# Near-Edge X-Ray Absorption Fine-Structure Spectra and Specific Dissociation of Phe-Gly and Gly-Phe

## TL;DR

This study uses X-ray absorption to explore how two dipeptides break apart under different energy conditions.

## Contribution

The study identifies specific dissociation patterns linked to molecular orbitals near the peptide bond in dipeptides.

## Key findings

- Excitation energy variations lead to selective dissociation of dipeptides.
- Dissociation behavior is closely tied to nodal planes of molecular orbitals near the peptide bond.
- Consistent dissociation patterns were observed in both small peptides and peptoids.

## Abstract

The total-ion-yield (TIY) near-edge X-ray absorption fine-structure (NEXAFS) spectra of two dipeptides were measured and analyzed to identify the excitation sites of core electrons and the corresponding destination molecular orbitals. Peptide molecules were transferred to the gaseous phase using traditional heating and MALDI methods, ensuring that the resulting NEXAFS spectra and fragmentation products were consistent across both approaches. Mass spectra obtained at various excitation energies revealed the branching ratios of products at each energy level, offering insights into specific dissociation phenomena. Notably, variations in excitation energy demonstrated a selective dissociation process, with certain products forming more efficiently. This specificity appears closely linked to dissociations near the peptide bond, where the nodal planes of destination molecular orbitals are located. These findings were validated using both small peptide models and peptoid molecules, highlighting consistent patterns in the dissociation behavior.