Electron-induced dissociation of protonated peptides yields backbone fragmentation consistent with a hydrogen-deficient radical

ArticleinRapid Communications in Mass Spectrometry 23(13):2099-101 · July 2009with9 Reads
DOI: 10.1002/rcm.4117 · Source: PubMed
    • "In as much as the triply charged radical of Substance P has been identified in an high-energy EID spectrum recorded at a resolving power of ~13,500 (m/z 674) with a QqTOF mass spectrometer in which an EMS ECD cell was installed [27], it is reasonable to expect that the preceding conclusion extends to an EMS ECD cell installed in a QqTOF mass spectrometer with the added benefit of that platform's greater resolving power. The levels of fragmentation efficiency evident in the product-ion spectra recorded in this study as well as in those recorded in earlier studies with FT ICR mass spectrometers [12,151617181920 is at the margin of analytical utility. Efforts by the present authors are underway to eliminate this shortcoming in the EMS cell. "
    [Show abstract] [Hide abstract] ABSTRACT: Dissociation of peptides induced by interaction with (free) electrons (electron-induced dissociation, EID) at electron energies ranging from near 0 to >30 eV was carried out using a radio-frequency-free electromagnetostatic (EMS) cell retrofitted into a triple quadrupole mass spectrometer. The product-ion mass spectra exhibited EID originating from electronically excited even-electron precursor ions, reduced radical cations formed by capture of low-energy electrons, and oxidized radical cations produced by interaction with high-energy electrons. The spectra demonstrate, within the limits of the triple quadrupole's resolving power, that high-energy EID product-ion spectra produced with an EMS cell exhibit essentially the same qualitative structural information, i.e., amino acid side-chain (SC) losses and backbone cleavages, as observed in high-energy EID spectra produced with a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer. The levels of fragmentation efficiency evident in the product-ion spectra recorded in this study, as was the case for those recorded in earlier studies with FT ICR mass spectrometers, is currently at the margin of analytical utility. Given that this shortcoming can be remedied, EMS cells incorporated into QqQ or QqTOF mass spectrometers could make tandem high-energy EID mass spectrometry more widely accessible for analysis of peptides, small singly charged molecules, pharmaceuticals, and clinical samples.
    Full-text · Article · Feb 2015
    • "Dissociation of the hydrogen rich radical cations often gives rise to c and z@BULLET ions, along with side-chain losses, through which they can convert quickly to hydrogen deficient radical ions192021. Hydrogen deficient cations can be generated by a variety of methods: laser ablation followed by ultraviolet (UV) photoionization [22, 23]; collision-induced dissociation (CID) of metal-ligand-peptide complexes242526; CID of peptide derivatives with labile bonds such as S-nitrosylation [27, 28], serine/homoserine nitrate esters [29], peroxycarbamates [30], 2,2,6,6-tetramethylpiperidine-1-oxy (TEMPO) [31, 32], and 4,4'-azobis(4-cyanopentanoic acid) (Vazo 68) [33] ; UV photolysis of iodinated tyrosine containing peptides [34] ; or noncovalent complexes with photolabile precursor [35] ; electroninduced dissociation of multiply charged ions [36, 37]. Hydrogen deficient radical anions can be formed by electron detachment [38] or photodetachment [39] from multiply deprotonated molecules, CID of peptide–metal complexes [40, 41], and photodissociation of iodinated peptide [42]. "
    [Show abstract] [Hide abstract] ABSTRACT: A variety of peptide sulfinyl radical (RSO•) ions with a well-defined radical site at the cysteine side chain were formed at atmospheric pressure (AP), sampled into a mass spectrometer, and investigated via collision-induced dissociation (CID). The radical ion formation was based on AP reactions between oxidative radicals and peptide ions containing single inter-chain disulfide bond or free thiol group generated from nanoelectrospray ionization (nanoESI). The radical induced reactions allowed large flexibility in forming peptide radical ions independent of ion polarity (protonated or deprotonated) or charge state (singly or multiply charged). More than 20 peptide sulfinyl radical ions in either positive or negative ion mode were subjected to low energy collisional activation on a triple-quadrupole/linear ion trap mass spectrometer. The competition between radical- and charge-directed fragmentation pathways was largely affected by the presence of mobile protons. For peptide sulfinyl radical ions with reduced proton mobility (i.e., singly protonated, containing basic amino acid residues), loss of 62 Da (CH(2)SO), a radical-initiated dissociation channel, was dominant. For systems with mobile protons, this channel was suppressed, while charge-directed amide bond cleavages were preferred. The polarity of charge was found to significantly alter the radical-initiated dissociation channels, which might be related to the difference in stability of the product ions in different ion charge polarities.
    Article · Aug 2012
    • "Applying these higher energy electrons to multiply charged peptides is known as hot electron capture dissociation (hECD) and has been shown to produce a significant increase in side chain fragmentation producing an even greater depth of information [20, 21]. More recently, the interaction between hotter electrons and singly charged cations has been shown to induce fragmentation and is referred to as electron induced dissociation (EID) [19,2223242526272829 . In a very recent study with pharmaceutical type molecules, EID produced extensive product ion data that largely complemented CID, was comparable to electron ionization (EI), and was more tolerant to a wider range of charge carrying species than CID [29]. "
    [Show abstract] [Hide abstract] ABSTRACT: LC ESI FTICR MS of a sample of cediranib identified this pharmaceutical target molecule plus an additional 10 compounds of interest, all of which were less than 10% total ion current (TIC) peak intensity relative to cediranib. LC FTICR tandem mass spectrometry using electron induced dissociation (EID) has been achieved and has proven to be the best way to generate useful product ion information for all of these singly protonated molecules. Cediranib [M + H](+) fragmented by EID to give 29 product ions whereas QTOF-CID generated only one very intense product ion, and linear ion trap-CID, which generated 10 product ions, but all with poor S/N. Twenty-six of the EID product ions were unique to this fragmentation technique alone. By considering the complementary LC-EID and LC-CID data together, all 10 unknown compounds were structurally characterized and proven to be analogous to cediranib. Of particular importance, EID produced unique product ion information for one of the low level cediranib analogues that enabled full characterization of the molecule such that the presence of an extra propylpyrrolidine group was discovered and proven to be located on the pyrrolidine ring of cediranib, solving an analytical problem that could not be solved by collision induced dissociation (CID). Thus, it has been demonstrated that EID is in harmony with the chromatography duty-cycle and the dynamic concentration range of synthetic compounds containing trace impurities, providing crucial analytical information that cannot be obtained by more traditional methodologies.
    Full-text · Article · Jan 2012
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