engleski

Comparing Mass Spectrometric Characteristics of Peptides and Peptoids

The collision-induced dissociation (CID) spectra of the [M + H](+) ions of a pentapeptide and the corresponding peptoid and retropeptoid have been compared, The spectra of the peptide and peptoid both exhibit B- and Y-n-type sequence ions at identical m/z values. In contrast to the peptide, the [M + H] (+) ion of the peptoid and all sequence ions containing an N-substituted glycine derivative corresponding to a tyrosine amino acid residue can easily lose a C7H6O molecule in a charge-remote fragmentation process, The presence of N-substituted glycine residues in a peptoid is further apparent from the presence of N- substituted immonium ions, which differ significantly in their fragmentation behaviour from the corresponding immonium ions observed in the spectra of common oligopeptides. Loss of the CH2=NH imine molecule is the dominant fragmentation reaction in the CID spectra of all peptoid immonium ions investigated in this study. The elimination of the CH=NH2 ylide analogue from common peptide immonium ions is energetically less favourable as shown by ab initio calculations. The relative heat of formation of the CH=NH2 ylide neutral appeared to be 168 kJ mol(-1) more than that of the CH2=NH inine molecule.

mass spectrometry ; peptides ; peptoides

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