Differences in binding of a cationic surfactant to cross-linked sodium poly(acrylate) and sodium poly(styrene sulfonate) studied by Raman spectroscopy

Raman spectroscopy has been used to investigate the structure of gel-surfactant complexes. Cross-linked sodium poly(acrylate) and sodium poly(styrene sulfonate) were immersed in solutions of the cationic surfactant dodecyl trimethylammonium bromide. During the deswelling process, two distinct regions could be observed for both types of gels. Looking at the Raman spectra, however, for the poly(styrene sulfonate), the surfactant could be found throughout the gel particle, whereas for poly(acrylate), essentially all the surfactant was bound in a surface layer.     

CYTOCHROME P-450/420 IN PLANT PLASMA MEMBRANES: A POSSIBLE COMPONENT OF THE BLUE-LIGHT-REDUCIBLE FLAVOPROTEIN-CYTOCHROME COMPLEX*

Abstract— Carbon monoxide difference spectra and pyridine binding spectra indicate the presence of cytochrome P-450/420 in plasma membranes from cauliflower inflorescences. Mild lithium dodecylsulfate polyacrylamide gel electrophoresis shows only one heme staining band in the plasma membrane fraction at an apparent molecular weight of 93 kiloDalton. This band is suggested to be due to a cytochrome P-450/420 dimer, in view of the known molecular weights of animal cytochromes P-450/420. The plasma membrane-bound cytochrome P-450/420 is probably identical to the blue-light-reducible b-type cytochrome of plant plasma membranes, which has been inferred to have a role in photomorphogenesis.     

ORIENTATION OF SHORT WAVELENGTH AND LONG WAVELENGTH PROTOCHLOROPHYLL SPECIES IN GREENING CHLOROPLASTS

Abstract— The orientation of protochlorophyll and Chi species with respect to the plane of thylakoid membranes was studied by measuring the fluorescence polarization ratio in magnetically oriented chloroplasts isolated from greening maize leaves and cucumber cotyledons. With viewing direction parallel to the plane of the photosynthetic membranes, in the spectral region of 620–660 nm, fluorescence polarization ratios of 1.0 were observed, whereas at longer wavelengths the fluorescence polarization ratios were much higher, and similar to that of fully green chloroplasts. The same result was obtained with chloroplasts isolated from leaves fed by δ-amino levulinic acid. These data indicate that the emitting oscillators of the short and long wavelength protochlorophyll species are oriented at random with respect to the plane of thylakoid membranes. Isotropy of the protochlorophyll species is discussed in terms of isotropic structures containing Chi precursors.     

Kinetics of the Formation of Nano-Sized Platinum Particles in Water-in-Oil Microemulsions

The association between low-charge-density polyelectrolytes adsorbed onto negatively charged surfaces (mica and silica) and an anionic surfactant, sodium dodecyl sulfate (SDS), has been investigated using surface force measurements, ellipsometry, and XPS. All three techniques show that the polyelectrolyte desorbs when the SDS concentration is high enough. The XPS study indicates that desorption starts at a SDS concentration of ca. 0.1 unit of cmc (8x10(-4) M) and that the desorption proceeds progressively as the SDS concentration is increased. Surface force measurements show that for the polyelectrolyte studied here, having 1% of the segments charged, the desorption proceeds without any swelling of the adsorbed layer. This behavior differs from that observed when polyelectrolytes of greater charge density are used. Copyright 2001 Academic Press.     

THE EFFECT OF THE ANTIPSORIATIC DRUG METABOLITE ETRETIN (Ro 10-1670) ON UVB IRRADIATION INDUCED CHANGES IN THE METABOLISM OF ARACHIDONIC ACID IN HUMAN KERATINOCYTES IN CULTURE

[¹⁴C]Arachidonic acid was avidly incorporated into human keratinocytes in culture and following exposure to UVB irradiation of 9 mJ/cm² (erythemally effective, EE) substantial amounts of ¹⁴C-radiolabel were released from the cells. The release of radiolabel was accompanied by a decrease in the labelling of phosphatidylethanolamine whereas the labelling of triacylglycerols and cholesteryl esters was increased. Keratinocytes produced significant amounts of prostaglandin E₂ (PGE₂) and following UVB irradiation of 9 mJ/cm² (EE) the formation of prostaglandin E₂ was increased.
Etretin (Ro 10-1670), the active metabolite of the antipsoriatic drug etretinate (Ro 10-9359), affected significantly neither the total release of radiolabel induced by UVB nor the formation of prostaglandin E₂. However, in the presence of etretin the UVB irradiation induced transfer of [^l4C]arachidonic acid into triacylglycerols and cholesteryl esters was not increased as much as in the corresponding experiments without etretin. On the basis of the present study it appears that etretin does not interfere with the release of arachidonic acid in amounts which could be related to the therapeutic effects of the combination of retinoids with UVB irradiation (Re-UVB) in the treatment of psoriasis.     

(Benzimidazol-1-yl)methyl]benzamides as bifunctional reagents for reliable inorganic-organic supramolecular synthesis

A series of ligands that utilize five-membered N-heterocycles as coordination sites, and the self-complementarity of the carboxamide functionality, have been employed in the supramolecular synthesis of Ag(I)-based extended networks. The crystal structures of eight compounds are reported: bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) tetrafluoroborate hydrate methanol, 1; bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) tetrafluoroborate, 2; bis[4-(5,6-dimethylbenzimidazol-1-yl)methylbenzamide]silver(I) tetrafluoroborate, 3; bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroarsenate methanol, 4; bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroarsenate methanol(0.5), 5; bis[4-(5,6-dimethylbenzimidazol-1-yl) methylbenzamide]silver(I) hexafluoroarsenate, 6; bis[4-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroantimonate, 7; and bis[3-(2-methylbenzimidazol-1-yl)methylbenzamide]silver(I) hexafluoroantimonate, 8. An analysis of motifs and structural patterns that result from the primary intermolecular interactions in these structures, reveals that this family of ligands is capable of providing quite reliable means for propagating the linear geometry of the complex ions into extended 1-D architectures via ligand-ligand, N-H...O, hydrogen-bond interactions.     

Brownian motion with negative drift and convex level sets in space-time

Suppose a, b, and are reals witha<b and consider the following diffusion equation

Modelling in the absence of data: a case study of fleet maintenance in a developing country

Adequate and relevant objective data for modelling maintenance decision problems are often incomplete or not readily accessible. This is particularly true in developing countries. In this paper the experience gained between 1991–95 in conducting a maintenance study of an inter-city express bus fleet in a developing country is presented. The lack of available maintenance records and operating data rendered the study the most data-starved maintenance modelling exercise the authors have met before or since. The study required the use of subjective methods to both define the problem and to estimate parameters, and the application of recently developed concepts in maintenance modelling along with snapshot analysis and delay time modelling. This imposed a structured approach to problem recognition and problem solution. The study contributed both directly and indirectly to a change in work culture and to a reduction in bus breakdown rate. The company was re-visited 5?years later specifically to seek evidence of lasting impact. Some evidence existed and is reported in the paper.     

On the influence of theory on research in mathematics education: the case of teaching and learning limits of functions

After an introduction on approaches, research frameworks and theories in mathematics education research, three didactical research studies on limits of functions with different research frameworks are analysed and compared with respect to their theoretical perspectives. It is shown how a chosen research framework defines the world in which the research lives, pointing to the difficult but necessary task to compare research results within a common field of study but conducted within different frameworks.     

Homogenization Based LES for Turbulent Combustion

In this work we propose a novel methodology for performing Large Eddy Simulations (LES) of premixed, non-premixed and partially premixed laminar and turbulent flames. The motivation behind this study is the need for more accurate and flexible LES computations of increasingly complex engineering applications, for which current LES models are limited. The main drawback of present LES methods for reactive flows is that most of the chemical activity, and thus also most of the exothermicity, occurs on the subgrid scales, and is hence subject to modeling using only information about the resolved scale flow. Reasonable results have been achieved in several studies with present LES models but improved accuracy, flexibility and reliability is needed. Here, we use a homogenization-based approach based on a multi-scale expansion technique to convert the reactive Navier–Stokes equations, with finite rate chemistry, into a cascade of equations for different scales. The equations of motion for the large-scale dependent variable dynamics are explicitly simulated, whereas the equations of motion for the small-scale dependent variable dynamics are simplified by reducing the spatial dimensions from three to one, thus permitting affordable simulations in a grid within the grid approach. Presently, the methodology is limited to low Ma number variable density flows, but can be extended to high Ma number reactive flows. This method has some similarities with the LES–LEM and the TLS models of Menon et al., but differs in some important aspects. The model developed is here applied to a bluff-body stabilized flame and comparisons with both experimental data and conventional flamelet and finite rate chemistry LES models are made. The results show that the performance of this model is as good or better than any of the other models, and to a reasonable computational cost.