Synthesis of a simplified bryostatin C-ring analogue that binds to the CRD2 of human PKC-alpha and construction of a novel BC-analogue by an unusual Julia olefination process

[structure: see text] The synthesis of two truncated bryostatin analogues 2 and 3 is described. High-field NMR measurements on the C-ring analogue 3 in C(2)H(3)CN containing 25% (2)H(2)O have shown that it binds to the CRD2 of human PKC-alpha at virtually the same position as phorbol-13-acetate (PA) and bryostatin 1 (1). NMR titration studies have also revealed that 3 binds to the CRD2 with a potency similar in magnitude to PA but much less potently than 1.     

Kinetic determination of magnesium and calcium by stopped-flow injection analysis

A kinetic method for the simultaneous determination of magnesium and calcium ions in solution is described. The method is based on the dissociation reactions of cryptand (2.2.2) complexes; a stopped-flow injection technique is used with spectrophotometric monitoring of the phthalein complexone complexes of the released metal ions. Analyses were done at a rate of 80 h^?1, with injected sample volumes of 80 μl. A microcomputer system for data acquisition and control of the system is described.     

Beitr?ge zur Bestimmung von Spurenverunreinigungen in UO2-Kernbrennstoff

Zusammenfassung Die für die Bestimmung geringer Gehalte an Phosphor, Silicium, Fluor, Chlor, Lithium, Natrium, Calcium und Kohlenstoff in UO₂-Kernbrennstoff angewandten chemischen Analysenverfahren werden beschrieben. Durch Kombination einfacher und blindwertfreier Abtrennungsverfahren (Extraktionen und Pyrohydrolysen) mit empfindlichen physikalischchemischen Bestimmungsmethoden (Spektralphotometrie, Flammenphotometrie, coulometrische Titration) lassen sich Nachweisgrenzen zwischen 0,1 und 10 ppm bei Probeneinwaage von 0,5–1 g UO₂ erreichen. Der Zeitaufwand für die Analysen kann durch simultane Bestimmung zweier oder dreier Elemente in einem Arbeitsgang niedriggehalten werden. Die beschriebenen Verfahren haben sich bei Reinheitskontrollen von Kernbrennstoffen gut bewährt.

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Summary Analytical methods have been developed for the determination of trace amounts of phosphorus, silicon, fluorine, chlorine, lithium, sodium, calcium, and carbon in UO₂ of nuclear purity. By combination of simple and rapid separation procedures (extraction, pyrohydrolysis) with highly sensitive methods of determination (spectrophotometry, flame photometry, coulometric titration) detection limits of 0.1–10 ppm have been obtained with sample sizes of 0.5–1 g. In order to reduce the time needed for analysis, some of the above elements are determined simultaneously. The methods described have been successfully applied to the purity control of nuclear fuels.

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Herrn Dr. W. Gebauhr danken wir für wertvolle Anregungen und Diskussionen.     

Quantitative Bestimmung der Catechine und Hydroxyzimts?uren in pflanzlichen Lebensmitteln

Zusammenfassung Die Problematik der Bestimmung von Catechinen und Hydroxyzimtsäuren in pflanzlichen Lebensmitteln wird diskutiert und gezeigt, daß es notwendig ist, eine ausreichende Vorreinigung (Säulen-Chromatographie an Polyamid und Dünnschicht-Chromatographie an Cellulose bzw. Kieselgel) mit einem geeigneten Bestimmungsverfahren (Spektralphotometrie mit Vanillin/Salzsäure bzw. direkt) zu kombinieren. Beispiele werden beschrieben.Plenarvortrag anläßlich der Tagung Spurenanalyse, 2.–5. April 1973 in Erlangen.     

Zur Fehlerermittlung bei der photometrischen Eisenbestimmung in Glassanden

Zusammenfassung Zur Bestimmung des Eisengehaltes in Glassanden eignet sich die o-Phenanthrolinmethode, da diese Methode frei ist von störenden Einflüssen der im Sand neben dem Eisen vorliegenden Fremdionen.Der Analysenfehler wird dabei aus den Eichmessungen nach den Methoden der Ausgleichsrechnung und mathematischen Statistik rechnerisch ermittelt und bei der Auswertung des Analysenergebnisses in geeigneter Form berücksichtigt.

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Summary For the determination of the iron content in glass sands the o-phenanthroline method is suitable because it is unaffected by foreign ions occuring in the sand besides iron.The analytical error is calculated from the calibrating measurements according to the methods of balancing computation and mathematical statistics, and is taken into account on interpreting the analytical result in a suitable form.

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Herrn Dr. Moritz danken wir für die Anregung zu dieser Arbeit, Herrn Dr.-Ing. habil. Klaus Doerffel für wertvolle Hinweise zur mathematischen Auswertung.     

In situ alkylation of cysteine residues in a hydrophobic membrane protein immobilized on polyvinylidene difluoride membranes by electroblotting prior to microsequence and amino acid analysis.

For identification of cysteine residues on microsequence analysis it is crucial to derivatize the sulfhydryl groups. This reaction requires a desalting step which often represents a major obstacle, especially if the sample consists of limited amounts of a hydrophobic membrane protein. An alkylation procedure is described, allowing efficient derivatization (greater than 90%) of cysteines and cystines even in low microgram quantities, as revealed by test analyses with lysozyme and a hydrophobic membrane protein. The modified protein is recovered in high yields in a form suitable for both microsequence analysis and amino acid analysis. The method involves electrophoretic desalting by miniaturized Tricine-sodium dodecyl sulfate-polyacrylamide gel electrophoresis and in situ alkylation after electro-transfer onto polyvinylidene difluoride membranes. Precautions against NH2-terminal blocking during sample preparations are provided. The general applicability of the method is illustrated by the structural characterization of the low abundance membrane receptor for human urokinase plasminogen activator.     

Propane fuel cells using phosphoric-acid-doped polybenzimidazole membranes

Propane fuel cells using H(3)PO(4)-doped polybenzimidazole polymer membranes produce low and unsustainable current densities at temperatures up to 250 degrees C under anhydrous conditions. Stable intermediate species blocked the surface of noble metal anode catalysts, and the intermediate species could not react further into desorbable final products. In contrast, when water was introduced by light humidification (S(r) 0.08%) of the propane stream, sustainable and higher current densities were achieved. Water participated in the reaction sequence to form surface-bound hydrocarbon and then oxygen-containing intermediates and thereby generated CO and CO(2) as the only carbon-containing products.     

Mild and practical method for the alpha-arylation of nitriles with heteroaryl halides

[reaction: see text] A mild and transition-metal-free method for the alpha-arylation of aliphatic nitriles with activated heteroaryl halides was developed using NaHMDS or KHMDS as base at ambient temperature. The key to the success of this method is generation of the nitrile anion in the presence of the heteroaryl halide. The method is applicable to both primary and secondary carbonitriles and a wide range of heteroaryl halides. Selective monoarylation was observed with primary carbonitriles. The operational simplicity and the mild reaction conditions add to the value of this method as a practical alternative to the preparation of alpha-heteroaryl carbonitriles.     

Synthesis and antiviral activity of monofluorinated cyclopropanoid nucleosides

Diastereopure monofluorinated cyclopropanoid nucleosides were synthesized for biological studies. As key intermediates cis- and trans-(+/-)-[1-fluoro-2-(acetoxymethyl)cyclopropyl]methanol were prepared starting from diastereopure fluorinated cyclopropanecarboxylates. The latter were synthesized by copper(i)-catalyzed cyclopropanation of [small alpha]-fluorostyrene with ethyl diazoacetate. After reduction and O-acetylation the diastereomeric (2-fluoro-2-phenylcyclopropyl)methyl acetates were obtained. Oxidative degradation using RuO(4) and reduction of the formed carboxyl group with borane gave the fluorinated alcohols, which were coupled with different nucleobases. After deprotection, the corresponding cyclopropanoid nucleosides of adenine, cytosine, guanine, thymine and uracil were obtained. Antiviral tests revealed for the cis-configured guanosine a low, but specific activity against HSV-1 and HSV-2. In addition low affinities of the adenine derivatives to adenosine receptors were detected.     

Surface tension of quantum fluids from molecular simulations

We present the first molecular simulations of the vapor-liquid surface tension of quantum liquids. The path integral formalism of Feynman was used to account for the quantum mechanical behavior of both the liquid and the vapor. A replica-data parallel algorithm was implemented to achieve good parallel performance of the simulation code on at least 32 processors. We have computed the surface tension and the vapor-liquid phase diagram of pure hydrogen over the temperature range 18-30 K and pure deuterium from 19 to 34 K. The simulation results for surface tension and vapor-liquid orthobaric densities are in very good agreement with experimental data. We have computed the interfacial properties of hydrogen-deuterium mixtures over the entire concentration range at 20.4 and 24 K. The calculated equilibrium compositions of the mixtures are in excellent agreement with experimental data. The computed mixture surface tension shows negative deviations from ideal solution behavior, in agreement with experimental data and predictions from Prigogine's theory. The magnitude of the deviations at 20.4 K are substantially larger from simulations and from theory than from experiments. We conclude that the experimentally measured mixture surface tension values are systematically too high. Analysis of the concentration profiles in the interfacial region shows that the nonideal behavior can be described entirely by segregation of H(2) to the interface, indicating that H(2) acts as a surfactant in H(2)-D(2) mixtures.