Dissociation Of Negative Ions Research Articles

Induced Charge and Dissociation of Negative Ions on a Conducting Surface

Induced Charge and Dissociation of Negative Ions on a Conducting Surface

Negative ion dissociation of peptides containing hydroxyl side chains

The dissociation of deprotonated peptides containing hydroxyl side chains was studied by electrospray ionization coupled with Fourier transform ion cyclotron resonance (ESI-FTICR) via sustained off-resonance irradiation collision induced dissociation (SORI-CID). Dissociation under post-source decay (PSD) conditions was performed by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF). This work included hexapeptides with one residue of serine, threonine, or tyrosine and five inert alanine residues. During SORI-CID and PSD, dissociation of [M-H](-) yielded c- and y-ions. Side-chain losses of formaldehyde (HCHO) from serine-containing peptides, acetaldehyde (CH(3)CHO) from threonine-containing peptides, and 4-methylene-2,5-cycohexadienone (C(7)H(6)O) from tyrosine-containing peptides were generally observed in the negative ion PSD and SORI-CID spectra. Side-chain loss occurs much less from tyrosine-containing peptides than from serine- and threonine-containing peptides. This is probably due to the bulky side chain of tyrosine, resulting in steric hindrance and poor geometry for dissociation reactions. Additionally, a selective cleavage leading to the elimination of the C-terminal residue from [M-H](-) was observed from the peptides with serine and threonine at the C-terminus. This cleavage does not occur in the dissociation of peptides with an amide group at the C-terminus or peptides with neutral or basic residues at the C-terminus. It also does not occur with tyrosine at the C-terminus. Both the C-terminal carboxylic acid group and the hydroxyl side chain of the C-terminal residue must play important roles in the mechanism of C-terminal residue loss. A mechanism involving both the C-terminal carboxylic acid group and a hydroxyl side chain of serine and threonine is proposed.

Gas-Phase Observation of the Heterolytic Dissociation of Negative Ions into Counter Ions: Dissociation of [Cu phthalocyanine (SO 3) 4Na] 3−

Ion pair formation proceeding in solution at room-temperature, where it is driven by energies of solvation, has been observed in the gas-phase in the collision-induced dissociation of [Cu phthalocyanine (SO3)4Na]3- and [Cu phthalocyanine (SO3)4Na2]2- at low energies. The gas-phase observation of these charge separations into positive and negative ions, seemingly counter-intuitive, is favored sufficiently by thermodynamics to proceed at low collision energies. The combination of a high stability of the negative product anion against electron detachment and a low recombination energy of the departing positive counter ion appears to be the key requirement for such dissociations to proceed at low energies in the gas-phase.

The Influence of Sialylation on Glycan Negative Ion Dissociation and Energetics

For the analysis of native glycans using tandem mass spectrometry (MS), it is desirable to choose conditions whereby abundances of cross-ring cleavages indicative of branch positions are maximized. Recently, negative ion tandem mass spectrometry has been shown to produce significantly higher abundances of such ions in glycans compared to the positive ion mode. Much of this prior work has concerned fragmentation patterns in asialo glycans. The present work compares the abundances of critical cross-ring cleavage ions using negative mode tandem mass spectrometry for milk oligosaccharides and N-linked glycans. For comparison, product ion formation was studied for deprotonated and nitrated ions formed from asialo glycans and deprotonated ions from sialylated glycans. Breakdown profiles demonstrate clearly that more energy was required to fragment sialylated compounds to the same extent as either their asialo or nitrate adducted counterparts. The extraction of a proton from a ring hydroxyl group during the ionization process may be viewed, qualitatively, as imparting significantly more energy to the ion than would that from a molecule bearing an acidic group, so that acidic glycans are more stable in the gas phase, as the negative charge resides on the carboxyl group. These results have strong practical implications because a major portion of glycans released from mammalian proteins will be sialylated.

Electric dissociation of negative ions at MeV energies

Electric dissociation of negative ions at MeV energies

Effect of tautomerization on the fast-atom bombardment tandem mass spectra of azo dyes

The effect of tautomerization on the collision-induced dissociation of negative ions produced from sulfonated azo dyes by fast-atom bombardment (FAB) was studied by analyzing the product ion spectra of several related compounds. The mechanisms by which azo dyes fragment were found to depend on the formation and stability of tautomers. The extent of tautomerization was affected by the number and location of hydroxy groups on the dye, as well as by the FAB matrix. Ions that retained a sodium were often inhibited from forming tautomers and gave different product ions. Substitution of deuterium for hydrogen on the hydroxy groups aided in the identification of ions having more than one possible structure and provided verification of proposed mechanisms. Mechanisms involving ions retaining a sodium were verified by substituting potassium for the sodium.

Electric dissociation of negative ions

As an alternative to naturally occurring negative ion discrimination, we consider the possibility of electric dissociation to discriminate between isobars, by destroying the weaker negative ion of a pair. The theoretical basis of negative ion dissociation using high electric gradients and an appropriate experimental setup are discussed. The possibility of negative ion destruction by electric dissociation during the first stage of tandem acceleration and at the ion source is also considered. In consequence, it is possible to place a limit on the electron affinity of some elements considering their survival in the AMS system. Mn −, Ca − and C −∗ among others are considered.

Collision-Induced Dissociations of Negative-Ions Formed by Reaction of HO- With Alkyl and Aryl Silanes. The Formation of Multiple Bonds to Silicon

Collisional activation of alkyl and aryl siloxide ions produces a variety of ions and neutrals containing double bonds to silicon. Sila enolate ions and sila acyl ions RSi =O are common features of the spectra of alkylsiloxide ions; ab initio calculations suggest these ions to have considerable multiple bond character. It is proposed that most reactions proceed through ion complex intermediates. Specific proton transfer reactions often occur for ions Me3SiCHR (R = C3H5, C3H3 or Ph), i.e. Me3SiCHR → -CH2(Me)2SiCH2R. In the particular case of the formation of PhCH2- from Me3SiCHPh, i.e. Me3SiCHPh → -CH2(Me)2SiCH2Ph → PhCH2- +Me2Si=CH2, the proton transfer competes with scrambling of all hydrogens in the decomposing ion.

Collision-activated dissociation of negative ions in an ion trap mass spectrometer

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCollision-activated dissociation of negative ions in an ion trap mass spectrometerScott A. McLuckey, Gary L. Glish, and Paul E. KelleyCite this: Anal. Chem. 1987, 59, 13, 1670–1674Publication Date (Print):July 1, 1987Publication History Published online1 May 2002Published inissue 1 July 1987https://doi.org/10.1021/ac00140a019RIGHTS & PERMISSIONSArticle Views207Altmetric-Citations67LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (661 KB) Get e-Alerts Get e-Alerts

Collision‐induced dissociation of negative ions in the gas phase: [Aryl S]−, [aryl SO]− and [aryl SO2]−

AbstractCollision‐induced dissociation of the ions [ArS]−, [ArSO]− and [ArSO2]− has uncovered a rich and varied ion chemistry. The major fragmentations of [ArS]− are complex and occur without prior ring hydrogen scrambling: for example, [C6H5S]−→[C2HS]− and [HS]−; [p‐CD3C6H4S]−→[C6H4S]−˙, [CD3C4S]− and [C2HS]−. In contrast, all decompositions of [C6H5CH2S]− are preceded by specific benzylic and phenyl hydrogen interchange reactions. [ArSO2]− and [ArSO2]− ions undergo rearrangement, e.g. [C6H5SO]−→[C6H5O]− and [C6H5S]−; [C6H5SO2]−→[C6H5O] −. The ion [C6H5CH2SO]− eliminates water, this decomposition is preceded by benzylic and phenyl hydrogen exchange.

Low energy electron impact on benzene and the fluorobenzenes. Formation and dissociation of negative ions

Electron attachment spectroscopy with nearly monoenergetic electrons is employed to study the formation and dissociation of negative ions in benzene and the fluorobenzenes. From all compounds, various negative ion fragments resulting from resonance dissociative electron attachment are observed. Electron affinities in the limit of the unknown excess energy are determined for the radicals C 6F 5 ·, C 6HF 4 ·, C 6H 2F 3 ·, and C 6H 2F 2 ·. Only in hexafluorobenzene is a long-lived parent molecular negative ion observed.

Electron-attachment spectroscopy: formation and dissociation of negative ions in the fluorochloroethylenes

The formation and dissociation of negative ions in C 2Cl 4, C 2FCl 3, 1,1-C 2F 2Cl 2, 1,2-C 2F 2Cl 2 (isomeric mixture), C 2F 3Cl and C 2F 4 have been studied employing (dissociative) electron-attachment spectroscopy with nearly monoenergetic electrons in the energy range 0–15 eV. All six compounds show low-lying resonances (below 4eV) associated with various dissociation channels leading to one negative and one neutral fragment. It is found that the resonance energy increases if Cl is replaced by F. Electron affinities in the limit of the unknown excess energy are given for the radicals C 2Cl 3, C 2F 2Cl 2, C 2F 2Cl and C 2F 3. For C 2Cl 4 and C 2F 2Cl 2 long-lived parent molecular anions are observed. Only tetrafluoroethylene gives fragments by cleavage of the double bond, as a result of the perfluoro effect.

Collision-induced dissociations of negative ions. α-Dicarbonyl parent negative ions

α-Dicarbonyl compounds form stable parent negative ions by capture of low-energy electrons. The parent negative ions undergo a variety of collision induced dissociations, the most characteristic being β cleavage to a carbonyl group, i.e. see diagram in paperCyclic α-dicarbonyl parent negative ions may also eliminate molecules of carbon monoxide, for example the fragmentations M- → [M-(R + CO)]- M- →[M - (R-2CO)]- and M- → [M-2CO]- occur in a number of cases.

Analysis of underivatised peptide mixtures by collision-induced dissociation of negative ions

Collision-induced decomposition of mass-selected negative ions has been used to provide useful sequence information from underivatised peptides and their mixtures.

Invited Paper-An H- Meson Facility

With the continuing evolution of the various types of meson factories the relative merits of the H- spiral ridge eyclotron appear to be improving. The development and design of such an accelerator has been led by UCLA. Recently three universities in British Columbia have combined personnel for a design study intended to lead to an H- meson facility called TRIUMF - Tri University Meson Facility). Among the various meson factories the H- facility is the only one which combines the following advantages: (1) large duty factor; (2) variable energy; (3) ease of beam extraction; (4) use of simultaneous beams; (5) high beam quality. Until recently it faced two problems: (a) uncertainty about field dissociation of negative ions; (b) lack of polarized ion sourees. Recent UCLA measurements of field dissociation and the advent of polarized H- ion sources and axial injection into cyclotrons remove these problems. The field dissociation measurements agree with Hiskes' calculations and enable the use of higher fields than previously proposed for H- facilities. The TRIUMF project concerns a machine whose beam characteristics (maximum energy 500 MeV; maximum beam radius 271 inches; beam current 20-100 μA) were selected for optimum use in nuelear structure experiments, for low cost and for operating simplieity.