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991.
Melina G. Carvalho Fátima D. Freire Fernanda N. Raffin Cícero Flávio Soares Arag?o Túlio F. A. L. Moura 《Chromatographia》2009,69(Z2):249-253
The aim of the present paper was to develop and validate a method to determine gallic acid and tannins by LC. Validation was
carried out in accordance with Brazilian Resolution 899/2003. The method showed satisfactory results for precision, accuracy,
specificity and linearity. Variations on the composition and flow rate of the mobile phase influenced the peak area and retention
time. The method was applied to determine the amount of hydrolysable tannins in preparations containing Schinus terebinthifolius Raddi. 相似文献
992.
Schmidt TF Pavinatto FJ Caseli L Gonzaga ML Soares SA Ricardo NM Oliveira ON 《Journal of colloid and interface science》2009,330(1):84-89
The use of natural substances in health applications may be hampered by the difficulties in establishing the mechanisms of action, especially at molecular-level. The protein-polysaccharide complex extracted from the mushroom Agaricus blazei Murill, referred to as CAb, has been considered for treating various diseases with probable interaction with cell membranes. In this study, we investigate the interaction between CAb and a cell membrane model represented by a Langmuir monolayer of dimyristoyl phosphatidic acid (DMPA). CAb affects the structural properties of DMPA monolayers causing expansion and increasing compressibility. In addition, interaction with DMPA polar heads led to neutralization of the electrical double layer, yielding a zero surface potential at large areas per molecule. CAb remained at the interface even at high surface pressures, which allowed transfer of Langmuir-Blodgett (LB) films onto solid supports with the CAb-DMPA mixture. The mass transferred, according to quartz crystal microbalance (QCM) measurements, increased linearly with the number of deposited layers. With UV-vis absorption, fluorescence and FTIR spectroscopies, we confirmed that the LB films contain polysaccharides, proteins and DMPA. Therefore, the CAb biological action must be attributed not only to polysaccharides but also to proteins in the complex. 相似文献
993.
Helena Hansson 《Talanta》2009,79(3):633-638
The utility of a dynamic hollow-fibre liquid phase microextraction method (optimized using a four-variable experimental design and response surface modelling) for extracting dinitrophenolic compounds from human plasma samples was evaluated. The investigated variables were donor phase salt concentration (10-400 mM), donor phase pH (2-6), acceptor phase pH (7-12), and donor/acceptor phase flow rates (30/7.5 to 70/17.5 μL min−1). Four dinitrophenol pesticides were used as model substances at concentrations of 0.1 μg mL−1 in spiked human plasma samples. Extraction efficiencies ranging from 42 to 77% with RSDs below 9 were achieved with the optimized method. The flow rate and acceptor pH were shown to strongly affect the extraction efficiency for all compounds, while the donor phase pH and salt concentration had minor effects. With a well-defined acceptor phase pH and flow rate the system exhibited high robustness. The limits of quantification for the investigated compounds, using the presented extraction method followed by liquid chromatography/electrospray ionization mass spectrometry in selected ion monitoring mode, ranged from 0.05 to 0.1 μg mL−1 plasma. 相似文献
994.
We prove an equivariant Riemann–Roch formula for divisors on algebraic curves over perfect fields. By reduction to the known
case of curves over algebraically closed fields, we first show a preliminary formula with coefficients in . We then prove and shed some further light on a divisibility result that yields a formula with integral coefficients. Moreover,
we give variants of the main theorem for equivariant locally free sheaves of higher rank. 相似文献
995.
A new recovery operator P :Qn^disc(T)→Qn+1^disc(M) for discontinuous Galerkin is derived. It is based on the idea of projecting a discontinuous, piecewise polynomial solution on a given mesh T into a higher order polynomial space on a macro mesh M. In order to do so, we define local degrees of freedom using polynomial moments and provide global degrees of freedom on the macro mesh. We prove consistency with respect to the local L2-projection, stability results in several norms and optimal anisotropic error estimates. As an example, we apply this new recovery technique to a stabilized solution of a singularly perturbed convection-diffusion problem using bilinear elements. 相似文献
996.
James P. Kelliher Milton C. Lopes Filho Helena J. Nussenzveig Lopes 《Annales de l'Institut Henri Poincaré (C) Analyse Non Linéaire》2009
We study the limiting behavior of viscous incompressible flows when the fluid domain is allowed to expand as the viscosity vanishes. We describe precise conditions under which the limiting flow satisfies the full space Euler equations. The argument is based on truncation and on energy estimates, following the structure of the proof of Kato's criterion for the vanishing viscosity limit. This work complements previous work by the authors, see Iftimie et al. (2009) [5], Kelliher (2008) [8]. 相似文献
997.
Robert Katava Franjo Zorko Ana Dunja Mance Helena Otmačić-Ćurković 《Molecular Crystals and Liquid Crystals》2017,642(1):29-37
Heterocyclic organic compounds containing nitrogen, sulfur or oxygen atoms are often used to protect metals from corrosion acting as organic corrosion inhibitors. Their inhibiting role is based on excellent ligand abilities and formation of stabile metal complex. Two requirements are essential for using selected class of organic inhibitors: (a) ligand capacity in the conditions of corrosion such as atmospheric conditions, acid or neutral corrosion, etc., and (b) nontoxicity, i.e., environmentally friendly inhibitors. Imidazole derivatives are capable to fulfil both requirements and they are, from that point of view, very promising and profound class of ligands. Synthesis and X-ray diffraction molecular and crystal structure of 4-methyl-1-N-(p-tolyl)imidazole has been reported, since it exhibits the most prominent corrosion inhibiting role. The synthesis, starting from 4-methylimidazole and 4-bromotoluene, is based on Ullmann-type coupling reaction by applying modifications of N-arylation by arylhalogenides and Cu2O as an efficient catalyst.
The molecular and crystal structure of prepared N-substituted imidazole derivative reveals non-planar molecular conformation and the supramolecular assembling of the molecules via C-H···N intermolecular hydrogen bonds between Csp2-H proton donor groups and basic imidazole nitrogen atom. The molecules are related by a 21 screw axis parallel to [0 1 0] in the form of infinite C(4) zig-zag 1D chains via C-H···N intermolecular hydrogen bonds. Such alignment produces additional weak stacking interaction between imidazole and phenyl ring of related chains. 相似文献
998.
Rinat Shoshnik Helena Elengoz Israel Goldberg 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(4):m187-m189
In the title compound, diaquabis(1,4‐di‐4‐pyridyl‐2,3‐diaza‐1,3‐butadiene)dimethanolzinc(II) bis(perchlorate) 1,4‐di‐4‐pyridyl‐2,3‐diaza‐1,3‐butadiene methanol 1.72‐solvate 1.28‐hydrate, [Zn(C12H10N4)2(CH4O)2(H2O)2](ClO4)2·C12H10N4·1.72CH4O·1.28H2O, determined at ca 110 K, the Zn cation and the extended dipyridyl ligand both lie across inversion centres in space group P. The structure consists of a network arrangement of the constituent species stabilized by a combination of coordination, hydrogen bonding and π–π forces. Uncoordinated methanol and water solvent molecules occupy the otherwise void spaces within and between the networks. 相似文献
999.
1000.
The solution polymerization of ethylene using rac-Et(Ind)2ZrCl2/MAO and (Dimethylsilyl(tert-butylamido)(tetramethyl- cyclopentadienyl)titanium Dichloride)(CGC-Ti)/MAO was studied in a semi-batch reactor at 120 °C under different monomer pressures and catalyst concentrations. The kinetics of ethylene polymerization with rac-Et(Ind)2ZrCl2/MAO can be described with first order reactions for polymerization and catalyst deactivation. When (CGC-Ti)/MAO is used, however, second order kinetics are observed for catalyst decay and the order of polymerization changes from 2 to 1 with increasing ethylene pressure. 相似文献