bluuebunny/crossref_metadata_2025_split huggingface dataset:
Impact of ion cloud densities on the measurement of relative ion abundances in Fourier transform ion cyclotron resonance mass spectrometry: experimental observations of coulombically induced cyclotron radius perturbations and ion cloud dephasing rates
Authors: Gordon Eric F. , Muddiman David C. 
Published: August 2002

AbstractFundamental research into the quantitative properties of Fourier transform ion cyclotron resonance mass spectrometry (FTICR‐MS) has yielded interesting observations, especially in terms of factors affecting the accuracy of relative ion abundances. However, most of the previous discussions have focused on theoretical systems, or systems of limited scope. In this paper, we document ion motion attributes of a 30 spectra (six samples, five replicates each) system previously established as linear over two orders of magnitude. Observed behaviors include the perturbation of one charged species (cyclosporin A, CsA) of low ion density to a cyclotron orbit of greater radius than that of an almost identical, but slightly mass‐separated species (CsG) with a higher ion density. This radial perturbation is attributed to the coulombic repulsion between the two ion clouds as they interact during the excitation process, as previously proposed by Uechi and Dunbar. Magnitudes of the perturbation were confirmed by making cyclotron radii determinations utilizing the ratio of the third‐to‐first harmonics for the charged species of interest. It was found that these radial differences can account for as much as a 55% signal bias in favor of CsA for a single sample and a >20% positive bias in the slope of the regressed data set. A second behavior noted that also contributes to the potential inaccuracy of relative ion abundance measurements is the difference in signal decay rates for CsA and CsG. Damping constants and initial time domain signal amplitudes were evaluated using segmented Fourier transforms. Discrepancies in decay rates were not expected from two species that have essentially identical collisional cross‐sections. However, it has been observed that the faster decay rates are observed by the species of lower ion cloud density. We have attributed this differential signal decay phenomenon to the rates of loss of phase coherence for the two ion clouds. Previously, others have reported that less dense ion clouds are more susceptible to shearing and other disruptive forces during the course of their excited cyclotron motion. Our experimental evidence supports that it is the loss of cloud coherence that accounts for the signal loss over time, with the less dense cloud de‐phasing more quickly. As the ion populations of the two investigated species near equivalence, so do their time constants. Copyright © 2001 John Wiley & Sons, Ltd.
Mass spectrometric studies on small open‐chain piperazine‐containing ligands and their transition metal complexes
Authors: Nuutinen Jari M. J. , Ratilainen Jari , Rissanen Kari , Vainiotalo Pirjo 
Published: August 2002

AbstractElectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry was used to characterize the complexes formed between open‐chain piperazine‐containing ligands and transition metal salts (Cobalt, Copper, Zinc, and Cadmium as chlorides, nitrates, and acetates). Only single‐charged complexes were observed, formed of one ligand (L) and mainly one metal ion (M). Since the net charge of the complexes was one, a counterion (X) was attached to some of the complexes, with formation of [L + M + X]+ complexes, and a proton was lost from others, as in [L − H + M]+ complexes. In most cases the composition of the complexes was more dependent on the ligand than the metal salt. Collision‐induced dissociation measurements showed that complexes with related composition often differed in structure, or that interactions between the ligand and the metal ion were not alike. The metal ion influenced considerably the fragmentation pathways of the ligands, so that the fragmentation products could be used to deduce the binding sites of the metal. The variations observed in fragmentation behavior of complexes possessing the same ligand but different metal ions can mostly be explained by the ionic radius and electronic configuration of the metal ion. The results indicated a preference of the piperazine ring of the coordinated ligand for the boat conformation. Copyright © 2001 John Wiley & Sons, Ltd.
Factors contributing to peak broadening and mass accuracy in the characterization of intact spores using matrix‐assisted laser desorption/ionization coupled with time‐of‐flight mass spectrometry
Authors: Ramirez Javier , Fenselau Catherine 
Published: August 2002

AbstractFactors contributing to peak broadening, accuracy and precision in mass assignment in the matrix‐assisted laser desorption/ionization characterization of a lipopeptide desorbed from intact Bacillus spores were investigated. These spores were studied as an example of a thick, topologically irregular sample, which present a more difficult target than a pure peptide or protein. The type of matrix, matrix:sample ratio, laser fluence, and localized repetitive laser irradiation were all found to affect the full‐width at half maximum of the biomarker. Both in‐source and post‐source phenomena were shown to contribute. Sample thickness had less effect. Precision and accuracy of mass assignment were also affected by matrix:sample ratio and laser fluence. In general, this sample was responsive to the same experimental variables as pure peptides, and the use of an internal standard produced significant improvements in precision and accuracy. Copyright © 2001 John Wiley & Sons, Ltd.
Formation of cryptophanes from their precursors as viewed by liquid secondary ion mass spectrometry
Authors: Brotin Thierry , Darzac Magali , Forest Danièle , Becchi Michel , Dutasta Jean‐Pierre 
Published: August 2002

AbstractThe formation of cryptophane‐A (C1) and the deuterated cryptophanes C2–C6 from their respective precursors P1–P6 in a mass spectrometer ion‐source was evidenced by liquid secondary ion mass spectrometry (LSIMS). Mass‐analyzed ion kinetic energy experiments performed on the precursor molecular ions suggested that cryptophane formation occurred mainly in the liquid‐matrix before desorption rather than in the gas phase. In addition, we observed that the presence of cations, such as lithium or sodium ions, inhibited the formation of the cryptophane molecular ions. In the light of these results we used the LSIMS technique to investigate the formation of the new cryptophanes C7–C13. All the data collected support the idea that a direct comparison can be made between these experimental findings and chemistry in solution. Copyright © 2001 John Wiley & Sons, Ltd.
Matrix‐assisted laser desorption/ionization collision‐induced dissociation of linear single oligomers of nylon‐6
Authors: Murgasova Renata , Hercules David M. 
Published: August 2002

AbstractMatrix‐assisted laser desorption/ionization, collision induced‐dissociation (MALDI‐CID) has been used to obtain structural information for linear single oligomers of nylon‐6. The effects of matrix and cationization agent in MALDI‐CID analysis have been investigated. Fragmentation mechanisms are proposed for the series of ions that are observed in the MALDI‐CID spectra of the hexamer, octamer and dodecamer. Fragmentation processes observed in the MALDI‐CID spectra include cleavage of the end groups followed by dissociation of the m/z 113 unit. Cleavage of the oligamide chain occurs at the amide linkage, as well as at adjacent bonds. For the four matrices and three cationization agents investigated, 2,5‐dihydroxybenzoic acid and sodium chloride showed the best performance for MALDI‐CID analysis of the dodecamer. In addition, yields of the fragment ions in MALDI‐CID spectra were found to be dependent on the chain length distribution. Copyright © 2001 John Wiley & Sons, Ltd.
Mapping the ion kinetic energy in a helium microwave plasma orthogonal acceleration time‐of‐flight mass spectrometer
Authors: Su Yongxuan , Jin Zhe , Duan Yixiang , Olivares José A. 
Published: August 2002

AbstractThe ion kinetic energy of a helium microwave plasma is studied using an orthogonal acceleration time‐of‐flight mass spectrometer. The ions produced in the plasma are extracted into the mass spectrometer in an ‘off‐cone’ mode (i.e. the helium plasma plume is off the sampler cone), and enter the repelling zone in the x‐direction, which is perpendicular to the flight tube. The information of ion initial kinetic energy was obtained from both theoretical calculations and experimental results. The potential influence of two x‐direction steering plates (X‐steering plates) on the ion energy and signal intensity was examined. The influence of gas composition on the ion kinetic energy was also investigated. The calculated results show that ions with different m/z have different velocity and kinetic energy when they enter the ion modulation zone, and lighter ions have higher velocity and lower kinetic energy. The experimental results obtained demonstrate that the ion signals of different m/z produced with an ‘off‐cone’ sampling helium microwave plasma show similar trends as calculated with the potential difference of the X‐steering plates, revealing their narrow kinetic energy distribution in the x‐direction. Under typical operating conditions, the x‐direction kinetic energy of ions detected mostly range from about 14.9 eV for 7Li+ to 16.8 eV for 208Pb+. Published in 2001 by John Wiley & Sons, Ltd.
Investigation of ion‐pair precipitates of selected alkoxylates and complex salts of specific metal cations by liquid secondary ion mass spectrometry
Authors: Frański Rafał , Szymański Andrzej , Gierczyk Błażej , Chlebicki Jan , Frańska Magdalena 
Published: August 2002

AbstractLiquid secondary ion (LSI) mass spectra of ion‐pair precipitates obtained for Triton X‐100 with strontium, lead, cadmium and mercury tetraphenylborates and for selected butoxylene–ethoxylene monoalkyl ethers with barium tetraiodobismuthate(III) are discussed. On the basis of LSI mass spectra, recorded in both positive and negative modes, the formulae of the ion‐pair precipitates were determined. On the basis of B/E mass spectra, the fragmentation routes of [M − H + Ba]+ ions for butoxylene–ethoxylene monoalkyl ether complexes of barium and [M − H + Cd]+ ions for the Triton X‐100 complex of cadmium are proposed. Copyright © 2002 John Wiley & Sons, Ltd.
Influence of a ring substituent on the tendency to form H2O adducts to Ag+ complexes with phenylalanine analogues in an ion trap mass spectrometer
Authors: Perera B. A. , Gallardo A. L. , Barr J. M. , Tekarli S. M. , Anbalagan V. , Talaty E. R. , Van Stipdonk M. J. 
Published: August 2002

AbstractIn a previous report we showed that certain binary Ag+–amino acid complexes formed adduct ions by the attachment of a single water and methanol molecule when stored in an ion trap mass spectrometer: complexes with aliphatic amino acids and with 4‐fluorophenylalanine formed the adduct ions whereas complexes with phenylalanine and tryptophan did not. In this study we compared the tendency of the Ag+ complexes derived from phenylalanine, 4‐fluorophenylalanine, 4‐hydroxyphenylalanine (tyrosine), 4‐bromophenylalanine, 4‐nitrophenylalanine and aminocyclohexanepropionic acid to form water adducts when stored, without further activation, in the ion trap for times ranging from 1 to 500 ms. Because the donation of π electron density to the Ag+ ion is a likely determining factor in complex reactivity, our aim in the present study was to determine qualitatively the influence of para‐position substituents on the aromatic ring on the formation of the water adducts. Our results show that the reactivity of the complexes is influenced significantly by the presence of the various substituents. Decreases in [M + Ag]+ ion abundance, and increases in adduct ion abundance, both measured as a function of storage time, follow the trend —NO2 > —Br > —F > —OH > —H. The complex of Ag+ with 4‐nitrophenylalanine was nearly as reactive towards water as the Ag+ complex with aminocyclohexanepropionic acid, the last being an amino acid devoid of π character in the ring system. Collision induced dissociation of the [M + Ag]+ species derived from the amino acids produces, among other products, Ag+ complexes with a para‐substituted phenylacetaldehyde: complexes that also form adduct species when stored in the ion trap. The trends in adduct ion formation exhibited by the aldehyde–Ag+ complex ions were similar to those observed for the precursor complexes of Ag+ and the amino acids, confirming the influence of the ring substituent. Copyright © 2002 John Wiley & Sons, Ltd.
Circulation of enteroviruses and persistence of meningitis cases in the winter of 1999–2000
Authors: Chambon Martine , Archimbaud Christine , Bailly Jean‐Luc , Henquell Cécile , Regagnon Christel , Charbonné Françoise , Peigue‐Lafeuille Hélène 
Published: August 2002

AbstractThe seasonal incidence of enterovirus meningitis was analyzed in a prospective study of patients admitted for suspected meningitis from October 1, 1998 to April 30, 2000. In‐house reverse transcription‐polymerase chain reaction (RT‐PCR) in cerebrospinal fluid (CSF) was used irrespective of cytological results. Fifty‐two (45.2%) of the 115 patients had positive RT‐PCR in CSF, including 44/86 children (51.2%) and 8/29 adults (27.6%). Six of the 52 (11.5%) had no pleocytosis. The numbers of CSF specimens with a predominance of lymphocytes or a predominance of neutrophils were closely similar. In 33 of the positive patients, an enterovirus, mainly echoviruses type 6 (48%) and 30 (24%), was recovered in one or more specimens. Sixteen cases of enteroviral meningitis were observed between November 1999 and March 2000 as against 2 cases between November 1998 and March 1999, showing that the disease persisted through the winter months of 1999–2000. During the same period, 96 enterovirus isolates were recovered from clinical specimens from other patients. The number of isolates was higher in the winter of 1999–2000 (P < 0.01) than in the winter of 1998–1999, indicating that the risk of enterovirus infection increased significantly in winter 1999–2000. Sixteen patients had aseptic meningitis, made a rapid recovery and had an enterovirus in throat swabs and stools (9/16) or in one of the two (7/16). RT‐PCR was not requested. Nine patients were admitted during the cold months. The clinical management of both adult and child patients could be improved by year‐round use of enterovirus generic RT‐PCR. J. Med. Virol. 65:340–347, 2001. © 2001 Wiley‐Liss, Inc.
Enteroviral meningitis in Northern Jordan: Prevalence and association with clinical findings
Authors: Meqdam Mamdoh M. , Khalousi Mohamed M. , Al‐Shurman Abdullah 
Published: August 2002

AbstractDuring the summer‐autumn of 1999, 390 specimens of cerebrospinal fluid were taken from infants and children younger than 15 years of age. They were suspected of having meningitis and were admitted to Princess Rahma Hospital, Northern Jordan. They were investigated for the presence of enteroviruses using shell vial culture and indirect immunofluorescence assays. Most cases (46.9%) occurred in children younger than 1 year of age in which males represented 71.9%. The common symptoms were fever, vomiting, and headache. Enteroviruses were isolated from 32 (8.2%) cases, coxsackievirus B types 2, 4, and 5 from 15 (46.9%) cases, and echovirus 9 (31.3%) was the most common identified serotype. The virus isolation rate was directly proportional to the number of leukocytes in the cerebrospinal fluid. However, enteroviral isolation was demonstrated in 4 (12.5%) of 32 cerebrospinal fluid specimens without pleocytosis. Leukocyte differential count revealed a predominance of polymorphonuclear cells in 71.4% of the cases. Hospitalization ranged from 1 day to 25 days with a mean of 7 days. The majority of enterovirus‐infected patients (88.9%) were treated with at least one type of antibiotic. These results emphasize the importance of shell vial culture assay for diagnosing enteroviruses, especially in laboratories that do not have access to advanced techniques such as polymerase chain reaction. J. Med. Virol. 66:224–228, 2002. © 2002 Wiley‐Liss, Inc.
Reduced number of functional glutamatergic synapses in hippocampal neurons overexpressing full‐length TrkB receptors
Authors: Klau Michele , Hartmann Matthias , Erdmann Kai S. , Heumann Rolf , Lessmann Volkmar 
Published: August 2002

AbstractBrain‐derived neurotrophic factor (BDNF) acutely modulates the efficacy of central glutamatergic synapses via activation of the receptor tyrosine kinase TrkB. On a longer time scale, recent evidence suggests an additional role of TrkB signaling in the formation of excitatory synaptic connections. Here, we have overexpressed full‐length TrkB receptors (fl‐TrkB) in hippocampal neurons, to investigate the contribution of BDNF signaling to the maturation of glutamatergic synapses. Using patch clamp recordings, we show a three‐fold reduction in glutamatergic excitatory autaptic and synaptic current amplitudes in neurons overexpressing fl‐TrkB, and application of saturating concentrations of BDNF and NT‐4/5 completely reverses this effect. Compatible with these overexpression data, in untransfected neurons, scavenging of endogenous BDNF and NT‐4/5 by TrkB‐IgGs reduces excitatory autaptic current (EAC) amplitudes. By overexpression of truncated TrkB receptors (TrkB.T1, TrkB.T2) and a chimeric receptor containing only the intracellular domain of fl‐TrkB, we show that intra‐ and extracellular domains of fl‐TrkB are necessary to observe the EAC reduction. Labeling of presynaptic terminals with FM 4‐64 revealed, that the reduced EAC amplitudes in fl‐TrkB overexpressing neurons are accompanied by a two‐fold reduction in synapse number. These results suggest, that ligand‐independent signaling through fl‐TrkB receptors can decrease glutamatergic synaptic strength, if sufficient amounts of BDNF or NT‐4/5 are not available. J. Neurosci. Res. 66:327–336, 2001. © 2001 Wiley‐Liss, Inc.
Toxic effect of L‐2‐chloropropionate on cultured rat cerebellar granule cells is ameliorated after inhibition of reactive oxygen species formation
Authors: Myhre O. , Bjugan B. , Fonnum F. 
Published: August 2002

AbstractOral administration of rats to L‐2‐chloropropionate (L‐CPA) causes selective necrosis to the granule cell layer of the cerebellum in vivo and to cultured rat cerebellar granule cells in vitro. The present study was conducted to characterize the involvement of reactive oxygen species (ROS) in cell death of L‐CPA to rat cerebellar granule cells in vitro. Exposure to L‐CPA (0.625–10 mM) produced a concentration dependent increase in formation of 2,7‐dichlorofluorescein (DCF) as a measure of formation of ROS. The elevation of ROS was inhibited after incubation of the cells with the ERK‐type of MAP kinases inhibitor U0126, the mitochondrial permeability transition pore inhibitor cyclosporin A (CSA), the antioxidant vitamin E, and the spin trap N‐tert‐butyl‐α‐(2‐sulfophenyl)‐nitrone (S‐PBN). Measurements of nitrite (NO2) in the cell culture supernatant using the Griess reagent indicate generation of nitric oxide (NO) after exposure to L‐CPA. Incubation with L‐CPA (10 mM) for 48 hr lead to cell death (90%). When the granule cells were incubated with L‐CPA in combination with the inhibitors of free radical production, the cell death was ameliorated. The results show that L‐CPA is toxic to granular cells by production of ROS. © 2001 Wiley‐Liss, Inc.
Brain metabolism and brain disease: Is metabolic deficiency the proximate cause of Alzheimer dementia?
Authors: Blass John P. 
Published: August 2002

AbstractThe potential of impairments in oxidative/energy metabolism to cause diseases of the brain had been proposed even before the major pathways of oxidative/energy metabolism were described. Deficiencies associated with disease are known in all the pathways of oxidative/energy metabolism and are associated with some of the most common disorders of the nervous system, including Alzheimer's disease (AD) and Parkinson's disease. A common mechanism in these conditions appears to be a downward mitochondrial spiral, involving abnormalities in energy metabolism, calcium metabolism, and free radicals (reactive oxygen and nitrogen species). In AD, the spiral appears to interact with abnormalities in the metabolism of the Alzheimer amyloid precursor protein (APP) and its Aβ fragment. Several lines of evidence indicate that the mitochondrial spiral may be a proximate cause of the clinical disabilities in AD. Decreases in cerebral metabolic rate (CMR) characteristically occur in AD and in other dementias. Inducing decreases in CMR leads to clinical disabilities characteristically associated with AD and with analogous problems in experimental animals. Treatments directed toward normalizing CMR appear to help at least some patients. Further studies of this possibility and of treatments designed to ameliorate the mitochondrial spiral may prove useful for treating AD and perhaps some other dementing disorders. © 2001 Wiley‐Liss, Inc.
Nitric oxide synthase‐positive neurons in the rat superior colliculus: Colocalization of NOS with NMDAR1 glutamate receptor, GABA, and parvalbumin
Authors: Soares‐Mota Marcia , Henze Isabela , Mendez‐Otero Rosalia 
Published: August 2002

AbstractWe analyzed the potential input and output components of nitric oxide synthase (NOS)‐containing neurons in the rat superior colliculus (SC). To identify whether NOS‐positive neurons receive glutamatergic input we investigated the colocalization of NOS with NMDA receptor subunit R1 (NMDAR1). In addition, to examine whether putative nitric oxide synthesizing neurons represent a neurochemically specific or distinct subpopulation of cells in the SC we studied the colocalization of NOS with the neurotransmitter GABA, the calcium‐binding proteins parvalbumin, calbindin and calretinin and with neuropeptides such as somatostatin, substance P and neuropeptide Y. We found that 90% of NOS‐positive neurons in the superficial layers of the rat SC express NMDAR1. Nearly 20% of the population of nitridergic neurons also expresses GABA and 15% of them express parvalbumin. NOS‐positive neurons in the superior colliculus did not contain calretinin, calbindin or either of the neuropeptides tested. The results of this study show that the capacity for synthesizing NO in the SC is largely restricted to neurons that receive glutamatergic inputs and that some of these neurons express GABA or parvalbumin. J. Neurosci. Res. 64:501–507, 2001. © 2001 Wiley‐Liss, Inc.
Ice crystal number concentration versus temperature for climate studies
Authors: Gultepe I. , Isaac G.A. , Cober S.G. 
Published: August 2002

AbstractIce crystal number concentration (Ni) is an important parameter, having a strong influence on the calculation of cloud optical and microphysical parameters. Cloud and precipitation parameterizations within climate and weather forecasting models, affecting the heat and moisture budget of the atmosphere, cannot be determined accurately if Ni is not estimated correctly. Previous studies of ice crystal number concentration versus temperature (T) have shown that Ni–T relationships are not unique. The present study uses observations made in the glaciated regions of stratiform clouds from two Arctic and two mid‐latitude field projects to study the Ni versus temperature relationship. Scatter plots of Ni versus T at the ice particle measurement level do not show a good correlation with T for ice crystals at sizes less than 1000 µm. For a given temperature, the variation in Ni is found to be up to two to three orders of magnitude for ice crystals with sizes larger than approximately 100 µm. A significant Ni–T relationship is found for precipitation sized particles with sizes greater than 1000 µm. The ice particle concentration for sizes between 100 and 1000 µm varied from 0.1 to 100 L−1, independent of geographic location where the measurements were made. Based on this work, it is concluded that modelling studies should be tested for the possible variations in Ni versus T. Copyright © 2001 Royal Meteorological Society