A quantum chemical study on the reactivity of four licorice flavonoids scavenging ·OOCl3C

Abstract

Isoliquiritigenin, liquiritigen, uralenol, and neouralenol are four natural licorice flavonoid compounds extracted from licorice, which have the ability of scavenging free radicals. In this paper, the density functional theory (DFT) was used to study the microscopic reaction mechanism of the four kinds of licorice flavonoids respectively scavenging ·OOCl3C in vivo. At the level of M06-2X/6-311+G(d,p), the geometries of all stationary points for hydrogen atom transfer (HAT) and radical adduct formation (RAF) pathways were optimized. The thermodynamic parameters and kinetic parameters of each reaction pathway were obtained, and the potential energy surface information of each reaction pathway was obtained too. Using the continuum solvation model based on solute electron density (SMD), the influence of the solvation effect on the reaction was calculated. The main mechanisms and reactive sites for the capture of ·OOCl3C by four licorice flavonoids, liquiritigen, isoliquiritigenin, uralenol, and neouralenol, were determined. Research indicates liquiritigen captures ·OOCl3C by HAT mechanism. The HAT pathway on the B′ ring of liquiritigen is the main reactive site. Isoliquiritigenin captures ·OOCl3C in the body through HAT and RAF mechanism. The RAF pathway is the dominant reaction pathway. The C1 site on the carbon–carbon double bond linking the two benzene rings is the main reactive site. Uralenol and neouralenol capture ·OOCl3C by HAT mechanism. The main reactive site of uralenol is B6 site, and the main reactive site of neouralenol is B′ 2 site. By this study, the potential energy surface information difficult to capture by experimental research is obtained, which provides a reliable theoretical basis for the further screening of highly active natural free radical scavengers of flavonoids in licorice and provides the support for the improvement of the development and application technology of licorice.