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71.
4-Monodeuterated NAD(P)H model compounds (1,4,6,7-tetrahydro-1,6,11-trimethyl-5-oxo-5H-benzo[c]pyrido[2,3-e]az epin; 11Me-MMPAH) have been oxidized with a series of p-benzoquinone and its derivatives in the presence of Mg2+. The models have an axial chirality with respect to the orientation of carbonyl dipole, the dihedral angle of which is larger than 55 degrees out of the plane of dihydropyridine ring. Without Mg2+, the anti- (with respect to the carbonyl dipole) hydrogen is 3 to 32 times more reactive than the corresponding syn-hydrogen, whereas, when Mg2+ is present in the system, the selectivity is shifted toward the syn-preferency. Mg2+ plays the role of a Lewis acid catalyst to control the stereochemistry at the same time as it catalyzes the reaction. 相似文献
72.
Tawada Y Tsuneda T Yanagisawa S Yanai T Hirao K 《The Journal of chemical physics》2004,120(18):8425-8433
We apply the long-range correction (LC) scheme for exchange functionals of density functional theory to time-dependent density functional theory (TDDFT) and examine its efficiency in dealing with the serious problems of TDDFT, i.e., the underestimations of Rydberg excitation energies, oscillator strengths, and charge-transfer excitation energies. By calculating vertical excitation energies of typical molecules, it was found that LC-TDDFT gives accurate excitation energies, within an error of 0.5 eV, and reasonable oscillator strengths, while TDDFT employing a pure functional provides 1.5 eV lower excitation energies and two orders of magnitude lower oscillator strengths for the Rydberg excitations. It was also found that LC-TDDFT clearly reproduces the correct asymptotic behavior of the charge-transfer excitation energy of ethylene-tetrafluoroethylene dimer for the long intramolecular distance, unlike a conventional far-nucleus asymptotic correction scheme. It is, therefore, presumed that poor TDDFT results for pure functionals may be due to their lack of a long-range orbital-orbital interaction. 相似文献
73.
Masataka Hiraide Kennich Ishikawa Zuo Sheng Chen Hiroshi Kawaguchi 《Mikrochimica acta》1994,117(1-2):7-13
Coprecipitation first with magnesium hydroxide, next with tin(IV) hydroxide is developed for the determination of traces of beryllium in sea-water. To a 200-ml sample is added a sodium hydroxide solution to form magnesium hydroxide at pH 11.5, on which beryllium is quantitatively coprecipitated. The precipitate is separated by centrifugation and dissolved in 2 ml of 12 mol/l hydrochloric acid. The resulting solution (ca. 10 ml) is mixed with 2 mg of tin (IV) carrier and the pH is adjusted to 5.0 to collect the beryllium on tin (IV) hydroxide, leaving magnesium ions in the solution. The tin (IV) hydroxide is centrifuged, dissolved in 0.1 ml of 5 mol/l hydrobromic acid, and then diluted to 1 ml with water. Magnesium is so added as to be 500 g/ml for increasing the sensitivity about four times, and the beryllium in the solution is determined by graphite furnace atomic absorption spectrometry. The experiments with synthetic seawater samples showed that pg — g amounts of beryllium can be coprecipitated on the metal hydroxides and beryllium at the low ng/1 level can be determined with reasonable precision (RSD < 10%). The detection limit of the proposed method is 0.5 ng/l of beryllium in seawater. 相似文献
74.
Diterpenes from the roots of Euphorbia kansui and their in vitro effects on the cell division of Xenopus (part 2) 总被引:2,自引:0,他引:2
Four new ingenane-type diterpenes, 3-O-(2,3-dimethylbutanoyl)-13-O-dodecanoyl-20-O-acetylingenol (1), 3-O-(2,3-dimethylbutanoyl)-13-O-dodecanoyl-20-deoxyingenol (2), 3-O-(2E,4Z-decadienoyl)-20-deoxyingenol (3), and 3-O-(2E,4E-decadienoyl)-20-deoxyingenol (4), two new jatrophane-type diterpenes, kansuinins D (9) and E (10), and four known ingenane-type diterpenes were isolated from the root of Euphorbia kansui. Their structures were elucidated by spectroscopic and chemical analysis, and individual Xenopus cells at the blastular stage were cultured with the diterpenes to test for biological activity. 20-Deoxyingenol diterpenes 3 and 4 induced the greatest cell cleavage arrest (0.5 micro g/ml of each compound resulted in >75% cleavage arrest), but cell cleavage inhibitory activity became weak when C-16 had an acyl residue. In contrast, the jatrophane diterpene kansuinin D (9) showed no activity. 相似文献
75.
Toru Tachihara Susumu Ishizaki Yoshiko Kurobayashi Hiroshi Tamura Youichi Ikemoto Atsushi Onuma Keisuke Yoshikawa Tetsuya Yanai Takeshi Kitahara 《Helvetica chimica acta》2003,86(2):274-279
All possible stereoisomers of imine derivatives 1 – 4 , which have the characteristic roast odor of seafood, were synthesized. As a result of odor evaluation of all isomers, we found that each isomer has a different and characteristic odor of roasted seafood. 相似文献
76.
In order to develop tumor-localizing fluorescent diagnostic agents without phototoxicity, various heterodimers linked by some spacers between a chlorine derivative and its Mn or Cu complex were synthesized. The representative agent of them was named HAT-D01 and has a molecular formula of m -phthalyl-{[13,17-bispropanoic acid-3-ethenyl-8-formylethylidene-7-hydroxy-2,7,12,18-tetramethyl-porphyrinate]-manganese (III)}-[3'-ethenyl-8'-formylethylidene-7'-hydroxy-2',7', 12', 18'-tetramethyl-porphine-13', 17'-bispropanoyl aspartic acid]-bishydrazone. 相似文献
77.
A procedure is described for recording evolved gas detection (thermal desorption spectra) of various FeOOH samples up to 400°. Characteristic curves of -,- and-FeOOH are discussed, based on the crystallographic structure which governs the sites for physisorbed H2O as well as OH groups producing H2O by dehydration. Examinations are also made of the variations of the desorption spectra with the progress of crystallization for -FeOOH, and with the distortion of the crystal structure caused by the addition of Cu(II) to -, - and-FeOOH. 相似文献
78.
Susumu Ohshiro 《Tetrahedron》1960,8(3-4):304-312
The configuration of positions 13 and 14 in N-methyl-8-aza-des-N-morphinan has been investigated. Potassium t-but-oxide in t-butanol converts N-acetyl-10-oxo-8-aza-des-N-morphinan (XVI) into 10-hydroxy-8,10-(-oxo-ethano)-8-aza-des-N-morphinan (XVII). Formation of these new lactams is possible only when rings B and C are cis. It follows, therefore, that 8-aza-des-N-morphinan synthesized in this investigation has B/C in cis and C/D in trans positions the same as the steric structure of morphinan (M). 相似文献
79.
[reaction: see text] Chiral C(4)-substituted (E)- or (Z)-1-alkynyl-1-trimethylsilyloxy-2-butene systems provide anti-(Z) or syn-(Z) conjugated dienyne, with a very high level of stereocontrol, on treatment with BF(3).OEt(2) in CH(2)Cl(2) at -50 degrees C in the presence of allyltrimethylsilane. The Cieplak conformation for (E)-substrates and neighboring-group participation for (Z)-substrates are considered to be responsible for the stereochemical consequences. 相似文献
80.
The method of orthonormality-constrained variation is extended using a dual-basis set instead of a single orthonormal basis. The complete and the partial variation methods are discussed and applied to electronic systems. It is found that the present formulation leads to the most general equation in the coupling operator method. 相似文献