Structural Insights into the Quinolone Resistance Mechanism of Mycobacterium tuberculosis DNA Gyrase

Mycobacterium tuberculosis DNA gyrase, an indispensable nanomachine involved in the regulation of DNA topology, is the only type II topoisomerase present in this organism and is hence the sole target for quinolone action, a crucial drug active against multidrug-resistant tuberculosis. To understand at an atomic level the quinolone resistance mechanism, which emerges in extensively drug resistant tuberculosis, we performed combined functional, biophysical and structural studies of the two individual domains constituting the catalytic DNA gyrase reaction core, namely the Toprim and the breakage-reunion domains. This allowed us to produce a model of the catalytic reaction core in complex with DNA and a quinolone molecule, identifying original mechanistic properties of quinolone binding and clarifying the relationships between amino acid mutations and resistance phenotype of M. tuberculosis DNA gyrase. These results are compatible with our previous studies on quinolone resistance. Interestingly, the structure of the entire breakage-reunion domain revealed a new interaction, in which the Quinolone-Binding Pocket (QBP) is blocked by the N-terminal helix of a symmetry-related molecule. This interaction provides useful starting points for designing peptide based inhibitors that target DNA gyrase to prevent its binding to DNA

Phosphorescence of C 5 N − in Rare Gas Solids

International audiencePhosphorescence of C5N− was discovered following the ArF-laser (193 nm) photolysis of cyanodiacetylene (HC5N) isolated in cryogenic argon, krypton, and xenon matrices. This visible emission, with an origin around 460 nm, is vibrationally resolved, permitting the measurement of frequencies for eight ground-state fundamental vibrational modes, including the three known from previous IR absorption studies. Phosphorescence lifetime amounts to tens or even hundreds of ms depending on the matrix host; it is five times longer than in the case of HC5N

High-Yield Formation of Substituted Tetracyanobutadienes from Reaction of Ynamides with Tetracyanoethylene.

The authors gratefully acknowledge Dr. L. Toupet from Institut de Physique de Rennes for solving X-ray structures, T. C. Nguyen for help in performing DFT calculations and Pr. A. Boucekkine for useful discussions.International audienceA high-yielding sequence of [2+2] cycloaddition-retroelectrocyclization of ynamides with tetracyanoethylene (TCNE) is described. The reaction provided tetracyanobutadiene (TCBD) species, which were characterized by various techniques. DFT and TD-DFT calculations were also performed to complement experimental findings

Low Temperature Synthesis and Phosphorescence of Methylcyanotriacetylene

International audienceThis paper reports on UV-stimulated synthesis of methylcyanotriacetylene carried out in cryogenic rare gas matrixes via coupling of smaller precursors: propyne and cyanodiacetylene. The detection was possible due to the strong visible ã 3A' → X̃ 1A1 phosphorescence of CH3C7N, discovered in the course of this work. The ensuing measurements of electronic spectroscopy revealed the formally forbidden B̃ 1E-X̃ 1A1 system, as well as the allowed one Ẽ 1A1-X̃ 1A1, with origins at approximately 3.32 and 5.4 eV, respectively. It was also possible to revisit the spectroscopic characterization of cyanotriacetylene, HC7N, formed in parallel to the title photoproduct. Spectral assignments were assisted with a density functional theory study

Synthesis and Electronic Phosphorescence of Dicyanooctatetrayne (NCN) in Cryogenic Matrixes

International audienceThe rodlike 1,8-dicyano-octa-1,3,5,7-tetrayne (NCN) molecule was synthesized with UV-assisted coupling of rare-gas matrix-isolated cyanobutadiyne (HCN) molecules. Detection of NCN molecule was possible due to its strong orange-red (origin at 618 nm) electronic luminescence. Excitation spectra of this emission (ã Σ-X̃ Σ phosphorescence) gave access to studying the fully allowed H̃ Σ-X̃ Σ UV system of NCN. The identification of observed spectral features was assisted with quantum chemical computations. Certain regularities shaping the electronic spectroscopy of NCN molecules have been discussed

Synthesis and spectroscopy of cyanotriacetylene (HC7N) in solid argon

International audienceUV laser irradiations of cryogenic solid argon matrices doped with a mixture of acetylene and cyanodiacetylene (HC5N) resulted in the formation of a longer carbon-nitrogen chain, cyanotriacetylene (HC7N). The identification of this species was accomplished based on IR vibrational spectroscopy (including the study of isotopically labeled compounds), on electronic luminescence spectroscopy, and on theoretical predictions. Additionally, IR absorption bands recognized as due to HC7N were detected in photolysed Ar matrices doped with a cyanoacetylene/diacetylene mixture; this assignment was confirmed with the mass spectrometry of gases released upon the warm-up of the sample

Spectroscopy of methylcyanodiacetylene revisited. Solid parahydrogen and solid neon matrix studies

International audienceElectronic phosphorescence and infrared absorption spectra of methylcyanodiacetylene (CH3C5N) are revisited using matrix isolation in solid parahydrogen and neon. Band assignments previously found for Ar, Kr, Xe, and N2 low-temperature host media were updated, with certain ambiguous attributions being resolved. A combined analysis of both dispersed phosphorescence and phosphorescence excitation spectra observed in different environments provides a means to estimate the singlet-triplet separation for the gas-phase and pure solid compound, where phosphorescence could not be observed

Cryogenic Photochemical Synthesis and Electronic Spectroscopy of Cyanotetracetylene

International audienceHC9N is a molecule of astrochemical interest. In this study, it was produced in cryogenic Ar and Kr matrices from UV-photolyzed diacetylene/cyanodiacetylene mixtures. Its strong phosphorescence was discovered and served for the identification of the compound. Vibrationally resolved phosphorescence excitation spectra gave insight into excited singlet electronic states. Two electronic systems were observed around 26 000-34 000 cm(-1) and 35 000-50 000 cm(-1). Energies of the second excited singlet and the lowest triplet state were derived from analysis of these systems. Vibrational and electronic spectroscopic features were assigned with the assistance of density functional theory calculations. Some trends concerning the electronic spectroscopy of HC2n+1N family molecules are presented

Electronic absorption and phosphorescence of cyanodiacetylene.

International audienceElectronic absorption and emission spectra have been investigated for cyanodiacetylene, HC(5)N, an astrophysically relevant molecule. The analysis of gas-phase absorption was assisted with the parallel rare gas matrix isolation experiments and with density functional theory (DFT) predictions concerning the excited electronic states. Mid-UV systems B (1)Delta<--X (1)Sigma(+) (origin at 282.5 nm) and A (1)Sigma(-)<--X (1)Sigma(+) (306.8 nm) were observed. Vibronic assignments have been facilitated by the discovery of the visible phosphorescence a (3)Sigma(+)<--X (1)Sigma(+) in solid Ar, Kr, and Xe. Phosphorescence excitation spectra, as well as UV absorption measurements in rare gas matrices, revealed the enhancement of A<--X transitions. The vibronic structure of dispersed phosphorescence spectra supplied new data concerning the ground state bending fundamentals of matrix-isolated HC(5)N. The experimental singlet-triplet splitting, 2.92 eV in Ar, closely matches the value of 3.0 eV predicted by DFT

Evolution of Health Care Consumption in the Knee and Hip Osteoarthritis Long Term Assessment Cohort, a French Population Based Cohort of Symptomatic Knee and/or Hip OA Patients

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