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See detailNkx6.1 and nkx6.2 regulate alpha- and beta-cell formation in zebrafish by acting on pancreatic endocrine progenitor cells.
Binot, Anne-Catherine; Manfroid, Isabelle ULg; Flasse, Lydie ULg et al

in Developmental Biology (2010), 340(2), 397-407

In mice, the Nkx6 genes are crucial to alpha- and beta-cell differentiation, but the molecular mechanisms by which they regulate pancreatic subtype specification remain elusive. Here it is shown that in ... [more ▼]

In mice, the Nkx6 genes are crucial to alpha- and beta-cell differentiation, but the molecular mechanisms by which they regulate pancreatic subtype specification remain elusive. Here it is shown that in zebrafish, nkx6.1 and nkx6.2 are co-expressed at early stages in the first pancreatic endocrine progenitors, but that their expression domains gradually segregate into different layers, nkx6.1 being expressed ventrally with respect to the forming islet while nkx6.2 is expressed mainly in beta-cells. Knockdown of nkx6.2 or nkx6.1 expression leads to nearly complete loss of alpha-cells but has no effect on beta-, delta-, or epsilon-cells. In contrast, nkx6.1/nkx6.2 double knockdown leads additionally to a drastic reduction of beta-cells. Synergy between the effects of nkx6.1 and nkx6.2 knockdown on both beta- and alpha-cell differentiation suggests that nkx6.1 and nkx6.2 have the same biological activity, the required total nkx6 threshold being higher for alpha-cell than for beta-cell differentiation. Finally, we demonstrate that the nkx6 act on the establishment of the pancreatic endocrine progenitor pool whose size is correlated with the total nkx6 expression level. On the basis of our data, we propose a model in which nkx6.1 and nkx6.2, by allowing the establishment of the endocrine progenitor pool, control alpha- and beta-cell differentiation. [less ▲]

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See detailNMDA-induced striatal brain damage and time-dependence reliability of thionin staining in rats
Haelewyn, B; Alix, Philippe ULg; Maubert, E et al

in Journal of Neuroscience Methods (2008), 168

Excitotoxic neuronal death induced by intracerebral injection of NMDA is a widely used model for investigating the potentially neuroprotective action of pharmacological agents against brain insults ... [more ▼]

Excitotoxic neuronal death induced by intracerebral injection of NMDA is a widely used model for investigating the potentially neuroprotective action of pharmacological agents against brain insults involving excitotoxic processes. Surprisingly, the time-course of NMDA-induced brain damage yet has not been investigated in the rat. Answering this question clearly needs to be assessed, given that the validity of preclinical neuroprotection studies requires to be insured that brain damage has reached a plateau that corresponds to the maximal extension of neuronal death at the time the brain is removed for histological analysis. Here, we investigated the time-course of neuronal death and the time-dependence validity of thionin coloration in rats that were given an intrastriatal injection of NMDA of 50 nmol or 70 nmol. Our results show that, whatever the dose used, NMDA-induced brain damage reaches its maximal value 24-48 h after the insult. They further indicate that the volume values of brain damage as estimated by thionin coloration constitute reliable data when the brain is removed up to 48 h after injection of NMDA. However, if the brain is removed more than 48 h after the excitotoxic insult onset, there is no alternative of using other techniques, such as immunochemical or neuroimaging techniques. [less ▲]

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See detailNMHC Climatology from Central European Mountain Observatories
Plass-Duelmer, C.; Reimann, S.; Wallasch, M. et al

in Geophysical Research Abstracts (2011), 13

NMHC (non-methane hydrocarbons) are a major group of atmospheric trace gases with impact on photochemical processes in the atmosphere, especially oxidant formation with ozone being the most prominent of ... [more ▼]

NMHC (non-methane hydrocarbons) are a major group of atmospheric trace gases with impact on photochemical processes in the atmosphere, especially oxidant formation with ozone being the most prominent of them, and contributions to SOA (secondary organic aerosols). By this, they are coupled to climate issues via the oxidizing capacity of the atmosphere, the greenhouse gas ozone and aerosol effects. NMHC monitoring was initiated in Europe in the “Tropospheric Ozone Research” project (1988-1995), and it was continued in EMEP and GAW (Global Atmosphere Watch) where it is an ongoing initiative which recently has been reinforced (GAW Report 171). In this presentation we will focus on time series from Central European mountain stations (46-49°N, 7-13°E): Hohenpeissenberg (985 m, DWD, Germany, 1998-ongoing), Rigi (1031 m, EMPA, Switzerland, 2003-ongoing), Junfraujoch (3580 m, EMPA, Switzerland, 2000-ongoing, and ULg (FTIR), Belgium, 1984-ongoing), Zugpitze (2650 m, UBA, Germany, 2000-ongoing), Schauinsland (1205 m, FZ-Jülich (1989-94), and UBA, Germany, 2004-ongoing), Brotjacklriegel (1016 m, UBA, Germany, 2000-2004), Donon (775 m, EMD, France, 1997-2007). Most sites used weekly flask samples but also on-line measurements were carried out with higher time resolution within the former TOR project and in the more recent time series at Hohenpeissenberg, Rigi, and Jungfraujoch. All samples were analysed by GC. Additionally to these GC measurements, a time series of column integrated acetylene and ethane by FTIR (Fourier Transform InfraRed spectrometry) is available from Jungfraujoch, from 1984 onwards. We focus here on time series of monthly averages of anthropogenic hydrocarbons over the 1997-2009 time period. They show quite similar patterns among the various stations over the whole period with pronounced seasonal cycles. Significantly lower mixing ratios were measured at the highest elevated sites, the Zugspitze and Jungfraujoch. Differences between the lower mountain sites (775-1200 m) are on first view surprisingly small. Generally, the differences between the high altitude and the other mountain sites are lowest in summer due to enhanced vertical mixing and thermal upslope winds. Downward trends for anthropogenic hydrocarbons are very similar at the various stations and are 2 %/yr for C2-C3 alkanes (+/- 1%), 3-6 %/yr for C4-C7 alkanes (+/- 2%), 2-3%/yr for C2-C3 alkynes and ethene (+/- 2%), 4 % /yr for propene and benzene (+/- 2%), and 5-10%/yr for toluene and xylenes (+/-3 and 5%, respectively). [less ▲]

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See detailNMR and X-ray diffraction analysis of 3-thioamido-5- phosphono-1-cyclohexene derivatives: Conformational and stereochemical assignments
Monbaliu, Jean-Christophe ULg; Tinant, Bernard; Marchand-Brynaert, Jacqueline

in Journal of Molecular Structure (2008)

[4 + 2] Cycloaddition; ; Vinyl phosphonate dienophiles; ; Cyclohexene conformations; NMR analysis; X-ray diffraction

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See detailNMR assignments of the major Cannabinoids and cannabiflavonoids isolated from flowers of Cannabis sativa
Choi, Y. H.; Hazekamp, A.; Peltenburg-Looman, A. M. G. et al

in Phytochemical Analysis (2004), 15(6, NOV-DEC), 345-354

The complete H-1- and C-13-NMR assignments of the major Cannabis constituents, Delta(9)-tetrahydrocannabinol, tetrahydrocannabinolic acid, A-tetrahydrocannabinol, cannabigerol, cannabinol, cannabidiol ... [more ▼]

The complete H-1- and C-13-NMR assignments of the major Cannabis constituents, Delta(9)-tetrahydrocannabinol, tetrahydrocannabinolic acid, A-tetrahydrocannabinol, cannabigerol, cannabinol, cannabidiol, cannabidiolic acid, cannflavin A and cannflavin B have been determined on the basis of one- and two-dimensional NMR spectra including H-1- and (13)-NMR, H-1-H-1-COSY, HMQC and HMBC. The substitution of carboxylic acid on the cannabinoid nucleus (as in tetrahydrocannabinolic acid and cannabidiolic acid) has a large effect on the chemical shift of H-1" of the C5 side chain and 2'-OH. It was also observed that carboxylic acid substitution reduces intermolecular hydrogen bonding resulting in a sharpening of the H-5' signal in cannabinolic acid in deuterated chloroform. The additional aromaticity of cannabinol causes the two angular methyl groups (H-8 and H-9) to show identical H-1-NMR shifts, which indicates that the two aromatic rings are in one plane in contrast to the other cannabinoids. For the cannabiflavonoids, the unambiguous assignments of C-3' and C-4' of cannflavin A and B were determined by HMBC spectra. Copyright (C) 2004 John Wiley Sons, Ltd. [less ▲]

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See detailNMR evidence for the structure of the complex between penicillin and the DD-carboxypeptidase of streptomyces R61
Degelaen, J.; Feeney, J.; Roberts, G. C. K. et al

in FEBS Letters (1979), 98(1), 53-56

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See detailNMR in the Pharmaceutical and Biomedical areas for identification and quantification of drugs and metabolomics applications
LAMBERT, Vincent ULg; Dufour, Gilles ULg; Chiap, Patrice ULg et al

Conference (2014, June 23)

Nuclear Magnetic Resonance (NMR) is probably, with mass spectrometry, the most powerful analytical tool for the structural determination of organic compounds. For a long time and due to technical ... [more ▼]

Nuclear Magnetic Resonance (NMR) is probably, with mass spectrometry, the most powerful analytical tool for the structural determination of organic compounds. For a long time and due to technical limitations, the main applications of NMR were focused on chemistry (organic, inorganic and medicinal chemistry) or biochemistry (i.e. proteins and proteins ligands analysis). Indeed, despite of very interesting potential in terms of structural information, reproducibility, specificity, quantification, NMR suffered of a lack of sensitivity and sometime of resolution in the case of complex mixture analysis in comparison with other technics. However, since several years, important technical improvements such as huge increase in sensitivity, hyphenation of NMR with LC system, automation and development of 2D and presaturation sequences have opened new putative applications for NMR, specifically in the pharmaceutical and biomedical areas. Then, beside the mass and chromatographic technics classically used for drug analysis, NMR represents an interesting and complementary tool for many applications. In this presentation, we will describe some NMR applications related to the pharma area. Starting from the identification of xenobiotic metabolites by coupling LC-SPE-NMR data with LC-MS/MS results, quantification of cyclodextrines in complex media, identification of illicit compounds, we will finish with our recent metabolomics NMR developments. [less ▲]

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See detailAN NMR INVESTIGATION OF THE ACTINIDE IONS AND THEIR COMPLEXES
Vidick, Geoffrey ULg; Bouslimani, Nouri; Desreux, Jean-François ULg

Poster (2010, January 28)

We currently use several advanced NMR techniques in order to fully characterize actinide ions and their complexes in water or in organic solvents. The dispersion of the longitudinal relaxation time T1 of ... [more ▼]

We currently use several advanced NMR techniques in order to fully characterize actinide ions and their complexes in water or in organic solvents. The dispersion of the longitudinal relaxation time T1 of solvent nuclei with the magnetic field (NMRD) yields information on the magnetic properties and on the dynamic behavior of paramagnetic species. 17O NMR allows the measurement of the water exchange times and 1H and 13C spectra yield information on the solution structures of the complexes and on the covalency of their coordination bonds. The application of NMR in actinide science will be illustrated with studies on the U, Np, Pu and Cm ions in different oxidation states and on their complexes. For instance, Cm3+ ion is the actinide analogue of Gd3+ but is not in a pure 8S state as indicated by much lower relaxation rates and much shortened electronic relaxation rates. In keeping with EPR studies1, Cm3+ does not have a perfectly spherical distribution of its unpaired electronic spins because of a much stronger spin-orbit coupling. Moreover, the Cm3+ relaxivity originates from three different processes: a dipolar coupling between the nuclear and electronic spins, a delocalization of unpaired electronic spins into the solvent orbitals (contact interaction) and a Curie contribution. Each process gives rise to an inflection point in the NMRD curves and the contact interaction reflects the partial covalency of the coordination bonds formed by Cm3+. A contact contribution is also observed in the NMR spectra of Cm3+ complexes. The sensitivity of NMR to the exact nature of the ground state of actinide ions is also illustrated by detailed studies on the U, Np and Pu ions in different oxidation states. For instance, a comparison of the NMRD curves of the 5f2 ions U4+, NpO2+ and PuO22+ indicates that the two dioxo cations have abnormally long electronic relaxation times. However, well-resolved 1H NMR spectra of their complexes can be obtained provided the solution species are sufficiently rigid. It will be shown that NpO2+ and PuO22+ induce dipolar paramagnetic shifts from which the solution structure can be deduced. [less ▲]

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See detailNMR investigation of the lanthanide and actinide complexes of bis-triazine extracting agents
Desreux, Jean-François ULg; Vidick, Geoffrey ULg; Bouslimani, Nouri

in Valuenza, Fernando L.; Moyer, Bruce A. (Eds.) 19th International Solvent Extraction Conference (2011, October 07)

Nuclear magnetic resonance spectroscopy (NMR) is applied to unravel the solution structure and the stoichiometry of the complexes formed between bis-triazine extracting agents (BTP and BTBP) and ... [more ▼]

Nuclear magnetic resonance spectroscopy (NMR) is applied to unravel the solution structure and the stoichiometry of the complexes formed between bis-triazine extracting agents (BTP and BTBP) and paramagnetic lanthanide ions. Highly rigid lanthanide perchlorate tris-complexes of threefold symmetry are formed by the pyridine bis-triazine BTP¿s while the bipyridine analogues (BTBP) form bis-complexes with a more open structure that leaves enough space for solvent molecules or anions. The nitrate ion is unable to enter the first coordination sphere of the tris-BTP complexes but the structure and stoichiometry of the bis-BTBP chelates are profoundly modified in presence of this ion. The NMR analysis is extended to actinides in various oxidation states despite technical difficulties. The NpO2+ ion is shown to form a 1:1 BTP complex in which the ligand is located in the plane perpendicular to the dioxo unit. No covalency contribution could be detected in the NMR spectra but such a contribution is clearly visible in the case of Am3+ and Cm3+. The latter induces very large paramagnetic shifts with a large contact contribution. [less ▲]

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See detailNMR relaxation and magnetic properties of superparamagnetic nanoworms
Gossuin, Yves; Disch, Sabrina; Vuong, Quoc L. et al

in Contrast Media & Molecular Imaging (2010), 5(6), 318-322

Maghemite particles are used as T-2 contrast agents for magnetic resonance imaging, especially for molecular and cellular imaging. Linear clusters of particles - called nanoworms - were recently developed ... [more ▼]

Maghemite particles are used as T-2 contrast agents for magnetic resonance imaging, especially for molecular and cellular imaging. Linear clusters of particles - called nanoworms - were recently developed to enhance the targeting efficiency. In this work, the magnetic and NMR relaxation properties of these nanoworms are studied at multiple magnetic fields. After the usual saturation at 0.5 T, the magnetization of the worms is still increasing, which results in an appreciable increase of the transverse relaxivity at high magnetic fields. The obtained relaxivities are typical of superparamagnetic particles of iron oxide (SPIOs). The transverse relaxation of the worms is clearly more efficient than for the isolated grains, which is confirmed by computer simulations. At high field, the longitudinal relaxation of the worms is less pronounced than for the grains, as expected for SPIOs. The nanoworms thus constitute a promising T-2 agent for cellular and molecular imaging. Copyright (C) 2010 John Wiley Sons, Ltd. [less ▲]

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See detailNMR Spectroscopy actinide complexes: In search of covalency effects
Desreux, Jean-François ULg; Vidick, Geoffrey ULg; Bouslimani, Nouri et al

Conference (2011, April 05)

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See detailNMR structure of a phosphatidylethanolamine binding protein from Drosophila
Rautureau, Gilles J P; Vovelle, Francoise; Schoentgen, Francoise et al

in Proteins (2010), 78(6), 1606-1610

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See detailNMR structure of Citrobacter freundii AmpD, comparison with bacteriophage T7 lysozyme and homology with PGRP domains.
Liepinsh, Edvards; Genereux, Catherine ULg; Dehareng, Dominique ULg et al

in Journal of Molecular Biology (2003), 327(4), 833-42

AmpD is a bacterial amidase involved in the recycling of cell-wall fragments in Gram-negative bacteria. Inactivation of AmpD leads to derepression of beta-lactamase expression, presenting a major pathway ... [more ▼]

AmpD is a bacterial amidase involved in the recycling of cell-wall fragments in Gram-negative bacteria. Inactivation of AmpD leads to derepression of beta-lactamase expression, presenting a major pathway for the acquisition of constitutive antibiotic resistance. Here, we report the NMR structure of AmpD from Citrobacter freundii (PDB accession code 1J3G). A deep substrate-binding pocket explains the observed specificity for low molecular mass substrates. The fold is related to that of bacteriophage T7 lysozyme. Both proteins bind zinc at a conserved site and require zinc for amidase activity, although the enzymatic mechanism seems to differ in detail. The structure-based sequence alignment identifies conserved features that are also conserved in the eukaryotic peptidoglycan recognition protein (PGRP) domains, including the zinc-coordination site in several of them. PGRP domains thus belong to the same fold family and, where zinc-binding residues are conserved, may have amidase activity. This hypothesis is supported by the observation that human serum N-acetylmuramyl-L-alanine amidase seems to be identical with a soluble form of human PGRP-L. [less ▲]

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See detailNMR Studies of Solutions of Actinide Ions and their Complexes. Relaxation and Spectroscopy
Braekers, Damien; Peters, Christelle; Vidick, Geoffrey ULg et al

Poster (2008, July)

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See detailNMR studies on radioactive actinide complexes. A completely foolish idea?
Vidick, Geoffrey ULg; Bouslimani, Nouri; Desreux, Jean-François ULg

Conference (2010, November 26)

The complete separation of actinides and lanthanides by solvent extraction is an important step in the reprocessing of nuclear wastes. The trivalent ions of these two families of f elements have very ... [more ▼]

The complete separation of actinides and lanthanides by solvent extraction is an important step in the reprocessing of nuclear wastes. The trivalent ions of these two families of f elements have very similar properties and it is only recently that an effective separation method has been developed. It is assumed that this separation can be achieved because of small differences in the covalency of the coordination bonds formed by the f ions but this has not been proved so far. We embarked into the first NMR study of the actinide complexes with the hope of better unravelling their solution structures and of clarifying the role of covalency. Nuclear magnetic resonance has nearly never been used for investigating actinide ions and their complexes not only because of their radioactivity and their toxicity but also because of the lack of dedicated spectrometers. It was also assumed that paramagnetism would cause excessive line broadenings. Many difficulties had thus to be overcome and the first step in our work was to show that well-resolved NMR spectra of actinide complexes (U to Cm) could indeed be obtained. Relatively narrow resonances have been observed for a variety of ions in different oxidation states provided their complexes are stable, symmetric and rigid. We used several advanced NMR techniques in order to fully characterize the actinide ions and their chelates in water or in organic solvents. The dispersion of the longitudinal relaxation time T1 of solvent nuclei with the magnetic field (NMRD) yields information on the magnetic properties and on the dynamic behaviour of paramagnetic species; 17O NMR allows the measurement of the water exchange times and 1H and 13C spectra yield information on the solution structures of the complexes. It will be shown that the paramagnetic shifts induced by the actinide ions originate from both a through space dipolar contribution and a through bonds contact contribution. The latter gives access to delocalized unpaired electron densities that are directly related to the covalency of the metal-ligand bonds. However, electron densities can only be obtained after separation of the two contributions. This could be accomplished thanks to variable temperature studies. In another approach, new ligands with rigid aliphatic substituents have been synthesized and contact contribution were deduced with the assumption that delocalization does not proceed to the 1H nuclei most removed from the metal center. This study has been extended to actinides in the trivalent, tetravalent and hexavalent states and new ligands have been synthesized in order to increase the magnetic anisotropy while keeping the symmetry and the rigidity needed to simplify the NMR analyses. [less ▲]

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See detailNMR study of ginkgolides by a suited ROESY approach
Grodent, Denis ULg; Llabres, Gabriel ULg

Poster (1992, August 15)

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