bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mass spectrometry of DNA mixtures by laser ablation from frozen aqueous solution
Authors: Schieltz David M. , Chou Chau‐Wen , Luo Cong‐Wen , Thomas Robert M. , Williams Peter , Becker C. H. 
Published: May 2005

AbstractWe report time‐of‐fight mass spectra of test mixtures of six single‐stranded DNA segments. The segments range in size from 8 to 60 nucleotides (molecular weight range 2413 to 18 602 Da). The best mass spectra were obtained by pulsed laser ablation of thin frozen films of an aqueous solution of the mixture from an oxidized copper substrate. These mass spectra are dominated by the molecular‐ion peak for each DNA segment, and show little evidence of fragmentation, peak broadening or cluster formation. In contrast, mass spectra obtained using UV laser ablation from an anthranilic acid matrix yield broad peaks with evidence of fragmentation, and DNA segments longer than 26 nucleotides are difficult to detect.
Thermospray high‐performance liquid chromatography/mass spectrometric determination of cyclosporins
Authors: Abián J. , Stone A. , Morrow M. G. , Creer M. H. , Fink L. M. , Lay J. O. 
Published: May 2005

AbstractThe cylic undecapeptides cyclosporin (Csp) A, CspD and dihydro CspC (HCspC) were analyzed by high‐performance liquid chromatography/thermospray‐mass spectrometry (HPLC/TSP‐MS) on line with 1–2 pmol injected on column. Mass spectra were characterized by signals corresponding to the [M + H]+ ion as well as fragment ions derived from he loss of 112 (CspA and CspD) or 44, 114 and 114+44 (HCspC) mass units from the parent ion. The same qualitative profile was observed for negative‐ion acquisition where the ions were formed by proton abstraction. The application of the technique to the characterization of CspA and its major hydroxylated and dealkylated metabolites in human blood samples is presented.
Opimizing signal and mass resolution for matrix‐assisted laser desorption utilizing a linear time‐of‐flight mass spectrometer
Authors: Brown R. S. , Glfrich N. L. 
Published: May 2005

AbstractResults are oresented for various instrumental configurations employed for matrix‐assisted laser desorption mass spectrometry. Mass resolution is determined for a linear time‐of‐flight mass spectrometer for various lengths of the field‐free region. A wire ion guide is utilized and is shown to improve ion transport efficiencies for longer field‐free regions. It is also determined experimentally that a modest mass resolution increase is often obtained in configurations employing the wire ion guide when compared to the mass resolution obtained with the same geometr without the wire ion guide. Optimal applied potentials are determined for the wire ion guide. No mass dependence on the opitmal applied potential (−100 V) for the wire ion guide is observed for samples of equine myoglobin (MW 16 951.5 Da) and a bacterial protease (MW 27 228.4 Da). The optimal applied voltage was also found to b identical (−100 V) for the singly through quadruply charged molecular ion species of rabbit gamma globulin (MW ≈︁ 150 000 Da). It is shown that a 2 m flight tube with a wire ion guide provides better signal‐to‐noise mass spectra than a 1 m flight tube without the wire ion guide and can more than double the mass resolution obtainable. Utilization obtainable. Utilization of a 4 m flight tube gives minimal mass resolution enhancement at the expense of signal‐to‐noise.
Investigation of some β‐lactam antibiotics by means of 2–35 keV cesium ion bombardment
Authors: Hamdan M. , Curcuruto O. , Tarzia G. , Harris F. M. 
Published: May 2005

AbstractA number of commercial β‐lactam antibiotics are investigated by means of cesium ion (Cs+) bombardment in the kinetic energy range 2–35 keV. The relative intensities of the protonated molecules, as well as some of the major fragment ions, are monitored as a function of the Cs+ kinetic energy. The dependence of the intact protonated molecule:fragment ion ratios on the primary‐ion kinetic energy is evident in some of the spectra investigated. An attempt is made to interpret these results in terms of existing secondary‐ion mass spectrometry data which have been obtained in a different kinetic energy range.
Matrix‐assisted laser desorption/ionization inside a quadrupole ion‐trap detector cell
Authors: Doroshenko Vladimikr M. , Cornish Timothy J. , Cotter Robert J. , Ross Mark M. 
Published: May 2005

AbstractAn ion‐trap detector has been modified for matrix‐assisted laser desorption/ionization using a pulsed frequency‐quadrupled Nd: YAG laser and extended mass range up to 3300 u using the resonant‐rejection mode of operation. The matric‐assisted laser desorption/ionization mass spectra of a number of peptides are reported, and the effects due to the synchronization of the laser pulses and the phase of the RF voltage applied to the ring electrode are described.
Cyclic boronates in the mass spectrometry of ecdysteroids
Authors: Vaisar Tomáš , Píš Jaroslav 
Published: May 2005

AbstractFor the structural elucidation of ecdysteroids a reaction with phenylboronic acid has been employed. This reaction takes place exclusively on the C20,C22 diol moiety, thus facilitating fast and easy detection of this moiety in the molecule od ecdysteroid. This derivatization also redirects fragmentation to C17/C20 bond cleavage with charge retention on both fragments enabling assessment of the structure both of the steroid nucleus and of the side‐chain. Possible reaction of phenylboronic acid with the diol moiety of the glycosyl group of the glycoside od ecdysteroid, producing di‐adduct, is demonstrated; participation of the 5β‐hydroxy group of 5β,20‐dihydroxyecdysone in the formation of such a di‐adduct is discussed; and the role of theenol form of the 6‐carbonyl group is proved.
Laser mass spectrometry of polydeoxyribothymidylic acid mixtures
Authors: Tang K. , Allman S. L. , Jones R. B. , Chen C. H. , Araghi S. 
Published: May 2005

AbstractMatrix‐assisted laser desorption/ionization mass spectrometry has been used to mass analyze synthetic oligomers of poly‐T ranging in size from 20 to 100 nucleotides. Both positively‐ and negatively‐charged parent molecular ions were observed.
Mass spectral fragmentation processes in nitronaphthalenes. A study using tandem mass spectrometry and collision‐induced dissociation
Authors: Yinon Jehuda 
Published: May 2005

AbstractMass spectral fragmentation processes and pathways of a series of nitro, dinitro and trinitro derivatives of naphthalene have been studied. Collision‐induced dissociation mass spectra were obtained using a tandem BB mass spectrometer. Major fragmentation pathways included loss of NO2 from the molecular ion, followed by loss of NO and/or CO. Additional fragmentations included loss of OH from the molecular ion ion some of the compounds investigated.
Dimerization of the ketene cation radical in the gas phase
Authors: Dass Chhabil 
Published: May 2005

AbstractThe dimerization of the ketene cation radical was investigated by using tandem mass spectrometry. Ketene was ionized by low‐energy charge‐exchange with CS· reagent ions. The high‐pressure environment in the ion source permits collisional stabilization of the ion/molecule adduct, which was characterized by obtaining its collisionally activated dissociation (CAD) mass spectrum. Comparison with the CAD spectrum of diketene+· revealed that the structure of the adduct is identical with that of the ionized diketene species. The singly occupied molecular orbital‐lowest unoccupied molecular orbital (SOMO‐LUMO) interaction was invoked to explain the formation of the ion/molecule adduct.
New methods for computational ion structure evaluation by means of tandem mass spectrometry
Authors: Hayek Erich W. H. , Stanek Wolfgang , Krenmayr Peter 
Published: May 2005

AbstractNew methods are presented for the evaluation of ion structures and fragmentation pathways using tandem mass spectrometry (MS/MS) with low energy collision‐induced dissociation. As an aid for mass spectroscopists, they incorporate a PC software package (named PDNL, written in Turbo‐PASCAL 5.5 (Borland), running under DOS (Microsoft) with mouse‐control). A database of almost 300 low energy MS/MS spetra is available for library searches. It utilizes a new, intensity‐based matching algorithm fitting to the demand of MS/MS data. Computational methods have been developed for (i) the separation of the spectra of unresolved isobaric ions and evaluation of the ratio of the ion abundances, (ii) the evaluation of single‐collision spectra using the multi‐collisional data map, and (iii) the elucidation of collision‐induced dissociation fragmentation pathways. Principal component analyses of sets of at least eight MS/MS spectra were used for a quick comparison of these spectra and for a summary of inter‐ion relationships.
The elusive HNCOH+ ion characterized by a double‐collision experiment in the mass spectrometer
Authors: McGibbon Graham A. , Terlouw Johan K. , Burgers Peter C. 
Published: May 2005

AbstractPrevious studies have shown that the gas‐phase protonation of isocyanic acid, HNCO, exclusively yields the N‐protonated ion, the aminoformylium ion, H2NCO+, 1, which is thermodynamically the most stable [H2, C, N, O]isomer. In the present paper it is shown that the O‐protonated species, the elusive isoformylaminylium ion, HNCOH+, 2, can be generated by successive degradation of ionized N‐methyl‐O‐methylcarbamate in a 3‐stage tandem (MS/MS/MS) type experiment: CH3NHC(O)OCH· → CH3NHCOH+· → HNCOH+· The species is identified from its characteristic collisional activation (CA) mass spectrum. From a comparison of the CA mass spectra of the2H‐labelled isotopomers DNCOH+ and HNCOD+ with that of the isomeric ion HDNCO+ it follows that collisionally excited ions (>400 kJ/mol) of 2 may isomerize into 1.
Differentiation of anomeric glycosyl azides using mass spectrometric methods
Authors: Kralj B. , Kramer V. , Žigon D. , Kobe J. , Štimac A. 
Published: May 2005

AbstractElectron ionization (EI), chemical ionization and mass‐analysed ion kinetic energy (MIKE) spectra have been applied with the aim of obtaining an unambiguous differentiation between the anomeric 2,3‐O‐isopropylidene α‐and β‐D‐ribofuranosyl azide derivatives. The MIKE spectra of their metastable [M  CH3]+ ions, originating from EI, showed a decomposition pattern allowing distinction between the anomers. The origin of the ions in the EI mass spectra, supported by examination of the deuterium‐labelled derivatives, makes it possible to identify the actual azido group orientation in a particular anomer.
Negative‐ion fast‐atom bombardment tandem mass spectrometry for the structural study of polyether compounds: Structural verification of yessotoxin
Authors: Naoki Hideo , Murata Michio , Yasumoto Takeshi 
Published: May 2005

AbstractWe have examined the applicability of tandem mass spectrometry to the structural elucidation of polyether compounds. The polyether toxin named yessotoxin was isolated from scallops which were implicated in food poisoning. The toxin consists of fused polycyclic ethers as does ciguatoxin, and bears two sulfate esters in the molecule. The negative‐ion fast‐atom bombardment tandem mass spectrum of the toxin showed a series of ions due to fragmentation at positions characteristic of cyclic ethers. With the mass spectrometric data alone, we succeeded in assigning the number and location of eleven ether rings in yessotoxin, which agreed with those previously deduced by nuclear magnetic resonance studies.
A model for peak shape in slow‐scan‐rate quadrupole ion trap mass spectronnetry
Authors: Amster I. Jonathan 
Published: May 2005

AbstractThe results of calculations are presented that address the effect of the scan rate on peak shape and position for slow‐scan‐irate detection in the quedrupole ion trap. The calculations are based on a model for signal detection that account for the change in the number of ions in the trap as the ejection field sweeps across a peak. The calculations predict that reduced scan rates lead to peak narrowing, peak asymmetry, and a shift in the apparent mass in the in resulting mass spectrum.
In situ reduction suitable for matrix‐assisted laser desorption/ionization and liquid secondary ionization using tris(2‐carboxyethyl)phosphine
Authors: Fischer Wolfgang H. , Rivier Jean E. , Craig A. Grey 
Published: May 2005

AbstractThe suitability of the hydrochloride salt of tris(2‐carboxyethyl)phosphine (TCEP) for in situ reduction with matrix‐assisted laser desorption/ionization (MALDI) and liquid secondary ionization (LSI) mass spectrometry is evaluated. TCEP can be used to irreversibly reduce organic disulfldes to thiols in water and is active at an acidic pH. We found that TCEP was suitable for partial reduction of bovine insulin deposited on the target and mixed with either sinapinic acid in MALDI or glycerol and m‐nitrobenzyl alcohol in LSIMS. When TCEP was added to insulin deposited on the target without prior mixing of sinapinic acid the in situ MALDI protocol resulted in almost complete reduction.
Sequeince‐ion studies in peptides: The generation of C″ ions
Authors: van Dongen W. D. , de Koster C. G. , Heerma W. , Haverkamp J. 
Published: May 2005

AbstractThe mechanism for the formation of C″‐type ions from protonated peptides, produced under conditions of fast‐atom bombardment and rollisional activation was investigated. Comparison of the tandem mass spectra of the [M + H]+ ions of a model peptide and the corresponding [Md + D]+ ions, in which all exchangeable hydrogens are replaced with deuterium, revealed that neither the carboxylic hydrogen not a hydrogen from a nitrogen atom is involved in the process of migration of a hydrogen which leads to the formation of Cn″‐type ions. The most feasible position from which the transferred hydrogen originates is that at the first C‐atom in the side‐chain of the adjacent ainino acid.
Translational energy spectroscopy. I. Theory and practical considerations
Authors: Enos Christopher S. , Brenton A. Gareth 
Published: May 2005

AbstractNon‐dissociative collision processes are classified and the accepted notation is given. The basic kinematics of binary collisions are derived and practical considerations based on Massey's adiabatic criterion together with the effects of pressure and temperature are discussed. A general description of instrumental developments and the performance achieved are given and the predictions of the Wigner spin conservation rule as regards the spectroscopic states of the products are summarized.
Analysis of cyclic nucleotide‐related enzymes by continuous‐flow fast‐atom bombardment mass spectrometry
Authors: Langridge James I. , Brenton A. Gareth , Walton Terence J. , Harris Frank M. , Newton Russell P. 
Published: May 2005

AbstractContinuous‐flow fast‐atom bombardment mass Spectrometry has been developed to directly monitor cyclic nucleotide (substrate) and its product levels from an on‐going phosphodiesterase reaction. Analysis of cAMP and cCMP phosphodiesterase incubates have been performed where the temporal evolution of the enzymic reaction is monitored and the effect of enzyme concentration upon the rate of reaction determined. Quantitative data on the enzyme kinetics have been obtained, in the form of Lineweaver‐Burke plots, that are shown to correlate well with well‐established radiometric methods.
Applications of electrospray mass spectrometry to studies on the structural properties of ribonuclease A and ribonuclease B
Authors: Camilleri P. , Haskins N. J. , Rudd P. M. , Saunders M. R. 
Published: May 2005

AbstractDeuterium‐exchange experiments were performed on ribonuclease A (RNase A) and its glycosylated form, ribonuclease B (RNase B), using electrospray ionization mass spectrometry. The number of exchangeable protons was found to be similar for both forms of the enzyme, indicating that the oligosaccharide moiety on RNase B does not exert any influence on protein conformation. Four main glycoform populations were identified in RNase B, each of which was homogeneous and associated with one phosphate group. Spectra for RNase A were heterogeneous due to the presence of 0–3 phosphate groups bound to the enzyme.
The collision‐induced fragmentations of deprotonated allyl alcohol and its monomethyl derivatives
Authors: Dua Suresh , Bowie John H. , Hayes Roger N. 
Published: May 2005

AbstractDeprotonated allyl alcohol undergoes collision‐induced losses of H2, CH2O and C2H4 with minor hydrogen randomization occurring prior to or during these dissociations. A further fragmentation involves loss of methane: labelling studies (with CH2CHCD2O−) suggest that this loss is preceded by the equilibration CH2CHCD2O− ⇌ CD2CHCH2O−. The methyl homologues of allyl alcohol form isomeric C3H ions: the charge reversal spectra of these isomers confirm that CH2CHCH, CH2C̄CMe and HC̄CHMe are separate species, and also suggest that all three of the corresponding positive ions are formed on the charge‐reversal time‐scale.
Differentiation between selected pairs of tripeptide diastereomers by tandem mass spectrometry on a hybrid tandem mass spectrometer
Authors: Schwartz Brenda L. , McClain Robert D. , Erickson Bruce W. , Bursey Maurice M. 
Published: May 2005

AbstractLow‐energy collisionally activated decomposition (CAD) and unimolecular decomposition of the [M + H]+ ions for X‐L‐Pro‐L‐Phe, where X is L‐Ala, D‐Ala, L‐Asp, or D‐Asp, allow easy differentiation between the LLL and DLL diastereomers. Tandem mass spectrometric (MS/MS) studies of the [M + H]+ ions formed by fast‐atom bombardment (FAB) at various ion kinetic energies (Elab values) on a hybrid tandem instrument produced ions of different intensities for the diastereomers. The ratio of NH3 to H2O loss is 0.3 for the L‐Ala peptide but 1.7 for the D‐Ala isomer at 5 eV. In some L‐Ala spectra, the [M + H − NH3]+ ion does not appear at all. The y2 ion is up to twice as abundant in the L‐Ala spectra as in the D‐Ala, while the b2 ion is somewhat more abundant for CAD of the D‐Ala peptide for most collision energies investigated. The D‐Asp peptide produces a b2 ion that is more than half‐again as abundant as in the case of the L‐Asp isomer, and an [M + H − H2O]+ ion that is up to twice as abundant in the D‐Asp CAD spectra as in those of the L‐Asp. The y1, a2, and phenylalanine immonium ions are each up to twice as abundant in the L‐Asp spectra as in those of the D‐Asp isomer. The major differences are correlated with force‐field calculations on hydrogen‐bonded tautomers.
Detection and characterization of fumonisin mycotoxins as their methyl esters by liquid chromatography/particle‐beam mass spectrometry
Authors: Young J. Christopher , Lafontaine Pierre 
Published: May 2005

AbstractThe diazomethane‐derived tetramethyl esters of fumonisins can be introduced readily into mass spectrometers using flow injection analysis or liquid chromatography (LC) via a particle‐beam interface to yield chemical ionization and electron‐ionization spectra. The esters of fumonisins B1, B2, and B3 were well resolved on a C18 reversed‐phase column when eluted with a gradient of water + methanol + acetonitrile in the presence of 0.05% trifluoroacetic acid. Enhancement of analyte transport through the particle‐beam interface to afford increased ion abundances was achieved by addition of carriers. Polyfunctional amino acid carriers, such as L‐glutamic acid or L‐serine, effected at least 100‐fold increases in sensitivity. In the LC mode, post‐column addition of aqueous L‐serine was the most advantageous because background interference was limited to lower masses, and because of higher solubility, and ease of cleaning.
Determination of saxitoxin by liquid chromatography/thermospray–mass spectrometry
Authors: Wils E. R. J. , Hulst A. G. 
Published: May 2005

AbstractThe determination of the paralytic shellfish poison saxitoxin by liquid chromatography/thermospray‐mass spectrometry (LC/TS‐MS) was investigated. It was found that a commercial sample contained an impurity, which was identified as the plasticizer tris(2‐butoxyethyl) phosphate. Spraying of saxitoxin in acid solution at pH 2 led to a useful TS mass spectrum, containing some fragment ions in addition to the protonated molecule. Using pentafluoropropionic acid as a counter‐ion, saxitoxin could be determined by LC/TS‐MS on a C18 re versed‐phase column. By injecting the relatively large volume of 1 mL, a concentration of 30 ng/mL could be measured.
Electron ionization‐tandem mass spectrometry of glycosphingolipids. Part II. The identification of a carbohydrate sequence corresponding to a novel repetitive blood group a heptaglycosylceramide
Authors: Holgersson Jan , Curtis Jonathan M. , Morris Michael R. , Teller Lee W. , Derrick Peter J. , Samuelsson Bo E. 
Published: May 2005

AbstractIn a previous paper, the presence in human kidney vein tissue of a novel blood group A heptaglycosylceramide based on the type‐3 carbohydrate chain GalNAcαl‐3(Fucαl‐2)Galα1‐3GalNAcαl‐3(Fucα1‐2)Galβl‐4Glcβl‐1 Ceramide, was suggested based on thin‐layer immunostaining and electron ionization mass Spectrometry. Ions corresponding lo a structure containing two deoxyhexoses, two hexosamines and three hexoses were identified, but no information was obtained from mass spectrometry concerning the carbohydrate sequence5. In the present paper, we report the identification of carbohydrate sequence ions corresponding to a type‐3 chain A heptaglyco‐sylceramide by electron ionization‐tandem mass spectrometry of a permethylated‐reduced glycosphingolipid mixture isolated from human kidney vein tissue. The use of a microchannel‐plate‐array detector increased the sensitivity for collision‐induced dissociation spectra by a factor of at least ten over a conventional electron multiplier.
Laser mass spectrometry of oligonucleotides with isomer matrices
Authors: Tang K. , Allman S. L. , Jones R. B. , Chen C. H. , Araghi S. 
Published: May 2005

AbstractVarious isomer matrices were used for laser‐desorption ionization of mixtures of oligomers. It was found that the efficiency of production of oligomer ions changed drastically when different isomers were used as matrices. For selected matrix materials, parent oligomer ions with sizes up to 64 bases were observed.
Spontaneous desorption: Dependence of the desorption rate on the grid parameters
Authors: Schoppmann Ch. , Voit H. 
Published: May 2005

AbstractThe desorption rate for ‘spontaneous desorption’ (SD) has been investigated using various grids with different geometrical dimensions (line width, line distance). The experimental results can be understood if one assumes that the keV ions which sputter ions from the sample in an SD process originate exclusively at the grid via field‐enhanced desorption of adsorbates (FEDA). This means that SD is a two‐step process. The first step is FEDA, the second step is a sputter process.
The loss of amine from electron ionized large‐ring cycloalkylamines
Authors: Lefèvre Odile , Mollova Névéna , Longevialle Pierre 
Published: May 2005

AbstractLarge‐ring ionized cycloalkylamines of low internal energy lose ammonia and homologous alkyl radicals competitively. It is shown by deuterium‐labelling experiments, that ammonia is lost mainly after ring‐contraction of the original parent ion to an alkyl‐monosubstituted cyclohexylamine isomer. This fragmentation is preceded by abundant hydrogen exchanges occurring mainly in this rearranged structure, but also, for the largest ring compounds, to some extent in the original structure.