The development of biological tools to aid in the genetic investigation of the black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros mitochondrial genomes
- Authors: Parsons, Michelle
- Date: 2015
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/56059 , vital:26769
- Description: The black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros are found in South Africa. A decline in the populations of these species has resulted due to human activities such as habitat fragmentation and poaching. This has contributed to the loss of genetic diversity amongst the black and white rhinoceros. Conservation and anti-poaching efforts are needed to help maintain genetic diversity. These efforts could be improved through the development of non-invasive techniques to examine DNA from threatened animals. The aim of this research was to develop a molecular technique which would allow for the identification of the black and white rhinoceros and to develop a molecular technique which would allow for intraspecies genetic variation to be examined. DNA extractions were performed on matched faecal and tissue samples that were collected from two regions in South Africa. Polymerase chain reaction (PCR) primer sets were designed to investigate several regions of the rhinoceros mitochondrial genome. PCR optimisation was completed for the target regions. Sequencing was conducted on all final PCR products. The cytochrome c oxidase subunit 1 (COIi) gene allowed for the rhinoceros family to be identified. This region was digested with the HindIII restriction enzyme, which allowed for the specific identification of either the black or white rhinoceros. A subsequent region of the cytochrome c oxidase subunit 1 (COIii) as well as the D-loop, hypervariable regions (HV1 and HV2), cytochrome b (cytb) and 16s rRNA regions were investigated. These regions displayed potential for establishing geographic origin for black rhinoceros samples, whereas the D-loop and HV2 show potential for the white rhinoceros. The white rhinoceros displayed sequence variation in the HV2 and cytb region, while variation was observed in the COIi and HV1 for the black rhinoceros. All investigated target regions allowed for the rhinoceros family to be identified. The COI (COIi and COIii), HV2 and cytb regions allowed for the subspecies of rhinoceros to be identified, however the D-loop was not able to identify the white rhinoceros species. The 16s rRNA and HV1 regions allowed for the correct subspecies of rhinoceros to be identified, however as the primers were only compatible for the black rhinoceros therefore a subsequent investigation is required for the white rhinoceros. The establishment of this novel PCR based technique to identify white and black rhinoceros will allow for efficient species identification in wildlife forensic cases. A biological method was established to study intraspecies variation for the white and black rhinoceros; however the investigated target regions did not yield sufficient genetic variation. The core techniques developed in this study will be valuable for future studies that wish to investigate genetic variation in mammal species.
- Full Text:
- Date Issued: 2015
- Authors: Parsons, Michelle
- Date: 2015
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/56059 , vital:26769
- Description: The black (Diceros bicornis) and white (Ceratotherium simum) rhinoceros are found in South Africa. A decline in the populations of these species has resulted due to human activities such as habitat fragmentation and poaching. This has contributed to the loss of genetic diversity amongst the black and white rhinoceros. Conservation and anti-poaching efforts are needed to help maintain genetic diversity. These efforts could be improved through the development of non-invasive techniques to examine DNA from threatened animals. The aim of this research was to develop a molecular technique which would allow for the identification of the black and white rhinoceros and to develop a molecular technique which would allow for intraspecies genetic variation to be examined. DNA extractions were performed on matched faecal and tissue samples that were collected from two regions in South Africa. Polymerase chain reaction (PCR) primer sets were designed to investigate several regions of the rhinoceros mitochondrial genome. PCR optimisation was completed for the target regions. Sequencing was conducted on all final PCR products. The cytochrome c oxidase subunit 1 (COIi) gene allowed for the rhinoceros family to be identified. This region was digested with the HindIII restriction enzyme, which allowed for the specific identification of either the black or white rhinoceros. A subsequent region of the cytochrome c oxidase subunit 1 (COIii) as well as the D-loop, hypervariable regions (HV1 and HV2), cytochrome b (cytb) and 16s rRNA regions were investigated. These regions displayed potential for establishing geographic origin for black rhinoceros samples, whereas the D-loop and HV2 show potential for the white rhinoceros. The white rhinoceros displayed sequence variation in the HV2 and cytb region, while variation was observed in the COIi and HV1 for the black rhinoceros. All investigated target regions allowed for the rhinoceros family to be identified. The COI (COIi and COIii), HV2 and cytb regions allowed for the subspecies of rhinoceros to be identified, however the D-loop was not able to identify the white rhinoceros species. The 16s rRNA and HV1 regions allowed for the correct subspecies of rhinoceros to be identified, however as the primers were only compatible for the black rhinoceros therefore a subsequent investigation is required for the white rhinoceros. The establishment of this novel PCR based technique to identify white and black rhinoceros will allow for efficient species identification in wildlife forensic cases. A biological method was established to study intraspecies variation for the white and black rhinoceros; however the investigated target regions did not yield sufficient genetic variation. The core techniques developed in this study will be valuable for future studies that wish to investigate genetic variation in mammal species.
- Full Text:
- Date Issued: 2015
Fungal remediation of winery and distillery wastewaters using Trametes pubescens MB 89 and the enhanced production of a high-value enzyme therein
- Authors: Strong, Peter James
- Date: 2008
- Subjects: Fungal remediation Distilleries -- Waste disposal Wine and wine making -- Waste disposal Bioremediation Laccase Enzymes -- Biotechnology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3932 , http://hdl.handle.net/10962/d1003991
- Description: In this study white-rot fungi were investigated for their efficiency at distillery wastewater remediation and the production of laccase as a valuable by-product. Distillery wastewaters are high in organic load and low in pH. The presence of phenolic compounds can lead to extremely colour-rich wastewaters and can be toxic to microorganisms. The presence of the inorganic ions may also affect biological treatment. White-rot fungi are unique among eukaryotic or prokaryotic microbes in possessing powerful oxidative enzyme systems that can degrade lignin to carbon dioxide. These ligninolytic enzymes, such as lignin peroxidase, manganese peroxidase and laccase, are capable of degrading a vast range of toxic, recalcitrant environmental pollutants and this makes the white-rot fungi strong candidates for the bioremediation of polluted soils and waters. The laccase enzyme alone has shown remediation potential in wastewaters such as beer production effluent, olive mill wastewater, alcohol distillery wastes, dye-containing wastewaters from the textile industry as well as wastewaters from the paper and pulp industry. It has been shown to be capable of remediating soils and waters polluted with chlorinated phenolic compounds, polyaromatic hydrocarbons, nitrosubstituted compounds and fungicides, herbicides and insecticides.
- Full Text:
- Date Issued: 2008
- Authors: Strong, Peter James
- Date: 2008
- Subjects: Fungal remediation Distilleries -- Waste disposal Wine and wine making -- Waste disposal Bioremediation Laccase Enzymes -- Biotechnology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3932 , http://hdl.handle.net/10962/d1003991
- Description: In this study white-rot fungi were investigated for their efficiency at distillery wastewater remediation and the production of laccase as a valuable by-product. Distillery wastewaters are high in organic load and low in pH. The presence of phenolic compounds can lead to extremely colour-rich wastewaters and can be toxic to microorganisms. The presence of the inorganic ions may also affect biological treatment. White-rot fungi are unique among eukaryotic or prokaryotic microbes in possessing powerful oxidative enzyme systems that can degrade lignin to carbon dioxide. These ligninolytic enzymes, such as lignin peroxidase, manganese peroxidase and laccase, are capable of degrading a vast range of toxic, recalcitrant environmental pollutants and this makes the white-rot fungi strong candidates for the bioremediation of polluted soils and waters. The laccase enzyme alone has shown remediation potential in wastewaters such as beer production effluent, olive mill wastewater, alcohol distillery wastes, dye-containing wastewaters from the textile industry as well as wastewaters from the paper and pulp industry. It has been shown to be capable of remediating soils and waters polluted with chlorinated phenolic compounds, polyaromatic hydrocarbons, nitrosubstituted compounds and fungicides, herbicides and insecticides.
- Full Text:
- Date Issued: 2008
Movement of coastal fishery species in Southern Africa: research trends, characterisation of behaviours and a case study on fishery implications
- Authors: Maggs, Jade Quinton
- Date: 2018
- Subjects: Fishery management -- Africa, Southern , Fisheries -- Africa, Southern , Fisheries -- Catch effort , Fisheries -- Environmental aspects , Fisheries --Monitoring , Biotelemetry , Sustainable fisheries -- Africa, Southern , Overfishing -- Africa, Southern
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60574 , vital:27798
- Description: Movement of fishes is an integral part of their daily life, but has significant implications for fishery management. As with nearly all coastal countries, South Africa relies on coastal fisheries as a renewable resource, but many stocks have been overexploited for decades. Although it has long been recognised that an understanding of fish movement is necessary for effective management, it is with some difficulty that the subject has been studied in the past. In recent years, however, improvements in technology have provided the means for more in-depth investigations into fish movement. This research has revealed a range of complex movement behaviours. Movement in fishes occurs on a variety of temporal and spatial scales leading to the characteristic patterns of distribution and abundance observed in marine ecosystems. Fishes move nearly constantly in search of food, shelter or reproductive opportunities. Observations of behaviours such as long-term site fidelity, longdistance migration and natal homing are enabling ecologists to understand patterns of distribution and abundance within a species' range. Fish movement around the South African coast has been studied on numerous occasions but this has largely been confined to studies on single species. Movement behaviour of multiple species has been studied, but this has been limited to spatially localised marine protected area research. There has been little attempt in southern Africa to synthesize interspecific movement behaviour over wide spatial scales.Unprecedented concern over the biological effects of overexploitation, together with rapid technological advances in biotelemetry, have provided the impetus for much research, on a global scale, into the movement of marine animals. I reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings. Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa. Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry. Overall, 26 fish families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications. Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine- scale habitat usage (33%) and protected areas (26%). The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population. Substantial progress has also been made in unravelling the complexities of fine-scale movements in marine reserves and habitat usage in estuaries. While this knowledge has enabled more effective management of South Africa's multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the extent of movement across reserve boundaries. Mark-recapture data, collected over the past 30 years by the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORICFTP), were used to investigate broad- scale movement patterns of 30 prominent coastal fishery species (Chapter 4). Fishes were tagged with plastic dart tags along the coastline of southern Africa from Angola to Mozambique. This exercise yielded more than 10000 recaptures. The 30 chosen species represented 14 families, although 12 species belonged to a single family (Sparidae). Overall, 67% of recaptures were reported from the original tagging locality and 73% were recorded within 5 km of the tagging locality. The remaining observations extended from 6-3000 km. Movements were assigned to four distance bins (0-5 km, 6-50km, 51-500km and >500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.
- Full Text:
- Date Issued: 2018
- Authors: Maggs, Jade Quinton
- Date: 2018
- Subjects: Fishery management -- Africa, Southern , Fisheries -- Africa, Southern , Fisheries -- Catch effort , Fisheries -- Environmental aspects , Fisheries --Monitoring , Biotelemetry , Sustainable fisheries -- Africa, Southern , Overfishing -- Africa, Southern
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/60574 , vital:27798
- Description: Movement of fishes is an integral part of their daily life, but has significant implications for fishery management. As with nearly all coastal countries, South Africa relies on coastal fisheries as a renewable resource, but many stocks have been overexploited for decades. Although it has long been recognised that an understanding of fish movement is necessary for effective management, it is with some difficulty that the subject has been studied in the past. In recent years, however, improvements in technology have provided the means for more in-depth investigations into fish movement. This research has revealed a range of complex movement behaviours. Movement in fishes occurs on a variety of temporal and spatial scales leading to the characteristic patterns of distribution and abundance observed in marine ecosystems. Fishes move nearly constantly in search of food, shelter or reproductive opportunities. Observations of behaviours such as long-term site fidelity, longdistance migration and natal homing are enabling ecologists to understand patterns of distribution and abundance within a species' range. Fish movement around the South African coast has been studied on numerous occasions but this has largely been confined to studies on single species. Movement behaviour of multiple species has been studied, but this has been limited to spatially localised marine protected area research. There has been little attempt in southern Africa to synthesize interspecific movement behaviour over wide spatial scales.Unprecedented concern over the biological effects of overexploitation, together with rapid technological advances in biotelemetry, have provided the impetus for much research, on a global scale, into the movement of marine animals. I reviewed 101 marine and estuarine fish movement studies from southern Africa, published from 1928 to 2014, with the aim of synthesising research trends and findings. Trends showed an increasing emphasis on fish movement research in publications in the sub-tropical and warm-temperate biogeographic regions along the south and east coasts of southern Africa. Although 63% of publications featured only marine studies, research into fine-scale habitat use in estuaries has been on the increase, concomitant with increasing accessibility of biotelemetry. Overall, 26 fish families were identified in the surveyed literature with regionally endemic sparids featuring in 32% of the publications. Ten movement themes were identified in the surveyed literature, including broad-scale movement patterns, which featured in 68% of studies, followed by fine- scale habitat usage (33%) and protected areas (26%). The most prominent phenomenon, emerging from this research, is that of partial migration, which describes the occurrence of resident and migratory behaviour within a coexisting animal population. Substantial progress has also been made in unravelling the complexities of fine-scale movements in marine reserves and habitat usage in estuaries. While this knowledge has enabled more effective management of South Africa's multi-user, multi-species fisheries, focus should now be directed at improving our understanding of the commonalities in movement behaviour, the associated driving forces behind this behaviour and the extent of movement across reserve boundaries. Mark-recapture data, collected over the past 30 years by the Oceanographic Research Institute’s Cooperative Fish Tagging Project (ORICFTP), were used to investigate broad- scale movement patterns of 30 prominent coastal fishery species (Chapter 4). Fishes were tagged with plastic dart tags along the coastline of southern Africa from Angola to Mozambique. This exercise yielded more than 10000 recaptures. The 30 chosen species represented 14 families, although 12 species belonged to a single family (Sparidae). Overall, 67% of recaptures were reported from the original tagging locality and 73% were recorded within 5 km of the tagging locality. The remaining observations extended from 6-3000 km. Movements were assigned to four distance bins (0-5 km, 6-50km, 51-500km and >500 km) and modelled with an ordinal logistic regression. Species, life-stage (juvenile/adult) and time- at-liberty were included as predictor variables. Model coefficients were then included in a cluster analysis, which produced two primary groupings of species (Category I and II), with two sub-groupings (Category IIa and IIb). Category I species were characterised by wide-ranging movements, greatest median recapture length and highest trophic levels. Category II species were characterised by residency, lower median recapture length and lower trophic levels. These findings have implications for fisheries management. Exploitation of resident species may lead to localised depletion, but their diffuse spatial distribution may offer some resilience. In contrast, even localised targeting of migratory species may pose a population level risk if individuals are known to aggregate. Life-cycle diversity or intra-population variability describes the existence of alternative strategies or tactics among coexisting individuals within an animal population (Chapter 5). Partial migration is a specific case of life-cycle diversity where coexisting groups exhibit either resident or migratory (wide-ranging) behaviour within a single population. Mark- recapture data collected under the auspices of the ORICFTP were used to investigate the occurrence and nature of life-cycle diversity in the movement behaviour of five non- diadromous fish species around the coastline of southern Africa. Among the five species were three teleosts (Category I and IIa) and two elasmobranchs (Category I). A fish was considered to have remained resident if recaptured within 0-5 km after 365 days at liberty. A fish was considered to have undertaken a wide-ranging movement if recaptured more than 50 km away from the release site in 365 days or less. A total of 1848 individuals from the five study species were recaptured during the study, of which 73% of the observations were classified as being resident. Binomial logistic regression confirmed that species, life-stage (juvenile/adult) and ecoregion were significant (p < 0.001) predictors of the probability of wide-ranging behaviour. A Gaussian model confirmed that species and ecoregion were also significant (p < 0.001) predictors of direction and distance of wide-ranging movement. However, the direction and distance of wide-ranging movements in juveniles did not differ significantly (p > 0.05) to that of adults. The median growth rate was mostly greater in wide- ranging individuals; however, this was only statistically significant (p < 0.05) in two cases. These findings provide unequivocal evidence of life-cycle diversity in five fish species, with vastly different life-histories. This ecological phenomenon may provide species resilience at the population level and needs to be considered in fisheries management initiatives. The movement of fishes is a fundamental aspect to consider when designing fishery management regimes. Unfortunately, traditional management strategies have often disregarded movement behaviour to the detriment of fish populations (Chapter 6). As a case study, the management of Lichia amia (Category I: wide-ranging) was evaluated in the context of its movement behaviour. Long-term catch-per-unit-effort (CPUE) datasets were examined for three South African recreational fishery sectors. The CPUE was standardised using generalized linear models (delta-Gamma/hurdle approach) to reduce the effect of factors other than abundance. Factors that were available for this purpose were year, month and locality/zone. Year was included in every model as the primary objective was to detect trends in abundance over time. Although standardised CPUE for all sectors showed an overall long-term decline, there was considerable variability in trends between the different recreational sectors and between datasets. Contrasting trends between competitive shore angling and general shore angling datasets were ascribed to hyperstability in competitive CPUE data. Hyperstability in this case was mostly influenced by rapidly improving technology, techniques and communication networks amongst competitive anglers. Month and locality were significant factors explaining the probability of catching L. amia. This suggests that the predictable aggregatory behaviour of this species could further compound the observed CPUE hyperstability. Although the CPUE responded positively for six years after implementation of the first minimum size and bag limits, and for one year after the decommercialisation of the species, these regulations and their amendments failed to arrest a long-term decline in the CPUE despite the ample evidence for hyperstability. It is clear from this case study that the predictable nature of wide-ranging behaviour in L. amia has made the population vulnerable to exploitation. This has led to the demise in the population, which could have been worse if not for the occurrence of intra-population variability in its movement behaviour, which may provide some measure of resilience.
- Full Text:
- Date Issued: 2018
A study of a class of invariant optimal control problems on the Euclidean group SE(2)
- Authors: Adams, Ross Montague
- Date: 2011
- Subjects: Matrix groups Lie groups Extremal problems (Mathematics) Maximum principles (Mathematics) Hamilton-Jacobi equations Lyapunov stability
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5420 , http://hdl.handle.net/10962/d1006060
- Description: The aim of this thesis is to study a class of left-invariant optimal control problems on the matrix Lie group SE(2). We classify, under detached feedback equivalence, all controllable (left-invariant) control affine systems on SE(2). This result produces six types of control affine systems on SE(2). Hence, we study six associated left-invariant optimal control problems on SE(2). A left-invariant optimal control problem consists of minimizing a cost functional over the trajectory-control pairs of a left-invariant control system subject to appropriate boundary conditions. Each control problem is lifted from SE(2) to T*SE(2) ≅ SE(2) x se (2)*and then reduced to a problem on se (2)*. The maximum principle is used to obtain the optimal control and Hamiltonian corresponding to the normal extremals. Then we derive the (reduced) extremal equations on se (2)*. These equations are explicitly integrated by trigonometric and Jacobi elliptic functions. Finally, we fully classify, under Lyapunov stability, the equilibrium states of the normal extremal equations for each of the six types under consideration.
- Full Text:
- Date Issued: 2011
- Authors: Adams, Ross Montague
- Date: 2011
- Subjects: Matrix groups Lie groups Extremal problems (Mathematics) Maximum principles (Mathematics) Hamilton-Jacobi equations Lyapunov stability
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5420 , http://hdl.handle.net/10962/d1006060
- Description: The aim of this thesis is to study a class of left-invariant optimal control problems on the matrix Lie group SE(2). We classify, under detached feedback equivalence, all controllable (left-invariant) control affine systems on SE(2). This result produces six types of control affine systems on SE(2). Hence, we study six associated left-invariant optimal control problems on SE(2). A left-invariant optimal control problem consists of minimizing a cost functional over the trajectory-control pairs of a left-invariant control system subject to appropriate boundary conditions. Each control problem is lifted from SE(2) to T*SE(2) ≅ SE(2) x se (2)*and then reduced to a problem on se (2)*. The maximum principle is used to obtain the optimal control and Hamiltonian corresponding to the normal extremals. Then we derive the (reduced) extremal equations on se (2)*. These equations are explicitly integrated by trigonometric and Jacobi elliptic functions. Finally, we fully classify, under Lyapunov stability, the equilibrium states of the normal extremal equations for each of the six types under consideration.
- Full Text:
- Date Issued: 2011
Networking: enabling professional development and institutionalisation of environmental education courses in Southern Africa
- Authors: Lupele, Justin Kalaba
- Date: 2007
- Subjects: SADC Regional Environmental Education Programme Education -- Africa, Southern Environmental education -- Africa, Southern Environmental education -- Study and teaching -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1678 , http://hdl.handle.net/10962/d1003561
- Description: This study was aimed at understanding how networking can enable or constrain professional development and institutionalisation of environmental education courses in southern Africa in the context of the Course Development Network (CDN), a project of the Southern Africa Development Community Regional Environmental Education Programme (SADC REEP). The study involved 12 institutions (each institution was represented in the CDN by a staff member) in eight SADC member states. It was contextualized through a review of social, political, environmental and educational developments in southern Africa, with specific reference to regionalization processes, as the SADC REEF is constituted under this post-colonial political framework. Relational philosophy informed the research process and methodology. The philosophy underpinned three distinct, yet related theoretical perspectives namely: critical realism, which provided the ontological perspectives of the study; Actor Network Theory; and Community of Practice, which provided the epistemological perspectives. Data was generated during a 33-month period in southern Africa and 12 months in the United Kingdom (and on a one week visit to Italy). During a 12 month Split Site Commonwealth Scholarship award, tenable at Manchester Metropolitan University in the United Kingdom, I studied the Environment and School Initiative (ENSI) and the Sustainability Education for European Primary Schools (SEEPS), to examine whether the same mechanisms that made them successful would apply to the CDN in the context of southern Africa. While these two case studies provided useful insight into the relationship between networking, professional development and institutionalization of environmental education programmes, they were not the main focus of the research. Data analysis was mainly through inductive, abductive and retroductive modes of inference. Inductive data analysis was done by means of Nvivo – a computer software package used for qualitative data analysis. The software aided in revealing features and relationships in the data in more depth as it allowed flexibility in working with data. Abduction is the interpretation of a phenomenon by means of a conceptual framework. In this study, I used Actor Network Theory (ANT) (Latour & Woolgar, 1979; Callon, 1986) and Community of Practice (COP) (Lave, 1988; Lave & Wenger, 1991; Fullan, 2003) as analytical conceptual frameworks to probe networking and professional development respectively. Data on institutionalisation of environmental education courses was analysed by means of retroductive mode of inference, which is a thought operation that enables the understanding of social reality beyond what is empirically observable or experienced. This study reveals that there were a number of necessary (internal) and contingent (external) factors that enabled or constrained networking, professional development and institutionalisation of environmental education courses in the context of the CDN. The key factors included existing cultural capital, donor political economy, power relations, poverty related factors and social transformation trends. The study found that relational approaches and the use of three relational theoretical lenses provided a broader lens which enabled this study to identify different dynamics, greater ontological depth and understanding of the relational dynamics and relations at play in the CDN beyond the participants' experience and observable events. The study also contends that networking can provide a support structure for social transformation and change in environmental education.
- Full Text:
- Date Issued: 2007
- Authors: Lupele, Justin Kalaba
- Date: 2007
- Subjects: SADC Regional Environmental Education Programme Education -- Africa, Southern Environmental education -- Africa, Southern Environmental education -- Study and teaching -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1678 , http://hdl.handle.net/10962/d1003561
- Description: This study was aimed at understanding how networking can enable or constrain professional development and institutionalisation of environmental education courses in southern Africa in the context of the Course Development Network (CDN), a project of the Southern Africa Development Community Regional Environmental Education Programme (SADC REEP). The study involved 12 institutions (each institution was represented in the CDN by a staff member) in eight SADC member states. It was contextualized through a review of social, political, environmental and educational developments in southern Africa, with specific reference to regionalization processes, as the SADC REEF is constituted under this post-colonial political framework. Relational philosophy informed the research process and methodology. The philosophy underpinned three distinct, yet related theoretical perspectives namely: critical realism, which provided the ontological perspectives of the study; Actor Network Theory; and Community of Practice, which provided the epistemological perspectives. Data was generated during a 33-month period in southern Africa and 12 months in the United Kingdom (and on a one week visit to Italy). During a 12 month Split Site Commonwealth Scholarship award, tenable at Manchester Metropolitan University in the United Kingdom, I studied the Environment and School Initiative (ENSI) and the Sustainability Education for European Primary Schools (SEEPS), to examine whether the same mechanisms that made them successful would apply to the CDN in the context of southern Africa. While these two case studies provided useful insight into the relationship between networking, professional development and institutionalization of environmental education programmes, they were not the main focus of the research. Data analysis was mainly through inductive, abductive and retroductive modes of inference. Inductive data analysis was done by means of Nvivo – a computer software package used for qualitative data analysis. The software aided in revealing features and relationships in the data in more depth as it allowed flexibility in working with data. Abduction is the interpretation of a phenomenon by means of a conceptual framework. In this study, I used Actor Network Theory (ANT) (Latour & Woolgar, 1979; Callon, 1986) and Community of Practice (COP) (Lave, 1988; Lave & Wenger, 1991; Fullan, 2003) as analytical conceptual frameworks to probe networking and professional development respectively. Data on institutionalisation of environmental education courses was analysed by means of retroductive mode of inference, which is a thought operation that enables the understanding of social reality beyond what is empirically observable or experienced. This study reveals that there were a number of necessary (internal) and contingent (external) factors that enabled or constrained networking, professional development and institutionalisation of environmental education courses in the context of the CDN. The key factors included existing cultural capital, donor political economy, power relations, poverty related factors and social transformation trends. The study found that relational approaches and the use of three relational theoretical lenses provided a broader lens which enabled this study to identify different dynamics, greater ontological depth and understanding of the relational dynamics and relations at play in the CDN beyond the participants' experience and observable events. The study also contends that networking can provide a support structure for social transformation and change in environmental education.
- Full Text:
- Date Issued: 2007
3-Methyl-1-phenyl-4-[(phenyl)(2-phenylhydrazin-1-yl)methylidene]-1H-pyrazol-5(4H)-one
- Identifier: http://vital.seals.ac.za8080/10353/7489 , http://hdl.handle.net/10353/5328 , vital:29192
- Full Text:
- Identifier: http://vital.seals.ac.za8080/10353/7489 , http://hdl.handle.net/10353/5328 , vital:29192
- Full Text:
The development of the emerging technologies sustainability assessment (ETSA) and its application in the design of a bioprocess for the treatment of wine distillery effluent
- Authors: Khan, Nuraan
- Date: 2005
- Subjects: Technology assessment , Wine and wine making -- Waste disposal , Distilleries -- Waste disposal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3953 , http://hdl.handle.net/10962/d1004012 , Technology assessment , Wine and wine making -- Waste disposal , Distilleries -- Waste disposal
- Description: Emerging Technologies Sustainability Assessment (ETSA) is a new technology assessment tool that was developed in order to compare emerging processes or technologies to existing alternatives. It utilizes infoIDlation modules, with the minimum use of resources such as time and money, in order to deteIDline if the process under development is comparatively favourable and should be developed beyond the early conceptual phase. The preliminary ETSA is vital in order to identify the gaps in the existing information and the specific methodologies to be used for data capture and analysis. The use of experimental design tools, such as Design-Expert, can facilitate rapid and efficient collection of necessary data and fits in well with the rationale for the ETSA. Wine distillery effluent (vinasse) is the residue left after alcohol has been distilled from fennented grape juice. It is an acidic, darkly coloured effluent, with a high COD and polyphenol content. The most popular method of disposal of this effluent, land application, is no longer viable due to stricter legislation and pressure on the industry to better manage its wastes. Although the ability of whiterot fungi to degrade a number of pollutants is well-known, fungal treatment of wine distillery effluent is still in the conceptual phase. The perfoIDlance of the fungal remediation system was assessed experimentally in terms of COD removal and laccase production using Design-Expert. Although Pycnoporus sanguine us was found to be most efficient at COD removal (85%) from 30% vinasse, laccase production was low (0.021 U/I). The optimum design for economically viable fungal treatment used Trametespubescens. This fungus was able to remove over 50% of the COD from undiluted vinasse while producing almost 800U/l of the valuable laccase enzyme within three days. Since the effluent from the fungal system did not meet the legal limits for wastewater disposal, a two-stage aerobicanaerobic system is suggested to improve the quality of the effluent prior to disposal. The ETSA was used to assess the fungal technology in relation to the two current methods of vinasse treatment and disposal, namely land application and anaerobic digestion. Based on the ETSA, which considered environmental, social and economic impacts, the fungal system proved to be potentially competitive and further development of the technology is suggested.
- Full Text:
- Date Issued: 2005
- Authors: Khan, Nuraan
- Date: 2005
- Subjects: Technology assessment , Wine and wine making -- Waste disposal , Distilleries -- Waste disposal
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:3953 , http://hdl.handle.net/10962/d1004012 , Technology assessment , Wine and wine making -- Waste disposal , Distilleries -- Waste disposal
- Description: Emerging Technologies Sustainability Assessment (ETSA) is a new technology assessment tool that was developed in order to compare emerging processes or technologies to existing alternatives. It utilizes infoIDlation modules, with the minimum use of resources such as time and money, in order to deteIDline if the process under development is comparatively favourable and should be developed beyond the early conceptual phase. The preliminary ETSA is vital in order to identify the gaps in the existing information and the specific methodologies to be used for data capture and analysis. The use of experimental design tools, such as Design-Expert, can facilitate rapid and efficient collection of necessary data and fits in well with the rationale for the ETSA. Wine distillery effluent (vinasse) is the residue left after alcohol has been distilled from fennented grape juice. It is an acidic, darkly coloured effluent, with a high COD and polyphenol content. The most popular method of disposal of this effluent, land application, is no longer viable due to stricter legislation and pressure on the industry to better manage its wastes. Although the ability of whiterot fungi to degrade a number of pollutants is well-known, fungal treatment of wine distillery effluent is still in the conceptual phase. The perfoIDlance of the fungal remediation system was assessed experimentally in terms of COD removal and laccase production using Design-Expert. Although Pycnoporus sanguine us was found to be most efficient at COD removal (85%) from 30% vinasse, laccase production was low (0.021 U/I). The optimum design for economically viable fungal treatment used Trametespubescens. This fungus was able to remove over 50% of the COD from undiluted vinasse while producing almost 800U/l of the valuable laccase enzyme within three days. Since the effluent from the fungal system did not meet the legal limits for wastewater disposal, a two-stage aerobicanaerobic system is suggested to improve the quality of the effluent prior to disposal. The ETSA was used to assess the fungal technology in relation to the two current methods of vinasse treatment and disposal, namely land application and anaerobic digestion. Based on the ETSA, which considered environmental, social and economic impacts, the fungal system proved to be potentially competitive and further development of the technology is suggested.
- Full Text:
- Date Issued: 2005
Agreement and coordination in XiTsonga, SeSotho and IsiXhosa: an optimality theoretic perspective
- Authors: Mitchley, Hazel
- Date: 2016
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/3423 , vital:20491
- Description: This thesis provides a unified Optimality Theoretic analysis of subject-verb agreement with coordinated preverbal subjects in three Southern Bantu languages: Xitsonga (S53), Sesotho (S33), and isiXhosa (S41). This analysis is then used to formulate a typology of agreement resolution strategies and the contexts which trigger them. Although some accounts in the Bantu literature suggest that agreement with coordinate structures is avoided by speakers (e.g. Schadeberg 1992, Voeltz 1971) especially when conjuncts are from different noun classes, I show that there is ample evidence to the contrary, and that the subject marker used is dependent on several factors, including (i) the [-HUMAN] specification on the conjuncts, (ii) whether the conjuncts are singular or plural, (iii) whether or not the conjuncts both carry the same noun class feature, and (iv) the order of the conjuncts. This thesis shows that there are various agreement resolution strategies which can beused: 1) agreement with the [+HUMAN] feature on the conjuncts, 2) agreement with the[-HUMAN] feature on the conjuncts, 3) agreement with the noun class feature on both conjuncts, 4) agreement with the noun class feature on the conjunct closest to the verb, and 5) agreement with the noun class feature on the conjunct furthest from the verb. Not all of these strategies are used by all languages, nor are these strategies interchangeable in the languages which do use them – instead, multiple factors conspire to trigger the use of a specific agreement strategy within a specific agreement featural context. I show that these effects can be captured using Optimality Theory (Prince and Smolensky 2004). The analysis makes use of seven constraints: RES#, MAX[+H], MAX[-H], DEP[-H], MAXNC, DEPNC, and AGREECLOSEST. The hierarchical ranking of these constraints not only accounts for the confinement of particular strategies to specific agreement featural contexts within a language, but also accounts for the cross-linguistic differences in the use of these strategies. I end off by examining the typological implications which follow from the OT analysis provided in this thesis.
- Full Text:
- Date Issued: 2016
- Authors: Mitchley, Hazel
- Date: 2016
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/3423 , vital:20491
- Description: This thesis provides a unified Optimality Theoretic analysis of subject-verb agreement with coordinated preverbal subjects in three Southern Bantu languages: Xitsonga (S53), Sesotho (S33), and isiXhosa (S41). This analysis is then used to formulate a typology of agreement resolution strategies and the contexts which trigger them. Although some accounts in the Bantu literature suggest that agreement with coordinate structures is avoided by speakers (e.g. Schadeberg 1992, Voeltz 1971) especially when conjuncts are from different noun classes, I show that there is ample evidence to the contrary, and that the subject marker used is dependent on several factors, including (i) the [-HUMAN] specification on the conjuncts, (ii) whether the conjuncts are singular or plural, (iii) whether or not the conjuncts both carry the same noun class feature, and (iv) the order of the conjuncts. This thesis shows that there are various agreement resolution strategies which can beused: 1) agreement with the [+HUMAN] feature on the conjuncts, 2) agreement with the[-HUMAN] feature on the conjuncts, 3) agreement with the noun class feature on both conjuncts, 4) agreement with the noun class feature on the conjunct closest to the verb, and 5) agreement with the noun class feature on the conjunct furthest from the verb. Not all of these strategies are used by all languages, nor are these strategies interchangeable in the languages which do use them – instead, multiple factors conspire to trigger the use of a specific agreement strategy within a specific agreement featural context. I show that these effects can be captured using Optimality Theory (Prince and Smolensky 2004). The analysis makes use of seven constraints: RES#, MAX[+H], MAX[-H], DEP[-H], MAXNC, DEPNC, and AGREECLOSEST. The hierarchical ranking of these constraints not only accounts for the confinement of particular strategies to specific agreement featural contexts within a language, but also accounts for the cross-linguistic differences in the use of these strategies. I end off by examining the typological implications which follow from the OT analysis provided in this thesis.
- Full Text:
- Date Issued: 2016
Comparative fish ecology in three periodically connected rivers in the upper Zambezi and Okavango ecoregions
- Authors: Taylor, Geraldine Claire
- Date: 2017
- Subjects: Fishes Ecology Zambia Zambezi District , Floodplain ecology Zambia Zambezi District , Stable isotopes , Fishes Food Zambia Zambezi District , Fishes Mortality Zambia Zambezi District , Fish populations Zambia Zambezi District , Fishes Growth
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/65055 , vital:28660 , DOI https://doi.org/10.21504/10962/65055
- Description: The Upper Zambezi, Kavango and Kwando rivers are three periodically interlinked floodplain rivers which share the same Upper Zambezian floodplain ichthyofauna. The aim of this thesis was to compare the biology and ecology of the fish communities in these three rivers. The objective was to test the hypothesis that fish community composition and assemblage structure, fish diets, food web structure and trophic dynamics, fish growth rates and total mortality are influenced by the differing flood magnitudes of the three rivers, in support of the flood pulse concept. To understand the abiotic characteristics of each river, water temperature, flood regime, total dissolved inorganic nitrogen concentrations and water quality parameters were measured and compared between rivers. Water temperatures varied seasonally, and seven day moving averages peaked above 30 °C in January, and fell to between 16 and 19 °C in June. The Zambezi River had the largest flood (6.14 m), followed by the Kavango River (3.80 m), while the Kwando River had the smallest flood (0.65 m). Total dissolved inorganic nitrogen concentrations were low in the Kavango and Zambezi Rivers (0.2 - 0.6 mg/l), and slightly higher in the Kwando River (<1 mg/l). Conductivity, total dissolved solids and total dissolved inorganic nitrogen concentrations decreased with the flood (dilution effect). Using biomass catch per unit effort data from experimental gillnets, fish community composition and assemblage structure was described, and differed between rivers in all hydrological seasons. In the Zambezi and Kavango rivers, fish assemblages varied with hydrological season as a result of the homogenising influence of the flood pulse, while in the Kwando River fish assemblages did not differ seasonally as flood pulses were small and often irregular. Differences in community composition were attributed to the abundance of Hydrocynus vittatus, a large bodied open water predator, in the Zambezi and Kavango rivers, and its relative absence in the Kwando River. Based on the results of the community composition, six focus species were chosen that were abundant and representative of the various feeding modes and life history strategies of the fish community. These were the striped robber Brycinus lateralis, sharptooth catfish Clarias gariepinus, blunttooth catfish Clarias ngamensis, African pike Hepsetus cuvieri, silver catfish Schilbe intermedius and purpleface largemouth Serranochromis macrocephalus. Stomach contents analysis was then used to compare the feeding ecology of the six example species between rivers. Clarias gariepinus, C. ngamensis and S. intermedius were piscivorous in the Zambezi and Kavango rivers, and preyed upon more invertebrates in the Kwando River, while Hepsetus cuvieri and S. macrocephalus were piscivorous in all three rivers. Differences in diets were attributed to seasonal prey abundance, with prey fishes abundant during falling and low water when the Zambezi and Kavango rivers were sampled, while invertebrates were abundant during rising and high water when the Kwando River was sampled. Prey mastication by B. lateralis made prey identification difficult. For other predators, the usefulness of stomach contents analysis for dietary descriptions was restricted by the high proportion of empty stomachs. As a result, whole ecosystem stable isotope analysis was used to gain a holistic understanding of the food web structure and fish feeding ecology of the three rivers. The Zambezi and Kavango river food webs were supported by C enriched resources such as C4 and C3 riparian vegetation from the floodplain, while the Kwando River food web was based on C depleted resources such as filamentous algae and aquatic macrophytes. The Zambezi River food web had a restricted nitrogen range, with reduced food chain length and the predators in this river did not occupy such elevated trophic positions compared to in the Kavango and Kwando river food webs. This was attributed to the overfishing of the primary and tertiary consumers in the Zambezi River, a phenomenon known to reduce food chain length. Focussing on predator communities, in the Zambezi and Kavango rivers, H. vittatus isotopic niche width was large and overlapped significantly with most other predators, while in the Kwando River predator niches were more distinct. This supported previously proposed hypotheses by describing H. vittatus as a dominant predator which excludes all other fishes by predation or competition. Despite the dominance of H. vittatus, C. gariepinus occupied the position of top predator in all three rivers, and information on the habitat use, feeding habits and trophic niches of the serranochromine cichlids added understanding of their ecology. Lastly, age was determined using sectioned sagittal otoliths for C. gariepinus, C. ngamensis, S. intermedius and S. macrocephalus and using whole asteriscus otoliths for B. lateralis and H. cuvieri, and growth was modelled using the von Bertalanffy growth equation. Growth performance was high in the Zambezi and Kavango rivers, and lower in the Kwando River, most likely in response to the varying flood magnitudes. Total mortality rates, estimated using Hoenig’s maximum-age based equation, were high in the Zambezi River as a result of the high fishing pressure on this river. Overall floodplain fish ecology in the Zambezi, Kavango and Kwando rivers was influenced by the flood pulse, as was predicted by the flood pulse concept. Periodic and equilibrium life history strategists were found to adapt either to the pulsing environments of the Zambezi and Kavango rivers, or to the more stable environment of the Kwando River, and large bodied, long lived periodic strategists such as C. gariepinus tended to be highly plastic and able to thrive in most conditions. Data also suggested that Zambezi River food web structure and fish mortality rates have been impacted by overfishing, for which more information is needed to conserve and manage this system. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2018
- Full Text:
- Date Issued: 2017
- Authors: Taylor, Geraldine Claire
- Date: 2017
- Subjects: Fishes Ecology Zambia Zambezi District , Floodplain ecology Zambia Zambezi District , Stable isotopes , Fishes Food Zambia Zambezi District , Fishes Mortality Zambia Zambezi District , Fish populations Zambia Zambezi District , Fishes Growth
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/65055 , vital:28660 , DOI https://doi.org/10.21504/10962/65055
- Description: The Upper Zambezi, Kavango and Kwando rivers are three periodically interlinked floodplain rivers which share the same Upper Zambezian floodplain ichthyofauna. The aim of this thesis was to compare the biology and ecology of the fish communities in these three rivers. The objective was to test the hypothesis that fish community composition and assemblage structure, fish diets, food web structure and trophic dynamics, fish growth rates and total mortality are influenced by the differing flood magnitudes of the three rivers, in support of the flood pulse concept. To understand the abiotic characteristics of each river, water temperature, flood regime, total dissolved inorganic nitrogen concentrations and water quality parameters were measured and compared between rivers. Water temperatures varied seasonally, and seven day moving averages peaked above 30 °C in January, and fell to between 16 and 19 °C in June. The Zambezi River had the largest flood (6.14 m), followed by the Kavango River (3.80 m), while the Kwando River had the smallest flood (0.65 m). Total dissolved inorganic nitrogen concentrations were low in the Kavango and Zambezi Rivers (0.2 - 0.6 mg/l), and slightly higher in the Kwando River (<1 mg/l). Conductivity, total dissolved solids and total dissolved inorganic nitrogen concentrations decreased with the flood (dilution effect). Using biomass catch per unit effort data from experimental gillnets, fish community composition and assemblage structure was described, and differed between rivers in all hydrological seasons. In the Zambezi and Kavango rivers, fish assemblages varied with hydrological season as a result of the homogenising influence of the flood pulse, while in the Kwando River fish assemblages did not differ seasonally as flood pulses were small and often irregular. Differences in community composition were attributed to the abundance of Hydrocynus vittatus, a large bodied open water predator, in the Zambezi and Kavango rivers, and its relative absence in the Kwando River. Based on the results of the community composition, six focus species were chosen that were abundant and representative of the various feeding modes and life history strategies of the fish community. These were the striped robber Brycinus lateralis, sharptooth catfish Clarias gariepinus, blunttooth catfish Clarias ngamensis, African pike Hepsetus cuvieri, silver catfish Schilbe intermedius and purpleface largemouth Serranochromis macrocephalus. Stomach contents analysis was then used to compare the feeding ecology of the six example species between rivers. Clarias gariepinus, C. ngamensis and S. intermedius were piscivorous in the Zambezi and Kavango rivers, and preyed upon more invertebrates in the Kwando River, while Hepsetus cuvieri and S. macrocephalus were piscivorous in all three rivers. Differences in diets were attributed to seasonal prey abundance, with prey fishes abundant during falling and low water when the Zambezi and Kavango rivers were sampled, while invertebrates were abundant during rising and high water when the Kwando River was sampled. Prey mastication by B. lateralis made prey identification difficult. For other predators, the usefulness of stomach contents analysis for dietary descriptions was restricted by the high proportion of empty stomachs. As a result, whole ecosystem stable isotope analysis was used to gain a holistic understanding of the food web structure and fish feeding ecology of the three rivers. The Zambezi and Kavango river food webs were supported by C enriched resources such as C4 and C3 riparian vegetation from the floodplain, while the Kwando River food web was based on C depleted resources such as filamentous algae and aquatic macrophytes. The Zambezi River food web had a restricted nitrogen range, with reduced food chain length and the predators in this river did not occupy such elevated trophic positions compared to in the Kavango and Kwando river food webs. This was attributed to the overfishing of the primary and tertiary consumers in the Zambezi River, a phenomenon known to reduce food chain length. Focussing on predator communities, in the Zambezi and Kavango rivers, H. vittatus isotopic niche width was large and overlapped significantly with most other predators, while in the Kwando River predator niches were more distinct. This supported previously proposed hypotheses by describing H. vittatus as a dominant predator which excludes all other fishes by predation or competition. Despite the dominance of H. vittatus, C. gariepinus occupied the position of top predator in all three rivers, and information on the habitat use, feeding habits and trophic niches of the serranochromine cichlids added understanding of their ecology. Lastly, age was determined using sectioned sagittal otoliths for C. gariepinus, C. ngamensis, S. intermedius and S. macrocephalus and using whole asteriscus otoliths for B. lateralis and H. cuvieri, and growth was modelled using the von Bertalanffy growth equation. Growth performance was high in the Zambezi and Kavango rivers, and lower in the Kwando River, most likely in response to the varying flood magnitudes. Total mortality rates, estimated using Hoenig’s maximum-age based equation, were high in the Zambezi River as a result of the high fishing pressure on this river. Overall floodplain fish ecology in the Zambezi, Kavango and Kwando rivers was influenced by the flood pulse, as was predicted by the flood pulse concept. Periodic and equilibrium life history strategists were found to adapt either to the pulsing environments of the Zambezi and Kavango rivers, or to the more stable environment of the Kwando River, and large bodied, long lived periodic strategists such as C. gariepinus tended to be highly plastic and able to thrive in most conditions. Data also suggested that Zambezi River food web structure and fish mortality rates have been impacted by overfishing, for which more information is needed to conserve and manage this system. , Thesis (PhD) -- Faculty of Science, Ichthyology and Fisheries Science, 2018
- Full Text:
- Date Issued: 2017
Synthesis and characterisation of lanthanide complexes with nitrogen- and oxygen-donor ligands
- Authors: Madanhire, Tatenda
- Date: 2016
- Subjects: Rare earth metals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13127 , vital:27154
- Description: The reactions of Ln(NO3)3∙6H2O (Ln = Pr, Nd or Er) with the potentially tridentate O,N,O chelating ligand 2,6-pyridinedimethanol (H2pydm) were investigated, and complexes with the formula, [Ln(H2pydm)2(NO3)2](NO3) (Ln = Pr or Nd) and [Er(H2pydm)3](NO3)3 were isolated. The ten-coordinate Pr(III) and Nd(III) compounds crystallise in the triclinic space group P-1 while the nine-coordinate Er(III) complex crystallises in the monoclinic system (P21/n). The reaction of PrCl3∙6H2O with H2pydm yielded the compound, [Pr(H2pydm)3](Cl)3, that crystallises in the monoclinic system, space group P21/c with α = 90, β = 98.680(1) and γ = 90°. The nine-coordinate Pr(III) ion is bound to three H2pydm ligands, with bond distances Pr-O 2.455(2)-2.478(2) Å and Pr-N 2.6355(19)-2.64(2) Å. X-ray crystal structures of all the H2pydm complexes reveal that the ligand coordinates tridentately, via the pyridyl nitrogen atom and the two hydroxyl oxygen atoms. The electronic absorption spectra of complexes show 4f-4f transitions. Rare-earth complexes, [Ln(H2L1)2(NO3)3] [Ln = Gd, Ho or Nd], were also prepared from a Schiff base. The X-ray single-crystal diffraction studies and SHAPE analyses of the Gd(III) and Ho(III) complexes shows that the complexes are ten-coordinate and exhibit distorted tetradecahedron geometries. With proton migration occurring from the phenol group to the imine function, complexation of the lanthanides to the ligand gives the ligand a zwitterionic phenoxo-iminium form. A phenolate oxygen-bridged dinuclear complex, [Ce2(H2L1)(ovan)3(NO3)3], has been obtained by reacting Ce(NO3)3∙6H2O with an o-vanillin derived Schiff base ligand, 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H2L1). Hydrolysis of the Schiff base occurred to yield o-vanillin, which bridged two cerium atoms with the Ce∙∙∙Ce distance equal to 3.823 Å. The Ce(III) ions are both tencoordinate, but have different coordination environments, showing tetradecahedron and staggered dodecahedron geometries, respectively. The reaction of salicylaldehyde-N(4)-diethylthiosemicarbazone (H2L2) in the presence of hydrated Ln(III) nitrates led to the isolation of two novel compounds: (E)-2[(ortho-hydroxy)benzylidene]-2-(thiomethyl)-thionohydrazide (1) and bis[2,3-diaza4-(2-hydroxyphenyl)-1-thiomethyl-buta-1,3-diene]disulfide. The latter is a dimer of the former. For this asymmetric Schiff base, 1 and the symmetric disulfide, classical hydrogen bonds of the O–H∙∙∙N as well as N–H∙∙∙S (for 1) type are apparent next to C–H∙∙∙O contacts. 4-(4-Bromophenyl)-1-(propan-2-ylidene)thiosemicarbazide was also prepared upon reacting 4-(4-bromophenyl)-3-thiosemicarbazide with acetone in the presence of ethanol and La(NO3)3∙6H2O. The C=S bond length was found to be 1.6686(16) Å which is in good agreement with other thioketones whose metrical parameters have been deposited with the Cambridge Structural Database. Classical hydrogen bonds of the N–H∙∙∙N and the N–H∙∙∙Br type are observed next to C–H∙∙∙S contacts. All synthesised compounds were characterised by microanalyses, single-crystal X-ray diffraction (except for [Nd(H2L1)2(NO3)3]), 1H NMR and IR spectroscopy.
- Full Text:
- Date Issued: 2016
- Authors: Madanhire, Tatenda
- Date: 2016
- Subjects: Rare earth metals
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/13127 , vital:27154
- Description: The reactions of Ln(NO3)3∙6H2O (Ln = Pr, Nd or Er) with the potentially tridentate O,N,O chelating ligand 2,6-pyridinedimethanol (H2pydm) were investigated, and complexes with the formula, [Ln(H2pydm)2(NO3)2](NO3) (Ln = Pr or Nd) and [Er(H2pydm)3](NO3)3 were isolated. The ten-coordinate Pr(III) and Nd(III) compounds crystallise in the triclinic space group P-1 while the nine-coordinate Er(III) complex crystallises in the monoclinic system (P21/n). The reaction of PrCl3∙6H2O with H2pydm yielded the compound, [Pr(H2pydm)3](Cl)3, that crystallises in the monoclinic system, space group P21/c with α = 90, β = 98.680(1) and γ = 90°. The nine-coordinate Pr(III) ion is bound to three H2pydm ligands, with bond distances Pr-O 2.455(2)-2.478(2) Å and Pr-N 2.6355(19)-2.64(2) Å. X-ray crystal structures of all the H2pydm complexes reveal that the ligand coordinates tridentately, via the pyridyl nitrogen atom and the two hydroxyl oxygen atoms. The electronic absorption spectra of complexes show 4f-4f transitions. Rare-earth complexes, [Ln(H2L1)2(NO3)3] [Ln = Gd, Ho or Nd], were also prepared from a Schiff base. The X-ray single-crystal diffraction studies and SHAPE analyses of the Gd(III) and Ho(III) complexes shows that the complexes are ten-coordinate and exhibit distorted tetradecahedron geometries. With proton migration occurring from the phenol group to the imine function, complexation of the lanthanides to the ligand gives the ligand a zwitterionic phenoxo-iminium form. A phenolate oxygen-bridged dinuclear complex, [Ce2(H2L1)(ovan)3(NO3)3], has been obtained by reacting Ce(NO3)3∙6H2O with an o-vanillin derived Schiff base ligand, 2-((E)-(1-hydroxy-2-methylpropan-2-ylimino)methyl)-6-methoxyphenol (H2L1). Hydrolysis of the Schiff base occurred to yield o-vanillin, which bridged two cerium atoms with the Ce∙∙∙Ce distance equal to 3.823 Å. The Ce(III) ions are both tencoordinate, but have different coordination environments, showing tetradecahedron and staggered dodecahedron geometries, respectively. The reaction of salicylaldehyde-N(4)-diethylthiosemicarbazone (H2L2) in the presence of hydrated Ln(III) nitrates led to the isolation of two novel compounds: (E)-2[(ortho-hydroxy)benzylidene]-2-(thiomethyl)-thionohydrazide (1) and bis[2,3-diaza4-(2-hydroxyphenyl)-1-thiomethyl-buta-1,3-diene]disulfide. The latter is a dimer of the former. For this asymmetric Schiff base, 1 and the symmetric disulfide, classical hydrogen bonds of the O–H∙∙∙N as well as N–H∙∙∙S (for 1) type are apparent next to C–H∙∙∙O contacts. 4-(4-Bromophenyl)-1-(propan-2-ylidene)thiosemicarbazide was also prepared upon reacting 4-(4-bromophenyl)-3-thiosemicarbazide with acetone in the presence of ethanol and La(NO3)3∙6H2O. The C=S bond length was found to be 1.6686(16) Å which is in good agreement with other thioketones whose metrical parameters have been deposited with the Cambridge Structural Database. Classical hydrogen bonds of the N–H∙∙∙N and the N–H∙∙∙Br type are observed next to C–H∙∙∙S contacts. All synthesised compounds were characterised by microanalyses, single-crystal X-ray diffraction (except for [Nd(H2L1)2(NO3)3]), 1H NMR and IR spectroscopy.
- Full Text:
- Date Issued: 2016
Reactivity of Rhenium (iii) and Rhenium (V) with multidentate NN-and no-donor ligands
- Yumata, Nonzaliseko Christine
- Authors: Yumata, Nonzaliseko Christine
- Date: 2010
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10373 , http://hdl.handle.net/10948/1085 , Rhenium , Ligands
- Description: The reaction of the potentially tridentate Schiff-base chelate Hhaep [Haep = N’-(1- (2-hydroxyphenyl)ethylidene)benzohydrazide] with [ReCl3(benzil)(PPh3)] and trans-[ReOCl3(PPh3)2] produced the neutral oxorhenium(V) complexes cis- [ReOCl2(mep)] [Hmep = 2-(1-iminoethyl)phenol] and cis-[ReOCI2(meb)(PPh3)] [Hmeb = N’-(propan-2-ylidene)benzohydrazide] in ethanol and acetone respectively. In both reactions the Hhaep molecule cleaves to give different coordinated bidentate NO-donor chelates coordinated to the rhenium(V) centers. The X-ray studies reveal that mep is present as a bidentate, monoanionic Schiffbase coordinating through the neutral imino nitrogen and the deprotonated phenolate oxygen in cis-[ReOCl2(mep)]. The bond distances and angles in cis- [ReOCI2(meb)(PPh3)] confirm that meb coordinates to the metal in the enolate form. The distorted octahedral complex fac-[ReCl3(dpa)(PPh3)] was prepared by the reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of dpa in acetonitrile under a nitrogen atmosphere. The compound dpa.HCl.2H2O was obtained as a by-product in the reaction of dpa with trans-[ReCI3(MeCN)(PPh3)2] in acetonitrile. The reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of 6- amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one (Hamp) in acetonitrile led to the isolation of cis-[ReCl2(bat)(PPh3)2]. On complexation to the metal center Hamp decomposed to give the coordinated benzoylacetone (bat). Bat is present as a monoanionic bidentate chelate. The complexes [ReVOCI(had)] and [ReIVCl(had)(PPh3)](ReO4) were prepared from the reaction of trans-[ReCl3(MeCN)(PPh3)2] with N,N-bis((2-hydroxybenzyl)-2- aminoethyl)dimethylamine (H2had) in ethanol under various reaction conditions. The treatment of [ReCl3(benzil)(PPh3)] with 2-[((2- pyridinylmethyl)amino)methyl]phenol (Hham) in a 2:1 molar ratio in acetonitrile led to the isolation of the hydrogen-bonded dimer [ReOCl2(ham)]2. The distorted octahedral complex [ReOCl(hap)] [H2hap = N,N-bis(2- hydroxybenzyl)aminomethylpyridine] was prepared from the reaction of trans- [ReCl3(MeCN)(PPh3)2] with a twofold molar excess of H2hap in acetonitrile. The X-ray crystal structure analysis shows that the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.
- Full Text:
- Date Issued: 2010
- Authors: Yumata, Nonzaliseko Christine
- Date: 2010
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10373 , http://hdl.handle.net/10948/1085 , Rhenium , Ligands
- Description: The reaction of the potentially tridentate Schiff-base chelate Hhaep [Haep = N’-(1- (2-hydroxyphenyl)ethylidene)benzohydrazide] with [ReCl3(benzil)(PPh3)] and trans-[ReOCl3(PPh3)2] produced the neutral oxorhenium(V) complexes cis- [ReOCl2(mep)] [Hmep = 2-(1-iminoethyl)phenol] and cis-[ReOCI2(meb)(PPh3)] [Hmeb = N’-(propan-2-ylidene)benzohydrazide] in ethanol and acetone respectively. In both reactions the Hhaep molecule cleaves to give different coordinated bidentate NO-donor chelates coordinated to the rhenium(V) centers. The X-ray studies reveal that mep is present as a bidentate, monoanionic Schiffbase coordinating through the neutral imino nitrogen and the deprotonated phenolate oxygen in cis-[ReOCl2(mep)]. The bond distances and angles in cis- [ReOCI2(meb)(PPh3)] confirm that meb coordinates to the metal in the enolate form. The distorted octahedral complex fac-[ReCl3(dpa)(PPh3)] was prepared by the reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of dpa in acetonitrile under a nitrogen atmosphere. The compound dpa.HCl.2H2O was obtained as a by-product in the reaction of dpa with trans-[ReCI3(MeCN)(PPh3)2] in acetonitrile. The reaction of trans-[ReCl3(MeCN)(PPh3)2] with a twofold molar excess of 6- amino-3-methyl-1-phenyl-4-azahept-2-ene-1-one (Hamp) in acetonitrile led to the isolation of cis-[ReCl2(bat)(PPh3)2]. On complexation to the metal center Hamp decomposed to give the coordinated benzoylacetone (bat). Bat is present as a monoanionic bidentate chelate. The complexes [ReVOCI(had)] and [ReIVCl(had)(PPh3)](ReO4) were prepared from the reaction of trans-[ReCl3(MeCN)(PPh3)2] with N,N-bis((2-hydroxybenzyl)-2- aminoethyl)dimethylamine (H2had) in ethanol under various reaction conditions. The treatment of [ReCl3(benzil)(PPh3)] with 2-[((2- pyridinylmethyl)amino)methyl]phenol (Hham) in a 2:1 molar ratio in acetonitrile led to the isolation of the hydrogen-bonded dimer [ReOCl2(ham)]2. The distorted octahedral complex [ReOCl(hap)] [H2hap = N,N-bis(2- hydroxybenzyl)aminomethylpyridine] was prepared from the reaction of trans- [ReCl3(MeCN)(PPh3)2] with a twofold molar excess of H2hap in acetonitrile. The X-ray crystal structure analysis shows that the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen.
- Full Text:
- Date Issued: 2010
Rhenium complexes with multidentate benzazoles and related N,X-donor (X = N, O, S) ligands
- Authors: Potgieter, Kim Carey
- Date: 2012
- Subjects: Rhenium , Benzimidazoles , Ligands (Biochemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10438 , http://hdl.handle.net/10948/d1020773
- Description: The coordination behaviour of 4-aminoantipyrine (H2pap) and its Schiff base derivatives with the oxorhenium(V) and tricarbonyl rhenium(I) cores are reported. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with H2pap were studied, and the complexes cis-[ReX2(pap)(H2pap)(PPh3)](ReO4) were isolated. The ligand pap is coordinated monodentately through the doubly deprotonated amino nitrogen as an imide, and H2pap acts as a neutral bidentate chelate, with coordination through the neutral amino nitrogen and the ketonic oxygen. The reactions of trans-[ReOBr3(PPh3)2] and cis-[ReO2I(PPh3)2] with -(2-aminobenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (H2nap) and 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (Hoap) are also reported. The complexes cis-[Re(nap)Br2(PPh3)]Br, [ReO(OEt)(Hnap)(PPh3)]I and [ReO(OMe)(oap)(PPh3)]I were isolated and structurally characterized. The reactions of the Schiff base derivatives 1,2-(diimino-4’-antipyrinyl)ethane (dae) and 2,6-bis(4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one)pyridine (bap) with [Re(CO)5X] (X = Br or Cl) produced fac-[Re(CO)3(dae)Cl] and fac-[Re(CO)3(bap)Br] respectively. A series of rhenium(I) tricarbonyl complexes containing bidentate derivatives of aniline was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3(κ1-Hpda)(κ2-Hpda)]Br was isolated, but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. The neutral complex [Re(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH3 group. In the complex [Re(CO)3(Htpn)Br] (Htpn = N-(2-(methylthio)benzylidene)benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthiol sulfur and imino nitrogen atoms only, with a free amino group. These rhenium(I) complexes, with the exception of [Re2(CO)7(spo)2], revealed broad emissions centred around 535 nm. The reactions of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) compounds [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 (ibsq = 2-iminothiobenzosemiquinonate, sbsq = 1,2-dithiobenzosemiquinonate, obsq = 2-hydroxothiobenzosemiquinonate) respectively. The complexes adopt a trigonal prismatic geometry around the rhenium centre with average twists angles between 3.20-26.10˚. The E1/2 values for the Re(III)/Re(IV) redox couple were found to be 0.022, 0.142 and 0.126 V for [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 respectively. The reactions of the benzoxazole ligands, 3-(benzoxazol-2-yl)pyridin-2-ol (Hbop) and 5-amino-2-(benzoxazol-2-yl)phenol (Habo) with a [ReO]3+ precursor led to the rhenium(III) complex, [ReCl2(bop)(PPh3)2], and the complex salt, [ReO(abo)I(PPh3)2]ReO4, respectively. A variety of benzothiazole and benzimidazole derivatives were reacted with [Re(CO)5Br]. In the case of bis(benzothiazol-2-ylethyl)sulfide (bts), the neutral complex fac-[Re(CO)3(bts)Br] was obtained. The dimeric complexes (μ-dbt)2[Re(CO)3]2 and (μ-mbt)2[Re(CO)3]2 were formed when 1,3-bis(benzothiazol-2-yl)thiourea (Hdbt) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) were used as ligands. The reaction of 2,2’-(oxybis(methylene))bis(benzimidazole) (bmb) with [Re(CO)5Cl] resulted in the rhenium(I) complex salt fac-[Re(CO)3(bmb)]+, with the tri-μ-chlorohexacarbonyl dirhenate [Re2(CO)6Cl3]- as the counter anion. The neutral complex fac-[Re(CO)3(btp)Cl] was isolated from the reaction of the 2,9-bis(benzothiazol-2-yl)-1,10-phenanthroline (btp) ligand and [Re(CO)5Cl]. The reactions of trans-[ReOCl3(PPh3)2] with bis(benzimidazol-2-ylethyl)sulfide (btn) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) led to the formation of the cationic compounds (μ-O)2[Re2O2(btn)2]I2 and [ReCl2(bte)(PPh3)2]Cl (bte = (benzothiazole-2-yl)-N-ethylidenemethanamine) respectively.
- Full Text:
- Date Issued: 2012
- Authors: Potgieter, Kim Carey
- Date: 2012
- Subjects: Rhenium , Benzimidazoles , Ligands (Biochemistry)
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10438 , http://hdl.handle.net/10948/d1020773
- Description: The coordination behaviour of 4-aminoantipyrine (H2pap) and its Schiff base derivatives with the oxorhenium(V) and tricarbonyl rhenium(I) cores are reported. The reactions of trans-[ReOX3(PPh3)2] (X = Cl, Br) with H2pap were studied, and the complexes cis-[ReX2(pap)(H2pap)(PPh3)](ReO4) were isolated. The ligand pap is coordinated monodentately through the doubly deprotonated amino nitrogen as an imide, and H2pap acts as a neutral bidentate chelate, with coordination through the neutral amino nitrogen and the ketonic oxygen. The reactions of trans-[ReOBr3(PPh3)2] and cis-[ReO2I(PPh3)2] with -(2-aminobenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (H2nap) and 4-(2-hydroxybenzylideneamino)-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one (Hoap) are also reported. The complexes cis-[Re(nap)Br2(PPh3)]Br, [ReO(OEt)(Hnap)(PPh3)]I and [ReO(OMe)(oap)(PPh3)]I were isolated and structurally characterized. The reactions of the Schiff base derivatives 1,2-(diimino-4’-antipyrinyl)ethane (dae) and 2,6-bis(4-amino-1,2-dihydro-2,3-dimethyl-1-phenylpyrazol-5-one)pyridine (bap) with [Re(CO)5X] (X = Br or Cl) produced fac-[Re(CO)3(dae)Cl] and fac-[Re(CO)3(bap)Br] respectively. A series of rhenium(I) tricarbonyl complexes containing bidentate derivatives of aniline was synthesized and structurally characterized. With 1,2-diaminobenzene (Hpda) the ‘2+1’ complex salt fac-[Re(CO)3(κ1-Hpda)(κ2-Hpda)]Br was isolated, but with 2-mercaptophenol (Hspo) the bridged dimer [Re2(CO)7(spo)2] was found. The neutral complex [Re(CO)3(ons)(Hno)] was isolated from the reaction of [Re(CO)5Br] with 2-[(2-methylthio)benzylideneimino]phenol (Hons; Hno = 2-aminophenol), with ons coordinated as a bidentate chelate with a free SCH3 group. In the complex [Re(CO)3(Htpn)Br] (Htpn = N-(2-(methylthio)benzylidene)benzene-1,2-diamine) the potentially tridentate ligand Htpn is coordinated via the methylthiol sulfur and imino nitrogen atoms only, with a free amino group. These rhenium(I) complexes, with the exception of [Re2(CO)7(spo)2], revealed broad emissions centred around 535 nm. The reactions of the rhenium(V) complex cis-[ReO2I(PPh3)2] with 2-aminothiophenol (H2atp), benzene-1,2-dithiol (H2tdt) and 2-hydroxybenzenethiol (H2otp) led to the formation of the rhenium(III) compounds [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 (ibsq = 2-iminothiobenzosemiquinonate, sbsq = 1,2-dithiobenzosemiquinonate, obsq = 2-hydroxothiobenzosemiquinonate) respectively. The complexes adopt a trigonal prismatic geometry around the rhenium centre with average twists angles between 3.20-26.10˚. The E1/2 values for the Re(III)/Re(IV) redox couple were found to be 0.022, 0.142 and 0.126 V for [Re(Hatp)(ibsq)2].OPPh3, [Re(sbsq)3].OPPh3 and [Re(obsq)3].OPPh3 respectively. The reactions of the benzoxazole ligands, 3-(benzoxazol-2-yl)pyridin-2-ol (Hbop) and 5-amino-2-(benzoxazol-2-yl)phenol (Habo) with a [ReO]3+ precursor led to the rhenium(III) complex, [ReCl2(bop)(PPh3)2], and the complex salt, [ReO(abo)I(PPh3)2]ReO4, respectively. A variety of benzothiazole and benzimidazole derivatives were reacted with [Re(CO)5Br]. In the case of bis(benzothiazol-2-ylethyl)sulfide (bts), the neutral complex fac-[Re(CO)3(bts)Br] was obtained. The dimeric complexes (μ-dbt)2[Re(CO)3]2 and (μ-mbt)2[Re(CO)3]2 were formed when 1,3-bis(benzothiazol-2-yl)thiourea (Hdbt) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) were used as ligands. The reaction of 2,2’-(oxybis(methylene))bis(benzimidazole) (bmb) with [Re(CO)5Cl] resulted in the rhenium(I) complex salt fac-[Re(CO)3(bmb)]+, with the tri-μ-chlorohexacarbonyl dirhenate [Re2(CO)6Cl3]- as the counter anion. The neutral complex fac-[Re(CO)3(btp)Cl] was isolated from the reaction of the 2,9-bis(benzothiazol-2-yl)-1,10-phenanthroline (btp) ligand and [Re(CO)5Cl]. The reactions of trans-[ReOCl3(PPh3)2] with bis(benzimidazol-2-ylethyl)sulfide (btn) and 1-(benzothiazol-2-ylidene)-3-methylthiourea (Hmbt) led to the formation of the cationic compounds (μ-O)2[Re2O2(btn)2]I2 and [ReCl2(bte)(PPh3)2]Cl (bte = (benzothiazole-2-yl)-N-ethylidenemethanamine) respectively.
- Full Text:
- Date Issued: 2012
Utilising value stream mapping to improve operations at Transwerk Uitenhage
- Authors: Silo, Andile Elliot
- Date: 2006
- Subjects: Production engineering , Production planning
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:8760 , http://hdl.handle.net/10948/604 , http://hdl.handle.net/10948/d1011684 , Production engineering , Production planning
- Description: Transwerk is a business uint of Transnet. It was established in 1940. Since 1940 unti 1994, Transwerk operated as the engineering section of Spoornet and was known as South African Railways. Transwerk emancipated in 1994 and had plants in all nine provinces of South Africa. In the past, trains were hauled by steam locomatives, which were manually operated. With the improvement of technology, steam locomotives were replaced by diesel locomotives. The recent technology improvement brought about electric locomotives which are more reliable than diesel locomotives.Trnaswerk has a plant in the Eastern Cape Province which is situated in Uitenhage. This plant focuses on refurbishing wagins for Spoornet. This research is about improving the refurbishing processes of Transwerk Uitenhage.
- Full Text:
- Date Issued: 2006
- Authors: Silo, Andile Elliot
- Date: 2006
- Subjects: Production engineering , Production planning
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: vital:8760 , http://hdl.handle.net/10948/604 , http://hdl.handle.net/10948/d1011684 , Production engineering , Production planning
- Description: Transwerk is a business uint of Transnet. It was established in 1940. Since 1940 unti 1994, Transwerk operated as the engineering section of Spoornet and was known as South African Railways. Transwerk emancipated in 1994 and had plants in all nine provinces of South Africa. In the past, trains were hauled by steam locomatives, which were manually operated. With the improvement of technology, steam locomotives were replaced by diesel locomotives. The recent technology improvement brought about electric locomotives which are more reliable than diesel locomotives.Trnaswerk has a plant in the Eastern Cape Province which is situated in Uitenhage. This plant focuses on refurbishing wagins for Spoornet. This research is about improving the refurbishing processes of Transwerk Uitenhage.
- Full Text:
- Date Issued: 2006
The synthesis, empirical and theoretical studies of various (N→B) diarylborinate esters
- Authors: Manana, Pholani Sakhile
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/53869 , vital:46027
- Description: A series of core-functionalized borinic acids was synthesized from Grignard reagents and tributylborate and reacted with ethanolamine, amino acids, 2-pyridylmethanol as well as 2-(ethyl amino ethanol). Among the borinic acids synthesized were the ones bearing: para-(2, 15, 16, 22, 27)-methyl, (3, 20, 25)-chloro, (4, 23, 26)-fluoro, (5)-methoxy; meta-(7, 17)-methyl, (9)-fluoro; ortho-(6)-methyl, (8)-chloro, (10, 18, 19)-methoxy substituents on their respective aromatic systems. All compounds obtained by condensation of the borinic acids with the aforementioned nitrogen-containing substrates were characterized structurally by means of diffraction studies based on single crystals and found to constitute chelate esters/amides featuring covalent B-O and dative N→B bonds. The chelate compounds researched in this study could be classified into four families and represent the compounds: ethanol amine: (1) 2,2-diphenyl-1,3,2-oxazaborolidines, (2) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (3) 2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (4) 2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (5) 2,2-bis(p-methoxyphenyl)-1,3,2-oxazaborolidines, (6) 2,2-bis(o-tolyl)-1,3,2-oxazaborolidines, (7) 2,2-bis(m-tolyl)-1,3,2-oxazaborolidines, (8) 2,2-bis(o-chlorophenyl)-1,3,2-oxazaborolidines, (9) 2,2-bis(m-fluorophenyl)-1,3,2-oxazaborolidines, (10) 2,2-bis(o-methoxyphenyl)-1,3,2-oxazaborolidines. α-amino acids : (14) 4-methyl-2,2-diphenyl-1,3,2-oxazaborolidin-5-ones, (15) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (16) 4-methyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (17) 4-isopropyl-2,2-bis(m-tolyl)-1,3,2-oxazaborolidin-5-ones, (18) 4-methyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (19) 4-acetamidyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (20) 4-phenylethane-2,2-bis(p-chlorophenyl)-1,3,2 oxazaborolidin-5-ones. 2-pyridylmethanol: (21) 1,3-hydroxypyridyl-2,2-diphenyl 1,3,2-oxazaborolidines, (22) 1,3-hydroxypyridyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (23) 1,3-hydroxypyridyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines 2-(ethyl amino ethanol): (24) 3-ethyl-2,2-diphenyl-1,3,2-oxazaborolidines, (25) 3-ethyl-2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (26) 3-ethyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (27) 3-ethyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines. Apart from structural studies in the solid state, the compounds were also characterized by means of multinuclear NMR spectroscopy (1H, 11B, 13C) as well as UV/vis and FTIR. The typical 11B resonances were found in the range of (4-10 ppm). A series of characteristic metrical parameters for the compounds in the solid state as well as typical NMR shifts for the chelate target molecules was established that allowed for the determination of the coordination induced shift. The carbon atom bonded to the oxygen atom shifted upfield, while the carbon atom bonded to the nitrogen atom shifted downfield. Factors mentioned in the literature that has an influence on the hydrolytic stability on the heterocyclic borinate motif have been taken into consideration and verified for the systems researched in this study. The substitution at the nitrogen atom with one ethyl group caused the greatest increases in the N→B bond length (27) 1.714 Å, due to the increase in the nitrogen Lewis basicity, making it the least hydrolytically stable, these include compounds (24-26). Furthermore, DFT calculations were performed by employing Becke’s three parameter hybrid exchange functional with Lee–Yang–Parr functional (B3LYP) method using the Gaussian 16 program package (Rev. B01) employing the basis set 6-311++G(d,p), to corroborate and correlate the experimental findings, which gave a general R-squared value of 0.9978 for calculated vs experimental 13C chemical shifts. Thermal properties are recorded for select compounds, indicating the ΔH and the melting points. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
- Full Text:
- Date Issued: 2021-12
- Authors: Manana, Pholani Sakhile
- Date: 2021-12
- Subjects: Port Elizabeth (South Africa) , Eastern Cape (South Africa) , South Africa
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10948/53869 , vital:46027
- Description: A series of core-functionalized borinic acids was synthesized from Grignard reagents and tributylborate and reacted with ethanolamine, amino acids, 2-pyridylmethanol as well as 2-(ethyl amino ethanol). Among the borinic acids synthesized were the ones bearing: para-(2, 15, 16, 22, 27)-methyl, (3, 20, 25)-chloro, (4, 23, 26)-fluoro, (5)-methoxy; meta-(7, 17)-methyl, (9)-fluoro; ortho-(6)-methyl, (8)-chloro, (10, 18, 19)-methoxy substituents on their respective aromatic systems. All compounds obtained by condensation of the borinic acids with the aforementioned nitrogen-containing substrates were characterized structurally by means of diffraction studies based on single crystals and found to constitute chelate esters/amides featuring covalent B-O and dative N→B bonds. The chelate compounds researched in this study could be classified into four families and represent the compounds: ethanol amine: (1) 2,2-diphenyl-1,3,2-oxazaborolidines, (2) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (3) 2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (4) 2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (5) 2,2-bis(p-methoxyphenyl)-1,3,2-oxazaborolidines, (6) 2,2-bis(o-tolyl)-1,3,2-oxazaborolidines, (7) 2,2-bis(m-tolyl)-1,3,2-oxazaborolidines, (8) 2,2-bis(o-chlorophenyl)-1,3,2-oxazaborolidines, (9) 2,2-bis(m-fluorophenyl)-1,3,2-oxazaborolidines, (10) 2,2-bis(o-methoxyphenyl)-1,3,2-oxazaborolidines. α-amino acids : (14) 4-methyl-2,2-diphenyl-1,3,2-oxazaborolidin-5-ones, (15) 2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (16) 4-methyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidin-5-ones, (17) 4-isopropyl-2,2-bis(m-tolyl)-1,3,2-oxazaborolidin-5-ones, (18) 4-methyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (19) 4-acetamidyl-2,2-bis(o-methoxyphenyl)-1,3,2- oxazaborolidin-5-ones, (20) 4-phenylethane-2,2-bis(p-chlorophenyl)-1,3,2 oxazaborolidin-5-ones. 2-pyridylmethanol: (21) 1,3-hydroxypyridyl-2,2-diphenyl 1,3,2-oxazaborolidines, (22) 1,3-hydroxypyridyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines, (23) 1,3-hydroxypyridyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines 2-(ethyl amino ethanol): (24) 3-ethyl-2,2-diphenyl-1,3,2-oxazaborolidines, (25) 3-ethyl-2,2-bis(p-chlorophenyl)-1,3,2-oxazaborolidines, (26) 3-ethyl-2,2-bis(p-fluorophenyl)-1,3,2-oxazaborolidines, (27) 3-ethyl-2,2-bis(p-tolyl)-1,3,2-oxazaborolidines. Apart from structural studies in the solid state, the compounds were also characterized by means of multinuclear NMR spectroscopy (1H, 11B, 13C) as well as UV/vis and FTIR. The typical 11B resonances were found in the range of (4-10 ppm). A series of characteristic metrical parameters for the compounds in the solid state as well as typical NMR shifts for the chelate target molecules was established that allowed for the determination of the coordination induced shift. The carbon atom bonded to the oxygen atom shifted upfield, while the carbon atom bonded to the nitrogen atom shifted downfield. Factors mentioned in the literature that has an influence on the hydrolytic stability on the heterocyclic borinate motif have been taken into consideration and verified for the systems researched in this study. The substitution at the nitrogen atom with one ethyl group caused the greatest increases in the N→B bond length (27) 1.714 Å, due to the increase in the nitrogen Lewis basicity, making it the least hydrolytically stable, these include compounds (24-26). Furthermore, DFT calculations were performed by employing Becke’s three parameter hybrid exchange functional with Lee–Yang–Parr functional (B3LYP) method using the Gaussian 16 program package (Rev. B01) employing the basis set 6-311++G(d,p), to corroborate and correlate the experimental findings, which gave a general R-squared value of 0.9978 for calculated vs experimental 13C chemical shifts. Thermal properties are recorded for select compounds, indicating the ΔH and the melting points. , Thesis (PhD) -- Faculty of Science, School of Biomolecular and Chemical Sciences, 2021
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- Date Issued: 2021-12
Synthesis, characterization, and biological studies of pyrazolone Schiff bases and their transition metal complexes
- Authors: Idemudia, Omoruyi Gold
- Date: 2014
- Language: English
- Type: Thesis , Doctoral , PhD (Chemistry)
- Identifier: vital:11340 , http://hdl.handle.net/10353/d1016068
- Description: Some new acylpyrazolone Schiff bases have been synthesized from the condensation reaction of two acylpyrazolone diketone precursors with phenylhydrazine, 2,4-dinitrophenylhydrazine and sulfanilamide. They have been fully characterized by elemental analysis and spectroscopic techniques (IR,1H and 13C NMR, and mass-spectra). The single crystal structure of the benzoyl derivative acylpyrazolone Schiff bases have been obtained and analyzed by X-ray crystallography technique. Solid state X-ray diffraction revealed a keto tautomer Schiff base in solid state. Mn(II), Co(II), Ni(II) and Cu(II) complexes with the Schiff bases have been synthesized and characterized by elemental analysis, IR and UV-VIS spectroscopy, magnetic susceptibility measurements, and thermal studies (TGA and DTG). An octahedral geometry around the transition metal ion, consisting of two bidentate Schiff base ligands bonding through the azometine nitrogen and ketonic oxygen have been proposed based on careful interpretation of available analytical and spectroscopic characterization results. Two water molecules as ligands complete the octahedral geometry in all cases. Using the invitro disc diffusion method for screening synthesized compounds against selected gram positive and gram negative bacterial at 40 mg/mL, and the DPPH free radical scavenging methods at 0.50, 0.25 and 0.13 mg/mL, the synthesized Schiff base and metal complexes showed varying biological activities. 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one sul29 fanilamide showed more activity generally, exhibiting a broad spectrum activity against all selected bacterial in some cases. Mn(II), Co(II) and Ni(II) complexes of sulfanilamide Schiff base with the acetylpyrazolone derivative 4-acetyl-3-methyl-1-phenyl-2-pyrazolin-5-one sulfanilamide, exhibited a stronger and very good DPPH radical scavenging activity as good as ascorbic acid on comparing, but not with Cu(II). As such they could be important antitumour candidates.
- Full Text:
- Date Issued: 2014
- Authors: Idemudia, Omoruyi Gold
- Date: 2014
- Language: English
- Type: Thesis , Doctoral , PhD (Chemistry)
- Identifier: vital:11340 , http://hdl.handle.net/10353/d1016068
- Description: Some new acylpyrazolone Schiff bases have been synthesized from the condensation reaction of two acylpyrazolone diketone precursors with phenylhydrazine, 2,4-dinitrophenylhydrazine and sulfanilamide. They have been fully characterized by elemental analysis and spectroscopic techniques (IR,1H and 13C NMR, and mass-spectra). The single crystal structure of the benzoyl derivative acylpyrazolone Schiff bases have been obtained and analyzed by X-ray crystallography technique. Solid state X-ray diffraction revealed a keto tautomer Schiff base in solid state. Mn(II), Co(II), Ni(II) and Cu(II) complexes with the Schiff bases have been synthesized and characterized by elemental analysis, IR and UV-VIS spectroscopy, magnetic susceptibility measurements, and thermal studies (TGA and DTG). An octahedral geometry around the transition metal ion, consisting of two bidentate Schiff base ligands bonding through the azometine nitrogen and ketonic oxygen have been proposed based on careful interpretation of available analytical and spectroscopic characterization results. Two water molecules as ligands complete the octahedral geometry in all cases. Using the invitro disc diffusion method for screening synthesized compounds against selected gram positive and gram negative bacterial at 40 mg/mL, and the DPPH free radical scavenging methods at 0.50, 0.25 and 0.13 mg/mL, the synthesized Schiff base and metal complexes showed varying biological activities. 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one sul29 fanilamide showed more activity generally, exhibiting a broad spectrum activity against all selected bacterial in some cases. Mn(II), Co(II) and Ni(II) complexes of sulfanilamide Schiff base with the acetylpyrazolone derivative 4-acetyl-3-methyl-1-phenyl-2-pyrazolin-5-one sulfanilamide, exhibited a stronger and very good DPPH radical scavenging activity as good as ascorbic acid on comparing, but not with Cu(II). As such they could be important antitumour candidates.
- Full Text:
- Date Issued: 2014
Contributions to the study of a class of optimal control problems on the matrix lie group SO(3)
- Authors: Rodgerson, Joanne Kelly
- Date: 2009 , 2013-07-12
- Subjects: Matrix groups , Lie groups , Maximum principles (Mathematics) , Elliptic functions , Extremal problems (Mathematics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5421 , http://hdl.handle.net/10962/d1007199 , Matrix groups , Lie groups , Maximum principles (Mathematics) , Elliptic functions , Extremal problems (Mathematics)
- Description: The purpose of this thesis is to investigate a class of four left-invariant optimal control problems on the special orthogonal group SO(3). The set of all control-affine left-invariant control systems on SO(3) can, without loss, be reduced to a class of four typical controllable left-invariant control systems on SO(3) . The left-invariant optimal control problem on SO(3) involves finding a trajectory-control pair on SO (3), which minimizes a cost functional, and satisfies the given dynamical constraints and boundary conditions in a fixed time. The problem is lifted to the cotangent bundle T*SO(3) = SO(3) x so (3)* using the optimal Hamiltonian on so(3)*, where the maximum principle yields the optimal control. In a contribution to the study of this class of optimal control problems on SO(3), the extremal equations on so(3)* (ident ified with JR3) are integrated via elliptic functions to obtain explicit expressions for the solution curves in each typical case. The energy-Casimir method is used to give sufficient conditions for non-linear stability of the equilibrium states. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Date Issued: 2009
- Authors: Rodgerson, Joanne Kelly
- Date: 2009 , 2013-07-12
- Subjects: Matrix groups , Lie groups , Maximum principles (Mathematics) , Elliptic functions , Extremal problems (Mathematics)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5421 , http://hdl.handle.net/10962/d1007199 , Matrix groups , Lie groups , Maximum principles (Mathematics) , Elliptic functions , Extremal problems (Mathematics)
- Description: The purpose of this thesis is to investigate a class of four left-invariant optimal control problems on the special orthogonal group SO(3). The set of all control-affine left-invariant control systems on SO(3) can, without loss, be reduced to a class of four typical controllable left-invariant control systems on SO(3) . The left-invariant optimal control problem on SO(3) involves finding a trajectory-control pair on SO (3), which minimizes a cost functional, and satisfies the given dynamical constraints and boundary conditions in a fixed time. The problem is lifted to the cotangent bundle T*SO(3) = SO(3) x so (3)* using the optimal Hamiltonian on so(3)*, where the maximum principle yields the optimal control. In a contribution to the study of this class of optimal control problems on SO(3), the extremal equations on so(3)* (ident ified with JR3) are integrated via elliptic functions to obtain explicit expressions for the solution curves in each typical case. The energy-Casimir method is used to give sufficient conditions for non-linear stability of the equilibrium states. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
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- Date Issued: 2009
Curcumin analogues as ligands for Re (I) and (V)
- Authors: Schmitt, Bonell
- Date: 2012
- Subjects: Rhenium , Ligands , Chemistry, Inorganic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10443 , http://hdl.handle.net/10948/d1020975
- Description: Coordination properties of 4-bromo-N-(diethylcarbamothioyl)benzamide (Hbeb) and 4-bromo-N-(diphenylcarbamothioyl)benzamide (Hbpb) with oxorhenium(V) and rhenium(I) are reported and discussed. Transition metal complexes of these ligands were studied due to the wide range of applications of thiourea derivatives in biological fields. N-[Di(alkyl/aryl)carbamothioyl]benzamide derivatives readily coordinate to metal ions as O,S-donors and the catalytic property of the complexes can be altered by these ligands, due to steric and electronic properties provided by various substituents. The coordination possibilities of curcumin with rhenium(V) are discussed, as well as the difficulties encountered. Analogues of curcumin have been made, which also contains a seven-spacer unit between the phenyl rings, which would be more reactive and more effective in bonding to rhenium and which have greater or a similar biological activity to curcumin. This was done by assessing the coordination properties of 1,5-bis(salicylidene)thiocarbohydrazide (H4salt) and 2,4-bis(vanilidene)thiocarbohydrazide (H4vant) with oxorhenium(V) and rhenium(I) starting materials. Two rhenium(V) complex salts of the core [ReX(PPh3)2]4+ (X = Br, I), containing a coordinated imido nitrogen, are reported. One is a ‘2+1’ complex, coordinating bi- and monodentately, with the other a similar ‘3+0’ complex containing a tridentate imido-coordinated Schiff base. Selected compounds were tested against oesophageal cancer cell lines in order to evaluate and compare their effectiveness in eliminating or reducing the cancer cells in the test medium during biological testing.
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- Date Issued: 2012
- Authors: Schmitt, Bonell
- Date: 2012
- Subjects: Rhenium , Ligands , Chemistry, Inorganic
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10443 , http://hdl.handle.net/10948/d1020975
- Description: Coordination properties of 4-bromo-N-(diethylcarbamothioyl)benzamide (Hbeb) and 4-bromo-N-(diphenylcarbamothioyl)benzamide (Hbpb) with oxorhenium(V) and rhenium(I) are reported and discussed. Transition metal complexes of these ligands were studied due to the wide range of applications of thiourea derivatives in biological fields. N-[Di(alkyl/aryl)carbamothioyl]benzamide derivatives readily coordinate to metal ions as O,S-donors and the catalytic property of the complexes can be altered by these ligands, due to steric and electronic properties provided by various substituents. The coordination possibilities of curcumin with rhenium(V) are discussed, as well as the difficulties encountered. Analogues of curcumin have been made, which also contains a seven-spacer unit between the phenyl rings, which would be more reactive and more effective in bonding to rhenium and which have greater or a similar biological activity to curcumin. This was done by assessing the coordination properties of 1,5-bis(salicylidene)thiocarbohydrazide (H4salt) and 2,4-bis(vanilidene)thiocarbohydrazide (H4vant) with oxorhenium(V) and rhenium(I) starting materials. Two rhenium(V) complex salts of the core [ReX(PPh3)2]4+ (X = Br, I), containing a coordinated imido nitrogen, are reported. One is a ‘2+1’ complex, coordinating bi- and monodentately, with the other a similar ‘3+0’ complex containing a tridentate imido-coordinated Schiff base. Selected compounds were tested against oesophageal cancer cell lines in order to evaluate and compare their effectiveness in eliminating or reducing the cancer cells in the test medium during biological testing.
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- Date Issued: 2012
Learners' perceptions of creating a collaborative hypermedia product: an exploratory case study at Mount Pleasant Primary School
- Authors: du Plessis, André
- Date: 2004
- Subjects: Computer-assisted instruction -- South Africa Computers -- Study and teaching -- South Africa Education, Elementary -- Activity programs Competency-based education -- South Africa Educational technology -- South Africa
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1663 , http://hdl.handle.net/10962/d1003546
- Description: The Ministry of Education (SICTE, 2002) states that the widespread introduction of computers in schools should support Curriculum 2005 and that computer technology is part and parcel of making schools the center of community life. The vision is to establish Smart Schools: schools that are reinvented in terms of teaching-learning practices to prepare learners for the information era (SICTE, 2002). Kafai (1996:71) has found that conventional school assignments rarely give learners the opportunity to spend a great deal of time on complex projects. As a result, many learners have little experience in design: planning, problem solving, researching, dealing with time constraints, modifying expectations and synthesizing everything in a project. Research by Carver, Lehrer, Connell and Erickson (1992); Lehrer, (1993); Lehrer, Erickson and Connell (1994); Kafai (1996); Liu and Hsiao (2002) and Liu (2002) indicates that the design of hypermedia artefacts can assist in providing experience in design. To date, no equivalent research has been conducted in South Africa to ascertain the perceptions of learners regarding the creation of a hypermedia artefact over an extended period of time and whether some of the critical outcomes specified in Curriculum 2005 can be addressed in such a learning-by-design hypermedia project. This study shows that design skills and aspects related to the critical outcomes of Curriculum 2005 can be achieved. Furthermore, it indicates that this kind of project encourages interest, motivation and collaboration. In addition, it suggests that learners experience the role of the teacher as different and prefer such a learning environment. In spite of the positive results, some aspects that need attention for future implementation are suggested.
- Full Text:
- Date Issued: 2004
- Authors: du Plessis, André
- Date: 2004
- Subjects: Computer-assisted instruction -- South Africa Computers -- Study and teaching -- South Africa Education, Elementary -- Activity programs Competency-based education -- South Africa Educational technology -- South Africa
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1663 , http://hdl.handle.net/10962/d1003546
- Description: The Ministry of Education (SICTE, 2002) states that the widespread introduction of computers in schools should support Curriculum 2005 and that computer technology is part and parcel of making schools the center of community life. The vision is to establish Smart Schools: schools that are reinvented in terms of teaching-learning practices to prepare learners for the information era (SICTE, 2002). Kafai (1996:71) has found that conventional school assignments rarely give learners the opportunity to spend a great deal of time on complex projects. As a result, many learners have little experience in design: planning, problem solving, researching, dealing with time constraints, modifying expectations and synthesizing everything in a project. Research by Carver, Lehrer, Connell and Erickson (1992); Lehrer, (1993); Lehrer, Erickson and Connell (1994); Kafai (1996); Liu and Hsiao (2002) and Liu (2002) indicates that the design of hypermedia artefacts can assist in providing experience in design. To date, no equivalent research has been conducted in South Africa to ascertain the perceptions of learners regarding the creation of a hypermedia artefact over an extended period of time and whether some of the critical outcomes specified in Curriculum 2005 can be addressed in such a learning-by-design hypermedia project. This study shows that design skills and aspects related to the critical outcomes of Curriculum 2005 can be achieved. Furthermore, it indicates that this kind of project encourages interest, motivation and collaboration. In addition, it suggests that learners experience the role of the teacher as different and prefer such a learning environment. In spite of the positive results, some aspects that need attention for future implementation are suggested.
- Full Text:
- Date Issued: 2004
Rhenium(V)-Imido complexes with potentially multidentate ligands containing the amino group
- Authors: Booysen, Irvin Noel
- Date: 2007
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10385 , http://hdl.handle.net/10948/479 , Rhenium , Ligands
- Description: The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab=1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada=2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re-Cl bond length trans to the Re=N bond is shorter than the two equatorial Re-Cl bond lengths. The reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3- dimethyluracil (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2](ReO4). The X-ray crystal structure shows that the ligand ddd is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated bidentately via the neutral amino nitrogen, which is coordinated trans to the imido nitrogen, and the singly deprotonated amido nitrogen, trans to the iodide. The reaction of equimolar quantities of [NH4(ReO4)] with H2ddd in methanol under reflux conditions led to the isolation of [C12H12N6O4] as only product. The [ReO4]- ion is therefore instrumental in the formation of [C12H12N6O4], and since the product contains no rhenium in any oxidation state, the conclusion is that [ReO4]- catalyses the oxidative deamination of H2ddd. The X-ray crystal structure consists of two centrosymmetric, tricyclic rings, comprising a central pyrazine ring and two terminal pyrimidine rings. The reaction of a twofold molar excess of H2apb (H2apb=2-(2-aminophenyl)-1Hbenzimidazole) with trans-[ReO2(py)4]Cl in ethanol gave the green product of the formulation [ReO(Hapb)(apb)] in good yield. The rhenium atom lies in a distorted trigonal-bipyramidal environment. The two imidazole N(2) atoms lie in the apical positions trans to each other, with the oxo-oxygen and two amido N(1) atoms in the trigonal plane. The complex has C2-symmetry. The two amino groups are singly deprotonated and provide a negative charge each, so that they are coordinated as amides. The oxo group provides two negative charges. In order to obtain electroneutrality for the rhenium(V) complex, the two coordinated imidazole nitrogens provide one negative charge. The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (H3mps=N-(2-amino-3- methylphenyl)salicylideneimine) was prepared by the reaction of trans- [ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The X-ray crystal structure shows that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in trans- [Re(mps)Cl(PPh3)2](ReO4) as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen. The [ReO4]- anion has approximately regular tetrahedral geometry. Two significant hydrogen bonds are formed between two of the perrhenyl oxygens and the water of crystallization. The six-coordinated complex cis-[Re(mps)Cl2(PPh3)2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps in benzene. The Xray crystal structure shows that the mps ligand coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen, the neutral imino nitrogen and the phenolate oxygen. The imide and phenolate oxygen coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.
- Full Text:
- Date Issued: 2007
- Authors: Booysen, Irvin Noel
- Date: 2007
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10385 , http://hdl.handle.net/10948/479 , Rhenium , Ligands
- Description: The complex trans-[Re(dab)Cl3(PPh3)2] (H2dab=1,2-diaminobenzene) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2dab in ethanol. The ligand dab is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. The complex trans-[Re(ada)Cl3(PPh3)2] (H2ada=2-aminodiphenylamine) was prepared from the reaction of trans-[ReOCl3(PPh3)2] with H2ada in acetonitrile. The ligand ada is coordinated to the rhenium(V) centre through a dianionic imido nitrogen only, in a distorted octahedral coordination geometry around the metal ion. Surprisingly, the Re-Cl bond length trans to the Re=N bond is shorter than the two equatorial Re-Cl bond lengths. The reaction of equimolar quantities of cis-[ReO2I(PPh3)2] with 5,6-diamino-1,3- dimethyluracil (H2ddd) in acetonitrile led to the formation of [Re(ddd)(Hddd)I(PPh3)2](ReO4). The X-ray crystal structure shows that the ligand ddd is coordinated monodentately through the doubly deprotonated amino nitrogen and is therefore present as an imide. The chelate Hddd is coordinated bidentately via the neutral amino nitrogen, which is coordinated trans to the imido nitrogen, and the singly deprotonated amido nitrogen, trans to the iodide. The reaction of equimolar quantities of [NH4(ReO4)] with H2ddd in methanol under reflux conditions led to the isolation of [C12H12N6O4] as only product. The [ReO4]- ion is therefore instrumental in the formation of [C12H12N6O4], and since the product contains no rhenium in any oxidation state, the conclusion is that [ReO4]- catalyses the oxidative deamination of H2ddd. The X-ray crystal structure consists of two centrosymmetric, tricyclic rings, comprising a central pyrazine ring and two terminal pyrimidine rings. The reaction of a twofold molar excess of H2apb (H2apb=2-(2-aminophenyl)-1Hbenzimidazole) with trans-[ReO2(py)4]Cl in ethanol gave the green product of the formulation [ReO(Hapb)(apb)] in good yield. The rhenium atom lies in a distorted trigonal-bipyramidal environment. The two imidazole N(2) atoms lie in the apical positions trans to each other, with the oxo-oxygen and two amido N(1) atoms in the trigonal plane. The complex has C2-symmetry. The two amino groups are singly deprotonated and provide a negative charge each, so that they are coordinated as amides. The oxo group provides two negative charges. In order to obtain electroneutrality for the rhenium(V) complex, the two coordinated imidazole nitrogens provide one negative charge. The complex salt trans-[Re(mps)Cl(PPh3)2](ReO4) (H3mps=N-(2-amino-3- methylphenyl)salicylideneimine) was prepared by the reaction of trans- [ReOCl3(PPh3)2] with a twofold molar excess of H3mps. The X-ray crystal structure shows that the trianionic ligand mps acts as a tridentate chelate via the doubly deprotonated amino nitrogen (which is present in trans- [Re(mps)Cl(PPh3)2](ReO4) as an imide), the neutral imino nitrogen and the deprotonated phenolic oxygen. The [ReO4]- anion has approximately regular tetrahedral geometry. Two significant hydrogen bonds are formed between two of the perrhenyl oxygens and the water of crystallization. The six-coordinated complex cis-[Re(mps)Cl2(PPh3)2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H3mps in benzene. The Xray crystal structure shows that the mps ligand coordinates as a tridentate chelate via the doubly deprotonated 2-amino nitrogen, the neutral imino nitrogen and the phenolate oxygen. The imide and phenolate oxygen coordinate trans to each other in a distorted octahedral geometry around the rhenium(V) centre, with the two chlorides in cis positions.
- Full Text:
- Date Issued: 2007
The coordination chemistry of Rhenium(V) with multidentate no-donor ligands
- Authors: Abrahams, Abubak'r
- Date: 2009
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10370 , http://hdl.handle.net/10948/912 , Rhenium , Ligands
- Description: The neutral distorted octahedral complexes [ReOCl(L)] {H2L = N,N-bis(2- hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H2had), N,N-bis(2-hydroxybenzyl) aminomethylpyridine (H2hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H2hae)} were prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H2L in ethanol. The X-ray structure determinations of [ReOCl(had)] and [ReOCl(hap)] were performed, and in both complexes the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen. Treatment of trans-[ReO2(py)4]I with two equivalents and one equivalent each of H2had in acetone afforded the iodide salts of the oxypyridinium-ammonium zwitterions N1-(2-hydroxybenzyl)-N2,N2- dimethyl-N1-((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [Hhpd]+ and N2,N2- dimethyl-N1-bis((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [dod]+ respectively. In [Hhpd]I, one of the 2-hydroxyphenyl groups of H2had is substituted by an oxypyridinium group, and in [dod]I, both 2-hydroxyphenyl groups are converted. The X-ray crystal structure determination of the starting material H2had, [Hhpd]I and [dod]I reveals trigonal pyramidal geometries around the central amino nitrogen. The complex salt [ReO(bsa)]PF6 (H2bsa=bis(N-methylsalicylicylideneiminopropyl) amine) was prepared from the reaction of cis-[ReO2I(PPh3)2] with H2bsa in toluene. The dianionic pentadentate ligand bsa is coordinated to the ReO3+ moiety via one secondary amino and two imino nitrogens, and two anionic phenolate oxygens. The complex was characterized by spectroscopy and analytical data, and the structure has been determined by single-crystal X-ray diffraction analysis. The complex exhibits a distorted octahedral geometry around the central rhenium(V) ion, with the basal plane being defined by a phenolate oxygen, two imino nitrogens and the secondary amino. ix A. Abrahams Nelson Mandela Metropolitan University The reaction of a two-fold molar excess of the potentially NN-donor ligand 2,2’- dipyridylamine (dpa) with trans-[ReO(OEt)Cl2(PPh3)2] in ethanol led to the isolation of [ReOCl2(OEt)(dpa)]. The X-ray crystal structure shows that the NN-chelated dpa is coordinated in the equatorial plane cis to the oxo and ethoxo groups, which are in trans positions relative to each other. The treatment of trans- [ReOCl3(PPh3)2] with a tenfold molar excess of dpa in ethanol at the refluxing temperature yielded the trans-dioxo complex [ReO2(dpa)2]Cl, but with a twofold molar excess only (μ-O)[{ReOCl2(dpa)}2] was isolated. Repeating the latter reaction with (n-Bu4N)[ReOCl4] as starting material in ethanol at room temperature a dark green product, also with the formulation (μ-O)[{ReOCl2(dpa)}2], was isolated. The reaction of equimolar quantities of bis(pyridin-2-yl)methyl)amine (HBPA) with (n-Bu4N)[ReOCl4] in acetone at room temperature led to the isolation of the sixcoordinate rhenium(V) complex [ReOCl(H2O)(BPA)]Cl. IR, NMR and X-ray crystallographic results indicate that BPA is coordinated as a tridentate uninegative chelate, with deprotonation of the amine nitrogen. The water molecule is coordinated trans to the oxo group, with the Re=O and Re-OH2 bond distances equal to 1.663(9) and 2.21(1) Å respectively. Complexes of the general formula [ReOX2{(C5H4N)CH(O)CH2(C5H4N)}] (X = Cl, I) were prepared by the reactions of trans-[ReOCl3(PPh3)2] and trans- [ReOI2(OEt)(PPh3)2] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. Experimental evidence shows that the coordinated DPE ligand has undergone addition of water at the ethylenic carbons, and that the (C5H4N)CH(O)CH2(C5H4N) moiety acts as a uninegative tridentate NON-donor ligand. The X-ray crystal structures of both complexes show a distorted octahedral geometry around the rhenium(V) centre. The treatment of trans-[ReOCl3(PPh3)2] with H2dbd in a 2:1 molar ratio in acetonitrile led to the isolation of the ligand-bridged dimer (μ-dbd)[ReOCl2(PPh3)]2. The X-ray crystal structure of the complex reveals a dinuclear structure in which two rhenium(V) ions are bridged by the dbd ligand. Each rhenium ion is in a x A. Abrahams Nelson Mandela Metropolitan University distorted octahedral geometry. The basal plane is defined by a phosphorus atom of the PPh3 group, two chlorides cis to each other, and a pyridyl nitrogen atom of dbd. The oxo group and alcoholate oxygen of dbd lie in trans axial positions. The complexes cis-[ReOX2(msa)(PPh3)] (X = Cl, Br, I) were prepared from trans- [ReOCl3(PPh3)2], trans-[ReOBr3(PPh3)2] or trans-[ReOI2(OEt)(PPh3)2] with 2-(1- iminoethyl)phenol (Hmsa) in acetonitrile. An X-ray crystallographic study shows that the bonding distances and angles in the comlexes are nearly identical, and that the two halides in each complex are coordinated cis to each other in the equatorial plane cis to the oxo group. The oxo-bridged dinuclear rhenium(V) complex [(μ-O){ReOCl(amp)}2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] and 6-amino-3-methyl-1-phenyl- 4-azahept-2-ene-1-one (Hamp) in acetone. The characterization of the complex by elemental analysis, infrared and 1H NMR spectroscopy and X-ray crystallography shows that amp is coordinated as a monoanionic NNO-donor chelate as an amino-amido ketone. However, the reaction of the similar ligand 7- amino-4,7-dimethyl-5-aza-3-octen-2-one (Hada) with [Re(CO)5Br] produced the product fac-[Re(CO)3Br(Hada)], with Hada coordinated as a neutral NN-donor amino-imino-ketone.
- Full Text:
- Date Issued: 2009
- Authors: Abrahams, Abubak'r
- Date: 2009
- Subjects: Rhenium , Ligands
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:10370 , http://hdl.handle.net/10948/912 , Rhenium , Ligands
- Description: The neutral distorted octahedral complexes [ReOCl(L)] {H2L = N,N-bis(2- hydroxybenzyl)-2-(2-aminoethyl)dimethylamine (H2had), N,N-bis(2-hydroxybenzyl) aminomethylpyridine (H2hap); N,N-bis(2-hydroxybenzyl)-2-(2-aminoethyl)pyridine (H2hae)} were prepared by the reaction of trans-[ReOCl3(PPh3)2] with a twofold molar excess of H2L in ethanol. The X-ray structure determinations of [ReOCl(had)] and [ReOCl(hap)] were performed, and in both complexes the chloride is coordinated trans to the tripodal tertiary amino nitrogen, with a phenolate oxygen trans to the oxo oxygen. Treatment of trans-[ReO2(py)4]I with two equivalents and one equivalent each of H2had in acetone afforded the iodide salts of the oxypyridinium-ammonium zwitterions N1-(2-hydroxybenzyl)-N2,N2- dimethyl-N1-((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [Hhpd]+ and N2,N2- dimethyl-N1-bis((2-oxypyridinium)-1-methyl)ethane-1,2-diamine [dod]+ respectively. In [Hhpd]I, one of the 2-hydroxyphenyl groups of H2had is substituted by an oxypyridinium group, and in [dod]I, both 2-hydroxyphenyl groups are converted. The X-ray crystal structure determination of the starting material H2had, [Hhpd]I and [dod]I reveals trigonal pyramidal geometries around the central amino nitrogen. The complex salt [ReO(bsa)]PF6 (H2bsa=bis(N-methylsalicylicylideneiminopropyl) amine) was prepared from the reaction of cis-[ReO2I(PPh3)2] with H2bsa in toluene. The dianionic pentadentate ligand bsa is coordinated to the ReO3+ moiety via one secondary amino and two imino nitrogens, and two anionic phenolate oxygens. The complex was characterized by spectroscopy and analytical data, and the structure has been determined by single-crystal X-ray diffraction analysis. The complex exhibits a distorted octahedral geometry around the central rhenium(V) ion, with the basal plane being defined by a phenolate oxygen, two imino nitrogens and the secondary amino. ix A. Abrahams Nelson Mandela Metropolitan University The reaction of a two-fold molar excess of the potentially NN-donor ligand 2,2’- dipyridylamine (dpa) with trans-[ReO(OEt)Cl2(PPh3)2] in ethanol led to the isolation of [ReOCl2(OEt)(dpa)]. The X-ray crystal structure shows that the NN-chelated dpa is coordinated in the equatorial plane cis to the oxo and ethoxo groups, which are in trans positions relative to each other. The treatment of trans- [ReOCl3(PPh3)2] with a tenfold molar excess of dpa in ethanol at the refluxing temperature yielded the trans-dioxo complex [ReO2(dpa)2]Cl, but with a twofold molar excess only (μ-O)[{ReOCl2(dpa)}2] was isolated. Repeating the latter reaction with (n-Bu4N)[ReOCl4] as starting material in ethanol at room temperature a dark green product, also with the formulation (μ-O)[{ReOCl2(dpa)}2], was isolated. The reaction of equimolar quantities of bis(pyridin-2-yl)methyl)amine (HBPA) with (n-Bu4N)[ReOCl4] in acetone at room temperature led to the isolation of the sixcoordinate rhenium(V) complex [ReOCl(H2O)(BPA)]Cl. IR, NMR and X-ray crystallographic results indicate that BPA is coordinated as a tridentate uninegative chelate, with deprotonation of the amine nitrogen. The water molecule is coordinated trans to the oxo group, with the Re=O and Re-OH2 bond distances equal to 1.663(9) and 2.21(1) Å respectively. Complexes of the general formula [ReOX2{(C5H4N)CH(O)CH2(C5H4N)}] (X = Cl, I) were prepared by the reactions of trans-[ReOCl3(PPh3)2] and trans- [ReOI2(OEt)(PPh3)2] with cis-1,2-di-(2-pyridyl)ethylene (DPE) in ethanol and benzene in air. Experimental evidence shows that the coordinated DPE ligand has undergone addition of water at the ethylenic carbons, and that the (C5H4N)CH(O)CH2(C5H4N) moiety acts as a uninegative tridentate NON-donor ligand. The X-ray crystal structures of both complexes show a distorted octahedral geometry around the rhenium(V) centre. The treatment of trans-[ReOCl3(PPh3)2] with H2dbd in a 2:1 molar ratio in acetonitrile led to the isolation of the ligand-bridged dimer (μ-dbd)[ReOCl2(PPh3)]2. The X-ray crystal structure of the complex reveals a dinuclear structure in which two rhenium(V) ions are bridged by the dbd ligand. Each rhenium ion is in a x A. Abrahams Nelson Mandela Metropolitan University distorted octahedral geometry. The basal plane is defined by a phosphorus atom of the PPh3 group, two chlorides cis to each other, and a pyridyl nitrogen atom of dbd. The oxo group and alcoholate oxygen of dbd lie in trans axial positions. The complexes cis-[ReOX2(msa)(PPh3)] (X = Cl, Br, I) were prepared from trans- [ReOCl3(PPh3)2], trans-[ReOBr3(PPh3)2] or trans-[ReOI2(OEt)(PPh3)2] with 2-(1- iminoethyl)phenol (Hmsa) in acetonitrile. An X-ray crystallographic study shows that the bonding distances and angles in the comlexes are nearly identical, and that the two halides in each complex are coordinated cis to each other in the equatorial plane cis to the oxo group. The oxo-bridged dinuclear rhenium(V) complex [(μ-O){ReOCl(amp)}2] was prepared by the reaction of trans-[ReOCl3(PPh3)2] and 6-amino-3-methyl-1-phenyl- 4-azahept-2-ene-1-one (Hamp) in acetone. The characterization of the complex by elemental analysis, infrared and 1H NMR spectroscopy and X-ray crystallography shows that amp is coordinated as a monoanionic NNO-donor chelate as an amino-amido ketone. However, the reaction of the similar ligand 7- amino-4,7-dimethyl-5-aza-3-octen-2-one (Hada) with [Re(CO)5Br] produced the product fac-[Re(CO)3Br(Hada)], with Hada coordinated as a neutral NN-donor amino-imino-ketone.
- Full Text:
- Date Issued: 2009