Redox‐Neutral Coupling between Two C(sp3)−H Bonds Enabled by 1,4‐Palladium Shift for the Synthesis of Fused Heterocycles

The intramolecular coupling of two C(sp³)?H bonds to forge a C(sp³)?C(sp³) bond is enabled by 1,4‐Pd shift from a trisubstituted aryl bromide. Contrary to most C(sp³)?C(sp³) cross‐dehydrogenative couplings, this reaction operates under redox‐neutral conditions, with the C?Br bond acting as an internal oxidant. Furthermore, it allows the coupling between two moderately acidic primary or secondary C?H bonds, which are adjacent to an oxygen or nitrogen atom on one side, and benzylic or adjacent to a carbonyl group on the other side. A variety of valuable fused heterocycles were obtained from easily accessible ortho‐bromophenol and aniline precursors. The second C?H bond cleavage was successfully replaced with carbonyl insertion to generate other types of C(sp³)‐C(sp³) bonds.     

Reduction of Tetrachloroaurate(III) at Boron-Doped Diamond Electrodes: Gold Deposition Versus Gold Colloid Formation

Tetrachloroaurate(III) dissolved in dilute aqueous aqua regia is electrochemically reduced at boron-doped diamond electrodes to form gold metal. The reduction process is studied by voltammetric, SEM, and XPS techniques. Both the deposition of gold and the anodic stripping process are detected. The ratio of cathodic to anodic charge or stripping efficiency, Q_anodic/Q_cathodic, is shown to depend on the concentration of AuCl and on the pretreatment of the boron-doped diamond electrode surface. Cathodic pretreatment of the boron-doped diamond electrode considerably increases the rate for both deposition and stripping. In the presence of power ultrasound emitted from a glass horn system (24 kHz, 8 Wcm⁻²) the current associated with the reduction of AuCl is considerably enhanced and two components in the mass transport controlled limiting current are identified as (i) the deposition of gold onto the boron-doped diamond and (ii) the formation of colloidal gold.     

Operators associated with a stochastic differential equation driven by fractional Brownian motions

In this paper, by using a Taylor type development, we show how it is possible to associate differential operators with stochastic differential equations driven by fractional Brownian motions. As an application, we deduce that invariant measures for such SDE’s must satisfy an infinite dimensional system of partial differential equations.     

High-throughput capillary electrophoresis for the identification and differentiation of seven species of Eimeria from chickens

A capillary electrophoretic approach has been evaluated for the identification of seven currently recognised species of Eimeria infecting chickens. The second internal transcribed spacer of ribosomal DNA is PCR-amplified from any of the seven species using a single set of oligonucleotide primers (one of which is fluorescently labelled). The amplicons are heat-denatured and subjected to capillary electrophoresis in a MegaBACE 1000 (Amersham). The chromatograms captured are stored electronically and then analysed using MegaBACE Fragment Profiler software. Using control DNA samples representing monospecific lines of Eimeria, specific peaks in the chromatograms were defined for the unequivocal identification of each of the seven species and their differentiation. Electrophoretic reading and analysis are carried out automatically, thus making it a time- and cost-effective method. This procedure should find applicability as a tool for the quality control of Eimeria vaccines, the monitoring of coccidiosis outbreaks and the high-throughput analysis of oocyst samples for epidemiological surveys.     

Cleavage of silicon- and germanium-transition metal bonds. Dependences of the stereochemistry on the nature of the ligands and the geometry of complexes

The cleavages of some new optically active complexes containing CoSi (orGe), MnSi (orGe), ReGe and WGe bonds are described. Electrophiles cleave the CoSi bond with good retention of configuration at silicon, while the MnSi bond is not cleaved under the same conditions. The M′Si and M′Ge bonds (where M'  transition metal) are cleaved by nucleophiles with retention or inversion of configuration. In the case of triginal bipyramidal geometry (cobalt complexes) the stereochemical outcome of the reaction is strongly dependent upon electronic effects, the size of the ligand trans to the CoSi (orGe) bond, and the nature of the nucleophilic reagant, in accord with the general rules for nucleophilic substitution at silicon. In contrast the transition metalsilicon orgermanium bonds in the octahedral complexes of manganese, rhenium and tungsten are always cleaved with poor retention of configuration regardless of the nature of the ligands or the nucleophilic reagent. The results provide the first cases in which the stereochemistry of nucleophilic displacement at silicon is independent of the electronic features of both the leaving group and the nucleophile.     

Scattering of ultrasonic shock waves in suspensions of silica nanoparticles

Experiments are carried out to assess, for the first time, the validity of a generalized Burgers' equation, introduced first by Davidson [J. Acoust. Soc. Am. 54, 1331-1342 (1973)] to compute the nonlinear propagation of finite amplitude acoustical waves in suspensions of "rigid" particles. Silica nanoparticles of two sizes (33 and 69 nm) have been synthesized in a water-ethanol mixture and precisely characterized via electron microscopy. An acoustical beam of high amplitude is generated at 1 MHz inside a water tank, leading to the formation of acoustical shock waves through nonlinear steepening. The signal is then measured after propagation in a cylinder containing either a reference solution or suspensions of nanoparticles. In this way, a "nonlinear attenuation" is obtained and compared to the numerical solution of a generalized Burgers' equation adapted to the case of hydrosols. An excellent agreement (corresponding to an error on the particles size estimation of 3 nm) is achieved in the frequency range from 1 to 40 MHz. Both visco-inertial and thermal scattering are significant in the present case, whereas thermal effects can generally be neglected for most hydrosols. This is due to the value of the specific heat ratio of water-ethanol mixture which significantly differs from unity.     

Two Distinct Structures of Membrane‐Associated Homodimers of GTP‐ and GDP‐Bound KRAS4B Revealed by Paramagnetic Relaxation Enhancement

KRAS homo‐dimerization has been implicated in the activation of RAF kinases, however, the mechanism and structural basis remain elusive. We developed a system to study KRAS dimerization on nanodiscs using paramagnetic relaxation enhancement (PRE) NMR spectroscopy, and determined distinct structures of membrane‐anchored KRAS dimers in the active GTP‐ and inactive GDP‐loaded states. Both dimerize through an α4–α5 interface, but the relative orientation of the protomers and their contacts differ substantially. Dimerization of KRAS‐GTP, stabilized by electrostatic interactions between R135 and E168, favors an orientation on the membrane that promotes accessibility of the effector‐binding site. Remarkably, “cross”‐dimerization between GTP‐ and GDP‐bound KRAS molecules is unfavorable. These models provide a platform to elucidate the structural basis of RAF activation by RAS and to develop inhibitors that can disrupt the KRAS dimerization. The methodology is applicable to many other farnesylated small GTPases.     

Chiral Catalysts for Pd0-Catalyzed Enantioselective C−H Activation

In the past few decades, processes that involve transition-metal catalysis have represented a major part of the synthetic chemist′s toolbox. Recently, the interest has shifted from the well-established cross-coupling reactions to C−H bond functionalization, thus making it a current frontier of transition-metal-catalyzed reactions. Constant progress in this field has led to the discovery of enantioselective methods to generate and control various types of stereogenic elements, thereby demonstrating its high value to generate scalemic chiral molecules. The present review is dedicated to enantioselective Pd⁰-catalyzed C−H activation, which may be considered as an evolution of Pd⁰-catalyzed cross-couplings, with a focus on the different chiral ligands and catalysts that enable these transformations.     

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