bluuebunny/crossref_metadata_2025 huggingface dataset:
Unimolecular fragmentations of long‐chain aliphatic iminium ions
Authors: Gross Jürgen H. , Veith Hans H.
Published: May 2005

The metastable ion characteristics of N‐alkyl‐N‐methylmethyleneiminium ions (\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm H}_2 {\rm C}=\!=\mathop {\rm N}\limits^ + ({\rm CH}_3){\rm R} $\end{document}, R = n‐CmH2m + 1, m = 3, 4, 5, 6, 8, 10, 14, 18) are reported and discussed. For R = n‐propyl, alkene loss by onium reaction and alkene loss by McLafferty rearrangement occur, whereas for the higher homologues only the latter reaction is observed. As a result of 2H and 13C labelling experiments, the mechanism of alkene loss by γ‐H transfer and β‐cleavage does not change with increasing chain length and the iminium ions do not isomerize prior to decomposition, neither by H–D scrambling nor by carbon skeleton rearrangement. Whereas the sequence of elementary steps during fragmentation is not affected, the energetics of the reaction change as the chain length increases. Resulting from thermodynamic estimations, the enthalpy of reaction ΔHr, critical energy E0 and reverse critical energy E0r diminish markedly as R increases from n‐propyl to n‐octadecyl. The knowledge of the reaction energetics including kinetic energy release data allows information about partitioning of excess energy into internal and translational degrees of freedom to be deduced.
Collision‐induced dissociation of glycoside–alkali metal adduct ions in fast atom bombardment mass spectrometry
Authors: Takayama Mitsuo
Published: May 2005

The collision‐induced dissociation (CID) spectra of glycoside–alkali metal adduct ions [M + C]+ (C = Li, Na, K and Rb) produced under fast atom bombardment (FAB) conditions are reported. The results obtained suggested that the CID spectra of the [M + C]+ ions of some flavonoid glycosides reflect the coordination structures because the CID patterns generally changed with the metal cation size. In diglycosides, the CID spectra showed that the relatively small cations Li+ and Na+ rather bind to the sugar moiety, whereas the large cations K+ and Rb+ rather bind to the aglycone moiety. In monoglycosides, the cations C+ rather bind to the aglycone moiety. It was concluded that the CID technique combined with FAB is useful for the structural elucidation of [M + C]+ ions and, in principle, the CID spectra reflect the coordination structures in the gas phase.
Identification of cyclic nucleotide derivatives synthesized for radioimmunoassay development by fast atom bombardment with collision‐induced dissociation and mass‐analysed ion kinetic energy spectroscopy
Authors: Newton Russell P. , Evans Andrea M. , Hassan Hamed G. , Walton Terence J. , Brenton A. Gareth , Harris Frank M.
Published: May 2005

The syntheses of 2′‐O‐succinyl, 2′‐O‐succinyltyrosinyl methyl ester and 2′‐O‐succinyliodotyrosinyl methyl ester derivatives of a cyclic nucleotide, derivatives necessary for the successful development of a specific radioimmuno‐assay, are described. Fast atom bombardment with collision‐induced dissociation and mass‐analysed ion kinetic energy spectroscopy were used to verify the positions of substitution and the retention of the 3′,5′‐cyclic phosphate moiety. Comparison of spectra produced after different iodination times permitted the optimization of the reaction conditions.
Surface‐induced ion neutralization with high energy deposition
Authors: Chorush Russell A. , Vidavsky Ilan , McLafferty Fred W.
Published: May 2005

Ion‐to‐neutral conversion at surfaces is found to be complementary to that with gas‐phase targets for neutralization–reionization mass spectrometry and to yield high‐energy neutral species. With an Ag surface deposited on an in‐line Si substrate, neutralization–reionization efficiencies of 0.01% are achieved using 9.8 keV CH, with the neutral CH4 receiving a median internal energy of 14 eV; with a conventional target of K vapor, the efficiency is 0.4% with a neutral energy of 8.2 eV expected from their ionization energy difference. The energy deposition can be increased by increasing the potential that deflects ions into the surface; in this way ∼15% of CH4 neutral species can be given >20 eV of internal energy. Product abundances from CH4 dissociation provide a useful estimate of the distribution of energy values deposited in neutralization.
Tandem mass spectrometry of peptides: Sequence information based on neutral losses. I—isomeric dipeptides
Authors: Cordero Marcela M. , Wesdemiotis Chrys
Published: May 2005

The neutral losses arising on the collisionally activated dissociation (CAD) of protonated dipeptides (MH+) are reionized by collision and detected in neutral fragment‐reionization (NfR) mass spectra. For the dipeptides investigated, which encompass Ala–Gly/Gly–Ala, Asp–Gly/Gly–Asp, Phe–Gly/Gly–Phe and Trp–Ala/Ala–Trp, the NfR spectra of each pair of isomers are distinct and permit the identification of the correct C‐terminal amino acid. The precise structure of this amino acid is elucidated by comparison of the NfR spectra with reference collision‐induced dissociative ionization (CIDI) mass spectra of authentic Gly, Ala, Asp, Phe and Trp, acquired from beams of these amino acids formed by dissociation of their proton‐bound dimers.
Fragmentation reactions of singly and doubly charged alkali metal ion–peptide complexes: A reaction specific to C‐terminal arginine residues
Authors: Tang Xue‐Jun , Thibault Pierre , Boyd Robert K.
Published: May 2005

Ionspray ionization of solutions containing peptides (M) plus alkali metal ions X+ produces [M + X]+, [M + H + X]2+ and [M + 2X]2+ ions. Low‐energy collision‐induced dissociation of these species demonstrated a marked trend towards decreased strength of the M–X+ interaction with increasing size of X+. For example, the [M +2X]2+ species yield predominantly [M + X]+ plus X+ for X+ = K+, Rb+, Cs+, but rich spectra of fragment ions incorporating X+ when X+ = Li+ or Na+. In general, these fragmentation reactions correspond to those established previously for the corresponding [M + X]+ precursor, including formation of [bi + X + OH]+ and [bi + X – H]+ fragments. As a special case, complexes of Li+ or Na+ with peptides having Arg (but not Lys or other basic residues) at the C‐terminus undergo a facile loss of 60 u. The resulting [M + X – 60]+ ions also fragment further to yield [yi′ + X – 60]+ fragments. Characterization of the 60 u neutral loss was undertaken by using tandem mass spectrometry plus hydrogen–deuterium exchange, and a mechanism is proposed to account for the characteristics of the process.
Intermediate ion–neutral complexes formed during the gas‐phase protonolysis of p‐(tert‐butyl)‐substituted α,ω‐diphenylalkanes
Authors: Matthias Carsten , Kuck Dietmar
Published: May 2005

Loss of isobutane is the exclusive fragmentation channel of long‐lived protonated tert‐butyl‐substituted α,ω‐diphenylalkanes with chain lengths n = 2–12. Methane chemical ionization/mass‐analysed ion kinetic energy spectrometry of the [M + H]+ ions and several deuterium‐labelled tert‐butyl‐substituted 1,2‐, 1,3‐ and 1,10‐diphenylalkanes revealed that the reaction involves with equal probability and maximum regioselectivity a hydride ion from both the adjacent and the remote benzylic methylene groups, irrespective of the length of the aliphatic chain. The isotope effect of the hydride abstraction step was found to be same in all cases, k[C4H10]/k[C4H9D] = 1.6 ± 0.1. A sterically restricted system, protonated 1‐benzyl‐4‐(tert‐butylbenzyl)benzene, shows the same behaviour. This implies, as a general phenomenon, the formation of intermediate ion–neutral complexes [C4H9+ Ar(CH2)n Ar] along with (or instead of) the corresponding π complexes [C4H9+ …︁ Ar(CH2)nAr] prior to isobutane elimination (Ar represents a phenyl or substituted‐phenyl group).
Structures of product ions C6H7+ and C6H9+ of ion–molecule reactions with allyl bromide
Authors: Zhu Zhiqing , Gäumann Tino
Published: May 2005

The ion–molecule reactions of allyl bromide with the molecular ion of allyl bromide and with its major fragment, the allyl ion, yield the C6H7+ and C6H9+ ions. The structure of these product ions was explored by means of photofragmentation with laser light in the 10 μm region and by proton transfer reaction to selected reagents. These product ions were also formed by other reactions and their reactivities compared. In both cases the presence of at least two populations is demonstrated. For C6H9+ these two populations are initially present, whereas for C6H7+ an isomer is formed by the infrared light before the loss of H2. When this ion is produced by photofragmentation of C6H7+, at least one third, stable isomer is formed. Two isomers of C6H5+ are formed in the photofragmentation of C6H7+, but only one form photofragments further by loss of C2H2. The use of non‐linear least‐squares fitting does not allow definite conclusions to be drawn concerning the kinetics of the consecutive photofragmentations.
Collision‐induced dissociation in a tandem time‐of‐flight mass spectrometer with two single‐stage reflectrons
Authors: Cornish Timothy J. , Cotter Robert J.
Published: May 2005

A tandem time‐of‐flight mass spectrometer was developed to be used for the study of collision‐induced dissociation (CID) products of peptides and small proteins. The instrument incorporates two single‐stage reflectrons, the first to energy focus the precursor ions to be fragmented and the second to both energy focus and disperse the product ions formed in the collision cell. Single‐stage rather than two‐stage reflectrons were used because the overall transmission is higher, interferences with grid wire fields are minimized and the mass calibration of product ion spectra is exactly linear with time. The CID product ion spectra of rhodamine and several peptides were acquired and found to exhibit very similar fragmentation patterns to those acquired in the B/E linked scan mode of a magnetic sector mass spectrometer.
The Precursor scan. A new type of experiment in neutralization–reionization mass spectrometry
Authors: Gu Ming , Tureček František
Published: May 2005

A new scan technique utilizing the tandem quadrupole acceleration–deceleration mass spectrometer is described. The technique is based on combined monitoring of neutral and ion precursors that fragment following collisional electron transfer to give rise to a selected low‐mass neutral species and its ion, respectively. PO˙ is found to be a stable neutral species formed by dissociations of a variety of oxidized phosphorus compounds, such as di‐ and trialkyl phosphites, phosphates and phosphonic esters. These compounds can be selectively monitored through PO˙. precursor scans in multi‐component mixtures. Interferences from isobaric neutral species, 35CIC˙, CH3S˙, CH330SiH2˙, and their precursors are discussed. Neutralization–reionization spectra of phosphorus‐containing radicals, PO˙, CH3OPH˙, CH3OPOH˙, ˙P(OCH3)2 and (CH3O)2PO˙, are also reported.
Skeletal rearrangements preceding CO loss from metastable phenoxymethylene ions derived from phenoxyacetic acid and anisole
Authors: Molenaar‐Langeveld Tineke A. , Ingemann Steen , Nibeering Nico M. M.
Published: May 2005

The loss of CH2˙ from the molecular ion of phenoxyacetic acid and the expulsion of an H˙ atom from ionized anisole lead to phenoxymethylen ions, which fragment predominantly by CO loss on the microsecond time‐scale. Carbon‐13 labelling reveals that ∼90% of the CO molecules expelled from the metastable ions derived from phenoxyacetic acid incorporate the carbon atom from the 1‐position of the phenyl group of the parent compound, whereas the residual CO molecules contain one of the other carbon atoms of the aromatic ring. The 2‐fluoro‐ and 2‐methylphenoxymethylene ions derived from the appropriate aryloxyacetic acids behave similarly, i.e. the carbon atom of the methylene group of the parent compound is not incorporated in the expelled CO molecules. In contrast, ∼45% of the CO molecules eliminated from the metastable phenoxymethylene ions formed from ionized anisole contain the carbon atom of the methyl group, while the remaining part contains the carbon atom from the 1‐position of the phenyl ring of the parent compound. This result is taken as evidence for the occurrence of a skeletal rearrangement of the anisole molecular ion leading to an interchange between the carbon atom of the methyl group and the carbon atom at the 1‐position of the ring. The elimination of CO from the metastable ions generated from either phenoxyacetic acid or anisole gives rise to a composite metastable peak. Conclusive evidence as to the formation of [C7H7O]+ isomers other than the phenoxymethylene ion is not obtained, indicating that the composite metastable peak is a result of two competing reactions both leading to CO loss. Possible mechanisms of these reactions are discussed together with the mechanism of the skeletal rearrangement of the molecular ion of anisole prior to H˙ loss.
Novel Ortho effects detected in the fast atom bombardment mass spectra of substituted bisaryl phosphate antagonists of platelet‐activating factor
Authors: Siegel Marshall M. , Tsao Rushung , Wissner Allan
Published: May 2005

A series of substituted bisaryl phosphate compounds, (R1CH2)+ ArOP = O(O−)(OArR2R3), was analyzed and characterized by fast atom bombardment mass spectrometry. Abundant fragment ions were observed and correlated with the proposed structures. From fragmentation pattersn, ‘ortho effect’ reactions were demonstrated to have occurred when the phosphoryl oxygen reacted with the (CH2R1)+ and CO(OCH3) substituents in the ortho position, relative to the phosphate group, and displaced the R1 and OCH3 groups, respectively, to produce phosphorus containing six‐membered rings fused to the aryl moiety. When the (CH2R1)+ substituents were in the meta position relative to the phosphate group, the ‘ortho effect’ reactions were not observed. However, when the CO(OCH3) substituent was in the meta position relative to the phosphate group, an abundant fragment ion containing a five‐membered phosphate ring fused to the aryl ring was detected with the original phosphoryl oxygen ortho to both the phosphate oxygen and a formyl group, formed from the original CO(OCH3) substituent. All other fragmentations not involving the ‘ortho effect’ reactions were nearly identical for the different structural isomers of the substituted bisaryl phosphate compounds.
Electrophilic bromination of gaseous aromatic compounds: Mechanism and linear free energy effects on reaction rates
Authors: Bortolini Olga , Yang Sheng Sheng , Cooks R. G.
Published: May 2005

Electrophilic bromination of monosubstituted aromatic compounds is effected in a pentaquadrupole mass spectrometer using BrCO+ and CH3NH2Br+ as mass‐selected reagent ions. Reaction normally occurs at the ring and the brominated product can be mass selected in turn and caused to dissociate by Br˙ loss upon collision‐induced dissociation. Linear free energy correlations with Brown substituent σ+ constants describe the extent of gas‐phase bromine cation addition under the non‐equilibrium, low‐pressure and solvent‐free conditions which pertain in quadruple collision cells. The electrophilic addition reaction proceeds via a σ‐complex to the ring as suggested by MS3 spectra, except in the case of nitrobenzene, where substituent bromination is suggested by the occurrence of a competitive process in which the nitrosubstituent is displaced by bromine. The reactivity parameters ρ are −0.23 and −0.56 for the gaseous reagents, BrCO+ and CH3NH2Br+, respectively. Both values are much less negative than corresponding values for bromination in solution. The greater reactivity of BrCO+ is evident by the fact that it reacts even with the strongly deactivated substrates and this is consistent with a weak BrCO bond. Competitive protonation occurs in the case of CH3NH2Br+ and, unlike bromination, the rate of this reaction does not correlate with σ+ values. This is suggested to be a consequence of protonation at the ring in some cases and at the substituent in others, including acetophenone and benzonitrile. Evidence for this is that, in contrast to its lack of correlation with substituent constants, the rate of protonation correlates linearly with proton affinity.
Rearrangements accompanying the fragmentation of ionized 1‐phenylalkan‐1‐ols
Authors: Budzikiewicz H. , Drabner G. , Hammes Ch.
Published: May 2005

Some aspects of the fragmentation sequence of 1‐phenylalkan‐1‐ols (C6H5CH(OH)R), which consists of the loss of R˙ followed by the elimination of CO and subsequently of H2, are discussed. Labelling studies and collision activation data of reference compounds allow a mechanism to be proposed for this rearrangement.
Intra‐ and intermolecular reactions of aromatic radical cations: An account of mechanistic concepts and methods in mass spectrometry
Authors: Grützmacher Hans‐Friedrich
Published: May 2005

Investigations in the authors's laboratory in Bielefeld and elsewhere on the mechanism of the intramolecular and intermolecular aromatic substitution via radical cations are reviewed with the aim of presenting an example for the development of mass spectrometric methods and concepts for the study of the mechanisms of gaseous ionic reactions. An intramolecular aromatic substitution resulting in the loss of a hydrogen or a substituent from an aromatic ring of the molecule ions by the attack of a nucleophilic heteroatom in the side‐chain was first observed in the normal electron impact (EI) mass spectra and was studied by substituent effects on ion abundance, ionization energy and appearance energy. This led to the construction of a two‐step mechanism of the intramolecular aromatic substitution with a rate‐determining first addition step. Subsequently, this fragmentation reaction was studied for a series of systems by tandem mass spectrometry, confirming the two‐step mechanism and yielding an excellent insight into the dynamics of the substitution process. The bimolecular variety of the nucleophilic aromatic substitution via radical cations was investigated recently by Fourier transform ion cyclotron resonance spectrometry. The results for a series of halogenated benzenes and NH3, CH3NH2 and (CH3)2NH as the nucleophile corroborate the conclusions drawn from the study of unimolecular reaction mechanisms. It is shown that in all cases the formation and further reaction of the addition intermediate play a crucial role. This can be perceived by the application of the configuration mixing reactivity model to the addition reaction, and by the concept of classical and distonic radical cations. This review on a specific reaction mechanism shows clearly the excellent techniques and methods which the developments in mass spectrometry have provided for a detailed study of the mechanisms of ionic reactions in the gas phase.
Sequencing membrane proteins by tandem mass spectrometry
Authors: Orlando Ron , Kenny Peter T. M. , Moquin‐Pattey Carole , Lerro Keith A. , Nakanishi Koji
Published: May 2005

Tandem mass spectrometry (MS/MS) is an attractive technique for sequencing membrane proteins because it can be applied to peptides in mixtures that are difficult to separate chromatographically. To evaluate the suitability of MS/MS sequencing for membrane proteins and to develop protocols for the preparation of the cleaved peptides, we employed the well characterized apoproteins of bacteriorhodopsin and bovine rhodopsin, i.e. bacterioopsin and opsin, respectively. Without separation, nine out of ten peptides resulting from cyanogen bromide cleavage of bacterioopsin were detected by fast atom bombardment MS, the single undetected fragment being a tetrapeptide that was presumably hidden in the low‐m/z matrix background. Furthermore, MS/MS was used to confirm the sequence of all the peptides detected with m/z values below 3.5 kDa (40% of the protein). Bovine opsin was analyzed in a similar fashion. Tandem MS/MS has thus allowed the sequencing of substantial portions of two integral membrane proteins by the analysis of unseparated peptide mixtures, demonstrating for the first time that this technique can obviate some of the most serious difficulties associated with sequencing membrane proteins, namely the difficult‐to‐achieve separation of the ‘sticky’ peptide fragments.
Some pitfalls in using the reaction intermediate scan (RIS)
Authors: Eller Karsten , Drewello Thomas
Published: May 2005

The reaction intermediate scan (RIS) represents a most instructive triple mass spectrometric (MS/MS/MS) experiment allowing the elucidation of sequential dissociation cascades. Preferably the RIS is performed by utilizing triple‐stage mass spectrometers. Considering experimental findings obtained with BEB‐ and BEqQ‐configurated instruments, some aspects regarding the collision processes and the applicability of linked scanning are discussed with special emphasis on the reliability of RIS.
Determination of glycosylation sites in O‐linked glycopeptides: A sensitive mass spectrometric protocol
Authors: Rademaker Geert Jan , Haverkamp Johan , Thomas‐Oates Jane
Published: May 2005

A sensitive mass spectrometric method for the specific identification of O‐glycosylation sites in glycopeptides is presented. Reductive β‐elimination liberates a peptide containing a specifically modified amino acid at the former site of carbohydrate attachment. Mass spectrometry is used to determine the sequence of the modified peptide, in which the position of the modified amino acid marks the site of O‐glycosylation. The method also provides information on the carbohydrate chain and is applicable at the low nanomolar level.
Intrinsic specificity of Ca2+–protein binding sites
Authors: Reiter Alex , Zhao Hong , Adams Jeanette
Published: May 2005

The gas‐phase chemistry of anionic [M + Cat2+ – 3H]− complexes between Ca2+‐specific peptides and the alkaline earth metal ions Mg2+, Ca2+ and Ba2+ is reported. The metal ion complexes were studied using fast atom bombardment, collision‐induced decomposition (CID) and molecular mechanical calculations. The CID reactions and molecular mechanical calculations revealed that the Ca2+–peptide complexes are bound differently to the Mg2+– and Ba2+–peptide complexes and that the intrinsic (gas‐phase) chemistry is reflected by known aqueousphase chemistry.
Systematic study of the effects of experimental parameters on the beam‐induced dehalogenation of chlorpromazine in liquid secondary ion mass spectrometry
Authors: Théberge R. , Paul G. J. C. , Bertrand M. J.
Published: May 2005

The effect of experimental parameters such as time of irradiation, analyte concentration, primary beam density, matrix selection and matrix additives on the beam‐induced dehalogenation of chlorpromazine in liquid secondary ion mass spectrometry (LSIMS) was investigated. It was found that dehalogenation of chlorpromazine in glycerol increased with increasing time of irradiation, analyte concentration and primary beam density. These results were compared with those obtained using 4‐chlorophenylalanine ethyl ester and the differences observed were rationalized in terms of compound surface activity. Evidence is given that matrix selection is the key experimental parameter affecting the extent of beam‐induced dehalogenation of chlorpromazine in LSIMS. Of the eleven matrices used, the greatest extent of dehalogenation was observed in glycerol. Sulfur‐containing matrices consistently exhibited a lower extent of dehalogenation than oxygen‐containing aliphatic matrices, implying that sulfur is implicated in mitigating the reduction process. Dehalogenation was totally inhibited in 2‐hydroxyethyl disulfide, 4‐hydroxybenzenesulfonic acid and 3‐nitrobenzyl alcohol. Similarly, the use of matrix additives such as 3‐nitrobenzyl alcohol and trifluoroacetic acid was found to be useful in inhibiting the extent of dehalogenation occurring in glycerol.
Photodissociation and collision‐induced dissociation of molecular ions from methylphenol and chloromethylphenol
Authors: Cassady C. J. , Afzaal S. , Freiser B. S.
Published: May 2005

The photodissociation of molecular ions from a series of methylphenols and chloromethylphenols was studied using Fourier transform ion cyclotron resonance mass spectrometry (FTMS). The photodissociation spectra contain both UV and visible absorption maxima. The positions of these bands correlate well with solution electronic absorption spectra and photoelectron spectra, respectively, suggesting that photodissociating populations of the molecular ions have not rearranged. The molecular ion of benzyl alcohol can be readily distinguished from the isomeric 2‐ and 4‐methylphenol ions on the basis of the position and intensity of the photodissociation bands, and the identity of the photoproduct. The p‐chlorophenol isomers, 4‐chloro‐2‐methylphenol and 4‐chloro‐3‐methylphenol, cannot be distinguished by their photodissociation spectra. Minor differences exist between these spectra and that of the o‐chlorophenol isomer 2‐chloro‐5‐methylphenol, suggesting that the relative positions of the chloro and hydroxy groups may have a greater effect on photodissociation than the position of the methyl group. For comparison, low‐energy collision‐induced dissociation using FTMS was also performed on the same ions.
Mass spectrometric fragmentation of isomeric 2‐alkyl‐substituted 1,3‐indandiones and 3‐alkylidenephthalides: a seven‐step consecutive isomerization of regular and distonic molecular radical cations
Authors: Kuck Dietmar
Published: May 2005

The electron impact‐induced fragmentation of 2,2‐dimethyl‐ and 2‐ethyl‐1,3‐indandione, 1 and 2, and their isomers, 3‐isopropylidene‐ and 3‐propylidenephthalide, 3 and 4, respectively, was studied in detail by mass‐analysed ion kinetic energy (MIKE) and collision‐induced dissociation (CID‐MIKE) spectrometry, including 2H and 13C. labelled analogues of 1 and 2. In all regimes of internal energy, the molecular ions 1+. 4+. interconvert by up to seven consecutive, reversible isomerization steps prior to the main fragmentation processes, viz. loss of CH3. and C2H4. 1,3‐Indandione and 3‐methylenephthalide ions with identical alkylidene moieties (i.e. 1+.⇌3+. and 2+.⇌4+.) equilibrate rapidly and completely prior to fragmentation, whereas these pairs of isomers interconvert only slowly via a five‐step rearrangement of the indandione ions 1+.⇌2+.. Distinct from the behaviour of simpler ionized carbonyl species, a 1,2‐C shift of a (formally) neutral carbonyl group is found to occur along with that of a protonated one. Also distinct from simpler cases, methyl loss does not take place from the ionized enol intermediates formed within the interconversion 1+.⇌2+. of the diketone ions but rather from the n‐propylidenephthalide ions 4+.. This follows from CID‐MIKE spectrometry of the [M  CH3]+ ions of 1–4 and two reference C10H7O2+ (m/z 159) ions of authentic structures (protonated 2‐methylene‐1,3‐indandione and protonated 1,4‐naphthoquinone). The characteristic CID fragmentation of the C10H7O2+ ions is rationalized. Finally, the multistep isomerization of ionized 1,3‐indandiones apparently also extends to higher homologues [e.g. 5+. from 2‐ethyl‐2‐methyl‐1,3‐indandione (5) and 6+. from 2,2‐diethyl‐1,3‐indandione (6)]: the ionized phthaloyl group of 1,3‐indandione radical cations 1+., 2+., 5+. and 6+., originally attached with its two acyl functionalities to the same carbon of the aliphatic chain, performs, in fact, a ‘multi‐step migration’.
Electron and chemical ionization mass spectrometry in stereochemical differentiation of some 1,3‐amino alcohols
Authors: Partanen Tuula , Vainiotalo Pirjo , Stájer Géza , Bernáth Gábor , Pihlaja Kalevi
Published: May 2005

Mass spectral fragmentations of two cyclopentane, eight cyclohexane and four norbornane/one 1,3‐amino alcohols were studied under electron ionization (EI) by low‐resolution, high‐resolution, metastable ion analysis and collision‐induced dissociation (CID) techniques. All stereoisomeric compounds gave rise to identical 70 eV EI mass spectra. However, the spectra of positional isomers clearly differed. The main fragmentation pathway for the saturated compounds began as an α‐cleavage reaction with respect to the nitrogen atom. For the norbornene compounds a retro‐Diels—Alder reaction was favoured. Relative to the aminomethyl‐substituted compounds the fragmentation patterns for the compounds having the amino group connected directly to the ring were more complicated. The chemical ionization (CI) mass spectra were recorded using ammonia, isobutane, methane, dichloromethane and acetone as reagent gas. From the norbornane/One compounds the di‐exo isomers decomposed more easily than the di‐endo isomers with most of the reagent gases used. Differences between stereoisomers were observed directly only under methane CI. The decomposition products of the [M + H]+ ions generated under ammonia and isobutane CI were studies by recording their CID mass spectra. These spectra allowed the differentiation of the stereoisomers, at least to some extent.
Dechlorination of polychlorinated biphenyls in electron‐capture negative‐ion chemical ionization mass spectrometry
Authors: Lépine Francois L. , Milot Sylvain M. , Reimer Mark L. J. , Mamer Orval A.
Published: May 2005

The electron‐capture negative‐ion chemical Ionization mass spectra of 36 35Cl mono‐ and di‐labelled penta‐ and hexachlorobiphenyls were studied. Under the conditions of the analyses, the dechlorination of these congeners probably proceeds through electrophilic hydrogen atom attachment followed by rapid loss of the chlorine atom at the same position. These dechlorination reactions occur regioselectively. When present, ortho‐chlorines are lost preferentially to meta‐ and para‐chlorines. The extent of the dechlorination reaction, as seen by the relative abundance of the [MH  Cl]− ions, decreases with increasing number of ortho‐chlorines.
Fast atom bombardment mass spectrometric study of benzyloxycarbonyl‐protected tetrapeptides containing proline
Authors: Tsunematsu Hideaki , Hanazono Hiroshi , Horie Kenichi , Fukuda Tsukasa , Yamamoto Magobei
Published: May 2005

Fragmentations of N‐benzyloxycarbonyl‐protected tetrapeptide ethyl esters containing L‐alanine and L‐proline, in which changes in the numbers and positions of prolyl residues were observed, were studied by negative‐ion fast atom bombardment mass spectrometry. A significant difference was found among the abundances of the molecule ions and the fragment ions formed by the cleavage of the benzyloxycarbonyl group, depending on the numbers and positions of prolyl residues in the derivatives. The results indicate that the conformational differences in the tetrapeptide derivatives due to the existence of proline affect fragmentations of molecules in the solution phase in negative‐ion fast atom bombardment mass spectrometry.
Study of two diastereomeric pairs of regiosomeric 2‐isoxazolines by tandem mass spectrometry with electron impact ionization
Authors: Selva Antonio , Auricchio Sergio , Truscello Ada M.
Published: May 2005

On electron impact (EI) ionization, two cis/trans pairs of 4‐methyl‐5‐phenyl and 4‐phenyl‐5‐methyl regioisomeric 3‐carbethoxy‐2‐isoxazolines showed normal mass spectra and mass‐analysed ion kinetic energy (MIKE) spectra of metastable (MI) and collision‐activated (CA) molecule ions, allowing unequivocal differentiation of the regioisomers. The cis/trans stereoisomers of each regioisomer showed very similar normal mass spectra. Very interestingly, the cis‐ and trans‐4‐phenyl‐5‐methyl stereoisomers appeared reasonably differentiated by the molecule ion MIKE spectra, whereas the 4‐methyl‐5‐phenyl regioisomeric pair of stereoisomers did not. The influence of the phenyl substituent to the fragmentation processes was notable. Some fragments of interest were studied by comparison of their MIKE spectra with those of model ions, generated by EI from suitable substrates, including (i) the isomeric α,β‐unsaturated oxime, namely ethyl (Z)‐2‐(hydroxymino)‐3‐methyl‐4‐phenylbut‐3‐enoate, a by‐product of importance for the mechanism(s) of the addition/cycloaddition reactions of nitrile oxides to alkenes and (ii) trans‐β‐methylstyrene, a dipolarophilic reactant in the same reactions. The favoured heterocyclic C(5)–O(1) bond cleavage occurred only for the ionized 4‐methyl‐5‐phenyl 2‐isoxazoline pair, leading to a distonic ion of relevance, as it can represent either a reasonable precursor for both the isomerization to the ionized α,β‐unsaturated oxime and the EI‐induced cycloreversion yielding ionized β‐methylstyrene, or the ionized form of a zwitterionic intermediate, which had been proposed previously for the addition/cycloaddition mechanism(s) in the solution phase, currently under study.
Differentiation among the four diastereomers of benzyloxycarbonyl‐protected γ‐hydroxyornithine in negative‐ion fast atom bombardment mass spectrometry
Authors: Tsunematsu Hideaki , Isobe Ryuichi , Mizusaki Koichi , Makisumi Satoru , Yamamoto Magobei
Published: May 2005

Discrimination among the four γ‐hydroxyornithine diastereomers was studied by fast atom bombardment mass spectrometry (FABMS). It is impossible to distinguish among the four diastereomers of this amino acid by positive‐ and negative‐ion FAB and collisionally activated dissociation MS, but benzyloxycarbonyl group protection of the α‐ and δ‐amino groups in γ‐hydroxyornithine allows differentiation among the diastereomers in negative‐ion FABMS. The negative‐ion mass spectra of benzyloxycarbonyl‐protected γ‐hydroxyornithine diastereomers showed differences among the abundances of the molecule ion [M – H]‐, the dehydrated ion [M — H — H2O]‐ due to the loss of the γ‐hydroxyl group and the fragment ions formed from both [M — H]‐ and [M — H — H2O]‐ ions. On the other hand, no difference was found between the fragmentations of the benzyloxycarbonyl‐protected enantiomers of ornithine in negative‐ion FABMS. These results indicate that the orientation of the γ‐hydroxyl group and the existence of two benzene rings in the benzyloxycarbonyl group are important factors which are responsible for the fragmentations of the four benzyloxycarbonyl‐protected γ‐hydroxyornithine diastereomers in negative‐ion FABMS. These studies also showed that the negative‐ion FABMS for benzyloxycarbonyl‐protected γ‐hydroxyornithine diastereomers is a useful method for determining the configuration of each diastereomer of γ‐hydroxyornithine.
Electron impact ionization mass spectra of lithocholyl amides: Evidence for a C(20) to C(23) rearrangement involving the loss of a C4H9 fragment
Authors: Nair Padmanabhan P. , Flanagan Vincent P. , Oliver James E.
Published: May 2005

Amides of lithocholic acid (3α‐hydroxy‐5β‐cholan‐24‐oic acid) with 6‐aminocaproic acid and 4‐aminobutyric acid were prepared and examined by electron impact ionization mass spectrometry. Both these compounds gave an unusual [M − 57]+ fragment. Since the product‐ion analysis of [M − 57]+ revealed the presence of fragments corresponding to the intact steroid nucleus in addition to that of the original amino acid (6‐aminocaproic acid or 4‐aminobutyric acid), we concluded that the integrity of the steroid amide had been retained in this fragment. The absence of this fragment from the product‐ion spectrum of [M − CH3]+ rules out the sequential loss from the molecular ion of 15 + 42 u as the origin of this signal. Mass spectrometry of the 24‐13C‐labelled lithocholylcaproylamide showed the retention of the label in the [M − 57]+ fragment. In contrast, the corresponding compound labelled with deuterium at C(23) showed a significant loss of the label during the formation of this product ion at [M − 58]+. In addition, through a combination of derivatization and tandem mass spectrometry, it was demonstrated that this loss of 57 u represented a rearrangement with the expulsion of a C4H9 radical from the side‐chain spanning C(20) to C(23) resulting in a truncated steroid‐amide fragment. This fragmentation pattern has not been observed in bile acid conjugates with N‐α‐amino acids.
Direct identification of organic inclusions in graphite on the basis of field desorption mass spectrometry
Authors: Kosevich M. V. , Pashinskaya V. A. , Shelkovsky V. S.
Published: May 2005

A method for the direct identification of organic inclusions in graphite on the basis of field desorption mass spectrometry is proposed, based on the possibility of using a fractured graphite sample as a field emitter. Under such circumstances, the organic inclusions adsorbed on the surface of the microcrystallites of modified graphites may be directly field desorbed and identified by their mass spectra without any pretreatment of the sample. Two differently modified types of graphite were analysed by this method and the nature of the admixtures was established: one sample appeared to contain a mixture of polymethylsiloxanes and the other and blend of dyes. For the latter sample, temperature fractionation of admixed substances was performed and the presence of three individual dyes was established. Such features of field desorption as the production of abundant molecular ions with negligible fragmentation and the possibility of obtaining of mass thermograms greatly facilitate the identification of individual components of mixture inclusions.
Characterization of explosives by liquid chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry using electrospray ionization and parent‐ion scanning techniques
Authors: Casetta Bruno , Garofolo Fabio
Published: May 2005

Analytical techniques for the detection of small amounts of explosives (in the picogram range) are now involved in various application. Some of them concern soil, water and air monitoring in order to face environmental problems related to improper handling procedures either in stocking or in wasting of the explosive products. Other areas are strictly related to forensic analysis of samples coming either from explosion areas where the matrix is various (metal, glass, wood, scraps), or from explosives transportation related to international terrorism. Generally speaking, for these applications the bulk of the matrix seriously interferes in the detection of the explosive analyte, which is usually present at trace levels. Unfortunately, despite some improvements, analytical techniques developed up today in this domain are still faced to two main constraints: the introduction of new products with unanticipated chemico‐physical properties and the requirement of a routine and fast analytical method which can handle any matrix with a minimal clean‐up and performing a sensitivity compatible either with the ever‐decreasing demanded detection limit and with the ever‐decreasing available specimen amount. These requirements can be fulfilled now by the new LC‐MS and LC‐MSMS techniques: mass spectrometry (MS) is likely an universal detector but even specific, especially when implemented in tandem MS (MSMS); LC is by far the most suitable technique to handle such a kind of compounds. Moreover, of a particular concern are some explosives which are reported to be thermally stable but difficult to dissolve. Some of the experiments on characterization of explosives [Octagen (HMX), Ethyleneglycol dinitrate (EGDN), Exogen (RDX), Propanetriol trinitrate (NG), Trinitrotoluene (TNT), N‐Methyl‐N‐tetranitrobenzenamine (TETRYL), Dintrotoluene (DNT), Bis‐(nitrooxy‐methyl) propanediol dinitrate (PETN), Hexanitrostilbene (HNS), Triazido‐trinitrobenzene (TNTAB), Tetranitro‐acridone (TENAC), Hexa‐nitrodiphenylamine (HEXYL), Nitroguanidine (NQ)] by LC‐MS and LC‐MSMS with the API‐IonSpray source and using the Parent‐Scan technique are presented.
Investigation of several aminoglycoside solutions containing one or more components by positive electrospray mass spectrometry
Authors: Curcuruto Ornella , Kennedy Gordon , Hamdan Mahmoud
Published: May 2005

Solutions containing one or more aminoglycosides have been investigated by positive electrospray mass spectrometry. The lack of extensive fragmentation in the acquired mass spectra permitted reliable identification of the individual components within the electrosprayed solutions. Results obtained at relatively high cone voltage allowed confident assignment of the major fragmentation pathways under electrospray conditions. The presented data also indicate that higher cone voltage favours the observation of sodium adduct ions, [M + Na]+. This experimental observation is tentatively attributed to a less efficient cone‐assisted collision‐induced dissociation of these species compared to their [M + H]+ counterparts.
Electrospray mass spectra of protein cations formed in basic solutions
Authors: Le Blanc J. C. Y. , Wang Jianyao , Guevremont Roger , Siu K. W. M.
Published: May 2005

The electrospray mass spectra of gramicidin S cations that originated from 0.2 M solutions of 18 nitrogen‐containing bases were examined. The relative abundances of the [M + 2H]2+ to the [M + H]+ ion were found to correlate not with the solution pH but with the proton affinities of the bases. It is postulated that some of the [M + 2H]2+ and the [M + H]+ ions exist as adducts with the nitrogen bases in solution, these adducts being desorbed into the gas phase during electrospray and dissociated in the lens region via collision‐induced dissociations to yield apparent proton attachment spectra. Some of these adducts were observed under nominally zero collision energy conditions.
Resonance electron capture for determining double bond and hydroxy group locations in fatty acids
Authors: Voinov Valery G. , Boguslavskiy Valentin M. , Elkin Yuri N.
Published: May 2005

The nature and location of modifications of fatty acids are determined by resonance electron capture (REC) ionization of free acids and their methyl esters and pyrrolidides. The molecular negative ions (MNI) formed in the high resonance region undergo both charge‐remote and charge‐driven decomposition. The spectra of fragments arising from dissociation of these high‐energy MNI contain decisive information on the original structure of the neutrals. The pyrrolidides of fatty acids result in simpler spectra on the one hand, and on the other hand these spectra give complete structure information.
TBA studies of prepreg curing behavior
Authors: Schneider N. S. , Gillham J. K.
Published: May 2005

The torsional braid analysis (TBA) equipment has been used as an automated torsion pendulum to characterize prepreg materials in the form of single ply strips (2‐1/2 × 1/8 in.). Compared to the use of coated glass braids, the main difference was a marked weakening of the gelation mechanical damping peak in isothermal runs. However, prepreg materials consisting of epoxy resins on glass, carbon or aramid fibers were successfully run isothermally to provide gelation and vitrification times as a function of temperature, or in constant heating rate scans to reveal the T < Tg and the Tg relaxations of the uncured resins, and at higher temperatures phenomena associated with gelation, vitrification and devitrification.
Use of mica in poly(vinyl chloride)
Authors: Bataille P. , Bui T. V.
Published: May 2005

A study was conducted to evaluate mica‐poly(vinyl chloride) (PVC) composites. A highly filled PVC pipe formulation was selected as reference and a gradual replacement by mica of the calcium carbonate was conducted. The mica improved the fluxing time of the formulation by a factor of three without markedly affecting the equilibrium or maximum, torque. The results are optimized when there is a partial replacement of the calcium carbonate by mica, Orientation of the mica flakes enhances the young's modulus as well as the yield stress. A theoretical analysis shows a discrepancy from experimental results for high levels of mica. The rheological properties were studied with a Brabender plastograph and mechanical properties with a model TM‐SM Instron.
Fatigue crack growth in fiber reinforced plastics
Authors: Mandell J. F.
Published: May 2005

Crack extension during fatigue loading is one of the primary causes of failure in engineering materials. While the fatigue crack resistance of homogeneous and even adhesive systems has received detailed study and characterization, relatively few and scattered results are available for fiber composites. One difficulty with obtaining such data for composites is their tendency to develop complex patterns of intra‐ and interlaminar damage which expand in a stable manner during fatigue. Such damage usually does not severely reduce the load carrying capacity of a structure but the complexity of the damage geometry has so far frustrated efforts to apply any unifying theories of growth. Measurement of the rate of macroscopic crack growth, through thickness crack extension, has been possible for certain composites and crack direction where the stable damage is constrained. These include cracks in 0°/90° laminates, woven fabric laminates, chopped strand mat laminates, sheet molding (SMC) materials, and short fiber reinforced thermoplastics. Macroscopic interlaminar cracks in continuous fiber systems have also received some recent attention. Fatigue crack growth in glass fiber composites for which most data are available, involves significant contributions from both static and cyclic load effects. A simple model for predicting fatigue crack growth rates from traditional S‐Ncurve and fracture toughness data has proven useful for certain well behaved systems. Limited study has also been made of the effects of moisture and salt water on the fatigue crack growth rate.
Fracture modes in off‐axis fiber composites
Authors: Sinclair J. H. , Chamis C. C.
Published: May 2005

Criteria have been developed for identifying, characterizing, and quantifying fracture modes in high‐modulus graphite‐fiber/resin unidirectional composites subjected to off‐axis tensile loading. Procedures are described which use sensitivity analyses and off‐axis data to determine the uniaxial strength of fiber composites. It was found that off‐axis composites failed by three fracture modes, which produce unique fracture surface characteristics. The stress that dominates each fracture mode and the load angle range of its dominance can be identified. Linear composite mechanics is adequate to describe quantitatively the mechanical behavior of off‐axis data are comparable to those measured in uneasily tests.
Structural performance of vinyl ester resin compression molded high strength composites
Authors: Enos J. H. , Erratt R. L. , Francis E. , Thomas R. E.
Published: May 2005

During the past few years the automotive industry has shown increasing interest in evaluating reinforced plastic composites (R/PC) for structural parts. The selection of R/PC systems is limited by economics and performance criteria; such as the ability to withstand temperature extremes, fatigue or other specific criteria depending upon the part. High Strength Molding Compound (HSMC) appears to be a promising R/PC technology. These performance requirements have lead to the development of HSMC based on vinyl ester or polyester resins for compression molding of automotive structural parts. This paper discusses static and dynamic physical properties as they relate to formulation and environmental variables for compression molded vinyl ester resin high strength composites. Static property data on tensile and flexural strength and modulus; coefficient of thermal expansion and Poisson's ratio for vinyl ester resin systems with 1 in. randomly chopped glass fiber levels from 37 to 72 weight percent at temperatures from −20 to 302°F are presented.
Application of uv resonance raman spectroscopy to the detection of monolayers of silane coupling agent on glass surfaces
Authors: Ishida Hatsuo , Koenig Jack L. , Asumoto Bruce , Kenney Malcolm E.
Published: May 2005

The silane, PcSi(OH)(OSi(CH3)2(CH = 2)), which has the potential of serving as a new type of coupling agent for fiber glass composites has been studied by UV resonance Raman spectroscopy. This silane is a member of a series of silanes which may lead to hydrolytically stable composites when used as coupling agents. Crystalline samples of the silane without glass and films on E‐glass fibers and high‐surface‐area silica at levels less than a monolayer have been investigated. The Raman line used in these investigations is at 1545 cm−1. This line is used because it gives a strong UV resonance Raman enhancement and because its frequency is dependent on the previous history of the sample. An attempt has been made to interpret the nature of the interaction of the silane with the glass surfaces in terms of the shifts of this line.