Spectrophotometric and electrochemical studies of the interaction between iron (II) tetrasulfophthalocyanine and histamine
- Authors: Oni, Joshua , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289629 , vital:56657 , xlink:href="https://doi.org/10.1142/S1088424602000233"
- Description: The interaction between iron(II) tetrasulfophthalocyanine ([FeIITSPc]4+) and histamine results in the oxidation of the central metal by oxygen in the former, with the formation of a complex denoted as [(His)FeIIITSPc]3− (where His = histamine). The rate constant for the formation of the complex is kf = 2.41 × 10−2dm3.mol−1.s−1 and an equilibrium constant of 6.3 dm3.mol-1 was obtained. The oxidation state of the central metal of [FeIITSPc]4− before and after the coordination of histamine is confirmed by spectroelectrochemistry. Further electrochemical oxidation of this [(His)FeIIITsPc]3− derivative results in a metal-based process proposed to involve an FeIV phthalocyanine species.
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- Date Issued: 2002
Synthesis, electrochemical and photochemical properties of unsymmetrically substituted zinc phthalocyanine complexes
- Authors: Matlaba, Pulane M , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289650 , vital:56658 , xlink:href="https://doi.org/10.1016/S0277-5387(02)01226-3"
- Description: The synthesis of symmetrically and unsymmetrically substituted zinc phthalocyanine (ZnPc) derivatives are reported. The ZnPc derivatives are synthesized by ring expansion of subphthalocyanine complexes. Ring substitution is effected with tert-butyl phenol, naphthol and hydroxybenzoic acid. Comparison of the redox potentials for complexes substituted with varying numbers of tert-butyl phenol: 1 (complex 5), 2 (complex 6), 3 (complex 7), 6 (complex 8) and 8 (complex 9) shows that the complexes with the highest number of substituents are more difficult to oxidize and easier to reduce. All the reported complexes are relatively photostable, with photobleaching quantum yields of the order of 10−5. Singlet oxygen quantum yields for the complexes ranged from 0.22 to 0.68.
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- Date Issued: 2002
Synthesis, photophysical and photochemical studies of germanium and tin phthalocyanine complexes
- Authors: Maree, Suzanne , Phillips, David , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289667 , vital:56661 , xlink:href="https://doi.org/10.1142/S108842460200004X"
- Description: This work reports on the synthesis of tin and germanium phthalocyanine complexes containing phenoxy and substituted phenoxy groups as phthalocyanine ring substituents. The compounds studied are: dichlorogermanium phthalocyanine complexes containing eight phenoxy (4a), o-methyl phenoxy (4b) or estrone (4c) groups on the ring. The corresponding dichlorotin complexes (5a, 5b and 5c) and diiodotin complex (6a) were also investigated, as well as diestrone phthalocyaninato tin (7). Germanium octaphenoxy phthalocyanine complexes undergo phototransformation rather than direct photobleaching, whereas tin octaphenoxy phthalocyanine complexes undergo a photobleaching process, which is mediated by photoreduction of the phthalocyanine ring. Tin octaphenoxy phthalocyanine complexes gave higher ΦΔ values than the corresponding germanium complexes. Also tin phthalocyanine complexes containing an unsubstituted ring gave higher ΦΔ values than the corresponding octaphenoxy substituted complexes. The triplet quantum yields increased with the increase in electron-donating power of the ring substituents.
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- Date Issued: 2002
The identification of the UV degradants of melatonin and their ability to scavenge free radicals
- Authors: Maharaj, Deepa S , Anoopkumar-Dukie, Shailendra , Glass, Beverley D , Antunes, Edith M , Lack, Barbara A , Walker, Roderick B , Daya, Santylal
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184303 , vital:44198 , xlink:href="https://doi.org/10.1034/j.1600-079X.2002.01866.x"
- Description: Ultraviolet (UV) light is known to induce the generation of free radicals in biological tissues such as skin. Of these free radicals, the O2–· and particularly the ·OH radical can induce cellular damage including lipid peroxidation. Thus, the use of antioxidants to prevent such damage induced by UV irradiation has received much attention recently. One such antioxidant, which has the potential to be incorporated into sunscreens, is the pineal secretory product melatonin. One of the concerns of using melatonin in sunscreens is its photostability. In the present study, we investigated the photostability of melatonin subjected to UV irradiation. In addition, we used liquid chromatography mass spectrometry (LC-MS) to identify the degradants and we also assessed the ability of the degradants to inhibit O2–· generation as well as lipid peroxidation in rat brain homogenate. The results show that UV irradiation of melatonin (0.1 mg/mL) using a 400-W lamp for 2 hr caused a significant decline of melatonin to 18% of its original concentration after 20 min, with the decline continuing until the melatonin concentration reaches zero at 120 min. The LC-MS results show that the degradants of melatonin are 6-hydroxymelatonin and N1-acetyl-N2-formyl-5-methoxykynurenamine (AFMK). These degradants were able to provide equipotent activity against potassium cyanide (KCN)-induced superoxide generation compared to non-irradiated melatonin. Thus, the study shows that although melatonin is rapidly degraded by UV irradiation, the degradants retain antioxidant activity, making melatonin a likely candidate for inclusion in sunscreens.
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- Date Issued: 2002
The role and value of savanna non-timber forest products to rural households in the Kat River Valley, South Africa
- Authors: Shackleton, Charlie M , Shackleton, Sheona E , Ntshudu, M , Ntzebeza, J
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/182820 , vital:43882 , xlink:href="https://www.cabdirect.org/cabdirect/abstract/20023145773"
- Description: The majority of South Africans reside in rural areas characterized by limited infrastructure and employment opportunities. Many, therefore, make extensive use of non-timber-forest products (NTFPs) as part of their daily livelihoods. However, until recently, there were relatively few quantitative studies on resources used, amounts and frequencies. This is especially so for the savanna biome in South Africa, even though it is the largest biome. This paper presents data from a quantitative study of resource use and value in three villages situated in the savannas of the poorest province of South Africa. The results demonstrated widespread use of a wide variety of NTFPs. There were no households that did not make use of at least one NTFP from the surrounding woodlands. The five contributing most to the total gross value per household were fuelwood, wild herbs, wild fruits, bushmeat and honey beer. The mean gross annual direct-use value at the three villages ranged from US$211 to US$324 per household, averaged across user and non-user households. The direct-use value to user households was approximately double this. The net value differed between specific NTFPs because of differential labour input. The net value represented between 39 and 86% of the gross value, with a mean of 63%. However, the use of opportunity costs of labour in such areas requires examination.
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- Date Issued: 2002
The toxicity of zinc to a selected macroinvertebrate, Adenophlebia auriculata (Ephemeroptera, Leptophlebiidae) method development
- Authors: Everitt, Victoria J , Scherman, Patricia A , Villet, Martin H
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/442370 , vital:73979 , https://doi.org/10.2989/16085914.2002.9626572
- Description: The South African water quality guidelines for the protection of the aquatic environment are constantly being updated. The Centre for Aquatic Toxicology of the Institute for Water Research, Rhodes University, uses artificial streams and toxicological methods to contribute to the development and refinement of these guidelines. This study involved the use of 96-hour acute toxicity tests, using zinc sulphate as the toxicant, to determine the suitability of Adenophlebia auriculata as a potential indicator species of zinc pollution. As it is known that experimental environments (e.g. still versus flowing water systems) can influence the tolerance of a test species, the experimental system most suited to this species' abiotic requirements was determined. Static and recirculating systems were compared, with LC50 values calculated for the static systems being 91% lower than those calculated for the recirculating systems. The increased sensitivity to the toxicant under static conditions may be due to the animals being additionally stressed by the less favourable static environment. This suggests that recirculating systems are more suited for toxicity tests using this mayfly. Adenophlebia auriculata appears to be tolerant to zinc when compared to zinc LC50 values for other test species in the literature, and may therefore not be a suitable indicator of zinc pollution in an aquatic environment.
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- Date Issued: 2002
The use of Daphnia spp. and indigenous river invertebrates in whole effluent toxicity testing in the Vaal Catchment.
- Authors: Muller, Nikite W J , Palmer, Carolyn G
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , report
- Identifier: http://hdl.handle.net/10962/438048 , vital:73431 , ISBN 1 86845 855 5 , https://wrcwebsite.azurewebsites.net/wp-content/uploads/mdocs/815-1-02.pdf
- Description: Freshwater is vital to societal, and environmental, well-being and any changes in the distribution, abundance and quality of water resources and ecosystems are detrimental to this societal and environmental sus-tainability. Increasing socio-economic activities world-wide have been accompanied by increased pollution stress on the aquatic environment. The need for improved efficiency in water quality management is urgent and immediate and it is important that policy to manage freshwater sys-tems is underpinned by sound science. Strategies to manage receiving water quality have been implemented world-wide and include chemical monitoring, biological monitoring and toxicological assessments, all of which are supported by on-going research. Water quality management in South Africa has come a long way since 1919, when it was first promulgated (Union Health Act 36 of 1919; van der Merwe and Grobler, 1990) but only included sewage effluent. Later amendments broadened water quality management to include effluent discharge from industry, mining and storm-water runoff. However, despite these and uniform, and general, effluent standards (UES), as well as DWAFs recognition of the need for integrated water resource management, water quality in the resources continue to deteriorate (DWAF, 1995; Basson etal 1997).
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- Date Issued: 2002
Use patterns and value of savanna resources in three rural villages in South Africa
- Authors: Shackleton, Sheona E , Shackleton, Charlie M , Netshiluvhi, T R , Geach, B S , Ballance, A , Fairbanks, D H K
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/182384 , vital:43825 , xlink:href="https://doi.org/10.1663/0013-0001(2002)056[0130:UPAVOS]2.0.CO;2"
- Description: Rural communities in South Africa harvest a diversity of wild resources from communal woodlands for home consumption and sale. The contribution these resources make to the rural economy has been little recognized, and few studies have attempted to place a monetary value on this use. This paper describes three case studies which aimed to determine the value of savanna resources for the livelihoods of rural households. Use patterns and values of resources in three villages of differing socioeconomic status were determined using household interviews, PRA techniques and key informant interviews. Questions were designed to establish the types of products used, frequency of use, quantities used, seasonality of use, longevity of durable resources, local prices, and the extent of trade. All households were procuring at least some woodland resources, with the most frequently used being fuel wood, wood for implements, edible herbs and fruits, grass for brushes, and insects. Patterns of resource use varied across villages. The most “rural” village used the greatest diversity of resources and had the highest number of users for most resources. Gross value of resources consumed per household per year ranged from R28I9 to R7238. Total value was highest in the less obviously resource dependent village, primarily the result of higher local prices due to greater extraction costs and a larger market for traded goods. Values are comparable to those contributed by other land-based livelihood activities such as subsistence cultivation and livestock production.
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- Date Issued: 2002
Voltammetric characterization of the self-assembled monolayer (SAM) of octabutylthiophthalocyaninatoiron (II)
- Authors: Ozoemena,Kenneth , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/290419 , vital:56748 , xlink:href="https://doi.org/10.1016/S0013-4686(02)00362-6"
- Description: The fabrication of a self-assembled monolayer (SAM) of 2,3,9,10,16,17,23,24-octa (butylthio)-phthalocyaninatoiron(II) [FePc(SBu)8] on gold electrode is described. The integrity of the SAM, with respect to its ability to block certain Faradaic processes, is interrogated using cyclic voltammetric experiments in aqueous solutions. The experiments show that this SAM provide an excellent blocking capability to the Faradaic processes emanating from gold surface oxidation, underpotential deposition (UPD) of copper and redox chemistry of Fe(NH4)(SO4)2 in HClO4. It is revealed by cyclic voltammetry that an ill-defined reversible couple of the SAM of FePc(SBu)8 can be greatly improved by a simple repetitive cycling of the modified electrode in a DMF solution containing TBAP within a short space of time (ca. 2 min). This ‘activation’ process provides good information concerning the surface coverage and orientation of the monolayer. The reversible redox wave shows a potential shift of about −57 mV per pH in the pH range of 2–9. A preliminary investigation indicates that FePc(SBu)8-SAM modified gold electrode shows electrocatalytic activity toward the oxidation of L-cysteine in acidic medium. The monolayer is stable and easily reproducible. However, due to its susceptibility to destruction via oxidative and reductive desorptions, its potential application as an electrochemical sensor would be much better in acidic and neutral than alkaline environments.
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- Date Issued: 2002
Voltammetric detection of vitamin B1 at carbon paste electrodes and its determination in tablets
- Authors: Oni, Joshua , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289692 , vital:56663 , xlink:href="https://doi.org/10.1002/1521-4109(200209)14"
- Description: The voltammetric behavior of vitamin B1 in alkaline medium at carbon paste electrode (CPE) is discussed. A method based on cyclic voltammetry for the determination of vitamin B1 at carbon paste electrode modified with manganese phthalocyanine (MnPc-CPE) is presented. In pH 10 buffer, the modified electrode showed catalytic activity towards the oxidation of vitamin B1 by considerably increasing the oxidation current of one of the observed waves compared to the oxidation current obtained at an unmodified electrode. The modified electrode was stable towards the determination of vitamin B1 compared to the unmodified electrode that is completely poisoned after a few scans. A linear relationship between the oxidation current and the concentration of vitamin B1 in solution was observed. The detection limit for vitamin B1 at the modified electrode was of the order of 10−5 mol dm−3. Commercial vitamin B1 tablets were analyzed using the modified electrodes.
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- Date Issued: 2002
Voltammetric detection of vitamin B1 at carbon paste electrodes and its determination in tablets
- Authors: Oni, Joshua , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/289678 , vital:56662 , xlink:href="https://doi.org/10.1002/1521-4109(200209)14"
- Description: The voltammetric behavior of vitamin B1 in alkaline medium at carbon paste electrode (CPE) is discussed. A method based on cyclic voltammetry for the determination of vitamin B1 at carbon paste electrode modified with manganese phthalocyanine (MnPc-CPE) is presented. In pH 10 buffer, the modified electrode showed catalytic activity towards the oxidation of vitamin B1 by considerably increasing the oxidation current of one of the observed waves compared to the oxidation current obtained at an unmodified electrode. The modified electrode was stable towards the determination of vitamin B1 compared to the unmodified electrode that is completely poisoned after a few scans. A linear relationship between the oxidation current and the concentration of vitamin B1 in solution was observed. The detection limit for vitamin B1 at the modified electrode was of the order of 10−5 mol dm−3. Commercial vitamin B1 tablets were analyzed using the modified electrodes.
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- Date Issued: 2002
Weaving cloths: Research design in contexts of transformation
- Authors: Lotz-Sisitka, Heila
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/184745 , vital:44268 , xlink:href="https://cjee.lakeheadu.ca/article/viewFile/259/136"
- Description: Through storytelling, I apply methodological and epistemological reflexivity to ask questions about the way in which environmental education research is framed in transformational settings. I ask questions about the role of research teachers/supervisors in the “weaving enterprise” or the research process. Do we have the dual task of developing contextually relevant frameworks, and of making sure that these frameworks are not adopted on an “industrial scale”—in other words, as new paradigms which have the potential to narrow research possibilities? The paper concerns itself with a broader question, notably the potentially debilitating effects of mass production of research, or the globalizing of knowledge production. The story I use to raise these, and other questions for consideration by teachers/supervisors of research is a research workers story (my own), constructed between 1992 and 1996, in a context of rapid socio-political and educational transformation in South Africa (Lotz, 1996). In addition to the above, the paper opens a debate about reflexivity as research methodological rigour.
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- Date Issued: 2002