Interaction of calf thymus DNA with new asymmetric copper(II) N,N-ethane bridged N2S2 macrocycle

Abstract

Novel asymmetric metalated Cu(II), Ni(II) double decker <i>N,N</i>-ethane bridged N₂S₂ macrocycles have been synthesized. Structure elucidation of the complexes has been done on the basis of elemental analysis, IR, UV-vis, EPR, Conductance measurements, ¹H NMR and ¹³C NMR spectroscopy. All the spectroscopic data indicate that the metal ions attain squareplanar geometry and are ionic in nature. The kinetic studies have been carried out with calf thymus DNA (CT-DNA) to ascertain the metal-DNA interaction by spectrophotometric method at the λ_max (446 nm) of Cu(II) complex at 30±1^oC. On interaction with CT-DNA, the absorption spectra exhibit a shift in wavelength, and also a steep decrease in absorbance

which clearly indicates strong binding of CT-DNA with the Cu(II) complex. The rate constants (<i>k</i>_obs)<i> </i>have been calculated under pseudo-first-order conditions and the plot of <i>k</i>_obs<i> </i>versus [DNA] gives a straight line. The electrochemistry of DNAmetal complex interaction has been carried out in H₂O/DMSO<i> </i>(95:5) solution at different scan rates. The shift in formal

potential (<i>E</i>⁰)<i> </i>after the interaction with CT-DNA clearly indicates the binding of Cu(n) complex to CT-DNA. Besides this, the ratio of anodic to cathodic peak currents <i>I</i>_pa/<i>I</i>_pc is ~0.8 for the free Cu(II) complex while for DNA bound metal complex, the ratio decreases to (0.5) suggesting that CT-DNA is bound strongly to the Cu(II) complex.