Ultrasonic and Thermophysical Properties of Cobalt Nanowires

Acoustical Physics - We have estimated elastic, mechanical, thermal and ultrasonic properties, in high temperature regime, of cobalt nanowires (Co-NWs) having a hexagonal close-packed (HCP)...     

WO3–SiO2 nanomaterials synthesized using a novel template-free method in supercritical CO2 as heterogeneous catalysts for epoxidation with H2O2

A series of tungsten oxide-silica (WO₃–SiO₂) composite nanomaterials were synthesized through a novel, template-free sol-gel method, in which supercritical-CO₂ (scCO₂) was utilized as synthesis medium. The efficacy of the synthesis method stems from a tailored reactor design that allows the contact of the reactants only in the presence of scCO₂. Selected synthetic parameters were screened with the purpose of enhancing the performance of the resulting materials as heterogeneous catalysts in epoxidation reactions with H₂O₂ as environmentally friendly oxidant. A cyclooctene conversion of 73% with epoxide selectivity of > 99% was achieved over the best WO₃–SiO₂ catalyst under mild reaction conditions (80 °C), equimolar H₂O₂ amount (1:1) and low WO₃ loading (~2.5 wt%). The turnover number achieved with this catalyst (TON = 328), is significantly higher than that of a WO₃–SiO₂ prepared via a similar sol-gel route but without supercritical CO₂, and that of commercial WO₃. A thorough characterization with a combination of techniques (ICP-OES, N₂-physisorption, XRD, TEM, STEM-EDX, SEM-EDX, FT-IR and Raman spectroscopy, XPS, TGA and FT-IR analysis of adsorbed pyridine) allowed correlating the physicochemical properties of the WO₃–SiO₂ nanomaterials with their catalytic performance. The high catalytic activity was attributed to: (i) the very high surface area (892 m²/g) and (ii) good dispersion of the W species acting as Lewis acid sites, which were both brought about by the synthesis in supercritical CO₂, and (iii) the relatively low hydrophilicity, which was tuned by optimizing the tetramethyl orthosilicate concentration and the amount of basic solution used in the synthesis of the materials. Our optimum catalyst was also tested in the reaction of cyclohexene with H₂O₂, resulting in cyclohexane diol as main product due to the presence of strong Brønsted acid sites in the catalyst, whereas the reaction with limonene yielded the internal epoxide as the major product and the corresponding diol as side product. Importantly, the catalyst did not show leaching and could be reused in five consecutive runs without any decrease in activity.     

Cyclotriphosphazene grafted silica: a novel support for immobilizing the oxo-vanadium Schiff base moieties for hydroxylation of benzene

The first report on the use of chlorotriphosphazenyl anchored mesoporous silica as a novel support for the immobilization of oxo-vanadium Schiff base moieties is described. The resulting heterogeneous material showed better catalytic activity than homogeneous as well as silica immobilized oxo-vanadium Schiff base for the hydroxylation of benzene with hydrogen peroxide.     

Intracellular Degradation of Elastin by Cathepsin K in Skin Fibroblasts— A Possible Role in Photoaging

Solar elastosis is observed in the dermis of photoaged skin and is characterized by an accumulation of abnormal elastin in the extracellular space. Several proteases that degrade elastin in the extracellular space have been implicated in its formation. The lysosomal protease cathepsin K (catK) has recently been described to be highly expressed in skin fibroblasts under certain pathologic conditions. As cat K is one of the most potent mammalian elastases, we hypothesized that catK-mediated intracellular elastin degradation may play a role in the formation of solar elastosis. Immunostaining of cultured skin fibroblasts incubated with labeled elastin demonstrated internalization of extracellular elastin to lysosomes and its degradation by catK. Induction of catK expression in fibroblasts was observed both in vitro and in vivo after exposure to longwave UVA. In contrast to fibroblasts from young donors, cells from old donors failed to activate catK in response to UVA. These data suggest a role of intracellular elastin degradation by catK in the formation of solar elastosis. We propose that an age-related decline in catK activity, in particular after UV exposure, may promote the formation of actinic elastosis through a decline of orderly intracellular elastin degradation and subsequent accumulation of elastin in the extracellular space.