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

Abstract

PostprintThis is the accepted version of a paper published in Physical Chemistry, Chemical Physics -PCCP. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination.Citation for the original published paper (version of record):Salen, P., Kaminska, M., Squibb, R J., Richter, R., Alagia, M. et al. (2014) Selectivity in fragmentation of N-methylacetamide after resonant K-shell excitation. 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 < 400 fs.

Highly Selective Dissociation of a Peptide Bond Following Excitation of Core Electrons

“…51 Although the K-edge spectra of amino acids and small peptides have been studied extensively, the dissociation pathways of peptides after core excitation has not been thoroughly investigated. 49,52 We demonstrate in the current study that the branching ratios after breakage of the peptide bond can be as high as 0.56−0.71. These large branching ratios of cleavage of the peptide bond in N-methylformamide and Nmethylacetamide can be rationalized according to the following characteristics.…”

“…49 On comparison with the mass spectra of the isotopically substituted compound CH 3 15 NHCO(CH 3 ) in this work, the formulas of these fragments are unambiguously determined. Moreover, we correct the assignments of two fragments made in the preceding work.…”

Mechanisms of site-specific photochemistry following core-shell ionization of chemically inequivalent carbon atoms in acetaldehyde (ethanal)

“…The photodissociation process has been widely studied using initial resonant core-electron excitation on atoms of different elements [5][6][7][8] in a process sometimes referred to as element-specific photochemistry, and on atoms of the same element but in different chemical environments [9][10][11][12] , which is referred to as site-specific photochemistry. The dissociation upon core ionisation is relatively less investigated.…”

NEXAFS spectroscopy and site-specific fragmentation of N-methylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide

“…If the anti-bonding orbital is localized one could further expect to preferentially break this bond. 3,4 Many experimental studies have been devoted to the investigation of siteselective bond breaking induced by core excitation both in the gas-phase [5][6][7][8][9][10][11][12][13][14][15] and on solid surfaces, 4,[16][17][18] and it has been demonstrated in both cases. Due to the high cross-section 4 and the potential anti-bonding character of the populated orbital, resonant excitation is expected to be more promising for selective fragmentation compared with core-ionization, a) Electronic mail: vitali.zhaunerchyk@physics.gu.se although selectivity has also been observed in the latter case.…”

“…In particular, we previously investigated the selectivity in the fragmentation of N-methylacetamide, CH 3 CONHCH 3 , upon excitation of different C, N, and O Kedge pre-edge resonances, and selective formation of specific fragments was demonstrated. 11 For example, the selective cleavage of the bonds connected with the N atom was observed upon excitation of the strongest N 1s resonance, although the site-selective dissociation channels were not dominant compared with other channels. Moreover, stronger tendencies towards selective bond breaking were found monitoring singly charged, compared with doubly charged, parent ion decay processes.…”