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Dubé,e, Vincent,Triboulet, Sé,bastien,Mainardi, Jean-Luc,Ethè,ve-Quelquejeu, Mé,lanie,Gutmann, Laurent,Marie, Arul,Dubost, Lionel,Hugonnet, Jean-Emmanuel,Arthur, Michel American Society for Microbiology 2012 Antimicrobial agents and chemotherapy Vol.56 No.8
<B>ABSTRACT</B><P>The structure ofMycobacterium tuberculosispeptidoglycan is atypical since it contains a majority of 3→3 cross-links synthesized byl,d-transpeptidases that replace 4→3 cross-links formed by thed,d-transpeptidase activity of classical penicillin-binding proteins. Carbapenems inactivate thesel,d-transpeptidases, and meropenem combined with clavulanic acid is bactericidal against extensively drug-resistantM. tuberculosis. Here, we used mass spectrometry and stopped-flow fluorimetry to investigate the kinetics and mechanisms of inactivation of the prototypicM. tuberculosisl,d-transpeptidase LdtMt1by carbapenems (meropenem, doripenem, imipenem, and ertapenem) and cephalosporins (cefotaxime, cephalothin, and ceftriaxone). Inactivation proceeded through noncovalent drug binding and acylation of the catalytic Cys of LdtMt1, which was eventually followed by hydrolysis of the resulting acylenzyme. Meropenem rapidly inhibited LdtMt1, with a binding rate constant of 0.08 μM<SUP>−1</SUP>min<SUP>−1</SUP>. The enzyme was unable to recover from this initial binding step since the dissociation rate constant of the noncovalent complex was low (<0.1 min<SUP>−1</SUP>) in comparison to the acylation rate constant (3.1 min<SUP>−1</SUP>). The covalent adduct resulting from enzyme acylation was stable, with a hydrolysis rate constant of 1.0 × 10<SUP>−3</SUP>min<SUP>−1</SUP>. Variations in the carbapenem side chains affected both the binding and acylation steps, ertapenem being the most efficient LdtMt1inactivator. Cephalosporins also formed covalent adducts with LdtMt1, although the acylation reaction was 7- to 1,000-fold slower and led to elimination of one of the drug side chains. Comparison of kinetic constants for drug binding, acylation, and acylenzyme hydrolysis indicates that carbapenems and cephems can both be tailored to optimize peptidoglycan synthesis inhibition inM. tuberculosis.</P>
Microstrip EHF Butler Matrix Design and Realization
Jean-Sébastien Néron,Gilles-Y. Delisle 한국전자통신연구원 2005 ETRI Journal Vol.27 No.6
This paper describes the design and realization of an extra high frequency band 8 × 8 microstrip Butler matrix. Operation at 36 GHz is achieved with a frequency bandwidth exceeding 400 MHz. The circuit is implemented on a bi-layer microstrip structure using conventional manufacturing processes. This planar implementation of a Butler matrix is a key component of a switched beam smart antenna with printed antenna elements integrated on-board. Conception details, simulation results, and measurements are also given for the components (hybrid couplers, cross-couplers, and vertical inter-connections) used to implement the matrix.
Borondifluoride complexes of hemicurcuminoids as bio-inspired push–pull dyes for bioimaging
Kim, Eunsun,Felouat, Abdellah,Zaborova, Elena,Ribierre, Jean-Charles,Wu, Jeong Weon,Senatore, Sé,bastien,Matthews, Cé,dric,Lenne, Pierre-Franç,ois,Baffert, Carole,Karapetyan, Artak,G The Royal Society of Chemistry 2016 Organic & Biomolecular Chemistry Vol.14 No.4
<P>Hemicurcuminoids are based on half of the pi-conjugated backbone of curcuminoids. The synthesis of a series of such systems and their borondifluoride complexes is described. The electrochemical and photophysical properties of difluorodioxaborine species were investigated as a function of the nature of electron donor and acceptor groups appended at either terminal positions of the molecular backbone. The emissive character of these dipolar dyes was attributed to an intraligand charge transfer process, leading to fluorescence emission that is strongly dependent on solvent polarity. Quasi-quantitative quenching of fluorescence in high polarity solvents was attributed to photoinduced electron transfer. These dyes were shown to behave as versatile fluorophores. Indeed, they display efficient two-photon excited fluorescence emission leading to high two-photon brightness values. Furthermore, they form nanoparticles in water whose fluorescence emission quantum yield is less than that of the dye in solution, owing to aggregation-induced fluorescence quenching. When cos7 living cells were exposed to these weakly-emitting nanoparticles, one-and two-photon excited fluorescence spectra showed a strong emission within the cytoplasm that originated from the individual molecules. Dye uptake thus involved a disaggregation mechanism at the cell membrane which restored fluorescence emission. This off-on fluorescence switching allows a selective optical monitoring of those molecules that do enter the cell, which offers improved sensitivity and selectivity of detection for bioimaging purposes.</P>