bluuebunny/crossref_metadata_2025 huggingface dataset:
Formation of CH3CH2OCH3+˙ and ˙CH2+OHCH2CH3 from ionized 2‐ethoxyethanol and theoretical and experimental studies of the reactions of ˙CH2+OHCH2CH3
Authors: McAdoo David J. , Hudson Charles E. , Ramanujam V. M. Sadagopa , George M.
Published: May 2005

It is concluded that C3H8O+˙ formed by dissociation of ionized 2‐ethoxyethanol (8) is a mixture of CH3CH2OCH3+˙ (7) and ˙CH2+OHCH2CH3 (2). Formation of 7 and CH3CH2+OHCH3 (12) is attributed to dissociations of species formed by the hydrogen transfers [CH3CH2OCH2+ ˙CH2OH] → [CH3CH2OCH2OCH3+˙ CH2O] → [CH3CH2+OHCH3HCO˙]. Production of 7 competes weakly with dissociation to CH3CH2 +OCH2 (13) and to 12. The low abundance of 7 is attributed to the simple dissociation 8 → 13 being both energetically and entropically favored, and a second H‐transfer to give 12 being energetically favored. The threshold for forming 7 is 45 kJ mol−1 above that for dissociation directly to 13, so formation of 7 is the first ion‐neutral complex‐mediated elimination found to have a threshold above that for the competing simple dissociation. The low abundance of 7 also demonstrates that ion–neutral complexes can be intermediates without obviously revealing their presence by direct dissociation. Experimental results suggest that 2 isomerizes to CH3CH2CH2OH+˙ (5) and then dissociates by eliminating water. Ab initio results support the feasibility of 2 → CH3+OHCH2CH2˙ (1) and 2 → 5. However, experimental observations suggest that 2 → 1 does not occur. This is attributed to strong competition from dissociation and isomerization to 5. The transition state for 2 → 5 resembles [CH3CH2CH2OH]+˙, and a cyclic transition state for 2 → 5 is ruled out. When the ethyl‐oxygen bond in 2 is simply lengthened, the charge is initially concentrated on ethyl, but it switches to CH2OH in a curve crossing at an apparent transition state for CO bond breaking.
Investigation of the ionization processes occurring in liquid‐assisted secondary ion mass spectrometry of derivatized monosaccharides
Authors: Paul G. J. C. , Théberge R. , Bertrand M. J. , Feng R. , Bailey M. D.
Published: May 2005

Several derivatized monosaccharides, the 2‐deoxy‐D‐ribofuranoses, have been studied by liquid‐assisted secondary ion mass spectrometry (LSIMS) in order to gain insight into the factors affecting ionization in FAB/LSIMS. Examination of the mass spectra for these compounds obtained in eight liquid matrices (diethanolamine, ethylene glycol, glycerol, 2‐hydroxyethyl disulfide, 2‐hydroxyphenethyl alcohol, 3‐nitrobenzyl alcohol, sulfolane and thioglycerol) reveals that in all cases the anomalous [M – H]+ ion is the predominant species in the molecular ion region and that [M + Na]+ species are observed in the presence of Na+. The analysis of these compounds by chemical ionization with ammonia shows [M + H]+ as the major species while [M – H]+ is essentially absent. This indicates that the ionization processes occurring in the two techniques are not analogous. Thermodynamic considerations based on the gas‐phase hydride ion affinities of the protonated matrices do not support a predominant gas‐phase mechanism for the formation of [M – H]+ in LSIMS. However, it is possible using solvation energies to rationalize the formation of [M – H]+ in terms of condensed‐phase ionization processes which take place either in the liquid matrix or in the dense selvedge region immediately above the surface where extensive solvation is present. Electrospray data obtained for one of the derivatized monosaccharides indicates that the [M – H]+ is not performed in the condensed phase in LSIMS and that it is the product of fast ion beam‐induced processes. While the nature of the matrix is seen to have little effect on the intensities of [M – H]+ and [M + H]+ it is observed to be an important factor for the intensity of M+˙ for one of the monosaccharides. This effect can be related to the electron‐scavenging properties of the matrices and reinforces the hypothesis that condensed phase processes are significant in ionization.
Matrix‐assisted laser desorption mass spectrometry of homopolymer oligodeoxyribonucleotides. Influence of base composition on the mass spectrometric response
Authors: Schneider Klaus , Chait Brian T.
Published: May 2005

Matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) has the potential for providing a rapid alternative to gel electrophoresis for DNA sequence analysis provided that an intense mass spectrometric response can be obtained from mixtures of DNA fragments containing up to 300 nucleotides. MALDI‐MS has not yet proved viable for such analyses because the MS response falls off rapidly for mixed‐base DNA fragments containing more than 20–30 nucleotides. Previous studies have demonstrated that base composition is a critical factor in the MALDI‐MS response of oligodeoxyribonucleotides. This paper describes an investigation of the physical roots of the observed influence of base composition on the mass spectrometric response, focusing on homopolymer oligodeoxyribonucleotides (dT7, dT10, dT18, dT36, dG7, dG10, dG18, dI18 and dU18) and dT5G5. Forty‐eight different matrix compounds were tested for their ability to produce laser desorption masses spectra from such homopolymer oligodeoxyribonucleotides. Considerably stronger mass spectrometric responses were obtained from polydeoxythymidines than from polydeoxyguanosines, polydeoxycytidines and polydeoxyadenosines. Although mass spectral peaks corresponding to dT18 were observed from 20 of the matrices studied, no discernible response was observed for dG18 from any of these matrices. To elucidate the physical basis for origins of the observed differences in response, a number of factors were investigated including the ionization efficiency, the tendency towards fragmentation and the extent to which the oligodeoxyribonucleotides were incorporated into the matrix crystals. The results of these experiments indicate that low ionization efficiency is not a likely main contributor to the low response to polydeoxyguanosines, fragmentation is a likely main contributor to the low response to polydeoxyguanosines, the overall incorporation of polydeoxyguanosines into matrix crystals is comparable to that for polydeoxythymidines and the exocyclic amino group of guanosine, adenosine and cytidine has a strong inhibitory effect on the mass spectrometric response.
Chemical ionization mass spectrometry of benzoyl peroxide: A radical aromatic substitution resulting in biphenylcarboxylic acid in the gas phase
Authors: Tu Ya‐Ping , Zou Da‐Peng , Tang Ming‐Sheng , Xin Bao‐Min , Jia Wei‐Ping , Liu Shu‐Ying
Published: May 2005

A radical aromatic substitution resulting in biphenylcarboxylic acid is inferred for the decomposition of benzoyl peroxide from the chemical ionization and collision‐induced dissociation mass spectra. The thermolysis of benzoyl peroxide gives rise to a benzoyloxy radical, which undergoes rapid decarboxylation and hydrogen abstraction leading to phenyl radical and benzoic acid, respectively. Attack of the resulting phenyl radical on the benzoic acid results in biphenylcarboxylic acid. On the other hand, the phenyl radical abstracts a hydrogen atom to yield benzene, which is then subjected to the attack of a benzoyloxy radical, affording phenyl benzoate. This substitution reaction rather than the recombination of benzoyloxy and phenyl radicals is found to be responsible for the formation of phenyl benzoate under the present conditions.
Fourier transform ion cyclotron resonance study of the dehydrogenative polymerization of allene and propyne induced by W+ in the gas phase
Authors: Ferhati Azedine , Sozzi Georges , Ohanessian Gilles
Published: May 2005

A Fourier transform ion cyclotron resonance study of the gas‐phase reaction of W+ with allene is reported. W+ successively dehydrogenates at least nine allene molecules, leading to the formation of a series of WC3nH ions, with WC27H as the largest product observed after a reaction delay of 40 s. Starting from the third reaction, there is a competition between elimination of H2 and C2H2 at each step. The activation of propyne was also investigated and found to lead to essentially the same sequence as with allene. The reaction of W+ with 1,1‐d2‐allene and collision‐induced dissociation spectra of product ions are used to discuss a plausible mechanism for the formation and structures of some of the species observed.
Matrix‐assisted laser desorption/ionization mass spectrometry with additives to 2,5‐dihydroxybenzoic acid
Authors: Karas Michael , Ehring Hanno , Nordhoff Eckhard , Stahl Bernd , Strupat Kerstin , Hillenkamp Franz , Grehl Matthias , Krebs Bernt
Published: May 2005

Selected benzoic acid derivatives and related substances were used as additives to 2,5‐dihydroxybenzoic acid (2,5DHB) and the performance of the mixtures in matrix‐assisted laser desorption/ionization mass spectrometry was investigated. Using benzoic acid derivatives substituted at position 2 and/or 5 or related substances as a co‐matrix in the 1–10% range with 2,5DHB results in improved ion yields and signal‐to‐noise ratio of analyte molecules, especially for the high‐mass range. The enhanced performance is prominent for 2‐hydroxy‐5‐methoxybenzoic acid and exists for both proteins and oligosaccharides. It is suggested that the improvement is caused by a disorder in the 2,5DHB crystal lattice allowing ‘softer’ desorption. Charge transfer from matrix ions to additive molecules at the expense of analyte ionization gives a simple explanation for the deteriorating effects of some tested additives.
Fast atom bombardment mass spectral study of tetracycline antibiotics
Authors: Harada Ken‐Ichi , Masuda Katsuyoshi , Suzuki Makoto , Oka Hisao , Ikai Yoshitomo , Hayakawa Junko
Published: May 2005

In the fast atom bombardment mass spectra of tetracyclines, ammonia elimination fragment ions, [M + H – NH3]+ and [M + H – NH3 – H2O]+, appeared with considerable abundances. A plausible mechanism for the loss of ammonia from [M + H]+ was discussed based on results by measurements on various types of tetracyclines and benzamides as the model compounds and B/E linked scanning. The results indicated that the loss of ammonia occurred in the carboxyamide moiety in the A ring and was accelerated by an ortho‐hydroxy group. The same fragmentations were observed in the electrospray mass spectra of tetracyclines with a skimmer‐capillary voltage differential of 150 V.
Structures and thermochemistry of ions formed by methane chemical ionization of Fe(CO)5. Site of protonation and determination of FeH and FeCO bond dissociation energies of HFe(CO)n+ ions
Authors: Ekeberg Dag , Hagen Solveig Isaksen , Hvistendahl Georg , Schulze Christian , Uggerud Einar , Vedde John
Published: May 2005

High‐energy collisional activation mass spectrometry of HFe(CO)5+ ions shows that Fe(CO)5 is protonated on the iron atom rather than on one of the ligands. This finding is supported by ab initio quantum chemical calculations. The value of the proton affinity of Fe(CO)5 was measured by high‐pressure mass spectrometry to be 857 kJ mol−1. The FeCO bond dissociation energies for HFe(CO)n+ (n = 1–5) were measured by energy‐variable low‐energy collisional activation mass spectrometry. The FeH bond dissociation energies in HFe(CO)n+ ions were also determined. A synergistic effect on the strengths of the FeH and FeCO bonds in HFe(CO)+ is noticed. It is demonstrated that the electronically unsaturated species HFe(CO)n+ (n = 3, 4) formed in exothermic proton‐transfer reactions with Fe(CO)5 form adducts with CH4. Adducts between C2H5+ or C3H5+ and Fe(CO)n are observed. These adducts are probably formed in direct reactions between the respective carbocations and Fe(CO)5.
Kinetic and thermodynamic considerations of the bracketing method: Entropy‐driven proton‐transfer reactions in a Fourier transform mass spectrometer
Authors: Gorman Gregory S. , Amster I. Jonathan
Published: May 2005

Several reports of experimentally derived proton affinity values and gas‐phase basicity values for amino acids and peptides have recently appeared in the literature. Here, we show that the thermodynamic quantity that is measured by the Fourier transform mass spectrometry proton transfer bracketing of amino acids and peptides is gas‐phase basicity and not proton affinity. Both experimental and theoretical evidence supports this conclusion. The difference between the values determined by proton transfer bracketing measurements for lysine versus leucine is consistent with a difference in gas‐phase basicity rather than proton affinity. The rate of proton transfer from protonated lysine to a series of reference compounds have been measured. Entropy‐driven, endothermic proton transfer is found to occur at the collision rate. Recent ab initio and semi‐empirical calculations of the proton affinity of lysine are found to agree with the value that is derived from bracketing studies when one assumes that gas‐phase basicity is measured. While entropy‐driven reactions have been observed previously in high‐pressure mass spectrometers, this is the first evidence for such reactions at low pressure in a Fourier transform mass spectrometer.
Activation of aromatic rings by early transition metal ions in the gas phase. Implications for the metal‐catalyzed [2 + 2 + 2] cycloaddition of alkynes and nitriles
Authors: Pope R. Marshall , Buckner Steven W.
Published: May 2005

The reactions of a series of monocyclic and bicyclic arenes with early transition metal ions (Sc+, Y+, Nb+ and Ta+) and their oxides and dioxides were studied in a Fourier transform ion cyclotron resonance mass spectrometer. Ring cleavage of the nitrogen‐containing heterocycles results in loss of HCN as the dominant pathway. Thermochemical considerations, secondary reactions and correlations with solution cyclotrimerization reactions indicate that the MC4H4+ product is a metallacyclopentadiene. Based on correspondence between the reactivities of a series of early metals with their valence electron counts, the reactivities of quinoline and isoquinoline and the decomposition behavior of the products, a metallacycloheptatriene intermediate is proposed for the heteroaromatic ring cleavage reaction. These results are compared to metal complexes in solution which catalyze the [2 + 2 + 2] cyclotrimerization of alkynes and nitriles.
Collison‐induced dissociation and photodissociation of nitroaromatic molecular ions: A unique isomerization for p‐nitrotoluene and p‐ethylnitrobenzene ions
Authors: Cassady Carolyn J. , McElvany Stephen W.
Published: May 2005

The photodissociation and low‐energy collision‐induced dissociation of p‐nitrotoluene and p‐ethylnitrobenzene molecular ions were studied using Fourier transform ion cyclotron resonance mass spectrometry. The dissociation of these ions is highly dependent on the time‐scale of the experiment and the pressure of the nitroaromatic compound. Collisions of the ions with nitroaromatic neutral species increase the abundance of fragment ions due to NO elimination, while collisions with inert gases such as sulfur hexafluoride and argon have no effect. Evidence is presented for the occurrence of an ion–molecule reaction between p‐alkylnitrobenzene ions and nitroaromatic neutral species that induces isomerization of the ion. This isomerization is proposed to involve a nitro‐to‐nitrite rearrangement. Although the mechanism of this process is unknown, isotopic labeling experiments have shown that it does not involve nitrogen atom transfer between the two reactants. The dissociations of o‐nitrotoluene, m‐nitrotoluene and nitrobenzene ions are also discussed. For these ions, no pressure‐ or time‐scale‐dependent behavior was observed, indicating that an isomerization did not occur.
Investigation of the effects of cooling after laser desorption before post‐ionization
Authors: Steenvoorden R. J. J. M. , Van Der Hage E. R. E. , Boon J. J. , Kistemaker P. G. , Weeding T. L.
Published: May 2005

To evaluate the necessity for cooling laser‐desorbed molecules to obtain molecular ions and minimal fragmentation, mass spectra of a series of methoxybenzenes were measured in two different experimental configurations. In one geometry, laser‐desorbed molecules were entrained in a pulsed supersonic jet before ionization. In the other, the molecules were ionized directly after laser desorption. The samples were ionized with laser‐generated vacuum ultraviolet radiation in a single‐photon process or ultraviolet radiation in a multi‐photon process.
Negative‐ion fast atom bombardment mass spectrometry of N‐phosphoamino acids
Authors: Yin Ying‐Wu , Ma Yuan , Zhao Yu‐Fen , Xin Bing , Wang Guang‐Hui
Published: May 2005

The fragmentation patterns of N‐phosphoamino acids in negative‐ion fast atom bombardment mass spectrometry (FABMS) showed different characteristics to those in positive‐ion FABMS. Six typical N‐diisopropyloxyphorphorylamino acids all had intense [M − 1]− peaks, and they underwent similar fragmentation pathways. In general, the elimination of one alkene molecule followed by the loss of one molecule of alcohol occurred. They also favoured an N → O rearrangement reaction, followed by fragmentation to (RO)2 PO2− and (RO) (HO)PO2−.
Evaluation of the dipole moments of organic ions in the gas phase
Authors: Bortolini O. , Olimpieri L. , Traldi P.
Published: May 2005

The dipole moments of a series of substituted benzene radical cations were evaluated on the basis of mass displacements from the expected instrumental value by ion trap experiments. Mass displacements represent a direct measure of the total polarizability, giving access to both the electronic and dipolar polarizabilities, depending on the characteristics of the analyte under investigation. A linear relationship was found between the dipolar polarizabilities and the dipole moments of the corresponding neutrals.
Electron impact‐induced fragmentation of 2,3‐dihydro‐1,5‐benzothiazepin‐4(5H)‐ones
Authors: Pócsfalvi Gabriella , Lévai Albert , Dinya Zoltán , Somogyi Árpád , Vékey Károly
Published: May 2005

The electron impact‐induced fragmentations of 2,3‐dihydro‐1,5‐benzothiazepin‐4(5H)‐ones and some related compounds were investigated. On the basis of low‐ and high‐resolution measurements, metastable ion studies by means of mass‐analysed ion kinetic energy spectroscopy and collision‐induced dissociation experiments, the main fragmentation pathways were established. The effect of methyl and phenyl substituents at the C(2) and C(3) positions of the heterocyclic ring on the fragmentations was also studied. The (1,3) ring splitting was investigated in some detail, using semi‐empirical molecular orbital calculations.
Mass spectral characterization of 3,4,6‐tri‐O‐benzyl‐β‐C‐glucopyranosides containing XC6H4S substituents of C(2)
Authors: Rozynov B. V. , Liukkonen R. J. , Carlson R. M. , Kuehl D. W. , Smoliakova I. P. , Caple R. , Kuehl C. J. , Smit W. A.
Published: May 2005

Electron impact mass spectra (70 eV) were generated for tri‐O‐benzyl‐D‐glucal and six XC6H5S substituted 3,4,6‐tri‐O‐benzyl‐β‐C‐glucosides which had been modified at C(2) by the introduction of an XC6H4S fragment (where X = CH3 or CI) in an effort to understand better fragmentation processes for the structural characterization of this important class of compounds. The model compounds which were synthesized were glucoside derivatives of CH2CHO, C(CH3)2CHO, , C6H5 and CN. For all O‐benzylated compounds, the benzyl moiety was the base ion; however, the molecule ion of each modified glucoside was significantly abundant. A characteristic feature of S‐containing C‐glucosides was an abundant CH3C6H5SCHCHCH2 ion at m/z 163. Fragmentation of these C‐glucosides was interpreted in terms of positive charge localization on the molecule ion according to rules for normal carbohydrates. Knowledge of the fragmentation on the S‐containing C‐glucosides should be useful for the characterization of additional new analogues.
Differentiation and electron ionization‐induced isomerization of 4,5‐Bis(alkylthio)‐1,3‐dithiole‐2‐thiones and 1,2‐dithiole‐3‐thiones
Authors: Andreu R. , Gayán I. , Garín J. , Orduna J. , Savirón M.
Published: May 2005

The electron impact ionization mass spectra of 4,5‐bis(alkylthio)‐1,3‐dithiole‐2‐thiones and their 1,2‐dithiole‐3‐thione isomers were studied by accurate mass measurements and linked scans. The relative abundance of ions formed following the extrusion of S2, CS or CS2 allows an unambiguous isomer differentiation. Isomerization of molecular ions was studied by means of metastable ion analysis and collision‐induced dissociation. The order of reactivity was analogous to that observed in isomerization under photochemical conditions.
Metastable ion studies: Ethyl(methoxy)(chloro)silanes
Authors: Hagen Arnulf P. , Hodge Shelly J. , Randolph Bruce B. , Laing John L.
Published: May 2005

Metastable ion scanning was used to investigate the fragmentation patterns of ethyl(trimethoxy)silane, ethyl(dimethoxy)chlorosilane and ethyl(methoxy)dichlorosilane, their deuterated counterparts and ethyltrichlorosilane. For these compounds the molecule ion has a low abundance using 70 eV electron impact ionization. In all cases the base peak corresponds to the loss of neutral C2H5. When chemical ionization is employed with isobutane, usable peaks representative of the molecule ions are observed.
Mass spectrometry of N‐substituted amino acids and their derivatives: Correlation of the abundances of the M+. and selected fragment ions of metamers
Authors: Wyrzykiewicz E. , Prukala D.
Published: May 2005

The mass spectral fragmentations of nineteen new metameric N‐(E)‐stilbenyloxyalkylcarbonyl‐ [or (E)‐(4′‐chlorostilbenyloxyalkylcarbonyl)]‐substituted amino acids and their metameric methyl esters and hydrazides were investigated. Fragmentation pathways are proposed on the basis of accurate mass and metastable transition measurements. The correlation between the intensities of M+. and the selected fragment ions of these compounds is discussed. The data obtained create the basis for distinguishing metamers.
Mass spectra of n‐butylboronate ester derivatives of the major metabolite of prostaglandin F
Authors: Ferretti Aldo , Flanagan Vincent P. , Roman John M.
Published: May 2005

The EI mass spectra of six n‐butylboronate ester derivatives of the major metabolite of prostaglandins F1α and F2α (PGF‐M) are presented and discussed. Proposed ion assignments and fragmentation pathways are based on substituent shifts, on data from a deuterium‐labeled methoxime derivative and on the analysis of collision‐induced dissociation spectra of selected ions. Fragment ions suitable for identification and quantification of PGF‐M in a biological matrix and diagnostically valuable ions for structure recognition are proposed.
Evidence for the existence of phosphoazonium (iminophosphenium) and arsenoazonium ions in the gas phase by mass spectrometry
Authors: Curtis Jonathan M. , Burford Neil , Parks Trenton M.
Published: May 2005

The first evidence for the existence of the methylphosphoazonium (methyliminophosphenium) ion CH3NP+ and the methylarsenoazonium ion (named in this work) CH3NAs+ (analogues of the methyldiazonium ion CH3NN+) is provided using electron impact mass spectrometry The ions are formed as fragment ions of some highly air‐sensitive phospholidinium and arsolidinium compounds that contain dicoordinate P and As centres. A combination of high‐resolution mass measurements and high‐ and low‐energy tandem mass spectra (fragment ion scans) suggest that the ions have NC bonds rather than the isomeric azophosphonium (CH3PN+) or azoarsenonium (CH3AsN+) forms.
Accurate mass measurements of positive ions in the desorption chemical ionization mode
Authors: Pergantis S. A. , Emond C. A. , Madilao L. L. , Eigendorf G. K.
Published: May 2005

Desorption chemical ionization mass spectrometry employing ammonia as the reagent gas has been extensively used to obtain molecular mass and structural information on a wide variety of compounds. Mass‐deficient reference standards normally used for calibration purposes in mass spectrometry do not provide adequate mass spectra under ammonia chemical ionization conditions. In order to overcome this problem a mixture of ammonia and methane as reagent gases was employed. In high‐resolution accurate mass measurement experiments, this gas mixture allows the simultaneous detection of mass spectra of perfluorokerosene adequate for calibration purposes and spectra containing molecular mass information of the analyte. A needle valve system was used to control the composition of the gas mixture introduced into the ion source. For positive‐ion accurate mass measurements of higher masses (up to m/z = 2300), Fomblin 18/8 oil was successfully used as a reference standard under ammonia, methane and isobutane desorption chemical ionization conditions.
Collision gas effects in the collision‐induced decomposition of protonated and cationized molecules of carbohydrate antibiotics
Authors: Florencio M. Helena , Despeyroux Dominique , Jennings Keith R
Published: May 2005

The collision‐induced decomposition (CID) mass spectra of the protonated and cationized molecules of a number of carbohydrate antibiotics of RMM ranging from 700 to 1500 were studied by means of a four‐sector mass spectrometer with a floated collision cell. Helium and argon were used as collision gases. This work illustrates that cationized rather than protonated carbohydrate antibiotics give an increased yield of high‐mass ions of diagnostic value. Further, when helium is replaced by argon as collision gas, differences in the CID spectra of MH+ ions become apparent only for molecules of RMM > 1400 whereas for [M + Na]+ ions differences are observed for molecules of RMM as low as 1000. These results have been attributed to the deposition of more internal energy in the precursor ion when argon is used, resulting in increased fragmentation.
Differentiation of diastereomeric chlorin derivatives by fast atom bombardment mass spectrometry
Authors: Schulze Peter , Kusch Dirk , Meier Axel , Montforts Franz‐Peter
Published: May 2005

The stereochemistry of six pairs of diastereomeric chlorin derivatives was investigated by electron impact (EI), fast atom bombardment (FAB) and direct chemical ionization DCI mass spectrometry. It was demonstrated that FAB and EI mass spectrometry are convenient and rapid methods for distinguishing between diastereomeric chlorin derivatives due to their different fragmentation patterns.
Collisional‐activated decomposition of benzyloxycarbonyl‐protected tripeptide derivatives containing proline in fast atom bombardment mass spectrometry
Authors: Tsunematsu Hideaki , Yamamoto Magobei , Isobe Ryuichi
Published: May 2005

The effect on the fragmentations of N‐benzyloxycarbonyl‐protected tripeptide ethyl esters due to the existence of L‐proline in the gas phase was examined by the collisional‐activated decomposition of the deprotonated molecule and the fragment ions produced by the cleavage of the tripeptide derivatives containing the neutral amino acids (L‐alanine, L‐leucine and L‐phenylalanine) and L‐proline, in which changes in both the numbers and positions of the prolyl residues were observed, in negative‐ion fast atom bombardment mass spectrometry. The cleavage patterns of these ions in the collisional‐activated decomposition mass spectra were observed to depend on the numbers and positions of prolyl residues in the peptide derivatives. These results indicate that the conformational differences in the peptide derivatives due to the existence of L‐proline affect the decomposition of the ions containing the neutral amino acids in the gas phase.
A mass spectrometric investigation on some 3‐[2‐(Nitroxy)alkyl]‐2H‐1,3‐benzoxazin‐4‐(3H)‐one derivatives
Authors: Rizzi Emanuele , Ferrario Francesco , Sala Alberto , Favretto Donata , Catinella Silvia , Traldi Pietro
Published: May 2005

The electron ionization mass spectrometric behaviour of ten 3‐[2‐(nitroxy)alkyl]‐2H‐1,3‐benzoxazin‐4‐(3H)‐one derivatives has been studied by means of metastable ion studies. By mass‐analysed ion kinetic energy spectrometry of the related molecular ions, clear differences have been evidenced between the 5‐methyl derivative and the other compounds, consisting of a highly favoured loss of NO2 radical. The same methodology has allowed easy characterization of isomeric compounds.
On the gas‐phase reaction of C3O2+. with C3O2
Authors: Pandolfo L. , Paiaro G. , Somogyi À. , Catinella S. , Traldi P.
Published: May 2005

The gas‐phase, ion molecule reaction between C3O2+. and C3O2 has been studied by both double‐focusing and ion trap mass spectrometry, rationalized by the formation of a dimeric, odd electron cation [C6O4]+. which decomposes extensively through sequential CO losses giving rise to [C5O3]+. and [C4O2]+. ions. The thermodynamics of this process have been investigated by means of ab initio calculation performed on the above species using different basis sets (STO‐3G, 3‐21G and 6‐31G*).
Proximity effects in mass spectrometry. Electron impact ionization‐induced cyclization of 1,2‐bis(1,4‐dithiafulven‐6‐yl)benzenes
Authors: Frère P. , Gorgues A. , Garín J. , Orduna J.
Published: May 2005

The electron impact ionization mass spectra of o‐, m‐ and p‐bis(1,4‐dithiafulven‐6‐yl)benzenes were studied by means of accurate mass measurements, metastable analysis and collision‐induced dissociation. Differences observed in the spectra of the ortho isomers are due to a cyclization reaction leading to molecular ions with the same structure as those generated from certain cyclic compounds, as confirmed by comparison of linked scans at constant B/E of metastable and collisionally activated molecular ions. Parallels of this cyclization of molecular ions with their electrochemical or acid‐induced isomerization are also discussed.
Gas chromatographic/mass spectrometric determination of vinyl acetate levels in air
Authors: Sturaro Alberto , Parvoli Giorgio , Doretti Lucio , Bancomina Cristina , Neonato Carlo
Published: May 2005

The determination of vinyl acetate at parts per 109 by volume (ppbv) levels in air by gas chromatography/mass spectrometry (GC/MS) was achieved by optimizing the GC conditions and choosing specific extraction solvents that are sufficiently pure. The ideal solvent should not give rise to fragment ions at m/z 43, in order to rule out any possible interference during the monitoring of the same vinyl acetate ion. Traces of acetone and butan‐2‐one in solvents suitable for this GC/MS determination may also mislead the detection of vinyl acetate. A 440 μl volume of a mixture of tetrachloroethylene containing 9% acetonitrile allowed the recovery of more than 90% of the ester with a detection limit of 1.5 ppbv in air together with a good linearity of response.
Potential of electrospray mass spectrometry for structural studies of O‐Glycoamino acids and ‐peptides with multiple α2,6‐Sialosyl‐Tn glycosylation
Authors: Peter‐Katalinić J. , Ashcroft A. , Green B. , Hanisch F.‐G. , Nakahara Y. , Ilijima H. , Ogawa T.
Published: May 2005

Non‐derivatized O‐glycosylated amino acids and peptides with multiple glycosylation yield molecular and fragment ions on electrospray ionization. Synthetic substrates were used to demonstrate the fragmentation behaviour of the sugar moiety in positive‐ and negative ion electrospray mass spectrometry (ESMS) at low and high skimmer potentials. The ion sensitivity is higher compared than when using fast atom bombardment desorption. The potential of ESMS for the sequencing of O‐glycans is discussed.
Structure determination of phosphoinositol oligosaccharides from parasitic protozoa using fast atom bombardment mass spectrometry
Authors: Wait Robin , Jones Christopher , Routier Françoise H. , Previato José Osvaldo , Mendonça‐Previato Lucia
Published: May 2005

Glycosylphosphatidylinositols (GPIs) are widely distributed membrane constituents of protozoa and higher eukaryotes, where they anchor proteins and other macromolecules to the cell surface. Free glycosylinositol phospholipids (i.e. not attached to protein or polysaccharide) have also been detected in some parasitic protozoa, and are thought play a role in the interaction of parasite and host. This paper describes the fast atom bombardment mass spectrometry (FABMS) of glycosylinositol phospholipids from the Trypanosomatid parasites Leptomonas samueli, Endotrypanum schaudinni and Leishmania adleri. FABMS in the positive‐and negative‐ion modes in conjunction with collisional activation permits the rapid determination of the monosaccharide composition, the sequence of residues, the branching pattern and the nature and location of non‐carbohydrate substituents. When supplemented by high‐field NMR, FABMS provides a highly efficient route to the complete structure elucidation of these materials.
Structure analysis of branched oligosaccharides using post‐source decay in matrix‐assisted laser desorption ionization mass spectrometry
Authors: Spengler Bernhard , Kirsch Dieter , Kaufmann Raimund , Lemoine Jérôme
Published: May 2005

Post‐source decay matrix‐assisted laser desorption ionization (PSD‐MALDI) of sodium ion‐attached branched oligosaccharides derived from glycoproteins was demonstrated as a method of structure analysis by reflectron time‐of‐flight (TOF) mass spectrometry. Mono‐, di‐ and triantennary structures were investigated. The fragmentation patterns of these (structurally related) substances as obtained in the positive‐ion mode showed characteristic differences correlated with branching sites and linkage positions. Two‐bond ring cleavages as known from fast atom bombardment/collision‐induced dissociation and IR laser desorption mass spectrometry were also observed. Internal fragment ions formed by up to four consecutive cleavages were obtained with high intensity, allowing the branching structure of complex carbohydrates to be identified. PSD‐MALDI of oligosaccharides is characterized by high sensitivity, very good signal‐to‐noise ratios and high reproducibility of fragmentation patterns and signal intensities.
Mechanics of intraply hybrid composites—properties, analysis, and design
Authors: Chamis C. C. , Sinclair J. H.
Published: May 2005

A mechanics theory is developed for predicting the physical thermal, hygral, and mechanical properties (including various strengths) of unidirectional intraply hybrid composites (UIHC) based on unidirectional properties of the constituent composites. Procedures are described which can use this theory in conjunction with composite mechanics computer codes and general purpose structural analysis finite element programs for the analysis/design of structural components made from intraply hybrid angleplied laminates (IHAL). Comparisons with limited data show that this theory predicts mechanical properties of UIHC and flexural stiffnesses of IHAL which are in good agreement with experimental data. The theory developed herein makes it possible to design and optimize structural components from IHAL based on a large class of available constituent fibers.
Syntatic foam pultrusion
Authors: Kwok F. T. , Wooddhams R. T.
Published: May 2005

A simple circular pultruded rod was used to evaluate the mechanical and economic performance of four commercially available hollow spherical fillers (microbubbes). The incorporation of such glass or silicate microbubbes in a pultruded rod produced a decrease in density, strength and modulus. However, the loss of strength and modulus was more than compensated for by the decrease in density so that a 50 percent material cost saving was possible without any sacrifice in flexural or torsional properties. Thus for simple profile (rods, bars. Panels) the use of hollow spherical fillers can be economically advantageous in reducing material costs. The syntactic pultrusions posses many of the desirable properties of wood such as toughess, low density, high strength and stiffness plus the ability to accommodate nails and screws. The operating conditions of the pultruder wee normal with the exception that half as much force was needed on the puller and the pultruder would only operate satisfactorily when the resin/glass fiber/microbubble concertrations were within specified boundaries. Pyrex type glass bubbles were found to be less prone to damage during processing and performed better than silicate type microbubbles.
Stress intensity factor measurements in composite laminates with various notch configurations
Authors: Roman I. , Harel H. , Marom G.
Published: May 2005

K‐calibration procedures were performed with a glass fiber‐reinforced epoxy angleply plate, a skin a sandwich structure. Different K‐calibration functions were obtained for various notch tip relative locations within the composite. In view of these observations and of the previously seen anisotropy of those functions it was concluded that the selection of an appropriate K‐calibration function depends on both the reinforcement geometry and on the notch tip location.
Evaluation of structural changes in epoxy systems by moisture sorption‐desorption and dynamic mechanical studies
Authors: Mikols W. J. , Seferis J. C. , Apicella A. , Nicolais L.
Published: May 2005

This work forms a basis for relating moisture solubilities and dynamic mechanical properties to the hygrothermal history of epoxy systems. Two different classes of epoxy systems were investigated; a low‐performance epoxy (DGEBA‐TETA) and a high‐performance system (TGDDM‐DDS) commonly used in carbon fiber composites. An increase in the equilibrium moisture content from TGDDM‐DDS epoxy samples having various DDS compositions was observed as a result of thermal cycling in a liquid environment. Interpretation of the experimental results suggest that hygrothermal interactions produce changes in the epoxy network structure and result in the observed moisture sorption behavior.
Elastic properties of intermingled hybrid composites
Authors: Gruber M. B. , Chou T.
Published: May 2005

The combination of different types of fibers in a common matrix, known as a hybrid composite, has the potential of achieving a balance between composite strength and ductility, as well as a more cost‐effective use of expensive fibers, not re‐alized in a single‐fiber compostie. The elastic properties of a continuous Kevlar®/glass intermingled hybrid composite have been investigated. Theoretical predictions utilizing a self‐consistent model and a bound approach are compared to the influence of the relative Kevlar®/glass fiber volume fraction on the elasstic material properties.
Studies of the simulation of silane coupling agent structures on particulate fillers; the pH effect
Authors: Miller James D. , Hoh Ka‐pi , Ishida Hatsuo
Published: May 2005

The molecular structure of γ‐methacryloxypropyltrimethoxysilane (γ‐MPS) deposited on the surfaces of particulate mineral fillers was modeled by adjusting the pH of an aqueous alcoholic solution of the silane in absence of a substrate. Hydrolyzates obtained from the solution were studied by gel permeation chromatography (GPC) and Fourier transform infrared spectroscopy (FT‐IR) and found to be polymethacryloxypropylsilsesquioxanes whose configuration and molecular‐weight distribution were dependent on the solution pH. In acidic environments (below pH 4) the polycondensation mechanism appeared to proceed in a selective manner to form polycyclic blocks which resemble a beaded chain following condensation between blocks. Under more neutral and basic conditions (at or above pH 4) the polycondensation mechanism, resulted in polymethacryloxypropylsilsesquioxanes with the more equilibrated double chain ladder configuration. The molecular weight distribution of these structures was dependent on the stability of the silanol or the silanolate ion. Extremely high‐molecular‐weight and polydisperse polymethacryloxypropylsilsesquioxanes were generated at near neutral pH due to the formation of the double chain ladder configuration and the high silanol instability in this pH range. The two different polymethacryloxypropylsilsesquioxane configurations were also observed on γ‐MPS modified metal oxide substrates. The structures help explain some of the previously observed trends with respect to γ‐MPS adsorption on particulate mineral fillers. In strongly basic environments the methacrylate function of γ‐MPS partially hydrolyzes to form sodium carboxylate, and carbon dioxide is absorbed from the air and reacts to form sodium carbonate.
Mechanical property enhancement in short‐fiber composites through the control of fiber orientation during fabrication
Authors: Goettler Lloyd A.
Published: May 2005

The mechanical properties of plastics and elastomers reinforced by short fibers are generally dictated by the selection of matrix and reinforcement. However, the high tensile properties attainable in these systems through laboratory processing techniques are frequently not obtained in conventional fabrication operations. To gain a wider latitude in meeting economic and performance constraints, the control of composite structure in the fabrication step should not be overlooked. Tool geometry and processing conditions can be manipulated specifically to control the fiber orientation distribution in the product. A study of fiber orientation in composite compounds during flow through runners, gates, and dies leads to recommendations for optimizing the directional strength and stiffness according to a kinematic model. Performance data on parts fabricated from various short‐fiber composite materials bear out these projections.
Deformation design for short‐fiber‐reinforced thermoplastics
Authors: McCammond D. , North P. A.
Published: May 2005

Stiffness matrices are predicted, using the Halpin‐Tsai laminate analogy, at different locations in 4 short glass‐fiber‐reinforced thermoplastic moldings, and the resulting anisotropy and inhomogeneity discussed, relative to quasi‐isotropic values. The predictions are based on actual material structure as obtained from contact microradiographs. Considerable anisotropy and inhomogeneity are noted. The response of the materials to tensile, flexure, and shear loads is calculated and it is shown that this deviates to a lesser degree from a quasiisotropic response. Finally the load deformation behavior in plate bending and twisting are predicted using both a quasiisotropic model and the stiffness properties based on actual structure and compared with previously available experimental data. It is concluded that, in the absence of a predictive approach to fiber orientation in short‐glass‐fiber‐reinforced thermoplastic moldings, the use of quasi‐isotropic stiffness data provides an acceptable means of performing deformation design analysis. Based on the analysis of the moldings considered, the quasi‐isotropic assumption could be expected to introduce errors of less than 20 percent in deformation predictions for planar moldings.
Paper‐like filled polyethylene films
Authors: Zboril V. G. , Harbourne D. A.
Published: May 2005

Filled high‐density‐polyethylene (HDPE) films for packaging applications have been developed. These films are of low permeability, are water and grease resistant, and can be heat‐sealed like HDPE films but have stiffness, deadfold, cuttability, and appearance similar to those of paper. The films are produced in thicknesses of 10 to 100 + μm by the standard film blowing technique. The effect of the filler type, resin parameters, and film blowing process variables on the resultant filled film properties is discussed. The commercialization of filled films and the market acceptance of the products is also briefly elaborated upon.
Recent developments in sheet molding compound technology
Authors: Newman Seymour , Fesko Donald G.
Published: May 2005

The molding of fiber‐reinforced thermoset components is a complex process involving a highly exothermic chemical reaction, which takes place in the presence of flow and thermal gradients. The flow in turn is complicated by time‐ and temperature‐dependent rheological characteristics. The industry has grown largely on the basis of empirical developments. However, numerous problems do remain which require increased understanding for solution. This report reviews work underway in numerous laboratories to characterize the flow and cure of sheet molding compounds and phenomena associated with these processes such as orientation, mechanical properties, residual internal stresses, mold fill, and surface defects.
Process induces fiber orientation: Numerical simulation with experimental verification
Authors: Gillespie John W. , Vanderschuren Jean A. , Pipes R. Byron
Published: May 2005

The performance of short fiber molded composite structures is determined uniquely by the properties of the molding material and the process induced fiber orientation. Consequently, the capability to accurately predict the fiber orientation distribution is of fundamental importance in computer‐aided mold design. Methodology for the numerical prediction of fiber orientation during the mold‐fill process is presented for a short glass fiber thermoset (57 percent phenolic resin, 10 percent calcium carbonate filler, and 33 percent glass fiber by volume). On the basis of a finite element flow characterization, Jeffery's orientation equation is numerically integrated along streamlines to calculate fiber orientation. Correlation of experimental and numerical results for an end‐gated bar with a molded‐in hole is reasonably good.
A radiant heat flux apparatus for measuring the thermal response of polymeric materials to high temperatures
Authors: Henderson J. B. , Hagen S. C.
Published: May 2005

An efficient and economical experimental apparatus has been designed and built which delivers a known radiant heat flux and simultaneously measures the in‐depth temperature profiles in polymeric materials. Test samples are maintained in a controlled environment and are heated radiantly by a silicon carbide heating element capable of producing heat fluxes up to 7.0 cal/cm2‐sec. The experimental data produced by this device are extremely accurate and therefore are suitable for use in verification of numerical models. The utility of the apparatus was demonstrated by measuring temperature profiles to approximately 1000°C in a glass‐filled phenol‐formaldehyde resin.
New potential silane coupling agents
Authors: Sounik David F. , Kenney Malcolm E.
Published: May 2005

The synthesis of two new potential silane coupling agents is described and commented on. These agents are HOSiPcOSi‐(CH3)2CH2CH2C6H4CH2I‐m and p and HOSiPcOSi(CH3)2‐CH2CH2C6H4CH2NHCH2CH2NH2‐m and p (Pc = phthalocyaninato ligand). In addition, a discussion of agents of the general class to which these two agents belong is given. In this discussion some of the special features of agents of this class are pointed out, e.g., the octahedral coordination of the silicon atoms in the agents having the potential to oxygen‐bridge to glass surfaces. Special features of the glass‐polymer linkages which these agents have the potential to form are also pointed out. Finally, the synthesis of the model isomer mixture HOSi‐PcOSi(CH3)2CH2CH2C6H4CH2N (CH2CH3)2‐m and p is described, and a very brief discussion of this model mixture is given.
Application of solid state carbon‐13 NMR spectroscopy to chemically modified surfaces
Authors: Zaper A. M. , Koenig J. L.
Published: May 2005

The nuclear magnetic resonance (NMR) techniques, high‐power decoupling, magic‐angle spinning, and cross polarization for high resolution in solid materials have been utilized to characterize surface‐modified silicas. Solid state Carbon‐13 NMR was used to study the chemical adsorption of a series of organosilane coupling agents on the silica surface. The type of information that can be obtained from such surface studies includes chemical bonding between the surface and the organosilane, the effects on steric hindrance of the hydrocarbon chains of the coupling agent, and other silane‐surface interactions. The approach for the analysis involved comparing the spectra of the treated silica to the spectra of the corresponding condensed coupling agents. Spectral differences in terms of changes in chemical shifts and line widths are observed. The results are interpreted in terms of chemical bonding and structural differences of the silane coupling agents adsorbed onto the surface.