Dipole-Supported Electronic Resonances Mediate Electron-Induced Amide Bond Cleavage

Area of Science:

• Physical Chemistry
• Chemical Physics
• Biomolecular Science

Background:

• Dissociative electron attachment (DEA) is crucial for understanding radiation damage in biomolecules.
• Electron capture in DEA is typically modeled via metastable valence states, followed by molecular fragmentation.
• Core-excited dipole-supported resonances are increasingly recognized as significant in DEA processes.

Purpose of the Study:

• To investigate the role of core-excited resonances in gas-phase dissociative electron attachment to simple peptides.
• To analyze the fragmentation patterns, specifically amide bond cleavage, in formamide, N-methylformamide (NMF), and N,N-dimethylformamide (DMF).
• To elucidate the nature of the resonances responsible for electron capture and subsequent fragmentation.

Main Methods:

• Combined experimental and theoretical investigations of gas-phase DEA.
• Measurement of ion yield curves for fragment ions.
• High-level electronic structure calculations to identify and characterize resonant states.

Main Results:

• Amide bond fragmentation was observed in formamide, NMF, and DMF, contrasting with positively charged peptide electron capture.
• Ion yield curves for amide bond cleavage products exhibited a double-peak structure between 5 and 8 eV.
• These peaks were assigned to Feshbach resonances, including core-excited dipole-supported resonances, with the lower peak linked to triplet state correlation.

Conclusions:

• Core-excited dipole-supported resonances significantly contribute to electron capture in the DEA process for these peptides.
• The observed amide bond cleavage highlights the importance of these resonances in biomolecular radiation damage.
• Optically spin-forbidden transitions, promoted by electron impact, play a role in DEA, particularly in forming core-excited resonances.