The development of single-molecule and super-resolution fluorescence techniques has revolutionised biological imaging. Nano-scale cellular structures and heterogeneous dynamic processes are now able to be visualised with unprecedented resolution in both time and space. The achievable localisation precision and therefore the resolution is fundamentally limited by the number of photons a single-fluorophore can emit. The ideal super-resolution dye would emit a large number of photons over a short period of time. On the contrary, an optimal single-molecule tracking probe would be highly photostable and undergo no transient dark-state transitions. Single-molecule instrument development is beginning to reach technological saturation and as the frontiers of bioimaging expand, exorbitant demands are placed on the gamut of available probes that often cannot be met. Thus, the next key challenge in the field is the development of the better fluorophores that underlie these techniques; this includes both the synthesis of new chemical derivatives and alternative novel strategies to augment existing technologies. The results of this thesis are divided into two distinct parts; Project One details the development of new synthetic fluorescent probes for the study of amyloid protein aggregates implicated in neurodegenerative diseases. This includes a study of the photophysical and binding properties of a novel fluorophore library based on the amyloid dye Thioflavin-T. Following on from this, is the presentation of novel bifunctional dyes capable of simultaneously identifying hydrogen peroxide and amyloid aggregates by combining existing tools for the independent detection of these species. The sensing capabilities of these dyes are explored at the bulk and single-molecule levels. Project Two describes a new photo-modulatable fluorescent-protein fusion construct that can undergo Förster resonance energy transfer (FRET) to an organic dye molecule. This FRET cassette is comprised of a photoconvertible fluorescent protein donor, mEos3.2 and acceptor fluorophore, JF646. This strategy imparts a strong photostabilising effect on the fluorescent protein and a resistance to photobleaching. The functionality of this approach is demonstrated with in vitro single-molecule fluorescence studies and its biological applicability shown by tracking single proteins in the nuclei of live embryonic stem cells. Furthermore, initial characterisations of the excited state dynamics in effect are presented through the systematic modification of parameters.

Faculty of Science School of Chemistry 9800165e govendor@aurum.wits.ac.za / Pyranonaphthoquinones are biologically important molecules found in a wide variety of bacteria, microbial fungi and plant species. Their biological activity is proposed to be a consequence of their ability to function as bioreductive alkylating agents. This class of compounds, which include monomeric and dimeric examples, contain the basic naphtho[2,3-c]pyran-5,10-dione skeleton, usually with substituents at the C-1 and C-3 positions of the pyran ring. The aim of the first part of the project was to develop a novel method for the synthesis of enantiomerically pure 5,8-dimethoxy-isochroman-4-ol, which will provide a handle for stereoselectively adding substituents to the C-1 and C-3 positions of the pyran nucleus. In the second part of the project we wished to attempt to synthesize the naturally occurring compound, cardinalin 3, the dimer of ventiloquinone L previously synthesized in the Wits laboratories. The synthesis of the enantiomerically pure isochromanol began with 2,5-dihydroxybenzoic acid, which was subjected to a diallylation followed by a Claisen rearrangement. The phenols were protected by a methylation reaction and the ester moiety was reduced to give (2-allyl-3,6- dimethoxyphenyl)methanol. It was then allylated to produce a suitable precursor for a one pot/two step ruthenium mediated isomerisation/ring closing metathesis reaction to produce 5,8-dimethoxy-1H-isochromene in an overall yield of 47%. It was converted to racemic 5,8-dimethoxy-isochroman-4-ol through a hydroboration-oxidation reaction in a yield of 84%. The separation of the enantiomers was achieved by acetylating the alcohol to form 5,8-dimethoxy-3,4-dihydro-1H-isochromen-4-yl acetate and then a lipase enzyme was used to stereospecifically deacetylate one enantiomer, while leaving the other enantiomer untouched. The second part of the dissertation discusses the progress towards the synthesis of cardinalin 3. This project began with the formation of the C-C biaryl axis starting from 1,3-dimethoxybenzene. The synthesis then continued with the diformylation of the biphenyl to give 2,2’,6,6’-tetramethoxy[1,1′-biphenyl]-3,3′-dicarbaldehyde. This was subjected to a Stobbe condensation and a Friedel-Crafts acylative cyclisation to produce diethyl [4,4′-diacetoxy-6,6′,8,8′-tetramethoxy-7,7′-binaphthalene]-2,2′- dicarboxylate. The synthesis will be continued in the PhD, using methodology previously developed for the formation of the monomer, as well as methodology developed here.

The primary purpose of this thesis was to assess the effects of a short verses long-term social skills training program on (a) enhancing adolescent and parent social skills, while Cb) reducing conflict and distress and enhancing warmth and cohesion. A modified pretest - posttest control group design was employed wherein the control group for the first experiment became a portion of the experimental group for the second experiment. The sample consisted of ~3 parent-adolescent dyads who volunteered to participate. Of those, 25 met the minimum criteria for being included in the analysis, 18 dyads from the experimental group and 7 from the control group. Results demonstrated that while the parents did perceive an improvement in skills assessed by the PARI sub-scores , the adolescents did not. Nonetheless, the findings demonstrated that the long-term program of one skill learned every week far eight weeks was mare effective than the concentrated one- week program of two skills learned per night far four nights.

Graduation date: 2003

The computation of texture and of stereoscopic depth is limited by a number of factors in the design of the optical front-end and subsequent processing stages in humans and machines. A number of limiting factors in the human visual system, such as resolution of the optics and opto-electronic interface, contrast, luminance, temporal resolution and eccentricity are reviewed and evaluated concerning their relevance for the recognition of texture and stereoscopic depth. The algorithms used by the human brain to discriminate between textures and to compute stereoscopic depth are very fast and efficient. Their study might be beneficial for the development of better algorithms in machine vision.

One of the key challenges in face perception lies in determining the contribution of different cues to face identification. In this study, we focus on the role of color cues. Although color appears to be a salient attribute of faces, past research has suggested that it confers little recognition advantage for identifying people. Here we report experimental results suggesting that color cues do play a role in face recognition and their contribution becomes evident when shape cues are degraded. Under such conditions, recognition performance with color images is significantly better than that with grayscale images. Our experimental results also indicate that the contribution of color may lie not so much in providing diagnostic cues to identity as in aiding low-level image-analysis processes such as segmentation.

Thesis (M.Sc. (Pharmaceutical Chemistry)--Potchefstroom University for Christian Higher Education, 2002.

Thesis (J.S.D.)--Stanford University, 1997. / Includes bibliographical references (leaves 101-105). Also available online.

Most of the 500 extra-solar planets detected to date have been discovered either by radial velocity measurements or photometric transits but very few by direct techniques. Direct imaging of exoplanets, however, gives access to a wider variety of information on the planet, from its orbital position to its spectrum, but is a difficult task to achieve because of the small angular separation between the star and its planet and the large flux ratio between them. For these two reasons, direct imaging of exoplanets has up to now been limited to the most favorable cases of bright giant exoplanets orbiting at large distances from their host stars. %The present work aims at developing the high dynamic range capabilities of single- and multi-aperture imaging techniques for the detection and characterization of planetary systems. The first part of this work reports studies of adaptive optics-aided ground-based telescopes and their complementarity with space-based facilities for the detection of extra-solar planets. Results obtained with the Well-Corrected Subaperture at Palomar observatory on narrow multiple systems are then used to illustrate this study. The second part of this work is dedicated to stellar and nulling interferometry. We first present a new data reduction technique for interferometry using the statistical distributions of the noise sources to significantly improve the precision of interferometric measurements. This technique is then applied to the Palomar Fiber Nuller instrument at Palomar observatory to constrain the presence of dust and companions in the innermost regions of Vega's stellar environment and to derive stellar angular diameters with very high accuracies. Finally, we introduce an on-going survey that we are pursuing with the AMBER interferometric instrument at the Very Large Telescope (Cerro Paranal, Chile) aiming at detecting sub-stellar companions around young main sequence stars.

The objective of this study was to explore the link between school climate and bullying behaviour through a case study of two high schools. Grade 10 students received the two day Cross-Cultural Conflict Resolution (XCCR) Module initiated by YOUCAN. Phase I of this study involved the development of an XCCR Logic Model, which aimed to clarify the objectives and key elements of the XCCR Module. Phase II involved the in depth analysis of the XCCR Module through an 84-item survey and qualitative semi-structured interviews with school and program staff. Data from this study did not indicate any changes in bullying behaviour or school climate between pre-and post-implementation. This study highlights a need to incorporate measures for program adherence and program fidelity in future studies. The results of this study provided two practical contributions, an XCCR Logic Model and information about bullying and school climate for the participating schools.