Density functional computations of the energetic and spectroscopic parameters of quercetin and its radicals in the gas phase and in solvent

Università della Calabria, Rende, Calabria, Italy
Theoretical Chemistry Accounts (Impact Factor: 2.23). 02/2004; 111(2):210-216. DOI: 10.1007/s00214-003-0544-1


Quercetin and its radicals were investigated at the B3LYP density functional level with the aim of determining the energetic and spectroscopic parameters and the factors that influence their antioxidant activity in the gas phase and in aqueous solution. The results indicated that the antioxidant ability of quercetin is mainly due to the orthodiphenolic moiety but also to the presence of the C=C double bond of the pyrone ring. Differences in the stability order of the isomers of quercetins radicals were found in going from vacuum to solvent. Hyperfine coupling constants were computed to help the interpretation of the intricate ESR spectrum of quercetin.


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    • "For quercetin, and, therefore, compound Q, there are a number of different conformers that can be considered [16, 54, 55] . The two most important parameters are the dihedral angle relating the orientation of ring B to ring C (δ = δ O 10 −C 2 −C 1 −C 2 ) and the possible hydrogen-bonding between 3 -ArOH and 4 -ArOH. "
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    • "Among the different possible stoichiometries that metal ions–aglycones complexes could exhibit, we have chosen to study those having the 1:2 ratio between cation and ligand. Despite there is not experimental indication about the ligand/metal ion combination ratio for this particular case, our choice was based on the fact that literature on similar subjects [29,35] suggests a predominance of complexes having the 2:1 ligand–metal ion stoichiometry with respect to those with 1:1 one. On the other hand, the structural features of daidzein are not those of a chelating agent being a monodentate ligand. "
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    • "Ultimately, we observed the following antioxidant order 3 > 6 > 7 > 4 > 5 % 2, whereas the reference experimental results indicated the order 3 > 4 > 6 % 5 > 7 % 2. The results obtained suggest that the most important factors in determining the scavenging ability of the examined molecules are, in decreasing order, the mutual position of the hydroxyl groups (the presence of catechol rings), their number and lastly the linkage between the 2 0 and 6 carbon atoms. On the basis of our previous experience in the study of polyphenolic systems (Iuga et al., 2012; Leopoldini, Chiodo, Russo, & Toscano, 2011; Leopoldini et al., 2004a Leopoldini et al., , 2004b Leopoldini et al., , 2006), we believe that our findings should be taken with confidence. On the other hand, the disagreement with respect to the experimental data could be due to the fact that the evaluation of the scavenging activity of phenanthrenes is referred to the reaction with the free radical (2,2-diphenyl-1-picrylhydrazyl), whereas our results are more general and do not take into account the possible differences due to a particular radical counterpart. "
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