Synthesis and spectroscopic calf thymus deoxyribonucleic acid binding investigations of luteolin – zinc(II) complex

Abstract

A luteolin–zinc(II) (lut–Zn) complex has been synthesized by the reaction of luteolin with copper acetate in alcohol. The binding mode of lut–Zn with calf thymus deoxyribonucleic acid (ctDNA) is studied by different spectroscopic methods in pH 7.4 tris(hydroxymethyl)aminomethane–HCl (Tris–HCl) buffer solution. Ultraviolet (UV)–visible absorption spectrophotometry and fluorescence spectroscopy as well as viscosity measurements have proved the formation of lut–Zn–ctDNA complex. Binding constant (K_a) of lut–Zn–ctDNA complex is 4.29 × 10⁴ L mol^-1 (310 K). Fluorophotometry measurements has proved that the quenching mechanism of fluorescence of acridine orange (AO)–ctDNA by lut–Zn is static quenching. The thermodynamic parameters entropy change (ΔS), enthalpy change (ΔH) and Gibbs free energy (ΔG) of binding reaction are calculated to be -20.87 J K^-1 mol^-1, -3.39 × 10⁴J mol^-1and -2.74 × 10⁴ J mol^-1 at 310 K, respectively. Negative values of ΔH and ΔS have indicated that there are hydrogen bonds and van der Waals forces in the binding reaction of lut–Zn with ctDNA. The fluorescence results and UV–visible absorption together have revealed that the interaction mode of lut–Zn to ctDNA is an intercalation mode. This conclusion is further confirmed by viscosity measurements.