Fluorescence “switch on” of conjugates of CdTe@ ZnS quantum dots with Al, Ni and Zn tetraamino-phthalocyanines by hydrogen peroxide
- Authors: Adegoke, Oluwasesan , Khene, Samson M , Nyokong, Tebello
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/241750 , vital:50966 , xlink:href="https://doi.org/10.1007/s10895-013-1222-x"
- Description: In this study, we have developed a novel nanoprobe for H2O2 based on the conjugation of CdTe@ZnS quantum dots (QDs) to different metal tetraamino-phthalocyanine (MTAPc): (M = (OAc)Al, {OAc = acetate}, Ni and Zn). Chemical coordination of the QDs to the MTAPc resulted in the fluorescence “switch off” of the linked QDs which was associated with Förster resonance energy transfer (FRET). In the presence of varying concentration of H2O2, the fluorescence of the linked QDs was progressively “switched on” and the FRET mechanism between the QDs and the MTAPc was disrupted. The sensitivity/limit of detection of the nanoprobe followed the order: QDs-ZnTAPc (2.2 μM) > QDs-NiTAPc (4.4 μM) > QDs-AlTAPc (9.8 μM) while the selectivity followed the order: QDs-NiTAPc > QDs-AlTAPc > QDs-ZnTAPc. The varying degree of sensitivity/selectivity and mechanism of detection is discussed in detail.
- Full Text:
- Date Issued: 2013
Influence of an intermittent food supply on energy storage by the subpolar deposit feeder Yoldia hyperborea (Bivalvia: Nuculanidae)
- Authors: Stead, R A , Richoux, Nicole B , Pereda, S V , Thompson, R J
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/457271 , vital:75621 , xlink:href="https://doi.org/10.1007/s00300-013-1353-1"
- Description: Food supply for deposit feeders varies from highly seasonal phytodetritus to a steady source of older organic matter, resulting in contrasting patterns of nutrient uptake and storage. To identify patterns in energy storage and feeding behaviour driven by different food conditions for the circumpolar deposit-feeding protobranch bivalve Yoldia hyperborea, we measured variations in cytological (digestive cell height) and biochemical (lipid class, fatty acid, glycogen, and protein content) components during controlled experiments. Three treatments with organisms in sediment with high refractory organic matter (12 % OM) were exposed to different feeding regimes resembling (a) the annual spring bloom settlement, (b) low food availability during winter, and (c) sporadic resuspension events. Yoldia exposed to a diatom-supplemented diet showed significantly higher mean values for digestive cell height (28.44 μm), glycogen (30.4 mg g−1 dry mass, DM), diatom-specific fatty acids, and total lipid (TL) levels (14.4 mg g−1 DM), but lower protein concentrations, than in non-supplemented treatments (digestive cell height 20.34 μm; glycogen 9.23 mg g−1 DM; TL 6.7 mg g−1 DM). All analyses showed no effect of resuspension events; thus, it was unlikely that resuspension improved sediment nutritional value. In the absence of recently deposited diatoms, Y. hyperborea did not increase nutrient storage, suggesting that significant amounts of older refractory OM are not used for growth or reproduction. The rapid storage of nutrients derived from diatoms demonstrates the role of seasonal episodic events of settling algae in the nutrition of subpolar Y. hyperborea and in the transfer of energy from the water column to the benthos.
- Full Text:
- Date Issued: 2013
Reconstructing the history of introduction and spread of the invasive species, Lantana, at three spatial scales in India
- Authors: Kannan, Ramesh , Shackleton, Charlie M , Shaanker, Ramanan U
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181015 , vital:43687 , xlink:href="https://doi.org/10.1007/s10530-012-0365-z"
- Description: This study sought to reconstruct the history of Lantana invasion and spread in India by considering two questions; (a) from where, by who, and when were Lantana species introduced into India? and (b) given its long history in the country, is it still spreading or more or less stable? We critically evaluated the archival and historical information on plant imports by the European powers into India during the period before and after British colonization. We then reconstructed the path of spread by analyzing the spatio-temporal patterns of occurrence and distribution of Lantana in India at both the national and local scale using a GIS platform. The spread of Lantana across the globe started as early as the 1690s. The European colonial powers moved the plants from Latin America to Europe and to their colonial countries in the early 1800s. Lantana species were introduced in India from 1807 onwards and thereafter the colonial powers moved this plant across the country. Following its introduction into India, the spread of Lantana across the country, either through subsequent multiple introductions from Europe to different British cantonments, or through moving the plants between cantonments within India, were reasonably rapid spanning only a few decades. In the absence of a rigorous control program, the spread of Lantana has gone on unabated and thereby impacting both wildlife and biodiversity.
- Full Text:
- Date Issued: 2013
The gold of one’s ring is not far more precious than the gold of one’s heart: Reported life satisfaction among married and cohabitating South African adults
- Authors: Botha, Ferdi , Booysen, Frikkie
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/396181 , vital:69156 , xlink:href=" https://doi.org/10.1007/s10902-012-9337-3"
- Description: This paper tests for differences in reported life satisfaction between married and cohabiting persons, i.e. the cohabitation gap, and in particular whether selection factors can explain the cohabitation gap. The paper also explores whether age at marriage and at start of cohabitation as well as the duration of relationship type matters for subjective well-being. Based on statistical and regression analysis of the 2008 National Income Dynamics Survey, married and cohabiting persons exhibit some differences in their respective determinants of life satisfaction. While the age at relationship commencement has no relationship with well-being, there is evidence to suggest that married people become more satisfied at a later stage in marriage, while cohabitants are more satisfied initially. A significant cohabitation gap exists (0.251), but after controlling for various selection factors, the cohabitation gap virtually disappears (0.042) and becomes insignificant, which suggests that marriage and cohabitation are very similar in South Africa. Relative income, absolute income, and education explain the largest part of the cohabitation gap. Against the global backdrop of an increasing trend towards cohabitation and declining marriage rates, the overall results of this paper suggest that, since a cohabitation gap no longer exists after controlling for selection factors, South Africans may as well not go the “official route” of entering into marriage, as cohabitation provides similar benefits in terms of its contribution to individual satisfaction with life.
- Full Text:
- Date Issued: 2013
Using a unified invasion framework to characterize Africa’s first loricariid catfish invasion
- Authors: Jones, Roy W , Weyl, Olaf L F , Hill, Martin P , Swartz, Ernst R
- Date: 2013
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/418081 , vital:71507 , xlink:href="https://doi.org/10.1007/s10530-013-0438-7"
- Description: This paper presents evidence of establishment of a loricariid population in the Nseleni River in South Africa and uses a unified framework to determine its invasion stage. Specimens were identified morphologically as Pterygioplichthys disjunctivus (Weber 1991), but genetic barcoding results indicated close association with specimens that may have a hybrid history. The species was introduced into South Africa via the pet trade and the first record of introduction into the wild was in 2004. Samples collected in 2011 and 2012 demonstrated that there were multiple length cohorts in the population including juveniles (12–130 mm total length TL) and large (>300 mm TL) adult fish. Gonadal assessment of adults demonstrated the presence of reproduction capable specimens. The concurrent occurrence of mature adults and juvenile fish demonstrated establishment. Locality records indicate that P. disjunctivus has already spread between two rivers through an inter basin water transfer. Using a unified framework for invasions this invasion was categorized as a self-sustaining population in the wild with individuals surviving and reproducing a significant distance from their original point of introduction. Containment is suggested as potential management strategy.
- Full Text:
- Date Issued: 2013
A comparative study on the sensitive detection of hydroxyl radical using thiol-capped CdTe and CdTe/ZnS quantum dots
- Authors: Adegoke, Oluwasesan , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/242778 , vital:51077 , xlink:href="https://doi.org/10.1007/s10895-012-1089-2"
- Description: Four types of water-soluble luminescent quantum dots (QDs) whose surface was functionlaized with thioglycolic acid (TGA), 3-mercaptopropionic acid (MPA), or glutathione (GSH), were investigated for the sensitive and selective detection of hydroxyl radical (●OH) in aqueous media. It was found that the type of capping agent and QD influenced the sensitivity of the probe. The order of sensitivity of the probe was: GSH-CdTe@ZnS > MPA-CdTe@ZnS > TGA-CdTe > MPA-CdTe QDs. Under the optimum conditions, a limit of detection as low as 8.5 × 10-8 M was obtained using GSH-CdTe@ZnS. The effects of foreign reactive oxygen species and the Fenton reactants and products as possible interferences on the proposed probe were negligible for CdTe@ZnS QDs. Besides, experimental results indicated that CdTe@ZnS QDs were more attractive for the selective recognition of ●OH than CdTe QDs. The mechanistic reaction pathway between the QDs and ●OH is proposed.
- Full Text:
- Date Issued: 2012
A lover’s shame
- Authors: Jones, Ward E
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/275692 , vital:55071 , xlink:href="https://doi.org/10.1007/s10677-012-9356-5"
- Description: Shame is one of the more painful consequences of loving someone; my beloved’s doing something immoral can cause me to be ashamed of her. The guiding thought behind this paper is that explaining this phenomenon can tell us something about what it means to love. The phenomenon of beloved-induced shame has been largely neglected by philosophers working on shame, most of whom conceive of shame as being a reflexive attitude. Bennett Helm has recently suggested that in order to account for beloved-induced shame, we should deny the reflexivity of shame. After arguing that Helm’s account is inadequate, I proceed to develop an account of beloved-induced shame that rightly preserves its reflexivity. A familiar feature of love is that it involves an evaluative dependence; when I love someone, my well-being depends upon her life’s going well. I argue that loving someone also involves a persistent tendency to believe that her life is going well, in the sense that she is a good person, that she is not prone to wickedness. Lovers are inclined, more strongly than they otherwise would be, to give their beloveds the moral benefit of the doubt. These two features of loving—an evaluative dependence and a persistent tendency to believe in the beloved’s moral goodness—provide the conditions for a lover to experience shame when he discovers that his beloved has morally transgressed.
- Full Text:
- Date Issued: 2012
Interaction of CdTe quantum dots with 2, 2-diphenyl-1-picrylhydrazyl free radical
- Authors: Adegoke, Oluwasesan , Chidawanyika, Wadzanai J U , Nyokong, Tebello
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/245751 , vital:51402 , xlink:href="https://doi.org/10.1007/s10895-011-1012-2"
- Description: The interaction of 2,2-diphenyl-1-picrylhydrazyl (DPPH●) free radical with thiol-capped CdTe quantum dots (QDs) has been studied by UV–vis spectroscopy, steady state and time resolved fluorescence measurements. Addition of DPPH● radical to CdTe QDs resulted in fluorescence quenching. The interaction occurs through static quenching as this was confirmed by fluorescence lifetime measurements. Time course absorption studies indicates that DPPH● may be reduced by interaction with QDs to the substituted hydrazine form (2,2-diphenyl-1-picrylhydrazine) DPPH-H. The mechanism of fluorescence quenching of CdTe QDs by DPPH● is proposed.
- Full Text:
- Date Issued: 2012
Spectral, photophysical and photochemical properties of tetra-and octaglycosylated zinc phthalocyanines
- Authors: Iqbal, Zafar , Masilela, Nkosiphile , Nyokong, Tebello , Lyubimtsev, Alexey , Hanack, Michael , Ziegler, Thomas
- Date: 2012
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/244428 , vital:51256 , xlink:href="https://doi.org/10.1039/c2pp05348a"
- Description: Photophysical and photochemical properties of a series of tetra- and octaglycosylated zinc phthalocyanines (ZnPcs) substituted with glucose and galactose moieties have been reported. Spectral properties of these phthalocyanines are compared in DMSO. Absorption spectra of the non-peripherally tetra-substituted ZnPcs 2 showed a significant red shift in their Q-band maxima as compared to the peripherally substituted analog 1. All the complexes gave high triplet quantum yields ranging from 0.68 to 0.88, whereas triplet lifetimes were in the range of 100–430 µs in argon-saturated solutions. The octagalactosylated ZnPc 3b showed the highest triplet quantum yield and singlet oxygen quantum yield of 0.88 and 0.69, respectively. The fluorescence quantum yields and lifetimes of all the compounds under investigation were within the range of zinc phthalocyanine complexes.
- Full Text:
- Date Issued: 2012
Being moved by a way the world is not
- Authors: Jones, Ward E
- Date: 2011
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/275631 , vital:55064 , xlink:href="https://doi.org/10.1007/s11229-009-9522-z"
- Description: At the end of Lecture 3 of The Empirical Stance, Bas van Fraassen suggests that we see the change of view involved in scientific revolutions as being, at least in part, emotional. In this paper, I explore one plausible way of cashing out this suggestion. Someone’s emotional approval of a description of the world, I argue, thereby shows that she takes herself to have reason to take that description seriously. This is true even if she is convinced—as a scientific community is when it considers alternative theories—that this description is false, that it is not the way the world is.
- Full Text:
- Date Issued: 2011
Comparative electrocatalytic behavior of self-assembled monolayer of thiol derivatised Co (II) phthalocyanines on gold disk, ultramicro cylinder and fiber electrodes
- Authors: Nombona, Nolwazi , Geraldo, Daniela A , Hakuzimana, Jean , Schwarz, Anne , Westbroek, Philippe , Nyokong, Tebello
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/263488 , vital:53632 , xlink:href="https://doi.org/10.1007/s10800-008-9716-y"
- Description: This paper reports on the use of thiol derivatised cobalt phthalocyanines as self assembled monolayers (SAMs) on gold disk electrode, gold ultramicro-cylinder electrode (UMCE) and on gold coated fiber for the detection of L-cysteine. The complexes are peripherally and non-peripherally substituted with phenylthio substituents. The SAM modified electrodes showed enhancement of catalytic currents and overpotential reduction occurred on the gold modified electrodes with different geometries. Electrocatalytic oxidation of L-cysteine on SAM modified gold coated fiber was reported for the first time. The gold coated fiber and ultramicro cylinder electrode were less stable towards the electrocatalytic oxidation of cysteine compared to its oxidation on the gold disk. The gold disk electrode gave better catalytic performance in terms of stability and reduction of overpotential.
- Full Text:
- Date Issued: 2009
Conservation, commercialisation and confusion: Harvesting of Ischyrolepis in a coastal forest, South Africa
- Authors: Shackleton, Charlie M , Parkin, Fiona , Chauke, Maphambe I , Downsborough, Linda , Olsen, Ashleigh , Brill, Greg , Weideman, Craig I
- Date: 2009
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181169 , vital:43704 , xlink:href="https://doi.org/10.1007/s10668-007-9106-3"
- Description: Harvesting of non-timber forest products is an integral component of rural livelihoods throughout the developing world. At times this is at odds with conservation objectives. Reconciliation of the two requires examination of local level contexts and needs. This paper reports on the harvesting needs for Ischyrolepis by a rural community in South Africa, against the setting that they had recently been prohibited from harvesting by the local conservation officials. Interviews were conducted with conservation officials to understand the reasoning for the prohibition. Local demand for Ischyrolepis was assessed by household surveys, as well as in-depth interviews with traders. The density and size class distribution of Ischyrolepis was determined using transects. The total annual demand for Ischyrolepis was determined to be approximately only 2.7% of the standing crop. The bulk of the annual demand was for small-scale trade, the income from which was a primary source of income for the few harvesters. Very little evidence could be found indicating that harvesting was damaging the resource or its habitat, and local knowledge suggested that the abundance of the species was stimulated by harvesting. Even if market demand were to increase, the size of the shoots required means that less than 20% of the standing crop could be harvested annually. Current regulations around harvesting are in a state of revision, and hence confusion prevails regarding if harvesting is permissible, and if so, under what conditions, which is detrimental to both conservation and livelihoods.
- Full Text:
- Date Issued: 2009
Volcano correlations for the reactivity of surface-confined cobalt N4-macrocyclics for the electrocatalytic oxidation of 2-mercaptoacetate
- 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
Assessing the effects of invasive alien species on rural livelihoods: Case examples and a framework from South Africa
- 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
Synthesis, photophysical and photochemical studies of new water-soluble indium (III) phthalocyanines
- Authors: Durmus, Mahmut , Nyokong, Tebello
- Date: 2007
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/283976 , vital:56007 , xlink:href="https://doi.org/10.1039/b618478b"
- Description: The preparation of water-soluble indium(III)phthalocyanine complexes is described for the first time in this study. Peripherally and non-peripherally 3-hydroxypyridine tetrasubstituted indium(III) phthalocyanines (5a, 6a) and their quaternarized derivatives (5b, 6b) have been synthesized and characterized by elemental analysis, IR, 1H NMR spectroscopy, electronic spectroscopy and mass spectra. The quaternarized compounds (5b, 6b) show excellent solubility in water, which makes them potential photosensitizers for use in photodynamic therapy (PDT) applications. Photochemical and photophysical measurements were conducted on 3-pyridyloxy appended indium(III) phthalocyanines in dimethylsulfoxide (DMSO) for non-ionic (5b, 6b) derivatives. General trends are described for quantum yields of photodegradation, fluorescence lifetimes, fluorescence quantum yields, triplet lifetimes and triplet quantum yields as well as singlet oxygen quantum yields of these compounds. The singlet oxygen quantum yields (ΦΔ), which give an indication of the potential of the complexes as photosensitizers in applications where singlet oxygen is required (Type II mechanism) are very high (ΦΔ > 0.55). Thus, these complexes may be useful as Type II photosensitizers.
- Full Text:
- Date Issued: 2007
Monetary valuation of livelihoods for understanding the composition and complexity of rural households
- 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.
- Full Text:
- Date Issued: 2005
Indomethacin reduces lipid peroxidation in rat brain homogenate by binding Fe2+
- Authors: Anoopkumar-Dukie, Shailendra , Lack, Barbara , McPhail, Kerry L , Nyokong, Tebello , Lambat, Zaynab , Maharaj, Deepat , Daya, Santy
- Date: 2003
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/304763 , vital:58487 , xlink:href="https://doi.org/10.1023/A:1021958016928"
- Description: One of the hallmarks of Alzheimer's disease (AD) is the progressive degeneration of cholinergic neurons in the cerebral cortex and hippocampus. It is generally accepted that this neuronal degeneration is due to free-radical-induced damage. These free radicals attack vital structural components of the neurons. This implies that agents that reduce free radical generation could potentially delay the progression of AD. Free radical generation in the brain is assisted by the presence of iron, required by the Fenton reaction. Thus, agents that reduce iron availability for this reaction could potentially reduce free radical formation. Since non steroidal anti-inflammatory drugs (NSAIDS) have been shown to reduce the severity of AD, we investigated the possible mechanism by which indomethacin could afford neuroprotection. Our results show that indomethacin (1 mM) is able to reduce the iron-induced rise in lipid peroxidation in rat brain homogenates. In addition, our NMR data indicate that indomethacin binds the Fe2+/Fe3+ ion. This was confirmed by a study using UV/Vis spectrophotometry. The results imply that indomethacin provides a neuroprotective effect by binding to iron and thus making it unavailable for free radical production.
- Full Text:
- Date Issued: 2003
Growth and fruit production of Sclerocarya birrea in the South African lowveld
- Authors: Shackleton, Charlie M
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181618 , vital:43752 , xlink:href="https://doi.org/10.1023/A:1020579213024"
- Description: Sclerocarya birrea (A.Rich.) Hochst. subsp. caffra (Sond.) Kokwaro. is a common species throughout the semiarid, deciduous savannas of much of sub-Saharan Africa. It is a favoured species and is frequently maintained in homestead plots and arable fields in an agroforestry situation. Although the abundance and popularity of this species has led to several initiatives to commercialise a number of marula products, the sustainability of the resource base with respect to fruit production has not been considered. This paper reports on a field experiment that monitored growth rates and fruit production of a sample of adult trees from several wild populations. Mean fruit production was 36.8 kg per tree in the first year, and negligible in the second. This was considerably less than previous estimates, which were based largely on small samples or anecdotal reports. The maximum recorded yield was 416.6 kg per tree. Fruit production was positively related to the size of the tree. Growth rates of adult trees were slow. There was a strong positive relationship between mean annual diameter increment and stem diameter. The slow growth rates and low fruit yields indicate that more attention is required regarding the sustainability of there source and its ability to provide sufficient fruit for the growing subsistence and commercial demand at both local and national scales.
- Full Text:
- Date Issued: 2002
Nearest-neighbour analysis and the prevelance of woody plant competition in South African savannas
- Authors: Shackleton, Charlie M
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/181640 , vital:43754 , xlink:href="https://doi.org/10.1023/A:1014795505362"
- Description: Inter- and intra-specific competition has long been regarded as a significant determinant of the structure and function of woody plant communities in African savannas. The most widely used approach to detect the presence or absence of competition has been the use of nearest-neighbour methods. Although several studies have been published reporting the presence of competition in Acacia dominated communities, less than 20 plots have been sampled across all these studies. Results from broad-leaved communities are variable, and also based on a small sample number. Consequently, this study sought to assess the prevalence of competition from a large number of savanna sites (45), and to identify abiotic and biotic factors characterising sites with competition relative to those without. Using the nearest-neighbour method only four sites (9.3%) indicated the presence of inter-specific competition; two were Acacia dominated communities (18.2% of Acacia sites) and two were broad-leaved communities (7.7%). These four sites had a significantly higher mean annual rainfall and fewer woody species than sites without inter-specific competition. There were also significant relationships between the inter-specific competition index and the dominance index and the number of species at a site. In terms of intra-specific competition only ten of the 31 sites tested revealed a significant correlation between nearest-neighbour distance and summed canopy volume of the two neighbours. Seven were for Acacia species (55.6% of the Acacia species comparisons) and three were for broad-leaved species (21.4% of the broad-leaved species comparisons). Sites lacking evidence of intra-specific competition were at a significantly lower slope position and had a smaller proportion of small stems. The lower prevalence of competition in South African savannas detected in this study using the same method as previous studies is discussed, and the appropriateness of nearest-neighbour analysis is examined.
- Full Text:
- Date Issued: 2002
pH study of the electrocatalytic SO2 detection at a glassy carbon electrode modified with iron (II) tetrasulfophthalocyanine
- Authors: Thamae, Mamothibe , Westbroek, Philippe , Nyokong, Tebello
- Date: 2002
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/304786 , vital:58490 , xlink:href="https://doi.org/10.1007/s00604-002-0914-8"
- Description: The electrocatalytic determination of SO2 is studied as a function of pH at a glassy carbon electrode modified with iron(II)tetrasulfophthalocyanine ([Fe(II)TSPc]4−). It was found in the literature that depending on pH, SO2·xH2O, HSO3 − and/or SO3 2− are the main compounds in solution, that these compounds behave differently at the electrode surface, and that the condition of the electrode surface is stable over the entire pH-range. The use of SO2(g) or sodium sulfite as starting material did result in identical curves except in the pH range from 7.5–9.0. A possible explanation could be given by proposing that SO2·xH2O is very unstable in the presence of SO3 2−. In strongly acidic medium, SO2·xH2O is the main compound, which can be oxidized as well as reduced with exchange of two electrons. HSO3 − is the main compound at pH = 4 and can also be oxidized and reduced with exchange of, respectively, two and four electrons. In alkaline solution sulfite is the main compound and can only be oxidized, also under exchange of two electrons. Detection limits are in the range of 4.0 ± 0.1 × 10−5 and 7.5 ± 0.1 × 10−5 mol L−1, dependent of pH and of the type of reaction (oxidation or reduction) used.
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- Date Issued: 2002