Near-edge X-ray absorption fine structure (NEXAFS) spectra of some peptide model molecules were measured and calculated with TDDFT. After locally exciting a core electron of carbon, nitrogen, or oxygen atom of a molecule, Auger decay would occur on 99% or more of them. One Auger electron leaves the molecule with high kinetic energy, and the molecular ion is formed with high internal energy followed by dissociation. A special phenomenon, specific dissociation, was discovered by Professor Eberhardt. To find out the connections between specific dissociation of locally and highly excited ions and peptide molecules, some peptide model molecules were selected to investigate. The intensity and branching ratio as functions of photon energy were obtained for all ionic products. The enhancement phenomena at specific excitation energies resulted from specific dissociation were recognized. To verify the dissociation paths, isotopic molecules were used to reveal the identities of the ionic fragments. It is interesting that most of the enhanced products were produced via breaking the peptide-bond which is attributed to the destination orbital. The branching ratios of breaking peptide bonds could be as high as 71% following a specific excitation. Adding a phenyl group on the peptide model, the branching ratios decrease dramatically to about 35% which is possibly due to the mixed destination molecular orbital. The specific dissociation also occurs on all peptide bonds while a molecule contains more than one peptide-bond.

Specific peptide-bond dissociation of some peptide model ions

254th National Meeting (2017)

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