Direct dynamics study ofN-protonated diglycine surface-induced dissociation. Influence of collision energy

Abstract

A quantum mechanical and molecular mechanical (QM + MM) direct dynamics classical trajectory simulation is used to study energy transfer and fragmentation in the surface-induced dissociation (SID) of N-protonated diglycine, (gly)2H+. The peptide ion collides with the hydrogenated diamond [111] surface. The Austin Model 1 (AM1) semiempirical electronic structure theory is used for the (gly)2H+ intramolecular potential and molecular mechanical functions are used for the diamond surface potential and peptide/surface intermolecular potential. The simulations are performed at collision energies Ei of 30, 50, 70, and 100 eV and collision angle of 0 degrees (perpendicular to the surface). The percent energy transfer to the peptide ion is nearly independent of Ei, while energy transfer to the surface increases with increase in Ei. A smaller percent of the energy remains in peptide translation as Ei is increased. These trends in energy transfer are consistent with previous trajectory simulations of SID. At each Ei the most likely initial pathway leading to fragmentation is rupture of the +H3NCH2-CONHCH2COOH bond. Fragmentation occurs by two general mechanisms. One is the traditional Rice-Ramsperger-Kassel-Marcus (RRKM) model in which the peptide ion is activated by its collision with the surface, "bounces off", and then dissociates after undergoing intramolecular vibrational energy redistribution (IVR). The other mechanism is shattering in which the ion fragments as it collides with the surface. Shattering is the origin of the large increase in number of product channels with increase in Ei, i.e., 6 at 30 eV, but 59 at 100 eV. Shattering becomes the dominant dissociation mechanism at high Ei.

Importance of shattering fragmentation in the surface-induced dissociation of protonated octaglycine

“…The distributions of energy-transfer to ⌬E int , ⌬E surf , and E f , for the i ϭ 0°collisions, are shown in Figure 2. Their forms are similar to those found previously [6,9,10,14,17,18] for simulations of the smaller gly n -H ϩ peptide ions and for the current study with i ϭ 45°.…”

“…For the work presented here, the much less expensive QM method AM1 was used. Previous work has shown that nearly the same energy-transfer efficiencies are obtained when either AMBER, AM1, or MP2/ 6-31G* are used to represent the peptide ion's intramolecular potential V ion [6,9,10,14]. In chemical dynamics simulations of gly-H ϩ SID, the same shattering probabilities are obtained when using either AM1 or MP2/6-316* for V ion [10,14].…”

“…In chemical dynamics simulations of SID, shattering has been observed for both protonated glycine [6,10] and diglycine, [9] i.e., gly-H ϩ and gly 2 -H ϩ . Experimentally, shattering has also been observed for the larger peptide ion protonated bradykinin [11].…”

Surface-induced dissociation of small molecules, peptides, and non-covalent protein complexes

“…Hase and colleagues have shown that several factors affect kinetic to internal energy conversion in the SID process, including collision energy, peptide size and conformation, incident collision angle, and surface target. Classical trajectory simulations of protonated diglycine and dialanine demonstrated that internal energy transfer in normal-incidence SID (collision perpendicular to the surface) decreases slightly with increasing collision energy [101,102]. The influence of peptide size has been explored by examining collisions of polyglycine (gly n -H ϩ , n ϭ 1-5) with a diamond surface.…”

“…Simulations of glycine colliding with a diamond surface revealed that as much as 55% of the total fragmentation observed could be attributed to shattering at the surface [99]. For simulations on diglycine, the shattering mechanism resulted in an increase in the number of fragmentation channels available from 6 at 30 eV to 59 at 100 eV and was strongly influenced by the orientation of the diglycine molecule as it collided with the surface [101].…”