The main purpose of this work is study of electrochemical hydrogen peroxide and ascorbate reactions on electrodes modified by Prussian blue (PB), with the aim to apply these electrodes in creation of sensors and biosensors. For this purpose, a detailed study of electrochemical reduction of hydrogen peroxide, as well as of oxidation of ascorbate at Prussian blue modified rotating disk electrode. In view of the results obtained, a mechanism for hydrogen peroxide reduction at PB modified electrode has been proposed. In accordance with this mechanism, electron transfer appears to be rate-limiting step. The kinetics of decomposition of PB modified electrode in the course of a cathodic reduction of hydrogen peroxide has been studied, and the influence of different factors to this process has been determined. Prototypes of sensors and biosensors, for different analytes have been elaborated and tested. / Darbo tikslas yra elektrocheminių vandenilio peroksido ir askorbato reakcijų tyrimas ant Berlyno mėlynuoju (BM) modifikuotų elektrodų, siekiant pritaikyti šiuos elektrodus jutiklių ir biojutiklių kūrimui. Ištirta vandenilio peroksido redukciją ir askorbato oksidaciją naudojant sukamojo disko elektrodą. Gauti rezultatai galimai įrodo stadijinį vandenilio peroksido katodinės redukcijos mechanizmą vykstantį ant BM modifikuoto elektrodo. Detaliai ištirta BM sluoksnio irimo kinetika vandenilio peroksido elektroredukcijos metu, ir nustatyti faktoriai, įtakojantys irimo proceso greitį. Sukurti jutiklių ir biojutiklių prototipai, kurie galėtų būti panaudoti biologiškai aktyvių medžiagų (vandenilio peroksido, askorbato, gliukozės) nustatymui.

Darbo tikslas yra elektrocheminių vandenilio peroksido ir askorbato reakcijų tyrimas ant Berlyno mėlynuoju (BM) modifikuotų elektrodų, siekiant pritaikyti šiuos elektrodus jutiklių ir biojutiklių kūrimui. Ištirta vandenilio peroksido redukciją ir askorbato oksidaciją naudojant sukamojo disko elektrodą. Gauti rezultatai galimai įrodo stadijinį vandenilio peroksido katodinės redukcijos mechanizmą vykstantį ant BM modifikuoto elektrodo. Detaliai ištirta BM sluoksnio irimo kinetika vandenilio peroksido elektroredukcijos metu, ir nustatyti faktoriai, įtakojantys irimo proceso greitį. Sukurti jutiklių ir biojutiklių prototipai, kurie galėtų būti panaudoti biologiškai aktyvių medžiagų (vandenilio peroksido, askorbato, gliukozės) nustatymui. / The main purpose of this work is study of electrochemical hydrogen peroxide and ascorbate reactions on electrodes modified by Prussian blue (PB), with the aim to apply these electrodes in creation of sensors and biosensors. For this purpose, a detailed study of electrochemical reduction of hydrogen peroxide, as well as of oxidation of ascorbate at Prussian blue modified rotating disk electrode. In view of the results obtained, a mechanism for hydrogen peroxide reduction at PB modified electrode has been proposed. In accordance with this mechanism, electron transfer appears to be rate-limiting step. The kinetics of decomposition of PB modified electrode in the course of a cathodic reduction of hydrogen peroxide has been studied, and the influence of different factors to this process has been determined. Prototypes of sensors and biosensors, for different analytes have been elaborated and tested.

The development of cellular senescence is not consistent in cultured bovine fibroblasts. Numerous factors may be contributing to the variable onset of cellular senescence, including oxidative stress, telomere shortening and DNA damage. Recent results indicate that cellular senescence is also associated with markers of DNA replication. This suggests that cells may be more likely to enter a senescent state depending on their cell cycle progression. The purpose of this study was to determine the effect of cell cycle phase on the development of stress-induced premature cellular senescence (SIPS). Bovine fibroblasts were synchronized at various cell cycle phases, followed by treatment with increasing doses of H2O2. Senescent cells were detected using SA-β-galactosidase staining assay. As H2O2 dosage increased, the amount of cell death by necrosis increased in both unsynchronized and cell cycle synchronized groups, while the amount of senescence varied depending on cell cycle phase. Our results suggest that the S phase of the cell cycle is the most resistant to oxidative damage, the G2/M phase is the most susceptible, and the G1/S phase is the most likely to enter senescence as a protective measure following low doses of H2O2. Increased senescence also resulted from an increased recovery time post-H2O2 treatment, and gene expression studies suggest SIPS bovine fibroblasts senesce via the p53-independent pathway. An improved understanding of SIPS has important implications for improving cloning efficiency and understanding age-related diseases.

<p>Aim and Objectives: To assess the effect of bleaching on the marginal integrity of Class V composite resin restorations. To determine the effect of a 6% hydrogen peroxide over the counter and a 38% hydrogen peroxide in-office vital bleaching treatment products on the microleakage of Class V composite restorations.</p>

The research presented in this thesis firstly concerns the use of electrochemical techniques to develop approaches to wool processing which have a lower impact on the environment than conventional chemical methods. Wool is a sulfur rich substrate and current methods used in wool processing often rely on sulfur-based reducing agents such as metabisulfite. However, due to increasing concern over the environmental impacts of metabisulfite, alternative methods are of interest. Electrochemical techniques have been applied to the process of wool setting in the presence of thiol setting agents. Wool disulfide bonds are reduced during this process and the thiol setting agent is converted to the disulfide. Efficient conversion of the disulfide back to the thiol setting agent would allow catalytic amounts of thiols to be used in wool setting. The electroreduction of cystine and 2-hydroxyethyl disulfide has been examined at a range of metal and carbon electrodes to find efficient methods of generating the corresponding thiols, cysteine and 2-mercaptoethanol respectively. Gold and silver were identified as the most efficient electrode materials. In industrial wool processing, the use of large-scale metal electrodes is expensive and therefore, high surface area gold and silver nanoparticle electrodes were fabricated by electrochemically depositing the metals onto low-cost carbon substrates. The most efficient electrochemical system for generating the thiol setting agent involved the electroreduction of cystine at the gold nanoparticle electrode and this system was used to successfully demonstrate that wool setting can be achieved using relatively low concentrations of cysteine. Further research was carried out to investigate methods for the controlled preparation of metal nanoparticle electrodes and their utility for detecting hydrogen peroxide was examined. A simple and versatile approach for the preparation of tethered gold nanoparticle assemblies was developed by exploiting electrostatic interactions between citrate-capped gold nanoparticles and amine tether layers attached to carbon surfaces. The nanoparticle assemblies were optimised for the detection of hydrogen peroxide by selecting the size and density of electrostatically assembled nanoparticles. The number of amine functionalities on the surface and the assembly conditions controlled the nanoparticle density. Nanostructured palladium electrodes fabricated using vapour deposition methods to immobilise palladium nanoparticles directly onto carbon substrates were also examined for the electroanalysis of hydrogen peroxide.

The significantly increased copper and oxidative stress levels are characteristic hallmarks of cancer cells. These differences provide a unique opportunity for selective targeting of cancer cells. D-penicillamine (D-pen) has been proposed to generate reactive oxygen species (ROS) in presence of copper. Therefore, these studies were aimed at investigating the potential application of a currently marketed copper chelator, D-pen, as a novel cytotoxic anti-cancer agent. D-pen was shown to produce ROS, specifically hydrogen peroxide (H2O2), in the presence of cupric sulfate through a copper catalyzed oxidation reaction. During this process D-pen was converted to D-pen disulfide. The experimental proof of the H2O2 generation was conclusively shown with the aid of a novel High Performance Liquid Chromatography (HPLC) assay. The in-vitro cytotoxicity of D-pen co-incubated with cupric sulfate was examined in human beast cancer (MCF-7 and BT474) and leukemia cells (HL-60, HL-60/VCR, and HL-60/ADR). D-pen was shown to cause concentration dependent cytotoxicity in both leukemia and breast cancer cells. A direct correlation between the detection of intracellular ROS and cytotoxicity was established. The treatment of D-pen plus cupric sulfate resulted in a significant reduction in the intracellular thiol content. D-pen is highly hydrophilic and is rapidly eliminated from the body; therefore to improve the intracellular uptake and to protect the thiol group of D-pen, we carried out the synthesis and the in-vitro characterization of a novel gelatin-D-pen conjugate. It was shown that D-pen alone does not enter cells. Confocal microscopy was employed to exhibit the uptake of the novel gelatin-D-pen conjugate by cancer cells. As the cancer cells in-vitro do not accumulate the same levels of copper as reported for cancer cells in-vivo, cancer cells were pre-treated with cupric sulfate to simulate the elevated copper levels. The cupric sulfate pretreatment resulted in reduced thiol level and significantly increased cellular copper content compared to untreated cells. Whereas both free D-pen and gelatin-D-pen conjugate lacked cytotoxicity in un-treated cells, both agents caused concentration dependent cytotoxicity in cupric sulfate pre-treated leukemia cells. Therefore, it was shown that the administration of D-pen as polymer conjugate would potentially provide cytotoxicity and specificity in the treatment of cancer.

Titanium and titanium based alloys are widely used in dentistry and orthopedics to replace hard tissue and to mend broken bones. It has become a material of choice due to its low density, high strength, good biocompatibility and its capacity to integrate closely with the bone. Today, modern materials and surgical techniques can enable patients to live longer, and aid in maintaining or regaining mobility for a more fulfilling life. There are, however, instances where implants fail, and one of the primary causes for implant failure is infection. This thesis deals with two possible ways of reducing or eliminating implant associated infections; TiO2 photocatalysis, where a surface can become antibacterial upon irradiation with UV light; and incorporation of silver, where a subsequent release of silver metal ions result in an antibacterial effect. For the TiO2 photocatalysis strategy, a simple and cost effective chemical oxidation technique, using hydrogen peroxide (H2O2) and water, was used to create an active TiO2 surface on titanium substrates. This surface was shown to effectively degrade an organic model substance (rhodamine B) by generating reactive oxygen species (ROS) under UV illumination. However, it was shown that Ti-peroxy radical species remaining in the surface after the H2O2-oxidation process, rather than generation of ROS from a heterogeneous photocatalytic process, was responsible for the effect. This discovery was further exploited in a TiO2/H2O2/UV system, which demonstrated synergy effects in both rhodamine B degradation tests and in antibacterial assays. For the silver ion release strategy, a combinatorial materials science approach was employed. Binary Ag-Ti oxide gradients were co-deposited in a reactive (O2) environment using a custom built physical vapor deposition system, and evaluated for antibacterial properties. The approach enabled synthesis and composition-structure-property evaluation unlikely to have been achieved by traditional means, and the gradient coatings demonstrated antibacterial properties against both S. aureus and S. epidermidis according to silver ion release. The release was shown to depend more on structural features, such as surface area, crystallinity and oxidation state, than on composition. Ag-Ti oxide gradients were also evaluated under UV illumination, as Ag deposits on crystalline TiO2 can enhance photocatalytic properties. In this work, however, the TiO2 was amorphous and UV illumination caused a slight reduction in the antibacterial effect of silver ions. This was attributed to a UV-induced SOS response in the S. epidermidis bacteria. The results of this thesis demonstrate that both TiO2 photocatalysis, or UV induced activation of Ti-peroxy radical species, as well as incorporation of silver are viable antibacterial strategies for titanium biomaterials. However, their clinical applications are still pending risk-benefit analyses of potential adverse host tissue responses.

Prior to full-scale implementation of process modifications at the Brantford WTP, a pilot-scale treatability study was conducted to investigate intermediate ozonation/AOP and to determine the most suitable granular media (anthracite, GAC, and Filtralite®) for deep-bed biological filtration. The primary objectives of this research were to provide insight into the destruction of natural and synthetic organics and assess ozonated and halogenated DBP formation. Ozone alone was unable to achieve the 1-log removal target for geosmin or MCPA, unless disinfection-level dosages were applied. No improvement was observed when adding hydrogen peroxide. A major obstacle to the implementation of ozonation in bromide-laden source waters is the formation of bromate. There is a direct correlation between ozone dose and bromate formation and by applying ozone dosages at disinfection levels, bromate is likely to exceed regulatory limits. However, adding hydrogen peroxide reduced the amount of bromate formed, and in most cases levels fell below regulatory limits. A linear correlation was established between bromate inhibition and increasing H2O2/O3 ratio at constant ozone dose. Amongst the three filtration media investigated, only GAC achieved 1-log removal for geosmin and MCPA. The superiority of GAC over anthracite and Filtralite® was attributed to its adsorption affinity. Filtralite® and anthracite media were both ineffective for MCPA removal due to its non-biodegradable nature under conventional water treatment conditions. At a 1 mg/L-ozone dose, GAC and Filtralite® filters achieved a 1-log geosmin removal. In contrast, a 1.44 mg/L ozone dose was required to meet this target with anthracite. The tandem of ozone followed by biological filtration was very effective for the control of distribution system TTHM production regardless of filter media, with levels well below current and anticipated provincial regulatory limits. The combination of intermediate ozonation followed by deep-bed biological filtration is well suited for treating Grand River water. Scale-up considerations include pairing the proper filter media to the size of the ozone generator. The best two treatment scenarios were: Option 1: select GAC media and size the ozone generator to produce a 1 mg/L dose. Option 2: select anthracite media and size the ozone generator to deliver a 2 mg/L dose.

Persistent organic pollutants (POPs) are organic compounds of anthropogenic origin that have been linked to the development of cancer, neurobehavioural impairment, and immune system biochemical alterations. These chemicals have various industrial applications as well as acting as pesticides. Dioxins and furans are some of these compounds that are unintentionally produced in combustion and industrial processes. By definition these compounds have 4 common qualities: they are highly toxic, they are resistant to environmental degradation, they are introduced into the air and water where they travel long distances, and they accumulate in fatty tissues. Photochemical degradation is a method that has been extensively researched in the last few decades. In the aqueous phase it has already been shown to be able to degrade a number of refractory organics, such as dioxins and furans. The ultimate products of this process tend to be carbon dioxide, water, and mineral anions. Air phase work has been also gaining attention in recent decades as a possible alternative to incineration methods in air pollution control. The advantages of photochemical degradation processes are that they can be initiated at low temperatures, are relatively low cost compared to incineration processes, environmentally benign, and have the potential for quick and complete degradation of organic compounds. The main aim of the research is to investigate the photochemical degradation potential of PCDD/ PCDFs in gaseous air streams as a potential air pollution control technology. In order to do this, the photodegradation reaction kinetics were determined for chlorobenzene as a suitable surrogate for PCDD/PCDFs. Three different photodegradation schemes were employed: direct photolysis, UV/O3, and UV/H2O2. In addition, ozonolysis reaction rates were also determined to evaluate the effects of on the overall photodegradation rates for the UV/O3 process. Factors such as humidity levels and temperature were investigated to determine their effects on degradation rates. Temperature and humidity were not greatly influential on the degradation rates of direct photolysis. The degradation rate of chlorobenzene at a temperature of 100°C and high humidity was noticeably reduced, but unchanged at the 10% RH and 60% RH levels for all temperatures. Ozonolysis of chlorobenzene was negligible at 30°C for all humidity levels. Ozonolysis reactions at the 60°C and 100°C levels were higher than direct photolysis rates and in the 100°C case exceeded the UV/O3 degradation rates. Ozone coupled with UV experiments proved to be the most destructive at the low temperature of 30°C and molar ratio of 10:1 ozone to chlorobenzene. There was a clear and positive relationship between the amount of ozone present in the reactor and the degradation rate. At lower ozone to chlorobenzene molar ratios the degradation rates were not much higher than those for direct photolysis of ozone. The 5:1 molar ratio saw a significant increase in degradation rates over the photolysis rates. The fastest degradation rate was achieved for the 10:1 molar ratio and high humidity, which was over 10 times the rate of direct photolysis. In addition, humidity had a noticeably significant positive effect in these reactions. The effect of temperature on the UV/ozone reaction scheme was determined for the 5:1 ozone to chlorobenzene ratio. Temperature had an interesting effect on the degradation rates at higher temperatures. As the reactor temperature increased, the degradation rates from ozonolysis and UV/O3 began to converge at 60°C, ultimately leading to the ozonolysis reaction being faster than the UV/O3. Exploratory experiments for the H2O2 scheme were performed. H2O2 had a positive influence on the degradation rate of chlorobenzene and was about 26% higher than the direct photolysis rates. However for similar conditions, the UV/O3 process had higher degradation rates as was expected from the difference in absorption values between ozone and hydrogen peroxide.

Objectives: This investigation adapted the LIVE/DEAD� Baclight[TM] bacterial viability stain for the quantitative determination of bacterial cell viability of the aerotolerant anaerobes Porphyromonas gingivalis ATCC 33277 and Prevotella intermedia ATCC 25611. The Live/Dead stain was used to determine the influence of haem availability on the resistance of P. gingivalis and P. intermedia to the reactive oxygen species (ROS) superoxide anion and hydrogen peroxide and compare the sensitivities between the haem-requiring periodontal bacteria to ROS. Neutrophils use oxidative and non-oxidative killing mechanisms. During phagocytosis, neutrophils kill bacteria via a respiratory burst, producing ROS. P. gingivalis and P. intermedia are oxygen-tolerant gram-negative bacteria found in the gingival crevice. These bacteria express superoxide dismutase (SOD) activity, which extends some protection against superoxide radicals. Methods: Initially, experiments were performed to validate the reliability and accuracy of the fluorogenic Live/Dead stain using Escherichia coli ATCC 10798 (K-12), followed by experiments using P. gingivalis. The Live/Dead stain distinguishes viable:non-viable proportions of bacteria using mixtures of green (SYTO 9) and red (propidium iodide) fluorescent nucleic acid stains respectively. Bacterial cell viability was assessed with fluorescence microscopy and subsequently quantitative measurement using a fluorescence microplate reader (BMG Fluorostar plus Optima). P. gingivalis and P. intermedia colonies were subcultured from frozen cultures, in Tryptic soy broth (TSB) (Difco) and incubated anaerobically for approximately five days. They were further subcultured in pre-reduced TSB, supplemented with menadione 0.5[mu]g/ml (TSB-M) and either 5 [mu]g/ml haemin (Haem 5), 50 [mu]g/ml haemin (Haem 50) or without supplemental haemin (Haem 0). Cultures were grown anaerobically at 37�C to early stationary phase (approximately 48 hours). For experimental purposes, bacteria were harvested, washed and resuspended in 10 mM Tris-buffered saline (pH 7.5) containing peptone (TBS-P) (0.1 mg/ml), with a final adjustment to OD₅₄₀ [approximately equals] 2.0 (which corresponds to 1 x 10⁹ bacteria/ml). Bacterial suspensions were diluted ([approximately equals] 10⁸/ml) into TBS-P containing the fluorogenic viability stain (BacLight, Molecular Probes). Either pyrogallol (0.02 - 2 mM) or hydrogen peroxide (0.01 - 100 mM) was added (except to control tubes); tubes were vortexed for ten seconds and incubated at 37�C. Viability was monitored fluorimetrically for three hours. Results: For both P. gingivalis and P. intermedia, a pyrogallol concentration of 0.2 mM resulted in 80 to 90% cell death; and a hydrogen peroxide concentration of 10 mM killed approximately 80 to 90% of cells. Irrespective of the haem status, no significant difference was determined between the overall maximum rate of killing of P. gingivalis and P. intermedia, in their response to either superoxide or hydrogen peroxide; with the exception that the P. intermedia Haem 0 group was significantly less susceptible to hydrogen peroxide than the P. gingivalis Haem 0 group. For the majority of the experiments, there was no significant difference between final bacterial cell viability in the Haem 0 and Haem 5 cells for both species, after 3 hours exposure to various concentrations of ROS. However, the Haem 50 cells showed a significant increased susceptibility (albeit, a small difference) to both hydrogen peroxide and superoxide. Conclusions: The Live/Dead bacterial viability stain provided a valuable method to monitor "real-time" killing, avoiding the difficulties associated with culture-based methods for assessing viability. Haem availability had no clear influence on the resistance to ROS of either P. gingivalis or P. intermedia Haem 0 and Haem 5 cells. The Haem 50 cells showed a very slight increase in susceptibility to hydrogen peroxide and superoxide. Although P. intermedia may be isolated in significant numbers from healthy gingivae, as well as from periodontally diseased sites, it was no more resistant to ROS than was P. gingivalis, which is associated with periodontal lesions and difficult to cultivate from relatively healthy (more oxygenated) sites. This suggests that resistance to ROS does not contribute to the ecological distinction between these two species. The finding that haem availability did not influence sensitivity implies that these bacteria do not accumulate haem for the purpose of protection from ROS.