186,221 research outputs found
Synthesis and catalytic activity of metal nanoclusters inside functional resins: an endeavour lasting 15 years
No full textCross-linked functional polymers (functional resins) are versatile, designable and useful supports for metal nanoclusters that are able to provide reasonably thermally and mechanically stable multi-functional metal catalysts characterized by good activity and selectivity. The paper reviews authors’ contributions to the field from the early 1990s to the present
Versatile plug flow catalytic cell for in situ transmission/fluorescence x-ray absorption fine structure measurements
No full textCross-Linked Polymers as Scaffolds for the Low-Temperature Preparation of Nanostructured Metal Oxides
No full textThe current state of the art of the use of cross-linked organic polymers, both insoluble (resins or gels) and soluble (micro- and nanogels), as aids for the low-temperature preparation of stable metal oxide nanoparticles or nanostructured metal oxides is reviewed herein. Synthetic strategies for inorganic oxide nanomaterials of this kind can greatly benefit from the use of cross-linked polymers, which may act as scaffolds/exotemplates during inorganic nanoparticle synthesis, or as stabilizers following post-synthetic modification of the nanoparticles. Furthermore, the peculiar properties of the organic cross-linked polymers add to those of the inorganic oxide nanoparticles, producing materials with combined properties. The potential applications of such highly promising composite nanomaterials will be also briefly sketched
Synthesis and characterization of iron(III) oxides as supports for Au(0)-based catalysts
No full textA series of iron(III) hydrated oxide/oxyhydroxide/oxide was prepared by precipitation from Fe(III) aqueous solutions, to obtain supports suitable as Au(0)-based catalysts. During synthesis, all parameters -pH, temperature and adding rate - were strictly controlled in order to achieve highly reproducible synthesis. The method of purification was also planned in order to remove nitrate ions that can influence the catalytic activity and/or the support properties, without modifying the structure or particle dimension of the support. Dialysis was identified as the best method for purifying the hydrated oxide/hydroxide, i.e., ferrihydrite and goethite; while ammonium carbonate washing proved to be the most successful for the other hydroxide/oxides. Mossbauer spectroscopy and X-ray powder diffraction pointed out the complexity of all these systems, proving the extreme importance of synthesis temperature for crystallinity, particle dimension, and amount of hydroxide/oxid
An Immunocompetent Environment Unravels the Proto-Oncogenic Role of miR-22
No full textMiR-22 was first identified as a proto-oncogenic microRNA (miRNA) due to its ability to post-transcriptionally suppress the expression of the potent PTEN (Phosphatase And Tensin Homolog) tumor suppressor gene. miR-22 tumorigenic role in cancer was subsequently supported by its ability to positively trigger lipogenesis, anabolic metabolism, and epithelial-mesenchymal transition (EMT) towards the metastatic spread. However, during the following years, the picture was complicated by the identification of targets that support a tumor-suppressive role in certain tissues or cell types. Indeed, many papers have been published where in vitro cellular assays and in vivo immunodeficient or immunosuppressed xenograft models are used. However, here we show that all the studies performed in vivo, in immunocompetent transgenic and knock-out animal models, unanimously support a proto-oncogenic role for miR-22. Since miR-22 is actively secreted from and readily exchanged between normal and tumoral cells, a functional immune dimension at play could well represent the divider that allows reconciling these contradictory findings. In addition to a critical review of this vast literature, here we provide further proof of the oncogenic role of miR-22 through the analysis of its genomic locus vis a vis the genetic landscape of human cancer
Resonant-XRD characterization of nanoalloyed Au-Pd catalysts for the direct synthesis of H2O2: Quantitative analysis of size dependent composition of the nanoparticles
No full textThe focus of this work is on the relationship between the quantitative structural characterization of bimetallic Au-Pd nanoparticles dispersed in an amorphous polymer matrix and their catalytic activity in the direct synthesis of hydrogen peroxide (DS reaction). Resonant X-ray powder diffraction with synchrotron radiation was employed to probe selectively and to reveal fine details of the structure of bimetallic nanoparticles embedded in the support. The semi-quantitative analysis of the resonant X-ray powdered diffraction data, made on a large number of metal nanoparticles, shows that in one of the polymer-supported Au-Pd catalyst for the DS reaction (P75) featured by an overall molar Pd/Au of about 5.54, the smallest metal nanoparticles (MNPs), which account for more than 99.9% of the total MNPs number and for more than 95% of the metal surface, are formed by practically pure palladium. The relative number of bimetallic alloyed nanoparticles is very small (less than 4 x 10(2) ppm) and they contribute to only about 2% of the total metal surface. In a second gold-enriched catalyst (P50) with an overall molar Pd/Au of 1.84, the proportion of the bimetallic alloyed nanoparticles increased to about 97% and they account for about 99% of the metal surface. As a result of the metal intermixing, the catalytic productivity for the DS reaction increased from 97 to 109 mmol(H2)O(2)/mol(H2), owing to the gold-promotion of palladium
Versatile plug flow catalytic cell for in situ transmission∕fluorescence x-ray absorption fine structure measurements
No full textA novel flow-through catalytic cell has been developed for in situ x-ray absorption spectroscopy (XAS) experiments on heterogeneous catalysts under working conditions and in the presence of a liquid and a gas phase. The apparatus allows to carry out XAS measurements in both the transmission and fluorescence modes, at moderate temperature (from RT to 50-80 ◦C) and low-medium gas pressure (up to 7-8 bars). The materials employed are compatible with several chemicals such as those involved in the direct synthesis of hydrogen peroxide (O2, H2, H2O2, methanol). The versatile design of the cell allows to fit it to different experimental setups in synchrotron radiation beamlines. It was used successfully for the first time to test nanostructured Pd catalysts during the direct synthesis of hydrogen peroxide (H2O2) in methanol solution from dihydrogen and dioxygen
Gel-type cross-linked functional polymers as template in the synthesis of size controlled metal nanoclusters
No full textCross-linked gel-type functional polymers (CFPs) are organic materials built up with interconnected polymer chains [1]. Pendants hanging from the polymer chains may render CFPs reactive materials particularly suitable for anchoring metal centres removed from a liquid phase, by means of covalent or ionic bonds [2]:
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Polymer-Hematite Nanocomposites: Templating Effect of Commercial Ion-Exchangers in the Growth of Size-Controlled Iron Oxide Nanoparticles
No full textGeneration of size-controlled Pd0 nanoclusters inside of the nanoporous domains of gel-type resins: diverse and convergent support to a strategy of "Template Controlled Synthesis"
No full textIn the realm of supported metal catalysis, the metal component
is usually present as nanoparticles dispersed on the
surface of suitable metal oxides or on active carbon.
Synthetic procedures are normally directed to the generation
of size-controlled metal nanoclusters, whose circumstances
become mandatory when reactions to be catalyzed are
“structure sensitive”.In general, size control has been achieved by: directly
manufacturing metal-oxide-supported catalysts;by the
generation of kinetically stabilized metal nanoclusters in the
liquid phase and subsequent transfer of the protected
nanoclusters on to suitable supports; by generating metal
nanoclusters inside isoporous inorganic materials such as
mesoporous silicas. Herein, we report on three independent, convergent
pieces of structural evidence of this template-controlled
synthesis strategy to obtain size-controlled metal nanoclusters
suitable for synthesizing resin-supported metal catalysts
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