Synthesis, separation and reactivities of multidentate phosphine ligands and investigation into dirhodium hydroformylation and hydrocarboxylation catalysis

A dirhodium homogeneous hydroformylation catalyst based on a tetraphosphine ligand, rac-Et2PCH2CH2P(Ph)CH2P(Ph)CH2CH2PEt2, rac-et,ph-P4, is under investigation. The ligand synthesis produces a racemic mixture and a facile and efficient method of separation of the racemic and meso diastereomers was achieved through reaction of et,ph-P4 with two equivalents of NiCl2 in EtOH to yield an almost quantitatively isolable precipitate of meso-Ni2Cl4(et,ph-P4) and the soluble rac-Ni2Cl4(et,ph-P4). Subsequent cyanolysis of these complexes liberates the et,ph-P4 ligand, and the formation of a thermodynamically favored racemic monometallic intermediate during cyanolysis facilitates isomerization of meso to racemic ligand. The addition of even small amounts of PPh3 to the dirhodium tetraphosphine hydroformylation catalyst synthesized from the diastereomerically pure rac-et,ph-P4 causes a dramatic drop in the aldehyde linear to branched regioselectivity (25:1 to 3:1) in acetone solvent (90 °C, 6.1 bar, 1-hexene). The results indicate extremely effective inhibition of the regioselective bimetallic hydroformylation catalyst and the formation of an inefficient monometallic catalyst system, but not fragmentation to generate free RhH(CO)(PPh3)2 catalysts. For the dirhodium hydroformylation catalyst the addition of 30% water (by volume) to the acetone solvent gives the highest rate (73 min-1) and highest selectivity (33:1 linear:branched (L:B) aldehyde ratio, \u3c1% isomerization or hydrogenation products) as compared to that in acetone with initial TOF of 20 min-1, 25:1 L:B, 2.5% isomerization, and 3.4% alkene hydrogenation for 1-hexene. The dramatic improvement is the result of the more polar water-acetone solvent system preventing phosphine ligand dissociation from the dirhodium catalyst and subsequent formation of inactive species. Comparisons of the catalytic results in water-acetone to those of four representative monometallic, rhodium, modified phosphine systems indicate that the dirhodium catalyst is one of the fastest and the most selective catalyst overall. The dirhodium catalyst also converts aldehydes, but more interestingly alkenes, to carboxylic acids in the presence of water and under hydrogen-depleted conditions. Alkenes are converted via a novel tandem catalysis reaction first involving hydroformylation then aldehyde-water shift catalysis

Saint-Pierre-d’Autils – Carrière GSM

Identifiant de l'opération archéologique : 11731, 11732, 11733, et 11734 Date de l'opération : 2006 (EX) Inventeur(s) : Honoré David (GAVS) Cette première phase d'intervention sur la future carrière a permis d'appréhender un ensemble de sites inédits et singuliers du Néolithique et de l'âge du Bronze. Une seconde phase de diagnostic devrait intervenir dans le courant de l'année 2007. Les découvertes du Néolithique ancien, moyen et récent appartiennent à des organisations de sites déjà illustr..

Yainville – Chemin rural no 6, 311 rue de L’Essart

L’opération de diagnostic a été réalisée dans le cadre d’un projet de lotissement d’un peu plus de 2 ha. Les travaux ont porté directement sur une portion du rempart de Yainville. La mise en évidence d’un ensemble inédit d’informations archéologiques apporte un nouveau regard sur le « Fossé Saint-Philibert », sa construction et sa chronologie. Un parement en gros appareil de pierres sèches, constitué de blocs de grès et de calcaire, est installé au pied de la levée de terre. Il domine deux pu..

On bipartite Rokhsar-Kivelson points and Cantor deconfinement

Quantum dimer models on bipartite lattices exhibit Rokhsar-Kivelson (RK) points with exactly known critical ground states and deconfined spinons. We examine generic, weak, perturbations around these points. In d=2+1 we find a first order transition between a ``plaquette'' valence bond crystal and a region with a devil's staircase of commensurate and incommensurate valence bond crystals. In the part of the phase diagram where the staircase is incomplete, the incommensurate states exhibit a gapless photon and deconfined spinons on a set of finite measure, almost but not quite a deconfined phase in a compact U(1) gauge theory in d=2+1! In d=3+1 we find a continuous transition between the U(1) resonating valence bond (RVB) phase and a deconfined staggered valence bond crystal. In an appendix we comment on analogous phenomena in quantum vertex models, most notably the existence of a continuous transition on the triangular lattice in d=2+1.Comment: 9 pages; expanded version to appear in Phys. Rev. B; presentation improve

Element content and expression of genes of interest in guard cells are connected to spatiotemporal variations in stomatal conductance

Element content and expression of genes of interest on single cell types, such as stomata, provide valuable insights into their specific physiology, improving our understanding of leaf gas exchange regulation. We investigated how far differences in stomatal conductance (g(s)) can be ascribed to changes in guard cells functioning in amphistomateous leaves. g(s) was measured during the day on both leaf sides, on well-watered and drought-stressed trees (two Populus euramericana Moench and two Populus nigra L. genotypes). In parallel, guard cells were dissected for element content and gene expressions analyses. Both were strongly arranged according to genotype, and drought had the lowest impact overall. Normalizing the data by genotype highlighted a structure on the basis of leaf sides and time of day both for element content and gene expression. Guard cells magnesium, phosphorus, and chlorine were the most abundant on the abaxial side in the morning, where g(s) was at the highest. In contrast, genes encoding H+-ATPase and aquaporins were usually more abundant in the afternoon, whereas genes encoding Ca2+-vacuolar antiporters, K+ channels, and ABA-related genes were in general more abundant on the adaxial side. Our work highlights the unique physiology of each leaf side and their analogous rhythmicity through the day

Identifying Relapsing Fever Borrelia, Senegal

We describe a nested polymerase chain reaction for the identification of Borrelia species from serum of patients with unidentified fevers. This technique, based on single nucleotide polymorphisms of the 16S ribosomal RNA gene, was used to test blood samples from 7,750 patients, 33 of whom were diagnosed with spirochete infections. Borrelia crocidurae was the only species identified

Zooplankton assemblages along the North American Arctic: Ecological connectivity shaped by ocean circulation and bathymetry from the Chukchi Sea to Labrador Sea

We defined mesozooplankton biogeography in the North American Arctic to elucidate drivers of biodiversity, community structure, and biomass of this key component of the Arctic marine ecosystem. A multivariate analysis identified four mesozooplankton assemblages: Arctic-oceanic, Arctic-shelf, Coastal-Hudson, and Labrador Sea. Bathymetry was a major driver of the distribution of these assemblages. In shallow waters, Cirripedia and the copepod Pseudocalanus spp. dominated the Coastal-Hudson and Arctic-shelf assemblages, which showed low species richness (19) and biomass (0.28 and 1.49 g C m-2 , respectively).The Arctic-oceanic assemblage occupied the entire North American Arctic, except for shallow breaks in the Canadian Arctic Archipelago downstream of sills blocking the Atlantic Water layer circulation below a depth of 200 m. This assemblage showed high copepod biomass (4.74 g C m-2 ) with a high share of Calanus hyperboreus, C. glacialis, and Metridia longa. In habitats below 200-m depth, C. hyperboreus represented 68% of the copepod biomass, underscoring its role as a keystone species in this ecosystem. Strong numerical representation by the borealAtlantic C. finmarchicus and Oithona atlantica stressed the strong Atlantic influence on the subarctic Labrador Sea assemblage on the northwestern Labrador Sea slope. The mixed Arctic-Atlantic composition of the Labrador Sea mesozooplankton resulted in high species richness (58) and biomass (5.73 g C m-2 ). The low abundance of Atlantic and Pacific taxa in the areas influenced by Arctic currents did not alter the Arctic status of the Arctic-oceanic, Arctic-shelf, and Coastal-Hudson assemblages.This study identifies hotspots of mesozooplankton biomass and diversity in Central Amundsen Gulf, Lancaster Sound, North Water Polynya and Baffin Bay, known for their high biological productivity and concentrations of vertebrate predators. The continental-scale zooplankton mapping furthers our understanding of the importance of bathymetry and ocean circulation for ecological connectivity in a vast and complex portion of the Arctic marine ecosystem