Optische Messungen an Amylose-Farbstoff-Komplexen

Zusammenfassung In neutralen wäßrigen Lösungen, die Amylose und Kongorot enthalten, treten im Bereich der Absorptionsmaxima Abweichungen von der normalen optischen Rotationsdispersion und mehrere induzierte Cotton-Effekte auf. Hieraus wird auf eine geordnete Assoziation der Farbstoffmoleküle an helicale Segmente der Amylose geschlossen. Bei Methylorange, -Naphtholorange und Chrysophenin G sind keine induzierten Cotton-Effekte zu beobachten.

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Summary Upon addition of Congo red, neutral aqueous solutions of amylose show several induced Cotton-effects in the regio of the dye absorption bands. It is assumed that Congo red forms sterically ordered adducts with helical amylose segments. With several other azo dyes (methyl orange, -naphthol orange, chrysophenin G), no induced Cotton-effects were observed.

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Mit 1 Abbildung in 3 Enzeldarstellungen

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Herrn Professor Dr.R. Tschesche mit freundlichen Grüßen zum 65, Geburtstag gewidmet.     

Particle size effects on the thermal behaviour of maghemite synthesised by flame pyrolysis

Thermal treatment of pure nanoscale maghemite (γ-Fe₂O₃) powders under argon yields different products depending on particle size. Particles with a mean diameter above 15 nm transform to hematite (-Fe₂O₃). Smaller particles, which were synthesised under identical conditions but from solutions with lower Fe³⁺ concentrations, transform into magnetite (Fe₃O₄) during thermal treatment. This phenomenon can be explained by adsorbed or incorporated reducing carboxylate groups. The origin of the reducing species and possible reaction mechanisms with the maghemite particles are discussed.     

New aminocoumarin antibiotics formed by a combined mutational and chemoenzymatic approach utilizing the carbamoyltransferase NovN

Five new aminocoumarin antibiotics were produced by a combined mutational and chemoenzymatic approach. For this purpose, the 3"-carbamoyltransferase NovN from the novobiocin producer Streptomyces spheroides was overexpressed in the heterologous host S. lividans as an N-terminal His(6) fusion protein and purified by nickel affinity chromatography. Five different 3"-unsubstituted aminocoumarin derivatives were isolated from mutants of the clorobiocin producer S. roseochromogenes, carrying single or multiple gene defects. All five compounds were readily accepted as substrates by NovN, and the 3"-carbamoylated products were isolated on a preparative scale. Their structures were elucidated by (1)H-NMR and mass spectroscopy, and their inhibitory activity on gyrase in vitro as well as their antibacterial activity was determined. The results give further insight into the structure-activity relationships of aminocoumarin antibiotics.     

Progress of thermal analysis in earth sciences

The historical origins of the present state of thermal analysis investigations in geosciences are outlined. The majority of about 80 contributions to ESTAC 4 concerning geosciences dealt with applied and technical mineralogy and crystallography. Others are discussed with respect to new of improved techniques, minerals and rocks, thermodynamics and kinetics of minerals, and archeometry. Finally, subjects are suggested that could be treated at future meetings.

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Zusammenfassung Der historische Ursprung des gegenwärtigen Standes thermoanalytischer Untersuchungen auf dem Gebiet der Geowissenschaften wird diskutiert. Von den auf dem ESTAC-4 vorgestellten ca. 80 Beiträgen zu Geowissenschaften mit Schwerpunkt Angewandte und Technische Mineralogie und Kristallographie werden einige unter den Aspekten: Neue oder verbesserte Methoden, Mineralien und Gesteine, Thermodynamik und Kinetik von Mineralen, Archäometrie diskutiert. Abschliessend werden Vorgeschläge für Themen künftiger Treffen gemacht.

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. 80 ESTAS 4 , . , , , , . , .

     

In vitro and in vivo production of new aminocoumarins by a combined biochemical, genetic, and synthetic approach

The aminocoumarin antibiotics clorobiocin, novobiocin, and coumermycin A(1) are inhibitors of bacterial gyrase. Their chemical structures contain amide bonds, formed between an aminocoumarin ring and an aromatic acyl component, which is 3-dimethylallyl-4-hydroxybenzoate in the case of novobiocin and clorobiocin. These amide bonds are formed under catalysis of the gene products of cloL, novL, and couL, respectively. We first examined the substrate specificity of the purified amide synthetases CloL, NovL, and CouL for the various analogs of the prenylated benzoate moiety. We then generated new aminocoumarin antibiotics by feeding synthetic analogs of the 3-dimethylallyl-4-hydroxybenzoate moiety to a mutant strain defective in the biosynthesis of the prenylated benzoate moiety. This resulted in the formation of 32 new aminocoumarin compounds. The structures of these compounds were elucidated using FAB-MS and (1)H-NMR spectroscopy.     

Describing Dzyaloshinskii–Moriya spirals from first principles

In magnetic systems lacking spatial inversion symmetry it is observed that the Dzyaloshinskii–Moriya interaction can entail long-ranged spin spirals with a unique sense of rotation. Here, we present a computationally efficient scheme to calculate these large magnetic structures within density functional theory and extract the interaction parameters using perturbative approaches of different order. We analyze the accuracy of these methods by investigating thin Fe films on W(1 1 0) and Mo(1 1 0) substrates.     

Deterministic Routing With Bounded Buffers: Turning Offline Into Online Protocols

In this paper we present a deterministic protocol for routing arbitrary permutations in arbitrary networks. The protocol is analyzed in terms of the size of the network and the routing number of the network. Given a network H of n nodes, the routing number of H is defined as the maximum over all permutations on {1, ..., n} of the minimal number of steps to route offline in H. We show that for any network H of size n with routing number R our protocol needs time to route any permutation in H using only constant size edge buffers. This significantly improves all previously known results on deterministic routing. In particular, our result yields optimal deterministic routing protocols for arbitrary networks with diameter or bisection width , constant. Furthermore we can extend our result to deterministic compact routing. This yields, e.g., a deterministic routing protocol with runtime O(R logn) for arbitrary bounded degree networks if only O(logn) bits are available at each node for storing routing information. Our protocol is a combination of a generalized ``routing via simulation' technique with an new deterministic protocol for routing h-relations in an extended version of a multibutterfly network. This protocol improves upon all previous routing protocols known for variants of the multibutterfly network. The ``routing via simulation' technique used here extends a method previously introduced by the authors for designing compact routing protocols. Received July 18, 1997     

Novel rearrangements of fused zwitterionic heterocyclic systems

(E)-2-Chlorodimethylstannyl-3-diethylboryl-2-pentene (1) reacts with the C-lithiated azoles 2 (derived from thiazole (2a), 4-methylthiazole (2b), 1,4-dimethylimidazole (2c), benzoxazole (2d) and benzthiazole (2e)) to eliminate LiCl, giving first mixtures containing compounds with either a coordinative N--- bond (3) or the zwitterionic isomer with an Sn---N bond (4), or both, and in some cases a rearranged product (5) with a 1,2,5-azastannaborole unit is also present. The zwitterionic compounds 4 tend to rearrange into the heterocycles 5 in which the heteroaromatic system is no longer present and two new C---C bonds, a new B---C and a new B---N bond are formed. The reactions were monitored by multinuclear NMR (¹H, ¹¹B, ¹³C, ¹⁴N and ¹¹⁹Sn NMR) which also served for the characterization of the final products. In the case of 5e, the molecular structure was determined by single-crystal X-ray analysis (monoclinic; space group P2₁/n; A=11.691(2), B=12.396(2), C=13.149(2) Å; β=93.41(2)°).     

Lithium carnallite,LiCl·MgCl2·7H2O

The title compound, lithium magnesium chloride heptahydrate, LiCl·MgCl₂·7H₂O, was analyzed in 1988 by powder X‐ray diffraction [Emons, Brand, Pohl & Köhnke (1988). Z. Anorg. Allg. Chem. 563 , 180–184] and a monoclinic crystal lattice was determined. In the present work, the structure was solved from single‐crystal diffraction data. A trigonal structure was found, exhibiting a network structure of Mg(H₂O)₆ octahedra and Li(H₂O)Cl₃ tetrahedra connected by H...Cl hydrogen bonds. The [Li(H₂O)]⁺ unit is coordinated by distorted edge‐connected Cl⁻ octahedra.