Synthesis and photophysical properties of lead phthalocyanines
- Modibane, D.K., Nyokong, Tebello
- Authors: Modibane, D.K. , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268636 , vital:54216 , xlink:href="https://doi.org/10.1016/j.poly.2007.12.004"
- Description: This work reports on the synthesis and photophysical parameters of tetra-and octa-substituted new lead phthalocyanines. The complexes synthesized are: 1,4-(tetraphenoxyphthalocyaninato)lead (7a), 1,4-(tetra-tert-butylphenoxyphthalocyaninato)lead (7b), 2,3-(tetraphenoxyphthalocyaninato)lead (8a), 2,3-(tetra-tert-butylphenoxyphthalocyaninato)lead (8b), 2,3-octaphenoxyphthalocyaninatolead (9a) 2,3-[octakis(4-t-butylphenoxyphthalocyaninato)]lead (9b). Photophysical properties were studied for these complexes in a dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.70 to 0.88 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and more than 10 μs in the rest of the solvents) were observed due to the presence of heavy atom.
- Full Text:
- Date Issued: 2008
- Authors: Modibane, D.K. , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268636 , vital:54216 , xlink:href="https://doi.org/10.1016/j.poly.2007.12.004"
- Description: This work reports on the synthesis and photophysical parameters of tetra-and octa-substituted new lead phthalocyanines. The complexes synthesized are: 1,4-(tetraphenoxyphthalocyaninato)lead (7a), 1,4-(tetra-tert-butylphenoxyphthalocyaninato)lead (7b), 2,3-(tetraphenoxyphthalocyaninato)lead (8a), 2,3-(tetra-tert-butylphenoxyphthalocyaninato)lead (8b), 2,3-octaphenoxyphthalocyaninatolead (9a) 2,3-[octakis(4-t-butylphenoxyphthalocyaninato)]lead (9b). Photophysical properties were studied for these complexes in a dimethylsulfoxide, dimethylformamide, toluene, tetrahydrofuran and chloroform. The fluorescence spectra were different from excitation spectra due to demetallation upon excitation. High triplet quantum yields ranging from 0.70 to 0.88 (in DMSO, DMF and toluene) and low triplet lifetimes (20–50 μs in DMSO, and more than 10 μs in the rest of the solvents) were observed due to the presence of heavy atom.
- Full Text:
- Date Issued: 2008
Synthesis and solvent effects on the photophysicochemical properties of novel cadmium phenoxy phthalocyanines
- Chidawanyika, Wadzanai J U, Antunes, Edith M, Nyokong, Tebello
- Authors: Chidawanyika, Wadzanai J U , Antunes, Edith M , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268649 , vital:54217 , xlink:href="https://doi.org/10.1016/j.jphotochem.2007.09.020"
- Description: The syntheses of novel cadmium phenoxy complexes; tetrakis{1,(4)-tert-butylphenoxyphthalocyaninato}cadmium(II) (5a), tetrakis{1,(4)-phenoxyphthalocyaninato}cadmium(II) (5b), tetrakis{2,(3)-tert-butylphenoxyphthalocyaninato}cadmium(II) (6a) and tetrakis{2,(3)-phenoxyphthalocyaninato}cadmium(II) (6b) are presented herein. The spectroscopic and photophysicochemical properties have also been carried out and discussed together with the influence of various organic solvents on these properties. Spectroscopic properties, i.e. ground state electronic absorption and fluorescence spectra have been found to vary as a function of substituent position on the phthalocyanine macrocycle, i.e. α-substitution versus β-substitution. The photophysical parameters are reported as well as the photodegradation and singlet oxygen quantum yields, where the complexes were found to exhibit good photostability with the production of appreciable amounts of singlet oxygen.
- Full Text:
- Date Issued: 2008
- Authors: Chidawanyika, Wadzanai J U , Antunes, Edith M , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268649 , vital:54217 , xlink:href="https://doi.org/10.1016/j.jphotochem.2007.09.020"
- Description: The syntheses of novel cadmium phenoxy complexes; tetrakis{1,(4)-tert-butylphenoxyphthalocyaninato}cadmium(II) (5a), tetrakis{1,(4)-phenoxyphthalocyaninato}cadmium(II) (5b), tetrakis{2,(3)-tert-butylphenoxyphthalocyaninato}cadmium(II) (6a) and tetrakis{2,(3)-phenoxyphthalocyaninato}cadmium(II) (6b) are presented herein. The spectroscopic and photophysicochemical properties have also been carried out and discussed together with the influence of various organic solvents on these properties. Spectroscopic properties, i.e. ground state electronic absorption and fluorescence spectra have been found to vary as a function of substituent position on the phthalocyanine macrocycle, i.e. α-substitution versus β-substitution. The photophysical parameters are reported as well as the photodegradation and singlet oxygen quantum yields, where the complexes were found to exhibit good photostability with the production of appreciable amounts of singlet oxygen.
- Full Text:
- Date Issued: 2008
Synthesis, electrochemical characterization of tetra-and octa-substituted dodecyl-mercapto tin phthalocyanines in solution and as self-assembled monolayers
- Khene, Samson M, Geraldo, Daniela A, Togo, Chamunorwa A, Limson, Janice L, Nyokong, Tebello
- Authors: Khene, Samson M , Geraldo, Daniela A , Togo, Chamunorwa A , Limson, Janice L , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264541 , vital:53743 , xlink:href="https://doi.org/10.1016/j.electacta.2008.08.018"
- Description: Non-peripherally (α) tetra- (9) and octa-(7) substituted dodecyl-mercapto tin(IV) phthalocyanines were synthesized and their electrochemical behavior studied. Cyclic voltammetry and spectroelectrochemistry show ring-based reductions for 7 and 9, the former shows two ring oxidations, while the latter shows only one ring-based oxidation. The adsorption kinetics of (7) and (9) on gold electrode were investigated by electrochemical impedance spectroscopy (EIS). The equilibrium constant (K) for the adsorption and the Gibbs free energy (ΔGads) of the SAMs were evaluated based on the Frumkin isotherm.
- Full Text:
- Date Issued: 2008
- Authors: Khene, Samson M , Geraldo, Daniela A , Togo, Chamunorwa A , Limson, Janice L , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/264541 , vital:53743 , xlink:href="https://doi.org/10.1016/j.electacta.2008.08.018"
- Description: Non-peripherally (α) tetra- (9) and octa-(7) substituted dodecyl-mercapto tin(IV) phthalocyanines were synthesized and their electrochemical behavior studied. Cyclic voltammetry and spectroelectrochemistry show ring-based reductions for 7 and 9, the former shows two ring oxidations, while the latter shows only one ring-based oxidation. The adsorption kinetics of (7) and (9) on gold electrode were investigated by electrochemical impedance spectroscopy (EIS). The equilibrium constant (K) for the adsorption and the Gibbs free energy (ΔGads) of the SAMs were evaluated based on the Frumkin isotherm.
- Full Text:
- Date Issued: 2008
Synthesis, photophysical and photochemical studies on long chain zinc phthalocyanine derivatives
- Ogunsipe, Abimbola, Durmus, Mahmut, Atilla, Devrim, Gürek, Ayşe Gül, Ahsen, Vefa, Nyokong, Tebello
- Authors: Ogunsipe, Abimbola , Durmus, Mahmut , Atilla, Devrim , Gürek, Ayşe Gül , Ahsen, Vefa , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/266019 , vital:53910 , xlink:href="https://doi.org/10.1016/j.synthmet.2008.06.007"
- Description: The synthesis and characterization of 2,9,16,23-chloro-3,10,17,24-triethyleneoxysulphanylphthalocyaninato zinc(II) (CTESZnPc) is described. The photophysics and photochemistry of CTESZnPc and those of tetrakis(triethyleneoxysulphanyl)zinc phthalocyanine (TTESZnPc) and octakis(triethyleneoxysulphanyl)zinc phthalocyanine (OTESZnPc), are presented and compared with those of unsubstituted zinc phthalocyanine (ZnPc). The presence of triethyleneoxysulphanyl substituents on the ZnPc ring gave rise to higher values of singlet oxygen (ΦΔ) and photodegradation (ΦPd) quantum yields in DMF. However, TTESZnPc, OTESZnPc and CTESZnPc are less fluorescent than ZnPc, judging from their fluorescence quantum yield (ΦF) values. Fluorescence was lower in toluene than in DMF due to aggregation in the former solvent. Triplet quantum yield (ΦT) values were found to increase with the presence of substituents on the ZnPc ring, while triplet lifetimes (τT) were found to vary linearly with the logarithms of solvent viscosities. The fluorescences of the substituted ZnPc complexes were effectively quenched by benzoquinone (BQ), and the quenching data analyzed by the Stern–Volmer equation. The Stern–Volmer constants and the diffusion-controlled bimolecular rate constants were calculated.
- Full Text:
- Date Issued: 2008
- Authors: Ogunsipe, Abimbola , Durmus, Mahmut , Atilla, Devrim , Gürek, Ayşe Gül , Ahsen, Vefa , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/266019 , vital:53910 , xlink:href="https://doi.org/10.1016/j.synthmet.2008.06.007"
- Description: The synthesis and characterization of 2,9,16,23-chloro-3,10,17,24-triethyleneoxysulphanylphthalocyaninato zinc(II) (CTESZnPc) is described. The photophysics and photochemistry of CTESZnPc and those of tetrakis(triethyleneoxysulphanyl)zinc phthalocyanine (TTESZnPc) and octakis(triethyleneoxysulphanyl)zinc phthalocyanine (OTESZnPc), are presented and compared with those of unsubstituted zinc phthalocyanine (ZnPc). The presence of triethyleneoxysulphanyl substituents on the ZnPc ring gave rise to higher values of singlet oxygen (ΦΔ) and photodegradation (ΦPd) quantum yields in DMF. However, TTESZnPc, OTESZnPc and CTESZnPc are less fluorescent than ZnPc, judging from their fluorescence quantum yield (ΦF) values. Fluorescence was lower in toluene than in DMF due to aggregation in the former solvent. Triplet quantum yield (ΦT) values were found to increase with the presence of substituents on the ZnPc ring, while triplet lifetimes (τT) were found to vary linearly with the logarithms of solvent viscosities. The fluorescences of the substituted ZnPc complexes were effectively quenched by benzoquinone (BQ), and the quenching data analyzed by the Stern–Volmer equation. The Stern–Volmer constants and the diffusion-controlled bimolecular rate constants were calculated.
- Full Text:
- Date Issued: 2008
The impact of aid dependence on social development: the case of Zimbabwe
- Authors: Nyatoro, Tinashe
- Date: 2008
- Subjects: Economic assistance , Zimbabwe
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/26649 , vital:65735
- Description: The purpose of this study was to look at how a foreign aid dependent economy is vulnerable to external manipulations. This study came up with the conclusion that foreign capital dependence is detrimental to long-term social, economic, and sustainable development of developing countries. The study also noted how foreign aid is used as a foreign policy instrument by western countries to influence the behaviour of the developing countries. The study noted that Zimbabwe is an aid dependent country hence its vulnerability to external manipulation. This has been demonstrated by capital flight from Zimbabwe since 1997. Multilateral Financial Institutions, the European Union, United States of America and other bilateral donors withdrew their financial support to the country due to policy disagreements with the Zimbabwean government. This incidence of donors withdrawing their financial support to Zimbabwe raises fundamental questions as to whether the African state is autonomous or is it possible for the African state to delink itself from the current global international market and at what costs? What has come out very clearly from this study is that a dependent state has no autonomy to decide on its domestic and foreign policies without considering the interests of its donors, and hence its vulnerability to external manipulations. , Thesis (MSoc) -- Faculty of Management and Commerce, 2008
- Full Text:
- Date Issued: 2008
- Authors: Nyatoro, Tinashe
- Date: 2008
- Subjects: Economic assistance , Zimbabwe
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/26649 , vital:65735
- Description: The purpose of this study was to look at how a foreign aid dependent economy is vulnerable to external manipulations. This study came up with the conclusion that foreign capital dependence is detrimental to long-term social, economic, and sustainable development of developing countries. The study also noted how foreign aid is used as a foreign policy instrument by western countries to influence the behaviour of the developing countries. The study noted that Zimbabwe is an aid dependent country hence its vulnerability to external manipulation. This has been demonstrated by capital flight from Zimbabwe since 1997. Multilateral Financial Institutions, the European Union, United States of America and other bilateral donors withdrew their financial support to the country due to policy disagreements with the Zimbabwean government. This incidence of donors withdrawing their financial support to Zimbabwe raises fundamental questions as to whether the African state is autonomous or is it possible for the African state to delink itself from the current global international market and at what costs? What has come out very clearly from this study is that a dependent state has no autonomy to decide on its domestic and foreign policies without considering the interests of its donors, and hence its vulnerability to external manipulations. , Thesis (MSoc) -- Faculty of Management and Commerce, 2008
- Full Text:
- Date Issued: 2008
The photophysical studies of a mixture of CdTe quantum dots and negatively charged zinc phthalocyanines
- Moeno, Sharon, Nyokong, Tebello
- Authors: Moeno, Sharon , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268663 , vital:54220 , xlink:href="https://doi.org/10.1016/j.poly.2008.03.007"
- Description: Fluorescence resonance energy transfer (FRET) studies were carried out with quantum dots capped with thioglycolic acid (TGA) and 2-mercaptoethanol (2-ME) and negatively charged phthalocyanines {Zn tetracarboxy (ZnTCPc), Zn octacarboxy (ZnOCPc) and Zn tetrasulfo (ZnTSPc) phthalocyinines} in a 0.1 NaOH:EtOH (50:50) solvent mixture. The best overlap between emission spectra of the donor (QDs) and the absorption spectra of the acceptor (ZnPc derivatives) was observed for TGA capped QDs, very little overlap was obtained for 2-ME QDs. ZnTSPc gave the highest FRET efficiency (0.3), with ZnOCPc and ZnTCPc giving a FRET efficiency of 0.2. The ΦT values of the MPcs generally decreased in the presence of the QD whereas the triplet lifetimes (τT) of the ZnPc derivatives were higher in the presence of QDs.
- Full Text:
- Date Issued: 2008
- Authors: Moeno, Sharon , Nyokong, Tebello
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268663 , vital:54220 , xlink:href="https://doi.org/10.1016/j.poly.2008.03.007"
- Description: Fluorescence resonance energy transfer (FRET) studies were carried out with quantum dots capped with thioglycolic acid (TGA) and 2-mercaptoethanol (2-ME) and negatively charged phthalocyanines {Zn tetracarboxy (ZnTCPc), Zn octacarboxy (ZnOCPc) and Zn tetrasulfo (ZnTSPc) phthalocyinines} in a 0.1 NaOH:EtOH (50:50) solvent mixture. The best overlap between emission spectra of the donor (QDs) and the absorption spectra of the acceptor (ZnPc derivatives) was observed for TGA capped QDs, very little overlap was obtained for 2-ME QDs. ZnTSPc gave the highest FRET efficiency (0.3), with ZnOCPc and ZnTCPc giving a FRET efficiency of 0.2. The ΦT values of the MPcs generally decreased in the presence of the QD whereas the triplet lifetimes (τT) of the ZnPc derivatives were higher in the presence of QDs.
- Full Text:
- Date Issued: 2008
The Postcolonial heart of African philosophy
- Authors: Tabensky, Pedro
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/305762 , vital:58610 , xlink:href="https://hdl.handle.net/10520/EJC96056"
- Description: This piece is one of among a handful that seek in the first instance to reveal the origin of African philosophy as an academic discipline, the source of its unity and distinctiveness. The discipline of African philosophy originates in tragedy, out of pain, confusion and rage stemming from colonial destruction; destruction that is responsible for what Fanon calls the ‘negro neurosis’ caused by what Biko would describe as the unbearable fusion of colonised and coloniser. I argue that the birth of African philosophy as an academic discipline is largely responsible for its character and, crucially, for its distinctive creative possibilities.
- Full Text:
- Date Issued: 2008
- Authors: Tabensky, Pedro
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/305762 , vital:58610 , xlink:href="https://hdl.handle.net/10520/EJC96056"
- Description: This piece is one of among a handful that seek in the first instance to reveal the origin of African philosophy as an academic discipline, the source of its unity and distinctiveness. The discipline of African philosophy originates in tragedy, out of pain, confusion and rage stemming from colonial destruction; destruction that is responsible for what Fanon calls the ‘negro neurosis’ caused by what Biko would describe as the unbearable fusion of colonised and coloniser. I argue that the birth of African philosophy as an academic discipline is largely responsible for its character and, crucially, for its distinctive creative possibilities.
- Full Text:
- Date Issued: 2008
Tuning the redox properties of Co-N4 macrocyclic complexes for the catalytic electrooxidation of glucose
- Villagra, Evelyn, Bedioui, Fethi, Nyokong, Tebello, Canales, J Carlos, Sancy, Mamie, Páez, Maritza A, Costamagna, Juan, Zagal, Jose H
- Authors: Villagra, Evelyn , Bedioui, Fethi , Nyokong, Tebello , Canales, J Carlos , Sancy, Mamie , Páez, Maritza A , Costamagna, Juan , Zagal, Jose H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268675 , vital:54221 , xlink:href="https://doi.org/10.1016/j.electacta.2008.02.006"
- Description: Graphite electrodes modified with four different cobalt N4 macrocyclics, namely Co tetrapentapyridinophthalocyanine, (CoTPenPyrPc), Co tetrapyridinoporphyrazine (CoTPyPz), Co octa(hydroxyethylthio)phthalocyanine (CoOEHTPc) and Co tetranitrophthalocyanine (CoTNPc) exhibit catalytic activity for the oxidation of glucose in alkaline media. The purpose of this work is to establish correlations between the catalytic activity of these complexes and their redox potential. The activity of the different modified electrodes was tested by linear voltammetry under hydrodynamic conditions using the rotating disk technique. Tafel plots constructed from mass-transport corrected currents give slopes ranging from 0.080 to 0.160 V/decade for the different catalysts which suggests that a first one-electron step is rate controlling with the symmetry of the energy barrier depending on the nature of the ligand of the Co complex. A plot of log I versus the Co(II)/(I) formal potential gives a volcano curve that also includes catalysts studied previously. This illustrates the concept that the formal potential of the catalyst needs to be tuned to a certain value for achieving maximum activity. A theoretical interpretation of these results is given in terms of Langmuir isotherms for the adsorption of glucose on the Co sites of the surface-confined metal complexes.
- Full Text:
- Date Issued: 2008
- Authors: Villagra, Evelyn , Bedioui, Fethi , Nyokong, Tebello , Canales, J Carlos , Sancy, Mamie , Páez, Maritza A , Costamagna, Juan , Zagal, Jose H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268675 , vital:54221 , xlink:href="https://doi.org/10.1016/j.electacta.2008.02.006"
- Description: Graphite electrodes modified with four different cobalt N4 macrocyclics, namely Co tetrapentapyridinophthalocyanine, (CoTPenPyrPc), Co tetrapyridinoporphyrazine (CoTPyPz), Co octa(hydroxyethylthio)phthalocyanine (CoOEHTPc) and Co tetranitrophthalocyanine (CoTNPc) exhibit catalytic activity for the oxidation of glucose in alkaline media. The purpose of this work is to establish correlations between the catalytic activity of these complexes and their redox potential. The activity of the different modified electrodes was tested by linear voltammetry under hydrodynamic conditions using the rotating disk technique. Tafel plots constructed from mass-transport corrected currents give slopes ranging from 0.080 to 0.160 V/decade for the different catalysts which suggests that a first one-electron step is rate controlling with the symmetry of the energy barrier depending on the nature of the ligand of the Co complex. A plot of log I versus the Co(II)/(I) formal potential gives a volcano curve that also includes catalysts studied previously. This illustrates the concept that the formal potential of the catalyst needs to be tuned to a certain value for achieving maximum activity. A theoretical interpretation of these results is given in terms of Langmuir isotherms for the adsorption of glucose on the Co sites of the surface-confined metal complexes.
- Full Text:
- Date Issued: 2008
Underlying mechanisms affecting institutionalisation of environmental education courses in Southern Africa
- Authors: Lupele, Justin
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/386926 , vital:68188 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/122773"
- Description: This paper discusses the underlying causal mechanisms that enabled or constrained institutionalisation of environmental education in 12 institutions in eight countries in southern Africa. The study was carried out in the context of the Southern Africa Development Community Regional Environmental Education Support Programme’s Course Development Network (CDN). This paper reports on part of the author's doctoral study and draws on critical realism as the ontological lens. Data analysis was done by means of a retroductive mode of inference, as articulated by Danermark, Ekström, Jakosben and Karlsson (2002). The paper demonstrates that there are a number of underlying causal mechanisms, which may enable or constrain institutionalisation of environmental education. They include factors at play at both national and institutional level; namely, responsiveness to national and institutional needs, recognition and ownership, accreditation and certification, institutional culture and politics, short course support structure and support from colleagues. As part of the discussions of the results of the study, I have advanced some retroductive theories that suggest causal mechanisms beyond the empirical data based on the participants’ experiences and events in the CDN.
- Full Text:
- Date Issued: 2008
- Authors: Lupele, Justin
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/386926 , vital:68188 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/122773"
- Description: This paper discusses the underlying causal mechanisms that enabled or constrained institutionalisation of environmental education in 12 institutions in eight countries in southern Africa. The study was carried out in the context of the Southern Africa Development Community Regional Environmental Education Support Programme’s Course Development Network (CDN). This paper reports on part of the author's doctoral study and draws on critical realism as the ontological lens. Data analysis was done by means of a retroductive mode of inference, as articulated by Danermark, Ekström, Jakosben and Karlsson (2002). The paper demonstrates that there are a number of underlying causal mechanisms, which may enable or constrain institutionalisation of environmental education. They include factors at play at both national and institutional level; namely, responsiveness to national and institutional needs, recognition and ownership, accreditation and certification, institutional culture and politics, short course support structure and support from colleagues. As part of the discussions of the results of the study, I have advanced some retroductive theories that suggest causal mechanisms beyond the empirical data based on the participants’ experiences and events in the CDN.
- Full Text:
- Date Issued: 2008
Volcano correlations for the reactivity of surface-confined cobalt N4-macrocyclics for the electrocatalytic oxidation of 2-mercaptoacetate
- Claußen, Jan A, Ochoa, Gonzalo, Páez, Maritza, Costamagno, Juan, Gulppi, Miguel, Nyokong, Tebello, Bedioui, Fethi, Zagal, José H
- Authors: Claußen, Jan A , Ochoa, Gonzalo , Páez, Maritza , Costamagno, Juan , Gulppi, Miguel , Nyokong, Tebello , Bedioui, Fethi , Zagal, José H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268688 , vital:54222 , xlink:href="https://doi.org/10.1007/s10008-007-0336-y"
- Description: We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin larger than Co–tetrasulfonatotetraphenylporphyrin larger than Co-2,2′,2″,2‴tetra-aminotetraphenylporphyrin and decreases for cobalt phthalocyanines as Co-3,4-octaethylhexyloxyphthalocyanine > Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.
- Full Text:
- Date Issued: 2008
- Authors: Claußen, Jan A , Ochoa, Gonzalo , Páez, Maritza , Costamagno, Juan , Gulppi, Miguel , Nyokong, Tebello , Bedioui, Fethi , Zagal, José H
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/268688 , vital:54222 , xlink:href="https://doi.org/10.1007/s10008-007-0336-y"
- Description: We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin larger than Co–tetrasulfonatotetraphenylporphyrin larger than Co-2,2′,2″,2‴tetra-aminotetraphenylporphyrin and decreases for cobalt phthalocyanines as Co-3,4-octaethylhexyloxyphthalocyanine > Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.
- Full Text:
- Date Issued: 2008
What future subordinates will value in their leaders
- Cox, Andrea, Amos, Trevor L, Baxter, Jeremy
- Authors: Cox, Andrea , Amos, Trevor L , Baxter, Jeremy
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/270992 , vital:54499 , xlink:href="https://hdl.handle.net/10520/EJC51031"
- Description: Leaders should not randomly choose a leadership style. To be effective, leaders need to ensure that their leadership style is congruent with what subordinates value. The focus of this study is on what the future South African graduate workforce will value in a leader. The female and male respondents in this study emphasise similar leadership values, indicating that there is no distinct set of competencies that will be valued separately by males and females. The same was found for respondents of different cultures, namely African, Coloured, Indian, White and other. With respect to both gender and culture, the respondents emphasise a mixture of African and Western leadership values. This supports the idea that to be effective in South Africa, leaders need to understand the prevailing national cultural values before simply applying ''foreign'' leadership models and theories based upon cultural values found in the West. This research finds that irrespective of gender and culture in the South African workplace, to be effective, leaders need to be loyal and inspirational, have vision and integrity and must be open and honest with their subordinates. Leaders should avoid being autocratic, strict, religious, ritualistic and traditional. They should also avoid using consensus and perceived external control.
- Full Text:
- Date Issued: 2008
- Authors: Cox, Andrea , Amos, Trevor L , Baxter, Jeremy
- Date: 2008
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/270992 , vital:54499 , xlink:href="https://hdl.handle.net/10520/EJC51031"
- Description: Leaders should not randomly choose a leadership style. To be effective, leaders need to ensure that their leadership style is congruent with what subordinates value. The focus of this study is on what the future South African graduate workforce will value in a leader. The female and male respondents in this study emphasise similar leadership values, indicating that there is no distinct set of competencies that will be valued separately by males and females. The same was found for respondents of different cultures, namely African, Coloured, Indian, White and other. With respect to both gender and culture, the respondents emphasise a mixture of African and Western leadership values. This supports the idea that to be effective in South Africa, leaders need to understand the prevailing national cultural values before simply applying ''foreign'' leadership models and theories based upon cultural values found in the West. This research finds that irrespective of gender and culture in the South African workplace, to be effective, leaders need to be loyal and inspirational, have vision and integrity and must be open and honest with their subordinates. Leaders should avoid being autocratic, strict, religious, ritualistic and traditional. They should also avoid using consensus and perceived external control.
- Full Text:
- Date Issued: 2008
Photovoltaic-powered wireless communication system for rural schools outside national utility grid
- Kaseke, Richmore https://orcid.org/0000-0002-8295-5016
- Authors: Kaseke, Richmore https://orcid.org/0000-0002-8295-5016
- Date: 2007-02
- Subjects: Photovoltaic system
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/25483 , vital:64284
- Description: Access to global information is inarguably one of the key ways of bringing development to any community. In developing worlds, many rural schools lie outside both the Internet Service Provider’s (ISP) cable network and the national utility grid. Rapid developments in information and communication technology (ICT) continue to widen the digital divide between urban and rural schools. In South Africa, although these rural areas are outside the ISP’s cable network, they enjoy excellent mobile (cellular) communications network coverage. Fortunately, leading mobile operators in the country (MTN and Vodacom) have incorporated mobile data packet services into their cellular communication networks since 2002. A stand-alone photovoltaic (PV) system for powering ICT equipment in off grid rural schools was designed and installed; and its performance monitored. Performance of the system was considered in two categories, which are; cost and service performance. In cost performance, return on investment (ROI) and payback period (PB) are the two critical considerations. The PV system designed in this study gave an impressive ROI and PB of 286percent and 5 years, respectively. In order to monitor and evaluate the service performance a data acquisition system (DAS) was designed and installed. Besides proving the potential of PV in powering ICT equipment, results from the DAS also suggested a more efficient way of employing PV as a power source for powering equipment that is based on Switched-Mode Power Supply Units. Concurrent and continuous change in irradiance and temperature result in a four-segment pattern of rising and falling module efficiency throughout the day. Generally, modules produce more energy on cooler sunny days than hotter sunny days. Infrared (IR) Thermography was also used as part of both indoor and outdoor module tests. During indoor tests at pre-deployment stage, IR Thermography showed development of hot spots in mismatched cells of reverse-biased modules. On the outdoors, IR Thermography reiterated the effect of bird droppings on module surfaces by showing hot spots forming on areas covered by the droppings. For internet connectivity, a customized Mobile Internet Device (MIDevice) was designed, built and tested. The device allows remote computer systems to be connected to the Internet via the already existing mobile communication network k using General Packet Radio Services (GPRS). An entire rural school local area network (LAN) can be connected to the Internet via a single MIDevice. An experimental setup was designed in order to monitor and evaluate performance of GPRS in specific and mobile Internet solutions in general. Results obtained proved that GPRS can indeed be a solution for remote Internet connectivity in rural schools. In order to improve performance of GPRS or mobile Internet connections, caching, pop-up blocking and proxy filtering are necessary. , Thesis (MSc) -- Faculty of Science and Agriculture, 2007
- Full Text:
- Date Issued: 2007-02
- Authors: Kaseke, Richmore https://orcid.org/0000-0002-8295-5016
- Date: 2007-02
- Subjects: Photovoltaic system
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/25483 , vital:64284
- Description: Access to global information is inarguably one of the key ways of bringing development to any community. In developing worlds, many rural schools lie outside both the Internet Service Provider’s (ISP) cable network and the national utility grid. Rapid developments in information and communication technology (ICT) continue to widen the digital divide between urban and rural schools. In South Africa, although these rural areas are outside the ISP’s cable network, they enjoy excellent mobile (cellular) communications network coverage. Fortunately, leading mobile operators in the country (MTN and Vodacom) have incorporated mobile data packet services into their cellular communication networks since 2002. A stand-alone photovoltaic (PV) system for powering ICT equipment in off grid rural schools was designed and installed; and its performance monitored. Performance of the system was considered in two categories, which are; cost and service performance. In cost performance, return on investment (ROI) and payback period (PB) are the two critical considerations. The PV system designed in this study gave an impressive ROI and PB of 286percent and 5 years, respectively. In order to monitor and evaluate the service performance a data acquisition system (DAS) was designed and installed. Besides proving the potential of PV in powering ICT equipment, results from the DAS also suggested a more efficient way of employing PV as a power source for powering equipment that is based on Switched-Mode Power Supply Units. Concurrent and continuous change in irradiance and temperature result in a four-segment pattern of rising and falling module efficiency throughout the day. Generally, modules produce more energy on cooler sunny days than hotter sunny days. Infrared (IR) Thermography was also used as part of both indoor and outdoor module tests. During indoor tests at pre-deployment stage, IR Thermography showed development of hot spots in mismatched cells of reverse-biased modules. On the outdoors, IR Thermography reiterated the effect of bird droppings on module surfaces by showing hot spots forming on areas covered by the droppings. For internet connectivity, a customized Mobile Internet Device (MIDevice) was designed, built and tested. The device allows remote computer systems to be connected to the Internet via the already existing mobile communication network k using General Packet Radio Services (GPRS). An entire rural school local area network (LAN) can be connected to the Internet via a single MIDevice. An experimental setup was designed in order to monitor and evaluate performance of GPRS in specific and mobile Internet solutions in general. Results obtained proved that GPRS can indeed be a solution for remote Internet connectivity in rural schools. In order to improve performance of GPRS or mobile Internet connections, caching, pop-up blocking and proxy filtering are necessary. , Thesis (MSc) -- Faculty of Science and Agriculture, 2007
- Full Text:
- Date Issued: 2007-02
Assessing the effects of invasive alien species on rural livelihoods: Case examples and a framework from South Africa
- Shackleton, Charlie M, McGarry, Dylan K, Fourie, Saskia, Gambiza, James, Shackleton, Sheona E, Fabricius, Christo
- Authors: Shackleton, Charlie M , McGarry, Dylan K , Fourie, Saskia , Gambiza, James , Shackleton, Sheona E , Fabricius, Christo
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181279 , vital:43715 , xlink:href="https://doi.org/10.1007/s10745-006-9095-0"
- Description: The detrimental impacts of invasive alien species (IAS) on ecosystem goods and services and local and regional economies are well documented. However, the use of IAS by rural communities is little understood, and rarely factored into IAS control programmes. Understanding the use of IAS by rural communities and factoring these into cost-benefit models is complex, depending upon a range of local-level attributes such as the time since invasion, abundance, and local-level costs and benefits. This paper reports on two case studies examining the role of IAS in rural livelihoods in the Eastern Cape, South Africa. In both cases, rural communities made widespread consumptive use of the IAS and generally would prefer higher densities, except in certain key localities. Several households traded in IAS products to generate supplementary income. We present a conceptual framework to guide interpretation of these and future case studies, considering attributes such as time since invasion, the competitiveness of the species, and the relative costs and benefits.
- Full Text:
- Date Issued: 2007
- Authors: Shackleton, Charlie M , McGarry, Dylan K , Fourie, Saskia , Gambiza, James , Shackleton, Sheona E , Fabricius, Christo
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181279 , vital:43715 , xlink:href="https://doi.org/10.1007/s10745-006-9095-0"
- Description: The detrimental impacts of invasive alien species (IAS) on ecosystem goods and services and local and regional economies are well documented. However, the use of IAS by rural communities is little understood, and rarely factored into IAS control programmes. Understanding the use of IAS by rural communities and factoring these into cost-benefit models is complex, depending upon a range of local-level attributes such as the time since invasion, abundance, and local-level costs and benefits. This paper reports on two case studies examining the role of IAS in rural livelihoods in the Eastern Cape, South Africa. In both cases, rural communities made widespread consumptive use of the IAS and generally would prefer higher densities, except in certain key localities. Several households traded in IAS products to generate supplementary income. We present a conceptual framework to guide interpretation of these and future case studies, considering attributes such as time since invasion, the competitiveness of the species, and the relative costs and benefits.
- Full Text:
- Date Issued: 2007
Assessment of antibacterial potentials of Garcinia Kola seed extracts and their interactions with antibiotics
- Authors: Sibanda, Thulani
- Date: 2007
- Subjects: Drug resistance in microorganisms , Garcinia , Antibiotics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/19236 , vital:43038
- Description: The antibacterial potency of the extracts of the seed of Garcinia kola (bitter kola) was investigated in this study against a panel of referenced, environmental and clinical bacterial strains. The killing rates of the active extract as well as their potential for combination antibacterial therapy with standard antibiotics were also elucidated using standard procedures. The aqueous and acetone extracts of the seed were screened for activity against 27 bacterial isolates. The aqueous extract exhibited activity mainly against Gram positive organisms with Minimum inhibitory concentration (MIC) values ranging from 5 mgml-1 – 20 mgml-1, while the acetone extract showed activity against both Gram negative and Gram positive organisms with MIC values ranging from 10 mgml-1 - 0.156 mgml-1. The acetone extract also showed rapid bactericidal activity against Staphylococcus aureus ATCC 6538 with a 3.097 Log10 reduction in counts within 4 hours at 0.3125 mgml-1 and a 1.582 Log10 reduction against Proteus vulgaris CSIR 0030 at 5 mgml-1 after 1 hour. In addition, the aqueous, methanol and acetone extracts of the seeds also exhibited activity against four clinical strains of Staphylococcus isolated from wound sepsis specimens. The MIC values for the aqueous extract were 10 mgml-1 for all the isolates while the acetone and methanol extracts had lower values ranging from 0.3125 - 0.625 mgml-1. The acetone extract was strongly bactericidal against Staphylococcus aureus OKOH3 resulting in a 2.70 Log10 reduction in counts at 1.25 mgml-1 within 4 hours of exposure and a complete elimination of the organism after 8 hours. The bactericidal activity of the same extract against Staphylococcus aureus OKOH1 was weak, achieving only a 2.92 Log10 reduction in counts at 1.25 mgml-1 (4× MIC) in 24 hours. In the test for interactions between the acetone extract of the seeds and antibiotics, synergistic interactions were observed largely against Gram positive organisms using the FIC indices, (indices of 0.52 - 0.875) with combinations against Gram negatives yielding largely antagonistic interactions (indices of 2.0 to 5.0). Synergy (≥ 1000 times or ≥ 3 Log10 potentiation of the bactericidal activity) against both Gram negative and Gram positive organisms was detected by time kill assays mainly involving the antibiotics tetracycline, chloramphenicol, amoxycillin and penicillin G. Combinations involving erythromycin and ciprofloxacin consistently gave antagonistic or indifferent interactions. We conclude that the acetone extract of Garcinia kola seeds possess strong bactericidal activities against both Gram positive and Gram negative organisms and can be therapeutically useful in the treatment of bacterial infections including the problematic staphylococcal wound infections. In addition, the acetone extract can be a potential source of broad spectrum resistance modifying compounds that can potentially improve the performance of antibiotics in the treatment of drug resistant infections. , Thesis (MSc)-- Microbiology, University of Fort Hare, 2007
- Full Text:
- Date Issued: 2007
- Authors: Sibanda, Thulani
- Date: 2007
- Subjects: Drug resistance in microorganisms , Garcinia , Antibiotics
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10353/19236 , vital:43038
- Description: The antibacterial potency of the extracts of the seed of Garcinia kola (bitter kola) was investigated in this study against a panel of referenced, environmental and clinical bacterial strains. The killing rates of the active extract as well as their potential for combination antibacterial therapy with standard antibiotics were also elucidated using standard procedures. The aqueous and acetone extracts of the seed were screened for activity against 27 bacterial isolates. The aqueous extract exhibited activity mainly against Gram positive organisms with Minimum inhibitory concentration (MIC) values ranging from 5 mgml-1 – 20 mgml-1, while the acetone extract showed activity against both Gram negative and Gram positive organisms with MIC values ranging from 10 mgml-1 - 0.156 mgml-1. The acetone extract also showed rapid bactericidal activity against Staphylococcus aureus ATCC 6538 with a 3.097 Log10 reduction in counts within 4 hours at 0.3125 mgml-1 and a 1.582 Log10 reduction against Proteus vulgaris CSIR 0030 at 5 mgml-1 after 1 hour. In addition, the aqueous, methanol and acetone extracts of the seeds also exhibited activity against four clinical strains of Staphylococcus isolated from wound sepsis specimens. The MIC values for the aqueous extract were 10 mgml-1 for all the isolates while the acetone and methanol extracts had lower values ranging from 0.3125 - 0.625 mgml-1. The acetone extract was strongly bactericidal against Staphylococcus aureus OKOH3 resulting in a 2.70 Log10 reduction in counts at 1.25 mgml-1 within 4 hours of exposure and a complete elimination of the organism after 8 hours. The bactericidal activity of the same extract against Staphylococcus aureus OKOH1 was weak, achieving only a 2.92 Log10 reduction in counts at 1.25 mgml-1 (4× MIC) in 24 hours. In the test for interactions between the acetone extract of the seeds and antibiotics, synergistic interactions were observed largely against Gram positive organisms using the FIC indices, (indices of 0.52 - 0.875) with combinations against Gram negatives yielding largely antagonistic interactions (indices of 2.0 to 5.0). Synergy (≥ 1000 times or ≥ 3 Log10 potentiation of the bactericidal activity) against both Gram negative and Gram positive organisms was detected by time kill assays mainly involving the antibiotics tetracycline, chloramphenicol, amoxycillin and penicillin G. Combinations involving erythromycin and ciprofloxacin consistently gave antagonistic or indifferent interactions. We conclude that the acetone extract of Garcinia kola seeds possess strong bactericidal activities against both Gram positive and Gram negative organisms and can be therapeutically useful in the treatment of bacterial infections including the problematic staphylococcal wound infections. In addition, the acetone extract can be a potential source of broad spectrum resistance modifying compounds that can potentially improve the performance of antibiotics in the treatment of drug resistant infections. , Thesis (MSc)-- Microbiology, University of Fort Hare, 2007
- Full Text:
- Date Issued: 2007
Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures
- Richoux, Nicole B, Froneman, P William
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457923 , vital:75695 , xlink:href="https://doi.org/10.1016/j.ecss.2006.09.007 "
- Description: Stable isotope analyses (δ13C and δ15N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ13C values of Zostera capensis and surface sediments near the salt marsh, the δ13C and δ15N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ13C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ13C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ15N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ13C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.
- Full Text:
- Date Issued: 2007
- Authors: Richoux, Nicole B , Froneman, P William
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457923 , vital:75695 , xlink:href="https://doi.org/10.1016/j.ecss.2006.09.007 "
- Description: Stable isotope analyses (δ13C and δ15N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ13C values of Zostera capensis and surface sediments near the salt marsh, the δ13C and δ15N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ13C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ13C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ15N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ13C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.
- Full Text:
- Date Issued: 2007
Characterization of self-assembled monolayers of iron and cobalt octaalkylthiosubstituted phthalocyanines and their use in nitrite electrocatalytic oxidation
- Matemadombo, Fungisai, Nyokong, Tebello
- Authors: Matemadombo, Fungisai , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/271182 , vital:54519 , xlink:href="https://doi.org/10.1016/j.electacta.2007.05.002"
- Description: Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.
- Full Text:
- Date Issued: 2007
- Authors: Matemadombo, Fungisai , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/271182 , vital:54519 , xlink:href="https://doi.org/10.1016/j.electacta.2007.05.002"
- Description: Cobalt and iron phenylthiosubstituted phthalocyanines have been deposited on Au electrode surfaces through the self-assembled monolayer (SAM) technique. The so formed layers were studied using voltammetric and impedance techniques. These SAMs blocked a number of Faradic processes and electrocatalyzed the oxidation of nitrite. The electrocatalytic parameters of the cobalt and iron phenylthiosubstituted phthalocyanines deposited on Au electrodes in nitrite solution were studied. Nitrite overpotentials which are lower than ever reported were obtained in this work for the iron phenylthiosubstituted phthalocyanines with very high stability.
- Full Text:
- Date Issued: 2007
Cobalt Phthalocyanine Molecular Electrode for the Electrochemical Investigation of the Release of Glutathione upon Copper-Catalyzed Decomposition of S-Nitrosoglutathione
- Sehlotho, Nthapo, Griveau, Sophie, Nyokong, Tebello, Bedioui, Fethi
- Authors: Sehlotho, Nthapo , Griveau, Sophie , Nyokong, Tebello , Bedioui, Fethi
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281201 , vital:55701 , xlink:href="https://doi.org/10.1002/elan.200603656"
- Description: Decomposition of S-nitrosoglutathione (GSNO) in phosphate buffer solution at physiological pH 7.4 in the presence of cuprous ion as a catalyst and sodium borohydride as a reducing agent is analyzed by observing the transient apparition of reduced glutathione GSH through its electrooxidation. Transient formation of GSH, upon decomposition of 1 mM GSNO in presence of 0.025 mM Cu(NO3)2 and 1 mM NaBH4 was detected by using an ordinary pyrolytic graphite electrode modified with an adsorbed monolayer of cobalt phthalocyanine at 0 V vs. SCE.
- Full Text:
- Date Issued: 2007
- Authors: Sehlotho, Nthapo , Griveau, Sophie , Nyokong, Tebello , Bedioui, Fethi
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281201 , vital:55701 , xlink:href="https://doi.org/10.1002/elan.200603656"
- Description: Decomposition of S-nitrosoglutathione (GSNO) in phosphate buffer solution at physiological pH 7.4 in the presence of cuprous ion as a catalyst and sodium borohydride as a reducing agent is analyzed by observing the transient apparition of reduced glutathione GSH through its electrooxidation. Transient formation of GSH, upon decomposition of 1 mM GSNO in presence of 0.025 mM Cu(NO3)2 and 1 mM NaBH4 was detected by using an ordinary pyrolytic graphite electrode modified with an adsorbed monolayer of cobalt phthalocyanine at 0 V vs. SCE.
- Full Text:
- Date Issued: 2007
Comparative electrooxidation of nitrite by electrodeposited Co (II), Fe (II) and Mn (III) tetrakis (benzylmercapto) and tetrakis (dodecylmercapto) phthalocyanines on gold electrodes
- Agboola, Bolade, Nyokong, Tebello
- Authors: Agboola, Bolade , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281212 , vital:55702 , xlink:href="https://doi.org/10.1016/j.aca.2007.01.031"
- Description: This work reports on the electrooxidation of nitrite using Co(II), Fe(II) and Mn(III) tetrakis (benzylmercapto) and tetrakis (dodecylmercapto) phthalocyanines electrodeposited onto a gold electrode. Good catalytic activity (in terms of lowering overpotential) was obtained for these molecules when compared to previously reported MPc catalysts. The catalytic current was found to vary linearly with nitrite concentration in the range employed in this work (0.1–1 mM) and high sensitivities ranging from 6.9 to 9.9 μA mM−1 were observed for all the modified electrodes.
- Full Text:
- Date Issued: 2007
- Authors: Agboola, Bolade , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281212 , vital:55702 , xlink:href="https://doi.org/10.1016/j.aca.2007.01.031"
- Description: This work reports on the electrooxidation of nitrite using Co(II), Fe(II) and Mn(III) tetrakis (benzylmercapto) and tetrakis (dodecylmercapto) phthalocyanines electrodeposited onto a gold electrode. Good catalytic activity (in terms of lowering overpotential) was obtained for these molecules when compared to previously reported MPc catalysts. The catalytic current was found to vary linearly with nitrite concentration in the range employed in this work (0.1–1 mM) and high sensitivities ranging from 6.9 to 9.9 μA mM−1 were observed for all the modified electrodes.
- Full Text:
- Date Issued: 2007
Comparative electrooxidation of sulphite by self-assembled monolayers (SAMs) of Co (II), Fe (II), Ni (II) and Mn (III) tetrakis benzylmercapto and dodecylmercapto metallophthalocyanines complexes on gold electrodes
- Agboola, Bolade, Nyokong, Tebello
- Authors: Agboola, Bolade , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281223 , vital:55703 , xlink:href="https://doi.org/10.1016/j.talanta.2006.11.042"
- Description: This work reports on the use of Co(II), Fe(II), Mn(III) and Ni(II) tetrakis benzylmercapto and dodecylmercapto phthalocyanine complexes for gold electrode modification for electrooxidation of sulphite ions. The complexes were successfully used to modify gold electrodes by self-assembled monolayer (SAM) technique. The self-assembled films are stable and showed blocking characteristics towards the following Faradaic processes; gold surface oxidation, underpotential deposition (UPD) of copper and solution redox chemistry of [Fe(H2O)63+]/[Fe(H2O)62+]. All the modified electrodes showed improved catalytic activities than the unmodified gold electrode towards sulphite ion electrooxidation with all the modified electrodes exhibiting high resistance to electrode surface passivation. Better catalytic performance were obtained for the CoPcs, FePcs and MnPcs which have metal based redox processes within the range of the sulphite electrooxidation peak, while the NiPcs which did not show metal based redox reaction performed less. The catalytic current was found to be linear with sulphite ion concentration in the concentration range employed in this work (0.1–1 mM) and sensitivities ranging from 1.68 to 2.96 μA/mM were observed for all the modified electrodes. Mechanisms of the catalytic oxidation of sulphite ions are proposed.
- Full Text:
- Date Issued: 2007
- Authors: Agboola, Bolade , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/281223 , vital:55703 , xlink:href="https://doi.org/10.1016/j.talanta.2006.11.042"
- Description: This work reports on the use of Co(II), Fe(II), Mn(III) and Ni(II) tetrakis benzylmercapto and dodecylmercapto phthalocyanine complexes for gold electrode modification for electrooxidation of sulphite ions. The complexes were successfully used to modify gold electrodes by self-assembled monolayer (SAM) technique. The self-assembled films are stable and showed blocking characteristics towards the following Faradaic processes; gold surface oxidation, underpotential deposition (UPD) of copper and solution redox chemistry of [Fe(H2O)63+]/[Fe(H2O)62+]. All the modified electrodes showed improved catalytic activities than the unmodified gold electrode towards sulphite ion electrooxidation with all the modified electrodes exhibiting high resistance to electrode surface passivation. Better catalytic performance were obtained for the CoPcs, FePcs and MnPcs which have metal based redox processes within the range of the sulphite electrooxidation peak, while the NiPcs which did not show metal based redox reaction performed less. The catalytic current was found to be linear with sulphite ion concentration in the concentration range employed in this work (0.1–1 mM) and sensitivities ranging from 1.68 to 2.96 μA/mM were observed for all the modified electrodes. Mechanisms of the catalytic oxidation of sulphite ions are proposed.
- Full Text:
- Date Issued: 2007
Comparative photocatalytic efficiency of oxotitanium (IV) phthalocyanines for the oxidation of 1-hexene
- 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/10962/271193 , vital:54520 , xlink:href="https://doi.org/10.1016/j.molcata.2007.04.005"
- Description: The comparative photocatalytic activities of aryloxy and arylthio tetrasubstituted oxotitanium(IV) phthalocyanine complexes for the oxidation of 1-hexene in DCM are reported for the first time. The singlet oxygen quantum yield, photostability and photocatalytic properties are investigated. The catalysts effectively catalyse 1-hexene to 1,2-epoxyhexane and 1-hexen-3-ol as major and minor products respectively. The photooxidation products are formed via two reaction mechanisms, namely via singlet oxygen (Type II) and radical (Type I) reaction pathways. These are also dependent on the singlet oxygen quantum yields and photostabilities of the phthalocyanines. Complex 1a that is peripherally substituted with phenoxy groups exhibited the best activity in terms of overall performance.
- 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/10962/271193 , vital:54520 , xlink:href="https://doi.org/10.1016/j.molcata.2007.04.005"
- Description: The comparative photocatalytic activities of aryloxy and arylthio tetrasubstituted oxotitanium(IV) phthalocyanine complexes for the oxidation of 1-hexene in DCM are reported for the first time. The singlet oxygen quantum yield, photostability and photocatalytic properties are investigated. The catalysts effectively catalyse 1-hexene to 1,2-epoxyhexane and 1-hexen-3-ol as major and minor products respectively. The photooxidation products are formed via two reaction mechanisms, namely via singlet oxygen (Type II) and radical (Type I) reaction pathways. These are also dependent on the singlet oxygen quantum yields and photostabilities of the phthalocyanines. Complex 1a that is peripherally substituted with phenoxy groups exhibited the best activity in terms of overall performance.
- Full Text:
- Date Issued: 2007