Synthesis of new piperazine derived Cu(II)/Zn(II) metal complexes, their DNA binding studies, electrochemistry and anti-microbial activity: Validation for specific recognition of Zn(II) complex to DNA helix by interaction with thymine base

New 3,4:9,10-dibenzo-2,11-dihydroxy-1,12-bispiperazine-5,8-dioxododecane complexes [C24H36N4O6Cu] (1), [C24H32N4O4Zn] (2) have been synthesized and characterized by elemental analysis, IR, NMR, Mass, EPR, UV–vis spectroscopy and molar conductance measurements. The complexes are non-ionic in nature and possess octahedral geometry around Cu2+, Zn2+ central metal ions. The binding studies of 1 and 2 with calf thymus DNA (CT-DNA) were investigated by UV–vis, fluorescence, cyclic voltammetery and viscosity measurements. The calculated binding constant Kb for 1 and 2 obtained from UV–vis absorption studies was 7.6 × 103 M−1, 80.8 × 104 M−1, respectively. The intrinsic binding constants were also estimated to be 7.0 × 104 M−1 and 7.53 × 105 M−1 for 1 and 2, respectively by using emission titrations. These experimental results suggest that complexes are groove binders and interact to CT-DNA with different affinities. Both the complexes in presence and absence of CT-DNA show quasireversible wave corresponding to CuII/CuI and ZnII/ZnI redox couple. The changes in E1/2, ΔE, Ipa/Ipc ascertain the interaction of 1 and 2 with CT-DNA. Further, decrease in viscosity of CT-DNA with increasing concentration of complexes was observed. In vitro, antimicrobial activity against fungi A. brassicicola, A. niger and bacteria E. coli, P. aeruginosa of complexes were carried out, which indicate that complex 2 is more active against both fungal and bacterial strains as shown by % inhibition data.