148 research outputs found
Co3O4 particles grown over nanocrystalline CeO2: influence of precipitation agents and calcination temperature on the catalytic activity for methane oxidation
Crystalline cobalt oxides were prepared by a precipitation method using three different precipitation
agents, ÄČNH4)2CO3, Na2CO3 and COÄČNH2)2. Cobalt oxide nanoparticles corresponding to a Co3O4 loading
of 30 wt% were also deposited over high-surface area nanocrystalline ceria by the same precipitation
agents. The effect of calcination temperature, 350 or 650 °C, on the morphological and structural properties
was evaluated. Characterization by BET, XRD, SEM, TEM, Raman spectroscopy, H2-TPR, XPS and
NH3-TPD was performed and the catalytic properties were explored in the methane oxidation reaction.
The nature of the precipitation agent strongly influenced the textural properties of Co3O4 and the
Co3O4âCeO2 interface. The best control of the particle size was achieved by using COÄČNH2)2 that
produced small and regular crystallites of Co3O4 homogeneously deposited over the CeO2 surface. Such a
Co3O4âCeO2 system precipitated by urea showed enhanced low-temperature reducibility and high surface
Co3+ concentration, which were identified as the key factors for promoting methane oxidation at
low temperature. Moreover, the synergic effect of cobalt oxide and nanocrystalline ceria produced stable
full conversion of methane in the entire range of investigated temperature, up to 700â800 °C, at which
Co3O4 deactivation usually occurs
Keggin heteropolyacid H3PW12O40 supported on different oxides for catalytic and catalytic photo-assisted propene hydration
Catalytic and catalytic photo-assisted hydration of propene to form 2-propanol in gasâsolid regime at
atmospheric pressure and 85 1C were carried out by using a heteropolyacid (POM) supported on different
oxides. Binary materials were prepared by impregnation of H3PW12O40 on different commercial and
home prepared supports (TiO2, SiO2, WO3, ZrO2, ZnO, Al2O3). Some of the composites were active both
for catalytic and catalytic photo-assisted reactions. The Keggin type POM was completely and partially
degraded, when supported on ZnO and Al2O3, respectively, and these binary solids always resulted as
inactive for both catalytic and catalytic photo-assisted reactions. The supported Keggin POM species
played a key role both for the catalytic and the photo-assisted catalytic reactions, due to their strong
acidity and ability to form strong oxidant species under UV irradiation, respectively. The contemporary
presence of heat and UV light improved the activity of almost all POM supported materials. All materials
were characterized by X-ray diffraction (XRD), scanning electron microscopy observations (SEM), diffuse
reflectance spectroscopy (DRS), determination of the conduction and valence band energy by photovoltage
measurements, Fourier transform infrared spectroscopy (FTIR), NH3-TPD experiments and time
resolved microwave conductivity (TRMC).
Introduction
Propene hydration to obtain 2-propanol is a reaction carried
out at moderate temperatures (ca. 150â200 1C) and pressure
(2MPa) in the presence of an acid catalyst;1 however the realization
of this reaction at ambient conditions is of great interest.
The us
Anti-angiogenic action of hyperthermia by suppressing gene expression and production of tumour-derived vascular endothelial growth factor in vivo and in vitro
Vascular endothelial growth factor is an important angiogenic factor for tumour progression because it increases endothelial-cell proliferation and remodels extracellular matrix in blood vessels. We demonstrated that hyperthermia at 42°C, termed heat shock, suppressed the gene expression and production of vascular endothelial growth factor in human fibrosarcoma HT-1080 cells and inhibited its in vitro angiogenic action on human umbilical vein endothelial cells. The gene expression of alternative splicing variants for vascular endothelial growth factor, VEGF121, VEGF165 and VEGF189, was constitutively detected in HT-1080 cells, but the VEGF189 transcript was less abundant than VEGF121 and VEGF165. When HT-1080 cells were treated with heat shock at 42°C for 4âh and then maintained at 37°C for another 24âh, the gene expression of all vascular endothelial growth factor variants was suppressed. In addition, HT-1080 cells were found to produce abundant VEGF165, but much less VEGF121, both of which were inhibited by heat shock. Furthermore, the level of vascular endothelial growth factor in sera from six cancer patients was significantly diminished 2â3 weeks after completion of whole-body hyperthermia at 42°C (49.9±36.5âpgâmlâ1, P<0.01) as compared with that prior to the treatment (177.0±77.5âpgâmlâ1). On the other hand, HT-1080 cell-conditioned medium showed vascular endothelial growth factor-dependent cell proliferative activity and the augmentation of pro-matrix metalloproteinase-1 production in human umbilical vein endothelial cells. The augmentation of endothelial-cell proliferation and pro-matrix metalloproteinase-1 production was poor when human umbilical vein endothelial cells were treated with conditioned medium from heat-shocked HT-1080 cells. These results suggest that hyperthermia acts as an anti-angiogenic strategy by suppressing the expression of tumour-derived vascular endothelial growth factor production and thereby inhibiting endothelial-cell proliferation and extracellular matrix remodelling in blood vessels
Interstitial fluid: the overlooked component of the tumor microenvironment?
Background: The interstitium, situated between the blood and lymph vessels and the cells, consists of a solid or matrix phase and a fluid phase, together constituting the tissue microenvironment. Here we focus on the interstitial fluid phase of tumors, i.e., the fluid bathing the tumor and stromal cells. Novel knowledge on this compartment may provide important insight into how tumors develop and how they respond to therapy. Results: We discuss available techniques for interstitial fluid isolation and implications of recent findings with respect to transcapillary fluid balance and uptake of macromolecular therapeutic agents. By the development of new methods it is emerging that local gradients exist in signaling substances from neoplastic tissue to plasma. Such gradients may provide new insight into the biology of tumors and mechanistic aspects linked to therapy. The emergence of sensitive proteomic technologies has made the interstitial fluid compartment in general and that of tumors in particular a highly valuable source for tissue-specific proteins that may serve as biomarker candidates. Potential biomarkers will appear locally at high concentrations in the tissue of interest and will eventually appear in the plasma, where they are diluted. Conclusions: Access to fluid that reliably reflects the local microenvironment enables us to identify substances that can be used in early detection and monitoring of disease
The mechanisms by which polyamines accelerate tumor spread
Increased polyamine concentrations in the blood and urine of cancer patients reflect the enhanced levels of polyamine synthesis in cancer tissues arising from increased activity of enzymes responsible for polyamine synthesis. In addition to their de novo polyamine synthesis, cells can take up polyamines from extracellular sources, such as cancer tissues, food, and intestinal microbiota. Because polyamines are indispensable for cell growth, increased polyamine availability enhances cell growth. However, the malignant potential of cancer is determined by its capability to invade to surrounding tissues and metastasize to distant organs. The mechanisms by which increased polyamine levels enhance the malignant potential of cancer cells and decrease anti-tumor immunity are reviewed. Cancer cells with a greater capability to synthesize polyamines are associated with increased production of proteinases, such as serine proteinase, matrix metalloproteinases, cathepsins, and plasminogen activator, which can degrade surrounding tissues. Although cancer tissues produce vascular growth factors, their deregulated growth induces hypoxia, which in turn enhances polyamine uptake by cancer cells to further augment cell migration and suppress CD44 expression. Increased polyamine uptake by immune cells also results in reduced cytokine production needed for anti-tumor activities and decreases expression of adhesion molecules involved in anti-tumor immunity, such as CD11a and CD56. Immune cells in an environment with increased polyamine levels lose anti-tumor immune functions, such as lymphokine activated killer activities. Recent investigations revealed that increased polyamine availability enhances the capability of cancer cells to invade and metastasize to new tissues while diminishing immune cells' anti-tumor immune functions
Different populations and sources of human mesenchymal stem cells (MSC): A comparison of adult and neonatal tissue-derived MSC
The mesenchymal stroma harbors an important population of cells that possess stem cell-like characteristics including self renewal and differentiation capacities and can be derived from a variety of different sources. These multipotent mesenchymal stem cells (MSC) can be found in nearly all tissues and are mostly located in perivascular niches. MSC have migratory abilities and can secrete protective factors and act as a primary matrix for tissue regeneration during inflammation, tissue injuries and certain cancers
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