Effects of lethal management on black-backed jackal population structure and source-sink dynamics
- Authors: Minnie, Liaan
- Date: 2016
- Subjects: Black-backed jackal Carnivorous animals
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/12658 , vital:27104
- Description: Lethal carnivore management, aimed at reducing carnivore impacts, threatens the persistence of carnivores globally. The effects of killing carnivores will depend on their life histories and social structures. Smaller canids, like black-backed jackals (Canis mesomelas), are highly adaptable and display variable population-level responses to mortality sources, which may contribute to their success in fragmented landscapes. Jackals, the dominant predator of livestock in South Africa, are widely hunted to reduce this predation. This hunting is heterogeneous across the landscape, focussed on livestock and game farms, with nature reserves acting as refuges. The aim of this research was to investigate the ecology and population dynamics of jackals in response to heterogeneous anthropogenic mortality. I hypothesized that the spatial variation in hunting results in the formation of a source-sink population structure, which contributes to the persistence of jackals. I addressed this hypothesis by evaluating two criteria, essential for the formation of a source-sink system in larger mammals. Firstly, I confirm that hunting pressures result in the formation of distinct subpopulations with asymmetrical dispersal (i.e. compensatory immigration) from unhunted reserves to neighbouring hunted farms. Secondly, I show that jackal subpopulation display asynchronous demographics, with farm populations displaying a relatively younger age structure and an associated increase in reproductive output (i.e. compensatory reproduction). This confirms the formation of a hunting-induced source-sink system. additionally, I show that jackals have a catholic diet, which confers a level of adaptability to direct (anthropogenic mortality, prey provisioning) and indirect (alteration in prey base) habitat modifications. This dietary flexibility allows jackals to obtain the appropriate resources to achieve reproductive condition. The relatively better body condition of younger jackals in sink habitats allows for compensatory reproduction which contributes to the success of jackals on hunted farms. Based on my findings, I hypothesize that the compensatory life history responses of jackals to anthropogenic mortality may be ascribed to two interconnected mechanism. Dispersal is presumably driven by density-dependent interference competition, as dominant territorial pairs outcompete subordinates in high-density reserve areas, forcing them to disperse onto low-density farms (i.e. ideal despotic model). Additionally, farms likely represent attractive habitats, owing to a reduction in conspecifics and a concomitant increase in resource availability (including anthropogenic resource provisioning). Therefore, dispersing subordinates presumably select for farms which are perceived as good quality habitats, as the high risks of anthropogenic mortality cannot be perceived by dispersing individuals. This results in the formation of an attractive sink or ecological trap. These compensatory processes will continue to counter population management actions as long as recruitment from unmanaged areas persists. This hypothesis provides a conceptual framework for future research directions in understanding jackal persistence and management (i.e. specifically focussing on controlling dispersal) of jackal populations.
- Full Text:
- Date Issued: 2016
Efficiency analysis of electricity distribution by South African Municipalities: a cost frontier approach
- Authors: Gqwaka, Aviwe Phelele Sebatian
- Date: 2016
- Subjects: Electric power distribution -- South Africa Public utilities -- South Africa Local government -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/10299 , vital:26650
- Description: Efficiency analysis in the public sector assesses the performance of municipal and government entities in their provision of services to the public. South Africa, in particular, has experienced a large degree of negative feedback with respect to the ability of the government and its municipal departments to provide basic services to citizens. This has led to a number of service delivery protests throughout the country. To remedy this, the ability of the municipality to provide basic services needs to be assessed in order for improvements to be made. A first step in this process would be to determine the efficiency with which municipalities are providing these services. This study focuses on a particular municipal service, namely electricity distribution. Primarily, the efficiency with which municipalities provide electricity to consumers is determined. This is achieved using the parametric cost frontier approach, which is appropriate since municipalities aim to reduce the costs incurred in distributing electricity. The municipalities are compared to a frontier (theoretical best practice) from which inferences on their performances can be made. Those municipalities whose performances are not optimal, deviate from the frontier. The deviations (errors) are then assumed to be caused by two factors, namely stochastic random noise and inefficiency. This composition accounts for effects for which municipalities cannot control (stochastic random noise) and those for which it can (inefficiency). The parametric nature of the cost frontier approach allows for distributional assumptions to be made on these factors. Stochastic random noise is always assumed to be normally distributed, while inefficiency is assumed to be one-sided and positively skewed.
- Full Text:
- Date Issued: 2016
Evaluation of p-menthane-3, 8-diol citronellal acetal as a suitable bio-plasticizer for polyvinyl chloride
- Authors: Ncanywa, Luphumlo
- Date: 2016
- Subjects: Polyvinyl chloride Chlorine compounds
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45898 , vital:39317
- Description: The main aim of this project is to test novel naturally-derived plasticizers (bio-plasticizers) synthesized at Innoventon and to determine if they are a suitable replacement for conventional plasticizers used to plasticize polyvinyl chloride. Polyvinyl chloride (PVC) is one of the most common plastics used in the world because of its durability and low cost. PVC when blended with plasticizers is a versatile thermoplastic and is used in many applications. A plasticizer is a substance that is added to a material, usually a polymer, to increase flexibility, softness and workability. Many elastomers and polymers are tough and dry; therefore they need plasticizers to make them useful. A plasticizer must be thoroughly incorporated in the elastomer or polymer in order for it to be effective. There are many types of plasticizers used in the world. Phthalate plasticizers are the most commonly used plasticizers of the past century. They comprise 92% of the global production of plasticizers. DEHP (di-ethyl hexyl phthalate) is the most widely used phthalate plasticizer. Phthalate plasticizers have been proved to be harmful to the environment and human beings. They can cause many harmful diseases to humans e.g. kidney failure, heart disease, liver failure, fertility and growth disorders. They lower testosterone in baby boys that are exposed through breast milk. In light of the above, the use of certain phthalates has been banned in cosmetics and consumer products. Since there is sufficient evidence to raise fears over the use of phthalate plasticizers, there is a great opportunity to find a way to replace phthalate plasticizers in PVC with bio-plasticizers. The current study represents the first step in developing alternative plasticizers for PVC and other polymers. These alternative plasticizers are characterized by low toxicity, low migration and are less harmful to the environment and human beings. p-menthane-3, 8-diol citronellal acetal is one such proposed bio-plasticizer which has a similar structure to the phthalates and has been previously reported by Innoventon to have potential plasticizing characteristics. During this study PVC was plasticized with PMD-citronellal acetal and tested for plasticizing properties. The plasticizing effect of PMD-citronellal acetal in PVC films was compared to that of conventional plasticizer dibutyl phthalate (DBP). The two plasticizers‟ performance was evaluated by preparing PVC films with varying amounts of each plasticizer and PMD-citronellal acetal subjecting the films to a series of tests. Tensile strength and elongation tests were performed on the plasticized and unplasticized films but these tests did not produce consistent results due to premature failures on the films. However, tensile strength was reduced in some films for both plasticizers compared to unplasticized film. Elongation and flexibility were increased in some samples as the percentage of plasticizer in each film was increased. Glass transition temperatures were determined for the plasticized and unplasticized PVC films. Glass transition temperature of both plasticizers was reduced as the percentage of plasticizer in each film was increased. Multiple regression analysis was done on the data to compare the similarity of the two plasticizers. The statistical tests showed that DBP and PMD-citronellal acetal have the same plasticization property with regard to glass transition temperature of PVC. The thermal stability of the PVC films with the two plasticizers was evaluated. Similar thermal stability was observed on the PVC, PVC with DBP and PVC with PMD-citronellal acetal. The leaching of the PMD-citronellal acetal and DBP were compared. The plasticizer loss increased as the percentage of each plasticizer in the PVC increased. The relationship between the percentage of the plasticizers and leaching rate was further analysed using multiple linear regressions. The two plasticizers were found to have the same leaching rate. FTIR analysis was performed on the plasticized and unplasticized PVC films to identify functional groups present and to determine whether the plasticizers formed any bonds with PVC functional groups. The characteristics bands of PVC were observed in FTIR. The FTIR spectra indicated that the plasticizers were incorporated into the PVC matrix without bonding. The results of the tests showed that PMD-citronellal acetal can be a suitable bio-plasticizer for PVC since it exhibited similar plasticization properties to DBP with regard to glass transition temperatures, leaching rates and thermal stability. Regarding tensile strength and elongation, further testing has to be done as the preliminary results were inconclusive. PMDcitronellal acetal was shown to be a possible alternative for DBP.
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- Date Issued: 2016
Factors influencing wetland distribution and structure, including ecosystem function of ephemeral wetlands, in Nelson Mandela Bay Municipality (NMBM), South Africa
- Authors: Melly, Brigitte Leigh , Gama, Phumelele T
- Date: 2016
- Subjects: Wetland management -- South Africa Wetland ecology -- South Africa -- Nelson Mandela Bay Municipality
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11721 , vital:26960
- Description: The Nelson Mandela Bay Municipality (NMBM) is a semi-arid area along the southern coastline of South Africa (SA). Until recently, there was no systematic approach to research on wetland systems in the NMBM. The systematic identification of wetlands was made more difficult by the relatively large number of small, ephemeral systems that can be difficult to delineate. This has meant that fundamental knowledge on wetland distribution, structure and function has been limited and, consequently, management and conservation strategies have been based on knowledge on systems from other regions of the country. Environmental processes occur at different spatial and temporal scales. These processes have an effect on the abiotic factors and biotic structure of wetlands, resulting in inherently complex systems. The location of the NMBM provides a good study area to research some of these environmental and biological attributes at different spatial scales, due to the variability in the underlying geology, geomorphology, vegetation types and the spatial and temporal variability in rainfall, within a relatively small area of 1951 km2. Thus, the aim of this study was to determine the factors influencing wetland distribution, structure and ecosystem functioning within the NMBM. The first Research Objective of work presented here was to identify wetlands using visual interpretation of aerial photographs. A total of 1712 wetlands were identified within the NMBM using aerial photographs, covering an area of 17.88 km2 (Chapter 5). The majority of these wetlands were depressions, seeps and wetland flats. Valley bottom wetlands (channelled and unchannelled) and floodplain wetlands were also identified. A range of wetland sizes was recorded, with 86% of the wetlands being less than 1 ha in size and the largest natural wetland being a floodplain wetland of 57 ha, located south of the Swartkops River. The identified wetlands were used to create a wetland occurrence model using logistic regression (LR) techniques (Chapter 5), in accordance with Objective 2 of the study. An accuracy of 66% was obtained, which was considered acceptable for a semi-arid climate with a relatively high degree of spatial and temporal rainfall variability. The model also highlighted several key environmental variables that are associated with wetland occurrence and distribution at various spatial scales. Some of the important variables included precipitation, evapotranspiration, temperature, flow accumulation and groundwater occurrence. Wetland distribution patterns were described in Chapter 6. Spatial statistics were used to identify whether wetlands are clustered and, therefore, form mosaics within the surrounding landscape (Objective 3). Systems were found to be highly clustered, with 43% of wetlands located within 200 m of another system. Clustering and wetland presence was especially prominent in the southern portion of the Municipality, which is also associated with a higher mean annual precipitation. Smaller wetlands were also significantly more clustered than larger systems (Average Nearest Neighbour statistic, p-value < 0.0001). Average distances also significantly varied according to HGM type, with depressions being the most geographically isolated wetland type compared to the other HGM types. Overall, distances between wetlands indicated good proximal connectivity. Potentially vulnerable areas associated with wetland systems were identified successfully using landscape variables, in accordance with Objective 4. These variables were: land cover, slope gradient, flow accumulation, APAN evaporation, mean annual precipitation (MAP) and annual heat units. The existing Critical Biodiversity Network was also used in connection with these variables to further identify potentially vulnerable areas. The abiotic and biotic characteristics were decribed for three hydrogeomorphic (HGM) types at a total of 46 wetland sites (Chapter 7), as per Objective 5. Depressions, seeps and wetland flats were sampled across the different geological, vegetation and rainfall zones within the NMBM. The wetland sites were delineated up to Level 6 of the Classification System used in SA, and the various abiotic and biotic characteristics of these systems were defined. A total of 307 plant, 144 aquatic macroinvertebrate and 10 tadpole species were identified. Of these species, over 90 species were Eastern Cape and SA endemic species, as well as three threatened species on the IUCN Red List. Multivariate analyses (including Bray-Curtis similarity resemblance analyses, distance-based redundancy analyses, SIMPER analyses and BIOENV analysis in Primer), together with environmental data, were used to define community structure at an HGM level, in accordance with Objective 5. The importance of the spatial scale of the environmental data used to define plant and macroinvertebrate community structure was described in Chapter 7, to address Objective 6. The results showed that both broad-scale and site-level characteristics were important in distinguishing community structure within the HGM types that superseded general location, the sample timing or the stage of inundation. These results also indicated that a combination of both landscape and site-level data are important in defining the community structure in the various HGM types. Some of the important environmental variables that explained some of species assemblages were similar to those in the wetland occurrence model (Chapter 5), with some additional hydrological and soil physico-chemical parameters (e.g. soil electrical conductivity, soil pH, and surface and subsurface water nutrients). These significant variables indicate the complex, multi-scalar role of environmental attributes on wetland distribution, structure and function.
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- Date Issued: 2016
Factors that influence the sustainability of rural crop production community projects in the Umzimvubu District
- Authors: Majiki, Fezeka
- Date: 2016
- Subjects: Sustainable agriculture -- South Africa -- Eastern Cape , Economic development projects -- South Africa -- Eastern Cape , Rural development -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/8089 , vital:24991
- Description: Maize production is the main cropping activity in the Umzimvubu district. This cereal crop is the staple food for the Eastern Cape’s rural communities and accounts for nearly 95 per cent of the crops cultivated in dry-land cropping programmes. Food security in rural areas has been a major concern for the South African government. In attempts to mitigate hunger and poverty, the government has initiated rural development maize production projects. The primary objectives of the projects were to achieve sustainable livelihoods and rural development for the poor. The projects were expected to improve the quality of rural life and provide basic nutritional requirements of the community. Historically the rural poor have had to fend for themselves through subsistence farming in adverse environments. Input costs for farming have become increasingly expensive; this resulted in major challenges for subsistence farming. The crop production projects initiated in the Umzimvubu district have not been sustainable and have fallen short of addressing the needs of the various communities. The study aims to identify the factors that influence the sustainability of the crop production projects in the Umzimvubu district. A triangulation research method was used to provide multiple viewpoints to examine the data; this allows for greater accuracy of the research. The mixed method approach in which the researcher collects and analyses data integrates the findings and draws inferences using both qualitative and quantitative methodology. The quantitative research methodology provided the demographics and biographical data on the participants. The qualitative research methodology concentrated on the focus group discussions that gave an insight into the participants' views, perceptions and concerns. Focus groups were used to examine the factors influencing the sustain-ability of the projects and to explore how these projects are perceived and under-stood by the community and people working on the projects. The research interest is not only in what the project beneficiaries think, but also in why they think as they do. The main data collection was obtained from the focus groups and individual face-to-face interviews with the beneficiaries of the crop projects in the Umzimvubu district. It was found that the farming areas required rehabilitation, were susceptible to erosion and degradation, and lacked adequate land use practices. The beneficiaries of the cropping programmes had small amounts of other crops growing in their individual household gardens for household use in conjunction with the maize received from the maize programmes. The income made from selling maize from the programmes was insignificant and did not contribute substantially to the household needs, as the communities in these projects were still failing to secure adequate food requirements. The maize yields do not substantiate the monetary investment from the beneficiaries. Furthermore, the findings indicated that the beneficiaries do not receive consistent income from the programmes. The participants consisted of large households comprising mainly elderly people who depended on social grants as a regular source of income. These elderly were burdened with taking care of their grandchildren, whose parents were employed in either urban areas or unemployed and formed part of the household. The unemployed young adults also depended on child support grants for income. The maize harvested had to be shared between a large number of community members and the livestock. The findings also suggested that there was dependency on outside contractors for cultivation and other practices. The study found that most of the beneficiaries felt disempowered, as they had not been involved in the decision-making process. Furthermore, policy-makers failed to acknowledge existing indigenous knowledge and practices of the rural communities (i.e. inter-cropping and green mealie harvesting). Indigenous practices should be included into the programmes instead of compelling beneficiaries to adhere to new forms of cultivation. The communities introduction to new large-scale and challenging, highly technological methods resulted in most of the communities being fully dependent on government support and guidance. Training and the empowerment of beneficiaries are imperative. Rural people should be included in development of strategies and the role of the women should be given more recognition. It should be acknowledged that rural households are diverse and that the model cannot apply to each village or community.
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- Date Issued: 2016
Foraging ecology of the gentoo penguin, pygoscelis papua, at Marion Island
- Authors: Carpenter-Kling, Tegan
- Date: 2016
- Subjects: Gentoo penguin -- Food
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/4912 , vital:20766
- Description: The distribution and subsequent availability of marine predators’ prey is highly variable and is linked to fluctuating oceanographic parameters. It is well documented that annual breeding success of seabirds is related to the temporal availability of prey. Knowledge of a seabird’s diet and at sea distribution is therefore critical in deducing the effect of a fluctuating environment on a seabirds’ population and, furthermore, to understand seabirds role in the environment. The gentoo penguin population at sub-Antarctic Marion Island experienced a decline of 52% between 1994 and 2012. It has been speculated that long term changes in the local marine environment, due to a southward shift of the sub-Antarctic Front (SAF), and subsequent changes in prey availability is the ultimate causal factor. Therefore, this thesis investigates the temporal variation in the diet these birds over three years, through the use of stomach content samples. It then investigates whether the composition of the diet has changed over the long term (approximately 18 years). Additionally, the at sea distribution of these birds was investigated using temperature-depth recorders (TDRs) and global positioning system (GPS) devices. This study represents the first to investigate variation in the diet over three years and over the long term. It is also the first study to track these birds fine scale movement. Over three years, the diet exhibited a high degree of variability. The birds primarily foraged on the fish, Lepidonotothen larseni and the crustaceans, Nauticaris marionis and Euphausia vallentiniy. Over three years, L. larseni became increasingly more important during the breeding season. This was attributed to an increase in availability of these fish during this time, as this time corresponded to the transition of these fish from the larval pelagic phase to the benthic adult phase. Furthermore, the proportions of N. marionis and E. vallentini in the diet varied significantly among years. This variation is possibly a result of the highly variable latitudinal position of the SAF. The diet changed over the long term. There was significantly less N. marionis and more E. vallentini in the diet during more recent years. The long term southward shift of the SAF is considered to be a leading cause of these significant changes in the diet. The shallow inter-island shelf between Marion and Prince Edward Island was an important foraging area possibly due to predictable prey resources. In addition, these birds exhibited an important and possibly unique foraging strategy. They performed short self-maintenance trips where after they return to land to roost for the night. The following day these trips were followed by a longer foraging trip that was followed by chick provisioning. This strategy is unique among seabirds longer trips are associated with self-maintenance and not chick provisioning. This study has provided important knowledge of the foraging ecology of the gentoo penguin at sub-Antarctic Marion Island. It highlights the necessity for continuation of diet and tracking studies of these birds if we are to fully understand the ultimate factors that are causing the decline in their breeding success and population numbers.
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- Date Issued: 2016
Formulation development and thermorheological properties of crumb rubber/eva modified bitumen
- Authors: Nare, Keith Dumisani
- Date: 2016
- Subjects: Crumb rubber Bitumen , Vinyl acetate
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/11974 , vital:27015
- Description: The study deals with the formulation development and thermorheological properties of crumb rubber/ethylene vinyl acetate (EVA) modified bitumen with the aim of optimizing the amount of crumb rubber and EVA loadings in bitumen based on thermorheological parameters complex shear modulus, phase angle and rutting parameter. In the modified binders EVA offers plastomer properties whereas the crumb rubber confers elasticity to the bitumen. 13.75% crumb rubber and 2.5% EVA loadings based on aging indices gave the best optimized mixture. The thermorheological behaviour of the best optimized mixture was compared to industrial grade EVA (AP-1) and crumb rubber (AR-1) modified bitumen. Improving aging behaviour of the bitumen was evaluated using four antioxidants: carbon black, hydrated lime, Irganox 1010 and Irgafos 168. The least aging indices at 58˚C and 64˚C were obtained from a 1:1:1 Irganox 1010/hydrated lime/carbon black mixture. SARA (saturates, aromatics, resins and asphaltene) analysis gave the chemical background for application of antioxidants to reduce the propensity of short term aging. To further improve the EVA/crumb rubber optimized mixture for workability FT wax (Sasobit®) was assayed at loadings from 0-2.5%. This was done to match the EVA content and maintain the original maximum loading of 2.5% in the optimized mixture. The phase change abilities of FT wax owing to the high latent heat enabled co-crystallization with the EVA with the elastomeric backbone of crumb rubber acting as support material. The energy-sustainability nexus was found to have worked at less than 1% loading of FT wax in the EVA/crumb rubber modified bitumen. Response surface methodology approach to all the sections of work was used to come up with the optimized mixtures based on rheological parameters complex shear modulus, phase angle and rutting parameter at test temperature 64˚C. The interaction chemistry of bitumen, crumb rubber, EVA and FT wax was found to be first and second order in all cases involving individual contributions and co-interaction amongst the factors. Project costing for each section of work (optimizing section, antioxidant section and FT wax section) was conducted involving the raw materials used, equipment used, labour involved and other costs incurred for all the project work.
- Full Text:
- Date Issued: 2016
Formulation of an optimal non-targeted liposome preparation for fusion with tumour cell line membranes
- Authors: Motala, Ismail Mohammed , Roux, Saartjie
- Date: 2016
- Subjects: Liposomes Cancer -- Adjuvant treatment Nanotechnology -- Cancer
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/12220 , vital:27045
- Description: The most common treatment used for cancer is chemotherapy. Chemotherapeutic agents have a greater affinity for rapidly dividing cells which is a characteristic of tumour cells. Although anti-cancer agents have their advantages in providing anti-cancer effects, they can be seen as highly toxic molecules posing a threat to normal healthy tissue within the human body. However, these toxic therapies need to be delivered to tumour sites without damaging healthy tissue. Liposomes can serve as a delivery system for these toxic molecules and be delivered to the tumour site via the EPR effect. Hence, liposomes that fuse with tumour cell line membranes are advantageous in delivering payloads of drugs directly into the tumour cell without damaging normal healthy tissue. The aim of the study was to formulate an optimised liposome preparation in order to enhance cellular uptake by MCF-7, Caco-2 and C3A cancer cell lines via membrane fusion. The optimal liposome formulation was aimed to be prepared utilising a statistical design approach in order to determine the ranges of the parameters that were furthermost optimal in formulating an ideal liposome preparation. The primary screening design was conducted using a 24-1 fractional factorial design that took into account the four parameters that were used to determine the optimisation of the liposomal preparation. The four variables used in the liposome preparation were the phospholipid type (PS or DOPE), the concentration of cholesteryl hemisuccinate (CHEMS) (10 – 40 %), the concentration of PEG2000-PE (0.5 – 4 %) and liposome size (100 or 200 nm). Liposomes were prepared using thin film hydration method and characterisation for size and zeta potential was carried out using photon correlation spectroscopy (PCS). Visual characterisation of liposome size was carried out using atomic force microscopy (AFM). Liposomes were exposed the cancer cell lines with visualisation and uptake being measured using fluorescent microscopy and flow cytometry, respectively. An optimal liposome preparation was prepared following the statistical design method. The optimal liposome preparation consisted of phospholipid type PS, 22.91 % of CHEMS, 4 % of PEG2000-PE and a liposome size of 200 nm. AFM analysis has shown that optimal liposome sizes ranged between 130 and 170 nm. Flow cytometry analysis indicated high level of liposome uptake with actual values falling below the predicted values set out by the statistical design. Fluorescence microscopy captured images of the fluorescent liposomes concentrated on the membrane of cells. The objective of the study was to determine from literature which variables would be desirable in preparing an optimal non-targeted liposome preparation. This was achieved by identifying four such variables and utilising them in a statistical design approach which was screened in order to determine the ideal parameters in preparing the optimised liposome batch. Therefore, from the results obtained it can be concluded that the aim of the study were met by preparing an optimal liposome preparation that has the ability to fuse with the tumour cell line membranes.
- Full Text:
- Date Issued: 2016
Higher order modulation formats for high speed optical communication systems with digital signal processing aided receiver
- Authors: Chabata, Tichakunda Valentine
- Date: 2016
- Subjects: Optical communications , Modulation (Electronics) , Signal processing
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/4775 , vital:20677
- Description: The drastic increase in the number of internet users and the general convergence of all other communication systems into an optical system have brought a sharp rise in demand for bandwidth and calls for high capacity transmission networks. Large unamplified transmission reach is another contributor in reducing deployment costs of an optical communication system. Spectrally efficient modulation formats are suggested as a solution to overcome the problems associated with limited channels and bandwidth of dense wavelength division multiplexing (DWDM) optical communication systems. Higher order modulation formats which are considered to be spectrally efficient and can increase the transmission capacity by transmitting more information in the amplitude, phase, polarization or a combination of all was studied. Different detection technologies are to be implemented to suit a particular higher order modulation format. In this research multilevel modulation formats, different detection technologies and a digital signal processing aided receiver were studied in a practical optical transmission system. The work in this thesis started with the implementation of the traditional amplitude shift keying (ASK) modulation and a differential phase shift keying (DPSK) modulation systems as they form the basic building block in the design of higher order modulation formats. Results obtained from using virtual photonics instruments (VPI)simulation software, receiver sensitivity for 10Gbpsnon-return-to-zero (NRZ), amplitude phase shift keying (ASK) and DPSK signals were measured to be -22.7 dBm and -22.0 dBm respectively. Performance comparison for the two modulation formats were done over different transmission distances. ASK also known as On-Off keying (OOK) performed better for shorter lengths whereas DPSK performed better for longer lengths of up to90km.Experimental results on a 10 Gbps NRZ- ASK signal gave a receiver sensitivity of -21.1 dBm from digital signal processing (DSP) aided receiver against -19.8 dBm from the commercial bit error ratio tester (BERT) yielding a small difference of 1.3 dB hence validating the reliability and accuracy of the digital signal processing (DSP) assisted receiver. Traditional direct detection scheme and coherent detection scheme performances were evaluated again on a 10 Gbps NRZ ASK signal. Coherent detection that can achieve a large unamplified transmission reach and has a higher passive optical splitting ratio was first evaluated using the VPI simulation software. Simulation results gave a receiver sensitivity of -30.4 dBm forcoherent detection and -18.3 dBm for direct detection, yielding a gain in receiver sensitivity of 12.1 dB. The complex coherently detected signal, from the experimental setup gave a receiver sensitivity of -20.6 dBm with a gain in receiver sensitivity of 3.5 dBm with respect to direct detection. A multilevel pulse amplitude modulation (4-PAM) that doubles the data rate per channel from10 Gbps to 20 Gbps by transmitting more information in the amplitude of the carrier signal was implemented. This was achieved by modulating the optical amplitude with an electrical four level amplitude shift keyed (ASK) signal. A receiver consisting of a single photodiode, three decision circuits and a decoding logic circuit was used to receive and extract the original transmitted data. A DSP aided receiver was used to evaluate the link performance. A receiver sensitivity of -12.8 dBm is attained with a dispersion penalty of about 7.2 dB after transmission through 25 km of G.652 fibre.
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- Date Issued: 2016
Investigating the effectiveness of microcatchments at enhancing transplant performance in Nama-Karoo riparian ecosystem restoration
- Authors: Jackson, Andrew St. John , Wigley, Benjamin , Schumann, Bonnie , Currie, Bianca
- Date: 2016
- Subjects: Arid regions agriculture , Environmental degradation , Range ecology
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/7469 , vital:21782
- Description: Globally agricultural rangelands have been subjected to degradation through over-utilization. The loss of productivity of agricultural rangelands around the world has led to the development of methods to restore the productivity of these areas. In South Africa, extensive areas of the Nama-Karoo have been degraded or transformed due in part to unsustainable agricultural activities. The development of restoration methods which are easily implementable and financially viable could increase the probability of stakeholders implementing restoration activities on privately owned land. The removal of the degrading factor is not sufficient to reverse the degradative trend in dryland environments. Active measures must be implemented to arrest the degradation cascade. The climatic conditions of the rangelands of South Africa are limiting to plant performance and the favourable conditions are sporadic. The translocation of plants should be combined with the amelioration of the local conditions. This study tested the restoration technique of microcatchments in association with plant translocation. The effects of microcatchments and planting combinations which were best suited to the survival and performance of the transplants were determined through a field trail. The results showed that microcatchments created microsites which were conducive to transplant survival and growth, including nutrient accumulation and increased soil moisture. The success of the method was dependent on the planting combination used. Plants which are adapted to inundation and the saline conditions of the site performed better. Plants which were older at the time of translocation had higher survival rates than younger transplants. In the conditions of this site, planting adjacent to the microcatchments was necessary to avoid inundation induced mortalities. The environmental conditions of the Nama-Karoo necessitate the coordination of restoration activities with the predicted favourable conditions in order to improve the success of restoration activities.
- Full Text:
- Date Issued: 2016
Investigating the effects of mopane worms (Imbrasia belina) on nutrients, Venetia-Limpopo Nature Reserve, South Africa
- Authors: De Swardt, Donovan Barry , O’Connor, Tim
- Date: 2016
- Subjects: Herbivores -- Ecology -- South Africa -- Limpopo , Phytophagous insects -- South Africa -- Limpopo , Mopane worm -- South Africa -- Limpopo , Soil fertility -- South Africa -- Limpopo
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/9273 , vital:26558
- Description: Ecologists have long been aware that large mammalian herbivores can alter ecosystem functioning in various ways, for example through changing where they defecate and urinate, which consequently affects nutrient cycling. The effects of herbivorous insects on ecosystems, however, have received limited attention until recently. Insects are capable of mass outbreaks, they can consume large volumes of vegetative material and can deposit large quantities of dung (frass), one example being the mopane worm, Imbrasia belina. This study looked at the effect of mopane worm frass on soil fertility in the mopane veld of the Venetia-Limpopo Nature Reserve and neighbouring Haakdoring farm. It found that mopane worms are capable of altering soil nutrient dynamics beneath the trees where they are browsing in three ways. Firstly, they increase the potential amount of nutrients deposited when compared with that deposited through conventional leaf litter. Secondly, they alter the rate of nutrient recycling by depositing nutrients in frass which decomposes more rapidly than conventional leaf litter. Lastly, they increase the amounts of potassium and phosphorus in the soil. While there is no conclusive data from this study that the mopane veld would become extinct if mopane worms were harvested to extinction, it has shown that there is relatively little evidence on how herbivorous insects could affect ecosystem functioning in the landscapes in which they occur. Further research is recommended that investigates how mopane worms influence soil fertility in more detail and over multiple geographical locations.
- Full Text:
- Date Issued: 2016
Leonotis leonurus: understanding the mechanism of anti-diabetic action and investigating a nano drug delivery system
- Authors: Odei-Addo, Frank , Levendal, Ruby-Ann
- Date: 2016
- Subjects: Diabetes Plant extracts
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/13116 , vital:27153
- Description: Diabetes mellitus is a metabolic disease characterised by hyperglycaemia resulting from defects in insulin secretion, insulin action, or both. The leaf extract of Leonotis leonurus and its active compound marrubiin, have been shown to possess anti-diabetic, antiplatelet, anti-inflammatory and anti-coagulation activity. In the present study, the mechanism by which L. leonurus and marrubiin exert their anti-diabetic properties, the cross-talk between the peripheral tissues and a nano drug delivery system were investigated. Marrubiin in the plant extract was effectively quantified by an optimised reversed phase highperformance liquid chromatography (HPLC) protocol using a pentafluorophenyl (PFP) column with water and acetonitrile (50:50) as mobile phase, and a flow rate of 1ml/min. The chemical structure was determined using liquid chromatography-tandem mass spectroscopy LC-MS/MS. Real-time quantitative polymerase chain reaction (RT-qPCR) gene expression of selected adipokines and proteins implicated in Type-2 diabetes (T2D) were investigated in specific peripheral tissues isolated from an in vivo obese rat model. An in vitro cell culture model was used to determine the crosstalk between the peripheral tissues and pancreatic (INS-1E) β-cells. Various nanoformulations of L. leonurus extract were prepared and their effect on cytotoxicity (in Chang liver and INS-1 cells), insulin-mediated glucose uptake (Change liver cells) and insulin secretion (INS-1) were investigated. The average yield of marrubiin from the plant extract was 10% (n=3), with a molecular mass of 333.20Da and a molecular formula of C20H29O4 +. Results from the in vivo study showed that the L. leonurus extract significantly (p<0.05) enhanced the gene expression of adiponectin, peroxisome proliferator-activated receptor gamma (PPAR-γ), glucokinase (GK), uncoupling protein-2 (UCP-2) and reduced leptin in adipose tissue, but resistin, glucose transporters (GLUT), fatty acid synthase (FAS), insulin receptor substrate -1 (IRS-1) and phosphoenolpyruvate carboxykinase (PEPCK) gene expression were not affected. Marrubiin decreased gene expression of leptin and resistin, and increased IRS-1 and glucokinase in adipose tissue. In liver and muscle tissues, marrubiin and the L. leonurus extract reduced gene expression of PPAR-γ, IRS-1, glucokinase and PEPCK. In the in vitro crosstalk study (under normoglycaemic and hyperglycaemic conditions), conditioned medium from 3T3-L1 cells significantly (p<0.01) enhanced insulin secretion. This was not observed in INS-1E cells exposed to muscle- and liver-conditioned medium, respectively. The in vitro studies using a nanostructured lipid formulation (NLC) of the plant extract was not cytotoxic to either INS-1 and Chang liver cells. The NLC formulation significantly (p<0.05) enhanced glucose uptake in Chang liver cells and improved chronic insulin release in INS-1 cells (p<0.05). Based on the above findings from the in vivo and in vitro studies, both L. leonurus and marrubiin exerted an insulinotropic effect via adipose tissue on pancreatic β-cells. The findings in the in vivo study showed that marrubiin and the L. leonurus extract were employing their major anti-diabetic action via the adipose tissue.
- Full Text:
- Date Issued: 2016
Modelling dispersal processes in impala-cheetah-lion ecosystems with infection in the lions
- Authors: Mbava, Willard
- Date: 2016
- Subjects: Predation (Biology) -- South Africa -- Kruger National Park Endangered species -- South Africa -- Kruger National Park
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/11782 , vital:26968
- Description: The study involved the predator-prey interaction of three species namely the predator (Cheetah Acinonyx jubatus), the super-predator (Lion Panthera leo), and their common prey (Impala Aepyceros melampus). The study area is the Kruger National Park. The predator being an endangered species, faces a survival problem. It is frequently killed by the super-predator to reduce competition for prey. The super-predator also scares away the predator o_ its kills. The prey forms the main diet of the predator. The plight of the predator motivated the author to formulate disease and reaction-diffusion models for the species interactions. The purpose of the models were to predict and explain the effect of large competition from the super-predator on the predator population. Important parameters related to additional predator mortality due to presence of super-predator, the disease incidence rate and induced death rate formed the focal points of the analysis. The dynamics of a predator-prey model with disease in super-predator were investigated. The super-predator species is infected with bovine Tuberculosis. In the study, the disease is considered as biological control to allow the predator population to regain from low numbers. The results highlight that in the absence of additional mortality on the predator by the super-predator, the predator population survives extinction. Furthermore, at current levels of disease incidence, the super-predator population is wiped out by the disease. However, the super-predator population survives extinction if the disease incidence rate is low. Persistence of all populations is possible in the case of low disease incidence rate and no additional mortality imparted on the predator. Furthermore, a two-species subsystem, prey and predator, is considered as a special case to determine the effect of super-predator removal from the system, on the survival of the predator. This is treated as a contrasting case from the smaller parks. The results show that the predator population thrives well in the total absence of its main competitor, with its population rising to at least twice the initial value. A reaction-diffusion three-species predator-prey model was formulated and analysed. Stability of the temporal and the spatio-temporal systems, existence and non-existence of stationary steady state solutions were studied. Conditions for the emergence of stationary patterns were deduced. The results show that by choosing the diffusion coeffcient d2 > _D 2 suffciently large, a non-constant positive solution is generated, that is, stationary patterns emerge, depicting dispersal of species. Predators were observed to occupy habitats surrounding prey. However, super-predators were observed to alternate their habitats, from staying away from prey to invading prey habitat. In the investigation, strategies to determine ways in which the predator species could be saved from extinction and its population improved were devised, and these included isolation of the predator from the super-predator.
- Full Text:
- Date Issued: 2016
Optimisation of clearcoat viscosity
- Authors: Bukula, Nwabisa Asanda
- Date: 2016
- Subjects: Coating processes , Automobiles -- Bodies -- Maintenance and repair
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/4814 , vital:20707
- Description: Modern automobiles are painted with basecoat, technology which is either metallic, solid colour or pearlescent. This requires protection from chemicals, scratching, weathering and UV light by applying a protective top coat (clearcoat) over the basecoat. For the clearcoat to cure into a hard protective shell it undergoes an irreversible crosslinking process. This usually takes place over the first four to five hours, depending on the formulation and weather conditions. The speed of crosslinking can be enhanced by temperature. Pot life is important as it can affect the overall quality of the painted surface. If crosslinking occurs too quickly, before the clearcoat is applied onto the surface, the clearcoat cannot be used to produce a good quality finish. The “expired” mixture is thus discarded. If used, the quality of the finished product cannot be guaranteed to last, and the paintwork may have to be redone. This often means removing the underlying paint and primer as well with the clearcoat film. Besides the time lost, the discarded clearcoat mixture often lands in the landfill, polluting ground water and the environment. It is thus important from the point of view of both the environment preservation and waste management, that as much clearcoat as possible is used without being wasted. It was proven in an earlier study (BSc Hon Formulation Science Treatise, 2011) that adding eugenol to a clearcoat mixture after crosslinking had started could reduce its viscosity, which is an indicator of crosslinking progress. Crosslinking subsequently resumed at a lower rate than in traditional blends. If stored away from oxygen and high temperatures, this blend could maintain optimum viscosity indefinitely. In this follow up study an optimum formulation was developed using D - optimal experimental design. It sought to extend the pot life to avoid waste to spray painters while saving the environment from pollution. The formulation that gave the desired viscosity after five hours of pot life was adopted. It was hypothesised that the optimum formulated clearcoat mixture would have a longer pot life than its traditional counterparts, and that it would perform just as well as the traditional clearcoat mixtures. To study the rate of crosslinking (disappearance of functional groups and appearance of the urethane bond), FTIR spectrometry was performed on a mixture produced from the optimized formula in comparison to that of a traditional mixture (the control). The rate of disappearance of functional groups was found to be lower in the eugenol mixture than in the control mixture. After six hours, eugenol was added into the control mixture, and this seemed to reduce the viscosity with the re-emergence of functional groups in the mixture. After 24 hours of crosslinking, an FTIR scan was done on the solid sample and this revealed that the eugenol mixture had crosslinked fully, with no detectable functional groups in the sample.
- Full Text:
- Date Issued: 2016
Perceptions and practices of small-scale piggery farmers towards animal welfare in the Nelson Mandela Bay Metropole
- Authors: Maqhajana, Mzwanele
- Date: 2016
- Subjects: Animal welfare -- South Africa -- Nelson Mandela Bay Municipality , Farms, Small -- South Africa -- Nelson Mandela Bay Municipality
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/8079 , vital:24719
- Description: There has been an increasing concern about animal welfare in small-scale farming as the farmers' agricultural practices shift towards intensive agriculture. It has become important to comprehend how small-scale farmers perceive and practice animal welfare relative to production and market integration. To solve the research problem, the research emphasis was on assessing the following practices; procedures adopted by the small-scale farmers, welfare levels verses industry equirements for market integration; determinants affecting small-scale perceptions and attitudes towards animal welfare and how has animal welfare affected farm development and production. The research focus for this study was to investigate the linkage between perceptions and this process. In order to achieve a more in-depth understanding of the study while also ensuring its validity and correctness a triangulation research method was applied, which consisted of a quantitative and qualitative method approach. The focus groups and structured research interview questions were used as the main data collections instruments. The study consisted of sixty-two piggery small-scale farmers from three areas of the Nelson Mandela Bay metropole. The study found that there was a disparity between the perceptions and practice of small-scale farmers. Farmers perceived their practices as acceptable. However, on most of the farms the pigs were farmed in an unhygienic environment, had limited handling facilities, the farmers had unconventional methods to handle the pigs; there was poor support from technical services, many of the farmers never administered animal welfare evaluations and applied questionable feeding practices. The study also indicated that less than 15% had suitable facilities to accommodate suitable reproduction and piglet care. The researcher recommended the following interventions to improve animal welfare approaches with small-scale farmers in the Nelson Mandela Bay metropole: Training and information campaigns to improve small-scale piggery farmers' perception and knowledge of animal welfare, as well as market standards and requirements. Strengthening the relationship between the small-scale piggery farmers and animal welfare stakeholders. Including active engagement between small scale piggery farmers and the Department of Rural Development, Agrarian Reform and Urban Agriculture Unit of the Nelson Mandela Bay Municipality. Encouraging farmers to strive for stronger markets to facilitate better income and care of animals.
- Full Text:
- Date Issued: 2016
Physical properties of solid-state erythromycin derived compounds
- Authors: Neglur, Rekha R
- Date: 2016
- Subjects: Erythromycin -- Thermal properties , Azithromycin -- Thermal properties
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/7228 , vital:21308
- Description: This thesis investigated the physical properties of the macrolide antibiotics: Erythromycin dihydrate (EM-DH), Roxithromycin monohydrate (RM-MH) and Azithromycin dihydrate (AZM-DH). The abovementioned hydrate compounds were investigated in terms of the hydrate-anhydrate crystal structure stability, dehydration and observed polymorphism under controlled temperature heating programs. Identified hydrate and anhydrate polymorphs were subjected to physical stability testing during controlled storage. EM-DH was characterized by thermal analysis (DSC, TGA), X-ray diffraction, FTIR and microscopy. Dehydration of EM-DH at temperatures of 100, 157 and 200°C (followed by supercooling to 25°C) produced the form (I) anhydrate (Tm =142.9°C), form (II) anhydrate (Tm = 184.7°C ) and amorph (II) (Tg = 118°C) respectively. The attempts to produce amorph (I) from melting (in vicinity of form (I) melt over temperature range 133°C to 144°C) and supercooling was unsuccessful due to the high crystallization tendency of the form (I) melt. Brief humidity exposure and controlled temperature (40°C)/ humidity storage for 4 days (0-96% RH) revealed hygroscopic behaviour for the anhydrate crystal (forms (I) and (II)) and amorph (II) forms. Form (II) converted to a nonstoichiometric hydrate where extent of water vapour absorption increased with increased storage humidity (2.1% absorbed moisture from recorded TGA at 96% RH). Amorph (II) exhibited similar trends but with greater water absorption of 4.7% (recorded with TGA) at 96% RH. The pulverization and sieving process of amorph (II) (at normal environmental conditions) was accompanied by some water vapour absorption (1.1%). A slightly lower absorbed moisture content of 3.3% (from TGA) after controlled 4 days storage at 40°C/ 96% RH was recorded. This suggested some physical instability (crystallization tendency) of amorph (II) after pulverization. The thermally induced dehydration of RM-MH by DSC-TG was evaluated structurally (SCXRD), morphologically (microscopy) and by kinetic analysis. Various kinetic analysis approaches were employed (advanced, approximation based integral and differential kinetic analysis methods) in order to obtain reliable dehydration kinetic parameters. The crystal structure was little affected by dehydration as most H-bonds were intramolecular and not integral to the crystal structure stability. Kinetic parameters from thermally stimulated dehydration indicated a multidimensional diffusion based mechanism, due to the escape of water from interlinked voids in crystal. The hygroscopicity of the forms RM-MH, Roxithromycin-anhydrate and amorph glass (Tg = 81.4°C) were investigated. Roxithromycinanhydrate (crystalline) converted readily to RM-MH which were found to be compositionally stable over the humidity range 43-96%RH. Amorphous glass exhibited increased water vapour absorption with increasing storage humidity (40°C/ 0-96% RH). TG analysis suggested a moisture content of 3.5% at 96% RH after 4 storage days. DSC and powder XRD analysis of stored pulverised amorphous glass indicated some physical instability due to water induced crystallization. Commercial AZM-DH and its modifications were characterized by thermal analysis (DSC, TGA), SC-XRD and microscopy. Thermally stimulated dehydration of AZM-DH occurred in a two-step process over different temperature ranges. This was attributed to different bonding environments for coordinated waters which were also verified from the crystal structure. Dehydration activation energies for thermally stimulated dehydration were however similar for both loss steps. This was attributed to similarities in the mode of H- bonding. Different forms of AZM were prepared by programmed temperature heating and cooling of AZM-DH. The prepared forms included amorphous glass (melt supercooling), amorphous powder (prepared below crystalline melting temperature), crystalline anhydrate and crystalline partial dehydrate. Humidity exposure indicated hygroscopic behaviour for the amorphous, crystalline anhydrate and crystalline partial dehydrate modifications. Both the crystalline anhydrate and partial dehydrate modifications converted to the stoichiometric dihydrate form (AZM-DH) at normal environmental conditions at ambient temperature. Both the amorph glass and amorph powder exhibited increased moisture absorption with increased humidity exposure. TG analysis of the pulverised amorph glass indicated a moisture content of 5.1% at 96% RH after 4 storage days. The absence of crystalline melt in DSC and presence of Tg (106.9°C) indicated the sample remained amorphous after pulverisation and storage for 4 days at 40°C/ 96% RH.
- Full Text:
- Date Issued: 2016
Quantitative microstructural evaluation of 12 Cr creep aged steels after welding
- Authors: Marx, Genevéve , Neethling, Jan
- Date: 2016
- Subjects: Stainless steel -- Welding , Electron microscopy
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/7232 , vital:21307
- Description: This dissertation focuses on the quantitative microstructural evaluation of new and creep aged X20 (12 Cr) stainless steel after welding. X20 stainless steel has been widely used in the high temperature and pressure pipework of coal-fired power plants. Consequently, this material has to withstand extreme conditions of high temperature and stress during service exposure. Under these conditions, creep deteriorates the strength of the material. The material’s resistance to creep damage due to its microstructure can be quantitatively described by the back-stress. There are four microstructural contributions to the back-stress: Precipitate Hardening, Sub-Boundary Hardening, Solid-Solution Hardening and Dislocation Hardening. Fusion welding is performed on creep aged materials when a component needs to be replaced. This high temperature process results in the formation of different microstructural regions within the weldment. These creep damaged components have a weldability limit as set by the life management strategy of the power plant company. Measuring techniques capable of quantifying the microstructural contributions (precipitates, subgrains and dislocations) were developed and evaluated in this study. These techniques were then used to characterise the different microstructural regions within a new and creep aged X20 steel weldment. Differences in the microstructure of the new and creep aged X20 steel was illustrated by the results of this study. The measured size and number densities of the precipitates in the creep aged X20 material showed that there is a decrease in PH during creep exposure. There was a decrease in SBH and DH stress for the creep aged X20 material due to coarsening of the subgrains and annealing of dislocations during creep exposure. The quantitative techniques demonstrated in this study opens up the possibility to perform life assessment on weldments with inhomogeneous microstructures by following a microstructural based approach.
- Full Text:
- Date Issued: 2016
Rhenium complexes with multidentate imine-, amine-, thione-, thiol-, hydroxy- and carboxamide chelates
- Authors: Habarurema, Gratien
- Date: 2016
- Subjects: Rhenium Metal complexes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/12679 , vital:27106
- Description: This study entails the synthesis, spectroscopic and structural characterization of new rhenium complexes with multidentate imine-, amine-, thione-, thiol-, hydroxy- and carboxamide chelates in various oxidation states. Rhenium(I) and (V) complexes with imidazolidine, pyrimidine and bridging pyridyl derivatives are reported in Chapter 3. The reactions of the potential tridentate N,N,Odonor ligand 2,2'-dipyridylketone (dpk) with trans-[ReOCl3(PPh3)2], (n-Bu4N)[ReOCl4] and trans-[ReOI2(OEt)(PPh3)2] led to the isolation of cis-[ReOCl2(edpm)], cis-[ReOCl2(dpk.OH)] and [ReO3(dpk.OH)] respectively (see Scheme 1). The reaction of (E)-N-((pyridine-2-yl)methylene)benzo[d]thiazol-2-amine (pbt) with trans- [ReOCl3(PPh3)2] produced a mononuclear oxorhenium(V) complex cis- [ReOCl2(epm)(PPh3)]. Both dpk and pbt exhibited a nucleophilic attack by acetonitrile (for Hedpm), water (for dpk) and ethanol (for pbt) leading to chelates that act as uninegative tridentate N,N,O- and bidentate N,O-donor chelates respectively. The reaction of [Re(CO)5Cl] with 2,3-dihydro-2,2-di(pyridin-2-yl)-1H-benzo[d]imidazole (H2dpb), (2,6-diaza-cyclohex-1-enylolonium)2-aza-benzoate (H2den) and 2-(2-(pyridine-2-yl)imidazolidin-2-yl)pyridine (H2pip) (see Scheme 1) gave rise to novel rhenium(I) complexes fac-[Re(CO)3(H2dmb)Cl], fac-[Re(CO)3(Hhdm)] and fac-[Re(CO)3(H2pip)]Cl respectively. The monomeric cationic salt fac-[Re(CO)3(H2salbam)]Br and ligand-bridged dimer fac- (μ-H2salet)[Re(CO)3]2 complexes were formed by the reactions of [Re(CO)5X] (X = Br or Cl) with the potentially heptadentate Schiff base 2,2,2-tris (salicylideneimino)- triethylamine (H3salet; Scheme 2) respectively. The reactions of the potentially hexadentate ligands acting as tridentate monoanionic N,N,O- or N,O,O-donor chelates N1-(3-(2-hydroxy enzylideneamino) propylamino) ethyl)benzylidenepropane-1,3-diamine (H2salpd) and N,N -bis(salicylidene) -3,6-dioxa-1,8-diaminooctane (H2saldane) (Scheme 2) with [Re(CO)5Cl] led to the isolation of the mononuclear and dinuclear complexes fac-[Re(CO)3(Hsaldane)] and fac-(μ-salpd)[Re(CO)3]2 respectively. The reactions of [Re(CO)5Cl] with the tetradentate ligands 2-{[2-hydroxy-3-{[(E)-(2- hydroxyphenyl)-methylidene]amino}propyl)imino]methyl}phenol (H2hmp), 6-((6E)- ((3E)-3-((oxocyclohexa-2,4-dienyl)methyleneamino)-2-hydroxypropylimino)methyl)- cyclohexa-2,4-dienone (H2hcd.H2O) zwitterion and 2-((1E)-1-((E)-3-(2-hydoxyphenylmethylideneamino)propylimino)methyl)phenol (H2hdp) (see Scheme 2) resulted in the formation of the neutral fac-[Re(CO)3(Hamp)], fac-[Re(CO)3(Hhetp)] and fac- [Re(CO)3(Happ)] respectively. The treatment of 2-((3-(2-hydroxybenzylamino)-propylamino)methyl)phenol (H2hbp) with [Re(CO)3Cl] and trans-[ReOCl3(PPh3)2] gave the fac-[Re(CO)3(Hhbp)] and (μ-O)[ReO(hbp)]2 complexes. The reactions of the ligands H2hmp, H2hdp and H2hap (see Scheme 2) with trans-[ReOBr3(PPh3)2] and trans-[ReOI2(OEt)(PPh3)2] produced dinuclear oxo-bridged rhenium(V) complexes (μ-O)[ReO(hmp)]2, [(μ-O)[ReO(hdp)]2 and (μ-O)[ReO(hap)]2 respectively. The neutral and anionic binding modes of thiosemicarbazones to the fac-[Re(CO)3]+, cis- [ReO2]+ and trans-[ReO2]+ cores have been investigated in Chapter 6. The reactions of the potentially tridentate ligand 1-{1-(2- hydroxyphenyl)ethylidene}-4- phenylthiosemicarbazide (H2hpt) (see Scheme 3) with [Re(CO)5Cl], cis-[ReO2I(PPh3)2]cand trans-[ReO2(py)4]Cl led to the isolation of the complexes fac-[Re(CO)3(H2hpt)2]Cl, [Re(hipt)(Hipht)(PPh3)] and trans-[ReO(hpt)(Hhpt)] respectively. The X-ray crystal analysis of the complexes show that the ligand H2hpt exhibits decomposition, thiol-enol tautomerism and a thiolate-iminium zwitterionic process, and coordinates in the neutral form via its thione sulfur and nitrogen and anionic through the azo nitrogen, thiolate sulfur and acetophenolic oxygen. A series of nitrogen-heterocyclic amide-, acid-, thiol- and diol-based ligands as well as their related monomeric rhenium(III) and (V) complexes have also been studied (see Chapter 7). The reaction of N-(2-(pyrazine-2-carboxamido)phenyl)pyrazine-2- carboxamide (H2ppc) (Scheme 3) with trans-[ReOBr3(PPh3)2] yielded the complex trans- [ReBr2(Hppca)(PPh3)2]. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with pyridine-2,6-dicarboxylic acid (H2pda) produced the neutral oxorhenium(V) complexes [ReOX2(epca)(PPh3)]. The treatment of trans-[ReOBr3(PPh3)2] with 2-mercaptopyridine- 3-carboxylic acid (H2mpc) gave rise to the rhenium(III) complex [Re(empc)3(PPh3)]. The reaction of 2,6-bis(hydroxymethyl)pyridine (H2bhp) with trans-[ReOI2(EOt)(PPh3)2], trans-[ReOBr3(PPh3)2] and [Re(CO)5Cl] gave the complexes [ReO(Hbhp)2(PPh3)]I.PPh3, cis-[ReOBr2(Hbhp)(PPh3)] and fac-(μ- O)2[Re(CO)3(Hbhp)]2 respectively. Their X-ray crystal structures indicate that the ligand acts as a bidentate monoanionic N,O-donor chelate leaving a free aliphatic hydroxyl group.
- Full Text:
- Date Issued: 2016
Rhenium complexes with pontentially multidentate ligands containing the amino, imino, hydroxy and thiol groups
- Authors: Mukiza, Janvier
- Date: 2016
- Subjects: Rhenium Thiols Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/12308 , vital:27053
- Description: The chemistry of rhenium has received considerable interest due to its versatility in various catalytic applications, fixation and especially the potential use of 186Re and 188Re radionuclides in nuclear medicine. This study investigates the synthesis and characterisation of rhenium complexes with potentially multidentate ligands containing the amino, imino, hydroxyl and thiol groups. It reports new rhenium complexes in the +1, +3, +4 and +5 oxidation states, which display structural diversity, from monomers to ligand-bridged dimers as well as metal-metal multiply bonded dimers. The reaction of orotic acid (H2oa) and 2-mercapto-orotic acid (H2moa) with trans- [ReOX3(PPh3)2] (X = Cl, Br) were studied and led to the formation of ligand-bridged dimers with metal-metal multiple bonds i.e. (μ-Br)(μ-O)(μ-oa)[Re2 IVBr(OEt)2(PPh3)2], (μ-X)(μ-O)(μ-oa)[Re2 IVX2(OiPr)(PPh3)2] and (μ-Cl)(μ-O)(μ-moa)2[Re(PPh3)]2. The reaction of H2oa with [ReO2(py)4]Cl, [Re(dab)Br3(PPh3)2] (H2dab = 1,2- diaminobenzene) and [Re(CO)5Cl] were also studied and monomeric complexes [ReO(py)2(OEt)(oa)], [Re(dab)Br(oa)(PPh3)2] and (Ph4P)[Re(CO)3(H2O)(oa)] were isolated. The treatment of 5-amino-orotic acid (H2aoa) with [ReOBr3(PPh3)2] led to dimers with metal-metal triple bonds ReIV≡ReIV i.e. (μ-Br)(μ-O)(μ-oa)[Re2 IVBr(OEt)2(PPh3)2], (μ-Br)(μ-O)(μ-oa)[Re2 IVBr2(OiPr)(PPh3)2], as well as the monomer [ReV(apd)Br(aoa)(PPh3)2] (apd2− = 5-imidopyrimidine-2,4-dione). The chelating ligand 5-aminopyrimidine-2,4-dione (H2apd) was formed by oxorhenium(V)-catalysed decarboxylation of 5-amino-orotic acid (H2aoa) (see Scheme 1). The reaction of the Schiff base derivative of 5-amino-ortic acid, salicylimine-orotic acid (H2soa), with trans-[ReOI2(OEt)(PPh3)2] in ethanol was also investigated and led to the formation of the rhenium(III) complex salt [Re(coa)I(PPh3)2]I [Hcoa = 5-(2- hydroxybenzylideneamino)pyrimidine-2,4(1H,3H)-dione]. The chelating Hcoa is also formed from the oxorhenium(V)-catalysed decarboxylation of H2soa and coordinates to the rhenium(III) ion as a monoanionic tridentate N,O,O-donor chelate via the phenolate and ketonic oxygens, and the imino nitrogen atom. However, decarboxylation of H2soa was not observed in its reaction with [ReOCl3(PPh3)2], which led to the isolation of [ReOCl(soa)(PPh3)]. The reaction of the carboxamide derivative of 5-aminoorotic acid, 5-(5-aminopyrimidine-2,4(1H,3H)- dioxamido)-1,2,3,6-tetrahedro-2,6-dioxopyrimidine-4-carboxylic acid (H2ampa) with [Re(CO)5Cl] in ethanol led to the formation of a zwitterionic rhenium(I) complex [Re(CO)3(H2O)(amef)] [amef = {5-(5-ammoniumpyrimidine-2,4(1H,3H)-dioxamido)- 1,2,3,6-tetrahedro-2,6-dioxopyrimidine-4-ethylformate}]. The chelating ion amef was formed from the combined tricarbonylrhenium(I)-catalysed esterification and aminoprotonation of H2ampa (see Scheme 1) and coordinates to the fac-[Re(CO)3]+ core as a dianionic bidentate N,N-donor chelate via the amido nitrgens.
- Full Text:
- Date Issued: 2016
Scalable chemistry involving diazonium salts
- Authors: Akwi, Faith Mary
- Date: 2016
- Subjects: Azo compounds -- Synthesis , Chemical processes
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10948/6909 , vital:21162
- Description: Herein an alternative approach aimed at reducing the cost of numbering up technique as a scale up strategy for chemical processes from the laboratory bench top to the industry is explored. The effect of increasing channel size on the reaction conversion of the synthesis of azo compounds is investigated. This was achieved via a systematic investigative understanding of the synthesis in microreactors where a proof of concept study was performed to determine the optimum reaction parameters in azo coupling reactions involving couplers with aminated or hydroxylated groups in Little Things Factory-MS microreactors (Channel diameter: 1.0 mm) It was found that at slightly alkaline conditions (pH 8.55) and at a temperature of 25 °C, excellent conversions were attained in the azo coupling reaction of the diazonium salt solution of 2,4-dimethylaniline to 2-naphthol. On the other hand, the azo coupling reaction of the diazonium salt solution of p-nitroaniline to diphenylamine was found to thrive at a pH of 5.71 and at a temperature of 25 °C. Using, these optimized reaction parameters, the in-situ and reactive quench of diazonium salts in LTF-MS microreactors was investigated where it was found that at a flow rate of 0.2 ml/min, 0.03 ml/min and 0.07 ml/min of diazotizable amine & HCl, sodium nitrite and coupler solutions respectively, a conversion of 98% is achieved in approximately 2.4 minutes. A library of azo compounds was thus generated under these reaction conditions from couplers with aminated or hydroxylated aromatic aromatic systems. The scaled up synthesis of these compounds in a homemade PTFE tubing (ID 1.5 mm) reactor system was thereafter investigated and comparable conversions were observed. Capitalizing on the benefits of a large surface area and the short molecular diffusion distances observed in microreactors, in-situ phase transfer catalyzed azo coupling reaction of diphenylamine to p-nitroaniline was also explored. In this investigation a rapid and easy optimization protocol that yielded a 99%, 22% and 33% conversion of diphenylamine, carbazole and triphenylamine respectively in approximately 2.4 minutes using Chemtrix microreactors was established. On increasing the microreactor channel internal diameter in the scaled up synthesis approach, it was found that a 0.5 mm increase in channel internal diameter does result in lower reaction conversions.
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- Date Issued: 2016