Spectroscopic studies on the interaction of morin-Eu(III) complex with calf thymus DNA

The interaction between morin-Eu(III) complex and calf thymus DNA in physiological buffer (pH 7.4) was investigated using UV-vis spectrophotometry, fluorescence spectroscopy, viscosity measurements and DNA melting techniques. Hypochromicity and red shift of the absorption spectra of morin-Eu(III) complex were observed in the presence of DNA, and the fluorescence intensity of morin-Eu(III) complex was greatly enhanced with the addition of DNA. Moreover, fluorescence quenching and blue shift of the emission peak were seen in the DNA-ethidium bromide (EB) system when morin-Eu(III) complex was added. The relative viscosity of DNA increased with the addition of morin-Eu(ill) complex, whereas the value of melting temperature of DNA-EB system decreased in the presence of morin-Eu(III) complex. All these results indicated that morin-Eu(III) complex can bind to DNA and the major binding mode is intercalative binding. The 3:1 morin:Eu(III) complex (estimated binding constant = 2.36 x 10(6) L mol(-1)) is stabilized by intercalation into the DNA. The Calculated binding constants of morin-EU(III) complex with DNA at 292, 301 and 310 K were 7.47 x 10(4), 8.89 x 10(4) and 1.13 x 10(5) L mol(-1), respectively. The thermodynamic parameters were also obtained: Delta H-0 was 20.14 kJ mol(-1) > 0 and Delta S-0 was 161.70 J mol(-1) K-1 > 0, suggesting that hydrophobic force plays a major role in the binding of morin Eu(III) complex to DNA. (c) 2009 Elsevier B.V, All rights reserved.