A conformational study of hydroxyflavones by vibrational spectroscopy coupled to DFT calculations.

The conformational preferences of a series of hydroxyflavones were studied by Raman and FTIR spectroscopies, coupled to Density Functional Theory calculations. Special attention was paid to the effect of hydroxyl substitution, due to its importance on the biological activity of these compounds. Their conformational preferences were found to be determined mainly by the orientation of the hydroxylic groups at C(7) and within the catechol moiety, leading to the occurrence of distinct conformers in the solid state. A complete assignment of the experimental spectra was carried out for these molecules, in the light of their most stable conformers and the corresponding predicted vibrational pattern.

Dietary chromones as antioxidant agents--the structural variable.

This study reports an evaluation of the free radical scavenging ability of a series of chromone derivatives, in the light of their structural features and conformational behaviour. The 2,2-diphenyl-1-picrylhydrazyl radical (DPPH˙) test for the assessment of radical scavenging properties was applied, and the interpretation of the experimental results was assisted by ab initio theoretical approaches that allowed relevant parameters, such as the enthalpy of formation of the radical species, to be predicted. From the eighteen tested compounds, three-fisetin, luteolin and quercetin-are shown to act as effective antiradicals. Consistent structure-activity relationships (SARs) were established regarding the antioxidant role of this type of chromone-based system.

Chromone-3-carboxylic acid as a potential electron scavenger: a surface-enhanced Raman scattering study.

A SERS study of chromone 3-carboxylic acid adsorbed on silver colloids was undertaken, in order to assess the ability of this compound to accept electrons in charge transfer (CT) processes. Theoretical SERS intensities under photoinduced CT resonant conditions have been carried out for both the neutral and the deprotonated species allowing to conclude, by comparison with the experimental data, that the recorded SER corresponds to the anionic form of the acid linked to the metal. It was shown that the SERS-CT mechanism predominates for this particular compound, thus explaining the strong enhancement of the band at ca. 1600 cm(-1) assigned to the 8a ring stretching mode. The identification of CT processes is of the utmost importance for understanding the mechanism through which these benzopyranes may act as antioxidants.