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dc.contributor.advisorSiu, K.W. Michael
dc.creatorWang, Yating
dc.description.abstractThis research work examines the dissociation chemistry of tripositive complexes formed by trivalent lanthanide ions and small peptides with tandem mass spectrometry under low-energy collision-induced dissociation (CID). By fragmentation of the tripositive lanthanide(III) cationized small peptide, a new route to generate peptide radical cations has been discovered. The dipositive b ions are also observed and the mechanisms by which they fragment are investigated by MSn. Tripositive complexes of lanthanide(III)/peptide have similar fragmentation chemistries in the gas phase when lanthanide = yttrium, lanthanum, cerium, samarium, gadolinium and terbium; [a3+H]2+ ions are formed and there are no peptide radical cations observed. When the lanthanide is europium(III), radical cations of tryptophan-, tyrosine-, phenylalanine-, methionine-containing peptides and of aliphatic peptides have been generated. Fragmentations of tripositive Ce(III)/peptide and Eu(III)/peptide complexes show very different behaviours. Abundant CO loss is only observed for dissociation of Ce(III)/peptide complexes, whereas CO2 loss is the predominant channel for Eu(III)/peptide complexes. Similarly, CO loss and CO2 loss are the predominant channels for the dissociations of [Ce(peptide-H)]2+ and [Eu(peptide-H)]2+, respectively. Peptide radical cations are only generated by the fragmentation of Eu(III)/peptide complexes, while protonated a and b ions are only observed when Ce(III)/peptide complexes dissociate. The dissociations of aliphatic [peptide]+ions generate [b3-H]+/ [b2-H]+ions for most peptides. In the dissociation of [a3+H]+ions, [b2-H]+ions are formed from most peptides. [a3+H]2+ ions usually cleave at the C-terminal amide bonds, creating two singly charged ions, a [b2]+ ion and an iminium ion derived from the C-terminal residue. Some [a3+H]2+ ions also lose small neutral molecules. The composition of the peptides dictates the preferred mode of the fragmentation of [b3+H]2+ ions, either loss of CO to form [a3+H]2+, or loss of CO plus H2O. Fragmentations of [Ce(peptide-H)]2+ ions show CO loss, and CO2 losses are observed for peptides with aromatic side chains or a methionine residue at C-terminus. For [Ce(peptide-H)(peptide)]2+ complexes, neutral losses are also observed but formation of two singly charged ions is dominant. The dissociation behaviour of [Ce(peptide-H)(CH3CN)]2+ and [Eu(peptide-H)(CH3CN)]2+ complexes are quite different. The former loses only CH3CN whereas the latter loses only CO2.
dc.rightsAuthor owns copyright, except where explicitly noted. Please contact the author directly with licensing requests.
dc.subjectAnalytical chemistry
dc.titleFragmentation of Lanthanide (III) Cationized Small Peptides: Generation of Peptide Radical Cations and Dipositive a and b ions.
dc.typeElectronic Thesis or Dissertation - Doctor of Philosophy
dc.subject.keywordsTandem Mass Spectrometry
dc.subject.keywordsElectrospray Ionization
dc.subject.keywordsMetal/Peptide Complex
dc.subject.keywordsTrivalent Metal Ion
dc.subject.keywordsSmall Peptide
dc.subject.keywordsRadical Cation
dc.subject.keywordsNew Route
dc.subject.keywordsDipositive b ion
dc.subject.keywordsDipositive a ion
dc.subject.keywordsTripositive Complex
dc.subject.keywordsDipositive Complex
dc.subject.keywordsAromatic Peptide
dc.subject.keywordsAliphatic Peptide
dc.subject.keywordsProline-containing Peptide

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