Intercalation of diafenthiuron insecticide with calf thymus DNA: spectroscopic and molecular dynamics analysis

A series of biophysical experiments like UV-Vis, fluorescence, circular dichroism (CD), competitive displacement assays, voltammetric studies, viscosity measurements and denaturation effect and metadynamics simulation studies were performed to establish the mode of binding of diafenthiuron (DF) insecticide with calf thymus DNA (CT-DNA). Analysis of absorption and fluorescence spectra in Tris-HCl buffer of pH 7.4 indicates the formation of a complex between DF and CT-DNA and the binding constant of which is in the order of 10(4) M-1. Competitive displacement assay with ethidium bromide (EB) and Hoechst 33258 suggests that the most probable mode of binding of DF with CT-DNA may be via intercalation mode. The results of other experiments such as CD spectral studies, viscosity measurements and the effect of denaturation agent urea support the intercalation of DF with CT-DNA. Thermodynamic parameters (Delta H-o, Delta S-o and Delta G(o)) reveal that hydrogen bonds (H-bonds) or van der Waals (vdW) force is the main binding force in the spontaneous interaction between DF and CT-DNA. Molecular dynamics (MD) simulation studies confirmed the intercalation of DF into the base pairs of CT-DNA. Communicated by Ramaswamy H. Sarma