|
|
UV-Vis and IR Spectroelectrocbemistry of Copper Complexes and Bioactive Compounds
Sokolová, Romana ; Obluková, Michaela ; Sýs, M. ; Mikysek, T. ; Wantulok, J. ; Nycz, J. E. ; Degano, I.
The interpretation of the change of absorption spectrum of an oxidized and reduced molecule\nrecorded during the electron transfer is an efficient tool for the determination of oxidation or\nreduction mechanism. This technique provides the information about the electroactive\nchromophore and is performed in two regimes of electrochemical measurement, cyclic\nvoltammetry and chronoamperometry, respectively. This approach was successfully applied to\nstudy the fundamental electrochemical behavior of recently synthesized copper complexes\nproviding biomimetic activity, ofpolyphenolic bioactive compounds, and also for the reduction\nof halogenated phenanthrolines. The identification of redox products was done by\nchromatographic techniques as HPLC-DAD and HPLC-ESI-MS/MS.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
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.
|
|
|
Some New Approaches to the Characterization of the Carbon Paste Electrodes
Mikysek, T. ; Švancara, I. ; Ludvík, Jiří ; Vytřas, K. ; Kalcher, K.
Uhlíkové pastové elektrody mají dvě hlavní výhody: jejich povrch lze snadno reprodukovatelně obnovovat a dále, je možné je modifikovat v objemu za účelem získání specifických senzorů. Příprava těchto elektrod však závisí jednak na použitých materiálech, tedy na uhlíkovém prášku i na olejovém médiu, jednak na jejich vzájemném poměru. To umožňuje velikou variabilitu vlastností, současně ale otázka charakterizace těchto elektrod je velmi významná. Bylo zjištěno, že graf závislosti odporu elektrody na jejím složení je ve tvaru dvou protínajících se přímek. K vysvětlení této závislosti byl navržen, testován a diskutován model vycházející z představy těsně uspořádaných koulí (známé z krystalografie). Další způsob charakterizace těchto elektrod je založen na interpretaci cyklických voltamogramů nějakého dobře reverzibilního systému. Obě tyto metody jsou kompatibilní, navíc umožňují vysvětlení dalších jevů spojených s morfologií a se stárnutím těchto elektrod.
|
guest ::
