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(III) 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 × 106 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 × 104, 8.89 × 104 and 1.13 × 105 L mol−1, respectively. The thermodynamic parameters were also obtained: ΔHθ was 20.14 kJ mol−1 > 0 and ΔSθ 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.