Structures of b and a Product Ions from the Fragmentation of Argentinated Peptides

Lee, Vicky W.-M.; Li, Hongbo; Lau, Tai‐Chu; Siu, Kin Wai Michael

doi:10.1021/ja9808245

Cited by 54 publications

(58 citation statements)

References 45 publications

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“…1 H NMR (400 MHz, CDCl 3 , 298 K) revealed ␦ 4.409 (s, 2H, NCH 2 CO), 7.473 (t, 2H, J ϭ 8.0 Hz, meta-H), 7.551 (t, 1H, J ϭ 6 Hz, para-H), and 7.977 (d, 2H, J ϭ 7.6 Hz, ortho-H). This spectrum is consistent with that previously published [47]. The ESI mass spectrum showed only the protonated molecule at m/z 162.…”

Section: Synthesis Of 2-phenyl-5-oxazolonesupporting

confidence: 92%

Why are a₃ ions rarely observed?

Allen

Racine

Berman

et al. 2008

J. Am. Soc. Mass Spectrom.

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It has been determined experimentally that a 3 ions are generally not observed in the tandem mass spectroscopic (MS/MS) spectra of b 3 ions. This is in contrast to other b n ions, which often have the corresponding a n ion as the base peak in their MS/MS spectra. Although this might suggest a different structure for b 3 ions compared to that of other b n ions, theoretical calculations indicate the conventional oxazolone structure to be the lowest energy structure for the b 3 ion of AAAAR, as it is for other b n ions of this peptide. However, it has been determined theoretically that the a 3 ion is lower in energy than other a n ions, relative to the corresponding b ions. Furthermore, the a 3 ¡ b 2 transition structure (TS) is lower in energy than other a n ¡ b nϪ1 TSs of AAAAR, compared with the corresponding b ions. Consequently, it is suggested that the b 3 ion does fragment to the a 3 ion, but that the a 3 ion then immediately fragments (to b 2 and a 3 *) because of the excess internal energy arising from its relatively low energy and the facile It has been shown that significant rearrangement can occur upon peptide dissociation, particularly in mass spectrometers with relatively long activation/dissociation times such as ion trapping instruments [23][24][25][26][27][28]. However, rearrangements are not limited to ion trapping mass spectrometers [29 -32]. In actuality even b and y ions are formed by rearrangements involving hydrogen atom transfers (y ions) or intramolecular cyclization (b ions). The ubiquitousness of the mechanism for formation of b and y ions has been shown through kinetic energy loss measurements [33].Initially it was thought that b ions had a simple acylium ion structure [5,34,35]. However, this theory was discredited because b 1 ions are not often observed in MS/MS spectra (i.e., these ions should also be acylium ions by the preceding rationale). The current consensus is that b ions most commonly have a protonated oxazolone structure [36 -39]. This has been demonstrated in gas-phase IR studies on the b 4 ions of YGGFL [38,40]. Additionally, recent experimental and theoretical data suggest that larger oxazolones can undergo head-to-tail cyclization to form cyclic-peptide isomers [32,40]. Further evidence supporting the conclusion that b ions have the protonated oxazolone structure is that the major dissociation products of b ions (a n and b nϪ1 ions) have product ion analogs in the MS/MS spectra of synthesized oxazolone compounds [37].Although formation of a n ions via the b n ¡ a n pathway is well understood [41], the actual mechanism of b nϪ1 formation is less clear. Two major mechanisms were considered here, the direct b n ¡ b nϪ1 [36] and indirect b n ¡ a n ¡ b nϪ1 [42] pathways. Metastable ion studies indicate that a n ions are formed with substantial release of kinetic energy (KER). On the other hand b nϪ1 fragments are formed from b n parents with small KER values [36,37]. This finding suggests that a direct b n ¡ b nϪ1 mechanism is preferred. Additionally, doubleresonance experimen...

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Section: Synthesis Of 2-phenyl-5-oxazolonesupporting

confidence: 92%

Why are a₃ ions rarely observed?

Allen

Racine

Berman

et al. 2008

J. Am. Soc. Mass Spectrom.

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“…It has been shown that the formation of [b n ] C or the analogous [b n 1 C Cat] C ions involves the formation of a five-membered ring oxazolin-5-one structure, initiated by the attack on the carbonyl carbon atom of the amide bond being cleaved by an oxygen atom on a carbonyl moiety located to the N-terminal side of the reaction site. 12,20,21 For Ag C cationized GG or GA, there are no such carbonyl groups to serve as nucleophiles, and the attack to produce the [b 1 …”

Section: Ag]mentioning

confidence: 99%

Formation of [b_n + 17 + Ag]⁺ product ions from Ag⁺ cationized native and acetylated peptides

et al. 2002

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We compared the tandem mass spectra of a range of native and acetylated Ag(+) cationized peptides to determine the influence of the derivatization step on the abundance of the [b(n) + 17 + Ag](+) product ions. Using tripeptides, the smallest for which the mechanisms to generate [b(2) - 1 + Ag](+) and [b(2) + 17 + Ag](+) products are both operative, we found that in most cases acetylation causes an increase in the abundance of the C-terminal rearrangement ion, [b(2) + 17 + Ag](+), relative to the rival N-terminal rearrangement ion, [b(2) - 1 + Ag](+). The presence of a free amino group to bind to the metal ion significantly influences the relative abundances of the product ions. We propose a mechanism for the formation of the [b(n) + 17 + Ag](+) that is based on the formation of a five-membered oxazolidin-5-one and tetrahedral carbon intermediate that may collapse to a peptide upon release of CO and an imine, aided by the fact that the ring formed during C-terminal rearrangement is both a hemiacylal and hemiaminal. We also identified an influence of amino acid sequence on the relative abundances of the [b(n) + 17 + Ag](+) and [b(n) - 1 + Ag](+) product ions, whereby bulky substituents located on the alpha-carbon of the amino acid to the C-terminal side of the cleavage site apparently promote the formation of the [b(n) + 17 + Ag](+) product over [b(n) - 1 + Ag](+) when the amino acid to the N-terminal side of the cleavage site is glycine. The latter ion is the favored product, however, when the bulky group is positioned on the alpha-carbon of the amino acid to the N-terminal side of the cleavage site.

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“…Interactions of metal cations with peptides and proteins in gas‐phase complexes have been studied intensively,1–16 as reviewed 17. Of particular interest has been the use of gas‐phase peptide complex dissociations for structure elucidation of peptides by mass spectrometry 18.…”

Section: Introductionmentioning

confidence: 99%

Sequence information, distinction and quantitation of C‐terminal leucine and isoleucine in ternary complexes of tripeptides with Cu(II) and 2,2′‐bipyridine

et al. 2001

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Tripeptides form ternary complexes with Cu(2+) and 2,2'-bipyridine (bpy) that self-assemble upon mixing the components in aqueous methanol solution. Electrospray ionization (ESI) of the complex solutions provides abundant singly charged [Cu(peptide -- H)bpy](+) and doubly charged [Cu(peptide)bpy](2+) ions. Collision-induced dissociation (CID) at low ion kinetic energies of several tripeptides, AGG, GGA, LGG, GGL, GGI, FGG, GGF, LGF, GLF, GFL, GYA and GAY, showed fragments that were indicative of the amino acid sequence in the peptide. In addition, CID of single and doubly charged complexes of isomeric tripeptides GGL and GGI provided unambiguous distinction of the isomeric leucine and isoleucine residues. Leucine peptides eliminated C(3)H(7) radicals from the amino acid side-chain whereas isoleucine eliminated C(2)H(5) radicals. CID of gas-phase doubly charged peptide complexes in a quadrupole ion trap produced a series of singly charged sequence fragments that following isolation and further CID furnished distinct fragments that allowed quantitation of leucine and isoleucine-containing peptides in mixtures.

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Structures of b and a Product Ions from the Fragmentation of Argentinated Peptides

Cited by 54 publications

References 45 publications

Why are a₃ ions rarely observed?

Why are a₃ ions rarely observed?

Formation of [b_n + 17 + Ag]⁺ product ions from Ag⁺ cationized native and acetylated peptides

Sequence information, distinction and quantitation of C‐terminal leucine and isoleucine in ternary complexes of tripeptides with Cu(II) and 2,2′‐bipyridine

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Structures of b and a Product Ions from the Fragmentation of Argentinated Peptides

Cited by 54 publications

References 45 publications

Why are a3 ions rarely observed?

Why are a3 ions rarely observed?

Formation of [bn + 17 + Ag]+ product ions from Ag+ cationized native and acetylated peptides

Sequence information, distinction and quantitation of C‐terminal leucine and isoleucine in ternary complexes of tripeptides with Cu(II) and 2,2′‐bipyridine

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Product

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Why are a₃ ions rarely observed?

Why are a₃ ions rarely observed?

Formation of [b_n + 17 + Ag]⁺ product ions from Ag⁺ cationized native and acetylated peptides