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Proton-transfer reactions are one of the most fundamental chemical reactions. However, the chemical dynamics of these processes remain elusive due to the difficulty of modeling these reactions. Establishing an experimental model system and using infrared absorption and two-dimensional infrared (2D IR) spectroscopies as means for detection, the chemical dynamics of the protonation states that are involved in a ground-electronic-state proton-transfer reaction in solution can be determined. In this study, experimental models are established with formic acid and nitrogenous bases in a low dielectric solvent. A hydrogen bond forms between the acid and the base, which will allow for the proton to transfer between the two molecules to form the neutral and the ion-pair protonation states. The carbon-deuterium (C-D) stretch and the carbonyl (C=O) stretch of the formic acid molecule are used as the reporter groups for the 2D IR measurements. The results of the C-D stretch demonstrate that there is a high sensitivity to the deprotonation, vibrational coupling, and vibrational dynamics trends that are linked to the solute-solvent interactions. The results of the C=O stretch demonstrate a sensitivity to the deprotonation and conformational disorder in which the position of the C=O changes the dynamics of the protonation state. Although, a proton-transfer is not detected, the experimental model system provides an understanding of the features that govern the chemical dynamics of proton-transfer reactions.

The present study was aimed at developing a new inexpensive and accurate analytical method for determining the glass content of slag and fly ash. Infrared absorption spectroscopy using an internal standard proved to be the method of choice. Both synthetic and commercial slags and fly ashes were investigated.

Articular cartilage helps in the motion of the diarthroidal joints by providing a near frictionless load bearing surface. Identification of changes in articular cartilage chemical and structural properties that arise from degeneration and suboptimal tissue repair have been the target of many studies. Current methods that evaluate these changes frequently involve destructive specimen preparation. Thus there is a need to develop a method to accurately evaluate changes in cartilage during disease or repair processes. Fourier transform infrared (FTIR) spectroscopy in the mid-infrared (MIR) spectral range is based on molecular vibrations and has been used to study the chemical and structural properties of biological tissues, including cartilage. However, this technique generally requires extensive sample preparation and modification of the intact tissue. An alternative approach is to use near-infrared spectroscopy (NIRS) which does not require sample preparation due to higher depth of penetration. This doctoral dissertation focuses on identification of NIR spectral features to evaluate the major components of cartilage. These NIR spectral features are then used to evaluate compositional changes in engineered and degraded cartilage, and the results validated with histological, biochemical, mechanical and MIR analysis of the same tissue. Together, these studies lay the groundwork for clinical and in situ applications of NIRS. / Bioengineering

Call number: LD2668 .T4 1966 P298 / Master of Science

Doctor of Philosophy / Department of Biology / Walter K. Dodds / Streams exist in a state of dynamic equilibrium with frequent floods and drought. The frequency and intensity of stream disturbances are projected to increase with greater water withdrawal for agriculture and biofuel production, watershed development, and altered climate. Changes in the hydrologic regime may alter stream ecosystems. I studied how stream communities return after disturbances and how nutrients, consumers, and substrata heterogeneity influence recovery trajectories. Large consumers were excluded from pools following a severe drought to assess how community structure and function returned in their absence. Large consumers reduced algal biomass, primary productivity, and nutrient uptake rates, and delayed macroinvertebrate recolonization. However, grazer effects were temporary and their influence weakened after five weeks. In a second experiment, I assessed the relative influence of grazer density and nutrient loadings on algal recovery from flood. Nutrients had a stronger effect on recovery than grazers, but the strength of each varied temporally. Grazer control decreased and nutrient control increased over time. A third experiment addressed the physical properties of stream substrata on algal development. The relationship among algal accumulation and substrata surface topography was assessed by growing algae on substrata with varying orientation and roughness. Total algal biomass decreased on surfaces with angles > 45 degrees, and peaked at an intermediate roughness (pit depth of [similar to]17 [Mu]m). Rougher surfaces collected more tightly attached (grazer resistant) forms and less loosely attached (grazer susceptible) forms. Individual algal forms responded differently to grazing pressure, nutrient availability, and surface features. I developed a method using Fourier-transform infrared microspectroscopy to measure single-cell physiological responses in benthic algae. Nutrients and consumers were strong regulators of ecosystem succession following disturbance, but nutrient influence was stronger. The influence of nutrients and consumers were context dependent, and changed over the course of recovery. Rougher surfaces increase algal growth and shifted algal assemblages to more grazer resistant forms, which may decrease the influence of large consumers on stream function. Altering the severity and frequency of disturbances can change the trajectory of stream recovery and ultimately change community composition and stream metabolic activity, which may alter ecosystem services such as water purification and recreation.

Vibrational and electronic absorption spectra of metal alloy molecules and small particles have been measured. The matrix isolation technique was used to produce the samples. Dissimilar metals were combined to provide far infrared vibrational activity. Through the study of the electronic and vibrational excitation spectra, metallic interatomic binding potential characteristics could be investigated. The absorption spectra of the molecular systems were modelled using the extended Hueckel method, for the electronic excitations, and a dynamical matrix-normal mode technique for the vibrational excitations. Surface plasmon absorption, from the metal alloy particles, could not be measured but surface phonon absorption was measured. Electronic and vibrational absorption lines in alloyed metal molecules were measured and compared to the calculations. A surface diffusion model was developed to explain the dependences of molecule and particle size on the experimentally controlled system parameters.

Thesis (MSc)--Stellenbosch University, 2004. / ENGLISH ABSTRACT: Please see fulltext for abstract / AFRIKAANSE OPSOMMING: Sien asb volteks vir opsomming

published_or_final_version / abstract / Botany / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Biological Sciences / Doctoral / Doctor of Philosophy