Scielo RSS http://www.scielo.org.za/rss.php?pid=0038-235320110002&lang=es vol. 107 num. 3-4 lang. es http://www.scielo.org.za/img/en/fbpelogp.gif http://www.scielo.org.za http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200001&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200002&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200003&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200004&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200005&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200006&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200007&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200008&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200009&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200010&lng=es&nrm=iso&tlng=es http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200011&lng=es&nrm=iso&tlng=es The paper reviews research conducted at Rhodes University towards the development of metal-selective ligands. The research has focused on the rational design, synthesis and evaluation of novel ligands for use in the formation of copper complexes as biomimetic models of the metalloenzyme, tyrosinase, and for the selective extraction of silver, nickel and platinum group metal ions in the presence of contaminating metal ions. Attention has also been given to the development of efficient, metal-selective molecular imprinted polymers. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200012&lng=es&nrm=iso&tlng=es The ever-increasing role of homogeneous gold catalysis in organic synthesis and the consequent need to be able to rationally control the rate and outcome of such reactions has emphasised the importance of each successive metal-carbon coordination step. Concentrating on alkyne and allene cyclisation and upon reaction mechanisms postulated on the basis of empirical and theoretical results, we have examined the coordination of gold fragments to triple bonds, the modification of gold(I) precatalysts to effect specific reaction pathways or enantioselectivity and the isolation of coordinated intermediates or model compounds thereof. Some of the recent advances that have been made in various laboratories are described in this compact review. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200013&lng=es&nrm=iso&tlng=es Materials made of carbon that can be synthesised and characterised at the nano level have become a mainstay in the nanotechnology arena. These carbon materials can have a remarkable range of morphologies. They can have structures that are either hollow or filled and can take many shapes, as evidenced by the well-documented families of fullerenes and carbon nanotubes. However, these are but two of the shapes that carbon can form at the nano level. In this review we outline the types of shaped carbons that can be produced by simple synthetic procedures, focusing on spheres, tubes or fibres, and helices. Their mechanisms of formation and uses are also described. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200014&lng=es&nrm=iso&tlng=es The Lake St Lucia estuarine system is the most important nursery ground for juvenile marine fish and prawns along the KwaZulu-Natal coast. The estuary mouth closed in June 2002 because of drought and remained so for 4 years and 9 months. A study to determine the impacts of extended mouth closure, hypersalinity and low lake levels on the mesozooplankton, macrobenthic invertebrates and fish fauna was initiated in 2004. Zooplankton and benthic invertebrate diversity declined, benthic invertebrate community composition changed and the diversity and abundance of fish decreased between 2004 and 2007. In the case of fish, the declines were related to die-offs in the lake and the failed recruitment of post-larvae and juveniles from the marine environment as a result of the mouth having been closed. Options for management intervention under closed-mouth conditions are limited at this time, particularly in the short term, to breaching the mouth and facilitating the inflow of sea water. In the medium term, as was the historical situation, the reconnection of the Mfolozi system to St Lucia should be viewed as a major priority. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200015&lng=es&nrm=iso&tlng=es In the 1850s Robert William Plant collected plants and other natural specimens in what is now KwaZulu-Natal. This one-time Englishman compiled a dictionary for gardeners before emigrating to Natal in 1850. There he worked as the agent for Samuel Stevens, the London dealer in 'curiosities of natural history'. Though Plant collected mainly plants, he also sent consignments of beetles, butterflies, bird skins and shells back to Britain. He published the first scientific paper on Zululand and was requested by the Royal Botanic Gardens at Kew to write the first Flora natalensis. It was while collecting for this never-to-be-completed treatise that Plant contracted malaria in Maputaland. He died in St Lucia in 1858 and in doing so became South Africa's martyr to botany. What emerges from this study is a picture of the difficulties faced by plant hunters in mid-19th-century South Africa, the sort of plants they collected and the necessity for them sometimes to diversify into other natural history products to survive. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200016&lng=es&nrm=iso&tlng=es Bean and tuber extracts of Tylosema esculentum (marama) - an African creeping plant - were obtained using ethanol, methanol and water. Based on information that T. esculentum is used traditionally for the treatment of various diseases, the antibacterial and anticandidal effects of tuber and bean extracts were investigated. The antimicrobial activity of the extracts was tested on methicillin-resistant Staphylococcus aureus (MRSA, ATCC 6538), Mycobacterium terrae (ATCC 15755), Corynebacterium diphtheriae (clinical) and Candida albicans (ATCC 2091). We performed the broth microdilution test for the determination of the minimum inhibitory concentration (MIC) and a method to determine survival of microorganisms after in vitro co-incubation with the highest concentrations of T. esculentum extracts, followed by assessment of colony counts. Ethanol and methanol (phenolic) bean extracts exhibited higher potency against bacteria and yeast than aqueous extracts. Marama bean seed coat crude ethanolic extract (MSCE) and seed coat polyphenolic fractions, especially soluble-bound fraction (MSCIB), were highly antimicrobial against M. terrae, C. diphtheriae and C. albicans. All marama bean polyphenolic fractions, namely cotyledon acidified methanol fraction (MCAM), seed coat acidified methanol fraction (MSCAM), cotyledon insoluble-bound fraction (MCIB), seed coat insoluble-bound fraction (MSCIB), cotyledon-free polyphenolic fraction (MCFP) and seed coat free polyphenolic fraction (MSCFP) had high antimicrobial effects as shown by low respective MIC values between 0.1 mg/mL and 1 mg/mL. These MIC values were comparable to those of control antimicrobials used: amphotericin B (0.5 mg/mL) and cesfulodin (0.1 mg/mL) against C. diphtheriae, streptomycin (1.0 mg/mL) and gentamicin (0.4 mg/mL) against M. terrae, and amphotericin B (0.05 mg/mL) against C. albicans. Marama seed coat soluble-esterified fraction (MSCS) had closer activity to that of cefsulodin against M. terrae. High amounts of phenolic substances, such as gallic acid, especially in the seed coats, as well as high amounts of phytosterols, lignans, certain fatty acids and peptides (specifically protease inhibitors) in the cotyledons contributed to the observed antibacterial and anticandidal activities. Marama extracts, especially phenolic and crude seed coat extracts, had high multi-species antibacterial and anticandidal activities at concentrations comparable to that of some conventional drugs; these extracts have potential use as microbicides. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200017&lng=es&nrm=iso&tlng=es Titanium dioxide (TiO2) nanostructured materials have attracted a great deal of attention because of their numerous applications. However, TiO2 applications depend strongly on the material's high homogeneity and definite phase composition, morphology, particle size, high surface area and porosity, which are dependent on the sample history, the method of preparation and heat treatment. We synthesised TiO2 nanopowder with an anatase structure by the sol-gel method using TiCl4-ethanol solution as a precursor in an argon gas environment, with and without applying ultrasonic waves. Our results show that the use of ultrasonic waves (after aging) has a significant effect on the homogeneity and size of TiO2 nanoparticles. A smaller crystallite size was obtained using ultrasonic waves. For this purpose, the average diameter of TiO2 nanoparticles was decreased by about 3 nm. The synthesised powder was characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200018&lng=es&nrm=iso&tlng=es Carbon-13 and oxygen-18 abundances were measured in large mammal skeletal remains (tooth enamel, dentine and bone) from the Chiwondo Beds in Malawi, which were dated by biostratigraphic correlation to ca. 2.5 million years ago. The biologic isotopic patterns, in particular the difference in carbon-13 abundances between grazers and browsers and the difference in oxygen-18 abundances between semi-aquatic and terrestrial herbivores, were preserved in enamel, but not in dentine and bone. The isotopic results obtained from the skeletal remains from the Chiwondo Beds indicate a dominance of savannah habitats with some trees and shrubs. This environment was more arid than the contemporaneous Ndolanya Beds in Tanzania. The present study confirms that robust australopithecines were able to live in relatively arid environments and were not confined to more mesic environments elsewhere in southern Africa. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200019&lng=es&nrm=iso&tlng=es Glycopolymers (synthetic sugar-containing polymers) have become increasingly attractive to polymer chemists because of their role as biomimetic analogues and their potential for commercial applications. Glycopolymers of different structures confer high hydrophilicity and water solubility and can therefore be used for specialised applications, such as artificial materials for a number of biological, pharmaceutical and biomedical uses. The synthesis and characterisation of a series of novel glycopolymer brushes, namely poly(2-(2-bromoisobutyryloxy) ethyl methacrylate)-g-poly(methyl 6-O-methacryloyl-α-D-glucoside) (P(BIEM)-g-P(6-O-MMAGIc)), poly(2-(2-bromoisobutyryloxy) ethyl methacrylate-co-methyl methacrylate)-g-poly(methyl 6-O-methacryloyl-α-D-glucoside) P(BIEM-co-MMA)-g-P(6-O-MMAGIc), poly(2-(2-bromoisobutyryloxy) ethyl methacrylate-b-methyl methacrylate)-g-poly(methyl 6-O-methacryloyl-α-D-glucoside) P(BIEM-b-MMA)-g-P(6-O-MMAGIc) and poly(4-vinylbenzyl chloride-alt-maleic anhydride)-g-poly(methyl 6-O-methacryloyl-α-D-glucoside) (P(Sd-alt-MAnh)-g-P(6-O-MMAGIc)) are described in this paper. Reversible addition-fragmentation chain transfer (RAFT)-mediated polymerisation was used to synthesise four well-defined atom transfer radical polymerisation (ATRP) macroinitiators (the backbone of the glycopolymer brushes). These ATRP macroinitiators were subsequently used in the 'grafting from' approach (in which side chains are grown from the backbone) to prepare high molar mass and low polydispersity index glycopolymer brushes with different grafting densities along the backbone. The number average molar mass of the glycopolymer brushes was determined using size exclusion chromatography with a multi-angle laser light scattering detector and further structural characterisation was conducted using ¹H-nuclear magnetic resonance spectroscopy. The results confirmed that glycopolymer brushes were successfully synthesised via a combination of RAFT-mediated polymerisation and ATRP. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200020&lng=es&nrm=iso&tlng=es This study presents an analysis of the performance of students from disadvantaged schools (DS)on first-year psychology examination questions. The analysis focuses on the process of enquiry that underpins different kinds of questions (factual, relational and conceptual) of increasing levels of difficulty. The findings indicate that success or failure is not simply a measure of the reproduction of content but is a function of the (in)appropriate form of responses that students generate in engaging with different kinds of questions. This has important implications for the conceptualisation of academic literacy and the development of responsive curricula in the South African higher education context. In order to further understand the reasons for the disproportionately high failure rate among students from disadvantaged schools, the responses of DS failing students are compared to those of their peers from advantaged schools (AS) who also failed the course. This comparative analysis reveals very different patterns of questioning engagement among the two failing groups of students, providing empirical support for the argument that underpreparedness is a distinct systemic phenomenon rather than simply failure by another name. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200021&lng=es&nrm=iso&tlng=es In today's climate of growing energy needs and increasing environmental concerns, alternatives to the use of non-renewable and polluting fossil fuels have to be investigated. One such alternative is solar energy. This study is based on the implementation of a mathematical computation - the PSA (Plataforma Solar de Almeria) computation developed at PSA (the European Test Centre for solar energy applications) - embedded in a control algorithm to locate the position of the sun. Tests were conducted on a solar parabolic trough (SPT) constructed at the Solar Thermal Applications Research Laboratory of the Mangosuthu University of Technology (Durban, South Africa) for optimal position control using the PSA value. The designed control algorithm embedded in an industrial Siemens S7-314 C-2PtP programmable logic controller compared the PSA computation to a measured position of the SPT to optimally rotate the SPT to a desired position with the constant movement of the sun. The two main angles of the sun relative to the position of the SPT on earth, the zenith angle and the azimuth angle, both calculated in the PSA from the vertical and horizontal planes, respectively, were applied to the control algorithm to generate an appropriate final tracking angle within a 0.007 radian (0º 24' 3.6") tolerance, in accordance to the construction specifications and solar collector testing standards of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE, 1991). These values, together with the longitude and latitude applicable to the geographical location of the SPT, were processed in the control software to rotate the SPT to an optimal position with respect to the position of the sun in its daily path, for solar-to-thermal conversion. http://www.scielo.org.za/scielo.php?script=sci_arttext&pid=S0038-23532011000200022&lng=es&nrm=iso&tlng=es We tested the hypothesis that acidic atmospheric pollution deposition, originating from the South African central industrial area, poses an environmental threat across a larger region within the dispersal footprint. A network of 37 passive monitoring sites to measure SO2 and NO2 was operated from August 2005 to September 2007. The area extended over the entire northern and eastern interior of South Africa. Monitoring locations were chosen to avoid direct impacts from local sources such as towns, mines and highways. Dry deposition rates of SO2 and NO2 were calculated from the measured concentrations. Concentrations of sulphur and nitrogen species in wet deposition from a previous study were used in conjunction with measured rainfall for the years 2006 and 2007 to estimate the wet deposition over the region. The calculated total (non-organic) acidic deposition formed the basis for an assessment of exceedance of critical loads based on sensitivity of the regional soils. Regional soil sensitivity was determined by combining two major soil attributes available in the World Inventory of Soil Emission Potentials (International Soil Reference and Information Centre). Results indicate that certain parts of the central pollution source area on the South African Highveld have the potential for critical load exceedance, while limited areas downwind show lower levels of exceedance. Areas upwind and remote areas up and downwind, including forested areas of the Drakensberg escarpment, do not show any exceedance of the critical loads.