Dataset Information

Dissociation Behavior of Tryptic and Intramolecular Disulfide-linked Peptide Ions Modified in the Gas Phase via Ion/Ion Reactions.

ABSTRACT: Protonated tryptic peptides, somatostatin-14, and oxytocin have been subjected to reactions with doubly deprotonated 4-formyl-1,3-benzenedisulfonic acid (FBDSA) in the gas phase. The major product is a negatively-charged complex comprised of the peptide and the reagent. Upon dehydration of the complex, all peptides show evidence for Schiff base formation involving a primary amine of the peptide. Some peptides also show evidence for the formation of a relatively strong electrostatic interaction without Schiff base formation (i.e., a mixture of isomeric precursor ions is generated upon dehydration of the complex). Ion trap collision-induced dissociation of the dehydration products from all peptides examined gave distinct product ion spectra relative to the deprotonated and protonated forms of the peptides. The distinct behavior of the modified ions is attributed to the highly stable charge carrying sulfonate group, which tends to inhibit intramolecular proton transfer in negatively charged species. Modified anions of the peptides with an intramolecular disulfide linkage show evidence for cleavage of both the disulfide linkage and an amide bond in the loop defined by the disulfide bond. Modification of protonated peptides via charge inversion with FBDSA is a useful means for generating novel and distinct ion-types that can provide complementary structural information upon subsequent activation to that obtained from dissociation of protonated or deprotonated forms of the peptide.

SUBMITTER: Stutzman JR

PROVIDER: S-EPMC3297198 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Dissociation Behavior of Tryptic and Intramolecular Disulfide-linked Peptide Ions Modified in the Gas Phase via Ion/Ion Reactions.

Stutzman John R JR Hassell Kerry M KM McLuckey Scott A SA

International journal of mass spectrometry 20120201

Protonated tryptic peptides, somatostatin-14, and oxytocin have been subjected to reactions with doubly deprotonated 4-formyl-1,3-benzenedisulfonic acid (FBDSA) in the gas phase. The major product is a negatively-charged complex comprised of the peptide and the reagent. Upon dehydration of the complex, all peptides show evidence for Schiff base formation involving a primary amine of the peptide. Some peptides also show evidence for the formation of a relatively strong electrostatic interaction w ...[more]

PMID: 22408389

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Project description:The intramolecular gas-phase reactivity of four oxoiron(IV) complexes supported by tetradentate N(4) ligands (L) has been studied by means of tandem mass spectrometry measurements in which the gas-phase ions [Fe(IV)(O)(L)(OTf)](+) (OTf = trifluoromethanesulfonate) and [Fe(IV) (O)(L)](2+) were isolated and then allowed to fragment by collision-induced decay (CID). CID fragmentation of cations derived from oxoiron(IV) complexes of 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane (tmc) and N,N'-bis(2-pyridylmethyl)-1,5-diazacyclooctane (L(8)Py(2)) afforded the same predominant products irrespective of whether they were hexacoordinate or pentacoordinate. These products resulted from the loss of water by dehydrogenation of ethylene or propylene linkers on the tetradentate ligand. In contrast, CID fragmentation of ions derived from oxoiron(IV) complexes of linear tetradentate ligands N,N'-bis(2-pyridylmethyl)-1,2-diaminoethane (bpmen) and N,N'-bis(2-pyridylmethyl)-1,3-diaminopropane (bpmpn) showed predominant oxidative N-dealkylation for the hexacoordinate [Fe(IV)(O)(L)(OTf)](+) cations and predominant dehydrogenation of the diaminoethane/propane backbone for the pentacoordinate [Fe(IV)(O)(L)](2+) cations. DFT calculations on [Fe(IV)(O)(bpmen)] ions showed that the experimentally observed preference for oxidative N-dealkylation versus dehydrogenation of the diaminoethane linker for the hexa- and pentacoordinate ions, respectively, is dictated by the proximity of the target C-H bond to the oxoiron(IV) moiety and the reactive spin state. Therefore, there must be a difference in ligand topology between the two ions. More importantly, despite the constraints on the geometries of the TS that prohibit the usual upright ? trajectory and prevent optimal ?(CH)-?*(z2) overlap, all the reactions still proceed preferentially on the quintet (S = 2) state surface, which increases the number of exchange interactions in the d block of iron and leads thereby to exchange enhanced reactivity (EER). As such, EER is responsible for the dominance of the S = 2 reactions for both hexa- and pentacoordinate complexes.

Dataset Information

Dissociation Behavior of Tryptic and Intramolecular Disulfide-linked Peptide Ions Modified in the Gas Phase via Ion/Ion Reactions.

Publications

Dissociation Behavior of Tryptic and Intramolecular Disulfide-linked Peptide Ions Modified in the Gas Phase via Ion/Ion Reactions.

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