bluuebunny/crossref_metadata_2025 huggingface dataset:
Metastable ion studies. IV—thermochemistry and ion structures among fragmenting [C3H6]+· ions
Authors: Holmes John. L. , Terlouw Johan. K.
Published: May 2005

Metastable ion peak shapes, dimensions and relative abundances have been measured for the three fragmentations [C3H6]+· → [C3H4]+· + H2, [C3H6]+· → [C3H5]+ + H· and [C3H6]+· → [C3H3]+ + H2 + H·. [C3H6]+· ions were derived from propene, cyclopropane, tetrahydrofuran, cyclohexanone, 2‐methyl but‐1‐ene and cis‐pent‐2‐ene. Activation energies for these fragmentations have been evaluated. Three daughter ion dissociations ([C3H5]+ → [C3H3]+ + H2, [C3H5]+ → [C3H4]+· + H· and [C3H4]+· → [C3H3]+ + H·) have been similarly examined.

Ion structures have been determined and the metastable energy releases have been correlated with the thermochemical data. It is concluded that the molecular ions of propene and cyclopropane become structurally indistinguishable prior to fragmentation and that differences in their metastable ion characteristics can be ascribed wholly to internal energy differences; the latter can be correlated with the photoelectron spectra of the isomers. The pathway for the consecutive fragmentation which generates the metastable ion peak (m/e 42 → m/e.39) has been shown to be

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It is likewise concluded that fragmentating [C3H6]+· ions generated from the various precursor molecules are also structurally indistinguishable and cannot be classified with either molecular ion of the isomeric C3H6 hydrocarbons.
The mass spectral fragmentation of 2,2′‐bis‐trimethylsilylbenzhydrylethers. An indication for transannular hydrogen/deuterium rearrangements and transannular elimination reactions
Authors: Akkerman O. S. , Evers E. A. I. M. , Kerkstra A.
Published: May 2005

The mass spectra of the methyl‐, trideuteromethyl‐, ethyl‐ and pentadeuteroethylethers of 2,2′‐bis‐trimethylsilylbenzhydrol are reported. The most significant ions arise from the [M – CH3]+ ion, formed by loss of a methyl radical from one of the trimethylsilyl groups. After ring formation by interaction of the siliconium ion centre with an aromatic nucleus, the ion loses (CH3)3SiOR (R = CH3, C2H5, CD3 and C2D5), giving ion m/e 223. The fragment (CH3)3SiOCH3 is also eliminated in the four ethers investigated from the ion [M – R]+. Attack of the siliconium ion. Indications are found for a transannular hydrogen/deuterium rearrangement and a transannular elimination reaction. The intensity of some peaks in the spectra are discussed in relation to group R.
The mechanism of loss of C2H2O from cinnamylalcohol
Authors: Köoppel C. , Schwarz H.
Published: May 2005

The mass spectra of ring deuterated and 13C labelled cinnamylalcohol give evidence of a partial hydrogen scrambling which is not accompanied by carbon skeleton rearrangements.
Electron impact studies. CXII—The properties of positive ions produced by charge stripping from negative ions. [C6H5O]+, [C6H5S]+ and [C7H7S]+
Authors: Benbow John A. , Bowie John H. , Klass Gunter
Published: May 2005

The dissociative spectrum of the [C6H5S]+ ion derived by charge inversion from [C6H5S]−, shows a variety of fragmentations including the competitive losses of H⋅, C3H4 and the formation of [CHS]+. The spectrum of a deuteriated derivative shows that these three processes are preceded or accompanied by H/D scrambling. The corresponding [C6H5O]+ species also undergoes hydrogen scrambling prior to fragmentation. In marked contrast, the ion [p‐MeC6H4S]+ does not undergo hydrogen randomization between the methyl and aryl groups, and positional integrity is retained during fragmentation. These results are compared with the properties of the same ions produced by conventional ionization.
Electron impact studies. CXIV—The occurance of metastable ions for two‐ and multi‐ stage decomposition of negative ions derived from p‐nitrophenyl carboxylic acids
Authors: Bowie John H. , Stapleton B. Jane
Published: May 2005

Pronounced metastable peaks are observed for the two‐stage decomposition and the multi ‐ stage elimination from p‐NO2C6H4(CH2)nCO2H (n>1). 2H and 18O labelling shows that each process involves elimination of atoms from both the nitro and carboxyl groups. A consideration of the spectrum of p‐nitrophenylcyclohexane‐4‐carboxylic acid leads to the proposition that interaction between the two functional groups is not a necessary prerequisite for the elimination of HO⋅.
Importance Relative des Isomères de I'Ion Moléculaire de Dérivés Substitués Polycycliques du Benzodioxinne 1,4
Authors: Dagaut Jacques , Ricard Michele , Brun Jean Pierre , Leblanc Danielle
Published: May 2005

Différents isomères de I'ion moléculaire de dérivés benzocyclobuténiques du benzodioxinne 1,4 spécifiquement marqués au deutérium ont été mis en évidence. L'abondance de l'Blimination des radicaux benzoyles et formyles différement marqués ont permis de déterminer l'importance relative des isomères de l'ion moléculaire.
Enthalpy considerations applied to the relatively slow unimolecular reactions of a series of homologous CnH2n radical cations
Authors: Bowen Richard D. , Williams Dudley H.
Published: May 2005

The concept that the slow, unimolecular reactions of the homologous series of radical cations are largely determined by the relative energetics of the possible product combinations is discussed. The concept is shown to provide a reasonably consistent rationalization of the known metastable dissociations of and correctly predicts the reactions undergone by . The concept may be useful in discussing the unimolecular chemistry of isomers.
Influence de l'Insaturation Δ20(22) sur la Fragmentation du Cycle D des Stéroides
Authors: Schmit Jean P. , Charette Jean J.
Published: May 2005

Les spectres de masse de deux séries de stéroides Δ20(22) insaturés ont été étudiés. L'analyse de la fragmentation du cycle D montre que la rupture da la liaison C‐15C‐16 est caractéristique de la présence d'une telle insaturation dans la chaîne latérale.
Studies in the chemistry of erythrina alkaloid derivatives IV—mass spectral studies of erythrinane derivatives
Authors: Migron Y. , Bergmann E. D.
Published: May 2005

The electron impact induced fragmentations of erythrinane, erythrinone and their derivatives, have been investigated and rationalized.
The Chemistry of C6H6O radical cations: A study of rearrangement reactions of halogen substituted ethyl phenyl ethers
Authors: Russell D. H. , Gross M. L. , Van Der Greef J. , Nibbering N. M. M.
Published: May 2005

New experimental data on the rearrangement reaction of various phenoxyethyl halides to give [C6H6O]+˙ are presented and compared with previous studies so that a coherent picture of this process can be developed. By examining the metastable kinetic energy release for low energy decomposing molecular ions of the phenoxyethyl halides, it has been concluded that formation of [C6H6O] occurs by competitive 1,2 and 1,3 hydrogen shifts from the alkyl carbons to oxygen followed by a rate determining CO bond cleavage. This is substantiated by the absence of a primary hydrogen isotope effect. For more highly activated molecular ions, a new mechanism comes into play as evidenced by the appearance of a small hydrogen isotope effect. It is postulated that this third mechanism involves transfer of the alkyl hydrogen to the ortho position of the ring by a rate determining 1,5 shift, followed by a 1,3 hydrogen shift from the ortho methylene group to oxygen and rapid CO bond cleavage. This 1,3 hydrogen shift to oxygen appears to be ‘catalysed’ by the halogen atoms yielding phenol ions. No indications have been found for the formation of tautomeric 2,4‐cyclohexadienone ions. Furthermore, highly activated molecular ions produce [C6H6O]+˙ which can undergo metastable decomposition to lose carbon monoxide. Kinetic energy release measurements for the latter reaction show that the majority of these [C6H6O]+˙ions have been formed as phenol ions as well. These arguments are supported by energetic measurements and by comparisons with previous ion cyclotron resonance and collisional activation studies.
Fragmentation de la Méthyl‐2 Indolizine sous Impact Electronique: perte de H˙ à partir de l'Ion Moléculaire; perte de HCN à partir de l'Ion [MH˙]+
Authors: Corval Madeleine , Brun Jean‐Pierre
Published: May 2005

L'origine du radical H⋅ éliminé dans la source D'ions à partir de l'ion moléculaire de la méthyl‐2 indolizine est étudiée au moyen de quatre variétés marquées au deutérium. La perte de H⋅ intéresse préférentiellement le substituant méthyle, mais les hydrogènes (ou certains des hydrogènes) de chacun des deux cycles interviennent également, particulièrement ceux du cycle substitué. Les résults de l'étude par balayage combiné de l'élimination de HCN à partir des ions métastables [M‐H˙]+ sont compatibles avec l'équivalence de tous les hydrogènes de l'ion précurseur vis‐à‐vis de ce processus, impliquant une réorganisation extensive préalablement à la fragmentation.
Mass spectroscopic study of halocyanoacetylenes: Appearance energies and thermochemical data
Authors: Büchler Ulrich , Vogt Jürgen
Published: May 2005

The mass spectra of the cyanoacetylenes XCCCN, X  H, F, CI, Br, I, are reported, together with electron impact appearance energies as determined using a modified second derivative method. From these data the enthalpies of formation and the CX as well as the CC bond energies are deduced. These bond energies are discussed in comparison with values of corresponding saturated and acetylenic compounds.
Keto and enol forms of methyl acetate molecular ions, their stability and interconvertibility prior to fragmentation in the gas phase
Authors: Holmes John L. , Lossing F. P.
Published: May 2005

The heats of formation of the keto and enol forms of the molecular ion of methyl acetate are 577 ± 4kJ mol−1 and 477 ± 4KJ mol−1 respectively. Fragmentation by loss of CH3O˙ takes place at the thermochemical threshold for [CH3CO]+ formation for both isomers, which may therefore freely interconvert at internal energies corresponding to this decomposition threshold.
Mass spectrometry of the simple N‐ vinylpyridinium salts
Authors: Ellingsen Peter , Hvistendahl Georg
Published: May 2005

N‐ Vinylpyridinium halides readily undergo a Hofmann type elimination, prior to evaporation in the mass spectrometer, with formation of pyridine, acetylene and hydrogen halide as volatile products. A second important reaction is thermally induced two electron reduction of the cation to the volatile N‐vinyldihydropyridine. Of minor importance is the formation of volatile compounds with the elemental composition of [cation + C2H] and [cation + C2H3]. The latter is suggested to have a divinyldihydropyridine structure. Its formation is explained as due to nucleophilic attack on the cation by the N‐vinyldihydropyridine present with displacement of pyridine.
Pyrones: V—The mass spectra and fragmentation mechanisms of some 3(5)‐methoxy‐4‐pyrones
Authors: McGillivray David L. , Poulton Gerald A.
Published: May 2005

The mass spectra of methyl kojate (2‐hydroxymethyl‐5‐methoxy‐4H‐pyran‐4‐one), two deuterated analogues and 14 related 3(5)‐methoxy‐4‐pyrones have been studied. These compounds fragment according to a common mechanism, initiated by primary rearrangement of the molecular ion(s). Guidelines which indicate the presence of 3(5)‐methoxy‐4‐pyrones and allow structural determinations to be made from their mass spectra are presented. For the majority of substituents studied, the nature of the substituent has no major effect upon the fragmentation pattern; the cyano group does. The hydroxy counterparts of the above compounds are readily converted for analysis by simple methylation.
The dependence of collision induced fragmentation pattern on the internal energy of the precursor ion
Authors: Porter C. J. , Proctor C. J. , Beynon J. H.
Published: May 2005

A Method is presented whereby product organic ions formed as the result of fragmentation of metastable ions can be selected on the basis of their internal energies. The method requires requires angular collimation of the beam of reactant ions issuing from the ion source and that the fragmentation of the metastable ions is studied in the first field free region of a reversed geometry double focusing mass spectrometer. The product ions that make up the metastable peak are allowed to fall on the intermediate resolving slit and, by adjusting the magnet current over a small range, ions contained in different regions of the peak can be allowed into the second field free region. It is shown that the position of an ion within the metastable peak correlates with its internal energy, ions near the edges of the peak being the least excited. The ions entering the second field free region can be investigated by collisional activation. This has been done for molecular ions of p‐chlorophenol, methylbenzoate, benzaldehyde, m‐chlorotoluene and n‐butane. The in which the collision induced fragmentation pattern varies with internal energy of the ions is illustrated.
The fragmentation of isotetronic acid O‐methyl ethers under electron impact
Authors: Bonini C. C. , Iavarone C. , Trogolo C. , Poulton G. A.
Published: May 2005

The mass spectra of a series of methyl ethers of isotetronic acids have been examined and the modes of fragmentation rationalized on the basis of two general schemes.
Thermal desorption of quasimolecular ions
Authors: Stoll R. , Röllgen F. W.
Published: May 2005

The thermal desorption of [M + Alkali]+ quasimolecular ions from a heated metal surface is reported for some alkali salts of carboxylic acids and mixtures of alkali halides with a crown ether, glucose and adenosine. No quasimolecular ion could be detected from sucrose. With benzo[15]crown‐5 the desorption of [M + Na]+ ions takes place even below the threshold temperature for thermionic emission of alkali ions. In addition, the desorption of intact [B(C6H5)4]− ions from a layer of NaB(C6H5)4 is reported.
Bifunctional interaction and its effect on the esterification of dicarboxylic acids in chemical ionization mass spectrometry
Authors: Wengang Chai , Guanghui Wang , Zhiling Xu , Jiongguang Pan , Shumin Duan
Published: May 2005

The chemical ionization mass spectra of different dicarboxylic acids, including saturated and unsaturated aliphatic, aromatic, hydroxyl and amino‐substituted dicarboxylic acids, have been studied using pure methanol as the reagent gas. Biomolecular monoesterification and diesterification product ions [M+15]+ and [M+29]+, and adduct ion [M+33]+, were observed, in addition to the protonated molecule [MH]+ and unimolecular water elimination product ions. The formation of a protonated molecule with bridged intramolecular hydrogen bond, and its effect on the esterification of dicarboxylic acids is discussed. Geometric isomers, such as maleic and fumaric acid, and ortho and meta isomers of phthalic acids can be distinguished from each other by methanol chemical ionization mass spectra. When ethanol was used as the reagent gas, similar mass spectra of some dicarboxylic acids were obtained.
Charge reversal of three alkylamide ions: Free nitrenium ions
Authors: Bursey Maurice M. , Harvan Donald J. , Parker Carol E. , Darden Thomas A. , Hass J. Ronald
Published: May 2005

The methylnitrenium, ethylnitrenium and dimethylnitrenium ions are prepared by charge reversal collisional activation (CR CA) of the corresponding negative ions; their collisional activation mass spectra are shown to support the assigned structures. MINDO/3 energies are used to evaluate relative energies of [CH4N]+ and [C2H6N]+ isomers, and to determine whether unstable forms rearrange spontaneously to stable ones. As in other examples, charge reversal here generates cations that do not exist in an energy well, but their transient existence is established because their fragmentation is more rapid than their rearrangement to a more stable form.
Mass and kinetic energy spectrometries of alkylketenes
Authors: Maquestiau A. , Flammang R. , Pauwels P.
Published: May 2005

Real‐time analysis of alkylketenes synthesized by flash vacuum thermolysis (FVT) of acid chlorides has been performed by mass spectrometric techniques using a triple sector (E/B/E) spectrometer. The major high energy reactions of the molecular ions consist of β‐cleavages relative to the CC bond of the ketene function, followed by decarbonylation. The unimolecular reactions of the metastable molecular ions are often different as shown by collisional activation of the fragment ions produced in a field‐free region of the spectrometer and also from estimated heats of formation.
A study of [C7H8]+˙ and [C7H8]2+ ions formed from different precursor molecules
Authors: Rabrenović M. , Brenton A. G. , Ast T.
Published: May 2005

On the basis of unimolecular and collisionally activated decompositions, as well as their charge stripping behaviour, [C7H8]+˙ and [C7H8]2+ ions from a variety of precursors have been studied. In particular, structural characteristics of molecular ions of toluene, cycloheptatriene, norborna‐2,5‐diene and quadricyclane have been compared to those of [C7H8]+˙ and [C7H8]2+ rearrangement fragment ions obtained from n‐butylbenzene, 2‐phenylethanol and n‐pentylbenzene. Severe interferences from [C7H7]2+˙ ion fragmentations have been observed and rationalized.
The collisionally induced dissociation of allyl and 2‐propenyl cations
Authors: Burgers Peter C. , Holmes John L. , Mommers Alexander A. , Szulejko Jan E.
Published: May 2005

Pure [CH2CHCH2]+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} ions are generated only in metastable fragmentations of [CH2CHCH2X]+˙, X=Cl, Br, I, and [CH3CXCH2]+˙, X=Br, I, respectively. For ion source generated [C3H5]+ ions there is some structural interconversion. The structure characteristic feature of their collisional activation mass spectra is the ratio m/z 27 ([C2H3]+): m/z 26 ([C2H2]+˙). For \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm{CH}}_{\rm{3}} \mathop {\rm{C}}\limits^{\rm{ + }} = {\rm{CH}}_{\rm{2}} $\end{document} the ratio is only weakly dependent upon the translational energy of the ion. For [CH2CHCH2]+, the ratio rises sharply as translational energy is reduced, from 0.9 at 8 kV to c. 3 at 1 kV. [CH2CHCH2]+ ions generated by charge reversal of [CH2CHCH2]− show higher ratios, resulting from their lower average internal energy content. It must therefore be emphasized that [C3H5]+ ion structure assignments should only be made using reference data which apply to specific experimental conditions. [C3H5]+ daughter ion structures for a number of well‐known fragmentations have been established. The heat of formation of the 2‐propenyl cation was measured to be 969±5 kJ mol−1. Labelling experiments show that at low internal energies, allyl cations do not undergo atom randomization in c. 1–2 μs; high internal energy ions of longer lifetime (c. 8 μs) show complete atom randomization. H˙ atom loss from [13CH3CHCH2]+˙ has been shown to generate [13CH2CHCH2]+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {}^{{\rm{13}}}{\rm{CH}}_{\rm{2}} \mathop {\rm{C}}\limits^{\rm{ + }} - {\rm{CH}}_{\rm{3}} $\end{document} without any skeletal rearrangement.
The energy surface for isomeric [C2H3O]+ ions: Further experimental evidence
Authors: Tureček FrantišEk , McLafferty F. W.
Published: May 2005

Mass spectra from collisionally activated dissociation (CAD) of [C2H3O]+ ions, including isotopically labeled analogs, provide further information on the isomers [CH3CO+] (a), [CH2CO+H] (b), [+CH2CHO] (c) and (d). Our data generally support the recent conclusions from theory by Radom and coworkers and from experiment by Terlouw, Holmes and coworkers. Most acetyl‐containing molecular ions form a ions in high purity only at low energies, consistent with isomerization of higher energy molecular ions to form the more stable enol which dissociates to b. Isomer d, prepared from (CICH2)2CHOH, undergoes facile hydrogen scrambling, presumably through a degenerate 1,2‐hydrogen shift. Theory suggests that c undergoes spontaneous isomerization to a and d; although [C2H3O]+ ions from BrCH2CHO appear to consist of a and ∼15% d, the latter are formed without substantial hydrogen scrambling.
Collision‐induced dissociation of ester enolate ions using fourier transform mass spectrometry
Authors: Froelicher Stephen W. , Lee Robert E. , Squires Robert R. , Freiser Ben S.
Published: May 2005

A series of ester enolates was investigated by the technique of collision‐induced dissociation (CID) using a Fourier transform mass spectrometer. Two primary modes of fragmentation were observed which led to CID products characteristic of the acyl and alkoxyl moieties of the ester enolates. An investigation of the fragmentation mechanism revealed that the primary fragmentation mode appears to be a sensitive function of the structure and the proton affinities of the two possible product ions. In most cases the anion (ketenyl or alkoxide) with the lower proton affinity was observed as the threshold product, suggestive of a proton‐bound dimer intermediate. Interesting secondary dissociations were observed to occur from the primary product ions, as alkoxide ions fragmented to enolate ions or other stabilized anions.
The reaction of the trichloromethylium ion with olefins
Authors: Stone John A. , Moote Nancy Joan
Published: May 2005

The reactions of [CCl3]+ with ethylene, 1‐hexene, cyclopentence, cyclohexene and styrene have been studied in a field‐free, high‐pressure ion source by time‐resolved ion collection following a short ionizing pulse of electrons. Ethylene is completely unreactive, while addition of [CCl3]+ to the olefinic bond of the other compounds is followed by loss of one or more HCl molecules to give unsaturated cations. Only styrene forms a stable adduct [MCCl3]+ which is an arenium ion produced by addition to the aromatic ring. Rate constants for the reaction of [CCl3]+ have been determined and show that whereas reaction with styrene occurs at almost every ion‐molecule collision, with 1‐hexene and cyclopentene only 15% of the collisions lead to reaction.
Electron impact mass spectrometry of some 2,3‐dihydro‐1‐benzofuran‐3‐acetic acids
Authors: Bravo Pierfrancesco , Ticozzi Calimero , Daolio Sergio , Traldi Pietro , Vecchi Enrico
Published: May 2005

The mass spectrometric behaviour of four 2,3‐dihydro‐1‐benzofuran‐3‐acetic acids has been studied in detail with the aid of exact mass measurements, linked scans, collisionally activated decomposition, mass analysed ion kinetic energy spectra and labelling experiments. Unusual fragmentation pathways are emphasized for which mechanisms are proposed.
Further mass spectral studies of flavones
Authors: Guidugli F. H. , Ardanaz C. E. , Kavka J. , Garibay M. E. , Joseph‐Nathan P.
Published: May 2005

Further evidence supporting the structure of the [M − 1]+ ion found in the mass spectrum of flavone as being the [dibenzo‐β‐tropolone − H]+ species was obtained by comparison of linked scan measurements performed in flavone, 3‐deuteroflavone, 5,6,7,8‐tetradeuteroflavone, 2′,3′,4′,5′,6′‐pentadeuteroflavone and dibenzo‐β‐tropolone. This fragmentation process has also been demonstrated in the case of 3‐methoxyflavone by high‐resolution measurements, deuterium labelling, metastable decompositions and evaluation of the subspectra of 9‐methoxyfluorenol, fluorenone and biphenylene. The structure of the ion at m/z 181 in the spectrum of flavone was found to be the [2‐phenylbenzoxetane − 1]+ species.
Oxidation reactions in triterpenes under chemical ionization conditions
Authors: Madhusudanan K. P. , Singh Chandan , Fraisse D.
Published: May 2005

From a collisional activation spectral study it has been found that certain triterpene alcohols with an ursane or oleanane skeleton undergo oxidation to the corresponding ketones under chemical ionization (NH3) conditions giving rise to abundant [M + NH4  2]+ ions. Mass‐analysed ion kinetic energy and B2/E scan results indicate that both [M + NH4]+ and [M + N2H7  2]+ ions contribute to the formation of the [M + NH4  2]+ ion.
Thermochemistry of HCOS+ and HCS2+
Authors: McAllister Trevor , Taylor Peter R. , Scarlett Margaret
Published: May 2005

Heats of formation for HCOS+ and HCS2+, obtained from high‐quality ab initio calculations, have been used to determine the thermochemistry of several reactions which may form these ions in interstellar clouds or mass spectrometer experiments. Radiative association of HCO+ or HCS+ with either O or S may be important in interstellar clouds, whereas proton transfer from H3+ or HCO+ to CS2 or COS may be a means of synthesizing these ions by mass spectrometry. In the latter case, the relevant heats of formation are: HCS2+(1A1) 1042 kJ mol−1 and HCOS+ (1A′) 996 kJ mol−1.
The correlation of the intensities of the M+˙ and [M − H]+ ions in electron impact mass spectra of cyclic acetals and thioacetals containing a phenylalkoxyester group
Authors: Konopski Leszek , Masłosz Józef
Published: May 2005

The correlation between the intensities of the M+˙ and [M − H]+ ions of 47 cyclic acetals and thioacetals of alkyl formylphenoxyacetates and propionates as well as the fragmentation patterns in the vicinity of the molecular ion are discussed. The characteristic differences between the spectra of 1,3‐dioxolanes, 1,3‐oxathiolanes, 1,3‐dithiolanes and 1,3‐dioxanes are presented.
Hydride abstraction in fast atom bombardment
Authors: Baldwin Michael A. , Welham Kevin J. , Toth Istvan , Gibbons William A.
Published: May 2005

Under fast atom bombardment conditions, compounds having long alkyl chains may exhibit [M − H]+ as the major quasimolecular ion species, which can lead to incorrect assignment of molecular masses. It is shown that for a long‐chain ether the loss of the hydride occurs from the hydrocarbon chain remote from the oxygen. This effect may yield information concerning ionization mechanisms in fast atom bombardment/mass spectrometry.
Mass spectrometry of charge‐transfer complexes of 7,7′,8,8′‐tetracyanoquinodimethane‐π‐donor systems
Authors: Kurono Sadamu , Tani Takeshi , Hirano Takashi , Tsujimoto Kazuo , Ohashi Mamoru
Published: May 2005

Electron impact (El) ionization and positive and negative liquid secondary ion mass Spectrometry (pLSIMS and nLSIMS) of eight charge‐transfer complexes of 7,7′,8,8′‐tetracyanoquinodimethane (TCNQ)‐aromatic systems and of the individual π‐donors and ‐acceptors was examined. The El spectra exhibited the molecular ions of both the donor and the acceptor of each complex. The molecular ion of the π‐donor was observed in pLSIMS using m‐nitrobenzyl alcohol (NBA) if its oxidation potential is lower than 1.2 V, but when the oxidation potential is higher than 1.9 V, no molecular ion was detected. On the other hand, nLSIMS exhibited the molecular ion of TCNQ in all cases. Participation of an excited state of NBA in the ionization process is suggested.
Mass spectrometry of thio analogues of pyrimidine bases: Correlation of the intensities of the M+˙ and the [M – ˙SH]+ ions of 2‐alkylthiouracils
Authors: Wyrzykiewicz E. , Bartkowiak G.
Published: May 2005

The mass spectral fragmentations of eight 2‐alkylthiouracils with C10, C12, C16 and C18 in the alkylthio group were investigated. Fragmentation pathways are proposed on the basis of accurate mass and matastable transition measurements. The correlation between the intensities of the M+˙ and [M ‐ ˙SH]+ ions of 36 2‐alkylthiouracils is discussed. The data obtained create the basis for distinguishing structural isomers.
Ion–molecule reactions of [ketene]+˙ as a diagnostic probe for distinguishing isomeric alkenes, alkynes and dienes: A study of the C4H8 and C5H8 isomeric hydrocarbons
Authors: Dass Chhabil , Stout Charles B.
Published: May 2005

The gas‐phase ion–molecular reactions of [ketene]+˙ with a number of isomeric alkenes, alkynes and dienes were studied by using tandem mass spectrometry. Ketene was reacted with C4H8 (but‐1‐ and −2‐ene and 2‐methylpropene) and C5H8 unsaturated hydrocarbons (isoprene, penta‐1,3‐ and −1,4‐diene, pent‐1‐ and −2‐yne, cyclopentene and methylenecyclobutane) in a high‐pressure chemical ionization source of a tandem mass spectrometer. The collisionally stabilized ion–molecule adducts were analyzed by use of collisionally activated dissociation (CAD) spectra. The three C4H8 alkenes were distinguishable on the basis of the distinct CAD spectra of their adducts with ketene. Similarly, the CAD data for the corresponding adducts derived from the C5H8 hydrocarbons point to different structures for the C5H8 compounds.
[M + 11]+˙ and [M + 11]−˙ ions in the nitrogen positive and negative ion chemical ionization mass spectra of aromatic amines
Authors: Stemmler Elizabeth A.
Published: May 2005

The N2 negative ion chemical ionization (NICI) mass spectra of aniline, aminonaphthalenes, aminobiphenyls and aminoanthracenes show an unexpected addition appearing at [M + 11]−˙. This addition is also observed in the N2 positive chemical ionization (PCI) mass spectra. An ion at [M – 15]− is found in the NICI spectra of aminoaromatics such as aniline, 1‐ and 2‐aminonaphthalene and 1‐ and 2‐aminoanthracene. Ion formation was studied using labeled reagents, variation of ion source pressure and temperature and examination of ion chromatograms. These experiments indicate that the [M + 11]−˙, [M – 15]−˙ and [M + 11]+˙ ions result from the ionization of analytes altered by surface‐assisted reactions. Experiments with 15N2, [15N] aniline, [2,3,4,5,6‐2H5] aniline and [13C6] aniline show that the [M + 11]−˙ ion corresponds to [M + N – 3H]−˙. The added nitrogen originates from the N2 buffer gas and the addition occurs with loss of one ring and two amino group hydrogens. Fragmentation patterns in the N2 PCI mass spectrum of aniline suggest that the neutral product of the surface‐assisted reaction is 1,4‐dicyanobuta‐1,3‐diene. Experiments with diamino‐substituted aromatics show analogous reactions resulting in the formation of [M – 4H]−˙ ions for aromatics with ortho‐amino groups. Experiments with methylsubstituted aminoaromatics indicate that unsubstituted sites ortho to the amino group facilitate nitrogen addition, and that methyl groups provide additional sites for nitrogen addition.
Collision‐induced decompositions of [M – H]− and [M + Li]+ ions from fast atom bombardment of dinucleoside phenylphosphonates
Authors: Madhusudanan K. P. , Katti S. B. , Hashmi S. A. N.
Published: May 2005

The collision‐induced decompositions of the [M – H]− and [M + Li]+ ions of a few dinucleoside phenylphosphonates were studied using fast atom bombardment and linked scanning at constant B/E. Deprotonation takes place on the base or sugar moieties. The [M – H]− ion decomposes mainly by cleavage on either side of the phosphonate linkage, leading to the formation of mononucleotide fragment ions and also by cleavage of the basesugar bond. Rupture of the 3′‐phosphonate bond is preferred. Unlike the normal charged nucleotides, these neutral nucleotides do not eliminate a neutral base from the [M – H]− ion. However, the mononucleotide fragment ions which can have the charge on the phosphorus oxygen eliminate neutral bases by charge‐remote fragmentation. The 4,4′‐dimethoxytrityl (DMT)‐protected nucleotides show the additional fragmentation of loss of DMT. Li+ attachment can occur at several sites in the molecule. As observed for the [M – H]− ion, the major cleavage occurs on either side of the phosphonate bond in the fully deprotected nucleotides, cleavage of the ester bond on C(3′) being preferred. Cleavage of the 5′‐phosphonate bond is not observed in the DMT‐protected nucleotides. Many of the fragmentations observed can be explained as arising from charge‐remote reactions.
An epoxy resin‐elastomer system for filament winding
Authors: Rinde J. A. , Mones E. T. , Moore R. L. , Newey H. A.
Published: May 2005

Tests characterizing an epoxy system that contains 5 percent rubber and is suitable for wet‐filament winding are described. The resin is a bisphenol‐A rubberized epoxy diluted with an aliphatic diglycidyl ether and cured with an aromatic amine. The viscosity and pot life were measured and the progress of cure was monitored so an optimum cure could be chosen. Mechanical tests were performed on the cured resin. The low viscosity (0.95 Pa's) and long pot life (29.3 h) make for ease of processing. A cure cycle of 1.5h at 90°C plus 2 h at 130°C gives a cured resin having a glass transition temperature of 104°C. The heat‐cured material has a tensile strength of 76.1 MPa and a modulus of 2.43 GPa. Kevlar 49 composites of 60‐, 65‐, and 70‐volume‐percent fiber were prepared and tested. Results are presented and compared to two other Kevlar 49/epoxy composites.
Interfacial interactions and the properties of filled polymers: I. Dynamic‐mechanical responses
Authors: Boluk M. Y. , Schreiber H. P.
Published: May 2005

The dynamic mechanical responses of rutile‐filled, chlorinated polyethylene (CPE) were studied as a function of temperature, of filler loading, and of filler surface condition. An objective was to establish the influence of matrix‐filler interactions on mechanical properties. Necessary information on potential interactions between matrix and filler was obtained from inverse gas chromatographic data, in the form of an acid‐base interaction parameter, Ω. The damping peak in filled CPE compounds was depressed by the pigment, as called for by theoretical models. The magnitude of the effect exceeded expectations, however, and clearly depended on the strength of interfacial interactions. These were consistent with the acid‐base ranking of CPE and the various rutiles, as given by Ω. It has been postulated that in the presence of acid‐base interactions, an immobilized layer of polymer in the vicinity of solid particles increases the effective particle dimension, thereby accounting for the observed variations in relative damping. Additional effects of matrix‐filler interaction were noted in the variation of storage moduli with loading and temperature. Again, the effects tend to be more pronounced when significant specific interactions between matrix and solid are operative. These observations point to the inadequacy of existing models as interpretative bases for dynamic mechanical properties in systems with significant specifie interactions among their components.
Electrical properties of exfoliated‐graphite filled polyethylene composites
Authors: Wang Y. S. , O'Gurkis M. A. , Lindt J. T.
Published: May 2005

An experimental study has been carried out to prepare and characterize high density polyethylene‐based composites filled with exfoliated graphite particles of varied aspect ratios. It has been demonstrated that the dielectric constant of the composite correlates with the in situ volumetric fraction of the compressible exfoliated filler particles. The dielectric constant has been found to range from 2.23 to 125. The minimum electrical resistivity of the composites obtained was 0.1 Ω.cm at a graphite content of 40 percent by volume. The use of these composites is intended in electromagnetic radiation interference (EMI) shielding.
High strain‐rate shear deformation of a polyurethane elastomer subjected to impact loading
Authors: Gupta Y. M.
Published: May 2005

Experimental techniques have been developed to produce and measure large amplitude one dimensional compression and shear waves in a polyurethane elastomer (Solithane 113). Experimental measurements consisted of time‐resolved compression and shear amplitude measurements at different distances from the impact surface. The data were analyzed to provide compression and shear wave velocities, and the corresponding stress‐stain curves on the microsecond time scale. The ability to measure directly the high stain rate shear response is a new development and has provided interesting results. The shear modulus varies between 3 and 9 kbar for compressive stresses ranging between 2 and 14 kbar. In contrast, shear modulus values inferred from quasi‐static measurements of bulk and Young's modulus under static high pressure are negligible. These comparisons suggest a high rate dependence of shear modulus in the glassy state. The shear strain curves suggest an elastic‐plastic response with yield strengths ranging from 0.12 kbar to 0.25 kbar with increasing compression for the compressive stress range investigated. Results of compression experiments are also presented.
Impact modification of poly(vinyl chloride) with chlorinated polyethylene II. Irreversible deformation
Authors: Siegmann A. , English L. K. , Baer E. , Hiltner A.
Published: May 2005

The mechanical behavior of chlorinated polyethylene (CPE)‐modified poly(vinyl chloride) (PVC) has been determined. The nature of the irreversible deformation processes which are responsible for mechanical energy absorption has been investigated by optical and electron microscopic techniques. Addition of CPE results in a decrease in the shear band initiation stress and an increase in void density and stability. The crazing to shear banding transition is observed at a blend composition between 2 and 7 percent CPE at the strain rate employed. It has been established that voiding occurs in the CPE rubber phase. Voiding accounts for at least part of the increased energy absorption of the blend. The stability of the voids to coalescence and fracture is attributed to strong adherence of the CPE to the primary PVC particles.
Fatigue behavior of medium‐density polyethylene pipes
Authors: Nishimura Hiroyuki , Narisawa Ikuo
Published: May 2005

A round bar specimen and a square bar specimen cut out from medium‐density polyethylene pipes with a notch were made and a fatigue test was conducted to cause a brittle fracture. The initiation and growth of a craze and crack at the tip of a notch was observed. In the range where loading cycles are few and displacement of the specimen does not increase, the craze prior to crack initiation occurs. Also, the effect of frequency was investigated. The pure creep failure and the fatigue failure at low frequency were compared. The lower the frequency, the smaller the reciprocal of the actual loading timeTfbecomes. It is also found that this tensile fatigue test is a useful test method to assure the quality of pipes.
Low Temperature Plasma‐Based Sterilization: Overview and State‐of‐the‐Art
Authors: Laroussi Mounir
Published: May 2005

Summary: Low temperature, high pressure, non‐equilibrium plasmas are now routinely used in several material processing applications, and in some cases are competing with low pressure plasmas in areas where these have historically been dominant. Etching and deposition are examples of such applications. Amongst the novel applications of non‐equilibrium plasmas, biomedical applications such as electrosurgery, surface modification of biocompatible materials, and the sterilization of heat‐sensitive medical tools are particularly interesting. In this paper, first a brief overview of recent research on reduced‐pressure plasma‐based sterilization/decontamination methods is given. Then a detailed review and discussion on the effects of atmospheric pressure non‐equilibrium plasmas on the cells of bacteria is presented. This includes the evaluation of the inactivation kinetics and the roles of the various plasma agents in the inactivation process. Measurements of the plasma temperature, the UV emission, and concentrations of various reactive species for the case of air plasma are presented. Plasma sub‐lethal effects are also briefly discussed, and the prospects of the use of “cold” plasmas in the biomedical field are outlined.

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Aerosol Charge Neutralization by a Radioactive Alpha Source
Authors: Liu Benjamin Y. H. , Pui David Y. H. , Lin Bing Y.
Published: May 2005

The performance of a Po‐210 radioactive ionizer for aerosol charge neutralization and bipolar charging has been evaluated. Monodisperse neutral and singly charged aerosols have been passed through the ionizer and their approach to the steady‐state Boltzmann charge measured by measuring the fraction of particles that are electrically charged. The result shows that an Nt of approximately 2.5 × 105 cm−3 s is needed for the development of a steady‐state charge fraction equal to that given by the Boltzmann' s law where N is the ion concentration and t is the residence time of the aerosol in the neutralizer. In addition, the performance of the ionizer for particle charge neutralization in a vibrating‐orifice aerosol generator has been evaluated and the result shows that the source is less effective for this application and the residual charge on the particles is considerably higher than that given by the Boltzmann's law.
Comparison of the three‐dimensional structure of two human rhinoviruses (HRV2 and HRV14)
Authors: Blaas Dieter , Kuechier Ernst , Vriend Gerrit , Arnold Edward , Luo Ming , Rossmann Michael G.
Published: May 2005

An attempt has been made to build a model of human rhinovirus 2 (HRV2) based on the known human rhinovirus 14 (HRV14) structure. HRV2 was selected because its amino acid sequence is known and because it belongs to the minor rhinovirus receptor class as compared to HRV14, which belongs to the major class. Initial alignment of HRV2 with HRV14 based on the primary sequence and the knowlege of the three‐dimensional structure of HRV14 showed that most probable position of the majority of insertions and deletions occurred in the vicinity of the neutralizing immunogenic sites (NIm). Out of a total of 855 amino acids present in one copy of each of the capsid proteins VP1 through VP4 of HRV14, 411 are different between the two viruses. There are also 6 amino acids residues inserted and 14 residues deleted in HRV2 relative to HRV14. Examination of amino acid interactions showed several cases of conservation of function, e.g., salt bridges or the filling of restricted space. The largest variation amongst the residues lining the canyon, the putative receptor binding site, was in the carboxy‐terminal residues of VP1.
Normal modes of vibration in bovine pancreatic trypsin inhibitor and its mechanical property
Authors: Nishikawa Tetsuo , Gō Nobuhiro
Published: May 2005

The normal mode analysis of conformational fluctuation is carried out for a small globular protein, bovine pancreatic trypsin inhabitor. Results are analyzed mainly to reveal the mechanical construction of the protein molecule. We take dihedral angles, including peptide ω angles, as independent variables for the normal mode analysis. There are 306 such angles in this molecule. Motions in modes with frequencies lower than 120 cm−1 are showned to involve atoms in the whole protein molecule, and spatial change of displacement vectors is continues, i.e., those of atoms near in space are similar. To quantitate the observation of the continuity, a correlation function of direction vectors of atomic displacement is calculated. From this function we define a Quantity that is interpreted as the wave length of an equivalent elastic plane wave. From this Quantity we deduce eefective young's modulus for each mode. For the mode with the lowest frequency 4.4 cm−1, it terned out to be 0.8 × 109 dyn cm−2, the value two orders magnitude softer than, for instance, α‐helices. Prompted by this observation, the four lowest frequency modes and also the harmonic motions in the thermal equilibrium are analyzed further mainly to detect relatively rigid structural elements in the molecule. From this analysis emerges a mechanical picture of the protein molecule that is made up of relatively rigid elements held together by very soft parts.
Validation of the first step of the heuristic refinement method for the derivation of solution structures of proteins from NMR data
Authors: Lichtarge Olivier , Cornelius Craig W. , Buchanan Bruce G. , Jardetzky Oleg
Published: May 2005

A new method for the analysis of NMR data in terms of the solution structure of proteins has been developed. The method consists of two steps: first systematic search of the conformational space to define the region allowed by the initial set of experimental constraints, and second, the narrowing of this region by the introduction of aaditional constraint and optional refinement procedures. The search of the conformational space is guided by heuristics to make it computationally feasible. The method is therfore called the heuristic refinement method and is coded in an expert system called PROTEAN. The paper describe the validation of the first step of the method using an artificial NMR data set generated from the known crystal structure of sperm whale carbon monoxymyoglodin. It is shown that the initial search procedure yields a low‐resolution structure of the myoglobin molecule, accurately reproducing its main topological features, and that the precision of the structure depend on the quality of the intial data set.
The building of protein structures form α‐carbon coordinates
Authors: Correa Paul E.
Published: May 2005

A procedure for the construction of complete protein structures from only αcarbon coordinates is described. This involves building the backbone by sequential addition of Pro, Gly, or Ala residues. This main chain structure is then refined using molecular dynamics. Side chains are constructed by sequential addition of atoms with intermediate molecular dynamics refinement. For α lytic protease (a structure that is mostly β sheet) a backbone root mean square deviation (RMSD) of 0.19 Å and an overall RMSD of 1.24 Å from the crystallographic coordinates are attained. For troponin C (67% β‐helix), where the coordinates are available only for the α‐carbons, a backbone RMSD of 0.41 Å and an overall RMSD of 1.68 Å are attained (fits kindly provided by Dr. Michael James and Natalie Strynadka). For flavodoxin a backbone RMSD of 0.49 Å and an overall RMSD of 1.64 Å were attained.
Purification, crystallization, and preliminary X‐ray diffraction analyses of the bacterial chemotaxis receptor modifying enzymes
Authors: West Ann H. , Djordjevic Snezana , Stock Ann M. , Martinez‐Hackert Erik
Published: May 2005

Bacterial chemotaxis receptor modifying enzymes from Salmonella typhimurium have been crystallized using microseeding techniques. The crystals of the S‐adenosyl‐L‐methionine‐dependent methyl transferase, CheR, belong to the monoclinic space group P21 with cell constants a = 55.1 Å, b = 48.1 Å, c = 63.1 Å, β = 112.3°. The crystals of the catalytic domain of the methylesterase, CheB, belong to the trigonal space group P3221 or P3121 with unit cell dimensions of a = b = 63.4 Å, c = 86.8 Å. Both crystals contain one molecule per asymmetric unit and have calculated Matthews' volumes of 2.4 Å3/Da. © 1995 Wiley‐Liss, Inc.
Crystallization and preliminary X‐ray diffraction studies of a bacterial flavohemoglobin protein
Authors: Ermler Ulrich , Siddiqui Roman A. , Cramm Rainer , Friedrich Bärbel , Schröder Dirk
Published: May 2005

A flavohemoglobin protein (FHP) was isolated from Alcaligenes eutrophus and has been crystallized by vapor diffusion methods using PEG 3350 as precipitant. The crystals of the FAD‐ and heme‐containing protein belong to the monoclinic space group P21 with unit cell parameters of 52.2 Å, 85.8 Å, 103.9 Å, and 81.8° corresponding to two molecules per asymmetric unit. The crystals diffract at least to a resolution of 2.0 Å and are suitable for an X‐ray structure analysis. © 1995 Wiley‐Liss, Inc.
Electrospray ionization mass spectrometry of some β‐agonists
Authors: Debrauwer Laurent , Bories Georges
Published: May 2005

Positive‐ion electrospray spectra of some β‐agonists have been acquired under various ion acceleration conditions. Collisional activation of β‐agonists allows control of their mass spectral patterns, i.e., the molecular ion or several characteristic fragmentations can be favored by changing the energy of the ions extracted into the vacuum system. Some preliminary observations are presented, showing the potential of electrospray ionization for the mass spectrometric analysis of β‐agonists.