Mechanisms of UV photodissociation of small protonated peptides.

Photofragmentation of protonated dipeptides by 263 nm photons is Investigated with,ill experimental technique based oil the detection in coincidence of the ionic and neutral fragments. With this method, it is possible to determine whether the fragmentation takes, place in one or several steps The timing of these steps call also be evaluated The interpretation of the various fragmentation pathways is tentatively developed along the same line IS that previously proposed for tryptophan The fragmentation call be explained by two types of mechanisms internal conversions and direct fragmentations triggered by the migration of the photoactive electron oil positive charged sties or oil oxygen sites