bluuebunny/crossref_metadata_2025 huggingface dataset:
Direct analysis of C60 and related compounds with electrospray mass spectrometry
Authors: Liu Tsang‐Yu , Shiu Lung‐Lin , Luh Tien‐Yau , Her Guor‐Rong
Published: May 2005

Without performing any charge transfer chemical reaction, C60 and its derivatives could be analyzed directly by electrospray mass spectrometry. Oxidation or reduction at the metal/solution interface of the probe tip was probably responsible for the formation of these radical cations and anions. This technique appeared to be superior to desorption chemical ionization and fast‐atom bombardment ionization in the analysis of C60 derivatives because the mass spectra were characterized by molecular ions with little or no fragmentation.
Utility of matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry for the analysis of low molecular weight compounds
Authors: Lidgard Ray , Duncan Mark W.
Published: May 2005

A range of low molecular weight compounds (<800 Da) have been examined by matrix‐assisted laser desorption time‐of‐flight mass Spectrometry to demonstrate the general analytical utility of this technique. The compound classes investigated included: carbohydrates, quaternary ammonium salts, sterols, nucleosides, purine and pyrimidine bases, amino acids, catecholamines, opioids, antibiotics, prostaglandins and a range of macrocyclic metal complexes of porphyrins and phthalocyanines. Many of the compounds tested are of biochemical, geochemical, industrial and/or therapeutic interest. Most organic analytes gave intense protonated molecules, but some were characterized by sodium adduct ions (i.e., [M + Na]+). The metal‐containing compounds formed radical‐cation molecular ions. In all instances the ions detected could be assigned, and excellent agreements between calculated and experimental mass values were obtained.
Effusive molecular beam from a capillary array for improved resolution time‐of‐flight and collision spectrometry
Authors: Bapat Bhas , Krishnakumar E.
Published: May 2005

We report here high mass resolution obtained with an electron impact, Wiley–McLaren type time‐of‐flight spectrometer employing an effusive molecular beam from a capillary array instead of the conventional gas cell. The improvement in resolution is due to the subthermal transverse velocity spread achievable from the well‐directed target beam produced by the capillary array. We also discuss the advantage of using the capillary array in various other spectrometry applications such as translational energy spectrometry and electron spectrometry where the energy resolution is limited by the thermal motion of the target gas.
Polycarbon sulfides CnS (n = 2–6) and corresponding hydrides HCnS.. Neutralization–reionization mass spectrometry and ab initio molecular orbital study
Authors: Flammang Robert , Van Haverbeke Yves , Wong Ming Wah , Wentrup Curt
Published: May 2005

A series of polycarbon sulfide radical cations, CnS+· (n = 2–6), have been detected in the 70 eV electron impact mass spectrum of benzothiazole. Application of collisional activation and neutralization–reionization mass spectrometry indicates their connectivity and the stability of the corresponding neutral molecules CnS in the gas phase. Closed shell HCnS+ ions (n = 2–6) and the corresponding radicals HCnS. have similarly been identified in the dilute gas phase of the mass spectrometer. The experimental results are supported by ab initio molecular orbital calculations at the QCISD(T)/6–311G** (based on additivity approximation) + ZPVE level.
Behaviour of catechin and ellagic acid subjected to thermally‐assisted hydrolysis–methylation/gas chromatography/mass spectrometry
Authors: Galletti Guido C. , Bocchini Paolo
Published: May 2005

Catechin and ellagic acid, two basic constituents of important natural polyphenols such as condensed tannins and ellagitannins, were subjected to thermally‐assisted hydrolysis–methylation in the presence of tetramethylammonium hydroxide (25% aq.). The reaction was carried out at 600°C for 5 s using a platinum filament pyrolyzer which, in turn, was connected to a gas chromatograph/ion trap detector mass spectrometer. The permethylated compounds determined in the pool of the reaction products suggest that the reaction occurring is different from a simple methylation of free hydroxyls after thermal degradation and entails thermal fission of different bonds than those involved in conventional pyrolysis or chemical hydrolysis as the main decomposition pathway. The mass spectra of the permethylated hydrolysis products of catechin and ellagic acid are of practical use in the analysis of plant materials containing condensed tannins and ellagitannins.
Immobilized human serum albumin: Liquid chromatography/mass spectrometry as a method of determining drug–protein binding
Authors: Tiller Philip R. , Mutton Ian M. , Lane Stephen J. , Bevan Christopher D.
Published: May 2005

A liquid chromatography/mass spectrometry methodology is described that enables the simultaneous estimation of the individual protein‐binding affinities of a mixture of compounds. This approach has proved to be robust and enables a series of molecules to be ranked according to their protein‐binding affinities within 20 minutes.
Tandem mass spectrometry analysis of synthetic opioid peptide analogs
Authors: Tseng Jih‐Lie , Yan Lin , Fridland Genevieve H. , Desiderio Dominic M.
Published: May 2005

Five synthetic opioid peptides that were designed to have specific opioid receptor‐binding properties were studied by low energy collision‐induced dissociation (CID) tandem mass spectrometry (MS/MS). The MS/MS data are required for the analysis of those peptides in ovine plasma in a study to determine the placental transfer of the peptide to the fetus. The synthetic enkephalin‐related peptides were: Tyr‐D‐Arg‐Phe‐Lys‐NH2, (DALDA), N,N‐diallyl‐Tyr‐Aib‐Aib‐Phe‐Leu‐OH, (ICI 174,864), Tyr‐D‐Thr‐Gly‐Phe‐Leu‐Thr, (DTLET), magnified image. Liquid secondary ion mass spectrometry (LSIMS) was used for sample desorption‐ionization, and a hybrid (E1BE2qQ) tandem mass spectrometer was used to collect the product‐ion spectra. A protonated molecule ion, [M + H]+, was observed for each peptide. Amino acid sequence‐determining fragment ions were produced by CID and collected by MS/MS for the three linear peptides, and also for the two disulfide‐bond‐containing peptides in their unreduced and dithiothreitol (DTT)‐reduced forms. The detection level for the [M + H]+ ion of DTLET was ca. 3 pmol; and the stabilities of the CTAP and ICI analogs in plasma were studied.
Possible applications of an external resonant circuit in Fourier transform ion cyclotron resonance
Authors: Gorshkov Michael V. , Kouzes Richard T.
Published: May 2005

The narrow‐band cooling of ion motion in the trap of a Fourier transform ion cyclotron resonance mass spectrometer (FTICR) using an external parallel resonant circuit is considered. The parameters of the circuit necessary for effective cooling of both axial and cyclotron ion motion are estimated. It is shown that the use of a resonant circuit may be helpful in studying the highly charged heavy ions produced in experiments with electrospray ionization combined with FTICR.
Excitation of neutral molecules: Probing the dynamics by translational energy spectrometry
Authors: Krishnamurthy M. , Mathur D.
Published: May 2005

High‐resolution translational energy spectroscopy has been applied to the study of collision‐induced excitation of neutral diatomic and polyatomic molecules using molecular projectile ions. Techniques to simulate the experimentally observed energy loss spectra are explored and information regarding the relative oscillator strengths to different electronic states of the neutral targets has been obtained. The effects of changing the quantal description of the projectile are studied and the results are understood within the domain of wavefunction overlaps. Concomitant calculations of the wavefunction overlap of the highest occupied molecular orbitals of the collision partners yield results which are consistent with the experimental observations.
Sorption technique in membrane‐inlet mass spectrometry
Authors: Rivlin A. A.
Published: May 2005

The combination of a membrane‐inlet system with an extra stage for the sorption of water has been achieved. The new device, used as an inlet system for a mass spectrometer, increases the sensitivity for the detection of organics in polar media such as water and broadens the range of substances that can be analysed.
Characterization of 1,3‐dioxolanes upon positive‐ion chemical ionization
Authors: Aubert C. , Rontani J.‐F.
Published: May 2005

Positive‐ion chemical ionization (CI) mass fragmentations were studied in the case of different 1,3‐dioxolanes. The formation in methane CI mass spectra of interesting fragment ions allowing the characterization of their parent carbonyl compounds and diols is discussed and some mechanisms (supported by D2O CI analyses) are proposed in order to explain these fragmentations.
A comparison of the combination of fast‐atom bombardment with tandem mass spectrometry and of gas chromatography with mass spectrometry in the analysis of a mixture of kaempferol, kaempferide, luteolin and oleouropein
Authors: Baracco Andrea , Bertin Giorgio , Gnocco Elia , Legorat Mauro , Sedocco Silvia , Catinella Silvia , Favretto Donata , Traldi Pietro
Published: May 2005

Two different approaches, i.e. fast‐atom bombardment tandem mass spectrometry and gas chromatography combined with mass spectrometry (GC/MS) have been employed for the characterization of a mixture of biologically relevant polyphenols (kaempferide, kaempferol, luteolin and oleouropein). The best results have been achieved by the first approach which allows an easy structural identification of the different compounds, also in the presence of isomers. GC/MS of the trimethylsilyl derivatives leads to a complex chromatogram due to the presence of derivatives exhibiting a different level of silylation; the only species related to oleouropein are due to pyrolysis products (silylated fragments of sugars) and there is no evidence for the related silylated aglycone.
On‐line combination of micellar electrokinetic chromatography and mass spectrometry using an electrospray–chemical ionization interface
Authors: Takada Yasuaki , Sakairi Minoru , Koizumi Hideaki
Published: May 2005

Micellar electrokinetic chromatography/mass spectrometry (MEKC/MS) using an electrospray–chemical ionization (ES‐CI) source is described. The interface between micellar electrokinetic chromatography and mass spectrometry consists of an electrospray‐type nebulizer and an atmospheric pressure chemical ionization source that uses a needle electrode. Aromatic amines (aniline, p‐nitroaniline, and 1‐naphthylamine) are analysed by MEKC/MS, using a phosphate buffer that includes 20 mM sodium dodecyl sulfate (SDS), and protonated molecular ions of the samples are clearly recorded on the ion electropherograms. The results show that the ES‐CI technique is very promising as an MEKC/MS interface since MEKC/MS uses a high concentration of nonvolatile salts and surfactants.
Identification of denatured double‐stranded DNA by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Benner William H. , Horn David , Katz Joe , Jaklevic Joseph
Published: May 2005

We created double‐stranded DNA (dsDNA) by annealing synthetic oligonucleotides and used matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry to measure the difference in molecular weight of the complementary strands after denaturation. Refined sample preparation and deliberate rectilinear construction of a linear mass spectrometer produced a mass resolution exceeding 1000 for single‐stranded DNA. We present methodologies and demonstrate the potential for analysing dsDNA by determining the mass of the complementary strands.
A fully integrated trap‐membrane inlet mass spectrometry system for the measurement of semivolatile organic compounds in aqueous solution
Authors: Leth Mads , Lauritsen Frants R.
Published: May 2005

A novel procedure to perform a membrane‐inlet mass spectrometry experiment is presented, which allows semi‐volatile organic compounds to be preconcentrated inside the membrane, before they are thermally released into the ion source. The method uses a standard membrane inlet with a tubular silicone membrane passing straight through the ion source of the mass spectrometer. A long slit in the ion source parallel to the membrane allows electrons from the filament to continuously bombard the membrane surface. The membrane is kept cold by a continuous flow of water or sample solution passing through the inlet. However, during a short interruption of the flow, the membrane is rapidly heated by the electron bombardment and organic compounds dissolved in the membrane are thermally released into the ion source. In this fashion a desorption peak is obtained. Using the areas of the desorption peaks, we have been able to detect semi‐volatile, hydrophobic organic compounds (boiling points above 200 °C) in aqueous solution at low and sub parts‐per‐billion levels. In general, the detection limits were 10–100 times lower than previously published results, where membrane‐inlet mass spectrometry has been used for the detection of the same compounds. Good linearity over 3 orders of magnitude was obtained and the standard deviation was 5%.
Fragmentation and intramolecular cyclization in cyclopentane‐4,5‐fused 2‐N‐phenyliminoperhydro‐1,3‐oxazines and related thiazines under electron impact ionization
Authors: Oksman Pentti , Pihlaja Kalevi , Fülöp Ferenc , Bernáth Gábor
Published: May 2005

The influence of cyclopentane fusion on the fragmentation behaviour of 1,3‐oxazines and related thiazines was studied. The differences observed in the rearrangement reactions between the hydrogen atom at the ortho position of the aromatic ring and one of the hetero atoms in the cyclohexane ring were also investigated. These rearrangements occur if the cyclohexane ring contains an electrophilic atom and the carbon atom next to it is substituted by a benzyl or arylamino group. The compounds examined were cis and trans isomers of the title compounds substituted with methyl and benzyl (in the latter case only the cis isomers) on the ring nitrogen. All the compounds exhibited a large [M  H]+ ion peak which decreased with increasing size of the substituent. This indicates an intramolecular cyclization prior to further fragmentation of the molecule. Methyl substitution seems to change the character of this intramolecular cyclization. The main routes of fragmentation resemble those of the cyclohexane‐fused analogues more than those of the corresponding 5,6‐fused compounds. The stereoisomers fragment so similarly that they cannot be distinguished from each other, except in the case of methyl substituted oxazines.
Sensitive detection and structural characterization of trimethyl(p‐aminophenyl)‐ammonium‐derivatized oligosaccharides by electrospray ionization–mass spectrometry and tandem mass spectrometry
Authors: Okamoto Masahiko , Takahashi Ken‐Ichi , Doi Tadashi
Published: May 2005

Mass spectrometric methodologies which use electrospray ionization (ESI) for oligosaccharide structural determination and which are linked to classical procedures, such as reductive amination, have been established. Several derivatives of a model oligosaccharide were prepared and their ionization efficiencies in electrospray ionization (ESI) and fast‐atom bombardment (FAB) mass spectrometry were investigated. The trimethyl‐(p‐aminophenyl)ammonium (TMAPA) derivatives showed extremely high sensitivity in positive‐ion ESI–MS and gave Y‐ and Z‐series sequence ions by ESI tandem mass spectromety (MS/MS). This study suggests that TMAPA‐derivatized oligosaccharides used in ESI‐MS and ESI‐MS/MS would be effective for structural characterization of oligosaccharides that are available only in limited quantities.
Determination of multiply labeled serine and glycine isotopomers in human plasma by isotope dilution negative‐ion chemical ionization mass spectrometry
Authors: Culea Monica , Hachey David L.
Published: May 2005

A gas chromatography/negative‐ion chemical ionization mass spectrometry method is presented to measure the isotopic enrichment of multiple serine and glycine isotopomers. The amino acid N‐heptafluorobutyryl n‐propyl ester derivatives were used. The method had good analytical linearity between 10 and 800 μg mL−1 and both precision and accuracy were 5% for plasma amino acids. Sensitivity permitted analysis of 100 pg amino acid on column. The method was applied to metabolic studies of the serine to glycine interconversion in humans. (α‐15N)serine and (1,2‐13C2)glycine were given as a single intravenous bolus to six healthy male subjects. Plasma concentration of glycine and serine were determined after addition of (α‐15N,1,2,3‐13C3) serine and (α‐15N,1,2‐13C2)glycine as internal standards to 500 μL of plasma. Since glycine and serine are rapidly interconverted by hepatic serine hydroxymethyl transferase, the resultant tracer spectrum requires deconvolution of the enrichment of four isotopomers of each amino acid. Deconvolution of the ion abundance ratios to yield tracer‐to‐tracee ratios for each isotopomer was done using Brauman's least squares approach.
Ionophores: Potential screening via supercritical‐fluid chromatography combined with mass spectrometry and tandem mass spectrometry
Authors: Ramsey E. D. , Berry A. J. , Lawrence S. D. , Games D. E. , Startin J. R.
Published: May 2005

A variety of ionophores have been studied by packed column supercritical‐fluid chromatography combined with mass spectrometry. One of the ionophores, lasalocid, provided particularly good multiple‐reaction monitoring signal‐to‐noise responses when analysed by tandem mass spectrometry and this approach shows considerable potential for the analysis of this compound in medicated animal feeds. A capillary supercritical‐fluid chromatograph has been interfaced to an unmodified benchtop quadrupole mass spectrometer and this combination has enabled the molecular weight determination of the sodium salt of an ionophore.
Mass spectrometric identification of N‐phenyllinoleamide metabolites in mouse peritoneal macrophages
Authors: Bioque G. , Abián J. , Bulbena O. , Roselló‐Catafau J. , Gelpí E.
Published: May 2005

N‐Phenyllinoleamide (NPLA), the anilide of linoleic acid, has been regarded as a marker of the case oils associated with toxic oil syndrome, but the mechanisms of toxic injury remain enigmatic. Experimental data have related an increased systemic toxic effect of heated linoleic anilides to chemical structural modifications that might also be possible by in vivo metabolism; however, little is known about their metabolism. Taking into account that NPLA is a derivative of linoleic acid, a fatty acid that can be metabolized by lipoxygenase activity to a vast array of derivatives possessing biological activity, the objective has been to elucidate the oxidative metabolism of NPLA by mouse peritoneal macrophages, a cellular model with high lipoxygenase activity. Cells were incubated with 0.1 mM NPLA spiked with N‐phenyl[1‐14C]linoleamide. The metabolites were separated by high‐performance liquid chromatography and individually collected prior to GC/MS analysis. Identification of trihydroxy‐, monohydroxy‐ and epoxy‐derivatives of NPLA, suggests that this xenobiotic can be metabolized via the same oxidative processes as for linoleic acid. Furthermore, identification of the non‐amidated monohydroxylated and trihydroxylated derivatives of linoleic acid arising from NPLA suggests an amidase‐like activity with release of aniline and the free fatty acid. These results provide information about possible biological structures arising from NPLA, and open the way to evaluate the biological significance of these metabolites in the inflammatory reactions associated with toxic oil syndrome.
Liquid chromatography mass/spectrometry multiresidue determination of sulfonylureas after on‐line trace enrichment
Authors: Volmer Dietrich , Wilkes Jon G. , Levsen Karsten
Published: May 2005

A multiresidue method was developed for the trace level determination of sulfonylurea herbicides in aqueous samples. The method employs on‐line solid‐phase extraction and electrospray and thermospray reversed‐phase liquid chromatography mass spectrometry. In combination with time‐scheduled selected‐ion monitoring, the method permits the detection of the sulfonylureas down to the 50–100 ng/L level with excellent recoveries of > 90% and reproducibilities between 2 and 8.5% for almost all of the investigated compounds. This improved method is superior to existing techniques because no special clean‐up step is necessary, and owing to the fast online preconcentration step, the technique can be used as a rapid screening and confirmatory method. The method can be used with either thermospray cr electrospray mass spectrometry, both of which provided mass spectra with at least three structure‐signficant ions necessary for an unambiguous identification in environmental samples.
Detection of ΔF508 mutation of the cystic fibrosis gene by matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Ch'Ang L.‐Y. , Schell M. , Ringelberg C. , Tang K. , Matteson K. J. , Allman S. L. , Chen C. H.
Published: May 2005

The most common mutation of the cystic fibrosis gene is characterized by the deletion of three nucleotides that code phenylalanine in the 508 position of the cystic fibrosis transmembrane conductance regulator. We report the first measurements by matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometry for the ΔLF508 mutation in cystic fibrosis carriers and patients. Furthermore, in a blind test, results from the normal and ΔLF508 mutant alleles in 30 clinical samples based on MALDI mass spectrometry and on conventional gel analysis of the DNA were in total agreement. These results demonstrate the utility of MALDI mass spectrometry in the molecular diagnosis of mutant alleles and point to its potential use for ultra‐fast detection in large‐scale screening of DNA mutations.
Matrix‐assisted laser desorption/ionization mass spectrometry: Improved matrix for oligosaccharides
Authors: Mohr Martin D. , OlafBörnsen K. , Widmer H. Michael
Published: May 2005

The aim of this article was to study the influence of different matrix molecules on the quality of matrix‐assisted laser desorption/ionization mass spectra of oligosaccharides. An important criterion was the sample preparation, i.e. the crystallization process leading to the matrix from which the analytes were desorbed and investigated. Quality criteria were, among others, the resulting molecular peak intensity, the mass resolution, and the suppression of unwanted matrix peaks. It was found that a mixture of 2,5‐dihydroxy benzoic acid (DHB) and 1‐hydroxy isoquinoline (HIC) in a weight ratio of 3:1 was best suited for the analytical investigation of oligosaccharides. In addition, this matrix mixture was found to be quite tolerant against all kinds of buffers, salts, and even additives such as sodium dodecyl sulfate (SDS). Furthermore, we determined the different affinities of the alkaline metals to the carbohydrates and found that cesium and potassium ions ionize oligosaccharides about three times better than sodium ions and therefore have an important influence on the quantum yield.
Thermal decomposition kinetics of protonated peptides and peptide dimers, and comparison with surface‐induced dissociation
Authors: Meot‐Ner (Mautner) Michael , Dongré Ashok R. , Somogyi Árpád , Wysocki Vicki H.
Published: May 2005

Rate constants for the unimolecular decomposition of peptide monomer and dimer ions by thermal and surface‐induced dissociation (SID) are measured and compared. Rate constants for thermal dissociation are measured in a heated wide‐bore capillary flow reactor attached in front of the capillary leading into the mass spectrometer. Thermal decomposition of the leucine enkephalin ion (YGGFL)H+ is observed between 600 and 680 K with rate constants of 20–200 s−1, and yields many of the same fragments as SID at 35 eV, although with different relative intensities. The thermal decomposition yields the Arrhenius parameters Ea = 38.3 kcal/mol, log A = 15.7. The decomposition of the monomer and dimer ions are also observed by using SID on C18 and fluorinated hydrocarbon surfaces, with rate constants of 2 × 104 to 40 × 104 s−1. The SID activated monomer ions are assigned equivalent temperatures of 710–840 K by extrapolation of the thermal activation parameters. The protonated dimer ion (YGGFL)2 H+ decomposes thermally at 500–540 K to yield the monomer ion. The dimer also decomposes by SID at low collision energies 10–20 eV on both surfaces to yield the monomer ion, and at much higher energies of 60–80 eV to yield fragments identical to the decomposition of the monomer. The large energy requirement for fragmentation from the dimer is due to energy deposition into more degrees of freedom plus the additional energy required for dissociation of the dimer to the monomer. It is assumed that the energy deposition is linear with collision energy up to 80 eV, and that the energy becomes randomized throughout the dimer, including energy flow through the hydrogen bond(s). These mechanistic assumptions are supported quantitatively by the SID energy relations between monomer and dimer fragmentation. Thermal decomposition of the larger, multiply protonated melittin ion [M + 3H]3+ occurs at substantially higher temperatures, between 810–840 K, than those required for thermal decomposition of (YGGFL)H+, to yield many of the same sequence ions as produced by SID at 135 eV on a fluorinated surface.
Electron‐impact induced decomposition of some 3‐alkyl‐5‐substituted‐6‐methyl uracils
Authors: Jovanović Bratislav Ž. , Perić Aleksandra A. , Vajs Vlatka V.
Published: May 2005

Mass spectrometry was used to study the main fragmentation routes of some 3‐alkyl‐5‐substituted‐6‐methyl uracils. Differences in fragmentation were caused by changes in the structure of the alkyl group in position 3 of the uracil ring, with the same substituent in position 5, and by differences in the substituent in position 5.
The effect of the central linkage on the mass spectrometric behaviour of extended tetrathiafulvalenes
Authors: Orduna Jesús , Garín Javier , Frère Pierre , Nguyen Thi‐Thao , Gorgues Alain , Sánchez Luis , Martín Nazario , Seoane Carlos
Published: May 2005

The electron ionization‐induced fragmentation pattern of extended tetrathiafulvalenes has been studied by exact mass measurements, metastable ion analysis and collision‐induced dissociation mass spectrometry. The influence on the fragmentation of the central bridge linking the dithiole moieties is discussed.
Asparaginyl endopeptidase mapping of proteins with subsequent matrix‐assisted laser desorption/ionization mass spectrometry
Authors: Kanda Fujihiro , Yoshida Seiichi , Okumura Tatsuya , Takamatsu Tasuku
Published: May 2005

A matrix‐assisted laser desorption/ionization (MALDI) mass spectrometric mapping strategy for the identification and characterization of isolated and purified proteins is described. The method, which employs the combined usage of a new site‐specific enzyme Asparaginyl endopeptidase (Asn‐EP) for proteolysis, and MALDI for subsequent mass analysis, is capable of rapidly and sensitively examining the components of complex mixtures without any chromatographic or electrophoretic separation steps. Subpicomole sample quantities typically suffice to permit the confirmation of deduced primary structures and/or the identification of possible post‐translational modifications. The data obtained should also prove useful for mass matching and sequence homology searching of computerised protein sequence data bases of known proteins.
Synthesis and mass spectral fragmentation patterns of some new heterocyclic bis‐carboxamides
Authors: Karminski‐Zamola Grace , Crnjak Andrina , Bajić Miroslav
Published: May 2005

The electron impact mass spectra of some newly synthesized heteropolycyclic bis‐carboxamides are discussed. The dominant peaks in all these spectra are formed by the cleavage of the CN bond on one side of the anilino group with the formation of a fragment ion C9H4OSCI+ m/z 195, as the base peak. Cleavage of the CN bond with charge retention on nitrogen leads to characteristic ions in some cases.
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

The 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

From 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

In 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

A 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

A 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

Single‐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

Capillary 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

Commercial 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

A 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

The 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

A 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

A 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

The 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

N1‐([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

Since 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

In 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.
Lane-switching and Jughandles in Contemporary Interpretations of Roman Poetry
Authors: Barchiesi Alessandro
Published: May 2005

My paper answers two of the conference organizer's questions: the first, what are you working on, by mentioning some difficulties I am having with my current research, the important related question, how does your approach differ from what it was ten years ago, by discussing some problems of interpretation that demonstrate a need to connect formal and textual with historical and material aspects of Roman culture. My six examples feature (1) the need for interdisciplinary discussion, (2) the significance of an intertextuality that is not demonstrably "causative," (3) the importance of taking seriously "literal" indications such as location and (4) architecture, (5 and 6) the use of deictics and numerology as pointers to, respectively, the economy of patronage and the agenda of Augustan ideology.
Critical Divergences: New Directions in the Study and Teaching of Roman Literature
Authors: Edmunds Lowell
Published: May 2005

Introduction to seven papers from the conference Critical Divergences: New Directions in the Study and Teaching of Roman Literature, held 24–25 October 2003 at Rutgers University.
Eduard Fraenkel on Horace and Servius, or Texts, Contexts, and the Field of "Latin Studies"
Authors: Farrell Joseph
Published: May 2005

This essay traces the recent trajectory of the field of "Latin Studies" using the example of interpretations of Horace's Carmen saeculare and showing, in particular, the increasingly comprehensive relevance attributed to historical context. It sketches a shift away from formalist interpretation and, to an even greater degree, away from practices, such as textual criticism, that once virtually defined the field.
Latin Literature between Text and Practice
Authors: Habinek Thomas N.
Published: May 2005

This paper contains an appeal to situate the study of Latin literature within a history of embodied practices. Art history, anthropology, and cognitive science can all contribute to a decentering of texts and textuality, and texts can be analyzed for their role in the organization of human beings' capacity for mimesis. Latin literature is a case study of the ongoing relationship between embodiment and symbolization.
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

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.