排序方式: 共有37条查询结果,搜索用时 578 毫秒
1.
Amphiphilic segmented polymer networks (SPNs) have been prepared by free radical copolymerization of methyl methacrylate with α,ω-bisacrylate terminated poly(2-methyl-2-oxazoline) and poly(2-ethyl-2-oxazoline). DSC and DMTA analysis demonstrated the influence of the copolymer composition, the molecular weight and nature of the poly(2-alkyl-2-oxazoline)s and the polymerization conditions on the final phase morphology of the networks. A comparative phase morphology study of the polymer blends and SPNs revealed the more compatible phase morphology of the networks. The compatibility could be further increased by UV-induced network formation. The investigation of the solvent uptake in different solvents clearly demonstrated the amphiphilic nature of the SPNs. 相似文献
2.
Tzoneva R Groth T Altankov G Paul D 《Journal of materials science. Materials in medicine》2002,13(12):1235-1244
The endothelization of cardiovascular implants is desirable to improve their blood compatibility. The capacity of the endothelial cells to attach, migrate, proliferate and function on the implant surface depends on the presence of matrix proteins such as fibronectin (FN) and fibrinogen (FNG). In this study, we show that the deposition of fibrinogen into extracellular matrix-like structures by human umbilical vein endothelial cells (HUVEC) is dependent on FN matrix formation. We found further that the process of organization of both adsorbed and soluble FN and FNG is dependent on the wettability of materials since it was observed only on a hydrophilic and not on a hydrophobic model surface. 3 integrin was involved in the process of cell attachment to adsorbed FNG, while the mechanism of FNG fibrillogenesis required the activity of the 1 integrin. Studies of EC morphology showed the predominant peripheral organization of actin filaments and the formation of distinct leading and trailing cell edges suggesting a motile phenotype of cells when they are seeded on FNG. In summary, we concluded that adsorbed fibrinogen may enhance the motility of HUVEC and that soluble FNG requires FN matrix assembly to be organized in fibrilar structures. 相似文献
3.
Summary It is shown that the combined use of gel permeation chromatography and the isocyanate method of determination of hydroxyl end groups extends the possibilities for studying complex oligomer mixtures of -caprolactone. Oligomer mixtures of -caprolactone obtained by (C6H5)3CSbCl6 and by (C6H5)3CK are investigated. At initiation by both the initiators — the cationic and the anionic one — a covalent bond between the initiator and the polymer chain is formed. In the case of the initiation by (C6H5)3CK intramolecular transesterification proceeds which results in cyclic oligomers. At initiation by (C6H5)3CSbCl6 linear oligomers are formed. It is assumed that the -caprolactone polymerization by (C6H5)3CSbCl6 proceeds by alkyl-oxygen bond scission. 相似文献
4.
Bakalova R Zhelev Z Jose R Nagase T Ohba H Ishikawa M Baba Y 《Journal of nanoscience and nanotechnology》2005,5(6):887-894
The present study describes an enhancement of the photoluminescence of CdSe quantum dots under long-term ultraviolet irradiation in organic solvents. The photoenhancement effect followed multiexponential kinetics and was found to depend on several factors: intensity of ultraviolet light, polarity of the solvent, presence of capping agents on the nanocrystal surface, and presence of free Cd and Se ions in the solution. High intensity ultraviolet irradiation provoked a rapid enhancement of the photoluminescence of CdSe nanocrystals, reaching the maximum with subsequent photoluminescence decay. Low-intensity ultraviolet irradiation provoked a comparatively slow enhancement of the photoluminescence of CdSe nanocrystals, reaching saturation after 5-6 hours of irradiation in organic solvents (butanol and chloroform). The photoenhancement effect was reversible or irreversible depending on the additional ingredients. The role of free Cd and Se in these processes was clarified. The results are discussed in the context of ultraviolet induced liberation of free Cd and Se ions from the nanocrystal surface and their hypothetical reversible deposition with trapping of the surface holes and influencing the efficiency of radiative versus nonradiative exciton decay during the enhancement of photoluminescence. 相似文献
5.
In the present study, we describe the synthesis of highly luminescent uncoated water-soluble CdSe quantum dots (QDs) possessing the following characteristics: approximately 2 nm in diameter, with very good size distribution (in 95% homodispersed) accompanied by a broad-band photoluminescent spectrum. The synthetic procedure is simple, is conducted at room temperature, in the absence of the most popular coordinating ligands (as TOPO or HDA), and is highly reproducible. The obtained CdSe core QDs possessed a comparatively long fluorescence half-life (approximately 30-90 ns, depending on the emission wavelength) detected by time-resolved spectroscopy. These QDs were further conjugated with antibodies and applied in several biochemical analyses. 相似文献
6.
Heterogeneous fenton and photo‐fenton oxidation for paracetamol removal using iron containing ZSM‐5 zeolite as catalyst
下载免费PDF全文
![点击此处可从《American Institute of Chemical Engineers》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Filipa Velichkova Henri Delmas Carine Julcour Bogdana Koumanova 《American Institute of Chemical Engineers》2017,63(2):669-679
Paracetamol is commonly found in wastewaters, as a consequence of its high consumption and incomplete elimination by conventional treatments. Homogenous (photo‐)Fenton oxidation has proved efficient for its remediation, but it suffers from uneasy dissolved iron recovery. Therefore this work examines the performance and stability of an iron containing zeolite (Fe/MFI) as catalyst for this reaction. Effects of reaction parameters (pH, temperature, catalyst and H2O2 concentrations, UV/vis irradiation) are investigated in batch conditions, by comparing the pollutant and Total Organic Carbon disappearance rates in solution, as well as the overall mineralization yield (including solid phase) and oxidant consumption. At near neutral pH paracetamol can be fully converted after 5 h, while TOC removal reaches up to 60%. Finally, thanks to good catalyst stability (low leaching), a continuous process coupling oxidation and membrane filtration is proposed, showing constant TOC conversion over 40 h and iron loss in the permeate <0.3 ppm. © 2016 American Institute of Chemical Engineers AIChE J, 63: 669–679, 2017 相似文献
7.
The present study describes a stabilization of single quantum dot (QD) micelles by a "hydrophobic" silica precursor and an extension of a silica layer to form a silica shell around the micelle using "amphiphilic" and "hydrophilic" silica precursors. The obtained product consists of approximately 92% single nanocrystals (CdSe, CdSe/ZnS, or CdSe/ZnSe/ZnS QDs) into the silica micelles, coated with a silica shell. The thickness of the silica shell varies, starting from 3-4 nm. Increasing the shell thickness increases the photoluminescence characteristics of QDs in an aqueous solution. The silica-shelled single CdSe/ZnS QD micelles possess a comparatively high quantum yield in an aqueous solution, a controlled small size, sharp photoluminescence spectra (fwhm approximately 30 nm), an absence of aggregation, and a high transparency. The surface of the nanoparticles is amino-functionalized and ready for conjugation. A comparatively good biocompatibility is demonstrated. The nanoparticles show ability for intracellular delivery and are noncytotoxic during long-term incubation with viable cells in the absence of light exposure, which makes them appropriate for cell tracing and drug delivery. The presence of the hydrophobic layer between the QD and silica-shell ensures an incorporation of other hydrophobic molecules with interesting properties (e.g., hydrophobic paramagnetic substances, hydrophobic photosensitizers, membrane stabilizers, lipid-soluble antioxidants or prooxidants, other hydrophobic organic dyes, etc.) in the close proximity of the nanocrystal. Thus, it is possible to combine the characteristics of hybrid materials with the priority of small size. The silica-shelled single QD micelles are considered as a basis for fabrication of novel hybrid nanomaterials for industrial and life science applications, for example, nanobioprobes with dual modality for simultaneous application in different imaging techniques (e.g., fluorescent imaging and functional magnetic resonance imaging). 相似文献
8.
Jose R Zhelev Z Nagase T Bakalova R Baba Y Ishikawa M 《Journal of nanoscience and nanotechnology》2006,6(3):618-623
A small portion of a reaction mixture including unpurified CdX (X = Se or Te) quantum dots (QDs), in which unreacted Cd and Se ions were left together with coordinating solvents, was dropped into an organic solvent. The CdX QDs in this organic solution showed enhancement of photoluminescence (PL) efficiency, growth of particles, and focusing of size distribution for more than 10 h at room temperature (RT, -23 degrees C). These effects were attributed to passivation of QDs' surface by Cd and X ions present in the solution. No external energy source was used for these achievements; therefore, the process is termed as self-surface passivation. The self-surface passivation was reproduced using purified CdX QDs with additional Cd and X ions in an organic solvent. The self-surface passivation method was applied to RT-synthesized CdSe QDs, which is characterized by a broad PL spectrum (fwhm - 150 nm) for monodispersed QDs, to modify their emission characteristics. On self-surface passivation, the broad PL spectrum was narrowed (fwhm - 35 nm) and the QDs were grown. The X-ray diffraction measurements of RT-synthesized CdSe QDs and that subsequently aged in 1-butanol showed that crystallinity of the samples was improved on aging. 相似文献
9.
Edwards SG Imathiu SM Ray RV Back M Hare MC 《International journal of food microbiology》2012,156(2):168-175
High levels of Fusarium mycotoxins HT-2 and T-2 have been detected in UK oats since surveys started in 2002. Fusarium langsethiae and the closely related species F. sporotrichioides have previously been associated with the contamination of cereals with type A trichothecenes HT-2 and T-2 in Nordic countries. Preliminary microbiological analysis of UK oat samples with high concentrations of HT-2 and T-2 detected and isolated F. langsethiae and F. poae but not the other type A trichothecene producing species F. sporotrichioides, F. sibiricum and F. armeniacum. Two hundred and forty oat flour samples with a known mycotoxin profile were selected from a previous four year study (2002-2005) to cover the full concentration range from below the limit of quantification (<20 μg/kg) to 9,990 μg/kg HT-2+T-2 combined. All samples were analysed for the DNA of F. langsethiae, F. poae and F. sporotrichioides based on previously published PCR assays. F. langsethiae was detectable in nearly all samples; F. poae was detected in 90% of samples whereas F. sporotrichioides was not detected in any sample. A real-time PCR assay was developed to quantify F. langsethiae DNA in plant material. The assay could quantify as low as 10(-4)ngF. langsethiae DNA/μl. Based on this assay and a previously published assay for F. poae, both species were quantified in the oat flour samples with known HT-2+T-2 content. Results showed a good regression (P<0.001, r(2)=0.60) between F. langsethiae DNA and HT-2+T-2 concentration. F. poae DNA concentration was not correlated to HT2+T2 concentration (P=0.448) but was weakly correlated to nivalenol concentration (P<0.001, r(2)=0.09). Multiple regression with F. langsethiae and F. poae DNA as explanatory variates identified that both F. langsethiae and F. poae DNA were highly significant (P<0.001) but F. poae DNA only accounted for an additional 4% of the variance and the estimate was negative, indicating that higher concentrations of F. poae DNA were correlated with slightly lower concentrations of HT2+T2 detected. A stronger regression (P<0.001, r(2)=0.77) between F. langsethiae DNA and HT-2+T-2 was obtained after extraction and quantification of DNA and mycotoxins from individual oat grains. The results from this study provide strong evidence that F. langsethiae is the primary, if not sole, fungus responsible for high HT-2 and T-2 in UK oats. 相似文献
10.
The influence of sucrose, wheat starch and sorbitol upon the heat- and mass-exchanging processes forming the structure of sponge cake was studied. Under the influence of wheat starch and sorbitol the structure of the sucrose-free sponge cake was formed at more uniform total moisture release. This process was done at lower temperatures and smoother change of the sponge cake height with respect to the sucrose-sweetened sponge cake. The porous and steady structure of both cakes was finally formed at identical time--between 18th and 19th minute, at the applied conditions for baking of each batter (metal pan with diameter 15.4 cm and depth 6.2 cm containing 300 g of batter and placed in an electric oven "Rahovetz-02", Bulgaria for 30 min at 180 degrees C). The water-losses at the end of baking (10.30% and 10.40% for the sucrose-sweetened cake and sucrose-free cake, respectively) and the final temperatures reached in the crumb central layers (96.6 degrees C and 96.3 degrees C for the sucrose-sweetened cake and sucrose-free cake, respectively) during baking of both samples were not statistically different. The addition of wheat starch and sorbitol in sucrose-free sponge cake lead to the statistically different values for the porosity (76.15% and 72.98%) and the volume (1014.17 cm3 and 984.25 cm3) of the sucrose-sweetened and sucrose-free sponge cakes, respectively. As a result, the sucrose-free sponge cake formed during baking had a more homogeneous and finer microstructure with respect to that ofthe sucrose-sweetened one. 相似文献