Study of fluorescence quenching mechanism between quercetin and tyrosine-H2O2-enzyme catalyzed product

Because of catalysis of horseradish peroxidase, the tyrosine reacted with H2O2 to form the product S which was a strong fluorescence substance. To the product S, the quercetin was acted as a quencher. The fluorescence quenching mechanism was studied by the measurement of fluorescence lifetime and based on the Stern–Volmer plot. The reaction mechanism, which was the static quenching process between quercetin and product S, was studied. The binding constant, K = 4.03 × 105 L mol−1 and the number of binding sites n = 1.09, were obtained against this reaction. The thermodynamic parameters were estimated. The data, ΔH = −75.68 kJ mol−1, ΔS = −147.9 J K−1 mol−1 and ΔG = −29.17 kJ mol−1 showed that the reaction was spontaneous and exothermic. What is more, both ΔH and ΔS were negative values indicated that van der Waals interaction and hydrogen bonding were the predominant intermolecular forces between quercetin and product S.