Optimizing the electrocatalytic activity of surface confined Co macrocyclics for the electrooxidation of thiocyanate at pH 4
- Tshangana, Charmaine, Pavez, Jorge, Gulppi, Miguel A, De Mattos, Ivanildo Luiz, Arratia-Perez, Ramiro, Linares-Flores, Cristian, Paez, Maritza, Nyokong, Tebello, Zagal, Jos H
- Authors: Tshangana, Charmaine , Pavez, Jorge , Gulppi, Miguel A , De Mattos, Ivanildo Luiz , Arratia-Perez, Ramiro , Linares-Flores, Cristian , Paez, Maritza , Nyokong, Tebello , Zagal, Jos H
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/247726 , vital:51612 , xlink:href="https://doi.org/10.1002/elan.201000599"
- Description: We have studied the trends in catalytic activity of several Co macrocyclics confined on the surface graphite electrodes for the oxidation of thiocyanate. A plot of log i (at constant E) versus the formal potential of the catalyst gives a volcano correlation, indicating that the Co(II/I) redox potential needs to be tuned, in order to achieve maximum reactivity. Graphite electrodes modified with Co phthalocyanine at pH 4 exhibit linear amperometric response for thiocyanate concentration in the range 10−7 and 10−3 M. Theoretical calculations show that electrocatalytic activity (as log i at constant E) plotted versus the energy of the LUMO of the Co complex also gives a volcano correlation.
- Full Text:
- Date Issued: 2011
- Authors: Tshangana, Charmaine , Pavez, Jorge , Gulppi, Miguel A , De Mattos, Ivanildo Luiz , Arratia-Perez, Ramiro , Linares-Flores, Cristian , Paez, Maritza , Nyokong, Tebello , Zagal, Jos H
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/247726 , vital:51612 , xlink:href="https://doi.org/10.1002/elan.201000599"
- Description: We have studied the trends in catalytic activity of several Co macrocyclics confined on the surface graphite electrodes for the oxidation of thiocyanate. A plot of log i (at constant E) versus the formal potential of the catalyst gives a volcano correlation, indicating that the Co(II/I) redox potential needs to be tuned, in order to achieve maximum reactivity. Graphite electrodes modified with Co phthalocyanine at pH 4 exhibit linear amperometric response for thiocyanate concentration in the range 10−7 and 10−3 M. Theoretical calculations show that electrocatalytic activity (as log i at constant E) plotted versus the energy of the LUMO of the Co complex also gives a volcano correlation.
- Full Text:
- Date Issued: 2011
Traditional Dealerships’ Operational Capacity to Sell Electric Vehicles
- Authors: Knoetze, Alicia Jo-mari
- Date: 2020
- Subjects: Electric vehicle industry Automobile industry and trade
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: http://hdl.handle.net/10948/48686 , vital:41059
- Description: The global automotive industry faces an emerging turning point where an unceasing dependence on costly fossil fuels and a growing concern over global warming is driving the industry to form new possibilities. A major challenge for decision makers is to assure that the consumer market is informed about both the advantages and disadvantageous of electric vehicle technology. A significant amount of research has been done on both the operational ability of electric vehicles and consumer resistance and preferences towards new technology and the marketing of electric vehicles. Given the retail relationship between key industry stakeholders such as the Original Equipment Manufacturers, franchised dealership network and potential electric vehicle consumers, the transition towards new electric vehicle technology represents an important strategic realignment for dealerships in order to sell electric vehicles along with traditional internal combustion engine vehicles and questions their operational capacity to do so successfully. The primary data was collected from a sample of forty respondents by means of an online questionnaire. The questionnaire was designed from literature and using similar extracts from other electric vehicle consumer resistance studies questionnaires. An email containing a Universal Resource Link (URL) to the questionnaire was sent and by means of snowball sampling, a representative sample of forty-eight respondents participated in the study who fully completed all the sections of the questionnaire. Interviews were conducted with Senior Management of local dealerships in the Port Elizabeth area. The interviews were executed in the same method as a ‘walk-in’ potential customer. Participation therefore was based on the willingness, readiness and availability of management. Three dealerships who already sell electric vehicles as well as two dealership who still only sell traditional internal combustion engine vehicles participated in the interviews. In addition, the National Automobile Dealers Association (NADA) commented on the strategic realignment of the South African industry as a whole. The results indicated that the majority of respondents believed that electric vehicles were a suitable alternative to the traditional internal combustion engine vehicle and were willing to personally contribute to improved sustainable mobility. Uncertainty remained with consumers and there was unwillingness to purchase and electric vehicle within the next five years. Electric vehicles were also believed to perform better but there was uncertainty about the return that would be achieved from investment in an electric vehicle despite the reduction in their carbon footprint and the associated image boost with family and colleagues. Furthermore, there appeared to be an alignment amongst the interviewees that South Africa does not face and immediate threat in terms of electric vehicles as the anticipated tipping point is envisaged to be in the region of 2030 onwards, however NADA as a professional industry body still warns that this is not a set point in time and that market forces could change the outlook and adaption dramatically.
- Full Text:
- Date Issued: 2020
- Authors: Knoetze, Alicia Jo-mari
- Date: 2020
- Subjects: Electric vehicle industry Automobile industry and trade
- Language: English
- Type: Thesis , Masters , MBA
- Identifier: http://hdl.handle.net/10948/48686 , vital:41059
- Description: The global automotive industry faces an emerging turning point where an unceasing dependence on costly fossil fuels and a growing concern over global warming is driving the industry to form new possibilities. A major challenge for decision makers is to assure that the consumer market is informed about both the advantages and disadvantageous of electric vehicle technology. A significant amount of research has been done on both the operational ability of electric vehicles and consumer resistance and preferences towards new technology and the marketing of electric vehicles. Given the retail relationship between key industry stakeholders such as the Original Equipment Manufacturers, franchised dealership network and potential electric vehicle consumers, the transition towards new electric vehicle technology represents an important strategic realignment for dealerships in order to sell electric vehicles along with traditional internal combustion engine vehicles and questions their operational capacity to do so successfully. The primary data was collected from a sample of forty respondents by means of an online questionnaire. The questionnaire was designed from literature and using similar extracts from other electric vehicle consumer resistance studies questionnaires. An email containing a Universal Resource Link (URL) to the questionnaire was sent and by means of snowball sampling, a representative sample of forty-eight respondents participated in the study who fully completed all the sections of the questionnaire. Interviews were conducted with Senior Management of local dealerships in the Port Elizabeth area. The interviews were executed in the same method as a ‘walk-in’ potential customer. Participation therefore was based on the willingness, readiness and availability of management. Three dealerships who already sell electric vehicles as well as two dealership who still only sell traditional internal combustion engine vehicles participated in the interviews. In addition, the National Automobile Dealers Association (NADA) commented on the strategic realignment of the South African industry as a whole. The results indicated that the majority of respondents believed that electric vehicles were a suitable alternative to the traditional internal combustion engine vehicle and were willing to personally contribute to improved sustainable mobility. Uncertainty remained with consumers and there was unwillingness to purchase and electric vehicle within the next five years. Electric vehicles were also believed to perform better but there was uncertainty about the return that would be achieved from investment in an electric vehicle despite the reduction in their carbon footprint and the associated image boost with family and colleagues. Furthermore, there appeared to be an alignment amongst the interviewees that South Africa does not face and immediate threat in terms of electric vehicles as the anticipated tipping point is envisaged to be in the region of 2030 onwards, however NADA as a professional industry body still warns that this is not a set point in time and that market forces could change the outlook and adaption dramatically.
- Full Text:
- Date Issued: 2020
Volatile constituents and biological activities of the leaf and root of Echinacea species from South Africa
- M. Nyalambisa, S.P. Songca, A.O. Oyedeji, I.A. Oyemitan
- Authors: M. Nyalambisa , S.P. Songca , A.O. Oyedeji , I.A. Oyemitan
- Date: 2017
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/11260/5543 , vital:44602
- Full Text:
- Authors: M. Nyalambisa , S.P. Songca , A.O. Oyedeji , I.A. Oyemitan
- Date: 2017
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/11260/5543 , vital:44602
- Full Text:
Volatile constituents and biological activities of the leaf and root of Echinacea species from South Africa
- M. Nyalambisa,, I.A. Oyemitan, B.N. Nkeh-Chungag, A.O. Oyedeji
- Authors: M. Nyalambisa, , I.A. Oyemitan , B.N. Nkeh-Chungag , A.O. Oyedeji
- Date: 2016
- Identifier: http://hdl.handle.net/11260/1568 , vital:37788
- Full Text:
- Authors: M. Nyalambisa, , I.A. Oyemitan , B.N. Nkeh-Chungag , A.O. Oyedeji
- Date: 2016
- Identifier: http://hdl.handle.net/11260/1568 , vital:37788
- Full Text:
Flammability of indigenous and invasive alien woody plants in coastal fynbos and thicket
- Msweli, Samukelisiwe Tholakele, Potts, Alastair J
- Authors: Msweli, Samukelisiwe Tholakele , Potts, Alastair J
- Date: 2020
- Subjects: Forest fires -- Environmental aspects , Forest fires -- Prevention and control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45875 , vital:39313
- Description: Globally, extreme fires have become more common in wildland-urban interface areas, and more recently, along the southern Cape coast of South Africa. The 2017 Knysna fires prompted greater understanding of the flammability of, and the fire risk posed by, different vegetation groups, which is essential to develop fire risk mitigation strategies. In this study, I experimentally assessed flammability of 30 woody plant species from the vegetation groups indigenous fynbos, thicket, and invasive alien plants (IAPs) that occur along the southern Cape coast. Live plant shoots were sampled across varying fire weather conditions and burnt experimentally to measure flammability in relation to fire weather conditions, fuel moisture, and fuel load. Flammability measures considered were: burn intensity, completeness of burn, time-to-ignition, and the likelihood of spontaneous ignition. I further assessed the flammability of partially dried plant material as a crude proxy for drought effects, to ascertain whether drying of fuels would differentially affect the flammability of the vegetation groups. I used generalized linear mixed-effects models to assess flammability measures in relation to the predictor variables: fire weather, fuel moisture, fuel load, vegetation groups, and species (as a random factor). Results showed that increasing severity of fire weather significantly increased flammability through increasing burn intensity, increasing completeness of burn, increasing the likelihood of spontaneous ignition, and also reducing time-to-ignition. Increasing fuel moisture significantly decreased burn intensity, completeness of burn, and the likelihood of spontaneous ignition. Fuel load significantly increased burn intensity and time-to-ignition. Flammability was highest in IAPs, intermediate in fynbos, and lowest in thicket. IAPs and fynbos showed significantly higher ignitability, and thus present risks under moderate and high fire weather conditions, whereas thicket presents lower risks under low and moderate fire weather conditions. The drying out of fuels considerably increased flammability equally in the three vegetation groups, and by implication, fire risk due to an increase in dead:live ratio. Flammability was furthermore assessed in relation to fuel traits, i.e. the proportion of fine fuels, coarse fuels, and dead fuels, fuel bed porosity, fuel load, and fuel moisture, using multiple regression analysis and stepwise selection of factors. This revealed that fuel moisture was the most important factor affecting flammability in terms of all the flammability measures. Results further showed that the increase in v the proportions of fine fuels increased flammability by increasing completeness of burn. Lastly, vegetation groups were compared (using Kruskal Wallis) in terms of their flammability and fuel traits. I found that fynbos and IAPs exhibited greater flammability on account of higher completeness of burn and more rapid ignition than thicket species, but no clear distinction was evident between fynbos and IAPs. Fynbos’ high flammability was attributed to high proportions of fine and porous fuels. Thicket’s low flammability was attributed to high proportions of coarse and dense fuels. Little distinction in fuel traits could be made between fynbos and IAPs, except that fynbos had a greater proportion of fine fuels. There is a potential risk posed by the IAPs in terms of increased flammability and fire severity, on an indigenous landscape that is invaded. Fire managers need to encourage the prioritization of the management of IAPs that present high flammability as an attempt to reduce fire risk along the southern Cape coast of South Africa.
- Full Text:
- Date Issued: 2020
- Authors: Msweli, Samukelisiwe Tholakele , Potts, Alastair J
- Date: 2020
- Subjects: Forest fires -- Environmental aspects , Forest fires -- Prevention and control
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/45875 , vital:39313
- Description: Globally, extreme fires have become more common in wildland-urban interface areas, and more recently, along the southern Cape coast of South Africa. The 2017 Knysna fires prompted greater understanding of the flammability of, and the fire risk posed by, different vegetation groups, which is essential to develop fire risk mitigation strategies. In this study, I experimentally assessed flammability of 30 woody plant species from the vegetation groups indigenous fynbos, thicket, and invasive alien plants (IAPs) that occur along the southern Cape coast. Live plant shoots were sampled across varying fire weather conditions and burnt experimentally to measure flammability in relation to fire weather conditions, fuel moisture, and fuel load. Flammability measures considered were: burn intensity, completeness of burn, time-to-ignition, and the likelihood of spontaneous ignition. I further assessed the flammability of partially dried plant material as a crude proxy for drought effects, to ascertain whether drying of fuels would differentially affect the flammability of the vegetation groups. I used generalized linear mixed-effects models to assess flammability measures in relation to the predictor variables: fire weather, fuel moisture, fuel load, vegetation groups, and species (as a random factor). Results showed that increasing severity of fire weather significantly increased flammability through increasing burn intensity, increasing completeness of burn, increasing the likelihood of spontaneous ignition, and also reducing time-to-ignition. Increasing fuel moisture significantly decreased burn intensity, completeness of burn, and the likelihood of spontaneous ignition. Fuel load significantly increased burn intensity and time-to-ignition. Flammability was highest in IAPs, intermediate in fynbos, and lowest in thicket. IAPs and fynbos showed significantly higher ignitability, and thus present risks under moderate and high fire weather conditions, whereas thicket presents lower risks under low and moderate fire weather conditions. The drying out of fuels considerably increased flammability equally in the three vegetation groups, and by implication, fire risk due to an increase in dead:live ratio. Flammability was furthermore assessed in relation to fuel traits, i.e. the proportion of fine fuels, coarse fuels, and dead fuels, fuel bed porosity, fuel load, and fuel moisture, using multiple regression analysis and stepwise selection of factors. This revealed that fuel moisture was the most important factor affecting flammability in terms of all the flammability measures. Results further showed that the increase in v the proportions of fine fuels increased flammability by increasing completeness of burn. Lastly, vegetation groups were compared (using Kruskal Wallis) in terms of their flammability and fuel traits. I found that fynbos and IAPs exhibited greater flammability on account of higher completeness of burn and more rapid ignition than thicket species, but no clear distinction was evident between fynbos and IAPs. Fynbos’ high flammability was attributed to high proportions of fine and porous fuels. Thicket’s low flammability was attributed to high proportions of coarse and dense fuels. Little distinction in fuel traits could be made between fynbos and IAPs, except that fynbos had a greater proportion of fine fuels. There is a potential risk posed by the IAPs in terms of increased flammability and fire severity, on an indigenous landscape that is invaded. Fire managers need to encourage the prioritization of the management of IAPs that present high flammability as an attempt to reduce fire risk along the southern Cape coast of South Africa.
- Full Text:
- Date Issued: 2020
Extended and Continuous Decline in Effective Population Size Results in Low Genomic Diversity in the World’s Rarest Hyena Species, the Brown Hyena
- Westbury, Michael V, Hartmann, Stefanie, Barlow, Axel, Wiesel, Ingrid, Leo, Viyanna, Welch, Rebecca J, Parker, Daniel M, Sicks, Florian, Ludwig, Arne, Dalén, Love, Hofreiter, Michael
- Authors: Westbury, Michael V , Hartmann, Stefanie , Barlow, Axel , Wiesel, Ingrid , Leo, Viyanna , Welch, Rebecca J , Parker, Daniel M , Sicks, Florian , Ludwig, Arne , Dalén, Love , Hofreiter, Michael
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124482 , vital:35616 , https://doi.org/10.1093/molbev/msy037
- Description: Hyenas (family Hyaenidae), as the sister group to cats (family Felidae), represent a deeply diverging branch within the cat-like carnivores (Feliformia). With an estimated population size of < 10,000 individuals worldwide, the brown hyena (Parahyaena brunnea) represents the rarest of the four extant hyena species and has been listed as Near Threatened by the IUCN. Here, we report a high-coverage genome from a captive bred brown hyena and both mitochondrial and low coverage nuclear genomes of 14 wild-caught brown hyena individuals from across southern Africa.We find that brown hyena harbor extremely low genetic diversity on both the mitochondrial and nuclear level, most likely resulting from a continuous and ongoing decline in effective population size that started_1Ma and dramatically accelerated towards the end of the Pleistocene. Despite the strikingly low genetic diversity, we find no evidence of inbreeding within the captive bred individual and reveal phylogeographic structure, suggesting the existence of several potential subpopulations within the species.
- Full Text:
- Date Issued: 2018
- Authors: Westbury, Michael V , Hartmann, Stefanie , Barlow, Axel , Wiesel, Ingrid , Leo, Viyanna , Welch, Rebecca J , Parker, Daniel M , Sicks, Florian , Ludwig, Arne , Dalén, Love , Hofreiter, Michael
- Date: 2018
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124482 , vital:35616 , https://doi.org/10.1093/molbev/msy037
- Description: Hyenas (family Hyaenidae), as the sister group to cats (family Felidae), represent a deeply diverging branch within the cat-like carnivores (Feliformia). With an estimated population size of < 10,000 individuals worldwide, the brown hyena (Parahyaena brunnea) represents the rarest of the four extant hyena species and has been listed as Near Threatened by the IUCN. Here, we report a high-coverage genome from a captive bred brown hyena and both mitochondrial and low coverage nuclear genomes of 14 wild-caught brown hyena individuals from across southern Africa.We find that brown hyena harbor extremely low genetic diversity on both the mitochondrial and nuclear level, most likely resulting from a continuous and ongoing decline in effective population size that started_1Ma and dramatically accelerated towards the end of the Pleistocene. Despite the strikingly low genetic diversity, we find no evidence of inbreeding within the captive bred individual and reveal phylogeographic structure, suggesting the existence of several potential subpopulations within the species.
- Full Text:
- Date Issued: 2018
Interaction of CdTe quantum dots with 2, 2-diphenyl-1-picrylhydrazyl free radical
- Adegoke, Oluwasesan, Chidawanyika, Wadzanai, Nyokong, Tebello
- Authors: Adegoke, Oluwasesan , Chidawanyika, Wadzanai , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245751 , vital:51402 , xlink:href="https://doi.org/10.1007/s10895-011-1012-2"
- Description: The interaction of 2,2-diphenyl-1-picrylhydrazyl (DPPH●) free radical with thiol-capped CdTe quantum dots (QDs) has been studied by UV–vis spectroscopy, steady state and time resolved fluorescence measurements. Addition of DPPH● radical to CdTe QDs resulted in fluorescence quenching. The interaction occurs through static quenching as this was confirmed by fluorescence lifetime measurements. Time course absorption studies indicates that DPPH● may be reduced by interaction with QDs to the substituted hydrazine form (2,2-diphenyl-1-picrylhydrazine) DPPH-H. The mechanism of fluorescence quenching of CdTe QDs by DPPH● is proposed.
- Full Text:
- Date Issued: 2012
- Authors: Adegoke, Oluwasesan , Chidawanyika, Wadzanai , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245751 , vital:51402 , xlink:href="https://doi.org/10.1007/s10895-011-1012-2"
- Description: The interaction of 2,2-diphenyl-1-picrylhydrazyl (DPPH●) free radical with thiol-capped CdTe quantum dots (QDs) has been studied by UV–vis spectroscopy, steady state and time resolved fluorescence measurements. Addition of DPPH● radical to CdTe QDs resulted in fluorescence quenching. The interaction occurs through static quenching as this was confirmed by fluorescence lifetime measurements. Time course absorption studies indicates that DPPH● may be reduced by interaction with QDs to the substituted hydrazine form (2,2-diphenyl-1-picrylhydrazine) DPPH-H. The mechanism of fluorescence quenching of CdTe QDs by DPPH● is proposed.
- Full Text:
- Date Issued: 2012
Firm age, collateral value, and access to debt financing in an emerging economy: evidence from South Africa
- Authors: Ezeoha,Abel , Botha, Ferdi
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396060 , vital:69147 , xlink:href="https://hdl.handle.net/10520/EJC31367"
- Description: This paper applies the Blundell and Bond system generalised method of moments (GMM) two-step estimator to examine the impact of age and collateral value on debt financing, using a panel of 177 non-financial companies listed on the Johannesburg Stock Exchange over the period 1999 to 2009. The results show that South African firms have target leverage ratios and adjust their capital structures from time to time to achieve their respective targets, that the relationship between firm age and debt financing is non-monotonic, and that firms with higher collateral value are likely to face fewer constraints on borrowing and therefore have greater access to medium-term and long-term debts. Robustness tests also reveal that during start-up and maturity stages, a firm's access to debt markets is significantly influenced by investments in assets that are acceptable to external creditors as collateral. These findings suggest that debt financing policies could be more critical for firms in the start-up and maturity stages.
- Full Text:
- Date Issued: 2012
- Authors: Ezeoha,Abel , Botha, Ferdi
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396060 , vital:69147 , xlink:href="https://hdl.handle.net/10520/EJC31367"
- Description: This paper applies the Blundell and Bond system generalised method of moments (GMM) two-step estimator to examine the impact of age and collateral value on debt financing, using a panel of 177 non-financial companies listed on the Johannesburg Stock Exchange over the period 1999 to 2009. The results show that South African firms have target leverage ratios and adjust their capital structures from time to time to achieve their respective targets, that the relationship between firm age and debt financing is non-monotonic, and that firms with higher collateral value are likely to face fewer constraints on borrowing and therefore have greater access to medium-term and long-term debts. Robustness tests also reveal that during start-up and maturity stages, a firm's access to debt markets is significantly influenced by investments in assets that are acceptable to external creditors as collateral. These findings suggest that debt financing policies could be more critical for firms in the start-up and maturity stages.
- Full Text:
- Date Issued: 2012
Synthesis and biological evaluation of truncated sarganaphthoquinoic acid derivatives as Hsp90 inhibitors
- Authors: Chiwakata, Maynard T
- Date: 2015
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/64708 , vital:28594
- Description: Hsp90 inhibition has been at the centre of attention in current research due to the possibility of “cracking down” on the entire process leading to the development of malignant cancers. Small underlying principles common in all types of cancers have been determined that govern the transformation of normal human cells into cancerous cells, with all relying on the ATPase activity of Hsp90 protein. Hsp90 protein is therefore an attractive drug target that if successfully inhibited can result in the remission of cancer tumours by one form of treatment. To date, no Hsp90 inhibitor has been sanctioned for cancer treatment as most are still in clinical development. Our research was therefore inspired by reports that indicated the potential of quinones / naphthoquinones to act as Hsp90 inhibitors. Preliminary results of a few selected marine natural product quinone systems i.e. sargaquinoic acid (SQA) (2.47) and lapachol (3.6) showed moderate cytotoxicity and weak interactions with the Hsp90 molecular chaperone, and evidence suggested C-terminal binding of these molecules. No correlation has been determined yet between cytotoxicity and Hsp90 inhibition, hence we aimed to develop natural product inspired molecules that exhibit both cytotoxic and Hsp90 inhibition properties. Due to limited amounts of the natural product that can be acquired from natural sources, synthetic analogues were opted for. Isolation of a few selected quinones was conducted to have material that could be used in biological assays. For structural modifications, a series of truncated naphthoquinone systems were prepared adopting the sarganaphthoquinoic acid (3.5) scaffold. The naphthoquinones were prepared via Diels-Alder reactions of relevant benzoquinones with myrcene, followed by aromatization reactions using MnO2. Various alkyl and aryl amines were then coupled to the C-2/3 position of the naphthoquinone using Michael’s addition reactions. Tricyclic naphthoquinones were also synthesized from reactions with hypotaurine and citral. Design of the analogues incorporated functionalities from known Hsp90 inhibitors e.g. geldanamycin (2.28) and its analogues. Preliminary results obtained showed that coupling of naphthoquinones with aryl-amines resulted in the most cytotoxic compounds (4.14-4.19) with IC50 values as low as 0.3 μM against Hs578T breast cancer carcinoma (triple negative). Most of the alkyl amines (4.20-4.25) had IC50 values greater than 50 μM except for 4.20 and 4.21 that showed IC50 values of 7.6 μM and 2.6 μM respectively. Tricyclic naphthoquinones (4.28-4.29) showed moderate cytotoxic activity of approximately 10 μM. Hsp90 inhibition was assessed by client protein degradation assays, of which SQA (2.47), showed the best Hsp90 inhibition properties, followed by compound 4.20. The most cytotoxic arylamino-naphthoquinone (4.16) and tricyclic naphthoquinones (4.28-4.29) showed only moderate inhibition. None of the compounds led to Hsp70 induction, suggesting possible binding to the C-terminus of Hsp90. Interactions at the binding site were assessed by molecular docking studies and saturation transfer difference (STD) NMR. Docking studies were conducted on the N-terminus of Hsp90 and better binding was observed for arylamino naphthoquinones (4.14-4.19) than for other series of compounds. Unfortunately, the co-crystal structure for the C-terminus of Hsp90 is unavailable, hence docking study comparisons on both domains could not be conducted. However, STD NMR offered a platform to assess binding interactions between the naphthoquinones and the N- or C-terminal domains of Hsp90. However no interactions were observed at both the N- and C- termini of Hsp90 due to either weak binding of ligands to the protein or poor water solubility of the ligands. From these preliminary results, naphthoquinones bind to Hsp90 protein but conclusive remarks to which terminal domain they bind to could not be made. The best candidate from amongst the series of naphthoquinones prepared that showed moderate cytotoxicity and promising Hsp90 inhibition was compound 4.20. We therefore succeeded in developing a new series of naphthoquinones that possess moderate cytotoxicity and show Hsp90 inhibition.
- Full Text:
- Date Issued: 2015
- Authors: Chiwakata, Maynard T
- Date: 2015
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/64708 , vital:28594
- Description: Hsp90 inhibition has been at the centre of attention in current research due to the possibility of “cracking down” on the entire process leading to the development of malignant cancers. Small underlying principles common in all types of cancers have been determined that govern the transformation of normal human cells into cancerous cells, with all relying on the ATPase activity of Hsp90 protein. Hsp90 protein is therefore an attractive drug target that if successfully inhibited can result in the remission of cancer tumours by one form of treatment. To date, no Hsp90 inhibitor has been sanctioned for cancer treatment as most are still in clinical development. Our research was therefore inspired by reports that indicated the potential of quinones / naphthoquinones to act as Hsp90 inhibitors. Preliminary results of a few selected marine natural product quinone systems i.e. sargaquinoic acid (SQA) (2.47) and lapachol (3.6) showed moderate cytotoxicity and weak interactions with the Hsp90 molecular chaperone, and evidence suggested C-terminal binding of these molecules. No correlation has been determined yet between cytotoxicity and Hsp90 inhibition, hence we aimed to develop natural product inspired molecules that exhibit both cytotoxic and Hsp90 inhibition properties. Due to limited amounts of the natural product that can be acquired from natural sources, synthetic analogues were opted for. Isolation of a few selected quinones was conducted to have material that could be used in biological assays. For structural modifications, a series of truncated naphthoquinone systems were prepared adopting the sarganaphthoquinoic acid (3.5) scaffold. The naphthoquinones were prepared via Diels-Alder reactions of relevant benzoquinones with myrcene, followed by aromatization reactions using MnO2. Various alkyl and aryl amines were then coupled to the C-2/3 position of the naphthoquinone using Michael’s addition reactions. Tricyclic naphthoquinones were also synthesized from reactions with hypotaurine and citral. Design of the analogues incorporated functionalities from known Hsp90 inhibitors e.g. geldanamycin (2.28) and its analogues. Preliminary results obtained showed that coupling of naphthoquinones with aryl-amines resulted in the most cytotoxic compounds (4.14-4.19) with IC50 values as low as 0.3 μM against Hs578T breast cancer carcinoma (triple negative). Most of the alkyl amines (4.20-4.25) had IC50 values greater than 50 μM except for 4.20 and 4.21 that showed IC50 values of 7.6 μM and 2.6 μM respectively. Tricyclic naphthoquinones (4.28-4.29) showed moderate cytotoxic activity of approximately 10 μM. Hsp90 inhibition was assessed by client protein degradation assays, of which SQA (2.47), showed the best Hsp90 inhibition properties, followed by compound 4.20. The most cytotoxic arylamino-naphthoquinone (4.16) and tricyclic naphthoquinones (4.28-4.29) showed only moderate inhibition. None of the compounds led to Hsp70 induction, suggesting possible binding to the C-terminus of Hsp90. Interactions at the binding site were assessed by molecular docking studies and saturation transfer difference (STD) NMR. Docking studies were conducted on the N-terminus of Hsp90 and better binding was observed for arylamino naphthoquinones (4.14-4.19) than for other series of compounds. Unfortunately, the co-crystal structure for the C-terminus of Hsp90 is unavailable, hence docking study comparisons on both domains could not be conducted. However, STD NMR offered a platform to assess binding interactions between the naphthoquinones and the N- or C-terminal domains of Hsp90. However no interactions were observed at both the N- and C- termini of Hsp90 due to either weak binding of ligands to the protein or poor water solubility of the ligands. From these preliminary results, naphthoquinones bind to Hsp90 protein but conclusive remarks to which terminal domain they bind to could not be made. The best candidate from amongst the series of naphthoquinones prepared that showed moderate cytotoxicity and promising Hsp90 inhibition was compound 4.20. We therefore succeeded in developing a new series of naphthoquinones that possess moderate cytotoxicity and show Hsp90 inhibition.
- Full Text:
- Date Issued: 2015
External Factors affecting Blackboard Learning Management System adoption by Students: Evidence from a Historically Disadvantaged Higher Education Institution in South Africa
- O. Matarirano, M. Panicker, N.R. Jere https://orcid.org/0000-0001-8966-2753, A. Maliwa
- Authors: O. Matarirano , M. Panicker , N.R. Jere https://orcid.org/0000-0001-8966-2753 , A. Maliwa
- Date: 2021
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/11260/3304 , vital:43306 , https://doi.org/10.20853/35-2-4025
- Description: Learning Management Systems (LMS) have the ability to transform learning experiences of students in Higher Education Institutions (HEI). In addition to the developmental benefits, LMS assist teaching and learning during student unrests, a common feature in historically disadvantaged institutions in South Africa. Regardless of the benefits of LMS platforms such as Blackboard, the utilisation by university students at the institution under study has been very low. Applying cross sectional electronic survey, this study identifies the key factors influencing technology adoption, as identified in the General Extended Technology Acceptance Model for E-Learning (GETAMEL), behind perceived ease of use and perceived usefulness in the adoption of technology. A sample of 125 students at a historically disadvantaged institution in South Africa was considered for the study. Data was collected to understand their perceptions on use of Blackboard Learning Management System (BB) for learning. Data was analysed with SmartPLS statistical analysis software. Results show that perceived ease of use of BB is influenced by computer self-efficacy, computer amusement and computer anxiety whilst perceived usefulness of BB is influenced by subjective norm and computer enjoyment. The findings also show computer experience to significantly affect computer self-efficacy and computer self-efficacy to affect computer enjoyment. The article presents the external factors that affect the usage of LMS at one of the historically disadvantaged HEI in South Africa. HEI leadership has to prioritise the identified external factors to increase chances of acceptance and utilisation of Blackboard by learners.
- Full Text:
- Date Issued: 2021
- Authors: O. Matarirano , M. Panicker , N.R. Jere https://orcid.org/0000-0001-8966-2753 , A. Maliwa
- Date: 2021
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/11260/3304 , vital:43306 , https://doi.org/10.20853/35-2-4025
- Description: Learning Management Systems (LMS) have the ability to transform learning experiences of students in Higher Education Institutions (HEI). In addition to the developmental benefits, LMS assist teaching and learning during student unrests, a common feature in historically disadvantaged institutions in South Africa. Regardless of the benefits of LMS platforms such as Blackboard, the utilisation by university students at the institution under study has been very low. Applying cross sectional electronic survey, this study identifies the key factors influencing technology adoption, as identified in the General Extended Technology Acceptance Model for E-Learning (GETAMEL), behind perceived ease of use and perceived usefulness in the adoption of technology. A sample of 125 students at a historically disadvantaged institution in South Africa was considered for the study. Data was collected to understand their perceptions on use of Blackboard Learning Management System (BB) for learning. Data was analysed with SmartPLS statistical analysis software. Results show that perceived ease of use of BB is influenced by computer self-efficacy, computer amusement and computer anxiety whilst perceived usefulness of BB is influenced by subjective norm and computer enjoyment. The findings also show computer experience to significantly affect computer self-efficacy and computer self-efficacy to affect computer enjoyment. The article presents the external factors that affect the usage of LMS at one of the historically disadvantaged HEI in South Africa. HEI leadership has to prioritise the identified external factors to increase chances of acceptance and utilisation of Blackboard by learners.
- Full Text:
- Date Issued: 2021
Media consumption and identity formation: the consumption of Latin American telenovelas in two neighbourhoods of Maputo in Mozambique
- Authors: Ofumane, Alvo Naftal
- Date: 2021-10-29
- Subjects: Television soap operas Mozambique Maputo , Identity (Psychology) and mass media Mozambique Maputo , Television soap operas History and criticism , Visual reception theory Mozambique Maputo , Mozambique Politics and government , Mozambique Social conditions , Mozambique Social life and customs
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/192287 , vital:45212
- Description: This study explores how the residents of two neighbourhoods in Maputo, KaMaxakeni and KaMpfumo interact with and make meanings of (Latin American) telenovelas, as part of their identity formation process. It is guided by questions on how the residents of these two neighbourhoods interact with telenovelas in their daily lives; how this shapes their own values and understanding of themselves and the world in which they live; what aspects of telenovelas they value, and what meanings they make from them; and, finally, what determines their choices of media consumption. The study adopted reception theory, rooted in qualitative methodology. This approach explores the ‘insider’s’ perspective of the research subjects, taking the actors’ perspective as the empirical point of departure. Using a purposive theoretical sampling procedure, targeting those families who are avid viewers of telenovelas, the data were generated through participant observation, focus groups discussions, and individual interviews. To understand and interpret the interface between the telenovela (medium) and its viewers (audience) in Maputo, the study used qualitative thematic content analysis of the telenovelas viewing process by the residents of KaMpfumo and KaMaxakeni. The data show that the residents of KaMpfumo and KaMaxakeni in Maputo interact and make sense of the telenovelas in various ways. Telenovelas are used as an educational tool; they are used to reinforce daily life world practices; they s shape people’s personal character; they become another family presence; they are used to build or strengthen physical and virtual viewing networks, and, “Pure” telenovela viewing is a relatively rare occurrence. , Thesis (MA) -- Faculty of Humanities, Journalism and Media Studies, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Ofumane, Alvo Naftal
- Date: 2021-10-29
- Subjects: Television soap operas Mozambique Maputo , Identity (Psychology) and mass media Mozambique Maputo , Television soap operas History and criticism , Visual reception theory Mozambique Maputo , Mozambique Politics and government , Mozambique Social conditions , Mozambique Social life and customs
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/192287 , vital:45212
- Description: This study explores how the residents of two neighbourhoods in Maputo, KaMaxakeni and KaMpfumo interact with and make meanings of (Latin American) telenovelas, as part of their identity formation process. It is guided by questions on how the residents of these two neighbourhoods interact with telenovelas in their daily lives; how this shapes their own values and understanding of themselves and the world in which they live; what aspects of telenovelas they value, and what meanings they make from them; and, finally, what determines their choices of media consumption. The study adopted reception theory, rooted in qualitative methodology. This approach explores the ‘insider’s’ perspective of the research subjects, taking the actors’ perspective as the empirical point of departure. Using a purposive theoretical sampling procedure, targeting those families who are avid viewers of telenovelas, the data were generated through participant observation, focus groups discussions, and individual interviews. To understand and interpret the interface between the telenovela (medium) and its viewers (audience) in Maputo, the study used qualitative thematic content analysis of the telenovelas viewing process by the residents of KaMpfumo and KaMaxakeni. The data show that the residents of KaMpfumo and KaMaxakeni in Maputo interact and make sense of the telenovelas in various ways. Telenovelas are used as an educational tool; they are used to reinforce daily life world practices; they s shape people’s personal character; they become another family presence; they are used to build or strengthen physical and virtual viewing networks, and, “Pure” telenovela viewing is a relatively rare occurrence. , Thesis (MA) -- Faculty of Humanities, Journalism and Media Studies, 2021
- Full Text:
- Date Issued: 2021-10-29
Efficacy of the rind physiological disorder oleocellosis control measures in lemon fruit (Citrus limon) under shade netting
- Authors: Njili, Zamazima
- Date: 2020
- Subjects: Citrus fruits--Storage--Diseases and injuries , Citrus--Diseases and pests Citrus fruit industry Citrus products
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49237 , vital:41613
- Description: Lemon growers aim to produce fruit with no blemishes on the rind. Fruit without blemishes is regarded as high value fruit required for the export market. Leakage of phytotoxic oil from the rind tissues damages them and results in the development of oleocellosis symptoms. Four experiments were conducted to investigate methods of avoiding and controlling the development of oleocellosis during harvest and post-harvest handling. The first experiment indicated that the rind oil release pressure (RORP) test is the method most effective at predicting oleocellosis incidents. The experiment also suggested that fruit not exposed to the sun are the most susceptible to oleocellosis due to low temperatures that cause high turgidity. Oleocellosis results when turgid fruit is mishandled. A cultivar experiment was carried out to ascertain the lemon cultivar most susceptible to oleocellosis. The results show that the Limoneira cultivar is the most susceptible to oleocellosis and 2PH seedless is the least susceptible cultivar when compared to other lemon cultivars such as Lisbon, Eureka and Genoa. When the use of shade netting was tested to determine its effect on oleocellosis severity, it was found that using shade netting did not have an effect. Fruit grown under shade netting had the same colour and average diameter as fruit grown in an open orchard. In the same experiment, mature fruit were shown to be more susceptible to oleocellosis than immature fruit. The final part of the project investigated harvesting and post-harvest practices to determine those that cause oleocellosis the most. It was found that fruit after degreening had greater oleocellosis due to exposure to moisture conditions and rough handling. Another practice that results in oleocellosis occurs before waxing when the fruit was roughly transferred from the bins into the packline. The third oleocellosis inducing practice was moving fruit along the conveyor belt while it is turgid. Improvement of handling procedures to reduce oleocellosis can increase export volume and result in higher value of fruit per carton.
- Full Text:
- Date Issued: 2020
- Authors: Njili, Zamazima
- Date: 2020
- Subjects: Citrus fruits--Storage--Diseases and injuries , Citrus--Diseases and pests Citrus fruit industry Citrus products
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/49237 , vital:41613
- Description: Lemon growers aim to produce fruit with no blemishes on the rind. Fruit without blemishes is regarded as high value fruit required for the export market. Leakage of phytotoxic oil from the rind tissues damages them and results in the development of oleocellosis symptoms. Four experiments were conducted to investigate methods of avoiding and controlling the development of oleocellosis during harvest and post-harvest handling. The first experiment indicated that the rind oil release pressure (RORP) test is the method most effective at predicting oleocellosis incidents. The experiment also suggested that fruit not exposed to the sun are the most susceptible to oleocellosis due to low temperatures that cause high turgidity. Oleocellosis results when turgid fruit is mishandled. A cultivar experiment was carried out to ascertain the lemon cultivar most susceptible to oleocellosis. The results show that the Limoneira cultivar is the most susceptible to oleocellosis and 2PH seedless is the least susceptible cultivar when compared to other lemon cultivars such as Lisbon, Eureka and Genoa. When the use of shade netting was tested to determine its effect on oleocellosis severity, it was found that using shade netting did not have an effect. Fruit grown under shade netting had the same colour and average diameter as fruit grown in an open orchard. In the same experiment, mature fruit were shown to be more susceptible to oleocellosis than immature fruit. The final part of the project investigated harvesting and post-harvest practices to determine those that cause oleocellosis the most. It was found that fruit after degreening had greater oleocellosis due to exposure to moisture conditions and rough handling. Another practice that results in oleocellosis occurs before waxing when the fruit was roughly transferred from the bins into the packline. The third oleocellosis inducing practice was moving fruit along the conveyor belt while it is turgid. Improvement of handling procedures to reduce oleocellosis can increase export volume and result in higher value of fruit per carton.
- Full Text:
- Date Issued: 2020
Volcano correlations for the reactivity of surface-confined cobalt N4-macrocyclics for the electrocatalytic oxidation of 2-mercaptoacetate
- Claußen, Jan A, Ochoa, Gonzalo, Páez, Maritza, Costamagno, Juan, Gulppi, Miguel, Nyokong, Tebello, Bedioui, Fethi, Zagal, José H
- Authors: Claußen, Jan A , Ochoa, Gonzalo , Páez, Maritza , Costamagno, Juan , Gulppi, Miguel , Nyokong, Tebello , Bedioui, Fethi , Zagal, José H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268688 , vital:54222 , xlink:href="https://doi.org/10.1007/s10008-007-0336-y"
- Description: We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin larger than Co–tetrasulfonatotetraphenylporphyrin larger than Co-2,2′,2″,2‴tetra-aminotetraphenylporphyrin and decreases for cobalt phthalocyanines as Co-3,4-octaethylhexyloxyphthalocyanine > Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.
- Full Text:
- Date Issued: 2008
- Authors: Claußen, Jan A , Ochoa, Gonzalo , Páez, Maritza , Costamagno, Juan , Gulppi, Miguel , Nyokong, Tebello , Bedioui, Fethi , Zagal, José H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268688 , vital:54222 , xlink:href="https://doi.org/10.1007/s10008-007-0336-y"
- Description: We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin larger than Co–tetrasulfonatotetraphenylporphyrin larger than Co-2,2′,2″,2‴tetra-aminotetraphenylporphyrin and decreases for cobalt phthalocyanines as Co-3,4-octaethylhexyloxyphthalocyanine > Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.
- Full Text:
- Date Issued: 2008
Population dynamics of the Zuurberg Cycad and the predicted impact of climate change
- Authors: Singh, Karishma
- Date: 2012
- Subjects: Cycads -- South Africa -- Eastern Cape , Encephalartos -- South Africa -- Eastern Cape , Climate change -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10633 , http://hdl.handle.net/10948/d1012857
- Description: Cycads first appeared about 300 million years ago and historical data indicates that they survived fluctuations of global temperature and carbon dioxide concentrations and reached peak abundance during periods where temperature and carbon dioxide concentrations were much higher than the present conditions as well as the predicted increased levels. With Africa being one of the most vulnerable regions to climate change and in the absence of an evaluation of predicted impacts of climate change on cycads, this study aims to contribute to our understanding of responses of Encephalartos longifolius to increased temperature. Encephalartos longifolius (Jacq.) Lehm is an Eastern Cape endemic and like most cycads has been around for millions of years with very little change to its basic structure. Photosynthetic rates showed E.longifolius seedlings have C3 photosynthesis and even under stress they do not switch over to CAM photosynthesis. The photosynthetic rates of seedlings showed a typical C3 -plant type response under elevated carbon dioxide levels. Increased temperatures could be detrimental to the species but coupled with elevated carbon dioxide levels the growth of Encephalartos longifolius are postulated to outweigh the negative impacts of increased temperatures. Whilst climatic conditions in the Eastern Cape might not impact the abundance of Encephalartos longifolius, the species however is declining rapidly to the present near-threatened status. Demographic studies revealed a high percentage of juvenile numbers in the wild; however juvenile plants are impacted on by animals thereby jeopardizing their survival. Adult plants are heavily impacted on by animals; this reduces the probability of new offspring being produced. Cycads are also very slow - growing which is the primary cause of their ruin in the wild. Encephalartos longifolius grows at just over approximately 1 cm per year with growth being more rapid in the juvenile plants. Once juvenile plants reach approximately 60 cm they stop growing in diameter but only get taller. Seed germination is also a very slow process with an optimum temperature of 28°C and a growth medium of at least 50 percent moisture. Regardless of the Eastern Cape predicted to become the hottest province in South Africa as a result of climate change, cycads will be able to adapt to the changing environment and conservation plans should focus on animal and human impacts that are the major force causing decreasing abundance of Encephalartos longifolius in the wild.
- Full Text:
- Date Issued: 2012
- Authors: Singh, Karishma
- Date: 2012
- Subjects: Cycads -- South Africa -- Eastern Cape , Encephalartos -- South Africa -- Eastern Cape , Climate change -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:10633 , http://hdl.handle.net/10948/d1012857
- Description: Cycads first appeared about 300 million years ago and historical data indicates that they survived fluctuations of global temperature and carbon dioxide concentrations and reached peak abundance during periods where temperature and carbon dioxide concentrations were much higher than the present conditions as well as the predicted increased levels. With Africa being one of the most vulnerable regions to climate change and in the absence of an evaluation of predicted impacts of climate change on cycads, this study aims to contribute to our understanding of responses of Encephalartos longifolius to increased temperature. Encephalartos longifolius (Jacq.) Lehm is an Eastern Cape endemic and like most cycads has been around for millions of years with very little change to its basic structure. Photosynthetic rates showed E.longifolius seedlings have C3 photosynthesis and even under stress they do not switch over to CAM photosynthesis. The photosynthetic rates of seedlings showed a typical C3 -plant type response under elevated carbon dioxide levels. Increased temperatures could be detrimental to the species but coupled with elevated carbon dioxide levels the growth of Encephalartos longifolius are postulated to outweigh the negative impacts of increased temperatures. Whilst climatic conditions in the Eastern Cape might not impact the abundance of Encephalartos longifolius, the species however is declining rapidly to the present near-threatened status. Demographic studies revealed a high percentage of juvenile numbers in the wild; however juvenile plants are impacted on by animals thereby jeopardizing their survival. Adult plants are heavily impacted on by animals; this reduces the probability of new offspring being produced. Cycads are also very slow - growing which is the primary cause of their ruin in the wild. Encephalartos longifolius grows at just over approximately 1 cm per year with growth being more rapid in the juvenile plants. Once juvenile plants reach approximately 60 cm they stop growing in diameter but only get taller. Seed germination is also a very slow process with an optimum temperature of 28°C and a growth medium of at least 50 percent moisture. Regardless of the Eastern Cape predicted to become the hottest province in South Africa as a result of climate change, cycads will be able to adapt to the changing environment and conservation plans should focus on animal and human impacts that are the major force causing decreasing abundance of Encephalartos longifolius in the wild.
- Full Text:
- Date Issued: 2012
The effect of structure on the electrochemical properties of 14 marine pyrroloquinoline metabolites
- Antunes, Edith M, Maree, Suzanne E, Nyokong, Tebello, Davies-Coleman, Mike T, Maree, M David
- Authors: Antunes, Edith M , Maree, Suzanne E , Nyokong, Tebello , Davies-Coleman, Mike T , Maree, M David
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286126 , vital:56242 , xlink:href="https://doi.org/10.3184/030823405775146915"
- Description: The electrochemical properties of 14 structurally related pyrroloquinoline metabolites (compounds 1–14) isolated from marine sponges were studied in pH-varied experiments using cyclic and square wave voltammetry. In general both substitution patterns and pH were observed to influence the reduction potentials of these molecules.
- Full Text:
- Date Issued: 2005
- Authors: Antunes, Edith M , Maree, Suzanne E , Nyokong, Tebello , Davies-Coleman, Mike T , Maree, M David
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286126 , vital:56242 , xlink:href="https://doi.org/10.3184/030823405775146915"
- Description: The electrochemical properties of 14 structurally related pyrroloquinoline metabolites (compounds 1–14) isolated from marine sponges were studied in pH-varied experiments using cyclic and square wave voltammetry. In general both substitution patterns and pH were observed to influence the reduction potentials of these molecules.
- Full Text:
- Date Issued: 2005
The safety of journalists: an assessment of perceptions of the origins and implementation of policy at two international television news agencies
- Authors: Venter, Sahm
- Date: 2005
- Subjects: Reuters Television , Associated Press Television News , Journalism -- Safety measures , Journalists -- Protection , News agencies -- Safety measures
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3491 , http://hdl.handle.net/10962/d1002946 , Reuters Television , Associated Press Television News , Journalism -- Safety measures , Journalists -- Protection , News agencies -- Safety measures
- Description: Being a journalist today can be a deadly pursuit, particularly for those covering conflict and other dangerous assignments. In 2004 more journalists and other media workers were killed than in the last ten years. While it is impossible to guarantee that journalists will not be killed or injured, kidnapped or detained, a policy has been created to help protect them in the course of their duties. This study examines the perceptions of journalists working for two international television news agencies about this safety policy called the ‘Joint code of practice for journalists working in conflict zones’. This policy was adopted in November 2000 by five major television companies including the television news agencies Reuters Television and Associated Press Television News. This study finds that the policy had significant flaws in how it was formulated and how it is communicated, implemented and reviewed. Recognising the existence of unequal relations of power and conflicting interests at play in any policy process, this study stresses that in the case of the journalist safety policy, all stakeholders should have participated in the relevant policy stages. This argument arises from researching the policy document as well as from the point of view of managers, and particularly journalists who work on dangerous assignments, either full-time or on a freelance basis for either of the two television news agencies. It finds that while journalists are not generally aware of the policy, they do practice many of its elements as well as a range of their own custom-made strategies to protect themselves. The result is to make the policy less effective than it could be.
- Full Text:
- Date Issued: 2005
- Authors: Venter, Sahm
- Date: 2005
- Subjects: Reuters Television , Associated Press Television News , Journalism -- Safety measures , Journalists -- Protection , News agencies -- Safety measures
- Language: English
- Type: Thesis , Masters , MA
- Identifier: vital:3491 , http://hdl.handle.net/10962/d1002946 , Reuters Television , Associated Press Television News , Journalism -- Safety measures , Journalists -- Protection , News agencies -- Safety measures
- Description: Being a journalist today can be a deadly pursuit, particularly for those covering conflict and other dangerous assignments. In 2004 more journalists and other media workers were killed than in the last ten years. While it is impossible to guarantee that journalists will not be killed or injured, kidnapped or detained, a policy has been created to help protect them in the course of their duties. This study examines the perceptions of journalists working for two international television news agencies about this safety policy called the ‘Joint code of practice for journalists working in conflict zones’. This policy was adopted in November 2000 by five major television companies including the television news agencies Reuters Television and Associated Press Television News. This study finds that the policy had significant flaws in how it was formulated and how it is communicated, implemented and reviewed. Recognising the existence of unequal relations of power and conflicting interests at play in any policy process, this study stresses that in the case of the journalist safety policy, all stakeholders should have participated in the relevant policy stages. This argument arises from researching the policy document as well as from the point of view of managers, and particularly journalists who work on dangerous assignments, either full-time or on a freelance basis for either of the two television news agencies. It finds that while journalists are not generally aware of the policy, they do practice many of its elements as well as a range of their own custom-made strategies to protect themselves. The result is to make the policy less effective than it could be.
- Full Text:
- Date Issued: 2005
Rhodeo: 1990 - August
- Date: 1990-08
- Subjects: Grahamstown -- Newspapers , Journalism, Students -- South Africa , Rhodes University -- Activate , Rhodes University -- Students , Student newspapers and periodicals -- South Africa
- Language: English
- Type: Text
- Identifier: vital:14759 , http://hdl.handle.net/10962/d1019631
- Description: Rhodeo is the Independent Student Newspaper of Rhodes University. Located in Grahamstown, Rhodeo was established in 1947, and renamed in 1994 as Activate. During apartheid Rhodeo became an active part of the struggle for freedom of expression as part of the now defunct South African Student Press Union. Currently Activate is committed to informing Rhodes University students, staff and community members about relevant issues, mainly on campus. These issues range from hard news to more creative journalism. While Activate acts as a news source, one of its main objectives it to be accessible as a training ground for student journalists. The newspaper is run entirely by the students and is published twice a term. Activate is a free newspaper which receives an annual grant from the Rhodes University Student Representative Council, however, majority of its revenue is generated through advertising.
- Full Text:
- Date Issued: 1990-08
- Date: 1990-08
- Subjects: Grahamstown -- Newspapers , Journalism, Students -- South Africa , Rhodes University -- Activate , Rhodes University -- Students , Student newspapers and periodicals -- South Africa
- Language: English
- Type: Text
- Identifier: vital:14759 , http://hdl.handle.net/10962/d1019631
- Description: Rhodeo is the Independent Student Newspaper of Rhodes University. Located in Grahamstown, Rhodeo was established in 1947, and renamed in 1994 as Activate. During apartheid Rhodeo became an active part of the struggle for freedom of expression as part of the now defunct South African Student Press Union. Currently Activate is committed to informing Rhodes University students, staff and community members about relevant issues, mainly on campus. These issues range from hard news to more creative journalism. While Activate acts as a news source, one of its main objectives it to be accessible as a training ground for student journalists. The newspaper is run entirely by the students and is published twice a term. Activate is a free newspaper which receives an annual grant from the Rhodes University Student Representative Council, however, majority of its revenue is generated through advertising.
- Full Text:
- Date Issued: 1990-08
Effects of injectable progestogen contraception versus the copper intrauterine device on HIV acquisition: sub-study of a pragmatic randomised controlled trial
- G Justus Hofmeyr, Mandisa Singata-Madliki, Theresa A Lawrie
- Authors: G Justus Hofmeyr , Mandisa Singata-Madliki , Theresa A Lawrie
- Date: 2017
- Language: English
- Type: Research
- Identifier: http://hdl.handle.net/11260/5570 , vital:44606
- Full Text:
- Authors: G Justus Hofmeyr , Mandisa Singata-Madliki , Theresa A Lawrie
- Date: 2017
- Language: English
- Type: Research
- Identifier: http://hdl.handle.net/11260/5570 , vital:44606
- Full Text:
Analysis of non-peptidic compounds as potential malarial inhibitors against plasmodial cysteine proteases via integrated virtual screening workflow
- Musyoka, Thommas M, Kanzi, Aquillah M, Lobb, Kevin A, Tastan Bishop, Özlem
- Authors: Musyoka, Thommas M , Kanzi, Aquillah M , Lobb, Kevin A , Tastan Bishop, Özlem
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123074 , vital:35403 , https://doi.10.1080/07391102.2015.1108231
- Description: Malaria is an infectious disease caused by a diverse group of erythrocytic protozoan parasites of the genus Plasmodium. It remains an exigent public health problem in the tropical areas of Africa, South America and parts of Asia and continues to take its toll in morbidity and mortality with half of the world’s population under a permanent risk of infection leading to more than half a million deaths annually (WHO, 2013). Five Plasmodium species, namely P. falciparum (Pf ), P. vivax (Pv), P. ovale (Po), P. malariae (Pm) and P. knowlesi (Pk), are known to infect humans with Pf responsible for more than 90% of the malarial fatalities reported in sub-Saharan Africa. The predominance of Pf is attributed to its adaptability (Ashley, McGready, Proux, & Nosten, 2006; Prugnolle et al., 2011). Although the high occurrence of the Duffy negative trait among African populations lowers the threat posed by Pv, it is the most frequent and widely causative agent of benign tertian malaria in other parts of the world (Mendis, Sina, Marchesini, & Carter, 2001). In addition to the listed human malarial parasite forms, several other Plasmodium species, which infect non-human laboratory models, have been identified and are of significant importance in understanding the parasite biology, the host–parasite interactions and in the drug development process (Langhorne et al., 2011).
- Full Text:
- Date Issued: 2016
- Authors: Musyoka, Thommas M , Kanzi, Aquillah M , Lobb, Kevin A , Tastan Bishop, Özlem
- Date: 2016
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123074 , vital:35403 , https://doi.10.1080/07391102.2015.1108231
- Description: Malaria is an infectious disease caused by a diverse group of erythrocytic protozoan parasites of the genus Plasmodium. It remains an exigent public health problem in the tropical areas of Africa, South America and parts of Asia and continues to take its toll in morbidity and mortality with half of the world’s population under a permanent risk of infection leading to more than half a million deaths annually (WHO, 2013). Five Plasmodium species, namely P. falciparum (Pf ), P. vivax (Pv), P. ovale (Po), P. malariae (Pm) and P. knowlesi (Pk), are known to infect humans with Pf responsible for more than 90% of the malarial fatalities reported in sub-Saharan Africa. The predominance of Pf is attributed to its adaptability (Ashley, McGready, Proux, & Nosten, 2006; Prugnolle et al., 2011). Although the high occurrence of the Duffy negative trait among African populations lowers the threat posed by Pv, it is the most frequent and widely causative agent of benign tertian malaria in other parts of the world (Mendis, Sina, Marchesini, & Carter, 2001). In addition to the listed human malarial parasite forms, several other Plasmodium species, which infect non-human laboratory models, have been identified and are of significant importance in understanding the parasite biology, the host–parasite interactions and in the drug development process (Langhorne et al., 2011).
- Full Text:
- Date Issued: 2016
Reactions towards the synthesis of the uncommon P57 cymarose moiety
- Authors: Mahanjana, Lungelwa
- Date: 2013
- Subjects: Chemistry, Organic , Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/6711 , vital:21136
- Description: The work described in this study aims to investigate methods that will improve a lengthy synthetic pathway in the synthesis of the P57 cymarose moiety, and to examine the conformational structure of certain glycosides in order to shed light on the problematic stereochemical issues surrounding the formation of the cymarose glycosyl donor. The cymarose moiety forms part of the trisaccharide derivative present in P57, an appetite suppressant molecule. Modification of reaction steps in the conversion of the stereochemistry at C-3 of a previously reported synthesis of the P57 cymarose moiety was carried out. The first step was the selective oxidation of D-glucal using Pd/C in the presence of acetonitrile. These reaction conditions are more appropriate for the oxidation step to avoid decomposition of the formed molecules. Successive protection of the free OH groups was followed by NaBH4 reduction under stereo-controlled conditions, influenced by CeCl3•7H2O. However, the reduced product could not be isolated from the starting material and this led to ambiguous results when attempting to confirm whether the conversion of the stereochemistry at C-3 had occurred or not. The effect of reaction conditions, such as change in reaction temperature, during the preparation of the cymarose glycosyl donor was studied in order to find suitable reaction conditions to produce α,β-allo derivatives with high stereoselectivity. Compared to the reported synthetic method, this set-up gave improved yields with, unfortunately, similar or slightly lower selectivity to the formation of α-altro:α,β-allo derivative. Examination of the conformational structure of the allal derivative, in order to understand the mechanism at work during the placement of the directing group at C-2, was carried out using molecular modelling. The mechanistic implications of this very short study are discussed and it provides some insights into the likely pathway of the iodination reaction and its selectivity in particular, to the D-allose system.
- Full Text:
- Date Issued: 2013
- Authors: Mahanjana, Lungelwa
- Date: 2013
- Subjects: Chemistry, Organic , Organic compounds -- Synthesis
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/6711 , vital:21136
- Description: The work described in this study aims to investigate methods that will improve a lengthy synthetic pathway in the synthesis of the P57 cymarose moiety, and to examine the conformational structure of certain glycosides in order to shed light on the problematic stereochemical issues surrounding the formation of the cymarose glycosyl donor. The cymarose moiety forms part of the trisaccharide derivative present in P57, an appetite suppressant molecule. Modification of reaction steps in the conversion of the stereochemistry at C-3 of a previously reported synthesis of the P57 cymarose moiety was carried out. The first step was the selective oxidation of D-glucal using Pd/C in the presence of acetonitrile. These reaction conditions are more appropriate for the oxidation step to avoid decomposition of the formed molecules. Successive protection of the free OH groups was followed by NaBH4 reduction under stereo-controlled conditions, influenced by CeCl3•7H2O. However, the reduced product could not be isolated from the starting material and this led to ambiguous results when attempting to confirm whether the conversion of the stereochemistry at C-3 had occurred or not. The effect of reaction conditions, such as change in reaction temperature, during the preparation of the cymarose glycosyl donor was studied in order to find suitable reaction conditions to produce α,β-allo derivatives with high stereoselectivity. Compared to the reported synthetic method, this set-up gave improved yields with, unfortunately, similar or slightly lower selectivity to the formation of α-altro:α,β-allo derivative. Examination of the conformational structure of the allal derivative, in order to understand the mechanism at work during the placement of the directing group at C-2, was carried out using molecular modelling. The mechanistic implications of this very short study are discussed and it provides some insights into the likely pathway of the iodination reaction and its selectivity in particular, to the D-allose system.
- Full Text:
- Date Issued: 2013