Applications of Baylis-Idllman methodology in the synthesis of chromene derivatives
- Authors: Nocanda, Xolani Wittleton
- Date: 2001
- Subjects: Heterocyclic chemistry , Heterocyclic compounds -- Derivatives
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4556 , http://hdl.handle.net/10962/d1018257
- Description: The reaction of salicylaldehyde with various activated alkenes, viz., methyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl sulfone, phenyl vinylsulfonate, acrolein and acrylonitrile, under Baylis-Hillman conditions, has been found to proceed with the chemoselective formation of chromene derivatives. The reaction conditions have been optimised and chromene derivatives have been obtained in isolated yields up to 87 %. The generality of the reaction, using 1,4-diazabicyclo[2.2.2]octane (DABCO), as the catalyst, and a heterogeneous (chloroform-water) solvent system, has been established using a range of salicylaldehyde derivatives,. including 2-hydroxynaphthaldehyde. The formation of chromene derivatives, under these conditions, has been assumed to proceed via an initial, Baylis-Hillman reaction, followed by cyclisation involving intramolecular conjugate addition, and subsequent dehydration. Evidence supporting this sequence has been obtained from the isolation ofBaylis-Hillman products from reactions involving the use of tertbutylclimethylsilyl-protected salicylaldehyde, 4-hydroxybenzaldehyde and tert-butyl acrylate as substrates. The potential of the ''Baylis-Hillman zwitterion" to participate as a donor species in Michael-type addition reactions has been explored and a series of climeric products has been isolated. The Baylis-Hillman methodology has also been successfully extended to the synthesis of sulfurcontaining heterocyclic systems, and a range of 3-substituted thiochromenes has been obtained in moderate yields, using 2,2'-dithiobenzaldehyde and various activated alkenes in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst. The electron-impact mass spectra of selected chromene and thiocbromene derivatives have been investigated permitting comparison of the fragmentation of the oxygen- and sulfur-containing analogues. In a study directed at the synthesis of potential HIV -1 protease inhibitors, chromene- and thiocbromene-containing analogues of the clinically useful drug, ritonavir, have been prepared. Thiochromene and chromene derivatives were converted to the corresponding 3 -carboxylic acids and coupled with a specially prepared, hydroxyethylene dipeptide isostere to afford ritonavir analogues containing cbromene and thiochromene termini in ca. 60% yield.
- Full Text:
- Date Issued: 2001
- Authors: Nocanda, Xolani Wittleton
- Date: 2001
- Subjects: Heterocyclic chemistry , Heterocyclic compounds -- Derivatives
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4556 , http://hdl.handle.net/10962/d1018257
- Description: The reaction of salicylaldehyde with various activated alkenes, viz., methyl vinyl ketone, ethyl vinyl ketone, phenyl vinyl sulfone, phenyl vinylsulfonate, acrolein and acrylonitrile, under Baylis-Hillman conditions, has been found to proceed with the chemoselective formation of chromene derivatives. The reaction conditions have been optimised and chromene derivatives have been obtained in isolated yields up to 87 %. The generality of the reaction, using 1,4-diazabicyclo[2.2.2]octane (DABCO), as the catalyst, and a heterogeneous (chloroform-water) solvent system, has been established using a range of salicylaldehyde derivatives,. including 2-hydroxynaphthaldehyde. The formation of chromene derivatives, under these conditions, has been assumed to proceed via an initial, Baylis-Hillman reaction, followed by cyclisation involving intramolecular conjugate addition, and subsequent dehydration. Evidence supporting this sequence has been obtained from the isolation ofBaylis-Hillman products from reactions involving the use of tertbutylclimethylsilyl-protected salicylaldehyde, 4-hydroxybenzaldehyde and tert-butyl acrylate as substrates. The potential of the ''Baylis-Hillman zwitterion" to participate as a donor species in Michael-type addition reactions has been explored and a series of climeric products has been isolated. The Baylis-Hillman methodology has also been successfully extended to the synthesis of sulfurcontaining heterocyclic systems, and a range of 3-substituted thiochromenes has been obtained in moderate yields, using 2,2'-dithiobenzaldehyde and various activated alkenes in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) as catalyst. The electron-impact mass spectra of selected chromene and thiocbromene derivatives have been investigated permitting comparison of the fragmentation of the oxygen- and sulfur-containing analogues. In a study directed at the synthesis of potential HIV -1 protease inhibitors, chromene- and thiocbromene-containing analogues of the clinically useful drug, ritonavir, have been prepared. Thiochromene and chromene derivatives were converted to the corresponding 3 -carboxylic acids and coupled with a specially prepared, hydroxyethylene dipeptide isostere to afford ritonavir analogues containing cbromene and thiochromene termini in ca. 60% yield.
- Full Text:
- Date Issued: 2001
Catalytic reactions of platinum group metal phthalocyanines
- Authors: Sekota, Mantoa Makoena C
- Date: 1999
- Subjects: Phthalocyanines Platinum group
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4396 , http://hdl.handle.net/10962/d1006151
- Description: The voltammetric behaviour of I-cysteine and other organic compounds such as hydrazine, hydroxylamine and methionine has been studied on GCE modified with phthalocyanine complexes of osmium, rhodium and ruthenium. For cysteine oxidation, the catalytic activity of the electrode was dependent the nature of the axial ligand. When cyanide and dimethylsulphoxide (DMSO) were used as axial ligands, giving (DMSO)(Cl)Rh(III)Pc, [(CN)₂Rh(III)Pc], (DMSO)₂0S(II)Pc and [(DMSO)₂Ru(II)Pc].2DMSO complexes, the peak current increased with repetitive scanning, indicating the increase in catalytic activity of the electrode after each scan. This behaviour was not observed when pyridine was used as axial ligand. The improvement of the catalytic activity of the GCE after the first scan has been attributed to the formation of the dimeric π-cation radical species at the electrode surface. Water soluble phthalocyanine complex ([(CN)₂Os(II)Pc]²⁻) and the tetramethyltetra-pyridinoporphyrazine complexes of Pd(II) and Pt(II), ([Pd(II)2,3Tmtppa(-2)]⁴⁺, [Pd(II)3,4Tmtppa(-2)]⁴⁺, [Pt(II)2,3Tmtppa(-2)]⁴⁺ and [Pt(II)3,4Tmtppa(-2)⁴⁺) have been prepared. [(CN)₂Os(II)Pc]²⁻ is soluble in water at pH greater 4 without the formation of dimers. The [M(II)Tmtppa(-2)]⁴⁺ (M = Pd or Pt) show high solubility in water and are stable only in acidic pHs. The cyclic voltammetry of the MPc and [M(II)Tmtppa(-2)]⁴⁺ complexes prepared, is also reported. The interactions of amino acids I-histidine and I-cysteine with the [M(II)Tmtppa(-2)]⁴⁺ complexes of Pd(II) and Pt(ll) were studied. All the [M(Il)Tmtppa(-2)]⁴⁺ are readily reduced to the monoanion species [M(Il)Tmtppa(-3)]³⁻ in the presence of histidine and cysteine. The rate constants for the interaction of [M(Il)Tmtppa(-2)]⁴⁺ complexes ofPt(II) and Pd(II), with histidine and cysteine range from approximately 2 x 10⁻³ to 0.26 dm³ mol⁻¹ s⁻¹. Kinetics of the interaction of [Co(Il)TSPc]⁴⁻ with amino acids, histidine and cysteine in pH 7.2 buffer were studied. The rate constants were found to be first order in both [Co(II)TSPc]⁴⁻ and the amino acid. The formation of [Co(III)TSPc]³⁻ in the presence of histidine occurred with the rate constant of 0.16 dm³ mol⁻¹ s⁻¹, whereas the formation of the [Co(I)TSPc]⁵⁻ species in the presence of cysteine gave the rate constant of 2.2 dm³ mo⁻¹ s¹. The relative quantum yield (QΔ) for singlet oxygen production by [(CN)₂Os(Il)Pc]²⁻, and [(CN)⁴Ru(II)Pc]²⁻ in DMF using diphenylisobenzofuran (DPBF) and a chemical quencher were determined. The quantum yield values were obtained as 0.39 ± 0.05 , and 0.76 ± 0.02 for [(CN₂Os(II)Pc]²⁻ and [(CN)₂Ru(II)Pc]²⁻ respectively. The differences in quantum yield values have been explained in terms of donor abilities of both the central metal and the axial ligands.
- Full Text:
- Date Issued: 1999
- Authors: Sekota, Mantoa Makoena C
- Date: 1999
- Subjects: Phthalocyanines Platinum group
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4396 , http://hdl.handle.net/10962/d1006151
- Description: The voltammetric behaviour of I-cysteine and other organic compounds such as hydrazine, hydroxylamine and methionine has been studied on GCE modified with phthalocyanine complexes of osmium, rhodium and ruthenium. For cysteine oxidation, the catalytic activity of the electrode was dependent the nature of the axial ligand. When cyanide and dimethylsulphoxide (DMSO) were used as axial ligands, giving (DMSO)(Cl)Rh(III)Pc, [(CN)₂Rh(III)Pc], (DMSO)₂0S(II)Pc and [(DMSO)₂Ru(II)Pc].2DMSO complexes, the peak current increased with repetitive scanning, indicating the increase in catalytic activity of the electrode after each scan. This behaviour was not observed when pyridine was used as axial ligand. The improvement of the catalytic activity of the GCE after the first scan has been attributed to the formation of the dimeric π-cation radical species at the electrode surface. Water soluble phthalocyanine complex ([(CN)₂Os(II)Pc]²⁻) and the tetramethyltetra-pyridinoporphyrazine complexes of Pd(II) and Pt(II), ([Pd(II)2,3Tmtppa(-2)]⁴⁺, [Pd(II)3,4Tmtppa(-2)]⁴⁺, [Pt(II)2,3Tmtppa(-2)]⁴⁺ and [Pt(II)3,4Tmtppa(-2)⁴⁺) have been prepared. [(CN)₂Os(II)Pc]²⁻ is soluble in water at pH greater 4 without the formation of dimers. The [M(II)Tmtppa(-2)]⁴⁺ (M = Pd or Pt) show high solubility in water and are stable only in acidic pHs. The cyclic voltammetry of the MPc and [M(II)Tmtppa(-2)]⁴⁺ complexes prepared, is also reported. The interactions of amino acids I-histidine and I-cysteine with the [M(II)Tmtppa(-2)]⁴⁺ complexes of Pd(II) and Pt(ll) were studied. All the [M(Il)Tmtppa(-2)]⁴⁺ are readily reduced to the monoanion species [M(Il)Tmtppa(-3)]³⁻ in the presence of histidine and cysteine. The rate constants for the interaction of [M(Il)Tmtppa(-2)]⁴⁺ complexes ofPt(II) and Pd(II), with histidine and cysteine range from approximately 2 x 10⁻³ to 0.26 dm³ mol⁻¹ s⁻¹. Kinetics of the interaction of [Co(Il)TSPc]⁴⁻ with amino acids, histidine and cysteine in pH 7.2 buffer were studied. The rate constants were found to be first order in both [Co(II)TSPc]⁴⁻ and the amino acid. The formation of [Co(III)TSPc]³⁻ in the presence of histidine occurred with the rate constant of 0.16 dm³ mol⁻¹ s⁻¹, whereas the formation of the [Co(I)TSPc]⁵⁻ species in the presence of cysteine gave the rate constant of 2.2 dm³ mo⁻¹ s¹. The relative quantum yield (QΔ) for singlet oxygen production by [(CN)₂Os(Il)Pc]²⁻, and [(CN)⁴Ru(II)Pc]²⁻ in DMF using diphenylisobenzofuran (DPBF) and a chemical quencher were determined. The quantum yield values were obtained as 0.39 ± 0.05 , and 0.76 ± 0.02 for [(CN₂Os(II)Pc]²⁻ and [(CN)₂Ru(II)Pc]²⁻ respectively. The differences in quantum yield values have been explained in terms of donor abilities of both the central metal and the axial ligands.
- Full Text:
- Date Issued: 1999
Characterization of the Hsp40 partner proteins of Plasmodium falciparum Hsp70
- Authors: Njunge, James Mwangi
- Date: 2014
- Subjects: Plasmodium falciparum , Heat shock proteins , Malaria -- Chemotherapy , Protein-protein interactions , Erythrocytes -- Biotechnology , Molecular chaperones , Host-parasite relationships , Mitochondria
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4117 , http://hdl.handle.net/10962/d1013186
- Description: Human malaria is an economically important disease caused by single-celled parasites of the Plasmodium genus whose biology displays great evolutionary adaptation to both its mammalian host and transmitting vectors. This thesis details the 70 kDa heat shock protein (Hsp70) and J protein chaperone complements in malaria parasites affecting humans, primates and rodents. Heat shock proteins comprise a family of evolutionary conserved and structurally related proteins that play a crucial role in maintaining the structural integrity of proteins during normal and stress conditions. They are considered future therapeutic targets in various cellular systems including Plasmodium falciparum. J proteins (Hsp40) canonically partner with Hsp70s during protein synthesis and folding, trafficking or targeting of proteins for degradation. However, in P. falciparum, these classes of proteins have also been implicated in aiding the active transport of parasite proteins to the erythrocyte cytosol following erythrocyte entry by the parasite. This host-parasite “cross-talk” results in tremendous modifications of the infected erythrocyte, imparting properties that allow it to adhere to the endothelium, preventing splenic clearance. The genome of P. falciparum encodes six Hsp70 homologues and a large number of J proteins that localize to the various intracellular compartments or are exported to the infected erythrocyte cytosol. Understanding the Hsp70-J protein interactions and/or partnerships is an essential step for drug target validation and illumination of parasite biology. A review of these chaperone complements across the Plasmodium species shows that P. falciparum possesses an expanded Hsp70-J protein complement compared to the rodent and primate infecting species. It further highlights how unique the P. falciparum chaperone complement is compared to the other Plasmodium species included in the analysis. In silico analysis showed that the genome of P. falciparum encodes approximately 49 J proteins, 19 of which contain a PEXEL motif that has been implicated in routing proteins to the infected erythrocyte. Most of these PEXEL containing J proteins are unique with no homologues in the human system and are considered as attractive drug targets. Very few of the predicted J proteins in P. falciparum have been experimentally characterized. To this end, cell biological and biochemical approaches were employed to characterize PFB0595w and PFD0462w (Pfj1) J proteins. The uniqueness of Pfj1 and the controversy in literature regarding its localization formed the basis for the experimental work. This is the first study showing that Pfj1 localizes to the mitochondrion in the intraerythrocytic stage of development of P. falciparum and has further proposed PfHsp70-3 as a potential Hsp70 partner. Indeed, attempts to heterologously express and purify Pfj1 for its characterization are described. It is also the first study that details the successful expression and purification of PfHsp70-3. Further, research findings have described for the first time the expression and localization of PFB0595w in the intraerythrocytic stages of P. falciparum development. Based on the cytosolic localization of both PFB0595w and PfHsp70-1, a chaperone – cochaperone partnership was proposed that formed the basis for the in vitro experiments. PFB0595w was shown for the first time to stimulate the ATPase activity of PfHsp70-1 pointing to a functional interaction. Preliminary surface plasmon spectroscopy analysis has revealed a potential interaction between PFB0595w and PfHsp70-1 but highlights the need for further related experiments to support the findings. Gel filtration analysis showed that PFB0595w exists as a dimer thereby confirming in silico predictions. Based on these observations, we conclude that PFB0595w may regulate the chaperone activity of PfHsp70-1 in the cytosol while Pfj1 may play a co-chaperoning role for PfHsp70-3 in the mitochondrion. Overall, this data is expected to increase the knowledge of the Hsp70-J protein partnerships in the erythrocytic stage of P. falciparum development, thereby enhancing the understanding of parasite biology.
- Full Text:
- Date Issued: 2014
- Authors: Njunge, James Mwangi
- Date: 2014
- Subjects: Plasmodium falciparum , Heat shock proteins , Malaria -- Chemotherapy , Protein-protein interactions , Erythrocytes -- Biotechnology , Molecular chaperones , Host-parasite relationships , Mitochondria
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4117 , http://hdl.handle.net/10962/d1013186
- Description: Human malaria is an economically important disease caused by single-celled parasites of the Plasmodium genus whose biology displays great evolutionary adaptation to both its mammalian host and transmitting vectors. This thesis details the 70 kDa heat shock protein (Hsp70) and J protein chaperone complements in malaria parasites affecting humans, primates and rodents. Heat shock proteins comprise a family of evolutionary conserved and structurally related proteins that play a crucial role in maintaining the structural integrity of proteins during normal and stress conditions. They are considered future therapeutic targets in various cellular systems including Plasmodium falciparum. J proteins (Hsp40) canonically partner with Hsp70s during protein synthesis and folding, trafficking or targeting of proteins for degradation. However, in P. falciparum, these classes of proteins have also been implicated in aiding the active transport of parasite proteins to the erythrocyte cytosol following erythrocyte entry by the parasite. This host-parasite “cross-talk” results in tremendous modifications of the infected erythrocyte, imparting properties that allow it to adhere to the endothelium, preventing splenic clearance. The genome of P. falciparum encodes six Hsp70 homologues and a large number of J proteins that localize to the various intracellular compartments or are exported to the infected erythrocyte cytosol. Understanding the Hsp70-J protein interactions and/or partnerships is an essential step for drug target validation and illumination of parasite biology. A review of these chaperone complements across the Plasmodium species shows that P. falciparum possesses an expanded Hsp70-J protein complement compared to the rodent and primate infecting species. It further highlights how unique the P. falciparum chaperone complement is compared to the other Plasmodium species included in the analysis. In silico analysis showed that the genome of P. falciparum encodes approximately 49 J proteins, 19 of which contain a PEXEL motif that has been implicated in routing proteins to the infected erythrocyte. Most of these PEXEL containing J proteins are unique with no homologues in the human system and are considered as attractive drug targets. Very few of the predicted J proteins in P. falciparum have been experimentally characterized. To this end, cell biological and biochemical approaches were employed to characterize PFB0595w and PFD0462w (Pfj1) J proteins. The uniqueness of Pfj1 and the controversy in literature regarding its localization formed the basis for the experimental work. This is the first study showing that Pfj1 localizes to the mitochondrion in the intraerythrocytic stage of development of P. falciparum and has further proposed PfHsp70-3 as a potential Hsp70 partner. Indeed, attempts to heterologously express and purify Pfj1 for its characterization are described. It is also the first study that details the successful expression and purification of PfHsp70-3. Further, research findings have described for the first time the expression and localization of PFB0595w in the intraerythrocytic stages of P. falciparum development. Based on the cytosolic localization of both PFB0595w and PfHsp70-1, a chaperone – cochaperone partnership was proposed that formed the basis for the in vitro experiments. PFB0595w was shown for the first time to stimulate the ATPase activity of PfHsp70-1 pointing to a functional interaction. Preliminary surface plasmon spectroscopy analysis has revealed a potential interaction between PFB0595w and PfHsp70-1 but highlights the need for further related experiments to support the findings. Gel filtration analysis showed that PFB0595w exists as a dimer thereby confirming in silico predictions. Based on these observations, we conclude that PFB0595w may regulate the chaperone activity of PfHsp70-1 in the cytosol while Pfj1 may play a co-chaperoning role for PfHsp70-3 in the mitochondrion. Overall, this data is expected to increase the knowledge of the Hsp70-J protein partnerships in the erythrocytic stage of P. falciparum development, thereby enhancing the understanding of parasite biology.
- Full Text:
- Date Issued: 2014
Enabling cumulative knowledge-building through teaching: a legitimation code theory analysis of pedagogic practice in law and political science
- Authors: Clarence, Sherran
- Date: 2014
- Subjects: Law -- Study and teaching (Higher) -- South Africa Political science -- Study and teaching (Higher) -- South Africa Education, Higher -- South Africa College teaching -- South Africa Knowledge, Theory of Social realism
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1966 , http://hdl.handle.net/10962/d1011763
- Description: Much current research and practice in teaching and learning in higher education tends to overfocus on social aspects of education; on how rather than what students are learning. Much of this research and practice is influenced by constructivism, which has a relativist stance on knowledge, generally arguing, contra positivism, that knowledge is constructed in socio-historical contexts and largely inseparable from those who construct it and from issues of power. This leads to a confusion of knowledge with knowing, and knowledge is thus obscured as an object of study because it is only seen or understood as knowing or as a subject of learning and teaching. This ‘knowledge-blindness’ (Maton 2013a: 4) is problematic in higher education because knowledge and knowing are two separate parts of educational fields, and while they need to be brought together to provide a whole account of these fields, they also need to be analysed and understood separately to avoid blurring necessary boundaries and to avoid confusing knowledge itself with how it can be known. Being able to see and analyse knowledge as an object with its own properties and powers is crucial for both epistemological access and social inclusion and justice, because knowledge and knowledge practices are at the heart of academic disciplines in universities. Social realism offers an alternative to the dilemma brought about by constructivism’s tendency towards knowledge-blindness. Social realism argues that it is possible to see and analyse both actors within social fields of practice as well as knowledge as something that is produced by these actors but also about more than just these actors and their practices; thus knowledge can be understood as emergent from these practices and fields but not reducible to them (Maton & Moore 2010). Social realism, drawing from Roy Bhaskar’s critical realist philosophy (1975, 2008), is intent on looking at the real structures and mechanisms that lie beneath appearances and practices in order to understand the ways in which these practices are shaped, and change over time. Legitimation Code Theory is a realist conceptual framework that has, as its central aim, the uncovering and analysis of organising principles that shape and change intellectual and education fields of production and reproduction of knowledge. In other words, the conceptual tools Legitimation Code Theory offers can enable an analysis of both knowledge and knowers within relational social fields of practice by enabling the analysis of the ways in which these fields, such as academic disciplines, are organised and how knowledge and knowing are understood in educational practice. This study draws on social realism more broadly and Legitimation Code Theory specifically to develop a relatively novel conceptual and explanatory framework within which to analyse and answer its central question regarding how to enable cumulative knowledge building through pedagogic practice. Using qualitative data from two academic disciplines, Law and Political Science, which was analysed using a set of conceptual and analytical tools drawn from Legitimation Code Theory, this study shows that the more nuanced and layered accounts of pedagogy that have been generated are able to provide valuable insights into what lecturers are doing as they teach in terms of helping students to acquire, use and produce disciplinary and ‘powerful’ knowledge (Young 2008b). Further, the study demonstrates that the organising principles underlying academic disciplines have a profound effect on how the role of the knower and the place or purpose of knowledge is understood in pedagogy and this affects how the pedagogy is designed and enacted. This study has argued that if we can research pedagogy rigorously using tools that allow us to see the real mechanisms and principles influencing and shaping it, and if we can reclaim the role of disciplinary knowledge as a central part of the pedagogic relationship between lecturer and students, then we can begin to see how teaching both enables and constrains cumulative learning. Further, we can change pedagogy to better enable cumulative learning and greater epistemological access to disciplinary knowledge and related practices for greater numbers of students. The study concludes by suggesting that the conceptual tools offered by Legitimation Code Theory can provide academic lecturers with a set of tools that can begin to enable them to 'see' and understand their own teaching more clearly, as well as the possible gaps between what they are teaching and what their students are learning. This study argues that a social realist approach to the study of pedagogy such as the one used here can begin not only to enable changes in pedagogy aimed at filling these gaps but also begin to provide a more rigorous theoretical and practical approach to analysing, understanding and enacting pedagogic practice. This, in turn, can lead to more socially just and inclusive student learning and epistemic and social access to the powerful knowledge and ways of knowing in their disciplines.
- Full Text:
- Date Issued: 2014
- Authors: Clarence, Sherran
- Date: 2014
- Subjects: Law -- Study and teaching (Higher) -- South Africa Political science -- Study and teaching (Higher) -- South Africa Education, Higher -- South Africa College teaching -- South Africa Knowledge, Theory of Social realism
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1966 , http://hdl.handle.net/10962/d1011763
- Description: Much current research and practice in teaching and learning in higher education tends to overfocus on social aspects of education; on how rather than what students are learning. Much of this research and practice is influenced by constructivism, which has a relativist stance on knowledge, generally arguing, contra positivism, that knowledge is constructed in socio-historical contexts and largely inseparable from those who construct it and from issues of power. This leads to a confusion of knowledge with knowing, and knowledge is thus obscured as an object of study because it is only seen or understood as knowing or as a subject of learning and teaching. This ‘knowledge-blindness’ (Maton 2013a: 4) is problematic in higher education because knowledge and knowing are two separate parts of educational fields, and while they need to be brought together to provide a whole account of these fields, they also need to be analysed and understood separately to avoid blurring necessary boundaries and to avoid confusing knowledge itself with how it can be known. Being able to see and analyse knowledge as an object with its own properties and powers is crucial for both epistemological access and social inclusion and justice, because knowledge and knowledge practices are at the heart of academic disciplines in universities. Social realism offers an alternative to the dilemma brought about by constructivism’s tendency towards knowledge-blindness. Social realism argues that it is possible to see and analyse both actors within social fields of practice as well as knowledge as something that is produced by these actors but also about more than just these actors and their practices; thus knowledge can be understood as emergent from these practices and fields but not reducible to them (Maton & Moore 2010). Social realism, drawing from Roy Bhaskar’s critical realist philosophy (1975, 2008), is intent on looking at the real structures and mechanisms that lie beneath appearances and practices in order to understand the ways in which these practices are shaped, and change over time. Legitimation Code Theory is a realist conceptual framework that has, as its central aim, the uncovering and analysis of organising principles that shape and change intellectual and education fields of production and reproduction of knowledge. In other words, the conceptual tools Legitimation Code Theory offers can enable an analysis of both knowledge and knowers within relational social fields of practice by enabling the analysis of the ways in which these fields, such as academic disciplines, are organised and how knowledge and knowing are understood in educational practice. This study draws on social realism more broadly and Legitimation Code Theory specifically to develop a relatively novel conceptual and explanatory framework within which to analyse and answer its central question regarding how to enable cumulative knowledge building through pedagogic practice. Using qualitative data from two academic disciplines, Law and Political Science, which was analysed using a set of conceptual and analytical tools drawn from Legitimation Code Theory, this study shows that the more nuanced and layered accounts of pedagogy that have been generated are able to provide valuable insights into what lecturers are doing as they teach in terms of helping students to acquire, use and produce disciplinary and ‘powerful’ knowledge (Young 2008b). Further, the study demonstrates that the organising principles underlying academic disciplines have a profound effect on how the role of the knower and the place or purpose of knowledge is understood in pedagogy and this affects how the pedagogy is designed and enacted. This study has argued that if we can research pedagogy rigorously using tools that allow us to see the real mechanisms and principles influencing and shaping it, and if we can reclaim the role of disciplinary knowledge as a central part of the pedagogic relationship between lecturer and students, then we can begin to see how teaching both enables and constrains cumulative learning. Further, we can change pedagogy to better enable cumulative learning and greater epistemological access to disciplinary knowledge and related practices for greater numbers of students. The study concludes by suggesting that the conceptual tools offered by Legitimation Code Theory can provide academic lecturers with a set of tools that can begin to enable them to 'see' and understand their own teaching more clearly, as well as the possible gaps between what they are teaching and what their students are learning. This study argues that a social realist approach to the study of pedagogy such as the one used here can begin not only to enable changes in pedagogy aimed at filling these gaps but also begin to provide a more rigorous theoretical and practical approach to analysing, understanding and enacting pedagogic practice. This, in turn, can lead to more socially just and inclusive student learning and epistemic and social access to the powerful knowledge and ways of knowing in their disciplines.
- Full Text:
- Date Issued: 2014
Interactions between figs (Ficus spp., Moraceae) and fig wasps (Chalcidoidea, Agaonidae)
- Authors: Ware, Anthony Brian
- Date: 1993
- Subjects: Fig -- South Africa Fig wasp -- South Africa Pollination Agaonidae Chalcid wasps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5719 , http://hdl.handle.net/10962/d1005405
- Description: Fig trees (Ficus spp., Moraceae) and fig wasps (Chalcidoidea, Agaonidae) are uniquely associated. In one fig wasp group, the pollinators (Agaoninae), each species is generally host species-specific. The relationship is one of obligate mutualism where the wasps provide pollination services and in return utilises some of the ovules for larval development. Non-pollinating fig wasps (generally belonging to subfamilies other than the Agaoninae) may be gallers or parasitoids, and can also be host species-specific. In the accompanying studies we examined the factors governing the interactions between fig wasps and their host trees. Surveys of fig trees and their associated pollinating fig wasps conducted in southern Africa, Madagascar and The Comores generally confirmed their specific relationships. An examination of F. sycomorlls in Madagascar resulted in the reclassification of F. sakalavarum as a distinct species with its own specific pollinator species. Biological and chemical evidence is presented demonstrating that the pollinators were able to distinguish their hosts through volatiles which emanated from the figs when they were ready to be pollinated. Environmental factors were found to influence wasp behaviour. Ambient temperature governed the timing of wasp emergence from their natal figs. When dispersing from their natal figs, the fig wasps flew upwards and then were blown downwind. Once nearing trees bearing figs ready to be pollinated, the wasps lost height and flew upwind towards the trees. E. baijnathi females apparently avoided figs which already contained a conspecific foundress. Scanning electron microscope studies of pollinating female fig wasp antennae showed that while all the species possessed multiporous plate sensilla, in only a few species were these sensilla elongated. Multiporous plate sensilla elongation is rare or absent among other female chalcids and may have evolved within the Agaoninae in order to facilitate their location on receptive host figs. Pollinator choice specificity appears to break down in a number of cases. In the first case examined, two pollinator species were recorded from the figs of African F. sycomorus. One. C. arabicus, pollinates the figs while the other, C. galili, acts as a 'cuckoo' by utilising some of ovules for oviposition without providing pollen. In the second case three pollinating fig wasp species were recorded from the rigs of F. lutea. Two were found to be incidental visitors and were not specifically attracted to the tree. The hybrid seeds from these crosses were successfully germinated but the seedlings did not grow passed the cotyledon stage of their development. In the concluding study the consequences of Ficus phenology and the structure of the fig's unusual inflorescence on the nonpollinating fig wasp community were examined. Various factors affecting the population levels and species richness were also examined. Future possible research directions were discussed.
- Full Text:
- Date Issued: 1993
- Authors: Ware, Anthony Brian
- Date: 1993
- Subjects: Fig -- South Africa Fig wasp -- South Africa Pollination Agaonidae Chalcid wasps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5719 , http://hdl.handle.net/10962/d1005405
- Description: Fig trees (Ficus spp., Moraceae) and fig wasps (Chalcidoidea, Agaonidae) are uniquely associated. In one fig wasp group, the pollinators (Agaoninae), each species is generally host species-specific. The relationship is one of obligate mutualism where the wasps provide pollination services and in return utilises some of the ovules for larval development. Non-pollinating fig wasps (generally belonging to subfamilies other than the Agaoninae) may be gallers or parasitoids, and can also be host species-specific. In the accompanying studies we examined the factors governing the interactions between fig wasps and their host trees. Surveys of fig trees and their associated pollinating fig wasps conducted in southern Africa, Madagascar and The Comores generally confirmed their specific relationships. An examination of F. sycomorlls in Madagascar resulted in the reclassification of F. sakalavarum as a distinct species with its own specific pollinator species. Biological and chemical evidence is presented demonstrating that the pollinators were able to distinguish their hosts through volatiles which emanated from the figs when they were ready to be pollinated. Environmental factors were found to influence wasp behaviour. Ambient temperature governed the timing of wasp emergence from their natal figs. When dispersing from their natal figs, the fig wasps flew upwards and then were blown downwind. Once nearing trees bearing figs ready to be pollinated, the wasps lost height and flew upwind towards the trees. E. baijnathi females apparently avoided figs which already contained a conspecific foundress. Scanning electron microscope studies of pollinating female fig wasp antennae showed that while all the species possessed multiporous plate sensilla, in only a few species were these sensilla elongated. Multiporous plate sensilla elongation is rare or absent among other female chalcids and may have evolved within the Agaoninae in order to facilitate their location on receptive host figs. Pollinator choice specificity appears to break down in a number of cases. In the first case examined, two pollinator species were recorded from the figs of African F. sycomorus. One. C. arabicus, pollinates the figs while the other, C. galili, acts as a 'cuckoo' by utilising some of ovules for oviposition without providing pollen. In the second case three pollinating fig wasp species were recorded from the rigs of F. lutea. Two were found to be incidental visitors and were not specifically attracted to the tree. The hybrid seeds from these crosses were successfully germinated but the seedlings did not grow passed the cotyledon stage of their development. In the concluding study the consequences of Ficus phenology and the structure of the fig's unusual inflorescence on the nonpollinating fig wasp community were examined. Various factors affecting the population levels and species richness were also examined. Future possible research directions were discussed.
- Full Text:
- Date Issued: 1993
L’etude comparative des elements merveilleux dans trois epopees africaines: Soundjata ou I’epopee mandingue, Emperor Shaka The Great: a Zulu Epic et Nsongo’a Lianja: I’epopee nationale des Nkundo
- Authors: Nkaongami, Josue Bosange
- Date: 2017
- Language: French , English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5590 , vital:20944
- Description: This thesis is a comparative study in Francophone literature which analyses the supernatural factors in three African epics, namely the Sundiata or Mandingo Epic from West Africa by Djibril Tasmir Niane (1960), Emperor Shaka The Great : A Zulu Epic from Southern Africa by Mazisi Kunene (1979), and Nsongo’a Lianja : the National Epic of Nkundo People from Central Africa by Edmond Boelaert (1949). The study analyses similarities and differences between the supernatural figures in these epics and their respective societies using contextual and socio-critical theories. In this thesis it is demonstrated that the presence of supernatural forces is a sine qua non condition for the existence of the epic in the sense that : “the essential mark of the heroic personality in many African folk epics is its reliance on supernatural resources” (Okpewho 1979 : 119). This study shows that in Africa, supernatural forces play vital roles in the society and therefore dominate the African oral epic traditions. Furthermore, the study is significant in the sense that it tries to describe the worldview, especially the religious and cultural beliefs of the particular society or group that produces the epic. The thesis is made up of six chapters. In the first chapter, I outline the study’s subject matter, its aims and objectives, its significance, its assumptions and methodology. In the second chapter, I examine the impact of supernatural devices on the lives of the epic heroes Sundiata, Shaka, and Lianja, the predictions and divinations about their births, childhoods, exiles or epic journeys, their ascension to the throne as well as their genealogies and deaths. Such analysis allows one to identify the supernatural factors surrounding each stage of the life of the heroes, and to understand further the importance of supernatural forces in the communities and institutions where the heroes exercise their powers. In the third chapter, I discuss the typology of the supernatural forces in the heroic epics Sundiata, Shaka and Lianja, using Greimas’s theory of actants. I divide the characters into protagonists, accessories and opponents. In the fourth chapter, I examine the sources of the supernatural forces prevailing on Sundiata, Shaka, and Lianja. The chapter shows how supernatural agents act on the epic heroes and how these supernatural beings make or mar them in the course of the narratives. In the fifth chapter, I investigate the supernatural factors acting on the heroes’ opponents, and in chapter six, I examine the supernatural forces and heroism of the women in the three epics. In the conclusion, I demonstrate that this analysis of supernatural factors enables us not only to appreciate their place and function in the three African epics under study, but also opens a window onto the culture of the Mandingo, Zulu, and Mongo People’s : their activities, beliefs, taboos and the rules which organise their respective societies. , This thesis is presented in two parts: French and English.
- Full Text:
- Date Issued: 2017
- Authors: Nkaongami, Josue Bosange
- Date: 2017
- Language: French , English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5590 , vital:20944
- Description: This thesis is a comparative study in Francophone literature which analyses the supernatural factors in three African epics, namely the Sundiata or Mandingo Epic from West Africa by Djibril Tasmir Niane (1960), Emperor Shaka The Great : A Zulu Epic from Southern Africa by Mazisi Kunene (1979), and Nsongo’a Lianja : the National Epic of Nkundo People from Central Africa by Edmond Boelaert (1949). The study analyses similarities and differences between the supernatural figures in these epics and their respective societies using contextual and socio-critical theories. In this thesis it is demonstrated that the presence of supernatural forces is a sine qua non condition for the existence of the epic in the sense that : “the essential mark of the heroic personality in many African folk epics is its reliance on supernatural resources” (Okpewho 1979 : 119). This study shows that in Africa, supernatural forces play vital roles in the society and therefore dominate the African oral epic traditions. Furthermore, the study is significant in the sense that it tries to describe the worldview, especially the religious and cultural beliefs of the particular society or group that produces the epic. The thesis is made up of six chapters. In the first chapter, I outline the study’s subject matter, its aims and objectives, its significance, its assumptions and methodology. In the second chapter, I examine the impact of supernatural devices on the lives of the epic heroes Sundiata, Shaka, and Lianja, the predictions and divinations about their births, childhoods, exiles or epic journeys, their ascension to the throne as well as their genealogies and deaths. Such analysis allows one to identify the supernatural factors surrounding each stage of the life of the heroes, and to understand further the importance of supernatural forces in the communities and institutions where the heroes exercise their powers. In the third chapter, I discuss the typology of the supernatural forces in the heroic epics Sundiata, Shaka and Lianja, using Greimas’s theory of actants. I divide the characters into protagonists, accessories and opponents. In the fourth chapter, I examine the sources of the supernatural forces prevailing on Sundiata, Shaka, and Lianja. The chapter shows how supernatural agents act on the epic heroes and how these supernatural beings make or mar them in the course of the narratives. In the fifth chapter, I investigate the supernatural factors acting on the heroes’ opponents, and in chapter six, I examine the supernatural forces and heroism of the women in the three epics. In the conclusion, I demonstrate that this analysis of supernatural factors enables us not only to appreciate their place and function in the three African epics under study, but also opens a window onto the culture of the Mandingo, Zulu, and Mongo People’s : their activities, beliefs, taboos and the rules which organise their respective societies. , This thesis is presented in two parts: French and English.
- Full Text:
- Date Issued: 2017
The investigation, development and characterisation of novel zirconium-based tanning agents
- Guthrie-Strachan, Jeffry James
- Authors: Guthrie-Strachan, Jeffry James
- Date: 2006
- Subjects: Zirconium Tanning Leather
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4319 , http://hdl.handle.net/10962/d1004977
- Description: Various oxygen- and nitrogen-donor ligands were investigated as potential zirconium masking agents in zirconium tanning. α-Hydroxycarboxylic acid ligands were identified as effective zirconium(IV) chelators in acidic aqueous solution. Glycolic acid, lactic acid, mandelic acid, 4-hydroxymandelic acid, 4-chloromandelic acid and 4-bromomandelic acid complexes were synthesised, isolated and characterised using a range of analytical techniques. Linear Free Energy Relationships were examined to optimise the stability of the zirconium complexes. Hammett [sigma] plots and Yukawa-Tsuno modified σ plots of the mandelate ligand and zirconium complex series indicated that inductive effects dominate within the benzene ring, however, mesomeric effects are significant outside the ring. Zirconium 4-hydroxymandelate complex solutions were identified as the most effective tanning agents and achieved shrinkage temperatures of 80 and 97ºC for hide powder and goatskin, respectively. The zirconium and 4-hydroxymandelic acid interact synergistically to yield leather equivalent to combination tanned leather in one step. Tanning was performed similarly to vegetable tanning processes with a pickle pH of approximately 5 and fixation was achieved upon acidification. Pilot-scale tanning of goatskin produced white tanned leathers and crust leathers which were physically and aesthetically comparable to matched chromium tanned material.
- Full Text:
- Date Issued: 2006
- Authors: Guthrie-Strachan, Jeffry James
- Date: 2006
- Subjects: Zirconium Tanning Leather
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4319 , http://hdl.handle.net/10962/d1004977
- Description: Various oxygen- and nitrogen-donor ligands were investigated as potential zirconium masking agents in zirconium tanning. α-Hydroxycarboxylic acid ligands were identified as effective zirconium(IV) chelators in acidic aqueous solution. Glycolic acid, lactic acid, mandelic acid, 4-hydroxymandelic acid, 4-chloromandelic acid and 4-bromomandelic acid complexes were synthesised, isolated and characterised using a range of analytical techniques. Linear Free Energy Relationships were examined to optimise the stability of the zirconium complexes. Hammett [sigma] plots and Yukawa-Tsuno modified σ plots of the mandelate ligand and zirconium complex series indicated that inductive effects dominate within the benzene ring, however, mesomeric effects are significant outside the ring. Zirconium 4-hydroxymandelate complex solutions were identified as the most effective tanning agents and achieved shrinkage temperatures of 80 and 97ºC for hide powder and goatskin, respectively. The zirconium and 4-hydroxymandelic acid interact synergistically to yield leather equivalent to combination tanned leather in one step. Tanning was performed similarly to vegetable tanning processes with a pickle pH of approximately 5 and fixation was achieved upon acidification. Pilot-scale tanning of goatskin produced white tanned leathers and crust leathers which were physically and aesthetically comparable to matched chromium tanned material.
- Full Text:
- Date Issued: 2006
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