Concentration-Dependent Fluorescence Emission of Quercetin

Abstract

Quercetin (Q) is an important antioxidant with high bioactivity and the potential of being used as SARS-CoV-2 inhibitor. The fluorescence (FL) emission from Q solutions made with different polar and non-polar solvents (methanol, acetone, and chloroform) was measured and compared with the FL emission from Q powder and from Q crystals. In the FL spectra of the solutions with high Q concentration, as well as in the spectra of Q in solid state, two features, at 615 nm and 670 nm, were observed. As the solution concentration decreases, the intensity of those peaks decreases and a peak at 505 nm arises. The FL emission of low concentration solutions displayed only that peak. Calculations for the Q molecule in each solvent, performed using time-dependent density functional theory (TDDFT), show that the emission at 505 nm is associated with the excited state intramolecular proton transfer (ESIPT) of the –OH3 group proton. Our calculations also show that the feature at 615 nm, which is observed in solid state Q and also in the emission of the high concentrated solutions, is related to the –OH5 proton transfer.

Experimental and Theoretical Study of Fluorescent Properties of Morin

“…To study FL properties of the M solid state, we used two different excitation wavelengths: 405 nm and 532 nm. At room temperature, the FL spectra obtained on M crystals and MH powder are very similar, reaching their maximum at approximately 615 nm; they are also similar to the spectra of Q shown in reference [ 16 ]. To our surprise, the FL spectrum at 10 K does not show significant changes.…”

“…On the other hand, its dissolution in water is very low. The same was observed on Q solutions [ 16 ].…”

“…In Figure 2 , M crystal images obtained by scanning electron microscope (SEM) are shown. M crystals are needle-like, sharp crystals, very similar to that of Q obtained by the same method and studied in our previous work [ 16 ]. The FL spectra of the crystals are shown in Figure 3 , and are compared with the spectra obtained on MH powder.…”

“…The present work is closely linked to our previous study of the dependence of the FL emission peak spectral position on the Q concentration in the solution [ 16 ]. In that paper, we studied how the FL emission of Q molecule changed with the variation of the concentration of solutions in different types of solvents.…”

Palladium Nanoparticle-Modified Carbon Spheres @ Molybdenum Disulfide Core-Shell Composite for Electrochemically Detecting Quercetin

“…Moreover, it also exerts a pro-apoptotic effect on cancer cells and blocks the growth of tumor cells [6]. Therefore, the accurate determination of QR in biochemistry and natural pharmaceutical chemistry has attracted increasing interest [7]. The typical methods for analyzing QR are high-performance liquid chromatography with ultraviolet detection [8], tandem mass spectrometry [9], and capillary electrophoresis [10].…”