A bioinorganic study of some cobalt(II) Schiff base complexes of variously substituted hydroxybenzaldimines
- Authors: Shaibu, Rafiu Olarewaju
- Date: 2008
- Subjects: Cobalt Schiff bases Artemia Spectrum analysis Ligands -- Analysis Bioinorganic chemistry Antineoplastic agents Cancer -- Chemotherapy Ligands -- Toxicity
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4394 , http://hdl.handle.net/10962/d1006009
- Description: Syntheses of Schiff bases were carried out by reacting salicylaldyhde, ortho-vanillin, para-vanillin or vanillin with aniline, 1-aminonaphthalene, 4- and 3-aminopyridine, and also with 2- and 3-aminomethylpyridine. The various Schiff bases obtained from the condensation reaction were reacted with CoCl₂.6H₂0, triethylamine stripped CoCl₂.6H₂0 or Co(CH₃COO)₂ to form cobalt(Il) complexes of ratio 2:1. The complexes obtained from cobalt chloride designated as the "A series" are of the general formulae ML₂X₂.nH₂0 , (L = Schiff base, X = chlorine) while those obtained from cobalt acetate or triethylamine stripped cobalt chloride denoted as "B" and C" are of the general formulae ML₂. nH₂0. The few complexes that do not follow the general formulae highlighted above are: IA [M(HL)₃.Cl₂], (L = N-phenylsalicylaldimine), 4A = (MLCl₂), (L = N-phenylvanaldiminato), 7 A and 21 A (ML₂), (L = N-naphthyl-o-vanaldiminato, and N-methy-2-pyridylsalicylaldiminato respectively), 8A = MLCI, (L = N-naphthylvanaldiminato), 12A = M₂L₃Cl₂, (L = N-4-pyridylvanaldiminato), 15A (MLCI), (L = N-3-pyridyl-o-vanaldiminato). The ligands and their complexes were characterized using elemental analyses and cobalt analysis using ICP, FT-IR spectroscopy (mid and far-IR), NIR-UV/vis (diffuse reflectance), UV/vis in an aprotic and a protic solvents, while mass spectrometry, ¹HNMR and ¹³CNMR, was used to further characterized the ligands. The tautomeric nature of the Schiff bases were determined by examining the behaviour of Schiff bases and their complexes in a protic (e.g. MeOH) and non-protic (e.g. DMF) polar solvents. The effects of solvents on the electronic behaviour of the compounds were also examined. Using CDCl₃, the NMR technique was further used to confirm the structures of the Schiff bases. The tentative geometry of the complexes was determined using the spectra information obtained from the far infrared and the diffuse reflectance spectroscopy. With few exceptions, most of the "A" series are tetrahedral or distorted tetrahedral, while the "B + C" are octahedral or pseudooctahedral. A small number of complexes are assigned square-planar geometry owing to the characteristic spectral behaviour shown. In order to determine their biological activity, two biological assay methods (antimicrobial testing and brine shrimp lethality assay) were used. Using disc method, the bacteriostatic and fungicidal activities of the various Schiff bases and their respective complexes to Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa as well as Aspergillus niger, were measured and the average inhibition zones are tabulated and analysed. Both the Schiff bases and their complexes showed varying bacteriostatic and fungicidal activity against the bacteria and fungus tested. The inhibition activity is concentration dependent and potential antibiotic and fungicides are identified. To determine the toxicity of the ligands and their corresponding cobalt(II) complexes, brine shrimp lethality assay was used. The LD₅₀ of the tested compounds were calculated and the results obtained were tabulated for comparison.
- Full Text:
- Date Issued: 2008
- Authors: Shaibu, Rafiu Olarewaju
- Date: 2008
- Subjects: Cobalt Schiff bases Artemia Spectrum analysis Ligands -- Analysis Bioinorganic chemistry Antineoplastic agents Cancer -- Chemotherapy Ligands -- Toxicity
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4394 , http://hdl.handle.net/10962/d1006009
- Description: Syntheses of Schiff bases were carried out by reacting salicylaldyhde, ortho-vanillin, para-vanillin or vanillin with aniline, 1-aminonaphthalene, 4- and 3-aminopyridine, and also with 2- and 3-aminomethylpyridine. The various Schiff bases obtained from the condensation reaction were reacted with CoCl₂.6H₂0, triethylamine stripped CoCl₂.6H₂0 or Co(CH₃COO)₂ to form cobalt(Il) complexes of ratio 2:1. The complexes obtained from cobalt chloride designated as the "A series" are of the general formulae ML₂X₂.nH₂0 , (L = Schiff base, X = chlorine) while those obtained from cobalt acetate or triethylamine stripped cobalt chloride denoted as "B" and C" are of the general formulae ML₂. nH₂0. The few complexes that do not follow the general formulae highlighted above are: IA [M(HL)₃.Cl₂], (L = N-phenylsalicylaldimine), 4A = (MLCl₂), (L = N-phenylvanaldiminato), 7 A and 21 A (ML₂), (L = N-naphthyl-o-vanaldiminato, and N-methy-2-pyridylsalicylaldiminato respectively), 8A = MLCI, (L = N-naphthylvanaldiminato), 12A = M₂L₃Cl₂, (L = N-4-pyridylvanaldiminato), 15A (MLCI), (L = N-3-pyridyl-o-vanaldiminato). The ligands and their complexes were characterized using elemental analyses and cobalt analysis using ICP, FT-IR spectroscopy (mid and far-IR), NIR-UV/vis (diffuse reflectance), UV/vis in an aprotic and a protic solvents, while mass spectrometry, ¹HNMR and ¹³CNMR, was used to further characterized the ligands. The tautomeric nature of the Schiff bases were determined by examining the behaviour of Schiff bases and their complexes in a protic (e.g. MeOH) and non-protic (e.g. DMF) polar solvents. The effects of solvents on the electronic behaviour of the compounds were also examined. Using CDCl₃, the NMR technique was further used to confirm the structures of the Schiff bases. The tentative geometry of the complexes was determined using the spectra information obtained from the far infrared and the diffuse reflectance spectroscopy. With few exceptions, most of the "A" series are tetrahedral or distorted tetrahedral, while the "B + C" are octahedral or pseudooctahedral. A small number of complexes are assigned square-planar geometry owing to the characteristic spectral behaviour shown. In order to determine their biological activity, two biological assay methods (antimicrobial testing and brine shrimp lethality assay) were used. Using disc method, the bacteriostatic and fungicidal activities of the various Schiff bases and their respective complexes to Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa as well as Aspergillus niger, were measured and the average inhibition zones are tabulated and analysed. Both the Schiff bases and their complexes showed varying bacteriostatic and fungicidal activity against the bacteria and fungus tested. The inhibition activity is concentration dependent and potential antibiotic and fungicides are identified. To determine the toxicity of the ligands and their corresponding cobalt(II) complexes, brine shrimp lethality assay was used. The LD₅₀ of the tested compounds were calculated and the results obtained were tabulated for comparison.
- Full Text:
- Date Issued: 2008
The rhizosphere as a bioprocess environment for the bioconversion of hard coal
- Authors: Igbinigie, Eric Egbe
- Date: 2008
- Subjects: Rhizosphere Biotechnology Bermuda grass Coal -- Microbiology Biomass conversion
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3924 , http://hdl.handle.net/10962/d1003983
- Description: Fundamental processes involved in the microbial degradation of coal and its derivatives have been well investigated and documented over the past two decades. However, limited progress in industrial application has been identified as bottleneck in further active development of the field. The sporadic and unanticipated growth of Cynodon dactylon (Bermuda grass) has been observed on the surface of some coal dumps in the Witbank coal mining area of South Africa. Preliminary investigations showed the formation of a humic soil-like material from the breakdown of hard coal in the root zone of these plants. The potential of this system to contribute to industrial scale bioprocessing of hard coal was investigated. This study involved an investigation of the C. dactylon/coal rhizosphere environment and demonstrated the presence of fungal species with known coal bioconversion capability. Amongst these Neosartorya fischeri was identified and its activity in coal bioconversion was described for the first time. Cynodon dactylon plant roots were also shown to be colonized by mycorrhizal fungi including Glomus, Paraglomus and Gigaspora species. The role of plant photosynthate translocation into the root zone, providing organic carbon supplementation of fungal coal bioconversion was investigated in deep liquid culture with the N. fischeri isolate used as the biocatalyst. Organic acids, sugars and complex organic carbon sources were investigated and it was shown that glutamate provided significant enhancement of bioconversion activity in this system. The performance of N. fischeri in coal bioconversion was compared with Phanaerochaete chrysosporium and Trametes versicolor, both previously described fungal species in the coal bioconversion application. Fourier transform infrared spectroscopy indicated more pronounced oxidation and introduction of nitro groups in the matrix of the humic acid product of coal bioconversion in N. fischeri and P. chrysosporium than for T. versicolor. Macro-elemental analysis of biomass-bound humic acid obtained from the N. fischeri catalyzed reaction showed an increase in the oxygen and nitrogen components and coupled with a reduction in carbon and hydrogen. Pyrolysis gas chromatography mass spectroscopy further supported the proposal that the mechanism of bioconversion involves oxygen and nitrogen insertion into the coal structure. The C. dactylon bituminous hard coal dump environment was simulated in a fixed-bed perfusion column bioreactor in which the contribution of organic supplement by the plant/mycorrhizal component of the system was investigated. The results enabled the proposal of a descriptive model accounting for the performance of the system in which the plant/mycorrhizal component introduces organic substances into the root zone. The non-mycorrhizal fungi utilize the organic carbon supplement in its attack on the coal substrate, breaking it down, and releasing plant nutrients and a soil-like substrate which in turn enables the growth of C. dactylon in this hostile environment. Based on these results, the Stacked Heap Coal Bioreactor concept was developed as a large-scale industrial bioprocess application based on heap-leach mineral processing technology. Field studies have confirmed that bituminous hard coal can be converted to a humic acid rich substrate in a stacked heap system inoculated with mycorrhizal and N. fischeri cultures and planted with C. dactylon.
- Full Text:
- Date Issued: 2008
- Authors: Igbinigie, Eric Egbe
- Date: 2008
- Subjects: Rhizosphere Biotechnology Bermuda grass Coal -- Microbiology Biomass conversion
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3924 , http://hdl.handle.net/10962/d1003983
- Description: Fundamental processes involved in the microbial degradation of coal and its derivatives have been well investigated and documented over the past two decades. However, limited progress in industrial application has been identified as bottleneck in further active development of the field. The sporadic and unanticipated growth of Cynodon dactylon (Bermuda grass) has been observed on the surface of some coal dumps in the Witbank coal mining area of South Africa. Preliminary investigations showed the formation of a humic soil-like material from the breakdown of hard coal in the root zone of these plants. The potential of this system to contribute to industrial scale bioprocessing of hard coal was investigated. This study involved an investigation of the C. dactylon/coal rhizosphere environment and demonstrated the presence of fungal species with known coal bioconversion capability. Amongst these Neosartorya fischeri was identified and its activity in coal bioconversion was described for the first time. Cynodon dactylon plant roots were also shown to be colonized by mycorrhizal fungi including Glomus, Paraglomus and Gigaspora species. The role of plant photosynthate translocation into the root zone, providing organic carbon supplementation of fungal coal bioconversion was investigated in deep liquid culture with the N. fischeri isolate used as the biocatalyst. Organic acids, sugars and complex organic carbon sources were investigated and it was shown that glutamate provided significant enhancement of bioconversion activity in this system. The performance of N. fischeri in coal bioconversion was compared with Phanaerochaete chrysosporium and Trametes versicolor, both previously described fungal species in the coal bioconversion application. Fourier transform infrared spectroscopy indicated more pronounced oxidation and introduction of nitro groups in the matrix of the humic acid product of coal bioconversion in N. fischeri and P. chrysosporium than for T. versicolor. Macro-elemental analysis of biomass-bound humic acid obtained from the N. fischeri catalyzed reaction showed an increase in the oxygen and nitrogen components and coupled with a reduction in carbon and hydrogen. Pyrolysis gas chromatography mass spectroscopy further supported the proposal that the mechanism of bioconversion involves oxygen and nitrogen insertion into the coal structure. The C. dactylon bituminous hard coal dump environment was simulated in a fixed-bed perfusion column bioreactor in which the contribution of organic supplement by the plant/mycorrhizal component of the system was investigated. The results enabled the proposal of a descriptive model accounting for the performance of the system in which the plant/mycorrhizal component introduces organic substances into the root zone. The non-mycorrhizal fungi utilize the organic carbon supplement in its attack on the coal substrate, breaking it down, and releasing plant nutrients and a soil-like substrate which in turn enables the growth of C. dactylon in this hostile environment. Based on these results, the Stacked Heap Coal Bioreactor concept was developed as a large-scale industrial bioprocess application based on heap-leach mineral processing technology. Field studies have confirmed that bituminous hard coal can be converted to a humic acid rich substrate in a stacked heap system inoculated with mycorrhizal and N. fischeri cultures and planted with C. dactylon.
- Full Text:
- Date Issued: 2008
Application of dermal microdialysis and tape stripping methods to determine the bioavailability and/or bioequivalence of topical ketoprofen formulations
- Tettey-Amlalo, Ralph Nii Okai
- Authors: Tettey-Amlalo, Ralph Nii Okai
- Date: 2008
- Subjects: Drugs -- Therapeutic equivalency Transdermal medication High performance liquid chromatography Nonsteroidal anti-inflammatory agents -- Bioavailability Nonsteroidal anti-inflammatory agents -- Effectiveness Nonsteroidal anti-inflammatory agents -- Testing Nonsteroidal anti-inflammatory agents -- Side effects
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3796 , http://hdl.handle.net/10962/d1003274
- Description: The widespread acceptance of topical formulations intended for local and/or regional activity has prompted renewed interest in developing a model to determine the bioavailability of drugs in order to establish bioequivalence as a means of evaluating formulation performance of multisource products and also for use during formulation development. Current in vivo techniques such as blister suction and skin biopsy amongst others used to determine the bioavailability and/or bioequivalence of topical formulations are either too invasive to generate appropriate concentration-time profiles or require large numbers of study subjects thereby making the study expensive and time-consuming. Moreover, there are currently no sampling techniques that can demonstrate dermal bioavailability and/or bioequivalence of topical formulations intended for local and/or regional activity. Dermal microdialysis is a relatively new application of microdialysis that permits continuous monitoring of endogenous and/or exogenous solutes in the interstitial fluid. The technique is involves the implantation of semi-permeable membranes which are perfused with an isotonic medium at extremely slow flow rates and collection of microlitre sample volumes containing diffused drugs. Tape stripping, a relatively older technique, has been extensively used in comparative bioavailability studies of various topical formulations. However, due to shortcomings arising from reproducibility and inter-subject variation amongst others, the published FDA guidance outlining the initial protocol was subsequently withdrawn. The incorporation of transepidermal water loss with tape stripping has garnered renewed interest and has been used for the determination of drug bioavailability from a number of topical formulations. Hence the primary objective of this research is to develop and evaluate microdialysis sampling and tape stripping techniques, including the incorporation of the determination of transepidermal water loss, to assess the dermal bioavailability of ketoprofen from topical gel formulations and to develop models for bioequivalence assessment. A rapid UPLC-MS/MS method with requisite sensitivity for the analysis of samples generated from dermal microdialysis was developed and validated which accommodated the microlitre sample volumes collected. An HPLC-UV method was developed and validated for the analysis of samples generated from the in vitro microdialysis and in vivo tape stripping studies. The work presented herein contributes to a growing body of scientific knowledge seeking to develop a model for the determination of bioequivalence of pharmaceutically equivalent topical formulations intended for local and/or regional activity in human subjects.
- Full Text:
- Date Issued: 2008
- Authors: Tettey-Amlalo, Ralph Nii Okai
- Date: 2008
- Subjects: Drugs -- Therapeutic equivalency Transdermal medication High performance liquid chromatography Nonsteroidal anti-inflammatory agents -- Bioavailability Nonsteroidal anti-inflammatory agents -- Effectiveness Nonsteroidal anti-inflammatory agents -- Testing Nonsteroidal anti-inflammatory agents -- Side effects
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3796 , http://hdl.handle.net/10962/d1003274
- Description: The widespread acceptance of topical formulations intended for local and/or regional activity has prompted renewed interest in developing a model to determine the bioavailability of drugs in order to establish bioequivalence as a means of evaluating formulation performance of multisource products and also for use during formulation development. Current in vivo techniques such as blister suction and skin biopsy amongst others used to determine the bioavailability and/or bioequivalence of topical formulations are either too invasive to generate appropriate concentration-time profiles or require large numbers of study subjects thereby making the study expensive and time-consuming. Moreover, there are currently no sampling techniques that can demonstrate dermal bioavailability and/or bioequivalence of topical formulations intended for local and/or regional activity. Dermal microdialysis is a relatively new application of microdialysis that permits continuous monitoring of endogenous and/or exogenous solutes in the interstitial fluid. The technique is involves the implantation of semi-permeable membranes which are perfused with an isotonic medium at extremely slow flow rates and collection of microlitre sample volumes containing diffused drugs. Tape stripping, a relatively older technique, has been extensively used in comparative bioavailability studies of various topical formulations. However, due to shortcomings arising from reproducibility and inter-subject variation amongst others, the published FDA guidance outlining the initial protocol was subsequently withdrawn. The incorporation of transepidermal water loss with tape stripping has garnered renewed interest and has been used for the determination of drug bioavailability from a number of topical formulations. Hence the primary objective of this research is to develop and evaluate microdialysis sampling and tape stripping techniques, including the incorporation of the determination of transepidermal water loss, to assess the dermal bioavailability of ketoprofen from topical gel formulations and to develop models for bioequivalence assessment. A rapid UPLC-MS/MS method with requisite sensitivity for the analysis of samples generated from dermal microdialysis was developed and validated which accommodated the microlitre sample volumes collected. An HPLC-UV method was developed and validated for the analysis of samples generated from the in vitro microdialysis and in vivo tape stripping studies. The work presented herein contributes to a growing body of scientific knowledge seeking to develop a model for the determination of bioequivalence of pharmaceutically equivalent topical formulations intended for local and/or regional activity in human subjects.
- Full Text:
- Date Issued: 2008
The impact of the identification process and the corporate social responsibility process on the effectiveness of multi-racial advertising in South Africa
- Authors: Johnson, Guillaume Desire
- Date: 2008
- Subjects: Marketing -- South Africa Advertising -- South Africa Sales promotion -- South Africa Consumers' preferences -- South Africa Marketing research -- South Africa Consumer behavior -- South Africa Consumption (Economics) -- Social aspect Attribution (Social psychology) South Africans -- Race identity Race awareness -- South Africa Ethnopsychology -- South Africa Group identity Racially mixed people
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1196 , http://hdl.handle.net/10962/d1008263
- Description: Selecting actors to appear in an advertisement is an important decision which has a crucial impact on the effectiveness of an advertising campaign. The same message, delivered by different actors, produces varying outcomes among consumers. This dilemma concerning the choice of actors occurs particularly in multi-racial societies, such as South Africa, where advertisers have to target different sectors of the community. In multi-racial societies, the choice of actors in advertisements goes beyond the usual commercial reasons. Indeed, two dimensions are generally conferred to multi-racial advertising. Firstly, the use of multi-racial representations allows for the targeting of a wider population that also owns a wider purchasing power. Marketers who want to market their brand use, for example, white and black actors so that white and black consumers can identify with the actors and recognize themselves as the target of the advertisement. Secondly, the multi-racial representations of this type of advertising hold a social role that counteracts the segregated depiction of the society. Consumers who are exposed to a multi-racial advertisement might perceive this social dimension and attribute a social responsibility to the advertisement. The purpose of this thesis is to examine the influence of the above dimensions on the effectiveness of a multi-racial advertisement. On the one hand, this study investigates the Identification Process followed by a consumer exposed to a multi-racial advertisement. On the other hand, it examines how consumers attribute a social responsibility to a specific multiracial advertisement and how this attribution, in turn, influences their responses to the advertisement and brand. Finally, the impacts of both of these dimensions on consumer behaviour are compared and the most persuasive dimension is identified. This thesis draws on Attribution Theory and Identification Theory in arguing that there are strong economic imperatives for adopting a multi-racial advertising approach. The thesis develops a conceptual framework and tests empirically hypotheses regarding the key constructs and moderating variables. The empirical results point out that both dimensions symbiotically influence the effectiveness of a multi-racial advertisement. Specifically, the results highlight that the social responsibility attributed by the viewers to the advertisement influences their behaviour more than the Identification Process.
- Full Text:
- Date Issued: 2008
- Authors: Johnson, Guillaume Desire
- Date: 2008
- Subjects: Marketing -- South Africa Advertising -- South Africa Sales promotion -- South Africa Consumers' preferences -- South Africa Marketing research -- South Africa Consumer behavior -- South Africa Consumption (Economics) -- Social aspect Attribution (Social psychology) South Africans -- Race identity Race awareness -- South Africa Ethnopsychology -- South Africa Group identity Racially mixed people
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1196 , http://hdl.handle.net/10962/d1008263
- Description: Selecting actors to appear in an advertisement is an important decision which has a crucial impact on the effectiveness of an advertising campaign. The same message, delivered by different actors, produces varying outcomes among consumers. This dilemma concerning the choice of actors occurs particularly in multi-racial societies, such as South Africa, where advertisers have to target different sectors of the community. In multi-racial societies, the choice of actors in advertisements goes beyond the usual commercial reasons. Indeed, two dimensions are generally conferred to multi-racial advertising. Firstly, the use of multi-racial representations allows for the targeting of a wider population that also owns a wider purchasing power. Marketers who want to market their brand use, for example, white and black actors so that white and black consumers can identify with the actors and recognize themselves as the target of the advertisement. Secondly, the multi-racial representations of this type of advertising hold a social role that counteracts the segregated depiction of the society. Consumers who are exposed to a multi-racial advertisement might perceive this social dimension and attribute a social responsibility to the advertisement. The purpose of this thesis is to examine the influence of the above dimensions on the effectiveness of a multi-racial advertisement. On the one hand, this study investigates the Identification Process followed by a consumer exposed to a multi-racial advertisement. On the other hand, it examines how consumers attribute a social responsibility to a specific multiracial advertisement and how this attribution, in turn, influences their responses to the advertisement and brand. Finally, the impacts of both of these dimensions on consumer behaviour are compared and the most persuasive dimension is identified. This thesis draws on Attribution Theory and Identification Theory in arguing that there are strong economic imperatives for adopting a multi-racial advertising approach. The thesis develops a conceptual framework and tests empirically hypotheses regarding the key constructs and moderating variables. The empirical results point out that both dimensions symbiotically influence the effectiveness of a multi-racial advertisement. Specifically, the results highlight that the social responsibility attributed by the viewers to the advertisement influences their behaviour more than the Identification Process.
- Full Text:
- Date Issued: 2008
Assembly of Omegatetravirus virus-like particles in the yeast Saccharomyces cerevisiae
- Authors: Tomasicchio, Michele
- Date: 2008
- Subjects: Helicoverpa armigera Imbrasia cytherea Viruses RNA viruses Insects -- Viruses Lepidoptera -- Viruses Saccharomyces cerevisiae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3930 , http://hdl.handle.net/10962/d1003989
- Description: The Tetraviridae are a family of ss (+) RNA viruses that specifically infect lepidopteran insects. Their icosahedral capsids are non-enveloped and approximately 40 nm in diameter with T=4 quasi-equivalent symmetry. The omegatetraviruses, which are structurally the best characterised in the family, include Helicoverpa armigera stunt virus (HaSV) and Nudaurelia capensis omega virus (NwV). The omegatetravirus procapsid is composed of 240 identical copies of the capsid precursor proteins, which undergo autoproteolytic cleavage at its carboxyl-terminus generating the mature capsid protein (b) and γ-peptide. This process occurs in vitro following a shift from pH 7.6 to pH 6.0. The viral capsid encapsidates two ss genomic RNAs: The larger RNA1 encodes the viral replicase as well as three small ORFs while RNA2 encodes the capsid precursor protein together with an overlapping ORF designated P17. While a wealth of structural data pertaining to the assembly and maturation of omegatetraviruses is available, little is known about how this relates to their lifecycle. The principle aim of the research described in this thesis was to use an experimental system developed in the yeast, Saccharomyces cerevisiae, to investigate the assembly of HaSV and NwV virus-like particles (VLPs) in terms of maturation and encapsidation of viral RNAs, in vivo. The yeast expression system used two promoter systems for expression of capsid precursor protein: in the first, a hybrid promoter (PGADH) was used for high-level expression, while the second, PGAL1, produced substantially lower levels of the virus capsid protein precursors. An increase in the level of HaSV capsid protein precursor (p71) via the PGADH promoter resulted in a dramatic increase in VLP assembly as compared with the PGAL system. A protein equivalent to the mature capsid protein (p64) appeared at later time intervals following induction of transcription. Transmission electron microscopic studies showed that p64 correlated with the presence of mature VLPs as opposed to procapsids in cells containing p71. This confirmed that the presence of p64 denoted maturation of VLPs in vivo. Further investigation indicated that maturation correlated with cell aging and the onset of apoptosis. It was shown that induction of apoptosis resulted in VLP maturation while inhibition of apoptosis prevented maturation. These results suggested that the process of apoptosis might be the trigger for maturation of virus procapsids in their host cells. The increase in the efficiency of VLP assembly observed in the high-level expression system was proposed to be due to an increase in the cellular concentrations of viral RNA. To test this hypothesis, HaSV P71 was co-expressed with either P71 mRNA or full length RNA2. An increase in the solubility of p71 was observed in cells expressing increased levels of both RNAs, but there was no increase in the efficiency of VLP assembly. Northern analysis of encapsidated RNAs revealed that there was no selective encapsidation of either P71 mRNA or viral RNA2. This data indicated that the increase in viral RNA was not the reason for increased efficiency of VLP assembly, but most likely resulted from higher concentrations of p71 itself. It was decided to determine whether a highly efficient nodavirus replication system developed in yeast for heterologous production of proteins, could be used as a method for expressing the capsid protein precursor. The aim of using this system was to determine if VLPs assembled in a replication system specifically encapsidated viral RNA. Transcripts encoding the NwV capsid protein precursor (p70) were generated in yeast cells by replication of a hybrid RNA template by the Nodamura virus (NoV) replicase. Western analysis confirmed the presence of p70 as well as a protein of 62 kDa corresponding to the mature NwV capsid protein. Northern analysis of purified VLPs showed that NoV RNA1 and RNA3 were encapsidated, but no RNA2 was detected. Taken together, the data lead to the conclusion that specific encapsidation of tetraviral RNAs required more than close proximity of the viral RNAs and assembling virus-like particles. Encapsidation specificity in the omegatetraviruses may require additional viral proteins such as p17 during encapsidation or specific viral RNA encapsidation was replication-dependent. Replication-dependent assembly has been shown in the nodaviruses.
- Full Text:
- Date Issued: 2008
- Authors: Tomasicchio, Michele
- Date: 2008
- Subjects: Helicoverpa armigera Imbrasia cytherea Viruses RNA viruses Insects -- Viruses Lepidoptera -- Viruses Saccharomyces cerevisiae
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3930 , http://hdl.handle.net/10962/d1003989
- Description: The Tetraviridae are a family of ss (+) RNA viruses that specifically infect lepidopteran insects. Their icosahedral capsids are non-enveloped and approximately 40 nm in diameter with T=4 quasi-equivalent symmetry. The omegatetraviruses, which are structurally the best characterised in the family, include Helicoverpa armigera stunt virus (HaSV) and Nudaurelia capensis omega virus (NwV). The omegatetravirus procapsid is composed of 240 identical copies of the capsid precursor proteins, which undergo autoproteolytic cleavage at its carboxyl-terminus generating the mature capsid protein (b) and γ-peptide. This process occurs in vitro following a shift from pH 7.6 to pH 6.0. The viral capsid encapsidates two ss genomic RNAs: The larger RNA1 encodes the viral replicase as well as three small ORFs while RNA2 encodes the capsid precursor protein together with an overlapping ORF designated P17. While a wealth of structural data pertaining to the assembly and maturation of omegatetraviruses is available, little is known about how this relates to their lifecycle. The principle aim of the research described in this thesis was to use an experimental system developed in the yeast, Saccharomyces cerevisiae, to investigate the assembly of HaSV and NwV virus-like particles (VLPs) in terms of maturation and encapsidation of viral RNAs, in vivo. The yeast expression system used two promoter systems for expression of capsid precursor protein: in the first, a hybrid promoter (PGADH) was used for high-level expression, while the second, PGAL1, produced substantially lower levels of the virus capsid protein precursors. An increase in the level of HaSV capsid protein precursor (p71) via the PGADH promoter resulted in a dramatic increase in VLP assembly as compared with the PGAL system. A protein equivalent to the mature capsid protein (p64) appeared at later time intervals following induction of transcription. Transmission electron microscopic studies showed that p64 correlated with the presence of mature VLPs as opposed to procapsids in cells containing p71. This confirmed that the presence of p64 denoted maturation of VLPs in vivo. Further investigation indicated that maturation correlated with cell aging and the onset of apoptosis. It was shown that induction of apoptosis resulted in VLP maturation while inhibition of apoptosis prevented maturation. These results suggested that the process of apoptosis might be the trigger for maturation of virus procapsids in their host cells. The increase in the efficiency of VLP assembly observed in the high-level expression system was proposed to be due to an increase in the cellular concentrations of viral RNA. To test this hypothesis, HaSV P71 was co-expressed with either P71 mRNA or full length RNA2. An increase in the solubility of p71 was observed in cells expressing increased levels of both RNAs, but there was no increase in the efficiency of VLP assembly. Northern analysis of encapsidated RNAs revealed that there was no selective encapsidation of either P71 mRNA or viral RNA2. This data indicated that the increase in viral RNA was not the reason for increased efficiency of VLP assembly, but most likely resulted from higher concentrations of p71 itself. It was decided to determine whether a highly efficient nodavirus replication system developed in yeast for heterologous production of proteins, could be used as a method for expressing the capsid protein precursor. The aim of using this system was to determine if VLPs assembled in a replication system specifically encapsidated viral RNA. Transcripts encoding the NwV capsid protein precursor (p70) were generated in yeast cells by replication of a hybrid RNA template by the Nodamura virus (NoV) replicase. Western analysis confirmed the presence of p70 as well as a protein of 62 kDa corresponding to the mature NwV capsid protein. Northern analysis of purified VLPs showed that NoV RNA1 and RNA3 were encapsidated, but no RNA2 was detected. Taken together, the data lead to the conclusion that specific encapsidation of tetraviral RNAs required more than close proximity of the viral RNAs and assembling virus-like particles. Encapsidation specificity in the omegatetraviruses may require additional viral proteins such as p17 during encapsidation or specific viral RNA encapsidation was replication-dependent. Replication-dependent assembly has been shown in the nodaviruses.
- Full Text:
- Date Issued: 2008
Melatonin and anticancer therapy interactions with 5-Fluorouracil
- Authors: Cassim, Layla
- Date: 2008
- Subjects: Melatonin Melatonin -- Therapeutic use Antineoplastic agents Fluorouracil Fluorouracil -- Toxicology Cancer -- Treatment
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3746 , http://hdl.handle.net/10962/d1003224
- Description: On the basis of clinical studies, some researchers have advocated that the neurohormone and antioxidant melatonin, shown to possess intrinsic anticancer properties, be used as co-therapy in cancer patients being treated with the antineoplastic agent 5-fluorouracil, as increased patient survival times and enhanced quality of life have been observed. The focus of this research was thus to investigate the mechanisms of this seemingly beneficial drug interaction between 5-fluorouracil and melatonin. Metabolism studies were undertaken, in which it was established that there is no hepatic metabolic drug interaction between these agents by cytochrome P450, and that neither agent alters the activity of this enzyme system. Co-therapy with melatonin is thus unlikely to alter plasma levels of 5-fluorouracil by this mechanism. Novel mechanisms by which 5-fluorouracil is toxic were elucidated, such as the induction of lipid peroxidation, due to the formation of reactive oxygen species; decreases in brain serotonin, dopamine and norepinephrine levels, possibly leading to depression; hippocampal shrinkage and morphological alterations and lysis of hippocampal cells, which may underlie cognitive impairment; and a reduction in the nociceptive threshold when administered acutely. All these deleterious effects are attenuated by the co-administration of melatonin, suggesting that the agent exhibits antidepressive and analgesic properties, in addition to its known antioxidative and free radical-scavenging abilities. This suggests that melatonin cotherapy can significantly decrease 5-fluorouracil-induced toxicity, but this may also exert a protective effect on cancer cells and thus compromise the anticancer efficacy of 5-fluorouracil. It was, furthermore, found that stimulation of indoleamine 2,3-dioxygenase activity, mediated by increases in superoxide anion and interferon-γ levels, may underlie resistance to 5-fluorouracil therapy. Melatonin was shown to increase superoxide anion levels in vivo, and this is believed to be by conversion to the metabolite and known oxidant 6- hydroxymelatonin. This highlights that the possible deleterious effects of melatonin metabolites should be studied further. Serum corticosterone levels and cytokine profiles are unaltered by both 5-FU and melatonin, suggesting that these agents may be used by HIV infected individuals without promoting the progression to AIDS. It can thus be concluded that melatonin co-therapy is potentially useful in countering 5-fluorouracil toxicity.
- Full Text:
- Date Issued: 2008
- Authors: Cassim, Layla
- Date: 2008
- Subjects: Melatonin Melatonin -- Therapeutic use Antineoplastic agents Fluorouracil Fluorouracil -- Toxicology Cancer -- Treatment
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3746 , http://hdl.handle.net/10962/d1003224
- Description: On the basis of clinical studies, some researchers have advocated that the neurohormone and antioxidant melatonin, shown to possess intrinsic anticancer properties, be used as co-therapy in cancer patients being treated with the antineoplastic agent 5-fluorouracil, as increased patient survival times and enhanced quality of life have been observed. The focus of this research was thus to investigate the mechanisms of this seemingly beneficial drug interaction between 5-fluorouracil and melatonin. Metabolism studies were undertaken, in which it was established that there is no hepatic metabolic drug interaction between these agents by cytochrome P450, and that neither agent alters the activity of this enzyme system. Co-therapy with melatonin is thus unlikely to alter plasma levels of 5-fluorouracil by this mechanism. Novel mechanisms by which 5-fluorouracil is toxic were elucidated, such as the induction of lipid peroxidation, due to the formation of reactive oxygen species; decreases in brain serotonin, dopamine and norepinephrine levels, possibly leading to depression; hippocampal shrinkage and morphological alterations and lysis of hippocampal cells, which may underlie cognitive impairment; and a reduction in the nociceptive threshold when administered acutely. All these deleterious effects are attenuated by the co-administration of melatonin, suggesting that the agent exhibits antidepressive and analgesic properties, in addition to its known antioxidative and free radical-scavenging abilities. This suggests that melatonin cotherapy can significantly decrease 5-fluorouracil-induced toxicity, but this may also exert a protective effect on cancer cells and thus compromise the anticancer efficacy of 5-fluorouracil. It was, furthermore, found that stimulation of indoleamine 2,3-dioxygenase activity, mediated by increases in superoxide anion and interferon-γ levels, may underlie resistance to 5-fluorouracil therapy. Melatonin was shown to increase superoxide anion levels in vivo, and this is believed to be by conversion to the metabolite and known oxidant 6- hydroxymelatonin. This highlights that the possible deleterious effects of melatonin metabolites should be studied further. Serum corticosterone levels and cytokine profiles are unaltered by both 5-FU and melatonin, suggesting that these agents may be used by HIV infected individuals without promoting the progression to AIDS. It can thus be concluded that melatonin co-therapy is potentially useful in countering 5-fluorouracil toxicity.
- Full Text:
- Date Issued: 2008
South Africa and Malaysia: identity and history in South-South relations
- Authors: Haron, Muhammed
- Date: 2008
- Subjects: Critical theory South Africa -- Foreign relations -- Malaysia Malaysia -- Foreign relations -- South Africa South Africa -- Politics and government -- History Malaysia -- Politics and government -- History South Africa -- Politics and government Malaysia -- Politics and government South Africa -- Social conditions -- History Malaysia -- Social conditions -- History South Africa -- Economic conditions Malaysia -- Economic conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2780 , http://hdl.handle.net/10962/d1002990
- Description: The focus of this thesis is on the bilateral relationship between South Africa and Malaysia. The thesis appropriates ‘critical theory,’ and as a flexible theoretical tool, and, as an open-ended, loose frame in order to give voice to the marginalized and voiceless from the South. The thesis thus looks at the politico-economic ties that have been developed and brings into view the socio-cultural relations that had been established between the peoples of the two sovereign nation-states during the apartheid and post-apartheid eras respectively. The basic purpose of this study was fivefold: (a) to contribute to the extant literature that concentrates on South Africa’s relations with Malaysia, (b) to examine the relationship at political and economic ties in some detail, (c) to demonstrate that apart from the afore-mentioned bonds IR specialists should also take into account the socio-cultural dimensions of international relations, (d) to bring to light the nation-state’s limitations when discussing the role of non-state actors and considering the contributions of other factors such as globalization, and (e) to stimulate further research on bilateral and multilateral relations in the South – particularly between South Africa and other states in Asia and Latin America - that would assist to better understand the past, present and perhaps the future.
- Full Text:
- Date Issued: 2008
- Authors: Haron, Muhammed
- Date: 2008
- Subjects: Critical theory South Africa -- Foreign relations -- Malaysia Malaysia -- Foreign relations -- South Africa South Africa -- Politics and government -- History Malaysia -- Politics and government -- History South Africa -- Politics and government Malaysia -- Politics and government South Africa -- Social conditions -- History Malaysia -- Social conditions -- History South Africa -- Economic conditions Malaysia -- Economic conditions
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:2780 , http://hdl.handle.net/10962/d1002990
- Description: The focus of this thesis is on the bilateral relationship between South Africa and Malaysia. The thesis appropriates ‘critical theory,’ and as a flexible theoretical tool, and, as an open-ended, loose frame in order to give voice to the marginalized and voiceless from the South. The thesis thus looks at the politico-economic ties that have been developed and brings into view the socio-cultural relations that had been established between the peoples of the two sovereign nation-states during the apartheid and post-apartheid eras respectively. The basic purpose of this study was fivefold: (a) to contribute to the extant literature that concentrates on South Africa’s relations with Malaysia, (b) to examine the relationship at political and economic ties in some detail, (c) to demonstrate that apart from the afore-mentioned bonds IR specialists should also take into account the socio-cultural dimensions of international relations, (d) to bring to light the nation-state’s limitations when discussing the role of non-state actors and considering the contributions of other factors such as globalization, and (e) to stimulate further research on bilateral and multilateral relations in the South – particularly between South Africa and other states in Asia and Latin America - that would assist to better understand the past, present and perhaps the future.
- Full Text:
- Date Issued: 2008
Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa
- Authors: Moeketsi, Daniel Mojalefa
- Date: 2008
- Subjects: Ionosphere -- Africa, Southern Electrons Ionospheric electron density -- Africa, Southern Ionosondes -- Africa, Southern Electromagnetic waves
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5489 , http://hdl.handle.net/10962/d1005275
- Description: The South African Global Navigation Satellite System (GNSS) network of dual frequency receivers provide an opportunity to investigate solar cycle effects on ionospheric Total Electron Content (TEC) over the South Africa region by taking advantage of the dispersive nature of the ionospheric medium. For this task, the global University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was adopted, modified and applied to compute TEC using data from the southern African GNSS Network. TEC values were compared with CODE International GNSS services TEC predictions and Ionosonde-derived TEC (ITEC) measurements to test and validate the UNB-IMT results over South Africa. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show pronounced seasonal variations with high TEC values around equinoxes for a year near solar maximum and less pronounced around solar minimum. Signature TEC depletions and enhanced spikes were prevalently evident around equinoxes, particularly for a year near solar maximum. These observations were investigated and further discussed with an analysis of the midday Disturbance Storm Time (DST) index of geomagnetic activity. The residual GTEC – ITEC corresponding to plasmaspheric electron content and equivalent ionospheric foF2 and total slab thickness parameters were computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for ionospheric research over South Africa. The UNB-IMT algorithm was applied to investigate TEC variability during different epochs of solar cycle 23. The results were investigated and further discussed by analyzing the GOES 8 and 10 satellites X-ray flux (0.1 – 0.8 nm) and SOHO Solar Extreme Ultraviolet Monitor higher resolution data. Comparison of UNB-IMT TEC derived from collocated HRAO and HARB GNSS receivers was undertaken for the solar X17 and X9 flare events, which occurred on day 301, 2003 and day 339, 2006. It was found that there exist considerable TEC differences between the two collocated receivers with some evidence of solar cycle dependence. Furthermore, the daytime UNB TEC compared with the International Reference Ionosphere 2001 predicted TEC found both models to show a good agreement. The UNB-IMT TEC was further applied to investigate the capabilities of geodetic Very Long Baseline Interferometry (VLBI) derived TEC using the Vienna TEC Model for space weather monitoring over HartRAO during the CONT02 and CONT05 campaigns conducted during the years 2002 (near solar maximum) and 005 (near solar minimum). The results verified the use of geodetic VLBI as one of the possible instruments for monitoring space weather impacts on the ionosphere over South Africa.
- Full Text:
- Date Issued: 2008
Solar cycle effects on GNSS-derived ionospheric total electron content observed over Southern Africa
- Authors: Moeketsi, Daniel Mojalefa
- Date: 2008
- Subjects: Ionosphere -- Africa, Southern Electrons Ionospheric electron density -- Africa, Southern Ionosondes -- Africa, Southern Electromagnetic waves
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5489 , http://hdl.handle.net/10962/d1005275
- Description: The South African Global Navigation Satellite System (GNSS) network of dual frequency receivers provide an opportunity to investigate solar cycle effects on ionospheric Total Electron Content (TEC) over the South Africa region by taking advantage of the dispersive nature of the ionospheric medium. For this task, the global University of New Brunswick Ionospheric Modelling Technique (UNB-IMT) was adopted, modified and applied to compute TEC using data from the southern African GNSS Network. TEC values were compared with CODE International GNSS services TEC predictions and Ionosonde-derived TEC (ITEC) measurements to test and validate the UNB-IMT results over South Africa. It was found that the variation trends of GTEC and ITEC over all stations are in good agreement and show pronounced seasonal variations with high TEC values around equinoxes for a year near solar maximum and less pronounced around solar minimum. Signature TEC depletions and enhanced spikes were prevalently evident around equinoxes, particularly for a year near solar maximum. These observations were investigated and further discussed with an analysis of the midday Disturbance Storm Time (DST) index of geomagnetic activity. The residual GTEC – ITEC corresponding to plasmaspheric electron content and equivalent ionospheric foF2 and total slab thickness parameters were computed and comprehensively discussed. The results verified the use of UNB-IMT as one of the tools for ionospheric research over South Africa. The UNB-IMT algorithm was applied to investigate TEC variability during different epochs of solar cycle 23. The results were investigated and further discussed by analyzing the GOES 8 and 10 satellites X-ray flux (0.1 – 0.8 nm) and SOHO Solar Extreme Ultraviolet Monitor higher resolution data. Comparison of UNB-IMT TEC derived from collocated HRAO and HARB GNSS receivers was undertaken for the solar X17 and X9 flare events, which occurred on day 301, 2003 and day 339, 2006. It was found that there exist considerable TEC differences between the two collocated receivers with some evidence of solar cycle dependence. Furthermore, the daytime UNB TEC compared with the International Reference Ionosphere 2001 predicted TEC found both models to show a good agreement. The UNB-IMT TEC was further applied to investigate the capabilities of geodetic Very Long Baseline Interferometry (VLBI) derived TEC using the Vienna TEC Model for space weather monitoring over HartRAO during the CONT02 and CONT05 campaigns conducted during the years 2002 (near solar maximum) and 005 (near solar minimum). The results verified the use of geodetic VLBI as one of the possible instruments for monitoring space weather impacts on the ionosphere over South Africa.
- Full Text:
- Date Issued: 2008
Camphor derivatives in asymmetric synthesis: a synthetic, mechanistic and theoretical study
- Authors: Lobb, Kevin Alan
- Date: 2008
- Subjects: Chemistry, Organic -- Research Esters Organic compounds -- Synthesis Alkylation Chemical reactions -- Computer simulation Chemical kinetics Camphor Cinnamomum
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4414 , http://hdl.handle.net/10962/d1006770
- Description: A series of 3,3-ethylenedioxy-exo- and endo- bornyl esters have been prepared and subjected to α-benzylation using lithium diisopropylamide and benzyl bromide. In the exo-series of esters the diastereofacial selectivity of benzylation was found to improve (up to 34% d.e.) as the steric bulk of the O-alkyl group increased, whereas in the endo-series, a surprising decrease in stereoselectivity was observed as the steric bulk increased – an observation attributed to flexibility of the metal-coordinated endo-enolate system, compared to the relative rigidity of the exo analogues. The conformational options for each series was explored at the density functional theory level. Reductive cyclization of a range of specially prepared N-carbobenzyloxy-amino acid esters has been shown to afford the corresponding derivatives, contrary to previous reports that the cyclization is limited to the glycine derivative. The cyclization sequence has been explored in detail, and the yield has been shown to be critically dependent on the stereochemistry of the α-amino acid moiety. Moreover, it seems that reductive cyclization occurs more readily with the endo- rather than the exo-bornyl N-CBZ-amino acid esters. Molecular modelling of relevant transition states at the DFT levels indicates that L-amino acid-derived systems should cyclize preferably in the exo-series and D-amino acid-derived systems should cyclize preferably in the endo series. Studies of alkylation of an iminolactone system have reported an interesting anomaly - exo-methylation is observed while endo-alkylation predominates for larger alkyl groups. This has been studied in detail at the DFT level, and the anomaly is attributed to thermodynamic control in the methyl case, whereas kinetic control is the norm in this system. Preliminary computer modelling of the intramolecular rearrangement of a 3,3-xylylbornyl system at the HF/STO-3G level raised doubts concerning the structure assigned by Evans to one of the rearrangement products, prompting an X-ray crystallographic analysis and leading to the revision of its structure from a pinene to a camphene derivative. The previously elusive spiro[bornane-3,2’-indan]-2-exo-tosylate has been successfully isolated, and the kinetics of its ready decomposition to the two camphene products has been followed by 1H NMR spectroscopy. The endo-tosylate analogue, on the other hand, was found to be remarkably stable. Kinetic data obtained for rearrangement of this exo-bornyl tosylate have indicated the operation of tandem autocatalytic and pseudo-first-order transformations leading sequentially to the two isomeric camphene products. An extensive coset analysis of all possible rearrangement processes of the initially-formed cation formed from decomposition of the exo-tosylate has afforded a graph containing 336 classical cations (modelled at the AM1 and B3LYP levels) and 526 transition-state complexes (modelled at the AM1 level). This analysis afforded a viable 4-step classical mechanism connecting the first camphene product with the second. A more realistic study, involving non-classical carbocations, has afforded a graph of all possible (classical and non-classical) cations that could be formed by rearrangment of the initiallyformed cation. The resulting graph confirms that the only energetically feasible path corresponds to the classical mechanism, but simply involves two steps, including a novel, concerted Wagner-Meerwein – 6,2-hydride shift – Wagner-Meerwein rearrangement.
- Full Text:
- Date Issued: 2008
- Authors: Lobb, Kevin Alan
- Date: 2008
- Subjects: Chemistry, Organic -- Research Esters Organic compounds -- Synthesis Alkylation Chemical reactions -- Computer simulation Chemical kinetics Camphor Cinnamomum
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4414 , http://hdl.handle.net/10962/d1006770
- Description: A series of 3,3-ethylenedioxy-exo- and endo- bornyl esters have been prepared and subjected to α-benzylation using lithium diisopropylamide and benzyl bromide. In the exo-series of esters the diastereofacial selectivity of benzylation was found to improve (up to 34% d.e.) as the steric bulk of the O-alkyl group increased, whereas in the endo-series, a surprising decrease in stereoselectivity was observed as the steric bulk increased – an observation attributed to flexibility of the metal-coordinated endo-enolate system, compared to the relative rigidity of the exo analogues. The conformational options for each series was explored at the density functional theory level. Reductive cyclization of a range of specially prepared N-carbobenzyloxy-amino acid esters has been shown to afford the corresponding derivatives, contrary to previous reports that the cyclization is limited to the glycine derivative. The cyclization sequence has been explored in detail, and the yield has been shown to be critically dependent on the stereochemistry of the α-amino acid moiety. Moreover, it seems that reductive cyclization occurs more readily with the endo- rather than the exo-bornyl N-CBZ-amino acid esters. Molecular modelling of relevant transition states at the DFT levels indicates that L-amino acid-derived systems should cyclize preferably in the exo-series and D-amino acid-derived systems should cyclize preferably in the endo series. Studies of alkylation of an iminolactone system have reported an interesting anomaly - exo-methylation is observed while endo-alkylation predominates for larger alkyl groups. This has been studied in detail at the DFT level, and the anomaly is attributed to thermodynamic control in the methyl case, whereas kinetic control is the norm in this system. Preliminary computer modelling of the intramolecular rearrangement of a 3,3-xylylbornyl system at the HF/STO-3G level raised doubts concerning the structure assigned by Evans to one of the rearrangement products, prompting an X-ray crystallographic analysis and leading to the revision of its structure from a pinene to a camphene derivative. The previously elusive spiro[bornane-3,2’-indan]-2-exo-tosylate has been successfully isolated, and the kinetics of its ready decomposition to the two camphene products has been followed by 1H NMR spectroscopy. The endo-tosylate analogue, on the other hand, was found to be remarkably stable. Kinetic data obtained for rearrangement of this exo-bornyl tosylate have indicated the operation of tandem autocatalytic and pseudo-first-order transformations leading sequentially to the two isomeric camphene products. An extensive coset analysis of all possible rearrangement processes of the initially-formed cation formed from decomposition of the exo-tosylate has afforded a graph containing 336 classical cations (modelled at the AM1 and B3LYP levels) and 526 transition-state complexes (modelled at the AM1 level). This analysis afforded a viable 4-step classical mechanism connecting the first camphene product with the second. A more realistic study, involving non-classical carbocations, has afforded a graph of all possible (classical and non-classical) cations that could be formed by rearrangment of the initiallyformed cation. The resulting graph confirms that the only energetically feasible path corresponds to the classical mechanism, but simply involves two steps, including a novel, concerted Wagner-Meerwein – 6,2-hydride shift – Wagner-Meerwein rearrangement.
- Full Text:
- Date Issued: 2008
Managing conflict across cultures, values and identities: a case study in the South African automotive industry
- Authors: Mayer, Claude-Hélène
- Date: 2008
- Subjects: Conflict management -- South Africa Automobile industry and trade -- South Africa Automobile industry workers -- South Africa Communication in management -- South Africa Intercultural communication -- South Africa Culture conflict -- South Africa Diversity in the workplace -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1174 , http://hdl.handle.net/10962/d1002790
- Description: Over the past fifty years, interest in the field of conflict management and peacekeeping has developed worldwide. During the same time, the potential for trans-ultural) conflict has escalated. This can mainly be attributed to the trend towards globalisation, as well as the growing complexity of societies increasingly experiencing more intercultural encounters or cultural transition situations and work-related or organisational conflicts. Cultural transition situations occur in the South African international automotive industry where the emergence of international co-operation, such as joint ventures (driven by globalisation) and new diversity management trends, have changed the way business is conducted. Due to these changes, employees of diverse origins with different cultures, values and identities work together, experiencing work-related conflicts. The purpose of this study was to assess managerial perspectives on conflict, identity and values, as well as on how (trans-cultural) conflict is managed in a selected international organisation in the South African automotive industry. The contribution of this study is twofold, namely to increase the understanding of the complexities of conflict in organisations; and to provide recommendations for conflict resolution strategies to manage (trans-cultural) conflict constructively by considering the values and identity aspects of those individuals involved. This study comprises a single explanatory case study which made use of qualitative data collection and analysis to investigate managerial perspectives on conflict, identity and values, as well as the management thereof, in the selected international organisation in the South African automotive context. Based on the main findings from this case study, it could be concluded that managers with diverse backgrounds experience work-related conflicts which are related to value and identity concepts in the selected organisation. The conflicts experienced fell into the categories of Communication and Treatment, Position and Competition, Organisation and Race and Gender.An overview of the occurrence frequency of value statements revealed that equality, communication and respect were the most commonly indicated values in conflicts. These value concepts include sub-concepts such as: · for equality: race, gender and human equality; · for communication: open, personal, free, decent, calm and proactive communication; and · for respect: mutual respect for self and others. With regard to value concepts and according to value domains of Schwartz (1994) and Schwartz and Bilsky (1987), the value dimensions of selftranscendence comprised the highest number of value statements. This dimension included the value domains of universalism and benevolence. Conflict in the data material was interlinked with identity. The extracts, based on the key words of the identity factors, demonstrated that the identity factors were related to either a weakening or strengthening effect on identities. Social and identity multiplicity in managers provides creativity spaces and flexibility in cases of strong identity patterns. Particularly with weak identities, the existence of conflict potentials could lead to complex conflicts and challenges in conflict management. Communication was most often mentioned as important to successful conflict resolution management and included examples such as round-table talks, smooth communication, face-to-face communication and room meetings. Communication was followed in frequency by strategies of internal intervention, which included the use of the formal structure of the organisation to resolve conflicts.
- Full Text:
- Date Issued: 2008
- Authors: Mayer, Claude-Hélène
- Date: 2008
- Subjects: Conflict management -- South Africa Automobile industry and trade -- South Africa Automobile industry workers -- South Africa Communication in management -- South Africa Intercultural communication -- South Africa Culture conflict -- South Africa Diversity in the workplace -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1174 , http://hdl.handle.net/10962/d1002790
- Description: Over the past fifty years, interest in the field of conflict management and peacekeeping has developed worldwide. During the same time, the potential for trans-ultural) conflict has escalated. This can mainly be attributed to the trend towards globalisation, as well as the growing complexity of societies increasingly experiencing more intercultural encounters or cultural transition situations and work-related or organisational conflicts. Cultural transition situations occur in the South African international automotive industry where the emergence of international co-operation, such as joint ventures (driven by globalisation) and new diversity management trends, have changed the way business is conducted. Due to these changes, employees of diverse origins with different cultures, values and identities work together, experiencing work-related conflicts. The purpose of this study was to assess managerial perspectives on conflict, identity and values, as well as on how (trans-cultural) conflict is managed in a selected international organisation in the South African automotive industry. The contribution of this study is twofold, namely to increase the understanding of the complexities of conflict in organisations; and to provide recommendations for conflict resolution strategies to manage (trans-cultural) conflict constructively by considering the values and identity aspects of those individuals involved. This study comprises a single explanatory case study which made use of qualitative data collection and analysis to investigate managerial perspectives on conflict, identity and values, as well as the management thereof, in the selected international organisation in the South African automotive context. Based on the main findings from this case study, it could be concluded that managers with diverse backgrounds experience work-related conflicts which are related to value and identity concepts in the selected organisation. The conflicts experienced fell into the categories of Communication and Treatment, Position and Competition, Organisation and Race and Gender.An overview of the occurrence frequency of value statements revealed that equality, communication and respect were the most commonly indicated values in conflicts. These value concepts include sub-concepts such as: · for equality: race, gender and human equality; · for communication: open, personal, free, decent, calm and proactive communication; and · for respect: mutual respect for self and others. With regard to value concepts and according to value domains of Schwartz (1994) and Schwartz and Bilsky (1987), the value dimensions of selftranscendence comprised the highest number of value statements. This dimension included the value domains of universalism and benevolence. Conflict in the data material was interlinked with identity. The extracts, based on the key words of the identity factors, demonstrated that the identity factors were related to either a weakening or strengthening effect on identities. Social and identity multiplicity in managers provides creativity spaces and flexibility in cases of strong identity patterns. Particularly with weak identities, the existence of conflict potentials could lead to complex conflicts and challenges in conflict management. Communication was most often mentioned as important to successful conflict resolution management and included examples such as round-table talks, smooth communication, face-to-face communication and room meetings. Communication was followed in frequency by strategies of internal intervention, which included the use of the formal structure of the organisation to resolve conflicts.
- Full Text:
- Date Issued: 2008
Molecular characterization of the Hsp70/Hsp90 organizing protein (Hop) phosphorylation, subcellular localization and interaction with Hsp90
- Authors: Daniel, Sheril
- Date: 2008
- Subjects: Molecular chaperones Phosphorylation Proteins Heat shock proteins Surface plasmon resonance Cytosol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3996 , http://hdl.handle.net/10962/d1004056
- Description: Hop (Hsp70-Hsp90 Organizing Protein) is a co-chaperone of two major molecular chaperones, Hsp70 and Hsp90, and acts by transferring substrates from Hsp70 to Hsp90. Although under normal conditions Hop is predominantly localized within the cytosol, Hop has been detected in the nucleus under certain conditions including cell cycle arrest. A putative nuclear localization signal (NLS) has been identified within Hop, which overlaps with the TPR2A domain (previously shown to be critical for Hop-Hsp90 interactions). Hop is phosphorylated in vitro by two cell cycle kinases, namely, casein kinase II (CKII) at S189 and cdc2-kinase at T198; both residues are found upstream of the putative NLS and TPR2A domain. Mimicking phosphorylation at either phosphorylation site appeared to affect the subcellular localization of Hop. The aim of this study was to characterize Hop with respect to its phosphorylation status in vivo, as well as its subcellular localization pattern under heat stress and determine how these properties affected its interaction with Hsp90 as a co-chaperone. Dephosphorylation of proteins under normal and heat shock conditions changed the isoform composition of Hop, providing strong evidence that Hop was phosphorylated in vivo. Surface plasmon resonance (SPR) and glutatione-S-transferase (GST) co-precipitation studies showed that a cdc2-kinase phosphorylated mimic of Hop disrupted Hop-Hsp90 binding. A full length Hop-EGFP construct, as well as substitution mutants of the predicted NLS residues within the Hop-EGFP construct, were transfected into baby hamster kidney (BHK)-21 cells in order to establish the subcellular localization of Hop under heat stress and to test whether predicted residues were critical for nuclear localization of Hop. Under normal conditions, both Hop-EGFP and the NLS mutants were predominantly cytosolic, but when the cells were subjected to heat stress, Hop and its NLS-mutants were localized to both the cytosol and the nucleus. SPR and GST co-precipitation studies showed that substitution of the residues within the major arm of the putative NLS abrogated Hop-Hsp90 interactions. The data obtained from this study, showed for the first time, that Hop was phosphorylated in vivo and suggested that phosphorylation of Hop by cdc2-kinase could inhibit Hop-Hsp90 interactions. Moreover, these results suggested that the subcellular localization of Hop was dependent on stress levels of the cell, particularly heat stress. We propose that the nuclear localization of Hop may be primarily regulated by stress and secondarily by cell cycle arrest. The major arm of the putative NLS did not affect the localization of Hop directly, but was shown to be critical for Hop-Hsp90 binding in vitro. The results of this study suggested that binding of Hop to Hsp90 sequestered Hop within the cytosol and that Hsp90 acted as a cytosolic retention factor for Hop. Both phosphorylation of Hop, and its subcellular localization, appeared to be intimately related to its interaction with Hsp90 as a co-chaperone.
- Full Text:
- Date Issued: 2008
- Authors: Daniel, Sheril
- Date: 2008
- Subjects: Molecular chaperones Phosphorylation Proteins Heat shock proteins Surface plasmon resonance Cytosol
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:3996 , http://hdl.handle.net/10962/d1004056
- Description: Hop (Hsp70-Hsp90 Organizing Protein) is a co-chaperone of two major molecular chaperones, Hsp70 and Hsp90, and acts by transferring substrates from Hsp70 to Hsp90. Although under normal conditions Hop is predominantly localized within the cytosol, Hop has been detected in the nucleus under certain conditions including cell cycle arrest. A putative nuclear localization signal (NLS) has been identified within Hop, which overlaps with the TPR2A domain (previously shown to be critical for Hop-Hsp90 interactions). Hop is phosphorylated in vitro by two cell cycle kinases, namely, casein kinase II (CKII) at S189 and cdc2-kinase at T198; both residues are found upstream of the putative NLS and TPR2A domain. Mimicking phosphorylation at either phosphorylation site appeared to affect the subcellular localization of Hop. The aim of this study was to characterize Hop with respect to its phosphorylation status in vivo, as well as its subcellular localization pattern under heat stress and determine how these properties affected its interaction with Hsp90 as a co-chaperone. Dephosphorylation of proteins under normal and heat shock conditions changed the isoform composition of Hop, providing strong evidence that Hop was phosphorylated in vivo. Surface plasmon resonance (SPR) and glutatione-S-transferase (GST) co-precipitation studies showed that a cdc2-kinase phosphorylated mimic of Hop disrupted Hop-Hsp90 binding. A full length Hop-EGFP construct, as well as substitution mutants of the predicted NLS residues within the Hop-EGFP construct, were transfected into baby hamster kidney (BHK)-21 cells in order to establish the subcellular localization of Hop under heat stress and to test whether predicted residues were critical for nuclear localization of Hop. Under normal conditions, both Hop-EGFP and the NLS mutants were predominantly cytosolic, but when the cells were subjected to heat stress, Hop and its NLS-mutants were localized to both the cytosol and the nucleus. SPR and GST co-precipitation studies showed that substitution of the residues within the major arm of the putative NLS abrogated Hop-Hsp90 interactions. The data obtained from this study, showed for the first time, that Hop was phosphorylated in vivo and suggested that phosphorylation of Hop by cdc2-kinase could inhibit Hop-Hsp90 interactions. Moreover, these results suggested that the subcellular localization of Hop was dependent on stress levels of the cell, particularly heat stress. We propose that the nuclear localization of Hop may be primarily regulated by stress and secondarily by cell cycle arrest. The major arm of the putative NLS did not affect the localization of Hop directly, but was shown to be critical for Hop-Hsp90 binding in vitro. The results of this study suggested that binding of Hop to Hsp90 sequestered Hop within the cytosol and that Hsp90 acted as a cytosolic retention factor for Hop. Both phosphorylation of Hop, and its subcellular localization, appeared to be intimately related to its interaction with Hsp90 as a co-chaperone.
- Full Text:
- Date Issued: 2008
Information technology support for transformation in higher educational institutions in South Africa
- Authors: Roets, Rina Annette
- Date: 2008
- Subjects: Education, Higher -- South Africa Educational change -- South Africa Universities and colleges -- South Africa Universities and colleges -- South Africa -- Administration Information technology -- South Africa Educational technology -- South Africa Education, Higher -- Technological innovations -- South Africa Knowledge management
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1145 , http://hdl.handle.net/10962/d1002775
- Description: Higher Education Institutions (HEIs) have been in a state of change, and in South Africa, the term “transformation” is used to describe the changes occurring. These changes have implications for the structure, processes and focus of HEIs, and as such have implications for Information Technology (IS/ICT) support for HEIs. IS/ICT support for organisations is predicated on several factors, such as effective informational and technical support at all levels of the organisation, but especially support for the strategic goals of the organisation (alignment). For organisations in a state of rapid change other issues need to be considered, such as flexibility, and new and diverse information and communication needs. This paper investigates the use of Information Technology to support HEIs in transformation. The research examines factors that make HEIs less amenable to rationalist techniques such as mixed management styles and a “different” value chain. The difficulties for IS/ICT support of HEIs at all managerial levels is discussed, especially the issue of alignment with institutional goals. Thereafter, transformation of HEIs and the possibility of IS/ICT support in achieving the ill-defined goal of transformation is examined. The research uses management and IS/ICT theories such as the widely used and reported Porter’s value chain, Anthony’s information model, and Minzberg’s organisational model to suggest an analysis model for HEIs (Applegate, McFarlan and McKenney, 1996; Minzberg, 1979; Ward and Peppard, 2002). Furthermore, from the analysis of the literature, a model of antecedent factors for successful HEI transformation supported by IS/ICT is proposed. The research makes use of a comparative case study approach in which 3 (three) South African HEIs are investigated through the “lens” of the developed model. The major finding of the research is that the potential use of IS/ICT support for HEIs is not optimal in the three cases examined. Results of the analysis suggest that: • IS/ICT alignment with organisational goals at HEIs is low and holistic IS/ICT strategic management is lacking. The areas of Knowledge Management and Communication Management are conducted informally and Knowledge Management, especially, is not fully exploited. • The greatest area of concern is the lack of IS/ICT support for academic management, where academics are increasingly required to perform administrative and managerial tasks. • The merger/incorporation information needs have not caused major system problems, but other intangible aspects of the mergers/incorporations could be better supported by IS/ICT. The research concludes with a set of actions that should ensure a higher level of support, amongst which are the more holistic management of IS/ICT especially for Academic management needs, and particularly the use of IS/ICT in innovative ways to overcome the challenges of the “transformed” Universities: There are areas of excellence but the full possibilities afforded by technology are not exploited maximally in support of transformation. Research suggests that the reasons for this are mainly the lack of holistic strategic management of IS/ICT.
- Full Text:
- Date Issued: 2008
Information technology support for transformation in higher educational institutions in South Africa
- Authors: Roets, Rina Annette
- Date: 2008
- Subjects: Education, Higher -- South Africa Educational change -- South Africa Universities and colleges -- South Africa Universities and colleges -- South Africa -- Administration Information technology -- South Africa Educational technology -- South Africa Education, Higher -- Technological innovations -- South Africa Knowledge management
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1145 , http://hdl.handle.net/10962/d1002775
- Description: Higher Education Institutions (HEIs) have been in a state of change, and in South Africa, the term “transformation” is used to describe the changes occurring. These changes have implications for the structure, processes and focus of HEIs, and as such have implications for Information Technology (IS/ICT) support for HEIs. IS/ICT support for organisations is predicated on several factors, such as effective informational and technical support at all levels of the organisation, but especially support for the strategic goals of the organisation (alignment). For organisations in a state of rapid change other issues need to be considered, such as flexibility, and new and diverse information and communication needs. This paper investigates the use of Information Technology to support HEIs in transformation. The research examines factors that make HEIs less amenable to rationalist techniques such as mixed management styles and a “different” value chain. The difficulties for IS/ICT support of HEIs at all managerial levels is discussed, especially the issue of alignment with institutional goals. Thereafter, transformation of HEIs and the possibility of IS/ICT support in achieving the ill-defined goal of transformation is examined. The research uses management and IS/ICT theories such as the widely used and reported Porter’s value chain, Anthony’s information model, and Minzberg’s organisational model to suggest an analysis model for HEIs (Applegate, McFarlan and McKenney, 1996; Minzberg, 1979; Ward and Peppard, 2002). Furthermore, from the analysis of the literature, a model of antecedent factors for successful HEI transformation supported by IS/ICT is proposed. The research makes use of a comparative case study approach in which 3 (three) South African HEIs are investigated through the “lens” of the developed model. The major finding of the research is that the potential use of IS/ICT support for HEIs is not optimal in the three cases examined. Results of the analysis suggest that: • IS/ICT alignment with organisational goals at HEIs is low and holistic IS/ICT strategic management is lacking. The areas of Knowledge Management and Communication Management are conducted informally and Knowledge Management, especially, is not fully exploited. • The greatest area of concern is the lack of IS/ICT support for academic management, where academics are increasingly required to perform administrative and managerial tasks. • The merger/incorporation information needs have not caused major system problems, but other intangible aspects of the mergers/incorporations could be better supported by IS/ICT. The research concludes with a set of actions that should ensure a higher level of support, amongst which are the more holistic management of IS/ICT especially for Academic management needs, and particularly the use of IS/ICT in innovative ways to overcome the challenges of the “transformed” Universities: There are areas of excellence but the full possibilities afforded by technology are not exploited maximally in support of transformation. Research suggests that the reasons for this are mainly the lack of holistic strategic management of IS/ICT.
- Full Text:
- Date Issued: 2008
Effects of coastal topography on physiology, behaviour and genetics of indigenous (Perna perna) and invasive (Mytilus galloprovincialis) mussels
- Authors: Nicastro, Katy R
- Date: 2008
- Subjects: Mussels -- Ecology -- South Africa , Perna -- Physiology -- South Africa , Perna -- Behavior -- South Africa , Mussels -- Behavior -- Environmental factors -- South Africa , Mussels -- Habitat -- South Africa , Mytilus galloprovincialis , Mytilus galloprovincialis -- Physiology -- South Africa , Mytilus galloprovincialis -- Behavior -- South Africa , Mytilus galloprovincialis -- Genetics -- South Africa , Coastal ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5833 , http://hdl.handle.net/10962/d1008262
- Description: Organisms inhabit environments that have many dimensions, each of which can vary temporally and spatially. The spatial-temporal variations of environmental stressors and disturbances may have major but different effects on indigenous and invasive species, favouring either of them at different times and places. The invasive mussel Mytilus galloprovincialis invaded the South African coast 30 years ago and, on the south coast of South Africa, it now competes and co-exists with the indigenous Perna perna in the lower eulittoral zone (referred to here as the mussel zone) The invasive and indigenous species dominate the upper and the lower mussel zones respectively, while the two co-exist in the mid-zone. My results show that intertidal mussels experience, and respond to, spatial and temporal fluctuations of several biotic and abiotic stressors. The invasive and the indigenous species adopt different strategies when reacting to environmental factors and their physiological and behavioural responses vary in time and in different habitats as different pressures become of overriding importance. Attachment strength of both species decreased in summer and increased in winter, and was higher on the open coast than in bays for both species, showing a strong positive correlation with wave force in time and space. P. perna had significantly higher attachment strength than M. galloprovincialis but, contrary to previous studies, the difference in gonad index between the two species varied according to the habitat. In bay habitats, M. galloprovincialis had a higher maximum reproductive effort than P. perna, however, on the open coast, there was no significant difference between the two species, suggesting that for the invasive species wave action is a limiting factor not only in terms of the attachment strength but also of energy availability for reproductive tissue development. Major spawning events occurred during periods of low wave action while minor spawning coincided with periods of intense hydrodynamic stress. On the open coast, gonad index was negatively correlated with attachment strength for both species while, in bays, there was no correlation between these two factors for either. The two species also showed different behaviour. In the field, M. galloprovincialis moved significantly more than P. perna over a period of six months. The higher mobility of the invasive species was also confirmed in the laboratory where, in general, M. galloprovincialis formed clumps more readily than P. perna. Taken collectively, these results suggest that channelling more energy into attachment strength limits reproductive tissue development and that, while the indigenous species invests more in byssal production, the invasive species adopts a more dynamic strategy looking for aggregation or a safer arrangement. Higher endolithic infestation and a greater expression of heat shock proteins (Hsps) in mussel populations on the open coast than in bays indicate that this habitat is a more stressful environment not only in terms of wave action. Endolith damaged mussels had significantly lower attachment strengths and condition indices than clean mussels, probably due to the need to channel energy into shell repair. The constant shell repair and expression of Hsps typical of open coast populations are energetically demanding processes. These observations suggest that on the open coast, mussels are subjected to more severe energetic constraints than in bay habitats. Wave and sand stress fluctuated seasonally with the former having a greater effect on mussel mortality on the open coast and the latter a higher impact on bay populations. Overall, mussel mortality rates were higher on the open coast than in bays. My results show that populations on the open coast had fewer private haplotypes and less genetic endemism than those inside bays. Gene flow analysis showed the relatively stable bay habitats act as source populations with greater genetic migration rates out of bays than into them. These differences in genetic structure on scales of las of kilometers show that coastal configuration strongly affects selection, larval dispersal and haplotype diversity. Environmental gradients that are key factors in species distribution over large geographical scales can also be responsible for micro-scale distributions. My results show that M. galloprovincialis colonizes the upper mussel zone where temperature is high, but is less tolerant to this stressor and has to maintain a high expression of Hsps. This suggests that temperature is probably a limiting factor in its invasion towards the sub-tropical east coast. There are inter- and intra-specific differences in responses to the environment which highlight the efforts of M. galloprovincialis and P. perna to optimize resource utilization for survival and reproduction. Determining these differences is crucial to understanding patterns of co-existence between competing indigenous and invasive species.
- Full Text:
- Date Issued: 2008
- Authors: Nicastro, Katy R
- Date: 2008
- Subjects: Mussels -- Ecology -- South Africa , Perna -- Physiology -- South Africa , Perna -- Behavior -- South Africa , Mussels -- Behavior -- Environmental factors -- South Africa , Mussels -- Habitat -- South Africa , Mytilus galloprovincialis , Mytilus galloprovincialis -- Physiology -- South Africa , Mytilus galloprovincialis -- Behavior -- South Africa , Mytilus galloprovincialis -- Genetics -- South Africa , Coastal ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5833 , http://hdl.handle.net/10962/d1008262
- Description: Organisms inhabit environments that have many dimensions, each of which can vary temporally and spatially. The spatial-temporal variations of environmental stressors and disturbances may have major but different effects on indigenous and invasive species, favouring either of them at different times and places. The invasive mussel Mytilus galloprovincialis invaded the South African coast 30 years ago and, on the south coast of South Africa, it now competes and co-exists with the indigenous Perna perna in the lower eulittoral zone (referred to here as the mussel zone) The invasive and indigenous species dominate the upper and the lower mussel zones respectively, while the two co-exist in the mid-zone. My results show that intertidal mussels experience, and respond to, spatial and temporal fluctuations of several biotic and abiotic stressors. The invasive and the indigenous species adopt different strategies when reacting to environmental factors and their physiological and behavioural responses vary in time and in different habitats as different pressures become of overriding importance. Attachment strength of both species decreased in summer and increased in winter, and was higher on the open coast than in bays for both species, showing a strong positive correlation with wave force in time and space. P. perna had significantly higher attachment strength than M. galloprovincialis but, contrary to previous studies, the difference in gonad index between the two species varied according to the habitat. In bay habitats, M. galloprovincialis had a higher maximum reproductive effort than P. perna, however, on the open coast, there was no significant difference between the two species, suggesting that for the invasive species wave action is a limiting factor not only in terms of the attachment strength but also of energy availability for reproductive tissue development. Major spawning events occurred during periods of low wave action while minor spawning coincided with periods of intense hydrodynamic stress. On the open coast, gonad index was negatively correlated with attachment strength for both species while, in bays, there was no correlation between these two factors for either. The two species also showed different behaviour. In the field, M. galloprovincialis moved significantly more than P. perna over a period of six months. The higher mobility of the invasive species was also confirmed in the laboratory where, in general, M. galloprovincialis formed clumps more readily than P. perna. Taken collectively, these results suggest that channelling more energy into attachment strength limits reproductive tissue development and that, while the indigenous species invests more in byssal production, the invasive species adopts a more dynamic strategy looking for aggregation or a safer arrangement. Higher endolithic infestation and a greater expression of heat shock proteins (Hsps) in mussel populations on the open coast than in bays indicate that this habitat is a more stressful environment not only in terms of wave action. Endolith damaged mussels had significantly lower attachment strengths and condition indices than clean mussels, probably due to the need to channel energy into shell repair. The constant shell repair and expression of Hsps typical of open coast populations are energetically demanding processes. These observations suggest that on the open coast, mussels are subjected to more severe energetic constraints than in bay habitats. Wave and sand stress fluctuated seasonally with the former having a greater effect on mussel mortality on the open coast and the latter a higher impact on bay populations. Overall, mussel mortality rates were higher on the open coast than in bays. My results show that populations on the open coast had fewer private haplotypes and less genetic endemism than those inside bays. Gene flow analysis showed the relatively stable bay habitats act as source populations with greater genetic migration rates out of bays than into them. These differences in genetic structure on scales of las of kilometers show that coastal configuration strongly affects selection, larval dispersal and haplotype diversity. Environmental gradients that are key factors in species distribution over large geographical scales can also be responsible for micro-scale distributions. My results show that M. galloprovincialis colonizes the upper mussel zone where temperature is high, but is less tolerant to this stressor and has to maintain a high expression of Hsps. This suggests that temperature is probably a limiting factor in its invasion towards the sub-tropical east coast. There are inter- and intra-specific differences in responses to the environment which highlight the efforts of M. galloprovincialis and P. perna to optimize resource utilization for survival and reproduction. Determining these differences is crucial to understanding patterns of co-existence between competing indigenous and invasive species.
- Full Text:
- Date Issued: 2008
A stable isotope approach to trophic ecology resolving food webs in intertidal ecosystems
- Authors: Hill, Jaclyn Marie
- Date: 2008
- Subjects: Stable isotopes Food chains (Ecology) Stable isotopes in ecological research Intertidal ecology Mussels -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5771 , http://hdl.handle.net/10962/d1005459
- Description: There are broad differences in regional oceanography and primary production around the South African coast, which we might expect to give rise to major differences in trophic pathways. δ⁻¹³C and δ⁻¹⁵N isotopic ratios of suspended particulate matter (SPM), mussels, various intertidal consumers and common macroalgae along the South African coastline were explored using stable isotope analysis to investigate biogeographic and temporal variability of isotopic signatures of marine intertidal consumers and their food sources around the coast of South Africa, with a focus on evaluating the dependence of intertidal mussels on phytoplankton and macroalgal-derived organic carbon. Isotopic equilibration rates of four mussel tissues were determined through laboratory feeding experiments, which established that adductor tissue had the slowest isotopic turnover rate, and was subsequently used as an indication of overall mussel diet. Biogeographic, temporal and nearshore/offshore trends of isotopic ratios of SPM were investigated along 10km transects perpendicular to the coast and SPM exhibited overall trends of carbon depletion when moving from west to east along the coastline and from nearshore to offshore water, in both cases suggesting a shift from macrophyte detritus to a phytoplankton signature. δ⁻¹³C signatures of SPM also revealed temporal and biogeographic variation that had strong ties to local oceanography, being closely correlated to regional hydrographic features and tidal influences. Mixing models indicated filter feeders demonstrated over 50% dependence on nearshore SPM for organic carbon and it was possible to categorize them into geographic groups based on their carbon and nitrogen signatures, suggesting biogeographic shifts in resources. Biogeographic shifts in diet were also seen in some grazers. Difficulties in relating macroalgae to mussel diet led to investigations into the isotopic changes associated with macroalgal decomposition. Variation in photosynthetic fractionation, leaching and microbial mineralization are believed to have resulted from species-specific patterns of degradation. Although the strong links between carbon signatures and local oceanography indicate that stable isotope analysis is a powerful tool for the study of water mixing and coastal hydrography in relation to food-web analyses, substantial variation in fractionation of primary consumers, along with different periods of time integration between consumers and their food sources must be considered in future studies, to resolve trophic links in marine food webs successfully.
- Full Text:
- Date Issued: 2008
- Authors: Hill, Jaclyn Marie
- Date: 2008
- Subjects: Stable isotopes Food chains (Ecology) Stable isotopes in ecological research Intertidal ecology Mussels -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5771 , http://hdl.handle.net/10962/d1005459
- Description: There are broad differences in regional oceanography and primary production around the South African coast, which we might expect to give rise to major differences in trophic pathways. δ⁻¹³C and δ⁻¹⁵N isotopic ratios of suspended particulate matter (SPM), mussels, various intertidal consumers and common macroalgae along the South African coastline were explored using stable isotope analysis to investigate biogeographic and temporal variability of isotopic signatures of marine intertidal consumers and their food sources around the coast of South Africa, with a focus on evaluating the dependence of intertidal mussels on phytoplankton and macroalgal-derived organic carbon. Isotopic equilibration rates of four mussel tissues were determined through laboratory feeding experiments, which established that adductor tissue had the slowest isotopic turnover rate, and was subsequently used as an indication of overall mussel diet. Biogeographic, temporal and nearshore/offshore trends of isotopic ratios of SPM were investigated along 10km transects perpendicular to the coast and SPM exhibited overall trends of carbon depletion when moving from west to east along the coastline and from nearshore to offshore water, in both cases suggesting a shift from macrophyte detritus to a phytoplankton signature. δ⁻¹³C signatures of SPM also revealed temporal and biogeographic variation that had strong ties to local oceanography, being closely correlated to regional hydrographic features and tidal influences. Mixing models indicated filter feeders demonstrated over 50% dependence on nearshore SPM for organic carbon and it was possible to categorize them into geographic groups based on their carbon and nitrogen signatures, suggesting biogeographic shifts in resources. Biogeographic shifts in diet were also seen in some grazers. Difficulties in relating macroalgae to mussel diet led to investigations into the isotopic changes associated with macroalgal decomposition. Variation in photosynthetic fractionation, leaching and microbial mineralization are believed to have resulted from species-specific patterns of degradation. Although the strong links between carbon signatures and local oceanography indicate that stable isotope analysis is a powerful tool for the study of water mixing and coastal hydrography in relation to food-web analyses, substantial variation in fractionation of primary consumers, along with different periods of time integration between consumers and their food sources must be considered in future studies, to resolve trophic links in marine food webs successfully.
- Full Text:
- Date Issued: 2008
Bioprocess development for removal of nitrogenous compounds from precious metal refinery wastewater
- Manipura, Walappuly Mudiyanselage Janakasiri Aruna Shantha Bandara
- Authors: Manipura, Walappuly Mudiyanselage Janakasiri Aruna Shantha Bandara
- Date: 2008
- Subjects: Factory and trade waste Centralized industrial waste treatment facilities Metals -- Absorption and adsorption Metals -- Environmental aspects Water -- Purification -- Mathematical models Water quality management Water reuse Metals -- Refining Microbiology -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4076 , http://hdl.handle.net/10962/d1007341
- Description: Removal of nitrogenous compounds from precious metal refinery (PMR) wastewater is important in terms of avoiding eutrophication (environmental protection), metal recovery (increased overall process efficiency and value recovery) and reuse of treated water (maximum use of natural resources). Extreme pH conditions (4 to 13 depending on the wastewater stream), high chemical oxygen demand (> 10,000 mg/I), numerous metals and high concentrations of those metals (> 20 mg/l of platinum group metals) in the wastewater are the main challenges for biological removal of nitrogenous compounds from PMR wastewater. Nitrogenous compounds such as NH₄⁺-N and N0₃-N are strong metal ligands, which make it difficult to recover metals from the wastewater. Therefore, a bioprocess was developed for removal of nitrogenous compounds from carefully simulated PMR wastewater. A preliminary investigation of metal wastewater was carried out to determine its composition and physico-chemical properties, the ability to nitrify and denitrify under different pH conditions and denitrification with different carbon Source compounds and amounts. Even at pH 4, nitrification could be carried out. A suitable hydraulic retention time was found to be 72 hours. There was no significant difference between sodium acetate and sodium lactate as carbon sources for denitrification. Based on these results, a reactor comparison study was carried out using simulated PMR wastewater in three types of reactors: continuously stirred tank reactor (CSTR), packed-bed reactor (PBR) and airlift suspension reactor (ALSR). These reactors were fed with 30 mg/l of Rh bound in an NH₄⁺ based compound (Claus salt: pentaaminechlororhodium (III) dichloride). Total nitrogen removal efficiencies of > 68 % , > 79 % and > 45 % were obtained in the CSTR, PBR and ALSR, respectively. Serially connected CSTR-PBR and PBR-CSTR reactor configurations were then studied to determine the best configuration for maximum removal of nitrogenous compounds from the wastewater. The PBR-CSTR configuration gave consistent biomass retention and automatic pH control in the CSTR. Ammonium removal efficiencies > 95 % were achieved in both reactors. As poor nitrate removal was observed a toxicity study was carried out using respirometry and the half saturation inhibition coefficients for Pt, Pd, Rh and Ru were found to be 15.81, 25.00, 33.34 and 39.25 mg/l, respectively. A mathematical model was developed to describe the nitrogen removal in PMR wastewater using activated sludge model number 1 (ASMl), two step nitrification and metal toxicity. An operational protocol was developed based on the literature review, experimental work and simulation results. The optimum reactor configuration under the set conditions (20 mg/I of Rh and < 100 mg/I of NH₄⁺-N) was found to be PBR-CSTR-PBR process, which achieved overall NH₄⁺-N and N0₃⁻-N removal efficiencies of > 90 % and 95 %, respectively. Finally, a rudimentary microbial characterisation was carried out on subsamples from the CSTR and PBRsecondary. It was found that the CSTR biomass consisted of both rods and cocci while PBRsecondary consisted of rods only. Based on these experimental works, further research needs and recommendations were made for optimisation of the developed bioprocess for removal of nitrogenous compounds from PMR wastewater.
- Full Text:
- Date Issued: 2008
- Authors: Manipura, Walappuly Mudiyanselage Janakasiri Aruna Shantha Bandara
- Date: 2008
- Subjects: Factory and trade waste Centralized industrial waste treatment facilities Metals -- Absorption and adsorption Metals -- Environmental aspects Water -- Purification -- Mathematical models Water quality management Water reuse Metals -- Refining Microbiology -- Research
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4076 , http://hdl.handle.net/10962/d1007341
- Description: Removal of nitrogenous compounds from precious metal refinery (PMR) wastewater is important in terms of avoiding eutrophication (environmental protection), metal recovery (increased overall process efficiency and value recovery) and reuse of treated water (maximum use of natural resources). Extreme pH conditions (4 to 13 depending on the wastewater stream), high chemical oxygen demand (> 10,000 mg/I), numerous metals and high concentrations of those metals (> 20 mg/l of platinum group metals) in the wastewater are the main challenges for biological removal of nitrogenous compounds from PMR wastewater. Nitrogenous compounds such as NH₄⁺-N and N0₃-N are strong metal ligands, which make it difficult to recover metals from the wastewater. Therefore, a bioprocess was developed for removal of nitrogenous compounds from carefully simulated PMR wastewater. A preliminary investigation of metal wastewater was carried out to determine its composition and physico-chemical properties, the ability to nitrify and denitrify under different pH conditions and denitrification with different carbon Source compounds and amounts. Even at pH 4, nitrification could be carried out. A suitable hydraulic retention time was found to be 72 hours. There was no significant difference between sodium acetate and sodium lactate as carbon sources for denitrification. Based on these results, a reactor comparison study was carried out using simulated PMR wastewater in three types of reactors: continuously stirred tank reactor (CSTR), packed-bed reactor (PBR) and airlift suspension reactor (ALSR). These reactors were fed with 30 mg/l of Rh bound in an NH₄⁺ based compound (Claus salt: pentaaminechlororhodium (III) dichloride). Total nitrogen removal efficiencies of > 68 % , > 79 % and > 45 % were obtained in the CSTR, PBR and ALSR, respectively. Serially connected CSTR-PBR and PBR-CSTR reactor configurations were then studied to determine the best configuration for maximum removal of nitrogenous compounds from the wastewater. The PBR-CSTR configuration gave consistent biomass retention and automatic pH control in the CSTR. Ammonium removal efficiencies > 95 % were achieved in both reactors. As poor nitrate removal was observed a toxicity study was carried out using respirometry and the half saturation inhibition coefficients for Pt, Pd, Rh and Ru were found to be 15.81, 25.00, 33.34 and 39.25 mg/l, respectively. A mathematical model was developed to describe the nitrogen removal in PMR wastewater using activated sludge model number 1 (ASMl), two step nitrification and metal toxicity. An operational protocol was developed based on the literature review, experimental work and simulation results. The optimum reactor configuration under the set conditions (20 mg/I of Rh and < 100 mg/I of NH₄⁺-N) was found to be PBR-CSTR-PBR process, which achieved overall NH₄⁺-N and N0₃⁻-N removal efficiencies of > 90 % and 95 %, respectively. Finally, a rudimentary microbial characterisation was carried out on subsamples from the CSTR and PBRsecondary. It was found that the CSTR biomass consisted of both rods and cocci while PBRsecondary consisted of rods only. Based on these experimental works, further research needs and recommendations were made for optimisation of the developed bioprocess for removal of nitrogenous compounds from PMR wastewater.
- Full Text:
- Date Issued: 2008
Purification, characterisation and application of inulinase and transferase enzymes in the production of fructose and oligosaccharides
- Authors: Mutanda, Taurai
- Date: 2008
- Subjects: Fructose Transferases Oligosaccharides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4448 , http://hdl.handle.net/10962/d1007734
- Description: Inulin hydrolysis can occur as a result of the action of exoinulinases and endoinulinases acting alone or synergistically. Exoinulinases cleave the non-reducing β-(2, I) end of inulin releasing fructose while endoinulinases act on the internal linkages randomly to release inulotrioses (F₃), inulotetraoses (F₄) and inulopentaoses (F₅) as major products. Fructosyltransferases act by cleaving a sucrose molecule and then transferring the liberated fructose molecule to an acceptor molecule such as sucrose or another oligosaccharide to elongate the short chain fructooligosaccharide. The production of high yields of oligosaccharides of specific chain length from simple raw materials such as inulin and sucrose is a challenge. Oligosaccharides of chain length up to degree of polymerisation (DP) 5 and fructose were produced using preparations of three commercial microbial enzymes. Production of these novel oligosaccharides was achieved by employing response surface methodology (RSM) with central composite experimental design (CCD) for optimising product yield. Using a crude Novozyme 960 endoinulinase preparation isolated from Aspergillus niger, the following conditions gave a high inulooligosaccharide (lOS) yield, temperature (60 ºC), 150 g/L inulin concentration, 48 h incubation; pH 6.0 and enzyme dosage of 60 U/ml. Under these conditions, inulotrioses (70.3 mM), inulotetraoses (38.8 mM), and inulopentaoses, (3.5 mM) were produced. Response surface regression predicted similar product levels under similar conditions. The crude endoinulinase was purified through a three step purification procedure with a yield of 1.11 % and 3.5 fold purification. The molecular weight of this endoinulinase was estimated to be 68 .1 kDa by SDS-PAGE and its endoinulinase nature was confirmed by native PAGE. The purified endoinulinase was more efficient in production of lOS than the crude endoinulinase preparation. The purified endoinulinase demonstrated a high affinity for the inulin substrate (Km[subscript] 3.53 mM, Vmax[subscript] 666.67 μmol/min/ml). Pectinex Ultra SP-L, a commercial crude enzyme preparation isolated from Aspergillus aculeatus is a cocktail of several enzymes including a fructosyltransferase. The crude enzyme showed both transfructosylation and hydrolytic activity in 200 to 600 g/L sucrose. The main fructooligosaccharides produced from sucrose were l-kestose (GF₂), nystose (GF₃) and fructofuranosyl nystose (GF₄). After the first RSM, with the coded independent variables of temperature, incubation time, pH and sucrose concentration, the highest levels of GF₂, was 68.61 mM, under sucrose concentration 600 g/L, temperature 60°C, enzyme dosage 20 U/ml , pH 5.6, after 4 h incubation. A sucrose concentration of 400 g/L favoured the synthesis of high levels of GF₃ and GF₄. In the second RSM the maximal yields of GF₂, GF₃ and GF₄ were 152.07 mM, 131.38 mM and 43.99 mM respectively. A purified fructosyltransferase did not synthesise GF₄. Ammonium ions were demonstrated to enhance the yield of FOS. A mixture of glucose and fructose was used as substrate for FOS synthesis and no FOS were formed. Glucose was shown to be an end product inhibitor of the fructosyltransferase and therefore hinders the formation of high FOS yield. Fructozyme, isolated from Aspergillus ficuum is a mixture of exo and endoinulinases with the former being predominant was used for fructose production from inulin hydrolysis. The exoinulinase was purified to electrophoretic homogeneity by a three step purification procedure. The molecular weight of the enzyme was estimated to be 53 kDa with a 2 I % yield and 4.2-fold. Response surface regression was used to predict the maximum fructose levels achievable under the combinations of temperature, enzyme dosage and incubation time. A reaction time (48 h), enzyme dosage (100 U/ml) and inulin concentration (150 g/l) at pH 5.0 at 50°C gave higher fructose levels (106.6 mg/ml) using crude exoinulinase as compared to 98.43 mg/ml using the purified exoinulinase. These findings indicate that higher levels of fructose require longer incubation periods and higher inulin substrate concentrations with higher enzyme dosage. The crude exoinulinase preparation gave fairly higher levels of fructose than the purified exoinulinase and this is due to the presence of other hydrolytic enzymes in the crude preparation. The conditions established by RSM and CCO were adequate in producing high yield of oligosaccharides and fructose and can therefore be applied for their industrial production since they are in high demand due to their health benefits as prebiotics.
- Full Text:
- Date Issued: 2008
- Authors: Mutanda, Taurai
- Date: 2008
- Subjects: Fructose Transferases Oligosaccharides
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4448 , http://hdl.handle.net/10962/d1007734
- Description: Inulin hydrolysis can occur as a result of the action of exoinulinases and endoinulinases acting alone or synergistically. Exoinulinases cleave the non-reducing β-(2, I) end of inulin releasing fructose while endoinulinases act on the internal linkages randomly to release inulotrioses (F₃), inulotetraoses (F₄) and inulopentaoses (F₅) as major products. Fructosyltransferases act by cleaving a sucrose molecule and then transferring the liberated fructose molecule to an acceptor molecule such as sucrose or another oligosaccharide to elongate the short chain fructooligosaccharide. The production of high yields of oligosaccharides of specific chain length from simple raw materials such as inulin and sucrose is a challenge. Oligosaccharides of chain length up to degree of polymerisation (DP) 5 and fructose were produced using preparations of three commercial microbial enzymes. Production of these novel oligosaccharides was achieved by employing response surface methodology (RSM) with central composite experimental design (CCD) for optimising product yield. Using a crude Novozyme 960 endoinulinase preparation isolated from Aspergillus niger, the following conditions gave a high inulooligosaccharide (lOS) yield, temperature (60 ºC), 150 g/L inulin concentration, 48 h incubation; pH 6.0 and enzyme dosage of 60 U/ml. Under these conditions, inulotrioses (70.3 mM), inulotetraoses (38.8 mM), and inulopentaoses, (3.5 mM) were produced. Response surface regression predicted similar product levels under similar conditions. The crude endoinulinase was purified through a three step purification procedure with a yield of 1.11 % and 3.5 fold purification. The molecular weight of this endoinulinase was estimated to be 68 .1 kDa by SDS-PAGE and its endoinulinase nature was confirmed by native PAGE. The purified endoinulinase was more efficient in production of lOS than the crude endoinulinase preparation. The purified endoinulinase demonstrated a high affinity for the inulin substrate (Km[subscript] 3.53 mM, Vmax[subscript] 666.67 μmol/min/ml). Pectinex Ultra SP-L, a commercial crude enzyme preparation isolated from Aspergillus aculeatus is a cocktail of several enzymes including a fructosyltransferase. The crude enzyme showed both transfructosylation and hydrolytic activity in 200 to 600 g/L sucrose. The main fructooligosaccharides produced from sucrose were l-kestose (GF₂), nystose (GF₃) and fructofuranosyl nystose (GF₄). After the first RSM, with the coded independent variables of temperature, incubation time, pH and sucrose concentration, the highest levels of GF₂, was 68.61 mM, under sucrose concentration 600 g/L, temperature 60°C, enzyme dosage 20 U/ml , pH 5.6, after 4 h incubation. A sucrose concentration of 400 g/L favoured the synthesis of high levels of GF₃ and GF₄. In the second RSM the maximal yields of GF₂, GF₃ and GF₄ were 152.07 mM, 131.38 mM and 43.99 mM respectively. A purified fructosyltransferase did not synthesise GF₄. Ammonium ions were demonstrated to enhance the yield of FOS. A mixture of glucose and fructose was used as substrate for FOS synthesis and no FOS were formed. Glucose was shown to be an end product inhibitor of the fructosyltransferase and therefore hinders the formation of high FOS yield. Fructozyme, isolated from Aspergillus ficuum is a mixture of exo and endoinulinases with the former being predominant was used for fructose production from inulin hydrolysis. The exoinulinase was purified to electrophoretic homogeneity by a three step purification procedure. The molecular weight of the enzyme was estimated to be 53 kDa with a 2 I % yield and 4.2-fold. Response surface regression was used to predict the maximum fructose levels achievable under the combinations of temperature, enzyme dosage and incubation time. A reaction time (48 h), enzyme dosage (100 U/ml) and inulin concentration (150 g/l) at pH 5.0 at 50°C gave higher fructose levels (106.6 mg/ml) using crude exoinulinase as compared to 98.43 mg/ml using the purified exoinulinase. These findings indicate that higher levels of fructose require longer incubation periods and higher inulin substrate concentrations with higher enzyme dosage. The crude exoinulinase preparation gave fairly higher levels of fructose than the purified exoinulinase and this is due to the presence of other hydrolytic enzymes in the crude preparation. The conditions established by RSM and CCO were adequate in producing high yield of oligosaccharides and fructose and can therefore be applied for their industrial production since they are in high demand due to their health benefits as prebiotics.
- Full Text:
- Date Issued: 2008
The effects of elephants at low densities and after short occupation time on the ecosystems of the Eastern Cape Province, South Africa
- Authors: Parker, Daniel Matthew
- Date: 2008
- Subjects: Elephants -- South Africa -- Eastern Cape Biotic communities -- South Africa -- Eastern Cape Animal populations -- South Africa -- Eastern Cape Plant communities -- South Africa -- Eastern Cape Mammals -- Ecology -- South Africa -- Eastern Cape Animal-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5678 , http://hdl.handle.net/10962/d1005363
- Description: Elephants (Loxodonta africana, Blumenbach) are recognised as keystone herbivores and ecosystem engineers in African ecosystems due to the noticeable impact they have on plant communities. This impact can influence other animal taxa and ecosystem processes, especially within enclosed systems. I investigated the effects of elephants in four vegetation types and the cascade effect on three associated taxa and two ecosystem processes at five sites with elephants and five paired sites without elephants in the Eastern Cape Province, South Africa, between April 2005 and July 2007. In grassland habitats, the physical structure of the vegetation was neither enhanced nor degraded in the presence of elephants. Within the locally important Thicket Biome, elephant browsing transformed relatively homogeneous stands of vegetation into more heterogeneous units. However, although seeds from thicket plant species were recorded in elephant dung, elephants did not promote the viability and germination success of these plants. In addition, elephant foraging on aloes caused declines in their populations. By contrast, the size of bushclumps was not reduced in the presence of elephants in bushclump savanna. The associated insect, bird and mammal communities appeared to benefit from elephant foraging in all vegetation types assessed, whereas vegetation patch dynamics and soil surface processes were neither enhanced nor degraded in the presence of elephants. I conclude that, at current densities, elephants do not (in most cases) negatively affect plant and animal communities or ecosystem processes in enclosed reserves. However, elephants have only been present at each site for a relatively short period and it is likely that their impact will be cumulative, increasing over time in these closed systems. Thus, future research along a continuum of elephant density and time since re-introduction is recommended.
- Full Text:
- Date Issued: 2008
- Authors: Parker, Daniel Matthew
- Date: 2008
- Subjects: Elephants -- South Africa -- Eastern Cape Biotic communities -- South Africa -- Eastern Cape Animal populations -- South Africa -- Eastern Cape Plant communities -- South Africa -- Eastern Cape Mammals -- Ecology -- South Africa -- Eastern Cape Animal-plant relationships -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5678 , http://hdl.handle.net/10962/d1005363
- Description: Elephants (Loxodonta africana, Blumenbach) are recognised as keystone herbivores and ecosystem engineers in African ecosystems due to the noticeable impact they have on plant communities. This impact can influence other animal taxa and ecosystem processes, especially within enclosed systems. I investigated the effects of elephants in four vegetation types and the cascade effect on three associated taxa and two ecosystem processes at five sites with elephants and five paired sites without elephants in the Eastern Cape Province, South Africa, between April 2005 and July 2007. In grassland habitats, the physical structure of the vegetation was neither enhanced nor degraded in the presence of elephants. Within the locally important Thicket Biome, elephant browsing transformed relatively homogeneous stands of vegetation into more heterogeneous units. However, although seeds from thicket plant species were recorded in elephant dung, elephants did not promote the viability and germination success of these plants. In addition, elephant foraging on aloes caused declines in their populations. By contrast, the size of bushclumps was not reduced in the presence of elephants in bushclump savanna. The associated insect, bird and mammal communities appeared to benefit from elephant foraging in all vegetation types assessed, whereas vegetation patch dynamics and soil surface processes were neither enhanced nor degraded in the presence of elephants. I conclude that, at current densities, elephants do not (in most cases) negatively affect plant and animal communities or ecosystem processes in enclosed reserves. However, elephants have only been present at each site for a relatively short period and it is likely that their impact will be cumulative, increasing over time in these closed systems. Thus, future research along a continuum of elephant density and time since re-introduction is recommended.
- Full Text:
- Date Issued: 2008
Plant aphid interactions : effects of diuraphis noxia and rhopalosiphum padi on the structure and function of the transport systems of leaves of wheat and barley
- Authors: Saheed, Sefiu Adekilekun
- Date: 2008
- Subjects: Russian wheat aphid Rhopalosiphum padi Aphids -- Host plants Wheat -- Diseases and pests
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4225 , http://hdl.handle.net/10962/d1003794
- Description: The infestation of the cultivated grain crops by phloem feeding aphids has generated a great deal of interest over the years, due to the serious damage they cause to the crops and yield losses that result. The mechanism of the interaction between aphids and host plants remains largely unknown in spite of efforts to understand the basis of aphid feeding on grain crops. Greater efforts are required to explain the mechanism(s) of this interaction in order to achieve sustainable agriculture. This thesis focused on an investigation of the mechanism of feeding by the Russian wheat aphid, Diuraphis noxia Mordvilko (RWA) and the bird cherry-oat aphid, Rhopalosiphum padi L. (BCA) on barley and wheat cultivars. These two aphids co-occur naturally, but they inflict very different feeding effects on host plants. Structural and functional approaches were employed to investigate their feeding habits and these were then related to the observed differences in their host plants. Transmission electron microscopy (TEM) techniques were used to study the ultrastructural damage, while fluorescence microscopy techniques – using aniline blue fluorochrome (a specific stain for callose) and 5, 6-CFDA (a phloem-mobile fluorophore) – were employed to investigate the functional response to damage via wound callose formation and phloem transport capacity respectively. RT-PCR and quantitative real-time RT-PCR techniques were used to investigate the regulation of the genes involved in callose synthesis and degradation at the transcriptional level. Morphological observation of the damage caused by the aphids show that infestation by RWA results in extensive leaf chlorosis, necrosis and rolling, while infestation by BCA does not lead to any observable symptoms within the same period. Interestingly, the population study shows that BCA breeds faster than RWA within the two-week experimental period. The ultrastructural study of feeding damage caused by the two aphids on the vascular bundles of susceptible barley cv Clipper, shows a different patterns of damage. Probing the vascular bundles results in the puncturing of vascular parenchyma by both aphids, but severe damage occurs in sieve tubes-companion cell complex during sustained feeding by RWA. In contrast, less damage occurs when BCA feeds on the phloem. Drinking from the xylem by RWA results in deposition of a large quantity of electron-dense watery saliva, which apparently seals the xylem vessels completely, by blocking all the pit membrane fields between the xylem vessels and associated parenchyma cells. In contrast, drinking from xylem by BCA results in deposition of a dense, granular saliva into the xylem vessels only, which does not appear to totally occlude the pit membrane fields. This is the first known report in which ultrastructural evidence of aphids’ drinking in xylem is provided. The comparative effects of RWA feeding on a susceptible Betta and resistant Betta-Dn1 wheat cultivars showed that after two weeks, the Betta cultivar expressed damage symptoms such as chlorosis, necrosis and leaf roll, while few chlorotic patches and necrotic spots occur in resistant Betta-Dn1 cultivars. An ultrastructural investigation of the feeding damage caused to all leaf tissues revealed, for the first time, that RWA is capable of both intra- and inter-cellular probing within mesophyll cells. Probing in the mesophyll cells induces a more severe damage in susceptible Betta than in the resistant Betta-Dn1 counterpart. Similar differences in damage occurred during feeding in the thin-walled sieve tubes of the phloem, with the sieve tubes of the Betta showing more damage than that of the resistant Betta-Dn1. However, drinking from xylem resulted in the characteristic occlusion of metaxylem vessels by copious deposition of saliva by RWA in both Betta and Betta-Dn1 cultivars. In all cases of probing, feeding, and drinking by RWA in both cultivars, all probed cells with evidence of salivary material deposit and those cells adjacent to salivary material deposit, exhibit significant damage in susceptible Betta cultivar, whereas similar cells in Betta-Dn1 cultivars do not show as damage as severe. Investigation of the functional response of the plants to feeding by aphids through the deposition of wound-induced callose shows that formation and deposition of wound callose occurs in both longitudinal and cross veins within 24h of feeding by RWA. This deposition increases through short-term feeding (72h) and prolonged feeding (14d). This is in sharp contrast to the observations with BCA feeding,where little or no callose formation occurs within the same time frame. Callose formation and deposition occurs only when a higher population of BCA feeds on barley leaves. This is the first report of aphid-induced wound callose by BCA. In all cases of callose deposition, aphid stylet tracks were associated with callose and the deposition of callose appears to be a permanent feature, because wound callose remained in the leaf tissues even after 120h of the aphids’ removal. Wound callose signals (defence and anti-defence) are discovered to be transported in the phloem tissues and are dependent on the direction of assimilate flow. Examination of the possible regulation of wound callose genes at the transcriptional level shows that the two expressed glucan synthase gene sequences (GSL – genes involved in callose formation) analysed did not show any significant increase or regulation upon aphid infestation. Contrary to expectation, all three aphid-induced β-1, 3-glucanases (genes which are thought to be involved in callose degradation) showed higher expression in RWA-infested tissue than in BCA-infested tissue. The results of the feeding damage on the transport capacity of the phloem shows that BCA infestation does not lead to a significant reduction in the phloem transport capacity during short-term feeding (72h), while RWA-infested leaves showed considerable reduction in the transport capacity of the phloem within the same period. However, prolonged feeding (14d) by BCA induces a considerable reduction on the transport capacity of the phloem on the infested tissues. In contrast, a marked reduction in the transport capacity of the phloem occurs in RWA-infested leaves and in most cases, complete cessation of transport ensues. In conclusion, these data collectively suggest that RWA is a serious and most destructive phloem feeder in comparison to the BCA. RWA causes severe damage to all cellular tissues of the host plants, which result in apoplasmic and symplasmic isolation of xylem and phloem tissues, while BCA infestation does not result in such isolation within the same time and population levels. Resistance genes appear to function by conferring resistance to cell damage on the resistant cultivars during aphid feeding. Responses by plants to aphid infestation via wound callose deposition are again shown to be species-specific. A quick response results when RWA feeds, even at a very low population level, while a response occurs only at a higher infestation level by BCA, and this response was shown as not regulated at the transcriptional level. Differences in the damage to leaf tissues and wound callose deposition eventually lead to varying degrees of damage to the transport capacity of the phloem. These differences in the damage signatures are hereby suggested to be the cause of the diversity in the observed damage symptoms and the yield losses upon infestation by the two aphid species.
- Full Text:
- Date Issued: 2008
- Authors: Saheed, Sefiu Adekilekun
- Date: 2008
- Subjects: Russian wheat aphid Rhopalosiphum padi Aphids -- Host plants Wheat -- Diseases and pests
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4225 , http://hdl.handle.net/10962/d1003794
- Description: The infestation of the cultivated grain crops by phloem feeding aphids has generated a great deal of interest over the years, due to the serious damage they cause to the crops and yield losses that result. The mechanism of the interaction between aphids and host plants remains largely unknown in spite of efforts to understand the basis of aphid feeding on grain crops. Greater efforts are required to explain the mechanism(s) of this interaction in order to achieve sustainable agriculture. This thesis focused on an investigation of the mechanism of feeding by the Russian wheat aphid, Diuraphis noxia Mordvilko (RWA) and the bird cherry-oat aphid, Rhopalosiphum padi L. (BCA) on barley and wheat cultivars. These two aphids co-occur naturally, but they inflict very different feeding effects on host plants. Structural and functional approaches were employed to investigate their feeding habits and these were then related to the observed differences in their host plants. Transmission electron microscopy (TEM) techniques were used to study the ultrastructural damage, while fluorescence microscopy techniques – using aniline blue fluorochrome (a specific stain for callose) and 5, 6-CFDA (a phloem-mobile fluorophore) – were employed to investigate the functional response to damage via wound callose formation and phloem transport capacity respectively. RT-PCR and quantitative real-time RT-PCR techniques were used to investigate the regulation of the genes involved in callose synthesis and degradation at the transcriptional level. Morphological observation of the damage caused by the aphids show that infestation by RWA results in extensive leaf chlorosis, necrosis and rolling, while infestation by BCA does not lead to any observable symptoms within the same period. Interestingly, the population study shows that BCA breeds faster than RWA within the two-week experimental period. The ultrastructural study of feeding damage caused by the two aphids on the vascular bundles of susceptible barley cv Clipper, shows a different patterns of damage. Probing the vascular bundles results in the puncturing of vascular parenchyma by both aphids, but severe damage occurs in sieve tubes-companion cell complex during sustained feeding by RWA. In contrast, less damage occurs when BCA feeds on the phloem. Drinking from the xylem by RWA results in deposition of a large quantity of electron-dense watery saliva, which apparently seals the xylem vessels completely, by blocking all the pit membrane fields between the xylem vessels and associated parenchyma cells. In contrast, drinking from xylem by BCA results in deposition of a dense, granular saliva into the xylem vessels only, which does not appear to totally occlude the pit membrane fields. This is the first known report in which ultrastructural evidence of aphids’ drinking in xylem is provided. The comparative effects of RWA feeding on a susceptible Betta and resistant Betta-Dn1 wheat cultivars showed that after two weeks, the Betta cultivar expressed damage symptoms such as chlorosis, necrosis and leaf roll, while few chlorotic patches and necrotic spots occur in resistant Betta-Dn1 cultivars. An ultrastructural investigation of the feeding damage caused to all leaf tissues revealed, for the first time, that RWA is capable of both intra- and inter-cellular probing within mesophyll cells. Probing in the mesophyll cells induces a more severe damage in susceptible Betta than in the resistant Betta-Dn1 counterpart. Similar differences in damage occurred during feeding in the thin-walled sieve tubes of the phloem, with the sieve tubes of the Betta showing more damage than that of the resistant Betta-Dn1. However, drinking from xylem resulted in the characteristic occlusion of metaxylem vessels by copious deposition of saliva by RWA in both Betta and Betta-Dn1 cultivars. In all cases of probing, feeding, and drinking by RWA in both cultivars, all probed cells with evidence of salivary material deposit and those cells adjacent to salivary material deposit, exhibit significant damage in susceptible Betta cultivar, whereas similar cells in Betta-Dn1 cultivars do not show as damage as severe. Investigation of the functional response of the plants to feeding by aphids through the deposition of wound-induced callose shows that formation and deposition of wound callose occurs in both longitudinal and cross veins within 24h of feeding by RWA. This deposition increases through short-term feeding (72h) and prolonged feeding (14d). This is in sharp contrast to the observations with BCA feeding,where little or no callose formation occurs within the same time frame. Callose formation and deposition occurs only when a higher population of BCA feeds on barley leaves. This is the first report of aphid-induced wound callose by BCA. In all cases of callose deposition, aphid stylet tracks were associated with callose and the deposition of callose appears to be a permanent feature, because wound callose remained in the leaf tissues even after 120h of the aphids’ removal. Wound callose signals (defence and anti-defence) are discovered to be transported in the phloem tissues and are dependent on the direction of assimilate flow. Examination of the possible regulation of wound callose genes at the transcriptional level shows that the two expressed glucan synthase gene sequences (GSL – genes involved in callose formation) analysed did not show any significant increase or regulation upon aphid infestation. Contrary to expectation, all three aphid-induced β-1, 3-glucanases (genes which are thought to be involved in callose degradation) showed higher expression in RWA-infested tissue than in BCA-infested tissue. The results of the feeding damage on the transport capacity of the phloem shows that BCA infestation does not lead to a significant reduction in the phloem transport capacity during short-term feeding (72h), while RWA-infested leaves showed considerable reduction in the transport capacity of the phloem within the same period. However, prolonged feeding (14d) by BCA induces a considerable reduction on the transport capacity of the phloem on the infested tissues. In contrast, a marked reduction in the transport capacity of the phloem occurs in RWA-infested leaves and in most cases, complete cessation of transport ensues. In conclusion, these data collectively suggest that RWA is a serious and most destructive phloem feeder in comparison to the BCA. RWA causes severe damage to all cellular tissues of the host plants, which result in apoplasmic and symplasmic isolation of xylem and phloem tissues, while BCA infestation does not result in such isolation within the same time and population levels. Resistance genes appear to function by conferring resistance to cell damage on the resistant cultivars during aphid feeding. Responses by plants to aphid infestation via wound callose deposition are again shown to be species-specific. A quick response results when RWA feeds, even at a very low population level, while a response occurs only at a higher infestation level by BCA, and this response was shown as not regulated at the transcriptional level. Differences in the damage to leaf tissues and wound callose deposition eventually lead to varying degrees of damage to the transport capacity of the phloem. These differences in the damage signatures are hereby suggested to be the cause of the diversity in the observed damage symptoms and the yield losses upon infestation by the two aphid species.
- Full Text:
- Date Issued: 2008
An interpretive inquiry into girls' educational choices and aspirations: a case study of Murang'a district, Kenya
- Authors: Mwingi, Mweru P
- Date: 2008
- Subjects: Education -- Kenya -- Case studies Education -- Economic aspects -- Kenya -- Case studies Student aspirations -- Kenya -- Case studies Women -- Vocational guidance -- Kenya -- Case studies Sex discrimination in education -- Kenya -- Case studies Sex discrimination against women -- Kenya -- Case studies Sexism in education -- Kenya -- Case studies Women -- Education -- Kenya -- Case studies Educational equalization -- Kenya
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1583 , http://hdl.handle.net/10962/d1003465
- Description: Global consensus on the importance of gender equity in education is perhaps one of the greatest agreements reached in the twentieth century. However, for countries in the sub Saharan African region where disparities of gender are wide and primary education takes priority, secondary education continues to remain in the periphery. As countries make progress towards the attainment of Universal Primary Education (UPE), the concerns for gender equity and equality have become associated with school access and pupil retention. Yet, patterns and trends in school enrollment suggest that disparities of gender are more complex. As lessons are learned from the achievements and challenges of attaining UPE, it is increasingly apparent that gender disparities within education occur in, within and beyond access to schooling. In other words, the challenge of making education gender equal goes beyond school access and school enrollment. Kenya is a signatory to the 1990 Jomtein Declaration on Education For All (EFA). It is also among the few countries in the sub Saharan Africa region with a significantly reduced gender gap in primary and secondary education. This is in tandem with the third of the eight Millennium Development Goals whose aims bear a broad social and economic development agenda. While education equity is important in Kenya and tremendous progress has been made in primary education, beyond the attainment of Universal Primary Education (UPE) there is an even more significant target; gender equity in education both in primary and secondary education by 2015. The attainment of this target requires more than access to schooling and for this reason it poses great challenges to governments and schools. In light of the progress made in Kenya and the need for more equitable education beyond primary education, this study conceives a need for an incisive examination of education equity priority areas in Kenya. The study argues on the need for a shift of concern and debate from primary education to secondary education because the gains of UPE only become meaningful when education equity is secured in secondary education. The study underscores that beyond school access and retention, education output and outcomes need to become prominent variables because they gauge trends and patterns and the quality of gains made where education is claimed to be both accessible and equitable. Using case study method, the study makes a critical interpretation of the schooling experiences, educational choices, preferences and aspirations of girls taking secondary education in single-sex schools in Murang’a district, Kenya. The study shows that girls schooling experiences are not homogenous and that there are contradictions in the ways that girls experience their schooling and make educational choices. It also shows that girls do not necessarily stand good chances with their education simply because they are enrolled in single-sex schools. The study reveals individual subjectivities and schooling culture to be at the centre of the differences between schools and the schooling experiences that girls have. The two have impact on how girls perceive themselves and their abilities, the preferences they nurture and the educational choices they make. The study draws attention to nuances in access and equity within girls’ education. It draws out issues and nuances linked to gender access, equity and equality with respect to school, teacher and subject access. Though the study is not generaliseable, it shows that in contexts where female access and survival is secured, there is need for attention to be paid to the environments that nurture educational choices and preferences so that the high rates in school access become translated into equally high educational output and outcomes.
- Full Text:
- Date Issued: 2008
- Authors: Mwingi, Mweru P
- Date: 2008
- Subjects: Education -- Kenya -- Case studies Education -- Economic aspects -- Kenya -- Case studies Student aspirations -- Kenya -- Case studies Women -- Vocational guidance -- Kenya -- Case studies Sex discrimination in education -- Kenya -- Case studies Sex discrimination against women -- Kenya -- Case studies Sexism in education -- Kenya -- Case studies Women -- Education -- Kenya -- Case studies Educational equalization -- Kenya
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:1583 , http://hdl.handle.net/10962/d1003465
- Description: Global consensus on the importance of gender equity in education is perhaps one of the greatest agreements reached in the twentieth century. However, for countries in the sub Saharan African region where disparities of gender are wide and primary education takes priority, secondary education continues to remain in the periphery. As countries make progress towards the attainment of Universal Primary Education (UPE), the concerns for gender equity and equality have become associated with school access and pupil retention. Yet, patterns and trends in school enrollment suggest that disparities of gender are more complex. As lessons are learned from the achievements and challenges of attaining UPE, it is increasingly apparent that gender disparities within education occur in, within and beyond access to schooling. In other words, the challenge of making education gender equal goes beyond school access and school enrollment. Kenya is a signatory to the 1990 Jomtein Declaration on Education For All (EFA). It is also among the few countries in the sub Saharan Africa region with a significantly reduced gender gap in primary and secondary education. This is in tandem with the third of the eight Millennium Development Goals whose aims bear a broad social and economic development agenda. While education equity is important in Kenya and tremendous progress has been made in primary education, beyond the attainment of Universal Primary Education (UPE) there is an even more significant target; gender equity in education both in primary and secondary education by 2015. The attainment of this target requires more than access to schooling and for this reason it poses great challenges to governments and schools. In light of the progress made in Kenya and the need for more equitable education beyond primary education, this study conceives a need for an incisive examination of education equity priority areas in Kenya. The study argues on the need for a shift of concern and debate from primary education to secondary education because the gains of UPE only become meaningful when education equity is secured in secondary education. The study underscores that beyond school access and retention, education output and outcomes need to become prominent variables because they gauge trends and patterns and the quality of gains made where education is claimed to be both accessible and equitable. Using case study method, the study makes a critical interpretation of the schooling experiences, educational choices, preferences and aspirations of girls taking secondary education in single-sex schools in Murang’a district, Kenya. The study shows that girls schooling experiences are not homogenous and that there are contradictions in the ways that girls experience their schooling and make educational choices. It also shows that girls do not necessarily stand good chances with their education simply because they are enrolled in single-sex schools. The study reveals individual subjectivities and schooling culture to be at the centre of the differences between schools and the schooling experiences that girls have. The two have impact on how girls perceive themselves and their abilities, the preferences they nurture and the educational choices they make. The study draws attention to nuances in access and equity within girls’ education. It draws out issues and nuances linked to gender access, equity and equality with respect to school, teacher and subject access. Though the study is not generaliseable, it shows that in contexts where female access and survival is secured, there is need for attention to be paid to the environments that nurture educational choices and preferences so that the high rates in school access become translated into equally high educational output and outcomes.
- Full Text:
- Date Issued: 2008
Studies in marine diterpene chemistry
- Van Wyk, Albert Wynand Wincke
- Authors: Van Wyk, Albert Wynand Wincke
- Date: 2008
- Subjects: Natural products Diterpenes Mollusks Marine metabolites Chemical oceanography
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4354 , http://hdl.handle.net/10962/d1005019
- Description: This thesis comprises both a natural product investigation and a synthetic component. The natural product investigations are presented in Chapters Two and Three. In Chapter Two the isolation and spectroscopic identification of the new isocopalane diterpene 12S,13R,14Sisocopalan- 13-ol-12,14-diacetate (2.1) and two known 3-(14S)-isocopal-12-ene-15-oyl-1- acetyl-sn-glycerol (2.2) and 3-(14S)-isocopal-12-ene-15-oyl-2-acetyl-sn-glycerol (2.3) from a single, large, unidentified sub-Antarctic nudibranch, collected near Marion Island, approximately 2000 km south of Cape Town are described. Chapter Three discusses the isolation, spectroscopic structure elucidation and anti-oesophageal cancer activity (3.1-3.4 only) of two known labdane diterpenes 6β,7α-diacetoxylabda-8,13E-dien-15-ol (3.1) and 2α,6β,7α-triacetoxylabda-8,13E-dien-15-ol (3.2) and one new 6β,7α,15-triacetoxylabda 8,13E-diene (3.3), as well as new 3α,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione (3.4) and cholest 7-en-3,5,7-triol (3.5) from the endemic pulmonate mollusc, Trimusculus costatus. The absolute configuration of 3.2, and hence 3.1 and 3.3 (from biogenetic arguments) was determined through X-ray diffraction of a single crystal of the camphanate ester of 3.2. The absolute configuration of the secondary hydroxyl at C-3 of 3.4 was established using the Modified Mosher’s method. The synthetic component of the thesis commences in Chapter Four with the semi-synthesis of labdane diterpene nitriles 9α-cyano-15,16-epoxy-7β-hydroxylabda-13(16),14-dien-6-one (4.1), 9α-cyano-15,16-epoxy-7-hydroxylabda-7,13(16),14-trien-6-one (4.2) and 9α-cyano-15,16- epoxy-6β,7β dihydroxylabda-13(16),14-diene (4.3) from the terrestrial labdane diterpene, hispanolone (4.4). This work is an extension of previous synthetic studies directed towards the synthesis of T. costatus metabolites. Diterpenes 4.1-4.3 exhibited in planta activity against the economically important crop pathogens, Magnaporthea grisea and Puccinia recondita. Chapter Five describes the successful semi-synthesis of two isomeric marine molluscan labdane diterpene aldehyde metabolites, labd-13E-ene-8β-ol-15-al (5.1) and labd-13Z-ene- 8β-ol-15-al (5.2) from the commercially available, terrestrial plant derived, labdane diterpene manool (5.3). Diterpenes 5.1 and 5.2, originally isolated from the Mediterranean nudibranch,Pleurobranchaea meckelii and selected diterpenes arising from this synthesis were evaluated for their activity against an oesophageal cancer cell line (WHCO1). Chapter Six further develops the research discussed in Chapter Five, where ethyl 17-norabiet-13(15)-E-en-8β-ol- 16-oate (5.49) and ethyl 17-norabiet-13(15)-Z-en-8β-ol-16-oate (5.50) were first semisynthesized serendipitously. Based on their structural relationship to naturally occurring tricyclic diterpenes with anti-plasmodial activity, tricyclic diterpenes, 17-norpimaran-13α- ethoxy-8,16-olactone (6.6), 17-norisopimar-15-ene-8β,13β-diol (6.7), 17-norisopimarane- 8β,16-diol (6.8) and 17-norabiet-13(15)-ene-8β,16-diol (6.9) were semi-synthesized from the terrestrial labdane diterpene, 5.3, and critically evaluated for their antimalarial potential from parasite inhibition and haemolytic studies.
- Full Text:
- Date Issued: 2008
- Authors: Van Wyk, Albert Wynand Wincke
- Date: 2008
- Subjects: Natural products Diterpenes Mollusks Marine metabolites Chemical oceanography
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4354 , http://hdl.handle.net/10962/d1005019
- Description: This thesis comprises both a natural product investigation and a synthetic component. The natural product investigations are presented in Chapters Two and Three. In Chapter Two the isolation and spectroscopic identification of the new isocopalane diterpene 12S,13R,14Sisocopalan- 13-ol-12,14-diacetate (2.1) and two known 3-(14S)-isocopal-12-ene-15-oyl-1- acetyl-sn-glycerol (2.2) and 3-(14S)-isocopal-12-ene-15-oyl-2-acetyl-sn-glycerol (2.3) from a single, large, unidentified sub-Antarctic nudibranch, collected near Marion Island, approximately 2000 km south of Cape Town are described. Chapter Three discusses the isolation, spectroscopic structure elucidation and anti-oesophageal cancer activity (3.1-3.4 only) of two known labdane diterpenes 6β,7α-diacetoxylabda-8,13E-dien-15-ol (3.1) and 2α,6β,7α-triacetoxylabda-8,13E-dien-15-ol (3.2) and one new 6β,7α,15-triacetoxylabda 8,13E-diene (3.3), as well as new 3α,11-dihydroxy-9,11-seco-cholest-4,7-dien-6,9-dione (3.4) and cholest 7-en-3,5,7-triol (3.5) from the endemic pulmonate mollusc, Trimusculus costatus. The absolute configuration of 3.2, and hence 3.1 and 3.3 (from biogenetic arguments) was determined through X-ray diffraction of a single crystal of the camphanate ester of 3.2. The absolute configuration of the secondary hydroxyl at C-3 of 3.4 was established using the Modified Mosher’s method. The synthetic component of the thesis commences in Chapter Four with the semi-synthesis of labdane diterpene nitriles 9α-cyano-15,16-epoxy-7β-hydroxylabda-13(16),14-dien-6-one (4.1), 9α-cyano-15,16-epoxy-7-hydroxylabda-7,13(16),14-trien-6-one (4.2) and 9α-cyano-15,16- epoxy-6β,7β dihydroxylabda-13(16),14-diene (4.3) from the terrestrial labdane diterpene, hispanolone (4.4). This work is an extension of previous synthetic studies directed towards the synthesis of T. costatus metabolites. Diterpenes 4.1-4.3 exhibited in planta activity against the economically important crop pathogens, Magnaporthea grisea and Puccinia recondita. Chapter Five describes the successful semi-synthesis of two isomeric marine molluscan labdane diterpene aldehyde metabolites, labd-13E-ene-8β-ol-15-al (5.1) and labd-13Z-ene- 8β-ol-15-al (5.2) from the commercially available, terrestrial plant derived, labdane diterpene manool (5.3). Diterpenes 5.1 and 5.2, originally isolated from the Mediterranean nudibranch,Pleurobranchaea meckelii and selected diterpenes arising from this synthesis were evaluated for their activity against an oesophageal cancer cell line (WHCO1). Chapter Six further develops the research discussed in Chapter Five, where ethyl 17-norabiet-13(15)-E-en-8β-ol- 16-oate (5.49) and ethyl 17-norabiet-13(15)-Z-en-8β-ol-16-oate (5.50) were first semisynthesized serendipitously. Based on their structural relationship to naturally occurring tricyclic diterpenes with anti-plasmodial activity, tricyclic diterpenes, 17-norpimaran-13α- ethoxy-8,16-olactone (6.6), 17-norisopimar-15-ene-8β,13β-diol (6.7), 17-norisopimarane- 8β,16-diol (6.8) and 17-norabiet-13(15)-ene-8β,16-diol (6.9) were semi-synthesized from the terrestrial labdane diterpene, 5.3, and critically evaluated for their antimalarial potential from parasite inhibition and haemolytic studies.
- Full Text:
- Date Issued: 2008