Stereo-controlled synthesis of polypropionate ester derivatives using titanium complexes

A method for the stereocontrolled synthesis of polypropionate ester derivatives by means of titanium complexes is described. The general procedure involves an allyltitanium complex which allows the formation of an enolsilane bearing two stereocentres and an alkoxy titanium complex used in a tandem aldol–Tischtschenko reaction. These two steps are very highly diastereoselective. We present here the study of the tandem aldol–Tischtschenko reaction involving enolsilanes possessing different steric hindrance. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SAStitanium complexes / aldol reaction / Tischtschenko reaction / asymmetric induction     

Electrocatalysis on nanoscale ruthenium-based material manufactured by carbonyl decomposition

The electrochemical characteristics of ruthenium-based particles synthesised from carbonyl chemical precursors in two solvent media are reported. Transmission electron microscopy (TEM) measurements revealed that this material in powder form, synthesised as described, is in the nanoscale range. Its reactivity with air depends on the solvent used in the manufacture of the powder. Micro-diffraction data revealed the nanocrystalline nature of the powder particles as well as the process leading to an amorphous state (oxide-like phase formation) when oxygen co-ordinates with the nanoscale ruthenium. This phenomenon influences the electrocatalytic process for the molecular oxygen reduction in acid medium.     

Amperometric determination of ascorbic acid on screen-printing ruthenium dioxide electrode

Ruthenium oxide (RuO₂) is commonly used in resistive pastes for screen printing. The electrochemical properties of a screen-printing planar RuO₂ electrode have hardly been studied. In this communication, planar electrochemical sensors with a RuO₂ working electrode, an Ag|AgCl reference electrode and a RuO₂ counter electrode are fabricated by screen printing. The electro-oxidation of ascorbic acid, uric acid, and hydrogen peroxide on these RuO₂ electrodes is investigated by means of cyclic voltammetry. Compared to uric acid and hydrogen peroxide, ascorbic acid can be easily oxidized at the low operating potential (<150 mV versus Ag|AgCl). The amperometric measurement of ascorbic acid at 100 mV on a RuO₂ electrode shows fast response and good linearity in the 0–4 mM range. Meanwhile, the electrochemical interference from uric acid and hydrogen peroxide at this potential is very small.     

克尔介质中场与级联三能级原子相互作用的熵特性

研究了在克尔介质中相干场与级联三能级原子相互作用的熵演化规律。讨论了克尔介质及初始平均光子数对场熵演化的影响。     

Radiation-induced graft polymerization and sulfonation of glycidyl methacrylate on to porous hollow-fiber membranes with different pore sizes

An epoxy group containing monomer, glycidyl methacrylate, was grafted on to a porous hollow-fiber membrane, made of polyethylene, whose different pore sizes ranged from 0.2 to 0.5 μm. The resulting epoxy group was converted into a sulfonic acid group as a cation-exchange group to capture metal ions. The porous network was retained after grafting and subsequent sulfonation because the poly-GMA chains invaded the polymer matrix. An increase in the SO₃H group density of the graft chain decreased the permeability of pure water because the graft chains expanded toward the pore interior due to their mutual electrostatic repulsion. The ion-exchange adsorption of Pb ions during the permeation of a Pb(NO₃)₂ solution through the pores edged by the cation-exchange graft chains was observed with a negligible diffusional mass-transfer resistance.     

银纳米颗粒负载TiO2复合薄膜的光催化活性及其光电流性质

制备了3种不同粒径的Ag纳米颗粒,将它们分别掺入二氧化钛溶胶, 制备成复合二氧化钛薄膜。利用TEM测定了Ag粒子的大小,测量TiO₂复合膜的光电流,以亚甲基蓝降解反应评价了Ag/TiO₂薄膜的光催化活性.结果表明,负载不同粒径Ag纳米粒子后,TiO₂薄膜的光电流和光催化活性均得到一定程度的提高.当负载平均粒径6.9 nm的Ag粒子后,薄膜具有最高的光电流和最强的光催化活性.     

Experimental observation of partial amplitude death in coupled chaotic oscillators

The dynamics of coupled Lorenz circuits is investigated experimentally. The partial amplitude death reported in {\em Phys. Rev.} E {\bf 72}, 057201 (2005) is verified by physical experiments with electronic circuits. With the increase of coupling constant, the coupled circuits undergo the transition from the breakdown of both the reflection symmetry and the translational symmetry to the partial amplitude death. Its stability is also confirmed by analysing the effects of noise.     

Formation of SrSnO3 shell-like inclusions in the Bi2Sr2CaCu2O8+x superconductor via chemical reaction

Superconducting composites Bi-2212–SrSnO₃ have been prepared by reacting between the Bi–Sr–Ca–Cu–O precursor and Sr₂SnO₄ or Ca₂SnO₄ at 800–950°C, followed by crystallisation of Bi-2212 from the partial melt at decreasing temperature. The samples have been characterised by powder X-ray diffraction, scanning electron microscopy and magnetic measurements. The materials consist of large Bi-2212 lamellae and complex-shaped fine inclusions of SrSnO₃. The composite obtained using Sr₂SnO₄ contains almost all the SrSnO₃ phase in the form of micron-sized spherical shells, which are partly included in Bi-2212 lamellae, partly agglomerated in-between. The shells are perforated, thus allowing the Bi-2212 crystals to grow through them. It has been found that the shell-like grains form at an early stage of the precursor thermal treatment between 800 and 850°C. A mechanism of the SrSnO₃ shell formation is proposed. The composites exhibit T_c in the range of 82–87 K and reveal up to five times better magnetic flux pinning at T≥30 K in comparison with the undoped Bi-2212 sample prepared using the same experimental procedure.     

Activation of cyclohexylhydroperoxide by diiron complexes: a new route for selective peroxide decomposition

The catalytic and selective decomposition of cyclohexylhydroperoxide has been demonstrated using dinuclear iron catalysts in acetonitrile. The complex, Fe₂OL₂(ClO₄)₄, [L=N,N′-dimethyl-2,11-diaza[3,3](2,6)pyridinophane] was found to be the most stable (up to 9 000 T.N.) and selective catalyst. Furthermore, cyclohexylhydroperoxide was found efficient as an oxidant during alkane oxidation. A free radical mechanism has been proposed for both peroxide decomposition and alkane oxidation, implicating the formation of iron–alkylhydroperoxo species.     

Electrocatalytic response of GMP on an ITO electrode modified with a hybrid film of Ni(II)–Al(III) layered double hydroxide and amphiphilic Ru(II) cyanide complex

A thin film of Ni(II)–Al(III) layered double hydroxide hybridized with an amphiphilic anionic Ru(II) complex ((N(C₂H₅)₄)₂[Ru(CN)₄(dc18bpy)]:dc18bpy=4,4^′-octadecyl-2,2^′-bipyridine) was prepared by the Langmuir–Blodgett (LB) method. Hybridization was performed by spreading a chloroform solution of (N(C₂H₅)₄)₂[Ru(CN)₄(dc18bpy)] onto an aqueous suspension of Ni(II)–Al(III) layered double hydroxide. The film was deposited onto a solid substrate such as an ITO electrode and mica. Atomic force microscopic (AFM) observation on the deposited film confirmed that about 9.0 nm thick Ni(II)–Al(III) layered double hydroxide particles were uniformly adsorbed by the monolayer of Ru(II) complex. Cyclic voltammograms on an ITO electrode modified with a single layer of the hybrid film gave quasi-reversible reduction–oxidation peaks due to Ni(II)/Ni(III) in a phosphate buffer at pH 7.67. When the mononucleotide of guanosine 5^′-monophosphate (GMP) was added in an electrolyte solution, the increase of oxidation current above 800 mV (vs SCE) was observed at the expense of the reduction peak of Ni(III). The results indicate that Ni(II) in the layered double hydroxide lattice acts as a mediator in oxidation of GMP. The modified electrode shows great enhancement in the oxidation of GMP in comparison with a bare ITO electrode.