Toward the prediction of the activity of antioxidants: Experimental and theoretical study of the gas-phase acidities of flavonoids

  • Hugo F. P. Martins
  • J. Paulo Leal
  • M. Tereza Fernandez
  • Victor H. C. Lopes
  • M. Natália D. S. Cordeiro
Article

Abstract

The relative gas-phase acidities were determined for eight flavonoids, applying the kinetic method, by means of electrospray-ion trap mass spectrometry. The experimental acidity order, myricetin > luteolin > quercetin > (±)-taxifolin > kaempferol > apigenin > (+)-catechin > (±)-naringenin shows good agreement with the order obtained by theoretical calculations at the B3LYP/6-311 + G(2d,2p)//HF/6-31G(d) level. Moreover, these calculations provide the gas-phase acidities of the different OH groups for each flavonoid. The calculated acidity values (ΔacH), corresponding to the most favorable deprotonation, cover a narrow range, 314.82013;330.1 kcal/mol, but the experimental method is sensitive enough to differentiate the acidity of the various flavonoids. For all the flavones and the flavanol, catechin, the 4′-hydroxyl group is the most favored deprotonation site whereas for the flavanones studied, taxifolin and naringenin, the most acidic site is the 7-hydroxyl group. On the other hand, the 5-hydroxyl, in flavones and naringenin, and the 3-hydroxyl, in taxifolin and catechin, are always the less acidic positions. The acidity pattern observed for this family of compounds mainly depends on the following structural features: The ortho-catechol group, the 2,3 double bond and the 4-keto group.

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Copyright information

© American Society for Mass Spectrometry 2004

Authors and Affiliations

  • Hugo F. P. Martins
    • 1
  • J. Paulo Leal
    • 1
    • 2
  • M. Tereza Fernandez
    • 1
  • Victor H. C. Lopes
    • 3
  • M. Natália D. S. Cordeiro
    • 3
  1. 1.Departamento de Química e Bioquímica, Faculdade de CiênciasUniversidade de LisboaLisboaPortugal
  2. 2.Departamento de QuímicaInstituto Tecnológico e NuclearSacavémPortugal
  3. 3.CEQUP/Faculdade de CiênciasUniversidade do PortoPortoPortugal

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