Preparation of titanocene and zirconocene dichlorides bearing bulky 1,4-dimethyl-2,3-diphenylcyclopentadienyl ligand and their behavior in polymerization of ethylene

New metallocene dichlorides [η⁵-(1,4-Me₂-2,3-Ph₂-C₅H)₂TiCl₂] (2), [η⁵-(1,4-Me₂-2,3-Ph₂-C₅H)₂ZrCl₂] (3) and [η⁵-(1,4-Me₂-2,3-Ph₂-C₅H)η⁵-(C₅H₅)ZrCl₂] (4) were prepared from lithium salt of 1,4-dimethyl-2,3-diphenylcyclopentadiene (1) and [TiCl₃(THF)₃], [ZrCl₄] and [η⁵-(C₅H₅)ZrCl₃(DME)], respectively. Compounds 2-4 were characterized by NMR spectroscopy, EI-MS and IR spectroscopy, and the solid state structure of 3 was determined by single crystal X-ray crystallography. The catalytic systems 3/MAO and 4/MAO were almost inactive in polymerization of ethylene at 30-50 °C, however, they exhibited high activity at temperature 80 °C. The catalyst formed from 2 and excess of MAO was practically inactive at all temperatures.     

Ultrafast laser processing of drug particles in water for pharmaceutical discovery

The laser fragmentation technique has been extensively used to produce inorganic nanoparticles, but its practice on organic materials, especially on drugs, is less common. Here, we briefly review the recent advances in laser micro-/nanonization of organic materials and the rationale of using laser fragmentation for drug discovery. We present our case studies of two drug models: fenofibrate and naproxen. Both drugs were fragmented in water with femtosecond (fs) laser and characterized in terms of particle size distribution and physicochemical properties. Effects of fs laser fragmentation were also compared with nanosecond (ns) laser fragmentation and with conventional media milling technique. Fs laser was more suitable to produce sub-micron size drug particles than ns laser, but degradation of drugs after nanonization was also more pronounced than micronization. Physicochemical transformations such as oxidation, hydration and amorphisation might occur during the laser–material interactions. Laser nanonization showed improved dissolution kinetics, similar to media milling. Unlike the conventional milling techniques, laser fragmentation enabled the treatment of minute amount (as small as several milligrams) of drugs with high efficiency, thus is a useful tool for particle size reduction during the early phases of drug discovery.     

The stereospecific epoxidation of olefins catalysed by ruthenium

Epoxidation of olefins by sodium periodate is effected by the catalysis of RuCl₃, (H₂O)_n associated with bipyridyl. The reaction is stereospecific for both cis and trans alkenes.     

Production of large quantities of “Janus” nanoparticles using wax-in-water emulsions

For the first time, large amount of Janus silica particles as small as 100 nm in diameter were prepared through a simple method based on the elaboration of Pickering emulsions of wax-in-water. Controlling the kinetic stabilization of wax droplets allows the fabrication of gram-sized quantities of regular asymmetric inorganic particles with high yield. In fact, our method is based on a limited coalescence process, which allows one to predict the quantity of interface which is produced when working with a known mass of wax, and thus to be sure that all introduced silica particles are adsorbed on the wax surface. To this end, the hydrophilic surface of the silica particles was made partially hydrophobic by adsorbing a known amount of surfactant: cetyltrimethylammonium bromide (CTAB). Varying the concentration in surfactant results in tuning the penetration rate of the particles in the wax droplets, leading to various dimension of the modified area. The broken spherical symmetry of the particle surface was thereafter revealed by the selective adsorption of gold nanoparticles on the amino-modified surface.     

Nanoclusters of TiO2 wetted with gold

We combined scanning tunneling microscopy and density functional theory to establish the structure-functionality relationship for nanometer-sized defects on TiO₂(1 1 0). Three-angstrom high topographically distinct dots are ascribed to stoichiometric TiO₂ nanoclusters with low coordination numbers. The under-coordinated O atoms of the nanocluster, with surface O atoms, provide exceptionally strong binding sites for Au nanoparticles. Our atomistic model elucidates a number of characteristics salient to low temperature CO oxidation by Au nanoparticles.     

Heterogeneous wires made of martensitic materials

In this paper we present a direct derivation of a theory of heterogeneous wires starting from three-dimensional nonlinear hyperelasticity augmented by an interfacial energy term. The derivation involves no a priori choice of asymptotic expansion or ansatz. It yields a wire theory with two Cosserat vector fields. The theory is applied to multiwell energy functions appropriate for martensitic materials. A formal derivation of higher theories of homogeneous wires is given, which yields three additional Cosserat vector fields and an explicit form for the bending and torsion energy. To cite this article: H. Le Dret, N. Meunier, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Production, chemical and isotopic separation of the178m2Hf high-spin isomer

The ^178m2Hf with its long-lived (T_1/2=31 y), high-spin I^π = 16⁺, isomeric state, is a challenge for new and exotic nuclear physics studies. The ^178m2Hf isomer has been produced in microweight quantities using the ¹⁷⁶Yb(α,2n) nuclear reaction, by irradiation with a high-intensity beam using the U-200 cyclotron in Dubna. Radiochemistry and mass separation methods have been developed, with the aim to separate and purify the produced Hf material. Thin targets of isomeric hafnium-178 on carbon backings have been prepared and used in experiments with neutron, proton and deuteron beams. This revised version was published online in August 2006 with corrections to the Cover Date.     

Information processing in three-state neural networks

We introduce networks of three-state neurons, where the additional state embodies the absence of information. Their dynamical behavior is studied from the standpoint of information processing. These networks display strong pattern completion capabilities. Moreover, inference naturally occurs between coherent patterns.     

Soft gluons in semi-inclusive deep inelastic experiments

The longitudinal and transverse properties of the QCD contribution to semi-inclusive deep inelastic scattering is worked out within the soft gluon resummation procedure. The Λ parameter needed to reproduce the data is in agreement with the value extracted from scaling violations. The intrinsic transverse momentum squared of a quark inside a proton is around 0.45 GeV². Predictions for the transverse correlations $\text{〈}\text{p}{}_{\mathrm{1\perp }}\text{·}\text{p}{}_{\mathrm{2\perp }}\text{〉}$ of two outgoing pions are guven.     

Field diffusion-like representation and experimental identification of a dynamic magnetization property

So as to fuse dynamic magnetization properties of soft materials with the electromagnetism theory, we investigate the inclusion of microscopic reversal processes related to domains and walls in macroscopic Maxwell equations. We first introduce a model for independent walls and the unidirectional motion mechanism; then we characterize one sample with measurements and analytical calculations in case of one-dimensional linear problems.