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

A QM + MM direct chemical dynamics simulation was performed to study collisions of protonated octaglycine, gly(8)-H(+), with the diamond {111} surface at an initial collision energy E(i) of 100 eV and incident angle theta(i) of 0 degrees and 45 degrees. The semiempirical model AM1 was used for the gly(8)-H(+) intramolecular potential, so that its fragmentation could be studied. Shattering dominates gly(8)-H(+) fragmentation at theta(i) = 0 degrees, with 78% of the ions dissociating in this way. At theta(i) = 45 degrees shattering is much less important. For theta(i) = 0 degrees there are 304 different pathways, many related by their backbone cleavage patterns. For the theta(i) = 0 degrees fragmentations, 59% resulted from both a-x and b-y cleavages, while for theta(i) = 45 degrees 70% of the fragmentations occurred with only a-x cleavage. For theta(i) = 0 degrees, 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 degrees these percentages are 26%, 12%, and 62%. The percentage energy-transfer to DeltaE(int) for theta(i) = 0 degrees is larger than that reported in previous experiments for collisions of des-Arg(1)-bradykinin with a diamond surface at the same theta(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.