bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrospray mass spectrometry of pentacosasaccharides of blood group I‐activity and related compounds
Authors: Ii Tadashi , Ohashi Yoko , Matsuzaki Yuji , Ogawa Tomoya , Nagai Yoshitaka
Published: May 2005

The structural characterization of large synthetic oligosaccharides and related glycoconjugates performed by the use of electrospray ionization mass spectrometry (ESIMS) is described. The largest molecules described here are unprotected and protected pentaantennary pentacosasaccharides 2 and 5 with average molecular masses of 4441 and 9416, respectively. The straight‐chain neutral ceramide decasaccharide (d18:1/c24:0) 6 and the disialoganglioside GD2 (d18:1/c24:0) 7 were also successfully analyzed by ESIMS. In addition to exact mass determination, collision‐induced dissociation (CID) spectrometry of these compounds provided saccharide chain sequence information.
Tandem mass spectrometry: From infancy to maturity in twenty‐five years
Authors: McLafferty Fred W.
Published: May 2005

When this journal was initiated in 1968, there were only hints of the important applications of tandem mass spectrometry that are so well recognized today. It appears particularly appropriate to review briefly this development when celebrating the silver anniversary of the first mass spectrometry journal.
Growing protein‐doped sinapic acid crystals for laser desorption: An alternative preparation method for difficult samples
Authors: Xiang Fan , Beavis Ronald C.
Published: May 2005

This paper describes several protocols for growing large, protein‐doped 3,5‐dimethoxy‐4‐hydroxy‐trans‐cinnamic acid crystals. Examination of these crystals using laser desorption shows that the mass spectra obtained from the crystals can be useful for biochemical analysis. One particular crystal growing protocol allowed a non‐covalently bound heme group of horse muscle myoglobin to remain attached to the polypeptide following laser ablation and ionization. Crystals could be grown in solutions that contained involatile solvents that normally inhibit polypeptide ion production, such as glycerol. These crystals were protein doped and produced acceptable analytical mass spectra. The results suggest that some problems associated with the frequently used droplet‐drying method of sample preparation are caused by the changing concentration conditions present in drying solutions.
Various energy minima and corresponding fragmentation processes: Alkylsilanes
Authors: Vékey Károly , Paizs Béla , Somogyi Árpád , Knausz Dezsö , Pócsfalvi Gabriella
Published: May 2005

Fragmentation of alkylsilanes, in particular trimethylethylsilane, were studied by mass‐analysed ion kinetic energy (MIKE) and collision‐induced decomposition MIKE techniques. Ab initio and semi‐empirical molecular orbital calculations were applied to explain the main fragmentation processes. These calculations indicate that more than one minimum can be located on the potential energy surface of a given ground‐state molecule ion. These differ from each other mainly in the length of the silicon–carbon bonds. The structures can be adequately described as complexes of a trivalent silyl ion and an alkyl radical. Each of these complexes fragments by the loss of the weakly bound alkyl radical. The calculated energetics of these reactions were found to be in good agreement with the observed energy dependence of the mass spectra.
Acetone chemical ionization studies. VII‐acetylation of some aromatic compounds
Authors: Vairamani M.
Published: May 2005

Acetone chemical ionization mass spectra of 14 monosubstituted aromatic compounds were studied. Benzene, toluene and halobenzenes give exclusively charge‐exchange spectra with very little fragmentation. Protonation is characteristic of compounds with higher proton affinities than acetone, with the exception of benzonitrile. Acetylation reactions are observed mainly with benzonitrile, phenol, anisole and aniline. The acetylation of phenol and aniline mostly occurs at the substitutent.
Structural studies of polyhydroxybis(tetrahydrofuran)acetogenins from Annona squamosa using the combination of chemical derivatization and precursor‐ion scanning mass spectrometry
Authors: Hirayama Kazuo , Akashi Satoko , Yuji Reiko , Niitsu Uno , Fujimoto Yoshinori
Published: May 2005

The structure of squamocin polyhydroxybis(tetrahydrofuran)acetogenin from Annona squamosa L., was characterized by a combination of the chemical derivatization and precursor‐ion scanning mass spectrometry. The lactone part of squamocin was modified with N,N‐dimethylethylenediamine in the vapour phase to afford a strong positive charge at one end of the skeleton. The derivative was ionized by fast atom bombardment (FAB), and the product ion spectrum from [M + H]+ and the precursor ion spectrum from the m/z 72 ion [CH2CHN+H(CH3)2] generated by low‐energy collision were acquired. The structure of the derivative could be characterized by the precursor‐ion spetrum from the m/z 72 ion, but little structural information could be obtained from the production spectrum from [M + H]+ of the derivative. By the attachment of a tertiary amino group to one end of the skeleton, charge‐remote fragmentation was facilitated and abundant and unique fragment ions were observed in the precursor‐ion spectrum. Structural characterization of six other isolated compounds was also carried out, and two novel compounds were found by this technique. A similar derivatization was applied in the peptide leu‐enkephalin, and full sequencing from the C‐terminus using precursor‐ion scanning from m/z 72 could be achieved.
1,2‐Versus 1,4‐reduction of α,β‐unsaturated carbonyl compounds in the gas phase
Authors: Ho Yeunghaw , Squires Robert R.
Published: May 2005

The regioselectivity involved in the gas‐phase hydride reduction of α,β‐unsaturated carbonyl compounds by pentacoordinate silicon hydride ions is investigated. The kinetics and product distributions of the reactions of acrolein, methyl vinyl ketone and cyclohex‐2‐enone with monoalkoxysiliconate ions of the general composition RSiH3(OR′)− were examined with the flowing afterglow–triple quadrupole technique. All three substrates react by hydride transfer and by formation of a siliconate adduct in which hydride reduction of the organic reactant has occurred. The structures of these adducts and the hydride transfer products were identified by various tandem mass spectrometric protocols, including analysis of competitive collision‐induced dissociation (CID) reactions and comparisons of CID spectra obtained from reference ions with known structures. 1,4‐Reduction forming an enolate ion product is found to be the dominant or exclusive process with all three substrates, i.e. acrolein (70 ± 5%), methyl vinyl ketone (72 ± 5%) and cyclohex‐2‐enone (100%). Comparisons are made between these gas‐phase results and the regioselectivity reported for analogous condensed‐phase reactions. The observed behavior is discussed in terms of the reaction thermochemistry.
Neutral counterparts of the C2H7O+ isomers
Authors: Sirois M. , George M. , Holmes J. L.
Published: May 2005

The neutral counterparts of the C2H7O+ isomers CH3O+ (H)CH3, CH3CH2OH2+ and \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $\end{document} were studied by neutralization‐reionization mass spectrometry. Protonated dimethyl ether and its —O(D)+ analogue were produced by protonation (deuteration) of dimethyl ether and also generated as a fragment ion from (labeled) ionized CH3OCH2CH(OH)CH3 by loss of CH3CO⋅. It was observed that the dissociation characteristics of the ions and the stability of their neutral counterpart depended on the internal energy of the protonated ether ions. Stable neutral CH3Ȯ(H)CH3 was only produced from energy‐rich ions. The classical protonated ethanol ion CH3CH2OH2+ (a) was produced at threshold by the loss of CH3CO⋅. from ionized butane‐2,3‐diol. Mixtures of a with the non‐classical ion \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm C}_2 \,{\rm H}_4 \,\, \cdot \cdot \cdot \mathop {\rm H}\limits^ + \, \cdot \cdot \cdot {\rm OH}_2 $\end{document} (b) were produced by reaction of C2H5+ ions with H2O. As for the protonated ether, only high‐energy a and/or b ions yielded stable hypervalent radicals. It is suggested that the stable C2H7⋅O radicals are Rydberg states.
The ortho effect in the mass spectra of ortho/para isomers of bisphenol a derivatives and related compounds
Authors: Pleshkova Alexandra P. , Uspenskaya Marina N. , Volkovitch Sergei V.
Published: May 2005

New examples of the ortho effect in bisphenol A derivatives including interaction of the hydrogen of the ortho‐hydroxy group with the neighbouring aromatic ring have been observed. The characteristic ions [M  PhOH]+middot; (m/z = 134) and [M  CH3  PhOH]+ (m/z = 119) were shown to form through the hydrogen transfer from hydroxy and isopropyl groups, respectively. The spectra of cyclic derivatives having ortho‐hydroxy functions show [M  43]+, [M  C8H9O]+, m/z = 147, m/z = 135 and [M  C9H10O]+ ions. The proposed mechanims of the corresponding transformations were supported by mass spectra of deuterated analogues, methyl and trimethyl silyl ethers.
Influence of fluorine atoms on the electron impact and chemical ionization mass spectrometric fragmentation of methyl x‐deoxy‐x‐fluoro‐per‐O‐methyl‐β‐D‐galactopyranosides
Authors: Kováčik V. , Kováč P.
Published: May 2005

Fully methylated methyl x‐deoxy‐x‐fluoro‐β‐D‐galactopyranosides were studied using electron impact (EI) and chemical ionization (CI) mass spectrometry and by gas chromatography (GC)/mass spectrometry. Metastable daughter‐ and parent‐ion measurements and high‐resolution measurements were used to evaluate the fragmentation schemes. Both the presence and the position of the electronegative fluorine atom influences the fragmentation pathways of the permethylated compounds. The individual methyl x‐deoxy‐x‐fluoro‐per‐O‐methyl‐β‐D‐ galactopy‐ranosides have different GC retention times. This, together with the characteristic differences present in the EI or CI (methane or isobutane) mass spectra, allows the location of fluorine in these substances to be unambiguously determined.
Fingerprinting stereoisomers by survivor‐ion mass spectrometry
Authors: Gu Ming , Turecek Frantisek
Published: May 2005

Survivor‐ion mass spectrometry is used to distinguish stereoisomeric cis‐ and trans‐4‐methylcyclohexanol. The method involves producing ions by electron impact ionization and submitting them without mass selection to collisional neutralization and reionization, followed by selective monitoring of non‐dissociating ions. The differences in the electron impact mass spectra of the stereoisomers, due to the different fragment ion elemental compositions and structures, are highlighted by collisional neutralization with Xe, NO and CH3SSCH3, followed by reionization with oxygen. The differences in the survivor‐ion spectra are due to different neutralization efficiencies of the isobaric and isomeric ions produced by electron impact ionization, different stabilities of the intermediate neutral species, different reionization efficiencies and reionized ion stabilities. Neutralization‐reionization spectra of the C7H12+., C6H9+, C3H6O+. and C3H5O+ ions from stereoisomeric 4‐methylcyclohexanols are also reported.
Unimolecular reactions of \documentclass{article}\pagestyle{empty}\begin{document}$ ^ \cdot {\rm CH}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm HCH}_2 {\rm CH}_2 {\rm CH}_3 $\end{document} βdistonic ion
Authors: Milliet Arielle , Lecarpentier Eric , Audier Henri‐Edouard
Published: May 2005

The β‐distonic ion \documentclass{article}\pagestyle{empty}\begin{document}$ ^ \cdot {\rm CH}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm HCH}_2 {\rm CH}_2 {\rm CH}_3 $\end{document} has been shown previously to be an intermediate in the fragmentation of ionized ethyl propyl ether. The reactions of this ion (generated by fragmentation in the ion source of alkyl propyl ethers of glycol) were studied in this work. Labelling showed that this ion undergoes competing hydrogen transfers leading to a series of isomeric distonic ions. Each of them was submitted to an isotope effect.
Matrix influence on stability constants of 15‐crown‐5‐alkali metal complexes measured by liquid secondary ion mass spectrometry
Authors: Giraud Denis , Laprévote Olivier , Das Bhupesh C.
Published: May 2005

The liquid secondary ion mass spectra of 15‐crown‐5 in the presence of equimolecular mixtures of three alkali metal salts show large changes in the relative abundances of the 15‐crown‐5‐cation complexes formed, depending on the relative concentrations of ligand and salts. These variations are due either to various desorption rates of the cationized species or to different affinities of 15‐crown‐5 toward the alkali metal cations. An original method allowing discrimination between desorption and complexation effects on the relative abundance of ligand‐metal complex ions is described and can be applied for the calculation of their stability constants. The spectral data obtained using two different matrices demonstrate that the matrix polarity has a very important effect on the two parameters considered, i.e. the stability constants of the 15‐crown‐5‐cation complexes and their desorption rates.
Evaluation of fast atom bombardment mass spectrometric and low‐energy collisional activation tandem mass spectrometric data for the structural elucidation of bisbenzylisoquinoline alkaloids
Authors: Caldwell Gary W. , Masucci John A. , Wu Wu‐Nan
Published: May 2005

The fast atom bombardment (FAB) mass spectra and low‐energy collisional activation mass spectra of ions generated under FAB were investigated for twelve bisbenzylisoquinoline (BBI) alkaloids. The relative molecular mass of the free base and diquaternary BBI alkaloids can be obtained from FAB data. However, monoquaternary ammonium salts produce only an [M — X]+ ion and the relative molecular mass cannot be determined. For Type A (single ether linkage) BBI alkaloids, fragmentation occurs primarily from benzylic and ether cleavages. Thus, the total number of aromatic substituents (OH, OCH3 or OCH2O) can be determined for rings A‐B, C‐D, E and F. For Type B (two either linkages) BBI alkaloids, fragmentation occurs primarily from double benzylic cleavages. Hence only the total number of aromatic substituents can be determined for the upper half of the Type B BBI alkaloids, i.e. rings A‐B and C‐D. An unknown alkaloid was examined to illustrate the utility of the fragmentation schemes.
Gas‐phase studies on reductive cyclization to a benzotriazole derivative from its precursors by liquid chromatography/thermabeam tandem mass spectrometry
Authors: Kuila Debasish , Huang Sunkwei
Published: May 2005

Liquid chromatography/Thermabeam mass spectrometry/mass spectrometry was carried out on the starting material, 2‐nitro‐2′hydroxy‐5′‐acetylazobenzene (1) and the intermediate N‐oxide (2) formed by dithionite reduction of the starting material (1). The mass spectra of (1) and the intermediate (2) showed an abundant fragment ion that corresponds to that of 2‐(2′‐hydroxy‐5′‐acetylphenyl)benzotriazole (3). These results show that 3 could be formed from both 1 and 2. The formation of 3 in the gas phase is analogous to the chemical reduction processes of the 2‐nitroazobenzene derivative 1 and the N‐oxide 2 in solution.
Fast atom bombardment mass spectrometric study of some unsaturated aryl C‐glycosides
Authors: Sinou Denis , Becchi Michel , Doyle Daves G.
Published: May 2005

Fast atom bombardment (FAB), FAB mass‐analysed ion kinetic energy (FAB MIKE) and collision‐activated dissociation (FAB CAD‐MIKE) mass spectra were obtained for two series of unsaturated anomeric aryl C‐glycosides. These tandem mass spectrometric techniques allowed the differentiation of the anomers by analysing either the [M + H]+ ion or the [M + met]+ ion (met=Li, Na).
Utility of nicotinoyl derivatives in structural studies of mono‐ and diacylglycerols by gas chromatography/mass spectrometry. Part 1
Authors: Zöllner P. , Lorbeer E. , Remberg G.
Published: May 2005

The 1‐ and 2‐monoacylglycerols and 1,2‐ and 1,3‐diacylglycerols of saturated and unbranched fatty acids with 8, 10, 12, 14, 16 and 18 carbon atoms were synthesized and subsequently derivatized with nicotinic acid chloride hydrochloride. The resulting nicotinoyl derivatives were examined by mass spectrometry in the case of pure substances and as mixtures by gas chromatography/mass spectrometry (GC/MS). From the electron impact mass spectra, differentiation between mono‐ and diacylglycerols and between the two positional isomers of mono‐acylglycerols and diacylglycerols is possible. The molecular masses of the partial acylglycerols and the identities of the bonded fatty acid were also determined. Similarly to the nicotinoyl derivatives of saturated fatty alcohols, the nicotinoyl derivatives of partial acylglycerols produce a fragmentation pattern that reflects every methylene group of the alkyl chains. These results offer rules for the structure elucidation of partially acylated acylglycerols and probably for mixed diacylglycerols by means of GC/MS, which includes the detection of double bonds and methyl branch positions at the fatty acid alkyl chains. The molecular formulae of all the important fragments in the mass spectra of the nicotinoyl derivatives were confirmed by high‐resolution mass spectrometry. Their structures and fragmentation pathways are proposed.
Structural and substituent effects on [M]+.vs. [MH]+ formation in fast atom bombardment mass spectra of simple organic compounds
Authors: Nakata Hisao , Tanaka Katsunori
Published: May 2005

The peak intensity ratios of [M]+. vs. [MH]+ were measured in the fast atom bombardment (FAB) mass spectra of readily available test compounds with 3‐nitrobenzyl alcohol as the matrix. For simple aromatic amines, the ratio increases as the ionization energy of the substrate decreases. 4‐Substituted benzophenones showed preferential formation of [MH]+ ions, regardless of the nature of the substituents. This is probably due to the fact that the benzophenoes have carbonyl groups which can form hydrogen bonds with the matrix molecule. The peak intensity ratio is roughly proportional to the Hammett σ+. Among 4‐substituted biphenyls, both bromo and chloro substituents afforded abnormally high peak intensity ratios. The effects of the substituents in these compounds are discussed semi‐quantitatively in terms of the Hammett correlation and the hard and soft acids and bases principle. The mechanism of ion formation in FAB and chemical ionization (CI) ion sources appeared to be different because some of the compounds studied showed an intense [M]+. peak with a relatively weak [MH]+ peak in FAB spectra but exhibited a strong [MH]+ peak in ordinary CI spectra.
Chemical ionization mass spectra of simple 1,3‐dioxolanes and their sulphur analogues recorded with methane, isobutane, ammonia and acetone as reagent gas
Authors: Leinonen Aki , Vainiotalo Pirjo
Published: May 2005

The mass spectral behaviour of nine 1,3‐dioxolanes, seven 1,3‐dithiolanes and seven 1,3‐oxathiolanes was studied under chemical ionization conditions with ammonia, isobutane, methane, acetone, acetone‐d6 or pentan‐3‐one as reagent gas. The proton affinity of the first members in each series was not large enough for ammonia to protonate them; instead, the ionization took place through unstable [M + NH4]+ ions. Isobutane, which gave rise to abundant [M + H]+ ions in all cases, was the best reagent gas for the determination of the molecular mass. Methane chemical ionization caused extensive fragmentations either through ring cleavage or through the elimination of the largest substituent from ring positions 2 as a neutral hydrocarbon. The ketones used as reagent gas reacted to form adduct ions. In the case of dioxolanes and oxathiolanes, the [M + RCO]+ adduct ion decomposed through ring opening and then, as a consequence of intramolecular nucleophilic substitution, through the elimination of a neutral carbonyl compound. Resonance‐stabilized dioxolanylium and oxathiolanylium ions were obtained for dioxolanes and oxathiolanes, respectively. This reaction was almost non‐existent for the dithiolanes.
A linear free‐energy correlation in the low‐energy tandem mass spectra of protonated tripeptides Gly–Gly–Xxx
Authors: Morgan Daniel G. , Bursey Maurice M.
Published: May 2005

The backbone cleavages of protonated tripeptide ions of the series Gly—Gly—Xxx, where Xxx  Gly, Ala, Val, d‐Leu, l‐Leu, Ile, Phe, Tyr, Trp, Pro, Met and Glu, were studied in a hybrid tandem mass spectrometer. C‐Terminal y‐type ions and N‐terminal a‐ and b‐type ions were noted. A linear relationship between log (y1/b2) and the proton affinity of the C‐terminal amino acid substituents was found: as the proton affinity of the C‐terminal residue increases, the fraction of y1 ion formation increases. When the C‐terminal substituent was more basic than Trp, the b2 ion was not observed. It is likely that the site of protonation changes from peptide bond to side‐chain for just these residues, Lys, His and Arg.
From green algae to calcium inside buckyballs
Authors: Rose Harry R. , Dance Ian G. , Fisher Keith J. , Smith Derek R. , Willett Gary D. , Wilson Michael A.
Published: May 2005

Coorongite and carbonaceous residues from coorongite pyrolysis at 450 and 500°C were studied by laser ablation Fourier transform mass spectrometry. Raw coorongite gave positive‐ion spectra having mainly protonated species of m/z 80–300 when laser ablated with a high laser power density. Endohedral fullerene positive ions of calcium were observed during the laser ablation of coorongite pyrolysis residues. Pyrolysis of the raw coorongite at 450 and 500°C produced residues which on laser ablation using the fundamental frequency of an Nd: YAG laser (1064 nm) gave a series of calcium fullerides. These ions were observed using low laser power densities (100–600 kW cm–2) Mixing the coorongite pyrolysis residue with barium sulphate gave M@Cn+ ions

The symbol ‘@’, as in Ca@60, is used to represent an endohedral complex, i.e. the adduct is located inside the carbon cage.

where M = calcium or barium. Mixing the coorongite pyrolysis residue with strontium oxalate also gave M@Cn+ ions where M = calcium or strontium. No ions containing two or more metals were detected.
Gas‐phase fragmentation reactions of protonated glycerol and its oligomers: Metastable and collision‐induced dissociation reactions, associated deuterium isotope effects and the structure of [C3H5O]+, [C2H5O]+, [C2H4O]+. and [C2H3O]+ ions
Authors: Dass Chhabil
Published: May 2005

The chemistry of glycerol subjected to a high‐energy particle beam was explored by studying the mass spectral fragmentation characteristics of gas‐phase protonated glycerol and its oligomers by using tandem mass spectrometry. Both unimolecular metastable and collision‐induced dissociation reactions were studied. Collision activation of protonated glycerol results in elimiation of H2O and CH3OH molecules. The resulting ions undergo further fragmentations. The origin of several fragment ions was established by obtaining their product and precursor ion spectra. Corresponding data for the deuterated analogs support those results. The structures of the fragment ions of compositions [C3H5O]+, [C2H5O]+, [C2H4O]+. and [C2H3O]+ derived from protonated glycerol were also identified. Proton‐bound glycerol oligomers fragment principally via loss of neutral glycerol molecules. Dissociation of mixed clusters of glycerol and deuterated glycerol displays normal secondary isotope effects.
Novel use of an isotope separator to determine the position of fluorine‐18 in labelled 1,1,1,2‐tetrafluoroethanes
Authors: Pike Victor W. , Waters Stephen L. , Aigbirhio Franklin I. , Makepeace John , Tanner Richard J. N.
Published: May 2005

A novel technique is described for measuring the site selectivity of methods for labelling the major CFC‐alternative, 1,1,1,2‐tetrafluoroethane (HFA 134a), with fluorine‐18 (t1/2 = 109.7 min). The carbon–carbon bond in radiofluorinated HFA 134a is broken in the ion source of an isotope separator. Radioactivity associated with the ion beam of the [CF2 18F]+. fragment (m/z = 68) is collected, measured and divided by the integrated mass of the simultaneously collected ion beam for the [CF3]+. fragment (m/z = 69) to give the ‘specific radioactivity’ (in nCi nmol–1) of the radiolabel in the 1‐position. Similarly, the ‘specific radioactivity’ of the radiolabel in the 2‐position is calculated from the measured radioactivity of the ion beam from the [CH2 18F]+. fragment (m/z = 32) and the integrated mass of the simultaneously collected ion beam from the [CH2F]+. fragment (m/z = 33). The selectivity of the labelling procedure for a particular position is then given by the decay‐corrected ratio of specific radioactivity at that position to the sum of specific radioactivities. The labelling of HFA 134a by the reaction of [18F] fluoride with trifluoroethylene was found to have 97% selectivity for the CF3 group, whereas labelling by the reaction of [18F] fluoride with 2,2,2‐trifluoroethyl p‐toluenesulphonate was found to have 91% selectivity for the CH2F group. This information is of value for tracer studies of the fate of HFA 134a in man following its inhalation as a drug propellant. The described technique is of potentially wider value for determining the position of fluorine‐18 in labelled polyfluorinated molecules.
Fast atom bombardment mass spectrometry of new polydentate schiff bases. 2. The case of mono‐ and bisaldimines containing pyridine groups
Authors: Coppola M. , Catinella S. , Traldi P. , Guerriero P. , Tamburini S. , Vigato P. A.
Published: May 2005

The mass spectrometric behaviour of seven polydentate Schiff bases derived from the condensation of formyl or diformyl precursors (2,3‐dihydroxy‐ or 2,5‐dihydroxy‐benzaldehyde, 3‐metoxy‐ or 3‐ethoxy‐salicylaldehyde, 3‐formyl‐salicyclic acid, 4‐methoxy‐ or 4‐chloro‐2,6‐diformylphenol) with 2‐aminomethylpyridine have been investigated by fast atom bombardment mass spectrometry and metastable ion studies.
Heats of formation of multi‐substituted positive ions of organic species
Authors: Luo Yu‐Ran , An Yan , Holmes John L.
Published: May 2005

The difference (ΔΔfH°) between heats of formation of many multi‐substituted odd‐ and even‐electron positive ions can be described by a linear equation: ΔΔfH° = A + Bm, where m is the number of substituents or ligands, relative to the unsubstituted reference ion, and m = 1, 2 or 3; A and B are the intercept and slope, respectively. The correlation quality for 59 types of odd‐ and 26 types of even‐electron ions, which involve C, Si, Sn, H, F, Cl, Br, I, O, S, N and P atoms, was analyzed. Unknown heats of formation of related ions and the proton affinities of some organic molecules were predicted using the linear equation.
Formation of M+. ions under matrix fast atom bombardment conditions: Does charge exchange reaction occur?
Authors: Takayama Mitsuo , Iwamura Michiko , Fuchibe Shohaku
Published: May 2005

The formation of molecular ions, M+., under fast atom bombardment (FAB) conditions using a liquid matrix was examined by using a new type of synthesized compounds in which preferential M+. peaks appear in their FAB spectra. The FAB spectra were compared with the corresponding mass spectra obtained by the electron impact (EI) ionization, chemical ionization (CI) and charge‐exchange ionization (CEI) methods. All of the spectra showed preferential peaks of M+. ion and a characteristic intense fragment ion peak originating from a β‐fission. The FAB spectra were similar in the fragment ions appearing in the EI spectra and were very similar in the fragmentation pattern to the CEI spectra using Ar+. and Xe+. as the reagent ions. Further, the FAB spectra did not show any doubly charged ion peaks, while the 70 eV EI spectra showed the peaks of doubly charged molecular and/or fragment ions. The isobutane CI spectra of the synthesized compounds suggested that the formation of M+. ions occurred through the CE reaction with isobutane ion, C4H10+., and the CI spectra showed a marked intense fragment ion peak originating from the β‐fission which seemed to occur characteristically in CEI processes. The results obtained suggested that the formation of M+. ions under matrix FAB conditions occurred mainly by CE reactions between the analytes M and matrix molecular ions B+. and/or fragment ions b+..
Mass spectrometric behaviour of simple oxazolidines under electron impact and chemical ionization
Authors: Lehtelä Pirjo‐Liisa , Smolander Risto , Vainiotalo Pirjo
Published: May 2005

The 70 eV electron impact mass spectra of 33 differently substituted oxazolidines were studied to determine the effect of substituents and the existence of the ring—chain tautomeric equilibrium on the decomposition of the molecular ions. Most of the fragmentations can be rationalized to start as the cleavage initiated by the radical site at nitrogen. Isomeric compounds showed different spectra and were easily differentiated. The position of the ring—chain equilibrium could be located only roughly. The chemical ionization mass spectra of the compounds were also recorded, with ammonia, isobutane, acetone or methane as reagent gas. Methane was the only reagent gas that promoted extensive fragmentation of the protonated molecules. However, no information about the position of ring‐chain tautomerism was obtained under these conditions. Analogously to other related five‐membered heterocycles, the oxazolidines reacted under acetone chemical ionization conditions to afford [M + CH3CO]+ adduct ions. These adducts were stable, however, and unlike those of 1,3‐dioxolanes and 1,3‐oxathiolanes, they did not decompose and form stable oxonium ions.
Multiphoton ionization and photodissociation at the second‐order space focus in a time‐of‐flight mass spectrometer: The amino acid tryptophan
Authors: Dey Michael , Grotemeyer Jürgen
Published: May 2005

Neutral IR‐desorbed molecules of the amino acid tryptophan entrained in a supersonic beam were post‐ionized by multiphoton ionization (MUPI) in the gas phase. Variations in the intensity of the ionization laser produced different degrees of fragmentation observed in the time‐of‐flight mass spectra of tryptophan according to the ladder‐switching model for MUPI fragmentation. From the number of absorbed photons the upper values for the appearance energies of specific fragment ions were obtained. A complete fragmentation pathway of tryptophan was established by using photodissociation of molecular ions and fragment ions formed by MUPI. Photodissociation was successfully performed by secondary excitation with a UV laser at the second‐order space focus of a reflection time‐of‐flight instrument. A fragmentation tree for a laser‐desorbed molecule obtained in a laser tandem time‐of‐flight instrument is shown for the first time.
Tandem mass spectrometric analysis of fixed‐charge derivatized oligosaccharides
Authors: Domon B. , Mueller D. R. , Richter W. J.
Published: May 2005

Various derivatives of a set of three isomeric (linear and branched) pentasaccharides (LNF‐1, LNF‐2 and LNF‐3) were prepared and investigated by high‐performance tandem mass spectrometry in order to compare their collision‐induced dissociation (CID) behaviour. The fast atom bombardment tandem mass spectra of [M + H]+ ions of peracetylated derivatives mainly display fragments containing the non‐reducing terminus (B‐type ions) and allow a straightforward assignment of sugar sequence and branching together with the identification of some interglycosidic linkages. Permethylated derivatives, which better accommodate the mass range of tandem mass spectrometers in the case of larger oligosaccharides, yield similar results, i.e. predominance of B ions, but the necessary information has to be retrieved from incomplete Bi and Yi ion series. By contrast, CID of permethyl or peracetyl derivatives carrying a preformed charge due to prior reductive amination of the oligosaccharides with trimethyl(p‐aminophenyl)ammonium chloride yields exclusively fragment ions comprising the reducing end. In this case, the four distinct series of fragments observed involve charge‐remote fragmentation processes. As a consequence, the spectral patterns are not significantly affected by the nature of the sugar O‐substituents additionally introduced (i.e. methyl or acetyl).
Liquid secondary ionization, tandem and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometric characterization of glycosphingolipid derivatives
Authors: Perreault Hélène , Costello Catherine E.
Published: May 2005

Permethylated, peracetylated and perbenzoylated derivatives of glycosphingolipids (GSLs) were prepared to compare their liquid secondary ionization mass spectrometric (LSIMS) and collision‐induced dissociation tandem mass spectrometric (CID/MS/MS) fragmentation patterns and also to determine sensitivity improvement in LSIMS and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS) relative to the native species. Permethylation was carried out in the liquid phase, whereas peracetylation and perbenzoylation could be effected using either liquid (bulk)‐phase or gas‐phase procedures. Lower amounts of starting material were required for the gas‐phase derivatization (⩽ 100 pmol) compared with the bulk phase (⩽1 nmol), because the former method permits more efficient sample handling. All three types of derivatives yielded sensitivity improvements of at least two orders of magnitude over the native species in both LSIMS and MALDI‐TOFMS. The behavior of the permethylated compounds was used as the benchmark for GSL structural information content in normal and tandem mass spectra. Fragments present in spectra of the three types of derivatives generated complementary information. Permethylated GSLs favored the formation of ions related to the ceramide moieties, whereas peracetylation enhanced the production of carbohydrate‐related ions. The LSI mass spectra of perbenzoylated GSLs contained information on both ceramide and sugar portions of the molecules. Each of the LSIMS, MS/MS and MALDI‐TOFMS techniques proved to be complementary to the others in this study; the use of all three is recommended for the generation of complete structural information.
Profiling glycosphingolipid structural detail: Periodate oxidation, electrospray, collision‐induced dissociation and tandem mass spectrometry
Authors: Reinhold Bruce B. , Chan Shui‐Yung , Chan Steven , Reinhold Vernon N.
Published: May 2005

Electrospray ionization mass spectrometry applied to methylated glycosphingolipid samples provides a sensitive molecular mass profile with no detectable fragmentation and little matrix background. In a bovine brain preparation, the components GM1a, GD1a/b and GT1a/b were characterized in detail and several minor entities, GT1, GM3, GA1, GM2, were mass profiled. Two additional materials, unrelated to the o‐, a‐, b‐ or c‐series, were characterized as hexosamine additions to GM1 and GD1a. Structural details of the major components within these samples were obtained by utilizing low‐energy collision tandem mass spectrometry and periodate oxidation, which could serve as a basis for more complex and higher molecular mass preparations. Fragment structures in the collision spectra were assigned with the assistance of C1H3 and C2H3 derivatization and by exploiting the natural carbohydrate and ceramide heterogeneity of the samples. Major fragments originate from C1O glycosidic rupture with few ring‐opening ions. Glycosidic fragments defined details that allow the determination of structural isomers, while specific fragments of the ceramide moiety differentiate sphingosine from N‐acyl heterogeneity. When contrasted with high‐energy (8 keV) tandem mass spectrometry, low‐energy collision‐induced dissociation of multiply charged molecular ions provided more abundant structurally diagnostic fragments.
Examination of complex oligosaccharides by matrix‐assisted laser desorption/ionization mass spectrometry on time‐of‐flight and magnetic sector instruments
Authors: Harvey D. J. , Rudd P. M. , Bateman R. H. , Bordoli R. S. , Howes K. , Hoyes J. B. , Vickers R. G.
Published: May 2005

Matrix‐assisted laser desorption/ionization (MALDI) spectra of underivatized oligosaccharides of the type attached to asparagine in glycoproteins (N‐linked oligosaccharides) were examined with linear time‐of‐flight (TOF) and magnetic sector instruments using 2,5‐dihydroxybenzoic acid (2,5‐DHB), α‐cyano‐4‐hydroxycinnamic acid, sinapinic acid, 1,4‐dihydroxynaphthalene‐2‐carboxylic acid or 2‐(4‐hydroxyphenylazo)benzoic acid (HABA) as the matrices. All compounds formed abundant [M + Na]+ ions with the strongest signals being obtained from 2,5‐DHB after recrystallization of the initially dried sample spot from ethanol. Only traces of fragmentation were detected from neutral oligosaccharides on the TOF system but more abundant fragment ions (about 5% relative abundance) were present in the spectra from the magnetic sector instrument. Fragmentation was dominated by Y‐type glycosidic cleavages (Domon and Costello nomenclature) between all sugar residues yielding sequence and branching information. Sialic acid‐containing oligosaccharides generally produced the sodium adduct of the sodium salt and gave much weaker signals than the neutral sugars in the positive‐ion mode. There was also considerable loss of the sialic acid moleties as the result of fragmentation on the magnetic sector instrument. The least fragmentation of both neutral and acidic sugars was caused by 2.5 DHB, which proved to be the most appropriate matrix for examination of oligosaccharide mixtures. Much better resolution of the oligosaccharides was obtained than by traditional methods such as the use of Bio‐Gel P‐4 gel filtration column chromatography. It is worth noting also that the measurements were considerably faster (a few minutes as opposed to about 16 h). In addition, no radiolabelling was necessary as required for detection on the P‐4 columns. Mixtures of oligosaccharides from several glycoproteins (ribonuclease B, human immunoglobulin G (IgG) transferrin, bovine fetuin and chicken ovalbumin) were examined and the patterns of the identified oligosaccharides were found to agree closely with the known compositions of the sugar mixtures. The mass spectrometric resolution on the magnetic sector instrument was very much better (up to 3000, FWHM) than could be obtained with the linear TOF systems (200–400). The technique was used as a detection system for the products of exoglycosidase digestion in experiments to determine the detailed structure of the oligosaccharide chains from human IgG.
Assessment of the potential for release of conductive fibers from advanced composites by means of thermogravimetric analysis and scanning electron microscopy
Authors: Wentworth Stanley E. , King Abram O. , Shuford Richard J.
Published: May 2005

Recently, there has been concern over the effects of accidentally released conductive carbon and graphite fibers on unprotected electrical circuits. Because of their thermal stability, such fibers could be released by the involvement of a resin matrix composite in a fire. A simple method based on thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) has been developed which permits the assessment of release potential from such composites. Dynamic TGA is used to determine temperatures at which significant events such as onset of resin matrix decomposition occur. Isothermal TGA permits a determination of the time required to produce releasable fibers at a given temperature. SEM examination of residues from TGA experiments serves to characterize their physical state which, in turn, permits a more precise assessment of release potential. This method has been used to examine a large number of materials composed of several different fibers in a variety of thermoset and thermoplastic matrices. It is concluded that release potential varies inversely with resin thermal‐oxidative stability and directly with fiber stability. The matching of matrix resin char and fiber stabilities is especially effective in suppressing fiber release.
Properties and structure of polymer concrete composite material with divinyl benzene as a crosslinking agent
Authors: Zeldin A. N. , Kukacka L. E. , Fontana J. , Carciello N.
Published: May 2005

A study has been performed to determine the effect of the use of divinyl benzene(DVB) as a crosslinking agent in polymeric binders consisting of mixtures of styrene, acrylonitrile, and acrylamide, on the thermal stability and structure of polymer concretes(PC), containing sand and cement as an aggregate. The results indicate that the inclusion of DVB results in improvements in the thermal and mechanical stability. The improvements are attributed to three‐dimensional cross‐linking of the polymer due to the inclusion of DVB. The influence of the sand‐cement ratio on the structure of PC samples at 240°C are also discussed.
Mechanical properties of polypropylene reinforced with short graphite fibers
Authors: Weiss R. A.
Published: May 2005

The Mechanical properties of injection molded and compression molded graphite fiber‐reinforced polypropylenes are discussed. In general, the tensile properties of polypropylene are significantly improved by reinforcement with graphite fibers and to a greater extent than achieved by glass fiber reinforcement. The failure mechanism of these materials involved a combination of matrix fracture and debonding of the fiber‐polymer interface. The use temperature of these materials is shown to increase with increasing fiber content and the notch sensitivity is reduced.
Viscoelastic behavior of galss‐reinforced epoxy resin
Authors: Nicolais L. , Guerra G. , Migliaresi C. , Nicodemo L. , Di Benedetto A. T.
Published: May 2005

The viscoelastic behavior of epoxy composites containing various percentage of glass microspheres and random short glass fibers was investigated over a wide range of temperatures. The effect of the second phase is to increase the relaxation moduli of the system and to shift the time dependency to higher times. All the data were shifted to a single master curve at a reference temperature by using independent shift factors that were a function of either temperature or filler content.
The rheology and mold flow of polyester sheet molding compound
Authors: Lee L. J. , Marker L. F. , Griffith R. M.
Published: May 2005

Flow properties of sheet molding compounds (SMC) were measured by several rhemeters. Shear viscosities of SMC paste can be fitted by the Carreau viscosity equation and reduced to a single master curve by plotting the reduced shear viscosity (η/η0) against reduced shear rate (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} η0/T). The deformation fo glass filled compounds under extensional forces. When the shear forced was applied, the compound defomed like a deck of cards being slid. It behaved essentially like a laminate of many layers. On the other hand, SMC compounds elongated much less before sample failure occurred under the extensional flow. The extensional viscosity was much higher than the shear viscosity. This phenomenon was explained by a solid composite theory and theories developed from local shear flows between adjacent fibers. The flow of SMC compounds during molding showed that the surface layers flowed further than the inner layers when the mold surfaces were hot. This casued inner plies to show through at the surface and resulting in some wavy glass orientation. This phenomenon was explained equalitatively by a heat penetration model.
Fatigue failure mechanisms in polymer composites
Authors: Dao K. C.
Published: May 2005

Axial fatigue of two, commercial, talc‐filled polypropylenes was studied. A significant result of our investigation was the identification and characterization of the failure mechanisms and the effects of frequency and hysteretic heating. Frequency was found to be important to the fatigue response of the polymers. At low frequency, fatigue failure appeared to be a process of crack initiation and growth with very little dissipative heating. At high frequency, the fatigue process was dominated by dissipative heating resulting in significant creep and modulus loss, and failure was much accelerated and due mainly to material softening and melting. Correlation of temperature rise with on‐line energy loss in selected experiments enabled us to extract information from the fatigue process. The results provided some quantitative understanding of the different fatigue failure mechanisms at low and high frequencies.
Behavior of discontinuous fiber composites: Fiber orientation
Authors: Byron Pipes R. , McCullough Roy L. , Taggart David G.
Published: May 2005

The behavior of polymeric materials reinforced by discontinuous. Descriptors for the planar and axial orientation distributions are discussed. Predictions of micromechanical models and experimental data are presented to illustrate the influence of orientation state upon elastic constants, thermal coefficients of expansion and tensile strength. Results are presented for the notched strength and compressive creep behavior of the glass/phenolic composite of two orientation states. Finally, the implications of these results upon the design of elements molded of discontinuous fiber composites are discussed.
Extension of the hole‐drilling method to birefringent composites
Authors: Prabhakaran R.
Published: May 2005

A complete stress analysis and reliable failure criteria are essential for important structural applications of composites in order to fully utilize their unique properties. The inhomogeneity, anisotropy and inelasticity of many composites make the use of experimental methods indispensable. Among the experimental techniques, transmission photoelasticity has been extended to birefringent composites in recent years. The extension is not straight‐forward, in view of the complex nature of the photoelastic response of such model materials. This paper very briefly reviews the important developments in the subject and then describes the theoretical basis for a new method of determining the individual values of principal stresses in composite models. The mehod consists in drilling very small holes at points where the state of stress has to be determined. Experiments are then described which verify the theoretical predictions. The limitations of the method are pointed out and it is concluded that valuable information concerning the state of stress in a composite model can be obtained through the suggested method.
Monitoring cure of autoclave‐molded parts by dielectric analysis
Authors: Chottiner J. , Sanjana Z. N. , Kodani M. R. , Lengel K. W. , Rosenblatt G. B.
Published: May 2005

A study was undertaken to determine the feasibility of using dielectric analysis as a means of monitoring and controlling cure of large closures during autoclave molding. In dielectric analysis, the dissipation factor (DF) and capacitance (C) of the sample are continuously monitored as a function of time, temperature, and frequency. Dissipation factor profiles were established for the suppliers' recommended cure cycle and for modified cure cycles, Good reproducibility was obtained in dissipation factor profiles on subsequent scaling up to production size (7 ft · 20 ft) autoclaves. Good correlation was also observed during production runs of fullscale closures. The effects of cure variables on the dissipation factor profiles and on the mechanical properties of the prepared laminates were analyzed for extent of correlation. Results of this study show: (1) dielectric analysis can be used to monitor autoclave cure of composites, and (2) within limits, process control may be feasible.