Studies of interaction of emodin and DNA in the presence of ethidium bromide by spectroscopic method

Emodin interacting with deoxyribonucleic acid (DNA) has been studied by different spectroscopic techniques, such as fluorescence, ultraviolet and visible (UV–vis), and fourier transform infared (FT-IR) spectroscopies, using ethidium bromide (EB) as a fluorescence probe of DNA. The decrease in the fluorescence of DNA–EB system on addition of emodin shows that the fluorescence quenching of DNA–EB complex by emodin occurs. The binding constants of emodin with DNA in the presence of EB are 6.02 × 104, 9.20 × 104 and 1.17 × 105 L mol−1 at 20, 35 and 50 °C, respectively. FT-IR spectrum further suggests that both the phosphate groups and the bases of DNA react with emodin. The reaction of DNA with emodin in the presence of EB is affected by ionic strength and temperature. The values of melting temperature (Tm) of DNA–EB complex and emodin–DNA–EB complexes were determined, respectively. From the experiment evidences, the major binding mode of emodin with DNA should be the groove binding.