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41.
Natsumi Tanaka Takahiro Suzuki Dr. Takehiko Matsumura Yosuke Hosoya Masahisa Nakada Prof. Dr. 《Angewandte Chemie (International ed. in English)》2009,48(14):2580-2583
Intelligent design : The total synthesis of the cytotoxic (?)‐FR182877 relies on 1) tandem Diels–Alder reactions to close rings A–D (see scheme), 2) a palladium‐mediated 7‐exo‐trig reaction, and 3) an iridium‐mediated isomerization followed by epimerization and stereoselective reduction.
42.
Xiao Y Fisher K Smith MC Newton WE Case DA George SJ Wang H Sturhahn W Alp EE Zhao J Yoda Y Cramer SP 《Journal of the American Chemical Society》2006,128(23):7608-7612
Nitrogenase catalyzes a reaction critical for life, the reduction of N(2) to 2NH(3), yet we still know relatively little about its catalytic mechanism. We have used the synchrotron technique of (57)Fe nuclear resonance vibrational spectroscopy (NRVS) to study the dynamics of the Fe-S clusters in this enzyme. The catalytic site FeMo-cofactor exhibits a strong signal near 190 cm(-)(1), where conventional Fe-S clusters have weak NRVS. This intensity is ascribed to cluster breathing modes whose frequency is raised by an interstitial atom. A variety of Fe-S stretching modes are also observed between 250 and 400 cm(-)(1). This work is the first spectroscopic information about the vibrational modes of the intact nitrogenase FeMo-cofactor and P-cluster. 相似文献
43.
We have succeeded in precisely determining the hyperfine interactions, particularly the isomer shifts, in the 149Sm Mössbauer transition. The difference in the nuclear radii between the ground and excited states is critical for the determination of isomer shifts but is relatively small in 149Sm. Therefore, the precise determination by 149Sm Mössbauer spectroscopy is difficult. The recent development of synchrotron-radiation-based Mössbauer spectroscopy allows the isomer shifts to be determined more precisely than previously with the help of wellcollimated synchrotron radiation. In particular, the time-window effect assists the precise determination of hyperfine interactions in the 149Sm Mössbauer transition because this effect enables us to measure spectra with higher energy resolution than natural linewidth determined by the lifetime of the excited states. Meanwhile, highenergy-resolution measurements to determine center shifts by SR-based Mössbauer spectroscopy enable us to observe the second-order Doppler shift, which has not been discussed, particularly for heavy Mössbauer nuclei. We have discussed the precise determination of isomer shifts and the observation of the second-order Doppler shift using 149Sm synchrotron-radiation-based Mössbauer spectroscopy. 相似文献
44.
A Cu-catalyzed γ-selective coupling reaction between propargylic phosphates and aryl- or alkenylboronates afforded aryl- or alkenyl-conjugated allenes. The reaction showed excellent functional group compatibility in both the propargylic substrates and the boronates. The reaction of an enantioenriched propargylic phosphate proceeded with excellent chirality transfer with 1,3-anti stereochemistry to give axially chiral aryl- and alkenylallenes. 相似文献
45.
Particle image velocimetry studies of a boundary layer perturbed by localized suction 总被引:1,自引:0,他引:1
Difference experiments were carried out in a low-Reynolds number (490 based on momentum thickness) flat-plate boundary layer.
Particle image velocimetry (PIV) was used to measure the two velocity components parallel to the plate in the boundary layer
with and without weak localized suction through two holes at suction speeds of less than 1% of the free-stream value under
otherwise identical conditions. The results from the preliminary PIV data show that suction does not affect the mean streamwise
velocity profile, but decelerates the boundary layer in the vicinity of the suction holes. This deceleration is on average
6% of the mean speed at 13 viscous length scales above the plate and persists for at least 10 hole diameters downstream of
the suction holes. Two-dimensional correlations of streamwise velocity fluctuations imply that even these low suction levels
reduce the cross-stream and streamwise length scales in the boundary layer.
Received: 22 December 1998/Accepted: 17 April 2000 相似文献
46.
L. Deák L. Bottyán R. Callens R. Coussement M. Major I. Serdons Y. Yoda 《Hyperfine Interactions》2006,167(1-3):709-715
The concept of the heterodyne/stroboscopic detection of nuclear resonance scattering of synchrotron radiation is extended to the grazing incidence geometry. Model calculations for an antiferromagnetic [57Fe/Cr]20 multilayer are shown and discussed. Principles and methodological aspects of stroboscopic synchrotron Mössbauer reflectometry are briefly reviewed. 相似文献
47.
Lisa Araki Maho Yamaguchi Natsumi Taniguchi Zheng-yun Zhao 《Tetrahedron letters》2004,45(12):2657-2661
A novel C4-linked imidazole ribonucleoside phosphoramidite was designed and successfully synthesized starting from tribenzylribofuranosylimidazole. This phosphoramidite product enables incorporation of the imidazole moiety into an RNA sequence and hence allows study of its role in the general acid and base catalysis of ribozymes. Pivaloyloxymethyl (POM) was first introduced as an N-protecting group for the imidazole ribonucleoside that can be readily removed under mild basic condition. 相似文献
48.
Otake K Kobayashi M Ozaki Y Yoda S Takebayashi Y Sugeta T Nakazawa N Sakai H Abe M 《Langmuir : the ACS journal of surfaces and colloids》2004,20(15):6182-6186
To confirm the surface activity of myristic acid in the dispersion polymerization of vinyl monomers in scCO2, the interfacial tension (IFT) at the polymer/supercritical carbon dioxide (scCO2) interface has been measured. For the IFT measurements, a high-pressure pendant drop apparatus was constructed. The IFT data was obtained by the axisymmetric drop shape analysis of melt polymer droplets formed at the tip of a capillary. The reliability of the apparatus was confirmed by measuring the IFT of polystyrene (PS)/scCO2 and polypropylene (PP)/CO2 systems. The IFT of the poly(methyl methacrylate) (PMMA)/scCO2 system with and without myristic acid was also measured. The IFT decreased on addition of myristic acid. The magnitude of the IFT depression due to the myristic acid was comparable to that of PS/scCO2 systems with the block copolymer surfactant, PS-b-poly(fluorooctyl acrylate). The surface activity of the myristic acid was confirmed by the decrease of IFT. 相似文献
49.
Reiko Yoda 《Mikrochimica acta》1982,78(3-4):271-278
Summary N,N-Ditnethyl-N-(4-methyl-5-nitro-2-thiazolyl)thiourea A new spectrophotometric method for the determination of palladium with N,N-dimethyl-N-(4-methyl-5-nitro-2-thiazolyl)thiourea (DMNT) is proposed. DMNT instantly forms a yellow chelate with Pd(II) at pH 2 at room temperature, which is readily extracted into organic solvents such as chloroform and shows a higher absorption maximum (=40,400) at 413 nm. The ratio of Pd(II) to reagent in the chelate is 12 as determined by the widely used method and also verified by synthesis of the authentic Pd-chelate. The chelate conforms well with the Lambert-Beer's law over a wide concentration range (3.3–22g in 10 ml chloroform). The optimum concentration range of palladium for spectrophotometry by the Ringbom plot is 5.6–18.6g in 10 ml of chloroform solution. This method gives a good reproducibility, high sensitivity and high accuracy in the presence of many foreign ions.
Spektrophotometrische Bestimmung von Palladium mit N,N-Dimethyl-N- (4-methyl-5-nitro-2-thiazolyl)-thioharnstoff (DMNT)
Zusammenfassung Eine neue spektrophotometrische Methode zur Bestimmung von Palladium mit DMNT wurde vorgeschlagen. Dieses Reagens bildet mit Pd(II) bei pH 2 und Zimmertemperatur ein gelbes Chelat, das mit Chloroform gut extrahierbar ist und bei 413 nm ein hohes Absorptionsmaximum (=40400) zeigt. Dessen Zusammensetzung wurde in üblicher Weise zu 12=Pd: DMNT bestimmt. Im Konzentrationsbereich 3,3–22g/10 ml entspricht das Chelat dem Lambert-Beerschen Gesetz. Die optimale Konzentration für die spektrophotometrische Bestimmung liegt zwischen 5,6 und 18,6g/10 ml Chloroform. Das Verfahren gibt gut reproduzierbare Ergebnisse, ist hoch empfindlich und auch in Anwesenheit vieler Fremdionen sehr genau.相似文献
50.
Highly regioselective transformations of the acyclic α,ω-terpenediols and their diacetates to the monoacetates using lipase were accomplished. The acetylation of the α,ω-terpenediols gave regioselectively the ω-monoacetates 3, whereas the α-monoacetates 2 were obtained by hydrolysis of the α,ω-diacetates. 相似文献