TDDFT prediction of UV–vis absorption and emission spectra of tocopherols in different media

• Published in: Journal of molecular modeling Vol. 21; no. 6; p. 158
• Main Authors: Bakhouche, Kahina, Dhaouadi, Zoubeida, Lahmar, Souad, Hammoutène, Dalila
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01-06-2015
• Subjects: Characterization and Evaluation of Materials; Chemistry; Chemistry and Materials Science; Computer Appl. in Life Sciences; Computer Applications in Chemistry; Models, Theoretical; Molecular Medicine; Original Paper; Solvents; Spectrophotometry, Ultraviolet - methods; Theoretical and Computational Chemistry; Tocopherols - chemistry; Solvent effect; Tocopherols; Absorption and emission wavelength; π→π transition; TDDFT
• ISSN: 1610-2940; 0948-5023
• DOI: 10.1007/s00894-015-2706-1

We use the TDDFT/PBE0/6-31+G* method to determine the electronic absorption and emission energies, in different media, of the four forms of tocopherol, which differ by the number and the position of methyl groups on the chromanol. Geometries of the ground state S
0
and the first singlet excited state S
1
were optimized in the gas phase, and various solvents. The solvent effect is evaluated using an implicit solvation model (IEF-PCM). Our results are compared to the experimental ones obtained for the vitamin E content in several vegetable oils. For all forms of tocopherols, the HOMO–LUMO first vertical excitation is a π–π* transition. Gas phase and non-polar solvents (benzene and toluene) give higher absorption wavelengths than polar solvents (acetone, ethanol, methanol, DMSO, and water); this can be interpreted by a coplanarity between the O-H group and the chroman, allowing a better electronic resonance of the oxygen lone pairs and the aromatic ring, and therefore giving an important absorption wavelength, whereas the polar solvents give high emission wavelengths comparatively to gas phase and non-polar solvents. Fluorescence spectra permit the determination, the separation, and the identification of the four forms of tocopherols by a large difference in emission wavelength values.
Graphical Abstract
Scheme from process methodological to obtain the absorption and emission spectra for tocopherols