Spectroscopic studies on the interaction between carbaryl and calf thymus DNA with the use of ethidium bromide as a fluorescence probe

The interaction between carbaryl and calf thymus DNA (ctDNA) was investigated under simulated physiological conditions (Tris–HCl buffer of pH 7.4) using ethidium bromide (EB) dye as a probe by UV–vis absorption, fluorescence and circular dichroism (CD) spectroscopy, as well as DNA melting studies and viscosity measurements. It can be concluded that carbaryl molecules could intercalate into the base pairs of DNA as evidenced by hyperchromic effect of absorption spectra, decreases in iodide fluorescence quenching effect, induced CD spectral changes, and significant increases in melting temperature and relative viscosity of DNA. The binding constants and thermodynamic parameters of carbaryl with DNA were obtained by the fluorescence quenching method. Furthermore, a chemometrics approach, parallel factor analysis (PARAFAC), was applied to resolve the measured three-way synchronous fluorescence spectral data matrix of the competitive interaction between carbaryl and EB with DNA, and the results provided simultaneously the concentration profiles and corresponding pure spectra for three reaction components (carbaryl, EB and DNA–EB complex) of the kinetic system at equilibrium. This PARAFAC analysis demonstrated the intercalation of carbaryl to the DNA helix by substituting for EB in the DNA–EB complex.