Collision-induced Decomposition Research Articles

Identification of isomeric tributylphosphate dimers formed by radiolysis using tandem mass spectrometry and stable isotopic labelling

Tributylphosphate (TBP) dimers, formed during radiolysis of the nuclear fuel reprocessing solvent, were studied using tandem mass spectrometry (MS/MS), stable isotopic labelling ( 2 H) and synthetic model compounds. The structures of isomeric dimers and their lower homologues were established, using GC/MS as well as electron impact and chemical ionisation GC/tandem mass spectrometry, with an extensive use of ion chromatograms of characteristic fragment ions from collision-induced decomposition in both nondeuterated and selectively deuterated series. An explanation of isomer ratios and of the restricted number of lower homologues as well as a radiolytic mechanism are advanced. The TBP-dimer fraction represented less than ~ 0.03% of the total mixture obtained from radiolysis of solvent.

High sensitivity mass spectral characterization of glycosphingolipids from bovine erythrocytes, mouse kidney and fetal calf brain

Stage-specific embryonic antigen (SSEA) glycosphingolipids (GSLs) found in the central nervous system are implicated in regulating cell-cell recognition, targeting and migration of cells during development. Through the action of fucosyltransferase enzymes, SSEA-1 (Lewis x) glycolipids are biosynthesized in the brain by fucosylation of lipid substrates with the neolacto series glycolipid core structure [Galβ1 → 4GlcNAcβ1 → 3Galβ1 → 4Glcβ1 → 1'Cer] (originally termed paragloboside) or its higher analogs. In order to optimize methodology for high sensitivity structural determinations of SSEA-1 type glycolipids from fetal calf brain, potential precursors and SSEA-1 glycolipids of previously established structure were first isolated from bovine erythrocytes and beige mutant mouse kidney, purified by column chromatography and characterized by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) MS, liquid secondary ionization mass spectrometry (LSIMS), and tandem mass spectrometry (MS/MS), among other techniques. Peracetylated derivatives were detected at the low femtomole level by MALDI-TOF MS and the subnanomole level by LSIMS. MALDI-TOF MS produced mainly [M + Na] + and [M + K] + species. On the basis of the direct and tandem mass spectral analyses of peracetylated and permethylated derivatives, the carbohydrate sequences in the selected bovine erythrocyte and mouse kidney GSL fractions were found to be consistent with those of glycolipids previously-reported from larger-scale studies of these sources. Their heterogeneous ceramide moieties were characterized by collision induced decomposition (CID) MS/MS of abundant Z 0-type ions in the LSI mass spectra of the permethylated GSLs. MALDI-PSD-TOF mass spectral analyses of low and subpicomole amounts of derivatized GSL fractions from fetal calf brain provided carbohydrate sequence information that indicates the presence of mono- and difucosylated SSEA-1 neolacto series glycolipids and their nonfucosylated analogs.

MALDI-TOF and electrospray tandem mass spectrometric analysis of fatty acyl-CoA esters

Coenzyme A (CoA) thioesters play a central role in many biochemical reactions, and methods for sensitive identification of these compounds are important for studies of cellular processes. The direct analysis of intact long-chain fatty acyl CoA esters was investigated using matrix assisted laser desorption time-of-flight and electrospray ionization mass spectrometry. Both techniques resulted in the formation of abundant positive and negative ions indicative of the molecular weight of the fatty acyl CoA molecular species. Several structurally significant fragment ions, in particular positive ions indicative of the fatty acyl portion of the molecule, were formed during ionization processes. Metastable (MALDI-TOF) and collision-induced decomposition (quadrupole tandem mass spectrometry) of these molecular ion species resulted in the formation of similar product ions independent of the mode of ionization. Abundant product ions, corresponding to the fatty acyl portion as well as the pantetheine-ADP portion of the molecule, were observed with both ionization techniques. Decomposition of the [M + H] + ion of hexadecyl coenzyme A (C16:0 CoA) at m / z 1006 yielded a prominent product ion at m / z 499 which was characteristic of the fatty acyl portion of the molecule. Similar fatty acyl product ion fragments corresponding to a neutral loss of 609 were found for the [M + H] + species of all the fatty acyl CoA esters investigated. This prominent and diagnostic fragment could be used to detect molecular species of CoA esters present in complex biological mixtures.

Effect of lithium cationization on oxygen atom transfer from the nitro group to the double bond during collision-induced decomposition in certain substituted β-nitrostyrenes

Effect of lithium cationization on oxygen atom transfer from the nitro group to the double bond during collision-induced decomposition in certain substituted β-nitrostyrenes

Electrospray ionization mass spectrometric study of oligomeric linear polysulfides: characterization of repeat units, end groups and fragmentation pathways

Electrospray ionization mass spectrometry is shown to offer excellent characterization of linear oligomeric polysulfides H(SC 2H 4OCH 2OC 2H 4S) n H with n = 1–24. Analysis of the mass spectra reveals the presence of individual oligomers, the presence in certain oligomers of repeat units containing additional oxyalkylene groups (and in some cases a monosulfide link rather than disulfide) and the presence of end groups such as epoxy. The attachment of polyacrylates during cure can also be detected. Assignments of individual peaks can be confirmed by collision-induced decomposition and precursor ion experiments: the fragmentation pathways are relatively few except for linear polysulfides of complex structure. The best signal-to-noise conditions are achieved with low-to-medium cone voltages and a mobile phase of acetone containing 0.5% KI.

Stereospecific Ion-Molecule Reactions of Nucleophilic Gas-phase Reagents with Protonated Bifunctional Tetracyclic Terpene Epimers in the Triple Quadrupole Collision Cell

Various nucleophilic reagents (methanol, acetone, ammonia and trimethylamine), characterized by different proton affinities, were introduced into the collision cell of the triple quadrupole as reactive gases for collisionally activated reaction (CAR) studies on stereoisomeric tetracyclic terpenes containing acetal and cyclobutanol functions. Under low-energy (Elab∽3 eV) and multiple collision conditions, proton transfer from protonated terpenes (MH+, selected by the first quadrupole) to the reagent gas was observed in each case, at varying efficiencies. At the same time, collision-induced decompositions (CIDs) were observed as competing processes in each tandem mass spectrum. For methanol, the reaction gas having the lowest proton affinity, CID processes were heavily favored, whereas CAR processes dominated only for trimethylamine (highest proton affinity) reacting with the exo terpene epimer. The latter reagent gas receives the proton in an exothermic transfer which is strikingly stereospecific. The underlying stereochemical effect is attributed not only to proton affinity differences which favor transfer from the exo epimer, but also to steric and kinetic factors which are evidently highly unfavorable for the endo configuration. © 1997 by John Wiley & Sons, Ltd.

Stereospecific IonMolecule Reactions of Nucleophilic Gasphase Reagents with Protonated Bifunctional Tetracyclic Terpene Epimers in the Triple Quadrupole Collision Cell

Various nucleophilic reagents (methanol, acetone, ammonia and trimethylamine), characterized by different proton affinities, were introduced into the collision cell of the triple quadrupole as reactive gases for collisionally activated reaction (CAR) studies on stereoisomeric tetracyclic terpenes containing acetal and cyclobutanol functions. Under low-energy (Elab∽3 eV) and multiple collision conditions, proton transfer from protonated terpenes (MH+, selected by the first quadrupole) to the reagent gas was observed in each case, at varying efficiencies. At the same time, collision-induced decompositions (CIDs) were observed as competing processes in each tandem mass spectrum. For methanol, the reaction gas having the lowest proton affinity, CID processes were heavily favored, whereas CAR processes dominated only for trimethylamine (highest proton affinity) reacting with the exo terpene epimer. The latter reagent gas receives the proton in an exothermic transfer which is strikingly stereospecific. The underlying stereochemical effect is attributed not only to proton affinity differences which favor transfer from the exo epimer, but also to steric and kinetic factors which are evidently highly unfavorable for the endo configuration. © 1997 by John Wiley & Sons, Ltd.

Formation of Radical Anion Adduct between Paclitaxel and Matrix under Fast-atom Bombardment

The effect of different matrices on the negative-ion fast-atom bombardment mass spectrum of Paclitaxel has been studied. It is found that the nitro-containing matrices, such as 3-nitrobenzyl alcohol, give rise to abundant radical anion adducts. Collision-induced decomposition of these adducts leads to the formation of deprotonated Paclitaxel and the matrix molecular anions. © 1997 John Wiley & Sons, Ltd.

Structural studies of the O-specific chain of Hafnia alvei strain 32 lipopolysaccharide

The structure of the O-specific side-chain of the Hafnia alvei strain 32 lipopolysaccharide has been investigated. Methylation analysis, partial acid hydrolysis, Smith degradations, NMR spectroscopy, MALDI-TOF and FAB mass spectrometry in combination with collision-induced decomposition MS/MS were the principal methods used. It is concluded that the polysaccharide is composed of pentasaccharide repeating units having the following structure which is partially O-acetylated in the 2- (20%) and 3- (50%) position of the → 4)-α- d-Gal p A-(1 → residue . ▪ A MALDI-TOF mass spectrum of the O-specific chains indicated that they consisted of up to 16 repeating units.

The Effects of Internal Energy Deposition During Ionization on the Collision-induced Decomposition Spectra of an Organic Polymer Additive

The Effects of Internal Energy Deposition During Ionization on the Collision-induced Decomposition Spectra of an Organic Polymer Additive

Transfer of Man9GlcNAc tol-fucose by endo-?-N-acetylglucosaminidase fromArthrobacter protophormiae

We have reported that transglycosylation activity of endo-β-N-acetylglucosaminidase fromArthrobacter protophormiae (endo-A) can be enhanced to near completion using GlcNAc as an acceptor in a medium containing 30% acetone (Fan J-Q, Takegawa K, Iwahara S, Kondo A, Kato I, Abeygunawardana C, Lee YC (1995)J Biol Chem270: 17723–29). In this paper, we found that the endo-A can also transfer an oligosaccharide, Man9GlcNAc, tol-Fuc using Man9GlcNAc2Asn as donor substrate in a medium containing 35% acetone. The transglycosylation yield was greater than 25% when 0.2m l-Fuc was used as acceptor. The transglycosylation product was purified by high performance liquid chromatography on a graphitized carbon column and the presence ofl-Fuc was confirmed by sugar composition analysis and electrospray mass spectrometry. Sequential exo-glycosidase digestion of pyridyl-2-aminated transglycosylation product, Man9GlcNAc-l-Fuc-PA, revealed that a β-anomeric configuration linkage was formed between GlcNAc andl-Fuc. The GlcNAc was found to be 1,2-linked tol-Fuc by two methods; i) collision-induced decomposition on electrospray mass spectrometry after periodate oxidation, reduction and permethylation of Man9GlcNAc-l-Fuc; and ii) preparation of Man9GlcNAc-l-Fuc-PA, its periodate oxidation and reduction, followed by hydrolysis and HPLC analysis. Thus, the structure of the oligosaccharide synthesized by endo-A transglycosylation was determined to be Man9GlcNAcβ(1,2)-l-Fuc. Methyl β-l-fucopyranoside,l-Gal are also acceptors for the enzymic transglycosylation. However, transglycosylation failed when methyl α-l-fucopyranoside,d-Fuc andd-Gal were used. These results indicate that the endo-A requires not only 3-OH and 4-OH to be equatorial but also a4C1-conformation or equivalent conformation of the acceptor to perform transglycosylation.

Collision-induced Decomposition of Nitrobenzyl Alcohol-derived Ions Under Fast Atom Bombardment

The collision-induced decomposition mass spectrum of protonated m-nitrobenzyl alcohol (NBA) was studied. The various cluster ions fragment mainly by loss of neutral NBA. Nitro-to-nitrite isomerization followed by loss of.NO is a favoured fragmentation pathway of the [MH] + ion. Eliminations of . OH, H 2 O and HNO 2 are among the other common fragmentation routes. Alkali metal cationization also leads to prominent loss of . NO. Accurate mass measurements and various linked scanning measurements were used to elucidate the fragmentation pathways.

Collisioninduced Decomposition of Nitrobenzyl Alcoholderived Ions Under Fast Atom Bombardment

Collisioninduced Decomposition of Nitrobenzyl Alcoholderived Ions Under Fast Atom Bombardment

A neutralization-reionization mass spectrometric study of alkyl hydroperoxide cation radicals and four distinguishable [C,H 3,O 2] + isomers

The cation radicals of simple alkyl hydroperoxides ROOH + (R = CH 3, C 2H 5, iso-C 3H 7, tert-C 4H 9) have been studied by various mass spectrometric techniques, and neutralization-reionization (NR) methods in particular. Collisional activation (CA) of the beam of fast neutrals before reionization (NCR) and collision experiments with the mass-selected survivor ions (NR/CA) demonstrate that the peroxide OO bond remains intact in ionized methyl hydroperoxide. In the series of hydroperoxides, the abundances of the survivor ions decrease with α-substitution, which can be traced back to increasing contributions of [ R + OOH ] ion/dipole complexes to the parent ion beam. For the elucidation of ion structures, +NR − experiments are shown to be particularly helpful; in addition, they also provide insight into the bonding situations in hydroperoxides. Unimolecular loss of H' from metastable ions (MI) of CH 3OOH + leads to hydroperoxy methyl cations, CH 2OOH +, which are characterized by their MI/CA mass spectra. For comparison, four distinguishable [C,H 3,O 2] + isomers (CH 2OOH +, CH 3OO +, HC(OH) 2 , and H 3O +·CO) have been generated and examined by MI, CA, and NR experiments. With the exception of the proton-bound species H 3O +·CO, the corresponding neutral [C,H 3,O 2] . radicals exist as well and do not interconvert into each other. In addition, HOCH 2O . radicals can be probed by −NR + experiments with HOCH 2O − anions. Unimolecular and collision-induced decomposition of CH 2OOH + gives rise inter alia to a composite [C,H 2,O] + peak, which consists of a narrow gaussian and a broad, dish-topped component. The narrow component vanishes in the +NR + experiment.

Electron impact ionization of tetramethylsilane (TMS)

We studied the electron impact ionization of tetramethylsilane (TMS), Si(CH 3) 4, which is utilized in plasma polymerization applications, using various mass spectrometric techniques. Absolute partial cross-sections for the formation of the parent ion and 15 fragment ions were measured in a high resolution double-focusing sector field mass spectrometer from threshold to 90 eV. Complementary measurements of mass spectral cracking patterns of TMS were also carried out using two quadrupole mass spectrometers. Dissociative ionization of TMS was found to be the dominant process. The Si(CH 3) 3 + ion is by far the most abundant fragment ion with a maximum cross-section of about 1 × 10 −15cm 2. In contrast, the maximum parent ionization cross-section is less than 2% of that value. On the basis of the measured partial ionization cross-sections, mass spectral cracking patterns and appearance energies of the various ionic products, we propose a collision-induced decomposition scheme for the TMS molecule. Three major decomposition channels were identified which all involve the total or partial removal of a methyl group. The agreement of our measured absolute partial ionization cross-sections with earlier data obtained by a different technique is generally poor.

Mass spectral characterization of oligomeric polysulfides by electrospray ionization combined with collision-induced decomposition

Polysulfide oligomers H(SC 2H 4OCH 2OC 2H 4S) nH with n = 1–24 can be characterized by electrospray ionization mass spectrometry. Samples prepared by the conventional method are shown to contain up to eight series of oligomers differing in structure by one of a small group of variants in one (or sometimes two) of the repeat units, e.g. with one less S atom or an additional CH 2O group. The composition of individual ions can be confirmed by collision-induced decomposition of cationized polysulfides, which yields unambiguous spectra of the fragmented ions.

Negative ion electrospray tandem mass spectrometric structural characterization of leukotriene B 4 (LTB 4) and LTB 4-derived metabolites

The low energy collision induced dissociation (CID) of the carboxylate anions generated by electrospray ionization of leukotriene B4 (LTB4) and 16 of its metabolites was studied in a tandem quadrupole mass spectrometer. LTB4 is a biologically active lipid mediator whose activity is terminated by metabolism into a wide variety of structural variants. The collision-induced dissociation spectra of the carboxylate anions revealed structurally informative ions whose formation was determined by the position of hydroxyl substituents and double bonds present in the LTB4 metabolite. Major ions resulted from charge remote α-hydroxy fragmentation or charge directed α-hydroxy fragmentation. The conjugated triene moiety present in some metabolites was proposed to undergo cyclization to a 1,3-cyclohexadiene structure prior to charge remote or charge driven a-hydroxy fragmentation. The mechanisms responsible for all major ions observed in the CID spectra were studied using stable isotope labeled analogs of the LTB4 metabolites. In general, the collision-induced decomposition of carboxylate anions produced unique spectra for all LTB4 derived metabolites. The observed decomposition product ions from the carboxylate anion could be useful in developing assays for these molecules in biological fluids.

Studies in organic mass spectrometry. Part 20: a hidden ortho effect in the electron ionisation mass spectra of some 2′-alkyl substituted 2-and 3-thiophenecarboxanilides

The electron-ionisation-induced amide-bond cleavage of some 2′-methyl- and 2′-ethyl-substituted 2- and 3-thiophenecarbox-anilides, which yields formally anilylium ions having relative intensities apparently in contrast with the Stevenson–Audier rule, has been investigated by mass-analysed ion kinetic energy (MIKE) spectrometry and compared to that of the 3′- and 4′-isomers. It has been shown that, in the case of the 2′-methyl and 2′-ethyl derivatives, the amide-bond cleavage is anchimerically assisted through the hidden migration of a benzyl hydrogen to the nitrogen. Analysis of the MIKE and collision-induced decomposition (CID) MIKE spectra of model compounds indicates that this cryptic ortho effect produces a stable ortho quinoide or aminotropylium structure.

Application of tandem mass spectral approaches to structural determinations of saponins.

Structural determinations of saponins present challenges to the analyst because of the variety of potential modification sites, the incorporation of both carbohydrate and non-carbohydrate moieties, and the occurrence of mixtures that may include isomeric species and highly-active minor components. These quite daunting features of the research problem represent an excellent opportunity for effective application of new analytical methodologies. Tandem mass spectrometry is a particularly logical choice: advances in sample preparation, ionization methods and analyzer techniques can now lessen the sample requirements, shorten the analysis time and provide detailed structural information for individual mixture components. We are utilizing liquid secondary ionization, matrix-assisted laser desorption/ ionization and electrospray ionization in conjunction with high- and low-energy collision-induced decomposition and post-source decay tandem mass analysis to probe the structures of saponins with established biological activities. Methods developed with known compounds are then used for the structural elucidation of unknowns. In the work described here, structures of saponins from a cardivascular active Chinese medicine were determined first and the fragmentation information was used as a guide in the interpretation of the spectra from more complex saponins found in extracts of the bark of Quillaja saponaria Molina that may have use as adjuvants in vaccines.

Hydration in the Gas Phase of the Orthophosphate Anion, (HO)2PO2-, and the Conversion of the Orthophosphate to the Metaphosphate, PO3-, Ion

The orthophosphate anion, (HO)2PO2-, was produced in the gas phase by electrospray. The hydration equilibria (HO)2PO2-(H2O)n-1 + H2O = (HO)2PO2-(H2O)n were determined after transfer of the ions into a reaction chamber containing known partial pressures of H2O, where thermal conditions prevailed. The and for steps (n−1,n) = (0,1) and (1,2) were obtained from equilibrium measurements in the 20−150 °C range. The ion concentration ratio was determined mass spectrometrically. The thermochemical data obtained are in good agreement with recent theoretical calculations. Under some conditions of the experiments, the equilibria (HO)2PO2-(H2O)n = PO3-(H2O)n-1 + H2O should have been observed according to reports in the literature. However, the formation of the metaphosphate ion, PO3-, and its hydrates was not observed. In separate experiments with a different apparatus setup, the kinetic energy threshold for the collision-induced decomposition (HO)2PO2- = PO3- + H2O was determined. The activation energy barrier obtained was high. The significance of these results to the possible conversion of the orthophosphate to metaphosphate, when a few hydrating molecules are available, is discussed.