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441.
Soxhlet extraction, ultrasound extraction, and accelerated solvent extraction (ASE), followed by RP-HPLC with a photodiode array detector was used for the determination of flavonoids in fruits of Peucedanum alsaticum. Three compounds were identified: a kaempherol derivative (astragalin), and two quercetin derivatives (quercitrin and hiperoside). The highest extraction yields of the selected compounds were obtained by use of exhaustive ASE. 相似文献
442.
Since the early 70s electrochemistry has been used as a powerful analytical technique for monitoring electroactive species in living organisms. In particular, after extremely rapid evolution of new micro and nanotechnology it has been established as an invaluable technique ranging from experiments in vivo to measurement of exocytosis during communication between cells under in vitro conditions. This review highlights recent advances in the development of electrochemical sensors for selective sensing of one of the most important neurotransmitters—dopamine. Dopamine is an electroactive catecholamine neurotransmitter, abundant in the mammalian central nervous system, affecting both cognitive and behavioral functions of living organisms. We have not attempted to cover a large time-span nor to be comprehensive in presenting the vast literature devoted to electrochemical dopamine sensing. Instead, we have focused on the last five years, describing recent progress as well as showing some problems and directions for future development. 相似文献
443.
The sol-gel procedure was applied to obtain powdery materials with different structures and morphology. It was possible to produce almost non-porous silica powder, with an extremely low surface area (ca. 4 m2/g) and very high uniformity of spherical particles as well as materials with various uniformity of particles and different porosity, most likely associated with increasing pore volume. Dependent on the properties of the carrier, the resulting supported vanadium catalysts (VOCl3/AlEt2Cl) showed significant differences concerning activity and stability. It was confirmed that improved hydrophobicity of the carrier’s surface may be useful and improve the activity of the system in the polymerization. It was found that the two-step modification procedure, involving a reaction with alkylaluminum, acts beneficially for the efficiency of supported catalysts. The system supported on sol-gel material with methyl groups, additionally pre-treated with diethylaluminum chloride, showed the highest activity as well as the lowest deactivation rate constant among all those studied. 相似文献
444.
Solid-phase extraction procedure for determination of phenolic acids and some flavonols in honey 总被引:2,自引:0,他引:2
The solid-phase extraction procedure (SPE) for isolation and preconcentration of phenolic acids (gallic, p-HBA, p-coumaric, vanillic, caffeic and syringic acid) and some flavonols (rutin, quercetin and kaempferol) from honey samples prior to their determination by HPLC is reported. Different solid sorbents such as Bond Elut octadecyl C(18), Oasis HLB, Strata-X and Amberlite XAD-2 were tested for this purpose. The best results were obtain when aqueous solution of honey (100 mL) was adjusted to pH 2 and passed through the microcolumn containing 2.5 g of Oasis HB followed by washing the sorbent with 50 mL of acidified water (pH 2). The analytes were then eluted with methanol. The proposed method permits the quantification of the studied compounds with the limit of detections ranged from 25 ng kg(-1) to 0.75 microg kg(-1) for p-HBA and quercetin, respectively. The precision of the overall analytical procedure was estimated by measuring the within-day repeatability and the relative standard deviations of the parallel (n=3) results were in the range of 1.9-10.1%. The method was tested for real honey samples from different botanical origins. 相似文献
445.
Kruczała K Szczubiałka K Łańcucki Ł Zastawny I Góra-Marek K Dyrek K Sojka Z 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2008,69(5):1337-1343
The research was focused on synthesis of proton conductive, easily degradable polymer membranes, which can be used as a model system to verify the efficiency of transition metal ions (TMI) in prevention of polymer degradation. Two polymers composed of 2-hydroxyethyl methacrylate (HEMA), 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS), and styrenesulfonic acid (SS) were synthesized. The copolymers were characterized by gel permeation chromatography (GPC), elementary analysis, and FTIR and fluorescence spectroscopies. The results allowed determination of weight-average molecular weight and the copolymer composition. The protons of sulfonic groups were substituted by paramagnetic transition metal ions of various spin states (Cr(3+), S=3/2 and Mn(2+), S=5/2) with the loading varying from 0.5 up to 10 mol%. The effectiveness of spin catalysis was checked by EPR. The results obtained indicate enhancement of polymer stability in the presence of Mn(2+). 相似文献
446.
Jańczyk A Wolnicka-Głubisz A Urbanska K Stochel G Macyk W 《Journal of photochemistry and photobiology. B, Biology》2008,92(1):54-58
Phototoxicity of titanium dioxide modified with platinum(IV)-chloride complexes, [TiO2/PtCl4], irradiated with visible light was tested on murine macrophage cell line (RAW 264.7) in vitro. Presence of antioxidants such as alpha-tocopherol or beta-carotene during photodynamic treatment significantly increased cells viability. Our results indicate that observed cell death induced by [TiO2/PtCl4] was due to photogeneration of reactive species. 相似文献
447.
A high-performance counter-current chromatography (HPCCC) method was applied for the first time for the preparative separation and purification of three rare compounds which occur as minor constituents in the fruits of Peucedanum alsaticum L.: 5-substituted coumarin notoptol and two dihydropyranochromones: divaricatol and ledebouriellol. A scale-up process from analytical to preparative in a very short time was developed. In order to purify a range of rare and minor compounds with different polarity two separate experiments were performed, one in reverse phase, the other in normal phase, using the same crude extract. A two-phase solvent system composed of n-hexane/ethyl acetate/methanol/water (1:1:1:1) was developed. The components purified and collected were analyzed by high-performance liquid chromatography. The method yielded 0.7 mg of notoptol, 1.46 mg of ledebouriellol at purity of 99.5%, and 10 mg of mixtures of divaricatol, alsaticol and alsaticocoumarin, where divaricatol present 22% by peak area. These amounts were obtained from 1 g of the crude extract in a single run. This is the first time when minor notoptol, ledebouriellol, and divaricatol were isolated in a single run using HPCCC method and first time when these were identified in plant from Peucedanum genus. 相似文献
448.
M. Radecka A. Kusior A. Lacz A. Trenczek-Zajac B. Lyson-Sypien K. Zakrzewska 《Journal of Thermal Analysis and Calorimetry》2012,108(3):1079-1084
TiO2/SnO2 nanocomposites are studied as potential candidates for gas sensors. Commercial metal oxide nanopowders milled for 1?h in ethanol are used for preparing nanocomposites with varied composition from 100?mol% TiO2 to 100?mol% SnO2. Brunauer?CEmmett?CTeller (BET) adsorption isotherms served to determine specific surface area, SSA. The particle size distribution is established by means of Dynamic Light Scattering, DLS technique. Differential Thermal Analysis and Thermogravimetry, DTA/TG measurements within the temperature range of 20?C900?°C indicate better stability of nanomaterials composed of bigger particles or agglomerates. The total mass loss varies from 0.9 to 8.5% for 100?mol% SnO2 and 100?mol% TiO2, respectively. The only gaseous products of decomposition are water and carbon dioxide. X-ray diffraction analysis of nanocomposites indicates two separate phases of different crystallite size, i.e., smaller rutile TiO2 (9?nm) and larger cassiterite SnO2 (28?nm). Gas sensor dynamic responses at 400?°C to the reducing gas??ammonia (NH3) are detected in the concentration range extending from 100?ppm to ?5000?ppm. Nanosensor of 50?mol% SnO2/50?mol% TiO2 is stable and sensitive to the interaction with NH3 and gives the highest response at 400?°C. 相似文献
449.
The dynamic interfacial tension for binary mixtures of hydrophobic metal ion extractants and a modifier were measured by using the drop volume technique. Four types of equimolar mixtures were considered: two chelating extractants: 2-hydroxy-5-nonylacetophenone oxime (HNAF) and beta-diketone (1-phenyldecan-1,3-dion), two solvating extractants: trioctylphosphine oxide (TOPO) and tributyl phosphate (TBP), chelating and solvating extractants TOPO and beta-diketone, and the chelating extractant HNAF and the modifier (decanol). With the aid of the Ward and Torday equation the values of the diffusion coefficients of individual compounds and their equimolar mixtures were estimated. It was found that in the case of two types of investigated mixtures, i.e., HNAF + beta-diketone and HNAF + decanol the compound HNAF that was dominant in the mixed adsorbed monolayer and the more interfacially active also determined the kinetics of adsorption in mixed systems. In contrary to the mixture of two chelating reagents, in the case of a mixture of two solvating extractants the mixed system behaves like the less active, though dominant at the interface, reagent TBP. The same effect was observed in both of the considered diluents (toluene and octane). 相似文献
450.
Janusz Kozakiewicz Gabriel Rokicki Krystyna Sylwestrzak Karolina M. Tomczyk 《Polymer Degradation and Stability》2010,95(12):2413-2420
Polyurethane and poly(urethane-urea) elastomers synthesized from oligocarbonate diols are characterized by very good mechanical properties, biocompatibility and excellent resistance to both oxidation and hydrolysis and therefore are widely used in medical applications. In this paper the results of studies on hydrolytic stability of poly(urethane-urea) elastomers (PURC) obtained by moisture-curing of corresponding urethane prepolymers synthesized from isophorone diisocyanate (IPDI) and four different oligocarbonate diols (OCD) are presented. OCD were synthesized from dimethyl carbonate and 1,6-hexanediol, from cyclic ethylene carbonate and 1,6-hexanediol as well as from trimethylene carbonate. The changes of the sample weight, mechanical properties and surface properties after immersion in a standard phosphate buffer solution (pH = 7.4) for up to 3 months at 70 °C were monitored. It was shown that neither sample weight nor mechanical properties changed significantly for PURC obtained from OCDs synthesized from 1,6-hexanediol and dimethyl carbonate or ethylene carbonate what confirms good resistance to hydrolysis of those PURC. Also SEM studies of those samples before and after immersion did not reveal any surface degradation effects. However, PURC sample obtained from OCD synthesized from trimethylene carbonate showed significant changes in mechanical properties and distinct change of appearance and surface erosion after 3 months immersion. The initial decrease and later increase of stress at break observed for PURC samples during immersion, was explained by the reaction of residual NCO groups present in PURC with water leading to molecular weight increase which proceeded during immersion period in parallel to hydrolysis of carbonate bond. 相似文献