The coordination mode of hesperidin with Zinc(II) was investigated by combined methods of Complete Neglect of Differential Overlap calculation (CNDO), continual variations of equimolar solutions, mole ratios, and IR spectra analysis. The results indicated that Zinc(II) ions and hesperidin form an ocher-yellow complex with an absorption maximum at 369 nm. Hesperidin can form a complex of 4:1 with Zinc(II) through its 4-carbonyl and 5-hydroxyl group. The relative stability constant of the complex, log β1 ranged from 2.79 at pH=8.50 to 4.48 at pH=10.50. The conditions for the spectrophotometric determination of hesperidin, by means of the complex formation reaction, were investigated. It was found that hesperidin can be determined in the concentration range from 2.00×10-4 to 2.00×10-3 mol/L. The application of the coordination reaction for determining the concentration of hesperidin in orange juice is demonstrated. All investigations were carried out in 70% methanol solutions at room temperature (28oC), constant values of pH (10.50), and ionic strength (0.01).

Boru Chen and Siming Zhu