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Effects of central metal on the photophysical and photochemical properties of non-transition metal sulfophthalocyanine

- Ogunsipe, Abimbola, Nyokong, Tebello

Authors: Ogunsipe, Abimbola , Nyokong, Tebello
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/289337 , vital:56623 , xlink:href="https://doi.org/10.1142/S1088424605000186"
Description: The photophysical and photochemical properties and quenching (by 1,4-benzoquinone) of metallophthalocyanine sulfonates of aluminium (AlPcSmix), zinc (ZnPcSmix), silicon (SiPcSmix), germanium (GePcSmix) and tin (SnPcSmix) are presented. The quantum yield values of fluorescence (ΦF), triplet state (ΦT), singlet oxygen (ΦΔ) and photodegradation (Φd) were determined and the observed trends in their variation among the complexes discussed in terms of aggregation and the heavy atom effect. 1,4-benzoquinone effectively quenched the fluorescence of the complexes. Quenching analyses gave positive deviations from Stern-Volmer behavior, suggesting the existence of static quenching in addition to dynamic quenching. The static and dynamic components of the quenching were separated using a modified Stern-Volmer equation and the “sphere of action quenching model”. The quenching constant was found to be a function of the radius of the central metal ion.
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Date Issued: 2005

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Electro-oxidation of phenol and its derivatives on poly-Ni (OH) TPhPyPc modified vitreous carbon electrodes

- Obirai, Joseph, Bedioui, Fethi, Nyokong, Tebello

Authors: Obirai, Joseph , Bedioui, Fethi , Nyokong, Tebello
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/289353 , vital:56625 , xlink:href="https://doi.org/10.1016/j.jelechem.2004.11.006"
Description: The electrochemical oxidation of phenol and its derivatives using poly-nickel hydroxy tetraphenoxypyrrolephthalocyanine (poly-Ni(OH)TPhPyPc) modified vitreous carbon electrodes are described. The films were formed by the electro-transformation of the electropolymerized pyrrole-substituted phenoxyphthalocyanine poly-NiTPhPyPc modified electrode in aqueous 0.1 M NaOH solution. The poly-Ni(OH)TPhPyPc films showed better stability and resistance to electrode fouling compared to poly-NiTPhPyPc and unmodified electrodes. The resistance to surface fouling and stability can be attributed to the structure of the ring substituent on the phthalocyanine macrocycle and to the particular O–Ni–O bridged architecture of the nickel phthalocyanine film.
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Date Issued: 2005

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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.
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Date Issued: 2005

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Electropolymerized Pyrrole-Substituted Manganese Phthalocyanine Films for the Electroassisted Biomimetic Catalytic Reduction of Molecular Oxygen

- Rodrigues, Nazaré Pereira, Obirai, Joe, Nyokong, Tebello, Bedioui, Fethi

Authors: Rodrigues, Nazaré Pereira , Obirai, Joe , Nyokong, Tebello , Bedioui, Fethi
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/289372 , vital:56626 , xlink:href="https://doi.org/10.1002/elan.200403064"
Description: We report for the first time on the electroassisted biomimetic activation of molecular oxygen by a newly prepared electropolymerized polypyrrole-manganese phthalocyanine film. The prepared films and their intervention in the electroassisted catalytic reduction of molecular oxygen were analyzed by cyclic voltammetry and UV-visible spectrophotometry on optically transparent electrodes. The obtained results demonstrate the probable existence of the key-steps responsible for the suggested formation of the highly reactive manganese oxo intermediate.
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Date Issued: 2005

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Estimating the potential role of commercial over-harvesting in resource viability: A case study of five useful tree species in South Africa

- Shackleton, Charlie M, Guthrie, G, Main, R

Authors: Shackleton, Charlie M , Guthrie, G , Main, R
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/181324 , vital:43719 , xlink:href="https://doi.org/10.1002/ldr.652"
Description: There is a growing commercialization of non-timber forest products (NTFPs) as a means of livelihood by rural communities throughout the developing world. This often occurs in the absence of any clear understanding of or guidelines regarding sustainable yields and ecological impacts, which may undermine the success of NTFP enterprises, especially from arid regions. This paper reports on the use of size class profiles and three quantitative indices to examine population profiles of five potentially useful tree species used as NTFPs in the semiarid lowveld of South Africa. We also contrast the population densities of the five tree species in 2003 with data from 1992. Low stem densities and population profiles indicated that three of the five species would preclude the establishment of NTFP enterprises based on their products. The other two species seem to have sufficient densities for some harvesting to take place, within an adaptive management framework. However, the longitudinal data indicated that the density of both these species had significantly declined over an eleven-year period, highlighting the need for appropriate management institutions. Additionally, the proportion of mature stems cut, and the degree of cutting per stem, had increased for all five species over the eleven years. The three quantitative indices of population stability were not correlated with one another, and hence provided a useful suite of measures sensitive to different aspects of size class profiles and their interpretation.
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Date Issued: 2005

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Five unpublished coins of Alexander the great and his successors in the Rhodes University collection

- Snowball, Jeanette D, Snowball, Warren D

Authors: Snowball, Jeanette D , Snowball, Warren D
Date: 2005
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/70359 , vital:29648 , http://dx.doi.org/10.7445/50-0-73
Description: The article briefly discusses the economic and political significance of the Alexander III(“the Great”) type silver tetradrachm and publishes three of his coins currently held by the Rhodes University Classics Museum. Based on stylistic elements, they are classified as from the Amphipolis and Arados mints and were probably minted during his lifetime. Two further tetradrachms from the empires of Alexander’s successors, Ptolemy II and Seleucus IV, are also published.
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Date Issued: 2005

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Hydrogen peroxide oxidation of 2-chlorophenol and 2, 4, 5-trichlorophenol catalyzed by monomeric and aggregated cobalt tetrasulfophthalocyanine

- Agboola, Bolade, Ozoemena, Kenneth I, Nyokong, Tebello

Authors: Agboola, Bolade , Ozoemena, Kenneth I , Nyokong, Tebello
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/289249 , vital:56612 , xlink:href="https://doi.org/10.1016/j.molcata.2004.10.041"
Description: Cobalt tetrasulfophthalocyanine (CoTSPc) was used to catalyze the oxidation of 2-chlorophenol (2-CP) and 2,4,5-trichlorophenol (TCP) using hydrogen peroxide (H2O2) as the oxidant. This CoTSPc catalyzed hydrogen peroxide oxidation of chlorophenols resulted in the formation of different types of oxidation products depending on the solvent conditions. In water/methanol conditions (where CoTSPc is mainly monomeric, and unionized forms of the phenols), phenol and hydroquinone were the main oxidation products, while in phosphate buffer solutions (pH 7 and 10 for TCP and 2-CP, respectively, where CoTSPc is mainly aggregated, and ionized forms of the phenols), benzoquinone was the main product. In contrast to CoTSPc, other MTSPc complexes studied (AlTSPc, CuTSPc and NiTSPc) exhibited no detectable catalytic effect on the oxidation of chlorophenols under the experimental conditions employed, thus proving the effect of the central metal ions on efficient catalysis of chlorophenol. Reaction pathways are proposed based on the relative time of oxidation products formation.
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Date Issued: 2005

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Immobilized cobalt (II) phthalocyanine–cobalt (II) porphyrin pentamer at a glassy carbon electrode

- Ozoemena, Kenneth I, Zhao, Zhixin, Nyokong, Tebello

Authors: Ozoemena, Kenneth I , Zhao, Zhixin , Nyokong, Tebello
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/300322 , vital:57916 , xlink:href="https://doi.org/10.1016/j.elecom.2005.04.019"
Description: This communication describes the electrochemistry of a novel cobalt phthalocyanine–cobalt porphyrin (cobalt(II)phthalocyanine–cobalt(II)tetra(5-phenoxy-10,15,20-triphenylporphyrin)) (CoPc-(CoTPP)4) immobilised onto a glassy carbon electrode (GCE). The GCE-CoPc-(CoTPP)4 displayed high efficiency as a potential amperometric sensor for hydrogen peroxide (H2O2) in neutral and alkaline pH conditions. Electrochemical and electrocatalytic properties of the pentamer seem to depend mostly on the central CoPc, and partly, on the synergistic effect of the CoPc/CoPP units. The GCE-CoPc-(CoTPP)4 showed very fast amperometric response (∼1 s), with linearities up to ⩾1.50 mM, low detection limits (μM range) and stability (8 weeks) towards the amperometric determination of laboratory and medical solutions of H2O2.
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Date Issued: 2005

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Marine Reserves: a guide to science, design, and use

- Booth, Anthony J

Authors: Booth, Anthony J
Date: 2005
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/124965 , vital:35714 , https://doi.10.2989/16085910509503862
Description: With the considerable pressures that are being placed on our marine resources, there is an urgent need to find alternative strategies to ensure their long-term sustainability. One measure that has been proposed, and which is rapidly gaining popularity, is the designation of Marine Protected Area (MPA). These are demarcated areas that prohibit (or at least restrict) consumptive or extractive uses, such that human interferences and impacts are minimised. In this edited collection of papers, most of which have been written or co-written by the authors themselves, Sobel and Dahlgren have presented an excellent synopsis of the rationale behind, and the scientific basis underpinning, the use of marine reserves as a management tool. In addition, they have devoted half the book to the provision of case studies.
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Date Issued: 2005

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Melatonin generates singlet oxygen on laser irradiation but acts as a quencher when irradiated by lamp photolysis

- Maharaj, Deepa S, Molell, H, Antunes, Edith M, Maharaj, Hiren, Maree, D M, Nyokong, Tebello, Glass, Beverley D, Daya, Santy

Authors: Maharaj, Deepa S , Molell, H , Antunes, Edith M , Maharaj, Hiren , Maree, D M , Nyokong, Tebello , Glass, Beverley D , Daya, Santy
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/300335 , vital:57917 , xlink:href="https://doi.org/10.1111/j.1600-079X.2004.00185.x"
Description: Melatonin, a naturally occurring chemical mediator, although assigned a diverse range of functions, has attracted interest in recent years because of its ability to function as a free radical scavenger. Because of the implications of singlet oxygen in neurotoxicity, the objective of the study was to investigate the ability of melatonin to quench singlet oxygen generated using laser irradiation or lamp photolysis. The results show that melatonin produces radicals upon laser irradation while the lamp photolysis studies show that melatonin is able to scavenge singlet oxygen produced by naphthalene. While melatonin is a free radical scavenger under biological conditions, it acts as a generator of singlet oxygen and or radicals (as ΦΔ is 1.41) when irradiated with laser light, implying that it has the potential to be used in photodynamic therapy in the destruction of tumors.
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Date Issued: 2005

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Methodological Decisions in Context: The dilemmas and challenges of novice African scholars

- Lupele, Justin, Mwingi, Mweru, Kinyanjui, Felistus, Kimani, Joyce, Kisamba, Christine

Authors: Lupele, Justin , Mwingi, Mweru , Kinyanjui, Felistus , Kimani, Joyce , Kisamba, Christine
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/373734 , vital:66717 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/122698"
Description: This paper emerges out of a panel discussion during a PhD week and subsequent 8th International Environmental Education Invitation Seminar held at Rhodes University in 2004 and 2005 respectively. It illuminates some insights into our struggles (as novice African researchers) in trying to respond to contextual realities as we research education and social change in African contexts, seeking insight into what counts as legitimate research in this context. The paper considers our struggles at conceptual, methodological, analytical and data generation levels, and in a politics of research. This is done by means of examples drawn from five current doctoral research projects being undertaken in east and southern African regions, using a review framework that represents fairly common dimensions of PhD research. We conclude that research, when defined rigidly within research disciplines/paradigms (as have been defined in some – primarily Western – research trajectories) may fail to take into account African social and contextual realities when applied uncritically. We argue that there is need for researchers in Africa to consider a multiplicity of approaches if research is to be meaningful in, and responsive to, social and contextual realities. In particular, we argue for taking account of socio historical and socio-cultural contexts in creating African epistemology in and through research.
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Date Issued: 2005

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Modelling the sustainable harvest of Sclerocarya birrea subsp. caffra fruits in the South African lowveld

- Emanuel, P L, Shackleton, Charlie M, Baxter, Jeremy

Authors: Emanuel, P L , Shackleton, Charlie M , Baxter, Jeremy
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/181312 , vital:43718 , xlink:href="https://doi.org/10.1016/j.foreco.2005.03.066"
Description: Levels of commercialization, size class profile and fruit production of Sclerocarya birrea (marula) trees were studied in the Bushbuckridge region of South Africa. A stage-based population matrix model was used to estimate the sustainable yield for S. birrea fruit. The trees begin to bear fruit at an average size of 42.8 cm in circumference and this relates to an approximate age of 19 years. For a stable size class profile, the population growth rate, λ, was 1.1828758. The observed size class profile did not conform to the stable stage size class profile, obtained from the model. Thus, it was not possible to predict the state of the observed population. Using the model, it was estimated that 92% of fruit could be removed without impacting the current population profile. The management of other more destructive forms of S. birrea resource use (such as bark or firewood harvesting), however, do need to be monitored to limit negative impacts on the population that may reduce fruit availability for regeneration or cropping.
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Date Issued: 2005

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Monetary valuation of livelihoods for understanding the composition and complexity of rural households

- Dovie, Delali B K, Witkowski, Ed T F, Shackleton, Charlie M

Authors: Dovie, Delali B K , Witkowski, Ed T F , Shackleton, Charlie M
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/181346 , vital:43721 , xlink:href="https://doi.org/10.1007/s10460-004-7233-0"
Description: There is, at present, little precise understanding of the relative contributions of the various income streams used by impoverished rural households in southern Africa. The impact of household profiles on overall income also is not well understood. There is, therefore, little consideration of these factors in national economic accounting. This paper is an attempt to reduce this gap in knowledge by reflecting on the relative contribution of agro-pastoralism, secondary woodland resources, and formal and informal cash income streams to households in the semi-arid rural village of Thorndale, Limpopo Province, South Africa. In the absence of jobs and confronted with high migrant labor, households with open access to natural resources derived more benefits from land-based livelihoods than cash income streams (i.e., 57.5 % vs. 42.5 %). Total livelihood income was valued at US$2887 per household per annum. A significant correlation between monetary values derived from crops and formal wages was established, and it was found that households with high cash incomes tended to invest more in crop production. Over 80 of households were male-headed. Of these heads of household, more than 60 were long-term migrants to urban areas, leaving household decision-making to the women. The low literacy rates of women have deprived them of paid jobs outside the area and, therefore, have increased their dependence on crops (62%) and secondary woodlands resources (60%). This was further reflected in the proportion of households in which females were the main contributors of cash income (9.7%), or joint contributors with men (24.4%). Various positive correlations were established between the number of women per household and the three land-based livelihoods. This implied that women’s total control over such activities was mostly a result of the absence of men and not a typical phenomenon. In spite of this control, it was not positively reflected in the lives of majority of the women. Households differed in their participation in livelihood activities. Household size influenced the level of production and was positively correlated with the value of secondary woodland resources and crops. The study shows the interdependence of land-based livelihood sources and the impact of household features on production and consumption. Policies that focus on livelihood options need to recognize and accommodate associated household dynamics.
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Date Issued: 2005

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Photochemical and photophysical properties of pentoxy-and naphthaloxy appended magnesium and zinc phthalocyanines

- Maqanda, Wesiwe, Nyokong, Tebello, Maree, David M

Authors: Maqanda, Wesiwe , Nyokong, Tebello , Maree, David M
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/289260 , vital:56613 , xlink:href="https://doi.org/10.1142/S1088424605000435"
Description: Photochemical and photophysical measurements were conducted on pentoxy and naphthaloxy appended zinc and magnesium phthalocyanines. We describe in this paper the synthesis as well as unexpected photodegradation behavior of naphthaloxy appended magnesium phthalocyanines. General trends are described for quantum yields of photodegradation, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds.
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Date Issued: 2005

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Photophysical and photochemical studies of sulphonated non-transition metal phthalocyanines in aqueous and non-aqueous media

- Ogunsipe, Abimbola, Nyokong, Tebello

Authors: Ogunsipe, Abimbola , Nyokong, Tebello
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/289271 , vital:56614 , xlink:href="https://doi.org/10.1016/j.jphotochem.2005.03.001"
Description: The photophysical and photochemical parameters for mixed sulphonated metallophthalocyanine complexes (AlPcSmix, SiPcSmix, GePcSmix, SnPcSmix, and ZnPcSmix) are reported in phosphate buffer saline (PBS, pH 7.4), PBS containing the surfactant Triton X-100, and in dimethylsulphoxide (DMSO). The ground state spectra of SiPcSmix, GePcSmix and SnPcSmix show splitting of the Q-band in DMSO, but the fluorescence spectra have only one band, suggesting that only some components of the mixed complexes fluoresce. In general the quantum yields of fluorescence (ΦF) were smaller in DMSO compared to the aqueous solvents, while quantum yields of triplet state (ΦT) were larger in DMSO. Triplet lifetimes were much lower in aqueous solutions (compared to DMSO) due to the fact that water absorbs strongly around 1108 nm, which corresponds to the triplet energy of a metallophthalocyanine complex. The MPcSmix complexes quenched hydroquinone, and the Stern–Volmer constants follow the order: AlPcSmix > SiPcSmix > GePcSmix > ZnPcSmix > SnPcSmix which is the order of the extinction coefficients (of the low energy band for complexes with split Q-band) of these molecules. The rate constants for fluorescence, intersystem crossing, internal conversion, and photodegradation were determined from the hydroquinone quenching data.
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Date Issued: 2005

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Photophysical properties of a water-soluble adjacently substituted bisnaphthalophthalocyanine

- Seotsanyana-Mokhosi, Itumeleng, Nyokong, Tebello

Authors: Seotsanyana-Mokhosi, Itumeleng , Nyokong, Tebello
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/286091 , vital:56237 , xlink:href="https://doi.org/10.1142/S1088424605000599"
Description: Spectral properties of a water soluble metal free tetracarboxyphenoxy bisnaphthalo-phthalocyanine (3) were studied in water and organic solvents. It was found that in protic solvents, complex 3 was highly aggregated. The surfactant, Triton X100, and bovineserum albumin (BSA) do not effect disaggregation while cetyl trimethylammonium chloride (CTAC) caused the molecule to disaggregate. The fluorescence quantum yields were higher in the presence of CTAC. Studying the interaction of BSA with complex 3 using fluorometry revealed that BSA is highly quenched by the latter. A 1:1 stoichiometric binding ratio between BSA and the Pc was found. Triplet quantum yields in water containing CTAC were higher than in organic solvents.
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Date Issued: 2005

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Playing musement games: Retroduction in social research, with particular reference to indigenous knowledge in environmental and health education

- Price, Leigh

Authors: Price, Leigh
Date: 2005
Subjects: To be catalogued
Language: English
Type: text , article
Identifier: http://hdl.handle.net/10962/373763 , vital:66722 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/122701"
Description: My aim here is to introduce the concept of musement (retroduction or abduction) as an appropriate alternative to deduction and induction, both in indigenous knowledge (IK) specifically and in social science generally. As an example, I will use musement to tentatively address some of the ethical problems of using indigenous knowledge (IK) in environmental education and health education. This paper will therefore be of use both to researchers/educators wanting a discussion of retroduction, and researchers/educators wanting a discussion of indigenous knowledge epistemology and its relationship with ethics. I am arguing, from a perspective that allows a stratified reality (things can be real even if not measurable or actually present), that, we admit retroduction into our list of allowable research logics. In terms of IK, the result of accepting retroduction as a valid logic is that we allow IK to be dynamic and non-reified. It also allows a previously ignored aspect of IK, its spiritual/non-empirical beliefs, to be validated through ethical outcomes experienced in our lives, rather than through the previous criteria of empirical validity. In other words, we ask for IK: does believing in (whatever) adequately explain experience and/or provide optimistic, long term, ethical, appropriate ways of living? Thus, retroduction has the potential to allow IK to contribute to a normative ethics.
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Date Issued: 2005

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