Internal glucose residue loss in protonated O-diglycosyl flavonoids upon low-energy collision-induced dissociation.

The low-energy collision-induced dissociation of protonated flavonoid O-diglycosides, i.e., flavonoid O-rutinosides and O-neohesperidosides, containing different aglycone types has been studied. The results indicate that the unusual [M + H - 162]+ ion formed by internal glucose residue loss, which in a previous study was shown to be a rearrangement ion, is strongly dependent upon the aglycone type. For 7-O-diglycosides, the internal glucose loss is very pronounced for aglycones of the flavanone type, but is completely absent for aglycones of the flavone and flavonol types. Internal glucose residue loss was found to correspond to a minor fragmentation pathway for flavonol 3-O-diglycosides. A plausible mechanism is proposed based on proton mobilization from the aglycone to the disaccharidic part of the flavonoid O-diglycosides which is supported by theoretical calculations and model building.