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61.
A. Yokoyama S. Morimoto T. Inoue J. Sanada H. Araki T. Saito H. Baba S. Shibata A. Shinohara T. Muroyama Y. Ohkubo 《Journal of Radioanalytical and Nuclear Chemistry》1999,239(1):143-149
Target-like products, that is,191–200Au,185–200Pt, and183–195Ir, from197Au target bombarded with12C ions at the energies of 180, 230, and 400 MeV/u were measured by using off-line gamma-ray spectrometry combined with chemical
separation procedures. Spallation systematics by Rudstam reproduces well the measured cross sections for formation of platinum
and iridium isotopes. It was found that the cross sections of gold nuclides increase with increase of the incident energy
in the range studied and they are enhanced if compared with the reported proton-induced reaction of gold at a similar incident
energy. It is suggested that the electromagnetic dissociation process plays a role for production of such gold nuclides. 相似文献
62.
Daisuke Suzuki Tomoyo Yamagata Koji Horigome Kiyoshi Shibata Akira Tsuchida Tsuneo Okubo 《Colloid and polymer science》2012,290(2):107-117
Influence of the gel size on the morphology, phase diagram, and reflection spectroscopy of the colloidal crystals of thermo-sensitive
gel spheres, poly (N-isopropylacrylamide) (pNIPAm), was discussed by adding the data of two gel samples of pNIPAm(400–5) and pNIPAm(600–5) of
412 nm (at 25 °C) and 220 nm (at 45 °C) and of 517 nm (at 20 °C) and 294 nm (at 45 °C), respectively. Colloidal single crystals
formed, but not so large compared with the giant crystals of small pNIPAm gels reported previously. The suspensions even with
ion-exchange resins were turbid and hard to observe the single crystals clearly with the naked eyes as gel size increased.
The critical concentration of melting decreased sharply as the suspensions were deionized with coexistence of the mixtures
of cation- and anion-exchange resins. The critical concentration increased as the gel size increased and/or dispersion temperature
increased. Density of the gel spheres increased as their size increased. These results demonstrated that the colloidal crystallization
takes place by the extended electrical double layers formed around the gel spheres in addition of the excluded volume effect of the gels. Contribution of the electrical double layers on the crystallization increased sharply as temperature increased
and gel concentration decreased, respectively. The contribution also increased slightly as sphere size increased, when comparison
was made at the same gel concentration in wt.%. The present work clarified that the colloidal interfaces, which are inevitable
for the formation of the electrical double layers, are formed between the water phase and gel spheres, though the gel spheres
contain a lot of water molecules at the inner sphere region. 相似文献
63.
Taniguchi S Kuroda K Doi K Tanabe M Shibata T Yoshida T Hatano T 《Chemical & pharmaceutical bulletin》2007,55(2):268-272
Gambir, the aqueous extract from Uncaria gambir (Rubiaceae), has been used as an astringent medicine in Asian countries. Investigation of the constituents in the extract led to the isolation of four chalcane-flavan dimers, gambiriin A1 (6), A2 (7), B1 (8), and B2 (9), in addition to (+)-catechin (1), (+)-epicatechin (2), and dimeric proanthocyanidins, procyanidin B1 (3), procyanidin B3 (4), and gambiriin C (5). The spectroscopic and chemical data obtained in the present study indicated that their previously proposed structures 6a, 7a, 8a, and 9a should be revised to 6, 7, 8, and 9, respectively. 相似文献
64.
Total Synthesis of cis‐Clavicipitic Acid from Asparagine via Ir‐Catalyzed CH bond Activation as a Key Step 下载免费PDF全文
Yu‐ki Tahara Mamoru Ito Dr. Kyalo Stephen Kanyiva Prof. Dr. Takanori Shibata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(32):11340-11343
4‐Substituted tryptophan derivatives and the total synthesis of cis‐clavicipitic acid were achieved in reactions in which Ir‐catalyzed C?H bond activation was a key step. The starting material for these reactions is asparagine, which is a cheap natural amino acid. The reductive amination step from the 4‐substituted tryptophan derivative gave cis‐clavicipitic acid with perfect diastereoselectivity. 相似文献
65.
Shuichi Nakamura Masashi Hayashi Yasutoshi Kamada Ryosuke Sasaki Yuichi Hiramatsu Norio Shibata Takeshi Toru 《Tetrahedron letters》2010,51(29):3820-3823
A catalytic enantioselective desymmetrization of meso-N-(heteroarenesulfonyl)aziridines with TMSN3 using chiral Lewis acids afforded products with high enantioselectivity. As proof of the utility of this procedure, the precursor of selective κ-opioid agonist (1S,2S)-(−)-U-50,488 was synthesized. 相似文献
66.
Sentaro Okamoto Hiroyuki Ishikawa Yoshimi Shibata Yu-ichiro Suhara 《Tetrahedron letters》2010,51(43):5704-5707
In the presence of a catalytic amount of 1,2-disubstituted or 1,2,3-trisubstituted imidazolium salts, γ-substituted allyl chlorides reacted with alkyl Grignard reagents to undergo substitution reactions in an SN2′-selective fashion, where the magnesium ate complexes [(N-heterocyclic carbene-MgR3)−(MgX)+] of imidazol-2-ylidenes or imidazol-4-ylidenes, generated in situ, were postulated as the active species. It was observed that the reactions with imidazol-4-ylidene catalysts were faster than those with imidazol-2-ylidenes. Enantioselective catalysis using a chiral imidazolium salt was preliminarily investigated. 相似文献
67.
Suzuka Kinoshita Ryota Yamano Dr. Yu Shibata Yusuke Tanaka Kyoichi Hanada Dr. Takashi Matsumoto Prof. Dr. Kazunori Miyamoto Dr. Atsuya Muranaka Prof. Dr. Masanobu Uchiyama Prof. Dr. Ken Tanaka 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(27):11113-11120
An S-shaped double helicene-like molecule (>99 % ee), possessing stable helical chirality, has been synthesized by the rhodium(I)/difluorphos complex-catalyzed highly diastereo- and enantioselective intramolecular double [2+2+2] cycloaddition of a 2-naphthol- and benzene-linked hexayne. The collision between two terminal naphthalene rings destabilizes the helical chirality of the S-shaped double helicene-like molecule, but the introduction of two additional fused benzene rings significantly increases the configurational stability. Thus, no epimerization and racemization were observed even at 100 °C. The enantiopure S-shaped double helicene-like molecule forms a trimer through the multiple C−H⋅⋅⋅π and C−H⋅⋅⋅O interactions in the solid-state. The trimers stack to form columnar packing structures, in which neighboring stacks have opposite dipole directions. The accumulation of helical structures in the same direction in the S-shaped double helicene-like molecule enhanced the chiroptical properties. 相似文献
68.
Shibghatullah Muhammady Fatimah A. Noor Rena Widita Yudi Darma 《International journal of quantum chemistry》2020,120(16):e26268
We study the structural, electronic, and magnetic properties of monolayer α-PbO0.875A0.125 (A = N, F), which are calculated using first principles. As a result, N doping induces local ferromagnetism centered at the N2− site, originating from the spin-down N 2p valence states. On the other hand, F doping induces nonmagnetism and induces ab-plane deformation, where F− receives one electron to its nearest-neighboring Pb1.75+ ions. N doping redshifts the bandgap of the undoped system and transforms it to be indirect, while F doping blueshifts the bandgap through the Burstein-Moss effect. The hybridization of Pb 6p and O 2p orbitals is stronger near the A site than that of the crystal structure edge. Our result shows new insights, predicting possible experimental results for future functional device applications. 相似文献
69.
The deformation of fresh and aged polybutene-1 spherulitic samples has been investigated by microscopic observation, interferometry, studying macroscopic and spherulitic birefringence changes, and study of light-scattering patterns. The spherulite deformation is not affine, the microscopic deformation ratio being less than the macroscopic deformation ratio of the sample and greater in the equatorial regions of the spherulite than in the polar regions. The deviation from affine deformation is less for fresh spherulites than for the aged, where void formation occurs in the equatorial part of the spherulite. This gives rise to large scattering by this part of the spherulite and to form birefringence. The spherulite birefringence and its change with elongation is dependent upon the degree of aging of the sample. The spherulite birefringence is more negative for the aged sample. In the polar regions of the spherulite, this negative birefringence decreases and turns positive at higher elongations, characteristic of a reorientation of the crystals with their optic axes turning from being perpendicular to parallel to the spherulite radius. The spherulite birefringence in the equatorial direction becomes somewhat more negative on stretching a fresh sample but less negative on stretching an aged one. Spherulite distortion and orientation changes are apparent from the light-scattering patterns of films possessing small spherulites. The changes in Vv and Hv scattering patterns upon stretch are different for the fresh and aged samples. The Vv patterns of the fresh samples decrease in intensity with time after stretching a fresh sample with the Hv patterns do not. 相似文献
70.
Stereoselective catalytic synthesis of 3-trifluoromethyl indolines through the [4+1] cycloaddition of benzoxazinones and sulfur ylides in a transition-metal-free manner was developed. In the presence of a catalytic amount of sodium hydride, aza-ortho-quinone methide intermediates were formed from trifluoromethyl benzoxazinones through decarboxylation after the first nucleophilic attack of sulfur ylides, which progressed to a second nucleophilic attack of sulfur ylides, resulting in the [4+1] cycloaddition. The key for this catalytic transformation is the dual attack of sulfur ylides on substrates. This unique transition-metal-free protocol is applicable to the synthesis of non-fluorinated vinyl-, ethynyl- or methyl-substituted indolines. The synthesis of 3-trifluoromethyl indoles was also achieved described under stoichiometric conditions. 相似文献