Study of interaction between kaempferol–Eu3+ complex and DNA with the use of the Neutral Red dye as a fluorescence probe

The interaction between kaempferol–Eu3+ complex and calf thymus DNA was investigated in physiological buffer (pH 7.4) using the Neutral Red (NR) dye as a spectral probe by UV–vis absorption and fluorescence spectroscopy, as well as viscosity measurements and DNA melting techniques. The results indicated that kaempferol–Eu3+ complex can bind to DNA and the major binding mode is intercalative binding. The binding constants K and number of binding sites n of kaempferol–Eu3+ complex with DNA were obtained by fluorescence quenching method. The thermodynamic parameters (ΔHθ, ΔSθ and ΔGθ) were calculated from the fluorescence data measured at three different temperatures, which showed that the binding of kaempferol–Eu3+ complex to DNA was driven mainly by hydrophobic interaction. Furthermore, the alternative least squares (ALS) method was applied to resolve a complex two-way array of the absorption spectra data, which provided simultaneously the concentration information for the three reaction components, NR, kaempferol–Eu3+ and DNA–NR. This ALS analysis indicated that the intercalation of the kaempferol–Eu3+ complex into the DNA proceeds by exchanging with the NR probe.