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171.
The systematic integration of the small 2π- and 4π-electron systems cyclopropenylium ion, cyclopropenone, oxo-cyclobutenylium ion, and cyclobutadiene into phane chemistry was initiated only a few years ago. [n2]Cyclopropenylophanes, [n2]cyclopropenonophanes, metal-capped [n4]cyclobutadienosuperphanes, and other new families of double-decker phane species became available from cycloalkydiynes through special methods of double [2+1]cycloaddition with carbenes and metal complex induced dimerization by double [2+2]cycloaddition. Phane-specific structural features were elucidated by X-ray structural analyses. Cyclic voltammetry and PE spectroscopy as well as MO calculations reealed considerable interactions between closely spaced π-electron systems. Decapping cyclobutadienosuperphanes formally extended the synthetic principle to threefold [2+2]cycloadditions resulting in [n4]-bridged tricyclo-[4.2.0.03, 5]octa-3,7-dienes, which represent a new type of cage compounds. Moreover, completion to fourfold [2+2]addition was achieved with the photoinduced transformation of [34]bridged tricyclo[4.2.0.03, 5]octa-3,7-diene into propella[34]cubane. 相似文献
172.
《Magnetic resonance in chemistry : MRC》2003,41(7):481-488
An electron spin resonance (ESR) spin probe study was performed on 1 : 1 by weight poly(acrylic acid) (PAA)/poly(ethylene oxide) (PEO) complex over the 100–450 K temperature range with a series of tetramethylpiperidyloxy‐based spin probes. Measurements of the parameters T5mT, Ta and Td demonstrated the effects of probe size and the strength of hydrogen bonding. The probes in the series Tempone, Tempo, Tempol and Tamine (respectively 4‐oxo‐, unsubstituted, 4‐hydroxy‐ and 4‐amino‐2,2,6,6,‐tetramethylpiperidine ‐1‐oxyl) displayed noticeable increases in the hydrogen‐bonding effect, as indicated by Ta and Td. These increases correlated with increasing hydrogen bond acceptor strength. On the other hand, as the probe size became larger, T5mT gradually increased due to the free volume decrease. These effects were analyzed using the established theoretical relationship of T5mT to probe volume expressed by f. Meanwhile, in order to investigate the effect of polymer matrix rigidity, a similar study was performed with a nitroxide spin probe, 2,2,6,6‐tetramethyl‐1‐piperidine‐1‐oxyl (Tempo), on PAA/PEO complexes of different weight compositions. The quantitative fast motion fraction in the composite ESR spectrum was calculated. The influence of changes in the composition of PAA on the molecular mobility was characterized by changes of the spectral parameters and τc. The molecular mobility was shown to diminish with increasing content of PAA in PAA/PEO blends duo to the restriction of the polymer matrix rigidity increase. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
173.
Binary organic-inorganic gels have been prepared by mixing a carbonaceous hydrosol and a Nb2O5 or Ta2O5 sol derived by hydrolysis of the alkoxides. The gels are pyrolyzed under an inert atmosphere into precursors in which carbon and the metal oxides are mixed very intimately. High temperature treatment converts the precursors into the cubic face centered carbides. The precursors as well as the carbides have been shown to be micro- and mesoporous materials. Measurements of nitrogen adsorption reveal a characteristic change of the shapes of the isotherms (Type I Type IV) and of the hysteresis loops (H4H2H1) during the thermal processes. Pore widening has been observed with rising temperature. The phenomena of crystallization, carbothermal reduction and sintering were found to control the pore shape and size. The results of the adsorption measurement correlate well with those of the thermoanalytical and X-ray diffraction studies.Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday 相似文献
174.
镍基气凝胶催化CH4-CO2重整制取合成气反应的研究 Ⅲ.影响催化剂积碳性能因素的探讨 总被引:3,自引:4,他引:3
考察了823K焙烧的干凝胶xNCA550、气凝胶aNCA550及浸渍型催化剂iNCA550在923K、1073K、1173K反应温度下的积碳行为,对催化剂表面碳的活性及类型进行了分析,并探讨了影响催化剂积碳的因素。实验结果表明,随反应温度的提高,催化剂的积碳能力减弱,尤以气凝胶催化剂aNCA550明显。催化剂的积碳主要发生在反应的初期,反应温度越高,到达积碳量相对稳定期所需要的时间越短;随着反应时间的延续,催化剂积碳量缓慢增长,并且表面碳的活性降低。催化剂的酸性和镍晶粒大小是影响其积碳性能的主要内在因素,而它们对积碳的影响程度受反应温度的影响,反应温度越高,催化剂表达酸性中心利于积碳的作用越小,小晶粒镍抑制催化剂积碳的能力越强。 相似文献
175.
用重复卷积法求解物理宽化函数吴万国,林嘉 (福州大学中心实验室,福州350002)(中国(福建)对外贸易中心集团,福州350001)关键词X射线衍射,晶粒度,晶格畸变,重复卷积粉末试样的X射线衍射谱线一般具有一定的宽度,引起话线宽化的主要原因有仪器致... 相似文献
176.
Hoebbel Dagobert Reinert Thomas Schmidt Helmut Arpac Ertugrul 《Journal of Sol-Gel Science and Technology》1997,10(2):115-126
The complexation degrees of Al-, Ti- and Zr-butoxide (M) with unsaturated and saturated -diketones (3-allylpentane-2.4-dione-APD, acetylacetone-ACAC) and -ketoesters (methacryloxyethyl-acetoacetate-MEAA, allylacetoacetate-AAA, ethylacetoacetate-EAA) as organic ligands (L) were examined by IR and 13 C NMR spectroscopy and were found to be L:M 1.5. The hydrolytic stability of the ligands of the metal alkoxide complexes (L:M = 1) during hydrolysis/condensation reactions at the molar ratio h (H2O : OR) = 0.5–2.0 decreases with increasing H
177.
Ryan Simon 《Analytica chimica acta》2005,542(1):104-110
The dependence of enantio-selective chromatographic performance on particle size, as measured by separation factor, was investigated for one-monomer molecularly imprinted polymers (OMNiMIPs) compared to traditionally formed EGDMA/MAA molecularly imprinted polymers (MIPs). Five particle size ranges were compared (<20 μm, 20-25 μm, 25-38 μm, 38-45 μm, and 45-63 μm), revealing that the particle sizes above 25 μm provided the highest separation factor, and thus the best enantiomer separation, for both imprinted polymers. Other chromatographic parameters such as the number of theoretical plates and resolution exhibited only minor changes for the OMNiMIPs as the particle size changed, except for particles 20 μm and below. However, the number of theoretical plates and resolution for EGDMA/MAA are higher for particles in the 20-25 μm range. Thus, chromatographic factors for the EGDMA/MAA polymers are better in this range, despite better enantioselectivity for particle sizes above 25 μm. In contrast, OMNiMIPs generally show the most favorable performance for particle sizes in the 38-45 μm range. It was also found that decreasing flow rate resulted in improved enantioselectivity for both MIPs for all particle sizes. 相似文献
178.
The effects of variant counterions with ionic strength of 0.05, 0.10, 0.20 and 0.25 mol·kg^-1 on the stability and particle size of silica sols have been studied using the traditional methods of Ubbelohde viscosity measurement, TEM and titration respectively, finding that the stability and particle size of the silica sols are all concerned with the acidic, positively electric properties and the sizes of the counterions, as well as the attraction between the counterions and surface silicon hydroxyl groups of the silica sols. The small positively charged counterions lead to the decrease in particle sizes, making the silica sol the most stable. But the larger weakly acidic counterions can restrict the particle sizes of the silica sols and easily make the sols coagulate. It was also found that there existed a linear relationship between log r and log η, which has not ever been reported. The effect of temperature on the stability and particle sizes was also discussed. 相似文献
179.
180.
The brightness of the X‐ray source in a W/Al‐film target used for X‐ray projection microscopy was studied by an approach using the Monte Carlo simulation. Since continuous X rays generated in a thin film have a specific angular distribution of emission, the brightness of the continuous X‐ray source cannot simply be estimated on the assumption that the angular distribution is homogeneous. The newly developed approach using the Monte Carlo simulation enables the evaluation of the effective source size, angular distribution, and brightness of a continuous X‐ray source with sufficient accuracy that it leads to the optimum design of a high‐brightness X‐ray source for uses such as X‐ray projection microscopy. The Monte Carlo calculations were performed for W(Δz)/Al (200 µm)‐film targets with different thicknesses of W film, Δz, under bombardment of 60 kV electrons. The results have suggested an optimum design consisting of a W (2 µm)/Al (200 µm)‐film target as most promising for providing an X‐ray source of higher brightness than the W (5 µm)/Al (200 µm)‐film target, which has already been in practice for X‐ray projection microscopy. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献