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. an + 1 and bn 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 an and dn formed via an + 1—were not due to the peculiarity of the excitation processes themselves, but due to quenching of the bn channels caused by the presence of arginine