List of Titles

Dual and targeted photodynamic therapy ablation of bacterial and cancer cells using phthalocyanines and porphyrins in the presence of carbon-based nanomaterials

Authors: Openda, Yolande Ikala
Date: 2022-10-14
Subjects: Phthalocyanines , Porphyrins , Active oxygen , Biofilms , Breast Cancer Treatment , Nanostructured materials , Combination therapy , Photochemotherapy
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365945 , vital:65804 , DOI https://doi.org/10.21504/10962//365946
Description: Phthalocyanines (Pcs) and porphyrins bearing substituents that possess antibacterial/anticancer properties are used as photosensitizers (PS) for the first time in the work. For targeting specificity and improved photoactivity, the PSs were afterward functionalized with carbon nanomaterials such as graphene quantum dots (GQDs) and detonation nanodiamonds (DNDs) via covalent conjugation (amide or ester bonds) or by non-covalent conjugation (π-π stacking and electrostatic interactions). Furthermore, the PSs-DNDs nanoconjugates were conjugated to either chitosan-capped silver nanoparticles (CSAg) via amide bonds or to the bare silver nanoparticles (Ag NPs) using the silver- nitrogen affinity. The as-synthesized nanoconjugates were also fully characterized by spectroscopic and microscopic methods together with thermal analysis. The potential photocytotoxicity of the complexes alone and their nanoconjugates against S. aureus and/or E. coli planktonic and biofilm cultures has been evaluated in vitro. Compared to the non- quaternized PSs, the cationic analogs exhibited a higher photodynamic inactivation against the planktonic cells with log10 reduction values above 9 in the viable count using a concentration of ca. 1.25 μM following 30 min exposure to light (Light dose: 943 J/cm2 for Pcs and 250 mW/cm2 for porphyrins). Whereas, at a concentration of ca. 100 μM the cationic PSs showed complete eradication of biofilms upon 30 min exposure to light. As a result of conjugation to carbon-based nanomaterials and silver nanoparticles, the compounds proved to be more effective as they exhibited stronger antibacterial and anti-biofilm activities on the multi-drug resistant bacteria strains due to synergetic effect, compared to PSs alone. This suggests that the newly prepared nanohybrids (PS concentration ca. 100 μM) could be used as potential antimicrobial agents in the treatment of biofilm-related infections. The target nanoconjugates showed all the advantages of two different groups existing on a single entity. In light of the potential advantages of combined chemotherapy and photodynamic antimicrobial chemotherapy (PACT), this work reports for the first time the use of PACT-ciprofloxacin (CIP) dual therapy using selected indium quaternized PSs which showed higher photoactivity with complete eradication of both Gram-positive and Gram-negative bacteria biofilms at concentrations of 8 μM of PS versus 2 μg/mL of the antibiotic following 15 min irradiation time (light dose: 471 J/cm2 for Pcs and fluence: 250 mW/cm2 for porphyrins) on S. aureus. Whereas the total killing of E. coli was obtained when combining 8 or 16 μM of PS combined with 4 μg/mL of CIP. The combined treatment resulted in the complete eradication of the matured biofilms with the highest log10 reduction values of 7.05 and 7.20 on S. aureus and E. coli, respectively. Used as a model, positively charged dimethylamino-chalcone Pcs also exhibited interesting photodynamic therapy (PDT) activity against MCF-7 cancer cells giving IC50 values of 17.9 and 7.4 μM, respectively following 15 min irradiation. Additionally, the TD-B3LYP/LanL2DZ calculations were run on the dimethylaminophenyl- porphyrins to compare the singlet excitation energies of quaternized and non-quaternized porphyrins in vacuo. the study shows excellent agreement between time-dependent density- functional theory (TD-DFT) exciting energies and the experimental S1>S0 excitation energies. The small deviation observed between the calculated and experimental spectra arises from the solvent effect. The excitation energies observed in these UV-Vis spectra mostly originated from electron promotion between the highest occupied molecular orbital (HOMO) for the less intense band and the HOMO-1 for the most intense band of the ground states to the lower unoccupied molecular orbital (LUMO) of the excited states. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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Date Issued: 2022-10-14

Effect of Helicosporidium sp. (Chlorophyta; Trebouxiophyceae) infection on Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), a biological control agent for the invasive Salvinia molesta D.S. Mitchell (Salviniaceae) in South

Authors: Mphephu, Tshililo Emmanuel
Date: 2022-10-14
Subjects: Salvinia molesta South Africa , Weeds Biological control , Cyrtobagous salviniae , Ketoconazole
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365815 , vital:65792 , DOI https://doi.org/10.21504/10962/365815
Description: The effectiveness of established biological control agents depends on biotic and abiotic interactions in the introduced range. The weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), was released as a biological control against Salvinia molesta D.S. Mitchell (Salviniaceae) in South Africa in 1985. This agent has been highly successful against S. molesta and has significantly reduced the weed’s populations around the country. However, in 2007, the parasitic alga, Helicosporidium sp. (an undescribed species), was detected in field-collected C. salviniae adults in South Africa. The distribution and impacts of this disease on the weevil and its efficacy as a control agent were not known. In this thesis, the prevalence, infection load, and impact of Helicosporidium sp. on C. salviniae was determined. In 2019, adult weevils were collected from 10 sites across the Eastern Cape, KwaZulu-Natal, Limpopo, and Western Cape provinces and screened to determine the occurrence, infection load, and geographic distribution of Helicosporidium sp. Transmission mechanisms of this disease in C. salviniae were then evaluated. The possible impact of Helicosporidium sp. was assessed by comparing the feeding rates and the reproductive output of the diseased and healthy adults of C. salviniae. An attempt was then made to eliminate the disease in C. salviniae through the application of the antibiotic, ketoconazole. Further, the role of temperature on infection load in C. salviniae was also assessed. Finally, recommendations for the long-term biological control programme against S. molesta in South Africa were made. The disease covers the entire distribution range of C. salviniae in South Africa, with the disease occurrence rate ranging from 92.15% to 100% insects infected per site. Helicosporidium sp. was found to transmit vertically within the populations of C. salviniae. Infection by the Helicosporidium sp. disease reduced the reproductive output of C. salviniae as well its impact on biomass reduction of S. molesta when a diseased culture was compared to a healthy culture from the USA. 98.44 to 98.55% of Helicosporidium sp. loads were reduced through multiple applications of ketoconazole concentrations under in vitro trials. In vivo treatments resulted in 70% control of Helicosporidium sp. in the adults of C. salviniae that were fed ketoconazole three times over a 21 day period. Adult C. salviniae feeding and survival performances were similar when fed fronds of S. molesta inoculated with ketoconazole and water. The lowest and highest disease loads of Helicosporidium sp. were recorded when the weevils were reared at 30°C and 14°C, respectively. As expected, the highest impact and reproductive output of C. salviniae were at 30°C. The evaluations discussed in this thesis highlight the role of diseases in biological control agents, and gaps in both the pre-release and post-release monitoring that should integrate screening of diseases in these studies. Although the combined application of the antibiotic and temperature will reduce Helicosporidium sp. loads and impact, this technology is most likely only applicable where the weevils are reared in small numbers in a rearing facility and not really applicable to the field situation. It is important to release healthy agents that will cause efficient control of the target weed plant species, therefore, when introducing new biological control agents, the health status of such agents needs to be understood. Therefore, long-term field monitoring and assessment of the impact of C. salviniae on S. molesta should be conducted to track all the changes that may result due to the presence of Helicosporidium sp. This long-term monitoring and assessment will give a more informative role of Helicosporidium sp. in field populations of C. salviniae. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
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Date Issued: 2022-10-14

Fucoidans from South African brown seaweeds: establishing the link between their structure and biological properties (anti-diabetic and anti-cancer activities)

Authors: Mabate, Blessing
Date: 2022-10-14
Subjects: Fucoidan , Diabetes Treatment , Cancer Treatment , Brown algae
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365677 , vital:65775 , DOI https://doi.org/10.21504/10962/365677
Description: Type 2 diabetes mellitus (T2DM) and cancer are major non-communicable diseases causing a heavy morbidity-mortality and economic burden globally. The therapeutic efforts in managing these diseases are primarily chemotherapeutic and are associated with demerits, including side effects and toxicity, limiting the prescribed amounts. These dosage limits may cause drug resistance, another major challenge in maintaining quality global health. The pursuit of novel natural bioproducts is a reasonable strategy to add to the arsenal against T2DM and cancer. Fucoidans, sulphated fucose polysaccharides abundant in brown seaweeds, have recently become popular for their biological activities, including anti-diabetic and anti-cancer properties. However, endemic South African brown seaweeds have not been adequately explored. Therefore, this study sought to characterise fucoidans extracted from South African brown seaweeds and elucidate their structure to their biological activities. Also, this study highlighted carbohydrate and glucose metabolism as major target processes in the control efforts of T2DM and cancer using fucoidans. Harvested brown seaweeds were identified as Ecklonia radiata and Sargassum elegans. E. maxima was kindly donated by KelpX. The fucoidans were then extracted using hot water, EDTA assisted, and acid extraction protocols. The integrity of the extracted fucoidan was confirmed through structural analysis using FTIR, NMR and TGA. The fucoidan extracts were then chemically characterised to determine their carbohydrate and monosaccharide composition and sulphate content. The characterised fucoidans were profiled for inhibiting the major amylolytic enzymes, namely α-amylase and α-glucosidase. The mode of inhibition by fucoidans and synergy experiments with the commercial anti-diabetic drug acarbose were also investigated. Furthermore, the fucoidans were screened for potential anti-cancer activities on the human colorectal HCT116 cancer cell line. The cytotoxicity of fucoidans was quantified using the resazurin assay. The effect of fucoidan on HCT116 cell adhesion on the tissue culture plastic was also investigated using the crystal violet-based cell adhesion assay. In addition, cancer antimigration properties of fucoidans were also investigated using 2D wound healing and 3D spheroid-based assays. Furthermore, the long-term survival of HCT116 cells was investigated through the clonogenic assay after treatment with fucoidans. Lastly, glucose uptake and lactate export assays revealed the influence of fucoidan on glucose uptake and the glycolytic flux of HCT116 cells. Fucoidans were successfully extracted with a yield between 2.2% and 14.2% on a dry weight basis. EDTA extracts produced the highest yields than the water and the acid extracts. Ecklonia spp. fucoidans displayed the highest total carbohydrate content, with glucose and galactose being the major monosaccharides. S. elegans and commercial Fucus vesiculosus had lower carbohydrate contents but contained more sulphates than the Ecklonia spp. fucoidans. Furthermore, the extracted fucoidan contained little to no contaminants, including proteins, phenolics and uronic acids. In addition, the extracted fucoidans were determined to be >100 kDa through ultracentrifugation. Mass spectrometry also detected the most abundant peak for all fucoidans to be around 700 Da (m/z). Extracted fucoidans inhibited the activity of α-glucosidase more strongly than the commercial anti-diabetic agent acarbose but were inactive on α-amylase. Fucoidans were also shown to be mixed inhibitors of α-glucosidase. Compellingly, fucoidans synergistically inhibited α-glucosidase in combination with the anti-diabetic agent acarbose, highlighting prospects for combination therapy. Finally, fucoidans demonstrated some anti-proliferative characteristics on HCT116 cancer cells by inhibiting their ability to adhere to the tissue culture plate matrix. Furthermore, some fucoidan extracts inhibited the migration of HCT116 cancer cells from 3D spheroids. Some of our fucoidan extracts also inhibited HCT116 colony formation, demonstrating inhibition of long-term cell survival. The E. maxima water extract also inhibited glucose uptake by HCT116 cells, thereby influencing the glycolytic flux. In conclusion, biologically active fucoidans were successfully extracted from South African brown seaweeds. These fucoidans demonstrated anti-diabetic and anti-cancer properties, revealing their relevance as potential drugs for these diseases. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
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Date Issued: 2022-10-14

Functional biogeography: evaluating community assemblage patterns and ecosystem functioning in intertidal systems using trait-based approaches

Authors: Gusha, Molline Natanah C
Date: 2022-10-14
Subjects: Biogeography , Marine algae , Benthic ecology , Invertebrates , Functional redundancy , Ocean temperature , Biology Classification
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365792 , vital:65790 , DOI https://doi.org/10.21504/10962/365792
Description: Analyses of taxonomic diversity patterns within coastal systems has been critical in the development of the theory of biogeography. Increasing evidence, however, shows that the variety of functions that species perform in ecosystems (rather than their taxonomic identity) is a better predictor of the influence of the environment on the species. This information has been useful in predictive ecology leading to the development of trait-based approaches (TBA). Until the late 1970s, however, limited effort (particularly in marine systems) was channeled towards patterns in functional species traits and how they may be affected by changes in environmental gradients. Here, I mapped the functional biogeography of the South African coastline based on a suite of species' reproduction and development traits. Because species composition is one of the key tools used by zoogeographers to map species distribution patterns, I expected lower variability in trait composition within main biogeographic regions than in intervening transition zones based on the habitat templet theory and following the biomass ratio and limiting similarity hypotheses. In brief, the habitat templet theory proposes that “the habitat provides a templet upon which evolution forges species characteristics”, while the biomass ratio hypothesis assumes that the most abundant species traits determine ecosystem functioning. The limiting similarity hypothesis also sometimes referred to as the niche complementarity hypothesis, however, predicts that species can coexist if their niches complement one another. In light of the habitat being an evolutionary templet, abiotic and biotic habitat patterns were measured as nearshore SST and chlorophyll-a gradients, respectively. I expected the SST gradient to act as the stronger key filter of trait diversification because temperature is often considered the most influential environmental factor affecting species survival with seasonality of SST affecting the timing of spawning and along with food availability, possibly influencing fecundity. Functional trait data were thus compiled for macroinvertebrate species collected from fifty-two rocky shore sites from three main bioregions (east, south, and west) and two transition zones (south-west and south-east). Biological trait analysis and functional diversity indices were used to evaluate how traits related to species development and reproduction respond to temperature and chlorophyll -a (used as a proxy for food availability) gradients along the coastline. GLMM and hierarchical cluster analyses showed distinct patterns/shifts in SST and chlorophyll-a gradients across bioregions, with two main breaks in SST separating the east and south-east overlap (SEO) bioregions from the south, south-west overlap (SWO) and west bioregions. In contrast, chlorophyll-a exhibited three major breaks with the east, SEO–south–SWO, and west clustering independently of each other. The RLQ analysis (a type of co-inertia analysis) which simultaneously ordinates 3-matrix datasets [i.e., (environment × site[R]), (species × site[L]) and (species × traits [Q])] showed that the higher SST gradient on the east and SEO promoted higher abundance and biomass of simultaneous hermaphrodites while higher chlorophyll-a gradients on the SWO and west coasts strongly promoted reproductive maturity at larger-sizes. The combined fourth-corner analyses showed that the modalities within the development trait domain responding to chlorophyll-a gradients primarily included filter feeders, sessile and swimming species and also species living on the infratidal zone. In addition, the reproduction trait domain showed higher sensitivity and association to differences in chlorophyll-a and SST gradients than development traits. Overall, SST and chlorophyll-a gradients influenced the distribution of the most dominant traits as indicated by shifts in community-weighted mean trait values across bioregions. This suggests the importance of habitat filtering on coastal species reproduction. A separate study evaluating the influence of large-scale biogeographic effects vs the micro-scale biogenic habitat structure offered by coralline seaweeds across 24 sites revealed some notable effects of both factors on the diversity and abundance of macroalgal epifauna. There was a notable biogeographic influence on epifauna, with the SEO recording the highest epifaunal species richness and abundance, followed by the south coast, then the SWO and lastly the west coast. In addition, the total biomass gradient of the corallines followed a similar trend. The epifauna however, showed no host-specificity, illustrating that epifauna may not be species–centric as commonly assumed, and the higher diversity of epifaunal diversity may well be simply because those corallines are the available habitat within the sampled part of the coastline. Lastly, macroinvertebrate trait distribution on the South African coastline confirms that the habitat, particularly the biotic filter (in this case chl-a) provides a templet upon which evolution forges species traits. However, since temperature is a proxy for nutrient availability (cold upwelling brings nutrients), then temperature drives chlorophyll-a. Subsequently this means the abiotic component indirectly drives trait distribution by influencing the biotic environment (chl-a). For epifauna species, also, the coralline diversity and composition can also be regarded as a biotic filter influencing the epifaunal abundances and composition across different bioregions. Moreover, since temperature is regarded as a conservative trait in seaweeds, temperature tolerance defines the biogeographical boundaries of seaweeds, therefore temperature may be indirectly affecting epifauna abundances through coralline species diversity and biomass. In summary, considering the deterministic processes governing ecosystem functioning and community assemblage, the mass ratio and limiting similarity hypotheses showed complementary effects. Different bioregions provided variable support for these two hypotheses, but overall, the mass ratio hypothesis (weighted by species biomass) received stronger support and may be more meaningful to the interpretation of ecosystem functioning and persistence within rocky shore systems. Lastly, although, the SWO showed some of the characteristics of a subtraction zone based on the relatively low abundance, diversity, and biomass measures. Nonetheless, there was evidence of high functional redundancy across all other four bioregions. This suggests that in the context of development and reproduction traits, the rocky shore ecosystem along the SA coastline may be functionally stable at this stage. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
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Date Issued: 2022-10-14

Human Development, the Capability Approach and the Mediating of Sustainable Rural Livelihoods: a case study of women’s empowerment through expansive learning in the Mzimvubu Catchment of the Eastern Cape province, South Africa

Authors: Conde Aller, Laura
Date: 2022-10-14
Subjects: Expansive learning , Social learning , Transformative learning , Capabilities approach (Social sciences) , Women's rights South Africa Mzimvubu River Watershed , Women Economic conditions , Women Social conditions , Sustainable agriculture South Africa Mzimvubu River Watershed
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/366236 , vital:65845 , DOI https://doi.org/10.21504/10962/366236
Description: This study makes a contribution to the field of sustainable agricultural development and women empowerment in rural South Africa by examining the transformations derived from an expansive learning process with a women farmers group in terms of their food production capability expansion and empowerment as well as the well-being of their local catchment or landscape where their activity was situated. The study took place in the Lutengele villages along the upper reaches of the lower Mzimvubu Catchment near Port St Johns in the Eastern Cape province of South Africa. Women in southern Africa are significant contributors to household livelihoods through their household food production practices and at the same time they are also one of the primary natural resource users in rural landscapes. In this case study, historical and contemporary ethnographic and situational data revealed disjuncture between existing practice and the fulfilment of women aspirations with regard to food security and social and ecological well-being at large. As a result, central to this study were the concepts of aspirations and capabilities and the role that these played in transformative learning processes via formative intervention research (after Engeström’s concept of expansive learning). Expansive learning emerges from Vygotsky’s early work on mediation of learning through language and culture, which gave raise to Cultural Historical Activity Theory (CHAT). Whereas the Capability Approach (CA) recognises that development interventions or initiatives should focus on “expanding the freedom that deprive people from enjoying their valued beings and doings” (Sen, 1999, p. 3), in other words, what people value or have reason to value. The Capability Approach coupled with CHAT deepens the contextual understanding of the agricultural activity system in light of the engendered power dynamics associated with women having access to productive resources, their culturally expected roles and responsibilities in the institution of their households, their families and the community at large, and most importantly, aspects of gerontocracy defined by their age and status in society. In addition, drawing on the Capability Approach as a lens to view agricultural development, social transformation and empowerment, provided the tools to conceptualise participants’ aspirations, their true value and the capabilities necessary for such aspirations to be realised in a context filled with socio-cultural and political power relations and dynamics faced especially by women. The first phase of the study set out to map the context in which the participants’ small-scale food production activity was situated, their aspirations relevant to sustainable agricultural livelihoods, food security, well-being and lastly, the main factors or contradictions inhibiting participants from attaining the aspired food production goals. During the initial phase of the expansive learning cycle I was able to address the first research question: What tensions and contradictions in aspiration-practice relationships shape household food security in the context of catchment management of the women farmers’ group or river forum in the Lutengele area? Twelve contradictions were identified from the historical and contemporary socio-cultural analysis of the home-based food production practices and agricultural activity in relation to the research participants’ envisaged aspirations, which under further scrutiny were thereafter considered by the participants as critical capabilities to pursue during the collective and transformative learning process in the second phase of the study. In the second phase of the study, a series of second stimuli were introduced in the form of conceptual and material tools and tasks with the aim to move participants along the expansive learning process. This led to the unfolding of the collectively defined Capability Learning Pathways for sustainable food production or expansion of their agricultural capability in the context of sustainability of the local micro-catchment or landscape. Through the various Change Laboratory workshops and supporting mini-cycles in the last stages of the formative interventionist research, participants’ learning and development was supported in a way that not only brought individuals together to co-design relevant solutions, strategies and working groups or committees, but also catalysed and amplified transformative agency and the expansion of food production capability, sustainable land use practices and ultimately empowerment. This answered the second and most important research question: Can, and if so, how can expansive social learning processes shape conversion factors for turning available resources into functionings that enhance household food security capabilities and ecological well-being? The methodology of expansive learning and formative interventionist research design intervention, with supporting mediating tools, has proven a positive intervention in the attainment of capabilities (or functionings) in relation to the participant’s aspired livelihoods and consequently improving their well-being as well as their ability to navigate through the various gendered power dynamics, especially for the young women participating in this study. The study proposes expansive learning as a suitable critical and transformative learning theory and methodology for the mediation of collective deliberations and the pursuit of capability development as charted by the learners’ collective and individual aspirations. This is a learning process that not only pursues the learners’ attainment of material and cognitive changes but also opens up new opportunities and most importantly, the freedom to exercise their agency no matter the circumstances they find themselves in – in other words, the freedom to aspire and to be, do and become what one values as instrumentally and intrinsically critical to live a life that they have reason to value. In sum, the unfolding of the expansive learning process happened at three levels: at the value clarification level in terms of human and non-human relationships and social relationality, the institutional level and the practices level. The study recommends further research on the suitability of expansive learning and Change Laboratories as a Capability Expansion Methodology involving human development and Capability Approach practitioners, particularly those with an interest in informal learning and community-based empowering initiatives. Additionally, further studies are also suggested for examining formative interventionist research as a participatory action research approach for capability development work in education and learning research and in different study fields and contexts. , Thesis (PhD) -- Faculty of Education, Education, 2022
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Date Issued: 2022-10-14

Identification and characterisation of microbial communities and their metabolic potential in meltwater ponds, Western Dronning Mau Land, Antarctica

Authors: Van Aswegen, Sunet
Date: 2022-10-14
Subjects: Uncatalogued
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365723 , vital:65779
Description: Thesis embargoed. Expected release date early 2024. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
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Date Issued: 2022-10-14

Identification of novel compounds against Plasmodium falciparum Cytochrome bc1 Complex inhibiting the trans-membrane electron transfer pathway: an In Silico study

Authors: Chebon, Lorna Jemosop
Date: 2022-10-14
Subjects: Malaria , Plasmodium falciparum , Molecular dynamics , Antimalarials , Molecules Models , Docking , Cytochromes , Drug resistance , Computer simulation , Drugs Computer-aided design , System analysis
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365666 , vital:65774 , DOI https://doi.org/10.21504/10962/365666
Description: Malaria continues to be a burden globally with a myriad of challenges deterring eradication efforts. With most antimalarials facing drug resistance, such as atovaquone (ATQ), alternative compounds that can withstand resistance are warranted. The Plasmodium falciparum cytochrome b (PfCytb), a subunit of P. falciparum cytochrome bc1 complex, is a validated drug target. Structurally, cytochrome b, cytochrome c1, and iron sulphur protein (ISP) subunits form the catalytic domain of the protein complex having heme bL, heme bH and iron-sulphur [2FE-2S] cluster cofactors. These cofactos have redox centres to aid in the electron transfer (ET) process. These subunits promote ET mainly through the enzyme’s ubiquinol oxidation (Qo) and ubiquinone reduction (Qi) processes in the catalytic domain. ATQ drug has been used in the prevention and treatment of uncomplicated malaria by targeting PfCytb protein. Once the mitochondrial transmembrane ET pathway is inhibited, it causes a collapse in its membrane potential. Previously reported ATQ drug resistance has been associated with the point mutations Y268C, Y268N and Y268S. Thus, in finding alternatives to the ATQ drug, this research aimed to: i) employ in silico approaches incorporating protein into phospholipid bilayer for the first time to understand the parasites’ resistance mechanism; ii) determine any sequence and structural differences that could be explored in drug design studies; and iii) screen for PfCytb-iron sulphur protein (Cytb-ISP) hit compounds from South African natural compound database (SANCDB) and Medicines for Malaria Venture (MMV) that can withstand the identified mutations. Using computational tools, comparative sequence and structural analyses were performed on the cytochrome b protein, where the ultimate focus was on P. falciparum cytochrome b and its human homolog. Through multiple sequence alignment, motif discovery and phylogeny, differences between P. falciparum and H. sapiens cytochrome b were identified. Protein modelling of both P. falciparum and H. sapiens cytochrome b - iron sulphur protein (PfCytb-ISP and HsCytb-ISP) was performed. Results showed that at the sequence level, there were few amino acid residue differences because the protein is highly conserved. Important to note is the four-residue deletion in Plasmodium spp. absent in the human homolog. Motif analysis discovered five unique motifs in P. falciparum cytochrome b protein which were mapped onto the predicted protein model. These motifs were not in regions of functional importance; hence their function is still unknown. At a structural level, the four-residue deletion was observed to alter the Qo substrate binding pocket as reported in previous studies and confirmed in this study. This deletion resulted in a 0.83 Å structural displacement. Also, there are currently no in silico studies that have performed experiments with P. falciparum cytochrome b protein incorporated into a phospholipid bilayer. Using 350 ns molecular dynamics (MD) simulations of the holo and ATQ-bound systems, the study highlighted the resistance mechanism of the parasite protein where the loss of active site residue-residue interactions was identified, all linked to the three mutations. The identified compromised interactions are likely to destabilise the protein’s function, specifically in the Qo substrate binding site. This showed the possible effect of mutations on ATQ drug activity, where all three mutations were reported to share a similar resistance mechanism. Thereafter, this research work utilised in silico approaches where both Qo active site and interface pocket were targeted by screening the South African natural compounds database (SANCDB) and Medicines for Malaria Venture (MMV) compounds to identify novel selective hits. SANCDB compounds are known for their structural complexity that preserves the potency of the drug molecule. Both SANCDB and MMV compounds have not been explored as inhibitors against the PfCytb drug target. Molecular docking, molecular dynamics (MD) simulations, principal component, and dynamic residue network (DRN; global and local) analyses were utilised to identify and confirm the potential selective inhibitors. Docking results identified compounds that bound selectively onto PfCytb-ISP with a binding energy ≤ -8.7 kcal/mol-1. Further, this work validated a total of eight potential selective compounds to inhibit PfCytb-ISP protein (Qo active site) not only in the wild-type but also in the presence of the point mutations Y268C, Y268N and Y268S. The selective binding of these hit compounds could be linked to the differences reported at sequence/residue level in chapter 3. DRN and residue contact map analyses of the eight compounds in holo and ligand-bound systems revealed reduced residue interactions and decreased protein communication. This suggests that the eight compounds show the possibility of inhibiting the parasite and disrupting important residue-residue interactions. Additionally, 13 selective compounds were identified to bind at the protein’s heterodimer interface, where global and local analysis confirmed their effect on active site residues (distal location) as well as on the communication network. Based on the sequence differences between PfCytb and the human homolog, these findings suggest these selective compounds as potential allosteric modulators of the parasite enzyme, which may serve as possible replacements of the already resistant ATQ drug. Therefore, these findings pave the way for further in vitro studies to establish their anti-plasmodial inhibition levels. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
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Date Issued: 2022-10-14

Land degradation and livelihood strategies in rural Zimbabwe: the case of two A1 farms in Shurugwi District

Authors: Nciizah, Tendai
Date: 2022-10-14
Subjects: Land degradation Zimbabwe , Sustainable livelihood , Shurugwi District , Conservation of natural resources Zimbabwe , Land reform Zimbabwe
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365989 , vital:65808 , https://doi.org/10.21504/10962/365989
Description: Land degradation is a global phenomenon which is having serious negative consequences for rural livelihoods, which depend quite fundamentally on land and its resources. At the same time, one of the key conditions contributing to land degradation relates to rural livelihood practices, insofar as these practices fail to protect the land. Hence, there sometimes exists a mutually-reinforcing process of decline, in relation to both land vitality and livelihoods vitality over time. This thesis seeks to investigate and understand this complex land-livelihoods process through a case study of two fast track farms in the Shurugwi District of contemporary Zimbabwe. In the year 2000, the Zimbabwean government introduced the fast track land reform programme which fundamentally reconfigured the rural landscape. In particular, it led to the formation of A1 farms (containing small-scale farming units called A1 plots), onto which people were resettled for purposes of enhancing their livelihoods. The case study focuses on two A1 farms in the district, namely, Selukwe Peak and Adare farms. Through a longitudinal study of land and livelihoods on these A1 farms, this study seeks to identify the multi-faceted character of land degradation on the farms, the multi-layered conditions (or causes) facilitating land degradation (specifically, the farm-based livelihood practices) and the effects of this land degradation on these very livelihood practices. This includes a focus on farmers’ understandings of land degradation and how these understandings may or may not condition livelihood practices on the two farms. Of particular importance is the presence of not only agricultural practices, but also high levels of illegal and legal mining on the farms and in the surrounding areas. In pursuing this study, the thesis draws upon the Sustainable Livelihoods Approach alongside Margaret Archer’s morphogenetic sociological perspective. Combined, they provide an intricate understanding of the relevance of both structure and agency to the analysis. A qualitative methodology was used, and this involved a questionnaire survey, in- depth interviews, life histories, focus group discussions and transect walks. The study concludes that the livelihood strategies undertaken by the villagers of Selukwe Peak and Adare farms are key causes of land degradation, as are the land-degrading activities of illegal and legal miners. The A1 villagers are aware that their activities are causing land degradation but they continue these activities because they are pushed by circumstances beyond their control. Hence, both proximate and underlying causes are of some significance in understanding land degradation and livelihoods on the two farms, and their interrelationships. , Thesis (PhD) -- Faculty of Humanities, Sociology, 2022
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Date Issued: 2022-10-14

Mechanistic analysis of two cytotoxic thiazolidinones as novel inhibitors of Triple-Negative Breast Cancer

Authors: Vukea, Nyeleti
Date: 2022-10-14
Subjects: Uncatalogued
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365734 , vital:65780
Description: Thesis embargoes. Expected release date early 2025. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
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Date Issued: 2022-10-14

Mentoring as social learning value creation in two South African environmental organisations: a social realist analysis

Authors: Hiestermann, Michelle
Date: 2022-10-14
Subjects: Social realism , Social learning , Mentoring , Environmental education South Africa
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/366248 , vital:65846 , https://doi.org/10.21504/10962/366248
Description: South Africa is facing overwhelming crises of educational quality, record rates of unemployment (especially amongst youth) and environmental issues and risks, further exacerbated by the Covid-19 pandemic. Environmental education research that addresses these challenges is critical to ensuring that future generations thrive in a warming climate. South Africa needs environmental leaders; we therefore need to understand and explore the possibilities of mentoring young professionals in environmental organisations in South Africa. Several initiatives have been developed to contribute to the mentoring of young professionals in South African environmental organisations. This study drew on a critical realist ontology, social realist meta-theory and domain specific theory on mentoring and evaluation to explore mentoring as a value creating proposition in two environmental organisations in South Africa that were part of the national Groen Sebenza youth employment creation programme which had a strong focus on mentoring. To strengthen conceptual analytical tools on mentoring, I undertook an immanent critique of domain specific mentoring theory to develop a more appropriate foundation for mentoring theory in the environmental sector that was not subject to the historical influence of human capital theory only (which has tended to dominate the field’s literature). I then developed in-depth understanding of mentoring in two case study contexts, namely a non-profit environmental organisation and an environmental consulting company, using qualitative research approaches that included contextual profiling, case study research and mirror data workshops. Analytically, I considered the case data drawing on the value creation evaluation framework of Wenger-Trayner and Wenger-Trayner (2014) which itself was developing as an analytical framework as the study developed. I strengthened the analytical framework with social realist interpretations drawing on Archer (1995). This offered me a way of developing an in-depth understanding of the factors which constrain or enable the value creation possibilities of mentoring, with a view to inform human capacity development initiatives that support mentoring in the environment sector. It was possible to explain the value creation possibilities of mentoring within two case study environmental organisations through considering mentoring as a social learning process of value creation and this overcame some of the shortfalls identified in other early learning theories as well as theories of mentoring. The research revealed how mentoring can provide a value creation social learning trajectory for unemployed youth. A social realist perspective explained how young professionals expanded their primary agency, through full participation in workplace communities of practice, to find their identity as corporate agents in the workplace with their mentors. In this research, Social Realist ontology, theory and methodology was able to achieve what Human Capital Theory could not and provided an account of the interplay of structure, culture and agency over time, through emergent properties and the separation of structure and agency. Thus, it was possible to avoid conflation and the limitation of theory of the present tense, with a deeper, ontologically robust explanation of mentoring as social learning and social change and a social realist orientation to human capacity development. South Africa has a history of oppression, inequality and injustice and requires social processes that are reflexive, critical, emancipatory and transformative. Therefore, this research required theory and approaches that could explain mentoring of unemployed youth, as a common good initiative for a more just and sustainable society. As shown in this study, a Social Realist approach can uncover the underlying generative mechanisms and make the implicit more explicit in research, policy and strategy, offering a robust alternative to the tenets of Human Capital Theory that have driven much mentoring research in South Africa and elsewhere to date. , Thesis (PhD) -- Faculty of Education, Education, 2022
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Date Issued: 2022-10-14

Negotiating marginalisation: A socio-economic history of the Kalanga of Mangwe, Zimbabwe, 1940-2015

Authors: Nyathi, Innocent
Date: 2022-10-14
Subjects: Marginalisation , Kalanga (African people) Race identity Zimbabwe , Ethnicity Zimbabwe , Zimbabwe Economic conditions , Zimbabwe Social conditions , Kalanga language (Botswana and Zimbabwe)
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/408705 , vital:70518 , DOI 10.21504/10962/408705
Description: The thesis explores the relationship between ethnicity, marginalisation, and survival mechanisms amongst the Kalanga people of Mangwe (southwestern Zimbabwe) from the 1940s up until the turn of the 21st century. The study showed how the Kalanga of Mangwe have used ethnicity as a concept to not only claim access to resources but also develop alternative survival strategies that help them seek to navigate their experiences of marginalisation by both the state and the hegemonic position of the Ndebele who dominate the region politically and linguistically. Using evidence from activities such as cross border migration and the mopane economy, I showed how the Kalanga express their displeasure at being dominated through engagement, as was shown in their attempt to fight for their language, for example in the 1940s through regionalised Kalanga organisations as the Kalanga Language and Cultural Development Society (KLCDS), to disengagement such as migration and illegal informal cross border trade. Using ‘conviviality’ and ‘the everyday’, as well as borrowing from the Race Relations Theory (RRT) of Robert Ezra Park as theoretical underpinnings, I demonstrated how amongst the Kalanga of Mangwe ethnic identity can lead to competition for resources, which in turn leads to marginalisation and discrimination which influences their social, political and economic choices that may in turn reinforce ethnic identity in a cycle like scenario. Everyday economic and social activities amongst the Kalanga of Mangwe that appear mundane and ordinary to an uninterested observer, help shape the everyday discourse of the Kalanga as they navigate marginalisation. , Thesis (PhD) -- Faculty of Humanities, History, 2022
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Date Issued: 2022-10-14

Regulation of Oct4 expression during cell stress

Authors: Samson, William John
Date: 2022-10-14
Subjects: Uncatalogued
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365712 , vital:65778
Description: Thesis embargoed. Expected release date early 2025. , Thesis (PhD) -- Faculty of Science, Biochemistry and Microbiology, 2022
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Date Issued: 2022-10-14

Revitalisation and indigenisation of the Science curriculum through drum making, drumming, music and dance

Authors: Liveve, Angelius Kanyanga
Date: 2022-10-14
Subjects: Curriculum change Namibia , Science Study and teaching (Secondary) Namibia , Traditional ecological knowledge Namibia , Drum Performance , Drum making , Pedagogical content knowledge , Social learning
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/405482 , vital:70175 , DOI 10.21504/10962/405482
Description: The integration of IK is a common phenomenon in many postcolonial states, where it is viewed as a means to redress the injustices of the colonial era. It is believed that the recognition of IK in education represents an acknowledgement of diversity and other ways of knowing. In Namibia, for instance, the National Curriculum for Basic Education encourages the integration of IK in Science teaching. However, this goal is still far from being achieved because the curriculum seems to be silent on how teachers should integrate IK into their teaching. As a result, research shows that many Science teachers in Namibia seem to find it difficult to integrate IK into their science teaching because they were not properly trained to do so during both their pre-service and in-service training. This suggests that there is a dire need to empower science teachers who are implementers of the curriculum on appropriate pedagogical content knowledge on how to integrate IK into their science teaching in particular. It is against this backdrop that this interventionist study sought to explore how to mobilise the indigenous technology of drum making, drumming, music and dance for cultural revitalisation and indigenisation of the science curriculum. The study is underpinned by an interpretivist paradigm and augmented with an indigenous research paradigm. The interpretivist paradigm enabled me to understand the teachers’ perspectives in their contexts. On the other hand, within the indigenous research paradigm, I used the Ubuntu perspective which afforded each of us an opportunity to understand each other’s ways of knowing, doing and being. Within these two complementary paradigms, a qualitative case study approach was employed. The case study was in the form of intervention with six Grade 10 Physics teachers from three senior secondary schools in the Kavango West Region in Namibia. Moreover, a critical friend who was a lecturer at the university and expert community members of the Unongo Cultural Youth Group who are the custodians of the cultural heritage. Data were generated using semi-structured interviews, workshop discussions (audio-recorded), observations (participatory and lesson observations), stimulated recall interviews as well as journal reflections. Vygotsky’s Socio-cultural Theory, Ogunniyi’s Contiguity Argumentation Theory and Mavhunga and Rollnick’s Topic-specific Pedagogical Content Knowledge were used as the theoretical lenses in this study. The data gathered were analysed thematically and then categorised into sub-themes and themes. The findings of the study revealed that tapping into the cultural heritage of community members through giving them a voice has great potential to revitalise and indigenise the science curriculum. It also emerged in this study that storytelling is a potential instructional strategy to make science accessible and relevant to learners. The use of the indigenous technology of drum making, drumming, music and dance contributed to the Physics teachers’ agency and empowered them to co-develop their learning and teaching support materials in the form of exemplar lesson plans that integrated IK. Moreover, their pedagogical content knowledge was enhanced through enacting such exemplar lessons and thereafter reflecting on them. The study thus recommends that those in academia should promote the use of indigenous technologies as hubs for mediating the learning of science concepts. It also recommends that learners should be taken out of their science classrooms into the community to learn IK and wisdom from expert community members, something which could assist them in understanding the science taught at school. This might also benefit teachers in effectively implementing the integration of IK in schools and thereby use learners’ cultural heritage as a starting point to enrich meaningful and authentic learning. , Thesis (PhD) -- Faculty of Education, Education, 2022
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Date Issued: 2022-10-14

Social upgrading or dependency?: Investigating the implications of the inclusion of commercial wine farms within South African Fairtrade certification

Authors: Bell, Joshua
Date: 2022-10-14
Subjects: Competition, Unfair South Africa , Wine industry South Africa Employees , Unfair labor practices South Africa , Fairtrade International , International trade , Economic development Moral and ethical aspects South Africa , Wine industry Moral and ethical aspects South Africa , Work environment South Africa
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/327155 , vital:61086 , DOI 10.21504/10962/327155
Description: The South African wine industry is one of the oldest sectors of the country’s economy, beginning in the early years of South African colonialism in the 17th century through the use of slave and slave-like labour. As an industry that has been defined by farm paternalism and dependency, the South African wine industry has had to demonstrate changes from its history of extreme racial and gendered exploitation to an industry that reflects the democratic values of a new South Africa. Ethical certifications are considered one way through which the post-apartheid South African wine industry can demonstrate that it has moved away from its historical practices and is now characterised by practices of decent work and social transformation. An important certificatory label that allows local wine producers entry into global wine production networks is Fairtrade International. While Fairtrade certification is often reserved for small-scale producers, this certification has been extended to large-scale, commercial producers within the South African wine industry despite its history of farm paternalism and dependency. This research asks if this inclusion promotes decent work through social upgrading or if it offers a platform for the continuation of farm dependency under the guise of ‘Fairtrade’. In this study, social upgrading has been defined through a ‘bottom-up’ approach that prioritises workers’ independence as a key means of improvement. Four key pillars are applied as embodying the concept of social upgrading: regular employment with set working hours; legally enforceable worker rights; social protection through collective and individual bargaining power; and non-discriminatory social dialogue that promotes significant socio-economic progression. A key finding of this research is that practices of dependency and paternalism continue on some large-scale commercial farms, despite their Fairtrade certification. Furthermore, the findings suggest that the benefits that farmworkers receive lock farmworkers into their position on the farm with marginally improved conditions and cease if workers depart from the Fairtrade wine farm. This suggests that, at best, this inclusion of commercial farmers within Fairtrade certification appears to create a top-down form of social upgrading that locks farmworkers into their position on the farm with marginally improved conditions and beneath a glass ceiling of development. At worst, this Fairtrade inclusion facilitates a global poverty network through paternalism and dependency under the guise of ‘Fairtrade’. As a result, where meaningful, bottom-up social upgrading may occur on South African wine farms, the study suggests that this is despite the presence of Fairtrade and not a result of it. , Thesis (PhD) -- Faculty of Humanities, Political and Interntional Studies, 2022
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Date Issued: 2022-10-14

Socio-historical analysis of organisational change: a case study of Zimbabwe posts (Zimpost), 2010–2020

Authors: Kambarami-Zengeni, Faith Chipo
Date: 2022-10-14
Subjects: Organizational change Zimbabwe , Fordism , Industrial management , Taylor, Frederick Winslow, 1856-1915 , Industrial relations , Postal service Management
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/327920 , vital:61170 , DOI 10.21504/10962/327920
Description: Postal organisations play an important role in the provision of basic communication services. In Zimbabwe, post offices have a large physical distribution network of over 240 post offices country-wide to make communication services accessible to the populace. However, e-substitution has threatened mail business significantly. Postal operators globally are experiencing declining mail volumes in the face of advanced information and communication technologies. The overall goal of this thesis was to undertake a socio-historical analysis of organisational change at ZimPost using Taylorism, Fordism and post-Fordism as broad ideal types to explain how industry evolves in different phases of capitalism. National politics and economics play an integral role in how Taylorism, Fordism and post-Fordism assumed at ZimPost. Studies on these broad organising types have mainly focused on private sector organisations. However, this thesis argues that these analytical paradigms are also valid in public sector organisations, but they will unfold differently given the context in which change is experienced. Using a qualitative approach, the study established that the 1980s and 1990s can best be described as the ‘golden years’ of postal services in Zimbabwe, characterised by mass production and mass consumption of postal products and services. At that time the Posts and Telecommunications Corporation enjoyed a monopoly of postal services in the country. The stable market share, competitive salaries for postal workers, increased unionisation and a fairly stable economy enabled a Fordist regime of accumulation to develop. The cycle broke down when the mode of regulation was weakened by national economic and political changes towards the late 1990s. PTC started to experience a decline in the consumption of postal products. The decline was also attributed to increased competition from smaller private courier operators that could provide specialised services to a market with changing needs. With increased competition, the advancement of information, and communication technologies, mail volumes dwindled. This period can best be described as the crisis of Fordism at ZimPost. In the year 2000, the government unbundled the posts and telecommunications corporation to create four companies including Zimbabwe Posts. This was perceived as one of the most radical organisational changes in the history of postal services in Zimbabwe. More organisational changes took place at ZimPost that can best be described as characteristics of post-Fordism. These changes were attempts by ZimPost to remain relevant in light of the economic, political and technological changes taking place in the country. The postal operator introduced customised products in the form of agency services, supported by increased use of information and communication technologies in the post office. Organisational changes at ZimPost were shaped mainly by the economic and political environment in which they took place. Organisational change is complex, changes do not follow a linear pattern, they are processual. , Thesis (PhD) -- Faculty of Humanities, Sociology, 2022
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Date Issued: 2022-10-14

Socio-historical analysis of organisational change: a case study of Zimbabwe Posts (Zimpost), 2010–2020

Authors: Kambarami-Zengeni, Faith Chipo
Date: 2022-10-14
Subjects: Uncatalogued
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/422518 , vital:71954 , DOI 10.21504/10962/422518
Description: Postal organisations play an important role in the provision of basic communication services. In Zimbabwe, post offices have a large physical distribution network of over 240 post offices country-wide to make communication services accessible to the populace. However, e-substitution has threatened mail business significantly. Postal operators globally are experiencing declining mail volumes in the face of advanced information and communication technologies. The overall goal of this thesis was to undertake a socio-historical analysis of organisational change at ZimPost using Taylorism, Fordism and post-Fordism as broad ideal types to explain how industry evolves in different phases of capitalism. National politics and economics play an integral role in how Taylorism, Fordism and post-Fordism assumed at ZimPost. Studies on these broad organising types have mainly focused on private sector organisations. However, this thesis argues that these analytical paradigms are also valid in public sector organisations, but they will unfold differently given the context in which change is experienced. Using a qualitative approach, the study established that the 1980s and 1990s can best be described as the ‘golden years’ of postal services in Zimbabwe, characterised by mass production and mass consumption of postal products and services. At that time the Posts and Telecommunications Corporation enjoyed a monopoly of postal services in the country. The stable market share, competitive salaries for postal workers, increased unionisation and a fairly stable economy enabled a Fordist regime of accumulation to develop. The cycle broke down when the mode of regulation was weakened by national economic and political changes towards the late 1990s. PTC started to experience a decline in the consumption of postal products. The decline was also attributed to increased competition from smaller private courier operators that could provide specialised services to a market with changing needs. With increased competition, the advancement of information, and communication technologies, mail volumes dwindled. This period can best be described as the crisis of Fordism at ZimPost. In the year 2000, the government unbundled the posts and telecommunications corporation to create four companies including Zimbabwe Posts. This was perceived as one of the most radical organisational changes in the history of postal services in Zimbabwe. More organisational changes took place at ZimPost that can best be described as characteristics of post-Fordism. These changes were attempts by ZimPost to remain relevant in light of the economic, political and technological changes taking place in the country. The postal operator introduced customised products in the form of agency services, supported by increased use of information and communication technologies in the post office. Organisational changes at ZimPost were shaped mainly by the economic and political environment in which they took place. Organisational change is complex, changes do not follow a linear pattern, they are processual. , Thesis (PhD) -- Faculty of Humanities, Sociology, 2023
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Date Issued: 2022-10-14

Stock structure of Patagonian toothfish Dissostichus eleginoides (Smitt 1898, family Nototheniidae) in the Southwest Atlantic

Authors: Lee, Brendon
Date: 2022-10-14
Subjects: Otoliths , Patagonian toothfish Geographical distribution , Fish tagging , Biogeography , Microstructure , Microchemistry
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365599 , vital:65763 , DOI https://doi.org/10.21504/10962/365599
Description: The identification of discrete self-sustaining productive units in marine populations is essential for achieving sustainable fisheries objectives. Marine fish populations frequently exhibit dynamic characteristics across their life-histories, displaying variability in spatial structure and mixing patterns, both within and among populations. The incoherent application of management boundaries on biological populations can bias stock assessment results and have important implications on sustainable fisheries management. Patagonian toothfish (Dissostichus eleginoides) is a long-lived, slow-growing, late-maturing, deep-sea, benthopelagic species. It forms the basis of important and highly lucrative industrial and artisanal fisheries across its distribution. Patagonian toothfish have complex life-histories characterised by high dispersal potential during the egg and larval phase, a wide depth range because of their ontogenetic migratory behaviour, and large adult size that is capable of undertaking long-distance active movements (>200 km). These characteristics provide opportunities for high levels of connectivity, and as such, the stock structure is not well understood. We applied an integrated, multidisciplinary approach to provide an improved understanding of the complex stock structure dynamics for Patagonian toothfish on the Patagonian Shelf, specifically in relation to the shelf, slope, and deep-sea plains around the Falkland Islands. Research results were focused on aspects pertaining to (1) geographic variation in phenotypic characters (otolith shape); (2) a description of the spatial-temporal distribution patterns; (3) the active movements of deep-sea adults (tag-recapture study); and (4) the identification of early life-history dispersal through otolith microstructure and microchemical chronologies. Results from the study indicate high regional connectivity during the early life-history stages derived from at least two spawning contingents into spatially discrete nursery areas (cohort groups) on the Falklands Shelf. Fish followed distinct ontogenetic pathways into deeper waters adjacent to the areas wherein juvenile settlement into a demersal habitat occurred. There is little to no evidence of mixing among cohort groups during their ontogenetic migration into deep-sea adult habitats, reflecting a mixed population based on oceanographically defined egg and larval dispersal. The majority of the adult component of the population continue to display high site fidelity. However, between 9 and 25% of the population, consisting predominantly of larger reproductively capable adults undertake long-distance dispersal behaviour, identified as home-range relocations from the adult deep-sea habitats towards three of the known southern spawning grounds in the region. Results are suggestive of a requirement for improved collaborative efforts for regionally-based management approaches with careful consideration of local stock contingents. Future monitoring and research priorities should focus on the identification of reproductive potential, dispersal pathways and settlement patterns of stock contingents to inform the dynamics of mixed stock origins across the Patagonian region. While many aspects regarding the stock structure remain unresolved, results derived from the current studies can be used to inform the development of management measures to ensure the continued recovery and sustainable management of Patagonian toothfish within the region. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2022
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Date Issued: 2022-10-14

Synthesis, characterization and host-guest complexes of supramolecular assemblies based on calixarenes and cucurbiturils

Authors: Baa, Ebenezer
Date: 2022-10-14
Subjects: Supramolecular chemistry , Calixarenes , Cucurbiturils , Metal-organic frameworks , Macrocyclic compounds , Drug delivery systems
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365621 , vital:65765 , DOI https://doi.org/10.21504/10962/365621
Description: The field of supramolecular chemistry has grown large and wide in both deepness of understanding, range of topics covered and scope and applications. Supramolecular self-assemblies are facilitated by a wide range of non-covalent intra and inter molecular interactions that range from hydrogen bonding to π-interaction and van der Waals. Macrocyclic compounds such as cucurbiturils and calixarenes have emerged as important classes of compounds with excellent potential of forming supramolecular assemblies. The porous nature of these compounds enables them to form host-guest supramolecular complexes stabilized by diverse range of non-covalent interactions. Furthermore, these compounds contain donor atoms capable of forming bonds with metal ions to yield metal complexes with interesting porous characteristics that deviate from their traditional hydrophobic cavity. The versatile nature of the resulting pores imply that they can accommodate diverse types of guests. This work explores the synthesis and characterization of a host of calixarenes and cucurbiturils. Self-assembly of these macrocycles with various metal ions results to the formation of porous metal organic framework (MOF) complexes. Four new calixarene typed compounds obtained from aromatic aldehydes and twenty-six cucurbituril metal complexes are reported. These macrocylces and their metal complexes also form supramolecular complexes with DMSO, methanol, isoniazid hydrochloride and ciprofloxacin hydrochlorides through either self-assembly, mechanochemistry and exposure to solvent vapors. The bulk materials have been characterized using nuclear magnetic resonance spectroscopy (NMR), Fourier transformed infrared spectroscopy (FTIR), powder and single crystal diffraction techniques and thermal studies thermogravimetric analysis (TGA) and differential thermal calorimetry (DSC). Data obtained from this study reveals that calixarenes can form supramolecular complexes with a frequently used laboratory solvents with BN22 showing appreciable selectivity for DMSO sorption from a solvent mixture. These compounds also form supramolecular complexes with drug molecules such as isoniazid and ciprofloxacin. Furthermore, the data reveals that choice of synthetic route of supramolecular ensembles dictates if the guest drug molecule will occupy the intrinsic or extrinsic pores of cucurbituril complexes. Biological studies on the obtained complexes reveal that the cucurbituril complexes are non-cytotoxic while the calixarenes show antibacterial activity against Escherichia coli and Staphylococcus aureus. Additionally, the study showed that ciprofloxacin can be successfully released from a calixarene host in a simulated body fluid although the host was also found to cross the dialysis membrane. The results of this study are important in that; - they can be exploited and developed in the selective sorption of certain guests and - that they can be used in the development of drug delivery systems that play a dual role of delivery and therapeutic activity. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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Date Issued: 2022-10-14

Synthesis, In-Silico molecular modelling and biological studies of 1,4-Dihydroxyanthraquinone and its derivatives

Authors: Kisula, Lydia Mboje
Date: 2022-10-14
Subjects: Computer simulation , Molecules Models , Dihydroxyanthraquinone , Trypanosomiasis , Leishmaniasis , Docking
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365828 , vital:65793 , DOI https://doi.org/10.21504/10962/365828
Description: This current study of investigation reports on the synthesis of 1,4-dihydroxyanthraquinone and its derivatives on explorations of their medicinal potential. The study initially aimed to synthesize an analogue of a natural anthraquinone, 1,3,6-trihydroxy-7-((S)-1- hydroxyethyl)anthracene-9,10-dione 5 using Friedel-Crafts acylation of phthalic anhydride and a benzene derivative. Synthetic transformation of anacardic acid 63, obtained as a by- product of the cashew industry successfully afforded 4-ethoxyisobenzofuran-1,3-dione 89. However, when attempted to couple 4-ethoxyisobenzofuran-1,3-dione 89 with 2- hydroxyacetophenone 91 in a Friedel-Crafts acylation manner to form 2-acetyl-1,8- dihydroxyanthracene-9,10-dione 87 the reaction did not work efficiently. A simple derivative of benzene which is; benzene-1,4-diol 102 was reacted instead with 3-ethoxyphthalic acid 71 and isobenzofuran-1,3-dione 96 to form 1,4,5-trihydroxy anthraquinone 72 and 1,4- dihydroxyanthraquinone 42, respectively. A modified Marschalk reaction was then used to introduce the hydroxyl alkyl group to 1,4-dihydroxy anthraquinone 42, which allowed further elaboration of the hydroxyl-substituent in moderate to good yields (22-80%). A molecular docking study was performed using Schrödinger software to predict the binding affinity of the test compounds to the target protein trypanothione reductase (PDB ID: 6BU7). An in-vitro screening of 1,4-dihydroxyanthraquinone derivatives and some selected precursors for antitrypanosomal, antiplasmodial, antibacterial, and cytotoxicity activities produced encouraging results. Derivatives of anacardic acid and cardanol from CNSL were found to have moderate activity against trypanosomes with no activity against Plasmodium falciparum. Almost 63% of synthesized 1,4-dihydroxyanthraquinone derivatives displayed activity against trypanosomes. The in-vitro evaluation and the in silico molecular docking studies revealed that 1,4-dihydroxyanthraquinone derivatives can be potential drug-like candidates active against T.brucei parasites (IC50 = 0.70-1.20 μM). Only four 1,4- iv dihydroxyanthraquinone derivatives with thiosemicarbazone, chloride, pyrrole, and diethanolamine functionality displayed activity against Plasmodium falciparum (IC50 = 3.17- 14.36 μM). In-vitro evaluated of test compounds against antibacterial screen and cytotoxicity effects significantly showed that 2-hydroxy-6-pentadecylbenzoic acid 63a and 2-((2- chlorophenyl)(piperazin-1-yl) methyl)-1,4-dihydroxyanthracene-9,10-dione 78 have potency against Staphylococcus aureus and reduced the viability of the cells below 20% at an initial concentration of 50 μg/mL. Only 1,4-dihydroxyanthraquinone derivatives with thiosemicarbazone 76, piperazine 78, and diethanolamine 80 motifs were active against HeLa cells and reduced the viability of cells below 20% at a concentration of 50 μg/mL. In conclusion, this current reported study has generated useful knowlege on the applicability of the agro-waste CNSL as an agent active against trypanosomiasis but also as a low-cost starting material to synthesize hydroxy anthraquinones. The study has further given an overview to the understanding of the medicinal value 1,4-dihydroxyanthraquinone derivatives as promising candidates towards developing drugs suitable for treating neglected tropical diseases particularly trypanosomiasis. , Thesis (PhD) -- Faculty of Science, Chemistry, 2022
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Date Issued: 2022-10-14

The impacts of anthropogenic fires in West African savanna woodlands and parklands: the case of the Guinea savanna, Ghana

Authors: Amoako, Esther Ekua Amfoa
Date: 2022-10-14
Subjects: Firemaking Ghana , Agroforestry Ghana , Parks Fire management Ghana , Nature Effect of human beings on Ghana , Land use Ghana , Savanna ecology Ghana , Traditional ecological knowledge Ghana
Language: English
Type: Academic theses , Doctoral theses , text
Identifier: http://hdl.handle.net/10962/365610 , vital:65764 , DOI https://doi.org/10.21504/10962/365610
Description: Fire is recognised as an important factor influencing the structure and function of tropical savannas. Despite the extensive studies conducted on the effects of fire on global savannas, there are relatively few studies focusing on fire-assisted land use practices in the agroforestry parkland of the Sudano-Guinean savannas of West Africa. The region experiences recurrent fires in the dry season which begins from November to April. The fires are anthropogenic and are mainly caused through rural livelihoods and cultural practices such as farming - to remove debris from crop fields and to improve soil fertility and hunting to flush out animals, among other reasons. This study therefore sought to: 1. contribute to the understanding of fire-assisted traditional land use practices, people’s knowledge and perceptions of fire use and fire regime: 2. analyse the effects of fire on vegetation, and 3. determine the effects of fire on soils in the Guinea savanna woodlands and parklands of Ghana. Study sites (burnt and unburnt land use types) were selected based on five-year daily fire counts (2013-2017) data, obtained from the Earth Observation Research and Innovation Centre (EORIC), Ghana in collaboration with the Council for Scientific and Industrial Research (CSIR) Meraka Institute, South Africa. Fire densities were calculated for the 18 districts in the Guinea savanna (Northern Region of Ghana). The districts were stratified into low, medium and high fire frequency areas. The East Gonja district recorded the highest fire density (1.0 fires km-2) while Tamale recorded the lowest fire density (0.3 fires km-2). Of the eighteen districts, six districts were purposively selected and ten communities sampled. Firstly, I investigated the frequency of fire use and control, perceptions of fire regime for selected livelihood and socio-cultural activities in the six districts. The majority of respondents (83%) across the study districts indicated that they used fire once a year for at least one of the following activities: land preparation, weed/grass/pest control, burning stubble after harvest, bush clearing around homesteads, firebreaks, charcoal burning and hunting. The study showed the highest frequency of fire use in the dry season was for land preparation for cropping. However, less than a fifth of the respondents (17%) indicated that they did not use fire for any of the above activities. The results of a multiple regression predicted fire activities in the dry season from gender, age, level of education, occupation and household size. Secondly, the study examined how fire influenced the population structure and abundance of two economically important woody species Vitellaria paradoxa C. F. Gaertn. (Shea tree) and Anogeissus leiocarpa (DC.) Guill. & Perr. (African Birch) in burnt and unburnt land-use types. Stand basal area, mean densities of juveniles and adult trees and Simpson’s index of dominance were determined. Eight diameter size classes of each species were analysed by comparing their observed distributions to a three-parameter Weibull distribution across the land use types. A total of 3,366 individuals of A. leiocarpa (n = 1,846) and V. paradoxa (n = 1,520) were enumerated. The highest total basal area of Anogeissus leiocarpa (16.9 m2/ha) was estimated in sacred groves whereas Vitellaria. paradoxa (20.6 m2 /ha) was found in unburnt woodland. The highest mean densities of A. leiocarpa (22.7±29.7 stems/ha) and V. paradoxa (15.3±2.2 stems/ha) were found in sacred in groves. Anogeissus leiocarpa was, however, absent in fallows and burnt crop fields. A somewhat inverse J-shaped distribution was found in sacred groves for both species. Thirdly, the study compared species composition in early burnt, late burnt and unburnt plots in a protected area where fire was regulated. Vitellaria paradoxa C. F. Gaertn., Terminalia avicennioides Guill. & Perr., Combretum adenogonium Steud. ex A. Rich. and Combretum molle R. Br. Ex. G. Don. were the most common and abundant in all treatments. Late burnt and unburnt plots recorded the lowest diversity amongst the three treatments. Unburnt plots had higher tree density than burnt plots. A Detrended Canonical Analysis showed a changing trend, indicating a moderately strong positive association between burning time and species composition. The first and second axes contributed 53% and 12% variation, respectively. Most of the species found in axis one had fairly strong positive association to early and late burnt treatment than unburnt treatments. Finally, the effects of fire on soil properties in burnt and unburnt crop fields and woodland in the ten communities were also investigated. A total of 151 composite samples in selected burnt and unburnt land use types (burnt crop field n=20; unburnt crop field n=27; burnt woodland n=53, unburnt woodland n=51) were analysed. The variables analysed were pH, soil organic carbon (SOC), total nitrogen (TN), available phosphorous (P), Exchangeable bases - potassium (K), magnesium (Mg), calcium (Ca), cation exchange and soil texture. Total N, SOC, pH and Ca differed significantly across the burnt and unburnt land-use types. A principal component analysis showed a stronger association and more positive gradient in woodlands than in crop fields. Total N showed a positive association with SOC, whereas silt showed a negative association to sand and clay. Traditional knowledge and perceptions of users of savanna agroforestry parklands can inform the formulation of local by-laws for community fire management as well as national policy regulation on fire use in the savanna through the interlinked analysis of social and ecological systems as have been elucidated in this study. The results on vegetation assessment revealed that fire practices and land uses influenced size class distribution of the two study species as well as the densities of woody species in traditional crop fields and the National Park. The unstable populations observed in most land uses and the absence of A. leiocarpa in crop fields and fallows call for education and policy actions on the use of fire in parklands of West Africa. Furthermore, fires positively influenced some soil properties in both woodlands and crop fields confirming one of the emphasised reasons why rural subsistence farmers use fire. As an environmental management decision and land use policy intervention, early dry season burning could be an option to curbing the indiscriminate and unplanned fire use. Also, the protection of trees on farm lands could check the unstable population structure of economically important woody species leading to the different structures that deviated from the recommended reverse J-shaped distribution curve observed in these agroforestry parklands. The management of socio-ecological systems such as the agroforestry parklands of West Africa require a holistic understanding of the complexity of the different resource systems, units and actors involved for sustainable management of these natural resources. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2022
Full Text:
Date Issued: 2022-10-14

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