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81.
Scott JP Oliver SF Brands KM Brewer SE Davies AJ Gibb AD Hands D Keen SP Sheen FJ Reamer RA Wilson RD Dolling UH 《The Journal of organic chemistry》2006,71(8):3086-3092
A practical asymmetric synthesis of the gamma-secretase inhibitor (-)-1 is described. As the key transformation, a highly diastereoselective intramolecular nitrile oxide cycloaddition forms the hexahydrobenzisoxazole core of 3 in four operations. Other aspects of the route include a highly stereoselective reduction of an isoxazole to form a cis-gamma-amino alcohol, an efficient chemical resolution, a dianion cyclization to construct a sultam ring, and the alpha-alkylation of a sultam with excellent diastereoselectivity. In each instance, the relative stereochemistry was evolved by way of substrate-based induction with > or = 96% ds. Kilogram quantities of the targeted drug candidate (-)-1 were obtained, without recourse to chromatography, by way of 10 isolated intermediates and in 13% overall yield. 相似文献
82.
We report muon spin rotation spectra in the narrow-gap semiconductors FeGa(3) and FeSb(2) consistent with a narrow band of small spin polarons (SPs). The characteristic sizes obtained for these SPs are R(FeGa(3)) ≈ 0.3-0.6 nm and R(FeSb (2)) ≈ 0.3 nm, respectively. Such SP states are expected to originate from the exchange correlations between localized and itinerant electrons. Our data suggest that SP bands are formed at low temperature, but are destroyed by thermal fluctuations above 10 K in FeGa(3) and above 7 K in FeSb(2). Formation of such SP band states can explain many of the low-temperature properties of these materials. 相似文献
83.
A. David Brewer George Ferguson Andrew A. Znotins 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(3):e109-e110
The structures of a 2‐oxa‐5‐thiabicyclo[4.1.0]heptane derivative, C7H10Cl2O3S, (I), and a 2H,3H,5H‐1,4‐dithiepine derivative, C7H9ClO4S2, (II), are reported. The six‐membered ring in (I) has an envelope conformation and the seven‐membered ring in (II) adopts a chair conformation. There are no untoward intermolecular interactions in (I), but two Cl atoms make a short intermolecular contact across an inversion centre in (II), with a Cl?Cl distance of 3.2784 (9) Å, some 0.22 Å less than the sum of the van der Waals radii. 相似文献
84.
G. M. Marshall A. Adamczak J. M. Bailey J. L. Beveridge G. A. Beer J. H. Brewer V. M. Bystritsky M. P. Faifman B. M. Forster M. C. Fujiwara T. M. Huber R. Jacot-Guillarmod P. Kammel K. R. Kendall N. P. Kherani S. K. Kim P. E. Knowles A. R. Kunselman M. Maier V. E. Markushin V. S. Melezhik G. R. Mason F. Mulhauser A. Olin C. Petitjean T. A. Porcelli L. A. Schaller V. A. Stolupin J. Zmeskal 《Hyperfine Interactions》2001,138(1-4):203-211
Since the discovery that muonic deuterium at energies near a few eV could travel distances of the order of 1 mm in condensed
hydrogen, and in particular that muonic tritium and muonic deuterium could emerge from the surface of a solid hydrogen layer,
the advantages of solid targets have enabled the study of several processes important in muon catalyzed fusion. A review of
the results is presented, emphasizing the strengths and limitations of the use of solid hydrogen layer targets.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
85.
The study of dilute Sc impurities in either heavier d-transition metals or in alkali metal hosts is difficult due to their limited solubility; however, the large host-impurity mismatch in these systems makes them particularly interesting in terms of local electronic structure. One way to overcome the solubility problem is implantation into the desired host; in particular, using recoil implantation following heavy-ion nuclear reactions, deep implantation into practically any host can be achieved. Here, we compare the implantation of 43Sc into Cs, studied in situ by the in-beam TDPAD method [1], with the implantation of 44m
Sc into Fe, studied by low-temperature nuclear orientation (LTNO) and related techniques (NMRON, thermal cycling) [2]. 相似文献
86.
87.
88.
We report the nuclear orientation of near-stoichiometric samples of ZrZn2 containing trace impurities of radioactive54Mn and60Co in the temperature range 6.5–60 mK and in applied fields between 0.2 and 5.7 T. Analysis of the resullts indicates that
in both cases, the transition-element impurities occupy two sites (the Zr and Zn sites) with about equal probablities. In
one site, most probably that of Zr, both impurities have positive hyperfine fields of +12.0 T and +3.8 T for Mn and Co, respectively;
in the other site, the corresponding hyperfine fields are negative, with the values −6.0 T and −6.9 T. The dynamic hyperfine
interaction of Mn in ZrZn2 has also been studied using the thermal cyclic method with a weak thermal link, and was analyzed for the two relaxation times
corresponding to the different lattice sites. 相似文献
89.
The presence of a nonvibratory segment of vocal folds after microlaryngeal surgery is often a cause of poor voice result. The etiology of a nonvibratory segment is due to full thickness epithelial defect followed by secondary wound closure and scar contracture. To reduce scar contracture and nonvibratory segment of the vocal folds, primary repair with a 6-0 chromic endo-knot suture technique was used to close defects and approximate microflaps of the vocal folds. This was done in 18 patients with epithelial defects after resection of benign vocal fold lesions. The pathologic findings included severe polypoid degeneration (n = 7), fusiform laryngeal polyps (n = 5), sulcus vocalis (n = 2), cyst (n = 2), and keratosis (n = 2). Voice was improved in all patients after surgery. Comparison of vocal fold vibration before and after surgery showed improvements in configuration, amplitude, and mucosal wave. Vocal folds that were sutured all had good vibratory characteristics; none had a nonvibrating segment at the site of suture placement. Voice and healing after microsuture technique were near normal by Day 10 and return of mucosal wave was often complete by Day 14. Endoscopic microsuture closure of microflaps of the vocal folds edge is safe and affords the surgeon an opportunity for primary repair with improved functional result. 相似文献
90.
We report the temperature dependence of the gamma-ray anisotropies from oriented160Tb nuclei produced by neutron activation of the central portion of a high-purity single crystal Tb slab. The magnetically
saturated sample was studied over a wide temperature range from 18 mK to 150 mK. The temperatures were determined using precision
resistance thermometry within situ calibration by a magnetically shielded six-element superconducting fixed point device. Temperature stability during data
acquisition was better than 0.1%, and least-squares fitting of the resulting temperature dependences of 0° and 90° anisotropies
allowed both the magnetic dipole and the electric quadrupole hyperfine interaction frequencies to be determined with good
accuracy. The weighted averages for 18 gamma rays arev
M=1393.8 (8.1) MHz andv
P=178.0 (2.1) MHz, in excellent agreement with NMR results on ion-implanted samples. 相似文献