bluuebunny/crossref_metadata_2025_split huggingface dataset:
Determination of N‐terminal myristoylation of proteins using a combined gas chromatographic/mass spectrometric assay of derived myristoylglycine: Electron impact‐induced fragmentation of acylglycine derivatives
Authors: McIlhinney R. A. Jeffrey , Harvey David J. 
Published: May 2005

AbstractA method based on gas chromatography/mass spectrometry is described for the detection of N‐terminal myristoylation of proteins. Myristoylglycine, derivatized as its trimethylsily (TMS) ester, gave an electron impact mass spectrum containing abundant molecular and and [M  CH3]+ ions, together with several ions diagnostic of the acyl glycine moiety, namely at m/z 145, 158, 172 and 189. The compositions of these ions and the mechanisms that produced them were investigated by high‐resolution mass measurements, deuterium labelling and the preparation of analogous compounds. As these were present in the spectra of all acylglycines examined, they could be used as markers for these compounds. A selected‐ion monitoring method for the detection of myristoylglycine was set up using the above ions and was used to confirm the presence of N‐terminal myristoylation in three reference peptides. A series of ions produced by radical‐induced cleavage of the alkyl chain following TMS group migration and elimination of carbon dioxide gave information on the structure of the chain and could be used to determine the structure of other potential acylglycines such as those with unsaturated acyl chains. Thus the derivatives could be used not only to detect myristoylation of protein, but also to detect and determine the structures of other acyl substituents.
Determination of β‐agonist residues in human plasma using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry and tandem mass spectrometry
Authors: Doerge D. R. , Bajic S. , Blankenship L. R. , Preece S. W. , Churchwell M. I. 
Published: May 2005

AbstractA multi‐residue gradient liquid chromatographic (LC) separation was developed for five β‐agonists (fenoterol, metaproterenol, terbutaline, salbutamol and clenbuterol) in human plasma and detection was made using LC/atmospheric pressure chemical ionization mass spectrometry (LC/APCI‐MS) in the selected‐ion monitoring (SIM) mode. Detection limits for the protonated molecules of the β‐agonists were <2.5 ppb in plasma or 100 pg on‐column and responses were highly linear over the range 2.5–50 ppb. A solid‐phase extraction (SPE) procedure, yielding recoveries of 67–104% from plasma spiked at 5 ppb with the five analytes, was also developed. In‐source collision‐induced dissociation was used to produce mass spectra containing diagnostic fragment ions and a common mechanism of fragmentation for all the β‐agonists was identified. The LC/APCI‐MS method was unable to determine salbutamol at levels <10 ppb in spiked plasma. To determine whether this resulted from low SPE efficiency or matrix interference, LC/APCI‐MS/MS was performed in the multiple reaction monitoring (MRM) mode to enhance the selectivity of the analysis. The MRM results showed that high recoveries were obtained for salbutamol, confirming the detrimental effect of co‐eluting interferences in the LC/MS analysis. This study demonstrates the feasibility of using SPE, gradient LC separation and highly sensitive/selective detection using LC/APCI‐MS and MS/MS for the multi‐residue analysis of β‐agonists at low ppb levels in a biological matrix.
Special feature: Perspective. Host–guest chemistry in the mass spectrometer
Authors: Vincenti Marco 
Published: May 2005

AbstractThe study of host–guest chemistry in the gas phase has been pursued systematically only in the last 5 years, after sporadic interest in the 1980s, despite extensive investigation of this chemistry in the condensed phase and the success encountered in several fields of application. Most gas‐phase studies have been performed under the controlled conditions that can be achieved inside a mass spectrometer, where solvent effects are not present. At this point, the first evaluation of the achievements and knowledge emerging from these mass spectrometric investigations can be attempted. At the same time, it is possible to evaluate the most promising subjects for future research. This review undertakes these tasks, by presenting (i) applications where mass spectrometry was used to investigate condensed phase equilibria and, more extensively, (ii) experiments where host–guest complexes were formed directly in the gas phase. The latter processes are discussed in detail in relation to the structural and electronic effects, the energetic requirements and the dependence on size, rigidity, spatial geometry and functional groups of both hosts and guests. All these effects combined are likely to contribute to the strength and multiplicity of the non‐covalent bonds that allow the complex to be formed. The macro(poly)cyclic hosts considered include crown ethers, cryptands, cyclodextrins, calixarenes, cryptophanes, cavitands, carcerands and macrolides. The guests are either metal cations or organic molecules and ions.
Distinguishing isobaric amino acids in sequence analysis of cyclosporins by fast atom bombardment and linked‐scan mass spectrometry
Authors: Havlíček Vladimír , Jegorov Alexandr , Sedmera Petr , Wagner‐Redeker Winfried , Ryska Miroslav 
Published: May 2005

AbstractAn analytical protocol suggested previously for the mass spectrometric sequence analysis of cyclosporins was extended by addition of methods for discrimination among isobaric amino acids differing either in the nature of the side‐chain or N‐substitution. The former goal was achieved by comparison of B/E linked‐scan mass spectra of corresponding collisionally activated immonium ions with those of standard amino acids and the latter by comparison of B/E fragment ion spectra of [M + H]+ and [Md + 2H]+ ions. The use of the improved protocol is illustrated by the structure elucidation of a novel natural cyclosporin, [Leu9]CS.
Gas chromatographic–mass spectrometric identification of chlorinated octadecanoic acids in eel lipids
Authors: Wesén Clas , Mu Huiling , Sundin Peter , Frøyen Paul , Skramstad Jan , Odham Göran 
Published: May 2005

AbstractGas chromatographic (GC) studies with halogen‐selective electrolytic conductivity detection (ELCD) showed that chlorinated carboxylic acids are major organochlorine compounds in lipids of eel (Anguilla anguilla) from the receiving waters of a chlorine bleaching sulphite pulp mill. To facilitate the recording of full mass spectra, chlorinated carboxylic acid methyl esters were cold‐trapped after capillary GC separation monitored with ELCD. Methyl dichlorooctadecanoate was identified using GC/mass spectrometry (GC/MS) with both electron impact (EI) and ammonia positive‐ion chemical ionization (PICI). Methyl tetrachlorooctadecanoate was indicated by GC/EIMS. Each chlorinated fatty acid was observed at two retention times, suggesting the presence of isomers. The original fatty acid methyl esters derived from the eel lipids were subjected to GC/MS in the selected‐ion monitoring mode; methyl dichlorooctadecanoate was detected using PICI and methyl tetrachlorooctadecanoate was detected using EI ionization.
Proton‐transfer reactions within ionized methanol clusters: Mass spectrometric and molecular orbital studies
Authors: Lee Sun Young , Shin Dong Nam , Cho Soo Gyeong , Jung Kyung‐Hoon , Jung Kwang Woo 
Published: May 2005

AbstractProton‐transfer reactions that proceed within methanol cluster ions were studied using an electron impact time‐of‐flight mass spectrometer. When CH3OH seeded in helium is expanded and ionized by electron impact, the protonated species, (CH3OH)nH+, are the predominant cluster ions in the low‐mass region. In CH3OD clusters, both (CH3OD)nH+ and (CH3OD)nD+ ions are observed. The ion abundance ratios, (CH3OD)nH+/(CH3OD)nD+, show a tendency to decrease as the methanol concentration increases, which is apparently related to the cluster structure and reaction energetics. The results suggest that the effective formation of (CH3OD)nH+ ions at low concentration of CH3OD in the expansion is the result of the relatively facile rotation of methanol molecules within the smaller clusters that tend to form at low CH3OD concentration. Ab initio molecular orbital calculations were carried out to investigate the rearrangement and dissociative pathways of ionized methanol dimer. Ion‐neutral complexes, [CH3OH2+…O(H)CH2] and [CH3OH2+…OCH3], are found to play an important role in the low‐energy pathways for production of CH3OH2+ + CH2OH (and OCH3) from ionized methanol dimer.
Comparison of gas‐phase basicities and ion–molecule reactions of aminobenzoic acids
Authors: Tang Ming , Isbell John , Hodges Bradley , Brodbelt Jennifer 
Published: May 2005

AbstractFunctional group interactions and substituent effects of o‐, m‐ and p‐aminobenzoic acids were examined in a quadrupole ion trap by evaluation of proton‐transfer and methylene substitution reactions. An electron‐withdrawing carboxylic acid group can enhance or reduce the gas‐phase basicity of aniline depending on its location and ability to participate directly in proton bridging. In fact, the gas‐phase basicity of o‐aminobenzoic acid is enhanced by ∼ 7 kcal mol−1 relative to the meta and para isomers in which the substituents do not have cooperative functional group interactions. Collisionally activated dissociation studies of deuterium‐labeled ions provide evidence of proton migration from the amino group to the carboxylic acid group prior to fragmentation. Results of semi‐empirical molecular orbital calculations provided structures for the various protonated aminobenzoic acids. For o‐aminobenzoic acid, the proton bridges between the acid and amine groups.
Fast atom bombardment, frit fast atom bombardment and electrospray ionization mass spectrometric study of organic salts C2+ 2X−: Matrix and anion effects
Authors: Aubagnac Jean‐Louis , Gilles Isabelle , Calas Michèle , Cordina Gérard , Piquet Gilles , Portefaix Philippe , Giral Louis 
Published: May 2005

AbstractThe fast atom bombardment (FAB), frit‐FAB and electrospray ionization mass spectra of bis‐ammonium salts, C2+ 2X−, were compared. The most informative spectra were the FAB mass spectra with m‐nitrobenzyl alcohol as matrix and the Frit‐FAB mass spectra. The nucleophilic character of the iodine anion was established.
Mass and sequence verification of modified oligonucleotides using electrospray tandem mass spectrometry
Authors: Barry John P. , Vouros Paul , Van Schepdael Ann , Law Say‐Jong 
Published: May 2005

AbstractElectrospray coupled with tandem mass spectrometry is shown to have utility in determining the molecular mass and the sequence of short modified oligonucleotides. The product ion spectrum of a triply deprotonated molecule precursor is dominated by ions formed via two fragmentation pathways: first, fragmentation across the 5′PO phosphate bond, and second, loss of a non‐terminal base with concomitant cleavage of the ribose 3′CO bond. If either of these two pathways is complete with fragmentation occurring at each equivalent position along the phosphodiester backbone, then the oligomer may be sequenced. Alternatively, if both these pathways are only partially complete, their complementarity may be used for more extensive sequencing. The inductive effect of the modification on the nucleobase is shown to influence the latter fragmentation process. The greater the electron affinity of the base modification, the more facile is the loss of that base when the molecule is collisionally activated. In fact, this latter fragmentation dominates the product ion spectrum when a nucleobase contains a substituent that is highly inductively withdrawing. This domination can be such that few other first‐generation fragment ions are present in the product ion spectrum. Sequence information may then require utilization of second‐generation product ions.
Identification of glucopyranosyl‐β‐1,4‐glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid, a new IAA catabolite, by liquid chromatography/tandem mass spectrometry
Authors: Östin Anders , Catalá Carmen , Chamarro Jesus , Sandberg Göran 
Published: May 2005

Abstract[5‐3H,13C6] Indole‐3‐acetic acid was fed to immature pericarp segments from fruits of tomato (Lycopersicon esculentum Mill., cv. Moneymaker), resulting, after 24 h of incubation, in five radiolabelled peaks when analysed by reversed‐phase high‐performance liquid chromatography with radiocounting. The fractions were numbered in order of decreasing polarity. Fractions 4 and 5 had earlier been shown to contain indole‐3‐acetyl‐N‐aspartic acid and indole‐3‐acetyl‐O‐glucose. Based on results from strong alkaline hydrolysis, it had been concluded that fractions 1 and 3 contain an amide conjugate with a modified indole ring. This paper presents data supporting the structure of the labelled compounds in fractions 1 and 3 to be diastereomers of glucopyranosyl‐β‐1,4‐glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid. The identification of glucopyranosyl‐β‐1‐N‐oxindole‐3‐acetyl‐N‐aspartic acid in fraction 2 is also reported. These structures were elucidated by liquid chromatography/frit fast atom bombardment tandem mass spectrometry.
Quantitation of fatty acids and hydroxy fatty acids by gas chromatography/mass spectrometry. Predictively useful correlations of relative response factors with empirical formula
Authors: Chaurasia Chandra S. , Williams Todd D. , Judson Charles M. , Hanzlik Robert P. 
Published: May 2005

AbstractRelative response factors (molar sensitivities relative to dibutyl phthalate) for homologous series of n‐alkanes (C12C26), trimethylsilyl esters of C10C20 fatty acids (FAs) and bistrimethylsilyl derivatives of C8C16 ω‐hydroxy fatty acids (HOF As) were determined by integration of total ion chromatograms obtained using a conventional gas chromatograph‐mass spectrometer in the electron impact ionization mode. For the alkanes up to C22 and for the FA‐TMS derivatives up to C18 (C21 including the TMS carbons), response factors increased linearly with total number of carbons (r2 > 0.99). The slope of this correlation (response factor = 0.0775n − 0.338, where n is the total number of carbon atoms in each analyte) is essentially identical with those determined in earlier studies for smaller molecules not containing silicon. For the HOFA derivatives up to C14 (C20 including TMS carbons), the molar response factors also increased linearly with total number of carbons, but for reasons not yet apparent the regression line for these homologs was different (response factor = 0.0330n + 0.456; r2 > 0.99). Response factors for higher homologs in all three series fell below the regression line for the lower homologs, the deviation increasing with increasing molecular mass and increasing GC retention time. In all three series the upper limit to the linear portion of the correlation corresponded to the homolog whose GC retention time was ca 15 min under the conditions used; a high injection port temperature was found to be the most critical factor in extending the linear range of the correlation.
Electron impact behaviour of trans‐4‐benzoylamino‐2H‐1‐benzopyran‐3‐ols: Evidence for an oxygen migration with loss of a benzopyranone
Authors: Evans John M. , Organ Andrew J. , Sims Jonathan L. 
Published: May 2005

AbstractCertain abundant peaks in the electron impact mass spectra of a series of trans‐4‐benzoylamino‐2H‐1‐benzopyran‐3‐ols involve the formation of a substituted N‐alkylated benzonitrile ion by a mechanism involving migration of oxygen, in a postulated four‐centre skeletal rearrangement, leading to the loss of a benzopyranone. The presence of a small range of differing substituents at three locations in this series was studied for their effects on this proposed mechanism.
Intramolecular aromatic substitution and amino‐Claisen rearrangement in substituted N‐(2‐propynyl)anilines on electron impact
Authors: Ramana D. V. , Sudha M. S. 
Published: May 2005

AbstractN‐(2‐Propynyl)anilines undergo amino‐Claisen rearrangement to a minor extent in the ion source, losing a molecule of HCN under electron impact conditions. However, metastable molecular ions with energies closer to threshold undergo Claisen rearrangement giving rise to more abundant [M − HCN]+· ions in the first field‐free region. Loss of a hydrogen from the molecular ion gives rise to the base peak in the mass spectrum of N‐(2‐propynyl)aniline. The hydrogen that is expelled for the formation of the [M − H]+ ion is observed to be from the amino nitrogen, propargylic carbon and the ortho‐carbon of the ring. The last process leads to a cyclic fragment involving intramolecular aromatic substitution. Double oxygen migration from the nitro group to the triple bond, due to the ortho effect, yields an abundant ion at m/z 105 in N‐(2‐propynyl)‐o‐nitroaniline. The proposed fragmentation pathways and ion structures are substantiated by high‐resolution data, B/E and B2/E linked‐scan spectra, collisionally activated dissociation–B/E linked‐scan spectra and deuterium isotopic labelling.
Application of reversed phase liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry to the determination of polycyclic aromatic sulfur heterocycles in environmental samples
Authors: Thomas Darren , Crain Sheila M. , Sim P. Greig , Benoit Frank M. 
Published: May 2005

AbstractReversed‐phase liquid chromatography (RPLC) was combined with atmospheric pressure chemical ionization mass spectrometry (APCI‐MS), via a heated pneumatic nebulizer interface, for the determination of the polycyclic aromatic sulfur heterocycle (PASH) content of samples obtained by the fractionation of an extract of a pond sediment contaminated by coke‐oven residues. Some of the samples produced by the fractionation procedure contained large amounts of other polycyclic aromatic compounds (PACs) which co‐eluted with the compounds of interest, making it difficult to obtain mass spectra suitable for compound identification and verification. Therefore, the use of tandem mass spectrometry (MS/MS), as a selective method for the identification of target analytes in complex matrices, was investigated. Initially, PASH standards were injected into the mass spectrometric system by flow injection and their collisionally induced dissociation mass spectra recorded. From these results, it was possible to select ions suitable for selected reaction monitoring (SRM) experiments on both the PASH standards (to establish detection limits and also retention times which could be used to identify these compounds) and the fractions (to establish the possible presence of the selected PASHs in the fractions). The RPLC‐SRM experiments led to a tentative identification of some of the PASH standards in the fractions. However, the use of multiple reaction monitoring experiments allowed the positive identification of dibenzothiophene, phenanthro [4,5‐bcd] thiophene, phenanthro [3,4‐b] thiophene and benzo [b] naphtho [2,3‐d] thiophene in the fractions, along with several of their isomers. Quantification of the PASH standards by RPLC‐SRM in the extracts found them to be present at high levels.
Glucose glass films: A matrix for mass spectrometry that mimics aqueous solution behavior
Authors: Song Siqing , Macfarlane Ronald D. 
Published: May 2005

AbstractThis study demonstrates that an amorphous film of glucose has many of the features of water as a medium for solvating ions and, at low concentrations, maintaining ion pair separation. Aqueous solutions of glucose containing dissolved salts are evaporated to form a homogeneous glucose glass where the distribution of the solute in solution is preserved in the evaporated glass film. Cluster ions form in aqueous solutions at high solute concentration, and glucose films made from these solutions form gas‐phase cluster when the film is excited by a high energy density pulse. These cluster ions do not form in dilute solutions and are not present in the mass spectrum of ions desorbed from films prepared from these solutions. Non‐polar ions concentrate at the surface of aqueous solutions owing to the hydrophobic interaction and glucose glass films prepared from these solutions show, by mass spectrometry, that these features are retained in the glucose film. The salts studied include KCl, NaBr, LiCF3SO3, (tert‐butyl)4NI and (C2H5)4NBF4. The concentration of the salt is the important variable in the study and ranges from a mole fraction of 0.1–10−4. For non‐polar ions, the abundance of the molecular ion is not significantly changed over a wide range of dilutions.
Determining calcium‐binding stoichiometry and cooperativity of parvalbumin and calmodulin by mass spectrometry
Authors: Hu Peifeng , Loo Joseph A. 
Published: May 2005

AbstractThe calcium‐binding properties of parvalbumin and calmodulin were investigated by electrospray ionization mass spectrometry (ESI‐MS). The two calcium sites of parvalbumin were found to be strongly cooperative in binding Ca2+ ion. Up to four calcium ions were found to bind to calmodulin at high calcium concentration levels. Strong cooperativity was detected between the third and fourth Ca2+ binding sites of calmodulin (ordered by loading sequence). Strong interactions were also indicated between the two halves of the calmodulin molecule. Demetallation of the gas‐phase ions can occur during the desolvation process, especially for ESI of aqueous solutions. However, the ESI‐MS methodology has the potential to provide insight into the intricate processes involved in metal site communications for other metalloproteins.
Effects of molecular geometry on the fragmentation of ionized maleic and fumaric acids; an overdue reappraisal
Authors: Chen Hongwen , Holmes John L. 
Published: May 2005

AbstractThe ionized geometric isomers maleic and fumaric acids ((Z)‐ and (E)‐ethenedicarboxylic acids) were studied by a variety of tandem mass spectrometric techniques. In agreement with much earlier work, the metastable ionized isomers do not reversibly interconvert. They do, however, have two dissociation channels, H2O and CO losses, for which common transition states are involved. Ionized maleic acid has one geometry‐specific dissociation, loss of CO2. Structures were assigned to all major fragment ions together with their heats of formation.