Study on the fluorescence spectra and electrochemical behavior of ZnL 2 and Morin with DNA

Abstract

The interactions of Morin (2′, 3, 4′, 5, 7-pentahydroxyflavone) and its Zn-complex, ZnL 2·3H 2O [L=Morin (2′-OH group deprotonated)], with calf thymus DNA have been studied using fluorimetric and electrochemical methods. ZnL 2·3H 2O has different spectral characteristics and electrochemical behavior from that of Morin in the presence of DNA. Increasing fluorescence is seen for ZnL 2·3H 2O with DNA addition whereas decreased fluorescence is observed for Morin. An isosbestic point appears at 560 nm for the DNA–ZnL 2·3H 2O system with ethidium bromide (EB) addition while no isosbestic point is detectable for Morin. Quenching fluorescence is observed for DNA–EB system when ZnL 2·3H 2O is added whereas no quenched fluorescence is seen for DNA–EB system with Morin addition. The above results suggest that Morin and ZnL 2·3H 2O can both bind to DNA, but the binding mode is different. The complex binds to DNA mainly by intercalation, while Morin binds in a non-intercalating mode. The binding constant and binding site sizes are derived from electrochemical methods. For ZnL 2·3H 2O, the binding constant is 5.0×10 4 l mol −1 at 20°C, and the binding site size n s is 5.