It is shown, that amphiphilic polymers--such as polysorbates and fatty esters of polyethylene glycol can be separated by comprehensive two-dimensional liquid chromatography using a reversed phase column (under critical conditions for the polyoxyethylene chain) and a HILIC column, which may arranged in different order. The mobile phases in both dimensions can be 93-97 wt% acetone water. As the retention of higher esters on the reversed phase column is very strong, this column should be used as the first dimension. On the HILIC column all fractions elute within a reasonably short time (at a flow rate of 2.5 ml/min within 2 min). With a flow rate of 0.1 ml/min in the first dimension, a full separation can be achieved in 90 min. 相似文献
This study was undertaken to investigate the herbicidal activity of mango (Mangifera indica L.) leaves against parthenium weed (Parthenium hysterophorus L.). The aqueous leaf extract at 15% concentration (on fresh weight basis) significantly reduced germination, shoot length and the shoot and root biomasses of parthenium seedlings. In a leaf residue incorporation pot trial, 2% residue incorporation treatment significantly suppressed the root and shoot biomasses of parthenium, while a 5% residue treatment completely stopped the growth of the weed. Five flavonoids, namely (-)-epicatechin-3-O-β-glucopyranoside (1), 5-hydroxy-3-(4-hydroxyphenyl)pyrano[3,2-g]chromene-4(8H)-one (2), 6-(p-hydroxybenzyl)taxifolin-7-O-β-D-glucoside (tricuspid) (3), quercetin-3-O-α-glucopyranosyl-(1 → 2)-β-D-glucopyranoside (4) and (-)-epicatechin(2-(3,4-dihydroxyphenyl)-3,4-dihydro-2H chromene-3,5,7-triol (5) were isolated from mango leaves. In a laboratory bioassay, 50 ppm solution of compounds 3 and 4 caused yellowing of the parthenium seedlings. A 250 ppm solution of compound 4 also significantly reduced germination and the root and shoot lengths of parthenium seedlings. This study concludes that compound 4 exhibits herbicidal activity against parthenium weed. 相似文献
Duboscic acid (1), a triterpenoid with a unique carbon backbone, was isolated from Duboscia macrocarpa Bocq. It is the first member of a new class of triterpenoids, for which the name "dubosane" is proposed. Duboscic acid has a potent α-glucosidase inhibition, and its structure was unambiguously deduced by a single-crystal X-ray diffraction study. 相似文献
The aim of this work is to establish an approach for obtaining improved design parameters for high temperature operation of terahertz quantum cascade lasers using a multi-objective evolutionary algorithm. For studying the lasing conditions of a quantum cascade laser, a self-consistent model is adopted. This model uses standard wave function approximation and effective mass approximation with relevant scattering mechanisms to solve Schrodinger’s equation for the cascaded quantum wells. Fermi’s Golden Rule is then used to calculate the corresponding lifetime of each eigen states. To describe the coherent evolution of wave functions and phase breaking, density matrix formalism is employed. Subsequently, laser rate equations are used for calculating the parameters related to electronic transport in the device. These parameters are then utilized for investigating the temperature dependence of existing terahertz quantum cascade lasers. Finally, using an optimization technique based on Genetic algorithm, design parameters for resonant-phonon quantum cascade laser are obtained within the terahertz frequency range. The results illustrate that this optimization process can offer improvement in the performance of quantum cascade lasers in terahertz region at an elevated temperature. Moreover, the results also reveal that significant increase in operating temperature of a resonant phonon terahertz QCL is unlikely and hence novel design approaches should be considered for operating THz QCLs at room temperature. 相似文献
Investigations have been performed to explore ultrashort laser irradiation effects on the surface topography as well as structural
and nonlinear absorption properties of a polymer CR-39. For this purpose, a CR-39 target was exposed in air to 25 fs, 800 nm
Ti:sapphire laser radiation at fluences ranging from 0.25 J cm−2 to 3.6 J cm−2. The surface features, structural changes and nonlinear absorption were explored by AFM, Raman Spectroscopy and a Z-scan
technique, respectively. Several topographical structures like bumps, explosions and nano cavities have been observed on the
irradiated surface. Raman spectroscopy reveals changes in the fundamental structure of the polymer after the irradiation.
Nonlinear absorption data contained by the Z-scan technique predict the dominance of three-photon absorption in case of pristine
CR-39. Furthermore, nonlinear absorption (three or two photon) increases with increasing laser fluences and is well correlated
with surface and structural changes revealed by AFM and Raman spectroscopy. 相似文献
In this article, we have theoretically demonstrated the mechanism of an active tractor beam for multiple fully immersed objects with additional abilities to yielding stable long distance levitation, a controlled rotation and a desired 3D trapping. This is demonstrated with a single optical set‐up by using two coaxial, or even non‐coaxial, superimposed higher order monochromatic Bessel beams of reverse helical nature and different frequencies. The superimposed beams can possess periodic intensity variations both along and around the beam‐axis due to a difference in longitudinal wave‐numbers and beam orders, respectively. The difference in frequencies of the two laser beams makes the intensity pattern to move along and around the beam‐axis in a continuous way without manual ramping of phase, which allows for bidirectional movement of completely immersed multiple particles. The condition for increasing or decreasing the dimension of binding regions is also proposed here to manipulate multiple immersed objects of different sizes under dipole approximation.
Sulfonamide Schiff bases were doped uniformly in silica sol–gels prepared from liquid precursors by a fast and easy way at room temperature and processed to form xerogels. Schiff bases are efficient chelating agents, bioactive and catalytically active compounds. The structures of the newly synthesized Schiff base doped xerogels were elucidated by their physical (morphology, surface area, porosity), spectral (FTIR) and analytical (CHNSO/Si) data. The powder X-ray diffraction studies were carried out to confirm the formation of single phase. Characterization confirmed that Schiff base molecules are entrapped inside the pores as well as physically bound onto the silica surface. All Schiff base doped xerogels are stable mesoporous materials showing hydrophilic properties. Loadings of Schiff bases from 0.10 to 0.23 g/g of xerogel were obtained resulting amorphous materials. The doping of Schiff bases with xerogel caused change in surface area, pore volume and pore diameter of xerogel without damaging the main framework of siliceous skeleton. Morphology and colour of xerogel was also changed after doping. The entrapment of Schiff bases in xerogel caused increase in their decomposition temperatures. The final Schiff base doped xerogels show remarkable thermal stability. 相似文献
In the present report, physically adsorbed rat liver microsomes were used in order to optimize the immobilization of membrane proteins on solid surfaces for use in biosensing and microreactor applications. Physical adsorption was used to form thin films on solid supports (gold, mica, macroporous aluminum oxide membrane). The characterization of the films was performed by surface plasmon resonance (SPR), atomic force microscopy (AFM) and environmental scanning electron microscopy (ESEM). Commercially available macroporous aluminium oxide membranes with a high surface area, allow the retention of a high amount of microsomal membranes in the form of a thin film. Microsomal film functionality was tested by monitoring the activities of several enzymes of phases I and II. Microsomal modified supports can be re-utilized for the same or different substrate after washing with appropriate buffer. 相似文献
Piperidine derivatives are reported to exhibit a variety of pharmacological activities. In this article, synthesis and aspartic protease inhibitory activity of three nitrophenacyl derivatives of N-methyl-4-hydroxy piperidine are reported. Enzyme assays showed that the attachment of a nitro group in the benzene ring plays an important role in the inhibition of plasmepsin-II of Plasmodium falciparum. The compound 1-methyl-1-(4'-nitrophenacyl)-4-hydroxypiperidinium bromide (3), consisting of a nitro group at the para position, was the most active at the concentration of 1.0?μM. The activity of the compounds was evaluated through the observed orientation and diagrammatic representation of nitrophenacyl derivatives of 4-hydroxy piperidine. 相似文献