bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of different ionization conditions on the mass spectrometric behaviour of some fluorinated acyclic nucleoside analogs
Authors: Favretto Donata , Traldi Pietro , Bravo Pierfrancesco , Viani Fiorenza , Tamas Jozsef , Czira Gabor , Somogyi Arpad 
Published: May 2005

AbstractThe behaviour of three fluorinated acyclic nucleoside analogs has been examined under different ionization conditions, i.e. by electron ionization, fast‐atom bombardment and positive‐ion chemical ionization using methane, isobutane and ammonia as reactant gases. The protonated molecules have been studied by collisional spectroscopy. In general, protonation takes place on the functional groups exhibiting a proton affinity higher than that of the reactant species but some discrepancies are present. They have been explained by the presence of quasi SHF structures implicating proton bridging between sulphur and fluorine atoms.
Unimolecular reaction of the (H3CO)3C+ cation
Authors: Nguyen Viet , Audier Henri Edouard , Milliet Arielle , Mourgues Philippe 
Published: May 2005

AbstractFrom metastable ion studies, Fourier transform ion cyclotron resonance experiments and semi‐empirical calculations, the unimolecular reaction of the (H3CO)3C+ cation 1 is discussed. The first step of the reaction is an irreversible, 1,3‐CH transfer giving the H3COC(O)O(CH3) ion, 2. This ion either cleaves or isomerizes into the ion‐neutral complex [H3COCO+, CH3OCH3], 3. Since the H3COCO+ cation is a very good CH donor, a CH transfgr then occurs within the complex, 3, to yield the predominant fragment (CH3)3O+.
Protonated dialkylbenzenes: Intermediacy of one or two π‐complexes?
Authors: Denhez J. P. , Audier H. E. , Berthomieu D. 
Published: May 2005

AbstractIn the gas phase, π‐complexes are common intermediates in unimolecular reactions of metastable protonated alkylbenzenes. The transient formation of two π‐complexes generated from protonated dialikylbenzenes has been proposed in the Literature, even when the substitution degree of the two benzylic carbons is different. For metastable tert‐C4H9C6H5R+ cations (R ‐ n‐C4H9, sec‐C4H9, iso‐C4H9), we demonstrate in this paper that the [tert‐C4H, C6H5‐R] π‐complex is produced and does not interconvert into the [tert‐C4H9C6H5, R+] π‐complex prior to fragmentation.
A combined magnetic sector–time‐of‐flight mass spectrometer for structural determination studies by tandem mass spectrometry
Authors: Bateman R. H. , Green M. R. , Scott G. , Clayton E. 
Published: May 2005

AbstractA combined magnetic sector–time‐of‐flight instrument has been constructed and used with both continuous (liquid secondary ion mass spectrometry and electrospray ionization) and pulsed (matrix‐assisted laser desorption/ionization) ion sources. The design includes provision for both low‐ and high‐energy gas collision induced decompositions and orthogonal acceleration of the product ions into the time‐of‐flight mass analyser. Tandem mass spectra may be acquired for singly and multiply charged precursor ions and reliable mass measurements are easily obtained. Product‐ion mass spectra are quite reproducible regardless of any instability in the precursor ion beam intensity.
Determination of aflatoxins in dust and urine by liquid chromatography/electrospray ionization tandem mass spectrometry
Authors: Kussak Anders , Nilsson Carl‐Axel , Andersson Barbro , Langridge Jim 
Published: May 2005

AbstractA liquid chromatography/electrospray ionization tandem mass spectrometry method is described for the determination of aflatoxins B1, B2, G1 and G2. Samples of naturally contaminated airborne dust and spiked urine were cleaned up on immunoaffinity columns and analysed by liquid chromatography using either mass spectrometry detection or post‐column derivatization with bromine and fluorescence detection. With tandem mass spectrometry, detection limits (S/N=3) calculated as amount ejected on column were: aflatoxin B1 4 pg, B2 4 pg, G1 5 pg, and G2 10 pg.
Collision‐induced dissociation of multiply charged peptides in an ion‐trap storage/reflectron time‐of‐flight mass spectrometer
Authors: Qian Mark G. , Zhang Yu , Lubman David M. 
Published: May 2005

AbstractSingle‐frequency collisional activation of multiply charged peptides has been studied via electrospray ionization in an ion trap storage/reflectron time‐of‐flight device (IT/reTOF). Several peptides with molecular weights ranging from 600 to 1700 were used to demonstrate that sequence information can be obtained with this hybrid instrument with a sensitivity in the low picomole level. Further, a resolution of nearly 1000 can be obtained for the fragment products, due to the cooling effects of the buffer gas in the trap before analysis by the reTOF. The influence of the primary structure of the peptides on the observed collision‐induced fragmentation patterns is discussed. Although the current study is limited by the electronics, in terms of its ion isolation capabilities, it is demonstrated that the device has the potential for obtaining sequence information for peptides with excellent sensitivity and relatively high resolution.
Capillary electrochromatography/mass spectrometry: Principles and potential for application in the pharmaceutical industry
Authors: Lane S. J. , Boughtflower R. , Paterson C. , Underwood T. 
Published: May 2005

AbstractCapillary electrochromatography (CEC) was coupled with electrospray (ESI) mass spectrometry and evaluated as an on‐line high resolution technique for the separation and characterization of some typical pharmaceutical compound mixtures. Dispersion effects were observed and are discussed in the context of an optimized CEC/MS interface.
Negative‐ion mass spectrometry in a commercial gas chromatography/ion‐trap mass spectrometer system
Authors: Catinella Silvia , Traldi Pietro , Jiang Xuewu , Londry Frank A. , Morrison Richard J. S. , March Raymond E. , Gregoire SÉBastien , Mathurin Jean‐Charles , Tabet Jean‐Claude 
Published: May 2005

AbstractCommercial gas chromatography quadrupole ion‐trap mass spectrometer (GC/ITMS) instruments have been used in a novel way for the study of negative ions formed from perfluorotributyl‐amine and polychlorinated biphenyl compounds. Negative ions, formed during a normal electron impact ionization period in which 70 eV electrons were used, were isolated in an ion trap by the application of a negative DC voltage to the ring electrode that caused all positive ions to be ejected from the ion trap; in the subsequent analytical scan, negatives ions were detected with an electron multiplier biased normally so as to detect positive ions. The major negative‐ion species detected from FC‐43 were m/z 252 to m/z 633; 34 other negative‐ion species were detected also, though in low abundance. The observed negative‐ion mass range extended from m/z 252 to m/z 633. The signal‐to‐noise ratio of negative‐ion mass spectra was enhanced by operation of the GC/MS instrument in GC mode and averaging the mass spectra acquired. In an examination of 3 hexachlorobiphenyl compounds, the molecular anion cluster around m/z 360 for the non‐ortho‐substituted congener 169 was observed with a signal‐to‐noise ratio of ca. 20 for 90 pg injected on column: the response for congener 169 was greater than that for congener 156 (mono‐ortho‐substituted) which, in turn, was greater than that for congener 153 (di‐ortho‐substituted).
Peptide characterization using bioreactive mass spectrometer probe tips
Authors: Nelson Randall W. , Dogruel David , Krone Jennifer R. , Williams Peter 
Published: May 2005

AbstractA method has been developed for the rapid and sensitive mass spectrometric characterization of peptides. The approach uses bioreactive mass spectrometer probe tips, incorporating covalently bound enzymes, which are capable of modifying biomolecules for analytical purposes. In the demonstrated cases, enzymatic proteolysis is initiated upon application of analyte to the probe tips, time is allowed for digestion, and the products are analyzed using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. The probe tips have been used for proteolytic mapping and partial sequence determination of picomole quantities of peptide. Analysis times were approximately 30 min. Two methods of database search were utilized. The first used limited peptide sequence information and parent molecular weight, while the second used exclusively the molecular weights of a number of endoproteolytic fragments. A simple method of comparing the match of experimental data for a tryptic digest with the results of a search is described.
Laser ablation of organic molecules from frozen matrices
Authors: Belov Mikhail E. , Alimpiev Sergei S. , Mlynsky Victor V. , Nikiforov Sergei M. , Derrick Peter J. 
Published: May 2005

AbstractThe technique of frozen matrix‐assisted laser ablation coupled with resonance‐enhanced multiphoton ionization and reflectron time‐of‐flight mass spectrometry was used to detect intact organic molecules directly from solutions. When frozen at the temperature of liquid nitrogen, the matrices of interest were ablated by a pulsed CO2 single‐mode laser. The analyte molecules emerging from the ablated plume were then ionized by a tunable XeCl excimer laser‐pumped dye laser and analysed with a gridless reflectron time‐of‐flight mass spectrometer. The ablation process from an ice matrix was studied with the amino acids tryptophan and tyrosine dissolved in an aqueous ethanol solution to a concentration level of 5 × 10−4 M. It was found that fragmentation of the analyte molecules is strongly dependent on the ablating laser fluence and that there is a laser fluence range just above the ablation threshold where the decomposition is negligible. The different fragmentation mechanisms are discussed and a cavitation under the liquid surface, causing the sonoluminescence signal from an ice matrix, was shown to be responsible for the decomposition of the analyte molecules ablated by a low photon energy IR laser. Under the appropriate conditions, the analyte molecules were found to have a low rotational temperature of about 150 K resulting from the jet‐like cooling in multiple collisions with matrix molecules.
Gas‐phase reactivity of protonated cyclodepsipeptidic toxins: The study of a systematic fragmentation pathway under fast‐atom bombardment desorption
Authors: Loutelier C. , Hubert M. , Marcual A. , Lange C. , Mercadier J‐L. , Cavelier F. , Verducci J. , Jacquier R. 
Published: May 2005

AbstractA systematic pathway of fragmentation for several protonated cyclohexadepsipeptides is demonstrated by positive‐ion fast‐atom bombardment linked‐scan mass spectrometry. It involves classical sequential acylium and immonium ions, but also, unusual fragment ions characteristic of this family of compounds.
Profiling new taxanes using LC/MS and LC/MS/MS substructural analysis techniques
Authors: Kerns Edward H. , Volk Kevin J. , Hill Susan E. , Lee Mike S. 
Published: May 2005

AbstractA rapid and systematic protocol based on liquid chromatography/mass spectrometry (LC/MS) profiling and liquid chromatography/tandem mass spectrometry (LC/MS/MS) substructural analysis techniques was utilized to identify novel taxane structures. Analyses of Taxus brevifolia, T. baccata and T. hicksii extracts and process intermediates have provided data for 24 novel taxanes and two side‐chain derivatives. Profiling of novel taxanes was based on comparing the mass spectrometric characteristics of unknown taxanes with the paclitaxel substructural ‘template’. The profiled structures incorporate four modifications from the paclitaxel template in the core and side‐chain substructures corresponding to: (i) substitution of the 3′ amide of the side‐chain with a series of homologs from acetamide through heptamide, (ii) substitution on the paclitaxel core substructure, (iii) absence of the paclitaxel side‐chain, and (iv) absence of the paclitaxel core. Detailed analytical data obtained for these novel compounds using a protocol based on LC/MS and LC/MS/MS are reported, including: high‐performance liquid chromatography (HPLC) relative retention time obtained under standard conditions, molecular weight, and MS/MS product ions indicative of specific substructures of the molecule.
Determination of positions of double bonds in di‐unsaturated esters and a di‐substituted γ lactone by means of GC/MS of dimethyl disulfide derivatives
Authors: Pepe C. , Balcar N. , Dizabo P. , Dagaut J. , Saliot A. , Couffignal R. , Sayer H. 
Published: May 2005

AbstractThe determination of the positions of double bonds after dimethyl disulfide (DMDS) addition is presented for linear or branched di‐unsaturated esters and a di‐substituted γ lactone. Different DMDS derivatives are studied according to the number, n, of methylene groups separating the double bonds. For n=0, a mono derivative is obtained following treatment with DMDS; for n = 1, 2 or 3, a cyclic thioether is synthesized. For n=0, only one double bond is located after a classical cleavage. For n = 1, 2 and 3, a systematic fragmentation pathway is observed allowing the determination of the positions of the double bonds and the molecular structures of the compounds.
Localization of serotonin 5‐HT2 receptors in living human brain by positron emission tomography using N1‐([11C]‐methyl)‐2‐BR‐LSD
Authors: Wong Dean F. , Lever John R. , Hartig Paul R. , Dannals Robert F. , Villemagne Victor , Hoffman Beth J. , Wilson Alan A. , Ravert Hayden T. , Links Jonathan M. , Scheffel Ursula , Wagner Henry N. 
Published: May 2005

AbstractN1‐([11C]‐Methyl)‐2‐Br‐LSD ([11C]‐MBL) has been developed as a positron emission tomography (PET) imaging agent for serotonin 5‐HT2 receptors. In vitro receptor binding assays with nonradioactive MBL show high‐affinity binding to serotonin 5‐HT2 receptors (Ki = 0.5 nM), a secondary interaction of 8‐fold lower affinity with dopamine D2 receptors, and low‐affinity interactions with α1‐adrenergic as well as serotonin 5‐HT1 receptors. Intravenous injection of [11C]‐MBL in a baboon led to selective labeling of cortical regions that was markedly blocked by prior administration of ketanserin, a selective 5‐HT2 receptor antagonist. Clinical trials with [11C]‐MBL have been conducted in seven normal human volunteers, and the regional distribution of radioactivity in the brain was distinctly serotonergic. Labeling was highest in frontal, temporal, and parietal cortex with lower levels observed in caudate and putamen. The tracer rapidly washed from the cerebellum and the low levels of activity in this brain region were used to define nonspecific binding. The maximum specificity was reached between 30 and 60 minutes postinjection when frontal cortex to cerebellum ratios ranged from 1.7 for a 52‐year‐old male to 2.7 for a 30‐year‐old male. In agreement with previous studies, a trend towards lower ratios (lower serotonin 5‐HT2 receptor levels) was observed in older volunteers. These studies indicate that [11C]‐MBL is a selective radioligand that can be used to monitor serotonin 5‐HT2 receptor densities in vivo in most regions of the human brain.
Human brain dopamine receptors in children and aging adults
Authors: Seeman Philip , Bzowej Natalie H. , Guan H.‐C. , Bergeron Catherine , Becker Lawrence E. , Reynolds Gavin P. , Bird E. D. , Riederer Peter , Jellinger Kurt , Watanabe Shuzo , Tourtellotte Wallace W. 
Published: May 2005

AbstractSince spontaneous oral dyskinesias are more prevalent in the elderly, and since these movements may be controlled by the balance of brain dopamine D1 and D2 dopamine receptors, we measured the densities of these receptors in 247 postmortem brain striata. In childhood, the densities of D1 and D2 dopamine receptors in the brain striatum rise and fall together. After age 20 years, D1 receptors disappear at 3.2% per decade while D2 receptors disappear at about 2.2% per decade. Overall, therefore, the D1/D2 ratio falls with age. Since perioral motion in rats is dominated by a high D1/D2 ratio, the observed decline in the human D1/D2 ratio with age suggests that the perioral control mechanisms for humans and rats may be different.
Immunohistochemical study of neurons containing corticotropin‐releasing factor in Alzheimer's disease
Authors: Powers Richard E. , Walker Lary C. , De Souza Errol B. , Vale Wylie W. , Struble Robert G. , Whitehouse Peter J. , Price Donald L. 
Published: May 2005

AbstractIn the brains of controls and individuals with Alzheimer's disease (AD), antisera to corticotropin‐releasing factor (CRF) were used to immunostain neurons and their processes. In AD, we identified abnormal CRF‐immunoreactive axons as well as neurites associated with deposits of amyloid in brain regions showing senile plaques. The number of immunoreactive fibers was decreased in individuals with AD. In contrast, CRF immunoreactivity was markedly increased in some neurons located within the paraventricular nucleus (PVN) of the hypothalamus. These findings support previous neurochemical studies indicating that certain CRF systems are affected in AD.
Funktionsmuster zur Gasdetektion auf Basis von Quantenkaskadenlasern (Functional Model for Gas Sensing Based on Quantum Cascade Lasers)
Authors: Steinbeck Thomas , Rohr Jürgen , Warnck Sven 
Published: May 2005

Abstract
Quantenkaskadenlaser stellen in der Gasanalytik eine ideale Strahlungsquelle dar. Sie erlauben im mittleren Infrarot sensitive und selektive Messungen. Die Detektion von Brandgasen zur frühen Branderkennung repräsentiert ein interessantes Anwendungsfeld, in der weitere technologische Vorteile der Laser zur Geltung kommen. In dem Vorhaben lagen die Schwerpunkte in der technischen Umsetzung des Demonstrators und seiner elektronischen Komponenten.
Biomaterials highlights III bone replacements: Implant materials and the modes of implant fixation
Authors: Heimke Günther 
Published: May 2005

Biomaterials Highlights III. In the third article of the series, the methods which are used to fix implants to the body's tissue are examined, which include cementing and mechanical fixation. The surfaces of the implants play an important role in interactions with the body. Various coatings are described and the application of isoelastic implants discussed. magnified image
High‐performance Silicon Nitride Materials
Authors: Boberski Cornelia , Hamminger Rainer , Peuckert P. , Aldinger Fritz , Dillinger Reinhard , Heinrich Jürgen , Huber Jürgen 
Published: May 2005

AbstractThe past decade has seen greatly increased interest in ceramic materials with special combinations of properties. Their hardness, high resistance to abrasive and erosive wear, and their good corrosion resistance when used under extreme mechanical and thermal conditions have made ceramics increasingly attractive for applications in mechanical and apparatus engineering. Silicon nitride (Si3N4) in particular, is suitable for the development of a high‐performance, high‐temperature material for vehicle engine construction. Although the properties of Si3N4 materials have been consistently improved in the last few years, they are still not adequate to allow these materials to be used in series production parts, for example as valves in automotive engines. One of the main reasons for this is the wide scatter and low reproducibility of the property parameters, which means that component reliability does not yet meet market requirements. Hence, one aim of Si3N4 materials development is to reduce the structural flaws resulting from physical and chemical inhomogeneity. This objective can only be achieved through a fundamental understanding of all the processing steps, from powder production to the final processing of the components.
Porous silicon: Quantum sponge structures grown via a self‐adjusting etching process
Authors: Lehmann Volker , Gösele Ulrich 
Published: May 2005

Electroluminescence in porous silicon at room temperature has recently been achieved. This is a crucial step in the realization of silicon‐based optoelecctronic devices but there is still work to be done, for example in improving the stability of the electroluminscence. The materials, the effect, and the potential of the materials in the study of quantum confinement effects in silicon sspongess (see figure) are discussed. magnified image
A novel tool for Surface Electronic Structure Calculations—insight into surface self‐diffusion on metals
Authors: Feibehnan Peter J. 
Published: May 2005

The diffusion of adatom clusters on surfaces and the nature and energetics of diffusion across a step are crucial in the synthesis of tailored materials, for example growing a structure involving atom A on substrate B. A recently developed method enables the study of such diffusion including concerted substitution diffusion, the mode in which atom A dives into the surface replacing atom B (see figure). The various aspects of the new method are presented. magnified image
Donor–acceptor substituted polyenes: Orientation in mono‐ and multilayers
Authors: Effenberger Franz , Niesert Claus‐Peter , Häußling Lukas , Ringsdorf Helmut , Bubeck Christoph , Neher Dieter 
Published: May 2005

Ordered structures of donor‐acceptor substituted polyenes (see Figure, where R'=phenyl or anthryl) formed using the Langmuir‐Blodgett technique are reported. The mono‐ and multilayers have been traansferred to solid supports and their nonlinear optical characteristics examined using angledependent second harmonic generation (SHG). magnified image
New redox‐responsive cryptands containing tetrathiafulvalene units
Authors: Gasiorowski Rafal , Jorgensen Tine , Møller Jørgen , Hansen Thomas K. , Pietraszkiewicz Marek , Becher Jan 
Published: May 2005

Cation‐sensitive electrochemically active systems have been provided with new potential model compounds in the form of recently synthesized TTF derivatives. The molecules, one of which is shown in the figure, are flexible and seem to be much better metal‐ion ligands than the previously reported TTF‐cage compounds. magnified image
Phase‐matched optical second‐harmonic generation in Langmuir–Blodgett film waveguides by mode conversion
Authors: Flörsheimer Mathias , Küpfer Munfred , Bosshard Christian , Looser Herbert , Günter Peter 
Published: May 2005

Phase‐matched second‐harmonk light generation by guided mode conversion has been observed for the first time in nonlinear optically active Langmuir‐Blodgett films. The sketch of the experimental setup (Figure) shows how the infrared fundamental beam is coupled via a grating into SiO2/TiO2‐DCNAP waveguides with various thicknesses of DCNAP film. The film with the correct thickness for phase matching guides a second‐harmonic mode, which is observed as a blue beam, as illustrated in a photograph in the article. magnified image
Ion implanted material in highly integrated GaAs ICs
Authors: Myers Frederick A. 
Published: May 2005

Selective ion implantation and epitaxy are beginning to increase the degree of integration of monolithic microwave ICs (MMICs). Most MMICs produced to date have only a single function per chip, for example the C‐band phased array radar T/R module illustrated in the Figure, but selective ion implantation has allowed a complex, multifunction GaAs MMIC to be realized recently. magnified image
Review of Polymer Synthesis in 1992
Authors: Schlüter Arnulf‐Dieter 
Published: May 2005

AbstractIn last year's review of polymer synthesis (Nachr. Chem. Tech. Lab. 1992, 40, 221), particular attention was paid to publications on metathesis and Ziegler–Natta polymerization, emphasizing the stormy and far‐reaching developments in these areas of polymer synthesis. This year's review will also stress specific points of interest, the most important one being anionic polymerization, where much has happened. Additionally, progress in other very different and less extensive areas of polymer synthesis will be presented. Like last year, areas of work in which polymers have been synthesized with new types of molecular structures will be somewhat preferentially treated.