Jump to main content
Jump to site search

Volume 195, 2016
Previous Article Next Article

Unimolecular dissociation of peptides: statistical vs. non-statistical fragmentation mechanisms and time scales

Author affiliations

Abstract

In the present work we have investigated mechanisms of gas phase unimolecular dissociation of a relatively simple dipeptide, the di-proline anion, by means of chemical dynamics simulations, using the PM3 semi-empirical Hamiltonian. In particular, we have considered two activation processes that are representative limits of what occurs in collision induced dissociation experiments: (i) thermal activation, corresponding to several low energy collisions, in which the system is prepared with a microcanonical distribution of energy; (ii) collisional activation where a single shock of hundreds of kcal mol−1 (300 kcal mol−1 in the present case) can transfer sufficient energy to allow dissociation. From these two activation processes we obtained different product abundances, and for one particular fragmentation pathway a clear mechanistic difference for the two activation processes. This mechanism corresponds to the leaving of an OH group and subsequent formation of water by taking a proton from the remaining molecule. This last reaction is always observed in thermal activation while in collisional activation it is less favoured and the formation of OH as a final product is observed. More importantly, we show that while in thermal activation unimolecular dissociation follows exponential decay, in collision activation the initial population decays with non-exponential behaviour. Finally, from the thermal activation simulations it was possible to obtain rate constants as a function of temperature that show Arrhenius behaviour. Thus activation energies have also been extracted from these simulations.

Back to tab navigation
Please wait while Download options loads

Publication details

The article was received on 10 May 2016, accepted on 23 Jun 2016 and first published on 23 Jun 2016


Article type: Paper
DOI: 10.1039/C6FD00126B
Citation: Faraday Discuss., 2016,195, 599-618
  •   Request permissions

    Unimolecular dissociation of peptides: statistical vs. non-statistical fragmentation mechanisms and time scales

    R. Spezia, A. Martin-Somer, V. Macaluso, Z. Homayoon, S. Pratihar and W. L. Hase, Faraday Discuss., 2016, 195, 599
    DOI: 10.1039/C6FD00126B

Search articles by author