Performance of Pt/SnO2 catalyst in the gas phase hydrogenation of crotonaldehyde

Selective hydrogenation of crotonaldehyde was performed on 5% Pt/SnO₂ catalysts, in gaseous phase, at atmospheric pressure, at 353 K. Two types of catalyst were prepared using H₂PtCl₆ and Pt(NH₃)₄(NO₃)₂ as metallic precursors. Their performances were compared as a function of the reduction temperature and both catalysts were characterised by X-ray diffraction after different reduction treatments. Using the ex-chloride catalyst, the selectivity values to the unsaturated alcohol (UOL) resulted into a maximum of 45% while a selectivity as high as 70–77%, in 0–25% conversion range, was achieved by using ex-nitrate catalyst reduced at 443 K. The formation of Pt–Sn alloy on the metal particles of platinum was thought to be necessary to improve the activity and the selectivity on these catalysts. In the contrast, a presence of PtSn₂ formed at a reduction temperature higher than 473 K led to a decrease of activity and selectivity.     

Étude de quelques dérivés de la pyrazoline-2: Spectres infrarouge et methode CNDO/2

The infrared spectra of some derivatives of 2-pyrazoline have been studied in the region of the CN and N-H stretching bands.The N-H stretching frequency seems to be related to Taft's σ^* constants of the substituents bound to the intracyclic carbon atoms. The “acidity” of this group seems to be considerably less than in pyrrole or in carboxylic amides.Absorption spectra of the pure compounds or of moderately concentrated solutions suggest the existence of intermolecular hydrogen bonding.The hybridization state of nitrogen atom (1) seems to be approximatively sp³, without any noticeable conjugation with the CN(2) double bond. In those cases where two conformers could be assumed to exist only one has been observed.These results are in accordance with those of a molecular orbital calculation by the CNDO/2 method. This calculation suggests that in 5-methyl-2-pyrazoline, the hydrogen atom bound to N(1) is trans with respect to the methyl group.     

A potentiometric and spectrophotometric study of gallium—benzohydroxamic acid complex formation

The complex formation of gallium with benzohydroxamic acid has been studied by potentiometry and spectrophotometry. Three successive complexes, GaL²⁺, GaL₂⁺, and GaL₃, are formed. The stability constants, log β₁, β₂, and β₃ , are 9.2 ± 0.1, 18.0 ± 0.1 and 25.3 ± 0.1, respectively, in 3 M NaClO₄ at 25°C.     

Catalytic hydrogenation of crotonaldehyde in the liquid phase using Pt and Ru/SnO<Subscript>2</Subscript> catalysts

Effects of the precursor of active metal and of the reduction temperature upon activity and selectivity in selective hydrogenation of crotonaldehyde by Pt/SnO₂ and Ru/SnO₂ catalysts were studied. Experiments were performed in the liquid phase with a group of solvents tested: propan-2-ol, toluene, hexane and tetrahydrofuran. The best results were achieved with catalysts from ex-nitrate precursors/Pt(NH₃)₄(NO₃)₂ and Ru(NO)(NO₃)₂/reduced at 150° C. Propan-2-ol was evaluated as the most appropriate solvent to gain high yields of crotylalcohol in this study. A new hydrogenation product, 2-methylprop-2-en-1-ol (methallylalcohol), was observed.     

Recognition of RNA by amide modified backbone nucleic acids: molecular dynamics simulations of DNA-RNA hybrids in aqueous solution

Thermodynamic and structural properties of a chemically modified DNA-RNA hybrid in which a phosphodiester linkage is replaced by a neutral amide-3 linkage (3'-CH(2)-CONH-5') were investigated using UV melting experiments, molecular dynamics simulations in explicit water, and continuum solvent models. van't Hoff analysis of the experimental UV melting curves suggests that the significant increase of the thermodynamic stability of a 15-mer DNA-RNA with seven alternated amide-3 modifications (+11 degrees C) is mainly due to an increased binding enthalpy. To further evaluate the origin in the observed affinities differences, the electrostatic contribution to the binding free energy was calculated by solving the Poisson-Boltzmann equation numerically. The nonelectrostatic contribution was estimated as the product of a hydrophobic surface tension coefficient and the surface area that is buried upon double strand formation. Structures were taken from 10 ns molecular dynamics simulations computed in a consistent fashion using explicit solvent, counterions, and the particle-mesh Ewald procedure. The present preliminary thermodynamic study suggests that the favorable binding free energy of the amide-3 DNA single strand to the complementary RNA is equally driven by electrostatic and nonpolar contributions to the binding compared to their natural analogues. In addition, molecular dynamics simulations in explicit water were performed on an amide-3 DNA single strand and the corresponding natural DNA. Results from the conformations cluster analysis of the simulated amide-3 DNA single strand ensembles suggest that the 25% of the population sampled within 10 ns has a pre-organized conformation where the sugar C3' endo pucker is favored at the 3'-flanking nucleotides. These structural and thermodynamic features contribute to the understanding of the observed increased affinities of the amide-3 DNA-RNA hybrids at the microscopic level.     

Catalytic and physicochemical properties of Pt/α-GeO<Subscript>2</Subscript> systems in reaction of selective hydrogenation of α,β-unsaturated aldehydes in a gas phase

Hydrogenation of crotonaldehyde in a gas phase over Pt/α-GeO₂ catalysts was investigated. The systems were characterized by BET, XRD, TPR, TEM, ToF-SIMS, and FTIR methods. The optimum pretreatment parameters were studied. The best catalytic performance shows the catalyst 5 wt % Pt/α-GeO₂ (69% selectivity to crotyl alcohol at 200 μmol s⁻¹ g _Pt ⁻¹ activity and 10% conversion of crotonaldehyde). Lower loaded catalysts (2 and 1 wt % Pt) show lower, but also promising activity and selectivity. This good catalytic performance was related to the physicochemical properties of the catalyst. GeO₂ in the presence of Pt undergoes a partial surface reduction at temperatures higher than 100°C probably leading to the creation of the active Pt-Ge centers responsible for high selectivity to crotyl alcohol. Reduction at a temperature≥200°C deactivates the catalytic systems due to the formation of inactive PtGe alloys. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 4, pp. 600–605. This article was submitted by the authors in English.     

Usefulness of autoantigens depletion to detect autoantibody signatures by multiple affinity protein profiling

Patients with cancer produce specific autoantibodies against protein antigens present in limited amount among a large background of immunoglobulins (Igs), nonrelevant as biomarkers, including natural antibodies. Multiple affinity protein profiling (MAPPing) that combines 2-D immunoaffinity chromatography, enzymatic digestion of the isolated proteins, and identification by MS/MS, may facilitate the identification of these so far unknown patient antibodies. The first immunoaffinity chromatography is crucial, as it is used for selectively removing proteins (autoantigens) recognized by natural antibodies. Application of this depletion step to colon cancer cell proteins is specifically described along with the identification of the natural autoantigens, as well as the coupling of this depletion step with the next steps. By enabling to separate antibody-binding proteins recognized by either natural autoantibodies or patient-specific antibodies this approach may contribute significantly towards the definition of autoantibody signatures.     

Synthesis of 9-substituted-1,4,5,8-tetraazaphenanthrenes

The synthesis of 9-substituted-1,4,5,8-tetraazaphenanthrenes was undertaken in the course of a study aimed at the preparation of organometallic complexing agents.