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Molecules 2017, 22(10), 1757; doi:10.3390/molecules22101757

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

1
Department of Chemistry, Renmin University of China, No. 59, ZhongGuanCun Street, Beijing 100872, China
2
Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK-1058 Frederiksberg C, Denmark
*
Authors to whom correspondence should be addressed.
Received: 22 September 2017 / Accepted: 16 October 2017 / Published: 18 October 2017
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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. View Full-Text
Keywords: genistein; copper; metal chelate; antioxidant genistein; copper; metal chelate; antioxidant
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Yang, J.; Xu, Y.; Liu, H.-Y.; Han, R.-M.; Zhang, J.-P.; Skibsted, L.H. Genistein Binding to Copper(II)—Solvent Dependence and Effects on Radical Scavenging. Molecules 2017, 22, 1757.

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