>Magister Scientiae - MSc / HIV and AIDS are among the world's pandemics that pose serious concern to almost every individual in the world. With the current level of availability of anti-retroviral (ARV) drugs and the ease of accessibility of treatment in many countries such as South Africa, the disease can be controlled by suppressing the viral load of an infected individual. These anti HIV drugs such as delavirdine are metabolised by enzymes which are found in the liver microsomes, particularly those of the cytochrome P450 family. Due to the fact that the metabolic rate of a patient determines the effect of the drug, the drug could either have a beneficial or an adverse effect once it is administered. It is therefore imperative that the metabolic profile of a patient is determined at point-of-care is necessary for proper dosing of the ARV drugs. In this project a nanobiosensor system was devised and used for the determination of the metabolism of delavirdine, a non-nucleoside reverse transcriptase inhibitor (NNRTI) ARV drug. The nanobiosensor was prepared by the entrapment of the isoenzyme CYP3A4 into a pre-formed electro active carrier matrice consisting of a dendrimeric copper generation-2 poly (propylene imine)-co-polypyrrole star copolymer (Cu(G2PPI)-co-PPy). The metallo-dendrimer was used as a host for the enzyme and provided thenecessary bio-compatible environment that allowed the direct transfer of electrons between the enzyme's active centres and platinum electrode surface. Copper was the choice of metal used in the study due to its properties. Copper is a malleable, ductile and a good conductor of both heat and electricity. It is a better conductor than most metals. Silver which also belongs to group 1b in the periodic table is a better electrical conductor than copper but copper has better corrosion resistance and is a more abundant and hence it is a cheaper material to use. Cu(G2PPI)-co-PPy was prepared by the incorporation of the copper metal into the G2PPI and the electropolymerization of pyrrole onto the Cu(G2PPI). The incorporation of Cu into G2PPI was determined by FTIR which did not show the presence of the Cu but showed an increase in the intensities of the peaks after the incorporation. The surface morphology of Cu (G2PPI) was confirmed by the use of HRSEM which showed a difference in the surface morphology of the dendrimer moiety with the addition of the copper metal. The HRSEM images after Cu incorporation resulted in the change from rough surface to smooth surface with open cavities which were essential for the entrapment of the biological systems (CYP3A4). Energy dispersive spectrometry (EDS) and HRTEM were used to confirm the presence of spherically shaped copper nanoparticles in the Cu (G2PPI) and were found to have a size distribution of 12-17 nm with an average particle size of 15nm. The star copolymer (Cu(G2PPI)-co-PPy) was characterised using cyclic voltammetrywhere it was confirmed that the material was electroactive and conducting due to electron movement along the polymer chain. A diffusion co-efficient (D₀) value of 8.64 x 10⁻⁵ cm²/s was determined for the material indicating a slow electron transfer kinetics within the diffusion layer. The constructed nanobiosensor was developed using copper poly (propylene imine) – polypyrrole star copolymer, bovine serum albumin and glutaraldehyde coupled to the enzyme CYP3A4. The resultant nanobiosensor parameters include a dynamic linear range (DLR) of 0.01-0.06 nM, a limit of detection (LOD) of 0.025 nM and a sensitivity value of0.379 μA/nM.

Cyclic dipeptides have been widely used as pharmaceutical agents due to their favourable properties and the fact that they are more stable and membrane permeable than their linear analogues. These characteristics make cyclic dipeptides attractive to protein-based drug developers (Martins & Carvalho, 2007). In this research study, the method of Milne et al. (1992) was used to synthesize the protected linear dipeptide esters. This was followed by boiling the unprotected, linear dipeptide esters under reflux in an oil bath (Sec-butanol: toluene (4:1)). This method gave good yields and pure cyclic dipeptides. Scanning electron microscopy, thermal analysis, X-ray powder diffraction and differential scanning calorimetry were used for evaluation of the physiochemical properties of the cyclic dipeptides. High-performance liquid chromatography and thin layer chromatography were used to determine the purity of the cyclic dipeptides. The structures of the cyclic dipeptides were elucidated using infrared spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy and molecular modeling and computational chemistry. The aim of the study was to determine the possible therapeutic activity of cyclo(D-Phe-4I-Pro) and cyclo(L-Phe-4I-Pro) with regard to antimicrobial, anticancer, antidiabetes and haematological effects. Both cyclic dipeptides showed a significant growth inhibition of Gram-positive, Gram-negative and fungal microorganisms in the antimicrobial study. Anticancer studies showed that both cyclic dipeptides caused growth inhibition of the MCF-7, HT-29 and HeLa cancer cell lines. Both cyclic dipeptides showed no antidiabetic activity. Haematological studies revealed that both cyclic dipeptides caused a significant effect on the clotting time and platelet aggregation. They caused an increase in clotting time and also inhibited platelet aggregation.

Cyclic dipeptides have limited conformational freedom due to their diketopiperazine backbone and their small size. They are relatively simple to synthesise, making them ideal subjects for investigation into their biological effects. Cyclic dipeptides have also been known for their multitude of biological activities, including antimicrobial, anticancer and haematological properties. In this study the cyclic dipeptides, cyclo(Phe-4Cl-Pro) and cyclo(D-Phe-4Cl-Pro), were synthesised from their corresponding linear precursors using a modified phenol-induced cyclisation procedure. The phenol induced cyclisation procedure resulted in good yields and purity of the cyclic dipeptides. Quantitative analysis and evaluation of the physiochemical properties of the cyclic dipeptides was achieved using high-performance liquid chromatography, scanning electron microscopy, thermal analysis and X-ray powder diffraction. Structural elucidation of the cyclic dipeptides was done by means of infrared spectroscopy, mass spectroscopy, nuclear magnetic resonance spectroscopy and molecular modelling. The study‟s aim was to determine the biological activity of cyclo(Phe-4Cl-Pro) and cyclo(D-Phe-4Cl-Pro) with respect to their anticancer, antimicrobial, haematological and ant-diabetic studies. Anticancer studies revealed that cyclo(Phe-4Cl-Pro) and cyclo(D-Phe-4Cl-Pro) inhibited the growth of HeLa (cervical cancer), HT-29 (colon cancer) and MCF-7 (breast cancer) cancer cell lines. Both cyclic dipeptides also inhibited the growth of certain selected Gram-positive, Gram-negative and fungal microorganisms in the antimicrobial study. Although the inhibition of growth in the anticancer and antimicrobial studies was statistically significant, the clinical relevance is questionable, since the inhibition produced by both cyclic dipeptides was very limited compared to other pre-existing anticancer and antimicrobial agents. Both cyclic dipeptides caused a significant shortening of the APTT and PT clotting times and an increase in the fibrin and D-Dimer formation. Cyclo(D-Phe-4Cl-Pro) at a screening concentration of 12.5 mM and 3.125 mM, showed significant anti-platelet activity. Both cyclic dipeptides failed to produce any inhibition of the α-Glucosidase enzyme and very limited inhibition of the α-Amylase enzyme.

Investment into offshore wind farms has been growing to address the growing threat of climate change. The majority of offshore wind turbines (both current and planned) are founded on monopiles, large circular steel pipe piles ranging from 4.0 m – 7.5 m in diameter. Based on available borehole records, most planned wind turbines in the UK will be founded in overconsolidated clay deposits. Monopile design is done via usage of the well established p-y curves. However, there are issues with the usage of the p-y curves. Firstly, the curves may be unsuitable to model the monopile’s behaviour as it is expected to behave similarly to a rigid pile rather than flexibly. Secondly, the curves may not accurately estimate the initial pile-soil stiffness. Thirdly, the curves are not comprehensive enough to account for the accumulated strain and stiffness changes resulting from cyclic loading. Considering these issues, research was carried out to improve the current design of monopiles in clay by carrying out displacement controlled monotonic and load controlled cyclic load tests in a centrifuge. Results from monotonic tests suggest that the DNV (2014) design methodology to construct p-y curves in clay based on Matlock’s (1970) soft clay criterion significantly underestimate stiffness. Findings suggested that the experimental p-y curves could be characterised through modification of the criterion. Modification of the criterion produced estimates that matched the 3.83 m monopile experimental curves. Pile toe shear force was observed to contribute little to ultimate lateral resistance and stiffness. Despite the marginal contribution, an effort was made to characterise the pile toe shear force. Estimates of the modified criterion on the 7.62 m monopile did not match the observations, indicating that further research should be carried out to improve the modified criterion. The cyclic tests displayed two distinct regimes; the stiffening regime and the softening regime. Results suggests that cyclic loads of different characteristics influence the locked in stress conditions of the soil which in turn influence the excess pore pressure behaviour, hence dictating whether the stiffening or softening regime takes place. Suggestions were made regarding the conditions that dictated whether the stiffening or softening regime would take place. In the stiffening regime, the stiffening rate decreased with increasing strain while as the accumulated rotation rate increased with vertical load for the same cyclic load magnitude. The softening regime was determined to be extremely detrimental as the high rates of softening and accumulated rotations could cause failure of the system in the short-term. Recommendations were made to estimate the cyclic stiffness and accumulated rotations resulting from both stiffening and softening regime.

No description available.

The Gilman's cyclic AMP binding assay was used to examine the possibility of adopting this method for adenylate cyclase determinations. Cyclic AMP determinations were not invalidated by the reagents used in the adenylate cyclase reaction. Cyclic AMP measured by the binding assay was directly proportional to adenylate cyclase activity. Although variability in recovery of cyclic AMP was obtained, it could be reduced by performing triplicate assays. Thus, the cyclic AMP binding assay, with some reservations, would appear applicable for measuring adenylate cyclase activity. Adenylate cyclase in rat brain was studied by using the cyclic AMP binding method for determination of product formed. Rat brain cortex was fractionated by the method of Whittaker. The highest adenylate cyclase activity was found in the fraction containing the highest acetylcholinesterase activity, and this fraction was shown by electronmicroscopic studies to be rich in synaptosomes. A modified sucrose gradient was used for isolating satisfactory synaptosomal fractions (the layer between 1.0 M and 1.1 M sucrose). Properties of synaptosomal adenylate cyclase were examined. The enzyme was dependent on the concentrations of ATP and Mg²⁺ or Mn²⁺ ion. The enzyme was stimulated by fluoride and inhibited by calcium ion. Synaptosomal adenylate cyclase was not sensitive to catecholamines or adenosine. No hormonal stimulation was obtained in the presence of GTP. In experiments where the effects of endogenous catecholamines were reduced by the addition of α and β adrenergic blocking agents or by prior treatment of the animals with reserpine, hormonal stimulation of adenylate cyclase in particulate preparations could not be demonstrated. / Medicine, Faculty of / Anesthesiology, Pharmacology and Therapeutics, Department of / Graduate

Spinal cord injuries (SCI) are characterized by the inability of mature neurons to regenerate or repair by themselves. In an attempt to overcome the SCI, a novel photo-sensitive cyclic Arg-Gly-Asp-Ser (RGDS) peptide was synthesized using solid phase peptide synthesis (SPSS) to control 3T3 fibroblast cell attachment on hyaluronic acid (HA) hydrogel. The circular RGDS peptide was designed using RGDS sequence labeled with Anp group (3-Na-fmoc-amino-3-(2-nitrophenyl) propionic acid) at the N terminus. The peptide was photo-labile cyclic caged to shelter its bioactivity and UV light was used to make the peptide uncaged. Accuracy of the cyclic caged RGDS peptide was confirmed by high-performance liquid chromatography (HPLC) and mass spectrum (MS). The molecular weight of cyclic caged RGDS peptide was confirmed as 881 by matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrum. Stability of the cyclic caged RGDS peptide under various pH conditions was verified by circular dichroism spectroscopy. The bioactivity of cyclic caged and uncaged RGDS peptide was tested by photo-controllable directing cell growth based on cell attachment study, cell counting study, and cell morphology study. Three dimensional model structures of cyclic caged and uncaged RGDS peptides were computed by Hyperchem program. The first order reaction theory of Anp uncaging reaction was confirmed by kinetic study. Bioactivity caging and uncaging property of the peptide was also fully confirmed by cell attachment study. This cyclic caged RGDS peptide would be a promising tool in cell patterning for repairing of SCI.

At an early age, i.e., up to about 1-2 years, humans learn to walk and subsequently develop a robust and flexible gait. This is learned by repetitively taking similar steps and the experience is stored in the muscle/reflexive memory. Over the last 30 years, a variety of humanoid bipedal robots have been developed to copy the human gait. However, walking/locomotion is still a relatively difficult control problem due to its complex hybrid nature because of non-smooth dynamics. Although, simple walking comprises of single support in which one leg swings forward, then it impacts with ground for a brief double support phase and further transition of the other support leg to start a new swing. The steps are repeated again and again in a similar manner for walking over an even surface. As the swinging leg strikes the ground, it is a non-linear impact which poses a challenge since it causes non-zero initial state errors for each step which depend on the error in the gait at last moment for previous step. The usual bipedal control relies on complex techniques based on inverse kinematics, ZMP (Zero-Moment Pole) and COP (Centre Of Pressure) to generate the required control inputs for the joints. However, a basic cognitive assumption is that walking is a relatively simple task which can be learned and the biological systems have achieved it by simple repetitions. This has been over-looked in these control techniques. In the past, ILC has been proposed to solve the repetitive learning problems. The Iterative Learning Controller learns to generate the desired set of input signals to compensate for the output tracking errors in a sequential manner such that in the initial iterations, the signals values at earlier time indices have faster rate than the later ones. So, at the last time index the convergence is achieved after all the earlier ones. ILC learns/adapts the joint control for repetitive gaits. In this thesis it has been proposed to be used as a muscle memory where control signals are learnt for a repetitive batch. Thus, ILC equates to “learning a sequence of action by muscles”. Due to the transfer of state error in a cyclic manner from the end of a previous step/repetition to the recent step/repetition, the convergence has to be established in joint control and state space. Similar is the case of continuous walking where the ground impacts transfer part of the error in the gait to the start of a new step representing an impacting Cyclic ILC scenario. Hence, the ILC problem is changed from finite to an infinite horizon. The second problem occurs with the non-constant length of the iteration due to change in step size. The two scenarios have been considered: Firstly, when the control input is updated using ILC with identical initial conditions at the start of each repetition. Secondly, control input update under varying initial conditions leading to Cyclic ILC. The batch to batch evolution of control inputs at each sample time within a batch is formulated. The sequential convergence of control input generated by ILC algorithms has been investigated. The exact relationship for the rate of convergence of the control input has been formulated down to the sample-time level. This provides deeper insight about the ILC algorithms and hence exact factors affecting the convergence could be established. Limits of the learning process have been clearly demonstrated as well. Although, simpler D-ILC converges for zero initial error but for cyclic non-zero initial errors, it has offset error which corresponds to the initial state error. With proportional part, the PD-ILC algorithm has eliminated the offset error which has been illustrated for a damped pendulum and further implemented to bipedal locomotion. For reasons of energy efficiency, passive dynamics has been chosen for the compass gait model of the biped. The walking problem for the compass gait robot has been solved using the modified PD-ILC which utilizes the acceleration error term as well. The steady gait has been achieved for the compass gait robot on flat surface which has been verified by the phase portraits.

The cyclic wetting and drying of a rock is considered to be one of a number of physical weathering processes that have an effect on the weathering of rock. While the presence of moisture is known to be of critical importance for the activation and enhancement of a number of other known weathering processes, such as cryogenic weathering, salt weathering and slaking it is possible that the mere cyclic application and removal of moisture over time may also have an effect on the physical structure of a rock. The precise nature of the process is not well understood, however. This document begins by investigating the studies that have previously been undertaken to determine how the wetting and drying weathering process is defined and to ascertain the current state of knowledge regarding this process. After an establishment of background context, a physical experiment is carried out on Clarens Formation sandstone and Marion Island basalt to note the relationship between cyclic wetting and drying and the changing physical properties of the rocks. The rocks were subjected to 105 wetting and drying cycles over a period of 21 weeks. At the beginning of the experiment, physical rock properties were measured by way of the method laid out by Cooke (1979) and again at the end of the experiment. Since the experiment was carried out under static environmental conditions, the comparison of physical rock properties gives a good indication of how the rocks have altered their structure over the experimental time period. The results obtained in this experiment show that different rock types will change in different ways when exposed to a common weathering process. The basalt samples experienced no mass loss at, while the sandstones did. The sandstones, which are rocks that are of common lithology and of very similar physical and chemical structure reacted to the wetting and drying weathering process in ways that could not be predicted without experimentation. The data does show a clear causal link between the application of external stimuli and rock property change, however. Changes in physical rock properties are not always straightforward and linear, but evolve dynamically over time, often yielding results that appear to oppose those intuitively predicted. A number of questions are asked regarding the philosophical approach that is taken to process isolation studies, with emphasis given to the careful consideration of the place that such studies have in the realm of process geomorphology. While process isolation studies may give an excellent indication of what a particular weathering process may be capable of under certain conditions and on certain rock types, they should not be regarded as indicative of what is occurring in the field. Additionally, it has become clear that it is not possible to predict how a specific rock type may respond to a specific weathering process without physical experimentation since the number of variables present in a typical weathering system are simply too vast to easily categorise. / Dissertation (MSc)--University of Pretoria, 2010. / Geography, Geoinformatics and Meteorology / MSc / Unrestricted

L'énergie électrique (de préférence d’origine renouvelable) peut être stockée dans des liaisons chimiques grâce à un électrolyseur approprié. Les réactions typiques comprennent la production d'hydrogène, la production d'hydrocarbures et la synthèse d'ammoniac. Ces électrocarburants permettent de faciliter l'intégration de sources d'énergie renouvelables dans le mix de production électrique. Ils sont compatibles avec l'infrastructure industrielle actuelle et la chaîne d'approvisionnement et peuvent être stockés facilement. En outre, ce procédé est à la fois un moyen de stocker l'électricité dans des liaisons chimiques (vecteurs énergétiques) et une technique de synthèse de composés chimiques à partir de matières premières comme le CO2 plutôt que de ressources fossiles.La thèse s’intéresse au développement de nouveaux catalyseurs moléculaires pour la conversion sélective du CO2 en CO en utilisant uniquement des matériaux abondants sur Terre, comme les porphyrines de Fer. Tout d'abord, les tentatives pour obtenir de nouveaux catalyseurs avec divers substituants sont détaillées. Une fois qu'un catalyseur hydrosoluble actif est identifié, une évaluation des performances est réalisée en utilisant des techniques électrochimiques telles que la voltammétrie cyclique / Electrical energy (preferably issued from renewable sources) can be stored in chemical bonds thanks to an appropriate electrolyzer. Typical reactions include hydrogen generation, the production of hydrocarbons and oxygenates, and ammonia synthesis. Such electrofuels supplement the integration of renewable energy sources in the electrical production mix; they are compatible with the current industrial infrastructure and supply chain, while they can be stored easily. Besides, they may be used either as a means to store the electricity in the chemical bonds of high-energy-content molecules or as various feedstocks to manufacture high value compounds.The thesis focused on the development of new molecular catalysts for the selective CO2-to-CO conversion in water using only earth-abundant materials, namely iron-based porphyrin derivatives. First, successful and unsuccessful attempts to derive new catalysts with various substituents are reviewed. Once an active water-soluble catalyst is identified, a performance assessment is completed using electrochemical techniques such as cyclic voltammetry investigations.Then, the immobilization of said catalysts onto the electrode surface is discussed. Once a robust integration in the catalytic film is secured, the coupling with a heterogeneous water-oxidation catalyst can be considered. The subsequent assembly of a whole electrolysis cell is reported, where a cobalt-based film was picked for the anode. Finally, economic perspectives provide a clear, rational basis for future optimization of the device