Spectroscopic characterization on the binding of interaction methylene blue with calf thymus DNA

Abstract

The calf thymus deoxyribonucleic acid (ct-DNA) binding properties of methylene blue (MB) including binding constant and thermodynamic parameter have been systematically studied by UV-vis absorption and fluorescence spectroscopy. The binding constant and stoichiometry were determined by analysis of optical absorption spectra of the MB dye at various ct-DNA concentrations using SQUAD software. The binding of MB to ct-DNA is quite strong as indicated by remarkable hypochromicity, red shift and equilibrium binding constant (K_b). Van't Hoff plot of 1/T versus ln K_b suggests that the MB dye binds exothermically to ct-DNA which is characterized by large negative enthalpy and entropy changes. The static mode of fluorescence quenching of MB by ct-DNA indicates the formation of a ground-state complex. The results showed that the MB molecule could intercalate into the double helix of the DNA.