Comparing the Affinities of Flavonoid Isomers with Protein by Fluorescence Spectroscopy

Abstract Dietary flavonoids can be detected in plasma as protein‐bound conjugates. Flavonoids–protein interaction is expected to modulate the bioavailability of flavonoids. In this work, the binding flavonoid isomers (galangin, baicalein, apigenin, and genistein; MW=270.25) and B‐ring hydroxylation flavonols (galangin, kaempferol, quercetin, and myricetin, which share the same structure on the A and C rings but have 0, 1, 2, and 3 moieties of ‐OH on the B‐ring, respectively) to protein were investigated by fluorescence quenching method. The apparent binding constants (K a ) of were flavonoid isomers determined as: flavones (106–107 L mol−1)>isoflavone≈flavonol (105 L mol−1). For B‐ring hydroxylation flavonols, the binding affinity increased with increasing number of hydroxyl groups on the B‐ring. The binding constants (K a ) were determined as follows: myricetin>quercetin>kaempferol>galangin.