Catalytic behaviour of metallophthalocyanines towards the detection of nitric oxide
- Authors: Vilakazi, Lea Sibulelo
- Date: 2002
- Subjects: Electrochemistry Nitric oxide
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4418 , http://hdl.handle.net/10962/d1006852
- Description: Electrocatalytic reduction and oxidation of nitric oxide (NO) using cobalt phthalocyanine complexes have been studied and compared to vitamin B₁₂ and other metallophthalocyanine (MPc) complexes. Modifying a glassy carbon electrode with these complexes resulted in improved sensitivity of the electrode allowing detection of NO to 10⁻⁹ mol dm⁻³. The mechanisms of catalysis were studied. Electrocatalysis of NO involves coordination of NO to the MPc complex. Hence catalytic activity is affected by the nature of the metal center. However coordination of NO to the MPc complex has to be reversible to eliminate poisoning of the electrode. Though FePc gave the best sensitivity and lowered the reduction potential more than CoPc, the strong Fe-NO bond resulted in the poisoning of the electrode hence, rendering the electrode unstable. Rate constants for NO coordination to the MPc complexes were studied. These rates were smaller than the studied NO porphyrin coordination rates. Electrocatalytic reduction of NO using MPc complexes involves a transfer of an electron from the metal center to the NO ligand. Hence, substitution of electron-donating grohps on the cobalt pthalocyanine complex resulted in improved sensitivity and catalytic activity. A CoPc modified microelectrode (11μm) was used to monitor NO in human blood components and to detect NO in a rat brain. Detections of NO were also done in aqueous solutions in the presence of interfering species such as dopamine and serotonin. An interaction between NO and serotonin was observed.
- Full Text:
- Date Issued: 2002
- Authors: Vilakazi, Lea Sibulelo
- Date: 2002
- Subjects: Electrochemistry Nitric oxide
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4418 , http://hdl.handle.net/10962/d1006852
- Description: Electrocatalytic reduction and oxidation of nitric oxide (NO) using cobalt phthalocyanine complexes have been studied and compared to vitamin B₁₂ and other metallophthalocyanine (MPc) complexes. Modifying a glassy carbon electrode with these complexes resulted in improved sensitivity of the electrode allowing detection of NO to 10⁻⁹ mol dm⁻³. The mechanisms of catalysis were studied. Electrocatalysis of NO involves coordination of NO to the MPc complex. Hence catalytic activity is affected by the nature of the metal center. However coordination of NO to the MPc complex has to be reversible to eliminate poisoning of the electrode. Though FePc gave the best sensitivity and lowered the reduction potential more than CoPc, the strong Fe-NO bond resulted in the poisoning of the electrode hence, rendering the electrode unstable. Rate constants for NO coordination to the MPc complexes were studied. These rates were smaller than the studied NO porphyrin coordination rates. Electrocatalytic reduction of NO using MPc complexes involves a transfer of an electron from the metal center to the NO ligand. Hence, substitution of electron-donating grohps on the cobalt pthalocyanine complex resulted in improved sensitivity and catalytic activity. A CoPc modified microelectrode (11μm) was used to monitor NO in human blood components and to detect NO in a rat brain. Detections of NO were also done in aqueous solutions in the presence of interfering species such as dopamine and serotonin. An interaction between NO and serotonin was observed.
- Full Text:
- Date Issued: 2002
Reconciling Western and African philosophy : rationality, culture and communitarianism
- Authors: Vitsha, Xolisa
- Date: 2002
- Subjects: Philosophy, African , Africa -- Intellectual life , Philosophy, Comparative , Philosophy , Communitarianism , Self
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2838 , http://hdl.handle.net/10962/d1003807 , Philosophy, African , Africa -- Intellectual life , Philosophy, Comparative , Philosophy , Communitarianism , Self
- Description: This thesis attempts to reconcile Western and African philosophy with specific reference to the issues of rationality, culture and communitarianism. It also discusses the post-Enlightenment, Western philosophical concept of liberal "atomism" and the primacy of the individual and the emergence of a communitarian critique in response. This thesis intends exploring how Western notions of individuality and the communitarian response can be reconciled with contemporary African philosophy and African communitarian thought in particular. To do this, it is necessary to explore the problem of liberal individualism and how African communitarianism might reinforce the Western communitarian critique. African communitarianism has a processual understanding of personhood that underpins its conception of the Self. In contrast to this view, Western communitarianism has a relational conception of the individual Self. Thus, this thesis argues that African communitarianism has a more profound understanding of the constitution of the Self. To demonstrate these claims, this study discusses notions of rationality which inform each of the philosophical traditions. This will enable a comparative analysis of the above-mentioned philosophical traditions with the intention of uncovering the concepts that provide the platform for their reconciliation.
- Full Text:
- Date Issued: 2002
- Authors: Vitsha, Xolisa
- Date: 2002
- Subjects: Philosophy, African , Africa -- Intellectual life , Philosophy, Comparative , Philosophy , Communitarianism , Self
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2838 , http://hdl.handle.net/10962/d1003807 , Philosophy, African , Africa -- Intellectual life , Philosophy, Comparative , Philosophy , Communitarianism , Self
- Description: This thesis attempts to reconcile Western and African philosophy with specific reference to the issues of rationality, culture and communitarianism. It also discusses the post-Enlightenment, Western philosophical concept of liberal "atomism" and the primacy of the individual and the emergence of a communitarian critique in response. This thesis intends exploring how Western notions of individuality and the communitarian response can be reconciled with contemporary African philosophy and African communitarian thought in particular. To do this, it is necessary to explore the problem of liberal individualism and how African communitarianism might reinforce the Western communitarian critique. African communitarianism has a processual understanding of personhood that underpins its conception of the Self. In contrast to this view, Western communitarianism has a relational conception of the individual Self. Thus, this thesis argues that African communitarianism has a more profound understanding of the constitution of the Self. To demonstrate these claims, this study discusses notions of rationality which inform each of the philosophical traditions. This will enable a comparative analysis of the above-mentioned philosophical traditions with the intention of uncovering the concepts that provide the platform for their reconciliation.
- Full Text:
- Date Issued: 2002
An assessment of the genetic diversity and origin of the invasive weed Chromolaena Odorata (L.) King and Robinson in South Africa
- Authors: Von Senger, Inge
- Date: 2002
- Subjects: Biodiversity -- South Africa , Chromolaena odorata -- Biological control -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4233 , http://hdl.handle.net/10962/d1003802 , Biodiversity -- South Africa , Chromolaena odorata -- Biological control -- South Africa
- Description: Chromolaena odorata (L.) King and Robinson is an alien invasive weed to most of the Old World tropical regions of the earth, including South Africa where it is morphologically distinct from most other C. odorata plants examined from both its native and invasive range. It is thought that these morphological differences are related to difficulties encountered in successful establishment of biological control agents on the South African population of C. odorata. It has been postulated that the source population of the South African population will harbour potential biocontrol agents that will be suited to successful establishment on the South African plants. Several morphological, cytological and isozyme studies have been attempted to identify the source population of the South African population, but these have failed to identify the origin of the South African population. In this dissertation two PCR-based methods were attempted, in an investigation into whether the morphological differences and difficulties in establishment of biocontrol agents have a genetic basis. The two techniques attempted were: Inter Simple Sequence Repeat (ISSR) amplification, and DNA sequencing. Results could not be obtained using the ISSR method, and the reason for this was not discovered despite extensive trials. The internal transcribed spacer region and the external transcribed spacer region sequences were obtained from five samples, and compared. It was found that the ETS region gave more phylogenetic signal at the intraspecific level than the ITS region. However, due to difficulties in amplification of the external transcribed spacer region, work here focussed on obtaining Internal Transcribed Spacer sequences for 61 samples. Each of the samples sequenced had a unique ITS sequence, displaying a high level of intraspecific genetic diversity. The degree of this diversity is discussed with reference to the possible influences of polyploidy and concerted evolution on genetic structure. The ITS data indicated that some of the physical traits used to define ‘morphotypes’ of C. odorata were not correlated to genotype. From discussion and comparison of morphological character distributions and the ITS-based phylogeography it is suggested that the geographical origin of the South African population is Greater Antilelan, rather than from the continents of North and South America, which is where the Australasian, West African and Mauritian infestations are suggested to have originated.
- Full Text:
- Date Issued: 2002
- Authors: Von Senger, Inge
- Date: 2002
- Subjects: Biodiversity -- South Africa , Chromolaena odorata -- Biological control -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4233 , http://hdl.handle.net/10962/d1003802 , Biodiversity -- South Africa , Chromolaena odorata -- Biological control -- South Africa
- Description: Chromolaena odorata (L.) King and Robinson is an alien invasive weed to most of the Old World tropical regions of the earth, including South Africa where it is morphologically distinct from most other C. odorata plants examined from both its native and invasive range. It is thought that these morphological differences are related to difficulties encountered in successful establishment of biological control agents on the South African population of C. odorata. It has been postulated that the source population of the South African population will harbour potential biocontrol agents that will be suited to successful establishment on the South African plants. Several morphological, cytological and isozyme studies have been attempted to identify the source population of the South African population, but these have failed to identify the origin of the South African population. In this dissertation two PCR-based methods were attempted, in an investigation into whether the morphological differences and difficulties in establishment of biocontrol agents have a genetic basis. The two techniques attempted were: Inter Simple Sequence Repeat (ISSR) amplification, and DNA sequencing. Results could not be obtained using the ISSR method, and the reason for this was not discovered despite extensive trials. The internal transcribed spacer region and the external transcribed spacer region sequences were obtained from five samples, and compared. It was found that the ETS region gave more phylogenetic signal at the intraspecific level than the ITS region. However, due to difficulties in amplification of the external transcribed spacer region, work here focussed on obtaining Internal Transcribed Spacer sequences for 61 samples. Each of the samples sequenced had a unique ITS sequence, displaying a high level of intraspecific genetic diversity. The degree of this diversity is discussed with reference to the possible influences of polyploidy and concerted evolution on genetic structure. The ITS data indicated that some of the physical traits used to define ‘morphotypes’ of C. odorata were not correlated to genotype. From discussion and comparison of morphological character distributions and the ITS-based phylogeography it is suggested that the geographical origin of the South African population is Greater Antilelan, rather than from the continents of North and South America, which is where the Australasian, West African and Mauritian infestations are suggested to have originated.
- Full Text:
- Date Issued: 2002
The ecology of the red-billed quelea Quelea Quelea (Linnaeus) and other granivorous birds at Eastern Cape feedlots
- Whittington-Jones, Craig Alun
- Authors: Whittington-Jones, Craig Alun
- Date: 2002
- Subjects: Quelea quelea -- South Africa -- Eastern Cape Granivores -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5618 , http://hdl.handle.net/10962/d1003286
- Description: Red-billed Quelea Quelea quelea have expanded their range in the Eastern Cape and now occur throughout the year in new areas. Recent changes in agricultural practice have probably been a contributing factor as flocks are larger than previously recorded and were more often associated with artificial food sources than natural grasses. Ringing and census data indicate that quelea have reduced movements during the non-breeding season and may display strong fidelity (over successive years) to dry season quarters with reliable food supplies. Although the recapture/recovery rate for quelea in the Eastern Cape (1.0-2.5%) was higher than the national average, it was still lower than expected and there may be considerable movement between nearby feeding sites. Some quelea breed locally, but most disperse during summer and their numbers at the feedlots were generally highest in winter and spring. The breeding season of quelea is later than other ploceids in the region and post-nuptial moult overlaps with winter. Replacement of primary wing feathers is relatively slow (124 days), and this is considered an adaptation to minimise disruption of flight capabilities and insulation. Significantly more quelea in the Eastern Cape have breeding plumage suffused with pink than in other southern African populations. However, during the non-breeding season there is apparently considerable intermixing between local populations and those from further north and the existence of a local sub-species is not supported. Seeds of two grass species, Echinochloa sp. and Urochloa panicoides, and two weed species, Amaranthus sp. and Chenopodium sp., were important in the diet of both quelea and Laughing Doves Streptopelia senegalensis. Maize comprised a large proportion of the diet of these species and losses at one ostrich feedlot were estimated at over R 17 000 in two years. Dependence on artificial food sources was generally greatest in winter and spring, but economically significant damage was not confined to this period. Alpha-chloralose showed good potential for reducing numbers of problem birds at livestock feedlots. However, the dynamic nature of problem bird populations favours a non-lethal management approach. Reduction of feed loss through manipulation of the ostrich ration could provide a relatively cheap and effective alternative to lethal control if applied appropriately.
- Full Text:
- Date Issued: 2002
- Authors: Whittington-Jones, Craig Alun
- Date: 2002
- Subjects: Quelea quelea -- South Africa -- Eastern Cape Granivores -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5618 , http://hdl.handle.net/10962/d1003286
- Description: Red-billed Quelea Quelea quelea have expanded their range in the Eastern Cape and now occur throughout the year in new areas. Recent changes in agricultural practice have probably been a contributing factor as flocks are larger than previously recorded and were more often associated with artificial food sources than natural grasses. Ringing and census data indicate that quelea have reduced movements during the non-breeding season and may display strong fidelity (over successive years) to dry season quarters with reliable food supplies. Although the recapture/recovery rate for quelea in the Eastern Cape (1.0-2.5%) was higher than the national average, it was still lower than expected and there may be considerable movement between nearby feeding sites. Some quelea breed locally, but most disperse during summer and their numbers at the feedlots were generally highest in winter and spring. The breeding season of quelea is later than other ploceids in the region and post-nuptial moult overlaps with winter. Replacement of primary wing feathers is relatively slow (124 days), and this is considered an adaptation to minimise disruption of flight capabilities and insulation. Significantly more quelea in the Eastern Cape have breeding plumage suffused with pink than in other southern African populations. However, during the non-breeding season there is apparently considerable intermixing between local populations and those from further north and the existence of a local sub-species is not supported. Seeds of two grass species, Echinochloa sp. and Urochloa panicoides, and two weed species, Amaranthus sp. and Chenopodium sp., were important in the diet of both quelea and Laughing Doves Streptopelia senegalensis. Maize comprised a large proportion of the diet of these species and losses at one ostrich feedlot were estimated at over R 17 000 in two years. Dependence on artificial food sources was generally greatest in winter and spring, but economically significant damage was not confined to this period. Alpha-chloralose showed good potential for reducing numbers of problem birds at livestock feedlots. However, the dynamic nature of problem bird populations favours a non-lethal management approach. Reduction of feed loss through manipulation of the ostrich ration could provide a relatively cheap and effective alternative to lethal control if applied appropriately.
- Full Text:
- Date Issued: 2002
Implementing non-photorealistic rendering enhancements with real-time performance
- Authors: Winnemöller, Holger
- Date: 2002 , 2013-05-09
- Subjects: Computer animation , Computer graphics , Real-time data processing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4580 , http://hdl.handle.net/10962/d1003135 , Computer animation , Computer graphics , Real-time data processing
- Description: We describe quality and performance enhancements, which work in real-time, to all well-known Non-photorealistic (NPR) rendering styles for use in an interactive context. These include Comic rendering, Sketch rendering, Hatching and Painterly rendering, but we also attempt and justify a widening of the established definition of what is considered NPR. In the individual Chapters, we identify typical stylistic elements of the different NPR styles. We list problems that need to be solved in order to implement the various renderers. Standard solutions available in the literature are introduced and in all cases extended and optimised. In particular, we extend the lighting model of the comic renderer to include a specular component and introduce multiple inter-related but independent geometric approximations which greatly improve rendering performance. We implement two completely different solutions to random perturbation sketching, solve temporal coherence issues for coal sketching and find an unexpected use for 3D textures to implement hatch-shading. Textured brushes of painterly rendering are extended by properties such as stroke-direction and texture, motion, paint capacity, opacity and emission, making them more flexible and versatile. Brushes are also provided with a minimal amount of intelligence, so that they can help in maximising screen coverage of brushes. We furthermore devise a completely new NPR style, which we call super-realistic and show how sample images can be tweened in real-time to produce an image-based six degree-of-freedom renderer performing at roughly 450 frames per second. Performance values for our other renderers all lie between 10 and over 400 frames per second on homePC hardware, justifying our real-time claim. A large number of sample screen-shots, illustrations and animations demonstrate the visual fidelity of our rendered images. In essence, we successfully achieve our attempted goals of increasing the creative, expressive and communicative potential of individual NPR styles, increasing performance of most of them, adding original and interesting visual qualities, and exploring new techniques or existing ones in novel ways. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2002
- Authors: Winnemöller, Holger
- Date: 2002 , 2013-05-09
- Subjects: Computer animation , Computer graphics , Real-time data processing
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4580 , http://hdl.handle.net/10962/d1003135 , Computer animation , Computer graphics , Real-time data processing
- Description: We describe quality and performance enhancements, which work in real-time, to all well-known Non-photorealistic (NPR) rendering styles for use in an interactive context. These include Comic rendering, Sketch rendering, Hatching and Painterly rendering, but we also attempt and justify a widening of the established definition of what is considered NPR. In the individual Chapters, we identify typical stylistic elements of the different NPR styles. We list problems that need to be solved in order to implement the various renderers. Standard solutions available in the literature are introduced and in all cases extended and optimised. In particular, we extend the lighting model of the comic renderer to include a specular component and introduce multiple inter-related but independent geometric approximations which greatly improve rendering performance. We implement two completely different solutions to random perturbation sketching, solve temporal coherence issues for coal sketching and find an unexpected use for 3D textures to implement hatch-shading. Textured brushes of painterly rendering are extended by properties such as stroke-direction and texture, motion, paint capacity, opacity and emission, making them more flexible and versatile. Brushes are also provided with a minimal amount of intelligence, so that they can help in maximising screen coverage of brushes. We furthermore devise a completely new NPR style, which we call super-realistic and show how sample images can be tweened in real-time to produce an image-based six degree-of-freedom renderer performing at roughly 450 frames per second. Performance values for our other renderers all lie between 10 and over 400 frames per second on homePC hardware, justifying our real-time claim. A large number of sample screen-shots, illustrations and animations demonstrate the visual fidelity of our rendered images. In essence, we successfully achieve our attempted goals of increasing the creative, expressive and communicative potential of individual NPR styles, increasing performance of most of them, adding original and interesting visual qualities, and exploring new techniques or existing ones in novel ways. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2002
The teaching of ecology in schools: a literature review
- Authors: Wiredu, Christopher Agyei
- Date: 2002
- Subjects: Environmental education Teachers -- In-service training -- South Africa Science -- Study and teaching -- South Africa Ecology -- Study and teaching
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1413 , http://hdl.handle.net/10962/d1003134
- Description: Project 1: This is a literature review on the teaching of ecology in South African schools. The importance of ecology education in the school curriculum is well reported. It is also reported that in spite of the apparent importance of the subject, not much ecology is taught or learned in schools. This report examines what ecology is supposed to be about and the challenges that confront its teaching. The approaches to teaching the subject are also discussed. It would seem that if teachers focus on teaching ecological concepts using constructivist teaching/learning strategies, students might be helped to learn ecology meaningfully. Project 2: 'Constructing eco-concepts' is a case study that reports the effects of a module whose design was informed by social constructivist ideas on the understanding of selected ecological concepts by college students. Social constructivism as a philosophy of learning has gained increasing attention in science education in recent times and yet the approach is so alien to so many. Many teachers still teach by the traditional teacher-centred approaches. This research project reports the conceptual change of students after undertaking the module. It also reports the students' perceptions about the teaching/learning strategies employed in the module. It would seem that the social constructivist strategies used in the module assisted the students to improve their frameworks of ecological concepts. Data also tend to reveal that the students enjoyed the approach to learning and had positive views about the social constructivist teaching/learning approach. Project 3: With the advent of the new curriculum framework for South Africa, the outcomes based curriculum, it would seem that teachers could no longer approach teaching by the traditional transmission methods. Colleges of education have been criticised for producing teachers who do not seem to be adequately prepared for their job. Presently, the argument seems to be that teachers would need in-service education on a wide scale and the colleges of education would seem to be important in-service teacher education centres. This research, using case study methodology, investigated the potential of one of the colleges of education to become an in-service teacher education institution based on its physical and human resources.
- Full Text:
- Date Issued: 2002
- Authors: Wiredu, Christopher Agyei
- Date: 2002
- Subjects: Environmental education Teachers -- In-service training -- South Africa Science -- Study and teaching -- South Africa Ecology -- Study and teaching
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: vital:1413 , http://hdl.handle.net/10962/d1003134
- Description: Project 1: This is a literature review on the teaching of ecology in South African schools. The importance of ecology education in the school curriculum is well reported. It is also reported that in spite of the apparent importance of the subject, not much ecology is taught or learned in schools. This report examines what ecology is supposed to be about and the challenges that confront its teaching. The approaches to teaching the subject are also discussed. It would seem that if teachers focus on teaching ecological concepts using constructivist teaching/learning strategies, students might be helped to learn ecology meaningfully. Project 2: 'Constructing eco-concepts' is a case study that reports the effects of a module whose design was informed by social constructivist ideas on the understanding of selected ecological concepts by college students. Social constructivism as a philosophy of learning has gained increasing attention in science education in recent times and yet the approach is so alien to so many. Many teachers still teach by the traditional teacher-centred approaches. This research project reports the conceptual change of students after undertaking the module. It also reports the students' perceptions about the teaching/learning strategies employed in the module. It would seem that the social constructivist strategies used in the module assisted the students to improve their frameworks of ecological concepts. Data also tend to reveal that the students enjoyed the approach to learning and had positive views about the social constructivist teaching/learning approach. Project 3: With the advent of the new curriculum framework for South Africa, the outcomes based curriculum, it would seem that teachers could no longer approach teaching by the traditional transmission methods. Colleges of education have been criticised for producing teachers who do not seem to be adequately prepared for their job. Presently, the argument seems to be that teachers would need in-service education on a wide scale and the colleges of education would seem to be important in-service teacher education centres. This research, using case study methodology, investigated the potential of one of the colleges of education to become an in-service teacher education institution based on its physical and human resources.
- Full Text:
- Date Issued: 2002
Synthetic approaches to marine labdane diterpenes
- Authors: Wisch, Gregory Albert
- Date: 2002 , 2013-05-10
- Subjects: Diterpenes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4289 , http://hdl.handle.net/10962/d1003131 , Diterpenes
- Description: The work presented in this thesis describes the synthesis of labd-13-en-8ß, 15-diol (46) a stable reduced derivative of an unstable marine natural product aldehyde [8ß-hydroxylabd-13E-en-15-al (6)] isolated by Cimino, et al. from the skin of a Notaspidean mollusc Pleurobranchaea meckelii. The rationale for the synthesis was to provide sufficient 46 for eventual mild oxidation to 6 and investigation of the biological activity of this latter compound. (-)-Sclareol (32), a common diterpene synthetic precursor, was the starting point for the ten step synthesis of 46 described in this thesis. A search of the literature revealed that only one non stereospecific synthesis of 46 had been previously reported. To provide the necessary background to the synthetic component of this thesis, both the occurrence of labdane and ent-labdane in the marine environment and the use of sclareol in the synthesis of marine natural products, was reviewed. The initial step in the synthesis of 46 was the potassium permanganate oxidation of sclareol to give a bisnorlabdane ketone. Reduction of this ketone with lithium aluminium hydride produced a mixture of diols which, through t-butyldimethysilyl triflate protection, afforded a quantitative route to protecting the C-13 ketone in an effort to prevent unwanted intramolecular cyclization reactions. Dehydration of the tertiary alcohol moiety at C-8 with phosphorous oxychloride yielded the Δ⁸·¹⁵ exocyclic alkene required for the next oxidation step. Ozonolysis succeeded in producing the desired C-8 ketone after much deliberation and research into alternative oxidation strategies. Methyl lithium methylation quantitatively afforded the desired a-methyl substitution at C-8, identified at the onset as the key step in the synthesis. Tetra-butylarnmonium fluoride deprotection yielded the 8ß,13-dihydoxylated product, which was in turn subjected to a Swern oxidition to give the desired 8ß-hydroxy-bisnorlabda-13-one. A modified Horner-Wadsworth-Emmons reaction allowed for elaboration at C-13 to yield a to Δ¹³ olefin with a terminal C-15 ethyl ester. Diisobutylaluminium hydride reduction of the ester produced the desired labd-13-en-8ß, 15-diol (46) in a low overall yield of 3.4%. Although opportunities for optimization of at least three steps in the synthesis exist, time constraints prevented both optimization of these steps and an investigation of the oxidation of 46 to 6. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2002
- Authors: Wisch, Gregory Albert
- Date: 2002 , 2013-05-10
- Subjects: Diterpenes
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4289 , http://hdl.handle.net/10962/d1003131 , Diterpenes
- Description: The work presented in this thesis describes the synthesis of labd-13-en-8ß, 15-diol (46) a stable reduced derivative of an unstable marine natural product aldehyde [8ß-hydroxylabd-13E-en-15-al (6)] isolated by Cimino, et al. from the skin of a Notaspidean mollusc Pleurobranchaea meckelii. The rationale for the synthesis was to provide sufficient 46 for eventual mild oxidation to 6 and investigation of the biological activity of this latter compound. (-)-Sclareol (32), a common diterpene synthetic precursor, was the starting point for the ten step synthesis of 46 described in this thesis. A search of the literature revealed that only one non stereospecific synthesis of 46 had been previously reported. To provide the necessary background to the synthetic component of this thesis, both the occurrence of labdane and ent-labdane in the marine environment and the use of sclareol in the synthesis of marine natural products, was reviewed. The initial step in the synthesis of 46 was the potassium permanganate oxidation of sclareol to give a bisnorlabdane ketone. Reduction of this ketone with lithium aluminium hydride produced a mixture of diols which, through t-butyldimethysilyl triflate protection, afforded a quantitative route to protecting the C-13 ketone in an effort to prevent unwanted intramolecular cyclization reactions. Dehydration of the tertiary alcohol moiety at C-8 with phosphorous oxychloride yielded the Δ⁸·¹⁵ exocyclic alkene required for the next oxidation step. Ozonolysis succeeded in producing the desired C-8 ketone after much deliberation and research into alternative oxidation strategies. Methyl lithium methylation quantitatively afforded the desired a-methyl substitution at C-8, identified at the onset as the key step in the synthesis. Tetra-butylarnmonium fluoride deprotection yielded the 8ß,13-dihydoxylated product, which was in turn subjected to a Swern oxidition to give the desired 8ß-hydroxy-bisnorlabda-13-one. A modified Horner-Wadsworth-Emmons reaction allowed for elaboration at C-13 to yield a to Δ¹³ olefin with a terminal C-15 ethyl ester. Diisobutylaluminium hydride reduction of the ester produced the desired labd-13-en-8ß, 15-diol (46) in a low overall yield of 3.4%. Although opportunities for optimization of at least three steps in the synthesis exist, time constraints prevented both optimization of these steps and an investigation of the oxidation of 46 to 6. , KMBT_363 , Adobe Acrobat 9.54 Paper Capture Plug-in
- Full Text:
- Date Issued: 2002
The evolution of a security community through a process of integration: problems and prospects for the SADC region
- Authors: Šebek, Vita
- Date: 2002
- Subjects: Political stability -- Africa, Southern , Southern African Development Community , National security -- Africa, Southern , Africa, Southern -- Economic integration
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2831 , http://hdl.handle.net/10962/d1003041
- Description: This thesis examines the security problematic of African states and focuses more particularly on the SADC region. It links the security problematic with the transactionalist approach to (supra)national integration and the concept of a security community, introduced into internatIonal relations theory by Karl Deutsch and his colleagues. In relation to the (in)security of SADC member states, the thesis attempts to demonstrate that national integration of these states (i.e. the establishment of an amalgamated security community) has at least to accompany if not precede the establishment of a security community at the regional level (i.e. a pluralistic security community). Since threats to the security of SADC member states are mainly nonmilitary in nature, the 'realist' concept of security is broadened to include political, economic, societal and environmental aspects of security at different levels. Furthermore, Deutsch's concept of a security community is redefined in line with the 'new security thinking' and adapted to the situation in African states. Moreover, this thesis attempts to demonstrate that it is essential for SADC member states to become strong and socio-economically cohesive in order to improve their competitiveness in relation to developed states, especially in their ability to deal with internal and ransnational/regional threats to their security, which are (in)directly caused and perpetuated by the lack of national integration, inefficient state-making and underdevelopment - the sources of their weakness.
- Full Text:
- Date Issued: 2002
- Authors: Šebek, Vita
- Date: 2002
- Subjects: Political stability -- Africa, Southern , Southern African Development Community , National security -- Africa, Southern , Africa, Southern -- Economic integration
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:2831 , http://hdl.handle.net/10962/d1003041
- Description: This thesis examines the security problematic of African states and focuses more particularly on the SADC region. It links the security problematic with the transactionalist approach to (supra)national integration and the concept of a security community, introduced into internatIonal relations theory by Karl Deutsch and his colleagues. In relation to the (in)security of SADC member states, the thesis attempts to demonstrate that national integration of these states (i.e. the establishment of an amalgamated security community) has at least to accompany if not precede the establishment of a security community at the regional level (i.e. a pluralistic security community). Since threats to the security of SADC member states are mainly nonmilitary in nature, the 'realist' concept of security is broadened to include political, economic, societal and environmental aspects of security at different levels. Furthermore, Deutsch's concept of a security community is redefined in line with the 'new security thinking' and adapted to the situation in African states. Moreover, this thesis attempts to demonstrate that it is essential for SADC member states to become strong and socio-economically cohesive in order to improve their competitiveness in relation to developed states, especially in their ability to deal with internal and ransnational/regional threats to their security, which are (in)directly caused and perpetuated by the lack of national integration, inefficient state-making and underdevelopment - the sources of their weakness.
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- Date Issued: 2002