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51.
Separation of andrographolide and neoandrographolide from the leaves of Andrographis paniculata using high-speed counter-current chromatography 总被引:4,自引:0,他引:4
The bioactive diterpenes andrographolide and neoandrographolide from the leaves of Andrographis paniculata NEES (Acanthaceae) were successfully separated by counter-current chromatography. A single 280-min separation yielded 189 mg of 99.9% andrographolide and 9.5 mg of 98.5% neoandrographolide applying water-methanol-ethyl acetate-n-hexane (2.5:2.5:4:1) solvent system. Structure confirmation was done by electrospray MS, one-dimensional NMR experiments, circular dichroism, optical rotation dispersion, and specific optical rotation [alpha]D. 相似文献
52.
Gerold Alsmeyer 《Journal of Theoretical Probability》2002,15(2):259-283
It is proved that for each random walk (S
n
)
n0 on
d
there exists a smallest measurable subgroup
of
d
, called minimal subgroup of (S
n
)
n0, such that P(S
n
)=1 for all n1.
can be defined as the set of all x
d
for which the difference of the time averages n
–1
n
k=1
P(S
k
) and n
–1
n
k=1
P(S
k
+x) converges to 0 in total variation norm as n. The related subgroup
* consisting of all x
d
for which lim
n P(S
n
)–P(S
n
+x)=0 is also considered and shown to be the minimal subgroup of the symmetrization of (S
n
)
n0. In the final section we consider quasi-invariance and admissible shifts of probability measures on
d
. The main result shows that, up to regular linear transformations, the only subgroups of
d
admitting a quasi-invariant measure are those of the form
1×...×
k
×
l–k
×{0}
d–l
, 0kld, with
1,...,
k
being countable subgroups of
. The proof is based on a result recently proved by Kharazishvili(3) which states no uncountable proper subgroup of
admits a quasi-invariant measure. 相似文献
53.
Gerold Alsmeyer 《Acta Appl Math》1994,34(1-2):135-150
The present work surveys some extensions of Blackwell's renewal theorem for a certain class of linear submartingalesS
which have been recently obtained by the author. The basic assumption onS
is that their conditional increment distribution functions with respect to some filtration
are bounded from above and below by integrable distribution functions. Under a further mean stability condition these random walks turn out to be natural candidates for satisfying Blackwell-type renewal theorems. The latter are derived by employing a coupling argument similar to that which has been used in the i.i.d. case by Lindvallet al. A number of applications are also presented. 相似文献
54.
A novel synthetic analog of adenosine: the 3′-deoxy-3′-C-dibromomenthylidene-adenosine The title compound ( 7 ) has been prepared by a sequence of classical synthetic steps from 3-deoxy-3-C-dibromomethylidene-1,2: 5,6-di-O-isopropylidene-α-D -ribo-hexofuranose ( 1 ). The β-configuration of the nucleoside was established by formation of a cyclonucleoside. 7 is very slowly deaminated by adenosine deaminase. In contrast with its dichloro analog, it does not inhibit the growth of Escherichia coli. 相似文献
55.
A. Fässler H. Schwarzenbach 《Zeitschrift für Angewandte Mathematik und Physik (ZAMP)》1979,30(2):190-200
Zusammenfassung Algorithmische Bestimmung von symmetriegerechten Polynomen (Kugelfunktionen) in kartesischen Koordinaten bezüglich einer beliebigen endlichen PunktgruppeGO
h
. Dabei erfolgt die Berechnung der zugehörigen Koeffizienten, im Gegensatz zur bisherigen Literatur,exakt.Als Anwendung des Algorithmus wird in einem ersten Beispiel für die volle Tetraedergruppe eine Tabelle symmetriegerechter Polynome bis zum Gradn=9 erstellt.In einem weiteren Beispiel erfolgt die Berechnung aller irreduziblen Darstellungen der eigentlichen Ikosaedergruppe aus ihrer Charakterentabelle.
Unserem verehrten Lehrer Professor E. Stiefel gewidmet 相似文献
The algorithmic determination of symmetry-adapted polynomials (spherical harmonics) in Cartesian coordinates is described.In contrast with the literature, all coefficients of these polynomials can be calculated exactly.A table of symmetry-adapted polynomials (degree up to 9) of the tetrahedral group is given as an application of the algorithm.In another example all the irreducible representations of the icosahedral group are calculated by using its character table.
Unserem verehrten Lehrer Professor E. Stiefel gewidmet 相似文献
56.
Gerold Wagner 《Monatshefte für Mathematik》1981,92(3):239-245
Letf be a periodic function on with period 1, piecewise continuously differentiable, satisfying
. For an arbitrary sequence = (
i
) in [0,1) put
and
. If
then
n
(f,) >c· logn holds for some positive constantc (depending onf only) and almost alln. In a certain sense the converse is also true: there is a class of functionsf with
such that
n
(f,) =o (logn).Support has been received from Netherlands Organization for the Advancement of Pure Research (Z. W. O.). 相似文献
57.
The proposed combination of a rather simple procedure for sample preparation with capillary gas-liquid chromatography using a barium carbonate/polyethyleneglycol 20,000 column and a Grob-type on-column injector permits measurement of bile acids in serum with high separation efficiency, short analysis time and complete separation of bile acids from cholesterol. The method can be adapted to combined capillary gas-liquid chromatography - mass spectrometry. 相似文献
58.
Preparative separation of flavonoid glycosides in leaves extract of Ampelopsis grossedentata using high-speed counter-current chromatography 总被引:3,自引:0,他引:3
Preparative separation of flavonoid glycosides in leaves extract of Ampelopsis grossedentata was conducted using high-speed counter-current chromatograph (HSCCC) with a solvent system composed of n-hexane-ethyl acetate-methanol-water (1:6:1.5:7.5, v/v). In a single operation, 28 mg of 5,7-dihydroxy-3',4'-trihydroxyflavone-3-O-6'-rhamnose and 18 mg of 5,7-dihydroxy-3',4'-dihydroxyflavone-3-O-6'-rhamnose was obtained from 150 mg of the extract. The chemical structure of the two compounds was elucidated by electrospray ionization (EIS) MS and NMR. 相似文献
59.
Weidong Dai Maria Ramos-Jerz Dongchao Xie Jiakun Peng Peter Winterhalter Gerold Jerz Zhi Lin 《Molecules (Basel, Switzerland)》2021,26(23)
N-Ethyl-2-pyrrolidinone-substituted flavanols (EPSF) are marker compounds for long-term stored white teas. However, due to their low contents and diasteromeric configuration, EPSF compounds are challenging to isolate. In this study, two representative epimeric EPSF compounds, 5′′′R- and 5′′′S-epigallocatechin gallate-8-C N-ethyl-2-pyrrolidinone (R-EGCG-cThea and S-EGCG-cThea), were isolated from white tea using centrifugal partition chromatography (CPC). Two different biphasic solvent systems composed of 1. N-hexane-ethyl acetate-methanol-water (1:5:1:5, v/v/v/v) and 2. N-hexane-ethyl acetate-acetonitrile-water (0.7:3.0:1.3:5.0, v/v/v/v) were used for independent pre-fractionation experiments; 500 mg in each separation of white tea ethyl acetate partition were fractionated. The suitability of the two solvent systems was pre-evaluated by electrospray mass-spectrometry (ESI-MS/MS) analysis for metabolite distribution and compared to the results of the CPC experimental data using specific metabolite partition ratio KD values, selectivity factors α, and resolution factors RS. After size-exclusion and semi-preparative reversed-phase liquid chromatography, 6.4 mg of R-EGCG-cThea and 2.9 mg of S-EGCG-cThea were recovered with purities over 95%. Further bioactivity evaluation showed that R- and S-EGCG-cThea possessed in vitro inhibition effects on α-glucosidase with IC50 of 70.3 and 161.7 μM, respectively. 相似文献
60.