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171.
From the ethyl acetate soluble fraction of twigs of Magnolia denudata (Magnoliaceae), seven new neolignan derivatives, 1-7, were isolated along with eighteen known lignan and neolignan derivatives, 8-25. The structures of the new neolignans were elucidated by means of spectral methods, especially by 1H-NMR and 13C-NMR spectra, and two dimensional NMR methods such as 1H-detected heteronuculear multiple bond connectivity1 (HMBC), 1H-detected multiple quantum coherence (HMQC) and 1H-1H-correlation spectroscopy (COSY). Compounds 1-4 have novel structures possessing a 6-oxabicyclo[3.2.2]nonane skeleton and compounds 5-8 also have novel structures possessing a bicyclo[3.2.1]octane skeleton. The anti-platelet-activating factor (PAF) activity of these compounds was tested by measurement of inhibition activity against acetyl transferase to lyso-PAF. 相似文献
172.
Characterization of clarithromycin polymorph was performed by solid-state cross polarization and magic angle spinning (CP/MAS) 13C-NMR spectroscopy. Two polymorphs, form II and form I, of clarithromycins indicated characteristic resonances of C1 carbonyl carbon at 176.2 and 175.2 ppm, respectively. Since each peak of C1 carbon was well separated in the spectrum of the two polymorphs, we performed quantitative analysis of the polymorphic fraction from the peak area of these peaks. The peak area of form I was found to linearly increase with an increase of its content, with a correlation coefficient of above 0.99. Solid-state NMR was found to be a useful technique to determine the characteristics of the polymorphic forms. 相似文献
173.
Nakamura I Mizushima Y Gridnev ID Yamamoto Y 《Journal of the American Chemical Society》2005,127(27):9844-9847
A new catalytic cyclization of o-alkynylbenzaldehyde acetals 1 to the functionalized indenes 2 was found to be strictly controlled by the number of triphenylphosphine ligands on the Pd catalyst. Only complexes with three available coordination sites on Pd catalyze this reaction. Mechanistic study suggests that pi-coordination of Pd to the benzene ring is a key step controlled by the number of vacant coordination sites. 相似文献
174.
Fumiyuki Ozawa Takashi Ito Yoshiyuki Nakamura Akio Yamamoto 《Journal of organometallic chemistry》1979,168(3):375-391
New palladium(0) complexes with a variety of coordinated olefins [Pd(olefin)(PMePh2)2] (II) (olefin = styrene, ethyl methacrylate, methyl methacrylate, methyl acrylate, methacrylonitrile, and dimethyl maleate), were prepared by the reactions of [PdEt2(PMePh2)2] (I) with corresponding olefins in toluene. These complexes were characterized by means of elemental analysis, IR and 1H NMR spectroscopy and the chemical reactions. The dissociation of the coordinated olefin from complex II in solution was confirmed by spectroscopic studies of [Pd(mma)(PMePh2)2] (mma = methyl methacrylate). From the variable temperature NMR study, kinetic parameters for the dissociation process were determined as Ea = 7 kcal/mol, and ΔS3 (293 K) = -30 cal/deg · mol. Some new hydrido complexes, [Pd(H)ClL2] (IV) (L = PMePh2, PEtPh2 and PEt2Ph), were prepared by the reactions of [Pd(olefin)L2] with dry HCl. 相似文献
175.
Akira Matsumoto Ikuo Tamura Masataka Yamawaki Masayoshi Oiwa 《Journal of polymer science. Part A, Polymer chemistry》1979,17(5):1419-1429
The polymerization of diallyl oxalate was conducted in the presence of radical initiators at a high temperature range of 80–180°C; a large decrease in degree of polymerization, an increase in residual unsaturation of the resulting polymer, and the evolution of carbon dioxide were observed with the elevation of temperature. These findings were reasonably interpreted by considering the dismutation of the uncyclized growing radical to yield the allyl radical, carbon dioxide, and polymer carrying a terminal double bond. The kinetics of the polymerization of diallyl oxalate in the evolution of carbon dioxide at elevated temperatures were also discussed in detail. 相似文献
176.
The molecular mechanism for 5-bromo-2'-deoxyuridine (BrdU) photosensitization was studied in thymine-requiring wild-type and uracil-DNA glycosylase (UDG)-deficient ung mutant cells of Escherichia coli K-12. Wild-type cells were more sensitive to BrdU photosensitiLation than ung mutant cells. IJV induced the identica/ numbers of alkaline sucrose single-strand breaks (SSB) in 5-bromouracil-DNA (BrU-DNA) of both the wild type and ung mutant. The ung mutant cells repaired SSB almost completely, whereas the wild-type cells with UDG produced more adverse SSB by 90 min after UV. Neutral agarose gel electrophoresis of minipreps indicated that UV induced (1) more smears of host BrU-DNA possibly by more double-strand breaks (DSB) and (2) a greater decline of pBR322 Form I BrU-DNA in the wild-type cells than the ung cells. These results indicated a greater induction of SSB by apyrimidinic (AP) endonucleases in wild-type cells. The ung/ wild ratios (=1.7–1.9) for cellular and plasmid BrdU sensitizations aftcr growth in 50% BrdU were similar. The extents of UDG-dependent and UDG-independent sensitizations in wild-type cells were ∼40 and ∼60%, respectively. The xth nfo double mutant defective in both exonuclcase III and endonucleasc IV was more sensitive to BrdU photosensitization than the wild type, indicating that an excess of AP sites remaining after uracil excision in the xth nfo mutant causes a greater BrdU photosensitization than SSB by AP endonucleases in wild-type cells. Conversely, the xth rfo ung triple mutant was more resistant to BrdU photosensitization than the xth nfo double mutant, so that UV-induced uracil residues in the BrU-DNA are tolerated and do not appear to be directly responsible for BrdU photosensitization. 相似文献
177.
The elemental analysis and morphology of individual particles indicate that the dominant suspended particles in river water are kaolin covered with hydrated iron(III) oxide which strongly sorbs humic substances. Suspended particles, about 1 mg, collected from 250 ml of water by centrifugation, are treated with 0.7 ml of 0.1M sodium hydroxide to desorb humic substances. Approximately 60% of copper and 30% of lead on or in suspended particles exist as humic complexes. 相似文献
178.
Nomura S Itoh T Nakasho H Uno T Kubo M Sada K Inoue K Miyata M 《Journal of the American Chemical Society》2004,126(7):2035-2041
Highly conjugated monomers, 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes (methoxy (1a), ethoxy (1b), isopropoxy (1c), benzyloxy (1d), chloroethoxy (1e), and bromoethoxy (1f)), were synthesized. Recrystallizations of 1a, 1c, 1e, and 1f yielded two crystal forms (prisms (1a-A) and needles (1a-B), needles (1c-A) and plates (1c-B), prisms (1e-A) and plates (1e-B), and prisms (1f-A) and needles (1f-B)), which have different molecular packing modes by X-ray crystal structure analysis, indicating that the crystals are polymorphic. In the photopolymerizations of these monomer crystals in the solid state, 1a-A, 1e-A, and 1f-A polymerized topochemically to give crystalline polymers. For their thermal polymerizations in the solid state, in addition to 1a-A, 1e-A, and 1f-A, 1e-B and 1f-B polymerized, but polymers formed from the 1e-B and 1f-B were amorphous. The packing of quinodimethane molecules in the crystals was defined by four kinds of parameters, stacking distance (d(s)), the distance between the reacting exomethylene carbon atoms (d(cc)), the angles formed between the stacking axis and longer axis of the monomer molecule (theta(1)), and the shorter axis of the monomer molecule (theta(2)), and then the polymerization reactivity of these quinodimethanes in the solid state was discussed on the basis of these parameters. 相似文献
179.
Masao Matsuoka Tsuyoshi Matsuda June Tamaki Yoshifumi Yamamoto Chiaki Iwakura 《Research on Chemical Intermediates》2006,32(5):389-402
Laves-phase hydrogen storage alloy has a high potential for use as negative electrode material as alternative for the misch-metal-based
material. In order to improve the energy density and the rate capability of negative electrode, chemical and mechanical modification
of Lavesphase alloy with different stoichiometric ratios was carried out. Discharge capacity and high-rate dischargeabilty
was evaluated by electrochemical methods and the characterization of Laves-phase alloy was made by X-ray diffraction, SEM
observation and PCT measurement. The best result in discharge capacity could be obtained for stoichiometric Laves-phase alloy
with a composition of Zr0.9Ti0.1Ni1.1Co0.1Mn0.5V0.2Cr0.1 by boiling in 10 M KOH solution. On the other hand, the high-rate dischargeability was increased remarkably by introducing
mechanical grinding before alkali treatment. The cause for improved performance was discussed on the basis of thermodynamic
stability of metal hydride and changes in crystal structure and surface morphology influencing on diffusion coefficient and
diffusion path length of hydrogen. 相似文献
180.
Masumi?Sato Masahiro?Nobe Toshiaki?DobashiEmail author Takao?Yamamoto Akira?Konno 《Colloid and polymer science》2005,284(3):293-300
We have found that the dialysis of curdlan dissolved in alkaline solution into aqueous solutions of metal salts yielded multifold gel structures. Aqueous sodium chloride and potassium chloride as well as pure water induced isotropic gels. Aqueous calcium salts induced liquid crystalline gel with refractive index gradient/amorphous gel alternative structure. Aqueous salts of trivalent aluminum and ferric cations induced a rigid liquid crystalline gel, which shrank above a threshold concentration of each salt. On the other hand, Liesegang ring-like pattern was observed with aqueous solutions of mixed salts of calcium chloride and magnesium chloride. The patterns have been classified to discuss the mechanism of forming the variety of structures. 相似文献