Fourfold tetraurea calix[4]arenes--potential cores for the formation of self-assembled dendrimers

Wide rim tetraurea calix[4]arenes monofunctionalized at the narrow rim by COOH or NH2 have been synthesized in five steps from t-butylcalix[4]arene tripropylether. Their covalent linkage via the narrow rim to a central calix[4]arene fixed in the 1,3-alternate conformation led to pentacalix[4]arenes 9 bearing four tetraurea derivatives in the cone conformation in a flexible tetrahedral arrangement. Their self-assembly via the formation of hydrogen bonded dimeric capsules has been studied under different conditions. A fourfold heterodimerisation of tetrakis-tetraurea derivatives of type 9 with tetratosylurea 10 has been confirmed by 1H NMR-spectroscopy and dynamic light scattering.     

First experiments on transmutation studies of129I and237Np using relativistic protons of 3.7 GeV

First experiments on the transmutation of long-lived¹²⁹I and²³⁷Np using relativistic protons of 3.7 GeV are described. Relativistic protons generate in extended Pb-targets substancial neutron fluences. These neutrons get moderated in paraffin and are used for transmutation as follows:¹²⁹I(n,)¹³⁰I and²³⁷Np(n,)²³⁸Np. The isotopes¹³⁰I (T _1/2-12.36 h) and²³⁸Np (T _1/2=2.117 d) were identified radiochemically. One can estimate the transmutation cross-section (n,) in the given neutron field as (¹²⁹I(n,))=(10±2)b and (²³⁷Np(n,))=(140±30)b The experiments were carried out in November 1996 at the Synchrophasotron, LHE, Dubna, Russia. The investigation has been performed at the Laboratory of High Energies, JINR, Dubna.     

Eine spezifische colorimetrische Methode zur Bestimmung der Sorbins?ure

Zusammenfassung Es wird eine einfache Methode zur schnellen Bestimmung (1 Std) von Sorbinsäure in Lebensmitteln beschrieben. Die Sorbinsäure wird durch Wasserdampfdestillation verlustlos vom Lebensmittel abgetrennt und im Destillat mit saurer Kaliumdichromatlösung oxydiert. Dabei entsteht unter anderem Malondialdehyd, der mit Thiobarbitursäure einen beständigen roten Farbstoff bildet, dessen Absorptionsmaximum bei 532 nm liegt. Die rote Lösung wird colorimetriert, und über eine Eichgerade, die mit 2–10 g Sorbinsäure aufgestellt worden ist, wird der Gehalt an Sorbinsäure bestimmt. Die Methode wird durch keinen der üblichen Konservierungsstoffe gestört. Verschiedenen Lebensmitteln zugesetzte Sorbinsäuremengen wurden zu 100±2% wiedergefunden. Der qualitative Nachweis kann in vielen Lebensmitteln ohne Destillation innerhalb weniger Minuten visuell durchgeführt werden.Vorgetragen auf der 18. Arbeitstagung des Arbeitskreises Südwestdeutschland der Fachgruppe Lebensmittelchemie und gerichtliche Chemie in der Gesellschaft deutscher Chemiker in Weinheim (Bergstra\e) am 19./20. 5. 1960.Meinem Assistenten, Herrn F. Nagel, sei für die gewissenhafte Durchführung einer gro\en Zahl von Versuchen aufrichtig gedankt.Wir danken ferner der Fa. Rostock Gebrüder Friedrich Söhne, Elmshorn/Holstein, fÜr die Überlassung von Margarineproben mit Sorbinsäure und den Hoechster Farbwerken fÜr die Bereitstellung verschiedener sorbinsäurehaltiger Lebensmittel.     

Synthesis of novel S-neoglycopeptides from glycosylthiomethyl derivatives

Reaction of glycosylthiomethyl azides with amino acid and peptide derivatives containing aspartate and glutamate thio acids gave the corresponding glycosylthiomethyl amides in excellent yields. Another type of neoglycopeptides was obtained via reaction of glycosylthiomethyl bromide with cysteine and homocysteine containing peptide derivatives, thus affording the corresponding S-(glycosylthiomethyl) peptides.     

Studies on the substrate specificity of Escherichia coli galactokinase

In vitro glycorandomization (IVG) technology is dependent upon the ability to rapidly synthesize sugar phosphates. Compared with chemical synthesis, enzymatic (kinase) routes to sugar phosphates would be attractive for this application. This work focuses upon the development of a high-throughput colorimetric galactokinase (GalK) assay and its application toward probing the substrate specificity and kinetic parameters of Escherichia coli GalK. The demonstrated dinitrosalicylic assay should also be generally applicable to a variety of sugar-processing enzymes. [reaction: see text]     

Kathodenstrahlpolarographische Bestimmung von Spuren Kobalt und Zink in Nickel und Nickelsalzen

Zusammenfassung Eine Methode zur kathodenstrahlpolarographischen Bestimmung von Spuren Kobalt und Zink in Nickel und Nickelsalzen wird beschrieben. Die Spuren werden untereinander und von der Matrix über den Anionenaustauscher Dowex 1X8 getrennt. Die Nachweisgrenzen betragen für Kobalt 5·10^–4% und für Zink 4·10^–4%.

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Summary A method is described for the cathode-ray polarographic determination of cobalt and zinc traces in nickel and nickel salts after separation by the anionexchange resin Dowex 1X8. Traces are detectable as low as 5·10^–4% and 4·10^–4%, respectively.

     

Kathodenstrahlpolarographische Bestimmung von Spurenelementen in Zinnchloriden

Zusammenfassung Eine Methode wird beschrieben, die die kathodenstrahlpolarographische Bestimmung von Spuren Ni, Pb, Mn, Co, Cu, Fe, Mo in Zinnchloriden in den Bereichen 10^–4% (Ni, Pb, Mn, Cu, Fe) und 10^–5% (Mo, Co) gestattet. Über den stark basischen Anionenaustauscher AG 1×8 wird das Zinn von den Spurenelementen getrennt.

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Cathode-ray polarographic determination of trace elements in tin chlorides

A method is described for the cathode-ray polarographic detemination of traces of Ni, Pb, Mn, Co, Cu, Fe, and Mo in tin chlorides. Tin is separated from the trace metals by ion exchange on the strong basic anion-exchange resin AG 1×8. The detection limits are within the ranges of 10^–4% and 10^–5%.

     

Structure analysis of [Be(NCS)2(C5H5N)2]

[Be(NCS)₂(C₅H₅N)₂] was prepared and characterized by chemical analysis, FT-IR-analysis, and single crystal X-ray structure analysis. The crystals are orthorhombic with a = 829.30(10) pm, b = 1292.1(2) pm, c = 1313.40(10) pm, space group Pnma. Z = 4. The structure is built up from tetrahedra. Hydrogen bonding between the S-atom of one Be-N-bonded thiocyanate and 1.3-H-atoms of pyridine ligands yield a three dimensional network consisting of folded sheets.     

Novel UDP-glycal derivatives as transition state analogue inhibitors of UDP-GlcNAc 2-epimerase

The "epimerisation" of UDP-GlcNAc to ManNAc, the first step in the biosynthesis of sialic acids, is catalyzed by UDP-GlcNAc 2-epimerase. In this paper we report the synthesis of transition state based inhibitors of this enzyme. To mimic the assumed first transition state of this reaction (TS 1), we designed and synthesized the novel UDP-exo-glycal derivatives 1-4. We also report herein the synthesis of 5 and 6, the first C-glycosidic derivatives of 2-acetamidoglucal, and the synthesis of the ketosides 7 and 8, which were designed as bis-substrate analogue and bis- product analogue, respectively, to mimic the second step of the reaction via the assumed second transition state TS 2.