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61.
A convergent total synthesis of leustroducsin B (1), which is known to exhibit a variety of biological activities, was successfully carried out. Notable features of our synthesis include construction of the C8 stereocenter by lipase-mediated desymmetrization of meso-diol 4 (90.2% ee) and preparation of the C9-C11 anti-diol moiety by the addition of alkynylzinc reagent 20 to the aldehyde 19. Furthermore, a new diol protecting group, p-silyloxybenzylidene, was developed for the deprotection from densely functionalized substrates under weakly acidic conditions. The protecting group was easily removed in a two-step procedure ((HF)3.Et3N; AcOH-THF-H2O). 相似文献
62.
63.
Ductile nickel-tungsten (Ni-W) alloys containing about 20–21 at.%W were electroplated onto copper substrates. The development
of the amorphous/nanocrystalline microstructure towards a complete crystallization by isochronal heat treatments in vacuum
was monitored by different methods. For medium annealing temperatures a solid-solution of W in the fcc-Ni lattice was achieved
resulting in an increased hardness. For temperatures of 600 °C and upward recrystallization started and thermodynamically
stable intermetallic compounds like Ni4W and NiW were formed. A third phase, containing more than 80 at.%W was also detected but could not be identified so far.
Only by combination of different methods and especially by use of analytical TEM structural analysis and phase identification
in these amorphous-nanocrystalline Ni-W alloys were successful. 相似文献
64.
In a recent publication [C.A. Bertulani, G. Cardella, M. De Napoli, G. Raciti, E. Rapisarda, Phys. Lett. B 650 (2007) 233] the validity of analysis methods used for intermediate-energy Coulomb excitation experiments was called into question. Applying a refined theory large corrections of results in the literature seemed needed. We show that this is not the case and that the large deviations observed in above mentioned reference are due to the use of the wrong experimental parameters in that publication. We furthermore show that an approximate expression derived in above mentioned reference is in fact equivalent to the theory of Winther and Alder, an analysis method often used in the literature. 相似文献
65.
66.
Combined DFT calculations and UV-vis-NIR, ESR, and SQUID measurements revealed that the ground-state electronic structure of a linear π-conjugated oligomer dication composed of two pyrrole and six or seven thiophene rings and methylthio end-capping units is dominated by a singlet biradical character. 相似文献
67.
Kensuke Okusa Yuki Suita Yukio Otsuka Mineo Tahara Tohru Ikegami Nobuo Tanaka Masayoshi Ohira Masakazu Takahashi 《Journal of separation science》2010,33(3):348-358
The effectiveness of several basic compounds for testing silica‐based stationary phases was reviewed by applying them to recent columns for reversed‐phase HPLC. Most octadecylsilylated (C18) stationary phases, prepared as a base‐deactivated material from high‐purity silica gel with endcapping, provided excellent peak shape and column efficiency for the bases including benzylamine and amitriptyline that once caused problems and were subsequently employed for testing silanol activities. However, a cyclic tertiary amine, dextrometorphan, was eluted as an acceptable peak from only a few columns at neutral pH. Such a more sensitive probe is expected to contribute to further improvement of the stationary phase for reversed‐phase HPLC. 相似文献
68.
69.
Kiminori Itoh Tohru Okamoto Shuhei Wakita Hiroshi Niikura Masayuki Murabayashi 《应用有机金属化学》1991,5(4):295-301
Thin films of peroxohetero(carbon)polytungstic acid (CW-HPA) and carbon-free isopolytungstic acid (W-IPA) were prepared, and examined in terms of optical and etching properties. Thermal decomposition was found to give good results in removing excess hydrogen peroxide (H2O2) during the preparation of CW-HPA and W-IPA. It was shown for the first time that thin films of CW-HPA and W-IPA have very high refractive indices (larger than 2.0) when sufficiently dried. Optical waveguide (OWG) characteristics of these films were examined using a slab-type OWG structure and ARROW (Antiresonance Reflection Optical Waveguide)-type structures. An embossing technique was applied to make diffractional grating couplers. 相似文献
70.
The exchange interaction in the radical pair in homogeneous solution has been investigated by using the CIDNP method. The experimental observations of the multiplet pattern were compared with the theoretical simulations in which the exchange integral was a variable parameter. The results show that 2-propanol is a unique solvent in that the exchange integral in the radical pair in this solvent is large. 相似文献