Structures of the a2 ions of Ala-Ala-Ala and Phe-Phe-Phe

Verkerk, Udo H.; Zhao, Jianxin; Lau, Justin Kai-Chi; Lam, Tim-Wai; Hao, Qiang; Steill, Jeffrey D.; Siu, Chi‐Kit; Hopkinson, Alan C.; Siu, Kin Wai Michael

doi:10.1016/j.ijms.2012.08.034

Cited by 12 publications

(13 citation statements)

References 53 publications

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“…Rearrangement mechanism of a 2 ions uponhead-to-tail cyclisation. Consistent results were obtained by Verkerk et al for the a 2 ions of protonated Ala 3 and Phe 3 , R 1 = R 2 = CH 3 and R 1 = R 2 = CH 2 C 6 H 5 , respectively [38], using a combination of quantum chemical calculations and IR spectroscopy in the 1000-2000 cm À1 region. A mixture of isomers C and E (see Scheme 2) was formed in the two cases.…”

Section: [ ( S C H E M E _ 2 ) T D $ F I G ]supporting

confidence: 87%

“…It was concluded that the cyclic isomer was also found to be predominant, and the second CQO band observed near 1727 cm À1 [24], with a weaker intensity than that of the cyclic CQO stretch, was found to be an evidence of the formation of the rearranged imine-amide structure [24]. It was later suggested that when a 2 ions are generated in the skimmer region of the high pressure region of the ion source [24], ion-molecule complexes may be formed with residual water or methanol molecules thus leading to solvent-assisted reactions [38] allowing for the formation of the rearranged imine-amide structure.…”

Section: [ ( F I G _ 2 ) T D $ F I G ]mentioning

confidence: 99%

“…Considering that the rearranged imine-amide structure could be formed when a 2 ions were formed in the high pressure region of the source [24], probably involving a solvent assisted 1,3-proton transfer [38], it was interesting to assess the effect of a side-chain on the rearrangement, especially in the case of small a n ions. The structure of the YG a 2 ion (of both protonated YGGFL and doubly protonated YGGFLR) was thus probed via infrared spectroscopy in both the 1000-2000 and 3000-4000 cm À1 regions [22].…”

Section: Quantifying Ion Populations Using Irmpd Spectroscopymentioning

confidence: 99%

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Rearrangement chemistry of a ions probed by IR spectroscopy

Hernandez

Paizs

Maı̂tre

2015

International Journal of Mass Spectrometry

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Section: [ ( S C H E M E _ 2 ) T D $ F I G ]supporting

confidence: 87%

Section: [ ( F I G _ 2 ) T D $ F I G ]mentioning

confidence: 99%

Section: Quantifying Ion Populations Using Irmpd Spectroscopymentioning

confidence: 99%

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Rearrangement chemistry of a ions probed by IR spectroscopy

Hernandez

Paizs

Maı̂tre

2015

International Journal of Mass Spectrometry

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“…Similar results were obtained by Siu and co-workers [57]. In principle, either the histidine or the phenylaniline side chains can do this, thereby lowering the barrier.…”

Section: Analysis Of a 2 Ion And [Cyclo-(hisphe)-co] + Ion Fragmentationsupporting

confidence: 87%

Proton Mobility in b₂ Ion Formation and Fragmentation Reactions of Histidine-Containing Peptides

Nelson

Abutokaikah

Harrison

et al. 2015

J. Am. Soc. Mass Spectrom.

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Abstract. A detailed energy-resolved study of the fragmentation reactions of protonated histidine-containing peptides and their b 2 ions has been undertaken. Density functional theory calculations were utilized to predict how the fragmentation reactions occur so that we might discern why the mass spectra demonstrated particular energy dependencies. We compare our results to the current literature and to synthetic b 2 ion standards. We show that the position of the His residue does affect the identity of the subsequent b 2 ion (diketopiperazine versus oxazolone versus lactam) and that energy-resolved CID can distinguish these isomeric products based on their fragmentation energetics. The histidine side chain facilitates every major transformation except trans-cis isomerization of the first amide bond, a necessary prerequisite to diketopiperazine b 2 ion formation. Despite this lack of catalyzation, trans-cis isomerization is predicted to be facile. Concomitantly, the subsequent amide bond cleavage reaction is rate-limiting.

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“…Initially, it was believed [10,35,43] that the a 2 ion was a substituted imine ion shown as Breakdown graph for the Tyr-Gly b 2 ion derived from Tyr-Gly-Gly a 2 in Scheme 1. However, the computational studies [31][32][33] as well as IRMPD studies [44][45][46] have shown that the cyclic structure is more stable and can be readily formed (Scheme 1). It should be noted that the calculations show [31][32][33] that the transition state for loss of CO is considerably higher than the energies of either a 2 or a 1 products.…”

Section: Mechanistic Considerationsmentioning

confidence: 99%

Formation of a₁ Ions Directly from Oxazolone b₂ Ions: an Energy-Resolved and Computational Study

Bythell

Harrison

2015

J. Am. Soc. Mass Spectrom.

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Abstract. It is well-known that oxazolone b 2 ions fragment extensively by elimination of CO to form a 2 ions, which often fragment further to form a 1 ions. Less well-known is that some oxazolone b 2 ions may fragment directly to form a 1 ions. The present study uses energy-resolved collision-induced dissociation experiments to explore the occurrence of the direct b 2 →a 1 fragmentation reaction. The experimental results show that the direct b 2 →a 1 reaction is generally observed when Gly is the C-terminal residue of the oxazolone. When the C-terminal residue is more complex, it is able to provide increased stability of the a 2 product in the b 2 →a 2 fragmentation pathway. Our computational studies of the relative critical reaction energies for the b 2 →a 2 reaction compared with those for the b 2 →a 1 reaction provide support that the critical reaction energies are similar for the two pathways when the C-terminal residue of the oxazolone is Gly. By contrast, when the nitrogen of the oxazolone ring in the b 2 ion does not bear a hydrogen, as in the Ala-Sar and Tyr-Sar (Sar=N-methylglycine) oxazolone b 2 ions, a 1 ions are not formed but rather neutral imine elimination from the N-terminus of the b 2 ion becomes a dominant fragmentation reaction. The M06-2X/6-31+G(d,p) density functional theory calculations are in general agreement with the experimental data for both types of reaction. In contrast, the B3LYP/6-31+G(d,p) model systematically underestimates the barriers of these S N 2-like b 2 →a 1 reaction. The difference between the two methods of barrier calculation are highly significant (PG0.001) for the b 2 →a 1 reaction, but only marginally significant (P=0.05) for the b 2 →a 2 reaction. The computations provide further evidence of the limitations of the B3LYP functional when describing S N 2-like reactions.

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Structures of the a2 ions of Ala-Ala-Ala and Phe-Phe-Phe

Cited by 12 publications

References 53 publications

Rearrangement chemistry of a ions probed by IR spectroscopy

Rearrangement chemistry of a ions probed by IR spectroscopy

Proton Mobility in b₂ Ion Formation and Fragmentation Reactions of Histidine-Containing Peptides

Formation of a₁ Ions Directly from Oxazolone b₂ Ions: an Energy-Resolved and Computational Study

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Structures of the a2 ions of Ala-Ala-Ala and Phe-Phe-Phe

Cited by 12 publications

References 53 publications

Rearrangement chemistry of a ions probed by IR spectroscopy

Rearrangement chemistry of a ions probed by IR spectroscopy

Proton Mobility in b2 Ion Formation and Fragmentation Reactions of Histidine-Containing Peptides

Formation of a1 Ions Directly from Oxazolone b2 Ions: an Energy-Resolved and Computational Study

Contact Info

Product

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Proton Mobility in b₂ Ion Formation and Fragmentation Reactions of Histidine-Containing Peptides

Formation of a₁ Ions Directly from Oxazolone b₂ Ions: an Energy-Resolved and Computational Study