Ion-Induced Dipole Interactions and Fragmentation Times: Cα-Cβ Chromophore Bond Dissociation Channel.

The fragmentation times corresponding to the loss of the chromophore (C alpha-C beta bond dissociation channel) after photoexcitation at 263 nm have been investigated for several small peptides containing tryptophan or tyrosine. For tryptophan-containing peptides, the aromatic chromophore is lost as an ionic fragment (m/z 130), and the fragmentation time increases with the mass of the neutral fragment. In contrast, for tyrosine-containing peptides the aromatic chromophore is always lost as a neutral fragment (mass = 107 amu) and the fragmentation time is found to be fast (<20 ns). These different behaviors are explained by the role of the postfragmentation interaction in the complex formed after the C alpha-C beta bond cleavage.