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The Electrochemistry of Natural Pigments
Sokolová, Romana ; Degano, I. ; Hromadová, Magdaléna ; Pospíšil, Lubomír
The electrochemical properties of flavonoid compounds (hemotoxylin, quercetin) were studied in buffered aqueous and non-aqueous solutions. The role of the preceding protonation/deprotonation on the electron transfer was estimated. The absorption spectra of these compounds, which contain a chromophore, were recorded during their oxidation. The electrochemical techniques were combined with GC-MS analysis in order to identify the degradation products. The mechanism of the formation of degradation products will be discussed.
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Některé nové přístupy k charakterizaci uhlíkových pastových elektrod
Mikysek, T. ; Švancara, I. ; Ludvík, Jiří ; Vytřas, K. ; Kalcher, K.
Carbon paste electrodes (CPEs) have several substantial advantages: their surface is easily renewable and it is possible to modify the electrode material in the bulk in order to prepare a specific sensor. The properties of the electrodes depend strongly on the used materials, that means on the carbon powder as well as on the oily binder, and on their proportions. Therefore the characterization of every type of such electrodes is very significant. We have found that the graph of the dependence of electrode resistance on the percentual composition manifests itself as two crossing lines. For the explanation of this dependence, a model based on the tight packing of spheres was suggested, formulated, tested and discussed. The other possibility how to characterize the electrodes is detailed interpretation of cyclic voltammetry of a reversible redox system. Both methods are compatible and enable to explain also problems with storage and ageing of electrodes.
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Intramolekulární elektronová interakce dvou typů dikarbonylových slouočenin a jejich derivátů – elektrochemická a kvantově chemická studie
Ludvík, Jiří ; Celik, H. ; Jirkovský, Jaromír ; Zuman, P.
V rámci studia molekul se dvěma redox centry byly studovány dva izomérní mnooximy odvozené od aryl alkyl-1,2-diketonu. Zatímco 1-fenyl-2-oxo-1-oximinopropan se v kyselém prostředí redukuje mechanismem typickým pro oximy, tedy čtyřmi elektrony na aminoketon, který pak v druhém kroku ztrácí reduktivně aminoskupinu, jeho izomér 1-fenyl-1-oxo-2-oximinopropan se redukuje na dále neredukovatelný 1-hydroxy-2-aminoolefin (enol forma), což je analogické redukci benzilu. Zde je zvláště překvapivé, že nesymetrická molekula se redukuje mechanismem typickým pro molekuly symetrické. Na základě elektrochemických dat a jejich korelace s kvantovými výpočty se podařilo důvod tohoto jevu vysvětlit.
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