Characteristics of photodissociation at 193 nm of singly protonated peptides generated by matrix-assisted laser desorption ionization (MALDI).

Photodissociation (PD) at 193 nm of various singly protonated peptides was investigated. These include peptides with an arginine residue at the C-terminus, N-terminus, at both termini, inside the chain, and those without an arginine residue. Monoisotopomeric selection was made for the precursor ions. Interference from the post-source decay (PSD) product signals was reduced as much as possible by using the deflection system (reported previously) and subtracting the remaining signals from the laser-on signals. The presence of an arginine residue and its position inside the peptide were found to significantly affect the PD spectra, as reported previously. Presence of a proline, aspartic acid, or glutamic acid residue hardly affected the PD spectral patterns. By comparing the PD spectra obtained at a few different wavelengths, it is concluded that the dissociation of the photoexcited ions occurs in their ground electronic states. Tentative explanations for the observed spectral correlations based on the statistical picture for the reactions are also presented.