Die kleinste Bedeckungszahl innerhalb einer Klasse von Flächenabbildungen

Ohne Zusammenfassung     

Ein biologischer Vergleich zwischen Benzol und Pyridin in kondensierten Ringsystemen

The synthesis of imidazo[4,5-b]pyridines and of [1,2,4]-triazolo[1,5-a]pyridines is described, and their biological activity in relation to the standard antiviral substance, 2-(α-hydroxybenzyl)benzimidazol, is discussed.     

Reaktionen mit Dimethylformamid, 4. Mitt. Notiz über den Chlor-Dimethylaminoaustausch und die partielle Hydrolyse von Nitrilen mit Dimethylformamid

Zusammenfassung Aromatisch gebundene Chloratome konnten nur bei gleichzeitiger Anwesenheit einer Nitrogruppe in 4-Stellung des aromatischen Kerns mit Dimethylformamid (DMF) und bei Anwesenheit von CuSO₄ gegen die Dimethylaminogruppe ausgetauscht werden. Die Reaktion von aromatischen Nitrilen mitDMF in Gegenwart von CuSO₄ führt jedoch überraschend zu Amiden (Ausb. rund 20%), wobei das CuSO₄ zu Metall reduziert wird.

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Reactions with Dimethyl formamide, IV: Notice Regarding the exchange of chlorine with the dimethylamino group and the partial hydrolysis of nitriles with dimethyl formamide

Only in the presence of a p-nitro group it was possible to exchange aromatically bonded chlorine atoms with the dimethylamino group using dimethyl formamide (DMF) and CuSO₄. The reaction, however, of aromatic nitriles withDMF in presence of CuSO₄ surprisingly formes amides (yield about 20%), whereby CuSO₄ is reduced to metallic Cu.

     

Rock porosity determination by combination of X-ray computerized tomography with mercury porosimetry

First results are described of coupling of mercury porosimetry with X-ray computerized tomography (CT) as a new combination technique for rock porosity studies. This technique is suitable for rock samples with a pronounced mercury intrusion-extrusion hysteresis and includes CT measurements before and after mercury intrusion. The entrapped portion of mercury, when the pressure after the intrusion into the rock sample is reduced to 0.1 MPa, serves as a contrast agent in the porous network to localize spatial distribution of rock porosity by CT. The results obtained show that the mercury intrusion and therefore the porosity were quite different for the separate mineral phases. Therefore the combination of mercury porosimetry and computer tomography can give 3-D data on mineral-specific porosity distributions with additional pore size information. In contrast to mercury porosimetry as a single method, results of the combination technique with CT represent a direct visualization of porosity variation and do not depend on any special pore network model. Received: 2 July 1996 / Revised: 20 November 1996 / Accepted: 22 November 1996     

Ansamycine, 5. Mitt., Chemie der Metacycloprodigiosine

In order to obtain a better partition of a prodigiosin derivative in biological media, two hydroxy groups were introduced into theansa-part of the molecule. The synthesis of the title compound is described in detail.     

Fundamentalsätze der quasielliptischen Differentialgeometrie

It is shown that in the quasielliptic space there exist two different sets of respectively quasielliptic congruent curves with the same natural equations =(s), =(s). On the curves of one set the sense of increasing arc length s corresponds with the positive orientation, to say with the sense of increasing x¹/x⁰; on curves of the other set the orientation of s is negativ. Further we prove that the fundamental quantities of surface theory as defined in [3] cannot always characterize an unique parametrized surface apart from quasielliptic motions. In the exceptional case one Christoffel symbol must be given too.     

The Synthesis of α‐Azidoesters and Geminal Triazides

Three simple methods for the synthesis of geminal triazides are described: Starting from 1) 3‐oxocarboxylic acids, 2) iodomethyl ketones, or 3) terminal olefins, a range of triazidomethyl ketones can be constructed under mild oxidative reaction conditions by the use of IBX‐SO₃K, a sulfonylated derivative of 2‐iodoxybenzoic acid (IBX), and NaN₃ as an azide source. This is the first report of representatives of this novel class of triazide compounds: Despite their high nitrogen content, the geminal triazides are easy to handle, even when preparative‐scale syntheses are performed. (Caution: These procedures still require protective measures!) The triazides are now broadly available for further studies regarding their properties and reactivity. Furthermore, we show how the method can be used to provide α‐azidoesters, which are potential building blocks for amino acids.     

GpdA-promoter-controlled production of glucose oxidase by recombinant aspergillus niger using nonglucose carbon sources

The gpdA-promoter-controlled exocellular production of glucose oxidase (GOD) by recombinant Aspergillus niger NRRL-3 (GOD3-18) during growth on glucose and nonglucose carbon sources was investigated. Screening of various carbon substrates in shake-flask cultures revealed that exocellular GOD activities were not only obtained on glucose but also during growth on mannose, fructose, and xylose. The performance of A. niger NRRL-3 (GOD3-18) using glucose, fructose, or xylose as carbon substrate was compared in more detail in bioreactor cultures. These studies revealed that gpdA-promoter-controlled GOD synthesis was strictly coupled to cell growth. The gpdA-promoter was most active during growth on glucose. However, the unfavorable rapid GOD-catalyzed transformation of glucose into gluconic acid, a carbon source not supporting further cell growth and GOD production, resulted in low biomass yields and, therefore, reduced the advantageous properties of glucose. The total (endo- and exocellular) specific GOD activities were lowest when growth occurred on fructose (only a third of the activity that was obtained on glucose), whereas utilization of xylose resulted in total specific GOD activities nearly as high as reached during growth on glucose. Also, the portion of GOD excreted into the culture fluid reached similar high levels (≅ 90%) by using either glucose or xylose as substrate, whereas growth on fructose resulted in a more pelleted morphology with more than half the total GOD activity retained in the fungal biomass. Finally, growth on xylose resulted in the highest biomass yield and, consequently, the highest total volumetric GOD activity. These results show that xylose is the most favorable carbon substrate for gpdA-promoter-controlled production of exocellular GOD.     

Ansamycine, 1. Mitt.: Chemie der Metacycloprodigiosine,Synthese des [9](2,4)Pyrrolophans

Some syntheses of [9](2,4)pyrrolophane are described.