Electrode modification through click chemistry using Ni and Co alkyne phthalocyanines for electrocatalytic detection of hydrazine
- O'Donoghue, Charles S, Shumba, Munyaradzai, Nyokong, Tebello
- Authors: O'Donoghue, Charles S , Shumba, Munyaradzai , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/242763 , vital:51076 , xlink:href="https://doi.org/10.1002/elan.201700084"
- Description: This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5-hexyn-oxy) cobalt(II) phthalocyanine (complex 2) and tetrakis(5-hexyn-oxy) nickel(II) phthalocyanine (complex 3) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3-dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP2-clicked-GCE and NiP3-clicked-GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc-GCE was 6.09 μM, while the NiPc-GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM−1 for the CoPc-GCE and 111.2 μA mM−1 for the NiPc-GCE.
- Full Text:
- Authors: O'Donoghue, Charles S , Shumba, Munyaradzai , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/242763 , vital:51076 , xlink:href="https://doi.org/10.1002/elan.201700084"
- Description: This work reports on the development of sensors for the detection of hydrazine using glassy carbon electrodes (GCE) modified with phthalocyanines through click chemistry. Tetrakis(5-hexyn-oxy) cobalt(II) phthalocyanine (complex 2) and tetrakis(5-hexyn-oxy) nickel(II) phthalocyanine (complex 3) were employed as electrode modifiers for hydrazine detection. The GCE was first grafted via the in situ diazotization of a diazonium salt, rendering the GCE surface layered with azide groups. From this point, the 1, 3-dipolar cycloaddition reaction, catalysed by a copper catalyst was utilised to “click” the phthalocyanines to the surface of the grafted GCE. The modified electrodes were characterized by scanning electrochemical microscopy, X-ray photoelectron spectroscopy and cyclic voltammetry. The electrografted CoP2-clicked-GCE and NiP3-clicked-GCE exhibited electrocatalytic activity towards the detection of hydrazine. The limit of detection (LoD) for the CoPc-GCE was 6.09 μM, while the NiPc-GCE had a LoD of 8.69 μM. The sensitivity was 51.32 μA mM−1 for the CoPc-GCE and 111.2 μA mM−1 for the NiPc-GCE.
- Full Text:
Electronic structure and NH-tautomerism of a novel metal-free phenanthroline-annelated phthalocyanine
- Martynov, Alexander G, Mack, John, Ngoy, Bokolombe P, Nyokong, Tebello, Gorbunova, Yulia G, Tsivadze, Aslan Yu
- Authors: Martynov, Alexander G , Mack, John , Ngoy, Bokolombe P , Nyokong, Tebello , Gorbunova, Yulia G , Tsivadze, Aslan Yu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/239643 , vital:50751 , xlink:href="https://doi.org/10.1016/j.dyepig.2017.01.072"
- Description: A novel low-symmetry A3B-type phthalocyanine annelated with a pyrazino[2,3-f]phenanthroline ring system and substituted with six solubilizing diisopropylphenoxy-groups (1) was synthesized by metalfree DBU-promoted cross-condensation of diiminoisoindolines derived from 4,5- bis(diisopropylphenoxy)phthalonitrile and pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile. The use of these particular precursors affords A3B phthalocyanine in 15% yield, while cross-condensation of the corresponding dinitriles yields only trace amounts of the target compound. Comparative studies of the A3B-type phthalocyanine and its symmetrical octa(diisopropylphenoxy)-substituted counterpart 2 reveal striking differences in the Q band regions of their UVevisible absorption (UVeVis) spectra, which could be readily rationalized through a comparison with calculated TD-DFT spectra. Since 1 can have two NH-tautomers with equivalent and non-equivalent NH-groups, and DFT calculations predict that the former tautomer is only 2.3 kcal/mol more stable than the latter one, a comprehensive analysis of 13C NMR spectra was carried out through the application of 1 He13C HMBC and HSQC techniques. It demonstrated that only the tautomer with equivalent NH-groups is present in solution.
- Full Text:
- Authors: Martynov, Alexander G , Mack, John , Ngoy, Bokolombe P , Nyokong, Tebello , Gorbunova, Yulia G , Tsivadze, Aslan Yu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/239643 , vital:50751 , xlink:href="https://doi.org/10.1016/j.dyepig.2017.01.072"
- Description: A novel low-symmetry A3B-type phthalocyanine annelated with a pyrazino[2,3-f]phenanthroline ring system and substituted with six solubilizing diisopropylphenoxy-groups (1) was synthesized by metalfree DBU-promoted cross-condensation of diiminoisoindolines derived from 4,5- bis(diisopropylphenoxy)phthalonitrile and pyrazino[2,3-f][1,10]phenanthroline-2,3-dicarbonitrile. The use of these particular precursors affords A3B phthalocyanine in 15% yield, while cross-condensation of the corresponding dinitriles yields only trace amounts of the target compound. Comparative studies of the A3B-type phthalocyanine and its symmetrical octa(diisopropylphenoxy)-substituted counterpart 2 reveal striking differences in the Q band regions of their UVevisible absorption (UVeVis) spectra, which could be readily rationalized through a comparison with calculated TD-DFT spectra. Since 1 can have two NH-tautomers with equivalent and non-equivalent NH-groups, and DFT calculations predict that the former tautomer is only 2.3 kcal/mol more stable than the latter one, a comprehensive analysis of 13C NMR spectra was carried out through the application of 1 He13C HMBC and HSQC techniques. It demonstrated that only the tautomer with equivalent NH-groups is present in solution.
- Full Text:
Enantioselective electrochemical carbon-chloride bond cleavage of hexachlorocyclohexanes (HCHs) catalyzed by Mn (III) Cl-phthalocyanine
- Wen, Junxia, Yu, Baoqui, Huang, Tingting, Mack, John, Wildervanck, Martijn, Nyokong, Tebello, Li, Minzhi, Zhu, Weihua, Liang, Xu
- Authors: Wen, Junxia , Yu, Baoqui , Huang, Tingting , Mack, John , Wildervanck, Martijn , Nyokong, Tebello , Li, Minzhi , Zhu, Weihua , Liang, Xu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189252 , vital:44831 , xlink:href="https://doi.org/10.1016/j.jelechem.2017.09.020"
- Description: A lipophilic and electron-rich metallophthalocyanine Mn(III)Cl(α,α′-n-OC5H11)8Pc has been synthesized and characterized. A series of electrochemical experiments demonstrate that the Mn(III)Cl(α,α′-n-OC5H11)8Pc complex can be used as a catalyst for highly efficient carbon-chloride bond cleavage of environmental toxic hexachlorocyclohexanes (HCHs) through electrochemical catalysis, and that the increased catalytic efficiency is related to the enantiomeric carbon-chloride σ-bond of HCHs.
- Full Text:
- Authors: Wen, Junxia , Yu, Baoqui , Huang, Tingting , Mack, John , Wildervanck, Martijn , Nyokong, Tebello , Li, Minzhi , Zhu, Weihua , Liang, Xu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189252 , vital:44831 , xlink:href="https://doi.org/10.1016/j.jelechem.2017.09.020"
- Description: A lipophilic and electron-rich metallophthalocyanine Mn(III)Cl(α,α′-n-OC5H11)8Pc has been synthesized and characterized. A series of electrochemical experiments demonstrate that the Mn(III)Cl(α,α′-n-OC5H11)8Pc complex can be used as a catalyst for highly efficient carbon-chloride bond cleavage of environmental toxic hexachlorocyclohexanes (HCHs) through electrochemical catalysis, and that the increased catalytic efficiency is related to the enantiomeric carbon-chloride σ-bond of HCHs.
- Full Text:
Environmental and social recovery asymmetries to large-scale disturbances in small island communities
- Aswani, Shankar, Van Putten, Ingrid, Miñarro, Sara
- Authors: Aswani, Shankar , Van Putten, Ingrid , Miñarro, Sara
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/67325 , vital:29073 , https://doi.org/10.1007/s11069-016-2685-2
- Description: publisher version , People’s livelihoods in tropical small-island developing states are greatly dependent on marine ecosystem services. Yet services such as fisheries and coastal buffering are being degraded at an alarming rate, thus making people increasing vulnerable to protracted and sudden environmental changes. In the context of the occurrences of extreme events such as earthquakes and tsunamis, it is vital to uncover the processes that make people in these island states resilient, or not, to environmental disruptions. This paper compares people’s perceptions of social and environmental impacts after an extreme event in the Western Solomon Islands (11 different villages on 8 different islands) to better understand how knowledge systems influence the coupling of human and natural systems. We examine the factors that contributed to perceptions of respective recovery in the environmental versus the social domains across communities with different traditional governance and modernization characteristics in a tsunami impact gradient. First, we separately assessed, at the community and individual level, the potential determinants of perceived recovery in the environmental and social domains. At the community level, the average values of the perceived environmental and social recovery were calculated for each community (1 year after the tsunami), and at the individual level, normally distributed environmental and social recovery variables (based on the difference in perceptions immediately and 1 year after the tsunami) were used as dependent variables in two General Linear Models. Results suggest that environmental and social resilience are not always coupled correspondingly and, less unexpectedly, that asymmetries during recovery can occur as a result of the underlying social and ecological context and existing adaptive capacity. More generally, the study shows how by evaluating post-disturbance perceptional data in tsunami-affected communities, we can better understand how subjective perceptions of change can affect the (de)-coupling of human and natural systems.
- Full Text: false
- Authors: Aswani, Shankar , Van Putten, Ingrid , Miñarro, Sara
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/67325 , vital:29073 , https://doi.org/10.1007/s11069-016-2685-2
- Description: publisher version , People’s livelihoods in tropical small-island developing states are greatly dependent on marine ecosystem services. Yet services such as fisheries and coastal buffering are being degraded at an alarming rate, thus making people increasing vulnerable to protracted and sudden environmental changes. In the context of the occurrences of extreme events such as earthquakes and tsunamis, it is vital to uncover the processes that make people in these island states resilient, or not, to environmental disruptions. This paper compares people’s perceptions of social and environmental impacts after an extreme event in the Western Solomon Islands (11 different villages on 8 different islands) to better understand how knowledge systems influence the coupling of human and natural systems. We examine the factors that contributed to perceptions of respective recovery in the environmental versus the social domains across communities with different traditional governance and modernization characteristics in a tsunami impact gradient. First, we separately assessed, at the community and individual level, the potential determinants of perceived recovery in the environmental and social domains. At the community level, the average values of the perceived environmental and social recovery were calculated for each community (1 year after the tsunami), and at the individual level, normally distributed environmental and social recovery variables (based on the difference in perceptions immediately and 1 year after the tsunami) were used as dependent variables in two General Linear Models. Results suggest that environmental and social resilience are not always coupled correspondingly and, less unexpectedly, that asymmetries during recovery can occur as a result of the underlying social and ecological context and existing adaptive capacity. More generally, the study shows how by evaluating post-disturbance perceptional data in tsunami-affected communities, we can better understand how subjective perceptions of change can affect the (de)-coupling of human and natural systems.
- Full Text: false
Eruptive history of the Karoo lava flows and their impact on early Jurassic environmental change:
- Moulin, Maud, Fluteau, Frédéric, Courtillot, Vincent, Marsh, Julian S, Delpech, Guillaume, Quidelleur, Xavier, Gérard, Martine
- Authors: Moulin, Maud , Fluteau, Frédéric , Courtillot, Vincent , Marsh, Julian S , Delpech, Guillaume , Quidelleur, Xavier , Gérard, Martine
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145098 , vital:38408 , https://doi.org/10.1002/2016JB013354
- Description: This paper reports new paleomagnetic and geochronologic data from a ~1500 m thick composite section belonging to the Drakensberg group, the thickest remnant of the Karoo lavas in Northern Lesotho. Flow‐by‐flow analysis of paleomagnetic directions reveals 21 magnetic directional groups, corresponding to single eruptive events, and 16 individual lava flows. The new age determinations of lava flows range from 180.1 ± 1.4 to 182.8 ± 2.6 Ma. These data, combined with previous results, allow us to propose that the main part of the Drakensberg group and the Karoo intrusive complex dated around 181–183 Ma may have been erupted over a period as short as 250 kyr and may have coincided with the two main phases of extinction in the Early Toarcian. This scenario agrees well with the discontinuous rhythm of environmental and biotic perturbations in the Late Pliensbachian‐Toarcian interval.
- Full Text:
- Authors: Moulin, Maud , Fluteau, Frédéric , Courtillot, Vincent , Marsh, Julian S , Delpech, Guillaume , Quidelleur, Xavier , Gérard, Martine
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/145098 , vital:38408 , https://doi.org/10.1002/2016JB013354
- Description: This paper reports new paleomagnetic and geochronologic data from a ~1500 m thick composite section belonging to the Drakensberg group, the thickest remnant of the Karoo lavas in Northern Lesotho. Flow‐by‐flow analysis of paleomagnetic directions reveals 21 magnetic directional groups, corresponding to single eruptive events, and 16 individual lava flows. The new age determinations of lava flows range from 180.1 ± 1.4 to 182.8 ± 2.6 Ma. These data, combined with previous results, allow us to propose that the main part of the Drakensberg group and the Karoo intrusive complex dated around 181–183 Ma may have been erupted over a period as short as 250 kyr and may have coincided with the two main phases of extinction in the Early Toarcian. This scenario agrees well with the discontinuous rhythm of environmental and biotic perturbations in the Late Pliensbachian‐Toarcian interval.
- Full Text:
Estimating δ15N fractionation and adjusting the lipid correction equation using Southern African freshwater fishes
- Taylor, Geraldine C, Hill, Jaclyn M, Jackson, Michelle C, Peel, Richard A, Weyl, Olaf L F
- Authors: Taylor, Geraldine C , Hill, Jaclyn M , Jackson, Michelle C , Peel, Richard A , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69124 , vital:29392 , https://0-doi.org.wam.seals.ac.za/10.1371/journal.pone.0178047
- Description: Stable isotope analysis is an important tool for characterising food web structure; however, interpretation of isotope data can often be flawed. For instance, lipid normalisation and trophic fractionation values are often assumed to be constant, but can vary considerably between ecosystems, species and tissues. Here, previously determined lipid normalisation equations and trophic fractionation values were re-evaluated using freshwater fish species from three rivers in the Upper Zambezian floodplain ecoregion in southern Africa. The parameters commonly used in lipid normalisation equations were not correct for the 18 model species (new D and I parameters were estimated as D = 4.46‰ [95% CI: 2.62, 4.85] and constant I = 0 [95% CI: 0, 0.17]). We suggest that future isotopic analyses on freshwater fishes use our new values if the species under consideration do not have a high lipid content in their white muscle tissue. Nitrogen fractionation values varied between species and river basin; however, the average value closely matched that calculated in previous studies on other species (δ15N fractionation factor of 3.37 ± 1.30 ‰). Here we have highlighted the need to treat stable isotope data correctly in food web studies to avoid misinterpretation of the data.
- Full Text:
- Authors: Taylor, Geraldine C , Hill, Jaclyn M , Jackson, Michelle C , Peel, Richard A , Weyl, Olaf L F
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69124 , vital:29392 , https://0-doi.org.wam.seals.ac.za/10.1371/journal.pone.0178047
- Description: Stable isotope analysis is an important tool for characterising food web structure; however, interpretation of isotope data can often be flawed. For instance, lipid normalisation and trophic fractionation values are often assumed to be constant, but can vary considerably between ecosystems, species and tissues. Here, previously determined lipid normalisation equations and trophic fractionation values were re-evaluated using freshwater fish species from three rivers in the Upper Zambezian floodplain ecoregion in southern Africa. The parameters commonly used in lipid normalisation equations were not correct for the 18 model species (new D and I parameters were estimated as D = 4.46‰ [95% CI: 2.62, 4.85] and constant I = 0 [95% CI: 0, 0.17]). We suggest that future isotopic analyses on freshwater fishes use our new values if the species under consideration do not have a high lipid content in their white muscle tissue. Nitrogen fractionation values varied between species and river basin; however, the average value closely matched that calculated in previous studies on other species (δ15N fractionation factor of 3.37 ± 1.30 ‰). Here we have highlighted the need to treat stable isotope data correctly in food web studies to avoid misinterpretation of the data.
- Full Text:
Evaluating the potential of monometallic and bimetallic nanomaterials as horseradish peroxidase mimetics
- Authors: Mvango, Sindisiwe
- Date: 2017
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65134 , vital:28694
- Description: This study presents the synthesis of citrate-capped gold nanoparticles (cit-AuNPs), copper oxide nanoparticles (CuONPs), glutathione-capped gold nanoparticles (GSH-AuNPs), 4- aminothiophenol-capped gold nanoparticles (4-ATP-AuNPs), 4-mercapto benzoic acid- capped gold nanoparticles (4-MBA-AuNPs) and copper oxide gold nanoalloys (CuO-Au nanoalloys). Microscopy and spectroscopy techniques were used to confirm the successful synthesis of these nanoparticles. The synthesized nanoparticles were studied their potential applications as horseradish peroxidase (HPR) enzyme mimetics and for the detection of glucose. The cit-AuNPs and GSH-AuNPs exhibited peroxidase-like activity towards hydrogen peroxide (H2O2) with high Michaelis-Menten (Km) values of 61.5 mM and 30.8 mM, respectively. The other nanoparticles, that is, 4-ATP-AuNPs, CuONPs and CuO-Au nanoalloys gave lower Km values of 4.74 mM, 1.92 mM and 4.05 mM, respectively. The obtained Km values were comparable to those of HRP enzymes which ranged from 0.214 - 3.70 mM with 4-ATP-AuNPs and CuO-Au nanoalloys slightly higher. These values were within the reasonable experimental values of the HRP enzyme. The studies showed that the gold nanoparticles had low adsorptive efficiency towards H2O2 compared to the copper-based nanoparticles (CuONPs and CuO-Au nanoalloys). The CuO-Au nanoalloys also showed the synergistic effect between the gold and copper nanoparticles with extended linear concentration range for the quantification of H2O2. The mechanism of catalysis was confirmed using UV-vis spectroscopy and electron paramagnetic resonance (EPR) in that the generation of reactive oxygen species was observed. The use of 1,3-diphenylisobenzofuran (DPBF) as radical quencher and 5,5- dimethyl-1-pyrroline N-oxide (DMPO) as a radical scavenger confirmed the production of reductive reactive oxygen species using UV-vis and EPR studies. The rate of production of reactive oxygen species in the gold-based nanoparticles was small compared to the copper-based nanoparticles, that is CuONPs and CuO-Au (bimetallic) nanoalloys. The synthesized nanoparticles were further studied their potential use in the colorimetric detection of glucose. The copper-based nanomaterials, CuONPs and CuO-Au nanoalloys, were excellent towards detection of glucose, with a limit of detection (LoD) of 9.34 pM for CuONPs and 6.75 pM for CuO-Au nanoalloys. The linear concentration (LCR) range of CuONPs was 0 to 70 pM and for CuO-Au nanoalloys the LCR was 0.0 - 30 pM. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
- Authors: Mvango, Sindisiwe
- Date: 2017
- Subjects: Uncatalogued
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10962/65134 , vital:28694
- Description: This study presents the synthesis of citrate-capped gold nanoparticles (cit-AuNPs), copper oxide nanoparticles (CuONPs), glutathione-capped gold nanoparticles (GSH-AuNPs), 4- aminothiophenol-capped gold nanoparticles (4-ATP-AuNPs), 4-mercapto benzoic acid- capped gold nanoparticles (4-MBA-AuNPs) and copper oxide gold nanoalloys (CuO-Au nanoalloys). Microscopy and spectroscopy techniques were used to confirm the successful synthesis of these nanoparticles. The synthesized nanoparticles were studied their potential applications as horseradish peroxidase (HPR) enzyme mimetics and for the detection of glucose. The cit-AuNPs and GSH-AuNPs exhibited peroxidase-like activity towards hydrogen peroxide (H2O2) with high Michaelis-Menten (Km) values of 61.5 mM and 30.8 mM, respectively. The other nanoparticles, that is, 4-ATP-AuNPs, CuONPs and CuO-Au nanoalloys gave lower Km values of 4.74 mM, 1.92 mM and 4.05 mM, respectively. The obtained Km values were comparable to those of HRP enzymes which ranged from 0.214 - 3.70 mM with 4-ATP-AuNPs and CuO-Au nanoalloys slightly higher. These values were within the reasonable experimental values of the HRP enzyme. The studies showed that the gold nanoparticles had low adsorptive efficiency towards H2O2 compared to the copper-based nanoparticles (CuONPs and CuO-Au nanoalloys). The CuO-Au nanoalloys also showed the synergistic effect between the gold and copper nanoparticles with extended linear concentration range for the quantification of H2O2. The mechanism of catalysis was confirmed using UV-vis spectroscopy and electron paramagnetic resonance (EPR) in that the generation of reactive oxygen species was observed. The use of 1,3-diphenylisobenzofuran (DPBF) as radical quencher and 5,5- dimethyl-1-pyrroline N-oxide (DMPO) as a radical scavenger confirmed the production of reductive reactive oxygen species using UV-vis and EPR studies. The rate of production of reactive oxygen species in the gold-based nanoparticles was small compared to the copper-based nanoparticles, that is CuONPs and CuO-Au (bimetallic) nanoalloys. The synthesized nanoparticles were further studied their potential use in the colorimetric detection of glucose. The copper-based nanomaterials, CuONPs and CuO-Au nanoalloys, were excellent towards detection of glucose, with a limit of detection (LoD) of 9.34 pM for CuONPs and 6.75 pM for CuO-Au nanoalloys. The linear concentration (LCR) range of CuONPs was 0 to 70 pM and for CuO-Au nanoalloys the LCR was 0.0 - 30 pM. , Thesis (MSc) -- Faculty of Science, Chemistry, 2017
- Full Text:
Evaluation of the acceptability of ambulatory blood pressure monitoring in a semi-rural, Eastern Cape population
- Authors: Chiwanza, Farisai
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MPharm
- Identifier: http://hdl.handle.net/10962/59161 , vital:27447
- Description: Expected release date-April 2019
- Full Text:
- Authors: Chiwanza, Farisai
- Date: 2017
- Language: English
- Type: text , Thesis , Masters , MPharm
- Identifier: http://hdl.handle.net/10962/59161 , vital:27447
- Description: Expected release date-April 2019
- Full Text:
Evidence for rangewide panmixia despite multiple barriers to dispersal in a marine mussel
- Lourenço, Carla R, Nicastro, Katy R, McQuaid, Christopher D, Chefaoui, Rosa M, Assis, Jorge, Taleb, Mohammed Z, Zardi, Gerardo I
- Authors: Lourenço, Carla R , Nicastro, Katy R , McQuaid, Christopher D , Chefaoui, Rosa M , Assis, Jorge , Taleb, Mohammed Z , Zardi, Gerardo I
- Date: 2017
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59952 , vital:27714 , doi:10.1038/s41598-017-10753-9
- Description: Oceanographic features shape the distributional and genetic patterns of marine species by interrupting or promoting connections among populations. Although general patterns commonly arise, distributional ranges and genetic structure are species-specific and do not always comply with the expected trends. By applying a multimarker genetic approach combined with Lagrangian particle simulations (LPS) we tested the hypothesis that oceanographic features along northeastern Atlantic and Mediterranean shores influence dispersal potential and genetic structure of the intertidal mussel Perna perna. Additionally, by performing environmental niche modelling we assessed the potential and realized niche of P. perna along its entire native distributional range and the environmental factors that best explain its realized distribution. Perna perna showed evidence of panmixia across 4,000 km despite several oceanographic breaking points detected by LPS. This is probably the result of a combination of life history traits, continuous habitat availability and stepping-stone dynamics. Moreover, the niche modelling framework depicted minimum sea surface temperatures (SST) as the major factor shaping P. perna distributional range limits along its native areas. Forthcoming warming SST is expected to further change these limits and allow the species to expand its range polewards though this may be accompanied by retreat from warmer areas.
- Full Text:
- Authors: Lourenço, Carla R , Nicastro, Katy R , McQuaid, Christopher D , Chefaoui, Rosa M , Assis, Jorge , Taleb, Mohammed Z , Zardi, Gerardo I
- Date: 2017
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59952 , vital:27714 , doi:10.1038/s41598-017-10753-9
- Description: Oceanographic features shape the distributional and genetic patterns of marine species by interrupting or promoting connections among populations. Although general patterns commonly arise, distributional ranges and genetic structure are species-specific and do not always comply with the expected trends. By applying a multimarker genetic approach combined with Lagrangian particle simulations (LPS) we tested the hypothesis that oceanographic features along northeastern Atlantic and Mediterranean shores influence dispersal potential and genetic structure of the intertidal mussel Perna perna. Additionally, by performing environmental niche modelling we assessed the potential and realized niche of P. perna along its entire native distributional range and the environmental factors that best explain its realized distribution. Perna perna showed evidence of panmixia across 4,000 km despite several oceanographic breaking points detected by LPS. This is probably the result of a combination of life history traits, continuous habitat availability and stepping-stone dynamics. Moreover, the niche modelling framework depicted minimum sea surface temperatures (SST) as the major factor shaping P. perna distributional range limits along its native areas. Forthcoming warming SST is expected to further change these limits and allow the species to expand its range polewards though this may be accompanied by retreat from warmer areas.
- Full Text:
Evil and the Hero-Villain Binary in Deon Meyer’s Post-Apartheid Crime Thriller, Devil’s Peak:
- Naidu, Samantha, van der Wielen, Karlien
- Authors: Naidu, Samantha , van der Wielen, Karlien
- Date: 2017
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/157991 , vital:40137 , ISBN 9781498533423
- Description: The Functions of Evil Across Disciplinary Contexts explores answers to two important questions about the age-old theme of evil: is there any use in using the concept of evil in cultural, psychological, or other secular evaluations of the world and its productions? Most importantly, if there is, what might these functions be? By looking across several disciplines and analyzing evil as it is referenced across a broad spectrum of phenomena, this work demonstrates the varying ways that we interact with the ethical dilemma as academics, as citizens, and as people. The work draws from authors in different fields—including history, literary and film studies, philosophy, and psychology—and from around the world to provide an analysis of evil in such topics as deeply canonical as Beowulf and Shakespeare to subjects as culturally resonant as Stephen King, Captain America, or the War on Terror. By bringing together this otherwise disparate collection of scholarship, this collection reveals that discussions of evil across disciplines have always been questions of how cultures represent that which they find socially abhorrent. This work thus opens the conversation about evil outside of field-specific limitations, simultaneously demonstrating the assumptions that undergird the manner by which such a conversation proceeds.
- Full Text:
- Authors: Naidu, Samantha , van der Wielen, Karlien
- Date: 2017
- Language: English
- Type: text , book
- Identifier: http://hdl.handle.net/10962/157991 , vital:40137 , ISBN 9781498533423
- Description: The Functions of Evil Across Disciplinary Contexts explores answers to two important questions about the age-old theme of evil: is there any use in using the concept of evil in cultural, psychological, or other secular evaluations of the world and its productions? Most importantly, if there is, what might these functions be? By looking across several disciplines and analyzing evil as it is referenced across a broad spectrum of phenomena, this work demonstrates the varying ways that we interact with the ethical dilemma as academics, as citizens, and as people. The work draws from authors in different fields—including history, literary and film studies, philosophy, and psychology—and from around the world to provide an analysis of evil in such topics as deeply canonical as Beowulf and Shakespeare to subjects as culturally resonant as Stephen King, Captain America, or the War on Terror. By bringing together this otherwise disparate collection of scholarship, this collection reveals that discussions of evil across disciplines have always been questions of how cultures represent that which they find socially abhorrent. This work thus opens the conversation about evil outside of field-specific limitations, simultaneously demonstrating the assumptions that undergird the manner by which such a conversation proceeds.
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Examining the nature of learning within an afterschool mathematics club : a case study of four learners
- Pohamba, Penehafo K, Graven, Mellony, Stott, Deborah A, Ashipala, Daniel O
- Authors: Pohamba, Penehafo K , Graven, Mellony , Stott, Deborah A , Ashipala, Daniel O
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70121 , vital:29623 , http://dx.doi.org/10.5430/irhe.v2n1p21
- Description: This study examined the nature of learning within an afterschool mathematics club established by the South African Numeracy Chair project. This study sought to establish what sort of progress in mathematical learning occurred in a grade 3 afterschool maths club, using assessment instruments associated with the Learning Framework in Number. The study also sought to understand the nature and effects of mentor mediation in the maths club, using Vygotsky’s notion of the Zone of Proximal Development (ZPD) together with the notion and practice of scaffolding. This study was interpretive in nature drawing on qualitative methods with some elements of quantification in relation to learners’ progression. The club consists of 10 learners of mixed ability (5 girls and 5 boys) at a township school in Graham’s town, South Africa. Learners in this case study were selected through purposive sampling. As part of the data collection strategies, the learners were interviewed twice in terms of their numeracy proficiency. The assessment interview results revealed that, in terms of proficiency in early arithmetical learning, all four learners showed progress after spending four months in an afterschool maths club. This study also recommended Wright et al.’s (2006) LFIN framework to be used in assessing learners’ progress in mathematics, as it could inform the refinement of instructional design within the school curriculum and teachers’ education in the Namibian context.
- Full Text:
- Authors: Pohamba, Penehafo K , Graven, Mellony , Stott, Deborah A , Ashipala, Daniel O
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/70121 , vital:29623 , http://dx.doi.org/10.5430/irhe.v2n1p21
- Description: This study examined the nature of learning within an afterschool mathematics club established by the South African Numeracy Chair project. This study sought to establish what sort of progress in mathematical learning occurred in a grade 3 afterschool maths club, using assessment instruments associated with the Learning Framework in Number. The study also sought to understand the nature and effects of mentor mediation in the maths club, using Vygotsky’s notion of the Zone of Proximal Development (ZPD) together with the notion and practice of scaffolding. This study was interpretive in nature drawing on qualitative methods with some elements of quantification in relation to learners’ progression. The club consists of 10 learners of mixed ability (5 girls and 5 boys) at a township school in Graham’s town, South Africa. Learners in this case study were selected through purposive sampling. As part of the data collection strategies, the learners were interviewed twice in terms of their numeracy proficiency. The assessment interview results revealed that, in terms of proficiency in early arithmetical learning, all four learners showed progress after spending four months in an afterschool maths club. This study also recommended Wright et al.’s (2006) LFIN framework to be used in assessing learners’ progress in mathematics, as it could inform the refinement of instructional design within the school curriculum and teachers’ education in the Namibian context.
- Full Text:
Exploiting Click Chemistry for the Covalent Immobilization of Tetra (4-Propargyloxyphenoxy) Metallophthalocyanines onto Phenylazide-Grafted Gold Surfaces
- Mwanza, Daniel, Mvango, Sindisiwe, Khene, Samson M, Nyokong, Tebello, Mashazi, Philani N
- Authors: Mwanza, Daniel , Mvango, Sindisiwe , Khene, Samson M , Nyokong, Tebello , Mashazi, Philani N
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189177 , vital:44824 , xlink:href="https://doi.org/10.1016/j.electacta.2017.09.115"
- Description: In this study, tetra-(4-propargyloxy)phenoxy phthalocyanines (MTPrOPhOPc) were covalently immobilized as thin films onto gold surfaces via click reaction. The gold electrode surfaces were pre-functionalized with phenylazide (Au-PAz) thin film using in-situ diazonium generation followed by electrografting. Copper (I) catalyzed alkynyl-azide cycloaddition (CuCAAC) reaction was used to covalently immobilize the MTPrOPhOPcs onto the gold electrode surfaces to form Au-PAz-MTPrOPhOPc. The MTPrOPhOPcs were further studied for their electrocatalytic and electroanalytical properties towards the detection of hydrogen peroxide. Au-PAz-MTPrOPhOPc exhibited good reproducibility and stability in various electrolyte conditions. Electrochemical and spectroscopic surface characterization of the functionalized gold electrode surfaces confirmed the presence of the phenylazide and MTPrOPhOPc thin monolayer films. The excellent electroanalysis of hydrogen peroxide with the limit of detection (LoD) and limit of quantification (LoQ) in the μM range was obtained. The electrocatalytic reduction peaks for H2O2 were observed at −0.37 V for Au-PAz-Mn(OAc)TPrOPhOPc and −0.31 V for Au-PAz-CoTPrOPhOPc when Ag|AgCl pseudo-reference electrode was used. The Au-PAz-Mn(OAc)TPrOPhOPc 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.
- Full Text:
- Authors: Mwanza, Daniel , Mvango, Sindisiwe , Khene, Samson M , Nyokong, Tebello , Mashazi, Philani N
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189177 , vital:44824 , xlink:href="https://doi.org/10.1016/j.electacta.2017.09.115"
- Description: In this study, tetra-(4-propargyloxy)phenoxy phthalocyanines (MTPrOPhOPc) were covalently immobilized as thin films onto gold surfaces via click reaction. The gold electrode surfaces were pre-functionalized with phenylazide (Au-PAz) thin film using in-situ diazonium generation followed by electrografting. Copper (I) catalyzed alkynyl-azide cycloaddition (CuCAAC) reaction was used to covalently immobilize the MTPrOPhOPcs onto the gold electrode surfaces to form Au-PAz-MTPrOPhOPc. The MTPrOPhOPcs were further studied for their electrocatalytic and electroanalytical properties towards the detection of hydrogen peroxide. Au-PAz-MTPrOPhOPc exhibited good reproducibility and stability in various electrolyte conditions. Electrochemical and spectroscopic surface characterization of the functionalized gold electrode surfaces confirmed the presence of the phenylazide and MTPrOPhOPc thin monolayer films. The excellent electroanalysis of hydrogen peroxide with the limit of detection (LoD) and limit of quantification (LoQ) in the μM range was obtained. The electrocatalytic reduction peaks for H2O2 were observed at −0.37 V for Au-PAz-Mn(OAc)TPrOPhOPc and −0.31 V for Au-PAz-CoTPrOPhOPc when Ag|AgCl pseudo-reference electrode was used. The Au-PAz-Mn(OAc)TPrOPhOPc 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.
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Exports, capital formation and economic growth in South Africa
- Feddersen, Maura, Nel, Hugo, Botha, Ferdi
- Authors: Feddersen, Maura , Nel, Hugo , Botha, Ferdi
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396035 , vital:69145 , xlink:href="https://www.ajol.info/index.php/aref/article/view/162150"
- Description: In South Africa the export sector is frequently accorded a special role in encouraging faster economic growth. Nonetheless, a question that remains unresolved is whether higher export growth indeed leads to higher economic growth and what particular role exports may play within the overall economic growth process of the country. This study applies Johansen’s cointegration procedure, impulse response functions, variance decomposition analysis and Granger causality tests to shed light on the channels through which export growth may impact South Africa’s economic growth rate. Quarterly time series data ranging from 1975q1 to 2012q4 is employed in the study’s empirical tests. The results support the notion that the role of exports lies in their ability to encourage investment and capital formation. While export growth directly supports higher economic growth in the short-run, the long-term effect was found to lie in supporting faster capital formation, and in turn, significantly increasing economic growth. Overall, a strategy of export-led growth that does not explicitly emphasize the export-capital-growth connection is likely to fall short of reflecting the dynamics contained within the exports-growth relationship in South Africa.
- Full Text:
- Authors: Feddersen, Maura , Nel, Hugo , Botha, Ferdi
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396035 , vital:69145 , xlink:href="https://www.ajol.info/index.php/aref/article/view/162150"
- Description: In South Africa the export sector is frequently accorded a special role in encouraging faster economic growth. Nonetheless, a question that remains unresolved is whether higher export growth indeed leads to higher economic growth and what particular role exports may play within the overall economic growth process of the country. This study applies Johansen’s cointegration procedure, impulse response functions, variance decomposition analysis and Granger causality tests to shed light on the channels through which export growth may impact South Africa’s economic growth rate. Quarterly time series data ranging from 1975q1 to 2012q4 is employed in the study’s empirical tests. The results support the notion that the role of exports lies in their ability to encourage investment and capital formation. While export growth directly supports higher economic growth in the short-run, the long-term effect was found to lie in supporting faster capital formation, and in turn, significantly increasing economic growth. Overall, a strategy of export-led growth that does not explicitly emphasize the export-capital-growth connection is likely to fall short of reflecting the dynamics contained within the exports-growth relationship in South Africa.
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Extended use of grey water for irrigating home gardens in an arid environment
- Al-Ismaili, Abdulrahim M, Ahmed, Mushtaque, Al-Busaidi, Ahmed, Al-Adawi, Seif, Tandlich, Roman, Al-Amri, Mohammed
- Authors: Al-Ismaili, Abdulrahim M , Ahmed, Mushtaque , Al-Busaidi, Ahmed , Al-Adawi, Seif , Tandlich, Roman , Al-Amri, Mohammed
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76048 , vital:30497 , https://doi.org/10.1007/s11356-017-8963-z
- Description: The use of treated grey water (GW) for home gardens, peri-urban agriculture and landscaping is becoming popular in many water stressed countries such as Oman. This study aims to investigate the treatment efficacy, health and chemical concerns, cost-benefits and maintenance protocol of a GW treatment system as well as the effect of irrigation with GW on crop yield. Therefore, a decentralized homemade GW treatment system was installed in a newly constructed house in Muscat, Oman and studied over a 2-year period. The treated GW was found to be suitable for irrigation as per Omani standards. GW when mixed with kitchen effluent substituted the use of nutrient supplements for plants and did not show any harmful chemical or biological contamination. The capital cost of the system was around US $980, and the annual operating cost was US $78 with annual income and savings from the system being around US $572 indicating a payback period of nearly 2 years. It was found that the system required simple but regular maintenance particularly cleaning of the top layer of the filter. It can be concluded from this study that such a GW system should be technically, economically and environmentally feasible in Oman. Also, wider acceptance by the general public to the idea of GW reuse will help in mitigating the water shortage problem of the country to some extent.
- Full Text:
- Authors: Al-Ismaili, Abdulrahim M , Ahmed, Mushtaque , Al-Busaidi, Ahmed , Al-Adawi, Seif , Tandlich, Roman , Al-Amri, Mohammed
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/76048 , vital:30497 , https://doi.org/10.1007/s11356-017-8963-z
- Description: The use of treated grey water (GW) for home gardens, peri-urban agriculture and landscaping is becoming popular in many water stressed countries such as Oman. This study aims to investigate the treatment efficacy, health and chemical concerns, cost-benefits and maintenance protocol of a GW treatment system as well as the effect of irrigation with GW on crop yield. Therefore, a decentralized homemade GW treatment system was installed in a newly constructed house in Muscat, Oman and studied over a 2-year period. The treated GW was found to be suitable for irrigation as per Omani standards. GW when mixed with kitchen effluent substituted the use of nutrient supplements for plants and did not show any harmful chemical or biological contamination. The capital cost of the system was around US $980, and the annual operating cost was US $78 with annual income and savings from the system being around US $572 indicating a payback period of nearly 2 years. It was found that the system required simple but regular maintenance particularly cleaning of the top layer of the filter. It can be concluded from this study that such a GW system should be technically, economically and environmentally feasible in Oman. Also, wider acceptance by the general public to the idea of GW reuse will help in mitigating the water shortage problem of the country to some extent.
- Full Text:
Extracellular Hsp90 and TGFP regulate adhesion, migration and anchorage independent growth in a paired colon cancer cell line model
- de la Mare, Jo-Anne, Jurgens, Tamarin, Edkins, Adrienne L
- Authors: de la Mare, Jo-Anne , Jurgens, Tamarin , Edkins, Adrienne L
- Date: 2017
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59920 , vital:27710 , https://doi.org/10.1186/s12885-017-3190-z
- Description: Tumour metastasis remains the major cause of death in cancer patients and, to date, the mechanism and signalling pathways governing this process are not completely understood. The TGF-ß pathway is the most commonly mutated pathway in cancer, however its role in cancer progression is controversial as it can function as both a promoter and a suppressor of metastasis. Although previous studies have suggested a role for the molecular chaperone Hsp90 in regulating the TGF-ß pathway, the level at which this occurs as well as the consequences in terms of colon cancer metastasis are unknown.
- Full Text:
- Authors: de la Mare, Jo-Anne , Jurgens, Tamarin , Edkins, Adrienne L
- Date: 2017
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59920 , vital:27710 , https://doi.org/10.1186/s12885-017-3190-z
- Description: Tumour metastasis remains the major cause of death in cancer patients and, to date, the mechanism and signalling pathways governing this process are not completely understood. The TGF-ß pathway is the most commonly mutated pathway in cancer, however its role in cancer progression is controversial as it can function as both a promoter and a suppressor of metastasis. Although previous studies have suggested a role for the molecular chaperone Hsp90 in regulating the TGF-ß pathway, the level at which this occurs as well as the consequences in terms of colon cancer metastasis are unknown.
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Facile synthesis of glutathione-l-Cysteine co-capped CdTe core shell system
- Daramola, Olamide A, Siwe-Noundou, Xavier, Krause, Rui W M, Marks, John A
- Authors: Daramola, Olamide A , Siwe-Noundou, Xavier , Krause, Rui W M , Marks, John A
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/195003 , vital:45518 , xlink:href="https://doi.org/10.1166/jnn.2017.13823"
- Description: Semiconductor nanoparticles also known as quantum dots (QDs) have been used in diverse areas of application due to their good optical and photo-physical properties. The synthesis of core–shell QDs have assisted to improve the stability of most nano-particles but the size and long term stability of such materials have been problematic. However, thiol-capped CdTe QDs have been regarded as some of the most widely synthesized nanoparticles due to their unique optical properties. The use of un-stable tellurium source such as NaHTe or highly toxic H2Te gas makes the reaction condition cumbersome. In this study, we prepared some CdTe QDs and core–shell QDs using K2TeO3 as a stable source of tellurium without inert gas protection. This was done using a co-capped bio-compatible coating such as cysteine and glutathione following a modified standard method to produce QDs in the yields of about 60 to 80%. All the synthesized materials were subsequently characterized using various characterization techniques. The systematic optimization of the reaction parameters such as reaction time, pH and mole ratio results with a drastic red shift in wavelength (546–600 nm) by the CdTe core proved that an extra material has been deposited unto the surface of the CdTe core. The 60 days stability test conducted demonstrated that the core–shell nanoparticles were quite stable. Since this reaction was performed under open air conditions and no special ligand or buffer solution was used, it may suitably be applied on an industrial scale.
- Full Text:
- Authors: Daramola, Olamide A , Siwe-Noundou, Xavier , Krause, Rui W M , Marks, John A
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/195003 , vital:45518 , xlink:href="https://doi.org/10.1166/jnn.2017.13823"
- Description: Semiconductor nanoparticles also known as quantum dots (QDs) have been used in diverse areas of application due to their good optical and photo-physical properties. The synthesis of core–shell QDs have assisted to improve the stability of most nano-particles but the size and long term stability of such materials have been problematic. However, thiol-capped CdTe QDs have been regarded as some of the most widely synthesized nanoparticles due to their unique optical properties. The use of un-stable tellurium source such as NaHTe or highly toxic H2Te gas makes the reaction condition cumbersome. In this study, we prepared some CdTe QDs and core–shell QDs using K2TeO3 as a stable source of tellurium without inert gas protection. This was done using a co-capped bio-compatible coating such as cysteine and glutathione following a modified standard method to produce QDs in the yields of about 60 to 80%. All the synthesized materials were subsequently characterized using various characterization techniques. The systematic optimization of the reaction parameters such as reaction time, pH and mole ratio results with a drastic red shift in wavelength (546–600 nm) by the CdTe core proved that an extra material has been deposited unto the surface of the CdTe core. The 60 days stability test conducted demonstrated that the core–shell nanoparticles were quite stable. Since this reaction was performed under open air conditions and no special ligand or buffer solution was used, it may suitably be applied on an industrial scale.
- Full Text:
Factors influencing the shape of CW-OSL signal obtained by stimulation of very deep traps in carbon-doped aluminium oxide: an experimental study
- Nyirenda, Angel N, Chithambo, Makaiko L
- Authors: Nyirenda, Angel N , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115493 , vital:34149 , https://doi.org/10.1016/j.jlumin.2017.07.016
- Description: The optically stimulated luminescence from carbon-doped aluminium oxide (α-Al2O3:C) displays a peak with time under certain measurement conditions. In this paper, we present factors that influence the peak-like shape of continuous-wave optically stimulated luminescence (CW-OSL) signal. The report is based on the experimental study of OSL signals obtained by stimulation of very deep traps in α-Al2O3:C. Methods exploiting post-irradiation annealing, variable dose and temperature dependent OSL measurements were used in the investigation. It is found that the rising part of the CW-OSL peak is obtained when the rate of retrapping at the most optically active trap (main trap) exceeds the rate of direct radiative recombination following optical release of charges from all optically active traps. This is possible if, during optical stimulation, the primary trap responsible for OSL i.e. the main trap, is substantially unoccupied and the very deep, donor traps are substantially filled up. The rate of charge retrapping itself is deduced to depend on the occupancy of the acceptor traps i.e. shallow, main and secondary traps; concentration of charge carriers in the very deep, donor traps; the post-irradiation annealing temperature and the temperature at which the OSL is measured.
- Full Text: false
- Authors: Nyirenda, Angel N , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/115493 , vital:34149 , https://doi.org/10.1016/j.jlumin.2017.07.016
- Description: The optically stimulated luminescence from carbon-doped aluminium oxide (α-Al2O3:C) displays a peak with time under certain measurement conditions. In this paper, we present factors that influence the peak-like shape of continuous-wave optically stimulated luminescence (CW-OSL) signal. The report is based on the experimental study of OSL signals obtained by stimulation of very deep traps in α-Al2O3:C. Methods exploiting post-irradiation annealing, variable dose and temperature dependent OSL measurements were used in the investigation. It is found that the rising part of the CW-OSL peak is obtained when the rate of retrapping at the most optically active trap (main trap) exceeds the rate of direct radiative recombination following optical release of charges from all optically active traps. This is possible if, during optical stimulation, the primary trap responsible for OSL i.e. the main trap, is substantially unoccupied and the very deep, donor traps are substantially filled up. The rate of charge retrapping itself is deduced to depend on the occupancy of the acceptor traps i.e. shallow, main and secondary traps; concentration of charge carriers in the very deep, donor traps; the post-irradiation annealing temperature and the temperature at which the OSL is measured.
- Full Text: false
Features of an annealing-induced thermoluminescence peak in 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/10962/116013 , vital:34289 , DOI: 10.1016/j.optmat.2017.05.034
- Description: We report the thermoluminescence glow curves of beta irradiated single crystal α-Al2O3:C,Mg after annealing at 700 and 900 °C. A glow curve measured at 1 °C/s from samples irradiated to 1 Gy following annealing at 700 and 900 °C shows a high intensity peak at 163 °C and seven secondary peaks of weaker intensity at 43, 73, 100, 195, 280, 329 and 370 °C. Comparing the position of the peaks in the annealed samples with those in an un-annealed one, it is observed that the peak at 100 °C appears only after annealing at and above 700 °C. Kinetic analysis of this annealing-induced peak was carried out using the initial rise, whole glow peak, peak shape, curve fitting and variable heating rate methods. The order of kinetics of the peak was determined as first order using various methods including the Tm-Tstop technique and the dependence of Tm on irradiation dose. The activation energy of the peak is about 1.01 eV and the frequency factor of the order of 1012 s−1. The peak was found to be affected by thermal quenching in analysis based on change of peak intensity with heating rate. The activation energy of thermal quenching was evaluated as 1.06 ± 0.08 eV. We speculate that the annealing-induced peak is due to formation of a new electron trap after destruction of the F22+(2 Mg) centre when the sample is annealed at 700 °C. The annealing-induced peak fades with storage between irradiation and measurement. It was also concluded that electrons from traps corresponding to secondary peaks get re-trapped at the main electron trap.
- Full Text: false
- Authors: Kalita, Jitumani M , Chithambo, Makaiko L
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/116013 , vital:34289 , DOI: 10.1016/j.optmat.2017.05.034
- Description: We report the thermoluminescence glow curves of beta irradiated single crystal α-Al2O3:C,Mg after annealing at 700 and 900 °C. A glow curve measured at 1 °C/s from samples irradiated to 1 Gy following annealing at 700 and 900 °C shows a high intensity peak at 163 °C and seven secondary peaks of weaker intensity at 43, 73, 100, 195, 280, 329 and 370 °C. Comparing the position of the peaks in the annealed samples with those in an un-annealed one, it is observed that the peak at 100 °C appears only after annealing at and above 700 °C. Kinetic analysis of this annealing-induced peak was carried out using the initial rise, whole glow peak, peak shape, curve fitting and variable heating rate methods. The order of kinetics of the peak was determined as first order using various methods including the Tm-Tstop technique and the dependence of Tm on irradiation dose. The activation energy of the peak is about 1.01 eV and the frequency factor of the order of 1012 s−1. The peak was found to be affected by thermal quenching in analysis based on change of peak intensity with heating rate. The activation energy of thermal quenching was evaluated as 1.06 ± 0.08 eV. We speculate that the annealing-induced peak is due to formation of a new electron trap after destruction of the F22+(2 Mg) centre when the sample is annealed at 700 °C. The annealing-induced peak fades with storage between irradiation and measurement. It was also concluded that electrons from traps corresponding to secondary peaks get re-trapped at the main electron trap.
- Full Text: false
Ferrocenyl and organic novobiocin derivatives: synthesis and their in vitro biological activity
- Mbaba, Mziyanda, Mabhula, Amanda N, Boel, Natasha, Edkins, Adrienne L, Isaacs, Michelle, Hoppe, Heinrich C, Khanye, Setshaba D
- Authors: Mbaba, Mziyanda , Mabhula, Amanda N , Boel, Natasha , Edkins, Adrienne L , Isaacs, Michelle , Hoppe, Heinrich C , Khanye, Setshaba D
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66189 , vital:28914 , https://doi.org/10.1016/j.jinorgbio.2017.04.014
- Description: publisher version , A focused series of novobiocin derivatives containing a ferrocene unit together with their corresponding organic novobiocin analogues have been synthesized in modest to good yields. These compounds were screened for biological activity against a chloroquine-sensitive strain of Plasmodium falciparum (3D7) and human breast cancer cell line (HCC38). With the exception of compounds 5c and 5d, the general trend observed is that incorporation of the ferrocene moiety into novobiocin scaffold resulted in compounds 6a–d/6f showing enhanced activity compared to organic analogues 5a–b and 5e–f.
- Full Text: false
- Authors: Mbaba, Mziyanda , Mabhula, Amanda N , Boel, Natasha , Edkins, Adrienne L , Isaacs, Michelle , Hoppe, Heinrich C , Khanye, Setshaba D
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/66189 , vital:28914 , https://doi.org/10.1016/j.jinorgbio.2017.04.014
- Description: publisher version , A focused series of novobiocin derivatives containing a ferrocene unit together with their corresponding organic novobiocin analogues have been synthesized in modest to good yields. These compounds were screened for biological activity against a chloroquine-sensitive strain of Plasmodium falciparum (3D7) and human breast cancer cell line (HCC38). With the exception of compounds 5c and 5d, the general trend observed is that incorporation of the ferrocene moiety into novobiocin scaffold resulted in compounds 6a–d/6f showing enhanced activity compared to organic analogues 5a–b and 5e–f.
- Full Text: false
Fibronectin is a stress responsive gene regulated by HSF1 in response to geldanamycin
- Dhanani, Karim C H, Samson, William J, Edkins, Adrienne L
- Authors: Dhanani, Karim C H , Samson, William J , Edkins, Adrienne L
- Date: 2017
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59931 , vital:27711 , https://doi:10.1038/s41598-017-18061-y
- Description: Fibronectin is an extracellular matrix glycoprotein with key roles in cell adhesion and migration. Hsp90 binds directly to fibronectin and Hsp90 depletion regulates fibronectin matrix stability. Where inhibition of Hsp90 with a C-terminal inhibitor, novobiocin, reduced the fibronectin matrix, treatment with an N-terminal inhibitor, geldanamycin, increased fibronectin levels. Geldanamycin treatment induced a stress response and a strong dose and time dependent increase in fibronectin mRNA via activation of the fibronectin promoter. Three putative heat shock elements (HSEs) were identified in the fibronectin promoter. Loss of two of these HSEs reduced both basal and geldanamycin-induced promoter activity, as did inhibition of the stress-responsive transcription factor HSF1. Binding of HSF1 to one of the putative HSE was confirmed by ChIP under basal conditions, and occupancy shown to increase with geldanamycin treatment. These data support the hypothesis that fibronectin is stress-responsive and a functional HSF1 target gene. COLA42 and LAMB3 mRNA levels were also increased with geldanamycin indicating that regulation of extracellular matrix (ECM) genes by HSF1 may be a wider phenomenon. Taken together, these data have implications for our understanding of ECM dynamics in stress-related diseases in which HSF1 is activated, and where the clinical application of N-terminal Hsp90 inhibitors is intended.
- Full Text:
- Authors: Dhanani, Karim C H , Samson, William J , Edkins, Adrienne L
- Date: 2017
- Language: English
- Type: article , text
- Identifier: http://hdl.handle.net/10962/59931 , vital:27711 , https://doi:10.1038/s41598-017-18061-y
- Description: Fibronectin is an extracellular matrix glycoprotein with key roles in cell adhesion and migration. Hsp90 binds directly to fibronectin and Hsp90 depletion regulates fibronectin matrix stability. Where inhibition of Hsp90 with a C-terminal inhibitor, novobiocin, reduced the fibronectin matrix, treatment with an N-terminal inhibitor, geldanamycin, increased fibronectin levels. Geldanamycin treatment induced a stress response and a strong dose and time dependent increase in fibronectin mRNA via activation of the fibronectin promoter. Three putative heat shock elements (HSEs) were identified in the fibronectin promoter. Loss of two of these HSEs reduced both basal and geldanamycin-induced promoter activity, as did inhibition of the stress-responsive transcription factor HSF1. Binding of HSF1 to one of the putative HSE was confirmed by ChIP under basal conditions, and occupancy shown to increase with geldanamycin treatment. These data support the hypothesis that fibronectin is stress-responsive and a functional HSF1 target gene. COLA42 and LAMB3 mRNA levels were also increased with geldanamycin indicating that regulation of extracellular matrix (ECM) genes by HSF1 may be a wider phenomenon. Taken together, these data have implications for our understanding of ECM dynamics in stress-related diseases in which HSF1 is activated, and where the clinical application of N-terminal Hsp90 inhibitors is intended.
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