Electron-capture induced dissociation of doubly charged dipeptides: on the neutral losses and N-Cα bond cleavages.

Electron capture by doubly charged peptide cations leads to neutral losses in addition to N-C(α) bond cleavages that give c and z fragments. In this work we discuss the influence of amino acid sequence on hydrogen versus ammonia loss and the propensity for subsequent partial side-chain cleavage after ammonia loss to give w fragment ions. Experiments were done on two series of doubly protonated dipeptides, [XK+2H](2+) and [XR+2H](2+), where X is one of the twenty common amino acid residues, excluding aspartic acid (D), and K and R are lysine and arginine, respectively.

Electron capture induced dissociation of dipeptide dications: where does the charge go?

Charge partitioning after electron capture induced dissociation of dipeptide dications is determined by proton mobility in the evanescent ion-molecule complex as the remaining proton has enough time to choose the fragment with the highest proton affinity.

On the charge partitioning between c and z fragments formed after electron-capture induced dissociation of charge-tagged Lys-Lys and Ala-Lys dipeptide dications.

Here we report on the charge partition between c and z fragments formed after femtosecond collisional electron-transfer from Cs atoms to charge-tagged peptide dications. Peptides chosen for study were Ala-Lys (AK) and Lys-Lys (KK) where one or both of the lysine epsilon-amino groups were trimethylated to provide one or two fixed charges. For peptides with only one charge tag, the other charge was obtained by protonation of an amino group.