Influence of Turn (or Fold) and Local Charge in Fragmentation of the Peptide Analogue Molecule CH3CO-Gly-NH2 Following Single-Photon VUV (118.22 nm) Ionization

The radical cationic reactivity of the peptide analogue molecule CH3CO-Gly-NH2 is addressed both experimentally and theoretically. The radical cation intermediate of CH3CO-Gly-NH2 is created by single-photon ionization of this molecule at 118.22 nm (∼10.5 eV). The two most stable conformers (C7 and C5) of this molecule exhibit different folds along the backbone: the C7 conformer has a γ-turn structure, and the C5 conformer has a β-strand structure. The experimental results show that the radical cation intermediate of CH3CO-Gly-NH2 dissociates and generates a fragment-ion signal at 73 amu that is observed through TOFMS. Theoretical results show how the fragment-ion signal at 73 amu is generated by only one conformer of CH3CO-Gly-NH2 (C7) and how local charge and specific hydrogen bonding in the molecule influence fragmentation of the radical cation intermediate of CH3CO-Gly-NH2. The specific fold of the molecule controls fragmentation of this reactive radical cation intermediate. Whereas the radical cation...