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排序方式: 共有245条查询结果,搜索用时 15 毫秒
81.
Gold(I)‐Catalyzed Asymmetric Desymmetrization of meso‐Alkynyl Diols and Kinetic Resolution of the Corresponding dl‐Diols: Effects of Celite Filtration and Silver Salts 下载免费PDF全文
Yumi Sota Masaaki Yamamoto Masato Murai Prof. Dr. Jun'ichi Uenishi Prof. Dr. Motokazu Uemura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(11):4398-4404
The asymmetric desymmetrization of meso‐2‐alkynylbenzenediols through the use of a combination of axially chiral diphosphine(AuCl)2 precatalysts and silver salt co‐catalysts gave optically active isochromene compounds with high enantioselectivities in good yields. The corresponding dl ‐diol isomers underwent efficient kinetic resolution to give the cyclized isochromenes and recovered diols with high enantioselectivities under similar conditions. The high reactivity and selectivity in the desymmetrization of the meso‐diols is independent of the combination of axially chiral diphosphine(AuCl)2 precatalyst and silver salt co‐catalyst, whereas the corresponding tricarbonylchromium complexes of alkynylbenzenediols were affected by the combination of the diphosphine(AuCl)2 and silver salt. The reactivity was largely dependent on the nature of the gold(I) species. 相似文献
82.
M. Oyasato K. Ichinose K. Fujiwara A. Tsujimura 《Journal of magnetism and magnetic materials》1987,70(1-3):233-235
The spin echo spectra of 89Y hyperfine fields in Y(Fe1−xTx)3 with low concentration x consist of two main lines and of satellite lines caused by the replacement of the Fe atoms by the T atoms. Values of the magnetic moments of the T atoms are estimated by observing the satellite lines. 相似文献
83.
Heat capacities of vanadium-oxygen alloys with various compositions, VO0.0834, VO0.1127, VO0.1245, and VO0.1296, were measured from 320 to 920K by adiabatic scanning calorimetry. A heat capacity anomaly due to order-disorder rearrangement of oxygen atoms was observed for all the compositions. The transition temperatures from α′ to β phase were found to be 780, 791, 786, and 768K for VO0.0839, VO0.1127, VO0.1245, and VO0.1296, respectively. The transition temperatures from β′ to β were also observed to be 665 and 660K for VO0.1245 and VO0.1296, respectively, but they shifted to lower temperatures in repeated measurements. The excess heat capacity due to order-disorder transition was obtained by assuming that the heat capacity can be expressed as the sum of a harmonic term of lattice vibration, a dilational term, an electronic term, and an anharmonic term of lattice vibration. The entropy changes due to the transition for VO0.0834, VO0.1127, VO0.1245, VO0.1296 were determined from the excess heat capacities to be 1.90, 2.88, 2.82, and 2.88 J K?1 mole?1, respectively, values which were explained by calculating the entropy changes due to the order-disorder rearrangement of oxygen atoms in the superstructures of VOx alloys. From the O/V dependence of the transition temperature and entropy change, the most stable composition of the α′ phase was thought to be V48O5. 相似文献
84.
Hideki Sugimoto Eiji Nakanishi Yumi Mizuno Takashi Yasumura Katsuhiro Inomata 《Colloid and polymer science》2008,286(6-7):777-786
In this study, two kinds of amphiphilic copolypeptide, C12-poly(N-hydroxyethyl L-glutamine-co-L-tryptophan) (C12-EGT-T) and C12-poly(L-glutamic acid-co-L-tryptophan) (C12-GAT-T) were prepared. By using the mixture of these amphiphilic copolypeptides, pH response of aggregate formation, critical aggregate concentration, the sizes of the aggregates and sustained-release behavior of model substances were investigated. The mixture of the amphiphilic copolypeptides formed aggregates in aqueous medium and showed the ability to uptake model substances such as pyrene and 5-fluorouracil into their hydrophobic moiety. Moreover, pH response was observed in the sustained-release behavior of model substances and the pH region where these properties changed was from pH 7.4 to pH 4.5 in the mixture of C12-EGT-T/C12-GAT-T at 50/50 (mol/mol). These results could be explained by dissociation of trifluoroacetic-acid-treated tryptophan residues in the hydrophilic moieties and destabilization of the aggregates by electrostatic repulsion. 相似文献
85.
Toyama M Hironaka M Yamahama Y Horiguchi H Tsukada O Uto N Ueno Y Tokunaga F Seno K Hariyama T 《Photochemistry and photobiology》2008,84(4):996-1002
There are two types of visual pigments in fish eyes; most marine fishes have rhodopsin, while most freshwater fishes have porphyropsin. The biochemical basis for this dichotomy is the nature of the chromophores, retinal (A1) and 3-dehydroretinal (A2), each of which is bound by an opsin. In order to study the regional distribution of these visual pigments, we performed a new survey of the visual pigment chromophores in the eyes of many species of fish. Fish eyes from 164 species were used to examine their chromophores by high-performance liquid chromatography--44 species of freshwater fish, 20 of peripheral freshwater fish (coastal species), 10 of diadromous fish and 90 of seawater fish (marine species) were studied. The eyes of freshwater fish, limb freshwater fish and diadromous fish had both A1 and A2 chromophores, whereas those of marine fish possessed only A1 chromophores. Our results are similar to those of previous studies; however, we made a new finding that fish which live in freshwater possessed A1 if living near the sea and A2 if living far from the sea if they possessed only one type of chromophore. 相似文献
86.
Hattori R Yamada K Hasegawa K Ishikawa Y Ito Y Sakamoto Y Yoshida N 《Rapid communications in mass spectrometry : RCM》2008,22(21):3410-3414
The isotope ratios of ethanol, an important constituent or ingredient of some foods and various beverages and fuels, provide information about biological and geographical origin and quality. We have developed an improved method for measuring the isotope ratio of ethanol in various samples by gas chromatography-high temperature conversion or combustion-isotope ratio mass spectrometry (GC-TC/C-IRMS) with headspace solid-phase microextraction (HS-SPME). A HS-SPME method was developed by optimizing several different parameters, including salt addition, incubation temperature and time, and extraction time. The HS-SPME method enabled us to determine the isotope ratio at low ethanol concentrations (0.08 mM) in 50 min with good precision (+/-0.3 per thousand for delta(13)C and +/-5 per thousand for deltaD). An advantage of this technique is that it can be adapted for use with samples which have high viscosity and contain many matrix compounds, such as alcoholic and non-alcoholic beverages. 相似文献
87.
Development of a mass spectrometric hydroxyl‐position determination method for the hydroxyindole metabolites of JWH‐018 by GC‐MS/MS 下载免费PDF全文
Maiko Kusano Kei Zaitsu Mayumi Yamanaka Kazuaki Hisatsune Tomomi Asano Kentaro Taki Yumi Hayashi Hitoshi Tsuchihashi Akira Ishii 《Journal of mass spectrometry : JMS》2016,51(5):350-357
One of the many issues of designer drugs of abuse like synthetic cannabinoids (SCs) such as JWH‐018 is that details on their metabolism has yet to be fully elucidated and that multiple metabolites exist. The presence of isomeric compounds poses further challenges in their identification. Our group has previously shown the effectiveness of gas chromatography‐electron ionization‐tandem mass spectrometry (GC‐EI‐MS/MS) in the mass spectrometric differentiation of the positional isomers of the naphthoylindole‐type SC JWH‐081, and speculated that the same approach could be used for the metabolite isomers. Using JWH‐018 as a model SC, the aim of this study was to differentiate the positional isomers of its hydroxyindole metabolites by GC‐MS/MS. Standard compounds of JWH‐018 and its hydroxyindole metabolite positional isomers were first analyzed by GC‐EI‐MS in full scan mode, which was only able to differentiate the 4‐hydroxyindole isomer. Further GC‐MS/MS analysis was performed by selecting m/z 302 as the precursor ion. All four isomers produced characteristic product ions that enabled the differentiation between them. Using these ions, MRM analysis was performed on the urine of JWH‐018 administered mice and determined the hydroxyl positions to be at the 6‐position on the indole ring. GC‐EI‐MS/MS allowed for the regioisomeric differentiation of the hydroxyindole metabolite isomers of JWH‐018. Furthermore, analysis of the fragmentation patterns suggests that the present method has high potential to be extended to hydroxyindole metabolites of other naphthoylindole type SCs in identifying the position of the hydroxyl group on the indole ring. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
88.
Yamano Y Fujita Y Mizuguchi Y Nakagawa K Okano T Ito M Wada A 《Chemical & pharmaceutical bulletin》2007,55(9):1365-1370
An improved synthesis of gamma-hydroxybutenolides 1a-d was achieved via crossed aldol condensation between aldehydes 2a-d and the protected gamma-hydroxy-beta-methylbutenolides 3 or 4 using the bulky Lewis acid, aluminum tris(2,6-diphenylphenoxide) (ATPH). Using this same methodology, the gamma-hydroxybutenolides 17a-d having various heteroaromatic rings were synthesized and their anti-tumor activities were evaluated. 相似文献
89.
Katsu T Tsunamoto Y Hanioka N Komagoe K Masuda K Narimatsu S 《Analytical and bioanalytical chemistry》2007,387(6):2057-2064
S,S,S-Tris(2-ethylhexyl) phosphorotrithioate proved to be an effective solvent mediator for constructing a mexiletine-sensitive
membrane electrode in combination with an ion-exchanger, sodium tetrakis[3,5-bis(2-methoxyhexafluoro-2-propyl)phenyl]borate.
Among a series of phosphorus compounds containing phosphoryl (P=O) groups, this solvent mediator showed the highest sensitivity
to mexiletine in phosphate-buffered physiological saline containing 0.15 mol L−1 NaCl and 0.01 mol L−1 NaH2PO4/Na2HPO4 (pH 7.4), giving a detection limit of 2 × 10−6 mol L−1 with a slope of 58.8 mV decade−1. This is the best reported detection limit of any mexiletine-sensitive electrode developed to date. Owing to its high selectivity
toward inorganic cations, the electrode was used to determine the level of mexiletine in saliva, the monitoring of which is
quite effective for controlling the dose of this drug noninvasively. The mexiletine concentrations determined with the mexiletine-sensitive
electrode compared favorably with those determined by high-performance liquid chromatography. 相似文献
90.
Hayashi Y Segawa Y Yamashita M Nozaki K 《Chemical communications (Cambridge, England)》2011,47(20):5888-5890
The present communication reports the chemistry of three linear triborane(5) compounds possessing bulky diamino substituents on the terminal boron atoms. Fluorotriborane 2 was synthesized by a reaction of boryllithium and BF(3)·OEt(2). Halogen exchange reaction of 2 took place by a treatment with ClSiMe(3) to give the corresponding chlorotriborane(5) 3. Addition of silver tetraarylborate to 3 in ether afforded a hydroxylated triborane(5) compound 5 probably via an unstable cationic boron intermediate 4. 相似文献