Analyte templating: enhancing the enantioselectivity of chiral selectors upon incorporation into organic polymer environments

A simple strategy for preserving and enhancing the chiral recognition capacity of polymer-embedded chiral selectors is proposed, capitalizing on a temporary blockage of the receptor binding site with tightly binding analytes during the polymerization process. We demonstrate that the copolymerization of a quinine tert-butylcarbamate selector monomer with chiral (and achiral) 3,5-dichlorobenzoyl amino acids allows one to control to a certain extent the binding characteristics of the resultant polymeric chiral stationary phases. The structural and stereochemical requirements of the templating analytes for maximizing the chiral recognition capacity of the polymer-embedded selectors are probed. The chromatographic chiral recognition characteristics of the analyte-templated polymeric chiral stationary phases are analyzed with respect to binding capacities and affinities and compared to those obtained with a conventional silica-based surface-grafted reference material. Changes in substrate-specific enantioselectivity originating from analyte templating are also addressed.     

Subject Index to Volume 28

Subject Index

Subject Index to Volume 28     

C++ im Nebenfachstudium: Konzepte und Erfahrungen

Eingegangen am 06.10.1995, in überarbeiteter Form am 03.07.1996     

Determination of effective macropore diffusion coefficients by digital image processing

In this contribution, a new method is proposed for determining effective macropore diffusion coefficients in porous media by digitized microphotographs of porous support materials and random walk simulations. The method introduced allows calculation of the effective diffusion coefficient as a function of the mean free path length over a wide variety of values. A versatile method for the preparation of porous substances for light microscopy is described. The frequently applied model of an active shell, which is used to model particle/solid collisions, was found to give incorrect results in conjunction with the application of the first passage time algorithm, which was applied to save computing time in the simulation of gas diffusion. It was possible to show that more realistic results are obtained if a Knudsen layer is used to model particle/solid collisions. Furthermore, in investigating diffusion in two- and three-dimensional representations of capillary tubes, it was found that results of simulations performed to calculate transport properties of fluids in porous media, based on two-dimensional model systems, cannot in any case be transferred to the corresponding three-dimensional systems.     

Verformungsvorgänge bei erosiver Beanspruchung und ihre Beeinflussung durch korrosive Medien

Deformation processes by erosive treatment and influences of corrosive media As a result of our solid impact experiments on steel increased wear was established, if aqueous media are added to the particle stream. Because of the absence of any corrosion mark on the worn surfaces in SEM topography changed deformation behaviour was supposed as the cause of the enhanced material loss. This paper deals with a survey of the deformation mechanisms of the erosive surface damage. Environmental influences of deformation processes are discussed by experimental results and by a literature review.     

Functionalized polyisobutenes by SH-en addition

Low molecular weight polyisobutenes can be transformed into macromonomers by means of SH-en addition, provided that the thiols contain an additional hydroxy group. The product structures formed by free-radical or electrophilic addition reactions can be determined on model compounds as well as on the polymers by ¹H- and ¹³C-NMR spectroscopy.     

Mobility of the growth promoters trenbolone and melengestrol acetate in agricultural soil: column studies

There is growing concern about environmentally released man-made chemicals suspected to be responsible for a number of adverse effects on endocrine function in wildlife species and possibly also in humans. Sex hormones are of particular interest due to their regulatory role in developmental processes such as sexual differentiation. Endogenous hormones of human or animal origin as well as exogenous sex steroids used for contraception or as anabolics for farm animals are excreted and reach the environment. We investigated the transport of the synthetic growth promoters trenbolone (TbOH) and melengestrol acetate (MGA) in agricultural soil by means of column experiments with aggregated soil materials (Ap and Bt horizons of a Luvisol). Column effluent concentrations and depth profiles of TbOH and MGA were determined with sensitive enzyme immunoassay systems and HPLC (RP-18), respectively. All procedures were confirmed by liquid chromatography-mass spectrometry. Small amounts of TbOH and MGA passed the columns very quickly. However, both hormones exhibited a high affinity to the organic matter of both horizons leading to a high retardation within the upper layers of the soil columns. Although we cannot deduce whether hormones of animal origin reach the ground water under field conditions, our model experiments show that their transition can be presumed.     

Light deflection from ferroelectric domain structures in congruent lithium tantalate crystals

Congruently grown lithium tantalate crystals containing ferroelectric domain structures have been illuminated with ultraviolet light along the crystallographic c axis with simultaneous application of an external electric field. This gives rise to a star-shaped light diffraction pattern in the transmitted beam. The characteristics of this phenomenon are investigated and compared with those observed in lithium niobate crystals.     

Curvature analysis and visualization for functions defined on Euclidean spaces or surfaces

Visualization of a scalar-valued function ƒ defined on Euclidean n-space ⁿ is often based on its graph-hypersurface . Particularly for curvature interrogation, it is natural to equip ^n-1 with a so-called isotropic metric and use isotropic measures of the graph instead of Euclidean invariants. The ideas are extended to functions defined on surfaces in ³. We present the central formulae for a curvature analysis of functions defined on surfaces. It is shown how to use them for visualization purposes and as a mathematical basis for the construction of interpolating or approximating functions on surfaces.     

Fixed bed reactor kalman filtering and optimal control—II Experimental investigation of discrete time case with stochastic disturbances

Discrete time linear quadraticoptimal control is investigated experimentally on a catalytic fixed-bed reactor with stochastic upstream disturbances. It is demonstrated that the discrete time variance evaluated with time intervals equal to the control intervals oscillates along the reactor axis due to the time discretization of the control action. However, if the variance is evaluated with much shorter time intervals than used for control, the oscillations are not present. The control system behaviour is demonstrated with both Gaussian and step disturbances.