The limited understanding of the electrochemical mechanism of Na-S battery systems is a barrier to further improve the performance of the Na-S energy storage. The characterization of sodium polysulfides in the Na-S battery systems can offer insightful information to understand the electrochemical reaction mechanism of the Na-S batteries and overcome the "inert" nature of short-chain polysulfides (Na2Sn, 1<n<4) during charge and discharge of the batteries. Up to now, there are limited studies on the sodium polysulfides compound in the Na-S batteries. Meanwhile, although many synthesis methods for sodium polysulfides have been reported, many related studies offer unclear and misleading parameters. This work examines several reported synthesis methods for sodium polysulfide. The results show that the sodium polysulfides cannot be obtained by the reaction of Na2S and S using anhydrous ethanol as the reaction media. In "dry" synthesis method, the pressure will influence the components in the product, and only Na2S4 can be synthesized at atmospheric pressure. This study also revises the synthesis method for Na2S2 and Na2S5, and detailed synthesis parameters are presented. The properties of sodium polysulfides in tetraethylene glycol dimethyl ether TEGDME were studied in this thesis. The solubility of Na2Sn in TEGDME increases with increasing sulfur in sodium polysulfide. The corresponding solution gets to longer-wavelength color and contains more long-chain polysulfides anions. / Master of Science / In recent decades, our society became more and more power-demanding, sodium-sulfur (NaS) energy storage systems attracted researchers’ attention due to their low cost and good performance. However, the limited understanding of the electrochemical mechanism of Na-S battery systems is a barrier to further improve the performance of the Na-S batteries. The characterization of sodium polysulfides in the Na-S battery systems can offer insightful information to understand the working mechanism of the Na-S batteries during charge and discharge of the batteries. Up to now, there are limited studies on the sodium polysulfides compound in the Na-S batteries. Meanwhile, although many synthesis methods for sodium polysulfides have been reported, many related studies offer unclear and misleading parameters. This work examines several reported synthesis methods for sodium polysulfide and offers complete processes with clear parameters for the synthesis of sodium polysulfide. Meanwhile, the sodium polysulfides solution in tetraethylene glycol dimethyl ether (TEGDME), an electrolyte solvent that was widely used in Na-S batteries, were analyzed to study the properties of sodium polysulfides in the Na-S battery system.

No description available.

4-Alkyl-L-proline derivatives (APD) are specialized precursors involved in the biosynthesis of at least three groups of different natural compounds: some pyrrolo-1,4-benzodiazepines with antitumor activity, bacterial hormone hormaomycin and clinically used lincosamide antibiotic lincomycin. These compounds share a biosynthetic pathway encoded by 5 or 6 homologous genes present in the biosynthetic gene clusters of the producing organisms. Similarities in biosynthesis and differences between APD structures of these compounds could be used to prepare a hybrid producing strain of biologically more effective lincomycin derivative. Unusual amino acid 4-propyl-L-proline (PPL) is the APD precursor of lincomycin. The originally proposed scheme of the PPL pathway does not comply with our current knowledge. Therefore, it was necessary to revise this scheme according to new results. The first two steps of the PPL pathway are functionally proved. Probing the next step was the main aim of this work. The protein LmbW was overproduced and its methyltransferase activity was confirmed in vitro. LmbW is able to directly methylate intermediate of second step of the pathway while the originally scheme proposed methylation at a later stage of biosynthesis. LmbW is also able to attach a longer alkyl chain to its substrate. This...

The thesis attemps to map the current situation of the variance process in masculines ended with epicene consonants -s and -z. Based on the description of the situation presented in language guides approximately since 1950s and with the help of Retrográdní slovník současné češtiny, the authoress compiled a list of masculines with this type of ending and afterwards she verified each noun via corpus databáze ČNK syn2010. To komplete the corpus results the authoress used the questionary survey on selected nouns. From acquired data there was set together a summary which should describe the current situation of this variance in these nouns.