Heme containing proteins and their reactivity play a central role in biological systems; they have a vast range of functions including electron transfer, catalysis, and respiration. Cytochromes c and heme c containing proteins have been used widely as model systems to understand how structure and dynamics lead toward function. In this thesis, a variety of biophysical methods are used to investigate two heme c containing model systems to gain insight into how redox potential and reactivity are modulated through changes in the local environment. Mitochondrial cytochrome c undergoes several pH dependent conformational rearrangements that involve different heme ligation and have associated changes in redox potential. Under basic conditions (pH greater than 8), the axial methionine (Met) residue is replaced by one of several nitrogen based ligands, usually a nearby lysine residue, and is coined the "alkaline transition". It is accompanied by a large downward shift in redox potential. The functional utility of this conformational change is not fully understood however it is strongly implicated in the signaling cascade for apoptosis. Bacterial monoheme cytochromes c exhibit similar phenomenological Met-loss behavior as a function of electrode material. In Chapter 2 we utilize Hydrogenobacter thermophilus cytochrome c552 as a model system for the assessment of redox thermodynamics and changes in redox potential associated with the Met-loss form. In Chapter 3 we extend our investigation to homologous cytochromes c. Bacterial cytochrome c peroxidases catalyze the two-electron reduction of hydrogen peroxide to water utilizing cytochrome c as an endogenous electron donor. Chapter 4 describes the first recombinant construct of the diheme Nitrosomonas europaea cytochrome c peroxidase (Ne CCP); a defining family member of constitutively active cytochrome c peroxidases. A variety of biophysical techniques were used to confirm similarity between the recombinant Ne CCP and native enzyme. Chapter 5 extends our investigation to the role of constitutively conserved glutamine and glutamic acid residues within the active site, and two conserved tryptophan residues; the first situated between hemes and the second distal to the active site. In Chapter 6, stopped flow spectroscopy is used to investigate the first intermediates of the Ne CCP catalytic mechanism.

No description available.

A kinetic study on polycrystalline platinum (Pt) in sulphuric acid is presented. An electrochemical kinetic mechanism of Pt oxide reduction and surface oxide structures are proposed. The reduction reaction was studied by cyclic voltammetry (CV) and various potential programs that combine sweep and hold periods by an assembled analog instrumentation. The reduction peak was studied under three surface conditions: same oxide coverage θ and same potential E, different θ and same E, and same θ but different E, to determine the influence of θ and E on the peak potential and peak shape. The double-layer charge measured previously by dynamic electrochemical impedance spectroscopy (dEIS) was used to correct the CV baseline. Differential-equation-based models as a function of θ and E were investigated to simulate the oxide reduction and oxidation, and estimate kinetic parameters. A simple mechanism combining desorption and multi-layer growth mechanisms showed good fit with both the spread-out oxidation peak and the sharp reduction peak. A microscopic surface oxide growth model was proposed to explain the surface oxides reduction mechanism. / Graduate

by Oi-Ming Cheng. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 104-108). / Chapter 1 --- INTRODUCTION / Chapter A) --- Sources of zinc and its functional role --- p.10 / Chapter B) --- Effects of excessive zinc intake --- p.11 / Chapter (a) --- Human --- p.11 / Chapter (b) --- Animal --- p.11 / Chapter (c) --- Fish --- p.12 / Chapter C) --- Techniques in zinc determination --- p.12 / Chapter 2 --- ANODIC STRIPPING VOLTAMMETRY / Chapter A) --- Basic principles --- p.16 / Chapter (a) --- Cell --- p.16 / Chapter (b) --- Electrodeposition and stripping --- p.20 / Chapter B) --- Major interferences in anodic stripping and the common solutions to these problems --- p.25 / Chapter (a) --- Intermetallic compound formation --- p.25 / Chapter (b) --- Overlapping peaks --- p.26 / Chapter (c) --- Organic compounds adsorbed at the electrode --- p.28 / Chapter 3 --- MUTUAL INTERFERENCE FROM ZINC AND COPPER / Chapter A) --- Introduction --- p.30 / Chapter B) --- Review of reported methods to remove copper interference --- p.31 / Chapter (a) --- Dual-working electrode approach --- p.31 / Chapter (b) --- Adjustment of the deposition potential --- p.31 / Chapter (c) --- Standard addition --- p.33 / Chapter (d) --- Addition of a third element --- p.33 / Chapter C) --- The proposed solution --- p.35 / Chapter 4 --- EXPERIMENTAL / Chapter A) --- Proposed method --- p.37 / Chapter (a) --- Apparatus --- p.37 / Chapter (b) --- Reagents --- p.38 / Chapter (c) --- Procedure --- p.40 / Chapter B) --- Reference method --- p.45 / Chapter (a) --- Apparatus --- p.45 / Chapter (b) --- Reagents --- p.45 / Chapter (c) --- Procedure --- p.47 / Chapter 5 --- RESULTS AND DISCUSSION / Chapter A) --- Optimization of instrumental parameters and working conditions --- p.49 / Chapter (a) --- Effect of plating potential on zinc peak current --- p.49 / Chapter (b) --- Effect of plating time on zinc peak current --- p.53 / Chapter (c) --- Effect of holding time and holding potential on zinc peak current --- p.56 / Chapter (d) --- Effect of sweep rate on zinc peak current --- p.58 / Chapter (e) --- Effect of final potential and strip time on zinc peak current --- p.61 / Chapter (f) --- Effect of pH on the peak current and recovery of zinc in the presence of copper after the sulphide treatment --- p.63 / Chapter (g) --- Effect of the concentration of buffer on the peak current --- p.66 / Chapter (h) --- Effect of the reaction time of sulphide with copper on the zinc recovery --- p.68 / Chapter B) --- "Calibration graph, precision and detection limit" --- p.71 / Chapter C) --- Effect of copper on the zinc determination by the proposed method --- p.78 / Chapter D) --- Interference studies --- p.80 / Chapter E) --- Recovery tests --- p.84 / Chapter F) --- Determination of zinc in real samples using the proposed method --- p.86 / Chapter (a) --- Clean water samples such as sea water and tap water --- p.86 / Chapter (b) --- Contaminated natural water and domestic wastewater samples --- p.91 / Chapter (c) --- Air samples --- p.93 / Chapter (d) --- Oyster tissue samples --- p.96 / Chapter (e) --- Sewage sludge and sediment samples --- p.99 / Chapter 6 --- CONCLUSION --- p.102 / REFERENCES --- p.104

No description available.

published_or_final_version / Chemistry / Master / Master of Philosophy

No description available.

Stimulant medications such as D-amphetamine, mixed-salts (75% D- and25% L-) amphetamine; Adderall®, and methylphenidate are first-line treatmentsfor Attention-Deficit/Hyperactivity Disorder (ADHD). In vivo studies havepredominantly focused on these stimulants in the context of drug abuse, andtheir therapeutic mechanistic properties are only theoretical. Previously, in vivotechniques have been limited by poor temporal and spatial resolution, andcharacterizations of these medications in rodent models have not been possibleat low, clinically relevant levels. In order to address these issues, our laboratoryused in vivo high speed chronoamperometric microelectrodes to characterize theeffects of local applications of D-amphetamine, L-amphetamine, D,Lamphetamine,and Adderall® at low levels in the striatum and nucleusaccumbens of 3-6 month old, male Fischer 344 (F344) rats. Our results showedsignificant differences between the faster kinetics of dopamine (DA) releasesignals caused by D,L-amphetamine and the slower kinetics resulting from Damphetamine.These data support that resulting DA concentrations evoked by DandD,L-amphetamine are correlated with the amount of D-amphetamine in thedrug and only the time courses of the signals are affected by L-amphetamine.Additionally, locally applied D- and L-amphetamine caused DA release signalswith similar amplitudes or concentrations of evoked DA; however, the signalswere significantly faster for L-amphetamine. Adderall® caused significantlygreater DA release that lasted over a longer time course compared to DA releasecaused by D- or D,L-amphetamine. These data support the hypothesis thatamphetamine isomers, alone or in combination, interact differently with the DAtransporter (DAT) to subsequently cause reversal of transport of DA out ofpresynaptic membranes of DA neuronal projections. Finally, reversemicrodialysis studies were carried out to assess low levels of D-amphetamine,Adderall® (75% D-, 25% L-amphetamine), methylphenidate, and a new mixedsaltsamphetamine that we referred to as Reverse Adderall (75% L-, 25% Damphetamine)in the striatum of F344 rats. These data reveal a stimulantconcentration-response curve for DA with double plateaus that may be explainedby dual mechanisms of reverse transport of DA through the DAT. In addition,reverse microdialysis of methylphenidate caused DA overflow similar to theeffects of the other stimulants.

Dramatic growth in substituted amphetamines (‘Ecstasy’) use since the 1980’s has correlated with increased incidence of acute toxicity and residual neuropsychological deficits. This thesis aimed to characterise the acute neurochemical mechanisms and residual neurochemical alterations produced by p-methoxyamphetamine (PMA), which is usually sold as ‘ecstasy’ and is associated with greater acute toxicity than 3,4-methylenedioxymethamphetamine (MDMA). While both PMA and MDMA primarily modulate dopaminergic and serotonergic neurotransmission, little is known of the differences in the neurochemical effects of PMA within the central nervous system, in vivo. This thesis used in vivo chronoamperometry to elucidate the acute neurochemical alterations in monoaminergic pharmacology in vivo after local application of PMA or MDMA within discrete brain nuclei in anaesthetised rats. Measurement of evoked release of monoamines including serotonin (5-HT), and inhibition of neurotransmitter uptake via membrane transporters were assessed. Initial studies compared pharmacodynamic responses of PMA and MDMA, showing PMA to have greater efficacy and potency for alteration of core body temperature in rats, a primary cause of acute toxicity, within minimal alteration in locomotion. Dose-response studies indicated local PMA application within striatum resulted in significantly greater 5-HT evoked release than MDMA, yet lesser dopaminergic release, as predicted by the pharmacodynamic data. Only PMA-evoked release could be partially blocked by pre-treatment with a 5-HT reuptake inhibitor (SERT). Differences in both the qualitative and quantitative nature of striatal evoked-release of 5HT and dopamine were noted for both drugs, which had not been previously seen. Both PMA and MDMA inhibited 5-HT clearance, but only MDMA inhibited dopamine clearance in striatum. Doseresponse studies in the CA3 region of hippocampus indicated PMA was also more efficacious than MDMA in the inhibition of 5-HT clearance in vivo. While the question of whether long term MDMA use induces selective neurodegeneration (reductions in serotonergic in vitro biomarkers) is still unclear, it was not known for PMA prior to this work. Repeated PMA administration was shown to result in reductions in cortical SERT (indicative of potential loss of 5-HT terminal axons), cortical 5-HT content was unaltered. A subsequent comprehensive study followed, comparing the residual effects of PMA or MDMA administration on in vitro serotonergic biomarkers (markers of selective neurodegeneration) and SERT function in vivo. PMA administration resulted in reductions in hippocampal SERT binding and [3H]-5HT synaptosomal uptake, correlating with in vitro biomarkers previously used. SERT function in vivo using chronoamperometric techniques was reduced, as would be predicted. However, hippocampal 5-HT content was again not reduced, indicating that selective neurodegeneration of 5-HT fibres may not in fact be occurring. MDMA administration reduced all measured in vitro serotonergic biomarkers, however SERT function in vivo was completely unaltered. These data indicate that reductions of in vitro biomarkers of 5-HT axonal degeneration do not necessarily predict the potential compensatory mechanisms that maintain SERT function in vivo. Compensatory mechanisms appear to exist in vivo to maintain clearance of extracellular 5- HT that may be disrupted or eliminated during tissue preparation for in vitro assays. In summary, while PMA produced significantly greater alterations, compared to MDMA, in processes intrinsic to 5-HT neurotransmission in both striatum and hippocampus, the magnitude of these responses did not explain the significantly higher risk of acute toxicity seen clinically with PMA use. The second component of the thesis extended beyond prior work, investigating the potential neurodegenerative effects of PMA and MDMA through the assessment of changes in key functional processes in 5-HT neurotransmisson. It is hoped this will contribute to the subsequent characterisation of the mechanism(s) of functional compensation in 5-HT neurotransmission which may lead to more targeted treatments to modulate potential psychological/psychiatric deficits that occur in regular ‘ecstasy’ users. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1346193 / Thesis (Ph.D.) - University of Adelaide, School of Medicine, 2008

Two thin film materials - intermetallic and porous silicon thin films, have been studied in this thesis. The first part focuses on the hydrogen storage and electrochemical properties of single layer LaNi5-based thin films fabricated by magnetron sputtering. The aim is to enhance their performance in mini hydrogen storage systems, and their application as electrodes in thin film Ni-MH micro-batteries. Such LaNi5-based thin films were fabricated by magnetron puttering. Using X-ray diffraction (XRD), these thin films revealed a crystalline structure with uniform chemical composition. Using AFM, SEM and TEM, they were found to have a unique microstructure: (1) Nanopores of approximately 15-40 nm which could possibly act as hydrogen reservoir (2) A dense, defect free cross sectional region which would ultimately improve the efficiency and lifetime of the thin film electrodes used in thin film battery. The hydrogen absorption/desorption behaviour of these thin films were determined by volumetric method. The maximum hydrogen content of the La-Ni-A1 film was found to be 1.45 wt% at 333 K which was very close to the theoretical capacity of 1.47 wt%; and higher than that of the La-Ni-AI powder materials (1.2 wt%). Electrochemical properties of the films were measured by simulated battery tests. When discharged at low current, the discharge capacity of the film was similar to that of powder materials - about 220 mAh/g for the first 30 cycles. When the thin film electrode was discharged at a high rate, 4C (current density of 100 mA/g), it could reach the maximum specific capacity of 200 mAh/g and maintained this capacity for 200 cycles; the value was not attainable for La-Ni-AI powder electrode. The presence of crack propagation in film during charge/discharge cycles would improve the electrochemical performance which was different to that of powder materials. Cyclic voltammetry reported that the efficiency of the film could maintain at 80% for the first 200 cycles and gradually decreased due to the formation of corrosion products on surface, which is consistent with the galvanostatic results. XPS (X-ray Photoelectron Spectroscopy) revealed that the corrosion products ??? A1203, La203 and La(OH)3 formed on the film surface after cyclic voltammetry. The second part reported the hydrogen absorption/desorption behaviour of porous silicon thin films. The hydrogen content was determined quantitatively by both volumetric method and thermogravimetric analysis (TGA) and found to be 15 wt% at 423 K under 15 atm of hydrogen pressure. This is an extraordinary amount of hydrogen absorption which supersedes the US Department of Energy's 2007 target of 6.5 wt%. Hydrogen depth profiles of the film after hydrogenation performed by Secondary Ion Mass Spectroscopy confirmed there was hydrogen within the film structure, this was an indication that hydrogen was not just physisorbed on the film surface, but chemisorbed into the porous Si lattice. X-ray diffraction found that there was a lattice contraction upon hydrogen insertion, again suggesting the hydrogen entered into the film structure by chemisorption.