THE EFFECT OF CHARGE-STATE AND THE LOCALIZATION OF CHARGE ON THE COLLISION-INDUCED DISSOCIATION OF PEPTIDE IONS

The effect that charge state has on the collision-induced dissociation (CID) of peptide ions is examined in detail for several representativ e peptides under high-energy collision conditions. The CID spectra of singly and doubly charged precursor ions (generated by fast-atom bomba rdment and electrospray ionization, respectively) are compared for sev eral peptides with similar primary structure. It is shown that for pep tides that contain highly basic amino acids, the dissociation of doubl y charged ions is strongly influenced by the position of these residue s within the peptide and the general observations reported concerning the dissociation of singly charged ions can be extended to precursors with higher charge states. Based on the dissociation behavior of the d oubly charged ions of these peptides, it is demonstrated that two char ges can reside in close proximity in the precursor ions, overcoming po ssible repulsion effects, when favored by a high concentration of basi c sites. Ln addition, this work illustrates that in the case of doubly charged ions, the charge state of some fragment ions can be determine d directly from the mass to-charge ratio assignments of the CID spectr um.