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Catalytic and adsorption properties of papain and its derivatives
Lachmanová, Štěpánka ; Hudeček, Jiří (advisor) ; Karpenko, Vladimír (referee)
The aminoacid sequence of papain (EC 3.4.22.2) consists of 212 aminoacids. It has only one free sulfhydryl group, which is located in the active site of the protein. Some organometallic complexes could be bonded only to this free -SH group due to their structure. The artificial metalloproteins synthesised by this way may have different electrochemical properties. In this work, we have studied the electrochemical properties of papain and its derivatives. We compared the ability of papain and its three artificial derivatives to catalyse the hydrogen evolution by the chronopotenciometry. The work was completed by the study of the electrochemical properties of the organometallic complexes of ruthenium, which were used for the artificial metalloprotein preparation. The electrochemical properties of the compounds were never studied before. The process of the hydrogen evolution catalysed by the proteins is held in the adsorbed state of the catalyst. Due to this fact we have also studied the adsorption properties of papain on the substrates with different level of hydrofobicity. (In Czech)
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Redox and catalytic properties of modified papain
Lachmanová, Štěpánka ; Zima, Jiří (referee) ; Hudeček, Jiří (advisor)
Redox and Catalytic Properties of Modified Papain Endopeptidase papain could be modified by the organometallic complex [(η6 -C6H5(CH2)2NHCO(CH2)Cl)Ru(N^N)Cl]Cl, (N^N) = 1,10-phenanthroline (TB11), which binds to the free sulfhydryl group of cysteine in the active centre of protein. This modification influences the catalytic properties of papain. The redox properties of the TB11 complex in its free form and when it is bound to papain were studied by the polarographic and voltammetric methods. Modified endopeptidase is reduced in the adsorbed state. Therefore, a phase-sensitive AC voltammetry is used for studies of the electron transfer in the TB11 modified papain. This method gives suitable methodology for studying the electron transfer rates in the systems influenced by adsorption. Using this method the catalytic hydrogen evolution process was detected not only in the TB11, but also for TB11 covalently-attached to the papain molecule. The results help better understand the catalytic mechanism of the hydrogenation reactions in the presence of TB11 modified enzyme. Adsorption properties of papain at different substrates were studied by AFM measurement. The formation of a compact monolayer was proved for the gold substrate modified by a layer of 11-mercaptoundecanoic acid.
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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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Comparison of Techniques for Single-Molecule Conductance Measurements of Expanded Pyridinium Molecules
Lachmanová, Štěpánka ; Hromadová, Magdaléna ; Sokolová, Romana ; Kocábová, Jana ; Gasior, Jindřich ; Mészáros, G. ; Lainé, P. P.
This work is focused on the comparison of two techniques of single-molecule conductance measurements: Scanning Tunneling Microscopy Break Junction technique and Mechanically Controlled Break Junction technique. The structure of studied compound 9-(pyridin-4-yl)benzo[c]benzo[1,2]quinolizino[3,4,5,6-ija][1,6]naphthyridin-15-ium allows the formation of the molecular bridge between two gold electrodes, which are connected to a source of the constant voltage in both of the used methods. The differences, advantages and disadvantages of both of the techniques will be discussed. Both techniques provided two values of conductance of studied compound depending on the experimantal conditions.
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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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