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11.
Spectroscopic and chemical evidence is presented in support of the structure of 7α,11β-diacetoxydihydronomilin (I) obtained from a benzene extract of the dehisced fruit capsules of . 相似文献
12.
Water adsorption on kaolinite is a specific cooperative adsorption which does not satisfy the fundamental hypothesis of the BET theory.The adsorption isotherms on different homoionic samples show the effect of the hydration energy of the active sites (exchangeable cations) on quantitative adsorption data.The corresponding calorimetric curves present a maximum which characterizes interactions in the adsorbed phase. A relationship is apparent between these interactions and the electric field or the polarizability of the fixed cation, these factors determining the nature of the bond between the surface and cation.From the experimental data, we may propose an approximative value for the number of molecules which compose the primary hydration sheath of the active sites. 相似文献
13.
Rolf Stomberg Knut Lundquist Marcelle Hauteville Hans Geiger 《Journal of chemical crystallography》1991,21(2):183-188
The crystal structure of protogenkwanin, C16H14O6, has been determined by single-crystal diffraction methods. The compound crystallizes in the monoclinic space groupP21/c witha=6.804(4),b=7.457(3),c=26.234(3)Å,=95.66(2)° andZ=4. A total of 3275 unique reflection intensities were recorded on a Rigaku AFC6R diffractometer (MoK radiation) at room temperature. The structure was solved by direct methods and electron density calculations. Full-matrix least-squares refinement gaveR=0.058 for 1257 observed [I>3(I)] reflections. Thecrystal structure confirms results from earlier studies on protogenkwanin and elucidates the steric orientation of the hydroxyl substituents of the cyclohexadiene ring: the hydroxyl groups aretrans orientated. 相似文献
14.
15.
Leszek Rycerz Ewa Ingier-Stocka Slobodan Gadzuric Marcelle Gaune-Escard 《Journal of Thermal Analysis and Calorimetry》2010,101(2):455-461
Differential Scanning Calorimetry was used to study phase equilibrium in EuBr2–RbBr binary system. It was established that this system includes two eutectics and three stoichiometric compounds. First
of them, Rb2EuBr4, decomposes peritectically at 778 K. Second one, RbEuBr3, undergoes the solid–solid phase transition at 732 K and melts incongruently at 852 K. Third compound, RbEu2Br5, melts congruently at 888 K. The composition and temperature values of eutectics were determined as x(EuBr2) = 0.316; T
eut = 776 K and x(EuBr2) = 0.797; T
eut = 859 K. Mixing enthalpy was measured by direct calorimetry on the whole composition range. The minimum of the mixing enthalpy
occurs around the composition x(EuBr2) ≈ 0.4. The electrical conductivity of liquid mixtures was also investigated over the whole composition range and measured
down to temperatures below solidification. The specific conductance (liquid phase) plotted against the mole fraction of EuBr2 shows a broad minimum at x(EuBr2) ~ 0.6. The activation energy for conductivity changes with temperature. Results obtained are discussed in terms of possible
complex formation. 相似文献
16.
Kouakou TH Dué EA Kouadio NE Niamké S Kouadio YJ Mérillon JM 《Applied biochemistry and biotechnology》2009,157(3):575-592
Two peroxidases, cPOD-I and rPOD-II, have been isolated and purified from cotton cell suspension and their biochemical characteristics
studied. rPOD-II from R405-2000, a non-embryogenic cultivar, has higher activity than cPOD-I derived from Coker 312, which
developed an embryogenic structure. The cPOD-I and rPOD-II had molecular mass of 39.1 and 64 kDa respectively, as determined
by SDS-PAGE. Both enzymes showed high efficiency of interaction with the guaiacol at 25 mM. The optimal pH for cPOD-I and
rPOD-II activity was 5.0 and 6.0, respectively. The enzyme had an optimum temperature of 25 °C and was relatively stable at
20–30 °C. The isoenzymes were highly inhibited by ascorbic acid, dithiothreitol, sodium metabisulfite, and β-mercaptoethanol.
Their activities were highly enhanced by Al3+, Fe3+, Ca2+, and Ni2+, but they were moderately inhibited by Mn2+ and K+. The enzyme lost 50% to 62% of its activity in the presence of Zn2+ and Hg2+. 相似文献
17.
From the fertile sprouts of Equisetum arvense L. have been isolated protogenkwanin 4'-glucoside and gossypitrin. The structure of protogenkwanin as 5-hydroxy-2-(1,4-dlhydroxy-2,5-cyclohexadienyl)-7-methoxy-4-chromenon is proved on the basis of chemical and physical evidence. It is demonstrated that articulatin a thiamine decomposing substance, from E. arvense, is identical with the known flavonol glycoside gossypitrin (= gossypetin-7-glucoside). The synthesis of 2,5-dihydroxy-2-(4 hydroxyphenyl)-7-methoxy-4-chromanon is reported. 相似文献
18.
Kudryavtsev V Felekyan S Woźniak AK König M Sandhagen C Kühnemuth R Seidel CA Oesterhelt F 《Analytical and bioanalytical chemistry》2007,387(1):71-82
A new general strategy based on the use of multiparameter fluorescence detection (MFD) to register and quantitatively analyse
fluorescence images is introduced. Multiparameter fluorescence imaging (MFDi) uses pulsed excitation, time-correlated single-photon
counting and a special pixel clock to simultaneously monitor the changes in the eight-dimensional fluorescence information
(fundamental anisotropy, fluorescence lifetime, fluorescence intensity, time, excitation spectrum, fluorescence spectrum,
fluorescence quantum yield, distance between fluorophores) in real time. The three spatial coordinates are also stored. The
most statistically efficient techniques known from single-molecule spectroscopy are used to estimate fluorescence parameters
of interest for all pixels, not just for the regions of interest. Their statistical significance is judged from a stack of
two-dimensional histograms. In this way, specific pixels can be selected for subsequent pixel-based subensemble analysis in
order to improve the statistical accuracy of the parameters estimated. MFDi avoids the need for sequential measurements, because
the registered data allow one to perform many analysis techniques, such as fluorescence-intensity distribution analysis (FIDA)
and fluorescence correlation spectroscopy (FCS), in an off-line mode. The limitations of FCS for counting molecules and monitoring
dynamics are discussed. To demonstrate the ability of our technique, we analysed two systems: (i) interactions of the fluorescent
dye Rhodamine 110 inside and outside of a glutathione sepharose bead, and (ii) microtubule dynamics in live yeast cells of
Schizosaccharomyces pombe using a fusion protein of Green Fluorescent Protein (GFP) with Minichromosome Altered Loss Protein 3 (Mal3), which is involved
in the dynamic cycle of polymerising and depolymerising microtubules. 相似文献
19.
Ferguson ML Senecal TD Groendyke TM Mapp AK 《Journal of the American Chemical Society》2006,128(14):4576-4577
Allylic phosphonium ylides are readily generated by the combination of an allylic alcohol, a carbene, and a chlorophosphite. Here we demonstrate that these intermediates undergo a thermal [3,3]-rearrangement to provide single isomers of homoallylic phosphonates in good to excellent yields. This new reaction manifold for phosphorus ylides is tolerant of a range of substitution patterns on the reactants and provides access to structurally complex intermediates for the synthesis of enzyme inhibitors, aminophosphonic acids, and natural products. 相似文献
20.
Beata Salamon Jan Kapała Marcelle Gaune-Escard 《Journal of Thermal Analysis and Calorimetry》2012,108(2):421-424
The original Calvet calorimeter, made from aluminum block, were instrumented. The cells for the solution calorimetry measurement
have been projected and constructed. The calibration of calorimeter was performed by measurement of the dependence of reference
material on temperature and the influence of mechanical events on thermograms. The enthalpies of solution in water and 0.01 M
HCl were investigated for chlorides and bromides of alkali metals (Na···Cs), PrBr3 and Rb3PrBr6. The enthalpies of solution of alkali halides have been compared to the reference data obtained for infinite solution. The
decomposition of Rb3PrBr6 at temperatures lower than 399 K has been stated. The enthalpy of solution PrBr3 at 298.15 K has been determined. 相似文献