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991.
The catalytic activity of a base metal-terpyridine complex immobilized on silica gel ( M(tpy)X2@SiO2/H2O : M=Mn, Fe, Co, Ni, Cu; X=Cl, Br) for hydrosilylation was investigated. Co(tpy)Br2@SiO2/H2O in the presence of NaBHEt3 exhibited the highest catalytic activity for hydrosilylation of 1-octene with diphenylsilane (Ph2SiH2) to form the anti-Markovnikov-type hydrosilylation compound as the main product. The reusability of Co(tpy)Br2@SiO2/H2O activated by NaBHEt3 was examined. It was found that the catalytic activity decreased with repeated use because of the peeling off of the Co complex anchor portion from the silica gel surface upon the attack of NaBHEt3. The introduction of Co(OAc)2 instead of CoBr2 to silica gel formed Co(tpy)(OAc)2- and Co(tpy)(OH)2-immobilized silica gel, which exhibited catalytic activity for the hydrosilylation in the absence of an activator such as NaBHEt3. The glassware in which Co(tpy)(OH)2 was immobilized on the inner wall was prepared. It was found that the hydrosilylation catalytically occurred on the surface of a pretreated glassware and that the catalytic activity did not decrease even after 10 repeated uses. 相似文献
992.
We show that if a smooth projective 4-fold M contains an ample divisor A which is P
1-bundle π :A→S over a smooth projective surface S, π is extended to a P
2-bundle π :S→S, unless $A$ is isomorphic to P
2×P
1.
Received: 28 September 1998 / Revised version: 16 August 1999 相似文献
993.
Using a scattering technique based on a parametrized linear combination of atomic orbitals Hamiltonian, we calculate the ballistic quantum conductance of multiwall carbon nanotubes. We find that interwall interactions not only block some of the quantum conductance channels, but also redistribute the current nonuniformly over individual tubes across the structure. Our results provide a natural explanation for the unexpected integer and noninteger conductance values reported for multiwall nanotubes by Stefan Frank et al. [Stefan Frank et al., Science 280, 1744 (1998)]. 相似文献
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998.
Chevallier J Sakai N Robert F Kobayashi T Gruenberg J Matile S 《Organic letters》2000,2(13):1859-1861
An expeditious route to synthetic lysobisphosphatidic acid S,S-1, its enantiomer, and regioisomers is reported. Synthetic difficulties concerning lipid stability and stereochemistry are bypassed using a phosphite triester approach in combination with multiple silyl protection. Spectroscopic studies evidence that acyl group migration in S,S-1 is accelerated by nonpolar solvents and inhibited by pyridine. 相似文献
999.
Nagase K Kobayashi J Kikuchi A Akiyama Y Annaka M Kanazawa H Okano T 《Langmuir : the ACS journal of surfaces and colloids》2008,24(19):10981-10987
We have prepared poly( N-isopropylacrylamide) (PIPAAm) brush-grafted surfaces with varied temperature-responsive hydrophobic properties through surface-initiated atom transfer radical polymerization (ATRP). These temperature-responsive surfaces were characterized by chromatographic analysis using modified silica beads as a chromatographic stationary phase in aqueous mobile phase. Mixed silane self-assembled monolayers (SAMs) comprising ATRP initiator and silanes with various terminal functional groups were formed on the silica bead surfaces. IPAAm was then polymerized by ATRP using the CuCl/CuCl2/Me6TREN catalyst system in 2-propanol at 25 degrees C for 16 h. The chromatographic retention behavior of steroids on the resulting PIPAAm brushes made on more polar silane components was distinct from that on more apolar silane interfaces. Retention times for steroids on PIPAAm mixed apolar silane graft interfaces were significantly longer than those on analogous polar silane interfaces due to enhanced dehydration of PIPAAm brushes on apolar silane-grafted surfaces. Changes in retention factor, k', on polar silane PIPAAm-grafted interfaces were relatively large compared to that on apolar PIPAAm grafted interfaces due to larger hydration/dehydration alterations of grafted PIPAAm brushes on the former surfaces. Applied step-temperature gradients from 50 to 10 degrees C show that PIPAAm brushes on polar silane interfaces tend to hydrate more, leading to shorter retention times. In conclusion, the polarity of the grafted interface significantly influences the grafted PIPAAm brush hydration/dehydration characteristics and subsequently also the temperature-modulated separation of bioactive compounds in all-aqueous chromatography. 相似文献
1000.
This review covers the structures, synthesis, biosynthesis, and bioactivity of a series of cytotoxic macrolides, named amphidinolides, isolated from symbiotic marine dinoflagellates of the genus Amphidinium which were separated from inside cells of marine flatworms. The structures of long-chain polyketides such as colopsinols isolated from Amphidinium sp. are also described. 相似文献