bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structurally‐selective gas‐phase ion‐molecule reactions of dibenzo‐16‐crown‐5 compounds
Authors: Liou Chien‐Chung , Isbell John , Wu Hui‐Fen , Brodbelt Jennifer S. , Bartsch Richard A. , Lee Jong Chan , Hallman Johnny L. 
Published: May 2005

AbstractSteric and substituent effects can play large roles in influencing the outcomes of organic reactions. In this work, the use of ion‐molecule reactions of dibenzo‐16‐crown‐5 compounds (lariat ethers) by tandem mass spectrometry to probe the influence of the pendant groups on the selectivity of their gas‐phase reactions was evaluated. Lariat ethers are macrocyclic ethers with pendant substituents that have been developed as new types of hosts for molecular recognition. Dimethyl ether (DME) was the reactant chosen because of its well characterized reactivity with various organic substrates possessing different functional groups. Only those dibenzo‐16‐crown‐5 compounds with no or at most one substituent at the center carbon of the three‐carbon bridge form the diagnostic [M + 13]+ product ion through a methylene substitution process. Dibenzo‐16‐crown‐5 compounds with geminal substituents on the center carbon of the three‐carbon bridge form the [M + 45]+ ion, but not the characteristic [M + 13]+ ion. Causative factors may be steric blocking of the reaction pathway by the geminal groups or a requirement for the presence of at least one hydrogen on the center carbon of the three‐center bridge for formation of the [M + 13]+ ion. CAD, deuterium labelling, molecular orbital calculations and comparisons with model compounds provide additional information about the reaction pathways.
Special feature: Tutorial. Translational energy spectrocopy
Authors: Brenton Anthony Gareth 
Published: May 2005

AbstractThe technique of translational energy spectroscopy (TES) is described, whereby a collision of a fast ion (a few keV in energy) with a neutral target gas can reveal spectroscopic information on the states of the participating species. Information on the dynamics of the collision, lifetimes of species, collision cross‐sections and populations of states can be revealed. Classification of collisional processes amenable to TES are given together with simple aspects of relevant collision theory, an appraisal of quantum selection rules for collisions, a description of typical high resolution instrumentation and two simple examples of TES experiments.
Gas‐phase H–D exchange reactions of protonated amino acids and peptides with ND3
Authors: Dookeran Nyla N. , Harrison Alex G. 
Published: May 2005

AbstractThe gas‐phase H‐D exchange reactions of protonated amino acids and small peptides with ND3 have been studied for reactions occurring in the quadrupole collision cell of a hybrid BEqQ mass spectrometer (B = magnetic sector, E = electric sector, q = quadrupole collision cell, Q = quadrupole mass analyzer). Protonated amino acids RCH(NH2)COOH· H+, including those with hydroxyl, carboxyl, and amine functions in the R group, exchange all active hydrogens readily. The amide hydrogens of protonated glutamine and asparagine exchange less readily as does the N‐bonded hydrogen of the imidazole ring of histidine. The phenolic hydrogen of protonated tyrosine and tyrosine‐containing peptides does not undergo significant exchange. Protonated arginine undergoes only limited exchange with ND3 and arginine‐containing peptides are essentially unreactive with ND3. Although simple protonated di‐ and tripeptides exchange all active hydrogens readily, peptides with amide groups in the side‐chain exchange the last two hydrogens slowly. Mechanisms for exchange of the active hydrogens are discussed in relation to the proton affinities of the various sites of the amino acids and the potential and limitations of the method for counting the labile hydrogens of unknown peptides is assessed.
Alumatrane revisited: Distribution of oligomeric ions in electron impact ionization, chemical ionization and liquid secondary ion mass spectra
Authors: Bartlett Michael G. , Burns Scot A. , Bruce David A. , Busch Kenneth L. 
Published: May 2005

AbstractOligomeric ions formed from aluminium 2,2′,2″‐nitriltriethoxide (alumatrane) are present in electron impact (EI) ionization, chemical ionization (CI), direct‐exposure probe chemical ionization (DCI) and liquid secondary ion (LSI) mass spectra. These oligomeric ions are most pronounced in the LSI mass spectrum, extending from monomeric to heptameric ions. The oligomeric ions exist there in the forms [Mn + H]+ and [Mn + (AIO)a + (Al2O3)b]+ where the sum of a and b can be as high as 5. In contrast to previous interpretations of EI and CI results, the LSI mass spectral data do not support a special stability for either the dimeric or tetrameric gas‐phase forms of alumatrane.
Oligosaccharide characterization using collision‐induced dissociation fast atom bombardment mass spectrometry: Evidence for internal monosaccharide residue loss
Authors: Kováčik V. , Hirsch J. , Kováč P. , Heerma W. , Thomas‐Oates J. , Haverkamp J. 
Published: May 2005

AbstractThe protonated and sodium cationized pseudomolecular ions of a series of reducing and non‐reducing oligosaccharides possessing aldopentopyranosyl, 6‐deoxyaldohexopyranosyl, ketohexofuranosyl, 4‐O‐methyl glucuronopyranosyl methyl ester and N‐acetyl 2‐deoxyglucopyranosylamine units were studied using collision‐induced dissociation (CID) fast atom bombardment (FAB) mass spectrometry. The CID spectra of the [M + H]+ ions provide information about the sequence of the monosaccharide units, while dissociation of the [M + Na]+ ions by two‐bond ring cleavage processes gives rise to fragment ions which allow differentiation of 1 → 2 and 1 → 4 linkages. The influence of the structure of the constituent monosaccharides on the dissociation of the [M + H]+ and [M + Na]+ ions is discussed. An unusual type of fragmentation, which we suggest involves the elimination of internal monosaccharides residues, has not only been observed in the FAB mass spectra but also in the unimolecular decomposition and CID spectra of both [M + H]+ ions and oxonium ions from several oligosaccharides containing monosaccharide residues with different masses.
Special feature: Tutorial. Glow discharge mass spectrometry: Trace element determinations in solid samples
Authors: King F. L. , Teng J. , Steiner R. E. 
Published: May 2005

AbstractGlow discharge mass spectrometry (GDMS) is a mature, versatile technique for the direct determination of trace elements in a variety of materials. The technique is an extension of the earliest forms of mass spectrometry. Processes inherent to the glow discharge, namely cathodic sputtering coupled with Penning ionization, yield an ion population from which semi‐quantitative results can be directly obtained. Quantification in GDMS is achieved both through standard elemental mass spectrometric procedures and more innovative approaches. The analytical performance of GDMS compares favorably with competing elemental mass spectrometric methods and newer experiments use this ionization method for both molecular and elemental analysis. As with any analytical technique, the future of GDMS lies in improvements with respect to instrumental implementation and extension to new areas of application. If the method is to remain competitive, commercial GDMS systems must incorporate advances in mass spectrometric technology to increase analytical performance while decreasing the size, complexity and cost of the technique. Continued efforts to develop improved quantitation procedures are needed to provide greater accuracy. The method should continue to mature as sustained efforts demonstrate its utility in the solution of new and more varied problems.
Negative‐ion fast atom bombardment tandem mass spectrometry of sodium salts of monensins and related compounds
Authors: Havlíček Vladimír , Ryska Miroslav , Pospíšil Stanislav 
Published: May 2005

AbstractThe negative‐ion collisionally induced dissociation fast atom bombardment mass spectra of sodium salts of monensins A and B, their 3‐O‐demethyl derivatives, laidlomycin and 26‐deoxylaidlomycin are reported. The nature of the R3 substituent appears to be important for the formation of sodium‐containing product ions. Fragment ion series observed in the mass spectra of the [M − H]− ions of monensins are characterized by alkali metal retention. In contrast to monensins, the product ions observed in the corresponding spectra of laidlomycins are sodium free. The affinity of monensins to alkali metals is a useful feature that may be used for the structure determination of unknown monensins, their metabolites and derivates. The structure of a novel natural monensin was elucidated based on its mass spectrometric behaviour.
Charged vs. neutral nucleobase loss from multiply charged oligonucleotide anions
Authors: McLuckey Scott A. , Vaidyanathan Gopalakrishnan , Habibi‐Goudarzi Sohrab 
Published: May 2005

AbstractTandem mass spectra of a variety of adenine‐containing deoxynucleic acid anions obtained using collisional activation in a quadrupole ion trap are described. Data are reported for singly charged mono‐, di‐ and trinucleotide species, and also for multiply charged anions derived from tri‐, tetra‐, penta‐ and hexanucleotides. Attention is focused on the first step in the unimolecular decomposition of these species, namely the loss of the nucleobase. Specifically, the competition between the loss of the nucleobase as a neutral versus its loss as an anion is addressed within the context of a proposed proton‐bound intermediate consisting of the nucleobase and a phosphodiester linkage. The data are interpreted on the basis of the energy surface involved in the break‐up of the proton‐bound intermediate, which can explain why the competition between loss of a neutral versus charged base is strongly dependent upon the charge of the parent ion.
Matrix‐assisted laser desorption/ionization mass spectrometry of phospholipids
Authors: Harvey D. J. 
Published: May 2005

AbstractPhosphatidylcholine, lysophosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylglycerol, phosphatidylinositol, phosphatidic acid and cardiolipin were examined by matrix‐assisted laser desorption/ionization mass spectrometry on both a time‐of‐flight and a magnetic sector instrument using several substituted cinnamic acids, benzoic acids and substituted coumarins as matrices. All of these phospholipids gave signals, with the strongest responses being obtained from α‐cyano‐4‐hydroxycinnamic acid, esculetin (6,7‐dihydroxycoumarin) and 2,5‐dihydroxybenzoic acid (2,5‐DHB). In the positive‐ion mode, most compounds produced mixtures of [M + H]+, [M + Na]+ and [M + K]+ ions from both the free acids and from the sodium salts to give a complex mixture of ions. The spectra were considerably simpler in the negative‐ion mode, where the molecular ion region contained mainly [M − H]− ions. Spectral simplification was also achieved in the positiveion mode by methylation with diazomethane to prevent salt formation. This procedure had the additional advantage of converting phosphatidylethanolamine and phosphatidylserine into their corresponding quaternary derivatives with a consequent gain in detection sensitivity. Fragmentation involving cleavages around the phosphate group was common, with the diacyl‐containing ion produced by loss of the substituted phosphate moiety being particularly abundant. Fragmentation appeared to be strongly dependent on the nature of the matrix and, particularly, on the presence or absence of water in the matrix solvent. With spectra recorded on the magnetic sector instrument, additional fragment ions produced by losses of the acyl groups were seen. These latter ions provided some information regarding the distribution of carbon atoms between the acyl chains.
Application of time‐of‐flight mass spectrometry to the analysis of phototransformation products of diclofenac in water under natural sunlight
Authors: Agüera A. , Pérez Estrada L. A. , Ferrer I. , Thurman E. M. , Malato S. , Fernández‐Alba A. R. 
Published: June 2005

AbstractExact mass capabilities of time‐of‐flight (TOF) mass spectrometry along with other mass spectrometric techniques have been evaluated to elucidate a complete range of dichlofenac phototransformation products. Photolysis experiments with diclofenac in water under direct solar irradiation were performed to characterise the main phototransformation products generated and to determine their stability. Photolysis experiments were performed in both demineralised water and reconstructed standard freshwater. Samples were extracted before analysis by solid phase extraction (SPE) with Oasis® HLB and MAX cartridges. Separation and identification of the transformation products were accomplished by the combined use of gas chromatography‐mass spectrometry (GC/MS) and liquid chromatography coupled with time‐of‐flight mass spectrometry (LC/TOFMS). Both techniques provided complementary information that enabled the identification of 13 phototransformation products. Six of them were identified by GC/MS through the structural information provided by the full scan mass spectra obtained under electron impact (EI) ionisation and the confirmation of the molecular mass provided by positive chemical ionisation (PCI) analyses. Accurate mass measurements obtained by LC/TOFMS provided the elucidation of seven polar transformation products. The low mass error observed (<2 ppm) enabled the assignment of highly probable empirical formulas as well as identification of a process dimerisation route. The photoproducts identified demonstrated that photolysis of diclofenac occurs by two main routes. One is the consequence of the initial photocyclisation of diclofenac into carbazole derivatives. The other route goes through the initial decarboxilation of diclofenac and further oxidation of the alkyl‐chain, which are typical photolytic process reactions. The main photoproduct identified was 8‐chloro‐9H‐carbazole‐1yl‐acetic acid. Copyright © 2005 John Wiley & Sons, Ltd.
Electrospray tandem mass spectrometric analysis of zeaxanthin and its oxidation products
Authors: Prasain Jeevan Kumar , Moore Ray , Hurst John S. , Barnes Stephen , van Kuijk Frederik J. G. M. 
Published: June 2005

AbstractCarotenoids have been implicated in protection of the eye from light‐mediated photo‐toxicity caused by free radicals. Under conditions of normal oxidative stress the carotenoids serve as protective antioxidants; however, when the oxidative stress exceeds the antioxidant capacity, carotenoids can be oxidized into numerous cleavage products. The determination and identification of oxidized carotenoids in biological samples remains a major challenge due to the small sample size and low stability of these compounds. We investigated the reaction of various zeaxanthin cleavage products with O‐ethyl hydroxylamine to evaluate their levels in a biological sample. For this, a sensitive and specific electrospray tandem mass spectrometry (ESI‐MS/MS) was developed, avoiding the classical lower sensitive and specific HPLC‐UV and fluorescence absorption methods. Protonated molecules [M + H]+ of carotenoids upon collision‐induced dissociation produced a number of structurally characteristic product ions. A series of complicated clusters of product ions differing in 14 (CH2)and 26 (C2H2)Da was characteristic of the polyene chain of intact carotenoids. All carotenoid ethyl oximes of zeaxanthin cleavage products were characterized by the losses of 60 and 61 Da in their MS/MS spectra. Through the application of the LC/MS/MS method, we identified two oxime derivatives of 3‐hydroxy‐β‐ionone and 3‐hydroxy‐14′‐apocarotenal with protonated molecules at m/z 252 and m/z 370 respectively, in a human eye sample. Copyright © 2005 John Wiley & Sons, Ltd.
Online microdialysis‐dynamic nanoelectrospray ionization‐mass spectrometry for monitoring neuropeptide secretion
Authors: Jakubowski Jennifer A. , Hatcher Nathan G. , Sweedler Jonathan V. 
Published: June 2005

AbstractAlthough mass spectrometric approaches offer a sensitive method for identifying cell–cell signaling peptides, the high salt‐containing environment of extracellular solutions often complicates characterization of these microscale samples. Accordingly, we have developed a miniature hollow‐fiber microdialysis device optimized for desalting small‐volume neuronal samples online, with the device directly connected to a modified dynamic nanoelectrospray ionization assembly interfaced with an ion trap mass spectrometer. Improvements over existing designs include placement of a capillary insert within the microdialysis fiber to minimize volume, as well as the use of a microinjector that enables 1 µl sample injections. We present detailed evaluation of peptide recoveries within the microdialysis fiber by liquid chromatography–electrospray ionization–ion trap–mass spectrometry analysis of tissue homogenate in artificial seawater with and without microdialysis. Analyte recoveries after microdialysis ranged from 6 to 78% with higher recoveries of more hydrophilic peptides, while little correlation between mass and percentage recovery was observed in the range studied (2000 to 6000 Da). Recoveries of peptides were the lowest for the analytes with the highest initial mass spectrometry signal intensity. Finally, we illustrate the utility of this microdialysis device for desalting neuropeptides secreted from preparations of the peptidergic bag cell neurons of the marine mollusk, Aplysia californica. Without microdialysis, the high concentration of salts (∼0.5 M) prevented detection of peptides, whereas following online microdialysis–dynamic nanoelectrospray mass spectrometry of stimulated releasate, three peptides (acidic peptide, acidic peptide 1‐24 and δ‐bag cell peptide) were detected. Copyright © 2005 John Wiley & Sons, Ltd.
Covalent modification of actin by 4‐hydroxy‐trans‐2‐nonenal (HNE): LC‐ESI‐MS/MS evidence for Cys374 Michael adduction
Authors: Aldini Giancarlo , Dalle‐Donne Isabella , Vistoli Giulio , Maffei Facino Roberto , Carini Marina 
Published: June 2005

AbstractWe demonstrate for the first time, by a combined mass spectrometric and computational approach, that G‐ and F‐actin can be covalently modified by the lipid‐derived aldehyde, 4‐hydroxy‐trans‐2‐nonenal, providing information on the molecular mass of modified protein and the mechanism and site of adduction.ESI‐MS analysis of actin treated with different molar ratios of HNE (1 : 1 to 1 : 20) showed the formation of a protein derivative in which there was an increase of 156 Da (42028 Da) over native actin (41872 Da), consistent with the adduction of one HNE residue through Michael addition. To identify the site of HNE adduction, G‐ and F‐actin were stabilized by NaBH4 reduction and digested with trypsin. LC‐ESI‐MS/MS analysis in data‐dependent scan mode of the resulting peptides unequivocally indicated that Cys374 is the site of HNE adduction. Computational studies showed that the reactivity of Cys374 residue is due to a significant accessible surface and substantial thiol acidity due to the particular microenvironment surrounding Cys374. Copyright © 2005 John Wiley & Sons, Ltd.
Screening for unknown synthetic steroids in human urine by liquid chromatography‐tandem mass spectrometry
Authors: Thevis Mario , Geyer Hans , Mareck Ute , Schänzer Wilhelm 
Published: June 2005

AbstractChemically modified steroids (designer steroids), including tetrahydrogestrinone and norbolethone, pose a threat to the integrity of the sport community. These compounds have recently been detected in urine specimens from athletes, resulting in temporary or permanent suspension from amateur and/or professional competition. Triple quadrupole mass spectrometers enable doping control laboratories to screen for unknown, anabolic, androgenic steroids utilizing precursor ion scans. On the basis of common dissociation patterns of steroids with common structural features, characteristic product ions were selected to serve as diagnostic markers for previously unidentified drugs or drug metabolites in human urine samples. An assay was established to complement standard screening procedures. Urine specimens were enzymically hydrolyzed, partitioned into ether, concentrated, and analyzed by precursor ion scanning. Spectra from samples fortified with eight standard compounds (methyltestosterone, ethyltestosterone, 1‐testosterone, gestrinone, dihydrogestrinone, tetrahydrogestrinone, norbolethone, and propyltrenbolone) and one deuterium‐labeled analog (d4‐tetrahydrogestrinone) at 50 ng/ml of urine, had precursor ion peaks other than those from common endogenous steroids. Subsequent product ion scan experiments on precursor ions of peaks of unknown origin provided structural identification of the unknown compounds. Copyright © 2005 John Wiley & Sons, Ltd.
Balance of xanthophylls molecular and protonated molecular ions in electrospray ionization
Authors: Guaratini Thais , Vessecchi Ricardo , Pinto Ernani , Colepicolo Pio , Lopes Norberto P. 
Published: June 2005

AbstractThis paper reports the chemical evidence of the balance between radical molecular ions and protonatedmolecules of xanthophylls (an oxygen‐containing carotenoid) with a conjugated π‐system (polyene) and oxygen as a heteroatom in ESI and HRESI mass spectrometry. The ionization energy of neutral xanthophylls was calculated by semi‐empirical methods. The results were compared with those previously published for carotenoids and retinoids, which have also been shown in ESI‐MS to form M+• and [M + H]+, respectively. This study demonstrates, for the first time, the correlation of an extended conjugation and the presence of oxygen in the formation and balance of M+• or [M + H]+ for the carotenoids, neoxanthin, lutein, violaxanthin and zeaxanthin. Copyright © 2005 John Wiley & Sons, Ltd.
Effect of nitrogen nutrition on salt tolerance of Pisum sativum during vegetative growth
Authors: de Almeida Paula Figueira Etelvina M. , Nunes Caldeira Gustavo C. 
Published: June 2005

AbstractThe influence of different nitrogen (N) forms on salt tolerance of Pisum sativum L. was investigated. Plants of the pea cultivar “Resal” were subjected to 0 (control) or 90 mM NaCl and one of the following nitrogen forms: 5 mM mineral N supplied as either NO$ _3^- $, NH$ _4^+ $, or NH4NO3 or N supplied by biological N2 fixation (inoculated with Rhizobium leguminosarum bv. viciae). Root and shoot biomass were determined 15, 30, 45, and 60 d after emergence, and Na+, K+, and Cl– concentrations were determined by capillary electrophoresis. Nitrogen sources induced significant differences in plant growth and in ion accumulation and distribution and in differentially affected salt tolerance. In the absence of salt, the largest biomass accumulation was obtained with NH4NO3. In the presence of NaCl, NO$ _3^- $‐fed plants experienced less salt toxicity than plants supplied with other N sources, as indicated by lower Na+ and Cl– and higher K+ concentrations in the shoot. The results also suggest that it is possible to establish an effective symbiosis under saline conditions, provided that a salt‐tolerant Rhizobium isolate with good N2‐fixing ability is used. The use of the appropriate N‐fertilizer source can enhance the growth of Pisum sativum. Hence, NH4NO3 may be preferably used under non‐saline and NO$ _3^- $ under moderately saline conditions.