bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simultaneous quantification of cyclosporin A and its major metabolites by time‐of‐flight secondary‐ion mass spectrometry and matrix‐assisted laser desorption/ionization mass spectrometry utilizing data analysis techniques: Comparison with high‐performance liquid chromatography
Authors: Muddiman David C. , Gusev Arkady I. , Karl‐Stoppek‐Langner  , Proctor Andrew , Hercules David M. , Tata Prasad , Venkataramanan Raman , Diven Warren 
Published: May 2005

AbstractSimultaneous quantification of cyclosporin A (CsA) and its major metabolite (AM1) in blood has been achieved using time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI/TOF‐MS). Previous investigations indicated that spectral interferences exist in the analysis of CsA blood samples by the above methods. In TOF‐SIMS, interference is caused by overlap of the Ag‐cationized internal standard, cyclosporin D (CsD), with the Ag‐cationized metabolite, AM1. To resolve this interference and obtain quantitative information, cross‐correlation analysis was applied to the TOF‐SIMS data. Application of damped non‐linear least squares curve‐fitting was carried out to resolve an interference in the MALDI/TOF‐MS data due to multiple cationization products (i.e. Na and K). Measurement of standard samples indicates that the minimum accuracy (95% confidence level) of the TOF‐SIMS method was better than 9% for CsA and 13% for AM1 using only one standard curve'. Similarly, the minimum accuracy of the MALDI/TOF‐MS method was determined to be 14% for CsA and better than 25% for AM1. Blood samples obtained from transplant patients receiving CsA were analyzed by polyclonal fluorescence polarization immunoassay, high‐performance liquid chromatography (HPLC), and by both TOF‐MS methods. Both TOF‐MS results for CsA and mono‐hydroxylated CsA are in good agreement with the HPLC results.
Electron capture negative chemical ionization mass spectrometry and tandem mass spectrometry analysis of β‐carotene, α‐tocopherol and their oxidation products
Authors: McClure Thomas D. , Liebler Daniel C. 
Published: May 2005

AbstractThe biological antioxidants α‐tocopherol, 1, and β‐carotene, 4, and products of their antioxidant reactions are potentially important indicators of biological antioxidant status and functions. Electron capture by compounds 1 and 4 and their oxidation products yields intense molecular anions with little fragmentation. Collision‐induced dissociation of the molecular anions was studied by linked‐scaning (B/E = constant) on a reverse‐geometry magnetic‐sector mass spectrometer. Both 1 and 4 and their products undergo extensive diagnostic cleavages of their hydrocarbon chains, apparently via charge‐remote fragmentation. Electron capture negative chemical ionization mass spectrometry appears uniquely suited to structure identification studies of antioxidants and their oxidation products. This methodology is used to identify oxidation products of 1 and 4 from a model biological membrane system subjected to peroxyl radical attack.
Liquid chromatography/fast atom bombardment and electrospray ionization mass spectrometry of gibberellin A3 1,2‐trans‐glycosyl esters
Authors: Schneider Gernot , Schmidt Jürgen , Moritz Thomas 
Published: May 2005

AbstractThe glucosyl ester (2b), the galactosyl ester (3b), the xylosyl ester (4b) and the arabinosyl ester (5b) of gibberellin A3 (GA3) as well as the glucosyl ester (7b) and the xylosyl ester (8b) of isoGA3 were synthesized and their structures confirmed especially by 1H nuclear magnetic resonance. In order to identify such conjugates in nature, the glycosyl esters 2b, 3b, 4b, 5b, 7b and 8b were subjected to mass spectrometry analysis using fast atom bombardment and electrospray ionization techniques. The spectra obtained from both negative and positive ions were compared and interpreted on the basis of tandem mass spectrometry experiments. The differences between the fragmentation of GA3 glycosyl ester and that of isoGA3 glucosyl ester are discussed. Diagnostic ions were evaluated, which should be useful for the identification of these conjugates by liquid chromatography/mass spectrometry.
Mass spectrometric and theoretical determination of polynuclear aromatic hydrocarbon proton affinities
Authors: Trouk‐Pointet Karine , Milliet Arielle , Renou‐Gonnord Marie‐France 
Published: May 2005

AbstractProton affinities (PAs) in the gas phase have been calculated for a series of polynuclear aromatic hydrocarbons by MOPAC 6.0 using AM1 and PM3 Hamiltonians and compared to the experimental values published in the literature. A correlation between PAs and the reactional competition leading to the respective formation of the molecular ion and the protonated molecular ion under ammonia positive‐ion chemical ionization (PICI) has been demonstrated. A method for estimating PAs from ion abundances in the ammonia PICI mass spectra is proposed.
Characterization of metabolites of Δ8,9‐dehydroestrone in dogs
Authors: Chandrasekaran A. , Osman M. , Raveendranath P. , Chan K. , Scatina J. A. , Sisenwine S. F. 
Published: May 2005

AbstractΔ8,9‐Dehydroestrone is the fifth most abundant component in the conjugated equine estrogen preparation Premarin®, representing about 2 to 6% of the total steroids in the tablet. The metabolism of this estrogen has been determined in female beagle dogs after acute peroral administration. 17β‐Dihydro‐Δ8,9‐dehydroestrone(17β‐Δ8,9‐dehydroestradiol) and 17α‐dihydro‐Δ8,9dehydroestrone(17α‐Δ8,9‐dehydroestradiol) have been identified as the major metabolites in plasma and urine. These metabolites, along with the unchanged drug, were isolated and purified by ether extraction and thin‐layer chromatography of the urine samples after enzyme hydrolysis. The trimethylsilyl ether derivatives of the isolated metabolites were characterized by comparison of their mass spectra and chromatographic properties with those of synthetic reference standards.
Special feature: Tutorial. Principles and instrumentation in time‐of‐flight mass spectrometry. Physical and instrumental concepts
Authors: Guilhaus Michael 
Published: May 2005

AbstractThe principles of time‐of‐flight mass spectrometry (TOFMS) are described with a view to understanding the strengths and weaknesses of this method of mass analysis in the context of current applications of mass spectrometry and the more familiar scanning instruments. Fundamental and instrumental factors affecting resolving power, sensitivity and speed are examined. Methods of gating ion populations and the special requirements in the detection and digitisation of the signals in the TOFMS experiment are discussed.
The role of the CC double bond in alcohol elimination from MH+ ions of unsaturated bicyclic esters upon chemical ionization
Authors: Khaselev N. , Mandelbaum A. 
Published: May 2005

AbstractMethyl and ethyl endo‐ and exo‐bicyclo [2.2.2] oct‐5‐ene‐2‐carboxylates exhibit different mass spectral behaviour under i‐Bu‐chemical ionization (CI) conditions and upon collision‐induced dissociation (CID) of their MH+ IONS. The endo‐esters exhibit m/z 135 [MH  MeOH]+ and [MH  EtOH]+ ions, which are absent in the i‐Bu‐CI mass spectra of the exo‐isomers. This stereospecific behavior is explained in terms of the proton bridging requirement in the alcohol elimination from MH+ ions of esters. Such proton bridging between the alkoxycarbonyl group and the double bond is possible in the endo‐esters, but not in the exo‐isomers. Hydrogen‐deuterium exchange processes, observed in the CID spectra of the MD+ ion of the endo‐esters, support the proposed mechanistic pathway. Hydrogen bridging with the double bond also plays a role in the alcohol elimination processes of stereoisomeric bicyclo [2.2.2] oct‐5‐ene‐2,3‐dicarboxylates.
Energy resolved mass spectrometry of diethyl alkyl phosphonates with an atmospheric pressure ionization tandem mass spectrometer
Authors: Wensing Michael W. , Snyder A. Peter , Harden Charles S. 
Published: May 2005

AbstractEnergy resolved mass spectrometry (ERMS) was used to characterize the dissociation processes of four diethyl alkyl phosphonates where the alkyl R group attached to the central phosphorus atom ranged from methyl to n‐butyl. An atmospheric pressure ionization triple quadrupole mass spectrometer was used in the analyses. Dissociation of the MH+ and further dissociation of the resulting progeny ions was induced between the atmospheric—vacuum sampling orifice and the first ion focusing RF‐only quadrupole, Q0, instead of the central Q2 quadrupole. The major dissociation pathways of the four phosphonates could be characterized by two sequential McLafferty rearrangements yielding an alkyl phosphonic acid. This acid further dissociated losing H2O followed by ROH to produce PO+, or the same process occurred but in the reverse order, i.e. first losing ROH followed by H2O to yield PO+. The latter process was the energetically favored process. The alkyl group attached to the phosphorus atom of the protonated alkyl phosphonic acid was observed to have a significant influence on the stability of the protonated alkyl phosphonic acid. As the R group increased in size with a concomitant increase in electron‐donating power, the alkyl phosphonic acid was less prone to dissociation than other alkyl phosphonic acids which possessed smaller R groups. A significant difference was also noted in the alkyl phosphonic acid dissociation processes; methyl phosphonic acid dissociated predominantly via H2O loss unlike the other acids which favored the loss of ROH over H2O.
Liquid chromatography–electrospray tandem mass spectrometry of dansylated polyamines and basic amino acids
Authors: Feistner Gottfried J. 
Published: May 2005

AbstractLiquid chromatogrpahy‐electrospray tandem mass spectrometry allows identification of dansylated basic amino acids and polyamines with a high degree of specificity, including unambiguous acid and 2 hydroxycadaverine, and N1‐ and N8‐acetylspermidine. In favorable cases, characteristic fragmentation mechanisms permit identification even in the absence of authentic reference compounds. The method readily identified acetyldiaminopropane, citrul‐line, and diacetylspermine as metabolic products of Erwinia amylovora.
The isomers of ionized dimethyl sulfoxide (C2H6OS+·) and their CH3OS+ fragments. An ab initio and multiple‐stage mass spectrometric (MSn) study
Authors: Gozzo Fábio Cesar , Eberlin Marcos N. 
Published: May 2005

AbstractThe relative stabilities, isomerizations and dissociations of ionized dimethyl sulfoxide (DMSO), its three C2H6OS+· isomers and of all their 14 conceivable CH3OS+ fragments (1–14), have been investigated by ab initio calculations at the MP2/6–31G(d,p)//6–31G(d,p) + ZPE and G2 levels of theory, and by multiple‐stage two‐ and three‐dimensional mass spectrometry performed in a pentaquadrupole instrument. The ab initio relative energies of the isomers, their connecting transition states, and their dissociation thresholds were used to elaborate potential energy surface diagrams that precisely corroborate and unify several previously divergent experimental observations on these systems. The most kinetically favorable isomerization of (CH3)2SO+· (I) to its aci‐form CH2S(OH)CH (II) displays a transition state considerably lower in energy than the threshold for its direct dissociation by CH3⋅ loss. Therefore, low‐energy, long‐lived metastable ions I are predicted to isomerize to II, and to dissociate in turn to CH2S+OH (2) upon CH3⋅ loss. Ions I excited a few electronvolts above the threshold are, on the other hand, predicted to dissociate directly to CH3S+O (1). Isomerization of I to the most stable C2H6OS+· ion, that is CH3SOCH (III), displays the most energetic transition state and should be negligible, whereas III is predicted to dissociate by CH3⋅ loss preferentially to 1 rather than 5 (CH3OS+). Nine CH3OS+ isomers, that is 1, 2, (HCS…OH2)+ (3), +CH2S(O)H (4), 5, HC(SH)OH+ (9), CH2OSH+ (10), CH2+OSH (11), and (HCO…SH2)+ (14), were found as true minima on the RHF/6–31G(d,p) potential‐energy surface, and some of their isomerization barriers and dissociation thresholds were estimated. Tandem and multiple‐stage (MS3) mass spectrometric experiments show that non‐dissociating DMSO+· ions produce, upon collision‐induced dissociation (CID), a mixture of approximately 40% of 1 and 60% of 2, whereas the CID chemistry of 1 and 2 is affected considerably by the collision energies employed. Both the experimental and theoretical results on 1 and 2 allow a detailed interpretation of their complex dissociation chemistry, which clarifies the nature of most of their indirect fragments. Such fragments are proposed to be formed via the common isomerization/dissociation sequences 1 → 2 → 9 ⇌ 3 → HCS+ (m/z 45) + H2O, and 1 → 2 → [7, HOCH2S+] → S + CH2OH+ (m/z 31). These processes are favored at lower collision energies, whereas direct dissociation of 1 to CH3+ (m/z 15) and SO+· (m/z 48), and of 2 to CH2S+· (m/z 46) occurs to greater extents at higher collision energies.
A method for counting disulfide bridges in small proteins by reduction with mercaptoethanol and electrospray mass spectrometry
Authors: Svoboda M. , Meister W. , Vetter W. 
Published: May 2005

AbstractA simple and rapid method for counting the number of internal disulfide bridges in a protein by incubation with 2‐mercaptoethanol and electrospray mass spectrometry analysis of the products was developed. 2‐Mercaptoethanol yields intermediate mixed disulfides during reduction of a protein. This results in a molecular weight increase of the protein by 78 Da per disulfide bond, which can easily be determined by electrospray mass spectrometry (ESMS). The number of mercaptoethanol adducts observed by ESMS reveals the number of disulfide bridges in the peptide or protein. Since the protein–mercaptoethanol–disulfide bonds are themselves further reduced by excess mercaptoethanol, the course of the reaction has to be followed in order to detect the maximum number of intermediates. Owing to the volatility of mercaptoethanol, samples can be taken out of the reaction solution for MS analysis without prior purification. Successful experiments were carried out using proteins with one, two, four or six SS‐bonds, covering a mass range from about 1 to over 23 kDa.
Electron impact ionization and fast atom bombardment mass spectrometry of some 3,3‐dimethyl‐1‐(isoxazol‐3‐yl)triazenes, a new class of potential anticancer agents
Authors: Orsatti Laura , Seraglia Roberta , Traldi Pietro , Diamantini Giuseppe , Tarzia Giorgio , Tontini Andrea 
Published: May 2005

AbstractA series of 3,3‐dimethyl‐1‐(isoxazol‐3‐yl)triazenes, potential anticancer agents, were studied by electron impact (EI) ionization and fast atom bombardment mass spectrometry. Their behaviour was compared with that of dacarbazine, 5‐(3,3‐dimethyl‐1‐triazenyl)‐(1H)‐imidazole‐4‐carboxamide, which is employed in the treatment of several neoplastic conditions. An interesting EI‐generated decomposition pathway was observed, consisting in the primary formation of [NH2CH3]+ cations, involved in the metabolic pathway of triazenes, as the alkylating agent responsible for the anticancer properties of the drug. A higher thermodynamic stability of the examined compounds than decarbazine was observed, which reasonably reflects the higher chemical stability.
Negative‐ion mass spectrometry of sulfonylurea herbicides
Authors: Winnik Witold , Brumley William , Betowski Leon 
Published: May 2005

AbstractSulfonylurea herbicides have been studied using negative‐ion desorption chemical ionization (DCI) mass spectrometry (MS) and DCI‐MS/MS techniques. Both [M  H]− and M−· ions were observed in the DCI mass spectra. The collisionally activated dissociation (CAD) spectra were characteristic of the structure of the herbicides examined. The fragmentation pattern was established based on the tandem mass spectra of the in situ deuterated sulfonylureas and on the comparison of the CAD spectra of sulfonylurea fragment ions with the CAD spectra of the ions derived from saccharin (o‐benzoic sulfimide) and methyl 2‐(aminosulfonyl)benzoate.
Investigation of doubly charged organic cations by electrospray ion cyclotron resonance mass spectrometry
Authors: Katritzky Alan R. , Shipkova Petia A. , Burton Richard D. , Allin Steven M. , Watson Clifford H. , Eyler John R. 
Published: May 2005

AbstractThe production and detection of doubly charged organic cations were studied using a previously unreported approach—electrospray ionization coupled with Fourier transform ion cyclotron resonance mass spectrometry. Owing to its ultra‐high mass resolution, accurate and stable mass calibration, multiple stages of collisionally activated dissociation (CAD) allowing tandem mass spectrometry and extremely long ion storage times (> 1 min), this technique has proven to be a powerful method for the detection and study of doubly charged organic compounds. CAD studies were used for the identification of ion–molecule reactions and for the investigation of the propensity towards gas‐phase SN1 and SN2 reaction pathways. To date exclusively SN1‐type reactions in the gas phase have been detected. Three doubly charged pyridinium salts were chosen as model compounds for this study.
A micromethod for the measurement of deuterium bound to carbon‐6 of glucose to quantify gluconeogenesis in vivo
Authors: Kalhan Satish C. , Trivedi Roopa , Singh Sheila , Chandramouli Visvanathan , Schumann William C. , Landau Bernard R. 
Published: May 2005

AbstractA method to measure the enrichment of deuterium in the hydrogens bound to C‐6 of glucose has been refined and taken to the micro‐scale. Glucose (≤0.2 mg) in small quantities of plasma samples is oxidized with sodium periodate. The formaldehyde formed contains the two hydrogens bound to C‐6 of glucose. The formaldehyde is condensed with ammonia to form hexamethylenetetramine (HMT), which can be directly determined by gas chromatography/mass spectrometry. All of the 12 hydrogens of HMT are from the formaldehyde and therefore deuterium enrichment as low as 0.1% on hydrogens bound to C‐6 of glucose can be measured with a coefficient of variation of less than 3%. The method can be used to quantify gluconeogenesis in vivo in humans by administering [2H2]O at an enrichment in total body water of only 0.5%, resulting in reproducibly measurable labeling of the hydrogens bound to C‐6 of glucose. The method is presented because of its potential value for the measurement of gluconeogenesis in humans in vivo at safe and acceptable doses of [2H2]O.
Linearized dipolar excitation and detection and quadrupolarized axialization in a cylindrical ion cyclotron resonance ion trap
Authors: Guan Shenheng , Huang Yulin , Marshall Alan G. 
Published: May 2005

AbstractAlthough cylindrical Penning ion traps are commonly used in atomic physics and in Fourier transform ion cyclotron resonance mass spectrometry (FT‐ICRMS or FTMS), such traps offer far from ideal dipolar excitation/detection and azimuthal quadrupolar axialization performance. Here it is shown that by applying r.f. voltages of just two (± V0) or three (0, ± V0) different amplitudes to appropriately spaced electrode segments, a cylindrical trap can produce nearly linear dipolar excitation/detection and nearly azimuthal quadrupolar excitation for ion axialization. Moreover, voltages are applied directly, rather than through a complex resistive or capacitive voltage dividing network as in prior designs. Advantages of the present design are confirmed by potential simulations and signal harmonic analysis.
Isolation and mass spectrometric characterization of an oxidized form of vasostatin I, an N‐terminal chromogranin A‐derived protein, from bovine chromaffin cells
Authors: Dillen L. , Zhang X. Y. , Claeys M. , Liang F. , De Potter W. P. , Van Dongen W. , Esmans E. L. 
Published: May 2005

AbstractAn N‐terminal proteolytic processing product of chromogranin A was obtained from bovine chromaffin granules using two steps of C18 solid‐phase extraction and reversed‐phase high‐performance liquid chromatography. Electrospray mass spectrometry revealed a protein with a molecular mass of 8632.0 for the fraction showing immunoreactivity against the N‐terminus of chromogranin A, which differed by 48 u from that of the N‐terminal processing product, vasostatin I (CGA1−76). Derivatization with mercaptoethanol showed that the peptide had an intact SS bridge, which is a key structural feature of vasostatin I. Peptide mapping experiments involving reduction/alkylation with vinylpyridine and trypsin digestion were consistent with oxidation of the three methionine residues of vasostatin I to their sulphoxide forms. The oxidation of the methionine residues was found to occur during the C18 solid‐phase extraction procedure. The use of freshly prepared Tris–HCl buffer and eluents and flushing the buffer and eluents with nitrogen were shown to result in the isolation of the non‐oxidized form of vasostatin I.
Gas‐phase complexes of amino acids with Cu(II) and diimine ligands. Part I. Aliphatic and aromatic amino acids
Authors: Gatlin Christine L. , Tureček František , Vaisar Tomáš 
Published: May 2005

AbstractGas‐phase complexes of Cu(II) with aliphatic and aromatic α‐amino acids (AA) and diimine ligands, 2,2′‐bipyridyl (bpy) and phenanthroline (phen) are obtained by electrospray ionization of their aqueous‐methanol solutions. The amino acids are found to bind to Cu(II) by their COO− and amino groups in the gas‐phase complexes. The [Cu(II)(AA – H)(bpy)]+· complexes (M+·) show distinct dissociations upon collisional activation. Decarboxylation produces stable (M – CO2)+· ions containing α‐amino alkyl residues coordinated to copper. Further dissociations of radicals derived from aliphatic amino acids involve fission of the CβCγ bond in the alkyl chain that reveals its branching. Leucine and isoleucine are readily distinguished by their different dissociation products. Complexes of aromatic amino acids undergo facile amine group transfer on to copper. Electron distributions in several copper complexes were obtained by ab initio calculations and used to discuss the dissociation products formed from gas‐phase [Cu(II)(AA – H)(bpy)]+· ions.
Gas‐phase complexes of amino acids with Cu(II) and diimine ligands. Part II. Amino acids with O, N and S functional groups in the side‐chain
Authors: Gatlin Christine L. , Tureček Frantiček , Vaisar Tomáš 
Published: May 2005

AbstractTernary complexes of amino acids, Cu(II) and diimine ligand 2,2′‐bipyridyl (bpy) are obtained in the gas phase by electrospray ionization (ESI). The amino acids are found to bind to Cu(II) by their deprotonated carboxylate groups in the gas‐phase complexes. Collisionally activated dissociations at low ion kinetic energies of the [Cu(II)(AA – H)(bpy)]+· complexes show decarboxylation followed by cleavages of the amino acid side‐chains that reveal interactions with the Cu atom of the side‐chain functional groups. Hydroxy, sulfide and disulfide groups are transferred on to the Cu atom following collisional activation, but do not displace the bpy ligand. The side‐chain functional groups and the CβH2CαHNH2 fragment are found to compete for coordination to Cu(bpy)+ in the products. The ε‐amino group in lysine and the guanidyl group in arginine displace the bpy ligand following decarboxylation. The fragmentations of the gas‐phase [Cu(II)(AA – H)(bpy)]+· complexes are highly specific for the amino acid residues. Arginine and lysine also form doubly charged ions by ESI that distinguish lysine from the isobaric glutamine.