The 6,6-spiroacetal segment of spirofungin A, an antifungal antibiotic isolated from Streptomyces violaceusniger Tü 4113, was efficiently prepared via the coupling reaction of the Weinreb amide and the alkyne which are readily available from the common intermediate. The synthesis includes the unsymmetrization through a stereoinversion at the C11 position and the transacetalization as the key steps. 相似文献
Phase equilibrium was established in the Y-Fe-O system at 1100°C by varying the oxygen partial pressure from −log(PO2/atm)=15.00 to 0, allowing construction of a phase diagram at 1100°C for the system Y2O3-Fe-Fe2O3. In the system, two ternary compounds, YFeO3 and Y3Fe5O12, were stable and had nonstoichiometric composition, whereas YFe2O4 was not found to be stable. The present result was different from that of previous studies at 1200°C, in which YFe2O4 was stable, along with the above two ternary compounds. Lattice constants of YFeO3 and Y3Fe5O12, prepared in air by a quenching method, were determined and compared with previous values, and showed close agreement. The standard Gibbs energy changes of the reactions in the Fe-O system, Fe+1/2O2=FeO, 3FeO+1/2O2=Fe3O4, and 2/3Fe3O4+1/6O2=Fe2O3, were determined, and the obtained values were compared with the previous values. The standard Gibbs energy changes of the reactions, Fe+1/2Y2O3+3/4O2=YFeO3, and 3YFeO3+2/3Fe3O4+1/6O2=Y3Fe5O12, were calculated from the oxygen partial pressures in equilibrium. 相似文献
The free radical polymerization of vinyl monomers such as styrene, methylmethacrylate, methyacrylate, acrylonitrile, vinylacetate, etc. in the presence of diphenylbutadiyne, was investigated. Both rates of polymerization and molecular weights of polymer decreased by the addition of diphenylbutadiyne. The degree of retardation depended on the stability of propagating radicals. The butadiyne does not react with the propagating radicals having high Q values, but it seems to trap the radicals temporarily thus retarding the polymerization 相似文献
This paper describes evaluation and correction of count rate characteristics of POSITOLOGICA II, a multi-slice whole body positron emission tomography system. The present study was performed using three phantoms; a 5 cm inner diameter, water-filled lucite cylinder, a 20 cm inner diameter, water-filled lucite cylinder and a chest phantom. After injection of high activity (about 1.85 GBq (50 mCi] of 13N ammonia into each phantom, rates of true coincidence, random coincidence and single photon detections were measured during decay of the isotope through more than two orders of magnitude of activity. At very high levels of activity, count rate characteristics of the system were saturated and limited to 660 kcps of total coincidence rate, which was the sum of rates in on-time and off-time windows, by the FIFO (first-in first-out) output frequency. Below those levels of activity the relationship between count loss and true coincidence rate was not unique but depended on the phantom configurations, suggesting that count loss correction using the above relationship was inadequate for quantitative study. However, the relationship between count loss and single rate was almost independent of the phantom configurations. Thus in conclusion count loss could be corrected using single rate for POSITOLOGICA II. A practical method of count loss correction was also proposed. 相似文献
The effect of Ce doping and pretreatment of Pt/Al2O3 on its catalysis of propane oxidation was investigated after aging the catalysts. The Ce amount and pretreatment conditions were varied, and the propane oxidation activity was measured. The properties of the catalysts were investigated by means of XRD, STEM-EDX, FT-IR, and H2-TPR. The size of the Pt nanoparticles (PtNPs) decreased for water-treated catalysts doped with a small amount of Ce, suggesting that water treatment of Ce-doped catalysts inhibits Pt sintering. The minimum PtNP size was obtained with ca. 3.6 wt% of Ce. The Ce species with less than 3.6 wt% existed in a dispersed state, whereas above this value, CeO2 particulates co-existed. The propane oxidation temperature of the water-treated catalysts was lowered to an extent that depended on the Ce content. This tendency is consistent with the PtNP size in the catalysts. It is considered that highly dispersed Ce species take a primary role in promoting propane oxidation on PtNPs. The reduction temperature of Ce species on water-treated catalysts was lower than that of untreated catalysts, probably owing to a stronger interaction between Pt and Ce, demonstrated by FT-IR measurements. The increased reducibility of Ce species may be the reason for the improved oxidation activity of the catalysts.
Some model experiments for functionalization of a polycarbonate were carried out. At first, reactivity of phenyl chloroformate with a few nucleophiles was examined. Reaction with alkyl amines gave corresponding carbamates, but in the case of aniline, formation of a byproduct diarylurea was observed. Reactions with alcohols and phenols afforded carbonates in moderate yields, in which p-nitrophenol and isopropyl alcohol were less reactive. On the basis of these results, 1-ethyl-4-phenoxycarboxymethyl-2,6,7-trioxabicyclo[2.2.2]octane (2) and 1-ethyl-4-ethoxycarboxymethyl-2,6,7-trioxabicyclo[2.2.2]octane (3) were prepared by the reaction of phenyl and ethyl chloroformates with 1-ethyl-4-hydroxymethyl-2,6,7-trioxabicyclo[2.2.2]octane in the presence of tert-amine. 2 polymerized cationically with BF3OEt2 at more than 80°C to give a polyether containing both ester and carbonate groups in the side chain, with contamination of a gelled polymer. 相似文献
The doublet instabilities of the restricted Hartree-Fock (RHF) solutions for the ion radicals of fulvalene systems, some of which have been known to show the lattice instabilities, are examined in the framework of the semiempirical SCF MO approximation. The RHF solutions for the anion radical of heptafulvalene and the cation radical of pentafulvalene are found to be doublet unstable at the conventional D2h nuclear arrangement. We calculate the broken-symmetry charge-density-wave (CDW) solutions lower in energy than the usual symmetry-adapted RHF solutions and examine their properties. It is shown that the energy lowerings due to the CDW solutions are very small in both the ion radicals, but their density matrix elements are remarkably different from those for the symmetry-adapted RHF solutions. It is also shown that the proton hyperfine splittings for the anion radical of heptafulvalene calculated assuming the CDW solution are in good agreement with the experimental values. Finally, we refer to the relationship between the doublet instability of the RHF solution and the lattice instability. 相似文献
(±)-Oxylubimin (1), the highest oxidized spirovetivane-type phytoalexin, was totally synthesized with high stereoselectivity using a novel method for α′-hydroxylation of α,β-unsaturated ketones. 相似文献