Search results for "activation"
showing 10 items of 2079 documents
Conformational properties of cyanomethoxy calix[4]arenes.
2005
O-Alkylation of the dinitro calix[4]arene 2, easily available by selective ipso-nitration of the di-cyanomethyl ether 1, with allylbromide (DMF/Cs2CO3) gave tetraethers 3 and 4 with anti- and syn-orientations of the two allyl ether residues. The two possible stereoisomers of 3 in the partial cone and 1,2-alternate conformation exist as an equilibrium mixture which could be quantitatively analysed by 1H NMR spectroscopy. The temperature dependence of this equilibrium leads to ΔH0 = − 7.6 to −9.7 kJ mol−1 in different solvents (tetrachloroethane, benzene, dimethylsulfoxide). Since 3(1,2-alt) could be obtained in pure form, its isomerisation to the equilibrium mixture with 3(paco) could be fol…
Effect of high temperature annealing (T > 1650 °C) on the morphological and electrical properties of p-type implanted 4H-SiC layers
2019
This work reports on the effect of high temperature annealing on the electrical properties of p-type implanted 4H-SiC. Ion implantations of Aluminum (Al) at different energies (30-200 keV) were carried out to achieve 300 nm thick acceptor box profiles with a concentration of about 10(20) at/cm(3). The implanted samples were annealed at high temperatures (1675-1825 degrees C). Morphological analyses of the annealed samples revealed only a slight increase of the surface roughness RMS up to 1775 degrees C, while this increase becomes more significant at 1825 degrees C (RMS = 1.2 nm). Room temperature Hall measurements resulted in a hole concentration in the range 0.65-1.34 x 10(18)/cm(3) and m…
Strategies to gain novel Alzheimer’s disease diagnostics and therapeutics using modulators of ABCA transporters
2021
Adenosine-triphosphate-(ATP)-binding cassette (ABC) transport proteins are ubiquitously present membrane-bound efflux pumps that distribute endo- and xenobiotics across intra- and intercellular barriers. Discovered over 40 years ago, ABC transporters have been identified as key players in various human diseases, such as multidrug-resistant cancer and atherosclerosis, but also neurodegenerative diseases, such as Alzheimer���s disease (AD). Most prominent and well-studied are ABCB1, ABCC1, and ABCG2, not only due to their contribution to the multidrug resistance (MDR) phenotype in cancer, but also due to their contribution to AD. However, our understanding of other ABC transporters is limited…
Statins and the squalene synthase inhibitor zaragozic acid stimulate the non-amyloidogenic pathway of amyloid-beta protein precursor processing by su…
2010
Cholesterol-lowering drugs such as statins influence the proteolytic processing of the amyloid-beta protein precursor (AbetaPP) and are reported to stimulate the activity of alpha-secretase, the major preventive secretase of Alzheimer's disease. Statins can increase the alpha-secretase activity by their cholesterol-lowering properties as well as by impairment of isoprenoids synthesis. In the present study, we elucidate the contribution of these pathways in alpha-secretase activation. We demonstrate that zaragozic acid, a potent inhibitor of squalene synthase which blocks cholesterol synthesis but allows synthesis of isoprenoids, also stimulates alpha-secretase activity. Treatment of human n…
Alpha-secretase as a therapeutic target.
2007
In the non-amyloidogenic pathway the alpha-secretase cleaves the amyloid precursor protein (APP) within the sequence of Abeta-peptides and precludes their formation. In addition, alpha-secretase cleavage releases an N-terminal extracellular domain with neurotrophic and neuroprotective properties. The disintegrin metalloproteinase ADAM10 has been shown to act as alpha-secretase in vivo, to prevent amyloid plaque formation and hippocampal defects in an Alzheimer disease mouse model. An increase in alpha-secretase activity therefore is an attractive strategy for treatment of AD and may be achieved by modulating selective signalling pathways. Functional characterization of the human ADAM10 prom…
Theoretical study of the NH tautomerism in free base porphyrin
1997
Abstract The NH tautomerism of free base porphyrin is investigated at the semiempirical spin-unrestricted AM1 (UAM1) and ab initio RHF/3-21G levels. The UAM1 method provides delocalized geometries for all stationary structures without imposing any symmetry constraint. RHF/3-21G geometry optimizations have to be performed under symmetry restrictions to ensure that realistic delocalized structures are obtained. Both the semiempirical and the ab initio calculations predict that the interconversion between trans tautomers proceeds in an asynchronous two-step process via intermediate cis tautomers. The cis tautomers are characterized as minima in the potential energy surface and are 8–10 kcal m…
<title>Hardening in LiF, induced by fast Kr and Ni ions, and recovery of the structure and properties under annealing</title>
2005
The recovery of optical and mechanical properties of LiF crystals irradiated with 790 MeV 78Kr and 640 MeV 58Ni ions at 10l2 ions/cm2 under annealing at temperatures up to 810 K is investigated. The optical absorbance and depth profiles of hardness before and after annealing were measured. A marked recovery of hardness and change in the optical absorption spectra were observed at temperatures above 520-530 K. An activation energy of 0.15±0.02eV, which is close to that for the thermal migration of H centers, is obtained from the annealing data. The results indicate a significant role of the H-center aggregates in the hardening and annealing processes. The maximum hardening is created and the…
Determination of phosphorus by instrumental neutron activation and bremsstrahlung measurement in bone samples
1997
A non destructive method based on the31P(n,γ)32P reaction for the assay of phosphorus in bone samples is described. This method involves a thermal neutron irradiation of 2 minutes in a reactor followed by the measurement of the bremsstrahlung produced by the β− of32P in a Ge-detector surrounded by an anti-Compton shield. Accuracy and precision were tested by analysing the certified NIST 1486 Bone Meal reference material and tri-calcium phosphate (Ca3(PO4)2) samples. The value obtained for the reference material was in good agreement with the certified value and with relative standard deviation of 4.1% the precision was acceptable. The value obtained for Ca3(PO4)2 shows a deviation of −6% fr…
Halogenated (arylsulfanyl)pyridines syntheses and their derivatives by C-S and C-X couplings catalyzed by palladium complexes
2018
C–H activation of aryl compounds directed by 2-sulfonylpyridine and 2-sulfanylpyridine moiety for the formation of C–X (X = F, Cl, Br, I) bonds was studied. First, the syntheses of thioethers (2-(arylsulfanyl)pyridines) and sulfones (2-(arylsulfonyl)pyridines) were necessary for the progress of this project. A C–S coupling catalyzed by palladium complexe between thioaryls and halogenated heterocycles was performed for the synthesis of thioethers. The cheap ligand bis(diphenylphosphino)ferrocene (dppf) was used for this convenient reaction. Then, oxidation of thioethers was performed to synthesize sulfones. Halogenation of these compounds was studied with ortho-directed C–H activation cataly…
Synthesis of novel organic-based fluorophores – Implementation to the design of fluorogenic enzyme substrates based on the principle of in situ synth…
2020
Detection and fluorescence imaging of biologic systems requires the implementation of efficient, robust and easy-to-use tools. Conventional fluorogenic probes currently used in microbiology lack efficiency since they are based on the single chemical modification of a fluorophore bearing an optically tunable reactive group, which often leads to incomplete fluorescence quenching. The main goal of my Ph.D thesis was to develop novel fluorogenic enzymatic substrates based on the "covalent assembly" principle. This approach also named "in situ synthesis" is based on the use of domino reactions to form a fluorescent moiety starting from a "caged" non-fluorescent molecule. In our case, the bioanal…