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111.
Matej Babjak 《Tetrahedron》2005,61(9):2471-2479
A total synthesis of (+)-goniothalesdiol, a 3,4-dihydroxy-2,5-disubstituted tetrahydrofuran isolated from Goniothalamus borneensis (Annonaceae), and its 7-epimer is reported using oxycarbonylation methodology for construction of polyhydroxylated substituted heterocycles. Diastereoselectivity of addition of organometallic reagents to 2,3-O-isopropylidene-d-threose derivatives using theoretical calculations based on the semiempirical PM5 was studied. 相似文献
112.
In our former investigations, the phenomenon high temperature corrosion (HTC) was described exemplarily on selected materialcoating combinations for blades of stationary gas turbines, mainly in the temperature region of up to 750° C. To answer the question, in which manner higher gas inlet and/or higher material surface temperature would influence the HTC behaviour, a special analytical technique—the integral layer profile analysis—was introduced to ameliorate concentration profile methods. By examining IN 738 LC specimens with CoCrAlY plasma spray coating, stressed by hot gas at 900° C, the limits of this system are shown by explaining the corrosion mechanism; the method is also used for other systems, e.g. U 520 with NiCrAlY coating at 750° C. 相似文献
113.
Electron micrographs of parallel arrays of negatively stained ramie cellulose protofibrils were analyzed using the two-dimensional digital autocorrelation function (ACF). The method is based upon the statistical analysis of images in real space. The ACF shows strong parallel streaks of high correlation, and the lateral distance between adjacent streaks allows the mean interfibrillar distance to be estimated as 3.7 nm. The intensity profile along the streaks shows a weak modulation with peaks occurring at integral multiples of 3 or 6 nm. These results provide direct evidence that there is a regular axial texture in the protofibrils, and corroborate the conclusions previously drawn from optical diffraction analysis. Using the difference vectors found in the ACF it has been possible to reduce the picture noise level by linear integration, thereby obtaining an enhanced image. A preliminary result obtained in this way suggests that the projected protofibril morphology associated with the observed axial periodicity is a ribbon-like zigzag structure. Possible applications of the method for future work are discussed. 相似文献
114.
James F. Rusling Barry J. Scheer Azita Owlia Thomas T.-t. Chou James M. Bobbitt 《Journal of Electroanalytical Chemistry》1984,178(1):129-142
1-Carbomethoxy-1,2,3,4-tetrahydrocarbazole (1) and its 7-methoxy derivative (2) were oxidized at carbon felt anodes in acetonitrile containing 0.2 M LiClO4 and 2-17 M water at potentials on the rising portion of the primary oxidation peak to yield products formed by formal substitution of the C-1 H atom with hydroxide. The resulting 1-hydroxy-l-carbomethoxy-1,2,3,4-tetrahydrocarbazole and its 7-methoxy derivative were isolated in 44 and 22% yields, respectively, when sodium bicarbonate was used to control acidity of the medium. Structures were elucidated by NMR, IR, elemental analysis, and mass spectrometry. Voltammetry at carbon-paste and glassy carbon electrodes showed that the oxidations proceed by an ECE or DISPI pathway. The rate-determining step is the reaction of water with a cation radical electrochemically generated from 1 or 2, involving either proton abstraction or nucleophilic addition. 相似文献
115.
The thermodynamics of the conversion of aqueous glucose to fructose has been investigated using both heat conduction microcalorimetry
and high pressure liquid chromatography (HPLC). The reaction was carried out in both aqueous Tris/HCl buffer and in aqueous
phosphate buffer in the pH range 7–8 using the enzyme glucose isomerase and the cofactors CoCl2 and MgSO4. The temperature range over which this reaction was investigated was 298.15–358.15 K. We have found that the enthalpy of
reaction is independent of pH over the range investigated. A combined analysis of both the HPLC and microcalorimetric data
leads to the following results at 298 15 K:ΔG° = 349 ± 53 J mol-1, ΔH° = 2.78 ± 0.20 kJ mol-1, and ΔC
p
°
= 76 ± 30 J mol-1 K-1. The stated uncertainties are based upon an analysis of both the random and systematic errors inherent in the measurements.
Comparisons are made with literature data. The percent conversion of glucose to fructose has been calculated for the temperature
range 300–373.15 K. 相似文献
116.
The degradation of acenaphthylene, acenaphthene, 2-methylnaphthalene, 2-methylindene, 3-methylindene and indene in water solutions was studied. These compounds at the 25-150 mug/l. level were almost totally degraded at ambient temperature within three days. The microbial population responsible for the degradation occurs naturally in ground-water taken from an aquifer in Ames, Iowa, which is contaminated with coal-tar products. These unidentified micro-organisms adapt readily to other waters when used as an inoculant for the degradation of aromatic compounds. The preservation of water to prevent such degradation was also investigated. Filtration through a 0.45-mum filter was found the most effective procedure for preserving the hydrocarbons in these waters. 相似文献
117.
The cis fused bicyclic sulfones 1a, 1c and 3a are lithiated in benzene with n-butyllithium under concomitant cis/trans isomerization of the ring fusion, involving intramolecular proton transfer. H/D exchange of the three α-hydrogens in protic solvents proceeds with retention of configuration. The lithiated sulfones are chlorinated with hexachloroethane (HCE) and show a strong preference for introduction of halogen at an equatorial α-position. 相似文献
118.
The Cr(CO)3(CH3CN)3 complex is found to catalyze the 1,4-addition of hydrogen to 1,3-dienes such as 2-methyl-1,3-butadiene, trans-1,3-pentadiene, and trans, trans-2,4-hexadiene at low temperature (40°) and low H2 pressure (20 psi). For trans, trans-2,4-hexadiene the only product obtained when D2 is used is 2,5-dideuterio-cis-3-hexene. The catalytic 1,4-hydrogenation can be carried out in neat dienes, and turnover numbers for the catalyst of greater than 3000 have been observed. 相似文献
119.
Simultaneous measurement of glucose and glutamine in aqueous solutions by near infrared spectroscopy 总被引:1,自引:0,他引:1
Hoeil Chung Mark A. Arnold Martin Rhiel David W. Murhammer 《Applied biochemistry and biotechnology》1995,50(2):109-125
A method is described for measuring the concentrations of both glucose and glutamine in binary mixtures from near infrared
(NIR) absorption spectra. Spectra are collected over the range from 5000–4000/cm (2.0–2.5μm) with a 1-mm optical path length.
Glucose absorbance features at 4710, 4400, and 4300/cm and glutamine features at 4700, 4580, and 4390/cm provide the analytical
information required for the measurement. Multivariate calibration models are generated by using partial least squares (PLS)
regression alone and PLS regression combined with a preprocessing digital Fourier filtering step. The ideal number of PLS
factors and spectral range are identified separately for each analyte. In addition, the optimum Fourier filter parameters
are established for both compounds. The best overall analytical performance is obtained by combining Fourier filtering and
PLS regression. Glucose measurements are established over the concentration range from 1.66–59.91 mM, with a standard error of prediction (SEP) of 0.32 mM and a mean percent error of 1.84%. Glutamine can be measured over the
concentration range from 1.10–30.65 mM with a SEP of 0.75 mM and a mean percent error of 6.67%. These results demonstrate
the analytical utility of NIR spectroscopy for monitoring glucose and glutamine levels in mammalian and insect cell cultures. 相似文献
120.
Andrzej Małecki Jalees A.K. Tareen Jean Pierre Doumerc Louis Rabardel Jean Claude Launay 《Journal of solid state chemistry》1985,56(1):49-57
Kinetics of thermal decomposition in vacuum of Co3O4 powder as well as single crystals has been investigated. Discrepancies with the results of previous authors have been discussed. Decomposition of Co3O4 proceeds through formation of a compact layer of CoO and hence diffusion is the rate-limiting factor. The experimental curves α(t) be described for 0.05 < α < 0.85 using a modified Ginstling-Brounshtein equation: 1 ? 2α/3 ? (1 ? α)2/3 = ktn where the activation energy varies with the degree of decomposition. 相似文献