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101.
Synthetic oligosaccharide constructs exhibiting tailored and well-defined heparan sulfate (HS) like sequences offer the potential to modulate dynamic HS-dependent biomolecular recognition processes. We report an efficient strategy for the generation of HS-like fragments [GlcA-beta-(1,4)-GlcNAc] and related dimerized (gemini) disaccharides (4a and 4b) via n-pentenyl glycoside formation. When a convergent synthetic approach was utilized, construction of target molecules was achieved through a combination of chemoselective protection/deprotection protocols, imidate and n-pentenyl glycosylations, and functional group manipulations followed by ozonolysis and reductive amination. For example, glycosylation of a 2-azido glycoside (25) with a trichloroacetimidate glucuronic acid donor (13), using a catalytic amount of TMSOTf, furnished heparin-like disaccharides (28a and 28b) that were equipped with an n-pentenyl tether at the anomeric end. In turn, heparinoid-like gemini disaccharides (4a and 4b) were produced by selective transformation of the olefinic unit in the n-pentenyl glycoside to the four-carbon aldehyde followed by reductive amination with ethylenediamine. The described synthetic approach provides access to structural variants of small heparinoid oligomers as versatile building blocks for generating novel HS mimetic pharmacotherapeutics, diagnostic reagents, and biomaterials. 相似文献
102.
A new, simple and rapid method based on the principle of liquid-liquid phase equilibria has been developed for the analysis of binary mixtures of chemically similar organic compounds. The method does not require elaborate instrumentation and can be used to analyse mixtures of members of homologous series. The application of the method has been illustrated by analysing binary mixtures of n-hexane and n-octane; the maximum uncertainty in this analysis is ~2%. 相似文献
103.
104.
A novel immunoassay format employing direct coating of small molecular hapten on microtiter plates is reported for the detection of atrazine and 2,4-dichlorophenoxyacetic (2,4-D). In this assay, the polystyrene surface of microtiter plates was first treated with an acid to generate -NO2 groups on the surface. Acid treated plates were further treated with 3-aminoprpyltriethoxysilane (APTES) to functionalize the plate surface with amino groups for covalent linkage to small molecular hapten with carboxyl groups. The modified plates showed significantly high antibody binding in comparison to plates coated with hapten-carrier protein conjugates and presented excellent stability as a function of the buffer pH and reaction time. The developed assay employing direct hapten coated plates and using affinity purified atrazine and 2,4-D antibodies demonstrated very high sensitivity, IC50 values for atrazine and 2,4-D equal to 0.8 ng mL−1 and 7 ng mL−1, respectively. The assay could detect atrazine and 2,4-D levels in standard water samples even at a very low concentration upto 0.02 and 0.7 ng mL−1 respectively in the optimum working range between 0.01 and 1000 ng mL−1 with good signal reproducibility (p values: 0.091 and 0.224 for atrazine and 2,4-D, respectively). The developed immunoassay format could be used as convenient quantitative tool for the sensitive screening of pesticides in samples. 相似文献
105.
Complexes of copper (II) aryl carboxylates with morpholine were prepared by the interaction of the copper carboxylate with the morpholine equimolar as well as in large excess quantities in acetone medium. The complexes isolated correspond to 1:1 and 1:2 stoichiometry. In continuation of our work on the preparation of complexes of copper (II) aryl carboxylates with nitrogen donors like aliphatic amines,1) heterocyclic amines2) and pyridine–N–Oxide3), the present communication deals with the preparation of complexes of copper (II) aryl carboxylates with morpholine. 相似文献
106.
Khajuria RK Suri KA Gupta RK Satti NK Amina M Suri OP Qazi GN 《Journal of separation science》2004,27(7-8):541-546
This paper describes a method for separation, identification, and quantification of selected withanolides in Withania somnifera plant extracts by HPLC-UV(DAD)-Mass Spectrometry (HPLC-MS). Withaferin-A (WS-3), 12-deoxywithastramonolide (WS-12DS), Withanolide A (WS-1), and Withanone (WS-2) were used as external standards. The compounds were isolated from Withania somnifera by repeated column chromatography of the root extract and their identity was established by 1H- and 13C-NMR and mass spectral data. The compounds were chromatographed on a Merck (250 x 4.6 mm ID, 5 microm) column and analyzed by Electrospray Ionization on a mass spectrometer in Selected Ion Mode (SIM). For quantification, [M + Na]+ ions were monitored. Linear calibration curves were obtained in the concentration range of 1.50 microg/mL to 6.5 microg/mL. The method was applied successfully to the detection and quantification of the said withanolides in a number of samples. 相似文献
107.
108.
We describe a kinetic data structure (KDS) that maintains the connected components of the union of a set of unit-radius disks
moving in the plane. We assume that the motion of each disk can be specified by a low-degree algebraic trajectory; this trajectory,
however, can be modified in an on-line fashion. While the disks move continuously, their connectivity changes at discrete
times. Our main result is an O(n) space data structure that takes O(log n\slash \kern -1pt log log n) time per connectivity query of the form ``are disks A and B in the same connected component?' A straightforward approach based on dynamically maintaining the overlap graph requires
Ω (n
2
) space. Our data structure requires only linear space and must deal with O(n
2 + ε
) updates in the worst case, each requiring O(log
2
n) amortized time, for any ε>0 . This number of updates is close to optimal, since a set of n moving unit disks can undergo Ω (n
2
) connectivity changes.
Received September 20, 2000, and in revised form January 19, 2001. Online publication April 6, 2001. 相似文献
109.
Abstract. We prove that a set of n disjoint unit balls in R
d
admits at most four distinct geometric permutations, or line transversals, thus settling a long-standing conjecture in combinatorial geometry.
The constant bound significantly improves upon the Θ (n
d-1
) bound for disjoint balls of unrestricted radii. 相似文献
110.
Fine crystals of samarium hexaboride were synthesized by molten salt electrolysis using samarium oxide, sodium tetraborate
and lithium fluoride. The electrolysis was performed at 900 °C in argon atmosphere at various current densities ranging from
1.0 to 2.3 A/cm2. The molar ratio of the reactants [Sm:B] was varied from 1:6 to 1:12. The deposited crystals were examined for the phase
purity using X-ray diffraction analysis. The effect of current density and the influence of molar concentration of the reactants
were evaluated. The morphological features of the crystals were examined using scanning electron microscopy (SEM). Pure crystals
of SmB6 are obtained at a current density of 1.8 A/cm2. The SEM images reveal that the crystals are packed in a cubic manner, exhibiting irregular morphology. The average crystallite
size of the powders is found to be between 72 and 83 nm. The mechanism of formation of SmB6 is explained by the joint deposition of B and Sm at the Mo cathode. 相似文献