|
|
Catalytic function of DNA-dependent RNA polymerases
Sýkora, Michal ; Vopálenský, Václav (advisor) ; Lichá, Irena (referee)
DNA-dependent RNA polymerase is a highly organised protein complex that is responsible for gene expression and its regulation. Multisubunit RNA polymerase with its several catalytic activities is responsible for transcription of genes to RNA copies in all cellular organisms. During transcription RNA polymerase undergoes substantial conformational changes depending on the conditions in a particular cell. RNA polymerase in a state designated as an elongation complex passes through repetitive cycles of adding a nucleotide to the growing RNA chain. The active center contains two magnesium ions which coordinate the reactive groups of substrates. Furthermore, the active center contains structural elements that participate in binding of substrate, propper orientation of substrate towards the template strand and translocation of the RNA polymerase. The most important of these mobile structural elements are the bridge helix and the trigger loop whose conformational changes accompanies nucleotide addition cycle. Advances in the structural and biochemical characterization of RNA polymerase open new possibilities in the understanding of the transcription mechanism, its fidelity and control.
|
|
|
Synthesis of aromatic compounds possessing the fluorene unit
Caivano, Ilaria ; Kotora, Martin (advisor) ; Starý, Ivo (referee) ; Tobrman, Tomáš (referee)
Thermal cyclotrimerization was first discovered in 1866 by Bertholet, then, in 1948, Reppe and Schweckendiek reported the first transition metal catalyzed [2+2+2] cyclotrimerization of alkynes using Ni complexes. In the following 70 years of research, transition metal catalyzed [2+2+2] cyclotrimerization have become a powerful method for the synthesis of variously decorated aromatic rings and new catalytic systems as well as reaction conditions have been successfully applied. Herein, I would like to show the use of this reaction for the synthesis of the important class of fluorene-based compounds. In particular, a regioselective cyclotrimerization of 2,4-disubstituted fluorenols was achieved by Ru-catalyzed partially intermolecular [2+2+2] cyclotrimerization of diynes with terminal alkynes. Rh-based complex proved to be a straightforward transition metal catalyst for the construction of selectively fluorinated [5] and [6]helical dispiroindenofluorenes using intramolecular [2+2+2] cycloaddition of triynediols as the key synthetic step. Moreover, Ni complexes demonstrated to be a valid choice for the selective synthesis of unsymmetrical [7]helical indenofluorenones, while other catalytic systems based on Rh, Ru, Pd and Co gave mixture of the desired cyclotrimerization compound together with the...
|
|
|
Metal nanoparticles in zeolites
Zhang, Yuyan ; Čejka, Jiří (advisor) ; Zima, Vítězslav (referee) ; Kubička, David (referee)
Zeolites with encapsulated metal nanoparticles have attracted a wide attention in heterogeneous catalysis due to their high catalytic activity, selectivity, and stability. The PhD thesis was focused on design and synthesis of metal@zeolite catalysts with small and uniformly distributed metal nanoparticles. The main interests were encapsulation of metal nanoparticles into zeolites by co-crystallization strategy and 2-dimensional to 3-dimensional zeolite transformation approach. The PhD work was performed at the Department of Synthesis and Catalysis at J. Heyrovský Institute of Physical Chemistry and Department of Physical and Macromolecular Chemistry, Faculty of Science at Charles University under the supervision of Prof. Jiří Čejka. Zeolites are inorganic crystalline aluminosilicates with microporous framework structures. The micropores of zeolites provide the ideal microenvironment to accommodate metal nanoparticles. During metal nanoparticles formation in zeolite micropores, they can be limited by a rigid framework, preventing the aggregation and leaching of metal during the reaction process. Furthermore, the diameters of zeolite micropores are usually in the range of 0.3-1.5 nm, which can be used to discriminate molecules depending on their size and shape, thus endowing the metal@zeolite...
|
|
|
Heterogeneous catalysis of terpenoid redox reactions
Kurucová, Svetlana ; Přech, Jan (advisor) ; Bulánek, Roman (referee)
Heterogeneous catalysts for Meerwein-Ponndorf-Verley (MPV) reduction of ketones and aldehydes are investigated due to issues connected with water sensitivity and separation problems of homogeneous catalysts. During MPV reduction, a hydrogen atom is transferred from the sacrificial alcohol onto the carbonyl group of the ketone/aldehyde forming corresponding alcohol. Tin and zirconium containing zeolites are active catalysts in this hydrogen transfer reaction. However, when using conventional 3D zeolites in the reduction of bulky molecules, e.g., terpenoid compounds, problems with active site accessibility for these bulky reactants may arise. The use of 2D pillared zeolites may represent a solution to the diffusion problem. Silica metal-oxide pillars increase the distance between individual layers of a 2D (lamellar) zeolite and thus improve the active site accessibility. 2D catalysts were prepared by pillaring a parent lamellar pure-Si MFI with a mixture of tetraethyl orthosilicate and Zr (IV) isopropoxide or Sn (IV) isopropoxide, while conventional 3D zeolites were synthesised hydrothermally. The activity of Sn and Zr containing pillared catalysts was compared with the activity of the 3D MFI and beta zeolites in MPV reduction of furfural and citronellal. The 2D zeolites, however, did not facilitate...
|
|
|
Shape selectivity of ADOR zeolites in gas-phase m-xylene isomerisation
Remperová, Natália ; Mazur, Michal (advisor) ; Kubička, David (referee)
Zeolites are microporous crystalline aluminosilicates. They are used as catalysts due to their acidity, shape selectivity, high surface area, high thermal, and chemical stability. New types of zeolitic materials are of interests as catalysts for various reactions. Isomerisation of m-xylene is sensitive to shape and dimensionality of pores, thus it is excellent model reaction for zeolites characterisation. The aim of this thesis is to investigate shape selectivity effects of isoreticular zeolites on the catalytic performance in m-xylene isomerisation. Isoreticular zeolites have the same crystalline layers connected in various way resulting in different, tuneable pore systems. The catalytic behaviour of the studied zeolites was compared to commercial ZSM-5 zeolite catalysts. Isoreticular zeolites were prepared via ADOR method. This new method is a top-down approach for zeolite synthesis providing materials with preserved crystalline layers, but different channel systems. Parent Al-UTL (14- and 12-ring channels) zeolite was prepared via hydrothermal synthesis. This material was utilised for the synthesis of daughter zeolites with various channel systems: Al-IPC-7 (14- and 12-ring, as well as 12- and 10-ring channels), Al-IPC-2 (12- and 10-ring channels), Al-IPC-6 (12- and 10-ring, as well as 10- and...
|
|
|
Preparation and properties of building blocks of specialty polymers
Šichová, Kristýna
This Diploma Thesis presents results obtained by solution of two partial projects: a) Preparation of monomers from renewable sources using metathesis and tandem hydrogenation catalyzed with ruthenium compounds - project solved during my Erasmus stay at the Université de Rennes 1 in France; b) Preparation and properties of ,-bis(tpy)quarterthiophene oligomers carrying ionic side groups as oligomonomers for polyelectrolyte conjugated dynamers - project solved at the Department of Physical and Macromolecular Chemistry, Faculty of Science, Charles University in Prague. Project a): Self-metathesis of 1,2-epoxyhex-5-ene (but-3-enyloxirane) and its cross-metathesis with methyl acrylate and acrylonitrile catalyzed with ruthenium compounds as well as tandem design of these metatheses and consecutive hydrogenation of their products by gaseous hydrogen have been optimized. The following influences have been studied and tuned: (i) type of the catalyst (Grubbs, Hoveyda, Zhan) and its concentration and method of dosing, (ii) concentration of reactants and additives, (iii) type of solvent, and (iv) reaction temperature. Reactions were monitored by the GC, GC and MS methods and the products were characterized by the NMR method. Methyl 6,7-epoxyheptanoate (methyl 5-oxiranylpentanoate) obtained by the tandem...
|
|
|
Activity of new nickel-complexes in coupling reactions
Plaček, Martin
In this work, we report the study of the catalytic activity of newly prepared coordination compounds of nickel(II) (complexes were prepared by prof. Kyritsis, University of Athens). The activities in model reactions of Kumada and Suzuki coupling and polymerization of 2,5- dibromo-3-hexylthiophene were tested. For Kumada coupling, the activity is comparable with known complex [Ni(dppp)Cl2]. On the other hand, selected complexes exhibit only limited activity for Suzuki coupling. GRIM polymerization of 2,5-dibromo-3-hexylthiophene was successful. Properties of prepared polymers are comparable with polymers prepared via known route with [Ni(dppp)Cl2].
|
|
|
Theoretical Investigation of Mechanisms of Chemical Reactions Taking Place in Microporous Materials
Položij, Miroslav
Mechanisms of three reactions catalyzed by microporous materials were investigated computationally; the reactions investigated include Friedländer and Knoevenagel reactions catalyzed by Cu3BTC2 metal organic framework (MOF) and an intramolecular cyclisation of unsaturated alcohols catalyzed by zeolite H-ZSM-5. It was found that the reaction mechanisms of all three reactions are controlled by a high concentration of active sites in materials. Reaction intermediates interact with more than one active site simultaneously. This novel concept of "multiple-site" interactions is described. The concerted effect of two catalytic sites leads to a decrease of activation barriers on reaction paths of Friedländer and Knoevenagel reactions. On the contrary, a simultaneous interaction of reactants with two active sites has a negative effect on reaction rate in case of alcohol cyclization catalyzed by H-ZSM-5; it was found that the interaction with dual sites results in the increase of activation barriers and diffusion limitations. In case of Knoevenagel reaction catalyzed by CuBTC, the adsorption of reaction precursor to the reaction site allows the creation of a dynamic defect in the MOF framework that subsequently catalyses the reaction. Both, the multiple sites effect and the dynamical defect formation effect...
|
|
|
Synthesis of the C15-C20 tiacumicin fragment
Havlíček, Vojtěch
In the diploma thesis, a method for preparation of the unsaturated C15-C20 tiacumicin fragment was developed. Tiacumicin is classified as a macrolidone antibiotic. Although three syntheses of tiacumicin have been recently published, this study has aimed to develop a novel pathway for its preparation utilizing catalytic reactions instead of stoichiometric ones. In the second part, an enantioselective allylation of (E)-3-jod-2-methylpropenal has been developed applying catalysis by a series of N,N'-dioxide catalysts. The asymmetric induction achieved in the allylation was up to 99% ee. This procedure allows relatively simple, straightforward and efficient preparation of wide range of natural products. Keywords tiacumicin, asymmetric synthesis, allylation, catalysis, chiral Lewis bases, organocatalysis
|
|
|
Study of physical and chemical properties of surface-modified tungsten oxide
Polášek, Jan ; Mašek, Karel (advisor)
Title: Study of physical and chemical properties of surface-modified tungsten oxide Author: Jan Polášek Department: Department of Surface and Plasma Science Supervisor: Doc. RNDr. Karel Mašek, Dr., Department of Surface and Plasma Science Abstract: This work can be divided into two parts. In the first part, we examine possibilities of preparation of monocrystalline tungsten and tungsten oxide na- noclusters by means of magnetron sputtering with gas aggregation. Clusters are prepared in the non-reactive (Ar) and reactive (Ar + O2) atmosphere and heated after the deposition or during the flight by IR radiation. Influence of oxygen in the aggregation process was described and possibilities of generating crystalline tungsten and tungsten oxide clusters were found. In the second part, we study reactivity of tungsten oxide layers, pure and doped with rare metals (Pt, Au), deposited on the silicon wafer and etched carbon, towards partial methanol oxi- dation. Influence of carbon substrate and metal doppants on reactivity was found and described, along with mofrological and chemical changes that occurs in the sample during the proces. Keywords: catalysis, tungsten oxide, clusters, partial oxidation of methanol, etched carbon 1
|
guest ::
