629 research outputs found
Doping and band-gap engineering of an intrazeolite tungsten(VI) oxide supralattice
New results are presented concerning the topotactic self-assembly, n-type
doping and band-gap engineering of an intrazeolite tungsten(VI) oxide supralattice
n(W03)-Na56Y, where 0 < η < 32, built-up of single size and shape (W03)2
dimers. In particular it has been found that the oxygen content of these dimers
can be quantitatively adjusted by means of a thermal vacuum induced reversible
reductive-elimination oxidative-addition of dioxygen. This provides access to new
n(W03.x)-Na56Y materials (0 < Ï ^ 1.0) in which the oxygen content, structural
properties and electronic architecture of the dimers are changed. In this way one
can precisely control the oxidation state, degree of η-doping and band-filling of a
tungsten(VI) oxide supralattice through an approach which can be considered akin
to, but distinct in detail to, that found in the Magneli crystallographic shear phases
of non-stoichiometric bulk W03.x . Another discovery concerns the ability to alter
local electrostatic fields experienced by the tungsten(VI) oxide moieties housed in
the 13Ă supercages of 16(W03)-M36Y, by varying the ionic potential of the
constituent supercage M + cations across the alkali metal series. This method
provides the first opportunity to fine-tune the band-gap of a tungsten(VI) oxide
supralattice. Î miniband electronic description is advanced as a qualitative first
attempt to understand the origin of the above effects. The implications of these
discoveries are that cluster size, composition and intrinsic electrostatic field effects
can be used to "chemically manipulate" (engineer) the doping and band
architecture of intrazeolite supralattices of possible interest in quantum electronics
and nonlinear optics
A novel hybrid material with calcium and strontium release capability
The preparation of PDMSâTEOSâCaO hybrid materials by solâgel techniques has been widely described in
previous works. Calcium nitrate is the most common source of calcium used in these preparations.
However, to remove possible toxic nitrate by-products a thermal treatment is necessary at temperatures
above 500 1C, which leads to the degradation of the polymeric components of the hybrids. Strontium has
already shown some promising results in the therapeutic area, being used in cases of osteoporosis and low
bone density. In this study a new potential bioactive hybrid material was prepared, by solâgel techniques,
using calcium acetate as a novel calcium source. Also, for the first time, incorporation of strontium in a
PDMSâTEOS hybrid system was evaluated. Samples were characterized before and after immersion in
Kokuboâs Simulated Body Fluid (SBF) by SEM, EDS, ICP and FT-IR spectroscopy
Synthesis and characterization of modified silica gel as an intermediate in the generation of gaseous standard mixtures
A possibility of extending analytical applications of chemically modified silica gels is described. This involves their utilization for the generation of gaseous standard mixtures consisting of methyl chloride as the analyte and nitrogen as a carrier gas to be used for the calibration of the GC-FID system. N-methylmorpholine was chemically bonded to the propylsilylated surface of silica gel forming chloride of an appropriate immobilized compound which, under certain conditions, undergoes thermal decomposition yielding a single, volatile component (methyl chloride). Such a method of generating specific amounts of a standard substance can be used both for a single point calibration and for checking the accuracy of an analytical instrument in a relatively wide measurement range. It was found that 3.40±0.081 mg of methyl chloride can be generated per 1 g of the modified gel
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The Ultra-Potent and Selective TLR8 Agonist VTX-294 Activates Human Newborn and Adult Leukocytes
Background: Newborns display distinct immune responses that contribute to susceptibility to infection and reduced vaccine responses. Toll-like receptor (TLR) agonists may serve as vaccine adjuvants, when given individually or in combination, but responses of neonatal leukocytes to many TLR agonists are diminished. TLR8 agonists are more effective than other TLR agonists in activating human neonatal leukocytes in vitro, but little is known about whether different TLR8 agonists may distinctly activate neonatal leukocytes. We characterized the in vitro immuno-stimulatory activities of a novel benzazepine TLR8 agonist, VTX-294, in comparison to imidazoquinolines that activate TLR8 (R-848; (TLR7/8) CL075; (TLR8/7)), with respect to activation of human newborn and adult leukocytes. Effects of VTX-294 and R-848 in combination with monophosphoryl lipid A (MPLA; TLR4) were also assessed. Methods: TLR agonist specificity was assessed using TLR-transfected HEK293 cells expressing a NF-ÎșB reporter gene. TLR agonist-induced cytokine production was measured in human newborn cord and adult peripheral blood using ELISA and multiplex assays. Newborn and adult monocytes were differentiated into monocyte-derived dendritic cells (MoDCs) and TLR agonist-induced activation assessed by cytokine production (ELISA) and co-stimulatory molecule expression (flow cytometry). Results: VTX-294 was âŒ100x more active on TLR8- than TLR7-transfected HEK cells (EC50, âŒ50 nM vs. âŒ5700 nM). VTX-294-induced TNF and IL-1ÎČ production were comparable in newborn cord and adult peripheral blood, while VTX-294 was ⌠1 log more potent in inducing TNF and IL-1ÎČ production than MPLA, R848 or CL075. Combination of VTX-294 and MPLA induced greater blood TNF and IL-1ÎČ responses than combination of R-848 and MPLA. VTX-294 also potently induced expression of cytokines and co-stimulatory molecules HLA-DR and CD86 in human newborn MoDCs. Conclusions: VTX-294 is a novel ultra-potent TLR8 agonist that activates newborn and adult leukocytes and is a candidate vaccine adjuvant in both early life and adulthood
Low-energy cross section of the 7Be(p,g)8B solar fusion reaction from Coulomb dissociation of 8B
Final results from an exclusive measurement of the Coulomb breakup of 8B into
7Be+p at 254 A MeV are reported. Energy-differential Coulomb-breakup cross
sections are analyzed using a potential model of 8B and first-order
perturbation theory. The deduced astrophysical S_17 factors are in good
agreement with the most recent direct 7Be(p,gamma)8B measurements and follow
closely the energy dependence predicted by the cluster-model description of 8B
by Descouvemont. We extract a zero-energy S_17 factor of 20.6 +- 0.8 (stat) +-
1.2 (syst) eV b.Comment: 14 pages including 16 figures, LaTeX, accepted for publication in
Physical Review C. Minor changes in text and layou
Core-coupled states and split proton-neutron quasi-particle multiplets in 122-126Ag
Neutron-rich silver isotopes were populated in the fragmentation of a 136Xe
beam and the relativistic fission of 238U. The fragments were mass analyzed
with the GSI Fragment separator and subsequently implanted into a passive
stopper. Isomeric transitions were detected by 105 HPGe detectors. Eight
isomeric states were observed in 122-126Ag nuclei. The level schemes of
122,123,125Ag were revised and extended with isomeric transitions being
observed for the first time. The excited states in the odd-mass silver isotopes
are interpreted as core-coupled states. The isomeric states in the even-mass
silver isotopes are discussed in the framework of the proton-neutron split
multiplets. The results of shell-model calculations, performed for the most
neutron-rich silver nuclei are compared to the experimental data
Molecular Mechanism of Thymidylate Synthase Inhibition by N 4 Hydroxy dCMP in View of Spectrophotometric and Crystallographic Studies
Novel evidence is presented allowing further clarification of the mechanism of the slow binding thymidylate synthase TS inhibition by N4 hydroxy dCMP N4 OH dCMP . Spectrophotometric monitoring documented time and temperature , and N4 OH dCMP dependent TS catalyzed dihydrofolate production, accompanying the mouse enzyme incubation with N4 OH dCMP and N5,10 methylenetetrahydrofolate, known to inactivate the enzyme by the covalent binding of the inhibitor, suggesting the demonstrated reaction to be uncoupled from the pyrimidine C 5 methylation. The latter was in accord with the hypothesis based on the previously presented structure of mouse TS cf. PDB ID 4EZ8 , and with conclusions based on the present structure of the parasitic nematode Trichinella spiralis, both co crystallized with N4 OH dCMP and N5,10 methylenetetrahdrofolate. The crystal structure of the mouse TS N4 OH dCMP complex soaked with N5,10 methylenetetrahydrofolate revealed the reaction to run via a unique imidazolidine ring opening, leaving the one carbon group bound to the N 10 atom, thus too distant from the pyrimidine C 5 atom to enable the electrophilic attack and methylene group transfe
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