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Chronopotentiometry of Papain Modified by Ruthenium Complexes
Nováková Lachmanová, Štěpánka ; Pospíšil, Lubomír ; Talbi, B. ; Salmain, M. ; Hromadová, Magdaléna
Catalytic hydrogen evolution reaction is one of known effects observed during the electrochemical studies of proteins. Constant current chronopotentiometric stripping technique is suitable tool for the study of catalytic hydrogen evolution reaction due to the formation of peak H. This contribution compares the catalytic behaviour of nonmodified papain and its artificial derivatives prepared by the interaction of organometallic complexes of ruthenium with free sulfhydryl group of protein. The comparison of the chronopotentiometric behaviour of papain and its derivatives would help to better understand the catalytic hydrogen evolution reaction in these derivatives.
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Determination of Roughness Factor and Fractal Dimension of Zirconium in its Native and Surface Modified State using Atomic Force Microscopy. Effect of the Hydrogen Evolution Reaction on the Surface Structure
Novák, M. ; Kocábová, Jana ; Kolivoška, Viliam ; Pospíšil, Lubomír ; Macák, J. ; Cichoň, Stanislav ; Cháb, Vladimír ; Hromadová, Magdaléna
Atomic force microscopy (AFM) was used to characterize surface morphology of pristine zirconium, Si modified and FeSi modified zirconium electrodes prior and after hydrogen evolution at potentials negative of the open circuit potential value. Two main characteristic parameters were obtained from the ex situ AFM height images, namely, the roughness factor and fractal dimension of the studied surface. The effect of hydrogen evolution reaction on the electrode surface morphology was discussed. Fractal dimension values were used successfully to explain the non ideality of the interfacial capacitance.
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Effect of pH on the Oxide Film Formation on a Pristine Zr Electrode
Hromadová, Magdaléna ; Kocábová, Jana ; Kolivoška, Viliam ; Pospíšil, Lubomír
Effect of pH on the oxidation of zirconium metal was studied by cyclic voltammetry in\naqueous borate buffer solutions as a function of the potential scan rate and pH from 4.80 to\n9.17. The results show that the oxide growth kinetics depends on pH of the electrolyte\nsolution and the total amount of irreversibly formed oxide under the potentiodynamic\nconditions decreases with decreasing buffer pH in accord with thermodynamic considerations.\nCathodic current corresponding to hydrogen evolution reaction diminishes in the presence of\nanodically modified electrode compared to bare zirconium.
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Dependence of Single-Molecule Conductance of Pyridinium Derivatives on Their Structure
Lachmanová, Štěpánka ; Hromadová, Magdaléna ; Kolivoška, Viliam ; Pospíšil, Lubomír ; Gasior, Jindřich ; Mészáros, G. ; Lainé, P. P.
The derivates of pyridinium belong to promising group of molecules applicable in molecular electronics. For this purpose, four expanded branched pyridinium compounds were synthetized and the influence of the molecular structure on their electrochemical properties and single-molecule conductances has been studied. The highest values of conductance provided compounds 9-(pyridin-4-yl)benzo[c]benzo[1,2]quinolizino[3,4,5,6-ija][1,6]naphthyridin-15-ium tetrafluoroborate and 3,5-dimethyl-2´,6´-diphenyl-[4,1´:4´,4´´-terpyridin]-1´-ium tetrafluoroborate. By the electrochemical reduction both of these compounds received two electrons in two separated one-electron steps. On the other hand, the compounds 2´,6´-diphenyl-[4,1´:4´,4´´-terpyridin]-1´-ium tetrafluoroborate and 2,6-diphenyl-4-(4-(pyridin-4-yl)phenyl)-[1,4´-bipyridin]-1-ium tetrafluoroborate are reduced by different mechanism and their conductance was lower.
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Electrochemical Properties of Branched Pyridinium Cations
Lachmanová, Štěpánka ; Hromadová, Magdaléna ; Pospíšil, Lubomír ; Lainé, P. P.
The electrochemical properties of branched extended pyridinium cations depend strongly on the structure of the molecule. This work is focused on the redox processes of the electron transfer of four derivatives of pyridinium. The electron transfer mechanism was studied by various electrochemical methods. Although the structures of the studied molecules seem to be quite similar, 1-N-methyl-2,4,6-triphenylpyridinium and 1',3',5'-trimethyl-2,4,6-triphenyl-1,4'-bipyridine-1,1'-diium are reduced in two separate one-electron transfer steps. On the other hand, 1'-methyl-2,4,6-triphenyl-1,4'-bipyridine-1,1'-diium and 1',3,5-trimethyl-2,4,6-triphenyl-1,4'-bipyridine-1,1'-diium accept two electrons, but in a single two-electron transfer. The heterogeneous rate constants of the electron-transfer processes were determined.
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Electrochemistry of halogenated benzenonitrils
Sokolová, Romana ; Pospíšil, Lubomír ; Hromadová, Magdaléna ; Ludvík, Jiří
Autoprotonation in reduction mechanism of 3,5-dihalogeno-4-hydroxy-benzonitriles was studied in dimethylsulfoxide by electrochemical methods. The overall one electron reduction process was found. Aryl radical formed by the cleavage of halogenide undergroes further electron transfer in EC type reaction. The anion is protonated by parent molecule resulting in total consumption of two electrons per two starting molecules. Addition of stronger proton donor increases the height of reduction wave up to two electrons per molecule. The addition of potassium hydroxide causes the decrease of the reduction wave. The reduction products were identified by GC/MS analysis in the absence and presence of strong proton donor.
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Fullerene C60 in Aqueous Medium
Kocábová, Jana ; Gál, Miroslav ; Hromadová, Magdaléna ; Kavan, Ladislav ; Pospíšil, Lubomír ; Sokolová, Romana
The aqueous solution of C60 was investigated by electrochemical and spectroscopis methods such as UV-Vis, Raman, FTIR and AFM techniques. The association constants of fullerene-gamma-cyclodextrin complex and ,ethanofullerene conjugates with beta-cyclodextrins in aqueous solution were evaluated from the shifts of the formal redox potential of complexed and uncomplexed fullerene. The most suitable techniques for electrochemical characterization of fullerene derivatives proved to be the low-frequency phase-sensitive AC polarography and the steady-state voltammetry.
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