[No abstract submitted] / Science, Faculty of / Physics and Astronomy, Department of / Graduate

[No abstract submitted] / Science, Faculty of / Physics and Astronomy, Department of / Graduate

In this thesis the Mossbauer effect in metallic iron has been studied as a function of the length of time of diffusion of the Co⁵⁷ source into metallic iron, of the source temperature over the range 156°K to 478°K, and of the absorber thickness. In each case, the line shape, width, intensity and shifts were measured. Measurements showed that the appearance of an appreciable Mossbauer effect, .122, arises within the first ten minutes of diffusion time at 900°C in a hydrogen atmosphere and that additional time is required to reduce the line width and to increase the intensity to .145. The observed temperature shift of the resonantly absorbed 14.4 kev radiation followed that which was predicted by the Josephson effect. However, corrections for an isomer and a hydrostatic compression shift were made to the data before comparing the measured shift with the theoretical shift. The results indicated a Debye temperature of Θ[subscript D] = (420±20)°K for both the source and absorber used. The measurements made over the temperature range indicated that the internal magnetic field H̰ followed the saturation magnetization curve (the Weiss Law) closely. For small temperature differences between the source and absorber, ΔΘ < 50°K, measurements were made indicating that the minimum line width occurred at ΔΘ = 24°K. These results indicated that the internal magnetic field at ΔΘ = 0°K for the source was .01x10⁵oe greater than that of the absorber. For ΔΘ ≥ 100°K, the Mossbauer line displayed a hyperfine structure arising from the temperature dependent difference in the internal magnetic field at the nuclei. The line profile, width, shift and intensity were measured for four absorber thicknesses - .0002", .00035", .00055", and .001". The detailed comparison of these line characteristics with the theoretical values required an extension of existing treatments, a discussion of which is given in chapter five. In each case it was observed that the Mossbauer line was accompanied by two small peaks, one on either side of the main line. The position of these peaks indicated that they were associated with a small or zero internal magnetic field at the site of some of the Fe⁵⁷ atoms. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

The Stark widths of seventeen N II and ten N III spectral lines, emitted by plasmas with free electron densities of .9 ± .1 x 10¹⁷, 2.2 ± .3 x 10¹⁷ and 2.9 ± .4- x 10¹⁷ cm⁻¹³, were measured. Nine of the N II linewidths and four of the N III linewidths have not been previously measured. The plasma source was a wall stabilized discharge filled with 50% helium and 50% nitrogen. The different electron densities were produced by varying the filling pressure and charging voltage. The electron temperature was determined from the intensity ratio of several N II to N III lines. The electron densities were estimated by measuring the Stark widths of He I 5876 and 6678. The nitrogen lines were measured at different plasma conditions to check linear scaling of Stark width vs electron density on the same device. However, the large errors in both the Stark widths and the electron density measurements, about half of which came from appreciable optical depths, made it difficult to check the scaling even over the limited range of this experiment. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Precision measurements of the Mössbauer fraction of the 14.4 kev Fe⁵⁷ transition were made using the black, wide absorber technique. The Fe⁵⁷ was diffused, as a dilute Mössbauer impurity, into 99.995% purity single crystal chips of Pt, Pd and Cu. By comparing the Debye form of -ln f, corrected for anharmonicity, with our data, we extracted a high and low temperature Debye theta, as well as an anharmonicity coefficient, є, for the three materials. We estimated the accuracy of our data to be ± 1%. From the data we concluded that the Fe⁵⁷ in Cu has stronger force constants and is more anharmonic than pure Cu, while Fe⁵⁷ in Pt and Pd has smaller force constants and about the same anharmonicity as the pure host materials.

Auger electrons have the potential for therapy mainly because of their short range and high level of toxicity. Biological effects of these electrons are critically dependent on the cellular and subcellular localization of their emitters. In this study 123I was used due to its relatively short half-life (13.2 h) and ideal y-ray energy (Ey=I59 keV). The short half-life is advantageous since it allows significant accumulation of disintegrations at normal physiological conditions without the need to freeze cells as required when long lived isotopes such as 1251 (T1/2=60.1 days) are used. The main objective of this study was to synthesize an organic compound that would deliver the radioactive 1231 into cellular DNA and to quantify the resulting damage from micronucleation. The higher degree of damage obtained in cell samples treated with 4-[123I]iodoantipyrine than with [123I]Nal is an indication of Auger electron effect. Also, micronuclei counts showed that 4-[123I]iodoantipyrine and [123I]Nal were prepared in a suitable manner and did not interfere with cellular kinetics. RBE values of 1.8 and 1.9 were obtained for CHO-Kl clone # 7 and # 16 cells, respectively, indicating lack of differential response for the two clones. When the current data is collectively analysed with that of other investigators using the same radiolabeled compounds, a reduction in Auger electron RBE is noticeable with radiosensitivity. This is consistent with the high-LET nature of Auger electrons. The extremely radiosensitive CHO-XRS 1 failed to give a dose-response as most cells underwent apoptosis. The significant radioprotection of CHO-K1 cells irradiated, in the presence of a chemical protector MEA, with 4-[ 123I]iodoantipyrine than with [123I]Nal showed that the mode by which Auger electrons cause damage is not the same as that of a-particles. Further studies involving the use of carriers that would specifically deliver radionuclides to nuclear DNA may be useful in understanding the mechanisms underlying the cellular responses to Auger electron exposure. / Thesis (M.Sc. (ARST) North-West University, Mafikeng Campus, 2005

archives@tulane.edu / Solubility is the ability of a molecule to favorably interact with a solvent. While seemingly simple in application many phenomena arise from knife-edge like conditions between solubility and insolubility. Herein, three of these phenomena; co-non-solvency, the hydrophobic effect, and the direct and reverse Hofmeister effects are investigated in detail to parse out a mechanistic view of solubility in each case. The first phenomenon, co-non-solvency, is the insolubility of a thermo-responsive polymer and a mixture of two good cosolvents. Host-guest systems are used to probe small molecule interactions in the presence of cosolvents for co-non-solvent effects. The second phenomenon, the hydrophobic effect, is often colloquially described as “oil and water do not mix.” However, this is much more complex when diving into the energetic contributions. Host-guest systems are used to determine structural effects novel hosts and guests have on the hydrophobic effect in collaboration with the computational community. The third phenomenon, the Hofmeister effects, are explored through the fine tuning of solubility of lysozyme through the addition of sodium perchlorate in varying pHs. This is used to determine a mechanistic view of protein solubility in the presence of salts. / 1 / Nicholas Ernst

Anesthesia, a state of being absent of sensation and consciousness, has been recognized since antiquity. Even today anesthesia is still best characterized by the lack of consciousness and sensations. Since anesthetic potency is correlated with lipid solubility, the site of action of general anesthetics has been thought to be hydrophobic in nature and to involve excitable membranes critical for interneuronal communications. Thus, general anesthetics may interact directly with functionally-relevant membrane proteins (via hydrophobic pockets) or indirectly, with the lipids surrounding these proteins. To better understand the details of general anesthetic action, I examined how halothane interacts with a functional synaptic protein, the acetylcholine receptor channel embedded in the membranes of cultured Xenopus myocytes. Next, I examined how changing the lipid composition, of these membranes, affected this interaction. Using the extracellular patch-clamp technique, I found that halothane, at clinically-relevant concentrations, shortened the burst duration of single receptor channels without affecting their conductance. Moreover, the halothane-induced reduction of burst durations was significantly attenuated after pretreatment with cholesterol-rich lipsomes which increased significantly the cholesterol content of these cells. These findings provide the first direct support for the role of membrane lipids in the mechanism of GA action. In particular, I demonstrated that increases in membrane cholesterol antagonize the anesthetic action of halothane. Although direct action of cholesterol on synaptic proteins cannot be ruled out, my data strongly suggest that membrane lipids are involved at a critical, but as yet undefined, site with which GAs interact. The exact manner by which increases in membrane cholesterol antagonize GA action remains to be eludicated.

No description available.

Triazenes, compounds containing a diazoamino moiety (–N(1)=N(2)–N(3)<), are known for their reversible cis-trans isomerization character and hence, have the potential to be used in photoswitchable devices and photostorage media. However, little is known about their cis-trans isomerization mechanism. In this thesis, kinetic studies on the thermal cis-to-trans isomerization of N-(phenylazo)-substituted nitrogen heterocycles are presented. It is shown that the isomerization rate constant increases as the size and electron-donating character of the cyclic amine increases, as the electron-withdrawing character of the para substituent group on the phenyl ring increases, and as the polarity of the solvent increases. All these trends are interpreted in terms of a rotational isomerization mechanism involving a dipolar transition state. In addition, photolytic cleavage of the N(2)–N(3) bond of target substrates is shown to be affected as well by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, with the result that the photolysis yield increases as the isomerization rate decreases. Theoretical calculations on target substrates both in the gas phase and various solvents were also performed based on DFT-B3LYP/6-31+G* method. Overall, the cis-to-trans isomerization is predicted to take place through rotation around the N(1)=N(2) bond. Furthermore, the calculated energy barriers are found to be influenced by the size and electronic character of the cyclic amine, the electronic character of the phenyl ring substituent, and the polarity of the solvent, consistent with the effects obtained experimentally from the kinetic studies.