Comparative study of collision-induced and surface-induced dissociation. 2. Fragmentation of small alanine-containing peptides in FT-ICR MS

Multiple-collision activation (MCA-CID) and surface-induced dissociation (SID) of protonated trialanine, (AAA)H+; tetraalanine, (AAAA)H+, pentaalanine. (AAAAA)H+; and prolyltetraalanine, (PAAAA)H+ were studied using a 7 T Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). Fragmentation efficiency curves obtained using both techniques were compared by converting the SID collision energy into an effective' center-of-mass frame using an arbitrary neutral partner of mass, M-N. The best overlap between the SID and MCA-CID fragmentation efficiency curves was obtained using very similar values of M-N for all the peptides, indicating that all the protonated precursor ions were undergoing similar interaction with terminal chemical groups on the fluorinated self-assembled monolayer (SAM) surface. Collision energy resolved fragmentation efficiency curves obtained using both methods are very similar, and both methods of collisional activation result in a quasi-thermal population of ion internal energies. We suggest that normal-incidence ion-surface collisions with self-assembled monolayer surface involve interactions of the projectile ion with chemical groups on the surface with efficient transfer of impact energy into the surface and into the internal energy of the ion. This mechanism, except for time frame for the activation process, is analogous to the sequential gas phase collisional activation of these model peptides.