Synthesis and photophysical studies of crown ether-bodipy dyes and the fabrication of bodipy embedded fluorescent nanofibers
- Authors: Stone, Justin
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4953 , vital:20746
- Description: This study has three major objectives: 1) to synthesize a series of structurally related BODIPY dyes, 2) to fabricate BODIPY embedded electrospun nanofibers, and 3) to investigate and characterize the photophysical properties of all synthesized BODIPY dyes with a special focus on their ability to generate singlet oxygen. This thesis first explores the acid catalysed condensation reaction to produce two structurally analogous meso-substituted BODIPY dyes based on cuminaldehyde and 4-dimethylaminobenzaldehdye. In order to enhance the rate of ISC and promote the generation of reactive oxygen species bromine atoms were then attached to the BODIPY 2,6-positions. These BODIPY dyes were then embedded in a polystyrene solution and electrospun into nanofibers. The resulting nanofibers were found to be highly fluorescent, but were no longer able to generate singlet oxygen. Ion-sensitive BODIPYs were prepared from the dibrominated BODIPY dyes by employing a modified Knoevenagel condensation reaction to form a styryl bond with 4’-formylbenzo-15-crown-5 at the 3,5-position of the BODIPY core. Changes in the morphology and position of the absorption and emission spectra of these crown ether-styryl BODIPY dyes were observed in the presence of sodium ions. These results imply that crown ether-substituted BODIPY dyes could function as ion sensors.
- Full Text:
- Authors: Stone, Justin
- Date: 2017
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4953 , vital:20746
- Description: This study has three major objectives: 1) to synthesize a series of structurally related BODIPY dyes, 2) to fabricate BODIPY embedded electrospun nanofibers, and 3) to investigate and characterize the photophysical properties of all synthesized BODIPY dyes with a special focus on their ability to generate singlet oxygen. This thesis first explores the acid catalysed condensation reaction to produce two structurally analogous meso-substituted BODIPY dyes based on cuminaldehyde and 4-dimethylaminobenzaldehdye. In order to enhance the rate of ISC and promote the generation of reactive oxygen species bromine atoms were then attached to the BODIPY 2,6-positions. These BODIPY dyes were then embedded in a polystyrene solution and electrospun into nanofibers. The resulting nanofibers were found to be highly fluorescent, but were no longer able to generate singlet oxygen. Ion-sensitive BODIPYs were prepared from the dibrominated BODIPY dyes by employing a modified Knoevenagel condensation reaction to form a styryl bond with 4’-formylbenzo-15-crown-5 at the 3,5-position of the BODIPY core. Changes in the morphology and position of the absorption and emission spectra of these crown ether-styryl BODIPY dyes were observed in the presence of sodium ions. These results imply that crown ether-substituted BODIPY dyes could function as ion sensors.
- Full Text:
Synthesis and physicochemical evaluation of a series of boron dipyrromethene dye derivatives for potential utility in antimicrobial photodynamic therapy and nonlinear optics
- Authors: Kubheka, Gugu Patience
- Date: 2017
- Subjects: Dyes and dyeing -- Chemistry , Photochemotherapy , Cancer -- Photochemotherapy , Anti-infective agents , Nonlinear optics , BODIPY
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4776 , vital:20723
- Description: A series of new BODIPY dye derivatives have been synthesized and characterized using various characterization tools such as 1H-NMR, MALDI-TOF mass spectrometry, FT-IR, UV-visible spectrophotometry and elemental analysis. The aniline-substituted BODIPY derivative was further coordinated with gold nanorods and the characterization was achieved by transmission electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS).In addition to this dye, quaternized BODIPY dyes were also synthesized and investigated for their potential utility as photosentitizers in antimicrobial photodynamic therapy (APDT).BODIPY dyes with pyrene substituted styryl groups were embedded in polymer thin film using poly(bisphenol A carbonate) (PBC) to study their optical limiting properties. The optical limiting values of these BODIPY dyes once embedded in thin films were found to be greatly improved and the limiting intensityof each film was well below the maximum threshold which is set to be 0.95 J.cm-². The physicochemical properties and NLO parameters of all of the synthesized dyes were investigated.
- Full Text:
- Authors: Kubheka, Gugu Patience
- Date: 2017
- Subjects: Dyes and dyeing -- Chemistry , Photochemotherapy , Cancer -- Photochemotherapy , Anti-infective agents , Nonlinear optics , BODIPY
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/4776 , vital:20723
- Description: A series of new BODIPY dye derivatives have been synthesized and characterized using various characterization tools such as 1H-NMR, MALDI-TOF mass spectrometry, FT-IR, UV-visible spectrophotometry and elemental analysis. The aniline-substituted BODIPY derivative was further coordinated with gold nanorods and the characterization was achieved by transmission electron microscopy (TEM), X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS).In addition to this dye, quaternized BODIPY dyes were also synthesized and investigated for their potential utility as photosentitizers in antimicrobial photodynamic therapy (APDT).BODIPY dyes with pyrene substituted styryl groups were embedded in polymer thin film using poly(bisphenol A carbonate) (PBC) to study their optical limiting properties. The optical limiting values of these BODIPY dyes once embedded in thin films were found to be greatly improved and the limiting intensityof each film was well below the maximum threshold which is set to be 0.95 J.cm-². The physicochemical properties and NLO parameters of all of the synthesized dyes were investigated.
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Synthesis of indium and lead phthalocyanine as photocatalysts for photodynamic antimicrobial chemotherapy and photo-oxidation of pollutants
- Authors: Oluwole, Oluyinka David
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5293 , vital:20805
- Full Text:
- Authors: Oluwole, Oluyinka David
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5293 , vital:20805
- Full Text:
Synthesis of indium and lead phthalocyanine as photocatalysts for photodynamic antimicrobial chemotherapy and photo-oxidation of pollutants
- Authors: Osifeko, Olawale L
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5221 , vital:20790
- Description: This thesis explores the synthesis of metallophthalocyanines as potential photosensitizers for application in photodynamic antimicrobial chemotherapy and phototransformation of environmental pollutants. The metallophthalocyanines containing amino substituent were conjugated with magnetic nanoparticle and semiconductor quantum dots via an amide bond and by chemisorption onto gold nanoparticles surface. Techniques such as time-resolved fluorescence measurements, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis, fourier transform infrared (FTIR), nuclear magnetic resonance (¹H, ¹³C, and cozy of symmetrical phthalocyanine), electronic spectroscopy, as well as mass spectroscopy were employed to characterize all metallophthalocyanines. Quarternized pyridyloxy substituted phthalocyanine and asymmetric (AB3) metallophthalocyanines were embedded in electrospun polystyrene fiber. General trends are described for quantum yields of fluorescence, triplet, singlet oxygen and photodegradation as well as lifetimes of fluorescence and triplet state of the compounds. There is an increase in triplet quantum yield for Pcs in the presence of gold nanoparticles (AuNPs) and semiconductor quantum dots (QDs), but not in the presence of magnetic nanoparticles (MNPs). Photodynamic inactivation of Escherichia coli with the quarternized photosensitizers at low concentrations totally inactivate the bacteria compared to non-charged photosensitiser. Also, a similar trend was observed for the magnetic nanoparticles conjugates. Photooxidations of bisphenol A and 4-chlorophenol were carried out in this study using two asymmetric Indium(III) phthalocyanines photosensitizers. The photooxidation reactions were compared with those of a symmetrical indium(III) phthalocyanines containing four quaternized 4-pyridyloxy substituents. The complexes were embedded in electrospun polystyrene fiber for heterogeneous photocatalysis. The immobilized photosensitizers possess good singlet oxygen generation potentials in aqueous media. The asymmetrical phthalocyanine containing 4-pyridylsulfanyl and one aminophenoxy showed the best photocatalytic behavior.
- Full Text:
- Authors: Osifeko, Olawale L
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/5221 , vital:20790
- Description: This thesis explores the synthesis of metallophthalocyanines as potential photosensitizers for application in photodynamic antimicrobial chemotherapy and phototransformation of environmental pollutants. The metallophthalocyanines containing amino substituent were conjugated with magnetic nanoparticle and semiconductor quantum dots via an amide bond and by chemisorption onto gold nanoparticles surface. Techniques such as time-resolved fluorescence measurements, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), elemental analysis, fourier transform infrared (FTIR), nuclear magnetic resonance (¹H, ¹³C, and cozy of symmetrical phthalocyanine), electronic spectroscopy, as well as mass spectroscopy were employed to characterize all metallophthalocyanines. Quarternized pyridyloxy substituted phthalocyanine and asymmetric (AB3) metallophthalocyanines were embedded in electrospun polystyrene fiber. General trends are described for quantum yields of fluorescence, triplet, singlet oxygen and photodegradation as well as lifetimes of fluorescence and triplet state of the compounds. There is an increase in triplet quantum yield for Pcs in the presence of gold nanoparticles (AuNPs) and semiconductor quantum dots (QDs), but not in the presence of magnetic nanoparticles (MNPs). Photodynamic inactivation of Escherichia coli with the quarternized photosensitizers at low concentrations totally inactivate the bacteria compared to non-charged photosensitiser. Also, a similar trend was observed for the magnetic nanoparticles conjugates. Photooxidations of bisphenol A and 4-chlorophenol were carried out in this study using two asymmetric Indium(III) phthalocyanines photosensitizers. The photooxidation reactions were compared with those of a symmetrical indium(III) phthalocyanines containing four quaternized 4-pyridyloxy substituents. The complexes were embedded in electrospun polystyrene fiber for heterogeneous photocatalysis. The immobilized photosensitizers possess good singlet oxygen generation potentials in aqueous media. The asymmetrical phthalocyanine containing 4-pyridylsulfanyl and one aminophenoxy showed the best photocatalytic behavior.
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Synthesis of silver nanoparticles from a Desmodium adscendens extract and its antibacterial evaluation on wound dressing material
- Lakkakula, Jaya R, Ndinteh, Derek T, van Vuuren, Sandy F, Olivier, Denise K, Krause, Rui W M
- Authors: Lakkakula, Jaya R , Ndinteh, Derek T , van Vuuren, Sandy F , Olivier, Denise K , Krause, Rui W M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/195025 , vital:45520 , xlink:href="https://doi.org/10.1049/iet-nbt.2017.0084"
- Description: The one-pot synthesis of silver nanoparticles (AgNPs) using the medium-polar extract of Desmodium adscendens (Sw.) DC. is presented here as an alternative synthesis of metal NPs. Characterisation of the formed NPs showed polydispersed AgNPs ranging from 15 to 100 nm where the concentration of metal ions was found to play a role in the size and shape of the prepared NPs. It could be established that the flavonoids, saponins, and alkaloids present in the extract acted as both reducing and stabilising agents during the formation of the capped metal NPs. This means of NP synthesis was also employed during the in situ immobilisation of AgNPs on gauze and plaster. An evaluation of the antibacterial activity of the medium-polar D. adscendens extract, AgNPs suspended in solution, and the immobilised AgNPs against Staphylococcus aureus (ATCC 25923), Bacillus cereus (ATCC 11778), and Escherichia coli (ATCC 25922) showed high efficacy against the latter in particular. This suggests that gauze, dilute silver nitrate solutions, and D. adscendens extract could be used successfully in the simple in situ preparation of effective antibacterial wound dressings.
- Full Text:
- Authors: Lakkakula, Jaya R , Ndinteh, Derek T , van Vuuren, Sandy F , Olivier, Denise K , Krause, Rui W M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/195025 , vital:45520 , xlink:href="https://doi.org/10.1049/iet-nbt.2017.0084"
- Description: The one-pot synthesis of silver nanoparticles (AgNPs) using the medium-polar extract of Desmodium adscendens (Sw.) DC. is presented here as an alternative synthesis of metal NPs. Characterisation of the formed NPs showed polydispersed AgNPs ranging from 15 to 100 nm where the concentration of metal ions was found to play a role in the size and shape of the prepared NPs. It could be established that the flavonoids, saponins, and alkaloids present in the extract acted as both reducing and stabilising agents during the formation of the capped metal NPs. This means of NP synthesis was also employed during the in situ immobilisation of AgNPs on gauze and plaster. An evaluation of the antibacterial activity of the medium-polar D. adscendens extract, AgNPs suspended in solution, and the immobilised AgNPs against Staphylococcus aureus (ATCC 25923), Bacillus cereus (ATCC 11778), and Escherichia coli (ATCC 25922) showed high efficacy against the latter in particular. This suggests that gauze, dilute silver nitrate solutions, and D. adscendens extract could be used successfully in the simple in situ preparation of effective antibacterial wound dressings.
- Full Text:
Synthesis, characterisation and evaluation of benzoxaborole-based hybrids as antiplasmodial agents
- Authors: Gumbo, Maureen
- Date: 2017
- Subjects: Malaria Chemotherapy , Antimalarials , Boron compounds , Drug resistance , Plasmodium falciparum , Drug development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/59193 , vital:27456
- Description: Malaria is a mosquito-borne disease, which continues to pose a threat to the entire humanity. About 40% of the world population is estimated to be at risk of infections by malaria. Despite efforts undertaken by scientific community, government entities and international organizations, malaria is still rampant. The major problem is drug resistance, where the Plasmodium spp have over the past decades developed drug resistance against available drugs. In order to counter this problem, novel antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Benzoxaborole derivatives have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported on the compounds such as 6-(2- (alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles, which showed good antimalarial activity against both W7 and 3D7 strains without significant toxicity. On the other hand, chloroquine (CQ) and cinnamic acids have a wide variety of biological activity including antimalarial activity. Herein, a hybridisation strategy was employed to synthesise new CQ-benzoxaborole and cinnamoyl-benzoxaborole hybrids. CQ-Benzoxaborole 2.12a-c and cinnamoylbenzoxaborole 2.11a-g hydrid molecules were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (1H and 13C NMR, and mass spectrometry). CQ-benzoxaborole compounds, however, showed instability, and only 2.12b was used for in vitro biological assay and showed activity comparable to CQ. Furthermore, in vitro biological assay revealed that compounds 2.11a-g poorly inhibited the growth of P. falciparum parasites. Interestingly, these compounds, however, exhibited satisfactory activity against Trypanosoma brucei with IC50 = 0.052 μM for compound 2.11g. The cell cytotoxicity assay of all final compounds confirmed that all CQ-benzoxaborole 2.12b and cinnamoyl-benzoxaborole 2.11a-g hybrids were non-toxic against HeLa cell lines. However, efforts to further expand the structure-activity relationship (SAR) of CQbenzoxaborole by increasing the length of the linker with one extra carbon (Scheme 2.10) were not possible as an important precursor 6-formylbenzoxaborole 2.29 could not be synthesized in sufficient yields. , Thesis (MSc) -- Faculty of Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Gumbo, Maureen
- Date: 2017
- Subjects: Malaria Chemotherapy , Antimalarials , Boron compounds , Drug resistance , Plasmodium falciparum , Drug development
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/59193 , vital:27456
- Description: Malaria is a mosquito-borne disease, which continues to pose a threat to the entire humanity. About 40% of the world population is estimated to be at risk of infections by malaria. Despite efforts undertaken by scientific community, government entities and international organizations, malaria is still rampant. The major problem is drug resistance, where the Plasmodium spp have over the past decades developed drug resistance against available drugs. In order to counter this problem, novel antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Benzoxaborole derivatives have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported on the compounds such as 6-(2- (alkoxycarbonyl)pyrazinyl-5-oxy)-1,3-dihydro-1-hydroxy-2,1-benzoxaboroles, which showed good antimalarial activity against both W7 and 3D7 strains without significant toxicity. On the other hand, chloroquine (CQ) and cinnamic acids have a wide variety of biological activity including antimalarial activity. Herein, a hybridisation strategy was employed to synthesise new CQ-benzoxaborole and cinnamoyl-benzoxaborole hybrids. CQ-Benzoxaborole 2.12a-c and cinnamoylbenzoxaborole 2.11a-g hydrid molecules were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (1H and 13C NMR, and mass spectrometry). CQ-benzoxaborole compounds, however, showed instability, and only 2.12b was used for in vitro biological assay and showed activity comparable to CQ. Furthermore, in vitro biological assay revealed that compounds 2.11a-g poorly inhibited the growth of P. falciparum parasites. Interestingly, these compounds, however, exhibited satisfactory activity against Trypanosoma brucei with IC50 = 0.052 μM for compound 2.11g. The cell cytotoxicity assay of all final compounds confirmed that all CQ-benzoxaborole 2.12b and cinnamoyl-benzoxaborole 2.11a-g hybrids were non-toxic against HeLa cell lines. However, efforts to further expand the structure-activity relationship (SAR) of CQbenzoxaborole by increasing the length of the linker with one extra carbon (Scheme 2.10) were not possible as an important precursor 6-formylbenzoxaborole 2.29 could not be synthesized in sufficient yields. , Thesis (MSc) -- Faculty of Faculty of Science, Chemistry, 2017
- Full Text:
Synthesis, characterisation and evaluation of ferrocene-containing Novobiocin analogues for anticancer and antiplasmodial activity through inhibition of Hsp90
- Authors: Mbaba, Mziyanda
- Date: 2017
- Subjects: Antibiotics Synthesis , Ferrocene , Heat shock proteins , Antimalarials , Cancer Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65111 , vital:28690
- Description: Novobiocin (Nb) is a coumarin type antibiotic isolated from the bacterium species of Streptomyces and possesses modest anticancer and antimalarial activities. Nb and analogues have been extensively explored as potential anticancer agents through inhibition of the C- terminal domain of heat shock protein 90 (Hsp90), which plays a pivotal role in the proteinfolding machinery of cells. There has been little effort in the exploration of Nb and derivatives for antimalarial activity. Incorporation of organometallic units, such as ferrocene (Fc), into bioactive chemical scaffolds remains an attractive approach for developing new therapeutic agents for treatment of several ailments. The current study sought to investigate the anticancer and antiplasmodial effects of incorporating ferrocene (Fc) into Nb scaffold presumably through inhibition of Hsp90. The ferrocenyl Nb analogues containing simplified structural motifs such as phenyl, benzyl, and piperidine were synthesized in six to nine steps employing conventional synthetic organic protocols adapted from literature, and the compounds were accessed in reasonable yields. For comparison purposes, a selection of organic Nb analogues were also included in the study. The target compounds were characterized by spectroscopic techniques including 1-dimensional nuclear magnetic resonance (1D NMR) and high-resolution mass spectroscopy. The synthesized compounds were evaluated in vitro for potential anticancer and antiplasmodial activities using the breast cancer cell line (HCC38) and chloroquine-sensitive strain (3D7) of the malaria parasite, Plasmodium falciparum. The presence of the Fc unit was found to enhance both anticancer and antiplasmodial activities of the resultant ferrocenyl Nb compounds with IC50 values in the low to mid micromolar range. Hsp90 inhibitory studies of the ferrocenyl Nb analogues possessing superior activities (2.13a and 2.20c) were also conducted using different yeast strains expressing both human and malarial Hsp90 isoforms: hHsp90a/p and PfHsp90, respectively. The results of Hsp90 inhibitory studies suggested no direct correlation between the observed activities of the analogues and Hsp90 inhibition. However, since the conditions of the assay were not optimised due to time constrains of the project, these observed data remained to be confirmed. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Mbaba, Mziyanda
- Date: 2017
- Subjects: Antibiotics Synthesis , Ferrocene , Heat shock proteins , Antimalarials , Cancer Chemotherapy
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65111 , vital:28690
- Description: Novobiocin (Nb) is a coumarin type antibiotic isolated from the bacterium species of Streptomyces and possesses modest anticancer and antimalarial activities. Nb and analogues have been extensively explored as potential anticancer agents through inhibition of the C- terminal domain of heat shock protein 90 (Hsp90), which plays a pivotal role in the proteinfolding machinery of cells. There has been little effort in the exploration of Nb and derivatives for antimalarial activity. Incorporation of organometallic units, such as ferrocene (Fc), into bioactive chemical scaffolds remains an attractive approach for developing new therapeutic agents for treatment of several ailments. The current study sought to investigate the anticancer and antiplasmodial effects of incorporating ferrocene (Fc) into Nb scaffold presumably through inhibition of Hsp90. The ferrocenyl Nb analogues containing simplified structural motifs such as phenyl, benzyl, and piperidine were synthesized in six to nine steps employing conventional synthetic organic protocols adapted from literature, and the compounds were accessed in reasonable yields. For comparison purposes, a selection of organic Nb analogues were also included in the study. The target compounds were characterized by spectroscopic techniques including 1-dimensional nuclear magnetic resonance (1D NMR) and high-resolution mass spectroscopy. The synthesized compounds were evaluated in vitro for potential anticancer and antiplasmodial activities using the breast cancer cell line (HCC38) and chloroquine-sensitive strain (3D7) of the malaria parasite, Plasmodium falciparum. The presence of the Fc unit was found to enhance both anticancer and antiplasmodial activities of the resultant ferrocenyl Nb compounds with IC50 values in the low to mid micromolar range. Hsp90 inhibitory studies of the ferrocenyl Nb analogues possessing superior activities (2.13a and 2.20c) were also conducted using different yeast strains expressing both human and malarial Hsp90 isoforms: hHsp90a/p and PfHsp90, respectively. The results of Hsp90 inhibitory studies suggested no direct correlation between the observed activities of the analogues and Hsp90 inhibition. However, since the conditions of the assay were not optimised due to time constrains of the project, these observed data remained to be confirmed. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
Synthesis, characterisation and evaluation of novel ferrocene-thiazole derivatives as antiplasmodial agents
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5304 , vital:20807
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/5304 , vital:20807
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
Synthesis, characterisation and evaluation of novel ferrocene-thiazole derivatives as antiplasmodial agents
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96068 , vital:31232
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
- Authors: Hakizimana, Emmanuel Victor
- Date: 2017
- Subjects: Plasmodium , Malaria -- Chemotherapy , Plasmodium falciparum , Plasmodium -- Inhibitors , Drug resistance in microorganisms , Thiaszoles
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/96068 , vital:31232
- Description: Malaria is mosquito-transmitted disease which continues to pose threat to humanity, despite the efforts undertaken by the scientific community, government entities and international organizations. The major problem is that Plasmodium species have developed resistance against available drugs. In order to counter this problem, antimalarial drugs that are efficacious and with novel mode of action are of great necessity. Thiazole derivatives, in particular aminomethylthiazole analogues, have been shown to exhibit promising antimalarial activity against Plasmodium falciparum strains. Previous studies reported the hit compound MMV010539, which showed good antimalarial activity against both K1 (CQ and multidrug resistant strains) and NF54 (CQ sensitive strain). In this study, MMV010539 was deemed to be as an attractive compound to generate novel analogues by addition of ferrocenyl organometallic unit. The ferrocene based compounds have shown biological activity; and with ferroquine currently in clinical trials there has been increasing research into identifying new ferrocenyl-containing molecules as potential antimalarial agents. Herein, thiazole ferrocene based molecules 3.22a-e were synthesised in low to good yields. Their structural identities were confirmed using conventional spectroscopic techniques (¹H and ¹³C NMR, FT-IR spectroscopy and mass spectrometry). The cell cytotoxicity assay of all final compounds confirmed that all ferrocene-thiazole blends 3.22a-e were non-toxic against HeLa cell lines. However, the in vitro biological assay revealed that despite the absence of cell cytotoxicity these compounds poorly inhibited the growth of Plasmodium falciparum parasite. As the aim was to expand further the structure-activity relationship (SAR) of MMV010539, this study confirmed the previous findings that there is a limited structural modification that could be accommodated as indicated in Figure 3.3 (Panel C). Moreover, the combination of ferrocenyl moiety and various alkylamines resulted in compounds with poor antiplasmodial potency, further suggesting that the free amine (Panel A, Figure 3.3) is important for activity.
- Full Text:
Synthesis, photophysical and nonlinear optical properties of a series of ball-type phthalocyanines in solution and thin films
- Nwaji, Njemuwa, Mack, John, Britton, Jonathan, Nyokong, Tebello
- Authors: Nwaji, Njemuwa , Mack, John , Britton, Jonathan , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188976 , vital:44803 , xlink:href="https://doi.org/10.1039/C6NJ03662G"
- Description: In this study, we report on the enhanced nonlinear optical properties of novel tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyaninato zinc(II)) (4), tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyaninato gallium chloride) (5) and tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyaninato indium chloride) (6) both in solution and when embedded in polymer thin films. Complexes 5 and 6 bearing heavy atoms showed enhanced triplet quantum yield and nonlinear optical response. The nonlinear third-order susceptibility and second-order hyperpolarizability values are also reported. Time dependent density functional theory (TD-DFT) calculations were performed in order to explain the origin of the observed UV-vis and magnetic circular dichroism (MCD) spectra of the complexes.
- Full Text:
- Authors: Nwaji, Njemuwa , Mack, John , Britton, Jonathan , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188976 , vital:44803 , xlink:href="https://doi.org/10.1039/C6NJ03662G"
- Description: In this study, we report on the enhanced nonlinear optical properties of novel tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyaninato zinc(II)) (4), tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyaninato gallium chloride) (5) and tetrakis-4-(hexadecane-1,2-dioxyl)-bis(phthalocyaninato indium chloride) (6) both in solution and when embedded in polymer thin films. Complexes 5 and 6 bearing heavy atoms showed enhanced triplet quantum yield and nonlinear optical response. The nonlinear third-order susceptibility and second-order hyperpolarizability values are also reported. Time dependent density functional theory (TD-DFT) calculations were performed in order to explain the origin of the observed UV-vis and magnetic circular dichroism (MCD) spectra of the complexes.
- Full Text:
Systematics and biogeography of forest snails, chondrocyclus (mollusca: gastropoda: caenogastropoda: cyclophoridae) in Southern Africa
- Authors: Cole, Mary Louise
- Date: 2017
- Subjects: Chondrocyclus , Mollusks -- South Africa , Cyclophoridae -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/4356 , vital:20651
- Description: This study presents a molecular phylogeny and systematic revision of Chondrocyclus, the major South African group of the large family of operculate terrestrial molluscs, the Cyclophoridae. Chondrocyclus snails are small gastropods found in forest and moist thicket throughout South Africa. This is the first detailed systematic treatment of a group of Cyclophoridae in mainland Africa and the first to provide molecular data. This study complements regional studies on the systematics of the family in Asia and provides comparative data for studies of higher level relationships within the Cyclophoridae. Phylogenetic reconstruction by BI and ML methods of combined and single gene datasets of 16S and CO 1 all showed Chondrocyclus to be monophyletic and recovered five well-supported clades that corresponded to groups of populations identifiable on the basis of combinations of morphological characters. Species were diagnosed morphologically and were shown to be genetically distinct lineages. Informative morphological features include shell dimensions, protoconch, periostracum, operculum, radula and penis. Two species in Afromontane regions of Zimbabwe and Malawi respectively are excluded from Chondrocyclus based on morphology and tentatively placed in Cyathopoma. Diversity recognised within the genus more than doubled, from a previous seven South African species to seventeen. Re-descriptions of established species and descriptions of new species are provided, together with photographs of morphological characteristics. New taxon names and nomenclatural acts within it are disclaimed and are therefore not available in the sense of the International Code of Zoological Nomenclature until validly published elsewhere. Several cryptic species within previously widespread “species” and unrecorded narrowly endemic species were documented. The clade consisting of populations of “Chondrocyclus isipingoensis”, now considered to be a species complex, was sister to a group containing the other four clades. The “Isipingoensis” clade occurs widely in Afromontane regions, along the Great Escarpment, and on the south-east coast. The other four clades occur from Zululand to the Cape Peninsula with a pattern of east-west lineage turnover. The biogeography of Chondrocyclus is interpreted by comparison with concordant patterns in other terrestrial molluscs and unrelated taxa with poor dispersal ability. This study complements other research on composition, spatial distribution and phylogenetic diversity of low-vagility invertebrates and expands the data available for biodiversity conservation in South Africa.
- Full Text:
- Authors: Cole, Mary Louise
- Date: 2017
- Subjects: Chondrocyclus , Mollusks -- South Africa , Cyclophoridae -- South Africa
- Language: English
- Type: text , Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/4356 , vital:20651
- Description: This study presents a molecular phylogeny and systematic revision of Chondrocyclus, the major South African group of the large family of operculate terrestrial molluscs, the Cyclophoridae. Chondrocyclus snails are small gastropods found in forest and moist thicket throughout South Africa. This is the first detailed systematic treatment of a group of Cyclophoridae in mainland Africa and the first to provide molecular data. This study complements regional studies on the systematics of the family in Asia and provides comparative data for studies of higher level relationships within the Cyclophoridae. Phylogenetic reconstruction by BI and ML methods of combined and single gene datasets of 16S and CO 1 all showed Chondrocyclus to be monophyletic and recovered five well-supported clades that corresponded to groups of populations identifiable on the basis of combinations of morphological characters. Species were diagnosed morphologically and were shown to be genetically distinct lineages. Informative morphological features include shell dimensions, protoconch, periostracum, operculum, radula and penis. Two species in Afromontane regions of Zimbabwe and Malawi respectively are excluded from Chondrocyclus based on morphology and tentatively placed in Cyathopoma. Diversity recognised within the genus more than doubled, from a previous seven South African species to seventeen. Re-descriptions of established species and descriptions of new species are provided, together with photographs of morphological characteristics. New taxon names and nomenclatural acts within it are disclaimed and are therefore not available in the sense of the International Code of Zoological Nomenclature until validly published elsewhere. Several cryptic species within previously widespread “species” and unrecorded narrowly endemic species were documented. The clade consisting of populations of “Chondrocyclus isipingoensis”, now considered to be a species complex, was sister to a group containing the other four clades. The “Isipingoensis” clade occurs widely in Afromontane regions, along the Great Escarpment, and on the south-east coast. The other four clades occur from Zululand to the Cape Peninsula with a pattern of east-west lineage turnover. The biogeography of Chondrocyclus is interpreted by comparison with concordant patterns in other terrestrial molluscs and unrelated taxa with poor dispersal ability. This study complements other research on composition, spatial distribution and phylogenetic diversity of low-vagility invertebrates and expands the data available for biodiversity conservation in South Africa.
- Full Text:
Talent management: a case study of Namibia’s Directorate of Civil Aviation (DCA) in securing talent for aviation safety, 2008 to 2014
- Authors: Simataa, George
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/7131 , vital:21220
- Description: This study is about talent management, focusing on a case study of the initiatives undertaken by the Directorate of Civil Aviation (DCA) of Namibia over the period 2008 to 2014 in securing talent for aviation safety. The International Civil Aviation Organisation (ICAO) regularly assesses the extent to which member states comply with their safety oversight responsibilities. According to a 1996 report by the ICAO, under the auspices of its Universal Safety Oversight and Security Audit Programme (USOSAP), Namibia’s safety oversight was found to be weak, as indicative of the State’s inability to guarantee the safety of aircraft operations within the national airspace (ICAO, 1996). One of the significant audit findings was the critical shortage of qualified professionals at the Directorate Civil Aviation (DCA) to effectively perform the State’s regulatory and oversight function as contained in the Chicago Convention of 1944. The shortage of qualified professionals resulted in Namibia being unable to respond to its obligations and responsibilities under the Chicago Convention and Namibia’s subsequent blacklisting by the ICAO Audit Result Review Board (ARRB). Consequently, a corrective action plan was undertaken. This study examines one aspect of this plan, namely the initiatives that were undertaken to secure the talent required for aviation safety posts. The aim of the research is, from the perspective of talent management, to analyse the corrective action plan of the Directorate of Civil Aviation (DCA), as a process of securing talent for strategic positions in aviation safety in Namibia. This initiative was analysed from the perspective of the fourth stream of talent management, which emphasises securing talent for strategic positions (Collings and Mellahi, 2009; Huselid & Becker, 2011). Taking into account the fact that Namibia was a racially and culturally divided society until about 25 years ago, the study also deals with issues of diversity management as they impacted upon the talent management of the civil aviation industry nationally. Furthermore, the study is located against the background of the Bantu Education System that was provided by the apartheid South African government to Namibians before independence in 1990. The research design of this study involved conducting a case study that followed a deductive approach. Data were collected using multiple methods and sources such as documentation, interviews and archival records. Content analysis was used in the analysis of collected data. The findings of the study showed the talent management strategies that were adopted in managing strategic positions, the challenges encountered and the impact of the programme. The findings were initially discussed from the perspective of stream four of talent management, with its focus on strategic positions in organisations. Some of the findings of the study were in line with this approach to talent management, but certain challenges that were encountered in carrying out the talent management programme could not be addressed from this perspective, thereby exposing the limits of this approach to talent management in an emerging economy like Namibia. Consequently, a proposed model of sustainable talent management for the DCA was developed. From the perspective of this model of sustainable talent management, recommendations were made for practice and further research.
- Full Text:
- Authors: Simataa, George
- Date: 2017
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/7131 , vital:21220
- Description: This study is about talent management, focusing on a case study of the initiatives undertaken by the Directorate of Civil Aviation (DCA) of Namibia over the period 2008 to 2014 in securing talent for aviation safety. The International Civil Aviation Organisation (ICAO) regularly assesses the extent to which member states comply with their safety oversight responsibilities. According to a 1996 report by the ICAO, under the auspices of its Universal Safety Oversight and Security Audit Programme (USOSAP), Namibia’s safety oversight was found to be weak, as indicative of the State’s inability to guarantee the safety of aircraft operations within the national airspace (ICAO, 1996). One of the significant audit findings was the critical shortage of qualified professionals at the Directorate Civil Aviation (DCA) to effectively perform the State’s regulatory and oversight function as contained in the Chicago Convention of 1944. The shortage of qualified professionals resulted in Namibia being unable to respond to its obligations and responsibilities under the Chicago Convention and Namibia’s subsequent blacklisting by the ICAO Audit Result Review Board (ARRB). Consequently, a corrective action plan was undertaken. This study examines one aspect of this plan, namely the initiatives that were undertaken to secure the talent required for aviation safety posts. The aim of the research is, from the perspective of talent management, to analyse the corrective action plan of the Directorate of Civil Aviation (DCA), as a process of securing talent for strategic positions in aviation safety in Namibia. This initiative was analysed from the perspective of the fourth stream of talent management, which emphasises securing talent for strategic positions (Collings and Mellahi, 2009; Huselid & Becker, 2011). Taking into account the fact that Namibia was a racially and culturally divided society until about 25 years ago, the study also deals with issues of diversity management as they impacted upon the talent management of the civil aviation industry nationally. Furthermore, the study is located against the background of the Bantu Education System that was provided by the apartheid South African government to Namibians before independence in 1990. The research design of this study involved conducting a case study that followed a deductive approach. Data were collected using multiple methods and sources such as documentation, interviews and archival records. Content analysis was used in the analysis of collected data. The findings of the study showed the talent management strategies that were adopted in managing strategic positions, the challenges encountered and the impact of the programme. The findings were initially discussed from the perspective of stream four of talent management, with its focus on strategic positions in organisations. Some of the findings of the study were in line with this approach to talent management, but certain challenges that were encountered in carrying out the talent management programme could not be addressed from this perspective, thereby exposing the limits of this approach to talent management in an emerging economy like Namibia. Consequently, a proposed model of sustainable talent management for the DCA was developed. From the perspective of this model of sustainable talent management, recommendations were made for practice and further research.
- Full Text:
Taste masking of clarithromycin with ion exchange resins
- Authors: Ntemi, Pascal Vitalis
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/65178 , vital:28701
- Description: Expected release date-May 2019
- Full Text:
- Authors: Ntemi, Pascal Vitalis
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10962/65178 , vital:28701
- Description: Expected release date-May 2019
- Full Text:
Tate Intensive: Art Matters
- Authors: Mulenga, Andrew
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/146711 , vital:38550 , https://www.tate.org.uk/whats-on/tate-modern/course/tate-intensive-art-matters
- Description: Tate Intensive: Art Matters took place 9-14 July 2017. A diverse group of 28 museum professionals – from Armenia, Australia, China, Colombia, Egypt, Ethiopia, Germany, Ireland, Kenya, Lithuania, New Zealand, Norway, Poland, South Africa, Singapore, South Korea, Turkey, the US, Zambia, Zimbabwe, and the UK – came together for a series of activities and workshops led by contributors including Tate staff and other culture professionals.
- Full Text:
- Authors: Mulenga, Andrew
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/146711 , vital:38550 , https://www.tate.org.uk/whats-on/tate-modern/course/tate-intensive-art-matters
- Description: Tate Intensive: Art Matters took place 9-14 July 2017. A diverse group of 28 museum professionals – from Armenia, Australia, China, Colombia, Egypt, Ethiopia, Germany, Ireland, Kenya, Lithuania, New Zealand, Norway, Poland, South Africa, Singapore, South Korea, Turkey, the US, Zambia, Zimbabwe, and the UK – came together for a series of activities and workshops led by contributors including Tate staff and other culture professionals.
- Full Text:
Teachers’ use of situated learning approaches to teach environmental topics in Natural Science and Health Education: a multi-case study of two Namibian teachers
- Authors: Mamili, Joy Z
- Date: 2017
- Subjects: Environmental education -- Namibia , Science -- Study and teaching -- Namibia -- Cast studies , Health education -- Namibia -- Case studies
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: http://hdl.handle.net/10962/40901 , vital:25037
- Description: This study focuses on the use of situated learning approaches in the teaching of environmental topics in Natural Science and Health Education (NSHED) and is the first of its kind in Namibia. Although situated learning approaches, as examples of learner-centred pedagogy, are advocated in national education policies, little empirical research has been conducted in Namibia into how situated learning approaches play out in classroom practice. Therefore, the goal of this study was to find out how NSHED teachers use situated learning approaches when teaching environmental topics. The study reviews the characteristics of situated learning theory and clarifies situated learning approaches as a form of learner-centred pedagogy which is actively promoted in the Namibian schooling system. The study commences with a contextual profile of the communities around the two selected schools. This describes the socio-economic and social-ecological context in which learners are taught about environmental topics. The profile also describes the under-performance of the schools in recent national assessments, especially in relation to environmental topics in NSHED. Drawing on data generated through document analysis, semi-structured interviews and classroom observations, the study concluded that: 1. NSHED teachers both knew about and wished to create an authentic context to enhance situated learning approaches. However, their understandings and applications of situated learning tended to be basic. 2. Teachers dominated the scaffolding process and their scaffolding strategies did not enable learners to increase independence in performing. 3. Despite the use of situated learning approaches, learners’ engagement with lesson content was superficial, and the teachers did little to encourage deeper reflections or critical thinking. 4. The teachers appeared to use situated learning approaches to clarify subject content but not to encourage broader environmental understanding, action-taking and change. Based on the research findings, the study recommends that situated learning approaches be integrated into pre- and in-service teacher training with the aim of enhancing teachers’ understanding regarding the use of situated learning approaches in the teaching of environmental topics in NSHED.
- Full Text:
- Authors: Mamili, Joy Z
- Date: 2017
- Subjects: Environmental education -- Namibia , Science -- Study and teaching -- Namibia -- Cast studies , Health education -- Namibia -- Case studies
- Language: English
- Type: Thesis , Masters , MEd
- Identifier: http://hdl.handle.net/10962/40901 , vital:25037
- Description: This study focuses on the use of situated learning approaches in the teaching of environmental topics in Natural Science and Health Education (NSHED) and is the first of its kind in Namibia. Although situated learning approaches, as examples of learner-centred pedagogy, are advocated in national education policies, little empirical research has been conducted in Namibia into how situated learning approaches play out in classroom practice. Therefore, the goal of this study was to find out how NSHED teachers use situated learning approaches when teaching environmental topics. The study reviews the characteristics of situated learning theory and clarifies situated learning approaches as a form of learner-centred pedagogy which is actively promoted in the Namibian schooling system. The study commences with a contextual profile of the communities around the two selected schools. This describes the socio-economic and social-ecological context in which learners are taught about environmental topics. The profile also describes the under-performance of the schools in recent national assessments, especially in relation to environmental topics in NSHED. Drawing on data generated through document analysis, semi-structured interviews and classroom observations, the study concluded that: 1. NSHED teachers both knew about and wished to create an authentic context to enhance situated learning approaches. However, their understandings and applications of situated learning tended to be basic. 2. Teachers dominated the scaffolding process and their scaffolding strategies did not enable learners to increase independence in performing. 3. Despite the use of situated learning approaches, learners’ engagement with lesson content was superficial, and the teachers did little to encourage deeper reflections or critical thinking. 4. The teachers appeared to use situated learning approaches to clarify subject content but not to encourage broader environmental understanding, action-taking and change. Based on the research findings, the study recommends that situated learning approaches be integrated into pre- and in-service teacher training with the aim of enhancing teachers’ understanding regarding the use of situated learning approaches in the teaching of environmental topics in NSHED.
- Full Text:
Technauriture as a platform to create an inclusive environment for the sharing of research
- Authors: Kaschula, Russell H
- Date: 2017
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/67005 , vital:29016 , http://books.openedition.org/obp/4209
- Description: publisher version , From Introduction: This chapter examines the importance of orality in rural communities using the paradigm of technauriture, which describes how technology, auriture2and literature intersect to transmit educational and other messages within communities. It uses oral literary research that has been conducted in the Eastern Cape region to show how technology can aid the data collection process, and how this technology can return such information to the communities from which it comes. This chapter also explores the process of orality fostered by community meetings, oral histories, oral poetry, beadwork, music and story-telling, and how this culture interacts with the recording process facilitated by modern technology. It will also consider the return of recorded oral material to educational and archival circles. These objectives are pursued using empirical data collected at Tshani near Port St. Johns, an area falling within the Mankosi tribal authority in the Eastern Cape Province of South Africa. They are also considered in relation to the work of oral poet, Bongani Sitole who lived in Mqhekezweni village near Qunu and Mthatha, as well as against the backdrop of research conducted in Keiskammahoek, and at the Broster Beadwork Collection, now housed at Walter Sisulu University in Mthatha.
- Full Text: false
- Authors: Kaschula, Russell H
- Date: 2017
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/67005 , vital:29016 , http://books.openedition.org/obp/4209
- Description: publisher version , From Introduction: This chapter examines the importance of orality in rural communities using the paradigm of technauriture, which describes how technology, auriture2and literature intersect to transmit educational and other messages within communities. It uses oral literary research that has been conducted in the Eastern Cape region to show how technology can aid the data collection process, and how this technology can return such information to the communities from which it comes. This chapter also explores the process of orality fostered by community meetings, oral histories, oral poetry, beadwork, music and story-telling, and how this culture interacts with the recording process facilitated by modern technology. It will also consider the return of recorded oral material to educational and archival circles. These objectives are pursued using empirical data collected at Tshani near Port St. Johns, an area falling within the Mankosi tribal authority in the Eastern Cape Province of South Africa. They are also considered in relation to the work of oral poet, Bongani Sitole who lived in Mqhekezweni village near Qunu and Mthatha, as well as against the backdrop of research conducted in Keiskammahoek, and at the Broster Beadwork Collection, now housed at Walter Sisulu University in Mthatha.
- Full Text: false
Temperature dependence of optically stimulated luminescence of α-Al2O3: C, Mg
- Kalita, Jitumani M, Chithambo, Makaiko L
- Authors: Kalita, Jitumani M , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115708 , vital:34217 , https://doi.org/10.1016/j.radmeas.2017.08.009
- Description: Thermal assistance and thermal quenching are two independently acting thermodynamic phenomena that simultaneously affect the stimulation of luminescence. We have studied thermal assistance to luminescence optically stimulated from α-Al2O3:C,Mg. Since thermal assistance causes only a minor change in the luminescence intensity, measurements were made after the sample had been pre-exposed to stimulating light to reduce its intensity significantly, that is, in the slow component of its decay curve. The luminescence intensity was monitored as a function of measurement temperature between 30 and 130 °C. The intensity goes through a peak at 60 °C due to competing effects of thermal assistance and thermal quenching. The initial increase of intensity is attributed to dominant thermal assistance whereas the subsequent decrease of intensity is ascribed to dominant thermal quenching. The activation energy for thermal assistance was calculated for the main electron trap of an un-annealed sample as 0.324 ± 0.020 eV and in a sample annealed at 900 °C as 0.416 ± 0.028 eV. Implications of such differences in the value of the activation energy for thermal assistance are considered.
- Full Text: false
- Authors: Kalita, Jitumani M , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115708 , vital:34217 , https://doi.org/10.1016/j.radmeas.2017.08.009
- Description: Thermal assistance and thermal quenching are two independently acting thermodynamic phenomena that simultaneously affect the stimulation of luminescence. We have studied thermal assistance to luminescence optically stimulated from α-Al2O3:C,Mg. Since thermal assistance causes only a minor change in the luminescence intensity, measurements were made after the sample had been pre-exposed to stimulating light to reduce its intensity significantly, that is, in the slow component of its decay curve. The luminescence intensity was monitored as a function of measurement temperature between 30 and 130 °C. The intensity goes through a peak at 60 °C due to competing effects of thermal assistance and thermal quenching. The initial increase of intensity is attributed to dominant thermal assistance whereas the subsequent decrease of intensity is ascribed to dominant thermal quenching. The activation energy for thermal assistance was calculated for the main electron trap of an un-annealed sample as 0.324 ± 0.020 eV and in a sample annealed at 900 °C as 0.416 ± 0.028 eV. Implications of such differences in the value of the activation energy for thermal assistance are considered.
- Full Text: false
Temperature-dependence of time-resolved optically stimulated luminescence and composition heterogeneity of synthetic α-Al2O3: C
- Chithambo, Makaiko L, Costin, G
- Authors: Chithambo, Makaiko L , Costin, G
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124172 , vital:35573 , https://doi.org/10.1016/j.jlumin.2016.10.038
- Description: The relationship of pulse-width, lifetime and measurement temperature in describing intensity of time-resolved luminescence optically stimulated at 470 nm from α-Al2O3:C is reported. The change of luminescence intensity with stimulation temperature is discussed in terms of the signal integrated over a complete time-resolved luminescence spectrum or in terms of ratios of the signal emitted either during or after pulsed stimulation to the total signal obtained per spectrum. The temperature-induced change in these parameters depends on whether the pulse-width is less or more than the luminescence lifetime. This is because the lifetime in α-Al2O3:C varies with measurement temperature. We have developed and applied new models to distinguish thermal assistance from different traps and to use this information as an additional means to analyse thermal quenching by using the luminescence intensity integrated from time-resolved spectra. Using a model based on use of the throughput, the activation energy for thermal assistance was determined for the shallow trap as 0.054±0.001 eV and as 0.53±0.03 eV for the main trap. The activation energy for thermal quenching was then evaluated using luminescence yield during the pulse as 1.09±0.01 eV and as 1.12±0.01 eV using the throughput after the pulse. Using the new analytical method based on integrated intensity, the activation energy for thermal quenching was found as 1.00±0.07 eV. These values are self-consistent and show that the methods for analyzing temperature-induced changes in intensity and the attendant thermal effects, such as thermal assistance can be successfully applied. We have also reported a general mathematical model that accounts for the temperature-dependence of time-resolved luminescence from α-Al2O3:C. The luminescence study was complemented by investigation of the phase and composition heterogeneity of the samples.
- Full Text: false
- Authors: Chithambo, Makaiko L , Costin, G
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/124172 , vital:35573 , https://doi.org/10.1016/j.jlumin.2016.10.038
- Description: The relationship of pulse-width, lifetime and measurement temperature in describing intensity of time-resolved luminescence optically stimulated at 470 nm from α-Al2O3:C is reported. The change of luminescence intensity with stimulation temperature is discussed in terms of the signal integrated over a complete time-resolved luminescence spectrum or in terms of ratios of the signal emitted either during or after pulsed stimulation to the total signal obtained per spectrum. The temperature-induced change in these parameters depends on whether the pulse-width is less or more than the luminescence lifetime. This is because the lifetime in α-Al2O3:C varies with measurement temperature. We have developed and applied new models to distinguish thermal assistance from different traps and to use this information as an additional means to analyse thermal quenching by using the luminescence intensity integrated from time-resolved spectra. Using a model based on use of the throughput, the activation energy for thermal assistance was determined for the shallow trap as 0.054±0.001 eV and as 0.53±0.03 eV for the main trap. The activation energy for thermal quenching was then evaluated using luminescence yield during the pulse as 1.09±0.01 eV and as 1.12±0.01 eV using the throughput after the pulse. Using the new analytical method based on integrated intensity, the activation energy for thermal quenching was found as 1.00±0.07 eV. These values are self-consistent and show that the methods for analyzing temperature-induced changes in intensity and the attendant thermal effects, such as thermal assistance can be successfully applied. We have also reported a general mathematical model that accounts for the temperature-dependence of time-resolved luminescence from α-Al2O3:C. The luminescence study was complemented by investigation of the phase and composition heterogeneity of the samples.
- Full Text: false
Tetra 4-(propargyloxy)phenoxy phthalocyanines: synthesis, spectroscopic, nonlinear optical and electrocatalytic properties
- Authors: Mwanza, Daniel
- Date: 2017
- Subjects: Phthalocyanines , Nonlinear optics , Electrocatalysis , Spectrum analysis , Thermogravimetry , Phthalocyanines Spectra
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65144 , vital:28695
- Description: This study presents the synthesis, spectroscopic, photophysical and theoretical characterisation of metal-free (H2TPrOPhOPc), cobalt (CoTPrOPhOPc) and manganese (MnTPrOPhOPc) tetra 4-(4-propargyloxy) phenoxy phthalocyanines. Thermal analysis using thermogravimetric analysis (TGA) confirmed the excellent thermal stability of synthesized tetra 4-(4- propargyloxy) phenoxy phthalocyanines. The metal complexes, CoTPrOPhOPc and MnTPrOPhOPc, exhibited better thermal stability when compared to H2TPrOPhOPc. The residual percentage weight remaining was approximately 70% for CoTPrOPhOPc and MnTPrOPhOPc and 45% for H2TPrOPhOPc after 600°C, clearly confirming the stability of the metal complexes. The MTPrOPhOPcs (where M = H2, Co and Mn) complexes exhibited excellent nonlinear optical properties with strong reverse saturable absorption (RSA), especially when 560 nm excitation laser was used. Their nonlinear optical properties followed this trend: H2TPrOPhOPc > CoTPrOPhOPc > MnTPrOPhOPc. According to the trend observed, the H2TPrOPhOPc was an excellent nonlinear optical limiter when compared to the CoTPrOPhOPc and MnTPrOPhOPc. All the investigated complexes exhibited optical limiting properties comparable to the phthalocyanine complexes reported in the literature. The MTPrOPhOPc complexes were further studied for their electrocatalytic and electroanalytical properties towards the detection of hydrogen peroxide. For the electrocatalytic studies, the synthesized complexes were immobilized onto gold electrode surfaces pre-functionalized with phenylazide (Au-PAz) monolayer. Copper (I) catalyzed alkynyl-azide cycloaddition reaction was used to covalently immobilize the MTPrOPhOPcs onto the gold electrode surfaces to form Au-PAz-MTPrOPhOPc. The MTPrOPhOPcs modified gold surfaces (Au-PAz-MTPrOPhOPc) exhibited good reproducibility and stability in various electrolyte conditions. Electrochemical and surface characterisation of the functionalised gold electrode surfaces confirmed the presence of the MTPrOPhOPcs and their electroanalysis was excellent towards electrocatalytic reduction of H2O2, with the limit of detection (LoD) and limit of quantification (LoQ) in the ^M range. The electrocatalytic reduction peaks for H2O2 were observed at -0.37 V for Au-PAz-MnTPrOPhOPc and -0.31 V for Au-PAz-CoTPrOPhOPc when Ag|AgCl pseudo-reference electrode was used. The Au-PAz-MnTPrOPhOPc and Au- PAz-CoTPrOPhOPc gold electrode surfaces showed good sensitivity and reproducibility towards the electrocatalytic reduction of hydrogen peroxide in pH 7.4 phosphate buffer solution. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Mwanza, Daniel
- Date: 2017
- Subjects: Phthalocyanines , Nonlinear optics , Electrocatalysis , Spectrum analysis , Thermogravimetry , Phthalocyanines Spectra
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65144 , vital:28695
- Description: This study presents the synthesis, spectroscopic, photophysical and theoretical characterisation of metal-free (H2TPrOPhOPc), cobalt (CoTPrOPhOPc) and manganese (MnTPrOPhOPc) tetra 4-(4-propargyloxy) phenoxy phthalocyanines. Thermal analysis using thermogravimetric analysis (TGA) confirmed the excellent thermal stability of synthesized tetra 4-(4- propargyloxy) phenoxy phthalocyanines. The metal complexes, CoTPrOPhOPc and MnTPrOPhOPc, exhibited better thermal stability when compared to H2TPrOPhOPc. The residual percentage weight remaining was approximately 70% for CoTPrOPhOPc and MnTPrOPhOPc and 45% for H2TPrOPhOPc after 600°C, clearly confirming the stability of the metal complexes. The MTPrOPhOPcs (where M = H2, Co and Mn) complexes exhibited excellent nonlinear optical properties with strong reverse saturable absorption (RSA), especially when 560 nm excitation laser was used. Their nonlinear optical properties followed this trend: H2TPrOPhOPc > CoTPrOPhOPc > MnTPrOPhOPc. According to the trend observed, the H2TPrOPhOPc was an excellent nonlinear optical limiter when compared to the CoTPrOPhOPc and MnTPrOPhOPc. All the investigated complexes exhibited optical limiting properties comparable to the phthalocyanine complexes reported in the literature. The MTPrOPhOPc complexes were further studied for their electrocatalytic and electroanalytical properties towards the detection of hydrogen peroxide. For the electrocatalytic studies, the synthesized complexes were immobilized onto gold electrode surfaces pre-functionalized with phenylazide (Au-PAz) monolayer. Copper (I) catalyzed alkynyl-azide cycloaddition reaction was used to covalently immobilize the MTPrOPhOPcs onto the gold electrode surfaces to form Au-PAz-MTPrOPhOPc. The MTPrOPhOPcs modified gold surfaces (Au-PAz-MTPrOPhOPc) exhibited good reproducibility and stability in various electrolyte conditions. Electrochemical and surface characterisation of the functionalised gold electrode surfaces confirmed the presence of the MTPrOPhOPcs and their electroanalysis was excellent towards electrocatalytic reduction of H2O2, with the limit of detection (LoD) and limit of quantification (LoQ) in the ^M range. The electrocatalytic reduction peaks for H2O2 were observed at -0.37 V for Au-PAz-MnTPrOPhOPc and -0.31 V for Au-PAz-CoTPrOPhOPc when Ag|AgCl pseudo-reference electrode was used. The Au-PAz-MnTPrOPhOPc and Au- PAz-CoTPrOPhOPc gold electrode surfaces showed good sensitivity and reproducibility towards the electrocatalytic reduction of hydrogen peroxide in pH 7.4 phosphate buffer solution. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
The abundance of an invasive freshwater snail Tarebia granifera (Lamarck, 1822) in the Nseleni River, South Africa
- Jones, Roy W, Hill, Jaclyn M, Coetzee, Julie A, Hill, Martin P, Avery, T S, Weyl, Olaf L F
- Authors: Jones, Roy W , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P , Avery, T S , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69077 , vital:29382 , https://doi.org/10.2989/16085914.2017.1298984
- Description: The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.
- Full Text: false
- Authors: Jones, Roy W , Hill, Jaclyn M , Coetzee, Julie A , Hill, Martin P , Avery, T S , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69077 , vital:29382 , https://doi.org/10.2989/16085914.2017.1298984
- Description: The invasive freshwater snail Tarebia granifera (Lamarck, 1822) was first reported in South Africa in 1999 and it has become widespread across the country, with some evidence to suggest that it reduces benthic macroinvertebrate biodiversity. The current study aimed to identify the primary abiotic drivers behind abundance patterns of T. granifera, by comparing the current abundance of the snail in three different regions, and at three depths, of the highly modified Nseleni River in KwaZulu-Natal, South Africa. Tarebia granifera was well established throughout the Nseleni River system, with an overall preference for shallow waters and seasonal temporal patterns of abundance. Although it is uncertain what the ecological impacts of the snail in this system are, its high abundances suggest that it should be controlled where possible and prevented from invading other systems in the region.
- Full Text: false