Studies on the interaction of apigenin with calf thymus DNA by spectroscopic methods

• Apigenin could insert into DNA base pairs to form a binary complex at physiological pH.
• The acting force between apigenin and DNA mainly included hydrophobic interactions.
• The stabilization of the ctDNA helix was increased in the presence of apigenin.
• The increase of ion strength has no significant effect to the binding of apigenin with DNA.
• The interaction between apigenin and ctDNA might occur via intercalative mode.

The interaction between apigenin and calf thymus deoxyribonucleic acid (ctDNA) in a pH 7.4 Tris–HCl buffer solution was investigated by UV–Vis spectroscopy, fluorescence spectroscopy, DNA melting techniques, and viscosity measurements. It was found that apigenin molecules could intercalate into the base pairs of DNA, forming a apigenin–DNA complex with a binding constant of K310K = 6.4 × 104 L mol−1. The thermodynamic parameters enthalpy change (ΔH), entropy change (ΔS) and Gibbs free energy (ΔG) were calculated to be 7.36 × 104 J mol−1, 329 J K−1 mol−1 and −2.84 × 104 J mol−1 at 310 K, respectively. Hydrophobic interaction was the predominant intermolecular force in stabilizing the apigenin–DNA complex. Thermal denaturation study suggested that the stabilization of the ctDNA helix was increased when the apigenin binding to ctDNA as indicated by the increase in thermal denaturation temperature of ctDNA at around 5.0 °C in the presence of apigenin. Spectroscopic techniques together with melting techniques and viscosity determination provided evidences of intercalation mode of binding for the interaction between apigenin and ctDNA.

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