Binding interactions of Toluidine Blue O with escherichia coli DNA: formation of bridged structure

Abstract

The interaction(s) of Toluidine Blue O (TBO) with DNA was investigated using absorption and emission spectral methods. The binding of TBO with DNA was understood from the observed hypochromism in the absorption spectra and decrease in the emission intensity of TBO. From the absorption and emission spectral data, two binding constants were estimated for the binding of TBO with DNA. Based on the binding constant values both intercalative and electrostatic interactions of TBO with DNA were suggested. The TBO-DNA binding constant values reveal that the electrostatic interaction of TBO with DNA is weaker than the intercalative interaction. The emission quenching and salt effect studies showed that the TBO was partially intercalated with DNA. The two modes of binding between TBO and DNA may lead to the formation of bridging of a pair of DNA duplexes by TBO molecule. The electrostatic interaction is more important for the formation of the bridged structure of TBO with DNA. This was verified by studying the interaction of an anionic dye, Eosin Y (EY).