Energetics and dynamics of fragmentation of protonated leucine enkephalin from time- and energy-resolved surface-induced dissociation studies.
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: E(0) = 1.20 eV and DeltaS++ = -20 eu(1) (MH(+)-->b(5)); E(0) = 1.14 eV and DeltaS++ = -14.7 eu (MH(+)-->b(4)); E(0) = 1.42 eV and DeltaS++ = -2.5 eu (MH(+)-->b(3)); E(0) = 1.30 eV and DeltaS++ = -4.1 eu (MH(+)-->a(4)); E(0) = 1.37 eV and DeltaS++ = -5.2 eu (MH(+)-->y ions); E(0) = 1.50 eV and DeltaS++ = 1.6 eu (MH(+)-->internal fragments); E(0) = 1.62 eV and DeltaS++ = 5.2 eu (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.
Laskin
Julia
J
Pacific Northwest National Laboratory, Fundamental Science Directorate, Richland, Washington 99352, USA. julia.laskin@pnl.gov
D000595:Amino Acid Sequence; D004735:Energy Transfer; D004743:Enkephalin, Leucine / Q000737:chemistry*; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011522:Protons; D013816:Thermodynamics
D011522:Protons; D004743:Enkephalin, Leucine