Year: 2024
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide N, N -Dimethylformamide (DMF) provides a useful small-molecule model for studying features of the peptide bond that forms the backbone of proteins. We report results from a comprehensive multimass velocity-map imaging study into the ultraviolet (UV) photolysis of the N, N -dimethylformamide cation (DMF + ) at wavelengths of 225, 245, and 280 nm. Electronic structure calculations on DMF and DMF + were employed to help interpret the experimental results. DMF + ions are generated by 118 nm single-photon ionization of neutral DMF. Subsequent UV photolysis is found to lead to selective cleavage of the N–CO amide bond. This yields HCO + NC 2 H 6 + as major products, with virtually all of the excess energy released into internal modes of the fragments. The data also indicate a small branching ratio into the HCO + + NC 2 H 6 product pair, which can be accessed from the 3 2 A′ electronic state of DMF + . N–CO bond dissociation can also be accompanied by simultaneous intramolecular hydrogen transfer from the oxygen to the nitrogen end of the amide bond, in which case NCH 4 + can be formed efficiently at all three wavelengths. The primary NC 2 H 6 + product is relatively long-lived, but the high degree of internal excitation often results in secondary fragmentation via a variety of pathways to form CH 3 +, NH 4 +, NCH 2 +, and NC 2 H 4 +, with secondary dissociation more likely at higher photon energies. The isotropic velocity-map images recorded for the various fragments attest to the long lifetime of NC 2 H 6 + and also imply that dissociation most probably occurs from the same set of electronic states at all wavelengths studied; these are thought to be the 1 2 A′ ground state and 2 2 A′ first excited state of the DMF + cation.
Institution: University of Oxford
Language: Hebrew
Subfield: Spectroscopy
Field: Chemistry
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4404968502