Genistein Binding to Copper(II)-Solvent Dependence and Effects on Radical Scavenging.

Jing Yang,Hao-Yu Liu,Jian-Ping Zhang,Yi Xu,Rui-Min Han,Leif Skibsted

doi:10.3390/molecules22101757

Abstract

Genistein, but not daidzein, binds to copper(II) with a 1:2 stoichiometry in ethanol and with a 1:1 stoichiometry in methanol, indicating chelation by the 5-phenol and the 4-keto group of the isoflavonoid as demonstrated by the Jobs method and UV-visible absorption spectroscopy. In ethanol, the stability constants had the value 1.12 × 1011 L2∙mol−2 for the 1:2 complex and in methanol 6.0 × 105 L∙mol−1 for the 1:1 complex at 25 °C. Binding was not detected in water, as confirmed by an upper limit for the 1:1 stability constant of K = 5 mol−1 L as calculated from the difference in solvation free energy of copper(II) between methanol and the more polar water. Solvent molecules compete with genistein as demonstrated in methanol where binding stoichiometry changes from 1:2 to 1:1 compared to ethanol and methanol/chloroform (7/3, v/v). Genistein binding to copper(II) increases the scavenging rate of the stable, neutral 2,2-diphenyl-1-picrylhydrazyl radical by more than a factor of four, while only small effects were seen for the short-lived but more oxidizing β-carotene radical cation using laser flash photolysis. The increased efficiency of coordinated genistein is concluded to depend on kinetic rather than on thermodynamic factors, as confirmed by the small change in reduction potential of −0.016 V detected by cyclic voltammetry upon binding of genistein to copper(II) in methanol/chloroform solutions.

Highlights

Polyphenols are a diverse group of phytochemicals acting as UV-light absorbers and singlet oxygen quenchers, protecting plant tissue against photodamage, and acting as chelators of ions of copper, iron, and other transition metals, protecting plant cells against oxidative degradation [1].Among the plant phenols, the flavonoids are considered to be important micronutrients from fruit and vegetables
The spectral changes observed were assigned to coordination of genistein to methanol/chloroform (7/3, v/v) change upon additon of the isoflavonoid genistein, as may be copper(II)
The spectral changes observed were assigned to coordination of genistein absorption band with a maximum at 262 nm and an absorption shoulder occuring between 320–400 to copper(II)

Summary

Introduction

Polyphenols are a diverse group of phytochemicals acting as UV-light absorbers and singlet oxygen quenchers, protecting plant tissue against photodamage, and acting as chelators of ions of copper, iron, and other transition metals, protecting plant cells against oxidative degradation [1].Among the plant phenols, the flavonoids are considered to be important micronutrients from fruit and vegetables. Benefits to human health of fruit and vegetables has been assigned to the anti-inflammatory, antiatherosclerotic, and antimutagenic activities of flavonoids. These and other positive effects of a high intake of flavonoids from fruit and vegetables on human health have often been assigned to radical scavenging capabilities [1,2,3,4]. The detailed mechanism behind such antioxidative protection seems, unclear, as most flavonoids under some conditions act as prooxidants [5,6]. The balance between prooxidative and antioxidative properties of flavonoids seems to be related to the presence of ions of transition metals.

Methods

Results

Conclusion