Abstract: The effect of pH of solution on the interaction between TH(thionine) and CT-DNA was studied using electrochemical and spectroscopic methods. The electrochemical results indicated that the interaction between TH and CT-DNA is in the intercalative mode in the pH 7.2 phosphate buffer solution, but both intercalative and electrostatic modes exist in the pH 6.5 phosphate buffer solution. Fluorescence spectroscopic results showed that the fluorescence intensity of TH is efficiently quenched by CT-DNA bases. The quenching constant, KSV obtained from the Stern-Volmer equation for the pH 6.5 solution is larger than that for the pH 7.2 solution indicating that the interaction between TH and CT-DNA in the pH 6.5 solution is stronger than that in the pH 7.2 solution. The conclusion is confirmed by the results of CD spectroscopic measurements.

Key words: Thionine, DNA, Electrochemical reaction, Fluorescence spectrum, 　Circular dichroism