Spectroscopic studies of the interactive model of methylene blue with DNA by means of β-cyclodextrin

The formation of the inclusion complex of methylene blue with beta-cyclodextrin is studied by spectroscopic and electrochemical methods and the binding constant of the inclusion complex is 4.5 x 10(3) 1 mol(-1). The interactive model of methylene blue with DNA has been investigated by means of the inclusion action of beta-cyclodextrin. Through the changes of absorption and fluorescence spectra, the intrinsic binding constant (k) of methylene blue with DNA and inclusion complex with DNA is obtained. Ln the case of 20 m mol l(-1) Tris buffer solution (pH 7.2), their values are 1.53 x 10(5) l mol(-1) and 9.98 x 10(4) l mol(-1), respectively. The experimental results suggest that the inclusion complex does not decompose when it interacts with DNA. The binding number (n) is 1 for both methylene blue and inclusion complex with DNA. According to the experimental results, it can be inferred that the interactive model of methylene blue with DNA is 'electrostatic binding'. This conclusion is able to explain the experimental phenomena clearly. (C) 1999 Elsevier Science B.V. All rights reserved.