On the collision-activated fragmentation of proferrioxamines: Evidence for a succinimide-mediated mechanism.

The fragmentation mechanism of acyclic proferrioxamines has been studied by tandem mass spectrometry in a triple stage quadrupole mass analyzer by using activation in the collision cell as well as in the high pressure region prior to the first mass analyzer. The data suggest that proferrioxamines fragment preferentially at the hydroxamate bonds via cyclic rearrangement to succinimide derivatives. This pattern was observed most clearly for the peracetyl derivatives, in which the influence of terminal functional groups was masked. Free amino or carboxylic acid functions may modify this basic fragmentation pattern. Using hydrogen-deuterium exchange, we also were able to show that the hydrogen atoms that are "recruited" in the formation of ammonium ions are "acidic" ones from elsewhere in the molecule or the matrix. At the same time, this rules out that they originate from "activated" methylene groups, as previously proposed.