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See detailMetal Ion Binding and Coordination Geometry for Wild Type and Mutants of Metallo-Beta -Lactamase from Bacillus Cereus 569/H/9 (Bcii): A Combined Thermodynamic, Kinetic, and Spectroscopic Approach
De Seny, Dominique ULg; Heinz, U.; Wommer, S. et al

in Journal of Biological Chemistry (2001), 276(48), 45065-78

One high affinity (nm) and one low affinity (microM) macroscopic dissociation constant for the binding of metal ions were found for the wild-type metallo-beta-lactamase from Bacillus cereus as well as six ... [more ▼]

One high affinity (nm) and one low affinity (microM) macroscopic dissociation constant for the binding of metal ions were found for the wild-type metallo-beta-lactamase from Bacillus cereus as well as six single-site mutants in which all ligands in the two metal binding sites were altered. Surprisingly, the mutations did not cause a specific alteration of the affinity of metal ions for the sole modified binding site as determined by extended x-ray absorption fine structure (EXAFS) and perturbed angular correlation of gamma-rays spectroscopy, respectively. Also UV-visible absorption spectra for the mono-cobalt enzymes clearly contain contributions from both metal sites. The observations of the very similar microscopic dissociation constants of both binding sites in contrast to the significantly differing macroscopic dissociation constants inevitably led to the conclusion that binding to the two metal sites exhibits negative cooperativity. The slow association rates for forming the binuclear enzyme determined by stopped-flow fluorescence measurements suggested that fast metal exchange between the two sites for the mononuclear enzyme hinders the binding of a second metal ion. EXAFS spectroscopy of the mono- and di-zinc wild type enzymes and two di-zinc mutants provide a definition of the metal ion environments, which is compared with the available x-ray crystallographic data. [less ▲]

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See detailMetal matrix nanocomposite coatings for improving the usage properties of metallic materials
Mertens, Anne ULg; Lecomte-Beckers, Jacqueline ULg

Conference (2015, January)

The use of metal matrix nanocomposite is at the present time not as widespread as for their polymer-based counterparts. Yet, the addition of nanoparticles in a metallic matrix also allows to significantly ... [more ▼]

The use of metal matrix nanocomposite is at the present time not as widespread as for their polymer-based counterparts. Yet, the addition of nanoparticles in a metallic matrix also allows to significantly improve its usage properties, thus opening new and interesting prospects in terms of applications. This presentation aims at providing a broad overview of the various usage properties that can be enhanced by the addition of nanoparticles as illustrated by a number of examples taken from the scientific literature as well as from the researches carried out by the Metallic Materials Science Unit at the University of Liege. [less ▲]

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See detailMetal plastic behaviour linked to texture analysis and FEM method
Duchene, Laurent ULg; Godinas, André; Habraken, Anne ULg

in 4th International Conference NUMISHEET 1999 (1999)

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See detailMetal response of transgenic tomato plants expressing P1B-ATPase
Barabasz, Anna; Wilkowska, Anna; Ruszczyńska, Anna et al

in Physiologia Plantarum (2012), 145

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See detailMetal-coordination: an effective lever for cobalt-mediated radical polymerization
Debuigne, Antoine ULg; Jérôme, Christine ULg; Jérôme, Robert ULg et al

in Polymer Preprints (2008), 49(27), 193-194

Detailed reference viewed: 24 (3 ULg)
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See detailMetal-Forming Simulation via Eulerian-Lagrangian FEM with Contact Problems
Ponthot, Jean-Philippe ULg

in Proc. of NUMETA'90, Numerical Meth. in Engineering: Theory & Applications (1990)

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See detailMetal-free strategies for the synthesis of functional and well-defined polyphosphoesters
Clement, Benoît ULg; Grignard, Bruno ULg; Koole, Leo et al

in Macromolecules (2012), 45(11), 4476-4486

We report here metal-free strategies using organocatalysis based on supramolecular recognition for the ring-opening polymerization (ROP) of several cyclic phosphate monomers (CPMs) by a variety of ... [more ▼]

We report here metal-free strategies using organocatalysis based on supramolecular recognition for the ring-opening polymerization (ROP) of several cyclic phosphate monomers (CPMs) by a variety of organocatalysts such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU), 1,5,7-triazabicyclo[4.4.0]undec-5-ene (TBD), and a bicomponent thiourea−tertiary amine catalyst. Each of these catalysts is efficient to produce linear polyphosphoesters (PPEs) from CPMs but with different sensitivity toward transesterification side reactions. The strong basicity of DBU is sufficient to activate an alcohol initiating the polymerization in the absence of any other cocatalyst. Nevertheless, side chain transfer reactions leading to branched and/or cyclic polymeric structures are observed, especially for high monomer conversion. Unlike DBU, TBD is a dual catalyst activating both the alcohol and the monomer. This dual activation allows shorter polymerization time, but SEC analyses of polyphosphates reveal bimodal molecular weight distribution due to chains coupling. Finally, a mixture of DBU and thiourea (TU) appears by far the most efficient catalyst to carry out fast and controlled polymerization while minimizing transesterification reactions, even at near-complete conversion. Compared with polymerizations carried out with Sn(Oct)2 as a metal catalyst, the control of polymerization is much better so that it is possible to prepare polyphosphoesters (PPEs) with molecular weight close to 70 000 g mol−1 and polydispersity index below 1.10. Simultaneous activation by TU of both CPMs and the alcohol group of the initiator by DBU proves to be an effective and robust ROP catalytic system to synthesize polymers with predictable molecular weight and narrow polydispersity. The chain extension experiments through the use of hydroxy end- capped PPEs as macroinitiators confirm the controlled/living nature of the DBU/TU-catalyzed ROP of CPMs and pave the way to the synthesis of block copolymers based on polyphosphates. [less ▲]

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See detailMetal-free synthesis of a glucosamine labeled amphiphilic polymer for drug delivery applications
Riva, Raphaël ULg; Boyère, Cécric; Debuigne, Antoine ULg et al

Poster (2014, May 19)

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See detailMétalangage et épistémologie
Badir, Sémir ULg

in Horizon sémiologie (2006)

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See detailMetallic nanowire networks for energy applications: experimental and modelling approaches
Langley, Daniel ULg; Lagrange, Mélanie; Munoz-Rojas, David et al

Conference (2014)

Research is increasingly being dedicated towards finding emerging materials aiming at playing a prominent role in energy issues. Transparent electrodes are a key component of devices such as solar cells ... [more ▼]

Research is increasingly being dedicated towards finding emerging materials aiming at playing a prominent role in energy issues. Transparent electrodes are a key component of devices such as solar cells or efficient lighting (such as OLED). Among emerging transparent conductive materials, metallic nanowire networks appear to be a very promising solution. This work aims at designing and optimizing metallic nanowire networks based on both experimental and modelling approaches. The influence on the networks physical properties of several key parameters such as the metal/alloy used, thermal annealing, network density, device size, etc. are explored. These percolating networks exhibit excellent properties (sheet resistances and optical transparency of about 10 Ω/ sq and 90%, respectively) fulfilling the requirements for solar or efficient opto-electronic applications. This makes them very appropriate for future uses involving large area and flexible photovoltaics or efficient lighting display technologies. A comprehensive understanding of the design and main physical properties of these promising nanostructured networks will be presented [less ▲]

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See detailMetallic nanowire networks: effects of thermal annealing on electrical resistance
Langley, Daniel ULg; Lagrange, Mélanie; Giusti, Gael et al

in Nanoscale (2014), 6

Metallic nanowire networks have huge potential in devices requiring transparent electrodes. This article describes how the electrical resistance of metal nanowire networks evolve under thermal annealing ... [more ▼]

Metallic nanowire networks have huge potential in devices requiring transparent electrodes. This article describes how the electrical resistance of metal nanowire networks evolve under thermal annealing. Understanding the behavior of such films is crucial for the optimization of transparent electrodes which find many applications. An in-depth investigation of silver nanowire networks under different annealing conditions provides a case study demonstrating that several mechanisms, namely local sintering and desorption of organic residues, are responsible for the reduction of the systems electrical resistance. Optimization of the annealing led to specimens with transmittance of 90% (at 550 nm) and sheet resistance of 9.5 Ω sq−1. Quantized steps in resistance were observed and a model is proposed which provides good agreement with the experimental results. In terms of thermal behavior, we demonstrate that there is a maximum thermal budget that these electrodes can tolerate due to spheroidization of the nanowires. This budget is determined by two main factors: the thermal loading and the wire diameter. This result enables the fabrication and optimization of transparent metal nanowire electrodes for solar cells, organic electronics and flexible displays. [less ▲]

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See detailThe metallicity gradient of the old halo
Parmentier, Geneviève ULg; Jehin, Emmanuel ULg; Magain, Pierre ULg et al

in Noels-Grötsch, Arlette; Magain, Pierre; Caro, Denise (Eds.) et al Liege International Astrophysical Colloquia (2000)

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See detailMetallicity Gradients in Globular Cluster Systems : the Trace of a Self-Enrichment Process ?
Parmentier, G.; Magain, Pierre ULg; Noels-Grötsch, Arlette ULg et al

in Geisler, E. K.; Grebel, E.; Minniti, D. (Eds.) Extragalactic Star Clusters (2002)

We have developed a model of globular cluster self-enrichment, based on the ability of the globular cluster gaseous progenitors to retain the ejecta of a first generation of Type II Supernovae. The key ... [more ▼]

We have developed a model of globular cluster self-enrichment, based on the ability of the globular cluster gaseous progenitors to retain the ejecta of a first generation of Type II Supernovae. The key point is that this ability depends on the pressure exerted on the progenitor cloud by the surrounding protogalactic medium and therefore on the location of the cloud in the protogalaxy. The model is able to explain the galactic halo metallicities and the metallicity gradient of the Old Halo which is thought to be the genuine galactic globular cluster system. The possibility that metallicity gradients are a common property of extragalactic globular cluster systems is also presented. [less ▲]

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See detailA metallo-beta-lactamase enzyme in action: Crystal structures of the monozinc carbapenemase CphA and its complex with biapenem
Garau, Gianpiero; Bebrone, Carine ULg; Anne, Christine et al

in Journal of Molecular Biology (2005), 345(4), 785-795

One strategy developed by bacteria to resist the action of beta-lactam antibiotics is the expression of metallo-beta-lactamases. CphA from Aeromonas hydrophila is a member of a clinically important ... [more ▼]

One strategy developed by bacteria to resist the action of beta-lactam antibiotics is the expression of metallo-beta-lactamases. CphA from Aeromonas hydrophila is a member of a clinically important subclass of metallo-beta-lactamases that have only one zinc ion in their active site and for which no structure is available. The crystal structures of wild-type CphA and its N220G mutant show the structural features of the active site of this enzyme, which is modeled specifically for carbapenem hydrolysis. The structure of CphA after reaction with a carbapenem substrate, biapenem, reveals that the enzyme traps a reaction intermediate in the active site. These three X-ray structures have allowed us to propose how the enzyme recognizes carbapenems and suggest a mechanistic pathway for hydrolysis of the beta-lactam. This will be relevant for the design of metallo-beta-lactamase inhibitors as well as of antibiotics that escape their hydrolytic activity. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailMetallo-beta-lactamases (classification, activity, genetic organization, structure, zinc coordination) and their superfamily
Bebrone, Carine ULg

in Biochemical Pharmacology (2007), 74(12), 1686-1701

One strategy employed by bacterial strains to resist beta-lactam antibiotics is the expression of metallo-beta-lactamases requiring Zn+2 for activity. In the last few years, many new zinc beta-lactamases ... [more ▼]

One strategy employed by bacterial strains to resist beta-lactam antibiotics is the expression of metallo-beta-lactamases requiring Zn+2 for activity. In the last few years, many new zinc beta-lactamases have been described and several pathogens are now known to synthesize members of this class. Metallo-beta-lactamases are especially worrisome due to: (1) their broad activity profiles that encompass most beta-lactam antibiotics, including the carbapenems; (2) potential for horizontal transference; and (3) the absence of clinically useful inhibitors. on the basis of the known sequences, three different lineages, identified as subclasses B1, B2, and B3 have been characterized. The three-dimensional structure of at least one metallo-p-lactamase of each subclass has been solved. These very similar 3D structures are characterized by the presence of an alpha beta beta alpha-fold. In addition to metallo-beta-lactamases which cleave the amide bond of the beta-lactam ring, the metallo-beta-lactamase superfamily includes enzymes which hydrolyze thiol-ester, phosphodiester and sulfuric ester bonds as well as oxydoreductases. Most of the 6000 members of this superfamily share five conserved motifs, the most characteristic being the His116-X-His118-X-Asp120-His121 signature. They all exhibit an alpha beta beta alpha-fold, similar to that found in the structure of zinc beta-lactamases. Many members of this superfamily are involved in mRNA maturation and DNA reparation. This fact suggests the hypothesis that metallo-beta-lactamases may be the result of divergent evolution starting from an ancestral protein which did not have a beta-lactamase activity. (c) 2007 Elsevier Inc. All rights reserved. [less ▲]

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See detailMetallo-beta-lactamases as emerging resistance determinants in Gram-negative pathogens: open issues
Cornaglia, G.; Akova, M.; Amicosante, G. et al

in International Journal of Antimicrobial Agents (2007), 29(4), 380-388

The rapid spread of acquired metallo-beta-lactamases (MBLs) among major Gram-negative pathogens is a matter of particular concern worldwide and primarily in Europe, one of first continents where the ... [more ▼]

The rapid spread of acquired metallo-beta-lactamases (MBLs) among major Gram-negative pathogens is a matter of particular concern worldwide and primarily in Europe, one of first continents where the emergence of acquired MBLs has been reported and possibly the geographical area where the increasing diversity of these enzymes and the number of bacterial species affected are most impressive. This spread has not been paralleled by accuracy/standardisation of detection methods, completeness of epidemiological knowledge or a clear understanding of what MBL production entails in terms of clinical impact, hospital infection control and antimicrobial chemotherapy. A number of European experts in the field met to review the current knowledge on this phenomenon, to point out open issues and to reinforce and relate to one another the existing activities set forth by research institutes, scientific societies and European Union-driven networks. (c) 2006 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved. [less ▲]

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See detailMetallo-supramolecular micellar gels: a structural study
Mugemana, Clément; Joset, Arnaud ULg; Guillet, Pierre et al

Poster (2013, July 10)

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See detailMetallo-supramolecular micellar gels: a structural study
Mugemana, Clément; Joset, Arnaud ULg; Guillet, Pierre et al

Conference (2013, May 17)

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See detailMetallocene catalyzed polymerization of ethylene in the presence of graphite. 1. Synthesis and characterization of the composites
Alexandre, Michaël ULg; Pluta, Miroslaw; Dubois, Philippe ULg et al

in Macromolecular Chemistry and Physics (2001), 202(11), 2239-2246

Polyethylene/graphite composites have been prepared by two different methods. In a first approach, the ethylene polymerization has been catalyzed by metallo-cene in the presence of neat graphite particles ... [more ▼]

Polyethylene/graphite composites have been prepared by two different methods. In a first approach, the ethylene polymerization has been catalyzed by metallo-cene in the presence of neat graphite particles (NGC composites). A second series of composites (TGC) has been prepared by the polymerization-filling technique, which requires that the metallocene/methylalumoxane catalyst is fixed onto the graphite surface prior to the ethylene polymerization. The two series of composites exhibit significantly different morphology and thermal properties. The filler distribution is very heterogeneous in the NGC series. The morphology changes from an intimate mixture of PE and filler particles at low graphite content to graphite covered by patches of PE at high filler loading. The graphite distribution is much more homogeneous in the TGC samples, and the morphology consists of particles covered by a layer of PE in the whole composition range. Differences in the thermal properties are discussed in relation to the morphology. [less ▲]

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