Mass spectral characterization of the thermal degradation of poly(propylene oxide) by electrospray and matrix-assisted laser desorption ionization

The thermal degradation of poly(propylene oxide) (PPO), M_n = 2000, can be characterized by electrospray (ESI) and matrix-assisted laser desorption ionization (MALDI). ESI and MALDI spectra of partially degraded PPO provide strong support for the thermal degradation pathway previously suggested by Griffiths et al. and Lemaire et al. Although these pathways differ in detail, it is not possible to distinguish between them from the masses of the resultant degradation species. Gel permeation chromatography data indicate that both mass spectrometric methods emphasize the presence of low-mass material, particularly in the degraded samples. This is attributed to the different sensitivities of the two techniques and some in situ fragmentation during mass spectrometric analysis.     

Physicochemical characteristics and biological activities of seasonal atmospheric particulate matter sampling in two locations of Paris

Fine particulate matter present in urban areas seems to be incriminated in respiratory disorders. The aim of this study was to relate physicochemical characteristics of PM2.5 (particulate matter collected with a 50% efficiency for particles with an aerodynamic diameter of 2.5 microm) to their biological activities toward a bronchial epithelial cell line 16-HBE. Two seasonal sampling campaigns of particles were realized, respectively, in a kerbside and an urban background station in Paris. Sampled-PM2.5 mainly consist of particles with a size below 1 microm and are mainly composed of soot as assessed by analytical scanning electron microscopy. The different PM2.5 samples contrasted in their PAH content, which was the highest in the kerbside station in winter, as well as in their metal content. Kerbside station samples were characterized by the highest Fe and Cu content, which appears correlated to their hydroxyl radical generating properties measured by electron paramagnetic resonance. Particles were compared by their capacity to induce cytotoxicity, intracellular ROS production, and proinflammatory cytokine release (GM-CSF and TNF-alpha). At a concentration of 10 microg/cm2, all samples induced peroxide production and cytokine release to the similar extent in the absence of cytotoxicity. In conclusion, whereas the PM2.5 samples differ by their PAH and metal composition, they induce the same biological responses likely either due to components bioavailability and/ or interactions between PM components.     

Morphological, structural and electrochemical analysis of sputter-deposited ceria and titania coatings for MCFC application

In order to protect the MCFC nickel cathode, TiO₂ and CeO₂ coatings were prepared by DC reactive magnetron sputtering. These oxides are stable thermodynamically whatever the cathode or anode gaseous conditions. Good quality, dense and homogeneous coatings were obtained at thicknesses lower than 1 μm. The structure of the deposits, as analysed by XRD, was the expected one. In this work only dense nickel substrates were used. After their direct immersion in a Li₂CO₃–Na₂CO₃ carbonate eutectic at 650 °C, which can be considered as extremely corrosive conditions with respect to the usual MCFC conditions, the coatings were affected. TiO₂ coatings were transformed into Li₂TiO₃, in agreement with thermodynamic predictions; however, they became progressively unstable, which was probably due to a problem of mechanical adhesion rather than to solubility. The thinner was the deposit, the higher was its conductance and the closer to that of a pure Ni electrode was its electrocatalytic activity. CeO₂ coatings were stable in a ceria form and their adhesion was better even though not fully satisfactory. These first preliminary results are promising regarding the direct contact of the coatings with the corrosive carbonate melt, but the improvement of the adhesion is one of the major problems to solve.     

η-Carbides (Co,Mo, or W) Nanoparticles from Octacyanometalates Precursors-Based Network

This paper describes a simple, two-steps chemical pathway to obtain bimetallic carbide nanoparticles (NPs) of general formula MxM″yC, also called η-carbides. This process allows for a control of the chemical composition of metals present in the carbides (M = Co and M″ = Mo or W). The first step involves the synthesis of a precursor consisting of a network of octacyanometalates. The second step consists in a thermal degradation of the previously obtained octacyanometalates networks under neutral atmosphere (Ar or N₂). It is shown that this process results in the formation of carbide NPs with diameter of ≈ 5nm, and the stoichiometries Co₃M’₃C, Co₆M’₆C, Co₂M’₄C for the Cs Co M’ systems.     

Synthesis,Characterization, and Reaction of Divinyl‐substituted Laddersiloxanes

Silicon - Silsesquioxanes with well-defined structures have been of great interest recently because of their superior properties. Among them, laddersiloxanes (ladder-type silsesquioxanes with...