Solvent effect on the third-order nonlinear optical properties of α-and β-tertbutyl phenoxy-substituted tin (IV) chloride phthalocyanines
- Louzada, Marcel, Britton, Jonathan, Nyokong, Tebello, Khene, Samson M
- Authors: Louzada, Marcel , Britton, Jonathan , Nyokong, Tebello , Khene, Samson M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188910 , vital:44797 , xlink:href="https://doi.org/10.1021/acs.jpca.7b07349"
- Description: This paper investigates the third-order nonlinear optical properties of 4α-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc) in different organic solvents. The third-order susceptibilities of α-SnOtBpPc and βSnOtBpPc are reported in different solvents, using Z-scan techniques with 10 ns laser pulses at 532 nm. Their nonlinear absorption coefficient and absorption cross sections were also determined. The molecular imaginary components of the secondorder hyperpolarizability Im[γ] of α-SnOtBpPc and β-SnOtBpPc were found to be 2.60 × 10−31 and 2.94 × 10−31 esu (tetrahydrofuran), 2.12 × 10−31 and 2.54 × 10−31 esu (chloroform), 3.06 × 10−31 and 2.54 × 10−31 esu (dichloromethane), and 1.27 × 10−31 and 1.50 × 10−31 esu (toluene), respectively. This study found that substitution at the α position has an effect of lowering the two-photon (2PA) cross section value for α-SnOtBpPc compared to that for β-SnOtBpPc, with values of 64.30 and 456.65 GM, respectively. The large 2PA cross section observed in β-SnOtBpPc is attributed to the decreased energy difference between the virtual state and the LUMO.
- Full Text:
- Authors: Louzada, Marcel , Britton, Jonathan , Nyokong, Tebello , Khene, Samson M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188910 , vital:44797 , xlink:href="https://doi.org/10.1021/acs.jpca.7b07349"
- Description: This paper investigates the third-order nonlinear optical properties of 4α-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (α-SnOtBpPc) and 4β-(4-tert-butylphenoxy) phthalocyaninato dichlorotin(IV) (β-SnOtBpPc) in different organic solvents. The third-order susceptibilities of α-SnOtBpPc and βSnOtBpPc are reported in different solvents, using Z-scan techniques with 10 ns laser pulses at 532 nm. Their nonlinear absorption coefficient and absorption cross sections were also determined. The molecular imaginary components of the secondorder hyperpolarizability Im[γ] of α-SnOtBpPc and β-SnOtBpPc were found to be 2.60 × 10−31 and 2.94 × 10−31 esu (tetrahydrofuran), 2.12 × 10−31 and 2.54 × 10−31 esu (chloroform), 3.06 × 10−31 and 2.54 × 10−31 esu (dichloromethane), and 1.27 × 10−31 and 1.50 × 10−31 esu (toluene), respectively. This study found that substitution at the α position has an effect of lowering the two-photon (2PA) cross section value for α-SnOtBpPc compared to that for β-SnOtBpPc, with values of 64.30 and 456.65 GM, respectively. The large 2PA cross section observed in β-SnOtBpPc is attributed to the decreased energy difference between the virtual state and the LUMO.
- Full Text:
Son of a dog
- Authors: Kolawole, Samuel
- Date: 2017
- Subjects: Creative writing (Higher education) South Africa , South African fiction (English) 21st century , African fiction (English) 21st century
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/7195 , vital:21228
- Description: Son of a Dog is inspired by a real-life figure whose exploits captured the Nigerian public imagination in the 1980s. Famously known as Ovbigbo (“The Law”), Lawrence Anini unleashed a nationwide reign of terror against law and order. Set against the backdrop of the political turmoil following the Nigerian civil war, the novel traces Anini’s formative years in menial jobs to his rise to the leadership of a notorious criminal gang. It fuses the established facts of his short meteoric career with my imagined version of his inner life and the contemporary myths that sprung up around his legend. It finally crosses the boundary between the real and the mythic as Lawrence Anini becomes truly invincible and elusive after a lust-struck encounter with a fantastical character. I draw inspiration from the dark visceral fiction of Michael Cisco and Brian Evenson, AyiKwei Armah’s unflinchingly descriptive prose and E.C. Osondu’s sharp contemporary humour.
- Full Text:
- Authors: Kolawole, Samuel
- Date: 2017
- Subjects: Creative writing (Higher education) South Africa , South African fiction (English) 21st century , African fiction (English) 21st century
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/7195 , vital:21228
- Description: Son of a Dog is inspired by a real-life figure whose exploits captured the Nigerian public imagination in the 1980s. Famously known as Ovbigbo (“The Law”), Lawrence Anini unleashed a nationwide reign of terror against law and order. Set against the backdrop of the political turmoil following the Nigerian civil war, the novel traces Anini’s formative years in menial jobs to his rise to the leadership of a notorious criminal gang. It fuses the established facts of his short meteoric career with my imagined version of his inner life and the contemporary myths that sprung up around his legend. It finally crosses the boundary between the real and the mythic as Lawrence Anini becomes truly invincible and elusive after a lust-struck encounter with a fantastical character. I draw inspiration from the dark visceral fiction of Michael Cisco and Brian Evenson, AyiKwei Armah’s unflinchingly descriptive prose and E.C. Osondu’s sharp contemporary humour.
- Full Text:
Sorptive and microbial properties of low-cost adsorbents used in the extraction of ciprofloxacin and isoniazid from aqueous solution
- Authors: Dube, Cyril Simbarashe
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSC
- Identifier: http://hdl.handle.net/10962/59178 , vital:27450
- Description: This work describes how coal fly ash (FA), kaolinite, perlite, talc and vermiculite were used to remove ciprofloxacin and isoniazid from aqueous solutions. The adsorptive features of the adsorbents were evaluated for ciprofloxacin and isoniazid with regards to the effects of contact time, pH, solid/liquid ratio and antibiotic concentration. All adsorbents were sterilised by dry heat before use to avoid the proliferation of antimicrobial resistance by the bacteria present on the adsorbents during experiments. The regression correlation coefficients indicate that the linearised form of the Langmuir isotherm gives the best fit for the sorption of both antibiotics onto FA and talc, ciprofloxacin onto kaolinite, and isoniazid onto perlite and vermiculite with R2 values ranging from 0.908 - 0.999. The linearised form of the Freundlich isotherm best describes the sorption of ciprofloxacin onto vermiculite and isoniazid onto kaolinite with R2 values of 0.999 for both. The linearised form of the Temkin isotherm best describes the sorption of ciprofloxacin onto perlite with an R2 = 0.997. The values of the Freundlich exponent, 1/n, range from 0.221 - 0.998, indicating a favourable adsorption of ciprofloxacin and isoniazid onto the adsorbents. The heat of sorption, B, calculated from the Temkin plots has values ranging from 0.018 - 10.460 J/mol, indicating a physical adsorption process (physisorption). Adsorption equilibrium on all adsorbents was achieved after 30 min for both antibiotics and the kinetic data obtained conforms best to the pseudo-second order equation with R2 values ranging from 0.998 - 0.999. The removal of ciprofloxacin and isoniazid by all adsorbents except FA was strongly influenced by the pH suggesting that electrostatic interactions play a major role in the adsorption processes. All adsorbents except FA removed showed excellent adsorption of ciprofloxacin from aqueous solutions with all of them achieving removals ranging from 80 - 99%. The adsorbents were less efficient in removing isoniazid and kaolinite gave the highest removal of 55 %. Furthermore, the microbial quality of the adsorbents was investigated and the results revealed that kaolinite, talc, perlite and vermiculite were heavily contaminated with microorganisms. FA was sterile. The fungi isolated from the mineral adsorbents were in concentrations ranging from 2.13 x 106 to 1.25 x 107 CFU/g and were mostly moulds; Penicillium spp., Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Cladosporium spp. and Rhizopus oryzae. One yeast was isolated and was identified as Candida albicans. The bacteria identified were in concentrations ranging from 4.96 x 106 - 1.19 x 109 CFU/g. E. coli, Enterobacter cloacae, Exiguobacterium spp., Pseudomonas aeruginosa, Bacillus spp. and Serratia liquefaciens. The leachability index (LI) values obtained for adsorbents indicated that it is highly unlikely that microorganisms could be leached out of the adsorbents by rain. Heat inactivation of the microorganisms at a 105 °C was totally unsuccessful. However, it was established that a dry heat dose of 160 °C for at least 15 min was sufficient to eradicate all microorganisms present in the adsorbents. The D-values for coliform bacteria from all samples were very similar ranging from 1.7-2.2 min indicating homogeneity in heat resistance by the microorganisms. The Pseudomonas aureginosa isolated had a D-value of 2.2 min. The fungi isolated from the samples had D-values ranging from 2.1-3.2 min.
- Full Text:
- Authors: Dube, Cyril Simbarashe
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSC
- Identifier: http://hdl.handle.net/10962/59178 , vital:27450
- Description: This work describes how coal fly ash (FA), kaolinite, perlite, talc and vermiculite were used to remove ciprofloxacin and isoniazid from aqueous solutions. The adsorptive features of the adsorbents were evaluated for ciprofloxacin and isoniazid with regards to the effects of contact time, pH, solid/liquid ratio and antibiotic concentration. All adsorbents were sterilised by dry heat before use to avoid the proliferation of antimicrobial resistance by the bacteria present on the adsorbents during experiments. The regression correlation coefficients indicate that the linearised form of the Langmuir isotherm gives the best fit for the sorption of both antibiotics onto FA and talc, ciprofloxacin onto kaolinite, and isoniazid onto perlite and vermiculite with R2 values ranging from 0.908 - 0.999. The linearised form of the Freundlich isotherm best describes the sorption of ciprofloxacin onto vermiculite and isoniazid onto kaolinite with R2 values of 0.999 for both. The linearised form of the Temkin isotherm best describes the sorption of ciprofloxacin onto perlite with an R2 = 0.997. The values of the Freundlich exponent, 1/n, range from 0.221 - 0.998, indicating a favourable adsorption of ciprofloxacin and isoniazid onto the adsorbents. The heat of sorption, B, calculated from the Temkin plots has values ranging from 0.018 - 10.460 J/mol, indicating a physical adsorption process (physisorption). Adsorption equilibrium on all adsorbents was achieved after 30 min for both antibiotics and the kinetic data obtained conforms best to the pseudo-second order equation with R2 values ranging from 0.998 - 0.999. The removal of ciprofloxacin and isoniazid by all adsorbents except FA was strongly influenced by the pH suggesting that electrostatic interactions play a major role in the adsorption processes. All adsorbents except FA removed showed excellent adsorption of ciprofloxacin from aqueous solutions with all of them achieving removals ranging from 80 - 99%. The adsorbents were less efficient in removing isoniazid and kaolinite gave the highest removal of 55 %. Furthermore, the microbial quality of the adsorbents was investigated and the results revealed that kaolinite, talc, perlite and vermiculite were heavily contaminated with microorganisms. FA was sterile. The fungi isolated from the mineral adsorbents were in concentrations ranging from 2.13 x 106 to 1.25 x 107 CFU/g and were mostly moulds; Penicillium spp., Aspergillus niger, Aspergillus fumigatus, Aspergillus flavus, Cladosporium spp. and Rhizopus oryzae. One yeast was isolated and was identified as Candida albicans. The bacteria identified were in concentrations ranging from 4.96 x 106 - 1.19 x 109 CFU/g. E. coli, Enterobacter cloacae, Exiguobacterium spp., Pseudomonas aeruginosa, Bacillus spp. and Serratia liquefaciens. The leachability index (LI) values obtained for adsorbents indicated that it is highly unlikely that microorganisms could be leached out of the adsorbents by rain. Heat inactivation of the microorganisms at a 105 °C was totally unsuccessful. However, it was established that a dry heat dose of 160 °C for at least 15 min was sufficient to eradicate all microorganisms present in the adsorbents. The D-values for coliform bacteria from all samples were very similar ranging from 1.7-2.2 min indicating homogeneity in heat resistance by the microorganisms. The Pseudomonas aureginosa isolated had a D-value of 2.2 min. The fungi isolated from the samples had D-values ranging from 2.1-3.2 min.
- Full Text:
South-South labour migration complexities and shifting visa policies in South Africa: a sociological analysis of Rhodes University academic labour migrants’ perceptions
- Authors: Domboka, Edward
- Date: 2017
- Subjects: Foreign workers -- South Africa , Foreign workers -- Government policy -- South Africa , College teachers, Foreign -- South Africa -- Attitudes , College teacher mobility -- Africa , Visas -- South Africa , Rhodes University -- Employees -- Attitudes
- Language: English
- Type: Thesis , Masters , MSocSc
- Identifier: http://hdl.handle.net/10962/46242 , vital:25593
- Description: International migration is an old phenomenon caused by many factors divided into push and pull factors. However, there is no enough coverage on the perceptions of the labour migrants. Although there is a vast body of writing on migration, this study delves into the experiential perceptions of academic labour migrants at Rhodes University. These academic labour migrants include professors, lecturers, researchers and postdoctoral research fellows. The study took a qualitative approach to document the experiential perceptions of academic labour migrants at Rhodes University. In-depth interviews were conducted with twelve respondents, to analyse how academic labour migrants perceive South Africa’s changing visa policies in the context of regional integration and development, migration networks and choice, host-migrant relations. The study is underpinned by Probsting’s (2015) concept of "spatial fix" in the context of capitalism and migration, to locate the positionality of academic labour migrants within a capitalist society. The study established that the increase in skilled labour migration is relatively linked to the expansion of capitalism. Based on the perceptions of the respondents, the study concluded that migration is inherently vital in providing cheap labour for capitalists. It established that changing visa policies is not without problems. Historical dispositions of the apartheid system, conflicting domestic versus international imperatives, neo-liberal policies and the widely condemned results of capitalism as an imperialist system and other factors influence migration management in South Africa.
- Full Text:
- Authors: Domboka, Edward
- Date: 2017
- Subjects: Foreign workers -- South Africa , Foreign workers -- Government policy -- South Africa , College teachers, Foreign -- South Africa -- Attitudes , College teacher mobility -- Africa , Visas -- South Africa , Rhodes University -- Employees -- Attitudes
- Language: English
- Type: Thesis , Masters , MSocSc
- Identifier: http://hdl.handle.net/10962/46242 , vital:25593
- Description: International migration is an old phenomenon caused by many factors divided into push and pull factors. However, there is no enough coverage on the perceptions of the labour migrants. Although there is a vast body of writing on migration, this study delves into the experiential perceptions of academic labour migrants at Rhodes University. These academic labour migrants include professors, lecturers, researchers and postdoctoral research fellows. The study took a qualitative approach to document the experiential perceptions of academic labour migrants at Rhodes University. In-depth interviews were conducted with twelve respondents, to analyse how academic labour migrants perceive South Africa’s changing visa policies in the context of regional integration and development, migration networks and choice, host-migrant relations. The study is underpinned by Probsting’s (2015) concept of "spatial fix" in the context of capitalism and migration, to locate the positionality of academic labour migrants within a capitalist society. The study established that the increase in skilled labour migration is relatively linked to the expansion of capitalism. Based on the perceptions of the respondents, the study concluded that migration is inherently vital in providing cheap labour for capitalists. It established that changing visa policies is not without problems. Historical dispositions of the apartheid system, conflicting domestic versus international imperatives, neo-liberal policies and the widely condemned results of capitalism as an imperialist system and other factors influence migration management in South Africa.
- Full Text:
Spatial differences in stunting and household agricultural production in South Africa:(re)-examining the links using national panel survey data
- Otterbach, Steffen, Rogan, Michael
- Authors: Otterbach, Steffen , Rogan, Michael
- Date: 2017
- Subjects: Human growth -- South Africa Malnutrition -- South Africa Poverty -- Case studies Economic development -- South Africa
- Language: English
- Type: Book , Text
- Identifier: http://hdl.handle.net/10962/59522 , vital:27622 , ISBN 9780868106342 , DOI 10.21504/10962/59522
- Description: One explanation for the increasing prevalence of stunting in South Africa over the past 15 years while other development indicators have improved is that Big Food retail chains have been contributing to a low quality diet across the country, particularly in poor urban households. We thus use nationally representative longitudinal data (2008–2014) to trace 6 years of stunting’s evolution among South African children, adolescents, and young adults aged 0–19, with particular attention to how the prevalence of under-nutrition differs between urban and rural areas and how the drivers of poor nutrition vary spatially. The results of our random-effects logistic regressions on the nutritional impact of household agricultural production suggest that, conditional on household income, subsistence farming is associated with a lower probability of stunting. Even more important, although under-nutrition retains a strong spatial component, once observable differences in living standards are controlled for, the higher tendency for children in deep rural households to suffer from (severe) stunting reverses.
- Full Text:
- Authors: Otterbach, Steffen , Rogan, Michael
- Date: 2017
- Subjects: Human growth -- South Africa Malnutrition -- South Africa Poverty -- Case studies Economic development -- South Africa
- Language: English
- Type: Book , Text
- Identifier: http://hdl.handle.net/10962/59522 , vital:27622 , ISBN 9780868106342 , DOI 10.21504/10962/59522
- Description: One explanation for the increasing prevalence of stunting in South Africa over the past 15 years while other development indicators have improved is that Big Food retail chains have been contributing to a low quality diet across the country, particularly in poor urban households. We thus use nationally representative longitudinal data (2008–2014) to trace 6 years of stunting’s evolution among South African children, adolescents, and young adults aged 0–19, with particular attention to how the prevalence of under-nutrition differs between urban and rural areas and how the drivers of poor nutrition vary spatially. The results of our random-effects logistic regressions on the nutritional impact of household agricultural production suggest that, conditional on household income, subsistence farming is associated with a lower probability of stunting. Even more important, although under-nutrition retains a strong spatial component, once observable differences in living standards are controlled for, the higher tendency for children in deep rural households to suffer from (severe) stunting reverses.
- Full Text:
Species identification of adult African blowflies (Diptera: Calliphoridae) of forensic importance:
- Lutz, Lena, Williams, Kristin A, Villet, Martin H, Ekanem, Mfon
- Authors: Lutz, Lena , Williams, Kristin A , Villet, Martin H , Ekanem, Mfon
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140620 , vital:37904 , DOI: 10.1007/s00414-017-1654-y
- Description: Necrophagous blowflies can provide an excellent source of evidence for forensic entomologists and are also relevant to problems in public health, medicine, and animal health. However, access to useful information about these blowflies is constrained by the need to correctly identify the flies, and the poor availability of reliable, accessible identification tools is a serious obstacle to the development of forensic entomology in the majority of African countries. In response to this need, a high-quality key to the adults of all species of forensically relevant blowflies of Africa has been prepared, drawing on high-quality entomological materials and modern focus-stacking photomicroscopy. This new key can be easily applied by investigators inexperienced in the taxonomy of blowflies and is made available through a highly accessible online platform. Problematic diagnostic characters used in previous keys are discussed.
- Full Text:
- Authors: Lutz, Lena , Williams, Kristin A , Villet, Martin H , Ekanem, Mfon
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140620 , vital:37904 , DOI: 10.1007/s00414-017-1654-y
- Description: Necrophagous blowflies can provide an excellent source of evidence for forensic entomologists and are also relevant to problems in public health, medicine, and animal health. However, access to useful information about these blowflies is constrained by the need to correctly identify the flies, and the poor availability of reliable, accessible identification tools is a serious obstacle to the development of forensic entomology in the majority of African countries. In response to this need, a high-quality key to the adults of all species of forensically relevant blowflies of Africa has been prepared, drawing on high-quality entomological materials and modern focus-stacking photomicroscopy. This new key can be easily applied by investigators inexperienced in the taxonomy of blowflies and is made available through a highly accessible online platform. Problematic diagnostic characters used in previous keys are discussed.
- Full Text:
Spectroscopic and electrochemical characterization of thio binuclear phthalocyanine complexes
- Authors: Makinde, Zainab Olusola
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/59287 , vital:27541
- Description: Expected release date-April 2019
- Full Text:
- Authors: Makinde, Zainab Olusola
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/59287 , vital:27541
- Description: Expected release date-April 2019
- Full Text:
Spectroscopic and nonlinear optical characterisation of alpha substituted binuclear phthalocyanines
- Authors: Ngubeni, Grace Nomthandazo
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5038 , vital:20757
- Full Text:
- Authors: Ngubeni, Grace Nomthandazo
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5038 , vital:20757
- Full Text:
Sports and competition law in South Africa: the need to account for the uniqueness of sport when applying the competition Act 89 of 1998 to the sports industry
- Authors: Sun, Huajun
- Date: 2017
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: http://hdl.handle.net/10962/7102 , vital:21217
- Description: Regulation of sport as an economic activity has become increasingly prevalent in a number of foreign jurisdictions. This thesis considers the applicability of competition law to the sports industry from a South African perspective. Although the Competition Act 89 of 1998 is yet to be applied in the context of organisation of professional sport, the sector is not free from the scrutiny of competition law authorities. It is necessary to subject sports organisers and governing bodies to competition law in order to ensure that their administrative powers, which effectively place them in positions of market dominance, are not misused for their own commercial interests. On the other hand, the unique characteristics of sports should also be taken into account when applying competition law to the sector. In particular, it should be noted that sporting activities are not purely economic in nature, and that they are also conducted in order to achieve various social objectives. This thesis examines foreign jurisprudence that have dealt with the relevance of purely sporting justifications under competition law, and conclude that South Africa law should take into account the unique nature of sport when determining whether a conduct should be per se prohibited under the Competition Act, as well as when the rule-of-reason enquiry is conducted. This would require an amendment to the Act, a draft of which is proposed in this thesis. Finally, the proposed approach is applied in the context of the player transfer rules in football, in order to highlight problematic aspects of the transfer system even when considered in light of the unique nature of sports.
- Full Text:
- Authors: Sun, Huajun
- Date: 2017
- Language: English
- Type: Thesis , Masters , LLM
- Identifier: http://hdl.handle.net/10962/7102 , vital:21217
- Description: Regulation of sport as an economic activity has become increasingly prevalent in a number of foreign jurisdictions. This thesis considers the applicability of competition law to the sports industry from a South African perspective. Although the Competition Act 89 of 1998 is yet to be applied in the context of organisation of professional sport, the sector is not free from the scrutiny of competition law authorities. It is necessary to subject sports organisers and governing bodies to competition law in order to ensure that their administrative powers, which effectively place them in positions of market dominance, are not misused for their own commercial interests. On the other hand, the unique characteristics of sports should also be taken into account when applying competition law to the sector. In particular, it should be noted that sporting activities are not purely economic in nature, and that they are also conducted in order to achieve various social objectives. This thesis examines foreign jurisprudence that have dealt with the relevance of purely sporting justifications under competition law, and conclude that South Africa law should take into account the unique nature of sport when determining whether a conduct should be per se prohibited under the Competition Act, as well as when the rule-of-reason enquiry is conducted. This would require an amendment to the Act, a draft of which is proposed in this thesis. Finally, the proposed approach is applied in the context of the player transfer rules in football, in order to highlight problematic aspects of the transfer system even when considered in light of the unique nature of sports.
- Full Text:
Stochastic models in finance
- Authors: Mazengera, Hassan
- Date: 2017
- Subjects: Finance -- Mathematical models , C++ (Computer program language) , GARCH model , Lebesgue-Radon-Nikodym theorems , Radon measures , Stochastic models , Stochastic processes , Stochastic processes -- Computer programs , Martingales (Mathematics) , Pricing -- Mathematical models
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/162724 , vital:40976
- Description: Stochastic models for pricing financial securities are developed. First, we consider the Black Scholes model, which is a classic example of a complete market model and finally focus on Lévy driven models. Jumps may render the market incomplete and are induced in a model by inclusion of a Poisson process. Lévy driven models are more realistic in modelling of asset price dynamics than the Black Scholes model. Martingales are central in pricing, especially of derivatives and we give them the desired attention in the context of pricing. There are an increasing number of important pricing models where analytical solutions are not available hence computational methods come in handy, see Broadie and Glasserman (1997). It is also important to note that computational methods are also applicable to models with analytical solutions. We computationally value selected stochastic financial models using C++. Computational methods are also used to value or price complex financial instruments such as path dependent derivatives. This pricing procedure is applied in the computational valuation of a stochastic (revenue based) loan contract. Derivatives with simple pay of functions and models with analytical solutions are considered for illustrative purposes. The Black-Scholes P.D.E is complex to solve analytically and finite difference methods are widely used. Explicit finite difference scheme is considered in this thesis for computational valuation of derivatives that are modelled by the Black-Scholes P.D.E. Stochastic modelling of asset prices is important for the valuation of derivatives: Gaussian, exponential and gamma variates are simulated for the valuation purposes.
- Full Text:
- Authors: Mazengera, Hassan
- Date: 2017
- Subjects: Finance -- Mathematical models , C++ (Computer program language) , GARCH model , Lebesgue-Radon-Nikodym theorems , Radon measures , Stochastic models , Stochastic processes , Stochastic processes -- Computer programs , Martingales (Mathematics) , Pricing -- Mathematical models
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/162724 , vital:40976
- Description: Stochastic models for pricing financial securities are developed. First, we consider the Black Scholes model, which is a classic example of a complete market model and finally focus on Lévy driven models. Jumps may render the market incomplete and are induced in a model by inclusion of a Poisson process. Lévy driven models are more realistic in modelling of asset price dynamics than the Black Scholes model. Martingales are central in pricing, especially of derivatives and we give them the desired attention in the context of pricing. There are an increasing number of important pricing models where analytical solutions are not available hence computational methods come in handy, see Broadie and Glasserman (1997). It is also important to note that computational methods are also applicable to models with analytical solutions. We computationally value selected stochastic financial models using C++. Computational methods are also used to value or price complex financial instruments such as path dependent derivatives. This pricing procedure is applied in the computational valuation of a stochastic (revenue based) loan contract. Derivatives with simple pay of functions and models with analytical solutions are considered for illustrative purposes. The Black-Scholes P.D.E is complex to solve analytically and finite difference methods are widely used. Explicit finite difference scheme is considered in this thesis for computational valuation of derivatives that are modelled by the Black-Scholes P.D.E. Stochastic modelling of asset prices is important for the valuation of derivatives: Gaussian, exponential and gamma variates are simulated for the valuation purposes.
- Full Text:
Stranded Action: Musa N Nxumalo’s ’16 Shots’
- Authors: Lila, Philiswa
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147115 , vital:38594 , https://artthrob.co.za/2017/05/23/stranded-action-musa-n-nxumalos-16-shots/
- Description: Musa Nxumalo’s exhibition ‘16 Shots’ at SMAC Johannesburg, reveals moments of particular and familiar events. It comprises a selection of sixteen black and white photographs focusing on #feesmustfall protest, youth parties, objects of still life and portraits of individuals. At face value, the images fall into the genre of documentary, reportage, of less excitement visually but meaningful as photo essays of relations between political and social matters of youth.
- Full Text:
- Authors: Lila, Philiswa
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147115 , vital:38594 , https://artthrob.co.za/2017/05/23/stranded-action-musa-n-nxumalos-16-shots/
- Description: Musa Nxumalo’s exhibition ‘16 Shots’ at SMAC Johannesburg, reveals moments of particular and familiar events. It comprises a selection of sixteen black and white photographs focusing on #feesmustfall protest, youth parties, objects of still life and portraits of individuals. At face value, the images fall into the genre of documentary, reportage, of less excitement visually but meaningful as photo essays of relations between political and social matters of youth.
- Full Text:
Street trees contribute to urban sustainability in South African towns
- Shackleton, Charlie M, Gwedla, Nanamhla
- Authors: Shackleton, Charlie M , Gwedla, Nanamhla
- Date: 2017
- Subjects: City planning -- Environmental aspects Sustainable urban development Community development -- Environmental aspects -- South Africa
- Language: English
- Type: text
- Identifier: http://hdl.handle.net/10962/54269 , vital:26440
- Description: Urban green spaces and trees are increasingly recognised as crucial elements in the quest for urban sustainability internationally, and for the promotion of urban liveability and quality of life in cities. So much so that many countries now have guidelines or regulations regarding either the amount of urban greenery that must be provided per capita, or the maximum distance that any dwelling can be from green spaces of stipulated sizes. For example, the European Union recently more than doubled its recommendation of 9 m2 of public green per person to 20 m2 per person.
- Full Text:
- Authors: Shackleton, Charlie M , Gwedla, Nanamhla
- Date: 2017
- Subjects: City planning -- Environmental aspects Sustainable urban development Community development -- Environmental aspects -- South Africa
- Language: English
- Type: text
- Identifier: http://hdl.handle.net/10962/54269 , vital:26440
- Description: Urban green spaces and trees are increasingly recognised as crucial elements in the quest for urban sustainability internationally, and for the promotion of urban liveability and quality of life in cities. So much so that many countries now have guidelines or regulations regarding either the amount of urban greenery that must be provided per capita, or the maximum distance that any dwelling can be from green spaces of stipulated sizes. For example, the European Union recently more than doubled its recommendation of 9 m2 of public green per person to 20 m2 per person.
- Full Text:
Strengthening postgraduate supervision
- McKenna, Sioux, Clarence-Fincham, Jenny, Boughey, Chrissie, Wels, Harry, Van den Heuvel, Henk
- Authors: McKenna, Sioux , Clarence-Fincham, Jenny , Boughey, Chrissie , Wels, Harry , Van den Heuvel, Henk
- Date: 2017
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/66645 , vital:28975 , ISBN 9781928357322 , https://doi.10.18820/9781928357323
- Description: Preface: Since 1996 the number of students enrolled for Master’s study in South Africa has more than doubled, while doctoral enrolments have almost tripled (Cloete, Mouton and Sheppard 2015). Such enormous growth has had major implications for supervision, especially in a context where only 39% of academics have doctorates themselves. If South Africa is to come close to the National Development Plan target of 5 000 doctoral graduates per year by 2030, the pressure on supervisors is likely to continue apace. But supervision is of course not simply a matter of applying technical skills to churn out highly competent postgraduate scholars. It is a teaching craft coupled with research acumen and deep personal commitment. This book reflects on how a range of supervisors are making sense of this complex endeavour. The Strengthening Postgraduate Supervision book brings together 15 chapters written by 18 academics from 16 disciplines in 11 institutions. The authors work across all three institutional types found in higher education in South Africa: traditional universities, comprehensive universities and universities of technology. Through this rich array of contributions, supervision is presented never as a ‘best practice’ to be generically implemented but rather as a nuanced pedagogy to be nurtured through critical reflection. The chapters mix theoretical considerations of the postgraduate process and personal narratives of supervision practice. Most of the authors can be described as emerging supervisors, with a few contributions from more experienced supervisors, but all have in common a deep desire to forge inclusive environments that foster meaningful postgraduate research and nurture a new generation of scholars. It is through the sharing of these academics’ concerns and constraints, competencies and celebrations that this book adds to our understanding of postgraduate supervision in South Africa.
- Full Text: false
- Authors: McKenna, Sioux , Clarence-Fincham, Jenny , Boughey, Chrissie , Wels, Harry , Van den Heuvel, Henk
- Date: 2017
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/66645 , vital:28975 , ISBN 9781928357322 , https://doi.10.18820/9781928357323
- Description: Preface: Since 1996 the number of students enrolled for Master’s study in South Africa has more than doubled, while doctoral enrolments have almost tripled (Cloete, Mouton and Sheppard 2015). Such enormous growth has had major implications for supervision, especially in a context where only 39% of academics have doctorates themselves. If South Africa is to come close to the National Development Plan target of 5 000 doctoral graduates per year by 2030, the pressure on supervisors is likely to continue apace. But supervision is of course not simply a matter of applying technical skills to churn out highly competent postgraduate scholars. It is a teaching craft coupled with research acumen and deep personal commitment. This book reflects on how a range of supervisors are making sense of this complex endeavour. The Strengthening Postgraduate Supervision book brings together 15 chapters written by 18 academics from 16 disciplines in 11 institutions. The authors work across all three institutional types found in higher education in South Africa: traditional universities, comprehensive universities and universities of technology. Through this rich array of contributions, supervision is presented never as a ‘best practice’ to be generically implemented but rather as a nuanced pedagogy to be nurtured through critical reflection. The chapters mix theoretical considerations of the postgraduate process and personal narratives of supervision practice. Most of the authors can be described as emerging supervisors, with a few contributions from more experienced supervisors, but all have in common a deep desire to forge inclusive environments that foster meaningful postgraduate research and nurture a new generation of scholars. It is through the sharing of these academics’ concerns and constraints, competencies and celebrations that this book adds to our understanding of postgraduate supervision in South Africa.
- Full Text: false
Strengthening teachers’ knowledge and practices through a biodiversity education professional development programme
- Songqwaru, Zintle, Shava, Soul
- Authors: Songqwaru, Zintle , Shava, Soul
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/436294 , vital:73255 , ISBN 978-3-319-45989-9 , https://doi.org/10.1007/978-3-319-45989-9_15
- Description: What constitutes adequate teacher professional development support that enables teachers to engage meaningfully with ESD learning processes? In an attempt to answer this question, this chapter focuses on how continuing teacher profes-sional development programmes can support teachers of Life Sciences to teach biodiversity as a grounding concept to strengthen educational quality and relevance of Life Sciences education. It reflects on how continuing teacher professional development programmes may be designed and implemented to support South African teachers to work creatively with a con-tent and assessment-referenced national school curriculum. The chapter focuses on what content knowledge, teaching and assessment approaches to include as well as teachers’ reflections on the impacts of such a programme.
- Full Text:
- Authors: Songqwaru, Zintle , Shava, Soul
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , book chapter
- Identifier: http://hdl.handle.net/10962/436294 , vital:73255 , ISBN 978-3-319-45989-9 , https://doi.org/10.1007/978-3-319-45989-9_15
- Description: What constitutes adequate teacher professional development support that enables teachers to engage meaningfully with ESD learning processes? In an attempt to answer this question, this chapter focuses on how continuing teacher profes-sional development programmes can support teachers of Life Sciences to teach biodiversity as a grounding concept to strengthen educational quality and relevance of Life Sciences education. It reflects on how continuing teacher professional development programmes may be designed and implemented to support South African teachers to work creatively with a con-tent and assessment-referenced national school curriculum. The chapter focuses on what content knowledge, teaching and assessment approaches to include as well as teachers’ reflections on the impacts of such a programme.
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Structural analysis of proteases from South African HIV-1 (subtype C) patients undergoing Lopinavir treatment, using comparative modeling, ligand-docking and molecular dynamics
- Authors: Sheik-Amamuddy, Olivier
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4931 , vital:20744
- Description: HIV is regarded as one of the most devastating infectious diseases of the last few decades, and has a high prevalence in South Africa, subtype C being the most common. Palliative measures used to fight HIV involve the use various types of inhibitors, including the use of HIV protease inhibitors. Representatives from this class of inhibitors are gradually losing their efficacy due to development of resistance mutations from HIV-1. In this study, compounds from the South African Natural Compound Database (SANCDB) were screened against HIV-1 protease models generated from protease protein sequences belonging to 11 South African HIV patients before and after treatment with Lopinavir. The effect of Lopinavir on the alteration of drug-binding affinity before and after treatment is investigated by molecular docking of the protease against other FDA-approved drugs and detection of mutation types using the HIVdb tool. A network representation of hydrogen bonding between docked ligands and their receptor proteases has been developed and a profiling method of visualizing receptor-ligand docking energies at the local level is presented. Four potential HIV-1 protease inhibitors were identified from the list of 599 natural compounds on the basis of receptor conformation and binding free energy. Ligand stabilities were monitored by 20ns molecular dynamics runs using the GROMACS software.
- Full Text:
- Authors: Sheik-Amamuddy, Olivier
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4931 , vital:20744
- Description: HIV is regarded as one of the most devastating infectious diseases of the last few decades, and has a high prevalence in South Africa, subtype C being the most common. Palliative measures used to fight HIV involve the use various types of inhibitors, including the use of HIV protease inhibitors. Representatives from this class of inhibitors are gradually losing their efficacy due to development of resistance mutations from HIV-1. In this study, compounds from the South African Natural Compound Database (SANCDB) were screened against HIV-1 protease models generated from protease protein sequences belonging to 11 South African HIV patients before and after treatment with Lopinavir. The effect of Lopinavir on the alteration of drug-binding affinity before and after treatment is investigated by molecular docking of the protease against other FDA-approved drugs and detection of mutation types using the HIVdb tool. A network representation of hydrogen bonding between docked ligands and their receptor proteases has been developed and a profiling method of visualizing receptor-ligand docking energies at the local level is presented. Four potential HIV-1 protease inhibitors were identified from the list of 599 natural compounds on the basis of receptor conformation and binding free energy. Ligand stabilities were monitored by 20ns molecular dynamics runs using the GROMACS software.
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Structural and optical properties of sol-gel derived α-Fe2O3 nanoparticles
- Mathevula, Langutani E, Noto, L L, Mothudi, Bakang M, Chithambo, Makaiko L, Dhlamini, M S
- Authors: Mathevula, Langutani E , Noto, L L , Mothudi, Bakang M , Chithambo, Makaiko L , Dhlamini, M S
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115467 , vital:34145 , DOI: 10.1016/j.jlumin.2017.07.055
- Description: α-Fe2O3 nanoparticles of crystallite size between 3.9 and 9.5 nm were synthesized by a simple sol-gel method using iron (III) nitrate nonahydrate (Fe(NO3)3·9H2O) as a precursor. Polyvinyl alcohol (PVA) was added as a capping agent to avoid agglomeration of the nanoparticles. A single pure phase was obtained when the sample was annealed at 300 °C and 600 °C. The purity was further confirmed with the Fourier Transform Infrared Spectroscopy. The energy band gap of the materials was extrapolated from the Kubelka-Munk relation and it ranges between 1.8 and 2.3 eV. The Photoluminescence of the 3 samples shows a broad emission spectrum centered at about 422 nm when excited by a 336 nm lamp. The emission peaks intensities increased with an increase in the annealing temperature, accept for the 576 nm peak, which was quenched as the temperature increased from 300 °C to 600 °C. The thermoluminescence glow curves were carried out at different heating rates and the samples were exposed to different beta particle doses (82–1315 Gy). The activation energy of the trapped electrons was determined.
- Full Text: false
- Authors: Mathevula, Langutani E , Noto, L L , Mothudi, Bakang M , Chithambo, Makaiko L , Dhlamini, M S
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115467 , vital:34145 , DOI: 10.1016/j.jlumin.2017.07.055
- Description: α-Fe2O3 nanoparticles of crystallite size between 3.9 and 9.5 nm were synthesized by a simple sol-gel method using iron (III) nitrate nonahydrate (Fe(NO3)3·9H2O) as a precursor. Polyvinyl alcohol (PVA) was added as a capping agent to avoid agglomeration of the nanoparticles. A single pure phase was obtained when the sample was annealed at 300 °C and 600 °C. The purity was further confirmed with the Fourier Transform Infrared Spectroscopy. The energy band gap of the materials was extrapolated from the Kubelka-Munk relation and it ranges between 1.8 and 2.3 eV. The Photoluminescence of the 3 samples shows a broad emission spectrum centered at about 422 nm when excited by a 336 nm lamp. The emission peaks intensities increased with an increase in the annealing temperature, accept for the 576 nm peak, which was quenched as the temperature increased from 300 °C to 600 °C. The thermoluminescence glow curves were carried out at different heating rates and the samples were exposed to different beta particle doses (82–1315 Gy). The activation energy of the trapped electrons was determined.
- Full Text: false
Structure-based analysis of single nucleotide variants in the renin-angiotensinogen complex:
- Brown, David K, Olivier, Sheik Amamuddy, Tastan Bishop, Özlem
- Authors: Brown, David K , Olivier, Sheik Amamuddy , Tastan Bishop, Özlem
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147994 , vital:38700 , https://doi.org/10.1016/j.gheart.2017.01.006
- Description: The renin-angiotensin system (RAS) plays an important role in regulating blood pressure and controlling sodium levels in the blood. Hyperactivity of this system has been linked to numerous conditions including hypertension, kidney disease, and congestive heart failure. Three classes of drugs have been developed to inhibit RAS. In this study, we provide a structure-based analysis of the effect of single nucleotide variants (SNVs) on the interaction between renin and angiotensinogen with the aim of revealing important residues and potentially damaging variants for further inhibitor design purposes.
- Full Text:
- Authors: Brown, David K , Olivier, Sheik Amamuddy , Tastan Bishop, Özlem
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/147994 , vital:38700 , https://doi.org/10.1016/j.gheart.2017.01.006
- Description: The renin-angiotensin system (RAS) plays an important role in regulating blood pressure and controlling sodium levels in the blood. Hyperactivity of this system has been linked to numerous conditions including hypertension, kidney disease, and congestive heart failure. Three classes of drugs have been developed to inhibit RAS. In this study, we provide a structure-based analysis of the effect of single nucleotide variants (SNVs) on the interaction between renin and angiotensinogen with the aim of revealing important residues and potentially damaging variants for further inhibitor design purposes.
- Full Text:
Student-generated content: an approach to harnessing the power of diversity in higher education
- Snowball, Jeanette D, McKenna, Sioux
- Authors: Snowball, Jeanette D , McKenna, Sioux
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66763 , vital:28991 , ISSN 1470-1294 , https://doi.org/10.1080/13562517.2016.1273205
- Description: Publisher version , Internationally, classes in higher education institutions are becoming larger and more diverse. Support for ‘non-traditional’ students has often taken the form of additional remedial classes offered outside the main curriculum, which has met with limited success. Sociocultural theories of learning argue that the potential clash between the sociocultural context of disciplinary knowledge and the very different home contexts of many non-traditional students needs to be acknowledged. One way to achieve this is to use student-generated content, which allows teachers to bring student experiences and voices into the community of practice and acknowledges the importance of their prior experiences in knowledge production. Building on such sociocultural approaches to teaching and learning, this paper focuses on the use of student-generated podcasts as a means to harness the diversity of student experiences in a large (nearly 600 students) first-year Economics class at a South African University.
- Full Text: false
- Authors: Snowball, Jeanette D , McKenna, Sioux
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66763 , vital:28991 , ISSN 1470-1294 , https://doi.org/10.1080/13562517.2016.1273205
- Description: Publisher version , Internationally, classes in higher education institutions are becoming larger and more diverse. Support for ‘non-traditional’ students has often taken the form of additional remedial classes offered outside the main curriculum, which has met with limited success. Sociocultural theories of learning argue that the potential clash between the sociocultural context of disciplinary knowledge and the very different home contexts of many non-traditional students needs to be acknowledged. One way to achieve this is to use student-generated content, which allows teachers to bring student experiences and voices into the community of practice and acknowledges the importance of their prior experiences in knowledge production. Building on such sociocultural approaches to teaching and learning, this paper focuses on the use of student-generated podcasts as a means to harness the diversity of student experiences in a large (nearly 600 students) first-year Economics class at a South African University.
- Full Text: false
Students’ perspectives of the relationship between the university and a community partner in the context of a service learning psycho-education programme
- Authors: Sibiya, Gillian
- Date: 2017
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/6968 , vital:21205
- Description: This qualitative case study aims to understand students’ perspectives of the relationship between the university and a community partner in the context of a service-learning programme. The study explores the experiences of three postgraduate psychology students that were involved in a service-learning programme at an under resourced school in the Eastern Cape. The data gathered was analysed thematically and major analytic themes were identified. The findings highlight the usefulness of service-learning for the student participants. However, student participants also argued that structural difficulties can make it harder for the community partner to enjoy the same benefits. The analysis brings forth the students’ concerns about managing stakeholder perceptions and the importance of broad-based participation and constant communication to ensure a good working relationship between partners. The findings highlight the students’ awareness of some of the difficulties of working in resource-constrained settings.
- Full Text:
- Authors: Sibiya, Gillian
- Date: 2017
- Language: English
- Type: Thesis , Masters , MA
- Identifier: http://hdl.handle.net/10962/6968 , vital:21205
- Description: This qualitative case study aims to understand students’ perspectives of the relationship between the university and a community partner in the context of a service-learning programme. The study explores the experiences of three postgraduate psychology students that were involved in a service-learning programme at an under resourced school in the Eastern Cape. The data gathered was analysed thematically and major analytic themes were identified. The findings highlight the usefulness of service-learning for the student participants. However, student participants also argued that structural difficulties can make it harder for the community partner to enjoy the same benefits. The analysis brings forth the students’ concerns about managing stakeholder perceptions and the importance of broad-based participation and constant communication to ensure a good working relationship between partners. The findings highlight the students’ awareness of some of the difficulties of working in resource-constrained settings.
- Full Text:
Studies in the thiophenol mediated substitution and reductive dehalogenation of 3 bromoacetylcoumarins
- Authors: Magwenzi, Faith N
- Date: 2017
- Subjects: 3-bromoacetylcoumarins , Coumarins , Halogens -- Decontamination , Thiols , Plasmodium falciparum , Malaria -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MPharm
- Identifier: http://hdl.handle.net/10962/45769 , vital:25546
- Description: A previous study conducted by our group identified indolyl-3-ethanone-a-thioethers (2.1a and 2.1b) as non-toxic, nanomolar, in vitro inhibitors of Plasmodium falciparum. Since the coumarin scaffold is associated with numerous biologically active compounds including antiprotozoal, anti-viral, anti-bacterial, and anti-inflammatory agents we were prompted to investigate coumaryl-3-ethanone-a-thioethers (2.1c) inspired by the activity of 2.1a and 2.1b against P. falciparum. We proposed a three-step synthesis of our target compounds 2.1c. The first step involved the Knoevenagel synthesis of 3-acetyl coumarins (2.3.1a - e) followed by a selective a-bromination to yield 3-bromoacetyl coumarin (2.2a). The final proposed step involved the nucleophilic displacement of the bromine by appropriately substituted thiophenols in either the presence or absence of base (K2CO3). Our initial findings revealed an unexpected major reductive dehalogenation of 2.2a into 2.3.1a. Further investigation revealed a close relationship between the electron withdrawing or donating nature of the thiophenol substituents and the relative formation of nucleophilic substitution or reductive dehalogenation products. Desired thioether products were obtained in higher yields when thiophenol was substituted with electron donating groups i.e. more nucleophilic thiophenols, while conversely, electron withdrawing substituents (i.e. lowered nucleophilicity) resulted in an increase of reductive dehalogenation. Furthermore, these results were consistent when experiments were conducted using either 2 or 1.2 equivalents of thiophenols which was an important observation in the context of two previous studies, by Oki et. al. and Israel et. al. Oki proposed that dehalogenation of a-chloro carbonyls occurs via sequential nucleophilic displacement of a-thioethers, while the study of Israel concluded that the dehalogenation of a-iodo carbonyls occurred in a single discreet step. Finally, in an effort to enhance nucleophilic substitution through the addition of K2CO3, we observed a Robinson annulation resulting in previously undescribed C-8 thiophenol functionalised dibenzo[b,d]pyran-6-ones (3.4a - e). In the introduction to this thesis, we briefly summarise the utility of coumarins in medicinal chemistry and related fields. Chapter two describes the rationalisation of our original research question and a retrosynthetic analysis of our desired compounds, followed by an initial description of the unexpected reductive dehalogenation. Chapter 3, begins with a brief review of reductive dehalogenation of a-halocarbonyls, and is followed by an analysis and discussion of our results in the context of the studies by Israel et. al. and Oki et. al.
- Full Text:
- Authors: Magwenzi, Faith N
- Date: 2017
- Subjects: 3-bromoacetylcoumarins , Coumarins , Halogens -- Decontamination , Thiols , Plasmodium falciparum , Malaria -- Chemotherapy
- Language: English
- Type: Thesis , Masters , MPharm
- Identifier: http://hdl.handle.net/10962/45769 , vital:25546
- Description: A previous study conducted by our group identified indolyl-3-ethanone-a-thioethers (2.1a and 2.1b) as non-toxic, nanomolar, in vitro inhibitors of Plasmodium falciparum. Since the coumarin scaffold is associated with numerous biologically active compounds including antiprotozoal, anti-viral, anti-bacterial, and anti-inflammatory agents we were prompted to investigate coumaryl-3-ethanone-a-thioethers (2.1c) inspired by the activity of 2.1a and 2.1b against P. falciparum. We proposed a three-step synthesis of our target compounds 2.1c. The first step involved the Knoevenagel synthesis of 3-acetyl coumarins (2.3.1a - e) followed by a selective a-bromination to yield 3-bromoacetyl coumarin (2.2a). The final proposed step involved the nucleophilic displacement of the bromine by appropriately substituted thiophenols in either the presence or absence of base (K2CO3). Our initial findings revealed an unexpected major reductive dehalogenation of 2.2a into 2.3.1a. Further investigation revealed a close relationship between the electron withdrawing or donating nature of the thiophenol substituents and the relative formation of nucleophilic substitution or reductive dehalogenation products. Desired thioether products were obtained in higher yields when thiophenol was substituted with electron donating groups i.e. more nucleophilic thiophenols, while conversely, electron withdrawing substituents (i.e. lowered nucleophilicity) resulted in an increase of reductive dehalogenation. Furthermore, these results were consistent when experiments were conducted using either 2 or 1.2 equivalents of thiophenols which was an important observation in the context of two previous studies, by Oki et. al. and Israel et. al. Oki proposed that dehalogenation of a-chloro carbonyls occurs via sequential nucleophilic displacement of a-thioethers, while the study of Israel concluded that the dehalogenation of a-iodo carbonyls occurred in a single discreet step. Finally, in an effort to enhance nucleophilic substitution through the addition of K2CO3, we observed a Robinson annulation resulting in previously undescribed C-8 thiophenol functionalised dibenzo[b,d]pyran-6-ones (3.4a - e). In the introduction to this thesis, we briefly summarise the utility of coumarins in medicinal chemistry and related fields. Chapter two describes the rationalisation of our original research question and a retrosynthetic analysis of our desired compounds, followed by an initial description of the unexpected reductive dehalogenation. Chapter 3, begins with a brief review of reductive dehalogenation of a-halocarbonyls, and is followed by an analysis and discussion of our results in the context of the studies by Israel et. al. and Oki et. al.
- Full Text: