排序方式: 共有49条查询结果,搜索用时 15 毫秒
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Suvi T.M. Simila 《Tetrahedron letters》2006,47(17):2933-2936
A concise synthesis of the azatricyclic core structure of FR901483, a potent immunosuppressant, has been accomplished. The key elements of the approach involve a nucleophilic addition to an acyl iminium ion, a ring closing metathesis and a lactone-lactam rearrangement to provide the tricyclic structure. 相似文献
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Trina M. Arola William H. Ojala Nell Herrera Barjeta Balidemaj Charles R. Ojala 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(4):o207-o211
Two isomeric pairs of Schiff bases, N,N′‐bis(2‐methoxybenzylidene)‐p‐phenylenediamine, C22H20N2O2, (I), and 2,2′‐dimethoxy‐N,N‐(p‐phenylenedimethylene)dianiline, C22H20N2O2, (II), and (E,E)‐1,4‐bis(3‐iodophenyl)‐2,3‐diazabuta‐1,3‐diene (alternative name: 3‐iodobenzaldehyde azine), C14H10I2N2, (III), and N,N′‐bis(3‐iodophenyl)ethylenediimine, C14H10I2N2 [JAYFEV; Cho, Moore & Wilson (2005). Acta Cryst. E 61 , o3773–o3774], differ pairwise only in the orientation of their imino linkages and in all four individual cases occupy inversion centers in the crystal, yet all four compounds are found to assume unique packing arrangements. Compounds (I) and (II) differ substantially in molecular conformation, possessing angles between their ring planes of 12.10 (15) and 46.29 (9)°, respectively. Compound (III) and JAYFEV are similar to each other in conformation, with angles between their imino linkages and benzene rings of 11.57 (15) and 7.4 (3)°, respectively. The crystal structures are distinguished from each other by different packing motifs involving the functional groups. Intermolecular contacts between methoxy groups define an R22(6) motif in (I) but a C(3) motif in (II). Intermolecular contacts are of the I⋯I type in (III), but they are of the N⋯I type in JAYFEV. 相似文献
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A modified derivative sign binary method is proposed to extract fringe skeletons from interferometric fringe patterns. A fringe direction map ranging from 0° to 360° is obtained with an unambiguous relationship between the grayscale and fringe tangent direction. Using this approach, the derivative sign binary map is detected without a fringe direction jump. The dark (light) fringe intensity minimum (maximum) can be extracted automatically to define fringe skeletons. In addition, two different anisotropic one-dimensional filters are described that can be used for further improving the fringe quality. Examples are provided for a holographic interferogram and a Moiré fringe pattern to illustrate applications and benefits of the approach. 相似文献
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Precise control and knowledge of surface structures are essential inorder to meet the requirements of today's and future materials. One possiblegrowth technique capable of meeting the requirements is atomic layer epitaxy(ALE). ALE is based on sequentially applied saturated gas-solid reactions,which provide the means for adsorption controlled material deposition atatomic layer level. In this paper the potentiality of the use of porousmaterials in a detailed study of adsorption controlled growth is discussed.At the same time the study promotes the application of adsorption controlledmaterials processing for advanced catalysts manufacturing. 相似文献
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Brown SD Strange P Bouchenoire L Zarychta B Thompson PB Mannix D Stockton SJ Horne M Arola E Ebert H Szotek Z Temmerman WM Fort D 《Physical review letters》2007,99(24):247401
We report measured dipolar asymmetry ratios at the LIII edges of the heavy rare-earth metals. The results are compared with a first-principles calculation and excellent agreement is found. A simple model of the scattering is developed, enabling us to reinterpret the resonant x-ray scattering in these materials and to identify the peaks in the asymmetry ratios with features in the spin and orbital moment densities. 相似文献
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Suvi T.M. Orr Shawn CabralDilinie P. Fernando Teresa Makowski 《Tetrahedron letters》2011,52(28):3618-3620
A variety of chiral azetidinepiperidines have been synthesized utilizing an expedient one-pot union of piperidine chloroaldehyde with chiral amines. This two step one-pot procedure provides access to an interesting set of compounds that retain the chiral purity of the starting chiral amine. 相似文献
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Ojanperä S Pelander A Pelzing M Krebs I Vuori E Ojanperä I 《Rapid communications in mass spectrometry : RCM》2006,20(7):1161-1167
An efficient method was developed for toxicological drug screening in urine by liquid chromatography coupled with electrospray ionization time-of-flight mass spectrometry. The method relies on a large target database of exact monoisotopic masses representing the elemental formulae of reference drugs and their metabolites. Mass spectral identification is based on matching measured accurate mass and isotopic pattern (SigmaFit) of a sample component with those in the database. Data post-processing software was developed for automated reporting of findings in an easily interpretable form. The mean and median of SigmaFit for true-positive findings were 0.0066 and 0.0051, respectively. The mean and median of mass error absolute values for true-positive findings were 2.51 and 2.17 ppm, respectively, corresponding to 0.65 and 0.60 mTh. For routine screening practice, a SigmaFit tolerance of 0.03 and a mass tolerance of 10 ppm were chosen. Ion abundance differences from urine extracts did not affect the accuracy of the automatically acquired SigmaFit or mass values. The results show that isotopic pattern matching by SigmaFit is a powerful means of identification in addition to accurate mass measurement. 相似文献
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