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991.
Quantum‐chemical analyses of aromaticity,UV spectra,and NMR chemical shifts in plumbacyclopentadienylidenes stabilized by Lewis bases 下载免费PDF全文
Toshiaki Kawamura Minori Abe Masaichi Saito Masahiko Hada 《Journal of computational chemistry》2014,35(11):847-853
We carried out a series of zeroth‐order regular approximation (ZORA)‐density functional theory (DFT) and ZORA‐time‐dependent (TD)‐DFT calculations for molecular geometries, NMR chemical shifts, nucleus‐independent chemical shifts (NICS), and electronic transition energies of plumbacyclopentadienylidenes stabilized by several Lewis bases, (Ph)2(tBuMe2Si)2C4PbL1L2 (L1, L2 = tetrahydrofuran, Pyridine, N‐heterocyclic carbene), and their model molecules. We mainly discussed the Lewis‐base effect on the aromaticity of these complexes. The NICS was used to examine the aromaticity. The NICS values showed that the aromaticity of these complexes increases when the donation from the Lewis bases to Pb becomes large. This trend seems to be reasonable when the 4n‐Huckel rule is applied to the fractional π‐electron number. The calculated 13C‐ and 207Pb‐NMR chemical shifts and the calculated UV transition energies reasonably reproduced the experimental trends. We found a specific relationship between the 13C‐NMR chemical shifts and the transition energies. As we expected, the relativistic effect was essential to reproduce a trend not only in the 207Pb‐NMR chemical shifts and J[Pb‐C] but also in the 13C‐NMR chemical shifts of carbons adjacent to the lead atom. © 2014 Wiley Periodicals, Inc. 相似文献
992.
Aplysiasecosterol A: A 9,11‐Secosteroid with an Unprecedented Tricyclic γ‐Diketone Structure from the Sea Hare Aplysia kurodai 下载免费PDF全文
Atsushi Kawamura Prof. Dr. Masaki Kita Prof. Dr. Hideo Kigoshi 《Angewandte Chemie (International ed. in English)》2015,54(24):7073-7076
A new 9,11‐secosteroid having an unprecedented tricyclic γ‐diketone structure, aplysiasecosterol A ( 1 ), was isolated from the sea hare Aplysia kurodai. The structure was determined by one‐ and two‐dimensional NMR spectroscopic analysis, molecular modeling studies, a comparison of experimental and calculated ECD spectra, and a modified Mosher′s method. Aplysiasecosterol A ( 1 ) exhibited cytotoxicity against human myelocytic leukemia HL‐60 cells. A biosynthetic pathway for 1 from a known cholesterol was proposed and includes twice α‐ketol rearrangements and an intramolecular acetalization. 相似文献
993.
CH Activation Generates Period‐Shortening Molecules That Target Cryptochrome in the Mammalian Circadian Clock 下载免费PDF全文
Tsuyoshi Oshima Dr. Iori Yamanaka Dr. Anupriya Kumar Dr. Junichiro Yamaguchi Dr. Taeko Nishiwaki‐Ohkawa Kei Muto Rika Kawamura Dr. Tsuyoshi Hirota Prof. Dr. Kazuhiro Yagita Prof. Dr. Stephan Irle Prof. Dr. Steve A. Kay Prof. Dr. Takashi Yoshimura Prof. Dr. Kenichiro Itami 《Angewandte Chemie (International ed. in English)》2015,54(24):7193-7197
The synthesis and functional analysis of KL001 derivatives, which are modulators of the mammalian circadian clock, are described. By using cutting‐edge C? H activation chemistry, a focused library of KL001 derivatives was rapidly constructed, which enabled the identification of the critical sites on KL001 derivatives that induce a rhythm‐changing activity along with the components that trigger opposite modes of action. The first period‐shortening molecules that target the cryptochrome (CRY) were thus discovered. Detailed studies on the effects of these compounds on CRY stability implicate the existence of an as yet undiscovered regulatory mechanism. 相似文献
994.
T. Inoue S. Ando T. Aoki H. Arikawa S. Ezure K. Harada T. Hayamizu T. Ishikawa M. Itoh K. Kato H. Kawamura A. Uchiyama T. Aoki K. Asahi T. Furukawa A. Hatakeyama K. Hatanaka K. Imai T. Murakami H. S. Nataraj T. Sato Y. Shimizu T. Wakasa H. P. Yoshida A. Yoshimi Y. Sakemi 《Hyperfine Interactions》2015,231(1-3):157-162
995.
Takayuki Atago Akihiro Tanaka Tomoyuki Kawamura Noritada Matsuo Yoo Tanabe 《Tetrahedron: Asymmetry》2009,20(9):1015-1019
We have developed an efficient practical resolution method for (1R,3R)-trans-chrysanthemic acid 1 and (1R,3S)-trans-2,2-dimethyl-3-(2,2-dichloroethenyl)cyclopropanecarboxylic acid 2, based on the preliminary results of the simpler analogues, (1R)-2,2-dichlorocyclopropanecarboxylic acid 3 and (1R)-2,2-dimethylcyclopropanecarboxylic acid 4, using a crystalline-liquid separation procedure (without column chromatography) with chiral 1,1′-binaphthol monoethyl ethers (R)-5b as the key auxiliary. Direct esterifications of 1, 2, 3, and 4 with (R)-5b gave four sets of (1R)- and (1S)-diastereomeric esters 8, 9, 6, and 7, respectively, with markedly different melting points. All of these diastereomers were easily obtained using a simple and one-step crystalline-liquid separation. The separated diastereomers 8 and 9 were easily hydrolyzed to the desired enantiopure acids 1 (>98%) and 2 (>99%), respectively, with recovery of (R)-5b (>90%). 相似文献
996.
Wide and small-angle X-ray scattering measurements were made, as well as differential scanning calorimetry, for amorphous Pd80Si20 before and after irradiation by neutrons (5 × 1020 neutrons/cm2, > 1 Mev), and the structural changes thereby produced are described.Before irradiation the structure is well assimilated with a dense random packing (DRP) structure except that the coherence between neighboring Pd atoms extends farther than expected from the DRP structure, the coherent length estimated from the X-ray scattering being about 8 Å.With irradiation the coherent regions of 8 Å diameter get separated from each other by a mean distance of 20 Å, thus producing structural inhomogeneities which do not exist at all before irradiation. The glass transition temperature is found to be increased by about 10 K after irradiation.The effects of irradiation are interpreted as being due to the structural imperfections produced by particle bombardment. The DPR structure is adopted as a model structure for the perfect amorphous solids. 相似文献
997.
T. Hakata H. Ohyama E. Simoen C. Claeys K. Miyahara K. Kawamura Y. Ogita Y. Takami 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(2):357-360
Results are presented of a study on the degradation and recovery of the electrical performance of MOSFETs processed on SIMOX
substrates, subjected to 1 and 2 MeV electron and to 20 MeV alpha-ray irradiations. The damage coefficient for alpha-ray irradiation
is about three orders of magnitude larger than the one for electron irradiation, which is attributed to the difference of
incident particle mass and the possibility of nuclear collision during radiation damage. 相似文献
998.
K. Ishida K. Nagamine T. Matsuzaki N. Kawamura S. N. Nakamura Y. Matsuda M. Kato H. Sugai M. Tanase K. Kudo N. Takeda G. H. Eaton 《Hyperfine Interactions》2001,138(1-4):225-234
Precise measurements of the absolute yields and the disappearance rates were carried out for both the X-rays from the (αμ)+ ion formed by muon to alpha sticking after the muon catalyzed fusion and for the fusion neutrons from 3He-free liquid and solid D/T mixtures. While the αμ X-ray yield does not contradict the values predicted by the atomic-process
theories, the effective sticking probability (ω
s
) obtained by neutron measurement is much smaller than that from any of the calculations published so far, suggesting, e.g.,
enhanced reactivation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
999.
The present paper considers the existence of continuous roots of algebraic equations with coefficients being continuous functions defined on compact Hausdorff spaces. For a compact Hausdorff space X, C(X) denotes the Banach algebra of all continuous complex-valued functions on X with the sup norm ∥⋅∥∞. The algebra C(X) is said to be algebraically closed if each monic algebraic equation with C(X) coefficients has a root in C(X). First we study a topological characterization of a first-countable compact (connected) Hausdorff space X such that C(X) is algebraically closed. The result has been obtained by Countryman Jr, Hatori-Miura and Miura-Niijima and we provide a simple proof for metrizable spaces.Also we consider continuous approximate roots of the equation zn−f=0 with respect to z, where f∈C(X), and provide a topological characterization of compact Hausdorff space X with dimX?1 such that the above equation has an approximate root in C(X) for each f∈C(X), in terms of the first ?ech cohomology of X. 相似文献
1000.
Shuyang Cao Shigehira Ozono Yukio Tamura Yaojun Ge Hironori Kikugawa 《Journal of Fluids and Structures》2010,26(5):685-702
Three-dimensional Direct Numerical Simulation (DNS) and Large Eddy Simulation (LES) are performed to investigate the shear effects on flow around a circular cylinder at Reynolds numbers of Re=60–1000. The shear parameter, β, which is based on the velocity gradient, cylinder diameter and upstream mean velocity at the center plane of the cylinder, varies from 0 to 0.30. Variations of Strouhal number, drag and lift coefficients, and unsteady wake structures with shear parameter are studied, along with their dependence on Reynolds number. The presented simulation provides detailed information for the flow field around a circular cylinder in shear flow. This study shows that the Strouhal number exhibits no significant variation with shear parameter. The stagnation point moves to the high-velocity side almost linearly with shear parameter, and this result mainly influences the aerodynamic forces acting on a circular cylinder in shear flow. Both the Reynolds number and shear parameter influence the movement of the stagnation point and separation point. Mode A wake instability is suppressed into parallel vortex shedding mode at a certain shear parameter. The lift force increases with increasing shear parameter and acts from the high-velocity side to the low-velocity side. In addition, a simple method to estimate the lift force coefficient in shear flow is provided. 相似文献