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31.
A new carotenoid glycoside, namely neo-rehmannioside (1), together with five known compounds, 6-O-seco-hydroxyaeginetoyl ajugol (2), oxyrehmaionoside B (3), ajugol (4), geniposidic acid (5) and geniposide (6) was isolated from the 95% ethanol extract of dry roots of Rehmannia glutinosa. The structure of the new compound (1) was determined based on MS, IR, 1-D and 2-D NMR spectral data. 相似文献
32.
Ruthenium complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane for atom and group transfer reactions
Sharon Lai-Fung Chan Yu-He Kan Ka-Lai Yip Jie-Sheng Huang Chi-Ming Che 《Coordination chemistry reviews》2011,255(7-8):899-919
With support by macrocyclic tertiary amine ligand 1,4,7-trimethyl-1,4,7-triazacyclononane (Me3tacn), a number of mononuclear metal–ligand multiple bonded complexes have been isolated. Starting with a brief summary of these complexes, the present review focuses on ruthenium-oxo and -imido complexes of Me3tacn. A family of monooxoruthenium(IV) complexes [RuIV(Me3tacn)O(N–N)]2+ (N–N = 2,2′-bipyridines) and a cis-dioxoruthenium(VI) complex cis-[RuVI(Me3tacn)O2(CF3CO2)]+ have been isolated, and the structures of [RuIV(Me3tacn)O(bpy)](ClO4)2 (bpy = 2,2′-bipyridine) and cis-[RuVI(Me3tacn)O2(CF3CO2)]ClO4 have been determined by X-ray crystallography. Oxidation of [RuIII(Me3tacn)(NHTs)2(OH)] (Ts = p-toluenesulfonyl) with Ag+ and electrochemical oxidation of [RuIII(Me3tacn)(H2L)](ClO4)2 (H3L = α-(1-amino-1-methylethyl)-2-pyridinemethanol) are likely to generate ruthenium-imido complexes supported by Me3tacn. DFT calculations on cis-[RuVI(Me3tacn)O2(CF3CO2)]+ and proposed ruthenium-imido complexes have been performed. Complexes [RuIV(Me3tacn)O(N–N)]2+ are reactive toward alkene epoxidation, and cis-[RuVI(Me3tacn)O2(CF3CO2)]+ efficiently oxidizes various organic substrates including concerted [3+2] cycloaddition reactions with alkynes and alkenes to selectively afford α,β-diketones, cis-diols, or CC bond cleavage products. Related oxidation reactions catalyzed by ruthenium Me3tacn complexes include epoxidation of alkenes, cis-dihydroxylation of alkenes, oxidation of alkanes, alcohols, aldehydes, and arenes, and oxidative cleavage of CC, CC, and C–C bonds, all of which exhibit high selectivity. Ruthenium Me3tacn complexes are also active catalysts for amination of saturated C–H bonds. 相似文献
33.
The effects of the coating amount of surfactant and the particle concentration on the impact strength of polypropylene (PP)/CaCO3 nanocomposites were investigated. Nanocomposites prepared with monolayer-coated CaCO3 nanoparticles had the best mechanical properties, including Young’s modulus, tensile yield stress and impact strength because of the good dispersion of the nanoparticles in the polymer matrix. In addition, the good dispersibility of the monolayer-coated nanoparticles allowed us to study the effects of particle concentration on the impact strength of the nanocomposites. H-PP and E-PP, which were the low and high molecular weight PPs, respectively, were used as polymer matrices. Critical particle concentrations of 10 and 25 wt% corresponding to an abrupt increase in the impact toughness were determined for the E-PP and H-PP nanocomposites, respectively. Good particle dispersion in a polymer matrix is the prerequisite for the calculation of the critical ligament thickness using the critical particle concentration. We propose that the observed critical ligament thickness actually corresponds to the critical thickness at which the plane-strain to plane-stress transition occurs. In addition, the critical ligament thickness of a nanocomposite depends on the properties of the polymer matrix, such as molecular weight, even for a given type of polymer. 相似文献
34.
The ability of stearate coated calcium carbonate nanoparticles to promote the nucleation of polypropylene (PP) was investigated systematically. The effects of surfactant coverage and CaCO(3) particle concentration were explored using differential scanning calorimetry as well as optical and atomic microscopies. The results indicate that at the crystallization temperature of PP, a monolayer stearate coating remains as a rigid layer and provides a noticeable nucleating effect. Insufficient or excess coating diminishes the nucleating effect, the former because of the formation of agglomerates, and the latter by forming a soft layer at the PP/CaCO(3) interface at high temperatures, leading to the weak nucleating ability. Monolayer-coated nanoparticles had the strongest nucleating effect. The crystallization temperature and crystallization rate increased with the concentration of the monolayer-coated nanoparticles up to 40wt.%. 相似文献
35.
Nitric oxide-releasing ruthenium nanoparticles were synthesized by the reaction of alkanethiolate-protected ruthenium nanoparticles with tert-butyl nitrite ((t)BuONO), and their water-soluble derivatives are able to deliver NO to proteins such as reduced myoglobin upon light irradiation in aqueous media. 相似文献
36.
A practical protocol has been developed for asymmetric cis-dihydroxylation of electron-deficient alkenes with Oxone catalysed by a manganese complex bearing a chiral tetradentate N(4)-donor ligand affording cis-diols in up to 95% yield with up to 96% ee. Analysis of the reaction mixture by high resolution ESI-MS revealed the formation of a cis-dioxomanganese(V) intermediate. 相似文献
37.
38.
Chi-Ming Chen 《Journal of Mathematical Analysis and Applications》2006,323(2):1231-1237
In this paper, first part, we establish some fixed point theorems for a k-set contraction map on the nearly-subadmissible subsets of a complete metric space. The second part, we deduce a generalization of the approximate fixed point theorem for the lower semicontinuous mappings on a metric space. 相似文献
39.
Xi Wang Weimin Hou Jianjun Zhou Lin Li Yang Li Chi-Ming Chan 《Colloid and polymer science》2007,285(4):449-455
The α- and β-form lamellae of isotactic polypropylene were developed at different temperatures. The melting behaviors of the
lamellae were observed in real time at elevated temperatures using a hot-stage atomic force microscopy. The melting behavior
of the α-form lamellae was determined by the lamellar defects. For the α-form lamellae developed at different undercoolings,
the larger the undercoolings, the relatively higher amount of defect in the lamellae was observed. The lamellae with defects
were melted into lamellar segments, and recrystallization took place during the heating process. The β-form lamellae had lower
thermal stability, and they melted firstly and separately from that of α-form. 相似文献
40.
In this note, we propose a general method to find cuts for a contingency table. Useful cuts are, in many cases, statistics S-sufficient for the nuisance parameter and S-ancillary for the parameter of interest. In general, cuts facilitate a strong form of parameter separation known to be useful for conditional inference [E.L. Lehmann, Testing Statistical Hypotheses, 2nd ed., Springer, New York, 1997, pp. 546–548]. Cuts also achieve significant dimension reduction, hence, increase computational efficiency. This is particularly true for the inference about cross-tabulated data, usually with a large number of parameters. Depending on the parameter of interest, we propose a flexible transformation to reparameterize the discrete multivariate response distribution. Inference on cell probabilities or odds ratios will require different parameterizations. The reparameterized distribution is not sum-symmetric. Thus, the finding in this paper expands the results in Barndorff-Nielsen [O.E. Barndorff-Nielsen, Information and Exponential Families in Statistical Theory, John Wiley, New York, 1978, pp. 202–206]. 相似文献