Stereoselective intermolecular carboazidation of chiral allylsilanes

[reaction: see text] Easily available chiral allylsilanes were used as substrate for carboazidation reactions. For the first time, a substantial control of the stereochemistry of the azidation of acyclic nonconjugated radicals was achieved.     

Structural analysis of partially acetylated glycosides by refocused-decoupled insensitive nuclei enhanced by polarization transfer (INEPT) experiments: a qualitative and quantitative method

The application of the refocused-decoupled INEPT pulse sequence in 13C-NMR spectroscopy allows, in conjonction with computer simulations, a straightforward editing of the spectra of a raw mixture of glycosidic compounds.     

A Time-Fractional Step Method for Conservation Law Related Obstacle Problems

We are interested in approximating the solution of a first-order quasi-linear equation associated with a forced unilateral obstacle condition. With this view, we make use of the time-splitting method developed classically to compute discontinuous solutions of nonhomogeneous scalar conservation laws. Here, one proves that this fractional step method converges in L¹ to the weak entropy solution of the considered obstacle problem. In the case of the Cauchy problem, an L¹-error bound in is established.     

Une approche nouvelle de la dualité locale de Tate

Sans résumé Received July 11, 1999 / Accepted September 25, 2000 / Published online February 5, 2001     

The real meaning of Nernst's steady diffusion layer concept under non-forced hydrodynamic conditions. A simple model based on Levich's seminal view of convection

A model accounting for the role of convection in macroscopically immobile solutions (viz., not submitted to any macroscopic flow or any density gradient) is developed to predict the resulting alterations on electrochemical experiments performed at long time durations. The model is based on a seminal idea introduced by Levich, and shows that in macroscopically still solutions microscopic chaotic motion has the same effect as an apparent diffusion coefficient that depends on the distance from the electrode, x. When the electrochemical perturbation affects only the viscous sub-layer adjacent to the electrode, this apparent diffusion coefficient varies as x⁴. The model remarkably predicts the experimental distortions of chronoamperometric currents from their ideal Cottrellian behavior. The model is thoroughly tested with success by comparing its predictions to experimental results (current and concentration profiles) obtained for the oxidation of Fe(CN)₆⁴⁻ in aqueous KCl.     

Synthesis of a new series of purine derivatives and their anti‐cyclin‐dependent kinase activities

The synthesis of new purine derivatives designed to inhibit cell cycle regulating cyclin‐dependent kinases (CDKs), is reported. These compounds, related to olomoucine and roscovitine, are characterised by the presence of apyrrolidine methanol substituent at C‐2 and a variety of ortho, meta and/or para substituents on the C‐6 arylamino group.     

Polymer/Laponite Composite Latexes: Particle Morphology,Film Microstructure,and Properties

Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.

     

A criterion of density for solutions of Poisson-driven SDEs

We construct a Dirichlet structure related to a Poisson measure on ℝ⁺×M, where M is a general measured space, with compensator dt⊗dv. We obtain a criterion of density for variables in the domain of the Dirichlet form and we apply it to S.D.E. driven by this Poisson measure. Received: 15 May 1999 / Revised version: 23 February 2000 / Published online: 12 October 2000     

A rosette cooling cell: More effective container for solubilization of single-walled carbon nanotubes under probe-type ultrasonic irradiation

Probe-type ultrasonication has been employed for surfactant-aided solubilization, or individualization, of single-walled carbon nanotubes (SWNTs). The resulting solution can be used not only for spectroscopic analyses such as absorption, photoluminescence, and circular dichroism, but also for separation by density gradient ultracentrifugation, dielectrophoresis, chromatography, and polymer wrapping. In spite of its importance, the sonochemical processing of SWNTs has not been considered seriously. Herein, we report on a more efficient cooling cell for probe-type ultrasonication. As compared with a conventional cylindrical cell, the concentration of the SWNTs solubilized in water was found to be almost double in a rosette cooling cell after ultracentrifugation. The efficiency of a rosette cell can be attributed to the higher efficiency in circulation and cooling of the SWNT dispersion as well as enhancement of the cavitation process.