Synthesis and Spectroscopic Calf Thymus Deoxyribonucleic Acid Binding Investigations of Luteolin – Zinc (II) Complex

Abstract

A luteolin–zinc (II) (lut–Zn) complex was synthesized by the reaction of luteolin with copper acetate in alcohol. The binding mode of lut–Zn with calf thymus deoxyribonucleic acid (ctDNA) was 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 proved the formation of lut–Zn–ctDNA complex. Binding constant (K_a) of lut–Zn–ctDNA complex was 4.29 × 10⁴ L mol^-1 (310K). Fluorophotometry measurements proved that the quenching mechanism of fluorescence of acridine orange (AO)–ctDNA by lut–Zn was static quenching. The thermodynamic parameters entropy change (∆S), enthalpy change (∆H) and Gibbs free energy (∆G) of binding reaction were calculated to be -20.87 J K^-1 mol ^-1, -3.39 × 10⁴ J mol^-1 and -2.74 × 10⁴ J mol^-1 at 310 K, respectively. Negative values of ΔH and ΔS indicated that there were hydrogen bonds and van der Waals forces in the binding reaction of lut–Zn with ctDNA. The fluorescence results and UV–visible absorption together revealed that the interaction mode of lut–Zn to ctDNA was an intercalation mode. This conclution was further confirmed by viscosity measurements.