Search results for "RPE"
showing 10 items of 2566 documents
Unmixing of Polymer Blends Confined in Ultrathin Films: Crossover between Two-Dimensional and Three-Dimensional Behavior
2006
The interplay between chain conformations and phase separation in binary symmetric polymer mixtures confined into thin films by "neutral" hard walls (i.e., walls that do not preferentially attract or repel one of the two components of the mixture) is studied by Monte Carlo simulations. Using the bond fluctuation model on a simple cubic lattice in the semi grand canonical ensemble, we locate the critical temperature of demixing via finite size scaling methods for a wide range of chain lengths (16/= N/= 256 effective monomers per chain) and film thicknesses (2/= D/= 19 lattice spacings). Simultaneously, we investigate the geometrical structure of the chains, showing that despite using melt de…
Dye-containing S∗cside-on/end-on copolymers
1995
Abstract Mesomorphic copolysiloxanes, which combine ‘normal’ end-on linked chiral mesogenic units inducing S∗c phases and side-on fixed chromophores were prepared. The interplay of the different orientational tendencies of these moieties, which are perpendicular (end-on linked mesogenic groups) or parallel (side-on fixed chromophores) to the polymer chain, lead to a strong destabilization of the S∗c phase. However, copolymers with up to about 10 mol % of chromophores still show a smectic C∗ phase. FTIR measurements show that both moieties orient parallel to each other and perpendicular to the polymer chains. These copolymers are interesting to consider as coloured guest-host S∗c materials f…
Polymer brushes under flow and in other out-of-equilibrium conditions
2011
Polymer brushes are formed from flexible linear macromolecules tethered at one chain end to a solid substrate, forming a dense polymeric layer of polymer chains which are more or less stretched in the direction perpendicular to the substrate surface. These systems find interest also due to numerous applications (colloid stabilization, improvement of lubrication properties when the surfaces are exposed to shear, protection of the surface against adsorption of nanoparticles or proteins, etc.), for which often the dynamic non-equilibrium response of these brushes to external perturbation is important. The present review summarizes recent computer simulation studies pertinent to these questions…
High speed X-ray analysis of plant enzymes at room temperature.
2013
X-ray measurements at room temperature (295 K) deliver high quality data sets with unprecedented speed (2 min), as shown for crystallized raucaffricine-O-β-D-glucosidase (RG), its mutant RG-Glu186Gln and several ligand complexes of the enzyme which participates in alkaloid biosynthesis in the plant Rauvolfia. The data obtained are compared with data sets measured under typical cryo conditions (100K). Under both conditions, density maps are highly comparable and favor the described protocol for room temperature measurements, potentially paving the way for future crystallographic studies capturing biosynthetic pathway intermediates.
Acylated triterpene saponins from the roots of Securidaca longepedunculata.
2009
Abstract Four triterpene saponins , 3- O -β- d -glucopyranosylpresenegenin 28- O -β- d -apiofuranosyl-(1 → 3)-β- d -xylopyranosyl-(1 → 4)-[β- d -apiofuranosyl-(1 → 3)]-α- l -rhamnopyranosyl-(1 → 2)-{4- O -[( E )-3,4,5-trimethoxycinnamoyl]}-β- d -fucopyranosyl ester, 3- O -β- d -glucopyranosylpresenegenin 28- O -β- d -apiofuranosyl-(1 → 3)-β- d -xylopyranosyl-(1 → 4)-[β- d -apiofuranosyl-(1 → 3)]-α- l -rhamnopyranosyl-(1 → 2)-[(6- O -acetyl)-β- d -glucopyranosyl-(1 → 3)]-{4- O -[( E )-3,4,5-trimethoxycinnamoyl]}-β- d -fucopyranosyl ester, 3- O -β- d -glucopyranosylpresenegenin 28- O -β- d -apiofuranosyl-(1 → 3)-β- d -xylopyranosyl-(1 → 4)-[β- d -apiofuranosyl-(1 → 3)]-α- l -rhamnopyranosyl-(…
Natural products and enzymes from plant cell cultures
1995
Plants represent an unlimited source of natural products. Many of the recently detected phytochemicals exhibit remarkable bioactivities, ranging from anticancer activity, phosphodiesterase inhibition to cytotoxicity against HIV-infected cells. Cultivated plant cells produce at their unorganized, dedifferentiated stage secondary metabolites, but in very different amounts in so far as new compounds are concerned. In fact, more than 140 novel natural products are presently known from plant cell cultures, which also include new metabolites formed by biotransformation. The biotransformation capacity of suspended cells is described and recent high yielding transformations, like the formation of a…
Preparation of 9a-Fluorinated Sesquiterpenic Drimanes and Evaluation of Their Antifeedant Activities
2010
19 pages, figures, and tables statistics.
Ein neues Butenolid ausConyza bonariensis
1991
A New Butenolide from Conyza bonariensis Extraction of aerial parts of Conyza bonariensis and chromatographic separation yielded the new butenolide 1, together with the acetylenic compounds trans-lachnophyllum lactone (2) and cis-lachnophyllum methyl ester (3), and the germacrane alcohol 4.
In vivo anti-inflammatory activity of saponins from Bupleurum rotundifolium
2001
Seven oleanane-type triterpene saponins were isolated from the methanolic extract of the aerial parts of Bupleurum rotundifolium. They were identified on the basis of their spectral data as 3-O-[alpha-L-rhamnopyranosyl (1--2)-beta-D-glucopyranosyl (1--2)-beta-D-glucopyranosyl]-28-O-[beta-D-glucopyranosyl (1--2)-beta-D-glucopyranosyl] echinocystic acid (saponin 1), 3-O-[alpha-L-rhamnopyranosyl (1--2)-beta-D-glucopyranosyl (1--2)-beta-D-fucopyranosyl] 11-methoxy-primulagenin A (saponin 2), rotundioside E (saponin 3), rotundioside F (saponin 4), 3beta-sulfate, 28-O-[beta-D-glucopyranosyl (1--6)-beta-D-glucopyranosyl (1--2)-beta-D-glucopyranosyl (1--2)-beta-D-glucopyranosyl] ester of primulagen…
Polymer chains confined into tubes with attractive walls: A Monte Carlo simulation
1994
A bead-spring off-lattice model of a polymer chain with repulsive interactions among repeating units confined into straight tubes of various cross sections, DT2, is studied by Monte Carlo simulation. We are also varying the chain length from N = 16 to 128 and the strength of a short-range attractive interaction between the repeating units and the walls of the tube. Longitudinal and perpendicular static linear dimensions of the chains are analyzed, as well as the density profile of repeating units across the tube. These data are interpreted in terms of scaling concepts describing the crossover between three-dimensional and quasi-one-dimensional chain conformations and the adsorption transiti…