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排序方式: 共有161条查询结果,搜索用时 250 毫秒
1.
2.
Kô Kaneko Mikako Tanaka Kimiaki Haruki Nobuaki Naruse Hiroshi Mitsuhashi 《Tetrahedron letters》1979,20(39):3737-3740
The 13C-NMR spectra of seven cavanine alkaloids isolated from Veratrum and Fritillaria plants were measured and their signals were assigned, and these results were applicated for structure elucidation of two new cevanine alkaloids, baimonidine and isoverticine, isolated from mature Fritillaria verticillata. 相似文献
3.
Yuji Naruse Atsushi Takamori Itsuki Nagasawa 《Phosphorus, sulfur, and silicon and the related elements》2020,195(7):523-525
AbstractWe previously designed and prepared the first molecules to exhibit observable CD spectra by n-σ* excitation, 2,6-dithiaspiro[3.3]heptane 2,6-dioxide. Spiro[3.3]heptane frameworks possess axial asymmetry due to puckering of 2 four-membered rings; the ring bonds are rich in p-character due to acute bond angles, which lowers the σ* energy levels. In contrast, the lone pairs are rich in s-character, which results in a good donor with conformational fixation. We expected that, instead of lone pairs as donating orbitals, the use of σ-electron-donating Si-Si bonds should result in UV absorption in the observable range (>180?nm), so that the Cotton effect could appear, at least partially, in that range. We designed 2,6-disilyl-2,6-disilaspiro[3.3]heptanes as models, and performed theoretical calculations to confirm our idea. 相似文献
4.
Lithium trialkylalkynylborates (1) react with oxiranes (2) to give non-isolable intermediates 3 which subsequently afford either γ-hydroxyketones 5, trisubstituted ethylenes of homoallylic alcohol type 6 or a tetrasubstituted ethylene 7 upon appropriate treatment with NaOH/H2O2, AcOH or NaOH/I2, respectively. The reaction of oxiranes with 1 proceeds in high regioselectivity and the resulting homoallylic alcohols 6 are of nearly 100% (E) configuration. A straight chain γ-hydroxyketone 16 is obtained in the reaction of methyloxirane with the ate-complex (1), which has been prepared from lithium acetylide ethylenediamine complex and trihexylborane. 相似文献
5.
Selective chemical treatment of cellular microdomains using multiple laminar streams 总被引:1,自引:0,他引:1
Takayama S Ostuni E LeDuc P Naruse K Ingber DE Whitesides GM 《Chemistry & biology》2003,10(2):123-130
There are many experiments in which it would be useful to treat a part of the surface or interior of a cell with a biochemical reagent. It is difficult, however, to achieve subcellular specificity, because small molecules diffuse distances equal to the extent of the cell in seconds. This paper demonstrates experimentally, and analyzes theoretically, the use of multiple laminar fluid streams in microfluidic channels to deliver reagents to, and remove them from, cells with subcellular spatial selectivity. The technique made it possible to label different subpopulations of mitochondria fluorescently, to disrupt selected regions of the cytoskeleton chemically, to dislodge limited areas of cell-substrate adhesions enzymatically, and to observe microcompartmental endocytosis within individual cells. This technique does not require microinjection or immobilization of reagents onto nondiffusive objects; it opens a new window into cell biology. 相似文献
6.
Takashi Yokoyama Kazuhiro Ikemoto Takatsugu Kihara Kouhei Teramura Keisuke Uryu Kohji Shimizu Motoki Bitoh Kohji Matsuzaki Michio Zenki 《Journal of solution chemistry》2006,35(5):639-657
Coordination equilibrium constants (K
NiS) of some donor solvent molecules to 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecanenickel(II) ([Ni(Me4[12]aneN4)]2+) were determined in nitrobenzene (a noncoordinating bulk solvent). The first (K
NiS1) and second stepwise coordination equilibrium constants (K
NiS2) for 1,4,7,10-tetraazacyclododecanenickel(II) ([Ni([12]aneN4)]2+), 1,4,8,11-tetraazac yclotetradecane- nickel(II) ([Ni([14] aneN4)]2+), 1,4,8,11-tetrathiacyclotetra-decanenickel(II) ([Ni([14]aneS4)]2+) were also reinvestigated. The K
NiS values for [Ni(Me4[12]aneN4)]2+ were compared to those of [Ni([12]aneN4)]2+, (1R,4S, 8R,11S)-1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecanenickel(II) (R,S,R,S-[Ni(Me4[14]aneN4)]2+), R,R,S,S-[Ni(Me4[14]aneN4)]2+, [Ni([14]aneN4)]2+, and [Ni([14]aneS4)]2+. Coordination of pyridine (Py), N,N,N′,N′-tetramethylurea (TMU), and N,N-dimethylacetamide (DMA) to [Ni(Me4[12]aneN4)]2+ was observed, although these donor solvent molecules did not coordinate to R,S,R,S-[Ni(Me4[14]aneN4)]2+. The K
NiS values for Py, TMU, and DMA are 7.9, 2.8, and 9.0 dm3⋅mol−1, respectively. Some hydrogen-bonding waters were coordinated to R,S,R,S-[Ni(Me4[14]aneN4)]2+, but such waters did not coordinate to [Ni(Me4[12] aneN4)]2+. Also, the K
NiS2 values were larger than the corresponding K
NiS1 values for [Ni([14]aneS4)]2+. Furthermore, the K
NiS1 values for [Ni([12]aneN4)]2+ were the largest among these nickel(II) complex cations. The K
NiS, K
NiS1, and K
NiS2 values are discussed in terms of properties of the donor solvents and steric strains of these nickel(II) complex cations. 相似文献
7.
8.
The studies of J. A. Ramírez, Hino–Ramírez, and Ariyoshi–Hino showed that an integrated version of Varadhan’s asymptotics holds for Markovian semigroups associated with arbitrary strong local symmetric Dirichlet forms. In this paper, we consider non-symmetric bilinear forms that are the sum of strong local symmetric Dirichlet forms and lower-order perturbed terms. We give sufficient conditions for the associated semigroups to have asymptotics of the same type. 相似文献
9.
We present tamper resistance in optical excitation transfer via optical near-field interactions based on the energy dissipation process occurring locally in nanometric devices such as quantum dots. A theoretical comparison with electrical systems is also shown, focusing on the required environmental conditions. Numerical simulations based on virtual photon models demonstrate high tamper resistance. 相似文献
10.
Koga T Seo YS Zhang Y Shin K Kusano K Nishikawa K Rafailovich MH Sokolov JC Chu B Peiffer D Occhiogrosso R Satija SK 《Physical review letters》2002,89(12):125506
We report an anomalous swelling of polymer thin films in carbon dioxide (CO(2)) which is associated (in both locus and form) with the density fluctuation ridge that forms along the extension of the coexistence curve of gas and liquid in the P-T phase diagram. Neutron reflectivity results showed that CO(2) could be sorbed to a large extent ( approximately 60%) in thin polymer films even when the bulk miscibility of the polymer with CO(2) is very poor. The anomalous swelling is found to scale with the polymer radius of gyration (R(g)) and extends to a distance approximately 10 R(g). 相似文献