The hydrogenation of olefins using a polymer supported ruthenium complex

RuCl₂(PPH₃)3 has been attached to a phosphinated polymer support (phosphinated polystyrene crosslinked with 2% divinylbenzene) and the reagent converted to the polymer supported analogue of RuClH(PPH₃)₃ in the presence of base. The polymer supported catalyst efficiently hydrogenates terminal olefins under ambient conditions. Hydrogenation of 1-hexene has revealed that the reaction rate is proportional to [Ru], [H₂] and [olefin]/(1 + [olefin]). The polymer support environment allows for selectivity in olefin hydrogenation and under suitable reaction conditions short chain terminal olefins are hydrogenated more rapidly than long chain terminal olefins. The extent of metal loading on the polymer and the reaction solvent composition also influence the reaction selectivity and these effects are discussed.     

A Systematic Study of the Use of DL-Tartaric Acid in the Synthesis of Silica Materials Obtained by the Sol-Gel Method

DL-tartaric acid was used as a template for the formation of silica nanotubes and spheres by the sol-gel method from tetraethylorthosilicate (TEOS) as silica source. The reactions were carried out in ethanol/water mixtures in the presence of aqueous ammonia, between 0°C and 75°C, using both stirred and non-stirred conditions. TEM and SEM images show that the yield and microstructure of the silica is influenced by the synthetic conditions (temperature, ammonia (aq) concentration, gelation time, solvent mixture). It was observed that the chiral form of the tartaric acid used and the diffusion of TEOS to the template determines the eventual silica structure.     

MnRe(CO)10: A review of the chemical and physical properties of a simple heterobimetallic non-bridged dimer

A review of the chemical and physical properties of MnRe(CO)₁₀ and its derivatives has been undertaken. This heterobimetallic complex is one of the simplest complexes known which contains a bond between two different metals and does not contain bridging groups. The review has revealed that high yield synthetic strategies are known for this complex and the synthetic strategies have bearing for the synthesis of other bimetallic complexes. Kinetic data suggest that information available on monometallic fragments can provide information on the reactivity trends expected for the dimer. However, the second metal is not a neutral spectator and provides a site forsecondary reactions eg for CO substitution. Data on the physical properties of the dimer are sparse and definitive statements ond _Mn-Re·v _Mn-Re, H_Mn-Re etc. cannot be made. This has significant implications for studies on related simple and complex dimer and cluster complexes.     

Cobalt Ion Incorporation into Periodic Mesoporous Organosilica Materials Synthesized by Co-condensation of 1,2-Bistrimethoxysilylethane with 3-Glycidoxypropyltriethoxysilane

Bifunctional periodic mesoporous organosilica materials with and without cobalt ion incorporation were synthesized by co-condensation of 1,2-bistrimethoxysilylethane (BTME) with 3-glycidoxypropyltriethoxysilane (GPTS) in the presence of cetyltrimethylammonium bromide. Nitrogen gas adsorption on samples with varying ratios of BTME:GPTS revealed that increasing the amount of GPTS affects pore size, surface area and pore volume as well as shapes of the isotherms and hysteresis loops. The hysteresis loops of the Type IV isotherms obtained for GPTS-modified ethane silica materials (without cobalt ion) change from Type H3 to Type H4 with increasing GPTS content. There is a tendency for pore sizes to change from mesopore to micropore when the amount of GPTS is increased. Isotherms of cobalt ion incorporated GPTS-modified ethane silica materials change from Type IV to Type I with increasing GPTS content. The surface area, pore volume and pore diameter decrease with increasing loading of GPTS as well as after cobalt ion incorporation. Thermogravimetric analysis and differential thermal analysis show that the surfactant is removed by solvent extraction. Cobalt ion incorporation is confirmed by powder X-ray diffraction and Raman spectroscopy.     

Alkylation of catechol with methanol to guaiacol over sulphate-modified zirconia solid acid catalysts

A series of sulphate-promoted ZrO₂ solid acid catalysts with different contents of SO₄ ²⁻ were calcined at 450°C in air for 4 h and tested for the liquid-phase alkylation of catechol to guaiacol in a fixed-bed down-flow reactor. The 5 wt.% SO₄ ²⁻ on ZrO₂ showed the best conversion (82%) and selectivity for guaiacol (84%) at 200°C and 1 bar pressure. A smooth correlation was observed between the catalytical activity and surface acidity of sulphated zirconia. Based on our results, a surface mechanism is proposed.     

The DNA sequence and analysis of human chromosome 13

Chromosome 13 is the largest acrocentric human chromosome. It carries genes involved in cancer including the breast cancer type 2 (BRCA2) and retinoblastoma (RB1) genes, is frequently rearranged in B-cell chronic lymphocytic leukaemia, and contains the DAOA locus associated with bipolar disorder and schizophrenia. We describe completion and analysis of 95.5 megabases (Mb) of sequence from chromosome 13, which contains 633 genes and 296 pseudogenes. We estimate that more than 95.4% of the protein-coding genes of this chromosome have been identified, on the basis of comparison with other vertebrate genome sequences. Additionally, 105 putative non-coding RNA genes were found. Chromosome 13 has one of the lowest gene densities (6.5 genes per Mb) among human chromosomes, and contains a central region of 38 Mb where the gene density drops to only 3.1 genes per Mb.     

Travelling fronts in integrodifferential equations

We provide results of the existence, uniqueness and asymptotic behavior of travelling-wave solutions for convolution equations involving different kinds of nonlinearities (bistable, ignition and monostable). We recover for these equations most of the known results about the standard equation $\text{?u}\text{?t}\text{+u″+f(u)=0}$. Some min–max formulas are also given. To cite this article: J. Coville, L. Dupaigne, C. R. Acad. Sci. Paris, Ser. I 337 (2003).     

Rapid traveling waves in the nonlocal Fisher equation connect two unstable states

In this note, we give a positive answer to a question addressed in Nadin et al. (2011) [7]. To be precise, we prove that, for any kernel and any slope at the origin, there exist traveling wave solutions (actually those which are “rapid”) of the nonlocal Fisher equation that connect the two homogeneous steady states 0 (dynamically unstable) and 1. In particular, this allows situations where 1 is unstable in the sense of Turing. Our proof does not involve any maximum principle argument and applies to kernels with fat tails.