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41.
Two new type dicoumarins (dicoumaro-p-menthanes), named dibothrioclinins I (1) and II (2) were isolated from the roots and rhizomes of Gerbera piloselloides (L.) CASS., collected in Yunnan Province, China. Their structures were elucidated on the basis of MS, 1D ((1)H-NMR, (13)C-NMR, DEPT and NOE) and 2D ((1)H-(1)H COSY, HMQC, HMBC) NMR spectral analyses. The relative structures of the two compounds were established by NOE difference spectroscopy and further confirmed by single-crystal X-ray diffraction studies. 相似文献
42.
Cao Ning-Jun Xu Qin Chen Chee-Shan Gong C. S. Chen L. F. 《Applied biochemistry and biotechnology》1994,(1):521-530
Cellulose gel with < 10% of crystallinity was prepared by treatment of microcrystalline cellulose, Avicel, with zinc chloride
solution at a ratio of zinc chloride to cellulose from 1.5 to 18 (w/w). The presence of zinc ions in the cellulose gels enhanced
the rate of hydrolysis and glucose yield. The evidence obtained from X-ray diffraction, iodine absorption experiments; and
Nuclear Magnetic Resonance spectra analysis suggested the presence of zinc-cellulose complex after Avicel was treated with
zinc chloride. Zinc-cellulose complex was more susceptible to hydrolysis than amorphous cellulose. Under the experimental
condition, cellulose gels with zinc ions were hyrolyzed to glucose with 95% theoretical yield and a concentration of 14% (w/v)
by cellulases within 20 h. The same gel was hydrolyzed by acid to glucose with 91.5% yield and a concentration of 13.4% (w/v). 相似文献
43.
XRD and XPS are used to study the dispersion state of CuO on ceria surface. The dispersion capacity values of CuO measured
by the two methods are consistent, which are of 1.20 mmol CuO/100 m2 CeO2. In addition, the results reveal that highly dispersed Cu2+ ions are formed at low CuO loadings and that increasing the CuO content to a value higher than its dispersion capacity produces
crystalline CuO after the surface vacant sites on CeO2 are filled. The atomic composition of the outermost layer of the CuO/CeO2 samples has been probed by using static secondary ion mass spectroscopy (SSIMS), and the ratim of Cu/Ce are found to be 0.93
and 0.46 for the 1.22 and 0.61 mmol CuO/CeO2 samples respectively. Temperature-programmed reduction (TPR) profile with two reduction peaks at 156 and 165°C suggests that
the reduction of highly dispersed Cu2+ ions consists of two steps and is easier than that of CuO crystallites, in which the TPR profile has only one reduction peak
at about 249°C. The above experimental results are in good agreement with the prediction of the incorporation model.
Project supported by the National Natural Science Foundation of China. 相似文献
44.
Reactions of the substituted 2‐formyl chromones with aroylhydrazines gave corresponding 2‐(aroylhydrazonomethylidyne) chromones. Then 2‐(3′‐acetyl‐5′‐aryl‐2′,3′‐dihydro‐1′,3′,4′‐oxadiazol‐2′‐yl) chromones were prepared by these 2‐(aroylhydrazonomethylidyne) chromones under refluxing with Ac2O. All target compounds were characterized through elemental analysis and IR, 1H NMR, MS. 相似文献
45.
The effects of four factors (different side chains, side-chain disorder, conformational change, and ions and water) on the energy band structures of proteins have been investigated with the aid of the CNDO/2 crystal orbital method. The results indicate that these factors are very important. The consequences of these effects on the semiconductive properties of proteins are discussed. 相似文献
46.
Highly ordered mesoporous silica can be regenerated from a mesoporous carbon CMK-3 that is a negative replica of mesoporous silica SBA-15, indicating reversible replication between carbon and inorganic materials. 相似文献
47.
We compute the quantum rate constant based on two extended stationary phase approximations to the imaginary-time formulation of the quantum rate theory. The optimized stationary phase approximation to the imaginary-time flux-flux correlation function employs the optimized quadratic reference system to overcome the inaccuracy of the quadratic expansion in the standard stationary phase approximation, and yields favorable agreements with instanton results for both adiabatic and nonadiabatic processes in dissipative and nondissipative systems. The integrated stationary phase approximation to the two-dimensional barrier free energy is particularly useful for adiabatic processes and demonstrates consistent results with the imaginary-time flux-flux correlation function approach. Our stationary phase methods do not require calculation of tunneling paths or stability matrices, and work equally well in the high-temperature and the low-temperature regimes. The numerical results suggest their general applicability for calibration of imaginary-time methods and for the calculation of quantum rate constants in systems with a large number of degrees of freedom. 相似文献
48.
Chen H Li G Zhang FF Sun L Chen HL Zhang SY 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(12):2767-2774
Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed. 相似文献
49.
Two pattern recognition (PR) techniques, principal component analysis-back propagation networks (PCA-BPN) and principal component analysis-nonlinear mapping (PCA-NLM), have been applied to the problem of classifying unknown energy levels of the first spectrum of curium (Cm I) according to their configurations. In comparison, with those reported by early PR techniques and counter propagation neural networks (CPN's), PCA-BPN has been demonstrated to possess much more prediction accuracy as to its performance on test sets. Obtained results further confirm the most previous assignments with these energy levels given by some early PR techniques and CPN. Moreover, the obtained results definitely reassign some energy levels' electronic configurations which were ambiguously conjectured in previous work. 相似文献
50.