Electrospray ionization tandem mass spectrometry fragmentation of protonated flavone and flavonol aglycones: a re‐examination

Abstract

Flavonoids are important phytochemicals which have been intensively studied in the last decades in view of their antioxidant activity, which is of particular importance in the case of flavones and flavonols, that differ in a single 3-OH group. Mass spectrometry has been used to elucidate the structures of many types of flavonoids and their metabolites. The work we present here is focused on the electrospray ionization tandem mass spectrometry (ESI-MS/MS) analysis of flavone and flavonols aglycones. Their fragmentation mechanisms in the positive ion mode are described and compared with previously reported mechanisms. We analyzed flavonoid derivatives produced by reaction of the flavonoids with chemically synthesized hypohalous acids (HOCl, HOBr and HOI) and peroxynitrite, reactive species involved in the inflammatory response. All the proposed pathways have been analyzed using computational chemistry methods in order to seek for possible variations and establish the most plausible ones. We observed that the losses of one and two CO molecules can be useful in terms of antioxidant activity prediction. Losses of one and two C(2)H(2)O groups are also informative in terms of structure and activity predictions. The retro-Diels-Alder fragmentations, and subsequent neutral losses, were reviewed and, according to our calculations, the most plausible structures for the product ions were established. These fingerprints will be of great value for differentiating flavonoids from other compounds in complex biological mixtures and for a thorough structural identification of flavonoid aglycones and their in vivo metabolites.

An integrated high resolution mass spectrometric and informatics approach for the rapid identification of phenolics in plant extract

“…Hence, the similarity of UV and MS data did not allow to distinguish between the two isomers. Quercetin was finally assigned by a manual examination of the MS/MS spectrum, revealing a diagnostic product ion at m/z 219 [M+H-2C 2 H 2 O] + which was reported to be characteristic for quercetin only [20].…”

Electrospray ionization mass spectrometric analysis of newly synthesized α,β‐unsaturated γ‐lactones fused to sugars

“…The product ions of the sodiated molecules (m/z values and relative abundances) are presented in [46][47][48][49][50][51][52] In order to determine the most probable protonation sites, the partial atomic charges for the neutral molecules, presented in Table 3, were computed using the Hamiltonean PM6 27 implemented in MOPAC2009. 28 The use of 20 According to the data presented in Table 3, for compounds 1, 2 and 3, the most probable protonation site will be the hydroxyl group linked to the C 4 atom of the sugar ring, whereas for compounds 4 and 5 the most probable site will be the sugar ring oxygen.…”

“…These methodologies have been successfully employed in mass spectrometry studies, for example in the fragmentation study of flavonoids and flavonoid diglycosides using both ESI-MS and semi-empirical calculations. 20,21 and in the study of fullerene derivatives. 26 The fragmentation pathways are greatly influenced by the type of the precursor…”

Strategies in the Analysis of Plant Flavonoids

“…Those authors also reported that, although MALDI-MS allows the detection of slightly higher DPs than ESI-MS, better discrimination of the lower molecular ions (DP < 15) is observed in ESI-MS. Structural identification of flavonoids based on MS analysis has been object of many good articles that can be consulted for more detailed information (Ma et al, 1997(Ma et al, , 2001Justesen, 2000;Stobiecki, 2000;Cuyckens and Claeys, 2004;Abad-Garcia et al, 2009;Justino, Borges, and Florencio, 2009;Vukics and Guttman, 2010).…”