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%.

     

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.     

A π-acceptor series for phosphines from51V N.M.R. data on [η5-CpV(CO)3L] complexes

Summary Qualitative molecular orbital considerations of the complexes [⁵-CPV(CO)₃ L] (L = substituted phosphane, SbPh₃, AsPh₃, CN^–) suggest that s' V chemical shift parameters () obtained for these compounds should correlate with the -acceptor abilities of L. Based on observed r-values, the ligands are arranged in sequence of their -acceptor ability, which lies in the order P(OR)₃ > CN^– > PR'₃3 SbPh₃ PPhF₂ > P(i-Bu)₃ P(NR ₂ )₃ > PPh₃ > AsPh₃ Nuclear spin-spin coupling constants J (⁵¹V-³¹ P), line widths H and i.r. data in the (CO) region are also presented.P(OR)₃ = P(OEt)₃, 4-Ethyl-l-phospha-2,6,7-trioxabicyclo[2.2.2]-octane; R = Me, n-Pr; R = Me, Et.     

Large electron polarization of H-like20Ne-ions traversing gd foils at very high velocities

It is shown that transient magnetic fields in Gd-host for²⁰Ne ions at a mean velocity of 12.5v₀(v₀=c/137), considerably beyond the Bohr velocity of 1s electrons of Ne ions (v_1s=10v₀), are dominated by the Fermi contact field of these electrons. The first excited 2⁺-state of²Ne was used as probe. The derived value for the mean degree of polarization p_1s=0.32(13), is surprisingly large, though still consistent with values obtained at lower velocities. Present calculations of spin exchange cross sections severely underestimate the observed polarization at this high velocity.The authors are grateful to the operating staff of the UNILAC for providing excellent beam conditions. They also thank Dr. P. Maier-Komor for preparing the delicate targets. Support by the BMFT is acknowledged.     

Upper limit for thermal direct photon production in heavy-ion collisions at 60 and 200A·GeV

The production of direct photons has been investigated in reactions ofp and¹⁶O projectiles at 60 and 200A·GeV with C and Au nuclei. Photon and ⁰ spectra have been measured in the pseudorapidity range 1.52.1 for the transverse momentum region 0.4 GeV/cp _T 2.8 GeV/c employing the lead-glass spectrometer SAPHIR. An upper limit of 15% at the 90% confidence level for the direct photon signal relative to the neutral pion production is obtained from the comparison of measured photon spectra with Monte Carlo simulations of the hadronic background based on the reconstructed yield of ⁰ and mesons. Consequences for a possible phase transition to a quark-gluon plasma are discussed.     

Muonic x-ray intensity measurements on a highT c superconductor

Muonic x-ray spectra from the high-T _c superconductor YBa₂Cu₃O_6.95 have been measured in the superconducting and normal states. No significant differences were found between the two spectra when comparing the intensities of 27 lines.Dedicated to Prof. Dr. H. J. Mang on the occasion of his 60th birthday     

New Methods for the Synthesis of Glycosides and Oligosaccharides—Are There Alternatives to the Koenigs-Knorr Method? [New Synthetic Methods (56)]

Glycoproteins, glycolipids, and glycophospholipids (glycoconjugates) are components of membranes. The oligosaccharide residue is responsible for intercellular recognition and interaction; it acts as a receptor for proteins, hormones, and viruses and governs immune reactions. These significant activities have stimulated interest in oligosaccharides and glycoconjugates. With their help it should be possible to clarify the molecular basis of these phenomena and to derive new principles of physiological activity. Major advances in the synthesis of oligosaccharides have been made by the use of the Koenigs-Knorr method, in which glycosyl halides in the presence of heavy-metal salts are employed to transfer the glycosyl group to nucleophiles. The disadvantages of this procedure have led to an intensive search for new methods. Such methods will be discussed in this article. Emphasis is placed on glycoside and saccharide formation by 1-O-alkylation, on the trichloroacetimidate method, and on activation through the formation of glycosylsulfonium salts and glycosyl fluorides.