Spectroscopic and voltammetric studies of the cobalt (II) complex of Morin bound to calf thymus DNA

Absorption and emission spectra, viscometric and electrochemical studies have been carried out on the interaction of Morin (2', 3, 4', 5, 7-pentahydroxyflavone) and its Co complex, CoL2.3H(2)O[L = Morin (2'-OH group deprotonated)], with calf thymus DNA. In the presence of DNA, the complex exhibits a hypochromism in the u.v.-vis. spectra and a large enhancement in emission spectra suggests that the complex binds to DNA via a weak partial intercalation, revealed by competitive experiments, viscosity and by electrochemical studies. The binding constant is ca. 2 x 10(3) M-1 at 20 degreesC. Both ZnL2.3H(2)O and CoL2.3H(2)O complexes have the same molecular structure, ZnL2.3H(2)O shows the spectral characteristics and electrochemical behaviour which agrees with observations for other intercalators in the presence and absence of DNA, whereas the CoL2.3H(2)O complex shows different spectral characteristics and electrochemical behaviour to that of ZnL2.3H(2)O, which suggests that the mode and affinity of the complex CoL2.3H(2)O binding to DNA are different from that of ZnL2.3H(2)O. Both ZnL2.3H(2)O and CoL2.3H(2)O complexes exhibited different antitumour activity. So the binding mode and affinity of complexes to DNA may play an important role in determining the antitumour activity.