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

Abstract

A QM ϩ MM direct chemical dynamics simulation was performed to study collisions of protonated octaglycine, gly 8 -H ϩ , with the diamond {111} surface at an initial collision energy E i of 100 eV and incident angle i of 0°and 45°. The semiempirical model AM1 was used for the gly 8 -H ϩ intramolecular potential, so that its fragmentation could be studied. Shattering dominates gly 8 -H ϩ fragmentation at i ϭ 0°, with 78% of the ions dissociating in this way. At i ϭ 45°shattering is much less important. For i ϭ 0°there are 304 different pathways, many related by their backbone cleavage patterns. For the i ϭ 0°fragmentations, 59% resulted from both a-x and b-y cleavages, while for i ϭ 45°70% of the fragmentations occurred with only a-x cleavage. For i ϭ 0°, the average percentage energy transfers to the internal degrees of freedom of the ion and the surface, and the energy remaining in ion translation are 45%, 26%, and 29%. For 45°these percentages are 26%, 12%, and 62%. The percentage energy-transfer to ⌬E int for i ϭ 0°is larger than that reported in previous experiments for collisions of des-Arg 1 -bradykinin with a diamond surface at the same i . This difference is discussed in terms of differences between the model diamond surface used in the simulations and the diamond surface prepared for the experiments. (J Am Soc Mass Spectrom 2009, 20, 939 -948)

Fragmentation and reactivity in collisions of protonated diglycine with chemically modified perfluorinated alkylthiolate-self-assembled monolayer surfaces

“…Despite this complication, we do see qualitatively similar behavior with the gly-H + + diamond {1 1 1}, 23 gly 8 -H + + diamond {1 1 1}, 25 and gly 8 -H + + H-SAM systems. A comparison of the fragmentation dynamics in previous studies is also complicated by the presence of reactivity between the peptide and the surface in our work.…”

“…[23][24][25] Semiempirical approaches are computationally inexpensive while yielding SID chemical dynamics trajectories that agree quite favorably with those determined using the higher level MP2 method for the QM atoms. [23][24][25] Semiempirical approaches are computationally inexpensive while yielding SID chemical dynamics trajectories that agree quite favorably with those determined using the higher level MP2 method for the QM atoms.…”

“…[23][24][25] Semiempirical approaches are computationally inexpensive while yielding SID chemical dynamics trajectories that agree quite favorably with those determined using the higher level MP2 method for the QM atoms. 23,26 The fragmentation pathways are primarily concerted [23][24][25][26] and the dynamics is complicated by the large number of fragmentation pathways. 23,26 The fragmentation pathways are primarily concerted [23][24][25][26] and the dynamics is complicated by the large number of fragmentation pathways.…”

“…The peptide-surface reactions are dominated by the formation of singlet products. [23][24][25][26] Although it is not correct to describe the peptide-surface dynamics as a primary reaction followed by secondary reactions, many of the peptide-surface reactions appear to be initiated by a four-centered TS structure as shown in Fig. Such dynamics was seen previously for O( 3 P) + C 2 H 6 reaction at hyperthermal energies 42 and for peptide-H + "shattering" SID.…”

Theoretical Methods for Vibrational Spectroscopy and Collision Induced Dissociation in the Gas Phase

“…AM1 results were in agreement with both Amber-(for energy transfer) and (for reactivity) MP2-based simulations [187], thus paving the way for using semi-empirical Hamiltonians in the puzzling study of gas phase reactivity of peptides. Protonated octaglycine SID was studied by Park et al [188], showing a dependence on the relevance of shattering on the collisional orientation between the ion and the surface. More recently, in our group we have studied the CID reactivity of N-formylalanylamide (a model dipeptide), pointing out that the semi-empirical Hamiltonian is able to provide a picture of reactivity in agreement with experiments, such that it becomes possible to provide a semi-quantitative theoretical MS-MS spectra [189].…”