Enhanced antioxidant activity, antibacterial activity and hypoglycemic effect of luteolin by complexation with manganese(II) and its inhibition kinetics on xanthine oxidase

The present study aims to improve the biological activities of luteolin by complexation with manganese(II). UV-visible spectroscopy, infrared spectroscopy, thermogravimetric analysis and elemental analysis were adopted to assess the relevant interaction of luteolin and manganese(II) ions and the chelation sites. The antioxidant activity, hypoglycemic effect and antimicrobial activity of luteolin–manganese(II) complex with respect to its parent luteolin and the inhibition effect of which on xanthine oxidase were investigated and compared. The spectroscopic data indicated that luteolin reacts with manganese(II) cations through the chelation sites of 5-hydroxy and 4-carbonyl in two luteolin molecules. Antioxidant and antibacterial activity were enhanced after the complexation of manganese(II) cations with luteolin. An inhibition effect assay found that luteolin and luteolin–manganese(II) complex reversibly inhibited xanthine oxidase in a competitive manner. Luteolin–manganese(II) complex had a more remarkable hypoglycemic effect than luteolin by increasing the glucose consumption in liver tissue.