Contributions to the study of nonholonomic Riemannian manifolds
- Authors: Barrett, Dennis Ian
- Date: 2017
- Subjects: Riemannian manifolds , Curvature , Lie groups , Geometry, Riemannian , Tensor fields
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/7554 , vital:21272 , DOI https://doi.org/10.21504/10962/7554
- Description: In this thesis we consider nonholonomic Riemannian manifolds, and in particular, left- invariant nonholonomic Riemannian structures on Lie groups. These structures are closely related to mechanical systems with (positive definite) quadratic Lagrangians and nonholo- nomic constraints linear in velocities. In the first chapter, we review basic concepts of non- holonomic Riemannian geometry, including the left-invariant structures. We also examine the class of left-invariant structures with so-called Cartan-Schouten connections. The second chapter investigates the curvature of nonholonomic Riemannian manifolds and the Schouten and Wagner curvature tensors. The Schouten tensor is canonically associated to every non- holonomic Riemannian structure (in particular, we use it to define isometric invariants for structures on three-dimensional manifolds). By contrast, the Wagner tensor is not generally intrinsic, but can be used to characterise flat structures (i.e., those whose associated parallel transport is path-independent). The third chapter considers equivalence of nonholonomic Rie- mannian manifolds, particularly up to nonholonomic isometry. We also introduce the notion of a nonholonomic Riemannian submanifold, and investigate the conditions under which such a submanifold inherits its geometry from the enveloping space. The latter problem involves the concept of a geodesically invariant distribution, and we show it is also related to the curvature. In the last chapter we specialise to three-dimensional nonholonomic Riemannian manifolds. We consider the equivalence of such structures up to nonholonomic isometry and rescaling, and classify the left-invariant structures on the (three-dimensional) simply connected Lie groups. We also characterise the flat structures in three dimensions, and then classify the flat structures on the simply connected Lie groups. Lastly, we consider three typical examples of (left-invariant) nonholonomic Riemannian structures on three-dimensional Lie groups, two of which arise from problems in classical mechanics (viz., the Chaplygin problem and the Suslov problem). , Thesis (PhD) -- Faculty of Science, Mathematics (Pure and Applied), 2017
- Full Text:
- Date Issued: 2017
- Authors: Barrett, Dennis Ian
- Date: 2017
- Subjects: Riemannian manifolds , Curvature , Lie groups , Geometry, Riemannian , Tensor fields
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/7554 , vital:21272 , DOI https://doi.org/10.21504/10962/7554
- Description: In this thesis we consider nonholonomic Riemannian manifolds, and in particular, left- invariant nonholonomic Riemannian structures on Lie groups. These structures are closely related to mechanical systems with (positive definite) quadratic Lagrangians and nonholo- nomic constraints linear in velocities. In the first chapter, we review basic concepts of non- holonomic Riemannian geometry, including the left-invariant structures. We also examine the class of left-invariant structures with so-called Cartan-Schouten connections. The second chapter investigates the curvature of nonholonomic Riemannian manifolds and the Schouten and Wagner curvature tensors. The Schouten tensor is canonically associated to every non- holonomic Riemannian structure (in particular, we use it to define isometric invariants for structures on three-dimensional manifolds). By contrast, the Wagner tensor is not generally intrinsic, but can be used to characterise flat structures (i.e., those whose associated parallel transport is path-independent). The third chapter considers equivalence of nonholonomic Rie- mannian manifolds, particularly up to nonholonomic isometry. We also introduce the notion of a nonholonomic Riemannian submanifold, and investigate the conditions under which such a submanifold inherits its geometry from the enveloping space. The latter problem involves the concept of a geodesically invariant distribution, and we show it is also related to the curvature. In the last chapter we specialise to three-dimensional nonholonomic Riemannian manifolds. We consider the equivalence of such structures up to nonholonomic isometry and rescaling, and classify the left-invariant structures on the (three-dimensional) simply connected Lie groups. We also characterise the flat structures in three dimensions, and then classify the flat structures on the simply connected Lie groups. Lastly, we consider three typical examples of (left-invariant) nonholonomic Riemannian structures on three-dimensional Lie groups, two of which arise from problems in classical mechanics (viz., the Chaplygin problem and the Suslov problem). , Thesis (PhD) -- Faculty of Science, Mathematics (Pure and Applied), 2017
- Full Text:
- Date Issued: 2017
Photophysical properties of a series of alloyed and non-alloyed water-soluble l-cysteine-capped core quantum dots
- Adegoke, Oluwasesan, Nyokong, Tebello, Forbes, Patricia B
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188486 , vital:44758 , xlink:href="https://doi.org/10.1016/j.jallcom.2016.10.276"
- Description: Photophysical properties of quantum dots (QDs) such as their photoluminescence (PL) quantum yield (QY), exciton lifetime and PL stability are important parameters used to unravel their chemical and physical characteristics. In this work, we have comparatively investigated the photophysical properties of a series of L-cysteine-capped non-alloyed (CdTe and CdSe) and alloyed (CdZnTe, CdSeS, CdSeTe and CdSeTeS) core QDs. Each of the QDs varied in their size and PL emission wavelength. We observe no physical relationship between the PL QY of the QDs and their PL stability. Based on the PL stability assessment, CdTe QDs with a high PL QY value of 88% exhibited poor PL stability while moderate PL stability was observed for CdZnTe (QY = 78%); CdSe (QY = 3%); and CdSeTe QDs (QY = ∼3%). Alloyed CdSeS (QY = ∼69%) and CdSeTeS (QY = 23%) QDs exhibited good PL stability and can serve as potential fluorophores for a wide range of chemical and biological applications. Generally, it is proposed that the structural nature of the QDs played a significant role in their overall photophysical properties. The information provided in this work will assist in the selection of core QDs suitable for different applications.
- Full Text:
- Date Issued: 2017
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188486 , vital:44758 , xlink:href="https://doi.org/10.1016/j.jallcom.2016.10.276"
- Description: Photophysical properties of quantum dots (QDs) such as their photoluminescence (PL) quantum yield (QY), exciton lifetime and PL stability are important parameters used to unravel their chemical and physical characteristics. In this work, we have comparatively investigated the photophysical properties of a series of L-cysteine-capped non-alloyed (CdTe and CdSe) and alloyed (CdZnTe, CdSeS, CdSeTe and CdSeTeS) core QDs. Each of the QDs varied in their size and PL emission wavelength. We observe no physical relationship between the PL QY of the QDs and their PL stability. Based on the PL stability assessment, CdTe QDs with a high PL QY value of 88% exhibited poor PL stability while moderate PL stability was observed for CdZnTe (QY = 78%); CdSe (QY = 3%); and CdSeTe QDs (QY = ∼3%). Alloyed CdSeS (QY = ∼69%) and CdSeTeS (QY = 23%) QDs exhibited good PL stability and can serve as potential fluorophores for a wide range of chemical and biological applications. Generally, it is proposed that the structural nature of the QDs played a significant role in their overall photophysical properties. The information provided in this work will assist in the selection of core QDs suitable for different applications.
- Full Text:
- Date Issued: 2017
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:
- Date Issued: 2017
- 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:
- Date Issued: 2017
Performing mindful creativity
- Authors: Krueger, Anton
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/225574 , vital:49236 , xlink:href="https://doi.org/10.5920/pam.2017.05"
- Description: This essay is grounded in the practical experience of three South African theatre practitioners who have all had some experience of mindfulness. It's based on interviews conducted with a performer (Andrew Buckland), a director (Janni Young), and a designer (Illka Louw). The aim of my conversations with these three was to explore ways in which mindfulness continues to enhance artistic practises, seeing our dialogues as a springboard to exploring intersections between creative practise and theories about mindfulness. To assist me in this process, I also interviewed Rob Nairn - co-founder of both the Mindfulness Association (UK) and Mindfulness Africa (RSA) - about key issues highlighting convergences between creativity and mindfulness. Some of the issues which are addressed include: the artist's relationship with fear, differing definitions of the value of conceptualisation, as well as whether or not the monkey mind (that is, the wandering mind) might hamper or help creativity.
- Full Text:
- Date Issued: 2017
- Authors: Krueger, Anton
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/225574 , vital:49236 , xlink:href="https://doi.org/10.5920/pam.2017.05"
- Description: This essay is grounded in the practical experience of three South African theatre practitioners who have all had some experience of mindfulness. It's based on interviews conducted with a performer (Andrew Buckland), a director (Janni Young), and a designer (Illka Louw). The aim of my conversations with these three was to explore ways in which mindfulness continues to enhance artistic practises, seeing our dialogues as a springboard to exploring intersections between creative practise and theories about mindfulness. To assist me in this process, I also interviewed Rob Nairn - co-founder of both the Mindfulness Association (UK) and Mindfulness Africa (RSA) - about key issues highlighting convergences between creativity and mindfulness. Some of the issues which are addressed include: the artist's relationship with fear, differing definitions of the value of conceptualisation, as well as whether or not the monkey mind (that is, the wandering mind) might hamper or help creativity.
- Full Text:
- Date Issued: 2017
Education in the Anthropocene: Ethico-moral dimensions and critical realist openings
- Authors: Olvitt, Lausanne L
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/372753 , vital:66620 , xlink:href="https://doi.org/10.1080/03057240.2017.1342613"
- Description: Human-induced changes in planetary bio-geo-chemical processes have tipped earth into a newly-proposed geological epoch: the Anthropocene, which places moral and ethical demands on people regarding who should take responsibility for the well-being of people and planet, how, and why. Drawing generally on critical realist ontology, and more particularly on Roy Bhaskar’s concept of the person as a ‘four-planar social being’ living in the world as a laminated ontological whole, the article examines the dimensions of people’s ethico-moral engagement with the Anthropocene and considers what types of learning processes might enable people to understand, live in, and co-create this period known as ‘the Anthropocene’ in just, care-filled and—where necessary—transformative ways. The article points to the need for a radical re-orientation of education systems in the light of ethico-moral challenges that come to prominence in the Anthropocene, and argues for learning processes that nurture individual and collective moral agency through transformative, even transgressive, learning processes that are relational, humble, interdisciplinary, multi-perspectival, systemic, reality-congruent and contextually responsive.
- Full Text:
- Date Issued: 2017
- Authors: Olvitt, Lausanne L
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/372753 , vital:66620 , xlink:href="https://doi.org/10.1080/03057240.2017.1342613"
- Description: Human-induced changes in planetary bio-geo-chemical processes have tipped earth into a newly-proposed geological epoch: the Anthropocene, which places moral and ethical demands on people regarding who should take responsibility for the well-being of people and planet, how, and why. Drawing generally on critical realist ontology, and more particularly on Roy Bhaskar’s concept of the person as a ‘four-planar social being’ living in the world as a laminated ontological whole, the article examines the dimensions of people’s ethico-moral engagement with the Anthropocene and considers what types of learning processes might enable people to understand, live in, and co-create this period known as ‘the Anthropocene’ in just, care-filled and—where necessary—transformative ways. The article points to the need for a radical re-orientation of education systems in the light of ethico-moral challenges that come to prominence in the Anthropocene, and argues for learning processes that nurture individual and collective moral agency through transformative, even transgressive, learning processes that are relational, humble, interdisciplinary, multi-perspectival, systemic, reality-congruent and contextually responsive.
- Full Text:
- Date Issued: 2017
Modelling dialectical processes in environmental learning
- Authors: Schudel, Ingrid J
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/294409 , vital:57219 , xlink:href="https://doi.org/10.1080/14767430.2017.1288061"
- Description: This paper describes a critical realist intensive case study, which develops and tests a ‘dialectic process model of transformative learning’. The model is inspired by Bhaskar's (1993) onto-axiological chain (or MELD Schema) as outlined in his formulation of dialectical critical realism. The study describes transformative environmental learning processes focusing on food security in two primary schools in rural South Africa. The model elaborates on the four links in the onto-axiological chain by describing four knowledge interests across the two cases: knowledge of ‘what is and what is not’, knowledge of ‘what could be’, knowledge of ‘what should be’, and knowledge of ‘what can be’. The model also highlights the emergent nature of epistemic relations in transformative learning processes. The paper discusses the model in relation to a transformative, open-ended and context specific approach to Environmental Education (EE)/ESD. The paper illustrates that Bhaskar’s MELD is a robust schema for investigating learning-led change in EE and suggests its relevance in other research contexts concerned with societal transformation.
- Full Text:
- Date Issued: 2017
- Authors: Schudel, Ingrid J
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/294409 , vital:57219 , xlink:href="https://doi.org/10.1080/14767430.2017.1288061"
- Description: This paper describes a critical realist intensive case study, which develops and tests a ‘dialectic process model of transformative learning’. The model is inspired by Bhaskar's (1993) onto-axiological chain (or MELD Schema) as outlined in his formulation of dialectical critical realism. The study describes transformative environmental learning processes focusing on food security in two primary schools in rural South Africa. The model elaborates on the four links in the onto-axiological chain by describing four knowledge interests across the two cases: knowledge of ‘what is and what is not’, knowledge of ‘what could be’, knowledge of ‘what should be’, and knowledge of ‘what can be’. The model also highlights the emergent nature of epistemic relations in transformative learning processes. The paper discusses the model in relation to a transformative, open-ended and context specific approach to Environmental Education (EE)/ESD. The paper illustrates that Bhaskar’s MELD is a robust schema for investigating learning-led change in EE and suggests its relevance in other research contexts concerned with societal transformation.
- Full Text:
- Date Issued: 2017
Aspect and slope as determinants of vegetation composition and soil properties in coastal forest backdunes of Eastern Cape, South Africa
- Ruwanza, Sheunesu, Shackleton, Charlie M
- Authors: Ruwanza, Sheunesu , Shackleton, Charlie M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180376 , vital:43358 , xlink:href="https://doi.org/10.1111/aje.12343"
- Description: Coastal sand dune ecosystems are subjected to many stress and disturbance factors that are particularly high in the foredunes compared to the backdunes. Although a few studies have been conducted on eastern coastline sand dunes of South Africa, none have examined the relationship between aspect and slope on vegetation composition and soil properties of coastal forest backdunes. Vegetation and soil sampling were conducted in 11 transects, each with four plots measuring 10 × 10 m, located on the seaward and landward sides and on middle and lower slopes of backdunes of Bathurst coastal forest. A total of 39 species were identified, of which 23 were trees and shrubs, thirteen were forbs and three were grasses. The data show that both aspect and slope had limited influence on vegetation community assemblage and soil properties, but had significant effects on individual species distribution. There was a grass-dominated community on the middle slope and a tree- and shrub- dominated community on the lower slope. These two plant communities act as the required coastal forest ecosystem engineer driving variability in soil properties between the slopes, the most prominent being high soil nutrients and moisture in the lower slopes compared to the middle slopes.
- Full Text:
- Date Issued: 2017
- Authors: Ruwanza, Sheunesu , Shackleton, Charlie M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180376 , vital:43358 , xlink:href="https://doi.org/10.1111/aje.12343"
- Description: Coastal sand dune ecosystems are subjected to many stress and disturbance factors that are particularly high in the foredunes compared to the backdunes. Although a few studies have been conducted on eastern coastline sand dunes of South Africa, none have examined the relationship between aspect and slope on vegetation composition and soil properties of coastal forest backdunes. Vegetation and soil sampling were conducted in 11 transects, each with four plots measuring 10 × 10 m, located on the seaward and landward sides and on middle and lower slopes of backdunes of Bathurst coastal forest. A total of 39 species were identified, of which 23 were trees and shrubs, thirteen were forbs and three were grasses. The data show that both aspect and slope had limited influence on vegetation community assemblage and soil properties, but had significant effects on individual species distribution. There was a grass-dominated community on the middle slope and a tree- and shrub- dominated community on the lower slope. These two plant communities act as the required coastal forest ecosystem engineer driving variability in soil properties between the slopes, the most prominent being high soil nutrients and moisture in the lower slopes compared to the middle slopes.
- Full Text:
- Date Issued: 2017
Ecosystem-scale impacts of non-timber forest product harvesting: Effects on soil nutrients
- Ruwanza, Sheunesu, Shackleton, Charlie M
- Authors: Ruwanza, Sheunesu , Shackleton, Charlie M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180099 , vital:43309 , xlink:href="https://doi.org/10.1111/1365-2664.12891"
- Description: The harvesting of non-timber forest products (NTFPs) is a global phenomenon, the sustainability of which has been studied for many species at the individual and population level. However, the broader scale impacts of NTFP harvesting have been acknowledged but rarely examined. We assessed plant size and the soil attributes undercanopy and in the open, in replicate, paired harvested and non-harvested sites for three NTFPs differing in the extent of biomass removed, i.e. timber for firewood from a tree (Acacia karroo), fruits from a cactus (Opunita ficus-indica) and flowering culms from a grass (Cymbopogon marginatus). Soil variables tested included pH, resistivity, P, total N, nitrate nitrogen, ammonium nitrogen, K, Na, Ca and Mg. The extent of loss of soil nutrients decreased across the three NTFPs relative to the proportion of biomass removed. Thus, significant differences in more soil variables were evident for the firewood species, least for the fruit species and intermediate for the grass species. Lower soil pH, P, C and K were evident in soils collected underneath A. karroo, while losses in cations of Na, Ca and Mg were reported in soils underneath C. marginatus, and only NO3N losses were recorded underneath O. ficus-indica. Our study reveals that while non-timber forest product (NTFP) harvesting may affect soil nutrients, this is not uniform between species and is likely to be a function of the extent of biomass removed and harvesting frequency. This indicates the need for caution in generalisations about the ecosystem-level impacts of NTFP harvesting as well as a concerted effort to better understand impacts at a greater range of scales than has been the case to date.
- Full Text:
- Date Issued: 2017
- Authors: Ruwanza, Sheunesu , Shackleton, Charlie M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180099 , vital:43309 , xlink:href="https://doi.org/10.1111/1365-2664.12891"
- Description: The harvesting of non-timber forest products (NTFPs) is a global phenomenon, the sustainability of which has been studied for many species at the individual and population level. However, the broader scale impacts of NTFP harvesting have been acknowledged but rarely examined. We assessed plant size and the soil attributes undercanopy and in the open, in replicate, paired harvested and non-harvested sites for three NTFPs differing in the extent of biomass removed, i.e. timber for firewood from a tree (Acacia karroo), fruits from a cactus (Opunita ficus-indica) and flowering culms from a grass (Cymbopogon marginatus). Soil variables tested included pH, resistivity, P, total N, nitrate nitrogen, ammonium nitrogen, K, Na, Ca and Mg. The extent of loss of soil nutrients decreased across the three NTFPs relative to the proportion of biomass removed. Thus, significant differences in more soil variables were evident for the firewood species, least for the fruit species and intermediate for the grass species. Lower soil pH, P, C and K were evident in soils collected underneath A. karroo, while losses in cations of Na, Ca and Mg were reported in soils underneath C. marginatus, and only NO3N losses were recorded underneath O. ficus-indica. Our study reveals that while non-timber forest product (NTFP) harvesting may affect soil nutrients, this is not uniform between species and is likely to be a function of the extent of biomass removed and harvesting frequency. This indicates the need for caution in generalisations about the ecosystem-level impacts of NTFP harvesting as well as a concerted effort to better understand impacts at a greater range of scales than has been the case to date.
- Full Text:
- Date Issued: 2017
The effects of expansive shrubs on plant species richness and soils in semi-arid communal lands, South Africa
- Sholto-Douglas, Craig, Shackleton, Charlie M, Ruwanza, Sheunesu, Dold, Tony
- Authors: Sholto-Douglas, Craig , Shackleton, Charlie M , Ruwanza, Sheunesu , Dold, Tony
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/398394 , vital:69408 , xlink:href="https://doi.org/10.1002/ldr.2745"
- Description: Expansion by expansive species can have severe ecological, social and economic impacts through the reduction of ecosystem goods and services and species richness. However, expansion by expansive species may also offer benefits to ecosystems and humans, through the supply of ecosystem goods and services (such as firewood, fodder and fruits), as well as potentially offering refugia in heavily used landscapes. Here, we examine the effects of four expansive dwarf shrub species (Aspalathus subtingens, Dicerothamnus rhinocerotis, Pteronia incana and Oedera genistifolia) on plant species richness (at the point scale), vegetation cover, soil properties and whether the expansive species offer refugia to other species. Plant species richness, cover and soil properties were recorded in 1-m2 quadrats located within a mosaic of expanded and non-expanded patches for the four expansive shrub species. Plant species richness was significantly higher in the non-expanded areas compared to the expanded ones for all four expansive species. Some of the expansive shrubs provided refugia to certain plant species and limited the frequency of other species. With regard to species composition, there was little separation of expanded and non-expanded samples within sites, indicating that the site factors were stronger determinants of plant species richness and composition than expansion. Therefore, it is more likely that the reduction in species richness in expanded sites is caused by multiple drivers, including vegetation attributes cover, litter cover and soil nutrients (organic C, Zn and P) and soil compaction.
- Full Text:
- Date Issued: 2017
- Authors: Sholto-Douglas, Craig , Shackleton, Charlie M , Ruwanza, Sheunesu , Dold, Tony
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/398394 , vital:69408 , xlink:href="https://doi.org/10.1002/ldr.2745"
- Description: Expansion by expansive species can have severe ecological, social and economic impacts through the reduction of ecosystem goods and services and species richness. However, expansion by expansive species may also offer benefits to ecosystems and humans, through the supply of ecosystem goods and services (such as firewood, fodder and fruits), as well as potentially offering refugia in heavily used landscapes. Here, we examine the effects of four expansive dwarf shrub species (Aspalathus subtingens, Dicerothamnus rhinocerotis, Pteronia incana and Oedera genistifolia) on plant species richness (at the point scale), vegetation cover, soil properties and whether the expansive species offer refugia to other species. Plant species richness, cover and soil properties were recorded in 1-m2 quadrats located within a mosaic of expanded and non-expanded patches for the four expansive shrub species. Plant species richness was significantly higher in the non-expanded areas compared to the expanded ones for all four expansive species. Some of the expansive shrubs provided refugia to certain plant species and limited the frequency of other species. With regard to species composition, there was little separation of expanded and non-expanded samples within sites, indicating that the site factors were stronger determinants of plant species richness and composition than expansion. Therefore, it is more likely that the reduction in species richness in expanded sites is caused by multiple drivers, including vegetation attributes cover, litter cover and soil nutrients (organic C, Zn and P) and soil compaction.
- Full Text:
- Date Issued: 2017
A perfect end: A study of syllable codas in South African Sign Language
- Köhlo, Mikhaela D.K., Siebörger, Ian, Bennett, William G
- Authors: Köhlo, Mikhaela D.K. , Siebörger, Ian , Bennett, William G
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/385295 , vital:68005 , xlink:href="https://www.ajol.info/index.php/splp/article/view/156629"
- Description: South African Sign Language (SASL) is an understudied language with a rich and interesting phonology. For instance, while the language allows onsetless syllables, it does not allow codaless syllables, except in a small class of signs which do not include path movement. This article identifies and defines possible constraints on syllable codas in SASL. Using a video dictionary as data, we have coded handshapes at locations occurring at the onset and coda of the more common signs in the lexicon. In handshape, it has been found that the selected fingers may move to create different handshapes in the coda position, but that these coda handshapes are often [1], [5], [A], [Å] or [S], which are the unmarked handshapes of the non-dominant hand in asymmetrical two-handed signs (Sandler and Lillo-Martin 2006). Furthermore, the joint specification for the selected fingers can also vary in the coda position, but there appear to be strict limitations on which joint combinations are permitted in the onset-coda relationship. There are also constraints on coda location. The major body region can change within a single syllable, and the preferred body regions in the coda position are [body] and [H2]. It is evident not only that handshape and location constraints occur at the coda position, but that these constraints show patterns similar to coda neutralisation in many spoken languages.
- Full Text:
- Date Issued: 2017
- Authors: Köhlo, Mikhaela D.K. , Siebörger, Ian , Bennett, William G
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/385295 , vital:68005 , xlink:href="https://www.ajol.info/index.php/splp/article/view/156629"
- Description: South African Sign Language (SASL) is an understudied language with a rich and interesting phonology. For instance, while the language allows onsetless syllables, it does not allow codaless syllables, except in a small class of signs which do not include path movement. This article identifies and defines possible constraints on syllable codas in SASL. Using a video dictionary as data, we have coded handshapes at locations occurring at the onset and coda of the more common signs in the lexicon. In handshape, it has been found that the selected fingers may move to create different handshapes in the coda position, but that these coda handshapes are often [1], [5], [A], [Å] or [S], which are the unmarked handshapes of the non-dominant hand in asymmetrical two-handed signs (Sandler and Lillo-Martin 2006). Furthermore, the joint specification for the selected fingers can also vary in the coda position, but there appear to be strict limitations on which joint combinations are permitted in the onset-coda relationship. There are also constraints on coda location. The major body region can change within a single syllable, and the preferred body regions in the coda position are [body] and [H2]. It is evident not only that handshape and location constraints occur at the coda position, but that these constraints show patterns similar to coda neutralisation in many spoken languages.
- Full Text:
- Date Issued: 2017
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:
- Date Issued: 2017
- 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:
- Date Issued: 2017
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:
- Date Issued: 2017
- 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:
- Date Issued: 2017
Integrating biodiversity considerations into urban golf courses: Managers’ perceptions and woody plant diversity in the Eastern Cape, South Africa
- Jarrett, Mitchell, Shackleton, Charlie M
- Authors: Jarrett, Mitchell , Shackleton, Charlie M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180353 , vital:43356 , xlink:href="https://doi.org/10.1080/1747423X.2017.1325525"
- Description: Rapid rates of urbanisation affect biodiversity through habitat fragmentation and loss. Because urban golf courses are large green spaces, they potentially harbour much biodiversity if managed for such. The area of untransformed land of golf courses in the Eastern Cape (South Africa) was determined using Geographic Information System (GIS), the woody plant composition of a subsample was determined by field sampling and the greenkeepers were interviewed. There was a significant relationship between climate and woody cover, species richness and percentage native plants but not species diversity. There was no relationship between management scores and species richness, diversity and percentage native. Significant relationships were evident between woody plant species richness and course income, number of grounds staff, number of club members and greenkeepers’ years of experience. These results suggest a complex suite of factors that play a role in the woody plant composition of urban golf courses and their contribution to urban biodiversity.
- Full Text:
- Date Issued: 2017
- Authors: Jarrett, Mitchell , Shackleton, Charlie M
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180353 , vital:43356 , xlink:href="https://doi.org/10.1080/1747423X.2017.1325525"
- Description: Rapid rates of urbanisation affect biodiversity through habitat fragmentation and loss. Because urban golf courses are large green spaces, they potentially harbour much biodiversity if managed for such. The area of untransformed land of golf courses in the Eastern Cape (South Africa) was determined using Geographic Information System (GIS), the woody plant composition of a subsample was determined by field sampling and the greenkeepers were interviewed. There was a significant relationship between climate and woody cover, species richness and percentage native plants but not species diversity. There was no relationship between management scores and species richness, diversity and percentage native. Significant relationships were evident between woody plant species richness and course income, number of grounds staff, number of club members and greenkeepers’ years of experience. These results suggest a complex suite of factors that play a role in the woody plant composition of urban golf courses and their contribution to urban biodiversity.
- Full Text:
- Date Issued: 2017
Investigation of photophysicochemical properties of zinc phthalocyanines conjugated to metallic nanoparticles
- Dube, Edith, Nwaji, Njemuwa, Oluwole, David O, Mack, John, Nyokong, Tebello
- Authors: Dube, Edith , Nwaji, Njemuwa , Oluwole, David O , Mack, John , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/233425 , vital:50089 , xlink:href="https://doi.org/10.1016/j.jphotochem.2017.09.020"
- Description: The syntheses of zinc(II) tetra–[3–(4–phenoxy) (propanoic acid) phthalocyanine] (2) and zinc(II) mono–[3–(4–phenoxy) (propanoic acid) phthalocyanine (3) are reported in this work. Compounds 2 and 3 were covalently linked to glutathione capped silver (AgNPs–GSH), gold (AuNPs–GSH) and silver-gold alloy (Ag3Au1NPs–GSH) nanoparticles (NPs) via an amide bond formation to afford the conjugates: 2–AgNPs–GSH, 3–AgNPs–GSH, 2–AuNPs–GSH, 3–AuNPs–GSH, 2-Ag3Au1NPs–GSH and 3-Ag3Au1NPs–GSH. The photophysicochemical behaviours of the compounds and their conjugates with NPs were assessed in solution. The conjugates afforded a decrease in fluorescence quantum yields and lifetimes with improved triplet quantum yields in comparison to the compounds. Accordingly, the AgNPs and AuNPs conjugates with the compounds afforded high singlet quantum yields. On the contrary, the conjugates of the alloy afforded decreased singlet quantum yields probably due to the screening effect. The compounds and their conjugates with NPs could serve as a viable and efficacious photosensitizer for photodynamic therapy.
- Full Text:
- Date Issued: 2017
- Authors: Dube, Edith , Nwaji, Njemuwa , Oluwole, David O , Mack, John , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/233425 , vital:50089 , xlink:href="https://doi.org/10.1016/j.jphotochem.2017.09.020"
- Description: The syntheses of zinc(II) tetra–[3–(4–phenoxy) (propanoic acid) phthalocyanine] (2) and zinc(II) mono–[3–(4–phenoxy) (propanoic acid) phthalocyanine (3) are reported in this work. Compounds 2 and 3 were covalently linked to glutathione capped silver (AgNPs–GSH), gold (AuNPs–GSH) and silver-gold alloy (Ag3Au1NPs–GSH) nanoparticles (NPs) via an amide bond formation to afford the conjugates: 2–AgNPs–GSH, 3–AgNPs–GSH, 2–AuNPs–GSH, 3–AuNPs–GSH, 2-Ag3Au1NPs–GSH and 3-Ag3Au1NPs–GSH. The photophysicochemical behaviours of the compounds and their conjugates with NPs were assessed in solution. The conjugates afforded a decrease in fluorescence quantum yields and lifetimes with improved triplet quantum yields in comparison to the compounds. Accordingly, the AgNPs and AuNPs conjugates with the compounds afforded high singlet quantum yields. On the contrary, the conjugates of the alloy afforded decreased singlet quantum yields probably due to the screening effect. The compounds and their conjugates with NPs could serve as a viable and efficacious photosensitizer for photodynamic therapy.
- Full Text:
- Date Issued: 2017
Cu (III) triarylcorroles with asymmetric push–pull meso-substitutions
- Liang, Xu, Niu, Yingjie, Zhang, Ojanchong, Mack, John, Yi, Xiaoyi, Hlatshwayo, Zweli, Li, Minzhi, Zhu, Weihua, Nyokong, Tebello
- Authors: Liang, Xu , Niu, Yingjie , Zhang, Ojanchong , Mack, John , Yi, Xiaoyi , Hlatshwayo, Zweli , Li, Minzhi , Zhu, Weihua , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232947 , vital:50040 , xlink:href="https://doi.org/10.1039/C7DT00716G"
- Description: The synthesis of four low symmetry A2B type Cu (III)triarylcorroles with meso-aryl substituents that provide electron donating (push) and withdrawing (pull) properties is reported, along with their structural characterization by NMR spectroscopy and X-ray crystallography. An analysis of the structure–property relationships in the optical and redox properties has been carried out by comparing their optical spectroscopy, electrochemistry, and spectroelectrochemistry to trends predicted in DFT and TD-DFT calculations. The results demonstrate that A2B type Cu(III)triarylcorroles are highly efficient catalysts for electrocatalyzed hydrogen evolution reactions (HERs) and that their reactivity can be modulated by changing the nature of the B-position meso-substituent.
- Full Text:
- Date Issued: 2017
- Authors: Liang, Xu , Niu, Yingjie , Zhang, Ojanchong , Mack, John , Yi, Xiaoyi , Hlatshwayo, Zweli , Li, Minzhi , Zhu, Weihua , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232947 , vital:50040 , xlink:href="https://doi.org/10.1039/C7DT00716G"
- Description: The synthesis of four low symmetry A2B type Cu (III)triarylcorroles with meso-aryl substituents that provide electron donating (push) and withdrawing (pull) properties is reported, along with their structural characterization by NMR spectroscopy and X-ray crystallography. An analysis of the structure–property relationships in the optical and redox properties has been carried out by comparing their optical spectroscopy, electrochemistry, and spectroelectrochemistry to trends predicted in DFT and TD-DFT calculations. The results demonstrate that A2B type Cu(III)triarylcorroles are highly efficient catalysts for electrocatalyzed hydrogen evolution reactions (HERs) and that their reactivity can be modulated by changing the nature of the B-position meso-substituent.
- Full Text:
- Date Issued: 2017
Nonlinear optical dynamics of benzothiazole derivatized phthalocyanines in solution, thin films and when conjugated to nanoparticles
- Nwaji, Njemuwa, Jones, Benjamin, Mack, John, Oluwole, David O, Nyokong, Tebello
- Authors: Nwaji, Njemuwa , Jones, Benjamin , Mack, John , Oluwole, David O , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/190426 , vital:44993 , xlink:href="https://doi.org/10.1016/j.jphotochem.2017.05.042"
- Description: Benzothiazole phthalocynines complexes: tetrakis[(benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] indium(III) chloride (1) and tetrakis[(benzo[d]thiazol-2-ylthio)phthalocyaninato] indium(III) chloride (2) were synthesisized and their nanosecond nonlinear optical behaviours in solution, solid state and when conjugated to metallic nanoparticles were examined and compared to those of the corresponding ZnPc and GaPc which are designated as: tetrakis[(4-benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] zinc(II) (3), tetrakis[(4-benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] gallium(III) chloride (4), tetrakis[(4-benzo[d]thiazol-2-ylthio)phthalocyaninato] zinc(II) (5) and tetrakis[(4-benzo[d]thiazol-2-ylthio)phthalocyaninato] gallium(III) chloride (6). Trends in the electronic structures were identified through a comparison of the UV–vis absorption and magnetic circular dichroism (MCD) spectroscopy of the complexes and calculated spectra predicted by time dependent density functional theory (TD-DFT). Of all the complexes and nanoconjugates, complex 2 (containing sulphur linkages and In as a central metal) gave the best optical limiting behaviour.
- Full Text:
- Date Issued: 2017
- Authors: Nwaji, Njemuwa , Jones, Benjamin , Mack, John , Oluwole, David O , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/190426 , vital:44993 , xlink:href="https://doi.org/10.1016/j.jphotochem.2017.05.042"
- Description: Benzothiazole phthalocynines complexes: tetrakis[(benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] indium(III) chloride (1) and tetrakis[(benzo[d]thiazol-2-ylthio)phthalocyaninato] indium(III) chloride (2) were synthesisized and their nanosecond nonlinear optical behaviours in solution, solid state and when conjugated to metallic nanoparticles were examined and compared to those of the corresponding ZnPc and GaPc which are designated as: tetrakis[(4-benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] zinc(II) (3), tetrakis[(4-benzo[d]thiazol-2-ylphenoxy)phthalocyaninato] gallium(III) chloride (4), tetrakis[(4-benzo[d]thiazol-2-ylthio)phthalocyaninato] zinc(II) (5) and tetrakis[(4-benzo[d]thiazol-2-ylthio)phthalocyaninato] gallium(III) chloride (6). Trends in the electronic structures were identified through a comparison of the UV–vis absorption and magnetic circular dichroism (MCD) spectroscopy of the complexes and calculated spectra predicted by time dependent density functional theory (TD-DFT). Of all the complexes and nanoconjugates, complex 2 (containing sulphur linkages and In as a central metal) gave the best optical limiting behaviour.
- Full Text:
- Date Issued: 2017
Halogen substituted A2B type Co (III) triarylcorroles
- Niu, Yingjie, Li, Minzhi, Zhang, Qianchong, Zhu, Weihua, Mack, John, Fomo, Gertrude, Nyokong, Tebello, Liang, Xu
- Authors: Niu, Yingjie , Li, Minzhi , Zhang, Qianchong , Zhu, Weihua , Mack, John , Fomo, Gertrude , Nyokong, Tebello , Liang, Xu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/233048 , vital:50051 , xlink:href="https://doi.org/10.1016/j.dyepig.2017.02.049"
- Description: Seven low symmetry A2B type Co(III)triarylcorroles with electron withdrawing meso-aryl substituents have been synthesized and characterized. A detailed analysis of the optical and redox properties has been carried out by comparing their optical spectroscopy, electrochemistry and spectroelectrochemistry to trends predicted in a series of DFT and TD-DFT calculations. The results demonstrate that Co(III)corroles are highly effective catalysts for hydrogen evolution reactions (HERs). Moreover, there is a marked enhancement in their homogenous catalytic ability when halogen atoms are introduced at the B position, which demonstrates that facile modifying the meso-aryl rings is a effective strategy for developing new HER catalysts. The electrochemical results demonstrate that an unusual two step modulation of HER reactions can be achieved by using singly and doubly electrochemical reduced cobalt triarylcorroles anions.
- Full Text:
- Date Issued: 2017
- Authors: Niu, Yingjie , Li, Minzhi , Zhang, Qianchong , Zhu, Weihua , Mack, John , Fomo, Gertrude , Nyokong, Tebello , Liang, Xu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/233048 , vital:50051 , xlink:href="https://doi.org/10.1016/j.dyepig.2017.02.049"
- Description: Seven low symmetry A2B type Co(III)triarylcorroles with electron withdrawing meso-aryl substituents have been synthesized and characterized. A detailed analysis of the optical and redox properties has been carried out by comparing their optical spectroscopy, electrochemistry and spectroelectrochemistry to trends predicted in a series of DFT and TD-DFT calculations. The results demonstrate that Co(III)corroles are highly effective catalysts for hydrogen evolution reactions (HERs). Moreover, there is a marked enhancement in their homogenous catalytic ability when halogen atoms are introduced at the B position, which demonstrates that facile modifying the meso-aryl rings is a effective strategy for developing new HER catalysts. The electrochemical results demonstrate that an unusual two step modulation of HER reactions can be achieved by using singly and doubly electrochemical reduced cobalt triarylcorroles anions.
- Full Text:
- Date Issued: 2017
A2B type copper (III) corroles containing zero-to-five fluorine atoms
- Li, Minzhi, Niu, Yingjie, Zhu, Weihua, Mack, John, Fomo, Gertrude, Nyokong, Tebello, Liang, Xu
- Authors: Li, Minzhi , Niu, Yingjie , Zhu, Weihua , Mack, John , Fomo, Gertrude , Nyokong, Tebello , Liang, Xu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/238275 , vital:50604 , xlink:href="https://doi.org/10.1016/j.dyepig.2016.10.044"
- Description: Four low symmetric A2B meso-substituted Cu(III)corroles with electron withdrawing meso-aryl rings have been synthesized and characterized. A detailed analysis of the optical and redox properties has been carried out by comparing their optical spectroscopy, electrochemistry and spectroelectrochemistry to a series of DFT and TD-DFT calculations. A series of experiments demonstrate that these Cu(III)corroles can be used as highly effective catalysts for hydrogen evolution reactions (HERs). Moreover, when the number of fluorine atoms at B meso-position is increased, there is a marked enhancement in the catalytic ability of the corrole complexes, which demonstrates that modification to the structures of low symmetry corroles is a useful strategy for developing new HER catalysts.
- Full Text:
- Date Issued: 2017
- Authors: Li, Minzhi , Niu, Yingjie , Zhu, Weihua , Mack, John , Fomo, Gertrude , Nyokong, Tebello , Liang, Xu
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/238275 , vital:50604 , xlink:href="https://doi.org/10.1016/j.dyepig.2016.10.044"
- Description: Four low symmetric A2B meso-substituted Cu(III)corroles with electron withdrawing meso-aryl rings have been synthesized and characterized. A detailed analysis of the optical and redox properties has been carried out by comparing their optical spectroscopy, electrochemistry and spectroelectrochemistry to a series of DFT and TD-DFT calculations. A series of experiments demonstrate that these Cu(III)corroles can be used as highly effective catalysts for hydrogen evolution reactions (HERs). Moreover, when the number of fluorine atoms at B meso-position is increased, there is a marked enhancement in the catalytic ability of the corrole complexes, which demonstrates that modification to the structures of low symmetry corroles is a useful strategy for developing new HER catalysts.
- Full Text:
- Date Issued: 2017
Highly efficient CCl bond cleavage and unprecedented CC bond cleavage of environmentally toxic DDT through molecular electrochemical catalysis
- Liang, Xu, Huang, Tingting, Li, Minzhi, Mack, John, Wildervanck, Martijn, Nyokong, Tebello, Zhu, Weihua
- Authors: Liang, Xu , Huang, Tingting , Li, Minzhi , Mack, John , Wildervanck, Martijn , Nyokong, Tebello , Zhu, Weihua
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188921 , vital:44798 , xlink:href="https://doi.org/10.1016/j.apcata.2017.07.026"
- Description: The electrocatalytic properties of a Co(II)octaalkoxyphthalocyanine complex (Co(II)Pc) with eight strongly electron-donating substituents provide the first example of the complete dechlorination of DDT through molecular electrocatalysis, rather than the use of metal electrodes which had been achieved previously. Interaction with a highly nucleophilic [Co(I)Pc]2− species results in rapid cleavage of the C(sp3) Cl, C(sp2) Cl and aromatic C(sp2) Cl bonds. Bis(p-chlorophenyl)methanone (BPCl2) is detected in high yield along with its full dechlorination product, diphenylmethanone (BP) and the conventional C Cl bond cleavage products, due to an unprecedented C C bond cleavage reaction that is followed by the formation of a C−O bond. Theoretical calculations are used to analyze trends in the electronic structure of the Co(II)octaalkoxyphthalocyanine complex that account for the efficiency of the C Cl bond cleavage reactions, and the reaction process and mechanism are analyzed in depth.
- Full Text:
- Date Issued: 2017
- Authors: Liang, Xu , Huang, Tingting , Li, Minzhi , Mack, John , Wildervanck, Martijn , Nyokong, Tebello , Zhu, Weihua
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/188921 , vital:44798 , xlink:href="https://doi.org/10.1016/j.apcata.2017.07.026"
- Description: The electrocatalytic properties of a Co(II)octaalkoxyphthalocyanine complex (Co(II)Pc) with eight strongly electron-donating substituents provide the first example of the complete dechlorination of DDT through molecular electrocatalysis, rather than the use of metal electrodes which had been achieved previously. Interaction with a highly nucleophilic [Co(I)Pc]2− species results in rapid cleavage of the C(sp3) Cl, C(sp2) Cl and aromatic C(sp2) Cl bonds. Bis(p-chlorophenyl)methanone (BPCl2) is detected in high yield along with its full dechlorination product, diphenylmethanone (BP) and the conventional C Cl bond cleavage products, due to an unprecedented C C bond cleavage reaction that is followed by the formation of a C−O bond. Theoretical calculations are used to analyze trends in the electronic structure of the Co(II)octaalkoxyphthalocyanine complex that account for the efficiency of the C Cl bond cleavage reactions, and the reaction process and mechanism are analyzed in depth.
- Full Text:
- Date Issued: 2017
Optical limiting properties of 3, 5-diphenyldibenzo-azaBODIPY at 532 nm
- Kubheka, Gugu, Achadu, Ojodomo J, Mack, John, Nyokong, Tebello
- Authors: Kubheka, Gugu , Achadu, Ojodomo J , Mack, John , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232761 , vital:50022 , xlink:href="https://doi.org/10.1039/C7NJ01503H"
- Description: Optical limiting properties of 3,5-diphenyldibenzo-azaBODIPY were investigated by using the z-scan technique at 532 nm in the nanosecond pulse range and a strong reverse saturable absorption (RSA) response was observed, which can be readily attributed to a two-photon absorption (TPA) assisted excited state absorption (ESA) mechanism in the singlet manifold based on a consideration of the other photophysical properties. The effect of solvent and incorporation into polymer thin films has been investigated in depth. The results indicate that the selection of solvents that enhance the population of the S1 excited state on the nanosecond timescale or embedding the azaBODIPY dye into polymer thin films significantly improves the optical limiting properties.
- Full Text:
- Date Issued: 2017
- Authors: Kubheka, Gugu , Achadu, Ojodomo J , Mack, John , Nyokong, Tebello
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232761 , vital:50022 , xlink:href="https://doi.org/10.1039/C7NJ01503H"
- Description: Optical limiting properties of 3,5-diphenyldibenzo-azaBODIPY were investigated by using the z-scan technique at 532 nm in the nanosecond pulse range and a strong reverse saturable absorption (RSA) response was observed, which can be readily attributed to a two-photon absorption (TPA) assisted excited state absorption (ESA) mechanism in the singlet manifold based on a consideration of the other photophysical properties. The effect of solvent and incorporation into polymer thin films has been investigated in depth. The results indicate that the selection of solvents that enhance the population of the S1 excited state on the nanosecond timescale or embedding the azaBODIPY dye into polymer thin films significantly improves the optical limiting properties.
- Full Text:
- Date Issued: 2017