The formation and fragmentation of flavonoid radical anions

Negative electrospray ionization of iron(III) salen complex of flavonoids, M, was used in conjunction with collision-induced dissociation (CID) to examine the formation and subsequent fragmentation reactions of their radical anions [M−2H]−. Sixteen different flavonoids were investigated from three different sub-groups (flavanone, flavone and flavanol). All formed the desired iron salen complex, [FeIII(salen)(M−2H)]−, and all but one of these complexes produced the radical anion upon CID. The CID fragmentation reactions of these radical anions, [M−2H]−, were compared to their even electron counterparts [M−H]−. Generally the former provided more structural information, with novel cross-ring cleavages of sugar(s) often being observed. Isomeric flavonoids can often be distinguished based on the differences in the fragmentation pathways of their radical anions.

Graphical abstractThe fragmentation of radical anions of flavonoids [M−2H]−, in comparison to fragmentation of their even electron counterparts [M−H]−, provides more structural information, with novel cross-ring cleavages of sugar(s) and the ability to distinguish between isomeric flavonoids.Figure optionsDownload full-size imageDownload high-quality image (35 K)Download as PowerPoint slideResearch highlights▶ CID of the [FeIII(salen)(M−2H)]− complex produces the flavonoid radical anion, [M−2H]−. ▶ Complexes incorporating a flavonoid containing a disaccharide, dissociation via the elimination of salen or fragmentation of the coordinated flavonoid competes with radical formation. ▶ Comparison of the CID spectra of the [M−2H]− radical anions with their corresponding even electron counterparts, [M−H]−, reveals that the radical anion provides a richer CID spectrum. ▶ CID of the radical anion may provide a means of distinguishing between isomeric flavonoids..