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排序方式: 共有195条查询结果,搜索用时 31 毫秒
31.
H. H. Willard J. J. Thompson E. Kasper P. Slawik A. W. Middleton K. Seelkopf H. Taeger P. Schmidt F. Weyrauch A. Necke H. Müller A. J. Lindsey B. Park E. J. Lewis O. B. Winter Helen M. Robinson F. W. Lamb E. J. Miller C. E. Willoughby E. S. Wilkins E. O. Kraemer A. Jílek J. Kota 《Analytical and bioanalytical chemistry》1936,106(4-6):200-207
32.
Errington RJ Petkar SS Middleton PS McFarlane W Clegg W Coxall RA Harrington RW 《Dalton transactions (Cambridge, England : 2003)》2007,(44):5211-5222
The tetra-n-butylammonium (TBA) salt of [(MeO)TiW(5)O(18)](3-) 1 was reacted with alcohols ROH to give primary, secondary and tertiary alkoxide derivatives [(RO)TiW(5)O(18)](3-) (R = Et 2, (i)Pr 3 and (t)Bu 4), whilst hydrolysis afforded [(mu-O)(TiW(5)O(18))(2)](6-) 5 rather than the hydroxo derivative (R = H). In reactions with (i)PrOH and (t)BuOH, impurity peaks observed at 1015 and 1020 ppm in the (17)O NMR spectra indicate alkoxide degradation and Ti=O bond formation via reactions analogous to those occurring at the surfaces of solid heteropolyacids. Aryloxides [(ArO)TiW(5)O(18)](3-) were prepared by reacting 1 with phenols ArOH (Ar = C(6)H(5) 6, C(6)H(4)Me-4 7, C(6)H(4)(t)Bu-4 8, C(6)H(4)OH-4 9, C(6)H(4)OH-3 10, C(6)H(3)(OH)(2)-3,5 11 and C(6)H(4)CHO-2 13). TiW(5)O(18) units were linked by reacting 1 with 9 to give [(mu-1,4-OC(6)H(4)O)(TiW(5)O(18))(2)](6-) 12. (17)O and (183)W NMR spectra are reported and X-ray crystal structures were obtained for TBA salts of anions 3-10 and 13, which showed that the titanium is six-coordinate in all cases. Reactions were monitored by (1)H NMR, including a 2D-EXSY study of methoxo exchange, and the slow rates observed are probably associated with the reluctance of titanium in these anions to achieve seven-coordination. 相似文献
33.
Simon G. Patching Rachel Edwards David A. Middleton 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2009,199(2):242-246
We demonstrate that individual H–C–C–H torsional angles in uniformly labelled organic solids can be estimated by selective excitation of 13C double-quantum coherences under magic-angle spinning at rotational resonance. By adapting a straightforward one-dimensional experiment described earlier [T. Karlsson, M. Eden, H. Luhman, M.H. Levitt, J. Magn. Reson. 145 (2000) 95–107], a double-quantum filtered spectrum selective for Cα and Cβ of uniformly labelled l-[13C,15N]valine is obtained with 25% efficiency. The evolution of Cα–Cβ double-quantum coherence under the influence of the dipolar fields of bonded protons is monitored to provide a value of the Hα–Cα–Cβ–Hβ torsional angle that is consistent with the crystal structure. In addition, double-quantum filtration selective for C6 and C1′ of uniformly labelled [13C,15N]uridine is achieved with 12% efficiency for a 13C–13C distance of 2.5 Å, yielding a reliable estimate of the C6–H and C1′–H projection angle defining the relative orientations of the nucleoside pyrimidine and ribose rings. This procedure will be useful, in favourable cases, for structural analysis of fully labelled small molecules such as receptor ligands that are not readily synthesised with labels placed selectively at structurally diagnostic sites. 相似文献
34.
Devon M. Middleton Feroze B. Mohamed Nadia Barakat Louis N. Hunter Sphoorti Shellikeri Jürgen Finsterbusch Scott H. Faro Pallav Shah Amer F. Samdani M.J. Mulcahey 《Magnetic resonance imaging》2014
Patient and physiological motion can cause artifacts in DTI of the spinal cord which can impact image quality and diffusion indices. The purpose of this investigation was to determine a reliable motion correction method for pediatric spinal cord DTI and show effects of motion correction on DTI parameters in healthy subjects and patients with spinal cord injury. Ten healthy subjects and ten subjects with spinal cord injury were scanned using a 3 T scanner. Images were acquired with an inner field-of-view DTI sequence covering cervical spine levels C1 to C7. Images were corrected for motion using two types of transformation (rigid and affine) and three cost functions. Corrected images and transformations were examined qualitatively and quantitatively using in-house developed code. Fractional anisotropy (FA) and mean diffusivity (MD) indices were calculated and tested for statistical significance pre- and post- motion correction. Images corrected using rigid methods showed improvements in image quality, while affine methods frequently showed residual distortions in corrected images. Blinded evaluation of pre and post correction images showed significant improvement in cord homogeneity and edge conspicuity in corrected images (p < 0.0001). The average FA changes were statistically significant (p < 0.0001) in the spinal cord injury group, while healthy subjects showed less FA change and were not significant. In both healthy subjects and subjects with spinal cord injury, quantitative and qualitative analysis showed the rigid scaled-least-squares registration technique to be the most reliable and effective in improving image quality. 相似文献
35.
X. Liang R. Chapman K.-M. Spohr M.B. Smith P. Bednarczyk S. Naguleswaran F. Haas G. de Angelis S.M. Campbell P.J. Dagnall M. Davison G. Duchêne Th. Kröll S. Lunardi D.J. Middleton 《The European Physical Journal A - Hadrons and Nuclei》2001,10(1):41-47
High-spin states in neutron-rich Dy isotopes, populated in deep-inelastic processes produced by the interaction of 234 MeV
37Cl ions with a 160Gd target, have been studied using the highly sensitive EUROBALL IV gamma-ray detector array. The previously known level schemes
for 159,160,161,162Dy have been extended to significantly higher spin ( ? 30?) and the i
13/2 band crossing in 159Dy has been observed for the first time. The experimental results are discussed within the framework of cranked shell model
and projected shell model calculations with particular reference to the observed delayed band crossing in 162Dy.
Received: 20 October 2000 / Accepted: 16 January 2001 相似文献
36.
A. K. Dinnis B. K. Middleton J. J. Miles 《Journal of magnetism and magnetic materials》1993,120(1-3):149-153
A theory of the digital magnetic recording process has been produced which facilitates the prediction of the recording properties of thick particulate and other media. It allows studies to be made of recorded patterns through the depths of media and the influence of these on overall recording properties. The theory is capable of dealing with particulate, thin-film and multilayer media. 相似文献
37.
Mark D. Middleton 《Tetrahedron》2006,62(45):10528-10540
A synthetic approach to the scabrosin family of antibiotics using a ruthenium carbene-catalyzed tandem metathesis and a Pd(II)-catalyzed cyclization is described. The chiral propargyl amino acid is furnished through enantioselective phase-transfer propargylation. The synthesis of the cyclohexadiene ring system is achieved through ring synthesis using tandem enyne metathesis, previously developed in our lab. The complementary methods of methylene-free and 1,5-hexadiene-alkyne metatheses are compared. The indoline heterocycles are formed using a two-step chloroacetoxylation (Bäckvall reaction) with subsequent nucleophilic attack by an amide nucleophile. The indoline subunits were joined and cyclized to furnish the core diketopiperazine ring. The stereochemical assignment of intermediates is also discussed. 相似文献
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