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201.
First-principles molecular-dynamics simulations of a hydrated electron in normal and supercritical water 总被引:1,自引:0,他引:1
A first principles study of a hydrated electron in water at ordinary and supercritical conditions is presented. In the first case, the electron cleaves a cavity in the hydrogen bond network in which six H2O molecules form the solvation shell. The electron distribution assumes an ellipsoidal shape, and the agreement of the computed and the experimental optical absorption seems to support this picture. At supercritical conditions, instead, the H-bond network is not continuous and allows us to predict that the electron localizes in preexisting cavities in a more isotropic way. Four water molecules form the solvation shell but the localization time shortens significantly. 相似文献
202.
Tatsuhiko Kanmera Haruhiko Aoyagi Michinori Waki Tetsuo Kato Nobuo Izumiya Kosaku Noda Tamio Ueno 《Tetrahedron letters》1981,22(37):3625-3628
Syntheses of cyclotetradepsipeptides, AM-toxin III and two analogs, were achieved, in which the Hofmann degradation method was used in order to derive a dehydroalanine residue from a 2,3-diaminopropionic acid residue in cyclodepsipeptide precursors. 相似文献
203.
Stereochemistry of β-hydroxydodecanoyl thioester dehydration catalyzed by fatty acid synthetase from
Kazuki Saito Akihiko Kawaguchi Yousuke Seyama Tamio Yamakawa Shigenobu Okuda 《Tetrahedron letters》1982,23(16):1689-1692
The -4 hydrogen of -α,β-dodecenoyl thioester was abstracted and a proton was added to the 2- face during the prototropic isomerization catalyzed by β-hydroxydodecenoyl thioester dehydrase. 相似文献
204.
205.
Wavelength dependence as well as relative humidity dependence of aerosol extinction to backscatter ratio was examined. The extinction to backscatter ratio is essential in solving lidar signal and was estimated from aerosol size distribution and refractive index (which were derived from angular light scattering measurements) using the Mie scattering theory. The extinction to backscatter ratios were calculated for wavelengths of 355 nm, 532 nm, 694 nm and 1064 nm, the major laser wavelengths used for lidars, where the refractive indices were assumed to be constant with wavelength. p ]When relating the aerosol extinction
1 to the backscatter
1 with a functional form of
1
1
k
1, the exponentk
1 was evaluated by the least square method and tabulated for the four wavelengths. The extinction to backscatter ratio defined asS
1=
1/
1 was calculated and their dependence on the wavelength and relative humidity was examined. Their dependence on the relative humidity is small whileS
1 in the average takes the value of 66 (±17), 60 (±13), 52 (±13) and 42 (±11) for the wavelengths 355 nm, 532 nm, 694 nm and 1064 nm, respectively 相似文献
206.
Sesquiterpenes and alkaloids from Lindera chunii and their inhibitory activities against HIV-1 integrase 总被引:4,自引:0,他引:4
Zhang CF Nakamura N Tewtrakul S Hattori M Sun QS Wang ZT Fujiwara T 《Chemical & pharmaceutical bulletin》2002,50(9):1195-1200
Three new eudesmane type sesquiterpenoid lindenanolides E (1), F (2) and G (3), and two new aporphine alkaloid lindechunines A (18) and B (20) were isolated from roots of Lindera chunii MERR., together with seven known sesquiterpenes including a new naturally-occurring lindenanolide H (4) and eight known aporphine alkaloids. The structures of these compounds were determined by spectroscopic means. Of the isolated compounds, hernandonine (14), laurolistine (16), 7-oxohernangerine (17) and lindechunine A (18) showed significant anti-human immunodeficiency virus type 1 (HIV-1) integrase activity with IC(50) values of 16.3, 7.7, 18.2 and 21.1 microM, respectively. The major alkaloids presented in the roots of L. chunii were quantitatively analyzed by an HPLC method. 相似文献
207.
New axially chiral 2,2'-bipyridine N,N'-dioxides 1 were obtained in an enantiomerically pure form by way of cyclic diesters 6 or 7 which were formed by the esterification of diols 2 with (R)-2,2'-bis(chlorocarbonyl)-1,1'-binaphthalene (5). Epimerization of the kinetic products at the ester formation (R(nap),S(pyr))-6 to the thermodynamically stable isomers (R(nap),R(pyr))-7 was observed in refluxing toluene or in the presence of trifluoroacetic acid. One of the N,N'-dioxides 1a which is substituted with phenyl groups at the 6 and 6' positions was found to be highly catalytically active and enantioselective for the asymmetric allylation of aldehydes with allyl(trichloro)silane giving homoallyl alcohols. 相似文献
208.
Shin Tsuge Yoshihiro Sugimura Tamio Nagaya 《Journal of Analytical and Applied Pyrolysis》1980,1(3):221-229
In order to obtain quantitatively specific and high-resolution pyrograms of high polymers, fundamental splitting conditions for pyrolysis—gas chromatography were studied using a vertical micro-furnace type of pyrolyzer attached to a glass capiliary separation column. High-resolution pyrograms were measured for polyolefins such as polyethylenes (PE), polypropylenes (PP) and various kinds of ethylen—propylene copolymers [P(E-co-P)] using a pyrolysis—hydrogenation device. Microstructures such as short branchings for PE, stereoregularities and chemical inversions for PP and sequence distributions for P(E-co-P) are discussed on the basis of the pyrograms. 相似文献
209.
Hayashi T Takahashi M Takaya Y Ogasawara M 《Journal of the American Chemical Society》2002,124(18):5052-5058
The catalytic cycle of asymmetric 1,4-addition of phenylboronic acid to an alpha,beta-unsaturated ketone catalyzed by a rhodium-binap complex was established by use of RhPh(PPh(3))(binap) as a key intermediate. The reaction proceeds through three intermediates, phenylrhodium, oxa-pi-allylrhodium, and hydroxorhodium complexes, all of which were observed in NMR spectroscopic studies. The transformations between the three intermediates, that is, insertion, hydrolysis, and transmetalation, were also observed. On the basis of the catalytic cycle, a more active chiral catalyst, [Rh(OH)(binap)](2), was found and used successfully for the asymmetric 1,4-addition reactions. 相似文献
210.
Hayashi T Yamasaki K Mimura M Uozumi Y 《Journal of the American Chemical Society》2004,126(10):3036-3037
The stereochemical pathway (syn or anti) of the oxypalladation step was studied in the palladium(II)-catalyzed Wacker-type cyclization of stereospecifically deuterated 6-(2-hydroxyphenyl)-3-deuteriocyclohexenes, cis-3-d-1 and trans-3-d-1, giving dihydrobenzofuran derivatives. The stereochemistry was determined to be syn in the reaction catalyzed by a dicationic palladium(II) catalyst generated from Pd(MeCN)4(BF4)2 and (S,S)-ip-boxax in the presence of benzoquinone in methanol, while it is mainly anti in the reaction catalyzed by PdCl2(MeCN)2 in the presence of a chloride ion. 相似文献