bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron and chemical ionization mass spectrometry in stereochemical differentiation of some 1,3‐amino alcohols
Authors: Partanen Tuula , Vainiotalo Pirjo , Stájer Géza , Bernáth Gábor , Pihlaja Kalevi 
Published: May 2005

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

AbstractThe silane, PcSi(OH)(OSi(CH3)2(CH = 2)), which has the potential of serving as a new type of coupling agent for fiber glass composites has been studied by UV resonance Raman spectroscopy. This silane is a member of a series of silanes which may lead to hydrolytically stable composites when used as coupling agents. Crystalline samples of the silane without glass and films on E‐glass fibers and high‐surface‐area silica at levels less than a monolayer have been investigated. The Raman line used in these investigations is at 1545 cm−1. This line is used because it gives a strong UV resonance Raman enhancement and because its frequency is dependent on the previous history of the sample. An attempt has been made to interpret the nature of the interaction of the silane with the glass surfaces in terms of the shifts of this line.
Spectroscopic determination of the in‐situ composition of epoxy matrices in glass fiber‐reinforced composites
Authors: Antoon M. K. , Zehner B. E. , Koenig J. L. 
Published: May 2005

AbstractComputerized infrared analysis is applied to the characterization of a glass‐reinforced crosslinked polyester. The method of factor analysis determines the number of independent components which constitute the polymeric matrix. Subsequently, the spectra of those components are fitted by a least‐squares criterion to spectra of the multicomponent matrix, or, if the glass spectrum is included as an additional component, to the spectra of composites. The least‐squares coefficients yield the matrix composition in terms of the initial reactant composition and the extent of crosslinking.
Some theoretical considerations on the long‐term stability of polymer concrete composites in reactive environments
Authors: Zeldin Arkady N. 
Published: May 2005

AbstractIn this report, a theoretical examination is made of the life span of polymer concrete (PC) composites in aggressive environments. Using well known physical chemistry laws, in can be shown that the durability of PC is dependent only on the temperature and concentration of the aggressive environment. This dependence can be extremely useful to potential users of PC materials in aggressive environments since the life span of such materials may be predicted with minimum experimental data.
A model of passive thermal nondestructive evaluation of composite laminates
Authors: Charles John A. , Wilson Dale W. 
Published: May 2005

AbstractA numerical model of passive thermal nondestructive evaluation (NDE) of composite laminates was developed. This model, based on a transient, three‐dimensional, finite difference solution to the heat conduction equations, can be used to characterize in‐plane defects in the laminates and to predict the laminate response to the thermal test. The model was experimentally verified using two material systems. A parametric study was then conducted to ascertain which variables were critical to the success of passive thermal NDE, and how flaw resolution might be improved.