This thesis deals with the mixing of liquids issues. The simulation of structure for mixing of liquids and evaluation of parametres which have most significant influence on mixing of liquids was made with help of COMSOL programm. In the next section of thesis the quality of electrodes used for cyclic voltammetry made on LTCC by thick layer technology was determined. In the end of this thesis the 3D structure for mixing of liquids was made. The quality of mixing was controlled by cyclic voltammetry.

This work deals with the preparation of gold nanostructures for future usage in electrochemical sensors and biosensors, methods for their characterization and production. The emphasis is focused on the template-based electrodeposition method of gold and on study of the effect of manufacturing conditions on physical properties, mainly electrical and topological of nanostructures. Thesis is focused also on overall function and sensitivity of the gold nanostructured electrode.

A series of Fischer mono- and biscarbene complexes of the type [MLn{C=(XR)R'}] was synthesized and characterized. The redox behavior of the complexes was studied by different techniques, including cyclic voltammetry, spectroelectrochemistry, ESR and computational methods. Different transition metals (M) and carbene substituents (XR, R') were employed to compare both the effect of the central metal atom as well as the carbene substituent. Thienyl, furyl and ferrocenyl chromium(0) mono- and biscarbene complexes with ethoxy and amino substituents were electrochemically studied in CH2Cl2. Results were mutually consistent with computational data showing that the carbene double bond of all complexes is reduced pseudo reversibly to an anion radical, -Cr-C•. The Cr centers are oxidized in two successive one electron transfer steps to Cr(II) via the Cr(I) intermediate. For all ferrocenyl carbene complexes the Fe(II) is oxidized after the first oxidation of Cr. It was found that with respect to the aryl substituents the donating effect decreases from Fc>Fu>Th. Stabilization from the XR substituent, where XR = NHR, also resulted in lower redox potentials compared to their OEt analogues. The inclusion of ferrocene in the carbene substituent was done, as its redox activity and increased donating effect are well known. Mono- and biscarbene complexes with ethoxy and amino substituents of both chromium and tungsten were electrochemically studied. Again experimental data were supported by computational studies. Similar to the ethoxy chromium complexes, reduction of the W=C fragment to -W-C• was observed. However oxidation of the Fc group occurred first before the electrochemically irreversible oxidation process for W(0) involving a three electron-mediated process as seen in chronocoulometric analyses. The tungsten oxidation was restricted to a W0/II, consistent with computational studies, by the use of the electrolyte [NnBu4][B(C6F5)4]. The short-lived W(II) species were calculated to be stabilized by agostic CH···W interactions, similar to the chromium analogues. To extend linkers between the metal-carbene termini and investigate metal-metal interaction, biferrocenyl and 2,5-thienylbiferrocenyl tungsten(0) mono-and biscarbene complexes were synthesized and studied by spectroelectrochemistry. A metal-metal charge transfer transition between the tungsten carbonyl increment and the biferrocenyl / 2,5-thienylbiferrocenyl unit was confirmed by infrared spectroelectrochemical studies. The electronic interaction in the corresponding cationic species can be described as weakly coupled class II systems according to Robin and Day. The cymantrenyl moiety, Mn(η5-C5H4)(CO)3, provides an interesting alternative to ferrocene as an organometallic molecular tag, however the instability of the radical cation impairs its use. Improved stability of the cation, monitored by electrochemical measurements, was accomplished by substituting a carbonyl with a ferrocenyl Fischer carbene ligand resulting in Mn(I) oxidation occuring at lower potentials than ferrocenyl oxidation. These uncommon Fischer carbene complexes is the first organometallic multi-tags reported. The mono cationic species, [CpMn(CO)2{=C(OEt)Fc}][PF6], could be isolated and characterized with ESR analysis. Finally, transmetallation from the tungsten(0) Fischer carbene complexes yielded examples of rare acyclic alkoxy- and aminocarbene complexes of gold(I). Single x-ray structures for all complexes could be obtained including the novel ferrocenophane dinuclear biscarbene Au(I) complex. All structures display unsupported aurophilic interactions, while the bridging biscarbene shows a semi-supported Au-Au interaction. In the case of the furanyl/thienyl methoxy monocarbene complexes, extended Au-Au interactions result in oligomeric structures. Although this study is of a fundamental nature, it is imperative for the understanding and design of gold compounds with specific applications. / Thesis (PhD)--University of Pretoria, 2013. / gm2014 / Chemistry / unrestricted

The goal of this master's thesis was to examine the possibility of oxidation of seven selected bile acids and evaluate whether such processes are suitable for analytical purposes. The secondary goal was to describe the oxidation products of bile acid electrolysis. The experiments were carried out in a non-aqueous medium of acetonitrile and in a mixed medium of acetonitrile:water using linear sweep and cyclic voltammetry. The working electrode materials employed for voltammetric experiments were: highly oriented pyrolytic graphite, -cyclodextrin modified glassy carbon and boron doped diamond. Preparative electrolysis was carried out on a platinum electrode in the non-aqueous medium of acetonitrile. Experiments have shown that neither the highly oriented pyrolytic graphite electrode nor the -cyclodextrin modified glassy carbon electrode are suitable for analytical purposes under conditions used. The results achieved on the boron doped diamond electrode, on the other hand, have not yet been described in the literature. Primary bile acids cholic and chenodeoxycholic were oxidized at approximately 0.5 V lower potential in the mixed medium of acetonitrile:water than in the papers using carbon electrodes published until now. Products of oxidation on the platinum electrode were separated by TLC and...

The aim of this thesis is preparation of inverse model catalyst CeOx/Pt(111) and its investigation using combination of surface physics methods and electrochemistry. New electrochemical cell was designed and built for electrochemical experiments. CeOx/Pt(111) samples were prepared and studied in UHV using STM and XPS methods. After that, samples were transferred to the electrolyte environment and studied by means of cyclic voltammetry and AFM. For high surface coverage of CeOx, new reaction was observed. We have identified this reaction as a combination of the reduction of cerium(IV) oxide by interaction with hydrogen adsorbed on the Pt(111) surface and oxidation of cerium(III) oxide by dissociative adsorption of water molecules. Powered by TCPDF (www.tcpdf.org)

Title: Cobalt phthalocyanines as sensors for determination of thiol groups Annotation: The possibility of employment of cobalt phthalocyanine as a material for the modification of HOPG electrode for construction of a sensor for quantification of thiol groups was studied. Thiol groups are occurring in various biologically active substances (sulfur amino acids). The electrochemical behavior of cobalt tetraneopentoxy-phthalocyanine (CoTNPc) in the water/organic phase system was studied, and individual peaks of cyclic voltammogram of the compound were identified. The electrodeposition of CoTNPc on HOPG electrode was found as a suitable method for construction of the sensor for quantification of thiol groups. The reproducibility of fabrication of the sensor and its time-stability was studied. The calibration dependencies for model analytes (cysteine hydrochloride and homocysteine) were measured. Key words: thiols, phthalocyanines, amperometric sensor, cyclic voltammetry

Voltammetric methods for determination of 1,3-dinitronaphthalene (1,3-DNN), 1,5-dinitronaphthalene (1,5-DNN) and 1,8-dinitronaphthalene (1,8-DNN) using DC voltammetry (DCV) and differential pulse voltammetry (DPV) at novel single crystal silver amalgam electrode (CAgAE) were developed in this work. Developed methods may be used for determination of 1,3-DNN within a concentration range 2 - 10 μmol.L-1 with LoQ 2 μmol.L-1 using DCV and 1 - 100 μmol.L-1 with LoQ 1 μmol.L-1 by DPV; 1,5-DNN wihin a concentration range 2 - 10 μmol.L-1 with LoQ 2 μmol.L-1 using DCV and 1 - 10 μmol.L-1 with LoQ 1 μmol.L-1 by DPV and 1,8-DNN within a concentration range 2 - 10 μmol.L-1 with LoQ 2 μmol.L-1 using DCV and 0,3 - 1 μmol.L-1 with LoQ 0,3 μmol.L-1 by DPV. An attepmt to decrease LoQ by adsorptive stripping differential pulse voltammetry was not successful. Process of electrochemical reduction of selected dinitronaphthalenes on the working electrode was also studied by cyclic voltammetry. This work verified the use of CAgAE as alternative electrode material to mercury electrodes for determination of electrochemically reducible organic compounds in aqueous-methanolic media. Small dimensions of the CAgAE are the main advantages which predetermine its use in voltammetric microvolume batch analysis and amperometric detection in...

The intracellular second messenger nitric oxide (NO) is implicated in a variety of physiological functions, including release and uptake of dopamine (DA). In the described study, in vivo microdialysis and differential pulse voltammetric techniques were used to determine the involvement of NO in release of DA and its metabolites (dihydroxyphenylalanine, DOPAC; homovanillic acid, HVA) in neostriatum of freely moving rats. While the NO donor molsidomine (30.0 mg/kg; MOLS) and neuronal NO synthase- (nNOS-) inhbitor 7-nitroindazole (10.0 mg/kg; 7-NI) had no effect on the basal in vivo microdialysate level of DA, 7-NI specifically enhanced D,L-amphetamine- (1.0 mg/kg i.p.; AMPH) evoked release of DA. Basal or AMPH effects on DOPAC and HVA levels were not influenced by MOLS or 7-NI. Findings indicate that nitrergic systems have an important role in mediating effects of AMPH on dopaminergic systems.

No description available.

Les cytochromes P450 sont des enzymes mononucléaires de fer qui catalysent l’oxydation de liaisons C-H en utilisant le dioxygène de l’air. L’activation de O2 nécessite sa réduction partielle par l'apport de deux protons et deux électrons. Ces derniers sont fournis par le réducteur naturel NADPH par l'intermédiaire d'une flavoprotéine qui permet de convertir l’adduit fer(II)-O2 en un intermédiaire de type fer(III)-peroxo dont les protonations successives permettent la rupture hétérolytique de la liaison O—O et l’obtention d’un intermédiaire de type fer-oxo responsable de l’oxydation du substrat.1 Ce projet s’inscrit dans le cadre de la chimie bio-inspirée, il a pour objectif de développer des catalyseurs de fer non-hémiques afin de réaliser l’oxydation de petites molécules organiques en utilisant le dioxygène de l’air. L’activation du dioxygène est assurée par le biais d’une électrode qui sert de source d’électrons mais également de sonde mécanistique. Pour comprendre le mécanisme de l’activation du dioxygène il est nécessaire (i) de générer les intermédiaires réactionnels oxydants (fer-oxo, fer-(hydro)peroxo) par le biais d’oxydants chimiques comme le PhIO et H2O2 puis (ii) de les caractériser par spectroscopie et électrochimie à basse température. Enfin (iii) l’étude expérimentale par voltampérométrie cyclique de la réaction du complexe de Fe(II) en présence de dioxygène couplée à des simulations de voltampérogrammes de cette même réaction (à l’aide de données thermodynamiques et cinétiques obtenues en (ii)) permettent ainsi de valider le mécanisme de l’activation réductrice du dioxygène de ce système. Ce travail a démontré que les complexes de FeII avec des ligands amines/pyridine peuvent activer le dioxygène à la surface d’une électrode en suivant un mécanisme proche de celui du cytochrome P450. A présent, la difficulté principale est de s’affranchir de la réduction prématurée des intermédiaires lorsqu’ils sont générés à l’électrode. En se basant sur ces résultats, l’essentiel du travail est à présent ciblé sur la compréhension des différents paramètres (première sphère de coordination, conditions expérimentales, …) qui peuvent modifier la stabilité des intermédiaires et donc l’efficacité de la catalyse. / Cytochrome P450 is a mononuclear iron enzyme, which catalyzes the oxidation of robust C-H bonds using O2. Activation of O2 is achieved at the Fe(II) center and requires an electron transfer to convert the iron(II)-dioxygen adduct into an iron(III)peroxo intermediate. After protonation, this latter may directly oxidize substrates or evolves to yield a powerful high valent iron-oxo moiety. In such natural systems, the necessary electrons are provided by a co-substrate NAD(P)H and are conveyed through a reductase.1The aim of this project is to develop non-heme iron(II) complexes as catalysts for the oxidation of small organic molecules by O2. Our objective is to use an electrode to deliver the electrons while providing mechanistic information at the same time thanks to a combined experimental/simulation approach using cyclic voltammetry. This work has shown that simple Fe(II) complexes bearing amine/pyridine ligands can activate O2 at an electrode surface following a mechanism that is reminiscent of the one of P450. However, the main scientific lock is to avoid the fast reduction of the reaction intermediates when they are generated at the electrode. We are currently studying how alterations of the first coordination sphere of the metal center and experimental conditions modulate the formation and the stability of these intermediates and thus, the efficiency of the catalysts.