A simple and efficient synthesis of new cyclic ureas

A facile access to a wide range of original saturated N-heterocyclic ureas is described using, as a key step, a Michael-type reaction involving isocyanates or amines on a piperidine framework possessing an α,β-unsaturated ester functionality.     

Palladium mediated direct coupling of silylated arylalkynes with propargylic chlorides: an efficient access to functionalized conjugated allenynes

Pd/Cu-catalyzed one-pot reaction of 1-trimethylsilyl-2-arylalkynes with propargylic chlorides in the presence of TBAF is described. The present new procedure is applicable to a wide range of silylated arylalkynes with both electron-withdrawing and electron-donating substituents. Functionalized allenynes can thus be obtained in good yields without prior deprotection of the alkynes.     

Friction Between Steel and a Confined Inert Material Representative of Explosives Under Severe Loadings

The ignition of a confined explosive submitted to an impact strongly depends on the friction conditions between the explosive and the confinement material (generally steel). A test has been developed to study the friction between steel and a material mechanically representative of an explosive. The scope of interest is that of high pressures and high relative velocities (respectively 20 MPa and 10 m/s). The friction device consists of making a cylinder, formed of the material, slide through a steel tube. Axial prestress enabling the steel-material contact stress to be generated is performed by means of a screw-nut system. This confinement state avoids any fracture of the material from occurring throughout the test. Two kinds of tests are carried out: low-velocity (around 1 mm/min) and high-velocity (around 10 m/s). The relative displacement is obtained using a testing machine during the low-velocity tests, and thanks to a Hopkinson bars system during the high-velocity tests. Examination of the measurements obtained during high-velocity tests shows that a workable steady state of equilibrium has been reached. As the interface stresses cannot be measured, the friction coefficient must be determined using indirect data: force measurements obtained from the machine or from the Hopkinson bars and strain measurements made on the exterior of the tube. The procedure to identify the steel-material friction coefficient from these measurements entails analytical modelling and finite element simulations of the mechanical behaviour of the tube-specimen assembly. The friction coefficient identified during the high-velocity tests is far higher than the coefficient identified during the low-velocity tests.     

Modulation of Relaxivity,Suspension Stability,and Biodistribution of Dendronized Iron Oxide Nanoparticles as a Function of the Organic Shell Design

Nanoparticles (NPs) with a mean diameter of 10 nm are functionalized with three dendrons: D1 a PEGylated PAMAM dendron of generation 0.5, D2 a hydrophilic oligoethyleneglycol‐derivatized dendron (D2) displaying a phosphonic acid at the focal point, and D2–2P the same dendron than D2 but with two phosphonic acid anchoring agents. Their grafting is confirmed by IR spectroscopy and elemental analysis. All dendronized NPs are stable over a long period of time in suspensions in water and in different physiological media and display a mean hydrodynamic diameter smaller than 50 nm whatever the molecule architecture. NMRD profiles and relaxivity measurements highlight the influence of the molecule architecture on the water diffusion close to the magnetic core thus influencing the relaxation properties at low magnetic field. The high hydrophilic architecture of the dendron D2 by contrast to dendron D1 allows maintaining the colloidal stability in different conditions while ensuring a very good accessibility of water molecule close to the magnetic core. Coupling of a fluorescent dye on dendrons have allowed investigating the biodistribution of dendronized NPs, which are found to be quickly eliminated through urinary and hepatobiliary pathways within 4 h. Furthermore, no enhanced permeation and retention effect in tumors can be observed.     

Determination of compound-specific Hg isotope ratios from transient signals using gas chromatography coupled to multicollector inductively coupled plasma mass spectrometry (MC-ICP/MS)

MeHg and inorganic Hg compounds were measured in aqueous media for isotope ratio analysis using aqueous phase derivatization, followed by purge-and-trap preconcentration. Compound-specific isotope ratio measurements were performed by gas chromatography interfaced to MC-ICP/MS. Several methods of calculating isotope ratios were evaluated for their precision and accuracy and compared with conventional continuous flow cold vapor measurements. An apparent fractionation of Hg isotopes was observed during the GC elution process for all isotope pairs, which necessitated integration of signals prior to the isotope ratio calculation. A newly developed average peak ratio method yielded the most accurate isotope ratio in relation to values obtained by a continuous flow technique and the best reproducibility. Compound-specific isotope ratios obtained after GC separation were statistically not different from ratios measured by continuous flow cold vapor measurements. Typical external uncertainties were 0.16‰ RSD (n = 8) for the ²⁰²Hg^/198Hg ratio of MeHg and 0.18‰ RSD for the same ratio in inorganic Hg using the optimized operating conditions. Using a newly developed reference standard addition method, the isotopic composition of inorganic Hg and MeHg synthesized from this inorganic Hg was measured in the same run, obtaining a value of δ ²⁰²Hg = −1.49 ± 0.47 (2SD; n = 10). For optimum performance a minimum mass of 2 ng per Hg species should be introduced onto the column.     

Manifestation of stereoelectronic effects on the calculated carbon-nucleophile bond lengths in nucleophilic addition to sterically unbiased ketones

Calculations at the B3LYP/6-311G(d,p) level of the structures of diastereoisomeric pairs of alcohols 1E-12E and 1Z-12Z, resulting from either reduction or methylation of sterically unbiased ketones show that the newly formed C-Nu bond lengths of the major isomers are larger than those of the minor isomers.