[Study on the interactions of Eu(III) complex of O-(thioxanthone-[2]-yl)-oxyacetic acid with DNA]

The interaction of the Eu(III) complex of O-(thioxanthone-[2]-yl)-oxyacetic acid and calf thymus DNA was studied using fluorimetric, UV-Vis and CD(circular dichroism) methods. It was found that the ultraviolet absorption intensity of Eu(III) complex of O-(thioxanthone-[2]-yl)-oxyacetic acid decreased as the concentration of DNA increased under the physiological condition of pH 7.10, and the compound remarkably influenced the negative peak in CD spectra of DNA when Eu(III) complex of O-(thioxanthone-[2]-yl)-oxyacetic acid interacted with DNA. The emission intensity of the Eu(III) complex evidently increased in the presence of DNA. The emission intensity of the DNA-EB system decreased as the concentration of the complex increasesd. And the presence of EB also led to the decrease in the emission intensity of the DNA-complex system. These changes observed here are often characteristic of intercalation. The above results strongly suggest that the complex can bind to DNA mainly by intercalation.