Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>The particles of the Pt metal were well dispersed on carbon nanotubes when EG was used and in isopropanol poor dispersion was observed and no further investigation was done on them. The platinum wt% on the supports observed from EDS was 21.8, 19.10 and 16.74wt% for Pt/EMWCNT, Pt/LPGCNT and Pt/ commercial CNT respectively. Pt/LPGMWCNT showed high electro-catalytic activity of 2.48 mA and active surface area of 76 m2/g, toward oxygen reduction, observed from cyclic voltammogram in iv sulfuric acid. Pt/LPGMWCNT also showed better tolerance toward methanol, however it was not highly active towards methanol, and hence the methanol oxidation peak current observed between 0.75 and 08 potential was the smallest. In this study a wide range of instruments was used to characterize the properties and behavior of Platinum nanoparticles on multi-wall carbon nanotubes. To add to the already mentioned, Scanning electrochemical microscopy (SEM), proton induced x-ray emission (PIXE), scanning electrochemical microscopy (SECM) and Brunauer-Emmett Tellar (BET) were also used.</p>

The field of industrial fluorine generation has not made significant progress in the past 60 years due to the difficulty and hazards surrounding the use of hydrofluoric acid (HF) and fluorine gas. This work examines various carbon materials for their use as electrodes in the electrochemical generation of elemental fluorine. An experimental apparatus was designed and constructed to melt and maintain the temperature of the KF·2HF electrolyte in a suitable range for electrochemical measurements. An electrochemical cell was designed and tested for operations in a highly corrosive atmosphere at elevated temperatures. The importance of safe operating procedures surrounding HF is outlined in this work. Various in-situ electrochemical techniques were used to study the ability of the different carbon anode materials in their ability to carry out the fluorine discharge reaction (FDR) as well as study the growth of passivating film. Ex-situ analytical techniques were used to examine the microstructure and composition of the carbon materials before and after electrochemical polarization. The results suggest that the level of non-carbon impurities had the most significant effect on the ability of the carbon material to carry out the FDR efficiently at most potentials tested. The results show that multiple analytical techniques are required to obtain a better understanding of a chemical system, and that no single method can be used to fully explain a single set of results. / UOIT

Tau, a microtubule associated protein, has been implicated in the formation of neurofibrillary tangles, a hallmark of Alzheimer’s disease.1 Resulting from the hyperphosphorylation of tyrosine, serine and threonine residues, protein kinases play an intricate role in the pathway of NFT formation.2 While a number of serine/ threonine kinases such as Glycogen Synthase Kinase 3 beta, have been implicated in the hyperphosphorylation of tau, and it is now believed that tyrosine phosphorylation plays a role. It appears that the degree to which tau is phosphorylated, and region in which phosphorylation occurs play a critical role in aggregate formation. Here we present the use of Ferrocene bioconjugates to monitor tyrosine-mediated hyperphosphorylation and aggregation. Electrochemistry, electron microscopy, surface plasmon resonance, Time of Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy were used to gain insight into the role of tyrosine phosphorylation on hyperphosphorylation.

Tau, a microtubule associated protein, has been implicated in the formation of neurofibrillary tangles, a hallmark of Alzheimer’s disease.1 Resulting from the hyperphosphorylation of tyrosine, serine and threonine residues, protein kinases play an intricate role in the pathway of NFT formation.2 While a number of serine/ threonine kinases such as Glycogen Synthase Kinase 3 beta, have been implicated in the hyperphosphorylation of tau, and it is now believed that tyrosine phosphorylation plays a role. It appears that the degree to which tau is phosphorylated, and region in which phosphorylation occurs play a critical role in aggregate formation. Here we present the use of Ferrocene bioconjugates to monitor tyrosine-mediated hyperphosphorylation and aggregation. Electrochemistry, electron microscopy, surface plasmon resonance, Time of Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy were used to gain insight into the role of tyrosine phosphorylation on hyperphosphorylation.

Ferrocene-peptide conjugates represent a hybrid area between organometallic chemistry and biochemistry. In these bioconjugates, the ferrocene (Fc) moiety can serve as molecular scaffold, chromophore, sensitive probe, biological marker, redox active site, etc. Disubstituted Fc systems, in which both cyclopentadienyl rings are substituted, provide influence over the supramolecular structure of the assemblies, and serve as starting materials for the design of electronic biomaterials. Recently, 1'-amino-ferrocene-1-carboxylic acid (Fca) and 1,1'-diaminoferrocene Fc[NH2]2 were recognized as useful tools in bioorganometallic chemistry. This work sketches some novel preparative and structural aspects of Fc-peptide conjugates and explores their applications as biosensors and as polymeric materials. <p>First, I demonstrated that Fca invariably induces a turn-like structure, which is stable in solution and the solid state. The obtained results showed different behaviour for Fca peptides depending on the chirality and position of the attached amino acid. The axial chirality of the Fca is completely dependent on the chirality of the first amino acid attached to the amino terminal of the Fca group.<p>Second, I was able to develop a surface based sensor for the electrochemical detection of papain based on Fc-peptide conjugates. The idea was to place a surface-bound redox probe in close proximity to the electrode surface. In addition, the redox-active Fca label will be part of the recognition site but will not interfere with the recognition process. My sensor provides an attractive alternative for the electrochemical detection of non-labelled non-redox active proteins, which under current detection schemes remains a significant challenge.<p>This work represents a truly important proof of concept for establishing this novel bioorganometallic approach for the electrochemical detection of important biological targets.<p>Last, I was successful in developing a very convenient method to synthesize 1,1'-bis(tert-butoxycarbonylamino)ferrocene as a stable derivative of Fc[NH2]2. This new synthetic approach has circumvented the problems encountered with the explosive diazide usually used as a precursor in the conventional synthons of Fc[NH2]2. Building on this achievement, a series of novel peptide-like oligomeric and polymeric ferrocenyl-amides were synthesized and fully characterized. The electrochemical investigations on these polymers suggested unresolved or no electronic interaction between the ferrocene groups in all systems. These results may reveal the influence of the amide groups on suppressing the electronic interaction between the iron centers in my polymers. <p>Thus, my systematic work on Fc-peptide conjugates lays solid foundations in the fields of structural control, biosensors, and material science.

Ferrocene-peptide conjugates represent a hybrid area between organometallic chemistry and biochemistry. In these bioconjugates, the ferrocene (Fc) moiety can serve as molecular scaffold, chromophore, sensitive probe, biological marker, redox active site, etc. Disubstituted Fc systems, in which both cyclopentadienyl rings are substituted, provide influence over the supramolecular structure of the assemblies, and serve as starting materials for the design of electronic biomaterials. Recently, 1'-amino-ferrocene-1-carboxylic acid (Fca) and 1,1'-diaminoferrocene Fc[NH2]2 were recognized as useful tools in bioorganometallic chemistry. This work sketches some novel preparative and structural aspects of Fc-peptide conjugates and explores their applications as biosensors and as polymeric materials. <p>First, I demonstrated that Fca invariably induces a turn-like structure, which is stable in solution and the solid state. The obtained results showed different behaviour for Fca peptides depending on the chirality and position of the attached amino acid. The axial chirality of the Fca is completely dependent on the chirality of the first amino acid attached to the amino terminal of the Fca group.<p>Second, I was able to develop a surface based sensor for the electrochemical detection of papain based on Fc-peptide conjugates. The idea was to place a surface-bound redox probe in close proximity to the electrode surface. In addition, the redox-active Fca label will be part of the recognition site but will not interfere with the recognition process. My sensor provides an attractive alternative for the electrochemical detection of non-labelled non-redox active proteins, which under current detection schemes remains a significant challenge.<p>This work represents a truly important proof of concept for establishing this novel bioorganometallic approach for the electrochemical detection of important biological targets.<p>Last, I was successful in developing a very convenient method to synthesize 1,1'-bis(tert-butoxycarbonylamino)ferrocene as a stable derivative of Fc[NH2]2. This new synthetic approach has circumvented the problems encountered with the explosive diazide usually used as a precursor in the conventional synthons of Fc[NH2]2. Building on this achievement, a series of novel peptide-like oligomeric and polymeric ferrocenyl-amides were synthesized and fully characterized. The electrochemical investigations on these polymers suggested unresolved or no electronic interaction between the ferrocene groups in all systems. These results may reveal the influence of the amide groups on suppressing the electronic interaction between the iron centers in my polymers. <p>Thus, my systematic work on Fc-peptide conjugates lays solid foundations in the fields of structural control, biosensors, and material science.

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The studies reported in the thesis deal with surface modification of non-platinum metals by coating with electronically conducting polymers, namely, polyanilne (PANI) and polypyrrole (PPY). The oxidation of Г/I2, hydroquinone/quinine and [Fe(CN)6]3-/ [ Fe(CN)6]4-are studied by cyclic voltammetry and chronoamperometry experiments. It has been shown tht the redox reactions, which do not occur on bare stainless steel electrode, occur through electron-transfer mediated by conducting polymers. The effect of heating of polyaniline (PANI) at 80 0C on its electrochemical activity is studies. Although the thermogravimetric analysis indicates that PANI is stable at temperatures up to about 250 0C and it undergoes decomposition at higher temperatures, its intrinsic redox electrochemical activity decreases with duration of heating at a temperature as low as 80 0C . The polymer completely loses its electrochemical activity. The decrease in lectrochemical activity of PANI is attributed to an irreversible loss of water molecules. The reaction order for degradation of PANI is found to be close to unity, and a value of 1.63 X 10-4 s-1 is obtained for the rate constant. The deactivated PANI does not recover its electrochemical activity even after a prolonged treatment in acidic electrolytes. The electrodeposition of PANI is carried out by galvanostatic, potentiostatic and potentiodynamic methods. The impedance data reflect a marked difference between the PANI deposited by static and dynamic methods. Furthermore, the impedance parameters vary with the sweep rate used in potentiodynamic method. Electrochemical impedance spectra of the electrodes are analyzed using a transmission line model consisting of two rails of finite resistances. Electrochemical deposition of polyaniline (PANI) is carried out on a porous carbon substrate for supercapacitor studies. PANI deposited at 100 mV s-1 sweep rate by potentiodynamic technique on porous carbon substrate is found to possess superior capacitance properties. Capacitance values as high as 1600 F g-1 are obtained and PANI coated carbon electrodes facilitate charge-discharge current densities as hgh as 45 mA cm-2 (19.8 A g-1 ). Electrodes are found to be fairly stable over a long cycle-life, although there is some capacitance loss during the initial stages of cycling. Electrooxidation of ascorbic acid on polyaniline is studied in a fuel-cell. Ascorbic acid (H2A) is employed as fuel and polyaniline (PANI) as the catalyst. H2A is an environmentally and biologically friendly molecule. The catalyst, namely PANI does not consist of any platinum group metal, and at 70 0C , a maximum power density of 4.3 mW cm-2 is obtained at a current density of 15 mA cm-2 . Also, studies on anodically deposited RuO2 for capacitor applications are reported. Cathodic deposition of RuO2 generally produces a mixture of Ru and RuO2 . On the other hand, the anodic depsotion on SS substrates is found to produce RUO2 which is characterized with high power supercapacitance properties. A capacitance value of 274 F g-1 is obtained at a current density of 20mA cm-2 .

Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references.