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The characterization of the interaction between Streptococcus pneumoniae PspC and Homo sapiens pIgR

  • Authors: Steyn, Sheldon
  • Date: 2019
  • Subjects: Streptococcus pneumoniae , Human evolution Microbiology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/44001 , vital:37091
  • Description: Streptococcus pneumoniae is a commensal bacterium in the human nasopharyngeal tract and is known to cause severe respiratory related diseases in humans. The pneumococcal surface protein C (PspC) has been demonstrated to interact with human polymeric immunoglobulin receptor (pIgR) and its free form secretory component (SC). S. pneumoniae utilizes the pIgR recycling mechanism to bypass the nasopharyngeal epithelial barrier of the host through the PspC-pIgR interaction. Studies have shown the YPT motifs in PspC R domains to be involved in this interaction (Hammerschmidt et al., 2000). The exact amino acid sequences in pIgR/SC have not yet been elucidated but Elm et al., (2004), Lu et al., (2003) and Venables et al., (2013) have demonstrated that Ig-like domains 3 and 4 of SC are mutually critical in this interaction. Mutagenesis studies were conducted to give insight into regions of these domains responsible for this interaction. In order to select possible candidates for mutagenesis, homology modelling, protein-protein docking and multiple sequence alignments were performed. PspC-SC interaction is human specific (Hammerschmidt et al., 2000) and the conservation between known species was used to select amino acids located on highly variable loop regions of the SC molecule. Amino acids Ser257, Asp312 and Gln373 were suggested by previous studies and investigated in this study. Protein-protein docking was performed with Cluspro 2.0 and Haddock 2.2 webservers. The docking results, coupled with conservation information resulted in Arg304 also being selected for investigation. Additional candidates were identified for future studies. Point mutations of the selected amino acids were introduced with overlap PCR and confirmed by DNA sequencing. The SC-D3D4 proteins were expressed in vitro and refolded by an on-column method developed by Venables et al., (2013). The Biorad ProteOn™ XPR36 protein interaction array system at Rhodes University was utilized for measuring the effects of the SC-D3D4 mutations on affinity for PspC-R1R2. The affinities of expressed SC-D3D4 mutants for PspC-R1R2 were compared to the wild type (WT) SC-D3D4 in concentration dependent kinetic analyses. The KD values for WT SC-D3D4 and Ser257, Arg304, Asp312 and Gln373 mutations were 1.4, 2.9, 4.1, 2.0, and 2.1 μM, respectively. It was concluded that these mutations had no impact on the affinity of SC-D3D4 with PspC-R1R2 and therefore probably excludes these four residues as interaction motifs for PspC.
  • Full Text:
  • Date Issued: 2019

The cultivation of Gracilaria gracilis in the Swartkops estuary, South Africa

  • Authors: Blewett, Alec
  • Date: 2019
  • Subjects: Gracilaria -- South Africa -- Port Elizabeth , Marine algae Algae -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/31446 , vital:31391
  • Description: Gracilaria gracilis (Stackhouse) M. Steentoft, L. M. Irvine & W. F. Farnham is a species of red macroalgae which occurs naturally within the Swartkops Estuary in South Africa. Bunches of the species were inserted into the lay of ropes, which were then either suspended in the water column at the Tiger Bay Marina, or staked at the surface of the sediment in the mudflats where the initial material was harvested from. The first site was used for the suspended growth trial, while the second site was for the bottom grown trial. Both of the growth trials ran for the same time period, which was approximately three weeks per season. This study examined three facets of the G. gracilis material that was grown. The growth rate and biomass were recorded in order to examine the potential for the growth of the species on longlines within the estuary. Secondly, the crude nutritional content of the species was determined in order to assess its potential for use as an abalone feed, specifically the dry and ashed weights, and the protein, carbohydrate and lipid contents. Lastly, the cultivated biomass was examined in terms of its agar gel yield and properties, which included the gel strength and the gel –melting and –forming temperatures. The growth rates for the cultivated G. gracilis were poor, and the largest positive growth rate of 1.17 ± 3.2% was found in spring, for the bottom grown trial. This season also saw the only increase in biomass above that which was seeded onto the line, and the final average weight after 22 days was 354.28 ± 68.04 g. All other growth rates were negative, and biomass declined in both growth trials across all the seasons. The suspended growth trials showed more extreme declines, and were heavily contaminated with epiphytic material, while the bottom grown trial had more gradual decrease, and it is likely that conditions associated with the culture systems were not ideal. The largest percentage of protein was found in autumn, where the bottom grown trial had a value of 88 ± 2.32%. For all the seasons, the lipid content had an average percentage of 1.80 ± 0.75% for the bottom grown trial, while the suspended trial was very similar, and had a value of 1.74 ± 0.58%. The nutritional composition of the cultivated biomass was not found to be a good abalone feed in comparison to other studies in land-based aquaculture facilities. Agar characteristics extracted in the present study showed the greatest potential for use as a valuable economic resource. The native agar extracted from the cultivated material was very close to the standards set by United States Pharmacopeia for all the characteristics, and has the potential to possibly be improved further by using an alkali treatment.
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  • Date Issued: 2019

The development of palladium nanoparticles for radiopharmaceutical application

  • Authors: Gandidzanwa, Sendibitiyosi
  • Date: 2019
  • Subjects: Nanotechnology , Nanostructures Nanofluids
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/42163 , vital:36631
  • Description: The dissertation describes an in-depth synthesis and optimisation of palladium(0) nanoparticles of three distinct size ranges, respective capping agents, and cellular uptake studies using a non-toxic concentration (10 μM), laying a foundation for the design of palladium-based folate receptor-targeted theranostic nanoradiopharmaceutical. In the preliminary selection to determine the optimal diamines for the study, ethylenediamine, hexamethylenediamine, 1,10-diaminodecane, 1,12-diaminododecane, 1,4- diaminobenzene, 4,4’-ethylenedianiline, 1,2-diphenyl-1,2-diaminoethane, and tetraaminophthalocyanine were employed. The characterisation of the nanoparticles obtained from the in situ reduction of palladium(II) salt at room temperature by either 1,2,3- trihydroxybenze (pyrogallol), citric acid, sodium metabisulphite, sodium borohydride, hydrazine hydrate, or formaldehyde was performed. Ethylenediamine and sodium borohydride were found to be the best diamine capping and reducing agent, respectively. Systematic investigations determined that the nanoparticle synthesis was dependent on various reaction parameters: such as reaction temperature, time, reductant reducing power, and capping agents. The parameters effects on the nanoparticle size, morphology, shape, stability, crystallinity, and surface charge were investigated. The optical properties, elemental composition, functional group, concentration and molecular weight for the synthesised nanoparticles or conjugates were determined. These properties were analysed using Ultraviolet–visible spectroscopy (UV-Vis), high resolution transmission electron microscopy (HRTEM) coupled with selective area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), zeta potential (ZP), dynamic light scattering (DLS), elemental analysis (EA), 1H and 13C-nuclear magnetic resonance (1H- and 13CNMR), Fourier-transform infrared spectroscopy (FTIR), inductively coupled plasma-optical emission spectroscopy (ICP-OES), and liquid chromatography-mass spectroscopy (LC-MS). The in vitro cytotoxicity, cell uptake, and internalisation studies of palladium nanoparticles (10 μM) ranging in size and different types of capping agent were performed using three breast cancer cell lines: MDA-MB-468 , MCF-7 and MDA-MB-231 , and a non-tumorigenic MCF-10A breast cell line. The cell uptake and internalisation were investigated using ICP-OES and TEM. A high dependence between reduction rate and concentration of palladium precursor was observed for the room temperature synthesis of palladium nanoparticles, and the employed synthesis procedure will be applied to the hot palladium isotope (109Pd). A facile, green, aqueous synthesis route for palladium nanoparticles at room temperature was developed, and the synthesised nanoparticles indicated narrow size distributions. A concentration dependence between cytotoxicity and palladium nanoparticles was observed, with lower concentrations (10 μM) exhibiting minimal cytotoxicity relative to higher concentrations (100 μM). The cellular uptake of palladium nanoparticles was found to be concentration, folate-receptor, capping agent, and cell line proliferation-dependent. Well-defined, monodispersed, and negatively charged folate-ethylenediamine and folate-phthalocyanine capped palladium nanoparticles were taken up by cells, with higher nanoparticle internalisation in folate receptor positive tumorigenic cells relative to folate receptor negative non-tumorigenic cells. It can be concluded that palladium(0) nanoparticles can be synthesised from the reduction of palladium(II) by sodium borohydride at room temperature. The folate-conjugated palladium nanoparticles are non-cytotoxic at 10 μM and were successfully optimised and selectively delivered to folate receptor-positive breast cancer cells (MDA-MB-231 and MCF-7) relative to non-tumorigenic breast cells (MCF-10A) and folate receptor negative cancer cells (MDA-MB-468).
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  • Date Issued: 2019

The distribution of South African loggerhead sea turtles (Caretta caretta) as indicated by epibionts and stable isotopes

  • Authors: Nolte, Christopher Robin
  • Date: 2019
  • Subjects: Sea turtles -- South Africa , Loggerhead turtle -- South Africa Sea turtles
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/31611 , vital:31625
  • Description: Many marine species undertake long-distance migrations as part of their life history strategies, and so form an important part of marine ecosystems performing a range of functions, across many habitats. However, these migratory species, including sea turtles, face multiple threats and anthropogenic impacts across their ranges and knowing their movement and distribution patterns enables more effective and appropriate conservation strategies to be devised. Satellite telemetry has provided invaluable information on spatial distribution of marine migrants, but applying this approach to a large proportion of a population is often unfeasible and costly. This study aimed to identify alternative, more cost effective methods that could assist with tracking animal movements across a larger proportion of a population of marine focal species, such as sea turtles. This study used nesting loggerhead sea turtles (Caretta caretta) from the iSimangaliso Wetland Park, South Africa as a model species to test these alternative methods and subsequently combine body condition, habitat use, and distribution range in the South West Indian Ocean. First, epibiont community assemblages were investigated as a proxy to determine sea turtle body condition. A body condition index was created using plastron shape, injuries and skin deformities. Sixty turtles were classified into four body condition categories ranging from poor to very good and this was reflected in their epibiont communities as both species abundance and richness increased with a decline in body condition. A total of twenty-eight epibiont taxa were identified from a range of systematic groups including, but not limited to, Amphipoda, Cirripedia, Brachyura and Polychaeta. The barnacle Chelonibia testudinaria showed the greatest variation among different body conditions with an increase in abundance as turtle body condition deteriorated. These results suggest that epibiont load can be used as an indicator of body condition that is easy to implement in the field. Second, a combination of organic δ13C and δ15N isotopic signatures of turtle epidermis and epibiont communities was used to infer foraging habitat. One hundred and seventy turtles were sampled for stable isotope analysis. These turtles were clustered into two groups based on δ13C at -13.61 ‰ with relative depletion or enrichment indicating foraging in oceanic or neritic environments, respectively. The epibiont communities of IV 80 turtles closely followed this cluster grouping; turtles with depleted δ13C had a higher abundance and frequency of oceanic epibiont species, such Lepas spp. Similarly, three neritic epibionts (Hyale grandicornis, Hyachelia tortugae and Podocerus africanus) were the other habitat-specific species driving community assemblages, with higher occurrence and abundance on turtles in the enriched δ13C cluster. Additionally, the size of the dietary niche was determined by a Bayesian analysis of δ13C and δ15N for 46 turtles in different body condition categories. Although there was overlap among categories, individuals in very good body condition had the smallest dietary niche. These results show the complementarity of using epibionts and stable isotope analysis in determining foraging area. Third, Chelonibia testudinaria barnacles on sea turtles were analysed for δ18O and inorganic δ13C. The δ18O of expected calcite fractionation was mapped for the known migration routes of eight turtles in the South West Indian Ocean. The inorganic carbon values were not very informative on movement, however, the δ18O analysis of the barnacle showed the range of the turtle host moving through the isoscape. Most of the turtles migrated from the north in the Mozambique Channel, to the southern rookery in South Africa, which is in accordance with reports from tag recoveries and satellite telemetry studies. Using this approach to track migratory species that have epibiotic barnacles can provide complimentary approach to satellite tracking that can be used on more individuals within a population. This study aids in providing alternative methods to study body condition, habitat use and regional movement of loggerhead sea turtles. These approaches can be applied to other sea turtle species and migratory marine fauna to help better understand their movement patterns thereby promoting more effective conservation strategies. Future work should consider incorporating different cohorts, examining other epibionts such as meiofauna and diatoms, including additional isotope and trace elements for analysis on habitat and improving the resolution of the isoscape data for δ18O of seawater in the SWIO.
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  • Date Issued: 2019

The ecology of Impala (Aepyceros melampus) in a dystrophic system: a case study from Welgevonden Game Reserve, Limpopo Province, South Africa

  • Authors: Pieterse, Marilize
  • Date: 2019
  • Subjects: Impala -- Habitat -- South Africa -- Limpopo province , Impala -- Feeding and feeds -- South Africa -- Limpopo province Ecology -- South Africa -- Limpopo province
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/43240 , vital:36768
  • Description: Impala (Aepyceros melampus) have been extensively researched and are known to flourish in Savanna ecosystems. They are a very adaptable species switching easily between grazing and browsing hence their classification as mixed feeders. However, little published research has been done on impala and their adaptability to sour nutrient-poor savannas. On Welgevonden Game Reserve (WGR), situated in the dystrophic Waterberg Mountain Range, impala have poor body condition and negative growth rates. Research shows that impala are on the threshold of being sexually dimorphic which can lead to a difference in the habitat selection and preference, diet composition and diet quality of adult male and female animals. This study served as a baseline study to understand the adaptability and ecology of impala in the Waterberg. The key research question was: How do male and female impala adapt to the area in terms of habitat selection and preference, and diet composition and quality, across the seasons of a year in the sour nutrient-poor Waterberg Mountain Range? This was the first study on impala in the area that looked at all the above-mentioned factors. A combination of observational studies, for habitat selection and preference, and faecal analysis, for diet composition and diet quality (faecal Nitrogen (Nf) and Phosphorous (Pf)), were used. It should be noted that WGR received below average rainfall and above average maximum temperatures over the past seven years. Impala on WGR are limited by the availability of suitable habitat and the quantity and quality of forage. They therefore suffer from nutrient deficiency. Spatial and ecological segregation between male and female animals occurred due to differences in sexual status and the constraints associated with this. Overall, very little variation in habitat use occurred between Wet and Dry seasons, emphasizing limited suitable impala habitat. Impala on WGR showed a distinct preference and avoidance of different habitat types. Both male and female preferred Short Grassland throughout the year. This is the smallest habitat type on the reserve and is dominated by Cynodon dactylon, which mostly occurs in the low-lying areas of the reserve. Both male and female impala avoided Hill Slope and Long Grassland throughout the year. These habitat types are characterized by steep slopes, medium to extensive rock cover, long sparse grass and dense tree cover. The Long Grassland habitat type consist mainly of old lands in different stages of regeneration dominated by dense unpalatable grasses. Both male and female impala were highly selective towards the most nutrient rich areas, which predominantly included the Short Grassland habitat type. The factors important to impala habitat selection are short to medium grass height (6-25 cm), ecotones in low lying areas between Short Grassland and woodland, proximity to water (0.96-1.5 km), moderate to no slopes, a burn interval of less than 3 years, the dominant occurrence of Cynodon dactylon, and the presence of Dichrostachys cinerea, Grewia flavescens, Dombeya rotundifolia and Indigofera melanodenia. The impala population on WGR appears to be limited by a lack of quality forage. The diet composition of impala on WGR followed a seasonal pattern, with a higher grass to browse content during the Wet seasons, and a higher browse to grass content during the Dry seasons. Furthermore, impala on WGR have a higher browse content in their diet than in other areas of South Africa. The higher content of browse in the impala’s diet on WGR is probably due to the impala optimizing their diet quality due to a lack of quality grasses, such as Cynodon dactylon, available to them on the reserve. Females consumed higher amounts of browse than males during lactation in order to optimize their diet quality. In general, impala experienced nutrient deficiencies during the Dry seasons as indicated by Nf and Pf values which were below the accepted threshold values for impala. This appears to have affected their body condition, reproductive success and survival. The below threshold values of Nf and Pf indicate that their numbers exceeded the ecological capacity of the reserve at the time of the study. This dystrophic savanna is marginal for impala. This indicates that even large reserves in the sour bushveld communities of the Waterberg Mountains are unlikely to sustain impala populations in a healthy productive state.
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  • Date Issued: 2019

The evolution of the Lepilemuridae-Cheirogaleidae clade

  • Authors: Andrews, Curswan Allan
  • Date: 2019
  • Subjects: Lemurs
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: http://hdl.handle.net/10948/40216 , vital:35989
  • Description: The Lepilemuridae and the Cheirogaleidae, according to recent molecular reconstructions, share a more recent common ancestor than previously thought. Further phylogenetic reconstructions have indicated that body size evolution in this clade was marked by repeated dwarfing events that coincided with changes in the environment. I aimed to investigate the morphological implications of changes in body size within the Lepilemur-cheirogaleid clade, testing four predictions. Together with Dr. Couette, I collected data on the overall palate shape and predicted that shape is likely to be influenced by several factors including phylogeny, body size and diet. Geometric morphometric analyses revealed that, although a strong phylogenetic signal was detected, diet had the major effect on palate shape. In a similar vein, when examining the arterial circulation patterns in these taxa, I predicted that changes in body size would result in changes and possible reductions in arterial size, particularly the internal carotid artery (ICA) and stapedial artery (SA). Analyses with micro-computed tomography (CT) and 3D imaging indicated that changes in body size led to reduction of a functional stapedial artery in Lepilemur, making it an intermediate stage between the daubentoniid, lemurid and indriid species with large stapedial arteries, and the smaller bodied cheirogaleids with an alternative blood supply in the form of an enlarged ascending pharyngeal artery. Lepilemur is the smallest living folivorous primate, and likely to be at the threshold body size to be able to subsist on such a poor diet. To investigate shifts in dietary patterns that accompanied changes in body size, I chose to explore the reported behaviour of caecotrophy as a possible means for the sportive lemurs to derive additional nutrient from their food sources. I predicted that, if caecotrophy is a way to assist folivory at small body size, the energy contained in “caecotrophic” and latrine faecal samples should be different. Analyses showed significant iv differences between the two types of faeces and, combined with an analysis of faecal bacterial diversity, support the occurrence of caecotrophy. Finally, I compared the digestive efficiency of two small, distantly related gummivorous primates that evolved their diets convergently. I studied the digestion of gum in Microcebus griseorufus and compared this with gum digestion in Galago moholi. I predicted that an evolutionary disposition to fermentation inherited from a folivorous ancestor would aid in the digestion of gum in mouse lemurs. Results indicated that retention time was prolonged by the presence of secondary compounds in Microcebus fed with Commiphora gum but relatively shorter (< 24 hrs) when fed Alantsilodenron gum, a preferred food. Despite the fact that G. moholi has an ansa coli, which is missing in M. griseorufus species, both are highly efficient at digesting gum. These data provide some of the first indicators of how dietary changes from a larger-bodied folivorous ancestor to partially gummivorous, small-bodied descendants may have occurred in evolutionary time.
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  • Date Issued: 2019

The extraction of bioactive compounds from spent coffee grounds and their application in a cosmetic formulation

  • Authors: Mdubeki, Ntokozo
  • Date: 2019
  • Subjects: Bioactive compounds , Plants -- bioactive compounds Plant biotechnology Coffee -- Processing Chemistry, Technical Cosmetics
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/41460 , vital:36485
  • Description: Residues obtained during coffee processing, known as spent coffee grounds, are an abundant, low-cost and versatile feedstock for a wide range of high-value biological compounds exhibiting a number of properties which include anti-cellulite and antioxidant properties for skin-care applications. The objective of the present work was to obtain a concentrated extract containing high-value biological methylxanthines and polyphenolic compounds with antioxidant activity from the spent coffee grounds. An investigation of the effect of extraction conditions on the concentration of the bioactive compounds in the extract was done. The recovery of both methylxanthines and the polyphenolic compounds with antioxidant activity was achieved through a one-step extraction method under reduced pressure using a non-toxic solvent blend. Various experimental designs were implemented with the aim of optimising the recovery of the selected bioactive compounds, namely, caffeine, theophylline and theobromine from spent coffee grounds by using solvent blends of water and ethanol. A number of factors considered were: (i) repeatability, (ii) extraction time, (iii) composition of solvent blends, (iv) extraction vacuum (pressure)/temperature settings and (v) operating variables. The results suggested that an optimal recovery of the bioactive compounds will be obtained at a two-hour extraction time with a solvent blend of 100% water to maximise caffeine, theophylline, total phenolic content and percentage antioxidant activity, while extraction of theobromine is optimal using aqueous ethanolic solvent mixtures. The optimal vacuum (pressure) setting was found to be 250 mbar to maximise percentage antioxidant activity. The methylxanthines and total phenolic content were not affected by the vacuum (pressure) and temperature settings. Freezedrying the spent coffee grounds before extraction ensured long-term stability of a reproducible sample and achieved better recovery of the important bioactive compounds. Extraction was performed under reduced pressure in order to reduce solvent reflux temperature and to improve extraction efficiency. The quantitative and qualitative determinations of the above-mentioned high-value compounds were performed by high-performance liquid chromatography (HPLC), which confirmed the presence of the methylxanthines in the extracts. In the extraction of methylxanthines, it was found that caffeine was more abundant in the extract as compared to theophylline and theobromine. The extracts were incorporated into three cosmetic gel formulations. Release studies of caffeine, theobromine and theophylline were performed using the three formulated cosmetic gels with the use of a Franz diffusion cell. It was found that theobromine and theophylline were not detected from the gel samples as they were present in too small amounts in the original extracts and there was no significant difference in the release rates of caffeine when comparing the three different gels. Caffeine was released within 15 minutes. All three gels displayed a pseudoplastic viscosity profile and the different viscosity values of the three gels did not influence the release of caffeine significantly.
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  • Date Issued: 2019

The hepatoprotective capacity of selected natural products from South Africa

  • Authors: Reddy, Shanika
  • Date: 2019
  • Subjects: Hepatology , Liver -- Physiology Liver -- Pathophysiology Liver -- Diseases
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/43622 , vital:36948
  • Description: Drug-induced liver injury (DILI) is recognized as a significant clinical problem, which may account for up to 50% of all cases of acute liver failure. DILI is initiated by the bioactivation of parent drug molecules to produce chemically reactive metabolites. These reactive intermediates induce mitochondrial dysfunction and oxidative stress leading to glutathione (GSH) depletion and damage to cellular proteins, lipids and nucleic acids, which eventually culminates in necrotic cell death. The principal objective of this study is to establish an in vitro screening platform to identify potential hepatoprotective natural products (plants and mushrooms) from South Africa (SA). Aqueous plant extracts (Cyclopia intermedia, Opuntia ficus indica and Kigelia africana), and aqueous and ethanolic macrofungal extracts (Ganoderma lucidum, Russula capensis, Pleurotus ostreatus and Lenzites elegans) were prepared and screened against HepG2 and VERO cells to assess their safety using Hoechst 33342-PI dual labelling. A drug-induced hepatotoxic model was established, using the dietary supplement menadione (vitamin K3). Hoechst 33342- PI, -CellROX® Orange and -TMRE dual labelling was used for necrosis, oxidative stress and mitochondrial membrane potential depolarization (ΔΨm) detection, respectively. The accuracy of the hepatoprotection model was confirmed through HepG2 cellbased assays (Hoechst 33342- PI, -CellROX® Orange and -TMRE dual labelling) that measured the protective effects of natural products against the menadione-induced toxicity, anti-oxidant assays (DPPH, NO, ORAC, CAPe and FRAP) that measured their anti-oxidant potential and enzyme assays (βglucuronidase, carboxylesterase and CYP450 isoform 3A4) that measured their effects on drug metabolism. Silymarin was used as a positive control for each assay. Menadione displayed significant cell death, increased oxidative stress and decreased ΔΨm at an elevated concentration of 100 μM; confirming the hepatotoxicity model, where necroptosis was suspected to be menadione’s cell death mode. Only ethanolic G. lucidum was cytotoxic. All three aqueous plant extracts demonstrated strong anti-oxidant capacities out of all the tested extracts; where C. intermedia displayed the most promising DPPH, NO, ORAC, CAPe and FRAP activity, followed by aqueous G. lucidum. Aqueous plant and ethanolic macrofungal extracts (C. intermedia, O. ficus indica, K. africana, and ethanolic P. ostreatus, R. capensis) displayed decreased menadione-induced ROS production and protected against menadione-induced ΔΨm depolarization, posing them and aqueous G. lucidum potential therapeutic interventions for DILI. Ethanolic L. elegans demonstrated the highest enzyme inhibition for each assay and presented genotoxicity, ruling it out as a therapeutic strategy against DILI. Together these assays addressed several aspects relating to DILI and hepatoprotection, and served as a good starting point in evaluating the therapeutic value of natural products from South Africa.
  • Full Text:
  • Date Issued: 2019

The hepatoprotective capacity of selected natural products from South Africa

  • Authors: Reddy, Shanika
  • Date: 2019
  • Subjects: Liver -- Physiology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/43611 , vital:36929
  • Description: Drug-induced liver injury (DILI) is recognized as a significant clinical problem, which may account for up to 50% of all cases of acute liver failure. DILI is initiated by the bioactivation of parent drug molecules to produce chemically reactive metabolites. These reactive intermediates induce mitochondrial dysfunction and oxidative stress leading to glutathione (GSH) depletion and damage to cellular proteins, lipids and nucleic acids, which eventually culminates in necrotic cell death. The principal objective of this study is to establish an in vitro screening platform to identify potential hepatoprotective natural products (plants and mushrooms) from South Africa (SA). Aqueous plant extracts (Cyclopia intermedia, Opuntia ficus indica and Kigelia africana), and aqueous and ethanolic macrofungal extracts (Ganoderma lucidum, Russula capensis, Pleurotus ostreatus and Lenzites elegans) were prepared and screened against HepG2 and VERO cells to assess their safety using Hoechst 33342-PI dual labelling. A drug-induced hepatotoxic model was established, using the dietary supplement menadione (vitamin K3). Hoechst 33342- PI, -CellROX® Orange and -TMRE dual labelling was used for necrosis, oxidative stress and mitochondrial membrane potential depolarization (ΔΨm) detection, respectively. The accuracy of the hepatoprotection model was confirmed through HepG2 cellbased assays (Hoechst 33342- PI, -CellROX® Orange and -TMRE dual labelling) that measured the protective effects of natural products against the menadione-induced toxicity, anti-oxidant assays (DPPH, NO, ORAC, CAPe and FRAP) that measured their anti-oxidant potential and enzyme assays (βglucuronidase, carboxylesterase and CYP450 isoform 3A4) that measured their effects on drug metabolism. Silymarin was used as a positive control for each assay. Menadione displayed significant cell death, increased oxidative stress and decreased ΔΨm at an elevated concentration of 100 μM; confirming the hepatotoxicity model, where necroptosis was suspected to be menadione’s cell death mode. Only ethanolic G. lucidum was cytotoxic. All three aqueous plant extracts demonstrated strong anti-oxidant capacities out of all the tested extracts; where C. intermedia displayed the most promising DPPH, NO, ORAC, CAPe and FRAP activity, followed by aqueous G. lucidum. Aqueous plant and ethanolic macrofungal extracts (C. intermedia, O. ficus indica, K. africana, and ethanolic P. ostreatus, R. capensis) displayed decreased menadione-induced ROS production and protected against menadione-induced ΔΨm depolarization, posing them and aqueous G. lucidum potential therapeutic interventions for DILI. Ethanolic L. elegans demonstrated the highest enzyme inhibition for each assay and presented genotoxicity, ruling it out as a therapeutic strategy against DILI. Together these assays addressed several aspects relating to DILI and hepatoprotection, and served as a good starting point in evaluating the therapeutic value of natural products from South Africa.
  • Full Text:
  • Date Issued: 2019

The hypolithic invertebrate community in the eastern Karoo: the role of rock size, microclimate and recolonization

  • Authors: Van der Westhuizen, Tara
  • Date: 2019
  • Subjects: Habitat (Ecology) -- South Africa -- Karoo , Biotic communities -- South Africa -- Karoo Invertebrates Ecosystem management -- South Africa -- Karoo Soil microbial ecology
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/44191 , vital:37128
  • Description: Hypolithic habitats are important for the persistence of fauna that utilize these habitats as refuges and resource patches. Little is known, however, about the composition and structure of this community in the semi-arid Karoo. The current study therefore aims to explore the patterns and processes behind hypolithic communities, through determining the effect of rock size and baboon presence on the hypolithic community, the influence of rock size on the microclimate experienced under rocks, as well as determining the short- (over five days) and long- (over 12 months) term colonisation of the hypolithic habitat following a rock rolling disturbance, in a semi-arid Karoo environment. The hypolithic fauna encountered, and the temperature and moisture content experienced under a range of rock sizes were measured. Additionally, hypolithic fauna under rocks that were rolled to mimic rock rolling by baboons were sampled after a set period (i.e. over five days and 12 months). Large rocks were found to provide a more stable microclimate than small rocks. The probability of hypolithic fauna presence was influenced by rock size and season, and hypolithic fauna abundance (except in the dry season), richness, body size and biomass did not correlate with rock size. Additionally, the probability of detecting hypolithic fauna under intermediate sized and larger rocks was greater in the presence of baboons than in the absence of baboons, and in the presence of baboons hypolithic fauna richness increased with rock size. Furthermore, it was shown that hypolithic fauna abundance and biomass did not differ under rolled rocks over a short- (i.e. over five days) or long- (i.e. over 12 months) term period. The short-term colonisation of hypolithic habitats was not influenced by season or rock density. Lastly, most of the change in hypolithic community composition (over 12 months) occurred in the first three months and thereafter the hypolithic community composition approached pre-disturbance levels in month 12. The hypolithic habitat was shown to be influenced by a variety of conditions and processes affecting hypolithic community composition and structure. This study therefore contributes to our understanding of the hypolithic invertebrate community in the eastern Karoo, and the influence of rock size, baboon presence, microclimate and colonisation on hypolithic community composition and structure.
  • Full Text:
  • Date Issued: 2019

The impact of re-establishment practices on tree survival, growth and uniformity in South African eucalypt plantations

  • Authors: Hechter, Ullrich
  • Date: 2019
  • Subjects: Forests and forestry -- South Africa -- KwaZulu-Natal , Forest nurseries -- South Africa -- KwaZulu Natal Forest management -- South Africa -- KwaZulu Natal
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/40338 , vital:36142
  • Description: Commercial forestry plantations in South Africa play an important role in the economy of the country, contributing 1.2% towards the gross domestic product, as well as with job creation in rural communities. Currently plantation forests occupy 1.1% (1.2 million hectares) of the South African land surface, of which 75 000 hectares are re-established each year. Eucalypts are the preferred species in the commercial forestry industry as they have the ability to grow fast. In addition, desirable characteristics from different eucalypt species can be combined to develop hybrids that can be used to further improve productivity. In South Africa, eucalypt plantations are mostly found in the warm temperate and sub-tropical zones situated in the KwaZulu-Natal and Mpumalanga Provinces. Various strategies are used to increase productivity and maximise site occupancy, including genetic tree improvement, site-species matching, optimising stand densities, management for risk (abiotic and biotic), as well as improved silviculture. Intensive silviculture is practiced by forest companies to maximise initial tree survival and reduce the time to canopy closure. This includes practices such as site preparation, slash management, tree protection, pruning and thinning, fertilisation and vegetation management treatments. Of the silvicultural aspects that are important during re-establishment, pitting, plant quality (plant size) and watering techniques/regimes have all been shown to influence short-term stand productivity. Despite research carried out on these individual components, recommendations as to best operating practices are varied and have changed over the years, with the application of these practices also varying across companies. Furthermore, there is limited published information related to the interaction between these practices, as well as any longer-term impacts of these factors on stand productivity. The objective of the present study was to gain an understanding of the impacts of pitting, plant quality (plant size), planting depth and watering on tree survival, growth and uniformity in South African Eucalyptus plantations. The study was carried out using three separate field trial series. In a first experiment, two field trials compared post-establishment performance of eucalypts planted using various pitting methods. The two trials were planted using Eucalyptus grandis and E. grandis x E. nitens on two contrasting sites, one at Greenhill in the KwaZulu-Natal Midlands and one at Vroegeveld in Mpumalanga. Four manual (notch, agricultural hoe, mattock, road pick) and three motor-manual heads (inverted A, Archimedes screw and Mondi-designed pitting head) were used to prepare and determine the effect of pit size/quality on tree survival, growth and uniformity. The notch pit implement created the smallest pit (1 L volume) compared to the other pitting implements (4 – 6 L volumes). For both trials, pitting method did not have a significant impact on the success of re-establishment or longer-term tree performance (6 yrs 7 mos at Greenhill and 3 yrs 7 mos at Vroegeveld). This indicates that for the sites and the species tested, all pitting implements could be considered viable alternatives. Other factors, such as operational costs, efficiency and ergonomics should be considered when selecting appropriate pitting methods together with tree performance. In a second experiment, three field trials were implemented to test three main factors: plant size (small and large); planting depth (standard and deep); and watering (dry and water planting). The eight treatments (2 x 2 x 2 factorial) were replicated four times and laid out in a randomised complete blocks design. The trials were established across a range of site types (Mt Home in Kwazulu-Natal, Vroegeveld in Mpumalanga and Trust in Zululand) in the summer rainfall region of South Africa using various eucalypt genera (E. dunnii, E. grandis x E. nitens and E. grandis x E. urophylla). Tree performance was assessed, with results up to four, six and seven years presented for the different sites. Results show that planting larger plants had the highest overall survival (x̄ = 81%) compared to smaller plants (x̄ = 58%), which also resulted in improved basal area and volume across all sites. Larger plants were able to tolerate a wider range of site conditions, thus providing an advantage for re-establishment. The cost-to-benefit of this however needs to be assessed, particularly in the context of current operational nursery standards. The benefits of deeper planting and applying water at planting are less clear, but appear to be beneficial under water stress conditions, such as on sandy sites when the weather is hot and dry. A third experiment tested the interaction between different methods of pit preparation (manual versus motor-manual), dry versus water planting, and re-watering at periodic intervals. The experiment consisted of one field trial established with E. dunnii in Greytown, KwaZulu-Natal. Twelve treatments (2 x 6 factorial) were replicated four times and laid out in a split-plot design, with the main factor of watering regime forming the whole plots, and pitting method the sub-plots. Differences in pit size, pit quality and tree performance were assessed. Pit dimensions and soil friability for the two pitting treatments were different, but pit volumes were similar (manually prepared pits = 4.7 L; motor-manually prepared pits = 4.4 L). Differences in pit soil moisture content were detected between dry planting (4.1%) and all other treatments (9.9%). Rainfall occurred in week 1 - 4 after planting (55.2 mm). Subsequently re-watering, relative to watering only at planting, was not beneficial. No significant growth differences occurred between the two pitting methods, nor was there any interaction between the main factors (pitting methods x watering regimes). Survival for dry planting (75%) was significantly lower than all the other treatments (92%), with a weakly significant difference in Biomass index (corrected) (BIc) at one year. Different pit qualities, determined by pitting method, will not significantly affect early eucalypt performance. However, the addition of water or hydrogel (as opposed to dry planting) will improve early eucalypt survival and growth. Eucalypt survival, growth and uniformity in South Africa continue to be impacted by an increase in mechanisation, changing climate conditions and the use of unskilled labour. It is therefore necessary to implement silvicultural practices which improve survival, growth and uniformity. Planting seedlings into good quality pits (regardless of pitting method) with water has shown to improve survival. It is also beneficial in terms of survival to plant larger (prime) plants at a deeper depth especially on sites with drought conditions. Despite all the establishment trials which have been implemented under controlled conditions, high mortality is still experienced and could be due to the lack of knowledge on the effects of plant quality and handling on post planting performance (particularly survival). In future, plant quality and handling in combination with various planting densities and the application of plant stress relievers should be considered to improve survival..
  • Full Text:
  • Date Issued: 2019

The influence of hands-on chemistry experimental interventions on the attitudes of grade 9 learners toward natural science

  • Authors: Swartbooi Tarryn Beatrix
  • Date: 2019
  • Subjects: Chemistry -- Study and teaching
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/44628 , vital:38168
  • Description: The primary purpose of this research was to explore the influence that interactive, hands-on chemistry experiments may have on grade 9 learners’ attitudes toward Natural Sciences. A pragmatic research philosophy was used to best answer the research question which asked “Do hands-on chemistry interventions have a positive effect on grade 9 learners cognitive, affective and behavioural attitude toward Natural Sciences?” and explore the problem statement “The conducting of relevant hands-on chemistry experiments and demonstrations are expected to positively affect learners’ attitudes (cognitive, affective and behavioural), which would in turn motivate learners to further explore science, both in and outside of the classrooms and increase their interest”. The attitudes of learners were studied at two quintile-1 ranked schools both situated in lower socio-economic areas. The main findings that for cognitive attitude from the achievement tests were that Quintile-1 schools based in low socio-economic areas have similar cognitive attitude outcomes (pre-tests, post-tests) except for scientific language. In addition, according to multiple linear regression testing, the hands-on chemistry intervention group (test group) had a more uniform understanding of the scientific topic under study when compared to the traditionally taught group of learners (control group). Key findings from the survey and focus group for affective attitude (School A n=56 and School B n=14) showed that most of the learners responded that science interests them. They also responded that they wanted science club as a permanent fixture at their school and enjoyed doing experiments practically. Main findings for the behavioural attitudes from the focus group and survey were that hands on chemistry experiments motivated grade 9 learners to select Physical Sciences in grade 10 and it also encouraged them to want follow a career in science. From the survey responses it was inferred that learners’ behavioural attitude (BA) toward science was positively affected by science demonstrations and experiments.
  • Full Text:
  • Date Issued: 2019

The medicinal chemistry of selected halogenated diketopiperazines CYCLO(CIS-PRO-4F-PRO) and CYCLO(L-PHE-4I-VAL)

  • Authors: Dakada, Vuyokazi
  • Date: 2019
  • Subjects: Medicinal plants , Drug development Cells -- Effect of drugs on
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/39370 , vital:35221
  • Description: Generally, peptides are selective and efficacious compounds; as a result, they are the best candidates for drug discovery and development. Most peptide-based drugs have been approved for clinical use. The 2,5-Diketopiperazines (DKPs), also known as cyclic dipeptides, are simple compounds which come from nature. Many DKPs are extracted from animals and plants. For example, cyclo(Proline(Pro)-Leucine(Leu)), cyclo(Proline-Valine(Val)), cyclo(Proline-Phenylalanine(Phe)) etc. In this study cyclo(cis-Proline(Pro)-4F-Proline(Pro)) and cyclo(L- Phenylalanine(Phe)-4I- Valine (Val)) were synthesized from their linear esters using a method modified by Milne et al. (1992). This method yielded good results. However, cyclo(L-Phe-4I-Val) degraded due to physicochemical stability attributes caused by hygroscopicity and photosensitivity. Quantitative analysis and evaluation of physicochemical properties of each dipeptide was achieved by using scanning electron microscopy, thermal analysis (differential scanning calorimetry and thermogravimetric analysis) and X-ray powder diffraction. To determine the purity of the cyclic dipeptide, high performance liquid chromatography and thin layer chromatography was used. The structural elucidation of the cyclic dipeptides was carried by employing infrared spectroscopy, mass spectrometry, nuclear magnetic resonance spectroscopy and, molecular modelling and computational chemistry. The aim of this research was to discover possible biological activity of cyclo(cis-Pro-4-F-Pro) and cyclo(L-Phe-4I-Val) with respect to their antimicrobial, anticancer, anti-diabetic and haematological effects. Cyclo(cis-Pro-4Fluoro-Pro) had no inhibitory effect on the antimicrobial strains tested, and cyclo(L-Phe-4Iodo-Val) could not be tested as the compound decomposed.
  • Full Text:
  • Date Issued: 2019

The prediction of, and changes in,medullated fibre levels when processing mohair into top

  • Authors: Van Zyl, Andreas Marius
  • Date: 2019
  • Subjects: Mohair Industry -- South Africa , Textile Fibers Testing
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/45767 , vital:38962
  • Description: The prediction of, and changes in, medullated fibre levels during early stage processing of mohair, from greasy to top, have been studied. Commercial lots, representative of the South African and Basuto mohair clips, covering a wide range of properties, with respect to objectionable medullated (kemp type) fibres, length and fibre diameter, were sampled for testing at three different processing stages, viz. greasy, preparatory gilled sliver, and top. All samples were tested with an Optical Fibre Diameter Analyser (OFDA100) for medullated- and fibre diameter related properties. Various statistical analyses were conducted to determine the most significant correlations and best prediction of changes in medullated fibre levels, during processing. As expected, the medullated fibre levels of the Basuto lots were much higher than those of the Cape lots. Moreover, the inclusion or exclusion of flat fibres, in combination with other medullated fibres, resulted in significant differences in the outcome of some of the statistical analysis. It was found that flat fibre levels were highly correlated with the standard deviation of fibre diameter at all processing stages, and also, the greasy standard deviation of fibre diameter was the best predictor of flat fibre levels in the top. Further, the percentage reduction in flat fibres, from greasy to preparatory gilled sliver, was more than double that of the reduction in flat fibres from preparatory gilled sliver to top. Similarly, the percentage reduction in objectionable medullated (including flat) fibres, from greasy to preparatory gilled sliver, was about 1.7 times more than that of the reduction from preparatory gilled sliver to top.
  • Full Text:
  • Date Issued: 2019

The social sustainability of low-cost housing: the role of social capital and sense of place

  • Authors: Williams-Bruinders, Leizel
  • Date: 2019
  • Subjects: Housing -- South Africa , City planning -- South Africa Cities and towns -- Research Urban geography
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/44390 , vital:37161
  • Description: In the past twenty years we have seen the South African government deliver the largest number of houses in the world (NDHS, 2011). However, this great effort does not appeal to the principles that policies have set out in terms of equality. Along with the delivery of this high level of state funded housing, many of the RDP dwellers feel as though they have been marginalised and forced out of the area of opportunity, namely, the CBD and the northern suburbs (Huchzermeyer, 2003). Many researchers believe that the South African housing delivery pattern resembles that of apartheid segregationist planning, which exacerbated the social inequalities in the country (Huchzermeyer, 2003; Donaldson, 2001; Harrison et al., 2003). To gain an in-depth understanding of the lived experiences of residents of a low-cost housing settlement, an interpretative phenomenological analysis was undertaken. The emergent themes emanating from the research study revealed that social problems were pertinent factors to the lack of formulation of community social cohesion. Without this aspect, community building will be hampered, and thus cohesive neighbourhoods will be lacking. To this end, social innovation is proposed as a solution to the Zanemvula development. The issue of social development needs to placed back on the housing agenda, as is stated in the latest Housing Act.
  • Full Text:
  • Date Issued: 2019

The socio-economic importance of indigenous vegetables to the Ntuze smallholder farming community in KwaZulu-Natal, South Africa

  • Authors: Qwabe, Qinisani Nhlakanipho
  • Date: 2019
  • Subjects: Indigenous crops -- Economic aspects -- South Africa -- KwaZulu Natal , Vegetables -- South Africa -- KwaZulu Natal Farmers -- Economic aspects -- South Africa -- KwaZulu Natal , Farms, Small -- South Africa -- KwaZulu Natal
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/30287 , vital:30927
  • Description: South Africa continues to face multiple socio-economic challenges – one of the direst being food insecurity, especially in rural areas. Compounding the challenges is the impact of changing weather patterns on agriculture. The current study presents evidence indicating that indigenous vegetables provide a sustainable yet inexpensive answer to several of these challenges. The research was aimed at determining the socio-economic impact of indigenous vegetables in the Ntuze community of northern KwaZulu-Natal. A mixed-methods methodology was employed to achieve a holistic understanding of the relationship between the use of indigenous vegetables and socio-economic influences. The study discovered that indigenous vegetables play an important role in the livelihood strategy of this rural farming community. Findings revealed that the utilisation of indigenous vegetables makes an essential contribution to the livelihoods and well-being of the Ntuze people, especially in terms of curbing food poverty, income generation and medicinal benefits. However, the value of these vegetables was found to be appreciated mostly by the elderly. Conclusions therefore indicate a possible decline in future production and use of indigenous vegetables if indigenous knowledge is not passed on to the next generation. Integration of indigenous knowledge in agricultural technology transfer programmes is therefore vital to promote production of indigenous vegetables as a sustainable food resource. Actively addressing the stigma attached to indigenous vegetables as being “low-status food” is also crucial to enhance perception and understanding of the value of these vegetables. This would contribute to both preserving cultural heritage and conserving valuable indigenous flora. Such intervention would safeguard this sustainable and renewable resource in its pivotal socio-economic role in terms of rural food security as is substantiated by this study.
  • Full Text:
  • Date Issued: 2019

The synthesis and assessment of thioxanthone- and xanthone- derived compounds as hosts for application in host-guest chemistry

  • Authors: Greyling, Lizé
  • Date: 2019
  • Subjects: Chemistry, Organic , Biochemistry
  • Language: English
  • Type: Thesis , Doctoral , DPhil
  • Identifier: http://hdl.handle.net/10948/42525 , vital:36665
  • Description: In this work, the host capabilities of two structurally related compounds, N,N’-bis(9-phenyl-9- thioxanthenyl)ethylenediamine (H1) and N,N’-bis(9-phenyl-9-xanthenyl)ethylenediamine (H2) were compared in the presence of a wide variety of guest species. Additionally, the selectivity displayed by these host compounds were examined when exposed to mixtures of guests in order to ascertain whether it would be feasible to employ them in alternative separation strategies for the purification of industrially relevant chemicals. H1 and H2 were synthesized by reacting thioxanthone and xanthone with phenylmagnesium bromide. The resultant alcohol was then treated with perchloric acid and, finally, two of these molecules were effectively linked by utilizing ethylenediamine to afford the two host compounds. Initially, H1 and H2 were investigated for their inclusion abilities by recrystallizing each from a number of potential isomeric and non-isomeric guest compounds such as the xylenes and ethylbenzene, methylanisoles and anisole, methylpyridines and pyridine, methylcyclohexanones and cyclohexanone, heterocyclic five- and six- membered ring compounds, alkylsubstituted benzenes, anilines, and dihaloalkanes. H1 displayed excellent inclusion ability when presented with the above-mentioned compounds, and a 1:1 H:G ratio was consistently preferred in each case. H2 also proved to be successful in this regard but did not include the methylcyclohexanones and cyclohexanone nor the heterocyclic five-membered ring solvents. Furthermore, varying host:guest ratios were observed for the complexes formed with H2. Mixed competition experiments were carried out in the presence of either isomeric or related but non-isomeric guest species. When H1 and H2 were independently recrystallized from mixtures of the former, selectivity orders correlated for both hosts, but it was observed that H2 exhibited an enhanced selectivity for the preferred guests in each case, compared with H1. Interestingly, in mixtures of the latter, host behaviours were distinctly opposing (with the exception of the dihaloalkanes). H1, and even more so H2, demonstrated very high selectivities for p-xylene, aniline and N,Ndimethylaniline from the xylene and aniline guest series, respectively, where selectivities were found to be ~90% or higher for host recrystallization experiments from respective mixtures of these guests. Single crystal X-ray diffraction, Hirshfeld surface and thermal analyses were employed in order to elucidate the reasons for any selectivity observations. The inclusion of these guests was, in most cases, found to be as a result of interactions between host and guest species, which included π∙∙∙π stacking, C‒H∙∙∙π, hydrogen bonding and various other short contact types. Guest compounds were accommodated in either cavities or channels and this was dependent on the nature of the guest. The host molecule conformations showed H1 to adopt a bent tricyclic fused ring system with the N atoms of the linker in a synclinal arrangement, while in complexes with H2, the fused ring system was near-planar and the N atoms adopted an antiperiplanar geometry. These key differences resulted in a very ordered host‒host packing for H2 as a direct result of the more planar O-containing ring and linear linker; for H1, on the other hand, the buckled S-containing ring and gauche-orientated N atoms resulted in a less ordered packing, which ultimately related to the differences in the behaviour of the two host species. Hirshfeld surface analyses, in general, did not provide much information to explain the host selectivities, with the exception of complexes containing the five-membered ring guest heterocyclics. Thermal analyses were completed on all suitable host-guest complexes and, in most cases but not all, the onset and peak temperatures (terms Ton and Tp, respectively) were related to the thermal stability of the complexes, which were used to rationalize the selectivities of these host compounds.
  • Full Text:
  • Date Issued: 2019

The synthesis, characterization, and application of peptide-capped magnetite nanoparticles for the targeting of cancer cells

  • Authors: Hickson, Matthew Victor
  • Date: 2019
  • Subjects: Nanomedicine -- Research , Nanostructured materials Cancer -- Alternative treatment
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/40172 , vital:35965
  • Description: In this study, a comparative analysis was performed upon three co-precipitation techniques for the synthesis of capped magnetite nanoparticles as to optimize the approach to the highest quality nanoparticles. Three techniques were applied whereby the capping agent either introduced before the stage of nanoparticle precipitation, simultaneously to the stage of precipitation, or after the stage of precipitation. The resultant nanoparticles were tested in terms of their size, dispersity, crystallinity, and magnetic characteristics. The three techniques gave nanoparticles of varying sizes and characteristics. Out of the three synthetic techniques, the post precipitation introduction method gave the highest quality nanoparticles in terms of size distribution, crystallinity and magnetic character. Three novel peptides were synthesized, incorporating amino acids to varying degrees. Structure was confirmed via IR and NMR spectroscopy. The peptides were studied potentiometrically to explore their acid nature and were explored computationally as to discern possible modes of interaction with the nanoparticles. These three peptides were further used in the capping of magnetite nanoparticles. For this set of nanoparticles, a higher synthesis temperature and larger iron content were used as to obtain larger nanoparticles. For the capping procedure, the post precipitation technique was used due to its previous positive results, once again yielding high quality nanoparticles with low size dispersity, high crystallinity, and high magnetic saturations. The nanoparticles were also seen to display positive zeta potentials, which are beneficial for cellular interactions. The peptides and peptide-capped nanoparticles were tested for biological activity against the healthy MCF-10A and cancerous MCF-7 cell lines. The MTT assay displayed increased proliferation for both the cell lines treated with the nanoparticles, while the peptide treatments decreased the MCF-10A cell lines proliferation and increased the MCF-7 proliferation. TEM analysis displayed nanoparticles in the cellular sections. An ICP-OES analysis on the cells showed that the capped nanoparticles of similar zeta potentials were seen to be taken up excessively by cells as compared to the uncapped. The nanoparticles of lower zeta potentials but higher L-glutamine content were taken up to a lesser degree.
  • Full Text:
  • Date Issued: 2019

The testing of natural and synthetic adjuvants to reduce herbicide-use and/or improve efficacy for the control of difficult-to-kill forest weeds

  • Authors: Letaoana, Josias Tshukudu
  • Date: 2019
  • Subjects: Weeds -- Control , Invasive plants -- South Africa Invasive plants -- Ecology -- South Africa Forest ecology -- South Africa Forests and forestry -- South Africa
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/40371 , vital:36153
  • Description: Commercial plantations within South Africa occur across diverse sites in terms of climate and physiography. Intensive silvicultural practices (site preparation, fertilisation, weed management etc.) are carried out during the establishment phase to ensure that the actual production of timber approximates the potential capacity for a site. Of these silvicultural practices, weed management is regarded as one of the most important, as if not carried out, competition from weeds may negatively influence seedling survival, growth and uniformity. During the establishment phase (planting to canopy closure), weed management operations are generally effective, as most competing species are still in a juvenile growth phase, and easily controlled. Due to limited weed-tree competition following canopy closure, weed management operations are reduced to a single event per annum (if necessary). This reduction in weed management often allows semi-shade/shade tolerant species to become established, together with an increase in the effort required for their control. The South African forest industry makes use of independent international auditing bodies to ensure that plantations are managed in a responsible, yet sustainable manner. Integrated management practices are considered the most effective as they reduce reliance on a single control method, such as the use of herbicides alone. In conjunction with integrated management, would be the need to reduce the overall quantities of herbicides used, yet at the same time ensuring improved efficacy of those herbicides that are used. The testing of these two aspects (reduced herbicide use and/or improved efficacy) was conducted on three diverse weeds that occur during the post-establishment phase within South African plantations, namely: Setaria megaphylla (setaria); Hedychium gardnerianum (wild ginger); and Solanum mauritianum (bugweed). The management of these species is considered problematic, as current herbicides and rates of application are not always completely effective. Four trials were implemented in KwaZulu-Natal (Midlands). Setaria megaphylla (setaria): Two trials were initiated (spring and autumn), to test the seasonal application of glyphosate + adjuvant combinations for improved efficacy (and hence reduced herbicide-use). A control (no herbicide applied), Select® (clethodim cyclohexanedione 120 g a.i. ℓ-1), Roundup® (glyphosate isopropylamine salt 360 g a.i. ℓ-1), and five Roundup® + adjuvant combinations were tested in both trials. iii The five adjuvants included three natural and two synthetic products that exhibited different properties and modes of action. At both sites, the eight treatments were replicated three times and laid out in a randomised complete blocks design. Setaria cover was assessed prior to spraying (0 days relative to spraying), and then again after two months (64 days relative spraying), with absolute changes in regrowth analysed. Although the application of Roundup® on its own provided good control within both trials, complete setaria control could not be obtained. Select® and the tested adjuvants did not improve Roundup® efficacy at the rates at which they were applied. The application of Roundup® in autumn (x̄ = 5.2% live cover) was more effective than the spring application (x̄ = 8.5% live cover), indicating that future studies should focus more on a combination of a season of application and subsequent follow-up operations, rather than the role of the adjuvants tested. Hedychium gardnerianum (wild ginger): Currently no herbicides are registered for the control of wild ginger in South Africa. One trial was implemented to test the potential for the control of wild ginger with herbicides applied to the foliage, cut-stems or rhizomes. In addition to an untreated control (no herbicide applied), Roundup® (glyphosate isopropylamine salt 360 g a.i. ℓ-1 at 4%) was applied as a foliar spray, either alone or with five adjuvants (three natural and two synthetic adjuvants). Brush- Off® (metsulfuron-methyl 6 g a.i. ℓ-1) or Roundup® was also applied to the cut-stems and rhizomes. Herbicide phytotoxicity was assessed up till 229 days after treatment application in terms of mortality, reduced and/or abnormal growth (of the resprouts) and foliar necrosis and/or discolouration. Although the foliar application of Roundup® (alone or with adjuvants) resulted in limited phytotoxicity, these treatments were ineffective in terms of killing wild ginger. The application of Roundup® or Brush-Off® to either the cut rhizome or cut-stems were equally effective, however, the cut-stem application would be preferred due to the reduced effort required. Future studies should further optimize the application of Roundup® (lowered rates + adjuvants) to the cut-stems/rhizome. Solanum mauritianum (bugweed): One trial was implemented on a stand of mature bugweed (located within a pine stand). The potential to reduce rates and/or improve the efficacy of Garlon® (triclopyr butoxyethyl ester 480 g a.i. ℓ-1®) was tested through the use of four adjuvants (two natural and two synthetic products) when applied as either a cut-surface or basal bark application. Two untreated controls (cut-surface or iv basal bark) were included for comparative purposes. The trial consisted of a 2 x 5 factorial arrangement of 10 treatments replicated three times and laid out as a randomized complete block design (RCBD). Although the cut-surface treatments were more effective than the basal bark treatments, no treatment provided complete control of bugweed. Of the cut-surface treatments, Garlon® + Break-Thru® (polyether-polymethylsiloxane-copolymer 1 000 g ℓ-1), Garlon® + Orosorb® (orange oil 50 g ℓ-1), and Garlon® + Actipron Super® (mineral oil 820 g ℓ-1) were equally effective, with Garlon® + Nu-Film P® (poly-1-menthene 975 g ℓ-1) the least effective. As the adjuvants tested did not improve the efficacy of Garlon® at the rates applied, the use of the most cost-effective and environmentally acceptable product would be preferable. For effective long-term control of mature bugweed, a cutsurface application is advisable, together with follow-up operations required. The results from these trials indicate that for bugweed and setaria, the currently registered herbicides remain the products of choice, albeit not 100% effective on wellestablished plants. In addition, the use of the adjuvants tested did not improve herbicide efficacy (and hence the opportunity for reducing rates of application) for all three species tested. However, Roundup® or Brush-Off® applied to either the cut rhizome or cut-stems were equally effective in terms of wild ginger control, indicating an opportunity for further testing to optimise rates of application.
  • Full Text:
  • Date Issued: 2019

The use of image processing to determine cell defects in polycrystalline solar modules

  • Authors: Banda, Peter
  • Date: 2019
  • Subjects: Polycrystals
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: http://hdl.handle.net/10948/36573 , vital:33996
  • Description: This research aims to use image processingtodetermine cell defects in polycrystalline solar modules. Image processing is a process of enhancing images for differentapplications. One domain that seems to not yet utilise the use of image processing, is photovoltaics. An increased use of fossil fuels is damaging the earth and a call to protect the earth has resulted in the emergence of pollutant-free technologies such as polycrystalline photovoltaic (PV) cells, which are connected to make up solar modules. However, defects often affect the performance of PV cells and consequently solar modules. Electroluminescence (EL) images are used to examine polycrystalline solar (PV) modules to determine if the modules are defective. The main research question that this research addressed is“How can an image processing technique be used to effectively identify defective polycrystalline PV cells from EL images of such cells?“. The experimental research methodology was used to address the main research question. The initial investigation into the problem revealed that certain sectors within industry, as well as the Physics Department at Nelson Mandela University(NMU), do not currently utiliseimage processing when examining EL images of solar modules. The current process is a tedious, manual process whereby solar modules are manually inspected. An analysis of the current processes enabled the identification of ways in which to automatically examine EL images of solar modules. An analysis of literatureprovided a better understanding of the different techniques that are used to examine solar modules, and it was identified how image processing can be applied to EL images. Further analysis of literatureprovided a better understanding of image processing and how image classification experiments using Deep Learning (DL) as an image processing technique can be used to address the main research question. The outcome of the experiments conducted in this research weredifferentadaptive models(LeNet, MobileNet, Xception)that can classify EL images of PV cellsaccording to known standardsused by the Physics Department at NMU. The known standards yielded four classes; normal, uncritical, critical and very critical, which were used for the classification of EL images of PV cells. The adaptive models were evaluated to obtain the precision, recall and F1–scoreof the models.The precession, recall, and F1–score were required to determine how effective the models were in identifying defective PV cells from EL images.The results indicated that an image processing technique canbe used to identify defective polycrystalline PV cells from EL images of such cells. However, further research needs to be conducted to improve the effectiveness of the adaptive models.
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  • Date Issued: 2019
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