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排序方式: 共有328条查询结果,搜索用时 15 毫秒
321.
Jukiya Sakamoto Yuhei Umeda Kenta Rakumitsu Prof. Dr. Michinori Sumimoto Prof. Dr. Hayato Ishikawa 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(32):13516-13524
A collective synthesis of glycosylated monoterpenoid indole alkaloids is reported. A highly diastereoselective Pictet–Spengler reaction with α-cyanotryptamine and secologanin tetraacetate as substrates, followed by a reductive decyanation reaction, was developed for the synthesis of (−)-strictosidine, which is an important intermediate in biosynthesis. This two-step chemical method was established as an alternative to the biosynthetically employed strictosidine synthase. Furthermore, after carrying out chemical and computational studies, a transition state for induction of diastereoselectivity in our newly discovered Pictet–Spengler reaction is proposed. Having achieved the first enantioselective total synthesis of (−)-strictosidine in just 10 steps, subsequent bioinspired transformations resulted in the concise total syntheses of (−)-strictosamide, (−)-neonaucleoside A, (−)-cymoside, and (−)-3α-dihydrocadambine. 相似文献
322.
323.
On the sharp constant for the weighted Trudinger–Moser type inequality of the scaling invariant form
Michinori Ishiwata Makoto Nakamura Hidemitsu Wadade 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2014
In this article, we establish the weighted Trudinger–Moser inequality of the scaling invariant form including its best constant and prove the existence of a maximizer for the associated variational problem. The non-singular case was treated by Adachi and Tanaka (1999) [1] and the existence of a maximizer is a new result even for the non-singular case. We also discuss the relation between the best constants of the weighted Trudinger–Moser inequality and the Caffarelli–Kohn–Nirenberg inequality in the asymptotic sense. 相似文献
324.
Sumimoto M Yokogawa D Komeda M Yamamoto H Hori K Fujimoto H 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2011,81(1):653-660
The molecular geometries, electronic structures, and excitation energies of NPh(3), NPh(2)Me, NPhMe(2), and NMe(3), were investigated using DFT and post-Hartree Fock methods. When the structural stabilities of these compounds were compared to results obtained by using MP4(SDQ) method, it was confirmed that the optimized geometries by using MP2 method were sufficiently reliable. The excited states with large oscillator strengths consisted of transition components from the HOMO. It should be noted that the orbitals of the nitrogen atom mix with the π-orbital of the phenyl group in an anti-bonding way in the HOMO, and the orbital energy increases with this mixing. The unoccupied orbitals are generated from bonding and anti-bonding type interactions between the π-orbitals of the phenyl groups; therefore, the number of phenyl groups strongly affects the energy diagram of the compounds studied. The differences in the energy diagram cause a spectral change in these compounds in the ultraviolet region. 相似文献
325.
A wavelength-calibration method for prism-based spectral imaging of single-molecule (SM) fluorescence was developed. With
this method, a wavelength reference is provided by photoluminescence from 50-nm-diameter gold nanoparticles (AuNPs) binding
with fluorophores. The AuNPs each bound with a SM fluorophore, either Alexa488 or Cy3, to form AuNP/fluorophore complexes
in tris-HCl buffer. Each complex was immobilized on a silica slide and then excited by total-internal-reflection illumination
to make it emit SM fluorescence and AuNP photoluminescence. The portion of the AuNP photoluminescence transmitted by a band-pass
filter gives the wavelength reference. A spectral-imaging system composed of a prism-based spectroscope (with a reciprocal
dispersion of about 4 nm/μm) and a charge-coupled device with 6.45-μm-square pixels was used to obtain an SM-fluorescence
spectrum and a wavelength-reference spectrum. Through smoothed differentiation of these two spectra, the peak location of
the former in relation to the latter was determined with subpixel precision. After that, the SM fluorophore was classified
as either Alexa488 or Cy3 according to the peak location. The error rate of the classification was estimated to be only 0.3%. 相似文献
326.
Oki M 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2010,86(9):867-883
Isolation of rotational isomer models of ethane-type molecules is described. We could experimentally prove that, if rotational isomers whose molecular shape was chiral, the molecule could be optically active, even though it did not carry an asymmetric carbon atom. As an extension, other types of stereochemically fundamental and optically active molecules were isolated and their absolute stereochemistry was determined. One example is the model of meso-tartaric acid, for which optical inactivity had been attributed to internal compensation but is now explained as follows. On dissolution of meso-tartaric acid in a solvent, the molecule gives two kinds of conformers, one of which is a C(i) molecule and the other is a C(1) molecule. Although the latter is intrinsically optically active, the optical activity is cancelled by its enantiomer. The theory of internal compensation is recommended to be abandoned. As an extension to another area, some reactions of conformers are also discussed. 相似文献
327.
328.
The title organoboron complex undergoes dissociation of the intramolecular B–S coordination bond much faster than the corresponding mono ethylthiomethyl complex as revealed by the dynamic NMR study. The facile dissociation is attributable to an SN2-type mechanism, where the uncoordinated ligand assists the dissociation of the coordinated ligand in the transition state. This mechanism is supported by the initio calculations of a model reaction system. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:241–245, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20005 相似文献