Viskoelastische Eigenschaften von Polyisobutylenen in verdünnten Lösungen

Zusammenfassung Die Speicher- und VerlustmodulnG undG verdünnter Lösungen (2–4%) dreier Isobutylenpolymerisate mit den Molekulargewichten 0,63, 1,29 und 11×10⁵ wurden in der Apparatur vonBirnboim undFerry über einen Frequenzbereich von 0,4–400 Hz und einen Temperaturbereich von –17,5 bis 25,0° bestimmt. Für die scharf fraktionierten Polymerisate von niederem Molekulargewicht ergab die Frequenzabhängigkeit der Moduln eine ausgezeichnete Übereinstimmung mit der Theorie vonZimm. Die aus den experimentell erhaltenen Kurven ermittelten Molekulargewichte und größten Relaxationszeiten waren von der erwarteten Größenordnung. Für das Polymerisat mit höherem Molekulargewicht entsprach die Frequenzabhängigkeit vonG undG – _s jedoch der Theorie vonRouse. Der Einfluß der hydrodynamischen Wechselwirkung in der Bewegung der Knäuelsegmente, in welchem der Unterschied zwischen den beiden Theorien besteht, erscheint als von der Größe des Molekulargewichts abhängig.

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Summary The storage and loss moduliG andG of dilute (2–4%) solutions of three polyisobutylenes of molecular weight 0.63, 1.29, and 11×10⁵ were determined in the apparatus ofBirnboim andFerry over a frequency range of 0.4 to 400 cps, and a temperature range of –17.0 to 25.0°. The sharply fractionated polymers of low molecular weight showed a frequency dependence in excellent agreement with the theory ofZimm. The experimentally determined molecular weights and terminal relaxation times were of the expected order of magnitude. The frequency dependence of the polymer of highest molecular weight, however, conformed more closely to the theory ofRouse. The influence of the hydrodynamic interaction on the motion of the coil segments, which constitutes the difference in the two theories, appears to depend on the magnitude of the molecular weight.

     

A Novel Environmentally Benign Method for the Selective Oxidation of Alcohols to Aldehydes and Ketones

In the presence of [Ru(terpyridine)(2,6‐pyridinedicarboxylate)], aliphatic and benzylic alcohols are oxidized to the corresponding aldehydes or ketones with high selectivity by using hydrogen peroxide as the oxidant. There is no need for the addition of co‐catalysts or organic solvents. By applying an optimized reaction protocol, high catalyst productivity (turnover number>10 000) and activity (turnover frequency up to 14 800 h^?1) has been achieved.     

Mechanism of the oxidation of cycloheptanone by chloramine-T

The oxidation kinetics of cycloheptanone by chloramine-T in alkaline media has been investigated. A mechanism involving the formation of an intermediate by the interaction between the enolic anion of cycloheptanone and chloramine-T in a slow step followed by its interaction with another molecule of chloramine-T in a fast step leading to products has been proposed. The scheme satisfactorily accords with the observed stoichiometry, negligible influence of ionic strength and a positive dielectric effect. Various rate parameters have been computed and 1.2-cycloheptanedione identified as the end product.With 2 Figures     

FLAVIN-PHOTOSENSITIZED MONOMERIZATION OF DIMETHYLTHYMINE CYCLOBUTANE DIMER IN THE PRESENCE OF MAGNESIUM PERCHLORATE

We have investigated the photosensitized monomerization of the cis,syn -cyclobutane dimer of 1,3-di-methylthymine using riboflavin tetraacetate and a 5-deazaflavin derivative as photosensitizer. Although little monomerization of the dimer is induced by photoexcitation of the flavins in the absence of any additives, the flavins can function as an efficient photosensitizer in the presence of magnesium perchlorate. Mechanistic studies involving spectroscopic, quantum-yield and flash-photolysis measurements demonstrated that the photosensitized monomerization exclusively proceeds through electron transfer from the dimer to the triplet flavins complexed with Mg²⁺. The effects of magnesium perchlorate are compared with those on the chloranil-photosensitized monomerization and also with the effects of HClO₄ on the flavin-photosensitized reaction.     

Anwendung mikroanalytischer Methoden zur Lösung kunst- und kulturgeschichtlicher Probleme

Zusammenfassung Mit bekannten mikroanalytischen Arbeitsmethoden — Oberflächenreaktionen, Abstrichuntersuchungen mit dem Korundstäbchen, Schutzschichtreaktionen sowie dem Abdruckverfahren — lassen sich archaeometrische Probleme einer Lösung näherbringen. Die Art der Korrosion kupferhaltiger Oberflächen wurde diskutiert.

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Application of microanalytical methods to the solution of artistic- and cultural historical problems

Summary Archeometrical problems are brought closer to a solution by means of known microanalytical procedures-surface reactions, surface scraping studies with the corundum rod, protective layer reactions as well as the imprint method. A discussion of the corrosion of copper-bearing surfaces is included.

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Vortrag anläßlich der Tagung Chemische Analysen — Kunst- und Kulturwissenschaften im Reiß-Museum in Mannheim, 19.–21. September 1974.     

Novel polycationic biocides: Synthesis and antibacterial activity of polymeric phosphonium salts

Various polymeric phosphonium salts and the corresponding low-molecular-weight model compounds were prepared and their antibacterial activities against Staphylococcus aureus and Escherichia coli were explored by the viable cell counting method in sterile distilled water. Antibacterial activity of the polymers was found to be higher than that of the corresponding model compounds, particularly against S. aureus. Furthermore, the polymeric phosphonium salt exhibited a higher activity by 2 orders of magnitude than the polymeric quaternary ammonium salt with the same structure except the cationic part. Compounds with the longest alkyl chain (octyl) studied were found to exhibit particularly high activity, and this finding may be ascribed to the contribution of the increased hydrophobicity of the compounds to the cidal activity. © 1993 John Wiley & Sons, Inc.     

Hole and Electron Doping of the 4d Transition-Metal Oxyhydride LaSr3NiRuO4H4

Hole or electron doping of phases prepared by topochemical reactions (e.g. anion deintercalation or anion-exchange) is extremely challenging as these low-temperature conversion reactions are typically very sensitive to the electron counts of precursor phases. Herein we report the successful hole and electron doping of the transition-metal oxyhydride LaSr₃NiRuO₄H₄ by first preparing precursors in the range La_xSr_4−xNiRuO₈ 0.5<x<1.4 and then converting into the corresponding La_xSr_4−xNiRuO₄H₄ phases. This is particularly noteworthy as the (Ni/Ru)H₂ sheets in the La_xSr_4−xNiRuO₄H₄ phases are structurally analogous to the CuO₂ sheets in cuprate superconductors and hole doping (Ni^1+/2+, Ru²⁺) or electron doping (Ni²⁺, Ru^1+/2+) yields materials with partial occupancy in Ni/Ru –H 1s bands which are analogous to the partially occupied Cu –O 2p bands present in the CuO₂ sheets of doped superconducting cuprates.     

A new technique for the identification of chloride ions by the formation of chromyl chloride

Summary A new technique is described for the identification of the chloride ion through the formation of chromyl chloride, based on the extraction of the latter with carbon tetrachloride. The identification limit is 2g of chloride. It is possible to carry out the test in the presence of many other anions, including fluoride, which cannot be present when the traditional distillation technique is employed.

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Zusammenfassung Vorgeschlagen wird eine neue Technik zum Chloridnachweis durch Bildung von Chromylchlorid. Dieser Nachweis beruht auf der Extraktion des Chromylchlorids mit Tetrachlorkohlenstoff. Die Nachweisgrenze liegt bei 2g Chlorid, wobei die Möglichkeit besteht, den Test auch in Gegenwart von Fluorid durchzuführen, das bei Anwendung der üblichen Destillationsmethoden nicht anwesend sein darf.

     

Molecular Recognition of Nucleic Acid Bases in Water by Hydrogen Bonding of Poly(vinyldiaminotriazine)

Poly(2-vinyl-4,6-diamino-1,3,5-triazine) efficiently binds nucleic acid bases and nucleosides in water by using complementary hydrogen bonding. The binding activity decreases in the order: U, T > A C, G. The corresponding monomer shows virtually no activity, indicating a predominant role of polymer effect for the molecular recognition in water.     

Proton Relaxometry of Long-Lived Spin Order

A study of long-lived spin order in chlorothiophene carboxylates at both high and low magnetic fields is presented. Careful sample preparation (removal of dissolved oxygen in solution, chelating of paramagnetic impurities, reduction of convection) allows one to obtain very long-lived singlet order of the two coupled protons in chlorothiophene derivatives, having lifetimes of about 130 s in D₂O and 240 s in deuterated methanol, which are much longer than the T₁-relaxation times (18 and 30 s, respectively, at a field =9.4 T). In protonated solvents the relaxation times become shorter, but the lifetime is still substantially longer than . In addition, long-lived coherences are shown to have lifetimes as long as 30 s. Thiophene derivatives can be used as molecular tags to study slow transport, slow dynamics and slow chemical processes, as has been shown in recent years.