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排序方式: 共有224条查询结果,搜索用时 15 毫秒
91.
SIMONA BADILESCU † RICARDO BICCA DE ALENCASTRO † HOA LE-THANH GUY RlCHER CAMILLE SANDORFY PIERRE-PAUL VAUDREUIL DANIEL VOCELLE 《Photochemistry and photobiology》1989,49(3):313-318
The hydrogen bonding-protonation equilibrium for retinyl Schiff base/propionic acid or 3-chloropropionic acid systems was examined by Fourier transform infrared spectroscopy in non polar solutions at temperatures ranging from 25 degrees C to about -150 degrees C. The spectra give evidence for the gradual increase in the degree of protonation as temperature is lowered. The bearing of this on applying low temperature spectroscopic results to physiological conditions in rhodopsin research is discussed. 相似文献
92.
We study properties of dynamic discrete-time linear systemswith the input or the state constrained to have integer components.The reachability of input-constrained systems is investigated,and consistency conditions for state-constrained systems aregiven. 相似文献
93.
本文首次报道了由钾分子-原子系统的混合激发和碰撞能量转移过程产生4F→3D受激辐射以及由钾原子的4S→4F偶极禁戒双光子共振产生4F→3D受激辐射和四波混频的研究结果。 相似文献
94.
为模拟和动态显示工作在液氦温区的两级4K脉冲管制冷机内部工作过程和参数变化规律,发展了一种新的欧拉法-拉格朗日法数值计算模型。采用拉格朗日方法,直接跟踪脉冲管中气体微元随周期性压力波动的具体运行轨迹;采用欧拉法,直接模拟蓄冷器内部的动态参数变化。本文简单介绍该模型,并模拟了一典型两级4 K脉冲管制冷机各参数的变化情况,分析了多层磁性蓄冷材料对制冷机性能的影响情况。 相似文献
95.
Polyoxometalates (POMs)containingKegginmoi etieshavebeenreceivingextensiveattentioninrecentyearsowingtotheirgreatfundamentalandpracticalinter est .1Especiallytheunusualelectronicproperty (highnegativecharges) ,oneofthemostimportantpropertiesofPOMs ,haspoten… 相似文献
96.
The time-resolved tryptophyl fluorescence of alpha-chymotrypsin A and alpha-chymotrypsin in the crystalline state and in buffer solution at room temperature was analyzed globally. Triple-exponential decay functions are necessary to adequately describe the tryptophyl fluorescence decay surfaces of the protein powders as a function of hydration and in solution. The fluorescence lifetimes of alpha-chymotrypsinogen A (tau 1 = 0.32, tau 2 = 1.30 ns, tau 3 = 3.98 ns) and alpha-chymotrypsin(tau 1 = 0.66 n s, tau 2 = 2.26 ns, tau 3 = 5.40 ns) are constant over the entire hydration range. The spectral positions of the decay-associated spectra of the hydrated powders do not shift as a function of hydration. This indicates that the structures of the zymogen and the active enzyme are unaffected by hydration. The lifetimes of alpha-chymotrypsinogen A in phosphate buffer pH 7.4 are tau 1 = 0.37 ns, tau 2 = 1.17 ns and tau 3 = 3.44 ns while the respective values of alpha-chymotrypsin are tau 1 = 0.47 ns, tau 2 = 1.40 and tau 1 = 3.89 ns. 相似文献
97.
Adrielli Tenfen Diogo Alexandre Siebert Celina Noriko Yamanaka Caio Maurício Mendes de Córdova Dilamara Riva Scharf Edésio Luiz Simionatto 《Natural product research》2016,30(17):2007-2011
This study describes the qualitative and quantitative chemical composition and evaluates the antibacterial activity of essential oil from Eugenia platysema leaves. Analysis by GC–FID and GC–MS allowed the identification of 22 compounds. Different from the other species of the Eugenia genus, the major compound found in the essential oil was the diterpene phytol (66.05%), being this the first report of the presence of this compound in the essential oils from Eugenia genus. The sesquiterpene elixene was the second most concentrated compound in the studied essential oil (9.16%). The essential oil from E. platysema was tested for its antibacterial activity against cell-walled bacteria and mollicute strains of clinical interest using the microdilution broth assay. The results showed that the essential oil of E. platysema was inactive until 1000 μg mL?1 against tested bacteria. 相似文献
98.
A new tropane alkaloid from the leaves of Erythroxylum subsessile isolated by pH‐zone‐refining counter‐current chromatography
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Rodrigo Alves Soares Cruz Henrique Almeida Caio Pinho Fernandes Pedro Joseph‐Nathan Leandro Rocha Gilda Guimarães Leitão 《Journal of separation science》2016,39(7):1273-1277
Tropane alkaloids are bioactive metabolites with great importance in the pharmaceutical industry and the most important class of natural products found in the Erythroxylum genus. However, these compounds are usually separated by traditional chromatographic techniques, in which the sample is progressively purified in multiple chromatographic steps, resulting in a time‐ and solvent‐consuming procedure. In this work we present the isolation of a novel alkaloid, 6β,7β‐dibenzoyloxytropan‐3α‐ol, together with the two known 3α‐benzoyloxynortropan‐6β‐ol and 3α,6β‐dibenzoyloxytropane alkaloids, directly from the crude alkaloid fraction from the leaves of Erythroxylum subsessile, by using a single run pH‐zone‐refining counter‐current chromatography method. The ethyl acetate/water (1:1, v/v) biphasic solvent system with triethylamine and HCl as retention and eluter agents, respectively, was used to isolate tropane alkaloids for the first time. The structures of the isolated alkaloids were elucidated by spectroscopic methods. 相似文献
99.
Tagusagawa C Takagaki A Hayashi S Domen K 《Journal of the American Chemical Society》2008,130(23):7230-7231
Layered HNbMoO6 was found to function as a strong solid acid catalyst, exceeding the activity of zeolites and ion-exchange resins for Friedel-Crafts alkylation. HNbMoO6 also exhibited high catalytic activity for esterification of hydrocarboxylic acid and hydration. The catalytic performance of layered HNbMoO6 is attributed to the intercalation of reactants into the interlayer and the development of strong acidity. 相似文献
100.