed that when the present

redox active copper complexes were interacted with DNA in the presence of hydrogen peroxide as an oxidant hydroxyl radicals Terminal deoxynucleotidyl transferase might be produced.22, 23 and 24 These hydroxyl radicals are responsible for cleavage of DNA. In order to establish the reactive species responsible for the cleavage of DNA, we carried out the experiment in the presence of histidine and DMSO. As seen in lanes 2–4 in Fig. 2, the cleavage activity was not found to be inhibited in the presence of histidine. This rules out the involvement of singlet oxygen in the cleavage activity. However, as seen in lanes 5–7, the cleavage activity was inhibited significantly in the presence of DMSO. This conclusively shows the involvement of the hydroxyl radical in the observed nuclease activity of the copper(II) complexes in the presence of peroxide. In summary, we have synthesized and characterized three new mononuclear mixed ligand copper(II) complexes having tridentate reduced Schiff bases and planar NN-donor heterocyclic bases. All the complexes show nuclease activity in the presence of hydrogen peroxide in converting supercoiled pUC19 DNA to its nicked circular form. The cleavage reactions are found to be inhibited in the presence of hydroxyl radical scavenger DMSO. All authors have none to declare. The authors thank the Head, Department of Chemistry, UDC, Trichy for providing laboratory facilities. “
“Copper is an essential trace element in plants and animals, but not some microorganisms.