A determination of the molar gas constant R by acoustic thermometry in helium

We have determined the acoustic and microwave frequencies of a misaligned spherical resonator maintained near the temperature of the triple point of water and filled with helium with carefully characterized molar mass M = (4.002 6032 ± 0.000 0015) g mol-1, with a relative standard uncertainty ur(M) = 0.37×10-6. From these data and traceable thermometry we estimate the speed of sound in our sample of helium at TTPW = 273.16 K and zero pressure to be u0 2 = (945 710.45 ± 0.85) m2 s-2 and correspondingly deduce the value R = (8.314 4743 ± 0.000 0088) J mol-1 K-1 for the molar gas constant. We estimate the value k = R/NA = (1.380 6508 ± 0.000 0015) × 10-23 J K-1 for the Boltzmann constant using the currently accepted value of the Avogadro constant NA. These estimates of R and k, with a relative standard uncertainty of 1.06 × 10-6, are 1.47 parts in 106 above the values recommended by CODATA in 2010

Synthesis of trehalose-based chemical tools for the study of the mycobacterial membrane

Corynebacteriales including the causative agent of many diseases such as tuberculosis are known to be extremely resistant against external stress as well as to antibiotic treatments which is believed to be related to the singular architecture of their mycomembrane. Over the last decades, both bioorthogonal chemical reporters and fluorescent probes for the metabolic labeling of bacterial cell glycans were developed including several trehalose-based probes to study the dynamics of mycomembrane components. This review presents an exhaustive view on the reported syntheses of trehalose-based probes enabling the study of the mycomembrane biogenesis

Champs acoustiques en melanges gaz-vapeurs saturees : diffusion moleculaire et precondensation aux parois

Un nouveau mod`ele pour d´ecrire le mouvement acoustique dans des m´elanges gazeux est pr´esent´e ici en partant des ´equations fondamentales de l’hydrodynamique et de la thermodynamique, et en y associant des conditions aux fronti`eres adapt´ees pour d´ecrire les ph´enom`enes d’´evaporation et de condensation sur les parois quand un des composants du m´elange se trouve au voisinage de son point de saturation. Les solutions analytiques g´en´erales de ces ´equations orent `a pr´esent une description unifi´ee de la propagation acoustique en espaces infinis, semi infinis et confin´es, loin de et dans les couches limites. Ces solutions tiennent compte des couplages forts entre le mouvement acoustique et les processus de diusion de chaleur et de concentration, incluant les ph´enom`enes de pr´econdensation sur les parois. Les r´esultats th´eoriques ainsi obtenus sont compar´es `a ceux issus de mod`eles propos´es et d’exp´eriences eectu´ees par le pass´e, mais ne susent toujours pas `a expliquer tous les r´esultats exp´erimentaux disponibles dans la litt´erature. Des exp´eriences sont en cours de pr´eparation, qui ont pour but de valider et compl´eter cette approche analytique par une caract´erisation empirique de certains param`etres li´es aux propri´et´es physiques des gaz utilis´es et `a l’´etat de surface des parois

Low frequency acoustic pressure meaurements based on a Fabry-Perot refractometer

International audienceThis paper presents the development, the operating principle, and the experimental results of an innovative technique for the measurement of acoustic pressures in the range of 40 mHz up to 5 Hz. This new measurement technique is based on the use of a Fabry Perot refractometer in which the air density variations related to an acoustic wave can be tracked and determined by measuring the optical frequency variations of a laser locked on a longitudinal mode of the Fabry Perot cavity. This approach covers a wider range in the low and infrasonic frequencies compared to conventional sensors

2′-Modified thymidines with bioorthogonal cyclopropene or sydnone as building blocks for copper-free postsynthetic functionalization of chemically synthesized oligonucleotides

International audienceThe development of facile methods for conjugating relevant probes, ligands, or delivery agents onto oligonucleotides (ONs) is highly desirable both for fundamental studies in chemical biology and for improving the pharmacology of ONs in medicinal chemistry. Numerous efforts have been focused on the introduction of bioorthogonal groups onto phosphoramidite building blocks, allowing the controlled chemical synthesis of reactive ONs for postsynthetic modifications. Among these building blocks, alkyne, cyclooctynes, trans-cyclooctene, and norbornene have been proved to be compatible with automated solid-phase chemistry. Herein, we present the development of novel 2′-functionalized nucleoside phosphoramidite monomers comprising bioorthogonal methylcyclopropene or sydnone moieties and their introduction for the first time to ON solid-phase synthesis. Traceless ON postsynthetic modifications with reactive complementary probes were successfully achieved through either inverse electron-demand Diels–Alder (iEDDA) reactions or strain-promoted sydnone–alkyne cycloaddition (SPSAC). These results expand the set of bioorthogonal phosphoramidite building blocks to generate ONs for postsynthetic labeling