Mass spectra of doubly charged ions

Abstract

The mass spectra of biological molecules, whose molecular mass exceeds 10 kDa, invariably contain multiply charged ions. For example, a survey scan of a small protein will produce singly, doubly and triply protonated molecules, the intensity of the doubly charged species often being greater than that of the singly charged entity. Although the spectra resulting from doubly charged peptides have not previously been studied, collisional activation of such doubly charged species may result in significant additional information pertaining to molecular structure. The techniques employed to study ions originating from multiply charged species were linked scanning of constant B/E and tandem mass spectrometry, namely low collision energy spectra acquired on a BEQQ hybrid instrument.The methodology was applied to model compounds whose tandem mass spectrometry characteristics are well known, e.g. gramicidin S and angiotensin I. The results for the product ions of the [M + 2H]*+ species of the models were obtained which highlight the methodology required for high-mass materiais.

Comparison between collision induced dissociation of electrosprayed protonated peptides in the up-front source region and in a low-energy collision cell

“…4(c)) is consistent with previous observations that doubly protonated peptides under low- energy CID conditions undergo facile fragmentation yielding redundant sequence information. 17,18,21,22 Our data are also consistent with the general concepts that low-energy decompositions are generally charge-directed, and that singly charged peptide ions which incorporate strongly basic residues undergo less facile fragmentation. 23 In doubly protonated peptides one proton is localised on the side-chain amino group of the C-terminal Lys, whereas the second proton resides on one of a number of sites, thereby promoting multiple fragmentation routes.…”

Conformation of Doubly Protonated Peptides Studied by Charge-separation Reactions in Mass Spectrometry

“…In FAB measurements, a cesium atom gun was used at 30 kV energy, the samples were dissolved in glycerol matrix and the intensity of doubly charged ions was increased by the addition of hydrochloric acid. 46 The observed metastable peak proÐles were analyzed by our computer program developed for the determination of KERD. 44 The algorithm used in the program is based on the calculation of the velocity of the ions formed in the metastable process.…”

Cycloreversion and other gas‐phase reactions of neutral and cationic pyrrolidine‐fused chlorins and isobacteriochlorins under ion bombardment and electrospray

“…Fragmentation of doubly charged ions by losses of charged moieties, triggered by both low-and high-energy collisions, is a well-known process. 30 Elimination of a methyl cation from a methoxy (-OCH 3 ) substituent, for disubstituted amino-s-triazines undergoing coulombic explosion reactions, has been reported. 31 In particular the loss of CH 3 þ from a doubly charged indoleamine cation has been described as occurring through partial location of the positive charge in the methyl group due to stretching of the bond prior to the separation of the two singly charged ions.…”