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101.
[reaction: see text] Aryl ketones were reduced to the corresponding alcohols with excellent enantioselectivity (up to 99.7% ee) by Cl3SiH in the presence of a catalytic amount of N-formyl-alpha'-(2,4,6-triethylphenyl)-L-proline as an activator. Both carboxyl group at the alpha-position of the activator and 2,4,6-triethylphenyl group at the alpha'-position were critical for the high enantioselectivity. 相似文献
102.
Sueishi Y Yoshioka D Yoshioka C Yamamoto S Kotake Y 《Organic & biomolecular chemistry》2006,4(5):896-901
Using a competitive spin trapping method, relative spin trapping rates were quantified for various short-lived radicals (methyl, ethyl, and phenyl radicals). High static pressure was applied to the competitive spin-trapping system by employing high-pressure electron spin resonance (ESR) equipment. Under high pressure (490 bar), spin trapping rate constants for alkyl and phenyl radicals increased by 10 to 40%, and the increase was dependent on the structure of nitrone spin traps. A maximum increase was obtained when tert-butyl(4-pyridinylmethylene)amine N-oxide (4-POBN) was used as a spin trap. Activation volumes (DeltaDeltaV(double dagger)) for the two spin trapping reactions were calculated to be -17-(-9) cm(3) mol(-1) for the 4-POBN system. 相似文献
103.
Toshio Morikawa Xuezheng Li Eriko Nishida Seikou Nakamura Kiyofumi Ninomiya Hisashi Matsuda Yoshimi Oda Osamu Muraoka Masayuki Yoshikawa 《Helvetica chimica acta》2010,93(3):573-586
The MeOH extract from the flowers of Bellis perennis was found to show pancreatic‐lipase inhibitory activity (IC50 455 μg/ml). From the extract, seven new triterpene saponins named perennisaponins G ( 1 ; IC50 163 μM ), H ( 2 ; 137 μM ), I ( 3 ; 147 μM ), J ( 4 ; 148 μM ), K ( 5 ; 223 μM ), L ( 6 ; 81.4 μM ), and M ( 7 ; 195 μM ) were isolated as pancreatic lipase inhibitors. The stereostructures of 1 – 7 were elucidated on the basis of chemical and spectroscopic evidence. 相似文献
104.
Using a competitive nitric oxide (NO)-trapping method between Fe–dithiocarbamate (DTC) complexes and liposome-encapsulated
2-[4-trimethylammonio]-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide (TMAPTIO), NO-trapping rates of Fe–DTC complexes in
the presence of phosphatidylcholine liposomes were quantified for five kinds of Fe–DTC complexes. We investigated how the
DTC ligand structure influences the NO-trapping rates of Fe–DTC complexes. The negatively charged liposomes give a higher
NO-trapping rate of Fe–DTC complexes than do the positively charged ones, suggesting that the presence of a charge on the
liposome surface affects the NO-trapping rate processes of Fe–DTC complexes. In addition, on the basis of the pressure dependence
experiments for the competitive reaction, we evaluated the difference in activation volumes between the NO-trapping reactions
by Fe–DTC complexes and TMA-PTIO, which allowed us to consider possible reaction mechanisms for the NO-trapping processes. 相似文献
105.
Yoshimi Egawa Hikoe Enomoto Ralph J. Faudree Hao Li Ingo Schiermeyer 《Journal of Graph Theory》2003,43(3):188-198
It is shown that if G is a graph of order n with minimum degree δ(G), then for any set of k specified vertices {v1,v2,…,vk} ? V(G), there is a 2‐factor of G with precisely k cycles {C1,C2,…,Ck} such that vi ∈ V(Ci) for (1 ≤ i ≤ k) if or 3k + 1 ≤ n ≤ 4k, or 4k ≤ n ≤ 6k ? 3,δ(G) ≥ 3k ? 1 or n ≥ 6k ? 3, . Examples are described that indicate this result is sharp. © 2003 Wiley Periodicals, Inc. J Graph Theory 43: 188–198, 2003 相似文献
106.
Ochiai M Nishi Y Hashimoto S Tsuchimoto Y Chen DW 《The Journal of organic chemistry》2003,68(20):7887-7888
In the presence of triethylamine, (Z)-(2-acetoxy-1-alkenyl)phenyl-lambda(3)-iodanes react with thioureas or thioamides in MeOH to give 2,4-disubstituted thiazoles directly in good yields. The reaction probably involves generation of highly reactive alpha-lambda(3)-iodanyl ketones through ester exchange of the beta-acetoxy group with liberation of methyl acetate, followed by nucleophilic substitutions with thioureas or thioamides. 相似文献
107.
UV irradiation at 275 K of the highly dispersed V/Vycor oxide catalyst in the presence of NO leads to the formation of N2 and O2. The decomposition reaction of NO proceeds photocatafytically. In the presence of CH4, UV-irradiation of the catalyst at 275 K leads to the formation of C2H6 and C2H4, but this reaction is found to accompany the reduction of the catalyst as well as the formation of CH3 radicals. A dynamic photoluminescence study of the catalyst in the absence and presence of the reactants indicates that the
charge transfer excited triplet state of the surface vanadyl-species (V=O) plays a significant role in these photoinduced
reactions of NO and CH4. On the other hand, UV-irradiation of the catalyst at 275 K in the presence of a mixture of NO and CH4 leads to the formation of CH3OH in addition to the above products. The higher the ratio of NO/CH4 in the mixture is, the larger the yield of CH3OH becomes and the smaller the yields of C2H6 and C2H4 become, the reaction proceeding catalytically. Thus, the present results not only imply that the highly dispersed supported
vanadium oxide catalysts can be utilized as a potential photocatalyst for de-NOx-ing and/or methane activation at normal temperature
but also suggest that the photo-formed oxygen species from NO molecules plays a significant role in the photoinduced CH3OH formation from CH4 and NO on V/Vycor oxide catalysts at 275 K. 相似文献
108.
Mitsumori T Bendikov M Dautel O Wudl F Shioya T Sato H Sato Y 《Journal of the American Chemical Society》2004,126(51):16793-16803
We report here the synthesis, X-ray structures, optical and electrochemical properties, fabrication of light-emitting devices, and density functional calculations for indolizino[3,4,5-ab]isoindole (INI) derivatives. Strongly luminescent heterocycles based on the INI unit were synthesized by 1,3-dipolar cycloaddition reactions between pyrido[2,1-a]isoindole (PIS) and acetylene or ethylene derivatives. They are indolizino[3,4,5-ab]isoindoles 2-9 and 14-15, benzo[1',2'-1,2]indolizino[3,4,5-ab]isoindoles 10, pyridazino[4',5':1,2]indolizino[3,4,5-ab]isoindoles 12-13, and 2,3-hydropyridazino[4',5':1,2]indolizino[3,4,5-ab]isoindole-1,4-dione 11. The relative luminescence quantum yield can be as high as 90%. Their reduction and oxidation potentials and high luminescence can make these heterocycles possible alternatives to tris(8-hydroxyquinolinato)aluminum (Alq(3)). The brightness of the light-emitting device reached as high as 10(4) cd/m(2) and indolizino[3,4,5-ab]isoindole 3 emits beautifully blue light. The X-ray crystal structures of INI derivatives were obtained for the first time. The geometries obtained from X-ray data and density functional theory calculations shed more light on an interesting formally antiaromatic 16pi system, which is divided into 10pi and 6pi aromatic systems. We also report a relatively easy protonation of INI, which occurs at a carbon, rather than nitrogen atom. 相似文献
109.
Yoshimi Egawa Ralph J. Faudree Ervin Györi Yoshiyasu Ishigami Richard H. Schelp Hong Wang 《Graphs and Combinatorics》2000,16(1):81-92
Dirac and Ore-type degree conditions are given for a graph to contain vertex disjoint cycles each of which contains a previously
specified edge. One set of conditions is given that imply vertex disjoint cycles of length at most 4, and another set of conditions
are given that imply the existence of cycles that span all of the vertices of the graph (i.e. a 2-factor). The conditions
are shown to be sharp and give positive answers to conjectures of Enomoto in [3] and Wang in [5].
Revised: July 28, 1999 相似文献
110.
K. Yamamoto M. Yoshimi Y. Tawada Y. Okamoto A. Nakajima S. Igari 《Applied Physics A: Materials Science & Processing》1999,69(2):179-185
The performances of thin-film poly-Si solar cells with a thickness of less than 5 μm on a glass substrate have been investigated.
The cell of glass/back reflector/n-i-p type Si/ITO is well characterized by the structure of naturally surface texture and
enhanced absorption with a back reflector (STAR), where the active i-type poly-Si layer was fabricated by plasma chemical
vapor deposition (CVD) at low temperature. The cell with a thickness of 2.0 μm demonstrated an intrinsic efficiency of 10.7%
(aperture 10.1%), an open-circuit voltage of 0.539 V and a short-current density of 25.8 mA/cm2 as independently confirmed by Japan Quality Assurance. No light-induced degradation is observed. The optical and transport
properties of poly-Si cells are summarized.
Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 7 July 1999 相似文献