Spectroscopic studies of cyanazine binding to calf thymus DNA with the use of ethidium bromide as a probe

The interaction between cyanazine and calf thymus DNA (ctDNA) in physiological buffer (pH 7.4) was investigated with the use of ethidium bromide (EB) as a spectral probe by UV–vis absorption, fluorescence, circular dichroism (CD) and Fourier transform infrared (FT-IR) spectroscopy, as well as viscosity measurements. The results revealed that intercalation binding should be the interaction mode of cyanazine to ctDNA and the binding constant was obtained to be 2.65 × 104 L mol−1 at 298 K. Analysis of the FT-IR spectra suggested that cyanazine mainly bound to guanine and cytosine of ctDNA bases and led to ctDNA duplex aggregation at higher cyanazine concentrations. The thermodynamic parameters, enthalpy change (ΔH°) and entropy change (ΔS°) suggested that hydrophobic interactions and hydrogen bonds played a predominant role in the binding of cyanazine to ctDNA. Furthermore, a chemometrics approach, the alternate least squares (ALS) algorithm, was applied to resolve the measured absorption spectral data array of the competitive reaction between cyanazine and EB with ctDNA, and the results provided simultaneously the concentration information and corresponding pure spectra for the three reaction components, cyanazine, EB and ctDNA–EB. The results obtained from the ALS analysis indicated that cyanazine intercalated into ctDNA by substituting for EB in the ctDNA–EB complex.