bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative Electronic Structure‐Activity Relations: The Influence of Basis Set Selection on Prediction Quality
Authors: Lahsen Joaquín , Schmidhammer Helmut , Spetea Mariana , Rode Bernd M. 
Published: June 2003

AbstractQuantitative electronic structure‐activity relations (QESAR) based on ab initio calculated atomic charge data have been investigated with respect to basis set influence on quality and predictability. A series of 11 nonpeptide δ‐opioid receptor ligands has been utilized to study the basis set effect, and to determine the active center of these compounds. The geometries were fully optimized using the semiempirical method AM1. Net atomic charges obtained from ab initio MO calculations were used as electronic predictors. Multivariate adaptive regression splines were applied to the data matrix for the construction of QESAR models, whose predictability was rated by PRESS. The best model yielded a PRESS value of 0.08 and it was obtained using the atomic charges derived from the basis set 6‐311G. This model contains the C(9), C(12), C(14), and O(19) atoms as predictors. The 3‐21G basis set supplies an almost equivalent model and can be seen as an economic alternative, therefore, for large compounds.
Flow injection of the lock mass standard for accurate mass measurement in electrospray ionization time‐of‐flight mass spectrometry coupled with liquid chromatography
Authors: Charles Laurence 
Published: June 2003

AbstractA method of flow injection of the lock mass for accurate mass measurement using electrospray ionization time‐of‐flight mass spectrometry is described. The reference compound is introduced in the chromatographic effluent via a six‐port valve placed post‐column, prior to the split connector. Flow injection is performed in such a way that the reference elution peak is superimposed in the total ion current and partially overlaps that of the investigated analyte, allowing independent ionization of the two compounds and thus accurate mass measurement with no ion suppression effects. Different lock mass molecules can be injected in a single analytical run to target various analytes. The performance of this methodology is demonstrated in both isocratic and gradient liquid chromatography modes. The molecular ion of the flow‐injected lock mass could also be used as a reference for mass measurement of the in‐source fragments of the analytes. Good mass accuracy, within 4 mDa of the theoretical values, was obtained. Copyright © 2003 John Wiley & Sons, Ltd.
Product ion spectral simplification using time‐delayed fragment ion capture with tandem linear ion traps
Authors: Hager James W. 
Published: June 2003

AbstractA new technique to generate product ion spectra as the internal energy of a collisionally activated precursor ion evolves is described. The precursor ion is activated by acceleration into a mass‐selective linear ion trap under conditions whereby some of the fragment ions formed are unstable within the trap. After a time delay the stability parameters of the ion trap are changed to allow capture of fragments that that were previously unstable. The result is a product ion spectrum that originates from precursor ions with a modified internal energy distribution. It is possible to follow the evolution of the precursor internal energy distribution for many milliseconds after admittance of the precursor ions into the linear ion trap. Time‐delayed fragmentation product ion spectra typically display reduced sequential fragmentation products leading to spectra that are more easily interpreted. Several important experimental parameters important to time‐delayed fragmentation have been identified and are discussed. The technique has applications for both small precursor ions and multiply charged peptides. Copyright © 2003 John Wiley & Sons, Ltd.
Structural analysis of oligosaccharides by a combination of electrospray mass spectrometry and bromine isotope tagging of reducing‐end sugars with 2‐amino‐5‐bromopyridine
Authors: Li Min , Kinzer Jeffery A. 
Published: June 2003

AbstractModel reducing‐end oligosaccharides were successfully labeled by a brominated aromatic amine reagent, 2‐amino‐5‐bromopyridine (ABP), through reductive amination. Using either a combination of liquid chromatography/electrospray ionization mass spectrometry (LC/ESI‐MS) with in‐source fragmentation or liquid chromatography/electrospray ionization tandem mass spectrometry (LC/ESI‐MS/MS), sequence information corresponding to the model oligosaccharides was revealed with little ambiguity via the diagnostic unique twin peaks arising from the bromine isotopes, for both the molecular ions of the derivatized oligosaccharides and their fragments. No fragment ions arising from loss of the bromine atom were observed. Copyright © 2003 John Wiley & Sons, Ltd.
Parallel high‐throughput accurate mass measurement using a nine‐channel multiplexed electrospray liquid chromatography ultraviolet time‐of‐flight mass spectrometry system
Authors: Fang Liling , Demee Michael , Cournoyer Jason , Sierra Teresa , Young Connie , Yan Bing 
Published: June 2003

AbstractA nine‐channel multiplexed electrospray (MUX) liquid chromatography ultraviolet time‐of‐flight mass spectrometry (LC/UV/TOFMS) system has been used to simultaneously measure accurate masses of eluting components from eight parallel gradient LC columns. Accuracies better than 5 and 10 ppm were achieved for 50 and 80% of samples, respectively, from a single batch analysis of ten plates (960 samples) of a Fmoc‐Asp(OtBu)‐OH and reserpine mixture. Combinatorial library compounds were analyzed using this parallel high‐throughput system in both positive and negative modes to rigorously verify expected products and identify side products. A mass accuracy of 10 ppm root mean square (RMS) is routinely obtained for combinatorial library samples from this high‐throughput accurate mass LC/MS system followed by automated data processing. This mass accuracy is critical in revealing combinatorial synthesis problems that would be missed by unit mass measurement. Copyright © 2003 John Wiley & Sons, Ltd.
Congener‐specific analysis of hexabromocyclododecane by high‐performance liquid chromatography/electrospray tandem mass spectrometry
Authors: Budakowski Wesley , Tomy Gregg 
Published: June 2003

AbstractA congener‐specific method based on high‐performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ES‐MS/MS) in the negative ion mode was developed for the analysis of hexabromocyclododecane (HBCDD). On a C18 analytical column, with a methanol/water mobile phase, the α‐isomer was completely resolved from the β‐ and γ‐isomers while the β‐ and γ‐isomers were sufficiently resolved at half their peak heights. The ES spray voltage strongly influenced the intensity of the ion signal. For MS, a source temperature of 500°C and a collision energy of 50 eV were found to be optimum for the [M–H]− to Br− transition. Run‐to‐run and day‐to‐day (n = 3) variability was minimal, with relative standard deviations of 2.6–4.1 and 2.4–4.4%, respectively. The limit of detection was 4–6 pg on‐column. When applied to tissue samples from Lake Winnipeg fish both α‐ and γ‐isomers of HBCDD were found in low‐ng/g (lipid corrected) concentrations. Copyright © 2003 John Wiley & Sons, Ltd.
Probing the mechanisms of the self ion‐molecule reactions of dopamine in an ion trap mass spectrometer
Authors: Wu Hui‐Fen , Chen Chien‐Hung , Lu Li‐Chi 
Published: June 2003

AbstractOur previous work was the first to report [M+CH]+ and [M+C2H3]+ ions in the self ion‐molecule reactions (SIMR) of two aza‐crown ethers in an ion trap mass spectrometer (ITMS). In this study, the CH and C2H3 addition ions were also found in the SIMR of dopamine. The SIMR of dopamine lead to the formation of the protonated molecules ([M+H]+), of adduct ions ([M+F]+, where F represents fragment ions), and of [M+CH]+, [M+C2H3]+ and [2M+H]+ ions. Based on the combination of the results of isolation experiments and semi‐empirical calculations, the reactive site for the formation of the [M+H]+ and [M+CH]+ ions of dopamine is proposed to be the amino group. Copyright © 2003 John Wiley & Sons, Ltd.
Electrospray ionization mass spectrometry of AZT H‐phosphonates conjugated with steroids
Authors: Xiao Qiang , Ju Yong , Yang Xinping , Zhao Yu‐Fen 
Published: June 2003

AbstractAZT H‐phosphonates conjugated with steroids were synthesized and determined by positive and negative ion electrospray ionization mass spectrometry (ESI‐MS) in conjunction with tandem mass spectrometry (MS/MS). The fragmentation pathways were investigated in detail. There are very different characteristic fragment ions in the positive and negative ion MS/MS spectra. The azide group of compounds 6a and 6b underwent either elimination of HN3 or rearrangement to an amine in both positive and negative ion mass spectrometry. Copyright © 2003 John Wiley & Sons, Ltd.
Cone voltage induced in‐source dissociation of glucuronides in electrospray and implications in biological analyses
Authors: Yan Zhengyin , Caldwell Gary W. , Jones William J. , Masucci John A. 
Published: June 2003

AbstractGlucuronidation is a common mechanism in drug metabolism. In‐source dissociation of glucuronides in electrospray generates fragment ions identical to those of the precursor ions of the original drugs. The effect of experimental parameters on the process was investigated in the present study using both commercially available compounds and glucuronides generated from microsomal glucuronidation incubations. It was found that cone voltage was the most critical parameter contributing to in‐source fragmentation of both O‐ and N‐glucuronides, whereas both the desolvation temperature and the source temperature had little effect. Additionally, the extent of in‐source dissociation varied for different glucuronides and could be minimized by lowering cone voltage. As demonstrated in real examples, minimizing in‐source dissociation can lead to higher sensitivity in detecting glucuronides in biological samples. In addition, product ions resulting from in‐source dissociation of glucuronides potentially interfere with accurate determinations of corresponding drug levels if chromatographic separation is not adequate. For cases in which chromatographic separation of glucuronides from the original drugs is not readily achieved or high‐throughput analyses are desired, interference caused by in‐source dissociation can usually be eliminated simply by using lower cone voltage. This approach has been proven to be effective in the analysis of more than 100 glucuronides generated from in vitro microsomal incubations. Copyright © 2003 John Wiley & Sons, Ltd.
Exact mass measurement of product ions for the structural confirmation and identification of unknown compounds using a quadrupole time‐of‐flight spectrometer: a simplified approach using combined tandem mass spectrometric functions
Authors: Clauwaert Karine , Casteele Sofie Vande , Sinnaeve Bart , Deforce Dieter , Lambert Willy , Van Peteghem Carlos , Van Bocxlaer Jan 
Published: June 2003

AbstractThis article describes a simple method to perform lock mass corrected accurate mass measurements in tandem mass spectrometry (MS/MS) with a quadrupole time‐of‐flight (Q‐TOF) mass spectrometer. The experimental approach consists of using the protonated molecule of a known compound, which is measured in a MS/MS function using low collision energy (no fragmentation), as mass calibrator. The unknown compound is acquired in MS/MS mode albeit using high collision energy. After the acquisition, the two MS/MS spectra of unknown and mass calibrator are combined, and the fragments of the unknown are lock mass corrected by using the protonated molecule of the mass calibrator. To prove this concept, 10 compounds were analyzed using this approach, the fragments interpreted and, where possible, related to structural data available in the literature. All the unequivocally assigned fragments were accurately mass measured with mass errors within appropriate limits, i.e. for m/z values <200 with a mass tolerance of 3 mDa while for m/z > 200 the mass tolerance is expressed as 10 ppm. Copyright © 2003 John Wiley & Sons, Ltd.
Charge state separation for protein applications using a quadrupole time‐of‐flight mass spectrometer
Authors: Chernushevich I. V. , Fell L. M. , Bloomfield N. , Metalnikov P. S. , Loboda A. V. 
Published: June 2003

AbstractA novel method for separating ions according to their charge state using a quadrupole time‐of‐flight mass spectrometer is presented. The benefits of charge state separation are particularly apparent in protein identification applications at low femtomole concentration levels, where in conventional TOF MS spectra peptide ions are often lost in a sea of chemical noise. When doubly and triply charged tryptic peptide ions need to be filtered from singly charged background ions, the latter are suppressed by two to three orders of magnitude, while from 10–50% of multiply charged ions remain. The suppression of chemical noise reduces the need for chromatography and can make this experimental approach the electrospray equivalent of conventional MALDI peptide maps. If unambiguous identification cannot be achieved, MS/MS experiments are performed on the precursor ions identified through charge separation, while the previously described Q2‐trapping duty cycle enhancement is tuned for approximately 1.4 of the precursor m/z to enhance intensities of ions with m/z values above that of the precursor. The resulting product ion spectra contain few fragments of impurities and provide quick and unambiguous identification through database search. The multiple charge separation technique requires minimal tuning and may become a useful tool for analysis of complex mixtures. Copyright © 2003 John Wiley & Sons, Ltd.
Mass spectral determination of skeletal/cardiac actin isoform ratios in cardiac muscle
Authors: Bergen H. Robert , Ajtai Katalin , Burghardt Thomas P. , Nepomuceno Angelito I. , Muddiman David C. 
Published: June 2003

AbstractSkeletal and cardiac muscle contains actin isoforms that vary by two juxtaposed amino acids and two amino acid substitutions (Met299Leu and Ser358Thr). This close sequence homology does not allow cardiac and skeletal actin isoforms to be resolved in traditional SDS‐PAGE analysis as the molecular weights (Δmass = 32 Da) are not significantly different and the pIs are identical (5.2). Although cardiac actin is the predominant form in cardiac muscle, there appears to be a specific skeletal/cardiac actin ratio in a normal heart that may vary in a compromised or diseased heart. In an effort to ascertain the validity of this hypothesis we developed a mass spectrometric technique to measure the ratio of skeletal to cardiac actin. The technique involves purification of muscle actin and subsequent liquid chromatography coupled with electrospray ionization Fourier transform ion cylcotron resonance (LC/FTICR‐MS) mass spectrometry. A 7 Tesla FTICR mass spectrometer was utilized to compare skeletal/cardiac actin isoform ratios. Additionally, a new dual electrospray ionization source was employed to determine accurate masses of the α‐skeletal and α‐cardiac actins. Copyright © 2003 John Wiley & Sons, Ltd.
High‐temperature elemental analysis and pyrolysis techniques for stable isotope analysis
Authors: Gehre Matthias , Strauch Gerhard 
Published: June 2003

AbstractA universal method for pyrolysis and elemental analysis, suitable for the online determination of deuterium, carbon, nitrogen and oxygen isotopes for organic and inorganic substances, is presented. The samples are pyrolytically decomposed in a high‐temperature pyrolysis (HTP) system, at a temperature exceeding 1400°C, in the presence of reactive carbon. The method is suitable for the analysis of stable isotope ratios from hydrogen, carbon, nitrogen and oxygen. The instrumentation and experimental procedure are simple and cost‐effective. The reproducibility of the delta values for D/H is better than 3‰, and for 18O, 13C (organic) and 15N (inorganic) it is ∼0.2‰. The HTP system is suitable for solid and liquid samples and can use an autosampler for the samples. Results are presented for the isotopic composition of international reference materials and selected laboratory reference materials, which demonstrate the precision and accuracy of the method. Possible problems in the measurement of nitrates and their solutions are particularly discussed. The analyses of oxygen isotopes in selected geological samples (carbonates, silicate, biotite) are demonstrated. Copyright © 2003 John Wiley & Sons, Ltd.
Solid‐state glycation of β‐lactoglobulin monitored by electrospray ionisation mass spectrometry and gel electrophoresis techniques
Authors: Fenaille François , Morgan François , Parisod Véronique , Tabet Jean‐Claude , Guy Philippe A. 
Published: June 2003

AbstractGlycation of β‐lactoglobulin (β‐Lg) with either lactose or galactose in a solid‐state medium was monitored using gel electrophoresis techniques and liquid chromatography coupled to electrospray ionisation mass spectrometry (LC/ESI‐MS). The kinetics of glycation monitored by SDS polyacrylamide gel electrophoresis showed a molecular weight increase over time of the β‐Lg bands for both sugars, but no significant amounts of aggregated proteins were observed. The isoelectric point of the protein, observed by isoelectric focusing gel electrophoresis, was dramatically affected by galactosylation. LC/MS measurements of β‐Lg variants A and B, over the whole glycation reaction time, showed a larger extent of glycation with galactose (from 4 up to 22 adducts) as compared with lactose (from 0 up to 14 adducts), and confirmed that early Maillard reaction products were the main species observed. Based on the relative abundances obtained from the deconvoluted mass spectra after a 8 h 15 min incubation time at 60°C, the mean values of lactose and galactose molecules bound to the protein species were calculated to be 10.4 and 17.9, and 10.5 and 18.6, for variants A and B, respectively. Furthermore, the charge state distribution data obtained by ESI‐MS was studied using different methanol percentages, and indicated that adduct formation with lactose, but more significantly galactose, tends to improve the stability properties of the native protein towards denaturation. Copyright © 2003 John Wiley & Sons, Ltd.
An efficient chemical method for dephosphorylation of phosphopeptides
Authors: Kuyama Hiroki , Toda Chikako , Watanabe Makoto , Tanaka Koichi , Nishimura Osamu 
Published: June 2003

AbstractPhosphate moieties found on serine, threonine or tyrosine residues in peptides, e.g., in proteolytic digests of proteins, were cleaved using hydrofluoric acid or hydrogen fluoride–pyridine without side reactions. Copyright © 2003 John Wiley & Sons, Ltd.
A simple method for oxygen‐18 determination of milligram quantities of water using NaHCO3 reagent
Authors: Ijiri Akira , Tsunogai Urumu , Gamo Toshitaka 
Published: June 2003

AbstractThis paper presents a modified H2OCO2 equilibration method for stable oxygen isotopic composition (δ18O) analysis of water. This method enables rapid and simple δ18O analysis of milligram quantities of water, by employing solid reagent NaHCO3 as the CO2 source, a small (0.6 mL) glass vial for the equilibration chamber, and an isotope‐monitoring gas chromatography/mass spectrometry (irm‐GC/MS) system for $\delta ^{18} {\rm O}_{{\rm CO}_{\rm 2} }$ analysis. This method has several advantages, including simple handling for the H2OCO2 equilibration (without purging and/or evacuation treatments), rapid and easy δ18O analysis of equilibrated CO2, and highly sensitive and highly precise δ18O analysis of H2O, using samples as small as 10 mg and with a precision of less than ±0.12‰. The time needed to attain oxygen isotopic equilibration between CO2 and water is also comparable (17 h for 10 mg H2O and 10 h for 100 mg H2O) to other previous methods using CO2 gas for the CO2 source. The extent of δ18O variation of sample water from its initial δ18O value due to isotope exchange with added NaHCO3 is also discussed. It is concluded that the correction needed is negligible (less than 0.1‰) as long as the oxygen atom ratio (${\rm O}_{{\rm NaHCO}_{\rm 3} } {\rm /O}_{{\rm H}_{\rm 2} {\rm O}}$) is less than 3.3 ± 10−3 and provided the $\delta ^{18} {\rm O}_{{\rm H}_{\rm 2} {\rm O}}$ determination is made by comparing δ18O of CO2 equilibrated with sample water and that equilibrated with standard water of a moderately close δ18O value, less than 30‰ difference. Copyright © 2003 John Wiley & Sons, Ltd.
Membrane fusion mediated by herpesvirus glycoproteins: the paradigm of varicella‐zoster virus
Authors: Cole Nancy L. , Grose Charles 
Published: June 2003

AbstractVaricella‐zoster virus (VZV) is well known for its propensity to cause polykaryons (syncytia) in the vesicles within infected skin. Similarly in cultured cells, VZV induces extensive syncytial formation by virus‐mediated cell‐to‐cell fusion. Statistical analyses of fusion parameters demonstrated three‐way interactive effects among all three tested variables (incubation temperature, cell type and virus strain). For example, fusion was greatly enhanced at 33°C vs 37°C; also fusion was pronounced in epidermal cells but negligible in fibroblast cells. As with all herpesviruses, VZV gH was a major fusogen. VZV cell fusion was inhibited by antibody to gH, but surprisingly was enhanced by antibody to gE. Other evidence implicating a role for VZV gE in the fusion process was provided by two mutant viruses, in which gE cell surface expression was enhanced. Under transfection conditions, VZV fusion formation occurred after expression of the gH/gL complex; in contrast, pseudorabies virus requires expression of gH, gL and gB, while the herpes simplex virus (HSV) types 1 and 2 require the quartet of gH, gL, gB and gD. VZV has no gD gene and no apparent gD functional homologue. On the other hand, VZV gE exerts a greater effect than HSV gE on membrane fusion. Taken together, the data in this review suggest that VZV has evolved viral glycoprotein machinery more geared toward cell‐to‐cell fusion (fusion‐from‐within) than toward virus‐to‐cell fusion (entry/fusion‐from‐without), as a means for syncytium formation within the human epidermis. Copyright © 2003 John Wiley & Sons, Ltd.
Cell‐mediated cytotoxicity in recovery from poxvirus infections
Authors: Müllbacher Arno 
Published: June 2003

AbstractThe availability of mutant and gene targeted knockout mice with defects in components of cellular cytotoxicity mediated by either the Fas or the exocytosis pathway permitted an analysis of their role in recovery from poxvirus infections. Ectromelia (EV), a natural mouse pathogen causing mousepox, the closely related orthopoxviruses cow pox (CPV) and vaccinia virus (VV), each encode serpins that inhibit Fas mediated apoptosis and lysis of target cells. Nevertheless, distinct differences were seen when the three viruses were inoculated into perforin‐;deficient mice: highly resistant C57Bl/6 mice became susceptible to low doses of EV; resistance to CPV increased whereas there was no effect on VV infections. Absence of the cytolytic granule associated granzymes (gzm) A and B rendered C57Bl/6 mice increasingly more susceptible to EV infections. Lack of both gzms rendered them as susceptible as perforin deficient mice, despite the presence of functionally active perforin. Elevated EV titres in liver and spleen of gzmA×B deficient mice, early after infection and before cytotoxic T cells were detectable, strongly suggests that these two gzms exert an antiviral effect by a mechanism distinct from effector molecules of NK and cytotoxic T cells. Copyright © 2003 John Wiley & Sons, Ltd.