230 resultados para lambda-carrageenan
Resumo:
A series of perovskite-like mixed oxides La(2-x)Sr(x)MO(4+lambda) (M=Cu, Co,Ni; x=0,1) was prepared and characterized using X-ray powder diffraction. The catalytic properties of these catalysts in NO decomposition were tested. The results showed that LaSrNiO4-lambda with K2NiF4 structure is very active and stable for the decomposition of NO.
Resumo:
A series of samples having the composition of La2-xSrxNiO4(0 less than or equal to x less than or equal to 1) were prepared and used as catalysts for NH3 oxidation. It was found that the La and oxygen vacancies exist in the La2-xSrxNiO4-lambda(0 less than or equal to x less than or equal to 1). The unit cell volume decreases with the increase of x. For bath c and a parameters there appeared a turning point at x = 0.5. Doping with a lower valence cation Sr2+ in the case of La2NiO4 resulted in an increase of Ni3+, consequently the formation of oxygen vacancies, the increase of reducing ability and the increase of catalytic activity. In the oxygen TPD of La2-xSrxNiO4(0 less than or equal to x less than or equal to 1) appeared three peaks, the alpha' peak at about 400K was attributed to the surplus oxygen desorption, the a peak at 700K which approaches to a maxium at x = 0.6 was attributed to the oxygen adsorbed at oxygen vacancies. The beta peak at about 1000K which depends closely on the x and favors the catalytic activity was attributed to the reduction of Ni3+. The catalytic activity of La-2-x SrxNiO4 mixed oxides in the NH3 oxidation in general could be attributed to the extent of the redox reaction: 2Ni(2+) + O-2 + V-0(..) reversible arrow 2Ni(3+) + 20(-) where V-0(..) representes the oxygen vacancies and O- the oxygen species adsorbed at the vacancies.
Resumo:
A series of mixed oxides La2-xSrxCoO4+/-lambda (x=0-2) with varying x values was synthesized. The crystal structure of this series of mixed oxides was studied by using XRD. The result showed that when x=0.25-1.5 the mixed oxides possessing K2NiF4 structure are formed. The valences of the transition metal Co and the relation between +/-lambda content and x value by using chemical analysis method have been measured, too. The redox property of this series of mixed oxides and different kinds of oxygen species were studied by IR, TPD, TPR, XPS and SEM methods. The catalytic activity in the complete oxidation of CO and CH4 was investigated and the relationships between the activity, composition and structure of the mixed oxides have been elucidated.
Resumo:
Two series of La1-xSrxNiO3-lambda and La1-1.333xThxNiO3-lambda catalysts have been prepared, and the relationships between the solid defect structure and catalytic activity for NH3 oxidation were measured. The results showed that in the range of x < 0.3, the samples possessed single perovskite-type structure, and as the content of Sr2+ decreased and that of Th4+ increased the catalytic activity increased which was paralleled with the Ni3+ concentration within the catalysts. The active oxygen species (O- or O2(2-)) were present not only on the surface but also in the bulk of the samples. The synergistic effect of transition metal ions with higher oxidation states and randomly distributed oxygen vacancies was the key factor determining catalytic activity of perovskite-type oxides. A redox mechanism for NH3 oxidation over ABO3 is proposed.
Resumo:
In order to study the relationship between chemical structure and properties of modified carrageenans versus antioxidant activity in vitro, K-carrageenan oligosaccharides were prepared through mild hydrochloric acid hydrolysis of the polysaccharide, and these were used as starting materials for the partial synthesis of their oversulfated, acetylated, and phosphorylated derivatives. The structure and substitution pattern of the oligosaccharides and their derivatives were Studied using FTIR and C-13 NMR spectroscopy, and their in vitro antioxidant activities were investigated. Certain derivatives of the carrageenan oligosaccharides exhibited higher antioxidant activity than the polysaccharides and oligosaccharides in certain antioxidant systems. The oversulfated and acetylated derivatives, which scavenge superoxide radicals, the phosphorylated and low-DS acetylated derivatives, which scavenge hydroxyl radicals, and the phosphorylated derivatives, which scavenge DPPH radicals, all exhibited significant antioxidant activities it, the systems examined. The effect of the molecular weight of the carrageenan on antioxidant activities, however, is not obvious from these studies. (c) 2005 Elsevier Ltd. All rights reserved.
Resumo:
Oligosaccharides were prepared through mild hydrochloric acid hydrolysis of kappa-carrageenan from Kappaphycus striatum to compare the antitumor activity with carrageenan polysaccharides. Oligosaccharide fractions were isolated by gel permeation chromatography and the structure of fraction 1 (F1) was studied by using negative- ion electrospray ionization-mass spectrometry (ESI-MS), and H-1 and C-13-NMR spectrometry. The in vitro antitumor effects in three human neoplastic cell lines (KB, BGC, and Hela) of polysaccharides and F1 were investigated. The bioassay results showed that F1 exhibited relatively higher antitumor activity against the three cancer cells than polysaccharides.
Resumo:
Antioxidant activity of kappa-carrageenan oligosaccharides (OM) and their chemical modification derivatives was investigated employing various established in vitro systems, such as reducing power, iron ion chelation, and total antioxidant activity using beta-carotene-linoleic acid system. The oversulfated (SD), lowly (LAD), and highly acetylated derivatives (HAD) in reducing power assay, the phosphorylated derivative (PD) in metal chelating assay, and oversulfated and phosphorylated derivatives in total antioxidant activity assay exhibited antioxidant activity higher than that of carrageenan oligosaccharides. The results indicated that the chemical modification of carrageenan oligosaccharides can enhance their antioxidant activity in vitro. The protective effects of the carrageenan oligosaccharides and their chemically modified derivatives against H2O2 and UVA (long-wave ultraviolet radiation) induced oxidative damage on rat thymic lymphocyte were investigated by measuring cell viability via 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT). Thymic lymphocyte exposure to H2O2 and UVA, a marked reduction in cell survival was observed, which was significantly prevented by carrageenan oligosaccharides and their derivatives (preincubated for 2 h) at 66.7-2000 mu g/mL. But both the carrageenan oligosaccharides and their different derivatives showed the similar protective effects on intracellular level. Taken together, these results suggest that carrageenan oligosaccharides and their derivatives show relevant antioxidant activity both in vitro and in a cell system. (C) 2005 Elsevier Ltd. All rights reserved.
Resumo:
The modulation of carrageenan oligosaccharides from Kappaphycus striatum on the immune system in S 180-bearing mice was investigated. The mice inoculated with S180 cell suspension were treated p.o. with carrageenan oligosaccharides (50, 100 and 200 mu g/g) for 14 days. The effects of carrageenan oligosaccharides on transplantable tumors and macrophage phagocytosis, quantitative hemolysis of sheep red blood cells (QHS),. lymphocyte proliferation, the activity of natural killer cells (NK), production of interleukin-2 (IL-2) and tumor necrosis factor-alpha (TNF-alpha) were studied. Carrageenan oligosaccharides could significantly inhibit the growth of transplantable sarcoma S180 and increase macrophage phagocytosis, the form of antibody secreted by spleen cells, spleen lymphocyte proliferation, NK cells activity, serumal IL-2 and TNF-alpha level in S 180-bearing mice. Considering all these results, it is suggested that carrageenan oligosaccharides exert their antitumor effect by promoting the immune system. (c) 2005 Elsevier Ireland Ltd. All rights reserved.
Resumo:
The interactions between granulocyte-colony stimulating factor (G-CSF) and dextran sulfate/kappa-carrageenan oligosaccharide were studied by capillary zone electrophoresis. Dextran sulfate could strongly interact with G-CSF and the complex was detected. The binding constant and stoichiometry were determined to be 1.2x10(6) (mol/L)(-1) and 3:1, respectively. However, the interaction between K-carrageenan oligosaccharide and G-CSF was not found.
Resumo:
针对氢/空气混合物,通过实验研究了其预混火焰在半开口管道中的火焰传播加速现象,结果表明,火焰传播状态随着氢气当量比的变化而发生改变。当氢/空气混合物被点燃后,由于障碍物的扰动,火焰在管道中不断加速传播,并最终到达一准稳态传播。在氢气当量比0.31附近时,火焰速度发生跃变。当氢气当量比足够大时,火焰传播由爆燃态转变为爆轰态。在本实验条件下,爆燃转准爆轰的临界条件是d/Lambda>=2.6(d是圆环形障碍物内径,人是爆轰格胞尺度)。障碍物阻塞比的变化对最大火焰速度和压力提升的影响不明显。
Resumo:
The characteristics of low-speed fluid streaks occurring under sheared air-water interfaces were examined by means of hydrogen bubble visualization technique. A critical shear condition under which the streaky structure first appears was determined to be u(tau) approximate to 0.19 cm/s. The mean spanwise streak spacing increases with distance from the water surface owing to merging and bursting processes, and a linear relationship describing variation of non-dimensional spacing <(
Resumo:
The three-dimensional compressible Navier-Stokes equations are approximated by a fifth order upwind compact and a sixth order symmetrical compact difference relations combined with three-stage Ronge-Kutta method. The computed results are presented for convective Mach number Mc = 0.8 and Re = 200 with initial data which have equal and opposite oblique waves. From the computed results we can see the variation of coherent structures with time integration and full process of instability, formation of Lambda-vortices, double horseshoe vortices and mushroom structures. The large structures break into small and smaller vortex structures. Finally, the movement of small structure becomes dominant, and flow field turns into turbulence. It is noted that production of small vortex structures is combined with turning of symmetrical structures to unsymmetrical ones. It is shown in the present computation that the flow field turns into turbulence directly from initial instability and there is not vortex pairing in process of transition. It means that for large convective Mach number the transition mechanism for compressible mixing layer differs from that in incompressible mixing layer.
Resumo:
Three adhesion contact models, JKR (Johnson-Kendall-Roberts), DMT (Derjaguin-Muller-Toporov) and MD (Maugis-Dugdale) are compared with the Hertz model in dealing with the nano-contact problems. It has been shown that the dimensionless load parameter, $\bar{P}=P/(\pi\Delta\gamma R)$, and the transition parameter, $\Lambda$, have significant influences on the contact stiffness (contact area) at micro/nano-scale and should not be ignored in shallow nanoindentation.
Resumo:
The plane strain asymptotic fields for cracks terminating at the interface between elastic and pressure-sensitive dilatant material are investigated in this paper. Applying the stress-strain relation for the pressure-sensitive dilatant material, we have obtained an exact asymptotic solution for the plane strain tip fields for two types of cracks, one of which lies in the pressure-sensitive dilatant material and the other in the elastic material and their tips touch both the bimaterial interface. In cases, numerical results show that the singularity and the angular variations of the fields obtained depend on the material hardening exponent n, the pressure sensitivity parameter mu and geometrical parameter lambda.