Vibrational spectra of quercetin and their interpretation with quantum-mechanical density-functional method

Abstract

Experimental vibrational (Raman and IR-absorption) spectra are obtained for microcrystalline powder of quercetin in the spectral range of 400−1800 cm −1 at the room temperature. Optimized geometries of two stable isomers of quercetin molecule are calculated with a density-functional method at the level CAM B3LYP/6-311++G(d,p). The isomers have an almost planar frame structure and differ by mirror orientations of one of the rings with respect to the other rings. Vibrational spectra of the isomers are calculated in harmonic approximation at the same level of theory. The scaling factors determined experimentally for each of the two isomers have been used when comparing the calculated and experimental data. The vibrational spectra are interpreted in the whole frequency range under test. Good correlation of the experimental and calculated vibrational spectra is obtained.

The Raman Active Vibrations of Flavone and Quercetin: The Impact of Conformers and Hydrogen Bonding on Fingerprint Modes

“…It can therefore be used to study molecules in their natural environment and can do so at high spatial resolution when coupled to optical, scanned probe, and electron microscopes. − Even single molecule spectra can be detected when the Raman scattering is enhanced by metal nanoparticle antennas. , DFT calculations can help identify the complex fingerprint vibrations of large molecules . Both Raman scattering and DFT have been applied to detect flavonoids and to help characterize the structure and stability of their microcrystalline powders. ,− Here, we use time dependent density functional theory (TDDFT) to identify Raman active vibrational modes of flavone and quercetin and to investigate the significant influence conformational variations and hydrogen bonding have on their spectra. Finally, we compare these results to Raman spectra of pollen grains known to contain flavonoids.…”