Bestimmung der Parameter des Potenzansatzes nach Ostwald-de Waele aus rheometrischen Messungen an einem Viskosimeter mit schnellrotierender Scheibe

Zusammenfassung Für die Bestimmung der Parameter desOstwaldde Waeleschen Modells zeigte sich die AbhÄngigkeit zwischen dem Momentkriterium und derReynolds- Zahl bei der Rotation einer Scheibe in einer nicht-Newtonschen Flüssigkeit, die durch Lösung der entsprechenden Bewegungsgleichungen unter der Voraussetzung Ähnlicher Geschwindigkeitsprofile gewonnen wurde, als geeignet.Der Gültigkeitsbereich dieser theoretisch berechneten AbhÄngigkeit wurde mit Hilfe experimenteller Daten bestimmt.Für die rasche Bearbeitung der aus Messungen mit einem Viskosimeter mit rotierender Scheibe gewonnenen Daten wurde eine graphische Methode für die Berechnung der rheologischen Parameter ausgearbeitet.     

Retention and selectivity tests of silica-based and metal-oxide bonded stationary phases for RP-HPLC

Chromatographic properties of silica-, zirconia- and alumina-based columns with octadecyl-, polyethylene glycol- and pentafluorophenylpropyl-bonded stationary phases were tested. Selectivities of nine columns for LC were characterized using chromatographic methods including Walters, Engelhardt, Tanaka and Galushko hydrophobicity and silanol activity tests, measurements of methylene selectivity in various aqueous-methanol and aqueous-acetonitrile mobile phases and of gradient lipophilic capacity as a measure of the effect of the sample hydrophobicity on gradient-elution separations. A semi-empirical interaction indices model, assuming a predominant role of the solvophobic interactions of test compounds with different polarities, was compared with the linear free energy relationships approach taking into account selective polar interactions. The interaction indices model was applied to both non-polar stationary phases bonded on silica, alumina and zirconia supports, and to the non-modified adsorbents in the normal-phase LC. The retention data of isomeric naphthalene disulfonic acids were used to compare the attractive and repulsive ionic interactions of the columns in purely aqueous mobile phases. The results of the hydrophobicity and polarity tests were consistent, and allowed column characterization and classification. Silanol activity was important with octadecyl silica columns, but was relatively insignificant with bonded polyethylene glycol and pentafluorophenylpropyl phases on silica gel support. Polar interactions with the alumina and zirconia support materials significantly affect the retention.     

Optical sensing system for ATP using porphyrin-alkaloid conjugates

Tetrabrucin-porphyrin as a sensor for ATP was designed and tested; selectivity for ATP was proved in the presence of ADP and AMP.     

Relative uniform convergence of a sequence of functions at a point and Korovkin-type approximation theorems

Positivity - We prove a Korovkin-type approximation theorem using the relative uniform convergence of a sequence of functions at a point, which is a method stronger than the classical ones. We give...     

Synthesis and application of a fluorous Lawesson's reagent: convenient chromatography-free product purification

[reaction: see text] A fluorous analogue of Lawesson's reagent for thionation of carbonyl compounds has been developed and its use demonstrated on a series of amides, esters, and ketones. The separation of the Lawesson's reagent-derived byproducts can be achieved by a simple fluorous solid-phase extraction.     

Korovkin-Type Approximation Theorem for Double Sequences of Positive Linear Operators via Statistical A-Summability

In this paper, using the concept of statistical A-summability which is stronger than the A-statistical convergence we provide a Korovkin-type approximation theorem on the space of all continuous real valued functions defined on any compact subset of the real two-dimensional space. We also study the rates of statistical A-summability of positive linear operators.     

On-Line Dimension of Semi-Orders

We analyze the on-line dimension of partially ordered sets as a value of a two-person game between Algorithm and Spoiler. The game is played in rounds. Spoiler presents an on-line order of width at most w, one point at a time. Algorithm maintains its realizer, i.e., the set of d linear extensions which intersect to the presented order. Algorithm may not change the ordering of the previously introduced elements in the existing linear extensions. The value of the game val(w) is the least d such that Algorithm has a strategy against Spoiler presenting any order of width at most w. For interval orders Hopkins showed that val $(w) \leqslant 4w-4$ . We analyze the on-line dimension of semi-orders i.e., interval orders admitting a unit-length representation. For up-growing semi-orders of width w we prove a matching lower and upper bound of w. In the general (not necessarily up-growing) case we provide an upper bound of 2w.     

A Highly Reactive Geminal P/B Frustrated Lewis Pair: Expanding the Scope to C−X (X=Cl,Br) Bond Activation

The geminal frustrated Lewis pair tBu₂PCH₂B(Fxyl)₂ ( 1 ; Fxyl=3,5‐(CF₃)₂C₆H₃) is accessible in 65 % yield from tBu₂PCH₂Li and (Fxyl)₂BF. According to NMR spectroscopy and X‐ray crystallography, 1 is monomeric both in solution and in the solid state. The intramolecular P ??? B distance of 2.900(5) Å and the full planarity of the borane site exclude any significant P/B interaction. Compound 1 readily activates a broad variety of substrates including H₂, EtMe₂SiH, CO₂/CS₂, Ph₂CO, and H₃CCN. Terminal alkynes react with heterolysis of the C?H bond. Haloboranes give cyclic adducts with strong P?BX₃ and weak R₃B?X bonds. Unprecedented transformations leading to zwitterionic XP/BCX₃ adducts occur on treatment of 1 with CCl₄ or CBr₄ in Et₂O. In less polar solvents (C₆H₆, n‐pentane), XP/BCX₃ adduct formation is accompanied by the generation of significant amounts of XP/BX adducts. FLP 1 catalyzes the hydrogenation of PhCH=NtBu and the hydrosilylation of Ph₂CO with EtMe₂SiH.     

Applying Mechanochemistry for Bottom‐Up Synthesis and Host–Guest Surface Modification of Semiconducting Nanocrystals: A Case of Water‐Soluble β‐Cyclodextrin‐Coated Zinc Oxide

Mechanochemistry has recently emerged as an environmentally friendly solventless synthesis method enabling a variety of transformations including those impracticable in solution. However, its application in the synthesis of well‐defined nanomaterials remains very limited. Here, we report a new bottom‐up mechanochemical strategy to rapid mild‐conditions synthesis of organic ligand‐coated ZnO nanocrystals (NCs) and their further host–guest modification with β‐cyclodextrin (β‐CD) leading to water‐soluble amide‐β‐CD‐coated ZnO NCs. The transformations can be achieved by either one‐pot sequential or one‐step three‐component process. The developed bottom‐up methodology is based on employing oxo‐zinc benzamidate, [Zn₄(μ₄‐O)(NHOCPh)₆], as a predesigned molecular precursor undergoing mild solid‐state transformation to ZnO NCs in the presence of water in a rapid, clean and sustainable process.