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排序方式: 共有244条查询结果,搜索用时 15 毫秒
41.
Warner JH Watt AR Thomsen E Heckenberg N Meredith P Rubinsztein-Dunlop H 《The journal of physical chemistry. B》2005,109(18):9001-9005
Steady-state and time-resolved photoluminescence spectroscopy are used to examine the photoluminescent properties of nanocrystal-polymer composites consisting of colloidal PbS nanocrystals blended with poly(2-methoxy-5(2-ethylhexyloxy)-p-phenylene vinylene). Quenching of the emission from the conjugated polymer due to the PbS nanocrystals is observed along with band edge emission from the ligand capped PbS nanocrystals. A decrease in the photoluminescence lifetime of MEH-PPV is also observed in the thin film nanocrystal-polymer composite materials. Photoluminescence excitation spectroscopy of the PbS nanocrystal emission from the composite shows features attributed to MEH-PPV providing evidence of a F?rster transfer process. 相似文献
42.
ÜMMÜHAN OCAK HALIT KANTEKIN YAŞAR GÖK H. BASIR ŞENTÜRK 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(1-2):87-91
The selective liquid–liquid extraction of various transition metal cations from the aqueous phase to the organic phase was carried out using a 14-membered N2O2S2-macrobicycle. Metal picrates such as Pb2+, Co2+, Zn2+, Ni2+,Cu2+ and Cd2+ were used in this extraction studies. It was found that the ligand showed moderate selectivity towards Pb2+ only among the other metals. The extraction constant (log K
ex) was determined to be 13.8 for Pb2+ complex. 相似文献
43.
W. R. Watt F. H. Fry H. Pobiner 《Journal of polymer science. Part A, Polymer chemistry》1968,6(10):2703-2713
Catalysts for the polymerization of ethylene were prepared from titanium (III) acetylacetonate and diethylaluminum chloride. Titanium (III) acetylacetonate is of interest because it is soluble in hydrocarbon solvents used as polymerization media. As its oxidation product oxobisacetylacetonatotitanium (IV) is also hydrocarbon-soluble, this system provides a vehicle for studying the effects of a change in valence on catalyst activity without an accompanying change of state, as occurs with titanium halides. Relatively high molar ratios (>20:1) of aluminum alkyl to titanium compound were required to give active catalysts. Precipitates generally formed in the catalyst mixtures, although dilute catalyst solutions in which no precipitate was visible still initiated polymerization. Catalyst mixtures were observed to undergo certain changes on standing. Light-scattering studies indicated an increase in catalyst particle size, and a gas identified as ethane was evolved. These changes were accompanied by a reduction in activity of the catalyst. Parallel polymerization tests were run for a comparison of catalysts prepared from titanium(III) acetylacetonate and catalysts prepared from oxobisacetylacetonatotitanium(IV). There was essentially no difference in yield or properties of polymer prepared using the two catalyst systems. The evidence suggests that both the trivalent and tetravalent titanium compounds yield the same catalytic intermediate when reacting with diethylaluminum chloride. 相似文献
44.
45.
I. C. Watt 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(5):1079-1089
The properties of keratin following the formation of polymers in situ have been studied. It is important to determine any effects of the initiatory system on keratin in order to assess the role of the added polymer, The water content of the copolymer usually differs from that of the keratin and polymer measured as separate entities and influences the observed physical properties. Deposition of polymer has little direct effect on properties unless reaction with the keratin structure occurs. Observed physical properties suggest that polymer is predominately formed in the matrix component. 相似文献
46.
47.
The Swern oxidation of acyclic and cyclic α-ketols delivered α-diketones or the tautomeric diosphenols in good yield. 相似文献
48.
49.
Frank Sobott Stephen J. Watt Julia Smith Mariola J. Edelmann Holger B. Kramer Benedikt M. Kessler 《Journal of the American Society for Mass Spectrometry》2009,20(9):1652-1659
Ubiquitination has emerged as one of the major post-translational modifications that decide on protein fate, targeting, and
regulation of protein function. Whereas the ubiquitination of proteins can be monitored with classic biochemical methods,
the mapping of modified side chains proves to be challenging. More recently, mass spectrometry has been applied to identify
ubiquitinated proteins and also their sites of modification. Typically, liquid chromatography tandem mass spectrometry (LC-MS/MS)
based approaches, including collision-induced fragmentation (CID), have been successfully used in the past. However, a potential
difficulty arises from the unstable nature of this modification, and also that the isopeptide bond linkage between C-terminal
glycine and the N(ε) lysyl side chain is susceptible to fragmentation under these conditions. Here we investigate the utility of electron-transfer
dissociation (ETD)-based fragmentation to detect ubiquitination sites in proteins. Our results indicate that ETD can provide
alternative fragmentation patterns that allow detection of gly-gly-modified lysyl side chains, in particular z+1 fragment
ions derived from triply charged precursor ions. We subsequently applied ETD fragmentation-based analysis and detected novel
ubiquitination sites on DNA polymerase B1 that were not easily observed using CID. We conclude that ETD can provide significant
alternative fragmentation information that complements CID-derived data to improve the coverage when mapping ubiquitination
sites in proteins. 相似文献
50.
Hypericin-photodynamic therapy (PDT) using an alternative treatment regime suitable for multi-fraction PDT 总被引:1,自引:0,他引:1
Thong PS Watt F Ren MQ Tan PH Soo KC Olivo M 《Journal of photochemistry and photobiology. B, Biology》2006,82(1):1-8
Photodynamic therapy (PDT) outcome depends on the conditions under which it is carried out. Maintaining the tumour tissue oxygen level is important for PDT efficacy and using a low fluence rate can improve outcome. In this work we studied the response of human nasopharyngeal carcinoma tumours in murine models to hypericin-PDT carried out under low fluence and fluence rate. A drug-light interval (DLI) of 1h or 6h was used for 1h-PDT and 6h-PDT, respectively. Evan's blue test was used to assess necrosis and TUNEL staining for apoptosis. Nuclear microscopy was used to quantify elemental concentrations in tumours. Serum vascular endothelial growth factor (VEGF) levels were also determined. TUNEL results showed that 6h-PDT induced significantly more apoptosis compared to 1h-PDT (p<0.01). This was supported by nuclear microscopy showing an increase in calcium and a decrease in zinc levels (both known triggers of apoptosis) in 6h-PDT tumours compared to non-PDT tumours (p<0.05). These results further imply a zinc-mediated pathway in hypericin-PDT induced apoptosis. 6h-PDT also resulted in a significant increase in copper concentrations compared to non-PDT tumours (p<0.05). Serum VEGF levels measured after 6h-PDT were lower than those obtained after 1h-PDT. Overall tumour response to hypericin-PDT under low fluence and fluence rate and using a 6h DLI showed increased apoptosis and lower serum VEGF levels. This treatment regime is suitable for the alternative approach of multi-fraction PDT in which the tumour can be exposed to multiple PDT fractions for complete tumour response. This alternative approach might yield improved outcome. 相似文献