Recyclable Heterogeneous Palladium Catalysts in Pure Water: Sustainable Developments in Suzuki,Heck, Sonogashira and Tsuji–Trost Reactions

This review summarizes the progress made essentially these last ten years on heterogeneous palladium catalysis in pure water. The work covers four important palladium‐catalyzed transformations for carbon‐carbon bond formation: Suzuki, Heck, Sonogashira and Tsuji–Trost reactions. The discussion focuses on the efficiency and reusability of the heterogeneous catalysts as well as on the experimental conditions from a sustainable chemistry point of view. The review is introduced by a discussion on mechanistic aspects inherent to heterogeneous catalysis.     

Faceting mechanisms of Si nanowires and gold spreading

We report detailed structural analysis of 〈111〉 oriented silicon nanowires (NWs) grown by UHV–CVD using the VLS process with a gold catalyst. STEM-HAADF observations have revealed an unexpected inhomogeneous distribution of gold nanoclusters on the NW surface. Gold is mainly distributed on three sides among the six {112}-sidewalls and is anchored on upward {111} facets. This original observation brought us a new comprehension of the faceting mechanisms. The stability of the 〈111〉 growth direction needs the formation of facets on {112}-sidewalls with energetically favorable planes. We demonstrate that the initial formation of covered facets with a three-fold symmetry is driven by the formation of {111} Au/Si interfaces between the nucleated Si NW and the Au droplet.     

The Synthesis and in vivo Evaluation of 2′,2′‐Difluoro KRN7000

The synthesis of 2′,2′‐difluoro KRN7000 is described. In vivo evaluation demonstrates that this fluorinated glycolipid induces CD1d‐dependent TCR activation of NKT cells, with a bias towards Th2 cytokine production.

     

Abnormal Expression of Synaptic and Extrasynaptic GABAA Receptor Subunits in the Dystrophin-Deficient mdx Mouse

Duchenne muscular dystrophy (DMD) is a neurodevelopmental disorder primarily caused by the loss of the full-length Dp427 dystrophin in both muscle and brain. The basis of the central comorbidities in DMD is unclear. Brain dystrophin plays a role in the clustering of central gamma-aminobutyric acid A receptors (GABA_ARs), and its loss in the mdx mouse alters the clustering of some synaptic subunits in central inhibitory synapses. However, the diversity of GABAergic alterations in this model is still fragmentary. In this study, the analysis of in vivo PET imaging of a benzodiazepine-binding site radioligand revealed that the global density of central GABA_ARs is unaffected in mdx compared with WT mice. In contrast, semi-quantitative immunoblots and immunofluorescence confocal imaging in tissue sections revealed complex and differential patterns of alterations of the expression levels and/or clustered distribution of a variety of synaptic and extrasynaptic GABA_AR subunits in the hippocampus, cerebellum, cortex, and spinal cord. Hence, dystrophin loss not only affects the stabilization of synaptic GABA_ARs but also influences the subunit composition of GABA_ARs subtypes at both synaptic and extrasynaptic sites. This study provides new molecular outcome measures and new routes to evaluate the impact of treatments aimed at compensating alterations of the nervous system in DMD.     

Nanodiamond‐Palladium Core–Shell Organohybrid Synthesis: A Mild Vapor‐Phase Procedure Enabling Nanolayering Metal onto Functionalized sp3‐Carbon

A novel approach for the bottom‐up construction of hybrid organic–inorganic nanocomposites with an intimate arrangement between sp³‐carbon 3D molecular‐size nanodiamonds (diamondoids) and a coated palladium surface as nanolayer is reported. The construction process is conducted stepwisely from the gas phase, using first controlled vapor‐phase self‐assembly of tailor‐made functionalized diamantane derivatives, followed by low‐temperature (45 °C) chemical vapor deposition of an organometallic complex in a reducing H₂ atmosphere over the self‐assembled diamondoid scaffold. The use of self‐assemblies of primary diamantane phosphine and phosphine oxide, which are produced with high structural uniformity and reproducibility, yields new hybrid diamondoid‐palladium materials incorporating Pd? O? PH? diamantane bonding motifs. Additional investigations provide evidence for a very challenging issue in the intimate construction of sp³‐C/metal scaffolds. Scanning electron microscopy and transmission electron microscopy microscopies combined with X‐ray photoelectron spectroscopy surface analysis and EDX bulk analysis confirm the formation of diamondoid‐palladium organohybrids with unique surface layering. The vapor phase‐controlled mild synthetic process allows excellent control over nanocomposite formation and morphology from molecular‐level modifications. As such, this bottom‐up composite building process bridges scales from the molecular (functionalized diamondoids) over nanoscopic (self‐assemblies) to microscopic regime (hybrids), in the challenging association of transition metals with an electronically saturated sp³‐carbon organic host material.     

Water vapour adsorption in highly porous carbons as seen by small and wide angle X-ray scattering

The adsorption of water vapour in a high surface area commercial carbon, as-received and after different surface chemical treatments was investigated as a function of relative humidity by three separate techniques. While gravimetry and small and wide angle X-ray scattering measurements are in reasonable agreement, volumetric observations yielded isotherms with substantially lower values for the water uptake. In each case, the results are sensitive to the surface chemistry of the sample. Several weeks were required to establish equilibrium, with strikingly different results being obtained for measurements carried out on shorter time scales. The slow kinetics of the uptake accounts for most of the discrepancies among the results of the different techniques. Immersion in water caused significant macroscopic swelling of the carbon matrix over a time scale comparable to the adsorption equilibrium time.     

Fabrication of silicon-on-insulator MEM resonators with deep sub-micron transduction gaps

The paper proposes and validates a low-cost technological process for the realization of mono-crystalline micro-electro-mechanical (MEM) resonators with deep sub-micron transduction gaps, on silicon-on-insulator (SOI) substrates. The MEM resonators are designed to work as bulk lateral resonators (BLR) in which the resonance of a suspended mass is excited and detected by lateral electrodes. For MEM BLRs, nano-scaled gaps (<200 nm) are essential to reduce the motional resistance in the order of few kΩ as well as to avoid the use of large DC applied voltages. Only standard optical lithography with 1 μm resolution and IC-compatible processing steps are employed to obtain 100–200 nm wide gaps with very high aspect-ratios of more than [40:1], allowing the fabrication of high Q resonators for MHz to GHz operating frequency range.     

Palladium‐Catalysed C?H Bond Electrophilic Fluorination of Highly Substituted Arylpyrazoles: Experimental and DFT Mechanistic Insights

A general protocol for palladium‐catalysed C H mono‐ and di‐fluorination of highly substituted arylpyrazoles is reported. Coupling pathways and substrate limitations are discussed in the light of complementary mechanistic experimental and density functional theory (DFT) studies. The mono‐ and di‐ortho‐fluorination of arylpyrazoles having substituted pyrazole groups and ortho‐, meta‐, or para‐substituted arene moieties is achieved. Various pyrazole groups can efficiently promote the direct C H activation/fluorination of substrates bearing valuable reactive ester, cyano, halide and nitro functions. The presence of methoxy, methyl and trifluoromethyl is tolerated on the pyrazole directing groups. However, steric substituent effects have a marked influence which is evidenced by calculations. DFT modelling suggested also a previously unseen outer‐sphere oxidative addition of N‐fluorobenzenesulfonimide (NFSI) to Pd(II) as an alternative mechanism to the commonly assumed Pd(II)/Pd(IV) process. This unprecedented proposal, which is supported by the mass spectrometry identification of a key Pd(II) monomer under the stoichiometric conditions deserves more attention. The influence of elaborate highly substituted directing groups on the course of Pd‐catalysed fluorination has generally received limited attention although this question has a crucial synthetic utility; herein, appropriate conditions for isolating pure products are reported.

     

A GHz Spintronic-Based RF Oscillator

A nano-sized oscillator for RF applications is presented which is based on two spintronic effects, the tunneling magnetoresistance (TMR) and the spin momentum transfer torque. The oscillation frequency is several GHz and can be tuned by both a DC bias current and an external DC magnetic field. High compactness, high tunability and full compatibility with standard CMOS process make this spin torque nano-oscillator (STNO) a promising candidate for future RF transceivers. The main issues to be addressed are spectral purity and output power. First measurements on a hybrid built connecting the STNO to a dedicated wideband amplifier show that today's performance in terms of power is close to but not yet compatible with telecommunication standard requirements. Using time domain analysis we show that frequency fluctuations are an issue for spectral purity. Frequency synthesis concepts based on STNOs are also discussed.