Characterization of the product ions from the collision-induced dissociation of argentinated peptides

Abstract

Tandem mass spectrometry performed on a pool of 18 oligopeptides shows that the product ion spectra of argentinated peptides, the [bn + OH + Ag]+ ions and the [yn - H + Ag]+ ions bearing identical sequences are virtually identical. These observations suggest strongly that these ions have identical structures in the gas phase. The structures of argentinated glycine, glycylglycine, and glycylglycylglycine were calculated using density functional theory (DFT) at the B3LYP/DZVP level of theory; they were independently confirmed using HF/LANL2DZ. For argentinated glycylglycylglycine, the most stable structure is one in which Ag+ is tetracoordinate and attached to the amino nitrogen and the three carbonyl oxygen atoms. Mechanisms are proposed for the fragmentation of this structure to the [b2 + OH + Ag]+ and the [Y2 - H + Ag]+ ions that are consistent with all experimental observations and known calculated structures and energetics. The structures of the [b2 - H + Ag]+ and the [a2 - H + Ag]+ ions of glycylglycylglycine were also calculated using DFT. These results confirm earlier suggestions that the [b2 - H + Ag]+ ion is an argentinated oxazolone and the [a2 - H + Ag]+ an argentinated immonium ion.

Novel fragmentation pathway for CID of (bn−1+Cat)+ ions from model, metal cationized peptides

“…The amino acid placed at position X either required a larger cyclic intermediate than the five-member ring presumably formed with ␣-amino acids (␤-alanine, ␥-aminobutyric acid, and -amino-n-caproic acid to generate 6-, 7-, or 9-member rings, respectively) or prohibited cyclization because of the inclusion of a rigid ring (para-and meta-aminobenzoic acid). For Ag ϩ , Li ϩ and Na ϩ cationized AcFGGX, formation of (b 3 ϩ 17 ϩ Cat) ϩ was suppressed when the amino acids requiring the adoption of larger ring intermediates were used, while amino acids that prohibit cyclization eliminated the reaction pathway completely-an observation in accord with proposed mechanisms for the formation of this important sequence ion [2][3][4][5][6][7][8].…”

“…The amino acid placed at position X either required a larger cyclic intermediate than the five-member ring presumably formed with ␣-amino acids (␤-alanine, ␥-aminobutyric acid, and -amino-n-caproic acid to generate 6-, 7-, or 9-member rings, respectively) or prohibited cyclization because of the inclusion of a rigid ring (para-and meta-aminobenzoic acid). For Ag ϩ , Li ϩ and Na ϩ cationized AcFGGX, formation of (b 3 ϩ 17 ϩ Cat) ϩ was suppressed when the amino acids requiring the adoption of larger ring intermediates were used, while amino acids that prohibit cyclization eliminated the reaction pathway completely-an observation in accord with proposed mechanisms for the formation of this important sequence ion [2][3][4][5][6][7][8].During subsequent experiments involving peptides containing similar "alternative" amino acids, we observed an unusual fragmentation pathway when the (b 3 Ϫ 1 ϩ Li) ϩ product ion derived from the synthetic peptide A(␤A)AG was subjected to collision-induced dissociation (CID). The pathway resulted in a neutral loss one mass unit (u) greater than the residue mass of the amino acid that composed the presumed oxazolinone ring [9 -15] of the (b 3 Ϫ 1 ϩ Li) ϩ species, and thus could not be attributed to the formation of the (b 2 Ϫ 1 ϩ Li) ϩ ion.…”

Glycine-Zn+/Zn2+ and their hydrates: On the number of water molecules necessary to stabilize the switterionic glycine-Zn+/Zn2+ over the nonzwitterionic ones

“…Recently, there has been a growing interest in the combination of metal ions with amino acid molecules [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and further combination with water molecules 16 due to its importance in the fields of catalysis, atmospheric chemistry or biochemistry, especially in the biochemical fields. The interaction between a metal ion and a single hydrated amino acid is essential building blocks for our understanding of the role of metal ions in the structure and function of proteins, nucleic acids and peptide hormones, which are yet often unknown, at the atomic and electronic level, while the nature of watermetal ion-biomolecule interactions remains nebulous.…”

Ion–molecule reactions reveal facile radical migration in peptides

“…Numerous methods (including electron initiated fragmentation, 1,2 direct bond homolysis by photolysis 3 or collisional activation, [4][5][6][7][8][9][10] and photoionisation 11 ) can be used to generate peptide radicals. Following radical generation, the subsequent fragmentation chemistry of the peptide is typically dominated by radical-directed processes, making the location of the radical crucial as the initiation point for fragmentation.…”