Ma?analytische Bestimmung des Quecksilbers

Ohne Zusammenfassung     

Complete biosynthesis of erythromycin A and designed analogs using E. coli as a heterologous host

Erythromycin A is a potent antibiotic long-recognized as a therapeutic option for bacterial infections. The soil-dwelling bacterium Saccharopolyspora erythraea natively produces erythromycin A from a 55 kb gene cluster composed of three large polyketide synthase genes (each ~10 kb) and 17 additional genes responsible for deoxysugar biosynthesis, macrolide tailoring, and resistance. In this study, the erythromycin A gene cluster was systematically transferred from S. erythraea to E. coli for reconstituted biosynthesis, with titers reaching 10 mg/l. Polyketide biosynthesis was then modified to allow the production of two erythromycin analogs. Success establishes E. coli as a viable option for the heterologous production of erythromycin A and more broadly as a platform for the directed production of erythromycin analogs.     

Novel fluoro-substituted benzo- and benzothieno fused pyrano[2,3-c]pyrazol-4(1H)-ones

A straightforward, two-step synthesis of fluoro substituted chromeno[2,3-c]pyrazol- and [1]benzothieno[2′,3′:5,6]pyrano[2,3-c]pyrazol-4(1H)-ones, respectively, is presented. Hence, treatment of 1-substituted or 1,3-disubstituted 2-pyrazolin-5-ones with fluoro substituted 2-fluorobenzoyl chlorides or 3-chloro-6-fluoro-1-benzothiophene-2-carbonyl chloride using calcium hydroxide in refluxing 1,4-dioxane gave the corresponding 4-aroylpyrazol-5-ols, which were cyclized into the fused ring systems. 5-Fluorochromeno[2,3-c]pyrazol-4(1H)-one was obtained upon treatment of the 1-(4-methoxybenzyl) protected congener with trifluoroacetic acid. Treatment of 5-fluorochromeno[2,3-c]pyrazol-4(1H)-ones with methylhydrazine afforded novel tetracyclic ring systems such as 2-methyl-7-phenyl-2,7-dihydropyrazolo[4′,3′:5,6]pyrano[4,3,2-cd]indazole. Detailed NMR spectroscopic investigations (¹H, ¹³C, ¹⁵N, ¹⁹F) with the obtained compounds were undertaken.     

Modified cyclodextrines as mass-sensitive coatings for solvent vapour detection

Advances in robustness, selectivity and sensitivity in organic solvent vapour detection can be achieved by the application of β-cyclodextrines as coatings for mass sensitive chemical sensors. Linking the cyclodextrines with e.g. diiodooctane combines the molecular recognition capabilities of host-guest chemistry with the high stability of polymeric layers. Special increase in selectivity is achieved with anhydro cyclodextrines, since their flattened conus is adapted to benzene derivatives as can also be shown by computer modelling. Furthermore methylation elongates the cavity, guaranteeing an optimised engulfing of the analytes. In this way even a differentiation between p- and m-xylene vapours and a QMB detection limit of some μL/L is possible.     

A straightforward method for analysing the grain-size distribution in tungsten carbide - cobalt hardmetals

Measurement of the grain-size distribution of sintered hardmetals is indispensable in research and production. In this study we present a method consisting of etching hardmetals in order to remove the cobalt binder and to analyse the remaining tungsten-cobalt (WC) crystallites on the basis of scanning electron microscopy images subjected to a PC-based image analysis by use of MATLAB®. Sample preparation is easy and quick to perform, i.e. it does not require metallographic polishing. It consists of either deep etching of the cobalt binder of cut and optionally hand-ground surfaces or etching of fracture surfaces. Two different computational routines and one combination thereof are described. Two hardmetal grades with average WC grain sizes slightly larger as well as smaller than 200 nm were investigated. The results of the computer algorithms are compared to data obtained by manual linear intercept analysis. The analysis has good potential to avoid time-consuming metallographic preparation and pre-treatment for grain-size analysis, which is especially true for hardmetals with extremely fine grain size.     

Chebyshev polynomials on symmetric matrices

In this paper we evaluate Chebyshev polynomials of the second kind on a class of symmetric integer matrices, namely on adjacency matrices of simply laced Dynkin and extended Dynkin diagrams. As an application of these results we explicitly calculate minimal projective resolutions of simple modules of symmetric algebras with radical cube zero that are of finite and tame representation type.