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

Abstract

The detection and analysis of flavonoids by Raman spectroscopy are of interest in many fields, including medicinal chemistry, food science, and astrobiology. Spectral interpretation would benefit from better identification of the fingerprint vibrational peaks of different flavonoids and how they are affected by intermolecular interactions. The Raman spectra of two flavonoids, flavone and quercetin, were investigated through comparisons between spectra recorded from pure powders and spectra calculated with time dependent density functional theory (TDDFT). For both flavone and quercetin, 17 peaks were assigned to specific molecular vibrations. Both flavonoids were found to have a split peak between 1250–1350 cm–1 that is not predicted by TDDFT calculations on isolated molecules. In each case, it is shown that the addition of hydrogen bonded molecules arranged based on crystal structures reproduces the split peaks. These peaks were due to a stretching vibration of the bond between benzopyrone and phenyl rings and represent a characteristic spectral feature of flavonoids. Spectra of pollen grains from Quercus virginiana were also recorded and exhibit several peaks that correspond to the quercetin spectrum.

A Raman spectral marker for the iso‐octyl chain structure of cholesterol

“…We have recently reported TDDFT calculated Raman spectra for anthraquinones and flavonoids and found good agreement with measured spectra since these fused‐ring structures are not subject to significant conformational variation 46,47 . These studies also showed distinct signatures of hydrogen bonding in specific bands of the spectrum.…”

“…45 We have recently reported TDDFT calculated Raman spectra for anthraquinones and flavonoids and found good agreement with measured spectra since these fused-ring structures are not subject to significant conformational variation. 46,47 These studies also showed distinct signatures of hydrogen bonding in specific bands of the spectrum. Here we investigate cholesterol through comparisons of TDDFT calculated Raman spectra to measurements on microcrystalline powder and solution phase lipid vesicles.…”