The mechanisms of the binding of quercetin·2H₂O and LaL₃·6H₂O to ctDNA

149-154The phenomenon of quercetin·2H2O (3', 3, 4', 5, 7-pentahydroxyflavone) and its complex LaL3·6H2O [L= quercetin (3-OH group deprotonated)] exhibiting different antitumour activities has been examined by the interactions of quercetin·2H2O and complex LaL3·6H2O with calf thymus DNA (ctDNA). The mechanisms for the binding of quercetin·2H2O and LaL3·6H2O to ctDNA have been studied by fluorometric and electrochemical methods. The complex interferes with the usual fluorescence enhancement of ethidium bromide (EB) by competing for intercalation sites on ctDNA. The intrinsic binding constant, K is 2.98×104 M-1 at 20°C, and the binding site size ns of the complex to ctDNA is 5, as determined by absorption titration in 5 mM Tris-HCl, 50 mM NaCl buffer (pH7.0). The results show that quercetin·2H2O and complex can both bind to DNA, but the binding modes and binding affinities are different. The complex LaL3·6H2O binds to DNA mainly by intercalation and quercetin·2H2O does so mainly by electrostatic attraction