Abstract
Total-ion-yield near-edge X-ray absorption fine-structure (NEXAFS) spectra of three oligo-peptide model molecules were recorded. The NEXAFS spectra were also calculated with time-dependent density functional theory; the calculated spectra are consistent with the experimental measurements. The ionic products from core-excited molecules and their branching ratios as functions of excitation energy show branching ratios 42%-75% of dissociation of the peptide bond, especially at resonant excitations. The major destination orbitals assigned at these excitation energies show significant antibonding character along peptide bonds, which causes large probabilities of bond cleavage.
Highlights
Core-level excitation, X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectra have been developed as powerful tools to study the electronic states of matter because of the excitation specificities of elements and sites
Eberhardt and co-workers pioneered research on the specific dissociation following a core excitation, utilizing mass spectra and NEXAFS spectra,6 Suzuki and his co-workers continued the research of core excited acetone without dramatic effect on site-specific decomposition
Since the main focus of the theoretical modeling in the current study is to assign the transition types corresponding to the major peaks of the experimental NEXAFS spectra, we chose to use the TD-B3LYP/6-31+G(d,p) method which, with appropriate energy shifts, gives overall better agreement with the experimental scitation.org/journal/adv spectra
Summary
Core-level excitation, X-ray photoelectron spectra (XPS) and near-edge X-ray absorption fine-structure (NEXAFS) spectra have been developed as powerful tools to study the electronic states of matter because of the excitation specificities of elements and sites. Eberhardt and co-workers pioneered research on the specific dissociation following a core excitation, utilizing mass spectra and NEXAFS spectra, Suzuki and his co-workers continued the research of core excited acetone without dramatic effect on site-specific decomposition. Varied phenomena of specific dissociation were investigated both in the gaseous phase and on a surface. The possible specific dissociation mechanisms and background sources were discussed in the literatures. For molecules containing a peptide bond, the branching ratio for dissociation of the peptide bond was measured to be as high as 71%. When the molecules contained both phenyl and amide groups, the products from the peptide-bond dissociation following the core excitation were still enhanced, but the branching ratios were found to be less than 35%.20. The identities of the functional groups that a molecule contains might significantly affect the specificity of the dissociation of a peptide bond. As those studied model molecules contained only. Three peptide model molecules (shown in Figures 1 and 2) containing two or three amide groups were investigated with measurement of the excitation of core-electron NEXAFS and mass spectra. Time dependent density functional theory has been applied to predict the NEXAFS spectra of the three molecules; the electronic transition orbitals corresponding to the NEXAFS spectral features have been assigned
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