bluuebunny/crossref_metadata_2025 huggingface dataset:
Glypican 4 modulates FGF signalling and regulates dorsoventral forebrain patterning inXenopusembryos
Authors: Galli Antonella , Roure Agnes , Zeller Rolf , Dono Rosanna
Published: August 2003

Heparan sulphate proteoglycans such as glypicans are essential modulators of intercellular communication during embryogenesis. In Xenopus laevis embryos, the temporal and spatial distribution of Glypican 4 (Gpc4) transcripts during gastrulation and neurulation suggests functions in early development of the central nervous system. We have functionally analysed the role of Xenopus Gpc4 by using antisense morpholino oligonucleotides and show that Gpc4 is part of the signalling network that patterns the forebrain. Depletion of GPC4 protein results in a pleiotropic phenotype affecting both primary axis formation and early patterning of the anterior central nervous system. Molecular analysis shows that posterior axis elongation during gastrulation is affected in GPC4-depleted embryos, whereas head and neural induction are apparently normal. During neurulation, loss of GPC4 disrupts expression of dorsal forebrain genes, such as Emx2, whereas genes marking the ventral forebrain and posterior central nervous system continue to be expressed. This loss of GPC4 activity also causes apoptosis of forebrain progenitors during neural tube closure. Biochemical studies establish that GPC4 binds FGF2 and modulates FGF signal transduction. Inhibition of FGF signal transduction, by adding the chemical SU5402 to embryos from neural plate stages onwards,phenocopies the loss of gene expression and apoptosis in the forebrain. We propose that GPC4 regulates dorsoventral forebrain patterning by positive modulation of FGF signalling.
Combinatorial function of the homeodomain proteins Nkx2.1 and Gsh2 in ventral telencephalic patterning
Authors: Corbin Joshua G. , Rutlin Michael , Gaiano Nicholas , Fishell Gord
Published: August 2003

Regional patterning of the mammalian telencephalon requires the function of three homeodomain-containing transcription factors, Pax6, Gsh2 and Nkx2.1. These factors are required for the development of the dorsal, lateral and medial domains of the telencephalon, respectively. Previous work has indicated that two of the genes encoding these factors, Pax6 and Gsh2,cross-repress one another in the formation of the border between dorsal and lateral region of the telencephalon. Here, we examine whether similar interactions are responsible for the establishment of other boundaries of telencephalic gene expression. Surprisingly, despite the fact that, at specific times in development, both Pax6 and Gsh2 maintain a complementary pattern of expression with Nkx2.1, in neither case are these boundaries maintained through a similar cross-repressive mechanism. Rather, as revealed by analysis of double-mutant mice, Nkx2.1 and Gsh2 act cooperatively in many aspects to pattern the ventral telencephalon. By contrast, as indicated by both loss- and gain-of-function analysis, Gsh2 expression in the medial ganglionic eminence after E10.5 may negatively regulate Nkx2.1 dependent specification of oligodendrocytes. Therefore, both integrative and antagonistic interactions between homeodomain-containing transcription factors contribute to the patterning of the telencephalon.
Integration of multiple signal transducing pathways on Fgf response elements of theXenopus caudalhomologueXcad3
Authors: Haremaki Tomomi , Tanaka Yasuko , Hongo Ikuko , Yuge Masahiro , Okamoto Harumasa
Published: August 2003

Early neural patterning along the anteroposterior (AP) axis appears to involve a number of signal transducing pathways, but the precise role of each of these pathways for AP patterning and how they are integrated with signals that govern neural induction step is not well understood. We investigate the nature of Fgf response element (FRE) in a posterior neural gene, Xcad3 (Xenopus caudal homologue) that plays a crucial role of posterior neural development. We provide evidence that FREs of Xcad3 are widely dispersed in its intronic sequence and that these multiple FREs comprise Ets-binding and Tcf/Lef-binding motifs that lie in juxtaposition. Functional and physical analyses indicate that signaling pathways of Fgf, Bmp and Wnt are integrated on these FREs to regulate the expression of Xcad3 in the posterior neural tube through positively acting Ets and Sox family transcription factors and negatively acting Tcf family transcription factor(s).
Egfr/Ras pathway mediates interactions between peripodial and disc proper cells inDrosophilawing discs
Authors: Pallavi S. K. , Shashidhara L. S.
Published: August 2003

All imaginal discs in Drosophila are made up of a layer of columnar epithelium or the disc proper and a layer of squamous epithelium called the peripodial membrane. Although the developmental and molecular events in columnar epithelium or the disc proper are well understood, the peripodial membrane has gained attention only recently. Using the technique of lineage tracing, we show that peripodial and disc proper cells arise from a common set of precursors cells in the embryo, and that these cells diverge in the early larval stages. However, peripodial and disc proper cells maintain a spatial relationship even after the separation of their lineages. The peripodial membrane plays a significant role during the regional subdivision of the wing disc into presumptive wing, notum and hinge. The Egfr/Ras pathway mediates this function of the peripodial membrane. These results on signaling between squamous and columnar epithelia are particularly significant in the context of in vitro studies using human cell lines that suggest a role for the Egfr/Ras pathway in metastasis and tumour progression.
Interaction of the actin cytoskeleton with microtubules regulates secretory organelle movement near the plasma membrane in human endothelial cells
Authors: Manneville Jean-Baptiste , Etienne-Manneville Sandrine , Skehel Paul , Carter Tom , Ogden David , Ferenczi Michael
Published: August 2003

The role of cytoskeletal elements in regulating transport and docking steps that precede exocytosis of secretory organelles is not well understood. We have used Total Internal Reflection Fluorescence (TIRF) microscopy to visualize the three-dimensional motions of secretory organelles near the plasma membrane in living endothelial cells. Weibel-Palade bodies (WPb), the large tubular storage organelles for von Willebrand factor, were labelled with Rab27a-GFP. By contrast, green fluorescent protein (GFP)-tagged tissue-type plasminogen activator (tPA-GFP) labelled submicron vesicular organelles. Both populations of GFP-labelled organelles underwent stimulated exocytosis. The movement of these morphologically distinct organelles was measured within the evanescent field that penetrated the first 200 nm above the plasma membrane. WPb and tPA-GFP vesicles displayed long-range bidirectional motions and short-range diffusive-like motions. Rotating and oscillating WPb were also observed. TIRF microscopy enabled us to quantify the contribution of actin and microtubules and their associated motors to the organelle motions close to the plasma membrane. Long-range motions, as well as WPb rotations and oscillations, were microtubule-and kinesin-dependent. Disruption of the actin cytoskeleton and inhibition of myosin motors increased the number of long-range motions and, in the case of WPb, their velocity. The actin and microtubules had opposite effects on the mobility of organelles undergoing short-range motions. Actin reduced the mobility and range of motion of both WPb and tPA vesicles, whereas microtubules and kinesin motors increased the mobility of WPb. The results show that the dynamics of endothelial secretory organelles close to the plasma membrane are controlled by the opposing roles of the microtubule and actin cytoskeletal transport systems.
The Hrp65 self-interaction is mediated by an evolutionarily conserved domain and is required for nuclear import of Hrp65 isoforms that lack a nuclear localization signal
Authors: Kiesler Eva , Miralles Francesc , Farrants Ann-Kristin Östlund , Visa Neus
Published: August 2003

Hrp65, an evolutionary conserved RNA-binding protein from the midge Chironomus tentans, has a conserved DBHS (Drosophila behavior, human splicing) domain that is also present in several mammalian proteins. In a yeast two-hybrid screening we found that Hrp65 can interact with itself. Here we confirm the Hrp65 self-interaction by in vitro pull-down experiments and map the sequences responsible for the interaction to a region that we refer to as the protein-binding domain located within the DBHS domain. We also show that the protein-binding domains of Drosophila NonA and human PSF, two other proteins with conserved DBHS domains, bind to Hrp65 in the yeast two-hybrid system. These observations indicate that the protein-binding domain can mediate homodimerization of Hrp65 as well as heterodimerization between different DBHS-containing proteins. Moreover, analyses of recombinant Hrp65 by gel-filtration chromatography show that Hrp65 can not only dimerize but also oligomerize into complexes of at least three to six molecules. Furthermore, we have analyzed the functional significance of the Hrp65 self-interaction in cotransfection assays, and our results suggest that the interaction between different Hrp65 isoforms is crucial for their intracellular localization.
Heterogeneous proliferative potential in regenerative adult newt cardiomyocytes
Authors: Bettencourt-Dias Mónica , Mittnacht Sybille , Brockes Jeremy P.
Published: August 2003

Adult newt cardiomyocytes, in contrast to their mammalian counterparts, can proliferate after injury and contribute to the functional regeneration of the heart. In order to understand the mechanisms underlying this plasticity we performed longitudinal studies on single cardiomyocytes in culture. We find that the majority of cardiomyocytes can enter S phase, a process that occurs in response to serum-activated pathways and is dependent on the phosphorylation of the retinoblastoma protein. However, more than half of these cells stably arrest at either entry to mitosis or during cytokinesis, thus resembling the behaviour observed in mammalian cardiomyocytes. Approximately a third of the cells progress through mitosis and may enter successive cell divisions. When cardiomyocytes divided more than once, the proliferative behaviour of sister cells was significantly correlated, in terms of whether they underwent a subsequent cell cycle, and if so, the duration of that cycle. These observations suggest a mechanism whereby newt heart regeneration depends on the retention of proliferative potential in a subset of cardiomyocytes. The regulation of the remaining newt cardiomyocytes is similar to that described for their mammalian counterparts, as they arrest during mitosis or cytokinesis. Understanding the nature of this block and why it arises in some but not other newt cardiomyocytes may lead to an augmentation of the regenerative potential in the mammalian heart.
Parkin is recruited to the centrosome in response to inhibition of proteasomes
Authors: Zhao Jinghui , Ren Yong , Jiang Qian , Feng Jian
Published: August 2003

Parkin is a protein-ubiquitin E3 ligase linked to Parkinson's disease. Although several substrates of parkin have been identified, the subcellular location for parkin to recognize and ubiquitinate its targets is unclear. Here we report that parkin was accumulated in the centrosome when SH-SY5Y or transfected HEK293 cells were treated with the proteasome inhibitor lactacystin. The specific recruitment of parkin was dependent on concentration and duration of the treatment, and was accompanied by the centrosomal accumulation of ubiquitinated proteins and CDCrel-1, a substrate of parkin. The recruitment of parkin was apparently mediated through its binding to γ-tubulin, which has been shown to accumulate in the centrosome in response to misfolded proteins. Furthermore, the effect was abrogated by the microtubule-depolymerizing drug colchicine or the microtubule-stabilizing drug taxol, which indicates that the intact microtubule network is required for the centrosomal recruitment of parkin. Taken together, our data suggest that the lactacystin-induced accumulation of parkin in the centrosome plays a significant role in the ubiquitination of misfolded substrates accumulated there. This process may provide a subcellular locale for parkin to ubiquitinate and degrade protein aggregates critically involved in the pathogenesis of Parkinson's disease.
Distinct centromere domain structures with separate functions demonstrated in live fission yeast cells
Authors: Appelgren Henrik , Kniola Barbara , Ekwall Karl
Published: August 2003

Fission yeast (Saccharomyces pombe) centromere DNA is organized in a central core region flanked on either side by a region of outer repeat (otr) sequences. The otr region is known to be heterochromatic and bound by the Swi6 protein whereas the central core region contains an unusual chromatin structure involving the histone H3 variant Cnp1 (S. pombe CENP-A). The central core is the base for formation of the kinetochore structure whereas the flanking region is important for sister centromere cohesion. We have previously shown that the ultrastructural domain structure of S. pombe centromeres in interphase is similar to that of human centromeres. Here we demonstrate that S. pombe centromeres are organized in cytologically distinct domains even in mitosis. Fluorescence in situ hybridization of fixed metaphase cells revealed that the otr regions of the centromere were still held together by cohesion even after the sister kinetochores had separated. In live cells, the central cores and kinetochores of sister chromosomes could be distinguished from one another when they were subjected to mitotic tension. The function of the different centromeric domains was addressed. Transacting mutations affecting the kinetochore (nuf2) central core domain (mis6) and the heterochromatin domain (rik1) were analyzed in live cells. In interphase, both nuf2 and mis6 caused declustering of centromeres from the spindle pole body whereas centromere clustering was normal in rik1 despite an apparent decondensation defect. The declustering of centromeres in mis6 cells correlated with loss the Ndc80 kinetochore marker protein from the centromeres. Interestingly the declustered centromeres were still restricted to the nuclear periphery thus revealing a kinetochore-independent peripheral localization mechanism for heterochromatin. Time-lapse microscopy of live mis6 and nuf2-1 mutant cells in mitosis showed similar severe misaggregation phenotypes whereas the rik1 mutants showed a mild cohesion defect. Thus, S. pombe centromeres have two distinguishable domains even during mitosis, and our functional analyses support the previous observations that the kinetochore/central core and the heterochromatin domains have distinct functions both in interphase and mitosis.
Weibel-Palade bodies recruit Rab27 by a content-driven, maturation-dependent mechanism that is independent of cell type
Authors: Hannah Matthew J. , Hume Alistair N. , Arribas Monica , Williams Ross , Hewlett Lindsay J. , Seabra Miguel C. , Cutler Daniel F.
Published: August 2003

The identification of organelles is crucial for efficient cellular function, yet the basic underlying mechanisms by which this might occur have not been established. One group of proteins likely to be central to organelle identity is the Rab family of small GTPases. We have thus investigated Rab recruitment to membranes using endothelial cells as a model system. We report that Weibel-Palade bodies, the Von Willebrand Factor storage compartment of human umbilical vein endothelial cells, contain Rab27a. We have also found that Weibel-Palade body-like structures induced in HEK-293 cells by the expression of von Willebrand factor can recruit endogenous Rab27a. In the absence of von Willebrand Factor, Rab27a is not lysosome associated, indicating that it can distinguish between the Weibel-Palade-body-like organelle and a classical lysosome. Finally, a time course of Weibel-Palade-body formation was established using a green-fluorescent version of von Willebrand factor. Newly formed Weibel-Palade bodies lack Rab27a, which is acquired some hours after initial appearance of the cigar-shaped organelle. We conclude that a lumenal cargo protein drives the recruitment of Rab27a to the organelle membrane by a novel mechanism that is indirect, maturation-dependent and cell-type independent.
Stacking Phenomenon of Self-assembled Monolayers and Bilayers of Thioalkyl-substituted Tetrathiafulvalene
Authors: Lu Jun , Zeng Qing-dao , Wang Chen , Wan Li-jun , Bai Chun-li
Published: August 2003

The self-assembled monolayer and bilayer of tetrakis (octadecylthio)tetrathiafulvalene (TODT-TTF) on highly orientated pyrolytic graphite (HOPG) surface were studied by scanning tunneling microscope (STM). Direct observation of the dimer of TODT-TTF formed by π-π interaction was achieved.
Efficient Photocycloreversion Reaction of Diarylethenes by Introduction of Cyano Subsutituents to the Reactive Carbons
Authors: Morimitsu Kentaro , Kobatake Seiya , Nakamura Shinichiro , Irie Masahiro
Published: August 2003

Highly efficient photocycloreversion reaction was observed for diarylethene derivatives with cyano groups at the reactive carbons of the thiophene rings. The cycloreversion quantum yield of 1,2-bis(2-cyano-5-phenyl-3-thienyl)perfluorocyclopentene was found to be ca. 30 times larger than that of 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene.
Excellent Catalytic Performances of SBA-15-supported Vanadium Oxide for Partial Oxidation of Methane to Formaldehyde
Authors: Lin Baomin , Wang Xiaoxing , Guo Qian , Yang Wei , Zhang Qinghong , Wang Ye
Published: August 2003

Vanadium oxide supported on SBA-15 exhibits superior catalytic performances for the partial oxidation of methane to formaldehyde. A space-time yield of formaldehyde as high as 93 mol kgcat.−1h−1 has been obtained with a formaldehyde selectivity of 94% over 3 wt % VOx/SBA-15 catalyst, significantly higher than those reported so far.
Large-scale Synthesis of Luminescent Y2O3:Eu Nanobelts
Authors: He Yu , Tian Ye , Zhu Yongfa
Published: August 2003

A two-step method was developed for the large-scale synthesis of luminescent Y2O3:Eu nanobelts. The structure and composition of the as-prepared Y2O3:Eu were characterized by XRD, TEM, and EDX. The luminescent performance of the nanobelts was also characterized and the result was different from that of the other Y2O3:Eu materials observed before.
1,2-Bis[(4-phenylpyridinio)methyl]benzene Dication. Its Unprecedented Selective Complexation with H2PO4−
Authors: Gono Hideyuki , Tamagaki Seizo
Published: August 2003

The anion complexation ability of 1,2-bis[(4-phenylpyridinio)methyl]benzene dichloride in MeCN was examined by UV-titration. The compound produced selectively the sufficiently strong H2PO4− complex in a 1:2 molar ratio. The presence of both of the 4-phenyl moieties was required for the H2PO4−-selection. The X-ray crystallography of the complex structure is presented.
Novel Selective Oxidation of Light Alkanes Using Carbon Dioxide. Oxidized Diamond as a Novel Catalytic Medium
Authors: Nakagawa Kiyoharu , Okumura Kimito , Shimamura Takahiro , Ikenaga Na-oki , Suzuki Toshimitsu , Kobayashi Tetsuhiko , Nishitani-Gamo Mikka , Ando Toshihiro
Published: August 2003

Carbon dioxide is an effective oxidant for the conversion of alkanes to chemical feedstocks. Oxidized diamond is useful as a novel catalytic support material. Oxidized diamond provided catalytic sites for the activation of alkanes under CO2 atmosphere. The present findings also suggest that the surface-properties of oxidized diamond may facilitate unique catalytic reactions, such as alkanes conversion in the presence of CO2.
Anisotropic Alignment Change of Columnar Liquid Crystal by Polarized Infrared Irradiation
Authors: Monobe Hirosato , Kiyohara Kenji , Terawasa Naohiro , Heya Manabu , Awazu Kunia , Shimizu Yo
Published: August 2003

Infrared photoinduced alignment change of liquid crystal domains was investigated and a uniform and anisotropic change of domains was observed. The texture observation and polarized microscopic IR spectra show that a change of the molecular alignment occurred and the direction of columns depends on the polarizing angle of an irradiating infrared light.
Reaction of Acetone on Coodinated Nitrile in β-Diketonato Ruthenium Complex, [Ru(acac)2(CH3CN)2] with the formation of β-Ketiminate
Authors: Hashimoto Takeshi , Hara Shuhei , Shiraishi Yumi , Natarajan Karuppannan , Shimizu Kunio
Published: August 2003

Synthesis and characterization of a new ruthenium complex, [Ru(acac)2(mhmk)] (1) with coordinated β-ketiminate ligand are described. The complex has been obtained by the reaction of acetone on coordinated acetonirile in [Ru(acac)2(CH3CN)2], the first such reaction to be observed. X-ray structure of 1 is similar to that of [Ru(acac)3]. Cyclic voltammetric studies of 1 show a negative shift for both reduction and oxidation indicating that there is large electron density on ruthenium containing β-ketiminate ligand when compared to ruthenium containing only β-diketonato ligands, [Ru(acac)3].
Photochemistry of a Tellurosilyl(carbonyl)iron(II) Complex. Generation of a Novel Te–Si–Fe Three-membered Cyclic Intermediate
Authors: Okada Hiroshi , Okazaki Masaaki , Tobita Hiromi , Ogino Hiroshi
Published: August 2003

The tellurosilyliron complex Cp*(CO)2FeSiMe2TePh (1) was synthesized by treatment of Cp*(CO)2FeSiMe2Cl with LiTePh. Irradiation of complex 1 and acetone in toluene led to dissociation of a CO ligand and insertion of acetone into the silicon–tellurium bond to afford the five-membered metallacycle Cp*(CO)Fe{κ2(Si,Te)-Me2SiOCMe2TePh}.
Photochemical mer → fac One-way Isomerization of Phosphorescent Material. Studies by Time-resolved Spectroscopy for Tris[2-(4′,6′-difluorophenyl)pyridine]iridium(III) in Solution
Authors: Karatsu Takashi , Nakamura Takeshi , Yagai Shiki , Kitamura Akihide , Yamaguchi Kentaro , Matsushima Yoshimasa , Iwata Takeshi , Hori Yoji , Hagiwara Toshimitsu
Published: August 2003

Photochemical characterization is reported for the mer-stereoisomer of fac-tris[2-(4′,6′-difluorophenyl)pyridine]iridium(III) (2), which has attracted attention as a electrophosphorescent material. The mer-2 has a much smaller emission-quantum yield and a shorter emission lifetime than those of the fac-isomer. The relation of the photophysical properties of mer-2 and one-way photoisomerization to fac-2 is discussed.
Changes in Post-Source Decay Fragmentation Behavior of Poly(Methyl Methacrylate) Polymers with Increasing Molecular Weight Studied by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry
Authors: Laine Olli , Trimpin Sarah , Räder Hans Joachim , Müllen Klaus
Published: August 2003

In order to investigate the systematic changes in fragmentation behavior of poly(methyl methacrylate) (PMMA) with increasing molecular weight, alkali–metal cationized PMMA 20-mer, 60-mer and 100-mer were selected for post-source decay (PSD) fragmentation study by matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry. PMMA polymers were cationized with lithium, potassium and cesium cations to explore the influence of the cation size on the fragmentation behavior of the polymers. All PMMA polymers could be fragmented by MALDI-PSD and fragmentation of the MALDI ionized synthetic polymer of molecular weight 10 kDa is reported here for the first time. It was shown that an increasing molecular weight of the PMMA chain required an increase in the size of the cation to improve the intensity and the number of the fragments in the PSD spectrum. Some instrumental parameters had to be optimized prior to a successful PSD analysis of the largest PMMA polymers.
Diffusion-Limited Extraction of Organic Ions by a Track-Membrane Interfaced Vacuum Inlet
Authors: Gridin V.V. , Kim T.K. , Bekkerman A. , Bulatov V. , Jung K.-H. , Schechtera I.
Published: August 2003

Glycerol-wetted track membranes (polyethylene terephthalate) were used to interface a low-vacuum facility (∼ 10−3 Torr) to an ambient pressure liquid analyte. High-field charge extraction conditions were routinely maintained between the liquid samples and a grid collector. The latter was positioned just near to the vacuum-facing side of such membranes. Upon establishing a steady-state charge-extraction regime, the collector currents were monitored and recorded at various solute concentration levels. The collector currents, which depend on solute concentration, were found to agree with recent theoretical treatments of such processes. Both positively- and negatively-charged species from organic solutions were routinely extracted. Ion injection for the low- and the high-mobility species has favored the diffusion-limited and the evaporation-limited schemes, respectively. Variable concentrations of 1-pyrenoyl-methylpyridinium bromide as well as naphthylacetic and anthracenecarboxylic acids in glycerol were used.
Charge Exchange in Tandem Mass Spectrometry: Dissociative Single Electron Capture by Doubly-Charged Toluene Cations
Authors: Fati Dorina , Leyh Bernard
Published: August 2003

Single electron capture by doubly-charged toluene cations upon collision with various target gases has been investigated by sector tandem mass spectrometry. Both non-dissociative and dissociative charge transfer reactions leading to C7H7+ + H and to C5H5+ + [C2,H3] are detected. Seven atomic or molecular target gases have been used with ionisation energies ranging from 8.8 eV to 14 eV. The branching ratios between the different non-dissociative and dissociative exit channels have been determined as well as the translational energy release on the dissociation products. The experimental data are compared to the predictions of a two-state semi-classical theoretical model that takes into account the non-adiabatic transition responsible for the charge transfer reaction. A wide reaction window shows up but the internal energies of the C7H8+ cations produced by single electron capture are observed to be larger than expected. We assign this effect partly to the influence of the large density of vibrational states and to the multichannel nature of the process. Excited states of the dication are also most probably involved in the charge exchange reaction.
Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Studies of Low Molecular Weight Dendrimers
Authors: Zhao Zhenwen , Xiong Shaoxiang , Liu Xiangwen , Xin Bin , Wang Guanghui
Published: August 2003

We report the application of matrix-assisted laser desorption/ionization time-of-flight (MALDI-ToF) mass spectrometry, with delayed extraction in the reflectron mode, for the characterization of low molecular weight dendrimers. 20 dendrimer samples were measured and 4 typical dendrimers, as examples, are discussedin detail. Several factors that affect the analysis including the matrices used, the concentrations of sample, the solvents and cationization reagent used, were investigated in detail. Experimental results indicate that the type of solvent can greatly influence exact mass measurement. However, sample preparation is generally not very critical for dendrimer analysis using MALDI-ToF since many kinds of matrices and a wide range of sample concentrations can be used efficiently. In addition, the Cs+ ion can be used to enhance the efficiency of cationization. Some reasons for this behavior are discussed on the basis of results of calculations using Gaussian94 software (a connected system of programs for performing a variety of semi-empirical and ab initio molecular orbital (MO) calculations).
MASSIS: A Mass Spectrum Simulation System. 1. Principle and Method
Authors: Chen HaiFeng , Fan BoTao , Xia HaiRong , Petitjean Michel , Yuan ShenGang , Panaye Annick , Doucet Jean-Pierre
Published: August 2003

A mass spectrum simulation system was developed. The simulated spectrum for a given target structure is computed based on the cleavage knowledge and statistical rules established and stored in pivot databases: cleavage rule knowledge, functional groups, small fragments and fragment-intensity relationships. These databases were constructed from correlation charts and statistical analysis of a large population of organic mass spectra using data mining techniques. Since 1980, several systems have been proposed for mass spectrum simulation, but at present there is no commercial software available. This shows the complexity and difficulties in the development of such a system. The reported mass spectral simulation system in this paper could be the first general software for organic chemistry use.
Reactions of the Ionised Enol Tautomer of Acetanilide: Elimination of HNCO via a Novel Rearrangement
Authors: Heydorn Lisa N. , Carter Lynn M. , Bowen Richard D. , Terlouw Johan K.
Published: August 2003

The reactions of ionised acetanilide, C6H5NH(=O)CH3•+, and its enol, C6H5NH(OH)=CH2•+, have been studied by a combination of tandem mass spectrometric and computational methods. These two isomeric radical cations have distinct chemistries at low internal energies. The keto tautomer eliminates exclusively CH2=C=O to give ionised aniline. In contrast, the enol tautomer loses H–N=C=O, via an unusual skeletal rearrangement, to form predominantly ionised methylene cyclohexadiene. Hydrogen atom loss also occurs from the enol tautomer, with the formation of protonated oxindole. The mechanisms for H–N=C=O and hydrogen atom loss both involve cyclisation; the former proceeds via a spiro transition state formed by attachment of the methylene group to the ipso position, whereas the latter entails the formation of a five-membered ring by attachment to the ortho position. The behaviour of labelled analogues reveals that these two processes have different site selectivities. Hydrogen atom loss involves a reverse critical energy and is subject to an isotope effect. Surprisingly, attempts to promote the enolisation of ionised acetanilide by proton-transport catalysis were unsuccessful. In a reversal of the usual situation for ionised carbonyl compounds, ionised acetanilide is actually more stable than its enol tautomer. The enol tautomer was resistant to proton-transport catalysed ketonisation to ionised acetanilide, possibly because the favoured geometry of the encounter complex with the base molecule is inappropriate for facilitating tautomerisation.
Gas-Phase Bimolecular Reactions between •CH2—(CH2)n—C+=O Distonic Ions and Pyridine: A Combined Experimental and Theoretical Study
Authors: Gerbaux Pascal , Wantier Pascale , Bury Micheline , De Meyer Claude , Finet Daniel , Van Haverbeke Yves
Published: August 2003

The gas-phase reactivities of the well-known •CH2CH2C+=O and •CH2CH2CH2C+=O distonic ions towards neutral pyridine were studied both experimentally (six sector hybrid mass spectrometer) and theoretically (density functional theory and Møller–Plesset ab initio calculations). Competitively to the charge exchange and protonation processes, both radical cations react with pyridine by an initial bonding between the positive charge site of the ion and the lone electron pair of the neutral molecule. At variance with previously reported studies in which such a nucleophilic interaction was proposed to play only a transient catalytic role, the initial C–N bond is likely to remain in the observed ion–molecule reaction products. The structures of the ion–molecule reactions products were probed by collisional activation at high kinetic energy and the reaction pathways were tentatively proposed on the basis of labeling experiments and ab initio molecular orbital calculations.
Potential Role of Methyl-Radical Adducts with Carbon Dioxide in the Martian Atmosphere
Authors: Schröder Detlef , Semialjac Marija , Schwarz Helmut
Published: August 2003

Neutralization reionization (NR) and charge reversal (CR) mass spectra of [CH3/CO2]−/+ ions are used to examine the behavior of the transient neutral radicals CH3OCO• and CH3COO•. While neutralization of the ionic species is associated with considerable changes of the geometries resulting in unfavorable Franck–Condon factors for vertical electron transfer in high-energy collisions, NR experiments nevertheless demonstrate the existence of both radicals in the gas phase. Analysis of the NR and CR spectra provides insight into the decomposition reactions of CH3OCO• and CH3COO•. For the former, loss of either CO or CO2 can occur at the neutral stage, whereas decarboxylation prevails in the latter case.
Ion—Molecule Reactions of [C, H3, S]+ Ions and Evidence for Long-Lived Triplet CH3S+
Authors: Teruel Mariano , de Moraes Patricia R.P. , Xavier Luciano A. , Riveros José M.
Published: August 2003

Gas-phase [C, H3, S]+ ions obtained by electron impact from (CH3)2S at 14 eV undergo two distinct low-pressure ion–molecule reactions with the parent neutral: proton transfer and charge exchange. The kinetics of these reactions studied by Fourier transform ion cyclotron resonance (FT-ICR) techniques clearly suggests the [C, H3, S]+ species to be a mixture of isomeric ions. While proton transfer is consistent with reagent ions displaying the CH2SH+ connectivity, the observed charge exchange strongly argues for the presence of thiomethoxy cations, CH3S+, predicted to be stable only in the triplet state. Charge exchange reactions are also observed in the reaction of these same [C, H3, S]+ ions with benzene, toluene and phenetole. For these substrates, the CH2SH+ ions can promote proton transfer and electrophilic methylene insertion in the aromatic ring with elimination of H2S. The results obtained for the different substrates suggest that the fraction of long-lived fraction of thiomethoxy cations obtained at 14 eV by electron ionization of dimethyl sulfide amounts to ∼(22 ± 4)% of the [C, H3, S]+ fragments.
Translational to Vibrational Energy Conversion during Surface-Induced Dissociation of N-Butylbenzene Molecular Ions Colliding at Self-Assembled Monolayer Surfaces
Authors: Jo Sung-Chan , Cooks R. Graham
Published: August 2003

Translational to vibrational (T→V) energy conversion in the course of inelastic collisions of n-butylbenzene molecular ions with thiolate self-assembled monolayer (SAM) gold surfaces is studied to better understand internal energy uptake by the hyperthermal projectile ions. The projectile ion is selected by a mass spectrometer of BE configuration and product ions are analyzed using a quadrupole mass analyzer after kinetic energy selection with an electric sector. The branching ratio for formation of the fragment ions m/z 91 and m/z 92, measured over a range of collision energies, is used to estimate the average internal energy with the aid of calculations based on unimolecular dissociation kinetics [Rice–Ramsperger–Kassel–Marcus (RRKM) theory]. The measured T→V conversion efficiencies (the fraction of the laboratory kinetic energy converted into internal energy) are 11∼12% for dodecanethiolate SAM (H-SAM) and 19∼20% for 2-perfluorooctylethanethiolate SAM (F-SAM), respectively, over ranges of a few 10s of eV. The values are similar to those reported earlier for other thermometer molecules undergoing surface collisions. Chemical sputtering leading to ionization of the surface is a prominent feature of the surface-induced dissociation (SID) spectra of n-butylbenzene acquired using the H-SAM surface but not the F-SAM surface because of the lower ionization energy of the former.
The Gas-Phase Basicity and Proton Affinity of 1,3,5-Cycloheptatriene—Energetics, Structure and Interconversion of Dihydrotropylium Ions
Authors: Salpin Jean-Yves , Mormann Michael , Tortajada Jeanine , Nguyen Minh-Tho , Kuck Dietmar
Published: August 2003

The hitherto unknown gas-phase basicity and proton affinity of 1,3,5-cycloheptatriene (CHT) have been determined by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Several independent techniques were used in order to exclude ambiguities due to proton-induced isomerisation of the conjugate cyclic C7H9+ ions, [CHT + H]+. The gas-phase basicity obtained by the thermokinetic method, GB(CHT) = 799 ± 4 kJ mol−1, was found to be identical, within the limits of experimental error, with the values measured by the equilibrium method starting with protonated reference bases, and with the values resulting from the measurements of the individual forward and reverse rate constants, when corrections were made for the isomerised fraction of the C7H9+ population. The experimentally determined gas-phase basicity leads to the proton affinity of cycloheptatriene, PA(CHT) = 833 ± 4 kJ mol−1, and the heat of formation of the cyclo-C7H9+ ion, Δ Hf0([CHT + H]+) = 884 ± 4 kJ mol−1. Ab initio calculations are in agreement with these experimental values if the 1,2-dihydrotropylium tautomer, [CHT + H(1)]+, generated by protonation of CHT at C-1, is assumed to be the conjugate acid, resulting in PA(CHT) = 825 ± 2 kJ mol−1 and Δ Hf0300([CHT + H(1)]+) = 892 ± 2 kJ mol−1. However, the calculations indicate that protonation of cycloheptatriene at C-2 gives rise to transannular C–C bond formation, generating protonated norcaradiene [NCD + H]+, a valence tautomer being 19 kJ mol−1 more stable than [CHT + H(1)]+. The 1,4-dihydrotropylium ion, [CHT + H(3)]+, generated by protonation of CHT at C-3, is 17 kJ mol−1 less stable than [CHT + H(1)]+. The bicyclic isomer [NCD + H]+ is separated by relatively high barriers, 70 and 66 kJ mol−1 from the monocyclic isomers, [CHT + H(1)]+ and [CHT + H(3)]+, respectively. Therefore, the initially formed 1,2-dihydrotropylium ion [CHT + H(1)]+ does not rearrange to the bicyclic isomer [NCD + H]+ under mild protonation conditions.
A Quantum Chemical Study of the Protonation of Phenylphosphine and its Halogenated Derivatives
Authors: Nam Pham-Cam , Gerbaux Pascal , Nguyen Minh Tho
Published: August 2003

The protonation and methylation of phenylphosphine (C6H5PH2) and its mono-halogenated derivatives have been studied using ab initio quantum chemical calculations. Density functional theory (B3LYP) calculations using the 6-311++G(d,p) basis set consistently confirm that protonation of phenylphosphines takes place at the phosphorus atom; the C4-protonated phenylphosphine lying about 66 kJ mol−1 above the P-protonated isomer. Similarly, methylation of phosphines consistently occurs at phosphorus. The proton and methyl cation affinities are estimated as follows: PA(phenylphosphine) = 863 ± 10 kJ mol−1 and MCA(phenylphosphine) = 515 ± 12 kJ mol−1. Mono-halogen substitution appears to reduce the proton affinites by up to 20 kJ mol−1. In this context, following P-protonation of either a meta- or a para-X–C6H4–PH2, an elimination of the halogen X-atom under collisional activation (CA) conditions is expected to lead to a distonic radical cation, a low-energy isomer being 50 kJ mol−1 above ionized phenylphosphine.
Is Allylphosphine a Carbon or a Phosphorus Base in the Gas Phase?
Authors: del Carmen Sicilia Maria , Mó Otilia , Yáñez Manuel , Guillemin Jean-Claude , Gal Jean-François , Maria Pierre-Charles
Published: August 2003

The gas-phase basicity of allylphosphine (2-propenylphosphine) was measured by means of Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry techniques. A complete survey of the allylphosphine-H+ potential energy surface, carried out through the use of high-level G2(MP2) and B3LYP/6-311+G(3df,2p) calculations, allows us to conclude that, under low-pressure, low-energy ICR conditions, the interaction between the protonated reference base, BrefH+, and allylphosphine leads to a complex in which BrefH+ attaches to the phosphorus atom of allylphosphine, where the electrostatic potential is strongly attractive. Hence, in the first step only the phosphorus protonated species should be formed. Its isomerization to yield the Cβ-protonated form, which is the global minimum of the potential energy surface, implies a very high activation barrier that cannot be overtaken under normal experimental ICR conditions. Therefore, the main conclusion of our study is that allylphosphine behaves as a phosphorus base in the gas phase, even though the Cβ-protonated structure is the most stable protonated species. We have also shown that both Cβ- and Cγ-protonation triggers a cyclization of the system. An analysis of the bonding of the different protonated species as compared with that of the neutral system is presented.
The Application of Liquid Chromatography-Electrospray Ionization Mass Spectrometry and Collision-Induced Dissociation in the Structural Characterization of Acylated Flavonol O-Glycosides from the Seeds of Carrichtera Annua
Authors: Cuyckens Filip , Shahat Abdelaaty A. , Van den Heuvel Hilde , Abdel-Shafeek Khaled A. , El-Messiry Moustafa M. , Nasr Medhat M. Seif-El , Pieters Luc , Vlietinck Arnold J. , Claeys Magda
Published: August 2003

The flavonoid fraction from the seeds of Carrichtera annua was studied using high-performance liquid chromatography simultaneously coupled to a photodiode array detector (LC/UV-DAD) and a mass spectrometer equipped with an electrospray source (LC/ESI-MS). Collision-induced dissociation (CID) mass spectral data obtained off-line by nanospray (nano-ESI) analysis provided a wealth of complementary structural information, which was consistent with structures established by NMR or led to the proposal of base structures of the flavonol O-glycosides present in the Carrichtera annua seed extract. The flavonoid fraction was found to contain 12 structurally related flavonol O-glycosides. Eleven flavonoids, of which several were new compounds, were acylated with one or more benzoyl, feruloyl or sinapoyl groups. These acyl groups gave rise to characteristic product ions in the [M + H]+ and [M + Na]+ CID spectra as well as to radicalar acid-related product ions at high-energy collisional activation. In addition to the characterization of the acyl substituents, the mass spectral data allowed the identification of the aglycone, the determination of the base structure and the differentiation of several positional isomers.
Electrospray Mass Spectrometry of 2-Aminotroponimines and 2-Aminotropones
Authors: Claramunt Rosa M. , Sanz Dionisia , Torralba Marta Pérez , Elguero José , Sanchez Pierre , Enjalbal Christine , Martinez Jean , Aubagnac Jean-Louis
Published: August 2003

A series of aminotroponimine and aminotropone derivatives were studied by electrospray mass spectrometry. MS and MS/MS data were acquired according to automated procedures. In the case of mono- and di-halogenated compounds, their specific behavior upon collisionally-activated dissociation conditions provided rapid structural assignments through inexpensive isotopic labeling MS/MS experiments.
The Kinetic Method as a Structural Diagnostic Tool: Ionized α-Diketones as Loosely One-Electron Bonded Diacylium Ion Dimers
Authors: Meurer Eduardo C. , Gozzo Fabio C. , Augusti R. , Eberlin Marcos N.
Published: August 2003

The kinetic method is used to corroborate the description of ground state ionized α-diketones as loosely electron-bonded acylium ion dimers: R1–C=O+—e−—+O=C–R2. The abundance ratio of both the acylium ion fragments R1CO+ and R2CO+ (summed to those of their respective secondary fragments) formed upon low energy (5 eV) collision-induced dissociation of several ionized α-diketones is found to correlate linearly with the ionization energies ( IEs) of the corresponding R1CO• and R2CO• free radicals as predicted by density functional theory calculations at the B3LYP/6-311++G(d,p) level. However, when these abundances are taken from 70 eV electron ionization mass spectra, lower and sometimes inverted ratios (2,3-pentanedione and 2,3-hexanedione) are observed. Inverted ratios are also observed via charge-exchange mass spectrometry/mass spectrometry (MS/MS) experiments for ionized 2,3-pentanodione formed with relatively high internal energies. Ionized α-diketones are found to display an effective temperature of 1705 K, which indicates an intermediate loosely-bonded nature. B3LYP/6-311++G(d,p) optimized geometries and charge and spin densities also corroborate the description of ground state ionized α-diketones as loosely electron-bonded diacylium ion dimers.
Reactions of CH3CHO•+ and of CH3COH•+ with Water upon Fourier Transform Ion Cyclotron Resonance Conditions
Authors: Nedev H. , van der Rest G. , Mourgues P. , Audier H.E.
Published: August 2003

The reactions of CH3CHO + and of CH3COH + with water yield the same products, at almost the same rate. It is shown, by using a characteristic reaction of the carbene structure, that a molecule of water converts CH3COH + into its more stable isomer CH3CHO +, which is a new example of catalyzed 1,2-H transfer. The dominant product is the proton-bound dimer of water which, in fact, comes from the [H2OH+…CH3] and [H2OH+…CO] primary products whose observed abundances are poor. In a related system, ionized formamide/water, a water molecule catalyzes the 1,3-transfer leading from the solvated carbene to the [H2O…H+…H2N–C=O] stable intermediate, which eliminates CO without back energy. In contrast, such a process does not take place in the studied system since the cleavage of the so formed [H2OH+…CH3CO] transient intermediate involves a high back energy; this is explained by the charge repartition within this intermediate. In fact, a different pathway takes place. The solvated acetaldehyde ion isomerizes into a terbody intermediate in which protonated water is bonded to a CO molecule on the one hand and to a methyl radical on the other hand. Simple cleavages of this complex yield the observed products.
Fragmentation Mechanisms of Protonated Benzylamines. Electrospray Ionisation-Tandem Mass Spectrometry Study and ab Initio Molecular Orbital Calculations
Authors: Bourcier Sophie , Hoppilliard Yannik
Published: August 2003

Our research into neurotransmitters in a biological fluid presented an opportunity to investigate the fragmentations under low collision energy characterising benzyl-amines protonated under electrospray ionisation (ESI) conditions in a triple quadrupole mass spectrometer. In this work we present the breakdown graphs of protonated 3,4-dihydroxybenzylamine, DHBAH+, and 3-methoxy, 4-hydroxybenzylamine, HMBAH+, at various source temperatures and various pressures in the collision cell, the collision energy varying from 0 to 46 eV in the laboratory frame. Both parent ions eliminate first NH3 at very low collision energy. The fragmentations of [MH – NH3]+ occur at high collision energy and are quite different for DHBAH+ and HMBAH+: formation of [MH – NH3 – H2O – CO]+ for the former; formation of the radical cation [MH – NH3 – CH3]+• for the latter. These fragmentations are interpreted by means of ab initio calculations up to the B3LYP/6-311+G(2d,2p) level of theory. The successive losses of H2O and CO involve first the rearrangement in two steps of benzylic ions formed by loss of NH3 into tropylium ions. The transition states associated with this rearrangement are very high in energy (about 400 kJ mol−1 above MH+) explaining (i) the absence of an ion corresponding to [DHBAH – NH3 – H2O]+. The determining steps associated with the losses of H2O and with H2O + CO are located lower in energy than the transition states associated with the isomerisation of benzylic ions into tropylium ions; explaining (ii) the formation of the radical cation [MH – NH3 – CH3]+•. The homolytic cleavage of CH3–O requires less energy than does the rearrangement.