bluuebunny/crossref_metadata_2025_split huggingface dataset:
Analysis of C60 derivatives by fast‐atom bombardment mass spectrometry as γ‐cyclodextrin inclusion complexes
Authors: Juo Chiun‐Gung , Shiu Lung‐Lin , Shen Clifton Kwang‐Fu , Luh Tien‐Yau , Her Guor‐Rong 
Published: May 2005

AbstractMany C60 derivatives form stable complexes with γ‐cyclodextrin in a ratio of 1:2. These complexes can be easily analyzed by fast‐atom bombardment mass spectrometry (FAB). Unlike the analysis of C60 derivatives directly by FAB, the spectra of these complexes were characterized by molecular ions with little or no fragmentation. The analysis of these complexes by FAB provides an easy and useful approach for the characterization of C60 derivatives. Most likely due to the size of the cavity, this approach is limited to C60 derivatives with molecular weights not significantly larger than that of C60 itself.
Experimental verification of an improved prefilter model
Authors: Simon M. , Bohátka S. , Futó I. , Trajber Cs. 
Published: May 2005

AbstractThe experimental verification of predictions of a new simulation model of quadrupole mass filters is presented. Computer calculations show that the transmission of the prefilter‐QMS system is periodical as a function of the prefilter length. The periodicity of the transmission is independent of the mass number of ions of equal velocity. Experimental proof of the simulation has been produced for low mass numbers and a more difficult procedure is required for higher masses (m/z > 100). This is realized with a closed ion source and tandem quadrupole mass spectrometer arrangement. Experimental results prove the mass‐independent behaviour predicted by the model.
Mass spectral study of diastereomers by electron impact
Authors: Vairamani M. , Prabhakar S. , Rama Devi A. , Madhusudanan K. P. 
Published: May 2005

AbstractThe electron impact mass spectra of some diastereomeric dialkyl tartrates and isopropylidine derivatives of dimethyl tartrate show diagnostic differences in the relative abundances of some ions. The differences have been explained based on preferred conformations of these isomers. The configuration of the carbomethoxy groups has been correlated with the configuration of carbomethoxy groups in dimethyl maleate and fumarate. The interaction between the two carbomethoxy groups is relatively larger in conformations where there is a gauche interaction between them. The results could also be correlated with the solution phase conformations of these compounds reported in the literature using nuclear magnetic resonance techniques. The difference, which is small in diastereomeric dimethyl tartrates, is very reproducible and has been confirmed using six different mass spectrometers.
Glycosyl compositions and structural characteristics of the potential immuno‐adjuvant active saponins in the Quillaja saponaria Molina extract Quil A
Authors: van Setten Dirk C. , van de Werken Gerrit , Zomer Gijsbert , Kersten Gideon F. A. 
Published: May 2005

AbstractFifty saponin components of Quil A, a commercially available extract from the bark of the South American tree Quillaja saponaria Molina, were partially structurally characterised. The molecular weights were determined by fast‐atom bombardment mass spectrometry. The glycosyl and elemental composition of all the saponins was determined by applying our recently developed method, monomer mapping, consisting of a computer program and accurate mass measurements. Support for the presumed identity of the aglycone, i.e. quillaic acid, was found in the accurate mass determination, 1H NMR measurement and chemical reactions. The saponin composition of Quil A was shown to consist of pairs. Within the 3‐O bound glycosyl moiety of a pair there was a structural difference: a pentose and rhamnose were interchanged. Structural differences between different pairs were located in the 28‐O bound glycosyl moiety. A structural element, unknown to date and of which the elemental composition was deduced to be C8H12O5, was found in the 28‐O bound glycosyl moiety of several saponins.
Negative‐ion electrospray mass spectra of peptides derivatized with 4‐aminonaphthalenesulphonic acid
Authors: Griffiths William J. , Lindh Ingemar , Bergman Tomas , Sjövall Jan 
Published: May 2005

AbstractThe detection limits of a series of small peptides derivatized with 4‐aminonaphthalenesulphonic acid have been determined using a magnetic sector mass spectrometer operated in the negative‐ion mode. The instrument (AutoSpec‐QFPD) is equipped with an electrospray ion source and both array and point detectors. Detection limits when using the array detector were on the sub‐femtomole level at a mass resolution of 2000 (full width half maximum height). Cone‐voltage and linked‐scan collision‐induced dissociation spectra were recorded using both the array and point detectors. When using the array detector, amino acid sequence information could be obtained from as little as 50 fmol of sample consumed.
High‐temperature mass spectrometric study of the thermodynamic properties of the CaOAl2o3 system
Authors: Stolyarova V. L. , Shornikov S. I. , Shultz M. M. 
Published: May 2005

AbstractUsing the Knudsen effusion mass spectrometric method, the composition of vapour and the partial pressures of vapour species over melts of the CaOAl2O3 system were studied for the temperature range 1833–2033 K. Thermodynamic functions of the CaOAl2O3 system were obtained, and the negative deviations from ideal behaviour were illustrated. The dependence of the Gibbs energies of formation of the CaOAl2O3 system on temperature and concentration of components was suggested.
The dependence of the resolving power and sensitivity of a discrete electrode detector array on the proximity of a microchannel‐plate electron multiplier
Authors: Langstaff David P. , Birkinshaw Keith 
Published: May 2005

AbstractA detector array has been designed which integrates all pulse sensing, data logging, control and interface circuitry on a single silicon chip. In conjunction with a microchannel‐plate electron multiplier (MCP) the array can be used to measure dispersed spectra of ions, electrons and photons (UV and higher energies). In order to increase the sensitivity of the pulse sensing circuitry, non‐standard steps are introduced into the fabrication process which increase cost and prototype development time. In the present work it is shown that by reducing the separation between the MCP output and the array to about 4.5 microns an improvement in performance is achieved which should enable the production of high performance devices using a standard fabrication process.
Contribution of mass spectrometry to the structural confirmation of components of the antibiotic GE2270 complex
Authors: Colombo L. , Stella S. , Selva E. 
Published: May 2005

AbstractThe GE2270 complex consists mainly of GE2270 A (MW 1289), a thiazolyl peptide antibiotic whose structure originates from the modification of a chain of 14 amino acids in a process which creates six thiazole rings and one pyridine. Together with the main component, a number of structurally related molecules are co‐produced in small quantities by fermentation. A preparative high‐performance liquid chromatrography method was developed to isolate GE2270 factors B1, B2, C1, Ca, C2a, C2b, D1, D2, E and T. Their structures, preliminarily determined by 1H‐nuclear magnetic resonance spectroscopy in comparison with GE2270 A, were confirmed by low and high resolution fast‐atom bombardment mass spectrometry and studies on the intact molecules and on their main hydrolysis products. Their molecular weights range from 1246 to 1306 Da. The structural differences between the factors lie in the extent of methylation and/or oxidation of thiazole rings (D and E) and asparagine, and in the aromatization of the oxazoline ring.
Automation of data acquisition and processing involving dynamically programmed scanning for a quadrupole ion trap mass spectrometer
Authors: Clarke Nigel J. , Franklin Anthony M. , Langford Marian L. , Penman Andrew D. , Thorner David A. , Todd John F. J. 
Published: May 2005

AbstractThis paper describes the use of dynamically programmed scanning in the automation of the acquisition and processing of data using a quadrupole ion trap mass spectrometer. The programs written to carry out the fixedion tandem mass spectrometry experiments and to automate the production of the three‐dimensional graphs are described. The use of three‐dimensional graphs to display familial data is also discussed, with examples of spectra given.
Amino acid composition and wavelength effects in matrix‐assisted laser desorption/ionization
Authors: Olumee Zohra , Sadeghi Mehrnoosh , Tang Xiaodong , Vertes Akos 
Published: May 2005

AbstractIon yields were investigated in matrix‐assisted laser desorption/ionization (MALDI) as a function of amino acid composition using a variable wavelength ion source. In the case of nitrogen laser excitation (337 nm), [M+H]+ ions were abundant for short peptides containing basic or polar amino acid residues. The lack of basic residues led to diminishing ion formation at 337 nm. Increasing the chain length led to enhanced ionization even for peptides with non‐polar side chains. In contrast to the liquid phase basicities the basic residues showed Arg > His > Lys order in their affinity to protons. Variations in the average ion yield showed decreasing trend with increasing basicity of the residues pointing to potential differences in the matrix incorporation of different guest molecules. Dye laser excitation at 280 nm resulted in extensive fragmentation and enhanced ion formation from peptides containing aromatic side chains indicating the possible role of analyte excited states in ion formation. Semi‐empirical quantum chemical calculations were used to explore the sites of protonation. Heat of formation diagrams of the matrix‐analyte complexes were examined as a function of their configuration. Investigation of the optimized geometries allowed the location of bifurcated and linear hydrogen bonds between the non‐polar analyte (e.g., Gly‐Gly) and matrix molecules. In addition to these intermolecular bonds, in the case of His‐His an intramolecular hydrogen bond was also formed within the analyte molecule. Proton affinity values were calculated for every dipeptide while the site of protonation was varied. The results seemed to indicate that for every dipeptide the amino terminus was more susceptible to protonation than the peptide bond. Due to increased stabilization effects in homo‐oligomers (Glyn), increasing the number of residues led to an increase in proton affinity. For basic diopeptides (e.g., His‐His), the side chains had the highest proton affinity, underlining their role in MALDI of proteins.
Concentration dependence of nucleoside fast‐atom bombardment mass spectra
Authors: Aksyonov Sergey A. , Sukhodub Leonid F. 
Published: May 2005

AbstractThe quantitative investigation of the four RNA nucleosides (adenosine, guanosine, cytidine and uridine) using fast‐atom bombardment mass spectra is reported. Nucleoside concentrations are varied in the 0.8–4% range. The nucleoside hydrogen‐bonded complexes are shown to form primarily on the liquid matrix surface.
Mass spectral fragmentation patterns of some 2‐methyl‐3‐furancarboxanilides and 2‐methyl‐3‐furancarbothioanilides. II
Authors: Karminski‐Zamola Grace , Fis̆er‐Jakić Lelja , And Miroslav Bajić , Boykin David W. 
Published: May 2005

AbstractThe electron impact mass spectra of some 2‐methyl‐3‐furancarboxanilides and 2‐methyl‐3‐furancarbothioanilides are discussed. Dominant peaks are formed by simple cleavage of a CN bond in the anilides as well as in the thioanilides. Thioanilides show some additional fragmentation pathways recently reported which are not seen in the anilides. (T. Jagodzinski and M. Stobiecki, Org. Mass Spectrom., Vol. 25, p. 333 (1990)).
Fast‐atom bombardment mass spectrometry coupled with collision‐induced dissociation of a hydantoin series for fragmentation studies
Authors: Henczi Maria , Weaver Donald F. 
Published: May 2005

AbstractPhenytoin is one of the most widely employed anticonvulsant drugs in the world. Because this drug has several side effects, an exhaustive structure‐toxicity study is needed. To find an easy and cost‐effective way to monitor phenytoin in metabolism and toxicity studies, 18 phenytoin derivatives were synthesized and analysed by fast‐atom bombardment tandem mass spectrometry.
Host–guest chemistry in the gas phase. Complexes of crown ethers with Fe(CO) ions
Authors: Gren' A. I. , Mazepa A. V. , Timofeev O. S. 
Published: May 2005

AbstractThe complexes formed between a series of 19 different crown ethers and Fe(CO) ions are described. It is found that the energy released in the reactions increases with the crown ether ring size. The bicyclic‐ring crown ethers can form sandwich type compounds with the reagent.
Fast‐atom bombardment mass spectrometry of 2,4‐diketonate complexes of transition metals [V(III), Cr(III), Mn(III), Fe(III), Co(III), Ru(III) and Os(III)]
Authors: Saraswathi Mandapati , Miller Jack M. 
Published: May 2005

AbstractThe tris(acetylacetonate) (L3) and tris(1,1,1‐trifluoromethyl‐2,4‐pentanedionate) (L′3) complexes of transition metals V, Cr, Mn, Fe, Co, Ru and Os in their +3 oxidation states were studied under fast‐atom bombardment (FAB) conditions using 3‐nitrobenzyl alcohol as a matrix. All complexes showed the formation of molecular ion and protonated molecules [ML2]+ and [ML′2]+ are the most abundant ions in the spectra of all the metal acetylacetonates (L) and trifluoroacetylacetonates (L′) studied. Interaction of matrix with metal complexes and polynuclear metal complexes led to the formation of polynuclear species with significant abundance especially for manganese and iron complexes. Formation of these metal ions was observed with relative intensities from 3–30%. Ions corresponding to ligand‐exchange reactions were observed with moderate to high abundance in all metal complexes studied except those of ruthenium and osmium. Experiments carried out with a split FAB probe tip suggested ligand–ligand exchange reactions were not due to gas‐phase reactions but only due to solution‐phase exchanges. Osmium and ruthenium complexes do not yield polynuclear species or ions due to matrix clustering. Instead they show neutral ligand losses and formation of acetyl ion.
Differentiation between natural and synthetic taurine using the 13C/12C isotope ratio
Authors: Gioacchini Anna Maria , Roda Aldo , Cipolla Antonio , Parenti Massimo , Baraldini Mario 
Published: May 2005

AbstractNatural taurine is an essential constituent of formula milk for infants and, because of the inferior nutritional value (δ), of synthetic forms, it is important to discriminate between these and taurines derived from a natural source. In this study we evaluated the ability of a method to make this distinction; it consisted of determination of the taurine 13C/12C ratio by means of a precision automated continuous flow mass spectrometric apparatus. This method was found to provide a powerful analytical tool for this purpose.
Localized charge distributions in stable n‐hexane radical cations
Authors: de Koster Chris G. , Beijersbergen Jaap H. M. 
Published: May 2005

AbstractThe potential energy surface of n‐hexane radical cations is probed theoretically. The structures with low internal energies are characterized by extensive lengthening of one of the three innermost CC bonds. This CC bond stretch is induced by localization of the positive charge. For an elongated terminal CC bond we calculated an energy which is 0.4 eV higher than that for a stretched central CC bond. The n‐hexane geometries with several CC bonds stretched do not represent stationary points on the potential energy surface. Comparison with previous dissociative‐neutralization experiments of low‐internal‐energy n‐hexane ions shows that the fragmentation pathways reflect the two lowest energy structures.
New matrices and accelerating voltage effects in matrix‐assisted laser desorption/ionization of synthetic polymers
Authors: Tang Xiaodong , Vertes Akos , Dreifuss Peter A. 
Published: May 2005

AbstractMost matrices used in matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) have been selected for their sound performance in the detection of proteins. We evaluated a series of new matrices for the analysis of synthetic polymers and compared their performance to that of conventional ones. Among substituted polycyclic aromatic hydrocarbons 1,4‐dihydroxy‐2‐naphthoic acid, 9‐anthracenecarboxylic acid (9‐ACA), and its mixtures with 5‐methoxysalicylic‐acid (‘super’ 9‐ACA) offered better signal quality for analysis of synthetic polymers. To test the performance of these new matrices, authentic standards of poly(ethylene glycol), poly(propylene glycol), Jeffamine, polybutadiene, poly(methyl methacrylate), poly(dimethyl siloxane), and some of their mixtures were analyzed. By generating mainly [M + Na]+ ions, 9‐ACA showed superior performance to most conventional matrices and provided higher effective mass resolution. The ‘super’ 9‐ACA composite matrix was found to be more suitable for larger polymer molecules (>8000 Da).Broader acceptance of MALDI‐MS for synthetic polymer analysis has been delayed by systematic differences observed between MALDI‐MS and gel permeation chromatography (GPC) in terms of oligomer size distributions (R. S. Lehrle and D. S. Sarson, Rapid Commun. Mass Spectrom.), Vol. 9, p. 91 (1995). We found that part of the discrepancy can be explained by the profound dependence of mass distributions on the accelerating voltage of the time‐of‐flight mass spectrometer. With decreasing accelerating voltage both the ion intensity and the mass resolution decreased, and the high‐mass end of the mass spectrum became truncated. For example, when the accelerating voltage was changed from 30 kV to 18 kV the center of the peak area distribution for poly(methyl‐methacrylate) (PMMA) 6000 shifted to lower values by about 210 Da. At the same time, the skewness of the distribution increased tenfold indicating serious discrimination phenomena. These detrimental effects of lower accelerating voltage were particularly strong for relatively large synthetic polymer molecules.
Amino acid sequence determination of phosphoenkephalins using liquid secondary ionization mass spectrometry
Authors: Dass Chhabil , Mahalakshmi P. 
Published: May 2005

AbstractLiquid secondary ionization mass spectrometry (LSIMS) operating in the positive‐ and negative‐ion modes was used to study fragmentation profiles and to obtain the amino acid sequences of a set of seven phosphoenkephalin peptides. The use of glycerol as the liquid matrix led to increase in fragmentation of phosphopeptides. The prominent amino acid sequence‐determining ions in the positive‐ion mode are y‐type C‐terminal ions; the N‐terminal sequence‐specific ions are observed sporadically. The most dominant ions in those mass spectra, however, are the immonium ions and a few low‐mass side‐chain cleavage products. The mass spectra in the negative‐ion mode are more information‐rich, and provide data complementary to that from the positive‐ion mode. The phosphate group marker ions, m/z 79 (PO) and 97 (H2PO), are prominent and both N‐ and C‐termini sequence ions are formed with equal facility in this mode of analysis. Both positive‐ and negative‐ion mass spectral data are useful in determining the amino acid sequence of all of the seven phosphoenkephalins. Thus, LSIMS alone can be a viable option to the tandem mass spectrometry approach when sufficient quantities (>50 nmol) of phosphopeptides are available.
Molecular weight distribution of poly(dimethylsiloxane) by combining matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry with gel‐permeation chromatography fractionation
Authors: Montaudo Giorgio , Montaudo Maurizio S. , Puglisi Concetto , Samperi Filippo 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) allows detection of large molecules such as those present in synthetic and natural macromolecules. Until recently, it was reported that MALDI‐TOF measurements can provide correct molecular weight (MW) estimates only for nearly monodisperse polymer samples. We have now developed a methodology for polydisperse samples. We recorded the gel‐permeation chromatography (GPC) trace of a polydisperse polymeric sample of poly(dimethylsiloxane) (PDMS), collecting 42 fractions. Selected fractions were analyzed by MALDI‐TOF and the average MW of each fraction was determined, allowing a calibration of GPC curves against absolute MW. The calibrated GPC trace was then used to compute average MW and molecular‐weight distribution (MWD) of the unfractionated poly(dimethylsiloxane) sample. In the spectra of low molecular‐weight fractions, the resolution is high enough to resolve the contributions of the various PDMS oligomers as separate signals.
Identification of chlorophyll transformation products in zooplankton faecal pellets and marine sediment extracts by liquid chromatography/mass spectrometry atmospheric pressure chemical ionization
Authors: Harris Philip G. , Eglinton Geoffrey , Carter James F. , Maxwell James R. , Head Robert N. , Harris Roger P. 
Published: May 2005

AbstractLiquid chromatography/mass spectrometry with an atmospheric pressure chemical ionization interface permits the routine study of mixtures of algal‐derived, chlorophyll transformation products isolated from biological and environmental samples. Interpretation of the mass spectra of standards of chlorophyll a and three of its commonly occurring transformation products has allowed the identification of components found in extracts from zooplankton faecal pellets and a marine surface sediment. This highly sensitive technique should prove valuable for pigment analysis in environmental studies.
Use of plasma desportion mass spectrometry for pesticide analysis: The s‐alkylaminotriazines
Authors: Bourcier S. , Hoppilliard Y. , Kargar T. 
Published: May 2005

AbstractThe 2‐substituted‐4, 6‐di‐(alkylamino)‐1,3,5‐triazines (s‐triazines) are well known pesticides. With the dramatic increase in usage patterns of pesticides, an urgent need has arisen to develop analytical techniques to assist in identification of such compounds. A comprehensive understanding of the major fragmentations of these molecules, after ionization, could aid in this task. The use of conventional ionization techniques such as electron impact or chemical ionization is limited because of the relatively low volatility of these compounds, or because of thermal limitations. Recently, there have been promising developments in desorption ionizaion techniques for analysis of thermolabile and low volatility compounds such as environmental compounds. Among these techniques, the desorption ionization technique called ‘plasma desorption’ (PD) leads to more informative mass spectra than those obtained with other ionization techniques. A systematic investigation of ion formation and decomposition processes of three families of 2‐X substituted‐s‐triazines (X = Cl, SCH3 and OCH3) under PD conditions is presented. Eight pesticides were studied in this work. The influence of the X and alkyl substituents on the fragmentation processes under PD conditions is investigated in detail. Specific molecular ions (adduct ion, substitution ions …) allow the differentiation of each family, while characteristic fragment ions lead to the identification of the 1,3,5‐triazine ring and/or of its substituents. The fragmentation processes are obtained by combining nominal masses of ions determined in positive‐ion mass spectra and metastable transitions of low internal energy ions. This study is extended to analysis of s‐triazine mixtures. The results obtained lead to the establishment of a desorption order of these compounds under PD conditions. The experimental results are supported by semi‐empirical molecular orbital calculations. Finally, the proton affinity of Ametryn (2‐methylthio‐4‐(isopropylamino)‐6‐(ethylamino)‐s‐triazine) was determined to be close to that of histidine i.e. 970 kJ/mol.