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See detailCatalytic epuration of biogaz
Claude, Vincent ULg; Toye, Dominique ULg; Heinrichs, Benoît ULg et al

Poster (2015, May 08)

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See detailCatalytic hydroprocessing of lignin under thermal and ultrasound conditions
Finch, Kenneth B.; Richards, Ryan; Richel, Aurore ULg et al

in Catalysis Today (2012), 196

Lignin isolated from Miscanthus x giganteus using acidic (FAL) and alkali (AL) conditions was thereafter subjected to the catalytic depolymerization under thermal or ultrasounds activation. The ... [more ▼]

Lignin isolated from Miscanthus x giganteus using acidic (FAL) and alkali (AL) conditions was thereafter subjected to the catalytic depolymerization under thermal or ultrasounds activation. The characterization of lignins was achieved by thermogravimetric analysis and FTIR. Three different classes of catalysts, containing nickel as active species, have been prepared in this scope: (i) nano-Ni by reduction of NiCl2 with NaBH4 under ultrasonication, (ii) Fe3O4-(NiMgAlO)x and (NiAlO)x by calcination of Mg(Ni)–Al hydrotalcite incorporated Fe3O4 followed by reduction with hydrogen, and (iii) NiO(111) nanosheets by reduction of Ni(NO3)2 with urea in benzyl alcohol. The catalysts were characterized by XRD and XPS techniques. Reduced mixed oxides displayed a moderate activity while a significant increase in conversion (up to 90%) was observed in the presence of nano-Ni(0). NiO(111) nanosheets catalysts performed very close to nano-Ni(0). The conversion and the mass distribution of the reaction products were strongly related to the procedure used for the extraction of ligning. In all the case AL led to a better depolymerization. The performances of the tested catalysts under ultrasound conditions were inferior to those tested under conventional heating conditions. The nature of the solvent was also found to be very important in this process. Thus, ionic liquid [BMIM]OAc led to the best results in autoclave conditions, and methanol under ultrasounds. [less ▲]

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See detailCatalytic layer for PEMFC based on carbon xerogels
Deschamps, Fabien ULg; Traina, Karl; Pirard, Jean-Paul ULg et al

in Proceedings of the Fundamentals and Development of Fuel cells 2013 conference (2013)

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See detailThe catalytic mechanism of beta-lactamases: NMR titration of an active-site lysine residue of the TEM-1 enzyme.
Damblon, Christian ULg; Raquet, X.; Lian, L. Y. et al

in Proceedings of the National Academy of Sciences of the United States of America (1996), 93(5), 1747-52

Beta-Lactamases are widespread in the bacterial world, where they are responsible for resistance to penicillins, cephalosporins, and related compounds, currently the most widely used antibacterial agents ... [more ▼]

Beta-Lactamases are widespread in the bacterial world, where they are responsible for resistance to penicillins, cephalosporins, and related compounds, currently the most widely used antibacterial agents. Detailed structural and mechanistic understanding of these enzymes can be expected to guide the design of new antibacterial compounds resistant to their action. A number of high-resolution structures are available for class A beta-lactamases, whose catalytic mechanism involves the acylation of a serine residue at the active site. The identity of the general base which participates in the activation of this serine residue during catalysis has been the subject of controversy, both a lysine residue and a glutamic acid residue having been proposed as candidates for this role. We have used the pH dependence of chemical modification of epsilon-amino groups by 2,4,6,-trinitrobenzenesulfonate and the pH dependence of the epsilon-methylene 1H and 13C chemical shifts (in enzyme selectively labeled with [epsilon-13C]lysine) to estimate the pKa of the relevant lysine residue, lysine-73, of TEM-1 beta-lactamase. Both methods show that the pKa of this residue is > 10, making it very unlikely that this residue could act as a proton acceptor in catalysis. An alternative mechanism in which this role is performed by glutamate-166 through an intervening water molecule is described. [less ▲]

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See detailCatalytic mechanism of the Streptomyces K15 DD-transpeptidase/penicillin-binding protein probed by site-directed mutagenesis and structural analysis
Rhazi, Noureddine ULg; Charlier, Paulette ULg; Dehareng, Dominique ULg et al

in Biochemistry (2003), 42(10), 2895-2906

The Streptomyces K15 penicillin-binding DD-transpeptidase is presumed to be involved in peptide cross-linking during bacterial cell wall peptidoglycan assembly. To gain insight into the catalytic ... [more ▼]

The Streptomyces K15 penicillin-binding DD-transpeptidase is presumed to be involved in peptide cross-linking during bacterial cell wall peptidoglycan assembly. To gain insight into the catalytic mechanism, the roles of residues Lys38, Ser96, and Cys98, belonging to the structural elements defining the active site cleft, have been investigated by site-directed mutagenesis, biochemical studies, and X-ray diffraction analysis. The Lys38His and Ser96Ala mutations almost completely abolished the penicillin binding and severely impaired the transpeptidase activities while the geometry of the active site was essentially the same as in the wild-type enzyme. It is proposed that Lys38 acts as the catalytic base that abstracts a proton from the active serine Ser35 during nucleophilic attack and that Ser96 is a key intermediate in the proton transfer from the Ogamma of Ser35 to the substrate leaving group nitrogen. The role of these two residues should be conserved among penicillin-binding proteins containing the Ser-Xaa-Asn/Cys sequence in motif 2. Conversion of Cys98 into Asn decreased the transpeptidase activity and increased hydrolysis of the thiolester substrate and the acylation rate with most beta-lactam antibiotics. Cys98 is proposed to play the same role as Asn in motif 2 of other penicilloyl serine transferases in properly positioning the substrate for the catalytic process. [less ▲]

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See detailCatalytic methods for the synthesis of stilbenes with an emphasis on their phytoalexins
Ferre-Filmon, Karine; Delaude, Lionel ULg; Demonceau, Albert ULg et al

in Coordination Chemistry Reviews (2004), 248(21-24), 2323-2336

This review aims at summarizing the recent significant advances in catalytic methods available for the synthesis of stilbene and functionalized stilbenes with an emphasis on their phytoalexins. Most ... [more ▼]

This review aims at summarizing the recent significant advances in catalytic methods available for the synthesis of stilbene and functionalized stilbenes with an emphasis on their phytoalexins. Most strategies developed so far involve palladium-mediated coupling reactions. Among them, the Heck and Suzuki reactions stand out for their synthetic versatility and efficiency, but the Stille and Negishi reactions have also found useful applications. Palladium also served as a catalyst to convert Z-stilbenes into the corresponding E-isomers. Other transition metal promoted stilbene syntheses include the McMurry coupling of aldehydes and ketones and alkene cross metathesis. Because non transition metal catalyzed syntheses of hydroxystilbenes continue to attract a lot of attention, significant recent developments in this area are also reported. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

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See detailCatalytic Properties of Class a Beta-Lactamases: Efficiency and Diversity
Matagne, André ULg; Lamotte-Brasseur, Josette; Frère, Jean-Marie ULg

in Biochemical Journal (1998), 330((Pt 2)), 581-98

beta-Lactamases are the main cause of bacterial resistance to penicillins, cephalosporins and related beta-lactam compounds. These enzymes inactivate the antibiotics by hydrolysing the amide bond of the ... [more ▼]

beta-Lactamases are the main cause of bacterial resistance to penicillins, cephalosporins and related beta-lactam compounds. These enzymes inactivate the antibiotics by hydrolysing the amide bond of the beta-lactam ring. Class A beta-lactamases are the most widespread enzymes and are responsible for numerous failures in the treatment of infectious diseases. The introduction of new beta-lactam compounds, which are meant to be 'beta-lactamase-stable' or beta-lactamase inhibitors, is thus continuously challenged either by point mutations in the ubiquitous TEM and SHV plasmid-borne beta-lactamase genes or by the acquisition of new genes coding for beta-lactamases with different catalytic properties. On the basis of the X-ray crystallography structures of several class A beta-lactamases, including that of the clinically relevant TEM-1 enzyme, it has become possible to analyse how particular structural changes in the enzyme structures might modify their catalytic properties. However, despite the many available kinetic, structural and mutagenesis data, the factors explaining the diversity of the specificity profiles of class A beta-lactamases and their amazing catalytic efficiency have not been thoroughly elucidated. The detailed understanding of these phenomena constitutes the cornerstone for the design of future generations of antibiotics. [less ▲]

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See detailCatalytic purification of biogas
Claude, Vincent ULg; Lambert, Stéphanie ULg

Poster (2012, December 05)

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See detailCatalytic reaction pathways approached by quantum chemistry: a challenge
Dive, Georges ULg; Dehareng, Dominique ULg; Ghosez, Léon

in Cellular and Molecular Life Sciences : CMLS (1998), 54(4), 378-382

This review explores the potential of quantum chemistry to help understand complex biochemical reactions such as enzyme catalysis. Starting from a historical background, the article introduces the reader ... [more ▼]

This review explores the potential of quantum chemistry to help understand complex biochemical reactions such as enzyme catalysis. Starting from a historical background, the article introduces the reader to the great diversity of problems than can be dealt with in the framework of quantum chemistry. [less ▲]

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See detailCatalytic reforming of biomass gasification tars with bi- or tri-doped catalysts optimized with organosilane precursors
Claude, Vincent ULg; Courson, Claire; Heinrichs, Benoît ULg et al

Conference (2016, June 08)

The thermochemical method called “biomass gasification” is generating emphatic interest for the production of bio-Syngas (CO + H2) since this process presents the advantage of being renewable without ... [more ▼]

The thermochemical method called “biomass gasification” is generating emphatic interest for the production of bio-Syngas (CO + H2) since this process presents the advantage of being renewable without emitting CO2. However, in practical applications, there are still some technical problems due to high tars concentration in the outlet gas which can condensate and clog the pipes. Many studies have highlighted the fact that the tar elimination via catalytic reforming seem to be the more practical and economical solution. The required properties of the catalysts are determined by its location: inside the reactor (primary catalyst) or outside of the reactor (secondary catalyst). Primary catalysts are generally robust, non-toxic, cheap and they are almost uniquely destined to fluidized bed reactors. Secondary catalysts can be used at the exit of both fluidized and fixed bed reactors. They are characterized by a tailored mesoporous shape, a controlled active site dispersion and an adapted elemental composition [1]. In this work , we decided to focus on designing materials for secondary catalytic applications, i.e. working at relatively low temperature (~650°C) with no mechanical stress. The supports were made of γ-Al2O3 synthesized via an easy Sol-Gel method. During their synthesis, these supports were doped with 10%wt of nickel and various combinations of metallic dopants (Co, Cu, Fe, Mn, Mo) in the aim of enhancing their catalytic activities and lifetime. [less ▲]

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See detailCatalytic transformation of CO2: from monomers to polymers
Alves, Margot ULg; Grignard, Bruno ULg; Boyaval, Amélie ULg et al

Conference (2016, May 24)

Valorising CO2 as a renewable C1 feedstock for producing added value building blocks is the scope of many academic and industrial researches. Carbon dioxide is a thermodynamically and kinetically stable ... [more ▼]

Valorising CO2 as a renewable C1 feedstock for producing added value building blocks is the scope of many academic and industrial researches. Carbon dioxide is a thermodynamically and kinetically stable molecule that can be converted into five membered cyclic carbonates by coupling with epoxides using organometallic complexes or organocatalysts. To date, the identification and development of highly efficient (organo)catalysts under mild experimental conditions still remains challenging. In particular, the synthesis of six membered cyclic carbonates by the CO2/oxetane coupling using such organocatalysts has never been reported to our knowledge. In this context, we developed a new highly efficient bicomponent homogeneous organocatalyst composed of an ammonium salt as the catalyst and fluorinated single or double hydrogen bond donor activators (HBD). First, the efficiency of this new organocatalyst for the fast and selective CO2/epoxide coupling was investigated through detailed kinetic studies by IR spectroscopy under pressure and results were compared with the most efficient organocatalysts reported in the literature. This study was completed by molecular modeling in order to elucidate the reaction mechanism. DFT calculations showed that the hexafluoroisopropanol functionalities of HBDs strengthened the proton donor capability and allowed a better stabilization by hydrogen bonding of the intermediates and transition states. Finally, the use of this dual organocatalyst was extended to the coupling of CO2 with less reactive oxetanes to produce hydroxyl telechelic oligocarbonates. [less ▲]

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See detailThe Catalytic, Glycosyl Transferase and Acyl Transferase Modules of the Cell Wall Peptidoglycan-Polymerizing Penicillin-Binding Protein 1b of Escherichia Coli
Terrak, Mohammed ULg; Ghosh, Tushar K.; van Heijenoort, Jean et al

in Molecular Microbiology (1999), 34(2), 350-364

The penicillin-binding protein (PBP) 1b of Escherichia coli catalyses the assembly of lipid-transported N-acetyl glucosaminyl-beta-1, 4-N-acetylmuramoyl-L-alanyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl ... [more ▼]

The penicillin-binding protein (PBP) 1b of Escherichia coli catalyses the assembly of lipid-transported N-acetyl glucosaminyl-beta-1, 4-N-acetylmuramoyl-L-alanyl-gamma-D-glutamyl-(L)-meso-diaminopimelyl+ ++- (L)-D-alanyl-D-alanine disaccharide pentapeptide units into polymeric peptidoglycan. These units are phosphodiester linked, at C1 of muramic acid, to a C55 undecaprenyl carrier. PBP1b has been purified in the form of His tag (M46-N844) PBP1bgamma. This derivative provides the host cell in which it is produced with a functional wall peptidoglycan. His tag (M46-N844) PBP1bgamma possesses an amino-terminal hydrophobic segment, which serves as transmembrane spanner of the native PBP. This segment is linked, via an congruent with 100-amino-acid insert, to a D198-G435 glycosyl transferase module that possesses the five motifs characteristic of the PBPs of class A. In in vitro assays, the glycosyl transferase of the PBP catalyses the synthesis of linear glycan chains from the lipid carrier with an efficiency of congruent with 39 000 M-1 s-1. Glu-233, of motif 1, is central to the catalysed reaction. It is proposed that the Glu-233 gamma-COOH donates its proton to the oxygen atom of the scissile phosphoester bond of the lipid carrier, leading to the formation of an oxocarbonium cation, which then undergoes attack by the 4-OH group of a nucleophile N-acetylglucosamine. Asp-234 of motif 1 or Glu-290 of motif 3 could be involved in the stabilization of the oxocarbonium cation and the activation of the 4-OH group of the N-acetylglucosamine. In turn, Tyr-310 of motif 4 is an important component of the amino acid sequence-folding information. The glycosyl transferase module of PBP1b, the lysozymes and the lytic transglycosylase Slt70 have much the same catalytic machinery. They might be members of the same superfamily. The glycosyl transferase module is linked, via a short junction site, to the amino end of a Q447-N844 acyl transferase module, which possesses the catalytic centre-defining motifs of the penicilloyl serine transferases superfamily. In in vitro assays with the lipid precursor and in the presence of penicillin at concentrations sufficient to derivatize the active-site serine 510 of the acyl transferase, the rate of glycan chain synthesis is unmodified, showing that the functioning of the glycosyl transferase is acyl transferase independent. In the absence of penicillin, the products of the Ser-510-assisted double-proton shuttle are glycan strands substituted by cross-linked tetrapeptide-pentapeptide and tetrapeptide-tetrapeptide dimers and uncross-linked pentapeptide and tetrapeptide monomers. The acyl transferase of the PBP also catalyses aminolysis and hydrolysis of properly structured thiolesters, but it lacks activity on D-alanyl-D-alanine-terminated peptides. This substrate specificity suggests that carbonyl donor activity requires the attachment of the pentapeptides to the glycan chains made by the glycosyl transferase, and it implies that one and the same PBP molecule catalyses transglycosylation and peptide cross-linking in a sequential manner. Attempts to produce truncated forms of the PBP lead to the conclusion that the multimodular polypeptide chain behaves as an integrated folding entity during PBP1b biogenesis. [less ▲]

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See detailCatalytically-inactive human cathepsin D triggers fibroblast invasive growth.
Laurent-Matha, V.; Maruani-Herrmann; Glondu, M. et al

in Journal of Cell Biology (2005), 168(3), 489-99

The aspartyl-protease cathepsin D (cath-D) is overexpressed and hypersecreted by epithelial breast cancer cells and stimulates their proliferation. As tumor epithelial–fibroblast cell interactions are ... [more ▼]

The aspartyl-protease cathepsin D (cath-D) is overexpressed and hypersecreted by epithelial breast cancer cells and stimulates their proliferation. As tumor epithelial–fibroblast cell interactions are important events in cancer progression, we investigated whether cath-D overexpression affects also fibroblast behavior. We demonstrate a requirement of cath-D for fibroblast invasive growth using a three-dimensional (3D) coculture assay with cancer cells secreting or not pro-cath-D. Ectopic expression of cath-D in cath-D–deficient fibroblasts stimulates 3D outgrowth that is associated with a significant increase in fibroblast proliferation, survival, motility, and invasive capacity, accompanied by activation of the ras–MAPK pathway. Interestingly, all these stimulatory effects on fibroblasts are independent of cath-D proteolytic activity. Finally, we show that pro-cath-D secreted by cancer cells is captured by fibroblasts and partially mimics effects of transfected cath-D. We conclude that cath-D is crucial for fibroblast invasive outgrowth and could act as a key paracrine communicator between cancer and stromal cells, independently of its catalytic activity. [less ▲]

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See detailCatamenial Pneumothorax: A Case Report and Review of the Literature
Pappalardo, E.; LAUNGANI, Alexis ULg; DURIEUX, Rodolphe ULg et al

in Acta Chirurgica Belgica (2007), 107(6, Nov-Dec), 695-6

Catamenial pneumothorax is a rare condition that is often misdiagnosed. It is defined as spontaneous pneumothorax occuring within 72 hours before or after onset of menstruation. Etiology is unknown but ... [more ▼]

Catamenial pneumothorax is a rare condition that is often misdiagnosed. It is defined as spontaneous pneumothorax occuring within 72 hours before or after onset of menstruation. Etiology is unknown but could be linked to endometriosis. Treatment is medicosurgical: thoracoscopy for pleural abrasion and hormonotherapy to avoid recurrence. [less ▲]

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See detailLe catastérisme chez Homère. Le cas d'Orion
Renaud, Jean-Michel ULg

in Gaia. Revue interdisciplinaire sur la Grèce archaïque (2003), 7

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See detailLe catastérisme d'Orion
Renaud, Jean-Michel ULg

in Bakhouche, Béatrice; Moreau, Alain; Turpin, Jean-Claude (Eds.) Les astres. Actes du Colloque International de Montpellier 23-25 mars 1995 (1996)

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See detailCatastrophe naturelle: Quand la communication se noie (c onfrontation Bénin / Tubize)
Ozer, Pierre ULg

Conference (2013, June 14)

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See detailCatastrophes naturelles et aménagement du territoire: de l’intérêt des images Google Earth dans les pays en développement
Ozer, Pierre ULg

in Geo-Eco-Trop : Revue Internationale de Géologie, de Géographie et d'Ecologie Tropicales (2014), 38(1), 209-220

More and more often, natural disasters linked to extreme weather events defined as extreme are charged to climate change. Here we demonstrate that -very often- these past, current or future disasters ... [more ▼]

More and more often, natural disasters linked to extreme weather events defined as extreme are charged to climate change. Here we demonstrate that -very often- these past, current or future disasters mainly result from the unexpected addition of human activities coupled with the lack of governance, through the non-application of laws and regulations relating to urban planning. To do this, in regions characterized by a patent lack of data, the use of satellite data available in open source via Google Earth can be a very effective tool to track certain processes (coastal erosion, gully erosion, urban sprawl in flood-prone areas) involved in the increasing risk. In addition, it is a very powerful educational tool to illustrate the speed of these phenomena that threaten property and people. To illustrate these assumptions, examples from Nouakchott (Mauritania) and Kinshasa (Democratic Republic of Congo) are successively presented [less ▲]

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