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Binding of baicalein, wogonin and baicalin to fish sperm DNA was studied by using ethidium bromide dye as a fluorescence probe. To study the binding mechanism, the absorption, fluorescence, melting temperature and viscosity measurement were carried out. The experimental results indicated that the planar of flavonoids intercalated to the DNA helix. When bound to DNA, flavonoids showed hyperchromic and blue shift in the absorption spectra and fluorescence quenching (>50%) in the fluorescence spectra. Furthermore, the intercalative binding was consistent with the red shift in the position of λ max in the fluorescence spectra. It was also found that ionic strength had little or no effect on the binding of flavonoids and DNA. Stern-Volmer plots at 25 and 37 • C showed that the quenching of fluorescence by flavonoids was a combined quenching process. The binding site number n, apparent binding constant K A at 25 and 37 • C, and the corresponding thermodynamic parameters G, H, S at 25 • C were obtained. The interaction of flavonoid-metal complexes with DNA was also studied by spectral methods, and the results suggested that the complexes intercalated into DNA.

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