Synthesis and derivatization of ethynyl alpha,alpha-dibromomethyl ketones: formation of highly functionalized vinyl triflates

[reaction: see text] We describe the synthesis of alpha,alpha-dibromomethyl ynones (8) and their subsequent derivatization to vinyl acetates (10). These vinyl acetates feature a 1,1-dibromo-olefin moiety, which is readily exploited in palladium-catalyzed Sonogashira, Stille, and Suzuki cross-coupling reactions with alkynes, stannanes, and boronic acids, respectively. A novel one-pot process then directly converts the resulting vinyl acetates 11-13 to the vinyl triflate derivatives 14a-j.     

Cloud-point preconcentration of fulvic and humic acids

The cloud-point extraction technique was used for preconcentration of fulvic and humic acids. The effect of the acidity of solution, the equilibration temperature and time, the amount of added surfactant (Triton X-100) and the time of centrifugation on the recovery were examined. The recoveries of fulvic and humic acids achieved under optimised conditions were 82% and 96%, respectively.     

The use of sample additives in flame emission spectrometry

New kinds of sample additives were investigated to increase the efficiencies of desolvation and atomization in flame spectrometry. Hydrazine and nigrosin were chosen as chemical and dye additives, respectively; an enhancement in the flame-emission signal was obtained in both cases. With nigrosin, it was possible to eliminate completely the interference of phosphate on a calcium emission signal. The increase in the signal for both additives was believed initially to be due to the more rapid evaporation of droplets in the sample aerosol. Further evidence, however, suggested that enhanced vaporization is responsible for the observed signal increase. It is suggested that similar sample additives might be useful also in inductively-coupled plasma emission spectrometry.     

Effect of zirconium,calcium, and barium on corrosion-electrochemical behavior of aluminum

The effect of zirconium, calcium, and barium on corrosion-electrochemical properties of aluminum was studied. A positive effect of alloying aluminum by these metals was revealed.Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11, 2004, pp. 1815–1818.Original Russian Text Copyright © 2004 by Ganiev, Barotov, Inoyatov.     

Unusual regiochemistry in a beckmann-like rearrangement of camphor. α-Camphidone via methylene migration.

Reaction of camphor with hydroxylamine-O-sulfonic acid affords the nitrogen insertion product α-camphidone by migration of the methylene group rather than the bridgehead. Since Beckmann rearrangements of trigonal oximes afford bridgehead cleavage products with camphor, an alternative synchronous rearrangement of a tetrahedral intermediate is proposed for this Beckmann-like reaction.     

Eine verbesserte Auswertungsmethode für die Röntgenkleinwinkelstreuung von Hochpolymeren

Zusammenfassung Die theoretischen und experimentellen Bedingungen für eine verbesserte Auswertung der Röntgenkleinwinkelstreuung von Hochpolymeren werden untersucht. Es wird gezeigt, daß genaue Messungen des Intensitätsverlaufes bei größeren Winkeln die Trennung der Kleinwinkelstreuung in eine reine Grenzflächenstreuung und eine Komponente der Dichteschwankungen innerhalb der Phasen ermöglicht.Diese Trennung erhöht die Genauigkeit der Bestimmung der Invarianten und gestattet die Berechnung der mittleren Durchschußlänge der kristallinen und amorphen Bereiche.Ein Vergleich dieses Längenparameters mit der Langperiode führt bei Annahme einer Lamellenstruktur zu einer Aussage über die Unebenheit der Grenzflächen.Der Absolutwert der Dichtefluktuation innerhalb der Phasen stellt einen zusätzlichen Strukturparameter dar, der besonders stark vom Unordnungsgrad der amorphen Bereiche abhängt.Ein Vergleich der experimentellen Ergebnisse mit Intensitätsverteilungen im Kleinwinkelbereich, die sich aus der Theorie des Parakristalls ergeben, zeigt, daß es nicht möglich ist, diese Theorie mit den Resultaten der Messungen in Einklang zu bringen.

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Summary The theoretical and experimental conditions for an improved method of evaluating the X-ray small-angle scattering of polymers are studied. It is shown that accurate measurements of the intensity distribution at wide angles makes it possible to decompose the small-angle scattering into a component due to the phase boundaries only and a component related to the density fluctuations within the phases.This separation increases the accuracy of the determination of the invariant and permits the calculation of the average length of segments of the crystalline and the amorphous regions.Assuming a lamellar structure, a comparison of this length parameter with the long period can be used to assess the planarity of the boundaries. The absolute value of the density fluctuations within the phases represents a supplementary structural parameter which is largely determined by the degree of disorder in the amorphous regions.A comparison of the experimental results with calculated intensity distributions in the small-angle region based on the theory of the paracrystal shows that it is impossible to bring this theory into agreement with the experimental results.

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung Berlin 1971 vom 9. bis 13. März des Regionalverbandes Physikalische Gesellschaft zu Berlin.

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Wir danken Herrn Dr.H. Tompa für das Programm zur Berechnung der in Abb. 9 wiedergegebenen Interferenzfunktion, Herrn Prof. Dr.G. Rehage für die Polystyrolpräparate und HerrnJ. P. Pauwels, HerrnJ. Braibant und dem Personal unseres Rechenzentrums für die Mitarbeit.     

Emission studies of pyrene solutions

Emission spectra of pyrene in hexane have been obtained over a temperature range (from 130 to 260 K) that has not been explored before for concentrations ranging from 10^?4 mole/? to 2 × 10^?2 mole/?. A conventional and new approximation which does not depend on the experimental set-up response functions has been used for evaluating pyrene excimer association energy W_DM and other pyrene parameters. In both methods W_DM agrees quite satisfactorlly, at all concentrations used, with that reported in the literature and obtained by other techniques. However, both approximation fail to yield the right values of the rate parameters at concentrations ? 2 g/?. This set the upper limit of sample solubility to be at C = 2g/? for our range of temperature. Furthermore, the new approximation can probably be used at higher concentration (for higher range of temperature) and even may be used for other organic molecules. There was also no difference in the ratio of the excimer (I_D) to monomer (I_M) quantum yields when an intense laser beam was used as a source of excitation rather than a super-pressure Hg-lamp. This suggested that the concentrations we used might not be large enough. As a result, the laser beam would not create enough density of excited molecules to affect the ratio of I_D/I_M.     

The formation of filamentous structures from iodinated neurotubules.

The porcine neurotubule and its basic subunit were found to be modified in vitro by iodination of amino acids (principally tyrosine) using lactoperoxidase. Iodide ion, H2O2, or lactoperoxidase singly or in any pairwise combination had virtually no effect on neurotubules. However, when all three reagents were present, permitting covalent iodination, it was found that at 0.1 iodotyrosines per tubulin dimer the microtubules unravel to form structures which morphologically resemble strands of protofilaments twisted or wound around each other. These abnormal tubules are stable at room temperature and 4 degrees C. Both monomers of tubulin are labeled to approximately the same extent. Iodinated tubulin (0.1 iodotyrosines/dimer) is unable to assemble in vitro under normal assembly conditions. Heavily iodinated microtubules (8 iodines per tubulin dimer) are similar in morphology to the slightly iodinated structures.     

MEASUREMENT OF THE TEMPERATURE DEPENDENCE OF THE FLUORESCENCE QUANTUM YIELD OF ORGANIC MOLECULES IN SOLUTION

A DETAILED investigation of the temperature dependence of the fluorescence quantum yield φ_f can yield–directly or indirectly–significant information about behavior of excited states of organic molecules, such as the temperature effect on radiationless transitions and on photochemical reactivity. Variation of the temperature changes the viscosity of the solvent and, in conjunction with measurements of φ_f( T ), allows investigations of diffusion-controlled processes. For example, energy transfer and quenching processes as well as excimer or exciplex formation fall into this category. Recent review articles by Weller (1962) and Birks (1970) deal with this topic. Moreover, Huber and Mantulin (1972) have suggested that restraints placed upon geometric modifications of the excited molecule by temperature-induced changes in the solvent cage (variation of site structure) are reflected in a varying φ_f.
The purpose of this note is to describe and verify a simple procedure, accurate to about ± 5%, for measuring the relative fluorescence quantum yield as a function of temperature. A quantum yield study of 9,10-diphenylanthracene between room temperature and 77°K is employed to demonstrate the capabilities of this method. In addition, we consider an example of diffusion-controlled quenching by oxygen measured over a wide temperature range.