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91.
92.
A Mössbauer spectroscopic study of orthorhombic Fe2P1–x
Si
x
withx 0.35 was performed. A large spread in magnetic hyperfine fields was found at the six Fe positions ranging from 10–26 T at 4.2 K. Small rearrangements in the crystal positions as compared to the hexagonal phase cause large changes in the magnetic field. Large changes in Fe magnetic moments have also been obtained in a spin-polarized LMTO band calculation performed on orthorhombic Fe2P as compared to a similar calculation of hexagonal Fe2P. 相似文献
93.
94.
Bräuner-Osborne H Bunch L Chopin N Couty F Evano G Jensen AA Kusk M Nielsen B Rabasso N 《Organic & biomolecular chemistry》2005,3(21):3926-3936
A set of ten azetidinic amino acids, that can be envisioned as C-4 alkyl substituted analogues of trans-2-carboxyazetidine-3-acetic acid (t-CAA) and/or conformationally constrained analogues of (R)- or (S)-glutamic acid (Glu) have been synthesized in a diastereo- and enantiomerically pure form from beta-amino alcohols through a straightforward five step sequence. The key step of this synthesis is an original anionic 4-exo-tet ring closure that forms the azetidine ring upon an intramolecular Michael addition. This reaction was proven to be reversible and to lead to a thermodynamic distribution of two diastereoisomers that were easily separated and converted in two steps into azetidinic amino acids. Azetidines 35-44 were characterized in binding studies on native ionotropic Glu receptors and in functional assays at cloned metabotropic receptors mGluR1, 2 and 4, representing group I, II and III mGlu receptors, respectively. Furthermore, azetidine analogues 35, 36, and 40 were also characterized as potential ligands at the glutamate transporter subtypes EAAT1-3 in the FLIPR Membrane Potential (FMP) assay. The (2R)-azetidines 35, 37, 39, 41 and 43 were inactive in iGlu, mGlu and EAAT assays, whereas a marked change in the pharmacological profile at the iGlu receptors was observed when a methyl group was introduced in the C-4 position, compound 36 versus t-CAA. At EAAT1-3, compound 35 was inactive, whereas azetidines 36 and 40 were both identified as inhibitors and showed selectivity for the EAAT2 subtype. 相似文献
95.
Fredrik Bergstr?m Ilya Mikhalyov Peter H?ggl?f Rüdiger Wortmann Tor Ny Lennart B A Johansson 《Journal of the American Chemical Society》2002,124(2):196-204
A ground-state dimer (denoted D(I)) exhibiting a strong absorption maximum at 477 nm (epsilon = 97 000 M(-1)cm(-1)) can form between adjacent BODIPY groups attached to mutant forms of the protein, plasminogen activator inhibitor type 1 (PAI-1). No fluorescence from excited D(I) was detected. A locally high concentration of BODIPY groups was also achieved by doping lipid phases (micelles, vesicles) with BODIPY-labeled lipids. In addition to an absorption band located at about 480 nm, a new weak absorption band is also observed at ca. 570 nm. Both bands are ascribed to the formation of BODIPY dimers of different conformation (D(I) and D(II)). Contrary to D(I) in PAI-1, the D(II) aggregates absorbing at 570 nm are emitting light observed as a broad band centered at about 630 nm. The integrated absorption band of D(I) is about twice that of the monomer, which is compatible with exciton coupling within a dimer. The F?rster radius of electronic energy transfer between a BODIPY excited monomer and the ground-state dimer (D(I)()) is 57 +/- 2 A. A simple model of exciton coupling suggests that in D(I) two BODIPY groups are stacked on top of each other in a sandwich-like configuration with parallel electronic transition dipoles. For D(II) the model suggests that the S(0) --> S(1) transition dipoles are colinear. An explanation for the previously reported (J. Am. Chem. Soc. 1994, 116, 7801) exceptional light spectroscopic properties of BODIPY is also presented. These are ascribed to the extraordinary electric properties of the BODIPY chromophore. First, changes of the permanent electric dipole moment (Delta(mu) approximately -0.05 D) and polarizability (-26 x 10(-40) C m(2) V(-1)) between the ground and the first excited states are small. Second, the S(0) <--> S(1) electronic transition dipole moments are perpendicular to Delta(mu). 相似文献
96.
This material is based upon work supported by the National Science Foundation under grant No. DMS-9207071. The US Government
has certain rights in this material. 相似文献
97.
Saeed Kamali-M Lennart Häggström Tore Ericsson Roger Wäppling 《Hyperfine Interactions》2006,168(1-3):995-999
The behaviour of small amounts of Fe in brass is investigated using Mössbauer spectroscopy. Different samples, made from the same ingot material, but run through different annealing temperatures and duration times and then quenched to room temperature, have different amount of γ-Fe. The present work shows that a suitable heat treatment can increase the amount of these precipitations and, that a heat treatment at 650°C is the optimal one for having the highest amount of this phase. 相似文献
98.
Angelika Kippert Katarina Trajkovic Dirk Fitzner Lennart Opitz Mikael Simons 《BMC neuroscience》2008,9(1):40
Background
During the development of the central nervous system, oligodendrocytes generate large amounts of myelin, a multilayered insulating membrane that ensheathes axons, thereby allowing the fast conduction of the action potential and maintaining axonal integrity. Differentiation of oligodendrocytes to myelin-forming cells requires the downregulation of RhoA GTPase activity. 相似文献99.
100.