Bioconjugates for tunable peptide fragmentation: free radical initiated peptide sequencing (FRIPS).

The free radical initiator Vazo 68 is coupled to a peptide and electrosprayed into an ion trap mass spectrometer. On collisional activation, the Vazo 68-peptide conjugate generates a free radical, which can be collisionally activated to cleave the peptide backbone. Mostly z-type fragments are formed, as in CAD of other radical peptides and ECD fragmentation. We present data for the Angiotensin II-Vazo 68 conjugate and discuss possible sites of H atom abstraction from the peptide. This experimental methodology for generating peptide fragments is a useful step toward the development of a completely gas-phase approach to protein sequencing.