Study of a lacunary solid phase I—Thermodynamic and crystallographic characteristics of its formation

The dehydration of the barium acid oxalate H₂C₂O₄·BaC₂O₄·2H₂O, depending on the conditions in which it is performed, can lead to two different anhydrous salts. That designated αH₂C₂O₄·BaC₂O₄ has all the features of a stable lacunary phase. Its crystalline structure has been determined and the atomic movements during this structure's formation are described. The other variety βH₂C₂O₄·BaC₂O₄ can be prepared either directly from the dihydrate or by transformation of the α form at higher temperature. An infinite number of nonstoichiometric hydrates (designated as H₂C₂O₄·BaC₂O₄·?H₂O with 0 < ? < 2) can be prepared in particular conditions, which identifies the “hydrate-vapor” system studied as divariant. A structural interpretation of this phenomenon is proposed; it takes into account the particular role of water molecules in the coordination polyhedron of the Ba²⁺ cations.     

Viscoelasticity of polydimethylsiloxane at the sol-gel threshold: structural effects

Five model polydimethylsiloxane (PDMS) networks were obtained by hydrosilation of a difunctional vinyl-terminated PDMS prepolymer with a SiH containing crosslinker. Viscoelastic experiments were performed in order to study the influence of molecular parameters on the dynamic properties at the sol-gel threshold. Critical parameters were determined close to and above the sol-gel threshold. The results obtained suggest that the critical exponents depend on the chemical structure of the incipient networks.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Catalytic asymmetric hydrogenation with the cluster Rh6(CO)10[(-)DIOP]3

Rh₆(CO)₁₀[(-)DIOP]₃ has been isolated after ligand exchange between Rh₆(CO)₁₆ and DIOP. The molecular cluster is an efficient catalyst for asymmetric reduction of various prochiral olefins; optical yields up to 47% have been achieved; the results are compared with those obtained with mononuclear rhodium (I) complexes.     

First principles NMR calculations of phenylphosphinic acid C6H5HPO(OH): assignments, orientation of tensors by local field experiments and effect of molecular motion

The complete set of NMR parameters for (17)O enriched phenylphosphinic acid C(6)H(5)HP( *)O(*OH) is calculated from first principles by using the Gauge Including Projected Augmented Wave (GIPAW) approach [C.J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials: NMR chemical shifts, Phys. Rev. B 63 (2001) 245101/1-245101/13]. The analysis goes beyond the successful assignment of the spectra for all nuclei ((1)H, (13)C, (17)O, (31)P), as: (i) the (1)H CSA (chemical shift anisotropy) tensors (magnitude and orientation) have been interpreted in terms of H bonding and internuclear distances. (ii) CSA/dipolar local field correlation experiments have allowed the orientation of the direct P-H bond direction in the (31)P CSA tensor to be determined. Experimental and calculated data were compared. (iii) The overestimation of the calculated (31)P CSA has been explained by local molecular reorientation and confirmed by low temperature static (1)H-->(31)P CP experiments.     

A highly efficient silver niobium alumina catalyst for the selective catalytic reduction of NO by n-decane

AgNb/Al(2)O(3) prepared by a nonhydrolytic sol-gel process is a highly efficient catalyst for NO(x) removal through selective catalytic reduction by hydrocarbons (HC-SCR). This result shows that the HC-SCR process remains a challenging method for lean engine DeNO(x).     

Both systemic and local application of Granulocyte-colony stimulating factor (G-CSF) is neuroprotective after retinal ganglion cell axotomy

Background  

The hematopoietic Granulocyte-Colony Stimulating Factor (G-CSF) plays a crucial role in controlling the number of neutrophil progenitor cells. Its function is mediated via the G-CSF receptor, which was recently found to be expressed also in the central nervous system. In addition, G-CSF provided neuroprotection in models of neuronal cell death. Here we used the retinal ganglion cell (RGC) axotomy model to compare effects of local and systemic application of neuroprotective molecules.     

Bioconversion of a L-carnitin precursor in a one- or two-phase system

Applied Biochemistry and Biotechnology - The ability of the yeastSaccharomyces cerevisiae to bioconvert stereo-selectively octyl-4-chloroacetoacetate (OCA) into the corresponding chiral alcohol,...     

Measurement of the spin correlation parameter Aoonn and of the analyzing power for pp elastic scattering in the energy range from 0.5 to 0.8 GeV

The spin correlation parameter A_oonn and the analyzing powers A_oono and A_ooon were measured simultaneously, in the energy range 0.5–0.8 GeV and in the angular region 40°–80° CM. The experiment used the polarized proton beam of SATURNE II and the Saclay frozen spin polarized target.