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Substituted catechols as complexing agents for the determination of bismuth, lead, copper and cadmium by adsorptive stripping voltammetry

  • Authors: Limson, Janice L , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293311 , vital:57074 , xlink:href="https://doi.org/10.1016/S0003-2670(96)00585-5"
  • Description: Copper, cadmium, lead and bismuth (> 5 μg ml−1) are determined by adsorptive cathodic stripping voltammetry (AdCSV) on a mercury film glassy carbon electrode, using catechol, 4-methylcatechol, 4-t-butylcatechol and resorcinol as complexing ligands. Complexes of lead, copper and bismuth with resorcinol showed the largest increase in current with increase in metal concentration, whereas complexes of these metals with 4-t-butylcatechol showed the lowest current response. Cadmium showed a different behaviour from the other three metals in that the highest current response was observed with 4-methylcatechol. The four metals could be determined simultaneously in the presence of resorcinol, although considerable interference was observed between bismuth and copper.
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  • Date Issued: 1997

The study of the interactions of cobalt (II) tetrasulfophthalocyanine with cysteine and histidine

  • Authors: Sekota, Mantoa , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293458 , vital:57087 , xlink:href="https://doi.org/10.1016/S0277-5387(97)00096-X"
  • Description: Kinetics for the interaction of cobalt(II) tetrasulfophthalocyanine ([CoIITSPc]4−, Pc(−2) = phthalocyanine dianion) with the amino acids, histidine and cysteine, in pH 7.2 phosphate buffer were studied. The rates were found to be first order in both the [CoIITSPc]4− and the amino acid. The formation of the [CoIIITSPc]3− species in the presence of histidine occurred with a rate constant of 0.16 dm3 mol−s−1, whereas the formation of the [CoITSPc]5− species in the presence of cysteine gave a rate constant of 2.2 dm3 mol−1.
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  • Date Issued: 1997

Towards sustainable conversation: Developing environmental education processes

  • Authors: Le Roux, Kim
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/389884 , vital:68492 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/137446"
  • Description: This paper highlights the importance of seeing environmental education as a process and considers the value of conversation and storytelling in environmental education processes. These processes are explored from a post-structural perspective within the context of the writer's own involvement in supporting environmental education processes.
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  • Date Issued: 1997

Troubled waters in south-western New Georgia, Solomon Islands: Is codification of the commons a viable avenue for resource use regularisation

  • Authors: Shankar, Aswani
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/440061 , vital:73732
  • Description: In recent decades there has been a growing interest in indigenous sea tenure institutions and their possible role in establishing a framework for sustainable resource use and conservation. Yet the feasibility of these institutions to cope with social and economic changes have been seldom explored. In this paper a case study is presented where internal deregularisation of the ‘commons’ is the result of existing socio-cultural principles combined with outside influences. Two territorial models are compared to elucidate emerging internal instabilities of sea tenure institutions and possible ways to correct existing problems. The codification of the commons is suggested here as a possible measure to strengthen indigenous common property regimes.
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  • Date Issued: 1997

Use of cobalt (II) phthalocyanine to improve the sensitivity and stability of glassy carbon electrodes for the detection of cresols, chlorophenols and phenol

  • Authors: Mafatle, Tsukutlane J , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293335 , vital:57076 , xlink:href="https://doi.org/10.1016/S0003-2670(97)00464-9"
  • Description: A cobalt(II) phthalocyanine-modified glassy carbon electrode (CoPc-GCE) was used for the detection of o-, m- and p-cresols, and of 2-chlorophenol, 4-chlorophenol and phenol. Modification of the glassy carbon electrode with CoPc increases the oxidation currents of these species and increases the stability of the electrode. CoPc-GCE showed less fouling by the oxidation products of these compounds than the unmodified GCE. Comparison of some first row transition metal phthalocyanines showed the following trend for the enhancement of the currents for the oxidation of cresols and phenols: Co(II)Pc > Mn(II)Pc > Fe(II)Pc > Ni(II)Pc > Cu(II)Pc > H2Pc > Zn(II)Pc > GCE. When [Co(II)TSPc]4− (TSPc=tetrasulfo Pc) was added to aqueous solutions containing the cresols and phenols, an enhancement of the oxidation currents was also observed.
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  • Date Issued: 1997

Voltammetric behavior of cysteine and metallothionein on cobalt (II) tetrasulfonated phthalocyanine modified glassy carbon electrodes

  • Authors: Limson, Janice L , Nyokong, Tebello
  • Date: 1997
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293346 , vital:57077 , xlink:href="https://doi.org/10.1002/elan.1140090314"
  • Description: Cysteine, and rat Cd, Zn-metallothionein (Cd, Zn-MT) have been studied electrochemically at glassy carbon electrodes modified with cobalt(II) tetrasulfonated phthalocyanine, [CoIITSPc]4−, where Pc(2-) = phthalocyanine dianion. The electrode was modified by electrodeposition of [CoIITSPc]4−. The anodic currents for the oxidation of cysteine on these electrodes are observed at 0.82 V (vs. Ag/AgCl) in acidic media. The anodic currents for the oxidation of Cd, Zn-MT are observed at 0.90 V at pH 8.4 (Tris buffer).
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  • Date Issued: 1997

Cyclic voltammetry and spectroelectrochemistry of osmium phthalocyanines in aqueous and non-aqueous solvents

  • Authors: Sekota, Mantoa , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293358 , vital:57078 , xlink:href="https://doi.org/10.1016/0277-5387(95)00581-1"
  • Description: Cyclic voltammetry of osmium phthalocyanine complexes, [(CN)2OsIIPc]2− and (py)2OSIIPc (PC = phthalocyanine dianion), show two oxidation couples and two reduction couples in acetonitrile and dimethy1formamide. Oxidation and reduction in these complexes occur at the ring to form cation and anion radical species, respectively. The [(CN)2OsIIPC]2− complexes show a remarkable ease of ring oxidation with oxidation potentials that are much lower than is typical for metallophthalocyanines. Half-wave potentials of 0.25 and 0.67 V (versus saturated calomel electrode, SCE) were obtained for the first and second ring oxidations, respectively. The [(CN)2OSIIPc]2− complex is soluble in water at pHs greater than 4. This complex shows one oxidation couple in pH 9 buffer at −0.11 V versus SCE.
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  • Date Issued: 1996

Electrocatalytic oxidation of cysteine by molybdenum (V) phthalocyanine complexes

  • Authors: Mafatle, Tsukutlane J , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293369 , vital:57079 , xlink:href="https://doi.org/10.1016/0022-0728(95)04519-8"
  • Description: Chemically modified electrodes, constructed by incorporating oxomolybdenum(V) phthalocyanine (OMo(V)(OH)Pc, Pc = phthalocyanine dianion) into graphite powder were used to catalyse the oxidation of cysteine. Solution catalysis of cysteine by oxomolybdenum(V) tetrasulfophthalocyanine, [OMo(V)(OH)TSPc]4−, was also investigated. A considerable reduction in overpotential for cysteine oxidation was observed. Cysteine oxidation occurred at 0.26 and 0.28 V vs. Ag/vbAgCl for catalysis by Omo(V)(OH)Pc and [OMo(V)(OH)TSPc]4− respectively as opposed to 0.77 V vs. Ag/vbAgCl observed on CoPc chemically modified electrodes. The anodic peak currents vary linearly with cysteine concentration in the range 0.02 to 0.08 mol dm−3 and 0.008 to 0.02 mol dm−3 for [OMo(V)(OH)TSPc]4− and OMo(V)Pc respectively.
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  • Date Issued: 1996

Perceptions of affirmative action

  • Authors: Scott, Judith , Amos, Trevor L , Richard Scott, W
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/270914 , vital:54491 , xlink:href="https://hdl.handle.net/10520/EJC-67e7bffd2"
  • Description: Private and public South African employers have instituted affirmative action policies meant to provide employment opportunities to Black South Africans. A body of literature suggests that because of affirmative action policies Black hopes have been raised while Whites view such policies as having a negative impact on their opportunities. However, no extant literature details an empirical investigation of these suggestions. Therefore, this study focusses on the affirmative action perceptions held by 350 South African university commerce students.
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  • Date Issued: 1996

Pharmacokinetics of cyclizine following intravenous administration to human volunteers

  • Authors: Kanfer, Isadore , Walker, Roderick B
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/184389 , vital:44214 , xlink:href="https://doi.org/10.1016/0928-0987(96)00177-7"
  • Description: The pharmacokinetics of cyclizine, a piperazine derivative useful in the prevention and treatment of nausea and vomiting, was investigated in six healthy male volunteers following an intravenous bolus dose. The drug is extensively distributed with a mean volume of distribution of 16.50 ± 3.33 l/kg and a mean total clearance of 0.870 ± 0.105 l/h per kg. Urinary excretion data showed that less than one percent of the dose was excreted up to 36 h as unchanged drug in the urine. The extremely low mean renal clearance (0.005 ± 0.002 l/h per kg) for the parent drug comprised only a small proportion of total clearance indicating that urinary excretion of parent drug is not a major route of elimination for cyclizine. The drug appears to exhibit biexponential pharmacokinetics and has a terminal elimination half-life of approximately 13 h.
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  • Date Issued: 1996

Photochemically induced electron transfer between sulfur dioxide and tin (IV) mono-and di-phthalocyanines

  • Authors: Nensala, Ngudiankama , Nzimande, Ayanda , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293402 , vital:57082 , xlink:href="https://doi.org/10.1016/1010-6030(96)04344-4"
  • Description: Photolysis, using radiation from a tungsten lamp, of tin diphthalocyanine (Pc2Sn(IV)) in dichloromethane containing SO2 results in the one-electron oxidation of this species to [Pc(−2)Sn(IV)Pc(−1)]+. The relative quantum yields for the formation of the oxidized species were in the order of 10−3. The one-electron oxidized complex was also formed when Pc2Sn was photolysed in an acetonitrile/dichloromethane solvent mixture. Photolysis of the monomeric (L)2Sn(IV)Pc(LOH−, Cl−, Br− and F−) in pyridine and in the presence of SO2 resulted in the reduction of these species to (L)2Sn(IV)Pc(−3)]− with quantum yields in the order of 10−2.
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  • Date Issued: 1996

Spectroelectrochemical studies of tin (IV) diphthalocyanine

  • Authors: Nensala, Ngudiankama , Nyokong, Tebello
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293436 , vital:57085 , xlink:href="https://doi.org/10.1016/0277-5387(95)00325-1"
  • Description: Cyclic voltammetry of tin(IV) diphthalocyanine (Pc2Sn) in dichloromethane containing TEAP shows two reduction couples at −0.56 and −0.89 versus saturated calomel electrode (SCE) and one oxidation couple at 0.35 V versus SCE; all were quasireversible one-electron couples. The oxidation couple corresponds to [Pc(−1)SnIVPc(−2)+/Pc(−2)SnIVPc(−2) and the reduction couples to Pc(−2)SnIVPc(−2)/[Pc(−3)SnIVPc(−2)]− and [Pc(−3)SnIVPc(−2)]−/[Pc(−3)SnIVPc(−3)]2−, respectively. The electronic absorption spectra of the various reduced or oxidized tin(IV) diphthalocyanine species are reported.
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  • Date Issued: 1996

Suppositories: An underutilized dosage form

  • Authors: Webster, Jessica A , Dowse, Roslind , Walker, Roderick B
  • Date: 1996
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/184697 , vital:44264 , xlink:href="https://hdl.handle.net/10520/AJA16836707_911"
  • Description: The rectal route is useful for the delivery of both local acting and systemic drugs. In certain cases suppositories are the best form of therapy, or else they are an effective alternative when oral therapy is not possible. However; doctors rarely prescribe them and patients are often reluctant to use them. Understanding how suppositories work, and their numerous uses, can overcome the aversion to this particular dosage form. Pharmacists are in an ideal position to educate doctors, other health care providers, and patients, on the benefits of using suppositories and their correct use, and to offer advice on any problems associated with their use.
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  • Date Issued: 1996

Tectonic and structural aspects at the Otjihase Mine, Matchless Belt, Namibia: A Systematic Review

  • Authors: Hartmann, K
  • Date: 1995-04
  • Subjects: Uncatalogued
  • Language: English
  • Type: Master's theses , text
  • Identifier: http://hdl.handle.net/10962/190232 , vital:44976
  • Description: The Otjihase pyritic massive sulphide deposit occurs within a 10km thick metasedimentary sequence of the Kuiseb Formation. The Kuiseb metasediments were deposited within the Khomas Trough, which forms the southernmost rift of the intracontinental arm of the Damara orogen. Amphibolite units of the Matchless member at Otjihase have a MORB-type geochemical character and occur within the Kuiseb schists, about 200m above the ore zone. The Otjihase mine is the largest of many Besshi-type deposits that occur in close proximity to the Matchless amphibolites. A depositional environment in a rift, slightly more advanced than the present-day Red Sea is envisaged. The five parallel, ruler-shaped, mineralised shoots at Otjihase occur on the same stratigraphic level. They have a plunge of approximately 6° to the west and a dip of approximately 16° to the northwest. The largest and best mineralised, is the northernmost shoot (the Main Shoot) which is ±250m wide, up to 12m thick and has a known length of 7,5km. The large length/breadth ratio is ascribed to the original setting along faults and thickening of the ore zone during thrusting. Intense ductile deformation has affected the ore bodies, with isoclinal refolding, boudinaging, duplexes of more competent bands and smearing of the schists. Squeezing and remobilisation of the sulphides into the schistosity and low pressure pods has taken place. Successive folding and thrusting during the D2 deformational event resulted in the dominant structural style. Fold axes of drag folds plot onto a great circle in stereographic projection, indicating the formation of sheath folds. The axial planar cleavages of competent layers is steeper than the S(0,1) foliation and suggests a structural right way-up. The presence of chloritic alteration above the ore shoots, is suggestive of footwall alteration indicating that the sequence was overturned during the D1 deformational event. Ore zone lithologies include stringery-, massive- and semi-massive sulphides, mineralised magnetite- quartzites and disseminated sulphide mineralisation within quartz-biotite-chlorite schists. Chalcopyrite is the main economic mineral and mainly occurs as matrix to pyrite and in coarse-grained pods. Lithological and metal zoning within the Main Shoot is distinct and is an indication that the macroscopic shape of the orebody is largely unaffected by later ductile deformation. North-south trending normal faults of the Windhoek Graben have disrupted the continuity of the ore shoots. In section, the faults appear to have a listric shape. The major faults have pronounced scissor movements and as a result the dips of the blocks within fault zones are affected. , Thesis (MSc) -- Faculty of Science, Exploration Geology, 2021
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  • Date Issued: 1995-04

Addendum to the paper Landcare: New directions in professional development for environmental education

  • Authors: Lotz-Sisitka, Heila
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/438672 , vital:73488 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/137475"
  • Description: During 1994-1995, we received correspondence from Tania Sadler of the University of Tasmania and from Debbie Heck, about the latter's paper published in volume 14. In response we publish the following addendum, which includes a list of references inadvertently left out of her paper. Ms Heck did supply these references to the SAJEE originally, and we apologise for any inconvenience to readers as a result of the mistake. (Ed.)
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  • Date Issued: 1995

Editorial

  • Authors: Janse van Rensburg, Eureta
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/438706 , vital:73493 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/137460"
  • Description: This edition of the SAJEE focuses on EEASA' s conference-and-workshops held in July 1995, at Kearsney College in Kwazulu Natal, South Africa. ln the 1994 issue we invited readers to explore Progress and Paradox, as a conference theme reflecting a new perspective on education and environment. We received a very positive response and the conference featured an excellent range of papers. From amongst the many worthy contributions the reviewers selected those papers that addressed the theme most directly, for publication in this, arguably EEASA' s best journal yet.
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  • Date Issued: 1995

Equilibrium and kinetic studies of the reaction between pyridine and cobalt (II) phthalocyanine in DMSO

  • Authors: Nyokong, Tebello
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293380 , vital:57080 , xlink:href="https://doi.org/10.1016/0277-5387(95)00090-F"
  • Description: Kinetics and equilibria for the reaction between pyridine and cobalt(II) phthalocyanine [CoPc] (H2Pc = phthalocyanine) in dimethyl sulphoxide (DMSO) were studied at 25°C. The complex, CoPc(py)2, is formed in two consecutive steps. The formation of the mono-substituted CoPc(py)(DMSO) occurs first with a pseudo-first-order rate constant of k1f = 7.7 ± 0.3 × 10−3 dm3 mol−1 s−1. The final disubstituted CoPc(py)2 complex is formed with k2f= 1.1 ± 0.1 × 10−4dm3mol−1−1. The equilibrium constants were found to be K1 = 160 ± 20dm3 mol−1 and K2 = 15 ± 3 dm3mol−1 for the formation of CoPc(py)(DMSO) and CoPc(py)2, respectively.
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  • Date Issued: 1995

Resource materials development in environmental education : Exploring some of the myths and tensions in participatory resource development in the We Care Primary Project

  • Authors: Lotz-Sisitka, Heila
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/438792 , vital:73500 , xlink:href="https://www.ajol.info/index.php/sajee/article/view/137472"
  • Description: This paper on environmental education resource materials development represents some of my 'lived experience' (Malone, 1994:20) as a researcher involved in clarifying the processes of materials development for junior primary classrooms. The sites of inquiry, action and reflection have been focussed around the development of the We Care Primary materials, shifts in orientations to environmental education and current educational change.
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  • Date Issued: 1995

The reaction of cyanide with iron (II) hexadecachlorophthalocyanine

  • Authors: Nyokong, Tebello
  • Date: 1995
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/293447 , vital:57086 , xlink:href="https://doi.org/10.1016/0277-5387(94)00291-L"
  • Description: Kinetics and equilibria for the reaction between cyanide and iron(II) hexadecachlorophthalocyanine ((Cl)16PcFe(DMSO)2, where Pc(−2) = phthalocyanine dianion) in dimethyl sulphoxide (DMSO) are reported. Only the spectrophotometric changes due to the formation of the dicyano, [(Cl)16PcFe(CN)2]2−, complex were observed. This complex is formed with the equilibrium constant, K3 = 1.6 × 103 dm3 mol−1 and a rate constant of k3f = 4.2 × 10−3 dm3 mol−1 s−1. The K2[(Cl)16PcFe(CN)2] complex dissolves in DMSO and dimethyl formamide (DMF) with ϵ = 110 000 and 92 000 dm3 mol−1 cm−1, respectively.
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  • Date Issued: 1995

Cyclic voltammetry and photooxidation of molybdenum (V) phthalocyanine

  • Authors: Nyokong, Tebello
  • Date: 1994
  • Subjects: To be catalogued
  • Language: English
  • Type: text , article
  • Identifier: http://hdl.handle.net/10962/295475 , vital:57344 , xlink:href="https://doi.org/10.1016/S0277-5387(00)86594-8"
  • Description: Cyclic voltammetry of OMoV(OH)Pc in chloronaphthalene shows two quasi-reversible oxidation couples at 0.38 and 1.22 V and three quasi-reversible reduction couples at −0.74, −1.15 and −1.85 V vs S.C.E. Bulk electrolysis of OMoV(OH)Pc (Pc2 = phthalocyanine dianion) shows that the first oxidation couple is due to the oxidation of the central MoV metal to MoVI and the first reduction couple due to reduction to OMoIVPc. Cyclic voltammetry and spectroelectrochemistry in DMSO also showed redox activity at the metal. Further reductions or oxidations in OMoVPc complexes occur at the phthalocyanine ring. OMoV(OH)Pc is readily photooxidized at the metal in the presence dichloromethane or dichlorobenzene, with the formation of OMoVIPc species.
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  • Date Issued: 1994
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