Dissociation lifetime studies of doubly deprotonated angiotensin peptides.

The doubly deprotonated [Asn,Val5] angiopeptide, in the gas phase, was irradiated with 266 nm photons. The time of flight (TOF) of the products formed following photoabsorption, namely, the monoanion and neutral fragments, was recorded with submicrosecond time resolution. Monte Carlo simulations of the TOF of the neutral fragments indicate that the dissociation occurs faster than 100 ns. A similar experiment performed on the Val5 angiopeptide also yielded a dissociation time shorter than 100 ns. We suggest dissociation mechanisms that account for the different number of photons required for the release of CO2.