Novel Bimetallic Complexes of Copper, Nickel and Manganese Derived from the Cobalt(III) Complex and their Interaction Studies with Calf Thymus DNA

Abstract

Synthesis of new bimetallic water-soluble complexes [C12H23N4O7CoCu]5H2O · Cl2(2), [C12H23N4O7CoNi]5H2O · Cl2(3) and [C12H23N4O7CoMn]5H2O · Cl2(4) has been achieved by reaction of the CoIII complex [C12H21N4O6Co]5H2O (1), with transition metal ions. Various physico-chemical techniques: elemental analysis, i.r., u.v.–vis., e.p.r,1H-, 13C- and 2D-n.m.r, spectroscopy, electrochemistry and molar conductance measurements were employed to characterize the complexes. The interaction of the monometallic complex (1) and bimetallic complexes (2–4) with calf thymus DNA have been carried out by u.v.–vis. titration, cyclic voltammetry (c.v.) and viscosity measurements. The intrinsic binding constant Kb of the complexes has been calculated. The absorption spectra of complexes exhibit a red shift with an overall ‘hyperchromic effect’ in the presence of CT-DNA. The binding affinity of the bimetallic complexes to calf thymus DNA is twofold in comparison with complex (1). The intrinsic binding constant value Kb of complex (1) was found to be 1.2 × 103 M−1, while the Kbvalue of complexes (2–4) were of the order of 1.4 × 103, 2.2 × 103 and 2.1 × 103 M−1, respectively. The Kb values are close to the border between classical and non-classical intercalation that indicates that the binding mode may be electrostatic, probably with covalent preference in bimetallic complexes. The electrochemical behavior of complexes (1–4) was studied in H2O and displays quasireversible CoII/CoI, CuII/CuI, NiII/NiI and MnII/MnIredox couples. The voltammetric studies of the complexes in the absence and in the presence of DNA exhibit a shift in the formal potential E0 and ratio of cathodic to anodic peak currents ipa/ipc, indicating binding of the complexes to calf thymus DNA. The viscosity of DNA decreases with increasing concentration of the complex, suggesting that complexes (2–4) bind to calf thymus DNA by electrostatic association with covalent preference.