Über den Anstieg von Flüssigkeiten in vertikalen makroskopischen Modellrohren unter Weltraumbedingungen

übersicht Der Anstieg einer Flüssigkeitssäule in makroskopischen kreiszylindrischen und konischen Rohren unter verminderter Schwereeinwirkung wird theoretisch und experimentell (Höhenforschungsrakete) untersucht. Das Verhalten von Flüssigkeiten unter Weltraumbedingungen (Restschwere, Mikrogravitation) ist von besonderem Interesse in der Raumfahrttechnik. Unter Berücksichtigung aller wesentlichen Kräfte ergibt sich trotz verschiedener Vereinfachungen in den theoretischen Ansätzen eine gute übereinstimmung zwischen numerischen Resultaten und den Meßergebnissen.

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On the rise of liquid columns into vertical tubes subjected to zero-gravity

Summary Theoretical and experimental information is given on the capillary rise of liquid into macroscopic vertical round tubes subjected to reduced gravity. The response in a low gravitational environment is of particular interest in studying the behaviour of liquid systems for space vehicles. An approximate analysis is presented to predict the transient rise and to interpret the experimental data. Agreement between numerical and experimental results is very good.

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Herrn Professor em. Dr. Dr.-Ing. E. h. Eberhard Mettler zur Vollendung des 75. Lebensjahres gewidmet     

Molecular Recognition with Model Systems

How structures fit together is the principal domain of molecular recognition, and current studies are evolving from the host–guest chemistry of ions to interactions between two molecules. Recent advances in the synthesis of sizable concave molecules, especially those featuring convergent functional groups, make it possible to bind smaller convex structures with considerable selectivity. One result is that hydrogen bonding can be addressed in model systems. The present review emphasizes the use of cleftlike structures as a means of probing the forces involved in nucleic acid recognition. The application of such molecules to the catalysis of chemical reactions, particularly those involved in self-replicating systems, is also described. Some implications for future pharmaceutical agents are suggested as a result of access to synthetic receptors for biologically relevant targets.     

Oxidative Ionization Under Certain Negative-Ion Mass Spectrometric Conditions

1,4-Hydroquinone and several other phenolic compounds generate (M – 2) ^–? radical-anions, rather than deprotonated molecules, under certain negative-ion mass spectrometric conditions. In fact, spectra generated under helium-plasma ionization (HePI) conditions from 1,4-hydroquinone and 1,4-benzoquinone (by electron capture) were practically indistinguishable. Because this process involves a net loss of H^? and H⁺, it can be termed oxidative ionization. The superoxide radical-anion (O₂ ^–?), known to be present in many atmospheric-pressure plasma ion sources operated in the negative mode, plays a critical role in the oxidative ionization process. The presence of a small peak at m/z 142 in the spectrum of 1,4-hydroquinone, but not in that of 1,4-benzoquinone, indicated that the initial step in the oxidative ionization process is the formation of an O₂ ^–? adduct. On the other hand, under bona fide electrospray ionization (ESI) conditions, 1,4-hydroquinone generates predominantly an (M – 1) ^– ion. It is known that at sufficiently high capillary voltages, corona discharges begin to occur even in an ESI source. At lower ESI capillary voltages, deprotonation predominates; as the capillary voltage is raised, the abundance of O₂ ^–? present in the plasma increases, and the source in turn increasingly behaves as a composite ESI/APCI source. While maintaining post-ionization ion activation to a minimum (to prevent fragmentation), and monitoring the relative intensities of the m/z 109 (due to deprotonation) and 108 (oxidative ionization) peaks recorded from 1,4-hydroquinone, a semiquantitative estimation of the APCI contribution to the overall ion-generation process can be obtained.

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An adjoint-based pressure correction scheme

Incompressible flows are solenoidal, i. e. the divergence of the flow field is zero. This is an algebraic constraint on the solution in time. The pressure has to be determined, so that the constraint is fulfilled. To calculate the pressure often a Poisson equation is derived, which is then solved by an iterative method. Instead of this the constraint is here formulated as an optimization problem. The objective functional is taken as the square of the norm of the divergence. A gradient based optimization is performed to calculate the pressure in every time step of the simulation. By this an alternative iterative scheme is derived. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A carbohydrate-conjugated deep cavitand permits observation of caviplexes in human serum

A deep cavitand was covalently modified with carbohydrates to provide solubility in biologically relevant environments and to investigate its receptor function. Specifically, a tetrakis(β-D-glucosyl) cavitand (1) that was soluble in neutral water or acid/base-buffered solutions was synthesized, and it formed complexes with hydrophobic small molecules. Extraction of the cavitand into aqueous sodium dodecyl sulfate micelles as simple membrane mimetics increased the scope of guests bound by 1 beyond that observed in only aqueous media. Complex formation was also detected in human serum. The findings show the functional compatibility of the receptor in both micelle-bound and serum-soluble forms.     

A light controlled cavitand wall regulates guest binding

Here we report a cavitand with a photochemical switch as one of the container walls. The azo-arene switch undergoes photoisomerization when subjected to UV light producing a self-fulfilled cavitand. This process is thermally and photochemically reversible. The reported cavitand binds small molecules and these guests can be ejected from the cavitand through this photochemical process.