Silber

Ohne Zusammenfassung     

Tetraarylester der μ-Imidodiphosphorsäure und ihre Thioderivate — Strukturuntersuchungen

Tetraarylesters of μ-Imido-Diphosphoric Acid and its Thio Derivatives — Structure Investigations New O,O′,O″,O?-tetratolyl- and ditolyl-diphenylesters of the μ-imido-diphosphoric acid and its mono and dithio derivatives were synthesized, compared with the corresponding tetraphenylesters and investigated by ¹H, ¹³C, and ³¹P NMR spectroscopy and X-ray crystal structure analysis. Structures of the O,O′,O″,O?-tetrakis-(2-methyl-phenyl)-μ-imidodiphosphate, 1b , as well as of the corresponding ortho-, meta- and para-tolylesters of the μ-imido-monothiodiphosphoric acid ( 2a , 2b , 2c ) were determined. All the compounds form dimers via N? H…?O hydrogen bonds in the crystal as well as in nonpolar solvents. The distances around the phosphorus atoms rise with decreasing electronegativity of the phosphorus substituents. Signs of the ²J_{P? N? P} coupling constants were determined by ¹³C{¹H, ³¹P} triple resonance experiments for some compounds. These constants become more negative owing to substitution of a phosphoryl by a thiophosphoryl group.     

De novo synthesis of 4'-ethoxy nucleoside analogues

Butenolides 5a and 13 were used as optically active templates in the de novo synthesis of 4'-disubstituted nucleoside analogues. The butenolides were reduced and acylated in situ to give acetates 10 and 14. Vorbrüggen coupling gave the protected nucleoside analogues 11 and 15. Reduction of 11 gave 4'-ethoxy-2',3'-dideoxythymidine (6) and deprotection of 15 gave 4'-ethoxy-2',3'-dideoxydidehydrothymidine (7). The cis-dihydroxylation of a variety of butenolides occurred with the major product formed from oxidation of the beta-face.     

Über die CH-Bestimmung in schwefelhaltigen Verbindungen

Zusammenfassung Verschiedene schwefelhaltige Verbindungen ergeben zu hohe Kohlenstoffwerte. Dieser Fehler kann behoben werden, indem die Einwaage im Verbrennungsschiffchen mit vorbehandeltem Cerdioxid abgedeckt oder vermischt wird.

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CH determination in containing compounds sulfur

Summary Various sulfur-containing compounds yield carbon values which are too high. This error can be eliminated by covering or mixing the aliquot in combustion boats with pretreated cerium dioxide.

     

Quantitative Bestimmung von DNA in Geweben durch Thymin-Analyse

Zusammenfassung Es wird über eine DNA-Bestimmung in biologischem Material durch Hochdruckflüssigkeits-Chromatographie an sphärischen Ionenaustauschern berichtet. Thymin wird durch Hydrolyse lyophilisierter Gewebe freigesetzt, durch Sublimation gereinigt und flüssigkeits-chromatographisch bei etwa 150 at Eingangsdruck bestimmt. Die Ausbeute des Verfahrens wird durch Isotopenverdünnungsanalyse überprüft. Der Einfluß von pH-Wert und Konzentration der Elutionspuffer und der Säulentemperatur wird ermittelt. Die untere quantitative Nachweisgrenze der Methode liegt bei etwa 0,5 g DNA in Geweben, die relative Standardabweichung betrug 10%.

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Quantitative determination of DNA in tissues by thymine-analysisII. Determination by high-pressure ionexchange liquid chromatography

A determination of DNA in biological material by high pressure, liquid chromatography of thymine on spherical ion-exchange resins is presented. After lyophilizing and hydrolyzing the tissues, thymine is separated by sublimation and determined by means of liquid chromatography at 150 at. Yields are controlled by isotope dilution analysis. Investigations on the effect of pH and concentration of eluents and of temperature are reported. The method is suitable for a minimal amount of 0.5 g DNA in tissues with a relative standard deviation of 10%.

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Teil I: diese Z. 259, 177 (1972).

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Geodia cydonium wurde uns dankenswerterweise von der meeresbiologischen Forschungsgruppe, Leitung Herr Prof. Dr. R. K. Zahn, zur Verfügung gestellt.     

An Analytical Method for the Separation and Determination of As(III) and As(V) in Seepage and Acid Mine Drainage Water

To avoid changes in the original As species distribution in natural water after sampling, a method of immediate separation of As(V) by anion exchange at the sampling site was developed. The procedure consists of two steps. The total concentration of arsenic is determined in one part of the water sample acidified on site. Another part of the water samples is pressed through a column filled with an anion exchanger. The As(III) species that is not redox-stable remains in the effluent of the sorbents column and can be analyzed with conventional methods after stabilization by addition of conc. HNO₃. As(V) is sorbed by the exchanger material. The As(V) concentration can be calculated as the difference between As_sol and As(III), neglecting very low contents of methylated species. Oxidation of Fe(II) by air followed by co-precipitation of arsenic with iron hydroxide was applied in field experiments to minimize the As concentration in seepage and mining water.     

C2-Symmetric 4,4′,5,5′-Tetrahydrobi(oxazoles) and 4,4′,5,5′-Tetrahydro-2,2′-methylenebis[oxazoles] as Chiral Ligands for Enantioselective Catalysis Preliminary Communication

The synthesis of a series of enantiomerically pure, C₂-symmetric 4,4′,5,5′-tetrahydro-2,2′-methylenebis[oxazoles] and 4,4′,5,5′-tetrahydro-2,2′-bi(oxazoles) is reported. Copper complexes with anionic tetrahydromethylenebis[oxazole] ligands are efficient catalysts for the enantioselective cyclopropane formation from olefins and diazo compounds (up to 96% ee in the reaction of styrene with menthyl diazoacetate). Tetrahydrobi(oxazole)iridium(I) complexes were found to catalyze transfer hydrogenations of aryl alkyl ketones with i-PrOH (up to 91% ee). Tetrahydrobi(oxazole)palladium complexes can be used as enantioselective catalysts for allylic nucleophilic substitution (up to 77% ee in the reaction of PhCH?CHCH(OAc)Ph with NaHC(COOMe)₂).     

Production of polarized baryons in polarized and unpolarizede + e − collisions

Polarized and unpolarizede ⁺ e ^? annihilation is considered in lowest order at energies 30–150 GeV taking γ andZ ⁰ exchange in the standardSU(2)×U(1) model into account. The fragmentation of polarized quarks into polarized baryons is described by two kinds of fragmentation functions; the first is based onSU(6) weights and empirical expressions for favoured and disfavoured fragmentation; the second is based upon a Monte Carlo model of the chain decay including helicities of quarks and hadrons. From the cross sections for \(e^ + e^ - \to q\bar q\) and the fragmentation functions we obtain predictions for the baryon polarization as function of the collision energy and of kinematical variables.