Our effort to provide an efficient route to serine glycosides with utility in glycopeptide synthesis has led to the identification of two particularly effective promoters of O-glycosylation. Indium(III) bromide and scandium(III) triflate were shown to be superior promoters of microwave accelerated O-glycosylation utilizing peracetyl carbohydrate donors. 247, 249 These Lewis acids afforded several advantages over previously described promoters including, increased yields, tolerance to moisture, decreased environmental toxicity, ease of work up, and increased reproducibility. Both affected the microwave accelerated glycosylation of Fmoc-ser-OH with sugar peracetates providing superior yields to previously reported methods. For larger scale work the two step route involving the glycosylation of Fmoc-Ser-OBn followed by removal of the benzyl protecting group via hydrogenolysis was preferred. Of the two Lewis acids, the minimally active indium (III) bromide was preferred, as it afforded slightly higher yields and was effective in catalytic quantities. Three groups of helical DAMGO glycopeptide analogs were synthesized in order to provide a better understanding of the structure activity relationships of these opioid peptides. Although the introduction of the amphipathic helix significantly affected binding of the DAMGO message, there was no correlation between binding affinity at the individual opioid receptors and the degree of helicity. In general, addition of the helical address imparted increased affinity for the kappa receptor. The nature of the linker connecting the N-terminal DAMGO sequence and the C-terminal helical address effected binding affinity only slightly. Successive addition of positive charges to the address increased binding at all three opioid receptors until a maximum was reached at a positive two address charge. Although, the amphipathic helix was shown to moderate receptor selectivity, the native mu preference of the DAMGO message was retained Two groups of fluorescent analogs of the mixed δ / μ opioid agonist MD100 were prepared. Within the first series, the fluorescent label was attached to the interior of the address sequence employing the pNZ moiety as a secondary protecting group. The second series of analogs was based on NovaTag™ resin, and allowed for attachment of the fluorophore at the carboxy terminus. The influence on helicity imparted by fluorophore conjugation depended on the nature and point of attachment of the label. The disruption of secondary structure associated with attachment of the fluorescent correlated with decreased binding affinity at the individual opioid receptors. Preliminary in vivo results were encouraging. The least parent like of the MD100 fluorescent analogs was shown to be taken up into endothelial cells. This suggests that the labeled glycopeptides are likely to cross the blood-brain barrier.

No description available.

No description available.

Suwannee River fulvic acid (SRFA) and humic acid (SRHA) were used as dissolved organic matter (DOM) and were applied to probe the effect of DOM. Addition of DOM resulted in decreased first order rate constants for all species selected. The inhibition became more significant as the hydrophobicity of the species increased. The decrease could not be simply attributed to the binding of hydrophobic species to DOM. This can be explained by the physical isolation of iron (II), which binds to hydrophilic sites of DOM and is the hydroxyl radical generation site, from hydrophobic pollutants which bind to hydrophobic sites of DOM. Accordingly, species which could compete agains t this physical isolation by DOM and bring iron (II) closer to target species could increase the degradation rates. This was observed with application of carboxymethyl-ß-cyclodextrin (CMßCD). Effects from concentration, structure of the target species and acidity etc., were studied. The increased degradation rates were observed even in the presence of DOM. Studies on ternary complexes of hydrophobic pollutants, iron (II) and CMßCD were carried with ESMS, UV and Fluorescence experiments and further calix[6]arene derivatives. Along with the fact that CMßCD can increase the solubility of hydrophobic species and remove them from contaminated sites, this indicates a potential application to in-situ degradation systems. Initial two -phase studies were carried out with quartz sand deposited with polycholobiphenyl (PCBs) and polycyclic aromatic hydrocarbons (PAHs). Successful degradations were observed with PCBs but not PAHs. The difference is attributed to the slow equilibrium of sorbed PAHs with dissolved CMßCD and the higher PAH loading used in these experiments. A halide sensor-molecule (1, 8-diphenylureaylnaphthalene), which performs with increasing fluorescence in the presence of fluoride and decreasing fluorescence with all other halides, was synthesized and reported. Studies using NMR and computer modeling with SPARTAN were carried out to compare the sensor-molecule with an analog, 2, 3-diphenylureaylnaphthalene. Both studies indicated that only fluoride can be accommodated in the space between the urea group protons to form a strong interaction. The sensor-molecule could to lead to improved sensors that overcome limitations with current fluorescence-quenching based anion sensors.

Faculty of Science School of Chemistry 0100505x jzeevaart@csir.co.za / The application of homogenous transition metal catalysis to the arylation of enolates to develop new synthetic procedures which are more environmentally benign, atomefficient and economically viable than current methods was the motivation behind the current work. The specific choice of molecules with an aromatic group in the a- position of a ketone, carboxylic acid, amide or other electron-withdrawing group arose from the fact that many natural products, pharmaceutical actives and synthetic intermediates contain such a substructure while the syntheses of these substructures are often cumbersome. The application of homogenous catalysis to various types of enolates was explored and in the process several developments were achieved and discoveries made. These included the use of inorganic bases under phase transfer conditions for the Heck reaction of acrylic acid as well as the synthesis and application of phosphine and phosphite ligands in the Heck reaction of acrylic acid esters. The successful use of low palladium loadings (as low as 0.01mol%) in the arylation of diethyl malonate using aryl chlorides and the application to the synthesis of ketoprofen and phenobarbital was demonstrated. The novel application of palladium catalysis to the arylation of methanesulfonamides and the first example of a bromoindole derivative as the aryl halide partner in an enolate arylation reaction was demonstrated. Ligand-free palladium catalysed phenylation of pinacolone followed by Baeyer Villiger oxidation led to a proposed novel synthetic route to tert-butyl esters of 2-arylacetic acids. The palladium and copper catalysed arylation of acetoacetate esters, with in situ decarbonylation, provided a different route to 2-arylacetic acid esters which are useful in the preparation of non-steroidal anti-inflammatory compounds.

Halide perovskite solar cells, with rapid efficiency improvements from ~10% to ~23% in 6 years, have attracted significant attention due to their remarkable performance, low processing cost and their potential to become a strong alternative candidate to silicon solar cells. Significant development has also been achieved in halide perovskite-based LEDs with EQE improved from below 1% to ~20% in less than 4 years. This remarkable progress can mainly be attributed to the optimisation of halide perovskite properties. This dissertation focuses on the correlation between optical and electrical properties of halide perovskites and their remarkable performance. Bandgap tunabilities of halide perovskites in blue to green regions through mixing Br-and Cl-and in near infra-red region by substituting Pb2+ with Sn2+ are demonstrated. The absorption and PL spectra are consistent with each other supporting the bandgap tunability. Corresponding EL spectra, which are consistent with their PL spectra, are also demonstrated for blue to green regions. Terahertz measurements coupled with PLQE and transient PL results reveal that the high carrier mobilities are the main reason behind the high efficiency of tin-rich samples. A novel perovskite-polymer-bulk heterostructure is introduced and studied comprehensively. Correlations between their optoelectronic properties and remarkable performance on timescales ranging from femtosecond to microsecond are presented. Transient optical spectroscopy reveals the energy transfer from 2D regions to 3D regions happens in 1 ps. The 20% EQE of the LEDs based in this structure is consistent with conventional thin-film optical models giving internal quantum efficiency of ~100%. This in agreement with near-unity PLQE value of the pristine emissive layer material and the dominant bimolecular recombination process observed in nanosecond-scale transient PL measurements. Two typical interfacial engineering methods to improve the quality of halide perovskite and device performance are then presented. Optimised NiOx is adopted to improve the anode interface. From transient photovoltaic measurements, we find the charge collection ability of NiOx is superior to that of PEDOT:PSS. This is also the main reason behind their better photovoltaic device performance. A unique anti-solvent treatment with additive modifies both the bulk and surfaces of halide perovskites and improves the device performance significantly. Transient PL and PLQE measurements demonstrate that non-radiative recombination pathways are significantly reduced.

This thesis investigates the relevance between the acoustic resonance and power harmonics on a metal halide lamp. First, a sinusoidal current ranging from 20 kHz to 400 kHz is used to drive a 70 W metal halide lamp. Second, a hybrid-current test circuit is designed to generate a current waveform consisting of a low-frequency square-wave and a high-frequency sinusoidal wave. Both of the frequency and the amplitude can be adjusted independently. The test lamp is deliberately driven at its acoustic-resonance eigen-frequencies to observe the effect of the power spectrum on the degree of the acoustic resonance. The experimental results indicate that the occurrence of acoustic resonance is indeed affected by the DC level and related power harmonics. The power harmonic spectrum that elucidates the initiation of acoustic resonance is deduced from the observations. It is found that the power harmonics that excites acoustic resonance can be divided into three categories. The first is independent of the average lamp power; it excites acoustic resonance only if the magnitude of its power exceeds a specific level. The thresholds of power harmonics belong to the second category are proportional to their DC powers. One can also find those remaining power harmonics belong to the third category. The power harmonic spectrum of the acoustic resonance is demonstrated by driving the test lamp with quasi-square-wave and triangle-wave currents. This work helps advance the understanding of the phenomena and mechanism of acoustic resonance in a metal halide lamp.

Conventionally, metal halide lamps were ignited by striking the lamp electrodes several times with high voltage pulses. Such a starting scenario causes uncomfortable light strobes to users. To solve this problem, this thesis attempts to ignite small-wattage metal halide lamps with a single pulse strike. At first, the forms of the high voltage pulses required for breaking down the electrodes are investigated. After being broken down, a continuous current is critical for sustaining the lamp arc. With conventional electronic ballasts, however, the lamp current tends to resonate to zero resulting in break of the lamp arc. This problem can be solved by adding an extra switch to remove the capacitor of the output filter during the ignition stage. An electronic ballast is designed and tested on 70 W metal halide lamps with an associated switch for single pulse striking. Experiments have demonstrated that the proposed ignition criteria can start up the lamps successfully with a single-pulse high voltage.

This study investigates the starting characteristics of metal halide lamps. A laboratory electronic ballast was built to drive metal halide lamps with a programmable low-frequency square-wave current. The lamp current at each stage of the starting transient can be independently adjusted. Experiments were conducted on 150-W metal halide lamps. By examining the waveforms of transient voltage, current and power, the starting period can be classified into four stages, breakdown, glow discharging, glow-to-arc transition, and thermal equilibrium. In addition, the stable operation is defined by observing the variations of the lamp arc, lighting spectrum and luminous output. Based on the investigation results, four starting scenarios are presented and examined to learn the different acceleration schemes. Experimental evidence shows that the starting time of a metal halide lamp can be effectively shortened by increasing the lamp current during the start-up transition. More importantly, a specifically-regulated operating power enables the lamp to further enhance the luminance producing, and hence to greatly reduce the starting transient period.

The research searches for an identification strategy which is able to recognize three small-wattage metal halide lamps rated at powers of 20-W, 35-W and 70-W from three world-wide prominent brands of GE, OSRAM and PHILIPS. A two-stage constant-power starting scenario is adopted to successfully start all three kinds of lamps without causing a tremendous power during the identification process. At the first stage, the tested lamps are started by a constant power of 25 W. The 20-W lamps can be distinguished from the others by their relatively high lamp voltages at the 30th seconds after being ignited. Then, the other lamps are driven up to 35 W to manifest the voltage difference of between the 35-W and 70-W lamps, and thus can be recognized at the 40th seconds. After being made out, the lamps are operated at their rated powers. Eventually, a verification checking with protection is introduced to prevent the tested lamps from over power operation. Experiments have been done on numerous new and aged lamps. The experimental results evidence that the electronic ballast with the proposed identification strategy can recognize three lamps¡¦ rated powers correctly during the starting transition, and drive the lamp to its rated power before entering the steady-state.