Binding studies of the antidiabetic drug, metformin to calf thymus DNA using multispectroscopic methods

Interaction between antidiabetic drug, Metformin and calf thymus DNA (CT-DNA) in (50mM Tris-HCl) buffer were studied by UV-Visible absorption, fluorescence, CD spectroscopy and viscosity measurements. In fluorimetric studies, the enthalpy and entropy of the reaction between the drug and CT-DNA showed that the reaction is exothermic (ΔH=-35.4522 kJ mol(-1); ΔS=-49.9523 J mol(-1)K(-1)). The competitive binding studies showed that the drug could release Hoechst 33258 completely. The complex showed absorption hyperchromism in its UV-Vis spectrum with DNA. The calculated binding constant, K(b), obtained from UV-Vis absorption studies was 8.3×10(4)M(-1). Moreover, the changes in the CD spectra in the presence of the drug show stabilization of the right-handed B form of CT-DNA. Finally, viscosity measurements revealed that the binding of the complex with CT-DNA could be surface binding, mainly due to groove binding.