Product ion yields in postsource decay and time-resolved photodissociation at 193 and 266 nm were measured for some peptide ions with lysine ([KF6 + H]+, [F6K + H]+, and [F3KF3 + H]+) formed by matrix-assisted laser desorption ionization. The critical energy (E0) and entropy (DeltaS(double dagger)) were determined by RRKM fitting of the data. The results were similar to those found previously for peptide ions with histidine. To summarize, the presence of a basic residue, histidine or lysine, inside a peptide ion retarded its dissociation by lowering DeltaS(double dagger). On the basis of highly negative DeltaS(double dagger), presence of intramolecular interaction involving a basic group in the transition structure was proposed.
Copyright 2009 John Wiley & Sons, Ltd.