bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of the excited states of ethylene by MRCI
Authors: Yamamoto Shigeyoshi , Tatewaki Hiroshi , Diercksen Geerd H. F. 
Published: January 2005

AbstractThe excited states of ethylene are systematically analyzed and characterized according to the natural orbitals (NOs) resulting from multireference configuration interaction singles and doubles (MRCISD) calculations. By comparing the shapes and nodal structures of the NOs with those of hydrogen atomic orbitals, the Rydberg series can be classified. Two or three different types of Rydberg series appear within five excited states for each symmetry of D2h. For example, in the 1Ag symmetry there are three series having np and two nf hydrogen‐like atomic orbitals. Electronic correlation effects for the (π→π*) V state are also discussed on the basis of a complete active space self‐consistent field (CASSCF) calculation, showing that electron correlation effects merely within the valence space cannot explain contraction of the V state. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005
Electrospray ionisation tandem mass spectrometric study of hydrogen‐bonding interactions of some disaccharides with lysine
Authors: Nagaveni V. , Prabhakar S. , Vairamani M. 
Published: January 2005

AbstractThe efficiency of formation of protonated heterotrimers of lysine with underivatised sugars (mono‐, di‐, and trisaccharides) and N‐acetylglucosamine (N‐AcGlc) was studied under electrospray ionisation conditions. The collision induced dissociation spectra of [Lys + sugar + NAcGlc + H]+ resulted in [Lys + NAcGlc + H]+ and [Lys + sugar + H]+ as the major product ions. Relative abundances of these two fragments reflect the extent of adduct formation of protonated lysine plus sugar, with reference to the reference compound NAcGlc. This relative abundance ratio was found to be characteristic of the sugar structure. In this way it was observed that the ability of lysine to form a protonated heterodimer with neutral sugars increases with an increase in the number of acetal oxygens. Lactose showed an anomalously high affinity for protonated Lys, possibly reflecting the axial hydroxyl at C4. The postulated involvement of the ϵ‐NH2 group of lysine in the formation of protonated heterodimers with sugars was supported by similar results of similar experiments with NH3 in place of lysine. Copyright © 2001 John Wiley & Sons, Ltd.
Proton mobility and main fragmentation pathways of protonated lysylglycine
Authors: Csonka István Pál , Paizs Béla , Lendvay György , Suhai Sándor 
Published: January 2005

AbstractTheoretical model calculations were performed to validate the ‘mobile proton’ model for protonated lysylglycine (KG). Detailed scans carried out at various quantum chemical levels of the potential energy surface (PES) of protonated KG resulted in a large number of minima belonging to various protonation sites and conformers. Transition structures corresponding to proton transfer reactions between different protonation sites were determined, to obtain some energetic and structural insight into the atomic details of these processes. The rate coefficients of the proton transfer reactions between the isomers were calculated using the Rice‐Ramsperger‐Kassel‐Marcus (RRKM) method in order to obtain a quantitative measure of the time‐scale of these processes. Our results clearly indicate that the added proton is less mobile for protonated KG than for peptides lacking a basic amino acid residue. However, the energy needed to reach the energetically less favorable but–from the point of view of backbone fragmentation–critical amide nitrogen protonation sites is available in tandem mass spectrometers operated under low‐energy collision conditions. Using the results of our scan of the PES of protonated KG, the dissociation pathways corresponding to the main fragmentation channels for protonated KG were also determined. Such pathways include loss of ammonia and formation of a protonated α‐amino‐ϵ‐caprolactam. The results of our theoretical modeling, which revealed all the atomic details of these processes, are in agreement with the available experimental results. Copyright © 2001 John Wiley & Sons, Ltd.
Monitoring organic reactions with on‐line atmospheric pressure ionization mass spectrometry: the hydrolysis of isatin
Authors: Brum Jeffrey , Dell'Orco Philip , Lapka Sara , Muske Kenneth , Sisko Joseph 
Published: January 2005

AbstractTime‐resolved electrospray ionization mass spectrometry (ESI‐MS) is a powerful tool for interrogating solution‐phase reaction systems. Both mechanistic and kinetic information can be obtained using this technique. The title reaction offers the opportunity to examine the effects of different ionization scenarios with regard to monitoring reactant consumption and product formation. The hydrolysis of isatin was monitored in real time using a variety of ESI schemes: positive ion ([M + H]+, [M + Li]+, [M + Na]+) and negative ion [M − H]−. The utility of each ionization approach, with respect to the spectral features afforded for reaction tracking was examined. A comparison of first‐order hydrolysis kinetics data obtained using negative ion mass spectrometry is made with data acquired via an optical technique. Copyright © 2001 John Wiley & Sons, Ltd.
Immobilized artificial membrane chromatography with mass spectrometric detection: a rapid method for screening drug‐membrane interactions
Authors: Liu Hanlan , Carter Guy T. , Tischler Mark 
Published: January 2005

AbstractA high‐performance liquid chromatography (HPLC)/electrospray ionization mass spectrometry method for measuring drug‐membrane interactions was developed using immobilized artificial membrane (IAM) fast‐screening mini‐columns. The HPLC mobile phase consisted of phosphate‐buffered saline (i.e., 5.0 mM phosphate buffer at pH 7.4, 1.35 mM KCl, and 68.5 mM NaCl) and acetonitrile. This method facilitated the measurement of IAM retention time of over ten compounds in one experiment, significantly reducing analysis time compared with the earlier IAM‐HPLC method. The particular electrospray source used demonstrated the ability to tolerate the high salt‐containing nonvolatile buffer used for retention time measurement. Copyright © 2001 John Wiley & Sons, Ltd.
Characterization of ammonium nitrate by electrospray ionization tandem mass spectrometry
Authors: Zhao Xiaoming , Yinon Jehuda 
Published: January 2005

AbstractMass spectra of ammonium nitrate were recorded in both positive‐ and negative‐ion mode by electrospray ionization mass spectrometry (ESI‐MS) and electrospray ionization tandem mass spectrometry with collision‐induced dissociation (ESI‐MS/MS‐CID). Characterization of ammonium nitrate by a series of typical cluster ions was further confirmed by using isotopically labeled ammonium nitrate (ammonium‐15N, nitrate‐15N, nitrate‐18O) and deuterated water. It was found that, at heated capillary temperatures in the range 55–150 °C, in the positive‐ion mode, cluster ions of the type [(NH4NO3)nNH4]+(n = 1–3) were dominant in the mass spectrum, which enables the characterization and identification of the integral ammonium nitrate molecule. Copyright © 2001 John Wiley & Sons, Ltd.
Resonant dissociation of polyatomic surface molecules by hyperthermal ions
Authors: Komarov V. V. , Popova A. M. , Stureiko I. O. , Schmidt L. , Jungclas H. 
Published: January 2005

AbstractA theoretical approach is suggested for the fragmentation of polyatomic surface molecules by scattering of hyperthermal atomic and molecular ions. It is assumed that the surface molecules contain chains of identical diatomic valence groups as substructures. These chains can accumulate collective vibrational excitations (excimols), leading to subsequent nonstatistical molecular fragmentation. Low‐energy incident ions at any incident angle are assumed to be reflected from the surface at atomic distances by the Coulomb potential, which acts for only a short period of time (10−13–10−12s). During this reflection period, the component of ion velocity normal to the surface is negligible, so ions move across the surface in a process that can be considered as a grazing collision. Analytical expressions are obtained for the fragmentation probabilities of surface molecules in grazing collisions with atomic and molecular ions. The probability of these processes strongly depends on the molecular structure and the incident ion velocity. The interaction between hyperthermal ions and molecules forming the outermost surface layer yields fragment molecules as a result of the mutual excitation processes. The experimental data on fragments generated from a fluorinated surface by action of incident ions are analyzed within the framework of the suggested model. Copyright © 2001 John Wiley & Sons, Ltd.
Sequence verification of oligonucleotides by electrospray quadrupole time‐of flight mass spectrometry
Authors: Ni Jinsong , Chan Kelvin 
Published: January 2005

AbstractThe combination of electrospray ionization (ESI) and quadrupole time‐of‐flight (Q‐Tof) mass spectrometry presents a powerful tool to verify/determine the sequence of oligonucleotides. An ESI‐Q‐Tof instrument provides better sensitivity and much higher resolution compared with either ESI‐triple quadrupole or ESI‐ion trap devices. With high‐resolution capability, the quadrupole time‐of‐flight instrument can provide an isotope pattern to support the charge state assignment. This will improve the reliability of the assignments of sequence‐related w or a‐Base series ions and lead to accurate determination of the oligonucleotide sequence. Copyright © 2001 John Wiley & Sons, Ltd.
A rapid, automated approach to optimisation of multiple reaction monitoring conditions for quantitative bioanalytical mass spectrometry
Authors: Higton David M. 
Published: January 2005

AbstractAn improvement to the procedure for the rapid optimisation of mass spectrometry (PROMS), for the development of multiple reaction methods (MRM) for quantitative bioanalytical liquid chromatography/tandem mass spectrometry (LC/MS/MS), is presented. PROMS is an automated protocol that uses flow‐injection analysis (FIA) and AppleScripts™ to create methods and acquire the data for optimisation. The protocol determines the optimum orifice potential, the MRM conditions for each compound, and finally creates the MRM methods needed for sample analysis. The sensitivitiesof the MRM methods created by PROMS approach those created manually. MRM method development using PROMS currently takes less than three minutes per compound compared to at least fifteen minutes manually. To further enhance throughput, approaches to MRM optimisation using one injection per compound, two injections per pool of five compounds and one injection per pool of five compounds have been investigated. No significant difference in the optimised instrumental parameters for MRM methods were found between the original PROMS approach and these new methods, which are up to ten times faster. The time taken for an AppleScript to determine the optimum conditions and build the MRM methods is the same with all approaches. Copyright © 2001 John Wiley & Sons, Ltd.
Probing reactive sites for ion‐molecule reactions of anthraquinones with dimethyl ether using an external source ion trap tandem mass spectrometer and computational chemistry
Authors: Wu Hui‐Fen , Chen Li‐Wei , Chen Chien‐Hung 
Published: January 2005

AbstractGas‐phase ion‐molecule reactions of anthraquinone derivatives with dimethyl ether (DME) were investigated using an external source ion trap mass spectrometer. Semi‐empirical calculations were executed to determine possible reactive sites for the product ions. Collision activated dissociation (CAD) was successfully performed for very low abundance of ion‐molecule products. Even for product ions with a relative intensity below 1%, CAD experiments can be successfully performed. Significantly more structural information could be elucidated based on this special feature. Importantly, the CAD spectra of very minor ions could be measured by this ion trap instrument, which significantly enhances the future role of the ion trap as a powerful analytical instrument. CAD of all product ions on anthraquinone compounds typically eliminates neutral molecules such as CO or H2O. A hydration phenomenon in the CAD processes resulting from the precursor ions incorporating one molecule of H2O and then eliminating one molecule of CO was observed in this study. Copyright © 2001 John Wiley & Sons, Ltd.
Size exclusion chromatography/mass spectrometry applied to the analysis of polysaccharides
Authors: Deery Michael J. , Stimson Elaine , Chappell Colin G. 
Published: January 2005

AbstractA novel method for analysing polysaccharide materials is described which employs size‐exclusion chromatography (SEC) followed by detection by on‐line electrospray ionisation mass spectrometry (ESI‐MS) and off‐line matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry (MALDI‐TOFMS). It is demonstrated through SEC/ESI ion trap mass spectrometry that the formation of multiply charged oligomer ions, which bind up to five sodium cations, allows the rapid analysis of polysaccharide ions with molecular weights in excess of 9 kDa. MALDI spectra generated from fractionation of the effluent collected from the same SEC separation are shown to be in good agreement with the ESI spectra with respect to molecular weight distributions and types of ions generated. ESI and MALDI mass spectra of samples obtained from sequential graded ethanol precipitation and SEC fractionation of acid and enzymatically digested arabinoxylan polysaccharides show important structural differences between polysaccharide fragments. In addition, a comparison is made between the mass spectra of native and permethylated SEC‐separated fragments of acid and enzymatically treated arabinogalactan. Linkage information of the permethylated arabinogalactan oligomers can be rapidly established through the use of on‐line SEC/ESI‐MS
n experiments. Copyright © 2001 John Wiley & Sons, Ltd.
Determination of cyclic polyester oligomers by gel permeation chromatography and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry
Authors: Laine Olli , Österholm Heidi , Seläntaus Maaria , Järvinen Hannele , Vainiotalo Pirjo 
Published: January 2005

AbstractPolyesters prepared from adipic acid (AA), phthalic anhydride (PA), isophthalic acid (IPA), terephthalic acid (TPA), and 2‐butyl‐2‐ethyl‐1,3‐propanediol (BEPD) were investigated by gel permeation chromatography (GPC) and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry(MALDI‐TOFMS). All polyesters were found to contain a fraction of low molecular weight molecules that were identified as cyclic ester oligomers. The most abundant cyclic oligomer varied with the diacid used in the synthesis but, in every case, it was either a dimer or a trimer. In addition, the relative amounts of the polyester starting materials influenced the amount of cyclic oligomers formed in the polyesterification reaction. Copyright © 2001 John Wiley & Sons, Ltd.
Rearrangement of P‐N to P‐O bonds in mass spectra of N‐diisopropyloxyphosphoryl amino acids/alcohols
Authors: Chen Jing , Chen Yi , Jiang Yang , Fu Hua , Xin Bin , Zhao Yu‐Fen 
Published: January 2005

AbstractThe cationized N‐diisopropyloxyphosphoryl amino acids/alcohols were analyzed by electrospray ionization tandem mass spectrometry. A rearrangement reaction leading to the P‐N to P‐O bond migration was observed, and cationized phosphoric acid isopropyl ester (PAIE) was formed. The rearrangement did not depend on the chain length of the amino acids/alcohols. A possible rearrangement mechanism was proposed. It was shown that the phosphoryl group has a strong affinity to the hydroxyl group in the gas phase. Copyright © 2001 John Wiley & Sons, Ltd.
Multiphoton dissociation/ionisation of dimethyl sulfide
Authors: Vatsa R. K. , Majumder C. , Jayakumar O. D. , Sharma P. , Kulshreshtha S. K. , Mittal J. P. 
Published: January 2005

AbstractMultiphoton dissociation/ionisation studies have been carried out at 355 nm for dimethyl disulfide (CH3SSCH3) using a time‐of‐flight‐mass spectrometer. The prominent ion signals observed are CH3+, S+, HCS+ and S2+. No evidence for the formation of a parent ion signal was observed. The laser power variation experiments show a two‐photon dependence for the most prominent HCS+ ion. The presence of a signal at m/e 30 is explained in terms of concerted elimination of ethane from the excited neutral CH3SSCH3 via a cyclic transition state. It is inferred that the multiphoton dissociation of CH3SSCH3 at 355 nm involves both S‐S and C‐S bond cleavage. Based on these results, it has been suggested that CH3S+ isomerises to CH2SH+, which undergoes unimolecular decay to produce HCS+ by H2 elimination. The results have been interpreted in terms of the dissociation of the parent molecule using two photons, followed by the ionisation of the fragments. Copyright © 2001 John Wiley & Sons, Ltd.
The elemental analyzer sample carousel: loading an autosampler made easy
Authors: Wooller Matthew , Collins Bert , Fogel Marilyn 
Published: January 2005

AbstractA newly developed device for loading samples into an autosampler attached to an elemental analyzer is described and evaluated. The purpose of the device is to reduce the time and number of errors experienced when loading samples into an autosampler. Tests show that the new device saves time when loading samples and, more importantly, reduces the chance of losing samples. In addition to analyzing the elemental components (e.g. % carbon and % nitrogen) and the elemental ratios (e.g. C/N) of a sample, the stable isotopic composition (e.g. δ13C and δ15N) can also be determined when an EA is attached to a stable isotope ratio mass spectrometer. Copyright © 2001 John Wiley & Sons, Ltd.
Impact desolvation of electrosprayed microdroplets – a new ionization method for mass spectrometry of large biomolecules
Authors: Aksyonov Sergei A. , Williams Peter 
Published: January 2005

AbstractImpact desolvation of electrosprayed microdroplets (IDEM) is a new method for producing gas‐phase ions of large biomolecules. Analytes are dissolved in an electrolyte solution which is electrosprayed in vacuum, producing highly charged micron and sub‐micron sized droplets (microdroplets). These microdroplets are accelerated through potential differences ∼5 − 10 kV to velocities of several km/s and allowed to impact a target surface. The energetic impacts vaporize the droplets and release desolvated gas‐phase ions of the analyte molecules. Oligonucleotides (2‐ to 12‐mer) and peptides (bradykinin, neurotensin) yield singly and doubly charged molecular ions with no detectable fragmentation. Because the extent of multiple charging is significantly less than in atmospheric pressure electrospray ionization, and the method produces ions largely free of adducts from solutions of high ionic strength, IDEM has some promise as a method for coupling to liquid chromatographic techniques and for mixture analysis. Ions are produced in vacuum at a flat equipotential surface, potentially allowing efficient ion extraction. Copyright © 2001 John Wiley & Sons, Ltd.
Secondary ion mass spectrometric investigation of Au‐based composites
Authors: Barison Simona , Piccirillo Clara , Fabrizio Monica , Daolio Sergio 
Published: January 2005

AbstractThe electrodeposition of thick gold layers plays an important role both in traditional and high‐tech productions, such as jewelry and microelectronics, respectively. In this work a secondary ion mass spectrometric study will be presented on Au co‐deposits with (sub‐)micrometric ceramic powders, in order to harden gold. Mass spectra are used to identify the components deposited, providing evidence of the additives and/or eventual contaminants introduced during electrolysis. Furthermore, analysis of ion depth profiles and the intensity distribution of ionic species along the film were studied. Copyright © 2001 John Wiley & Sons, Ltd.
Deceleration of high‐energy matrix‐assisted laser desorption/ionization ions in an open cell for Fourier transform ion cyclotron resonance mass spectrometry
Authors: Frankevich Vladimir , Zenobi Renato 
Published: January 2005

AbstractA new method of ion deceleration in a Fourier transform ion cyclotron resonance (FTICR) open cell is described that improves the performance of FTICR‐MS instruments equipped with an internal source for laser desorption/ionization. Ion deceleration occurs in the front trapping cylinder of an open cylindrical cell. Decelerating voltages up to 100 V can be applied for 10–500 µs to the front cylinder during ion introduction. The deceleration field is uniformly distributed along the cylinder length giving a ‘smooth’ deceleration, which means that the deceleration is effective over a large time interval and a large m/z range. This results in improved trapping efficiency of high‐energy ions. We demonstrate efficient trapping of high (m/z 66 kDa) mass ions and the possibility to reduce the width of the kinetic energy distribution of MALDI ions with this arrangement. Copyright © 2001 John Wiley & Sons, Ltd.
Quantitative determination of medroxyprogesterone acetate in plasma by liquid chromatography/electrospray ion trap mass spectrometry
Authors: Kim Seong‐Mo , Kim Dong‐Hyun 
Published: January 2005

AbstractA sensitive and rapid liquid chromatography/electrospray ion trap mass spectrometry (LC/MS/MS) method has been developed for the quantitative determination of medroxyprogesterone acetate (MPA) in human plasma. Plasma samples (1.0 mL) were simply extracted with pentane and the extracts were analyzed by HPLC with the detection of the analyte in the selective reaction monitoring (SRM) mode. The determination of MPA was accurate and reproducible, with a limit of quantitation of 0.05 ng/mL in plasma. The standard calibration curve for MPA was linear (r = 0.998) over the concentration range 0.05–6.0 ng/mL in human plasma. Analysis precision over the concentration range of MPA was lower than 18.8% (relative standard deviation, RSD) and accuracy was between 96.2 and 108.7%. Copyright © 2001 John Wiley & Sons, Ltd.
Drug screening of pharmaceutical discovery compounds by micro‐size exclusion chromatography/mass spectrometry
Authors: Wabnitz Paul A. , Loo Joseph A. 
Published: January 2005

AbstractMicro‐size exclusion chromatography coupled with capillary liquid chromatography (capLC) and mass spectrometry (MS) provides a rapid and simple approach to the preliminary screening of active ligands toward a specific target macromolecule. In this study, the effectiveness of this technique is demonstrated by a number of small molecule ligands with known binding affinities towards the protein target. All ligands were incubated together with a target protein under native conditions. Separation was then achieved by microcentrifugation where the high molecular weight (MW) compounds were selectively passed through the size‐exclusion material. The retained low MW compounds were then recovered and analyzed by capLC/MS. The absence of the ligand indicated strong affinity towards the target, while ligand detection indicated inactivity. This assay demonstrated the drugs that were acting as strong inhibitors of Co‐PDF from those showing to be comparatively inactive. The relative binding rank order of the drugs towards Co‐PDF was also determined. The results were validated by a corresponding set of control experiments in which the target molecules were excluded from the process. In principle, high‐throughput micro‐size exclusion chromatography, coupled with capLC/MS, offers a powerful technique as a preliminary screen in determining both the strong binding affinity and the relative affinity rank ordering of ligands towards a specific target macromolecule, and is complementary with other analytical drug screening techniques. Copyright © 2001 John Wiley & Sons, Ltd.