排序方式: 共有47条查询结果,搜索用时 11 毫秒
1.
Afarin Moezzi Marylin M. Olmstead Doris C. Pestana Philip P. Power 《无机化学与普通化学杂志》1995,621(11):1933-1938
The reaction of either Li2PPh or Li2AsPh with the diborane(4) derivative B2(NMe2)2Br2 affords the compounds [PhP(BNMe2)2]2 ( 1 ) or [PhAs(BNMe2)2]2 ( 2 ) in good yield. Both 1 and 2 have cyclic structures featuring non-planar P2B4 or As2B4 six-membered rings which have chair configurations. Although all four borons in each ring have planar coordination, the two phosphorus or arsenic centers have different degrees of pyramidalization. Bond distances within the rings indicate that the B? B, B? P or B? As bonds are single, whereas the exo-B? N bond lengths are consistent with significant π-bonding. The ring structures of 1 and 2 are in sharp contrast to the related boron-nitrogen species (t-BuN)2N4Me4 which has a nido-N2B4 framework. The attempted synthesis of the nitrogen analogue of 1 or 2 by using a similar approach did not result in the isolation of [PhN(BNMe2)2]2, instead the tetramino diborane(4) species [B(NMe2)NHPh]2 ( 3 ), which has a structure similar to other tetramine diborane(4) compounds, was isolated. 相似文献
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Alicia Cantón Ana Granados Domingo Pestana José M. Rodríguez 《Central European Journal of Mathematics》2013,11(10):1817-1830
We prove that under appropriate assumptions adding or removing an infinite amount of edges to a given planar graph preserves its non-hyperbolicity, a result which is shown to be false in general. In particular, we make a conjecture that every tessellation graph of ?2 with convex tiles is non-hyperbolic; it is shown that in order to prove this conjecture it suffices to consider tessellation graphs of ?2 such that every tile is a triangle and a partial answer to this question is given. A weaker version of this conjecture stating that every tessellation graph of ?2 with rectangular tiles is non-hyperbolic is given and partially answered. If this conjecture were true, many tessellation graphs of ?2 with tiles which are parallelograms would be non-hyperbolic. 相似文献
4.
Teresa Avilés António Dinis Michael G. B. Drew Vitor Félix 《Monatshefte für Chemie / Chemical Monthly》2000,6(1):1305-1310
The self-assembly of Ag[BF4] with trans-azobenzene in dichloromethane yields a new coordination polymer ([Ag(μ-trans-azobenzene)H2O][BF4])n which was characterized by X-ray single crystal diffraction. The crystal consists of 1-D zigzag cationic chains made up from [Ag(H2O)]+ units linked by trans-azobenzene bridges and BF− 4 anions. Hydrogen bonding interactions between the chains and BF− 4 anions occur via intermolecular C*H⋯F and O*H⋯F contacts, and the crystal displays a 2-D supramolecular structure. 相似文献
5.
Oil-in-water lecithin-based microemulsions as a potential delivery system for amphotericin B 总被引:1,自引:1,他引:1
Pestana KC Formariz TP Franzini CM Sarmento VH Chiavacci LA Scarpa MV Egito ES Oliveira AG 《Colloids and surfaces. B, Biointerfaces》2008,66(2):253-259
In this work the structural features of microemulsions (MEs) containing the pharmaceutical biocompatible Soya phosphatidylcholine/Tween 20 (1:1) as surfactant (S), Captextrade mark 200 as oil phase (O), and phosphate buffer 10mM, pH 7.2 as aqueous phase (W) were studied. Systems obtained with different proportions of the components were described by pseudo-ternary phase diagrams in order to characterize the microemulsions studied here. MEs were prepared with and without the polyene antifungal drug amphotericin B (AmB). The maximum AmB incorporation into the ME system was dependent on both the oil phase and surfactant proportions with 6.80 and 5.7mg/mL in high contents, respectively. The incorporation of AmB into the ME systems significantly increased the profile of the droplet size of the ME for all ranges of surfactant proportions used in the formulations. The microstructures of the system were characterized by dynamic light scattering (DLS) and rheological behavior. The DLS results showed that the size of the oil droplets increases 4.6-fold when AmB is incorporated into the ME system. In all cases the increase in the proportion of the oil phase of the ME leads to a slight increase in the diameter of the oil droplets of the system. Furthermore, for both the AmB-loaded and AmB-unloaded MEs, the size of the oil droplets decrease significantly with the increase of the S proportion in the formulations, demonstrating the efficiency of the surfactant in stabilizing the ME. Depending on the ME composition, an anti-thixotropic behavior was found. The maximum increases of the consistency index caused by the increase of the oil phase of the ME were of 17- and 25-times for the drug-loaded and drug-unloaded MEs, respectively. However, the observed effect for the drug-loaded ME was about 4.6 times higher than that for the drug-unloaded one, demonstrating the strong effect of the drug on the rheological characteristics of the ME system. Therefore, it is possible to conclude that the investigated ME can be used as a very promising vehicle for AmB. 相似文献
6.
Maria Margarida Mateus Dinis Guerreiro Olga Ferreira João Carlos Bordado Rui Galhano dos Santos 《Cellulose (London, England)》2017,24(2):659-668
A clear, direct and rapid analysis of the preliminary results concerning the acid liquefaction of Eucalyptus globulus’ bark is herein presented. The results led to a methodology for the selective liquefaction of hemicellulose and amorphous cellulose. Liquefaction was conducted at various temperatures, as well as different reaction times. The process results are heuristically explained in view of the experiments of ATR-FTIR, hydroxyl number, and acid value. The procedure method allows reusing the wastes arising from the paper industry. Valuable products and chemical building blocks from lignocellulosic biomass, mostly based on cellulose can be thus accessed. 相似文献
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We present a bounded modified realisability and a bounded functional interpretation of intuitionistic nonstandard arithmetic with nonstandard principles.The functional interpretation is the intuitionistic counterpart of Ferreira and Gaspar's functional interpretation and has similarities with Van den Berg, Briseid and Safarik's functional interpretation but replacing finiteness by majorisability.We give a threefold contribution: constructive content and proof-theoretical properties of nonstandard arithmetic; filling a gap in the literature; being in line with nonstandard methods to analyse compactness arguments. 相似文献
8.
Kayla Belanger Tony M. Dinis Sami Taourirt Guillaume Vidal David L. Kaplan Christopher Egles 《Macromolecular bioscience》2016,16(4):472-481
The repair of large crushed or sectioned segments of peripheral nerves remains a challenge in regenerative medicine due to the complexity of the biological environment and the lack of proper biomaterials and architecture to foster reconstruction. Traditionally such reconstruction is only achieved by using fresh human tissue as a surrogate for the absence of the nerve. However, recent focus in the field has been on new polymer structures and specific biofunctionalization to achieve the goal of peripheral nerve regeneration by developing artificial nerve prostheses. This review presents various tested approaches as well their effectiveness for nerve regrowth and functional recovery.
9.
Dinis F. Silva Alexandre M. Viana Isabel Santos-Vieira Salete S. Balula Luís Cunha-Silva 《Molecules (Basel, Switzerland)》2022,27(5)
An effective and sustainable process capable of simultaneously execute desulfurization and denitrogenation of fuels is in fact an actual necessity in the refinery industry. The key to achieve this goal is the parallel oxidation of sulfur and nitrogen compounds present in fuels, which is only achieved by an active and recovered catalyst. A novel heterogeneous catalyst was successfully prepared by the encapsulation of an imidazolium-based polyoxometalate (POM) into a ZIF-8 framework ([BMIM]PMo12@ZIF-8). This composite material revealed exceptional catalytic efficiency to concurrently proceed with the oxidative desulfurization and denitrogenation of a multicomponent model fuel containing various sulfur and nitrogen compounds. A complete removal of all these compounds was achieved after only one hour and the catalyst system was able to be reused for ten consecutive cycles without loss of efficiency. In fact, an ionic liquid POM was incorporated in the ZIF-8 for the first time, and this composite compound was originally applied as a catalyst for simultaneous oxidative desulfurization and denitrogenation processes. 相似文献
10.
Fernando Pestana Da Costa 《NoDEA : Nonlinear Differential Equations and Applications》1998,5(1):23-37
The asymptotic behaviour of solutions to the generalized Becker-D?ring equations is studied. It is proved that solutions
converge strongly to a unique equilibrium if the initial density is sufficiently small.
Received July 19, 1996 相似文献