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101.
da Silva Cunha IB Salomão K Shimizu M Bankova VS Custódio AR de Castro SL Marcucci MC 《Chemical & pharmaceutical bulletin》2004,52(5):602-604
Extracts from different samples of Brazilian propolis were obtained by Soxhlet extraction or maceration at room temperature using ethanol, water, and accombination of both solvents. Analysis of their composition using HPLC revealed that no major differences were seen when a propolis sample was subject to different extraction methods. The activity of the 15 extracts was assayed against bloodstream trypomastigotes of Trypanosoma cruzi, the etiologic agent of Chagas' disease. Multivariate analysis was applied to evaluate the efficiency of the different extracts and the trypanocidal activity. The extracts could be divided into two groups. In the first, in which, extracts were obtained by reflux in Soxhlet using 100% ethanol, there was a lower content of bioactive compounds and consequently lower trypanocidal activity. Extract 136-Et100 stands out in this group, since it had the highest levels of bioactive compounds together with highest activity against the parasite when compared with all other extracts. The second group comprises extracts with intermediate levels of bioactive compounds and higher activity against T. cruzi. 相似文献
102.
103.
J Lukkari M Salom?ki A Viinikanoja T A?ritalo J Paukkunen N Kocharova J Kankare 《Journal of the American Chemical Society》2001,123(25):6083-6091
Electronically conducting polyanion and polycation based on poly(alkoxythiophene) derivatives, poly-3-(3'-thienyloxy)propanesulfonate (P3TOPS) and poly-3-(3'-thienyloxy)propyltriethylammonium (P3TOPA) have been synthesized. Both polymers are water-soluble and exhibit high conjugation length in solution and in the solid state. These polyelectrolytes were used to prepare conducting and electroactive polyelectrolyte multilayers by the sequential layer-by-layer adsorption technique. In aqueous solutions multilayers of P3TOPS with inactive polyelectrolytes (e.g., poly(diallyldimethylammonium chloride), PDADMA) displayed electrochemical and optical behavior similar to polythiophene films prepared in organic media. Their in-plane conductivity was low (ca. 1.6 x 10(-)(5) S cm(-)(1)). The conductivity could, however, be increased by a factor of ca. 40 in "all-thiophene" films, in which P3TOPA was substituted for the inactive polycation (PDADMA). The interpenetration of layers is of prime importance in films containing conducting components. The interpenetration of P3TOPS was studied by measuring the charge-transfer rate across an insulating polyelectrolyte multilayer between the substrate and the P3TOPS layer with modulated electroreflectance. The extent of interpenetration was 8-9 polyelectrolyte layers, the length scale (7-15 nm) depending on the nature of the insulating layer and, especially, on the ionic strength of the solution used for the adsorption of P3TOPS. 相似文献
104.
Nieto-Oberhuber C López S Jiménez-Núñez E Echavarren AM 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(23):5916-5923
Three pathways actually compete in metal-catalyzed cyclizations of enynes in which the metal selectively activates the alkyne: an endocyclic process and two exo-cyclizations, one proceeding by anti attack of the alkene and a second one resulting in a syn addition. Although cyclobutenes may be formed in transition-metal-catalyzed cyclization of some enynes, particularly, 1,7-enynes, these compounds are not necessarily the intermediates in the skeletal rearrangement. Cyclobutenes are formed by ring expansion of syn-cyclopropyl metal-carbenes formed in the syn pathway. 相似文献
105.
106.
Carmen Cortázar Manuel Elgueta Jorge García-Melián Salomé Martínez 《Journal of Evolution Equations》2016,16(1):209-232
We consider the following nonlocal equationwhere J is an even, compactly supported, Hölder continuous kernel with unit integral and g is a continuous positive function. Our main concern will be with unbounded functions g, contrary to previous works. More precisely, we study the influence of the growth of g at infinity on the integrability of positive solutions of this equation, therefore determining the asymptotic behavior as \({t\to +\infty}\) of the solutions to the associated evolution problem in terms of the growth of g.
相似文献
$$\int J\left(\frac{x-y}{g(y)}\right) \frac{u(y)}{g(y)} dy -u(x)=0\qquad x\in \mathbb{R},$$
107.
Margarita G. Prolongo C. Arribas Catalina Salom Rosa M. Masegosa 《Journal of Thermal Analysis and Calorimetry》2007,87(1):33-39
Diglycidyl
ether of bisfenol-A (DGEBA)/poly(vinyl acetate) (PVAc)/poly(4-vinyl phenol)
brominated (PVPhBr) ternary blends cured with 4,4’-diaminodiphenylmethane
(DDM) were investigated by differential scanning calorimetry (DSC), dynamic
mechanical thermal analysis (DMTA) and scanning electron microscopy (SEM).
Homogeneous (DGEBA+DDM)/PVPhBr networks with a unique T
g
are generated. Ternary blends (DGEBA+DDM)/PVAc/PVPhBr are initially miscible
and phase separate upon curing arising two T
gs
that correspond to a PVAc-rich phase and to epoxy network phase. Increasing
the PVPhBr content the T
gof
the PVAc phase move to higher temperatures as a consequence of the PVAc-PVPhBr
interactions. Different morphologies are generated as a function of the blend
composition. 相似文献
108.
A highly stereocontrolled and efficient synthesis for a fully functionalized C 10-C 22 fragment of pectenotoxin 2 is described using a convergent sequence involving a stereoselective methylation of beta-hydroxyketone as a key step. 相似文献
109.
Eckert AK Rodríguez-Morgade MS Torres T 《Chemical communications (Cambridge, England)》2007,(40):4104-4106
Genuine B-B linked subphthalocyanine dimers are synthesized through Wurtz coupling of readily accessible chlorosubphthalocyanines. 相似文献
110.
Rodríguez-Morgade MS Claessens CG Medina A González-Rodríguez D Gutiérrez-Puebla E Monge A Alkorta I Elguero J Torres T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(4):1342-1350
A new and general synthetic method for the preparation of fluoro-substituted subazaporphyrins is reported that involves the treatment of the corresponding chloro- or aryloxy-substituted subazaporphyrins (SubAPs) with BF(3).OEt(2). The strategy has been applied to both subphthalocyanines (SubPcs) and subporphyrazines (SubPzs). The yields were high for the latter, although low yields were obtained for the benzo derivatives. In contrast to the corresponding chloro derivatives, fluorosubazaporphyrins are quite robust towards hydrolysis. All of the new compounds were characterized by several spectroscopic techniques, which included (1)H, (13)C, (19)F, (15)N, and (11)B NMR spectroscopy, IR spectroscopy, UV/Vis spectrophotometry, and mass spectrometry (both high and low resolution). In addition, DFT calculations provided theoretical NMR spectroscopy values that are in good agreement with the experimental ones. The high dipole moments exhibited by the fluorosubazaporphyrins as a result of the presence of a fluorine atom in an axial position are responsible for the spontaneous and singular supramolecular aggregation of the macrocycles in the crystalline state. The molecular and crystal structures of two one-dimensional fluorine SubAPs, namely, a SubPc and a SubPz, are discussed. Molecules of the same class stack in alternating configurations along the c axis, which gives rise to columns that contain large numbers of monomers. SubPz 3 c forms aggregates with the macrocycles arranged in a parallel fashion with the B-F bonds perfectly aligned within a column, whereas with SubPc 3 b the neighboring columns cause a commensurate sinusoidal distortion along the columns in the c direction, which prevents the alignment of the B-F bonds. However, the most remarkable feature, common to both crystalline architectures, is the extremely short and unusual intermolecular F...N distances of the contiguous molecules, which are shorter than the sum of the corresponding van der Waals radii. Theoretical calculations have shown that these short distances can be explained by the existence of a cooperativity effect as the number of monomers included in the cluster increases. 相似文献