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Title: Gas-phase structures and proton affinities of N-terminal proline containing b2 + ions from protonated model peptides
Authors: Karaca, Sıla
Atik, Ahmet Emin
Elmacı, Nuran
Yalçın, Talat
Keywords: Diketopiperazine
Proton affinity
Quantum calculation
Issue Date: Dec-2015
Publisher: Elsevier Ltd.
Source: Karaca, S., Atik, A.E., Elmacı, N., and Yalçın, T. (2015). Gas-phase structures and proton affinities of N-terminal proline containing b2 + ions from protonated model peptides. International Journal of Mass Spectrometry, 393, 1-8. doi:10.1016/j.ijms.2015.09.011
Abstract: In this study, we investigated the effect of the second amino acid identity of hexapeptides on gas-phase structures and the proton affinities of N-terminal proline containing b2 + ions produced from the fragmentation of b6 + ions under low-energy collision-induced dissociation (CID) tandem mass spectrometry (MS/MS). It should be noted that, among all other fragments, the b2 + and nominally b4 + (AAAA) ions ([M+H]+ → b6 + → b2 + (PX+) + b4 + (AAAA+) were mainly considered in this study. This is a unique example of consecutive cleavage of b6 + ions which fragments to b2 + and nominal b4 + ions. All structural and proton affinity calculations for b2 + ions were carried out with the B3LYP/6-31+G(d,p) level of theory. The study utilized C-terminal amidated model peptides consisting of PAAAAA-NH2 and PXAAAA-NH2 where X is phenylalanine (F), glutamic acid (E), tryptophan (W), and histidine (H) residue. Two main structural isomers of b2 + ions, namely oxazolone and diketopiperazine, have been considered for the computations. The results demonstrated that the proton affinities of oxazolone isomers of PX are greater than its diketopiperazine isomers. Higher correlation coefficient is calculated if the structure of PX is considered as oxazolone rather than diketopiperazine isomer. Additionally, a linear fit is observed between intensity ratio (PX/AAAA) and calculated proton affinities of PX ions. Additionally, MS/MS results revealed that the relative intensities of b2 +-PA, PF, and PE- ions are lower compared to the relative intensity of AAAA fragment ion. In contrast, b2 +-PW and PH- ions have higher relative intensities compared to the AAAA ion. This behavior is explained by the proton affinities of fragment ions computationally.
ISSN: 1387-3806
Appears in Collections:Chemistry / Kimya
Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection

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