Kinetic investigations of the hydrogen production step of a thermochemical cycle using mixed iron oxides coated on ceramic substrates

A two‐step thermochemical cycle for solar hydrogen production using mixed iron oxides as the metal oxide redox system has been investigated. The ferrite is coated on a honeycomb structure, which serves as the absorber for solar irradiation and provides the surface for the chemical reaction. Coated honeycomb structures have already been tested in a solar receiver reactor in the solar furnace of DLR in Cologne with respect to their water splitting capability and their long‐term stability. The concept of this new reactor design has proven feasible and constant hydrogen production during repeated cycles has been shown. For a further optimization of the process and in order to gain reliable performance predictions more information about the process especially concerning the kinetics of the oxidation and the reduction step are essential. To examine the hydrogen production during the water splitting step a test rig has been built up on a laboratory scale. In this test rig small coated honeycombs are heated by an electric furnace. The honeycomb is placed inside a tube reactor and can be flushed with water vapour or with an inert gas. A homogeneous temperature within the sample is reached and testing conditions are reproducible. Through analysis of the product gas the hydrogen production is monitored and a reaction rate describing the hydrogen production rate per gram ferrite can be formulated. Using this test set‐up, SiC honeycombs coated with zinc ferrite have been tested. The influences of the temperature and the water concentration on the hydrogen production during the water splitting step have been investigated. An analysis of the ferrite conversion was performed using the Shrinking Core Model. A mathematical approach for the peak reaction rate at the beginning of the water splitting step was formulated and the activation energy was calculated from the experimental data. An activation energy of 110 kJ mol⁻¹ was found. Copyright © 2009 John Wiley & Sons, Ltd.     

In Vitro Metabolism of Six C-Glycosidic Flavonoids from Passiflora incarnata L.

Several medical plants, such as Passiflora incarnata L., contain C-glycosylated flavonoids, which may contribute to their efficacy. Information regarding the bioavailability and metabolism of these compounds is essential, but not sufficiently available. Therefore, the metabolism of the C-glycosylated flavones orientin, isoorientin, schaftoside, isoschaftoside, vitexin, and isovitexin was investigated using the Caco-2 cell line as an in vitro intestinal and epithelial metabolism model. Isovitexin, orientin, and isoorientin showed broad ranges of phase I and II metabolites containing hydroxylated, methoxylated, and sulfated compounds, whereas schaftoside, isoschaftoside, and vitexin underwent poor metabolism. All metabolites were identified via UHPLC-MS or UHPLC-MS/MS using compound libraries containing all conceivable metabolites. Some structures were confirmed via UHPLC-MS experiments with reference compounds after a cleavage reaction using glucuronidase and sulfatase. Of particular interest is the observed cleavage of the C–C bonds between sugar and aglycone residues in isovitexin, orientin, and isoorientin, resulting in unexpected glucuronidated or sulfated luteolin and apigenin derivatives. These findings indicate that C-glycosidic flavones can be highly metabolized in the intestine. In particular, flavonoids with ortho-dihydroxy groups showed sulfated metabolites. The identified glucuronidated or sulfated aglycones demonstrate that enzymes expressed by Caco-2 cells are able to potentially cleave C–C bonds in vitro.     

Tailoring Chitosan/LTA Zeolite Hybrid Aerogels for Anionic and Cationic Dye Adsorption

Chitosan (CS) is largely employed in environmental applications as an adsorbent of anionic dyes, due to the presence in its chemical structure of amine groups that, if protonated, act as adsorbing sites for negatively charged molecules. Efficient adsorption of both cationic and anionic dyes is thus not achievable with a pristine chitosan adsorbent, but it requires the combination of two or more components. Here, we show that simultaneous adsorption of cationic and anionic dyes can be obtained by embedding Linde Type A (LTA) zeolite particles in a crosslinked CS-based aerogel. In order to optimize dye removal ability of the hybrid aerogel, we target the crosslinker concentration so that crosslinking is mainly activated during the thermal treatment after the fast freezing of the CS/LTA mixture. The adsorption of isotherms is obtained for different CS/LTA weight ratios and for different types of anionic and cationic dyes. Irrespective of the formulation, the Langmuir model was found to accurately describe the adsorption isotherms. The optimal tradeoff in the adsorption behavior was obtained with the CS/LTA aerogel (1:1 weight ratio), for which the maximum uptake of indigo carmine (anionic dye) and rhodamine 6G (cationic dye) is 103 and 43 mg g⁻¹, respectively. The behavior observed for the adsorption capacity and energy cannot be rationalized as a pure superposition of the two components, but suggests that reciprocal steric effects, chemical heterogeneity, and molecular interactions between CS and LTA zeolite particles play an important role.     

Pro-Inflammatory Microenvironment Modulates the Transfer of Mutated TP53 Mediated by Tumor Exosomes

Exosomes released from tumor cells are instrumental in shaping the local tumor microenvironment to allow cancer progression. Recently, it has been shown that tumor exosomes carry large fragments of dsDNA, which may reflect the mutational status of parental cells. Although it has been described that a stressful microenvironment can influence exosomal cargo, the effects on DNA packing and its transfer into recipient cells have yet to be investigated. Here, we report that exosomes derived from SW480 (human colorectal adenocarcinoma cell line) cells can carry dsDNA fragments containing the entire coding sequence of both TP53 and KRAS genes, harboring the SW480-related TP53 c.818G > A and KRAS c.35G > T typical mutations. We also report the following: that cell stimulation with lipopolysaccharides (LPS) promotes the selective packaging of the TP53 gene, but not the KRAS gene; that exosomes secreted by SW480 cells efficiently transfer the mutated sequences into normal CCD841-CoN colon epithelial and THLE-2 hepatic cells; that this mechanism is more efficient when the cells had been previously incubated with pro-inflammatory cytokines; that the TP53 gene appears actively transcribed in both recipient cells; and that mutated mRNA levels are not influenced by cytokine treatment. Our data strongly suggest that pro-inflammatory stimulation promotes the horizontal transfer of an oncogene by exosomes, although this remains a rare event. Further studies are needed to assess the impact of the oncogenic transfer by exosomes in malignant transformation and its role in tumor progression.     

Ion-conducting lithium bis(oxalato)borate-based polymer electrolytes

Poly(2-ethoxyethyl methacrylate) polymer gel electrolytes containing immobilised lithium bis(oxalato)borate in aprotic carbonates: propylene carbonate (PC), propylene carbonate–ethylene carbonate (PC–EC 50:50 vol.%) and diethyl carbonate–ethylene carbonate (DEC–EC 50:50 vol.%) were prepared by a direct radical polymerisation. The electrolyte composition was optimised to achieve suitable ionic conductivity 0.5 and 2.4 mS cm⁻¹ at 25 and 70 °C respectively along with good mechanical properties. The electrochemical stability up to 5.1 V vs. Li/Li⁺ was determined on gold electrode by voltammetrical measurements. The polymer electrolytes with high-boiling solvents (PC and PC/EC) showed higher thermal stability (up to 110–120 °C) compared to the liquid electrolytes. The proposed area of application is in the lithium-ion batteries with cathodes operating at elevated temperatures of 70 °C, where higher electrochemical stability of the polymer electrolytes is employed.     

Quantitative pressure and strain field analysis of helium precipitates in silicon

The structural properties of overpressurised helium precipitates formed by low dose ion implantation and subsequent annealing of silicon are investigated by quantitative transmission electron microscopy techniques. These precipitates, which show pronounced platelet geometry, are analysed with respect to their geometry, crystallographic orientation and their particular gas pressure values. The dependence of the measured platelet pressure versus the radius is discussed in terms of a Griffith crack. Experimental results on the shape and the crystallographic orientation of the platelets are discussed in the framework of anisotropic elastic properties and surface energies of silicon. The ability of the precipitates to punch-out dislocation loops is discussed in terms of associated threshold shear stress values and evaluated with regard to the defect size dependency.     

Activated Poly(hydromethylsiloxane)s as Novel Adhesion Promoters for Metallic Surfaces

A poly(hydromethylsiloxane) (PHMS) was bound to aluminum, copper and steel surfaces via activation with cis-[PtCl₂(PhCH = CH₂)₂] in solution at room temperature. The attached polymer promotes the adhesion to two-component silicone resins where the curing process is based on catalytic hydrosilylation of olefins. In lap-shear or peel tests, cohesive failure was always observed. An example shows that the adhesive joint withstood boiling water for 200 h without considerable loss of adhesive strength. It is suggested that a small fraction of the olefinic component of the resin, e.g., a poly(dimethylsiloxane) containing some olefinic groups, is also connected with the attached PHMS via catalytic hydrosilylation, thus binding the silicone resin to the surface via the PHMS layer.     

Operational strategy of a two-step thermochemical process for solar hydrogen production

A two-step thermochemical cycle process for solar hydrogen production from water has been developed using ferrite-based redox systems at moderate temperatures. The cycle offers promising properties concerning thermodynamics and efficiency and produces pure hydrogen without need for product separation.     

S1P Lyase Regulates Intestinal Stem Cell Quiescence via Ki-67 and FOXO3

Background: Reduction of the Sphingosine-1-phosphate (S1P) degrading enzyme S1P lyase 1 (SGPL1) initiates colorectal cancer progression with parallel loss of colon function in mice. We aimed to investigate the effect of SGPL1 knockout on the stem cell niche in these mice. Methods: We performed immunohistochemical and multi-fluorescence imaging on tissue sections of wildtype and SGPL1 knockout colons under disease conditions. Furthermore, we generated SGPL1 knockout DLD-1 cells (SGPL1^−/−M.Ex1) using CRISPR/Cas9 and characterized cell cycle and AKT signaling pathway via Western blot, immunofluorescence, and FACS analysis. Results: SGPL1 knockout mice were absent of anti-Ki-67 staining in the stem cell niche under disease conditions. This was accompanied by an increase of the negative cell cycle regulator FOXO3 and attenuation of CDK2 activity. SGPL1^−/−M.Ex1 cells show a similar FOXO3 increase but no arrest of proliferation, although we found a suppression of the PDK1/AKT signaling pathway, a prolonged G1-phase, and reduced stem cell markers. Conclusions: While already established colon cancer cells find escape mechanisms from cell cycle arrest, in vivo SGPL1 knockout in the colon stem cell niche during progression of colorectal cancer can contribute to cell cycle quiescence. Thus, we propose a new function of the S1P lyase 1 in stemness.     

Effect of transition metal catalysts on the microstructure of carbide-derived carbon

Carbon materials with different microstructure can be produced by a carbide-derived carbon (CDC) approach varying the carbide precursor and the reaction conditions for the selective etching of the metal. CDC was produced using biomorphic TiC and SiC ceramics derived from paper preforms by a chemical vapor infiltration and reaction technique. In this work the effect of transition metal salt catalysts such as Ru(III), Fe(II), Fe(III) or Ru(III)/Fe(III) on the chlorination process at temperatures in the range 600-1200 °C as well as on the microstructure of the resulting carbon was investigated. The produced CDC was characterized by its degree of order and pore structure using Raman spectroscopy, high resolution transmission electron microscopy and low temperature nitrogen adsorption. A higher etching rate as well as a higher degree of order at lower reaction temperatures was observed if a catalytically active metal was present during the chlorination process. This effect was mostly pronounced in the case of a Ru(III)/Fe(III) bimetallic catalyst. The higher degree of order of the carbon is associated with an increased amount of mesopores and with a decrease in specific surface area. Therefore, the CDC processing in the presence of catalysts offers another way to produce ordered carbon structures at lower temperatures.