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71.
Tomonori Ichibakase Tetsuya Kaneko Yuya Orito Shunsuke Kotani Makoto Nakajima 《Tetrahedron》2012,68(22):4210-4224
The aldol reactions of trimethoxysilyl enol ethers catalyzed by lithium binaphtholate were found to be powerful tools for the construction of quaternary asymmetric carbon centers. The stereoselectivities were greatly affected by the presence of water. Trimethoxysilyl enol ether derived from a cyclic ketone, such as cyclohexanone, was used as a substrate to obtain the anti-adduct preferentially under anhydrous conditions; by contrast, the syn-adduct was preferentially obtained under aqueous conditions with high stereoselectivity. The aldol-Tishchenko reaction of a trimethoxysilyl enol ether derived from acyclic ketones proceeded to give monoacyl 1,3-diol derivatives in high enantioselectivities. 相似文献
72.
Koichi Machida Akira Kotani Yuzuru Hayashi Hideki Hakamata 《Journal of mass spectrometry : JMS》2022,57(8):e4877
ISO 11843 part 7 (ISO 11843-7) can provide a standard deviation (SD) of area measurements of a target peak through the stochastic behaviors of instrumental noises. The purpose of this study is to demonstrate that ISO 11843-7 can be applied to assess repeatability in an isocratic liquid chromatography–tandem mass spectrometry (LC–MS/MS) system without repetitive measurements. The relative standard deviation (RSD) of the peak area of ergosterol picolinyl ester, which was used as an example, on a multiple reaction monitoring (MRM) chromatogram was determined by ISO 11843-7. The RSD by ISO 11843-7 (N = 1) was within a 95% confidence band of the RSD by repetitive measurements (N = 6). Moreover, the effects of digital smoothing, such as moving average, were also examined on the repeatability assessment in LC–MS/MS by ISO 11843-7. From the results of the comparisons of the RSDs obtained by ISO 11843-7 and the repetitive measurements, it was shown that suitable RSDs of the peak area were obtained from the smoothed MRM chromatograms by the moving average for narrow data point windows (e.g., one-sixth of the peak width). In conclusion, the utility of repeatability assessment based on ISO 11843-7 has been expanded for the validation of an LC–MS/MS system. 相似文献
73.
The dynamics of the low-lying excited states of vanadyl octaethylporphyrin (OEPVO) in frozen solution is investigated by transient electron paramagnetic resonance (TREPR). The observation of spin-polarized TREPR spectra from the lowest excited trip-quartet state of OEPVO, reported in the preceding paper, opens a new avenue for investigation of the excited states of such molecules. Here, a model based on the back-and-forth transitions between the trip-quartet and trip-doublet states is developed and used to explain the time dependence of the low-temperature laser flash-induced electron spin polarization of OEPVO. At early times, the TREPR spectra show predominantly multiplet polarization, whereas strong net polarization develops at later times. An analysis of the time dependence reveals two well-separated processes: (i) fast evolution of the polarization from the multiplet pattern to the net absorptive pattern and (ii) very slow decay of the net polarization. Both processes are temperature dependent and are faster at higher temperature. All of these observed features can be reproduced, and the experimental data can be simulated within the framework of the model. For simplicity, only the two nearly degenerate orbital states resulting from the a(1) --> e triplet excitation of the porphyrin are considered. Each of these is split into a trip-doublet and trip-quartet giving a total of four low-lying excited states. Transitions between the trip-doublet and trip-quartet states are assumed to be governed by spin-orbit coupling, which mixes the four low-lying states. It is known that following light excitation, the molecule initially decays to the lowest trip-doublet state and then to the trip-quartet state. In agreement with the observed TREPR spectra, the model predicts that this decay results in predominantly multiplet polarization of the trip-quartet. However, a small amount of net polarization is also predicted due to the spin selectivity associated with the Zeeman interaction. Because the energy gap between the trip-doublet and trip-quartet states is small, back-and-forth electronic transitions between the trip-doublet and trip-quartet are expected to occur as thermal equilibrium is established. The model predicts that it is these transitions that lead to the observed evolution of the initial multiplet polarization to net absorptive polarization. 相似文献
74.
X-ray magnetic circular dichroism at rare-earth L23 absorption edges in various compounds and alloys
Theoretical interpretations of X-ray magnetic circular dichroism (XMCD) at rare-earth (called R hereafter) L23 absorption edges are reviewed using differing models, depending on the material under investigation. In the first chapter, we present an overview of recent developments for XMCD in XAS with a few general remarks, especially at R atom absorption edges. In Section 2, we first describe basic mechanism of XMCD at L23 edges of R systems, and then we essentially discuss two examples of XMCD spectra in: (i) R2Fe14B metallic compounds, with the help of a cluster model, and (ii) RFe2 Laves-phase compounds, using a tight-binding approximation for R 5d and Fe 3d conducting states. A good agreement between theory and experiment for R2Fe14B suggests that a cluster model provides a valuable method to quantitatively calculate XMCD spectra of R systems, even with quite complicated atomic arrangements. For RFe2 systems the XMCD spectral shape, especially for the L2 edge of heavy R elements, is more complicated than those of R2Fe14B systems, and this is explained by the competition of some different XMCD mechanisms. In Section 3, we focus on special series of Ce systems, related to XAS and XMCD studies at the Ce L23 edges. Two clearly differing cases are interpreted: (i) A well localized 4f1 system, i.e. CeRu2Ge2; (ii) A less localized 4f1 system, i.e. CeFe2, with a 3d partner. Then, from a more experimental point of view, we investigate the influence of substitution on the low temperature properties of CePd3 compounds, i.e. Ce(Pd1-xMnx)3 alloys where x is about 0.03, giving rise to (CePd3)8Mn ordered structure. We give another example: Ce(Pd1-xNix)3 alloys with x taken up to about 0.25. Also the Ce L23 XMCD signal measured in pure CePd3 demonstrates that in the Ce based dense Kondo materials, only the 4f1 channel yields a magnetic response. 相似文献
75.
76.
Much effort has focused on methods for detecting various genetic differences in individuals, including single nucleotide polymorphisms (SNPs). SNP can be characterized as a substitution, insertion, or deletion at a single base position on a DNA strand. There is expected to be on average one SNP for every 1000 bases of the human genome, and some variations located in genes are suspected to alter both the protein structure and the expression level. Therefore, highly sensitive techniques with a simple procedure would be desirable for a high-throughput screening of millions of SNPs widely dispersed throughout the human genome. In this short review, we consider recently reported unique techniques for genotyping in a homogeneous solution, and organize them in terms of the chemical and physical processes accelerated on DNA. 相似文献
77.
A central limit theorem for a generalized Harper operator ona crystal lattice is obtained. As the limit, the continuoussemigroup of a uniform magnetic Schrödinger operator iscaptured on a vector space equipped with a special Euclideanstructure. The standard realization of the crystal lattice isa key to the Euclidean structure and a linear vector potentialon the Euclidean space from combinatorial data of the generalizedHarper operator. 相似文献
78.
[reaction: see text] When carbonyl compounds were allowed to react with phenyl trimethylsilyl selenide and tributylstannyl hydride in the presence of a catalytic amount of AIBN as a radical initiator, the hydrosilylation of the carbonyl compounds efficiently proceeded to give the corresponding silyl ethers in moderate to good yields. 相似文献
79.
Akira Sugimoto Takeshi Kotani Junko Tsujimoto Shigeo Yoneda 《Journal of heterocyclic chemistry》1989,26(2):435-438
In order to examine the “capto-dative” substitution-effect on the electrical conductivity, five compounds which have capto-dative substituents were prepared. Electron withdrawing (capto) group was nitro- or cyano-substituted phenyl and electron donating (dative) one was 5-methyl-5,10-dihydrophenazinyl moiety. The character of intramolecular electron donor acceptor complex of the five compounds were demonstrated by their uv spectra. Electron donor acceptor complexes of them with tetracyanoquinodimethane were prepared and their electrical resistivities were measured. 相似文献
80.
The reaction of oleanane triterpenoid 1b with a FeIII(PA; picolinate)3/H2O2/MeCN system (reagent system A), a simple model system for mono-oxygenase, gave the 11 alpha-hydroxyl derivative 3 as major product, along with 11-oxo derivative 4 and 12-oxo derivative 6. The reaction of lupane triterpenoid 2b with reagent system A gave only oxidative rearrangement compounds, (20R)-aldehyde 8 and (20S)-aldehyde 9 were epimeric isomers. Then, we have found that iron(III) picolinate complex, FeIII(PA)3 is efficient in effecting the rearrangement of triterpenoid epoxides 5 and 7 into the corresponding carbonyl compounds, 6, 8 and 9 with 1,2-shift of the hydride. 相似文献