Study on the interaction between methylene violet and calf thymus DNA by molecular spectroscopy

The fluorescence and solid surface room temperature phosphorescence (SS-RTP) spectral properties of methylene violet (MV) were investigated. And the factors influencing the phosphorescence emission were discussed. The interaction of MV and ctDNA was studied by molecular spectroscopy. Deduced from the fluorescence, SS-RTP and resonance light-scattering spectral data, there were two different interaction mechanism involved in the whole interaction process depending on the R-values(R: the molar ratio of MV to ctDNA) at pH = 7.56. The value R = 1.9 is the turning point; when R < 1.9, enhanced resonance light-scattering (RLS) was observed, which indicated long range assembly of MV on the ctDNA molecular surface. In this process long-range assembly is the main binding mode. The second process occurs when R > 1.9, where MV intercalated into the ctDNA helix, the intercalative binding is predominant, supported by fluorescence polarization experiment and potassium iodide quenching study. Based on the fluorescence quenched experiment of MV by ct DNA, the binding constant of MV binding to ctDNA was 1 × 106 L/mol, the binding site was 1.0.