Interpretation of the IR and Raman spectra of morin by density functional theory and comparative analysis

Density functional theory calculations, with M05-2X functional and 6-311++G(d,p) basis set implemented in the Gaussian 09 package, are performed with the aim to support molecular structure and spectroscopic characteristics of morin, a bioflavonoid molecule known for its antiproliferative, antitumor, and anti-inflammatory effects. Detailed vibrational spectral analysis and the assignments of the bands, done on the best-fit basis comparison of the experimentally obtained and theoretically calculated IR and Raman spectra, match quite well indicating DFT calculations as very accurate source of normal mode assignments. The assignment of the most prominent normal modes of morin is qualitatively verified through comparative spectral analysis with quercetin, a structurally isomeric molecule of morin which differs only by the substitution pattern of the B ring. Performed comparative analysis reflects quite accurately all the structural differences between the investigated molecules additionally proving the applied theoretical method.

Graphical abstractTheoretically predicted vibrational wavenumbers of morin were compared with available IR and Raman experimental data. Spectral assignments done on the basis of the best-fit comparison of the experimentally obtained and theoretically calculated spectra match quite well indicating DFT calculations as very accurate source of normal mode assignments.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► The geometrical parameters of morin are calculated by using M05-2X/6-311++G(d,p) level of theory. ► Interpretation of the IR and Raman spectra of morin by DFT is performed. ► Description of the largest vibrational contributions to the normal modes is given. ► The hyperconjugative interaction or charge transfer are investigated by NBO analysis. ► The assignment of the bands is proposed on the basis of fundamentals.