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201.
202.
Magnetic beads as interfacial nanoprobes 总被引:1,自引:0,他引:1
Helseth LE Wen HZ Heinig P Fischer TM 《Langmuir : the ACS journal of surfaces and colloids》2004,20(16):6556-6559
We use paramagnetic beads to probe strongly localized magnetic fields from one-dimensional nanomagnets. Using a polarization microscope in reflection mode, we find that light reflected from beads exhibits intensity fluctuations which may help us understand Brownian motion near interfaces. We estimate the height fluctuations and femtonewton forces acting on the beads. 相似文献
203.
Gerhard W. Fischer 《Journal of heterocyclic chemistry》1995,32(5):1557-1561
The acid-catalyzed reaction of substituted phenylhydrazines 1 with 1-aryl-5-(2-dimethylaminovinyl)-1H-tetrazoles 2 afforded (1-aryl-1H-tetrazol-5-yl)acetaldehyde phenylhydrazones 3 which on heating in acetic acid/perchloric acid underwent a Fischer indolization to give substituted 3-(1-aryl-1H-tetrazol-5-yl)-indoles 4a-k. Indoles of this type are also formed on subjecting 1 and 2 directly to indolization conditions; thus, starting from phenylhydrazine the tetrazolylindoles 41-s were obtained by a one-pot procedure. Indolization of corresponding Nα-methylphenylhydrazones 5 resulted in 1-methyl-3-(1-aryl-1H-tetrazol-5-yl)indoles 6 . 相似文献
204.
Two compounds janoxepin (1) and brevicompanine B (2) were isolated from the fungus Aspergillus janus and the structures elucidated by one- and two-dimensional NMR spectroscopic methods and mass spectrometry. Janoxepin is a novel oxepin derivative with a rare d-leucine incorporated. Brevicompanine B has previously only been isolated from Penicillium brevicompactum. Both compounds were tested in antimicrobial assays and found to be active against the malaria parasite Plasmodium falciparum 3D7 (IC50-values of 28 and 35 mg/ml, respectively). However, no activity was observed in antifungal or antibacterial assays. 相似文献
205.
T. P. Fischer S. Shuttleworth P. A. O’Day 《Analytical and bioanalytical chemistry》1998,362(5):457-464
The accurate measurement of ultra-trace concentrations of rare metals and platinum group elements in volcanic fluids is complicated by interferences, complex matrices, and preferential element partitioning. We analyzed condensed, high-temperature magmatic fluids collected from Kudryavy volcano (Kurile Islands, Russia) for Be, B, Rb, Sr, Mo, Ru, Rh, Pd, Cd, W, Re, Pt, Pb, Bi, and U using ICP-MS. The samples had three different matrices: 5 mol L–1 sodium hydroxide (NaOH, pH = 11), gas condensates of sulfuric acid (H2SO4, pH = 0), and solid elemental sulfur. Interferences and suppression/enhancement effects were investigated using standards in concentrated NaOH and H2SO4 solutions to determine adequate dilution for sample analyses, which then required very low levels of element detection (< 1 μg L–1 for most elements). Depending on the field sampling technique of volcanic gas vents, our results show significant differences in concentrations of some trace elements due to the precipitation of solid sulfur during gas condensation and variations in element volatility as a function of temperature. 相似文献
206.
Determination of polycyclic aromatic hydrocarbons in water samples using high-performance liquid chromatography with amperometric detection 总被引:2,自引:0,他引:2
The determination of polycyclic aromatic hydrocarbons (PAHs) using high-performance liquid chromatography (HPLC) with UV and fluorescence detection has been well established. Although most of the PAHs can be detected by these methods, some environmentally important polyaromatic compounds, such as acenaphthylene, do not show fluorescence and can only be determined by UV detection at higher concentrations. A sensitive and selective determination of acenaphthylene, acenaphthene and the six PAHs listed in the TVO, the German drinking water standard, is also possible by amperometric detection following HPLC separation. The method was applied to the determination of PAHs in different water samples after solid-phase extraction (SPE). The efficiency of the amperometric determination was found to be superior to UV detection (λ = 300 nm). 相似文献
207.
208.
Radicals H2N? ?H? COOH and H2N? ?H? COO? which have different ESR. spectra are observed during the reaction of hydroxyl radicals with glycine in aqueous solution. Rapid and reversible exchange between the different dissociated radicals is induced by addition of phosphoric acid. The pH dependence of the ESR. spectra yields the pK value and rate constants for proton transfer reactions between the radicals and phosphoric acid. 相似文献
209.
Interactions of three types of tetraalkylammonium cations (tetrapropyltetrabutyl-and tri-isoamylbutyl- ammonium) with perchlorate and tetraphenylborate anions were studied by the conductivity method in 2-butanone from –45°C to 25°C. Conductance data obtained for diluted solutions (5×10–5 – 2×10–3 mol-dm–3) were used to calculate the limiting molar conductivities and associationconstants. The conductance equation of Fuoss-Hsia including the Chen term and the chemical model assumption were applied. Limiting ion conductivities were calculated assuming equal limiting conductivities of the i-Am3BuN+ and BPh
4
–
ions at all temperatures. Gibbs energies and entropies of ion pair formation, calculated from the dependence of association constants on temperature, are presented including the contributions due to short-range forces. 相似文献
210.
Ulrich Ch . Fischer Paul Towner Dieter Oesterhelt 《Photochemistry and photobiology》1981,33(4):529-537
Abstract— Bacteriorhodopsin (BR) from the purple membrane of Haiobacterium halobium contains covalently bound retinal in the 13- cis and all- trans configurations. Several forms of bacteriorhodopsin are known, with different absorption maxima which are designated as BRλmax (nm). At acidic pH, BR605 is formed from BR560. The following sequence of reactions was found, which is initiated by irradiation of BR605 with red light:
An all- trans /13- cis to 9- cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560. 相似文献
An all- trans /13- cis to 9- cis isomerisation occurs in the light induced reaction BR605 ∼ BR500. BR500 seems to contain covalently bound retinal, whereas BR390 contains free retinal. By irradiation with light, BR500, BR450 and BR390 can be reconverted to BR560. 相似文献