355 research outputs found
Restructuring of supported Pd by green solvents: an operando Quick EXAFS (QEXAFS) study and implications for the derivation of structure-function relationships in Pd catalysis
Transmission electron microscopy (TEM) is commonly used as an ex-situ technique to determine structural changes by comparing images of catalyst particles before and after a reaction. This requires the use of an alcoholic solvent to disperse the particles on a grid. In this work, we will show that Pd catalysts can be transformed during the procedure, by using EXAFS to determine the structure of Pd catalysts in different environments (as dry or wet samples). Supported palladium nanoparticles exposed to aqueous ethanolic solution (50% w/v) are transformed to a common, reduced, and hydrogen-contaminated state, irrespective of their initial habit or support. Catalysts comprised of nanosize PdO are reduced at ca. 350 K, whereas samples comprised of very small (ca. ≤ 10 atoms) Pd particles react with the solvent at just above room temperature and agglomerating with considerable loss of dispersion. As such any potential benefits to catalysis sought through the synthesis of very highly dispersed metallic Pd supported upon a range of inorganic dispersants will be rapidly erased through the action of such solvents
Effect of Fetal Striatal and Astrocyte Transplants into Unilateral Excitotoxin-Lesioned Striatum
Studies have suggested that neurotrophic
mechanisms may underlie transplant-induced
functional recovery. Astrocytes have been
reported to be a source of neurotrophic factors.
The present study examined the possible role of
cultured astrocytes in promoting recovery of
apomorphine-induced rotation behavior in rats
with unilateral kainic acid (KA) lesions of the
striatum. Five weeks after the lesions, one group
of rats received fetal striatal tissue (E17)
transplants, another group received transplants
of cultured astrocyte suspension, and the
remaining rats received sham transplants and
served as controls. Apomorphine-induced
rotation behavior was tested 4 weeks after the
KA lesions, and 5 and 10 weeks following the
transplantation. The KA-induced rotation
behavior was reduced by the striatal transplants
but not by the cultured astrocyte transplants 5
and 10 weeks following the transplantation.
Histochemicai analysis indicated that the striatal
transplants had survived and grown and
contained neurons and glia with similar
morphology to those in the host brain.
Immunocytochemical analysis of the astrocyte
transplant sites revealed heavy glial fibrillary
acidic protein and OX-42 staining in the
transplant areas, suggesting that the
transplanted astrocytes may have survived in the host brain. Although fetal striatal
transplants can ameliorate apomorphine-induced
rotation behavior, transplants of
astrocytes alone may not be sufficient to reverse
the functional deficits produced by KA lesions
Effect of retained chlorine in ENCAT™ 30 catalysts on the development of encapsulated Pd: insights from in situ Pd K, L₃ and Cl K-edge XAS
In situ X-ray absorption spectroscopy (XAS) and Pd K, LIII, and Cl K-edges shows that Cl can be present in significant amounts in ENCATâ„¢ 30 catalysts and that it can severely retard Pd nanoparticle (NP) development in flowing solvents. We also show that whilst polymeric encapsulation protects the Pd against solvent induced agglomeration of Pd nanoparticles the evidence suggests it does not prevent the formation PdHx through reaction with the aqeous ethanol solvent, and that, as received, ENCATâ„¢ 30 NP catalysts are not, for the most part, comprised of nanoparticulate Pd0 irrespective of the presence of Cl
Metabolically stable bradykinin B2 receptor agonists enhance transvascular drug delivery into malignant brain tumors by increasing drug half-life
<p>Abstract</p> <p>Background</p> <p>The intravenous co-infusion of labradimil, a metabolically stable bradykinin B2 receptor agonist, has been shown to temporarily enhance the transvascular delivery of small chemotherapy drugs, such as carboplatin, across the blood-brain tumor barrier. It has been thought that the primary mechanism by which labradimil does so is by acting selectively on tumor microvasculature to increase the local transvascular flow rate across the blood-brain tumor barrier. This mechanism of action does not explain why, in the clinical setting, carboplatin dosing based on patient renal function over-estimates the carboplatin dose required for target carboplatin exposure. In this study we investigated the systemic actions of labradimil, as well as other bradykinin B2 receptor agonists with a range of metabolic stabilities, in context of the local actions of the respective B2 receptor agonists on the blood-brain tumor barrier of rodent malignant gliomas.</p> <p>Methods</p> <p>Using dynamic contrast-enhanced MRI, the pharmacokinetics of gadolinium-diethyltriaminepentaacetic acid (Gd-DTPA), a small MRI contrast agent, were imaged in rodents bearing orthotopic RG-2 malignant gliomas. Baseline blood and brain tumor tissue pharmacokinetics were imaged with the 1<sup>st </sup>bolus of Gd-DTPA over the first hour, and then re-imaged with a 2<sup>nd </sup>bolus of Gd-DTPA over the second hour, during which normal saline or a bradykinin B2 receptor agonist was infused intravenously for 15 minutes. Changes in mean arterial blood pressure were recorded. Imaging data was analyzed using both qualitative and quantitative methods.</p> <p>Results</p> <p>The decrease in systemic blood pressure correlated with the known metabolic stability of the bradykinin B2 receptor agonist infused. Metabolically stable bradykinin B2 agonists, methionine-lysine-bradykinin and labradimil, had differential effects on the transvascular flow rate of Gd-DTPA across the blood-brain tumor barrier. Both methionine-lysine-bradykinin and labradimil increased the blood half-life of Gd-DTPA sufficiently enough to increase significantly the tumor tissue Gd-DTPA area under the time-concentration curve.</p> <p>Conclusion</p> <p>Metabolically stable bradykinin B2 receptor agonists, methionine-lysine-bradykinin and labradimil, enhance the transvascular delivery of small chemotherapy drugs across the BBTB of malignant gliomas by increasing the blood half-life of the co-infused drug. The selectivity of the increase in drug delivery into the malignant glioma tissue, but not into normal brain tissue or skeletal muscle tissue, is due to the inherent porous nature of the BBTB of malignant glioma microvasculature.</p
Crystallographic Phase Transition and High-Tc Superconductivity in LaFeAsO:F
Undoped LaFeAsO, parent compound of the newly found high-Tc superconductor,
exhibits a sharp decrease in the temperature-dependent resistivity at ~160 K.
The anomaly can be suppressed by F doping and the superconductivity appears
correspondingly, suggesting a close associate of the anomaly with the
superconductivity. We examined the crystal structures, magnetic properties and
superconductivity of undoped (normal conductor) and 14 at.% F-doped LaFeAsO (Tc
= 20 K) by synchrotron X-ray diffraction, DC magnetic measurements, and ab
initio calculations to demonstrate that the anomaly is associated with a phase
transition from tetragonal (P4/nmm) to orthorhombic (Cmma) phases at ~160 K as
well as an antiferromagnetic transition at ~140 K. These transitions can be
explained by spin configuration-dependent potential energy surfaces derived
from the ab initio calculations. The suppression of the transitions is ascribed
to interrelated effects of geometric and electronic structural changes due to
doping by F- ions.Comment: 22 pages, 8 figures, 2 tables, Supplementary information is included
at the end of the document, accepted for publication in Supercond. Sci.
Techno
The Structure and Dynamics of the Upper Chromosphere and Lower Transition Region as Revealed by the Subarcsecond VAULT Observations
The Very high Angular resolution ULtraviolet Telescope (VAULT) is a sounding
rocket payload built to study the crucial interface between the solar
chromosphere and the corona by observing the strongest line in the solar
spectrum, the Ly-a line at 1216 {\AA}. In two flights, VAULT succeeded in
obtaining the first ever sub-arcsecond (0.5") images of this region with high
sensitivity and cadence. Detailed analyses of those observations have
contributed significantly to new ideas about the nature of the transition
region. Here, we present a broad overview of the Ly-a atmosphere as revealed by
the VAULT observations, and bring together past results and new analyses from
the second VAULT flight to create a synthesis of our current knowledge of the
high-resolution Ly-a Sun. We hope that this work will serve as a good reference
for the design of upcoming Ly-a telescopes and observing plans.Comment: 28 pages, 11 figure
Induction of Selective Blood-Tumor Barrier Permeability and Macromolecular Transport by a Biostable Kinin B1 Receptor Agonist in a Glioma Rat Model
Treatment of malignant glioma with chemotherapy is limited mostly because of delivery impediment related to the blood-brain tumor barrier (BTB). B1 receptors (B1R), inducible prototypical G-protein coupled receptors (GPCR) can regulate permeability of vessels including possibly that of brain tumors. Here, we determine the extent of BTB permeability induced by the natural and synthetic peptide B1R agonists, LysdesArg9BK (LDBK) and SarLys[dPhe8]desArg9BK (NG29), in syngeneic F98 glioma-implanted Fischer rats. Ten days after tumor inoculation, we detected the presence of B1R on tumor cells and associated vasculature. NG29 infusion increased brain distribution volume and uptake profiles of paramagnetic probes (Magnevist and Gadomer) at tumoral sites (T1-weighted imaging). These effects were blocked by B1R antagonist and non-selective cyclooxygenase inhibitors, but not by B2R antagonist and non-selective nitric oxide synthase inhibitors. Consistent with MRI data, systemic co-administration of NG29 improved brain tumor delivery of Carboplatin chemotherapy (ICP-Mass spectrometry). We also detected elevated B1R expression in clinical samples of high-grade glioma. Our results documented a novel GPCR-signaling mechanism for promoting transient BTB disruption, involving activation of B1R and ensuing production of COX metabolites. They also underlined the potential value of synthetic biostable B1R agonists as selective BTB modulators for local delivery of different sized-therapeutics at (peri)tumoral sites
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