While much is known about the toxicity of polychlorinated biphenyls (PCBs), there are tens of thousands of natural and synthetic chemicals in the environment that can activate the aryl hydrocarbon receptor (AhR) and thus cause toxicity. Since it would be difficult to conduct studies of the toxicity of each and every compound, here is presented a new model based on first-principles taking into account the basic electronic and electron trans- fer characteristics of PCBs, but can be used to predict the toxicities of other AhR-active compounds. The predictive model is based on Density Functional Theory. The model predicts that the energy gap between highest occupied (HOMO) and lowest unoccupied (LUMO) molecular orbitals is the overarching indicator of toxicity of PCBs, but not the only factor. The model explains why chlorination of both para-positions is required for maximum toxic potency. To rank potency of PCBs, the dipole moment in relation to the most chemically active chlorine-sites is critical. The theory is consistent with the accepted toxic equivalency factor (TEF) model for these molecules and is also able to improve on ranking toxic potency of PCBs with similar TEFs. This new model also includes a 13th dioxin-like PCB, PCB 74, not considered in the current TEF model developed by the World Health Organization (WHO). The model was applied to HOMO-LUMO gap mea- surements of a set of PCBs and the measurements are consistent with the model. Values of HOMO-LUMO gap can also be used to predict bio-accumulation of PCBs. The model provides an in silico method to screen a wide range of chemicals to predict their ability to act as an AhR agonist.

M.Sc., Faculty of Science, University of the Witwatersrand, 2011 / The objective of the study was to investigate the preparation of glass beads for base metal analysis of mining samples prior to x-ray fluorescence analysis. The research method used included the investigation of different fluxes, oxidising, non-wetting agents, fusion temperature and time. The experiments were carried out using different fusion instruments: Electrofluxer and Katanax followed by both EDXRF and WDXRF analysis. The x-ray spectrometers were calibrated with standards prepared from pure oxides and the results compared to values determined by alternative techniques. Different statistical methods were used to validate the experiments including factorial designs. Not all the elements and oxides were recovered successfully, however, perfect glass beads were prepared. The two areas of concern were addressed successfully: firstly the loss of copper was overcome by using an alternative heating mechanism of the Katanax and sodium iodide as the non-wetting agent. Secondly, the sulphur was successfully oxidised and retained in the glass beads.

by Chan Wing-yee. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1993. / Includes bibliographical references (leaves 93-95). / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / Chapter CHAPTER 1 --- INTRODUCTION --- p.1 / Chapter 1.1 --- General Introduction --- p.1 / Chapter 1.2 --- "Clinical Significance of Fe, Cu and Zn" --- p.2 / Chapter 1.3 --- Alternative Methods of Analysis --- p.5 / Chapter 1.4 --- Principles of Energy Dispersive X-ray Fluorescence Spectrometry --- p.11 / Chapter 1.5 --- Research Plan --- p.20 / Chapter CHAPTER 2 --- EXPERIMENTAL --- p.22 / Chapter 2.1 --- Energy Dispersive X-ray Fluorescence Analysis --- p.22 / Chapter 2.1.1 --- Apparatus --- p.22 / Chapter 2.1.2 --- Reagents --- p.25 / Chapter 2.1.3 --- Procedure --- p.28 / Chapter 2.2 --- Atomic Absorption Spectrometric Analysis --- p.32 / Chapter 2.2.1 --- Apparatus --- p.32 / Chapter 2.2.2 --- Reagents --- p.32 / Chapter 2.2.3 --- Procedure --- p.34 / Chapter CHAPTER 3 --- RESULTS AND DISCUSSION --- p.38 / Chapter 3.1 --- Optimisation of Excitation Conditions --- p.38 / Chapter 3.1.1 --- Effect of Filter --- p.38 / Chapter 3.1.2 --- Effect of Tube Voltage --- p.43 / Chapter 3.1.3 --- Effect of Tube Current --- p.44 / Chapter 3.2 --- Optimisation of Preconcentration Procedure --- p.46 / Chapter 3.2.1 --- Effect of Sample Area and Collimator Size --- p.46 / Chapter 3.2.2 --- Effect of pH --- p.51 / Chapter 3.2.3 --- Effect of Ligand Concentration --- p.54 / Chapter 3.2.4 --- Effect of Mixing Time --- p.57 / Chapter 3.2.5 --- Effect of Standing Time --- p.59 / Chapter 3.2.6 --- Study of Sample Homogeneity --- p.61 / Chapter 3.3 --- Optimisation for Deproteination --- p.63 / Chapter 3.3.1 --- Effect of Different Protein Precipitants --- p.63 / Chapter 3.3.2 --- Effect of Trichloroacetic Acid Concentration --- p.65 / Chapter 3.3.3 --- Effect of Hydrochloric Acid Concentration --- p.67 / Chapter 3.3.4 --- Effect of Temperature --- p.69 / Chapter 3.3.5 --- Effect of Incubation Time --- p.71 / Chapter 3.4 --- Study of Blanks --- p.74 / Chapter 3.5 --- Construction of Calibration Curves --- p.77 / Chapter 3.6 --- Determination of Detection Limit and Sensitivity --- p.84 / Chapter 3.7 --- Accuracy and Reproducibility Tests --- p.86 / Chapter 3.8 --- Parallel Check --- p.89 / Chapter CHAPTER 4 --- CONCLUSION --- p.92 / REFERENCES --- p.93

by Ho Sing Yiu. / Thesis (M. Phil.)--Chinese University of Hong Kong, 1991. / Includes bibliographical references. / ACKNOWLEDGEMENT --- p.i / ABSTRACT --- p.ii / Chapter CHAPTER 1 --- GENERAL INTRODUCTION --- p.1 / Chapter PART I --- DERIVATIVE SPECT3ROPHOTOMETRIC METHOD FOR THE SIMULTANEOUS DETERMINATION OF COPPER AND NICKEL IN ALLOYS / Chapter CHAPTER 2 --- INTRODUCTION --- p.5 / Chapter CHAPTER 3 --- EXPERIMENTAL --- p.14 / Chapter CHAPTER 4 --- RESULTS AND DISCUSSION --- p.18 / Chapter PART II --- X-RAY FLUORESCENCE SPECTROMETRIC METHOD FOR THE SIMULTANEOUS DETERMINATION OF SEVEN METALS IN WATER SAMPLES / Chapter CHAPTER 5 --- INTRODUCTION --- p.43 / Chapter CHAPTER 6 --- EXPERIMENTAL --- p.58 / Chapter CHAPTER 7 --- RESULTS AND DISCUSSION --- p.65 / Chapter CHAPTER 8 --- CONCLUSION --- p.99 / REFERENCES --- p.101

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Ph.D. / Biochemistry and Molecular Biology / The human copper chaperone to superoxide dismutase (hCCS) is a zinc and copper containing protein that delivers copper to the active site of the cytoplasmic protein superoxide dismutase (SOD). hCCS is a three domain protein with three possible copper binding sites: Domain I is called the Atx-like domain and contains the copper binding motif MXCXXC; Domain II is the SOD-like domain and includes the slightly altered histidine rich copper binding site seen in SOD; and Domain III is a short C-terminal tail that has the copper binding motif of CXC. Studies of the WT protein using EXAFS showed that the protein contained a binuclear copper-sulfur cluster. Initially, it was unknown whether this cluster was formed between domain I and domain II of the protein or formed intermolecularly between two hCCS monomers. Further studies, on the cysteine to serine mutants of the residues in the Domain I and Domain II motifs, showed that while the Domain I motif is capable of binding Cu(I), it is Domain III that is the site of the copper cluster and the cluster is formed between two hCCS monomers. Additional studies with cysteine to alanine mutants of the residues in the copper binding motifs of Domain I and Domain III showed that Domain III is not only the site of the copper cluster but also the site of transfer of copper from hCCS to SOD and also a imerization interface for hCCS. While Domain I can bind copper and may play a role in regulation of activity, it is Domain III that contains the activity of hCCS.

<p>Gamma ray spectroscopy has provided enormous amounts of information on the behaviour and structure of atomic nuclei [SHA88, BEA92, EBE08]. Most of the major discoveries in experimental nuclear physics over the last five decades are strongly associated with improvements in detector technologies. Inorganic scintilators led to the discovery in 1963 of the first excited states of a rotational band based on the ground state of 162Dy. Improvements in peak-to-background ratios and detector resolutions obtained with germanium led to the first evidence of backbending which is associated with a two quasi-particle excitation in 162Dy [SHA88]. More recently the development of composite and highly-segmented Ge detectors has significantly increased the performance and power of detection systems. The Clover detector is such a detector system and is in use at iThemba LABS. This study concerns the evaluation of the particle transport code MCNPX 2.5.0 as a tool to model complex composite detectors such as the Clover. Lanthanum silicate (LSO) and Lead tungstate (PbWO) are also evaluated as possible suppressor shield materials. It is shown that reasonable agreement between experiment and simulation is found when the experiment is accurately reproduced. However, when complex detection modes are implemented in the detector based on the number of elements that fire, MCNPX cannot be used to model the detector performance exactly. Differences between simulated and experimental results are found in suppressed add-back mode. It is proposed that the discrepancies are due to limitations in implementation of the pulse-height and special anti-coincidence tally in MCNPX. LSO and PbWO are compared to BGO as suppressor shield materials. It is found that LSO is not an ideal material for a suppression shield. PbWO is shown to give performance values similar to that of BGO. The back-plug is shown to have no effect on the Peak-to-Total ratio but is effective at reducing the background at lower energies.</p>

An overview of synchrotrons and synchrotron radiation is presented, along with the theory and practical considerations behind several types of X-ray spectroscopy. The theory and practical considerations of density functional theory are also given, with direct reference to some specific software packages.<p> Some synchrotron-excited X-ray spectroscopy measurements and density functional theory calculations of selenium and arsenic-doped selenium films are then outlined. The physical structure of crystalline and amorphous selenium and the electronic structure of amorphous selenium are discussed and comparison is made to the experimental results.<p> A weak feature in the conduction band is identified as a "fingerprint" of the degree of crystallization in amorphous selenium from X-ray absorption measurements. Similarly, a weak feature corresponding to lone-pairs in the valence band is identified as a "fingerprint" of the arsenic concentration from X-ray emission measurements.<p> Finally a detailed model of the structure of amorphous selenium is explained, and compared to experiment. This model is tested both by direct calculations and by a reverse Monte Carlo approach. The implications of this model with respect to the structure of amorphous and arsenic-doped amorphous selenium are discussed. Calculations suggest that simply randomizing the arrangement of "perfect" trigonal selenium is unable to reproduce the measurements of amorphous selenium; a moderate variation in the bond angle of "perfect" trigonal selenium is also necessary.

An overview of synchrotrons and synchrotron radiation is presented, along with the theory and practical considerations behind several types of X-ray spectroscopy. The theory and practical considerations of density functional theory are also given, with direct reference to some specific software packages.<p> Some synchrotron-excited X-ray spectroscopy measurements and density functional theory calculations of selenium and arsenic-doped selenium films are then outlined. The physical structure of crystalline and amorphous selenium and the electronic structure of amorphous selenium are discussed and comparison is made to the experimental results.<p> A weak feature in the conduction band is identified as a "fingerprint" of the degree of crystallization in amorphous selenium from X-ray absorption measurements. Similarly, a weak feature corresponding to lone-pairs in the valence band is identified as a "fingerprint" of the arsenic concentration from X-ray emission measurements.<p> Finally a detailed model of the structure of amorphous selenium is explained, and compared to experiment. This model is tested both by direct calculations and by a reverse Monte Carlo approach. The implications of this model with respect to the structure of amorphous and arsenic-doped amorphous selenium are discussed. Calculations suggest that simply randomizing the arrangement of "perfect" trigonal selenium is unable to reproduce the measurements of amorphous selenium; a moderate variation in the bond angle of "perfect" trigonal selenium is also necessary.

Thesis (Ph. D.)--University of Canterbury, 2008. / Typescript (photocopy). Includes bibliographical references (p. 126-133).