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Electrochemical Study of Oxazaborine Chromophores
Mikysek, T. ; Josefík, F. ; Vytřas, K. ; Ludvík, Jiří
This contribution describes a basic electrochemical study of a series of newly synthesized chromophores based on the oxazaborine core. The attention was focused on determination of the first oxidation and the first reduction potentials, their difference and the relationship to the calculated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies. The oxidation is mostly a two-electron irreversible process, the first reduction is also irrevesible, but involving one-electron. For better understanding of the relationship between the structure and redox properties, the approach using sigma (para) constants of Hammett type was applied, the difference between E(ox) and E(red) was correlated with the HOMO-LUMO gap.
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Electrochemistry of Polynitrocalix-[4]-arenes
Liška, Alan ; Ludvík, Jiří
Calix[4]arene is a suitable inert and stable frame for building "smart" molecules and supramolecular assemblies. Polynitrocalix[4]arenes where reducible nitro groups are located at the upper rim are promising precursors for aimed development of sensors. In this work a series of mono-, di-, tri- and tetra nitroderivatives was reduced, the sequence of individual steps was described and the mechanism discussed. It was found that in this molecule with several redox centers all nitro groups are electronically isolated and thus are reduced independently yielding poly-radical ions. Two different couples of equivalent nitro groups were proved in tetranitro derivatives. The experimental results were confirmed by quantum chemical calculations.
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New Characterisation Approaches for Carbon Ionic Liquid Electrodes (CILES)
Mikysek, T. ; Stočes, M. ; Švancara, I. ; Vytřas, K. ; Ludvík, Jiří
Within this study, some new approaches to characterize the carbon paste mixtures and the respective carbon ionic liquid electrodes (CILEs) are presented and their properties discussed. Particular attention has been paid to the changes of the resistivity, relative to the dependence on composition of the CILE. Three types of carbon ionic liquid pastes were examined, and for the interpretation of experimental data, the results were compared with those of "classic" carbon paste electrode (CPE) based on graphite powder. Some problems connected with homogeneity and stability of carbon pastes are also discussed.
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Electrochemical Reduction of 1,3-Alt-tetranitrothiacalix[4]arenes
Liška, Alan ; Ludvík, Jiří
Calixarenes are organic molecules which contain several aromatic units (in this work four) connected by methylene („calixarenes“) or sulfur („thiacalixarenes“) bridges. Calix[4]arenes can exist in four defined conformations: cone-, partial cone-, 1,2- and 1,3-alternating (Fig. 1). The conformational stability of a (thia)calix[4]arene is controlled by the size of the substituents on the upper or the lower rim, or by other interactions (e.g. hydrogen bonds). These compounds are very attractive for supramolecular chemists, since they have the shape of a cavity, being able to exhibit host-guest interaction according to the substitution 1,2. The calixarene skeleton itself is not reducible. Therefore it´s necessary to introduce a suitable redox probe in the calixarene frame in order to use electrochemical methods for investigations of calixarene properties. For the purpose of this study the nitro group was chosen because its electrochemical reduction proceeds easily in a well-defined way.
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Electrochemical Study of Triazaborine Chromophores
Mikysek, T. ; Josefík, F. ; Ludvík, Jiří
This contribution describes a basic electrochemical behaviour of a series of newly synthesized chromophores based on triazaborine core. The main attention has been paid to the investigation of the first oxidation and first reduction process of such compounds using cyclic voltammetry, rotating disk voltammetry and polarography. The oxidation is mostly a two-electron irreversible process, whereas the first reduction is in most cases revesible, involving one-electron. For better understanding of the relationship between the structure and redox properties, the Linear Free Energy relationship (LFER) approach using sigma (para) constants of Hammett type was applied, the oxidation and reduction centers were localized, the difference between E(ox) and E(red) was correlated with the HOMO-LUMO gap and the anomalous cases were elucidated.
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Funding of public universities with focus on qualitative criteria
Ludvík, Jiří ; Urbánek, Václav (advisor) ; Kubík, Rudolf (referee)
The bachelor's thesis as a whole deals with funding of public universities in the Czech Republic. The bachelor's thesis deals at first with education system in the Czech Republic and defines the term "university education" as such itself. Step by step gets it to the problematics of funding public universities and describes this process in the Czech Republic in detail. As a main issue the bachelor's work analyses qualitative touchstones in funding of public universities and finally investigates the impact of these intermediate indicators on budget of the University of Economics in Prague.
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FOX-7 - Study of Reduction Products of Spectroelectrochemical Methods
Šimková, Ludmila ; Dmitrieva, E. ; Klíma, Jiří ; Dunsch, L. ; Ludvík, Jiří
A new energetic material 2,2-dinitroethene-1,1-diamine (FOX-7) is recently broadly tested because of its high performance and very low sensitivity. On the other hand, its electrochemical and redox properties have not been studied yet. Our results show that FOX-7 is reduced in aprotic solvents only by two one-electron steps up to -2.9 V. The color changes during reduction of FOX-7 and reversibility of the redox process indicate the presence of radical intermediates. Therefore in situ UV-vis-NIR and ESR spectroelectrochemical investigations were performed. The products after exhaustive electrolyses were separated by HPLC and are identified by mass spectrometry. The possible formation of gaseous products was followed online EC-GC.
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Electrochemical and spectrometric study of FOX-7 in aprotic solvents
Šimková, Ludmila ; Ludvík, Jiří ; Klíma, Jiří
2,2-Dinitroethene-1,1-diamine (FOX-7) is a recently developed and broadly tested energetic material with high efficiency and low sensitivity. Generally, explosion is based on thermally initiated chain of intramolecular redox reactions. Recently it has been found that electrochemical reduction in aqueous solutions is also able to provoke the chain of follow-up processes leading to total decomposition of the parent substance yielding gaseous products analogously like during explosion. Similarly, results from reductive electrolysis of FOX-7 in aprotic solvents show analogous course of degradation. The first transferred electron activates the molecule and initiated the formation of colored radical intermediates that have been spectroscopically characterized
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Carbon nanotubes - material for carbon paste electrodes, possibilities of preparation and characterization
Mikysek, T. ; Stočes, M. ; Švancara, I. ; Ludvík, Jiří
In this article, some new approaches to characterize the carbon paste mixtures and the respective carbon nanotube paste electrodes (CNTPEs) are presented, discussed. Particular attention has been paid to the changes of the ohmic resistance, relative to the dependence on composition of the CNTPE, the materials used, the time. Four types of carbon nanotube pastes were examined, and for the interpretation of experimental data. Some problems connected with homogeneity and stability of carbon pastes, their storage, or eventual aging effects are also discussed.
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