FOCUS: PEPTIDE FRAGMENTATION Dissociation of the N–C Bond and Competitive Formation

Dissociations at the N–C bond of tryptophan and tyrosine residues are the prevalent pathways in the fragmentations of radical cations of tripeptides that contain such as residues. This process involves a proton transfer from the -carbon of the tryptophan or tyrosine residue to the carbonyl oxygen of the amide group, followed by cleavage of the N–C bond, generating low-lying proton-bound dimers that dissociate to give each an ionic and a neutral product. Formation of the [zn – H] • or [cn 2H] ion is a competition between the two incipient fragments for the proton in a dissociating proton-bound dimer. (J Am Soc Mass Spectrom 2008, 19, 1799–1807) © 2008 Published by Elsevier Inc. on behalf of American Society for Mass Spectrometry