[Fluorescence and visible spectroscopic studies on interaction of beta-cyclodextrin-thionine inclusion complex with...

The inclusion of beta-cyclodextrin (CD) for thionine (TH) and the interaction of DNA with CD-TH inclusion complex were investigated by fluorescence and visible absorption spectrometry. TH with beta-CD formed a 1 : 1 inclusion complex with the stability constant of 527 L x mol(-1) (visible spectrometry)/444 L x mol(-1) (fluorescence) in the pH 7.2 PBS buffer solutions. The addition of DNA makes the absorbance of the inclusion complex decrease and the absorption spectrum shift toward long wavelengths. The fluorescence experiments indicated that the presence of DNA makes the emission peak of CD-TH shift toward short wavelengths and the fluorescence of inclusion complex quench, and the quenching constant was calculated to be 6.12 x 10(4) L x mol(-1) by Stern-Volmer method. All the data confirmed that CD-TH reacted with DNA in intercalative mode, and the binding numbers and the binding constant were estimated to be 1 and 3.47 X 10(4) L x mol(-1) by spectrophotometry.