study on the interaction between isatin-β-thiosemicarbazone and calf thymus dna by spectroscopic techniques

the interaction between isatin-β-thiosemicarbazone (ibt) and calf thymus dna (ct-dna) was investigated in physiological buffer (ph 7.4) using neutral red (nr) dye as a spectral probe by uv–vis absorption and fluorescence spectroscopy, as well as viscosity measurements. the ibt is stabilized by intercalation in the dna ( k [ibt –dna] =1.03×105 m−1), and displaces the nr dye from the nr–dna complex. the binding constants kf and number of binding sites (n≈1) of ibt with dna were obtained by fluorescence quenching method at different temperatures. furthermore, the enthalpy and entropy of the reaction between ibt and ct-dna showed that the reaction is enthalpy-favored and entropy-disfavored. the changes in the base stacking of ct-dna upon the binding of ibt are reflected in the circular dichroic (cd) spectral studies. the viscosity increase of ct-dna solution is another evidence to indicate that, ibt is able to be intercalated in the dna base pairs.