On the efficiency of energy transfer in collisional activation of small peptides

We present a study of the efficiency of the internal excitation of small peptide ions upon multiple-collision activation with Ar and ion-surface interaction with self-assembled monolayers of fluorinated alkylthiol on gold. Internal energy distributions are extracted from RRKM modeling of collision energy-resolved fragmentation efficiency curves for protonated tri-, tetra-, and penta-alanine, and polyltetra-alanine. The efficiency of T-->V transfer in surface collisional activation decreases for larger peptides. This is readily rationalized by the corresponding decrease in the center-of-mass collisions energy. For all peptides except protonated dialanine, energy transfer upon multiple-collision activation is rather insensitive to the peptide size and composition. The average energy deposited into protonated dialanine is substantially lower than the excitation level achieved for other peptides. Master equation modeling revealed that energy-transfer efficiency in peptide collisions with Ar is the same for all peptides excluding (AA)H+. The results suggest that protonated dialanine has a more extended structure than larger peptides studied in this work. (C) 2002 American Institute of Physics.