Selectivity in fragmentation of N-methylacetamide after resonant K-shell excitation

• Published in: Physical chemistry chemical physics : PCCP 2014-01, Vol.16 (29), p.15231-15240
• Main Authors: Salén, Peter, Kamińska, Magdalena, Squibb, Richard J, Richter, Robert, Alagia, Michele, Stranges, Stefano, van der Meulen, Peter, Eland, John H D, Feifel, Raimund, Zhaunerchyk, Vitali
• Format: Article
• Language: English
• Subjects: Acetamides - chemistry; Atom and Molecular Physics and Optics; Atom- och molekylfysik och optik; Ions; Models, Chemical; Peptide Fragments - chemistry; X-Ray Absorption Spectroscopy
• ISSN: 1463-9076; 1463-9084; 1463-9084
• DOI: 10.1039/c4cp01067a

The fragmentation pattern of the peptide model system, N-methylacetamide, is investigated using ion time-of-flight (TOF) spectroscopy after resonant K-shell excitation. Corresponding near-edge X-ray absorption fine structure (NEXAFS) spectra recorded at high resolution at the C1s, N1s and O1s edges are presented. Analysis of the ion TOF data reveals a multitude of fragmentation channels and dissociation pathways. Comparison between the excitation of six different resonances in the vicinity of the C1s, N1s and O1s edges suggests evidence for site-selective bond breaking. In particular the breaking of the peptide bond and the N-C(α) bond show a clear correlation with resonant excitation at the N1s edge. Also, stronger tendencies towards site-selective bond breaking are found for the generation of single ions compared with ion pairs. Analysis of angular distributions of ions from breakage of the peptide bond yields a fragmentation time of