An oxidative stress in the form of H2O2 exposure previously has been shown to cause a transient increase in NO??oduction and a chronic increase in eNOS protein levels. Nevertheless, oxidative stress can cause an uncoupling of catalytic activity resulting in decreased NO??d increased O2??roduction from eNOS. This uncoupling seems to be mediated predominantly by oxidation of tetrahydrobiopterin (BH4), an eNOS required cofactor. To study how these phenomena regulate the physiological balance of reactive oxygen species (ROS), H2O2-induced NO??oduction was measured in bovine aortic endothelial cells (BAECs) using an NO??ecific electrode. Following H2O2 exposure, NO??ncentrations initially increased; however, if cells were challenged a second time with H2O2, the increase in NO??oduction was attenuated. We postulated that the decline in NO??oduction after H2O2 exposure resulted from BH4 oxidation and tested this by supplementing cells with BH4 prior to the second H2O2 exposure. This resulted in a recovery of NO??oduction. Since H2O2 also activates NADPH oxidase to produce superoxide (O2?? we tested whether the decrease in NO??oduction during the second H2O2 exposure could be explained by increased NADPH oxidase-dependent oxygen free radical production, including O2??peroxynitrite (ONOO-), and hydroxyl radicals (??. A reduction in H2O2-induced NO??lease was prevented in apocynin-and PEG-SOD-treated cells and in p47phox-knockout mouse aortic endothelial cells (MAECs), which lack a critical subunit of the NADPH oxidase. These results suggest that O2??roduced by NADPH oxidase leads to eNOS dysfunction. Scavenging ONOO- resulted in a full recovery of NO??oduction, and scavenging ??resulted in a partial recovery of NO??oduction. This implies roles for these O2??erivatives in the reduced NO??sponse to repeated H2O2 exposures.

In the study, a self-developed electrolytic micro-machining tester is employed to investigate the effects of the supply voltage and the highest position of the workpiece relative to the tool on the geometry of the tungsten rod. The peripheral surface of the iron needle (tool) is insulated by an insulator and its tip with a diameter of 50£gm is exposed to the electrolyte as a cathode. The tungsten rod (workpiece) with 200£gm in diameter reciprocates as an anode. Both the cathode and the anode are dipped into an aqueous electrolyte of 2wt % sodium hydroxide to proceed electrochemical machining. Experimental results show that since the length and the diameter of the workpiece are varied during the machining process, it is necessary to manually adjust the highest position and the gap between the workpiece and the tool in each reciprocating motion to achieve a uniform tungsten rod. Moreover, because of the higher removal rate of the workpiece at the higher supply voltage, it is hard to control the geometry of the workpiece. On the contrary, the geometry of the workpiece can be controlled at the lower supply voltage. Finally, the workpiece is first machined at the higher supply voltage, and then the supply voltage is switched to the lower one to achieve a uniform tungsten rod with 2£gm in diameter and 200£gm in length, or 100 in aspect ratio.

Electrochemical Mechanical Polishing (ECMP) has become increasingly important due to the continuous decrease of the device size in integrated circuit (IC) fabrication. Tantalum (Ta) is a promising material as a substitute for copper in ICs. This dissertation studies the tribology and electrochemistry of Ta ECMP. The present research uses experimental combined analysis approaches. A specially designed experimental setup assembling a tribometer and a potentiostat was used to carry out Ta ECMP. The friction force and electrochemical reactions were measured simultaneously. Using this setup, we found the factors which affected the frictional behaviors of Ta during ECMP. The technique of single frequency electrochemical impedance spectroscopy (EIS) was employed to investigate the material removal mechanisms in Ta ECMP. The results presented the competing mechanisms of removal and formation of a surface oxide layer of Ta. In order to further the investigation in a nanoscale, the atomic force microscope (AFM) was used to measure the material removal rate. The Preston equation for the Ta ECMP was established. A new methodology was developed to study the oxidation state and process of Ta during ECMP. Through comparing the material removal rate measured by using the AFM and the calculated one via the Faraday’s law, the distribution of the Ta suboxides and pentoxide, as well as the oxidation process, was revealed. The oxidation process was strongly dependent of the applied anodic potential, thickness of the oxide layer, mechanical forces, and surface orientation. A polymer environmental cell was designed and produced. Using this cell and AFM, it was found that the material removal in the nanometer scale was a function of the surface orientations. This research is beneficial for optimization of the Ta ECMP process. This dissertation includes six chapters. After Introduction and Motivation and Objectives, the material, setup, and testing conditions are discussed in Chapter III. Chapter IV discusses the tribology and material removal mechanisms in Ta ECMP, while Chapter V the oxidation of Ta during ECMP, followed by Conclusions and Future Work.

Amperometric dectection of heparin and glucosamine in flow injection analysis

Perchloroethylene (PCE) is a toxic contaminant that has been introduced into the environment over many years through industrial and agricultural wastes. Research has been done in the past to investigate PCE degradation by zero-valent iron (ZVI), green rust (GR) and a mixture of both. The combination of ZVI and green rust has been reported to be more effective for degrading PCE than either of them alone. Forming green rust electrochemically has the potential for depositing GR more effectively on the surface of ZVI where it will be able to more easily transfer electrons from ZVI to contaminants such as PCE. Therefore, the goal of this research was to determine the feasibility of electrochemically depositing green rust on zero-valent iron and to characterize it in terms of its composition, crystal properties and amount produced. XRD analysis was conducted to determine composition and crystal properties and a procedure was developed to measure the amount produced. Equipment was constructed to deposit green rust electrochemically onto ZVI. A chain of experiments with varying voltage, pH, time and amounts of ZVI were conducted to determine feasible experimental conditions for GR formation. Then, a method was developed to accurately measure the amount of surface oxides of iron deposited on the zero-valent iron substrate. This method was tested and found useful for measuring iron in: i) standard solutions of soluble iron with different concentrations of reagents; ii) suspensions with solid iron hydroxides by themselves; and iii) suspensions with solid iron hydroxides and ZVI. Electrochemical experiments were conducted and the amounts of iron hydroxides deposited on the ZVI surface were measured. XRD analysis of the deposits on the surface was conducted and the patterns of XRD-peaks were compared to that of type 2 – sulfate green rust.

Structural determinations and electrochemical properties in the series of multinuclear ferrocenyl-ethynyl complexes with formula [(£b5-C5(CH3)5)(P2)MII-C¡ÝC-(fc)n-C¡ÝC-MII(P2)(£b5-C5(CH3)5)] (fc = ferrocenyl; M = Fe(II), Ru(II), Os(II); R = H, CH3; P2 = Ph2PCH2CH2PPh2 (dppe)) are reported. Complexes with more electron-rich ligand environment, were prepared with regard to the understanding of electronic coupling mechanism. These complexes undergo sequential reversible oxidation events from -0.2 V to 1.0 V referred to the Ag/AgCl electrode in anhydrous CH2Cl2 solution and the low-pontential waves have been assigned to the end-capped metallic centers. The magnitude of the electronic coupling between two terminal metallic centers in the series of complexes was estimated by electrochemical technique. Based on the correlation between the £GE1/2 values and the second redox potentials of the end-capping metallic centers in the series of complexes, a qualitative explanation for the different magnitude of the electronic coupling is given.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

Thesis (Ph. D.) in Chemistry--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 181-196).

Thesis (Ph. D.)--University of Michigan. 1931. / "By Alfred L. Ferguson. Richard Hitchens and Kenneth Van Lentes." From Transactions of the Electrochemical society, v. 71, 1937.

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xvi, 149 p.; also includes graphics (some col.). Includes abstract and vita. Advisor: Sheikh Akbar, Dept. of Materials Science and Engineering. Includes bibliographical references (p. 138-149).