Time-resolved photodissociation of singly protonated peptides with an arginine at the N-terminus: a statistical interpretation.

Time-evolution of product ion signals in ultraviolet photodissociation (UV-PD) of singly protonated peptides with an arginine at the N-terminus was investigated by using a tandem time-of-flight mass spectrometer equipped with a cell floated at high voltage. Observation of different time-evolution patterns for different product ion types--an apparently nonstatistical behavior--could be explained within the statistical framework by invoking consecutive formation of some product ions and broad internal energy distributions for precursor ions. a(n) + 1 and b(n) ions were taken as the primary product ions from this type of peptide ions. Spectral characteristics in post-source decay, UV-PD, and collisionally activated dissociation at low and high kinetic energies could be explained via rough statistical calculation of rate constants. Specifically, the striking characteristics in high-energy CAD and UV-PD--dominance of a(n) and d(n) formed via a(n) + 1--were not due to the peculiarity of the excitation processes themselves, but due to quenching of the b(n) channels caused by the presence of arginine.