Binding and photocleavage of DNA by mixed ligand Co(III) and Ni(II) complexes of thiophene[2, 3-b] quinoline and phenanthrolie/bipyridine

In order to systematically perform an experimental and theoretical study on DNA binding and photocleavage properties of transition metal complexes of the type [M(L)(2)(L-1)](PF6)(n) center dot xH(2)O (where M = Co(III) or Ni(II), L = 1,10- phenanthroline or 2.2' bipryidine, L-1 = Thiophene [2,3-b] quinoline (qt), n = 3 or 2 and x = 5 or 2) have been synthesized and characterized by elemental analysis, IR, H-1 NMR, UV and magnetic susceptibility data. The DNA-binding properties of these complexes have been investigated with UV-Vis, viscosity measurements, thermal denaturation and cyclic voltametric studies. It is experimentally found that all the complexes are bound to DNA via intercalation in the order [Co(bpy)(2)(qt)](PF6)(3) > [Co(phen)(2)(qt)](PF6)(3) > [Ni(phen)(2)(qt)](PF6)(2) > [Ni(bpy)(2)(qt)](PF6)(2). The photocleavage studies with pUC19 DNA shows that all these complexes promoted the conversion of SC form to NC form in absence of 'inhibitors'.