Voltammetric characterisation of the self-assembled monolayers (SAMs) of benzyl-and dodecyl-mercapto tetra substituted metallophthalocyanines complexes
- Agboola, Bolade, Westbroek, Philippe, Ozoemena, Kenneth I, Nyokong, Tebello
- Authors: Agboola, Bolade , Westbroek, Philippe , Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281414 , vital:55723 , xlink:href="https://doi.org/10.1016/j.elecom.2006.08.047"
- Description: Voltammetric characterisations of cobalt, iron, manganese, nickel and zinc phthalocyanine complexes tetra substituted with benzyl- and dodecyl-mercapto ring substituents and immobilisation on gold electrodes via the self-assembling technique are presented. The self-assembled films are stable and showed blocking characteristics towards the following Faradaic processes; gold surface oxidation, under potential deposition of copper and solution redox chemistry of [Fe(H2O)6 3+ ]/[Fe(H2O)6 2+ ]. The solution chemistry of [Fe(CN)6]−3/[Fe(CN)6]−4 redox process was used to study the orientation of the CoPcs-SAMs and this revealed a possible deviation from flat orientation of the complexes on the gold electrodes when the SAM formation times were greater than 24 h. For SAM formation time at 24 and 48 h, CoTDMPc-SAM showed more inhibition of the [Fe(CN)6]−3/[Fe(CN)6]−4 redox process than the CoTBMPc-SAM counterpart, indicating more blocking characteristics of the dodecylmercapto ring substituents compared to the benzylmercapto counterpart. To avoid SAM desorption, the potential application should be limited to −0.2 to +0.8 V vs. Ag∣AgCl (NaCl, sat’d) in acidic and neutral pH.
- Full Text:
- Date Issued: 2007
- Authors: Agboola, Bolade , Westbroek, Philippe , Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281414 , vital:55723 , xlink:href="https://doi.org/10.1016/j.elecom.2006.08.047"
- Description: Voltammetric characterisations of cobalt, iron, manganese, nickel and zinc phthalocyanine complexes tetra substituted with benzyl- and dodecyl-mercapto ring substituents and immobilisation on gold electrodes via the self-assembling technique are presented. The self-assembled films are stable and showed blocking characteristics towards the following Faradaic processes; gold surface oxidation, under potential deposition of copper and solution redox chemistry of [Fe(H2O)6 3+ ]/[Fe(H2O)6 2+ ]. The solution chemistry of [Fe(CN)6]−3/[Fe(CN)6]−4 redox process was used to study the orientation of the CoPcs-SAMs and this revealed a possible deviation from flat orientation of the complexes on the gold electrodes when the SAM formation times were greater than 24 h. For SAM formation time at 24 and 48 h, CoTDMPc-SAM showed more inhibition of the [Fe(CN)6]−3/[Fe(CN)6]−4 redox process than the CoTBMPc-SAM counterpart, indicating more blocking characteristics of the dodecylmercapto ring substituents compared to the benzylmercapto counterpart. To avoid SAM desorption, the potential application should be limited to −0.2 to +0.8 V vs. Ag∣AgCl (NaCl, sat’d) in acidic and neutral pH.
- Full Text:
- Date Issued: 2007
Effect of doping vs covalent linking of a low symmetry zinc phthalocyanine to silica nanoparticles on singlet oxygen production
- Peteni, Siwaphiwe, Nyokong, Tebello
- Authors: Peteni, Siwaphiwe , Nyokong, Tebello
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/187873 , vital:44705 , xlink:href="https://doi.org/10.1016/j.ica.2018.06.029"
- Description: Tris[(4-(pyridin-4-ylthio)-2-thio-4-methylthiazol-5-yl)acetic acid phthalocyaninato] zinc (II) (3) was covalently linked to and doped onto SiNPs. An increase in triplet quantum yields for 3-SiNPs (linked) with decreasing lifetimes was observed. For 3-SiNPs (doped) there was a decrease in both the triplet quantum yield and lifetimes when compared to 3 alone. There was an increase in singlet oxygen quantum yields for 3-SiNPs (linked) compared to 3 from 0.67 to 0.80, while there was a decrease for 3-SiNPs (doped) to 0.25.
- Full Text:
- Date Issued: 2018
- Authors: Peteni, Siwaphiwe , Nyokong, Tebello
- Date: 2018
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/187873 , vital:44705 , xlink:href="https://doi.org/10.1016/j.ica.2018.06.029"
- Description: Tris[(4-(pyridin-4-ylthio)-2-thio-4-methylthiazol-5-yl)acetic acid phthalocyaninato] zinc (II) (3) was covalently linked to and doped onto SiNPs. An increase in triplet quantum yields for 3-SiNPs (linked) with decreasing lifetimes was observed. For 3-SiNPs (doped) there was a decrease in both the triplet quantum yield and lifetimes when compared to 3 alone. There was an increase in singlet oxygen quantum yields for 3-SiNPs (linked) compared to 3 from 0.67 to 0.80, while there was a decrease for 3-SiNPs (doped) to 0.25.
- Full Text:
- Date Issued: 2018
Anti-cancer and anti-trypanosomal properties of alkaloids from the root bark of Zanthoxylum leprieurii Guill and Perr
- Eze, Fabian I, Siwe-Noundou, Xavier, Isaacs, Michelle, Patala, Srivinas, Osadebe, Patience O, Krause, Rui W M
- Authors: Eze, Fabian I , Siwe-Noundou, Xavier , Isaacs, Michelle , Patala, Srivinas , Osadebe, Patience O , Krause, Rui W M
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193352 , vital:45324 , xlink:href="http://dx.doi.org/10.4314/tjpr.v19i11.19"
- Description: Purpose: To isolate the anti-cancer and anti-trypanosomal principles of Zanthoxylum leprieurii, a medicinally versatile wild tropical plant used for managing tumours, African trypanosomiasis, and inflammation in southeastern Nigeria. Methods: The pure compounds were isolated using chromatographic methods. The structural elucidation of the pure compounds was based on their NMR (1D and 2D) and mass spectral data as well as chemical test results. Structure-activity relationships were based on the structural differences among the compounds. The cytotoxicity of the extracts and compounds (1, 2, 3, and 4) was evaluated in HeLa (human cervix adenocarcinoma) cell line while the trypanocidal activities were evaluated on Trypanosoma brucei brucei. Results: Two acridone alkaloids, 1-hydroxy-3-methoxy-10-methylacridin-9 (10H)-one, named fabiocinine (1), and 1-hydroxy-2,3-dimethoxy-10-methylacridin-9 (10H)-one (arborinine, 2), together with a furoquinoline alkaloid, skimmianine (3), and a chelerythrine derivative, 6-acetonyl-5,6-dihydrochelerythrine (4) were isolated from the root bark of Zanthoxylum leprieurii. Skimmianine (3) exhibited cytotoxicity and anti-trypanosomal IC50 of 12.8 and 13.2 µg/mL respectively (p less than 0.05). Compound (1) and arborinine (2) were selectively cytotoxic to HeLa cells with cytotoxicity IC50 of 28.49 and 62.71 µg/mL, respectively, while (4) did not show significant activity (p less than 0.05). Conclusion: Zanthoxylum leprieurii root bark contains cytotoxic and trypanocidal compounds, and is thus a potential source of anti-cancer and anti-trypanosomal leads.
- Full Text:
- Date Issued: 2020
- Authors: Eze, Fabian I , Siwe-Noundou, Xavier , Isaacs, Michelle , Patala, Srivinas , Osadebe, Patience O , Krause, Rui W M
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193352 , vital:45324 , xlink:href="http://dx.doi.org/10.4314/tjpr.v19i11.19"
- Description: Purpose: To isolate the anti-cancer and anti-trypanosomal principles of Zanthoxylum leprieurii, a medicinally versatile wild tropical plant used for managing tumours, African trypanosomiasis, and inflammation in southeastern Nigeria. Methods: The pure compounds were isolated using chromatographic methods. The structural elucidation of the pure compounds was based on their NMR (1D and 2D) and mass spectral data as well as chemical test results. Structure-activity relationships were based on the structural differences among the compounds. The cytotoxicity of the extracts and compounds (1, 2, 3, and 4) was evaluated in HeLa (human cervix adenocarcinoma) cell line while the trypanocidal activities were evaluated on Trypanosoma brucei brucei. Results: Two acridone alkaloids, 1-hydroxy-3-methoxy-10-methylacridin-9 (10H)-one, named fabiocinine (1), and 1-hydroxy-2,3-dimethoxy-10-methylacridin-9 (10H)-one (arborinine, 2), together with a furoquinoline alkaloid, skimmianine (3), and a chelerythrine derivative, 6-acetonyl-5,6-dihydrochelerythrine (4) were isolated from the root bark of Zanthoxylum leprieurii. Skimmianine (3) exhibited cytotoxicity and anti-trypanosomal IC50 of 12.8 and 13.2 µg/mL respectively (p less than 0.05). Compound (1) and arborinine (2) were selectively cytotoxic to HeLa cells with cytotoxicity IC50 of 28.49 and 62.71 µg/mL, respectively, while (4) did not show significant activity (p less than 0.05). Conclusion: Zanthoxylum leprieurii root bark contains cytotoxic and trypanocidal compounds, and is thus a potential source of anti-cancer and anti-trypanosomal leads.
- Full Text:
- Date Issued: 2020
Zinc (II) 2, 9, 16, 23-tetrakis [4-(N-methylpyridyloxy)]-phthalocyanine anchored on an electrospun polysulfone polymer fiber: Application for photosensitized conversion of methyl orange
- Zugle, Ruphino, Nyokong, Tebello
- Authors: Zugle, Ruphino , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232741 , vital:50020 , xlink:href="https://doi.org/10.1016/j.molcata.2012.10.001"
- Description: In this work, a comparative study of photodegradation of methyl orange, an azo dye, in homogeneous aqueous solution of a quarternized cationic zinc phthalocyanine and a heterogeneous catalytic system based on the same phthalocyanine anchored on polysulfone polymer fiber is presented. In both cases, conversion involved the azo bond of the dye with no detectable opening up of the aromatic benzene rings. The reaction kinetics in both cases were consistent with first order with the conversion occurring in the homogeneous system being faster than when the functionalized polymer fiber was used. The reaction products consisted of a coupling product as well as a series of oligopolymeric products.
- Full Text:
- Date Issued: 2013
- Authors: Zugle, Ruphino , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/232741 , vital:50020 , xlink:href="https://doi.org/10.1016/j.molcata.2012.10.001"
- Description: In this work, a comparative study of photodegradation of methyl orange, an azo dye, in homogeneous aqueous solution of a quarternized cationic zinc phthalocyanine and a heterogeneous catalytic system based on the same phthalocyanine anchored on polysulfone polymer fiber is presented. In both cases, conversion involved the azo bond of the dye with no detectable opening up of the aromatic benzene rings. The reaction kinetics in both cases were consistent with first order with the conversion occurring in the homogeneous system being faster than when the functionalized polymer fiber was used. The reaction products consisted of a coupling product as well as a series of oligopolymeric products.
- Full Text:
- Date Issued: 2013
Positioning non-timber forest products on the development agenda
- Shackleton, Charlie M, Pandey, Ashok K
- Authors: Shackleton, Charlie M , Pandey, Ashok K
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180992 , vital:43679 , xlink:href="https://doi.org/10.1016/j.forpol.2013.07.004"
- Description: Non-timber forests products (NTFPs) provide multiple livelihood benefits to local communities and regional and national economies. And yet this knowledge is rarely drawn upon in debates around and design of poverty alleviation or land use policies, strategies and projects. Unless the accumulating wealth of empirical evidence can be translated into policies and approaches at higher levels, and integrated into poverty alleviation programmes, it will have little impact on local and national poverty profiles. In this paper we propose and briefly discuss eight steps to facilitate integration of NTFPs into the development agenda, for the benefit of local communities. These include: (1) proper inventory of NTFP stocks, (2) research on NTFP ecology and sustainable harvest levels, (3) introduction of extension services for NTFPs, (4) inclusion of NTFPs in land management and trade-off decisions, (5) integration of NTFPs into sectoral policies, (6) ensuring NTFP commercialisation is not at the expense of local livelihood needs, (7) promoting security of access and use, and (8) examination of local contextual drivers of unsustainable use. Each is presented along with examples or proposals towards implementation.
- Full Text:
- Date Issued: 2014
- Authors: Shackleton, Charlie M , Pandey, Ashok K
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180992 , vital:43679 , xlink:href="https://doi.org/10.1016/j.forpol.2013.07.004"
- Description: Non-timber forests products (NTFPs) provide multiple livelihood benefits to local communities and regional and national economies. And yet this knowledge is rarely drawn upon in debates around and design of poverty alleviation or land use policies, strategies and projects. Unless the accumulating wealth of empirical evidence can be translated into policies and approaches at higher levels, and integrated into poverty alleviation programmes, it will have little impact on local and national poverty profiles. In this paper we propose and briefly discuss eight steps to facilitate integration of NTFPs into the development agenda, for the benefit of local communities. These include: (1) proper inventory of NTFP stocks, (2) research on NTFP ecology and sustainable harvest levels, (3) introduction of extension services for NTFPs, (4) inclusion of NTFPs in land management and trade-off decisions, (5) integration of NTFPs into sectoral policies, (6) ensuring NTFP commercialisation is not at the expense of local livelihood needs, (7) promoting security of access and use, and (8) examination of local contextual drivers of unsustainable use. Each is presented along with examples or proposals towards implementation.
- Full Text:
- Date Issued: 2014
pH study of the electrocatalytic SO2 detection at a glassy carbon electrode modified with iron (II) tetrasulfophthalocyanine
- Thamae, Mamothibe, Westbroek, Philippe, Nyokong, Tebello
- Authors: Thamae, Mamothibe , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/304786 , vital:58490 , xlink:href="https://doi.org/10.1007/s00604-002-0914-8"
- Description: The electrocatalytic determination of SO2 is studied as a function of pH at a glassy carbon electrode modified with iron(II)tetrasulfophthalocyanine ([Fe(II)TSPc]4−). It was found in the literature that depending on pH, SO2·xH2O, HSO3 − and/or SO3 2− are the main compounds in solution, that these compounds behave differently at the electrode surface, and that the condition of the electrode surface is stable over the entire pH-range. The use of SO2(g) or sodium sulfite as starting material did result in identical curves except in the pH range from 7.5–9.0. A possible explanation could be given by proposing that SO2·xH2O is very unstable in the presence of SO3 2−. In strongly acidic medium, SO2·xH2O is the main compound, which can be oxidized as well as reduced with exchange of two electrons. HSO3 − is the main compound at pH = 4 and can also be oxidized and reduced with exchange of, respectively, two and four electrons. In alkaline solution sulfite is the main compound and can only be oxidized, also under exchange of two electrons. Detection limits are in the range of 4.0 ± 0.1 × 10−5 and 7.5 ± 0.1 × 10−5 mol L−1, dependent of pH and of the type of reaction (oxidation or reduction) used.
- Full Text:
- Date Issued: 2002
- Authors: Thamae, Mamothibe , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/304786 , vital:58490 , xlink:href="https://doi.org/10.1007/s00604-002-0914-8"
- Description: The electrocatalytic determination of SO2 is studied as a function of pH at a glassy carbon electrode modified with iron(II)tetrasulfophthalocyanine ([Fe(II)TSPc]4−). It was found in the literature that depending on pH, SO2·xH2O, HSO3 − and/or SO3 2− are the main compounds in solution, that these compounds behave differently at the electrode surface, and that the condition of the electrode surface is stable over the entire pH-range. The use of SO2(g) or sodium sulfite as starting material did result in identical curves except in the pH range from 7.5–9.0. A possible explanation could be given by proposing that SO2·xH2O is very unstable in the presence of SO3 2−. In strongly acidic medium, SO2·xH2O is the main compound, which can be oxidized as well as reduced with exchange of two electrons. HSO3 − is the main compound at pH = 4 and can also be oxidized and reduced with exchange of, respectively, two and four electrons. In alkaline solution sulfite is the main compound and can only be oxidized, also under exchange of two electrons. Detection limits are in the range of 4.0 ± 0.1 × 10−5 and 7.5 ± 0.1 × 10−5 mol L−1, dependent of pH and of the type of reaction (oxidation or reduction) used.
- Full Text:
- Date Issued: 2002
Sustainable Human Resource Practices for Organizational Competitiveness Post the Covid-19 Pandemic
- Asoba, Samson Nambei, Patricia, Nteboheng Mefi
- Authors: Asoba, Samson Nambei , Patricia, Nteboheng Mefi
- Date: 2021
- Subjects: Personel Management Covid-19 (Disease) Article
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/11260/8118 , vital:61396 , xlink:href="https://www.abacademies.org/articles/Sustainable-human-resource-practices-for-organizational-competitiveness-post-the-covid-19-1528-2686-27-2-480.pdf"
- Description: The study was formulated to tap into the future of HRM given the disruptions arising from the Covid-119 pandemic as well as the progression of the global technological environment to the fourth industrial revolution. The aim of the study was to: the Covid-19 induced HRM practices underpinning future organizational competitiveness. A literature review strategy was adopted to achieve the study objective. The study established seven emerging themes to inform HRM practices for the competitiveness of organizations in future following the Covid-19 disturbances. These themes are: primacy of HRM, increased cyber influences, digitalization, remote HRM, human-machine interface skills, human-organisation strategic links as well as human-technology interface competencies. Based on the study findings, the study recommended HRM departments to move to HR 4.0 through the adoption of industry 4.0 technologies, increased automation, and digitalization as well as strengthen virtualization systems.
- Full Text:
- Date Issued: 2021
- Authors: Asoba, Samson Nambei , Patricia, Nteboheng Mefi
- Date: 2021
- Subjects: Personel Management Covid-19 (Disease) Article
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/11260/8118 , vital:61396 , xlink:href="https://www.abacademies.org/articles/Sustainable-human-resource-practices-for-organizational-competitiveness-post-the-covid-19-1528-2686-27-2-480.pdf"
- Description: The study was formulated to tap into the future of HRM given the disruptions arising from the Covid-119 pandemic as well as the progression of the global technological environment to the fourth industrial revolution. The aim of the study was to: the Covid-19 induced HRM practices underpinning future organizational competitiveness. A literature review strategy was adopted to achieve the study objective. The study established seven emerging themes to inform HRM practices for the competitiveness of organizations in future following the Covid-19 disturbances. These themes are: primacy of HRM, increased cyber influences, digitalization, remote HRM, human-machine interface skills, human-organisation strategic links as well as human-technology interface competencies. Based on the study findings, the study recommended HRM departments to move to HR 4.0 through the adoption of industry 4.0 technologies, increased automation, and digitalization as well as strengthen virtualization systems.
- Full Text:
- Date Issued: 2021
Photocatalytic transformation of chlorophenols under homogeneous and heterogeneous conditions using palladium octadodecylthio phthalocyanine
- Ogunbayo, Taofeek B, Nyokong, Tebello
- Authors: Ogunbayo, Taofeek B , Nyokong, Tebello
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/246816 , vital:51516 , xlink:href="https://doi.org/10.1016/j.molcata.2011.09.003"
- Description: Homogeneous and heterogeneous photosensitized transformations of 4-chlorophenol (4-CP) and pentachlorophenol (PCP) using palladium octadodecylthiophthalocyanine (PdODPc) were investigated. Under heterogeneous conditions, the photosensitizer was supported on functionalized single walled carbon nanotubes (SWCNTs). Homogeneous photosensitization proved to be more effective than the heterogeneous reaction in terms of percentage of transformation achieved. The kinetics of heterogeneous catalysis proved that ads-PdODPc–SWCNT–COOH (where SWCNT has been functionalized with COOH groups) was reusable for 4-CP while its activity degenerated when reused for PCP. Singlet oxygen was confirmed as playing an active role in the reactions.
- Full Text:
- Date Issued: 2011
- Authors: Ogunbayo, Taofeek B , Nyokong, Tebello
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/246816 , vital:51516 , xlink:href="https://doi.org/10.1016/j.molcata.2011.09.003"
- Description: Homogeneous and heterogeneous photosensitized transformations of 4-chlorophenol (4-CP) and pentachlorophenol (PCP) using palladium octadodecylthiophthalocyanine (PdODPc) were investigated. Under heterogeneous conditions, the photosensitizer was supported on functionalized single walled carbon nanotubes (SWCNTs). Homogeneous photosensitization proved to be more effective than the heterogeneous reaction in terms of percentage of transformation achieved. The kinetics of heterogeneous catalysis proved that ads-PdODPc–SWCNT–COOH (where SWCNT has been functionalized with COOH groups) was reusable for 4-CP while its activity degenerated when reused for PCP. Singlet oxygen was confirmed as playing an active role in the reactions.
- Full Text:
- Date Issued: 2011
Stock returns and Friday the 13th effect in five African countries
- Authors: Botha, Ferdi
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396127 , vital:69152 , xlink:href="https://www.ajol.info/index.php/aref/article/view/91060"
- Description: This study is concerned with Friday the 13th and daily stock market returns in five African countries. Using the MSCI Global Equity Indices during various periods, the evidence overwhelmingly suggests that there is no Friday the 13th effect.
- Full Text:
- Date Issued: 2013
- Authors: Botha, Ferdi
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396127 , vital:69152 , xlink:href="https://www.ajol.info/index.php/aref/article/view/91060"
- Description: This study is concerned with Friday the 13th and daily stock market returns in five African countries. Using the MSCI Global Equity Indices during various periods, the evidence overwhelmingly suggests that there is no Friday the 13th effect.
- Full Text:
- Date Issued: 2013
Electrocatalytic activity of arylthio tetra-substituted oxotitanium (IV) phthalocyanines towards the oxidation of nitrite
- Tau, Prudence, Nyokong, Tebello
- Authors: Tau, Prudence , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281234 , vital:55704 , xlink:href="https://doi.org/10.1016/j.electacta.2006.12.059"
- Description: This paper investigates the catalytic activities of arylthio substituted oxotitanium phthalocyanine (OTiPc) complexes that are immobilized on the glassy carbon electrode by electropolymerization, towards the oxidation of nitrite. The complexes are peripherally and non-peripherally substituted with phenylthio and benzylthio groups, namely 1a, 1b, 2a and 2b. All the modified electrodes exhibited improved electrocatalytic oxidation of nitrite than the unmodified electrodes by a two-electron mechanism producing nitrate ions. Catalytic currents are enhanced and nitrite overpotential reduced to ∼0.60 V. Kinetic parameters are determined for all complexes and a mechanism is proposed.
- Full Text:
- Date Issued: 2007
- Authors: Tau, Prudence , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281234 , vital:55704 , xlink:href="https://doi.org/10.1016/j.electacta.2006.12.059"
- Description: This paper investigates the catalytic activities of arylthio substituted oxotitanium phthalocyanine (OTiPc) complexes that are immobilized on the glassy carbon electrode by electropolymerization, towards the oxidation of nitrite. The complexes are peripherally and non-peripherally substituted with phenylthio and benzylthio groups, namely 1a, 1b, 2a and 2b. All the modified electrodes exhibited improved electrocatalytic oxidation of nitrite than the unmodified electrodes by a two-electron mechanism producing nitrate ions. Catalytic currents are enhanced and nitrite overpotential reduced to ∼0.60 V. Kinetic parameters are determined for all complexes and a mechanism is proposed.
- Full Text:
- Date Issued: 2007
Indium phthalocyanine–CdSe/ZnS quantum dots nanocomposites showing size dependent and near ideal optical limiting behaviour
- Sanusi, Kayode, Nyokong, Tebello
- Authors: Sanusi, Kayode , Nyokong, Tebello
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189921 , vital:44947 , xlink:href="https://doi.org/10.1016/j.optmat.2014.09.021"
- Description: Indium phthalocyanine–CdSe/ZnS quantum dots (QDs) nanocomposites (InPc–CdSe/ZnS) of three sizes (5.57, 8.12 and 8.75 nm) were synthesized according to known procedures. The particle size of the CdSe/ZnS QDs alone are 3.95, 6.02, and 6.66 nm, and are denoted as QD1, QD2 and QD3 respectively. The nonlinear absorption (NLA) properties of the nanoconjugates (InPc–CdSe/ZnS) were investigated with nanosecond laser radiation at 532 nm wavelength. Enhanced NLA properties compared to the InPc alone were observed in the conjugates. The NLA was found to increase with the size of the CdSe/ZnS particles attached to the phthalocyanine. The observed increase was due to the availability of more free-carrier ions in the larger QDs, thus giving rise to the enhanced free-carrier absorption. The measured free-carrier absorption cross-sections (σFCA) are 1.10, 1.65 and 1.95 (×10−19 cm2) for InPc-QD1, InPc-QD2 and InPc-QD3 respectively. The nanoconjugates (InPc–CdSe/ZnS) showed a much lower threshold for optical limiting together with a much lower transmission at high fluences, than the previously reported nanocomposite limiters.
- Full Text:
- Date Issued: 2014
- Authors: Sanusi, Kayode , Nyokong, Tebello
- Date: 2014
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/189921 , vital:44947 , xlink:href="https://doi.org/10.1016/j.optmat.2014.09.021"
- Description: Indium phthalocyanine–CdSe/ZnS quantum dots (QDs) nanocomposites (InPc–CdSe/ZnS) of three sizes (5.57, 8.12 and 8.75 nm) were synthesized according to known procedures. The particle size of the CdSe/ZnS QDs alone are 3.95, 6.02, and 6.66 nm, and are denoted as QD1, QD2 and QD3 respectively. The nonlinear absorption (NLA) properties of the nanoconjugates (InPc–CdSe/ZnS) were investigated with nanosecond laser radiation at 532 nm wavelength. Enhanced NLA properties compared to the InPc alone were observed in the conjugates. The NLA was found to increase with the size of the CdSe/ZnS particles attached to the phthalocyanine. The observed increase was due to the availability of more free-carrier ions in the larger QDs, thus giving rise to the enhanced free-carrier absorption. The measured free-carrier absorption cross-sections (σFCA) are 1.10, 1.65 and 1.95 (×10−19 cm2) for InPc-QD1, InPc-QD2 and InPc-QD3 respectively. The nanoconjugates (InPc–CdSe/ZnS) showed a much lower threshold for optical limiting together with a much lower transmission at high fluences, than the previously reported nanocomposite limiters.
- Full Text:
- Date Issued: 2014
Electrocatalytic oxidation and detection of hydrazine at gold electrode modified with iron phthalocyanine complex linked to mercaptopyridine self-assembled monolayer
- Ozoemena, Kenneth I, Nyokong, Tebello
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286065 , vital:56235 , xlink:href="https://doi.org/10.1016/j.talanta.2005.02.030"
- Description: Electrocatalytic oxidation and detection of hydrazine in pH 7.0 conditions were studied by using gold electrode modified with self-assembled monolayer (SAM) films of iron phthalocyanine (FePc) complex axially ligated to a preformed 4-mercaptopyridine SAMs. The anodic oxidation of hydrazine in neutral pH conditions with FePc-linked-mercaptopyridine-SAM-modified gold electrode occurred at low overpotential (0.35 V versus Ag|AgCl) and the treatment of the voltammetric data showed that it was a pure diffusion-controlled reaction with the involvement of one electron in the rate-determining step. The mechanism for the interaction of hydrazine with the FePc-SAM is proposed to involve the Fe(III)Pc/Fe(II)Pc redox process. Using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), hydrazine was detected over a linear concentration range of 1.3 × 10−5 to 9.2 × 10−5 mol/L with low limits of detection (ca. 5 and 11 μM for OSWV and CV, respectively). At concentrations higher than 1.2 × 10−4 mol/L the anodic peak potential shifted to 0.40 V (versus Ag|AgCl), and this was interpreted to be due to kinetic limitations resulting from the saturation of hydrazine and its oxidation products onto the redox-active monolayer film. This type of metallophthalocyanine-SAM-based electrode is a highly promising electrochemical sensor given its ease of fabrication, good catalytic activity, stability, sensitivity and simplicity.
- Full Text:
- Date Issued: 2005
- Authors: Ozoemena, Kenneth I , Nyokong, Tebello
- Date: 2005
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/286065 , vital:56235 , xlink:href="https://doi.org/10.1016/j.talanta.2005.02.030"
- Description: Electrocatalytic oxidation and detection of hydrazine in pH 7.0 conditions were studied by using gold electrode modified with self-assembled monolayer (SAM) films of iron phthalocyanine (FePc) complex axially ligated to a preformed 4-mercaptopyridine SAMs. The anodic oxidation of hydrazine in neutral pH conditions with FePc-linked-mercaptopyridine-SAM-modified gold electrode occurred at low overpotential (0.35 V versus Ag|AgCl) and the treatment of the voltammetric data showed that it was a pure diffusion-controlled reaction with the involvement of one electron in the rate-determining step. The mechanism for the interaction of hydrazine with the FePc-SAM is proposed to involve the Fe(III)Pc/Fe(II)Pc redox process. Using cyclic voltammetry (CV) and Osteryoung square wave voltammetry (OSWV), hydrazine was detected over a linear concentration range of 1.3 × 10−5 to 9.2 × 10−5 mol/L with low limits of detection (ca. 5 and 11 μM for OSWV and CV, respectively). At concentrations higher than 1.2 × 10−4 mol/L the anodic peak potential shifted to 0.40 V (versus Ag|AgCl), and this was interpreted to be due to kinetic limitations resulting from the saturation of hydrazine and its oxidation products onto the redox-active monolayer film. This type of metallophthalocyanine-SAM-based electrode is a highly promising electrochemical sensor given its ease of fabrication, good catalytic activity, stability, sensitivity and simplicity.
- Full Text:
- Date Issued: 2005
Fluorescence quenching and energy transfer in conjugates of quantum dots with zinc and indium tetraamino phthalocyanines
- Britton, Jonathan, Antunes, Edith M, Nyokong, Tebello
- Authors: Britton, Jonathan , Antunes, Edith M , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/262638 , vital:53539 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.12.013"
- Description: CdTe QDs capped with mercapto propionic acid (MPA) and thioglycolic acid (TGA) were covalently linked to zinc and indium tetraaminophthalocyanines (TAPcs) using N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) as the coupling agents. The results presented give evidence in favour of formation of an amide bond between the MTAPc and CdTe QDs. Both the linked ZnTAPc–QD complexes and the mixture of QDs and ZnTAPc (without chemical linking) showed Förster resonance energy transfer (FRET), whereas the QD interactions with InTAPc yielded no evidence of FRET. Both MTAPcs quenched the QDs emission, with quenching constants of the order of 103–104 M−1. High energy transfer efficiencies were obtained in some cases (as high as 93%), due to the low donor to acceptor distances.
- Full Text:
- Date Issued: 2010
- Authors: Britton, Jonathan , Antunes, Edith M , Nyokong, Tebello
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/262638 , vital:53539 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.12.013"
- Description: CdTe QDs capped with mercapto propionic acid (MPA) and thioglycolic acid (TGA) were covalently linked to zinc and indium tetraaminophthalocyanines (TAPcs) using N-ethyl-N(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) as the coupling agents. The results presented give evidence in favour of formation of an amide bond between the MTAPc and CdTe QDs. Both the linked ZnTAPc–QD complexes and the mixture of QDs and ZnTAPc (without chemical linking) showed Förster resonance energy transfer (FRET), whereas the QD interactions with InTAPc yielded no evidence of FRET. Both MTAPcs quenched the QDs emission, with quenching constants of the order of 103–104 M−1. High energy transfer efficiencies were obtained in some cases (as high as 93%), due to the low donor to acceptor distances.
- Full Text:
- Date Issued: 2010
Synthesis, photophysics and photochemistry of novel tetra (quinoxalinyl) phthalocyaninato zinc (II) complexes
- Erdoğmuş, Ali, Ogunsipe, Abimbola, Nyokong, Tebello
- Authors: Erdoğmuş, Ali , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263441 , vital:53628 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.04.007"
- Description: The syntheses and spectral, photophysical and photochemical properties of some zinc phthalocyanine derivatives – {2, (3)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (β-ZnPc) and 1, (4)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (α-ZnPc)} – are presented. The β-substituted complex is more fluorescent and exhibits lower tendencies to undergo intersystem crossing than its α-substituted counterpart, as judged by the former's higher fluorescence quantum yield (ΦF) and lower triplet quantum yield (ΦT) than the latter's in three solvents (DMSO, DMF and toluene). Singlet oxygen quantum yield (ΦΔ) values show the same trends as ΦT values. The differences in the spectral and photophysical properties of α-ZnPc and β-ZnPc are partly attributed to greater molecular distortions in the former. Studies of the interaction of the triplet states of α-ZnPc and β-ZnPc with triplet oxygen showed that α-ZnPc is more vulnerable to oxygen quenching than β-ZnPc. Also, the smallest quenching rate constants were observed in DMSO, which is attributed to the higher viscosity of DMSO than DMF and toluene.
- Full Text:
- Date Issued: 2009
- Authors: Erdoğmuş, Ali , Ogunsipe, Abimbola , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263441 , vital:53628 , xlink:href="https://doi.org/10.1016/j.jphotochem.2009.04.007"
- Description: The syntheses and spectral, photophysical and photochemical properties of some zinc phthalocyanine derivatives – {2, (3)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (β-ZnPc) and 1, (4)-tetra(quinoxalinyl)phthalocyaninato zinc(II), (α-ZnPc)} – are presented. The β-substituted complex is more fluorescent and exhibits lower tendencies to undergo intersystem crossing than its α-substituted counterpart, as judged by the former's higher fluorescence quantum yield (ΦF) and lower triplet quantum yield (ΦT) than the latter's in three solvents (DMSO, DMF and toluene). Singlet oxygen quantum yield (ΦΔ) values show the same trends as ΦT values. The differences in the spectral and photophysical properties of α-ZnPc and β-ZnPc are partly attributed to greater molecular distortions in the former. Studies of the interaction of the triplet states of α-ZnPc and β-ZnPc with triplet oxygen showed that α-ZnPc is more vulnerable to oxygen quenching than β-ZnPc. Also, the smallest quenching rate constants were observed in DMSO, which is attributed to the higher viscosity of DMSO than DMF and toluene.
- Full Text:
- Date Issued: 2009
The use of experimental design for the development of a capillary zone electrophoresis method for the quantitation of captopril
- Mukozhiwa, S Y, Khamanga, Sandile M, Walker, Roderick B
- Authors: Mukozhiwa, S Y , Khamanga, Sandile M , Walker, Roderick B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/183828 , vital:44073 , xlink:href="https://doi.org/10.1691/ph.2017.7071"
- Description: A capillary zone electrophoresis (CZE) method for the quantitation of captopril (CPT) using UV detection was developed. Influence of electrolyte concentration and system variables on electrophoretic separation was evaluated and a central composite design (CCD) was used to optimize the method. Variables investigated were pH, molarity, applied voltage and capillary length. The influence of sodium metabisulphite on the stability of test solutions was also investigated. The use of sodium metabisulphite prevented degradation of CPT over 24 hours. A fused uncoated silica capillary of 67.5cm total and 57.5 cm effective length was used for analysis. The applied voltage and capillary length affected the migration time of CPT significantly. A 20 mM phosphate buffer adjusted to pH 7.0 was used as running buffer and an applied voltage of 23.90 kV was suitable to effect a separation. The optimized electrophoretic conditions produced sharp, well-resolved peaks for CPT and sodium metabisulphite. Linear regression analysis of the response for CPT standards revealed the method was linear (R2 = 0.9995) over the range 5-70 μg/mL. The limits of quantitation and detection were 5 and 1.5 μg/mL. A simple, rapid and reliable CZE method has been developed and successfully applied to the analysis of commercially available CPT products.
- Full Text:
- Date Issued: 2017
- Authors: Mukozhiwa, S Y , Khamanga, Sandile M , Walker, Roderick B
- Date: 2017
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/183828 , vital:44073 , xlink:href="https://doi.org/10.1691/ph.2017.7071"
- Description: A capillary zone electrophoresis (CZE) method for the quantitation of captopril (CPT) using UV detection was developed. Influence of electrolyte concentration and system variables on electrophoretic separation was evaluated and a central composite design (CCD) was used to optimize the method. Variables investigated were pH, molarity, applied voltage and capillary length. The influence of sodium metabisulphite on the stability of test solutions was also investigated. The use of sodium metabisulphite prevented degradation of CPT over 24 hours. A fused uncoated silica capillary of 67.5cm total and 57.5 cm effective length was used for analysis. The applied voltage and capillary length affected the migration time of CPT significantly. A 20 mM phosphate buffer adjusted to pH 7.0 was used as running buffer and an applied voltage of 23.90 kV was suitable to effect a separation. The optimized electrophoretic conditions produced sharp, well-resolved peaks for CPT and sodium metabisulphite. Linear regression analysis of the response for CPT standards revealed the method was linear (R2 = 0.9995) over the range 5-70 μg/mL. The limits of quantitation and detection were 5 and 1.5 μg/mL. A simple, rapid and reliable CZE method has been developed and successfully applied to the analysis of commercially available CPT products.
- Full Text:
- Date Issued: 2017
Optical properties of water-soluble L-cysteine-capped alloyed CdSeS quantum dot passivated with ZnSeTe and ZnSeTe/ZnS shells
- Adegoke, Oluwasesan, Nyokong, Tebello, Forbes, Patricia B C
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B C
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193609 , vital:45352 , xlink:href="https://doi.org/10.1016/j.optmat.2015.05.024"
- Description: Alloyed quantum dots (QDs) passivated with shell materials have valuable optical characteristics suitable for a wide array of applications. In this work, alloyed ternary CdSeS QDs passivated with ZnSeTe and ZnSeTe/ZnS shells have been synthesized via a hot-injection method and a ligand exchange reaction employing L-cysteine as a thiol ligand has been used to obtain these water-soluble nanocrystals for the first time. The photoluminescence (PL) quantum yield (QY) of alloyed L-cysteine-capped CdSeS was 71.2% but decreased significantly to 5.2% upon passivation with a ZnSeTe shell. The red shift in PL emission of the CdSeS/ZnSeTe QDs was attributed to be strain-induced whilst a lattice-induced process likely created defect states in the core/shell interface hence contributing to the decline in the PL QY. Nonetheless, the fluorescence stability of CdSeS/ZnSeTe QDs in aqueous solution was unperturbed. Further passivation with a ZnS shell (CdSeS/ZnSeTe/ZnS) improved the PL QY to a value of 58.7% and thus indicates that the defect state in the QDs core/shell/shell structure was reduced. PL lifetime exciton measurements indicated that the rates of decay of the QDs influenced their photophysical properties.
- Full Text:
- Date Issued: 2015
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello , Forbes, Patricia B C
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/193609 , vital:45352 , xlink:href="https://doi.org/10.1016/j.optmat.2015.05.024"
- Description: Alloyed quantum dots (QDs) passivated with shell materials have valuable optical characteristics suitable for a wide array of applications. In this work, alloyed ternary CdSeS QDs passivated with ZnSeTe and ZnSeTe/ZnS shells have been synthesized via a hot-injection method and a ligand exchange reaction employing L-cysteine as a thiol ligand has been used to obtain these water-soluble nanocrystals for the first time. The photoluminescence (PL) quantum yield (QY) of alloyed L-cysteine-capped CdSeS was 71.2% but decreased significantly to 5.2% upon passivation with a ZnSeTe shell. The red shift in PL emission of the CdSeS/ZnSeTe QDs was attributed to be strain-induced whilst a lattice-induced process likely created defect states in the core/shell interface hence contributing to the decline in the PL QY. Nonetheless, the fluorescence stability of CdSeS/ZnSeTe QDs in aqueous solution was unperturbed. Further passivation with a ZnS shell (CdSeS/ZnSeTe/ZnS) improved the PL QY to a value of 58.7% and thus indicates that the defect state in the QDs core/shell/shell structure was reduced. PL lifetime exciton measurements indicated that the rates of decay of the QDs influenced their photophysical properties.
- Full Text:
- Date Issued: 2015
The challenges of alleviating poverty through ecological restoration: Insights from South Africa's “working for water” program
- McConnachie, Matthew M, Cowling, Richard M, Shackleton, Charlie M, Knight, Andrew T
- Authors: McConnachie, Matthew M , Cowling, Richard M , Shackleton, Charlie M , Knight, Andrew T
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181003 , vital:43680 , xlink:href="https://doi.org/10.1111/rec.12038"
- Description: Public works programs have been posited as win–win solutions for achieving societal goals for ecological restoration and poverty alleviation. However, little is documented regarding the challenges of implementing such projects. A commonly cited example is South Africa's invasive alien plant control program “Working for Water” (WfW), which aims to create employment via restoring landscapes invaded with alien plants. Recent studies have raised questions over the effectiveness of this program in achieving both its restoration and poverty alleviation goals. This is the first study that we are aware of that synthesizes the knowledge of managers on both the poverty alleviation and environmental outcomes of a public works project. Herein, we sought to understand the challenges and constraints faced by 23 WfW managers in fulfilling the program's environmental and poverty alleviation objectives. We found that the challenges most frequently cited by managers related to the capacity and competence of managers and teams, followed by challenges relating to planning and coordination, specifically the challenges of being flexible and adaptive when constrained by operating procedures. In addition, the current focus on maximizing short-term employment was perceived by some as limiting the efficiency and long-term effectiveness of the WfW program in achieving its environmental and social goals. We suggest that improving the conditions and duration of employment could improve the effectiveness of invasive alien plant control and ecological outcomes. We also suggest that WfW measure the impacts of their interventions through an adaptive management approach so that it can learn and adapt to the challenges it faces.
- Full Text:
- Date Issued: 2013
- Authors: McConnachie, Matthew M , Cowling, Richard M , Shackleton, Charlie M , Knight, Andrew T
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181003 , vital:43680 , xlink:href="https://doi.org/10.1111/rec.12038"
- Description: Public works programs have been posited as win–win solutions for achieving societal goals for ecological restoration and poverty alleviation. However, little is documented regarding the challenges of implementing such projects. A commonly cited example is South Africa's invasive alien plant control program “Working for Water” (WfW), which aims to create employment via restoring landscapes invaded with alien plants. Recent studies have raised questions over the effectiveness of this program in achieving both its restoration and poverty alleviation goals. This is the first study that we are aware of that synthesizes the knowledge of managers on both the poverty alleviation and environmental outcomes of a public works project. Herein, we sought to understand the challenges and constraints faced by 23 WfW managers in fulfilling the program's environmental and poverty alleviation objectives. We found that the challenges most frequently cited by managers related to the capacity and competence of managers and teams, followed by challenges relating to planning and coordination, specifically the challenges of being flexible and adaptive when constrained by operating procedures. In addition, the current focus on maximizing short-term employment was perceived by some as limiting the efficiency and long-term effectiveness of the WfW program in achieving its environmental and social goals. We suggest that improving the conditions and duration of employment could improve the effectiveness of invasive alien plant control and ecological outcomes. We also suggest that WfW measure the impacts of their interventions through an adaptive management approach so that it can learn and adapt to the challenges it faces.
- Full Text:
- Date Issued: 2013
The influence of livelihood dependency, local ecological knowledge and market proximity on the ecological impacts of harvesting non-timber forest products
- Steele, Melita Z, Shackleton, Charlie M, Shaanker, Ramanan U, Ganeshaiah, Kotiganahalli N, Radloff, Sarah E
- Authors: Steele, Melita Z , Shackleton, Charlie M , Shaanker, Ramanan U , Ganeshaiah, Kotiganahalli N , Radloff, Sarah E
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180908 , vital:43669 , xlink:href="https://doi.org/10.1016/j.forpol.2014.07.011"
- Description: It is well established that non-timber forest products make significant contributions to rural incomes throughout most of the developing world. NTFP use frequently raises concerns about the sustainability of, or ecological impacts associated with, NTFP harvesting, as well as local contextual factors which may limit or reduce the impacts. Here we test the conceptual model first advanced by Uma Shaanker et al. (2004) relating to the factors that may limit or exacerbate the ecological impacts associated with NTFP harvesting. These were the extent of local dependence on NTFPs, the degree of marketing and the level of local ecological knowledge. Data were collected via household questionnaires and ecological surveys of woody plants from eight villages throughout South Africa. We found no significant relationships between measures of ecological impact with local ecological knowledge or market proximity and engagement. There was a strong positive relationship between ecological impacts and NTFP dependency as indexed through mean annual direct-use value for NTFPs. This indicates that the higher the dependency and demand for NTFPs, the greater is the possibility of high impacts to the local environment. However, other contextual drivers not included in the original Uma Shaanker et al. (2004) model may also play a role, particularly the strength of local resource governance institutions.
- Full Text: false
- Date Issued: 2015
- Authors: Steele, Melita Z , Shackleton, Charlie M , Shaanker, Ramanan U , Ganeshaiah, Kotiganahalli N , Radloff, Sarah E
- Date: 2015
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/180908 , vital:43669 , xlink:href="https://doi.org/10.1016/j.forpol.2014.07.011"
- Description: It is well established that non-timber forest products make significant contributions to rural incomes throughout most of the developing world. NTFP use frequently raises concerns about the sustainability of, or ecological impacts associated with, NTFP harvesting, as well as local contextual factors which may limit or reduce the impacts. Here we test the conceptual model first advanced by Uma Shaanker et al. (2004) relating to the factors that may limit or exacerbate the ecological impacts associated with NTFP harvesting. These were the extent of local dependence on NTFPs, the degree of marketing and the level of local ecological knowledge. Data were collected via household questionnaires and ecological surveys of woody plants from eight villages throughout South Africa. We found no significant relationships between measures of ecological impact with local ecological knowledge or market proximity and engagement. There was a strong positive relationship between ecological impacts and NTFP dependency as indexed through mean annual direct-use value for NTFPs. This indicates that the higher the dependency and demand for NTFPs, the greater is the possibility of high impacts to the local environment. However, other contextual drivers not included in the original Uma Shaanker et al. (2004) model may also play a role, particularly the strength of local resource governance institutions.
- Full Text: false
- Date Issued: 2015
An assessment of the efficacy of two lysine microencapsulation techniques to determine the quantitative lysine requirement of the South African abalone, Haliotis midae L
- Shipton, Thomas A, Britz, Peter J, Walker, Roderick B
- Authors: Shipton, Thomas A , Britz, Peter J , Walker, Roderick B
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184289 , vital:44197 , xlink:href="https://doi.org/10.1046/j.1365-2095.2002.00204.x"
- Description: The quantification of the essential amino acid requirements of a species is a prerequisite to the formulation of biologically optimized diets. In this study, crystalline L-lysine was used in an attempt to determine the quantitative lysine requirement of juvenile Haliotis midae. Two microencapsulation techniques [gelatine/acacia and cellulose acetate phthalate (CAP)] were used to retard leaching of crystalline L-lysine incorporated into semipurified test diets. An assessment of the efficacy of the encapsulation techniques, revealed that despite effective lysine supplementation, H. midae fed semipurified test diets containing encapsulated crystalline L-lysine failed to promote significant improvements in either growth, feed or protein efficiency (P > 0.05). The failure of the crystalline L-lysine to illicit growth and nutritional responses is discussed.
- Full Text:
- Date Issued: 2002
- Authors: Shipton, Thomas A , Britz, Peter J , Walker, Roderick B
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184289 , vital:44197 , xlink:href="https://doi.org/10.1046/j.1365-2095.2002.00204.x"
- Description: The quantification of the essential amino acid requirements of a species is a prerequisite to the formulation of biologically optimized diets. In this study, crystalline L-lysine was used in an attempt to determine the quantitative lysine requirement of juvenile Haliotis midae. Two microencapsulation techniques [gelatine/acacia and cellulose acetate phthalate (CAP)] were used to retard leaching of crystalline L-lysine incorporated into semipurified test diets. An assessment of the efficacy of the encapsulation techniques, revealed that despite effective lysine supplementation, H. midae fed semipurified test diets containing encapsulated crystalline L-lysine failed to promote significant improvements in either growth, feed or protein efficiency (P > 0.05). The failure of the crystalline L-lysine to illicit growth and nutritional responses is discussed.
- Full Text:
- Date Issued: 2002
Efficient energy transfer in ethynyl bridged corrole–BODIPY dyads
- Yan, Yu, Wu, Fan, Qin, Jiawei, Xu, Haijun, Shi, Maohu, Zhou, Jingfeng, Mack, John, Fomo, Gertrude, Nyokong, Tebello, Shen, Zhen
- Authors: Yan, Yu , Wu, Fan , Qin, Jiawei , Xu, Haijun , Shi, Maohu , Zhou, Jingfeng , Mack, John , Fomo, Gertrude , Nyokong, Tebello , Shen, Zhen
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240899 , vital:50883 , xlink:href="https://doi.org/10.1039/C6RA12271J"
- Description: A series of new corrole–BODIPY dyads bridged by ethynyl linker moieties have been synthesized in high yields and fully characterized. The direction of energy transfer upon electronic excitation has been explored, and was found to be dependent on the number of corrole rings and their connection position on the BODIPY core. Intense bands in the absorption spectrum cover most of the visible region, which is potentially advantageous for capturing solar energy. Studies on the excitation spectra and lifetimes suggest that the energy transfer efficiency between the BODIPY and corrole moieties reaches almost 85%, which appears to be efficient in the context of energy transfer within the singlet manifold.
- Full Text:
- Date Issued: 2016
- Authors: Yan, Yu , Wu, Fan , Qin, Jiawei , Xu, Haijun , Shi, Maohu , Zhou, Jingfeng , Mack, John , Fomo, Gertrude , Nyokong, Tebello , Shen, Zhen
- Date: 2016
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/240899 , vital:50883 , xlink:href="https://doi.org/10.1039/C6RA12271J"
- Description: A series of new corrole–BODIPY dyads bridged by ethynyl linker moieties have been synthesized in high yields and fully characterized. The direction of energy transfer upon electronic excitation has been explored, and was found to be dependent on the number of corrole rings and their connection position on the BODIPY core. Intense bands in the absorption spectrum cover most of the visible region, which is potentially advantageous for capturing solar energy. Studies on the excitation spectra and lifetimes suggest that the energy transfer efficiency between the BODIPY and corrole moieties reaches almost 85%, which appears to be efficient in the context of energy transfer within the singlet manifold.
- Full Text:
- Date Issued: 2016