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See detailThe Electron and Proton Energy Input Into The Auroral Thermosphere During Substorms: Remote Sensing With Image-fuv
Hubert, Benoît ULg; Gérard, Jean-Claude ULg; Meurant, M. et al

in EGS XXVII General Assembly, Nice, 21-26 April 2002 (2002)

This paper investigates the dynamical properties of the Eta model, a state-of-the- art nested limited-area model, following the approach previously developed by the present authors. It is first shown that ... [more ▼]

This paper investigates the dynamical properties of the Eta model, a state-of-the- art nested limited-area model, following the approach previously developed by the present authors. It is first shown that the intrinsic dynamics of the model depends crucially on the size of the domain, with a non-chaotic behavior for small domains, supporting earlier findings on the absence of sensitivity to the initial conditions in these models. The quality of the predictions of several Eta model versions differing by their domain size is next evaluated and compared with the Avn analyses on a targeted region, centered on France. Contrary to what is usually taken for granted, a non-trivial relation between predictability and domain size is found, the best model versions be- ing the ones integrated on the smallest and the largest domain sizes. An explanation in connection with the intrinsic dynamics of the model is advanced. [less ▲]

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See detailElectron and proton excitation of the FUV aurora: Simultaneous IMAGE and NOAA observations
Coumans, Valérie ULg; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in Journal of Geophysical Research. Space Physics (2002), 107

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in different spectral channels. The Wideband Imaging Camera (WIC) is sensitive to ... [more ▼]

The Far Ultraviolet (FUV) imaging system on board the IMAGE satellite provides a global view of the north auroral region in different spectral channels. The Wideband Imaging Camera (WIC) is sensitive to the N[SUB]2[/SUB] LBH emission and NI emissions produced by both electron and proton precipitations. The SI12 camera images the Lyman-alpha emission due to incident protons only. We compare WIC and SI12 observations with model predictions based on particle measurements from the TED and the MEPED detectors on board NOAA-TIROS spacecraft. Models of the interaction of auroral particles with the atmosphere are used together with the in situ proton and electron flux and characteristic energy data to calculate the auroral brightness at the magnetic footprint of the NOAA-15 and NOAA-16 orbital tracks. The MEPED experiment measures the precipitating particles with energy higher than 30 keV, so that these comparisons include all auroral energies, in contrast to previous comparisons. A satisfactory agreement in morphology and in magnitude is obtained for most satellite overflights. The observed FUV-WIC signal is well modeled if the different spatial resolution of the two sensors is considered and the in situ measurements properly smoothed. The calculated count rate includes contributions from LBH emission, the NI 149.3 nm line, and the OI 135.6 nm line excited by electrons and protons. The proton contribution in WIC can locally dominate the electrons. The comparisons indicate that protons can significantly contribute to the FUV aurora at specific times and places and cannot be systematically neglected. The results confirm the shift of the proton auroral oval equatorward of the electron oval in the dusk sector. We also show that in some regions, especially in the dusk sector, high-energy protons dominate the proton energy flux and account for a large fraction of the Lyman-alpha and other FUV emissions. [less ▲]

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See detailElectron and proton shock aurora observed by IMAGE-FUV
Meurant, M.; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in EGS - AGU - EUG Joint Assembly (2003, April 01)

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the ... [more ▼]

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the molecular N_2 LBH and the atomic NI emissions at 140-180 nm. The two channels of the Spectrographic Imager (SI) observe the Doppler shifted Lyman-α emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). Three simultaneous snapshots are recorded each 2 minutes. In this study, the FUV instrument allows a global viewing of the aurora with a high temporal resolution both in proton and electron. It is used to study the shock aurora resulting from the disturbance caused by the arrival of a coronal mass ejection on the front of the magnetosphere. A comparison between electron and proton injection features at global scale is performed for different isolated events with positive and negative interplanetary B_z. A correlation with IMF and solar wind parameters is presented as well as a description of the magnetosphere morphology given by the Tsyganenko model in the shock aurora period. [less ▲]

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See detailElectron and proton shock aurora observed by IMAGE-FUV
Meurant, M.; Gérard, Jean-Claude ULg; Hubert, Benoît ULg et al

in EGS - AGU - EUG Joint Assembly (2003, April 01)

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the ... [more ▼]

The FUV instrument on the IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) satellite monitors the aurora in three different spectral regions. The Wideband Imaging Camera (WIC) observes the molecular N_2 LBH and the atomic NI emissions at 140-180 nm. The two channels of the Spectrographic Imager (SI) observe the Doppler shifted Lyman-α emission at 121.8 nm due to precipitating protons (SI12) and the electron auroral emission of OI at 135.6 nm (SI13). Three simultaneous snapshots are recorded each 2 minutes. In this study, the FUV instrument allows a global viewing of the aurora with a high temporal resolution both in proton and electron. It is used to study the shock aurora resulting from the disturbance caused by the arrival of a coronal mass ejection on the front of the magnetosphere. A comparison between electron and proton injection features at global scale is performed for different isolated events with positive and negative interplanetary B_z. A correlation with IMF and solar wind parameters is presented as well as a description of the magnetosphere morphology given by the Tsyganenko model in the shock aurora period. [less ▲]

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See detailElectron backscattered diffraction of aluminium alloy 7075 samples after heat treatment
Vaneetveld, Grégory ULg; Rassili, Ahmed ULg; Lecomte-Beckers, Jacqueline ULg et al

in International Journal of Material Forming (2009)

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular ... [more ▼]

Thixoforging is a type of semi-solid metal processing at high solid fraction (0.7<fs<1), which involves the processing of alloys in the semi-solid state. The use of semi-solid material with globular microstructure helps to decrease forming load. But the introduction of a liquid phase in the material is a source of defects that limit mechanical properties of thixoforged parts. One of these defects is the hot cracking for some hot crack-sensitive wrought aluminium alloys. Hot cracking occurs because of strain and deformation during last step of solidification. This paper shows how thixoforging process should help to lower hot cracking tendency without modification of the alloy composition by decreasing strain and deformation due to shrinkage. Different experimental tests by extrusion of 7075 aluminium alloys are used. [less ▲]

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See detailElectron detachment dissociation (EDD) pathways in oligonucleotides
Kinet, Catherine ULg; Gabelica, Valérie ULg; Balbeur, Dorothée ULg et al

in International Journal of Mass Spectrometry (2009), 283

Electron detachment dissociation (EDD) and electron photodetachment dissociation (EPD) are two novel fragmentation methods yielding radicals from negatively charged ions. With the goal of comparing EDD ... [more ▼]

Electron detachment dissociation (EDD) and electron photodetachment dissociation (EPD) are two novel fragmentation methods yielding radicals from negatively charged ions. With the goal of comparing EDD, EPD and the more traditional Collision-Induced Dissociation (CID) and Infrared Multiphoton Disscociation (IRMPD) fragmentation processes in oligonucleotides, we studied here the EDD fragmentation pathways of oligonucleotides of varying length. We chose polythymine oligonucleotides because these are the least prone to secondary structure formation, and found complete sequence coverage by EDD for up to dT20. We also found that the fragmentation pathways change with oligonucleotide length: electron detachment is a mandatory step in the fragmentation of larger sequences, while shorter oligonucleotides can also fragment via direct electronic or vibrational excitation by the electrons. This is supported by (1) the fact that continuous ejection of the charge reduced species does not totally prevent fragmentation of short oligonucleotides dT5 and dT6, (2) the fact that CID and EDD fragments are more similar for small oligonucleotides (although double resonance experiments show that they are not all issued from the same mechanisms), and (3) the fact that electron-induced dissociation (EID) of singly charged dT3 and dT4 gives similar fragments as EDD of doubly charged dT5 and dT6. Finally, the detachment efficiency as a function of the nature of the nucleobase was studied. The effect of base on electron detachment in EDD (G > T > A > C) is different than in EPD (G > A > C > T), indicating different electron loss mechanisms. [less ▲]

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See detailThe electron excited ultraviolet spectrum of HD: Cross sections and transition probabilities
Ajello, J.; Palle, P. V.; Abgrall, H. et al

in Astrophysical Journal Supplement Series (2005), 159(2), 314-330

We have analyzed the high-resolution ultraviolet (UV) emission spectrum of molecular deuterium hydride (HD) excited by electron impact at 100 eV under optically thin, single-scattering experimental ... [more ▼]

We have analyzed the high-resolution ultraviolet (UV) emission spectrum of molecular deuterium hydride (HD) excited by electron impact at 100 eV under optically thin, single-scattering experimental conditions. The high-resolution spectrum (FWHM = 160 m angstrom) spans the wavelength range from 900 to 1650 angstrom and contains the two Rydberg series of HD: (1)Sigma(u)(+) 1s sigma, np sigma(B, B', B '', n = 2, 3, 4) --> X (1)Sigma(g)(+) and (1)Pi(u)(+)1s sigma, np pi(C, D', D '', D '', n = 2, 3, 4, 5) --> X (1)Sigma(g)(+). A model spectrum of HD, based on newly calculated transition probabilities and line positions including rovibrational coupling for the strongest band systems, B 1 Sigma(u)(+)- X (1)Sigma(+)(g), B' (1)Sigma(u)(+)- X (1)Sigma(g)(+), C (1)Pi(u) - X (1)Sigma(g)(+), and D (1)Pi(u) X (1)Sigma(g)(+), is in excellent agreement with observed intensities. The cross sections for direct excitation at 100 eV of the B (1)Sigma(u)(+), B' (1)Sigma(u)(+), C (1)Pi(u), and D (1)Pi(u) states were derived from a model analysis of the experimental fluorescence spectrum to the ground state. The absolute cross section values for excitation to the B (1)Sigma(u)(+), B' (1)Sigma(u)(+), C (1)Pi(u), and D (1)Pi(u) states were found to be (2.57 +/- 0.26) x 10(-17), (0.22 +/- 0.06) x 10(-17), (2.54 +/- 0,25) x 10(-17), and (0.17 +/- 0.04) x 10(-17) cm(2), respectively. We have also determined the dissociative excitation cross sections at 100 eV for the emission of Ly alpha at 1216 angstrom and Ly beta at 1025 angstrom lines, which are (7.98 +/- 1.12) x 10(-18) and (0.40 +/- 0.10) x 10(-18) cm(2), respectively. The summed excitation function of the closely spaced pair of lines, H Ly alpha and D Ly alpha, resulting from dissociative excitation of HD, has been measured from the threshold to 800 eV and is analytically modeled with a semiempirical relation. The model cross sections are in good agreement with the corrected Ly alpha cross sections of Mohlmann et al. up to 2 keV. Based on measurements of H, D (2s) production cross section values by Mohlmann et al., the H, D (n = 2) cross section is estimated to be 1.6 x 10(-17) cm(2) at 100 eV. [less ▲]

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See detailElectron localization in lithium niobate
Veithen, M.; Ghosez, Philippe ULg

in AIP Conference Proceedings (2002), 626

Using a plane-wave pseudopotential approach to density functional theory, we investigate the degree of electron localization in lithium niobate. We pay a particular attention to its variation during the ... [more ▼]

Using a plane-wave pseudopotential approach to density functional theory, we investigate the degree of electron localization in lithium niobate. We pay a particular attention to its variation during the phase transition and to the relationship with the electronic structure and the Born effective charges in this material. A band-by-band decomposition allows us to focus on the different bands composing the energy spectrum of this compound. At variance with previous calculations based on finite differences, the localization tensor has been obtained using linear-response techniques. [less ▲]

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See detailElectron localization: Band-by-band decomposition and application to oxides
Veithen, M.; Gonze, X.; Ghosez, Philippe ULg

in Physical Review. B, Condensed Matter and Materials Physics (2002), 66

Using a plane-wave pseudopotential approach to density functional theory we investigate the electron localization length in various oxides. For this purpose, we first set up a theory of the band-by-band ... [more ▼]

Using a plane-wave pseudopotential approach to density functional theory we investigate the electron localization length in various oxides. For this purpose, we first set up a theory of the band-by-band decomposition of this quantity, more complex than the decomposition of the spontaneous polarization (a related concept), because of the interband coupling. We show its interpretation in terms of Wannier functions and clarify the effect of the pseudopotential approximation. We treat the case of different oxides: BaO, alpha-PbO, BaTiO3, and PbTiO3. We also investigate the variation of the localization tensor during the ferroelectric phase transitions of BaTiO3 as well as its relationship with the Born effective charges. [less ▲]

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See detailElectron microscope localization of ribosomal RNA and DNA after in situ hybridization
Thiry, Marc ULg; Thiry-Blaise, Lydia

in Harris, J R; Zbarsky, I B (Eds.) Nuclear structure and function (1990)

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See detailElectron microscopic study of measles virus infection: cell fusion and hemadsorption
Rentier, Bernard ULg; Hooghe-Peters, Elisabeth L.; Dubois-Dalcq, Monique

in Journal of Virology (1978), 28(2), 567-577

Virus-induced cell fusion has been studied after infection of Vero cells with measles virus. Scanning and transmission electron microscopy were combined with immunoperoxidase labeling of measles antigens ... [more ▼]

Virus-induced cell fusion has been studied after infection of Vero cells with measles virus. Scanning and transmission electron microscopy were combined with immunoperoxidase labeling of measles antigens to correlate viral production and distribution of virus-induced erythrocyte binding sites with progress of fusion-Release of infectious virus started before syncytia were detected and decreased while the number and size of syncytia were increasing. Most virions were seen budding from mononucleated cells or from the periphery of syncytia where cells were being recruited. Moving inward, the surfaces of syncytia were covered with numerous ridges containing viral antigen, but few viral buds were seen, suggesting that syncytia might be sites of defective viral formation. Hemadsorption occurred predominantly within the confines of syncytia. Erythrocytes were scattered sparsely over immature syncytia but were densely packed in the center of mature syncytia. Active binding sites for erythrocytes were located on cell villi and ridges covered with measles antigens. Hemadsorption was completely inhibited in measles virus-infected cultures pretreated with virus- specific immunoglobulin G for 1 h at 4°C. However, when these cultures were shifted to 37°C, hemadsorbing sites were recovered at the periphery of enlarging syncytia. Virus-induced sites for erythrocyte adsorption were found to move centripetally on syncytium membranes as fusion progressed. [less ▲]

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See detailElectron microscopic study of measles virus infection: unusual antibody-triggered redistribution of antigens on giant cells
Hooghe-Peters, Elisabeth L.; Rentier, Bernard ULg; Dubois-Dalcq, Monique

in Journal of Virology (1979), 29(2), 666-676

Vero cells infected with measles virus fuse to form multinucleated cells which incorporated virus- specific antigens in their membrane. The distribution of these antigens was analyzed after a brief ... [more ▼]

Vero cells infected with measles virus fuse to form multinucleated cells which incorporated virus- specific antigens in their membrane. The distribution of these antigens was analyzed after a brief treatment with human anti-measles immunoglobulin G, using autoradiography and immunoperoxidase labeling combined with transmission and scanning electron microscopy. Virus-specific antigens were distributed over the entire surface of giant cells treated at 4°C with human anti-measles immunoglobulin G and labeled Protein A. When cells were shifted to 37°C, labeled antigen-antibody complexes were redistributed in two stages. Patch formation occurred in 5 to 15 min. Later, antigen- antibody complexes became concentrated in a paracentral "ring" rather than typical caps. Patch formation occurred in the presence of metabolic inhibitors, whereas ring formation was inhibited by metabolic inhibitors. These rings contained membrane folds, villi, and viral buds, whereas the rest of the membrane was smooth. In addition, shedding, endocytosis of antigen-antibody complexes, and reexpression of antigens were observed. Antibodies to nonviral membrane antigens induced the same pattern of redistribution. Infected cells treated with anti-measles Fab' fragments maintained a homogeneous distribution of label throughout the experiments. In conclusion, intact immunoglobulins, but not Fab' fragments, were able to induce a dramatic redistribution of viral antigen on the membrane of giant cells infected with measles virus. [less ▲]

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See detailElectron microscopical investigations of hexagonal phase precipitation in Zn---12 wt% Al---1 wt% Cu and Zn---27 wt% Al---2 wt% Cu alloys
Rachev, P.; Terziev, L.; Lecomte-Beckers, Jacqueline ULg et al

in Acta Metallurgica et Materialia (1991), 39(9), 2177-2182

In Zn---12 wt% Al---1 wt% Cu and Zn---27 wt% Al---2 wt%Cu alloys aged at 100° and 250°C the precipitation of h.c.p. phases was studied by means of transmission electron microscopy. The presence of the ... [more ▼]

In Zn---12 wt% Al---1 wt% Cu and Zn---27 wt% Al---2 wt%Cu alloys aged at 100° and 250°C the precipitation of h.c.p. phases was studied by means of transmission electron microscopy. The presence of the metastable ηm and ηx-phases was established using the Moiré pattern method. The ηm → η phase transition was observed. Screw dislocations are visualized in (114) with b logical and {220} in η phase precipitates by means of Moiré fringes. [less ▲]

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See detailElectron microscopy on Banzi Virus particle and its development in the sucking mice brains
Calberg-bacq, C. M.; Rentier-Delrue, Françoise ULg; Osterrieth, P. et al

in Journal of Ultrastructure Research (1975)

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See detailElectron microscopy proves Jo-1 antigen to be predominantly cytoplasmic but also nuclear.
Thiry, Marc ULg; Humbel, R.; Dicato, M. et al

in Biomedicine & Pharmacotherapy (1988), 42(7), 469-71

The Jo-1 antigen is a specific marker for autoimmune myositis with an excellent correlation with associated interstitial lung disease. Using an electron microscopy immunogold technique, we were able to ... [more ▼]

The Jo-1 antigen is a specific marker for autoimmune myositis with an excellent correlation with associated interstitial lung disease. Using an electron microscopy immunogold technique, we were able to show that the antigen was predominantly cytoplasmic. [less ▲]

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See detailElectron partitioning between the two branching quinol-oxidizing pathways in Acanthamoeba castellanii mitochondria during steady-state state 3 respiration.
Jarmuszkiewicz, W.; Sluse-Goffart, C.; Hryniewiecka, L. et al

in Journal of Biological Chemistry (1997), 273(17), 10174-10180

Amoeba mitochondria possess a respiratory chain with two quinol-oxidizing pathways: the cytochrome pathway and the cyanide-resistant alternative oxidase pathway. The ADP/O method, based on the non ... [more ▼]

Amoeba mitochondria possess a respiratory chain with two quinol-oxidizing pathways: the cytochrome pathway and the cyanide-resistant alternative oxidase pathway. The ADP/O method, based on the non-phosphorylating property of alternative oxidase, was used to determine contributions of both pathways in overall state 3 respiration in the presence of GMP (an activator of the alternative oxidase in amoeba) and succinate as oxidizable substrate. This method involves pair measurements of ADP/O ratios plus and minus benzohydroxamate (an inhibitor of the alternative oxidase). The requirements of the method are listed and verified. When overall state 3 respiration was decreased by increasing concentrations of n-butyl malonate (a non-penetrating inhibitor of succinate uptake), the quinone reduction level declined. At the same time, the alternative pathway contribution decreased sharply and became negligible when quinone redox state was lower than 50%, whereas the cytochrome pathway contribution first increased and then passed through a maximum at a quinone redox state of 58% and sharply decreased at a lower level of quinone reduction. This study is the first attempt to examine the steady-state kinetics of the two quinol-oxidizing pathways when both are active and to describe electron partitioning between them when the steady-state rate of the quinone-reducing pathway is varied. [less ▲]

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See detailElectron photodetachment dissociation of DNA anions with covalently or noncovalently bound chromophores
Gabelica, Valérie ULg; Rosu, Frédéric ULg; De Pauw, Edwin ULg et al

in Journal of the American Society for Mass Spectrometry (2007), 18(11), 1990-2000

Double stranded DNA multiply charged anions coupled to chromophores were subjected to UV-Vis photoactivation. in a quadrupole ion trap mass spectrometer. The chromophores included noncovalently bound ... [more ▼]

Double stranded DNA multiply charged anions coupled to chromophores were subjected to UV-Vis photoactivation. in a quadrupole ion trap mass spectrometer. The chromophores included noncovalently bound minor groove binders (activated in the near UV), noncovalently bound intercalators (activated with visible light), and covalently linked fluorophores and quenchers (activated at their maximum absorption wavelength). We found that the activation of only chromophores having long fluorescence lifetimes did result in efficient electron photodetachment from the DNA complexes. In the case of ethidium-dsDNA complex excited at 500 nm, photodetachment is a multiphoton process. The MS3 fragmentation of radicals produced by photodetachment at lambda = 260 nm (DNA excitation) and by photodetachment at lambda > 300 nm (chromophore excitation) were compared. The radicals keep no memory of the way they were produced. A weakly bound noncovalent ligand (m-amsacrine) allowed probing experimentally that a fraction of the electronic internal energy was converted into vibrational internal energy. This fragmentation channel was used to demonstrate that excitation of the quencher DABSYL resulted in internal conversion, unlike the fluorophore 6-FAM. Altogether, photodetachment of the DNA complexes upon chromophore excitation can be interpreted by the following mechanism: (1) ligands with sufficiently long excited-state lifetime undergo resonant two-photon excitation to reach the level of the DNA excited states, then (2) the excited-state must be coupled to the DNA excited states for photodetachment to occur. Our experiments also pave the way towards photodissociation probes of biomolecule conformation in the gas-phase by Forster resonance energy transfer (FRET). [less ▲]

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See detailElectron photodetachment dissociation of DNA polyanions in a quadrupole ion trap mass spectrometer
Gabelica, Valérie ULg; Tabarin, Thibault; Antoine, Rodolphe et al

in Analytical Chemistry (2006), 78(18), 6564-6572

We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6-20-mer ... [more ▼]

We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6-20-mer single strands and 12-base pair double strands. In all cases, laser irradiation causes electron detachment from the multiply charged DNA anions. Electron photodetachment efficiency directly depends on the number of guanines in the strand, and maximum efficiency is observed between 260 and 275 nm. Subsequent collision-induced dissociation (CID) of the radical anions produced by electron photodetachment results in extensive fragmentation. In addition to neutral losses, a large number of fragments from the w, d, a*, and z* ion series are obtained, contrasting with the w and (a-base) ion series observed in regular CID. The major advantage of this technique, coined electron photodetachment dissociation (EPD) is the absence of internal fragments, combined with good sequence coverage. EPD is therefore a highly promising approach for de novo sequencing of oligonucleotides. EPD of nucleic acids is also expected to give specific radical-induced strand cleavages, with conservation of other fragile bonds, including noncovalent bonds. In effect, preliminary results on a DNA hairpin and on double strands suggest that EPD could also be used to probe intra- and intermolecular interactions in nucleic acids. [less ▲]

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See detailElectron Photodetachment of DNA Polyanions: Photoelectron Spectroscopy and UV Action Spectroscopy
Gabelica, Valérie ULg; Rosu, Frédéric ULg; De Pauw, Edwin ULg et al

Conference (2008, April 15)

DNA polyanions trapped in a mass spectrometer undergo electron detachment following irradiation with UV light [1-3]. Electron photodetachment is a 1-photon process, and its efficiency depends on: - The ... [more ▼]

DNA polyanions trapped in a mass spectrometer undergo electron detachment following irradiation with UV light [1-3]. Electron photodetachment is a 1-photon process, and its efficiency depends on: - The nature of the DNA bases: guanine-containing strands are the most prone to electron photodetachment, followed by adenine, cytosine, and finally thymine. - The excitation wavelength: electron detachment is maximum around 260 nm, corresponding to base excitation. - The charge of the polyanion: higher charge state ions undergo more efficient electron detachment because of the Coulombic repulsion. Here we will discuss the electron photodetachment mechanism in the light of the most recent experimental results. Because the base-dependence of electron photodetachment efficiency is correlated with the base ionization potential and is maximum at wavelengths corresponding to the base absorption, we initially proposed that electron photodetachment might occur directly from the base, and that the photodetachment yield was correlated with the electron binding energy to the base [2]. Photoelectron spectroscopy experiments were performed on DNA multiply charged anions with varying base composition to probe how the electron binding energies changes with the base composition. Finally, the electron detachment channel was used to perform UV spectroscopy experiments on large DNA polyanions trapped in the gas phase. Gas-phase UV spectra of DNA duplexes and G-quadruplexes containing up to 24 bases (> 7000 Da) will be presented. [1] V. Gabelica, T. Tabarin, R. Antoine, F. Rosu, I. Compagnon, M. Broyer, E. De Pauw, and P. Dugourd, Anal. Chem. 78, 6564 (2006). [2] V. Gabelica, F. Rosu, T. Tabarin, C. Kinet, R. Antoine, M. Broyer, E. De Pauw, and P. Dugourd, J. Am. Chem. Soc. 129, 4706 (2007). [3] V. Gabelica, F. Rosu, E. De Pauw, R. Antoine, T. Tabarin, M. Broyer, and P. Dugourd, J. Am. Soc. Mass Spectrom. 18, 1990 (2007). [less ▲]

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See detailAn Electron Spin Resonance (Esr) Study on the Mechanism of Ascorbyl Radical Production by Metal-Binding Proteins
Mouithys-Mickalad, Ange ULg; Deby, Carol; Dupont, Ginette ULg et al

in Biometals (1998), 11(2), 81-8

The mechanism of ascorbate oxidation by metal-binding proteins (ceruloplasmin, albumin and transferrin) was investigated in vitro and in isolated plasma by the measurement of the ascorbyl free radicals ... [more ▼]

The mechanism of ascorbate oxidation by metal-binding proteins (ceruloplasmin, albumin and transferrin) was investigated in vitro and in isolated plasma by the measurement of the ascorbyl free radicals (AFR) by electron spin resonance (ESR). In plasma of 13 healthy volunteers, a spontaneous and variable production of AFR was detected, which was increased by a 10(-4) M ascorbate overloading; however, this increase was not correlated to the intensity of the spontaneous AFR signal. The addition of Cu2+ and ceruloplasmin to plasma increased the ESR signal, while the addition of transferrin decreased the signal intensity in a dose-dependent manner. In vitro, we demonstrated that ascorbate was oxidized by human serum albumin and by ceruloplasmin, and that this oxidase-like activity was lost by trypsin or heat treatment of these proteins. These two proteins positively interacted in the oxidation of ascorbate, since addition of crude albumin to a solution of ascorbate and ceruloplasmin increased the intensity of ESR signal in a dose-dependent manner. The treatment of albumin by a metal chelator (DDTC) abolished these positive interactions. The respective roles of copper and iron in ascorbate oxidation were studied and showed a dose-dependent effect of these ions on ascorbate oxidation. The role of iron was confirmed by the inhibiting effect of metal-free transferrin on iron-dependent ascorbate oxidation. Concerted actions between iron carrying albumin and copper carrying ceruloplasmin appear responsible for the production of AFR in vitro and in vivo. [less ▲]

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