Binding of quercetin with human serum albumin: A critical spectroscopic study

Abstract

Flavonols are plant pigments that are ubiquitous in nature. Quercetin (3,3',4',5,7-pentahydroxyflavone) and other related plant flavonols have come into recent prominence because of their usefulness as anticancer, antitumor, anti-AIDS, and other important therapeutic activities of significant potency and low systemic toxicity. Quercetin is intrinsically weakly fluorescent in aqueous solution, showing an emission maximum at approximately 538 nm. Upon binding to human serum albumin (HSA), quercetin undergoes dramatic enhancement in its fluorescence emission intensity, along with the appearance of dual emission behavior, consisting of normal and excited-state proton transfer (ESPT) fluorescence. In addition, the occurrence of a third emitting species has been noted for the first time. This is attributed to a electronic ground-state complex formed in the protein environment. High values of the fluorescence anisotropy (r) are obtained in the presence of HSA for the ESPT tautomer (r = 0.18), as well as the complex species (r = 0.37) of quercetin, indicating that the precursor ground-state molecules for both these emitting species of quercetin molecules are located in the motionally constrained sites of HSA. The steady-state emission data suggest that quercetin binds to two distinct sites in HSA from which the emissions from the normal tautomer and complex species take place. The preliminary results of studies on emission decay kinetics are also reported herein. Studies by far-UV circular dichroism spectroscopy reveal that binding of quercetin induces no significant perturbation in the secondary structure of HSA.

A steady‐state and time‐resolved fluorescence, circular dichroism study on the binding of myricetin to bovine serum albumin

“…The 295 nm light excites tryptophan residues, while the 280 nm light excites both tryptophan and tyrosine residues. Comparison of quenching effects at 280 nm with 295 nm excitation can tell which intrinsic fluorophores are mainly quenched (15)(16)(17), thus the mechanism of interaction can be obtained. The comparison of fluorescence quenching effect on the BSA can be seen in Fig.…”

Study on the Interactions of Kaempferol and Quercetin with Intravenous Immunoglobulin by Fluorescence Quenching, Fourier Transformation Infrared Spectroscopy and Circular Dichroism Spectroscopy

“…1) and other related plant flavonols have come into recent prominence because of their usefulness as anticancer, antitumor, anti-AIDS, and other important therapeutic activities of significant potency and low systemic toxicity. [15][16][17][18] It is non-specific and reversible that many of these agents bind to serum proteins, and the binding affects their pharmacological and pharmacokinetic properties.…”

“…12) Therefore a study on the binding of 16,17) Furthermore, the interaction of IVIG with drugs in fact represents the behavior of IgG and it is of much more clinical use.…”

Spectroscopic Investigation on the Interaction of a Cyanine Dye with Serum Albumins

“…1 Considering their clinical and pharmaceutical importance, much attention has therefore been paid to investigating the complexation of albumins with a number of natural and synthetic ligands. [4][5][6] Among the reported compounds, cyanine dyes and their derivates attracted much attention due to their moderate fluorescence quantum yields and sensitivity to the environmental conditions such as temperature and viscosity. 7 Once binding with the biomolecules, the fluorescence quantum yield of the dyes was enhanced a lot because of the rotation hindrance.…”