PNNL

Abstract

Dissociation of singly protonated leucine enkephalin (YGGFL) was studied using surface-induced dissociation (SID) in a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially configured for studying ion activation by collisions with surfaces. The energetics and dynamics of seven primary dissociation channels were deduced from modeling the time- and energy-resolved fragmentation efficiency curves for different fragment ions using an RRKM based approach developed in our laboratory. The following threshold energies and activation entropies were determined in this study: E0=1.20 eV and ?S‡=-20 e.u.1 (MH+?b5); E0=1.14 eV and ?S‡=-14.7 e.u. (MH+?b4); E0=1.42 eV and ?S‡=-2.5 e.u. (MH+?b3); E0=1.30 eV and ?S‡=-4.1 e.u. (MH+?a4); E0=1.37 eV and ?S‡=-5.2 e.u. (MH+?y ions); E0=1.50 eV and ?S‡=1.6 e.u. (MH+?internal fragments); E0=1.62 eV and ?S‡=5.2 e.u. (MH+?F). Comparison with Arrhenius activation energies reported in the literature demonstrated for the first time the reversal of the order of activation energies as compared to threshold energies for dissociation.