Harrison, Alex G.Taşoğlu, ÇağdaşYalçın, Talat2017-03-282017-03-282013Harrison, A.G., Taşoğlu, Ç., and Yalçın, T. (2013). Non-direct sequence ions in the tandem mass spectrometry of protonated peptide amides - An energy-resolved study. Journal of the American Society for Mass Spectrometry, 24(10), 1565-1572. doi:10.1007/s13361-013-0707-91044-03051879-1123https://doi.org/10.1007/s13361-013-0707-9https://hdl.handle.net/11147/5155The fragmentation reactions of the MH+ ions of Leu-enkephalin amide and a variety of heptapeptide amides have been studied in detail as a function of collision energy using a QqToF beam type mass spectrometer. The initial fragmentation of the protonated amides involves primarily formation of bn ions, including significant loss of NH3 from the MH+ ions. Further fragmentation of these bn ions occurs following macrocyclization/ring opening leading in many cases to bn ions with permuted sequences and, thus, to formation of non-direct sequence ions. The importance of these non-direct sequence ions increases markedly with increasing collision energy, making peptide sequence determination difficult, if not impossible, at higher collision energies. [Figure not available: see fulltext.]eninfo:eu-repo/semantics/openAccessNon-direct sequence ionsPeptide amidesTandem mass spectrometryIonsArticle2-s2.0-8488455523910.1007/s13361-013-0707-9