bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metastable and collision‐induced fragmentation of selected C3H6S+· isomers; evidence for extensive isomerization
Authors: Hop Cornelis E. C. A. 
Published: May 2005

AbstractThe metastable ion (MI) and collision‐induced dissociation (CID) mass spectra of five C3H6S+· isomers were examined. The MI mass spectra were virtually identical, which suggests that C3H6S+· ions having a substantial amount of internal energy can freely interconvert and isomerize into a common structure prior to fragmentation. However, the CID mass spectra are distinctly different and the differences can be related to the structure of the C3H6S+· isomers. It was even possible to distinguish the distonic ion H2CCH2SCH2+· from its conventional counterpart magnified image. The smaller amount of internal energy of the ions probed in CID experiments obviously limits isomerization.
Determination of both linkage position and anomeric configuration in underivatized glucopyranosyl disaccharides by electrospray mass spectrometry
Authors: Mulroney Brad , Traeger John C. , Stone Bruce A. 
Published: May 2005

AbstractNegative‐ion electrospray mass spectrometry was used to determine directly both glycosidic linkage position and anomeric configuration in the complete glucopyranosyl disaccharide series without the need for derivatization or tandem mass analysis. A series of empirical criteria were developed which first differentiate between the linkage positions and then the anomeric configurations using selected diagnostic peaks and their relative intensities. The use of standard mass spectral library searching methods for structural analysis was also investigated.
Formation by fast atom bombardment of molecular radical cations by electron donor–acceptor complexes from tosylated amino acid esters
Authors: Athanassopoulos Constantions , Papaioannou Dionissios , Napoli Anna , Siciliano Carlo , Sindona Giovanni 
Published: May 2005

AbstractN‐Alkyl‐N‐tosyl amino acid esters were ionized by fast atom bombardment (FAB) in a nitrobenzyl alcohol matrix through oxidative processes leading to molecular radical cations (M+·). The addition to the matrix of Cu11 salts induces the ionization through proton attachment whereby [M + H]+ are exclusively displayed by the positive‐ion FAB spectra. The formation of electron donor–acceptor complexes between the analytes and the matrix lowers the critical energy for the ionization by one‐electron removal from the substrates.
Analysis of the chemical defence system in an insect larva by tandem mass spectrometry
Authors: Gfeller Hans , Schlunegger Urs P. , Schaffner Urs , Boevé Jean‐Luc , Ujvary Istvan 
Published: May 2005

AbstractLarvae of the sawfly Rhadinoceraea nodicornis Konow (Hymenoptera, Tenthredinidae) living on the plant Veratrum album L. (Liliales, Melanthiaceae) are efficiently protected against ants and spiders. Moreover, when their haemolymph was offered in a sugar solution, ants were still deterred. The chemical defence system of these larvae was investigated and the structures of the biologically active compounds determined by tandem mass spectrometry. Plant‐derived alkaloids both in original and metabolized form were found in the larval haemolymph.
Identification and determination of cystathionine sulfoxide and NAc‐cystathionine sulfoxide in the urine of a patient with cystathioninuria using liquid chromatography/atmospheric pressure chemical ionization mass spectrometry
Authors: Zhang Jianying , Masuoka Noriyoshi , Ubuka Toshihiko , Kodama Hiroyuki 
Published: May 2005

AbstractNovel cystathionine metabolities, cystathionine sulfoxide and NAc‐cystathionine sulfoxide, were identified in the urine of a patient with cystathioninuria using liquid chromatography/mass spectrometry with an atmospheric pressure chemical ionization interface system. NAc‐cystathionine sulfoxide was discovered as a new metabolite of cystathionine in the urine of a cystathioninuric patient. The concentrations of cystathionine sulfoxide and NAc‐cystathionine sulfoxide in this urine were also determined for the first time using this method, and were 28.69 ± 0.44 and 10.51 ± 0.49 mg g−1 creatinine, respectively. Neither compound was detected in the urine of healthy subjects.
Matrix‐assisted laser desorption/ionization mass spectrometry of sphingo‐ and glycosphingo‐lipids
Authors: Harvey David J. 
Published: May 2005

AbstractSphingo‐ and glycosphingo‐lipids were examined by matrix‐assisted laser desorption/ionization mass spectrometry on a time‐of‐flight (TOF) and a magnetic sector mass spectrometer with 2,5‐dihydroxybenzoic acid (2,5‐DHB), sinapinic acid, α‐cyano‐4‐hydroxycinnamic acid, 2‐(4‐hydroxyphenylazo)benzoic acid (HABA) and esculetin as the matrices. Strong signals were produced by all lipids tested, with many of the compounds producing structurally useful fragment ions. Neutral glycosphingolipids gave the best signals in the positive‐ion mode with 2,5‐DHB, α‐cyano‐4‐hydroxycinnamic acid and esculetin. When 2,5‐DHB was used as the matrix, glycosphingolipids that did not contain HexNAc residues tended to fragment between the sugar and ceramide moieties to give ions revealing the saccharide and lipid contents. Other matrices tended not to induce this fragmentation but, instead, produced ions resulting from loss of that acylamide from the ceramide moiety. These ions revealed the distribution of carbon atoms between the acyl and sphingosine chains. Fragmentation of the oligosaccharide chain of glycolipids that did contain HexNAc groups tended to be more random than that seen when HexNAc was absent and provided considerable sequence information. The acidic gangliosides produced broad, unresolved fragment ion peaks on the TOF spectrometer. Fragmentation was the result of both decarboxylation and loss of sialic acids. On the magnetic sector instrument, these fragment ions were sharp and well resolved. Additional fragment ions resulting from glycosidic cleavages provided information about the sequence of sugars in the oligosaccharide chain. Negative‐ion signals ([M − H])− from the acidic glycosphingolipids were generally better defined than those in the positive‐ion spectra as the result of a reduction in alkali metal adduct and salt formation.
GC/MS analysis of [2H5]phenylalanine at very low enrichment: Measurement of protein synthesis in health and disease
Authors: Slater Christine , Preston Tom , McMillan Donald C. , Falconer J. Stuart , Fearon Kenneth C. H. 
Published: May 2005

AbstractA gas chromatographic/mass spectrometric (GC/MS) method has been developed for the precise and accurate analysis of high enrichment (1–10 mol.% excess) and very low enrichment (0.005–0.12 mol.% excess) 2H5‐labelled phenylalanine. Tracer enrichment in free phenylalanine was measured by GC/electron impact MS analysis of the tert‐butyldimethylsilyl (TBDMS) derivative. The measurement of very low tracer enrichment, typical of that found in protein hydrolysates, was accomplished by careful control of sample yield during preparation and analysis of the TBDMS derivative of purified β‐phenylethylamine, produced by enzymatic decarboxylation and solvent extraction. The new method was illustrated by measurement of albumin synthesis in healthy patients using a rapid protocol which showed good patient acceptability and was straightforward to manage in the clinical setting. The mean (SEM) albumin fractional synthetic rate was 9.54% (0.81%) per day, in agreement with previous studies that used more complex clinical protocols and analytical procedures. Use of the same derivative for analysis of amino acid precursor and protein samples facilitated consecutive analysis on the same instrument without interruption, permitting rapid feedback of results to the clinician and the possibility of using the method in intervention studies. The method should prove useful in the study of the synthetic rate of other proteins and mixed tissue protein, which will help our understanding and management of protein metabolism in health and disease. The possibility of extending the use of multiple‐atom tracers combined with GC/MS analysis to other substrate metabolism studies was identified.
‘Underflow’ introduction system for solid and liquid samples in bench‐top gas chromatographic/mass spectrometric systems
Authors: Favretto Donata , Cecchinato Francesco , Traldi Pietro , March Raymond E. 
Published: May 2005

AbstractA simple, inexpensive inlet system was developed for the introduction of liquid and solid samples, to be employed in commercial gas chromatographic/mass spectrometric instruments, and not requiring sample injection through the chromatographic column. The system does not need any modifications of the ion source housing and pumping system and is based on admitting the sample vapour as an underflow to the normal helium flow through the chromatographic column at a location near the transfer line.
Special feature: Perspective. Mass spectrometric detection of carcinogen adducts
Authors: Farmer P. B. , Sweetman G. M. A. 
Published: May 2005

AbstractGenotoxic carcinogens interact with nucleic acids and proteins to yield covalently bound products (adducts), the quantitative determination of which has been proposed as a biomonitor of human exposure to carcinogens. Mass spectrometry is playing a leading role both in the structural characterisation and in the quantitative determination of these carcinogen adducts. In particular electrospray ionisation and matrix assisted laser desorption ionisation are being increasingly used in nucleotide and protein adduct detection and in sequencing of carcinogen‐modified oligonucleotides and peptides. Quantitative determination of carcinogen‐modified nucleic acid bases and protein amino acids is generally carried out by GC/MS or GC/MS/MS, the highest sensitivity being achieved using negative ion chemical ionisation. These techniques are now being applied to samples from humans exposed to carcinogens from environmental, medicinal and occupational sources.
Identification of amperozide metabolites in urine from rats, rabbits, dogs and man by Frit‐FAB LC/MS using deuterated solvents to gain additional structural information
Authors: Edlund P. O. 
Published: May 2005

AbstractA general procedure for screening of amperozide, N‐ethyl‐4‐[4,4‐bis(p‐fluorophenylbutyl)]‐1‐piperazine carboxamide, labelled with 3H and 14C was developed. Urine extracts were first fractionated by preparative reversedphase chromatography with an acetonitrile gradient elution. The collected fractions were finally analysed using a methanol gradient on packed capillary LC columns with an internal diameter of 0.32 or 0.5 mm connected to the Frit‐FAB probe of a Jeol SX‐102 mass spectrometer for structural analysis. A micro‐gradient system dedicated for the use of deuterated solvents was constructed from two six‐port switching valves to reduce the consumption of the eluents. The number of hydrogens bound to heteroatoms (OH, NH) was determined by comparing the spectra recorded from mobile phases using water and deuterium oxide. The mass spectra recorded during elution with deuterated solvents was also useful for the interpretation of the fragmentation pattern of standard compounds and unknown metabolites. The technique proved especially useful to differentiate between hydroxylation and N‐oxidation which gave the same increase in molecular mass by 16 u but a difference in the number of exchangeable protons. Metabolites formed by oxidative N‐dealkylation of amperozide either at the basic nitrogen or at the N‐ethylcarboxamide nitrogen were identified. Additional metabolites derived from deethylated amperozide inovlving N‐oxidation of the basic nitrogen of the piperazine ring and/or hydroxylation of the piperazine ring were identified. Metabolites formed by oxidative N‐dealkylation and opening of the piperazine ring were also identified.
Detection of testosterone esters in human plasma
Authors: de la Torre Xavier , Segura Jordi , Polettini Aldo , Montagna Maria 
Published: May 2005

AbstractThe detection of testosterone misuse in sports is currently based on the urinary testosterone to epitestosterone ratio, although in some rare instances physiological or pathological conditions could compromise the application of this general criterion. The detection in the body of traces of the unchanged testosterone esters really ingested would offer unequivocal confirmation of testosterone administration. In this work, the detectability of testosterone esters in humans was studied. Liquid–liquid extraction of human blood plasma and appropriate derivatization of nine testosterone esters are described. Different acyl (trifluoroacetyl, pentafluoropropionyl and heptafluorobutyryl) and trimethylsilyl derivatives were studied. The trimethylsilyl derivatives appear to be the best for screenign purposes based on the characteristics of their mass spectra, with abundant molecular ions in the high‐mass range. They also offered good conditions for tandem mass spectrometric analysis, needed to achieve the required sensitivity after oral administration of the drugs. The method was successful in the detection and determination of intramuscularly administered testosterone propionate and testosterone enanthate and orally ingested testosterone undecanoate.
Fast atom bombardment mass spectrometry of phospholipids in human cerebrospinal fluid
Authors: Mollova Nevena N. , Moore Ida Marie (Ki) , Hutter John , Schram Karl H. 
Published: May 2005

AbstractLipid extracts of cerebrospinal fluid (CSF) collected from children with leukemia were separated on normal‐phase high‐performance liquid chromatography (HPLC) and analyzed by fast atom bombardment mass spectrometry (FABMS) and tandem FABMS/MS. CSF samples from 13 children with leukemia receiving chemotherapy and radiation treatment were analyzed. Analysis of the results permits the identification of phosphatidylcholine (PC), sphingomyelin (SM), diacylglycerol (DAG) and lysophosphatidylcholine (LPC) molecular species. The following changes in the CSF phospholipid composition during treatment with chemotherapy were identified: (i) presence of DAGs and LPCs and (ii) increase in SM relative to PC. A predominance of the C18:1 SM was observed during radiation treatment. To our knowledge, this is the first report of the application of HPLC and FABMS for the analysis of human CSF. The possibility of using FABMS and FABMS/MS for the direct analysis of the total CSF lipid extracts in cancer patients is demonstrated.
Configurational effects on internal proton transfers and ion–neutral complex formation in stereoisomeric 1,4‐di(alkoxymethyl)cyclohexanes on chemical ionization
Authors: Denekamp C. , Mandelbaum A. 
Published: May 2005

AbstractCis‐ and trans‐1,4‐dimethyl‐1‐d3‐methoxymethyl‐4‐(2‐methoxy‐2‐propyl)cyclohexane (3a‐c and 3a‐t), the isomeric 1,4‐dimethyl‐1‐methoxymethyl‐4‐(2‐d3‐methoxy‐2‐propyl)cyclohexanes (3b‐c and 3b‐t) and 1,4‐dimethyl‐1‐methoxymethyl‐4‐(2‐d3‐methoxy‐2‐propyl)cyclohexanes (3b‐c and 3b‐t) and 1,4‐dimethyl‐1‐ethoxymethyl‐4‐(2‐methoxy‐2‐propyl)cyclohexanes (3c‐c and 3c‐t) give rise to different isobutane chemical ionization (CI) mass spectra. The cis isomers exhibit abundant [MHROH]+ ions (100%, ROH originating from the tertiary alkoxy group), while no MH+ or [MHR′OH]+ ions (R′OH originating from the primary alkoxyl) were detected in the mass spectra. This behaviour indicates an efficient proton transfer between the two ether functions in the transient MH+ ions of the cis isomers, resulting in the total and exclusive elimination of methanol from the tertiary position. In contrast to the cis diethers, the trans isomers 3a‐t, 3b‐t and 3c‐t afford relatively abundant [MHROH]+ and [MHR′OH]+ ions. This behaviour is consistent with protonation on each of the two distant non‐interacting ether groups, resulting in two isomeric MH+ ions, each of which eliminates the corresponding alcohol. The highly stereospecific behaviour of the cis and trans diethers 3c and 3t is dependent on the presence of the methyl substituents at positions 1 and 4: identical mass spectra were obtained for cis‐ and trans‐1‐ alkoxymethyl‐4‐(2‐alkoxy‐2‐propyl)cyclohexanes (4‐c and 4‐t) (four pairs with different 1‐ and 4‐alkoxy groups), and both stereoisomers exhibit exclusive elimination of ROH originating from the tertiary methoxy group in each pair. The absence of [MHR′OH]+ and MH+ ions in the isobutane CI mass spectra of 4‐t requires proton transfer from the primary OR′ to the tertiary OR group prior to the elimination of ROH, despite the large distance between them in the trans configuration. These results indicate isomerization of the fragmenting MH+ ions of 4‐t to structures which allow a facile proton transfer from the primary the tertiary alkoxyl. The similarity of the mass spectra of 4‐c and 4‐t suggests trans → cis isomerization, which may occur via an ion–neutral complex.
Tandem mass spectrometry of peptides. III—differentiation between leucine and isoleucine based on neutral losses
Authors: Squire Nicole L. , Beranová Šárka , Wesdemiotis Chrys 
Published: May 2005

AbstractThe neutral species generated during the collisionally activated dissociation (CAD) of the protonated dipeptides Ala–Leu, Ala–Ile, Leu–Ala and Ile–Ala are post‐ionized by collision and detected in neutral fragment‐reionization (+NfR+) mass spectra. These spectra are dominated by fragment ions diagnostic for the C‐terminal amino acid, as confirmed by comparison with reference collision‐induced dissociative ionization (CIDI) mass spectra of authentic Ala, Leu and Ile. CIDI of Leu and Ile yields distinct and structurally indicative products. These are also observed upon +NfR+ of [Ala–Leu]H+ and [Ala–Ile]H+, respectively, thus allowing one to deduce the correct sequence. In contrast, [Leu–Ala]H+ and [Ile–Ala]H+, which possess identical C‐termini, form no differentiating neutral losses upon CAD.
Selective enhancement of ion signal of charged surfactant in fast atom bombardment mass spectrometry
Authors: Chen Yu‐Chie , Shiea Jentaie 
Published: May 2005

AbstractThe addition of sodium dodecylsulfate (SDS) to a glycerol solution containing equal concentrations of a series of quaternary amines has been found to have a significant effect on the relative fast atom bombardment (FAB) response factors for each analyte. The relative FAB signals of quaternary amines with different alkly chain length were found to be either enhanced or degraded under different SDS concentrations. The effect observed can be correlated with the difference in the rate of ion‐pair precipitate formation between negatively charged dodecylsulfate and positively charged quaternary amine. It is also demonstrated that, in much the same way, SDS can be used to enhance the response of the less surface‐active component in an industrial dye by FAB analysis.
Origin of [M + H]+ ions in electron impact mass spectra of tertiary nitrosonitriles
Authors: Grela Karol , Konopski Leszek 
Published: May 2005

AbstractThe presence of [M + H]+ ions was observed in the electron impact mass spectra of the series of dimers of aliphatic tertiary β‐, γ‐ and δ‐nitrosonitriles. Neither M+· nor [M + H]+ ions are observed in the spectra of α‐nitrosonitriles or after introduction of voluminous substituents into the molecule, so the geometric factor is very important. It was found that this effect was probably due to the rearrangement of the hydrogen atom in the fragmentation pattern of the dimer molecular ions 2M+· of β‐ and δ‐nitrosonitriles. Aliphatic nitrosocompounds exist even in the gas phase in equilibrium with their dimers. The existence of dimers was confirmed by the presence of the [2M + H]+· ion in the liquid secondary ion mass spectrum of a γ‐nitrosonitrile. Using deuterium labelling, as distinct to the nitrosoketones and esters, it was unexpectedly found that the origin of hydrogen in the [M + H]+ ions was the methyl groups in the position vicinal to the tertiary nitroso group (CH3)2C(NO)R.
Stable isotope labelling and quantitative determination of enalaprilate in human plasma by GC–NICI–MS
Authors: Leis H. J. , Gleispach H. , Windischhofer W. 
Published: May 2005

AbstractA method for the quantitative determination of enalaprilate, the active metabolite of the angiotensin‐converting enzyme inhibitor enalapril, is presented. The asay is based on gas chromatography–negative ion chemical ionization–mass spectrometry. The preparation of 18O4‐labelled enalaprilate for use as an internal standard is described. The method involves solid phase extraction and derivation to the pentafluorobenzyl diester–trifluoroacetamide derivatives. The detection limit was found to be 0.5 pg, and a lower limit of quantitation was reached down to 40 pg ml−1 plasma. The method was applied to pharmacokinetics of the metabolite in humans.
Thermospray liquid chromatography–mass spectrometry of the DNA adducts formed between 2′‐deoxynucleosides and bisphenol A diglycidyl ether
Authors: Vanhoutte K. , Joos P. , Lemière F. , Van Dongen W. , Esmans E. L. , Claeys M. , Van den Eeckhout E. 
Published: May 2005

AbstractThe adducts formed between 2′‐deoxyadenosine (dAdo), 2′‐deoxycytidine (dCyd), 2′‐deoxycytidine (dUrd), 2′‐deoxyguanosine (dGuo) and bisphenol A diglycidyl ether (BPADGE) were analysed by high‐performance liquid chromatography (HPLC) and thermospray liquid chromatography–mass spectrometry. An HPLC method was developed using a 5RP8 select B column (125 × 4 mm i.d.) and a mobile phase of MeOH/0.1 M NH4OAc at a flow‐rate of 0.8 ml min−1. A sample enrichment procedure using solid phase extraction was developed and was found to result in an enrichment factor with a mean value of 9. Mono‐adducts were characterized by intense [BH + H]+, [BH + Na]+ and [S]+ ion signals. Imidazole ring opening was observed for the BPADGE/dGuo adduct indicating that the alkylation occurs at N‐7. The alkylation site in the BPADGE/dCyd adduct was assigned to N‐3 because a hydrolytic deamination reaction was observed leading to the BPADGE/dUrd adduct. Crosslinking was not observed.
Matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) of membrane proteins and non‐covalent complexes
Authors: Rosinke Burkhard , Strupat Kerstin , Hillenkamp Franz , Rosenbusch Jürg , Dencher Norbert , Krüger Ulrike , Galla Hans‐Joachim 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization (MALDI) mass spectra and methods to improve their quality are reported for three hydrophobic, membrane‐bound proteins: porin from Escherichia coli, bacteriorhodopsin from Halobacterium salinarium and cholesterolesterase from Pseudomonas fluorescens. Several commonly used UV and IR matrices have been tested. In addition, the susceptibility of MALDI mass spectrometry to various neutral and ionic detergents, known usually to degrade the quality of MALDI mass spectra, has been tested systematically. For porin, consisting of three identical non‐covalently bound subunits, a new sample preparation is reported, resulting in the desorption of the intact quaternary protein structure. This leads to a better understanding of the way a given analyte is embedded into the host matrix crystals.