Showing items 41 - 60 of 452

Your selections:

Zozagne

Prade

Saraka

LaPaix

Diop

Ti Gbeu

Ramde

Sankirtan

Abissa

Remix Abissa

Ah! les hommes

Lekoussa

Belesky

Moya

Minwoun

Maudit soit de jour

Structural and synthetic investigations of South African marine natural products

  • Authors: Beukes, Denzil Ronwynne
  • Date: 2000
  • Subjects: Natural products -- South Africa Marine invertebrates -- South Africa Marine metabolites -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:4350 , http://hdl.handle.net/10962/d1005015
  • Description: A chemical investigation of six different marine invertebrates, collected along the South African coastline, resulted in the isolation and structural elucidation of fifteen previously undescribed secondary metabolites along with seven known compounds. The structures of the new metabolites were determined by a combination of spectroscopic and chemical methods. The endemic false limpet Siphonaria capensis was shown to contain two unusual polypropionate metabolites capensinone (162) and capensifuranone (163) as well as 2,4,6,8-tetramethyl-2-undecenoic acid (164) and the known polypropionates (E)- and (Z)siphonarienfuranone (149 and 161). Capensinone is the first example of a marine polypropionate containing a cyc1opentenone moiety. An investigation of the endemic South African soft coral Pieterfaurea unilobata yielded six new, highly oxygenated, pregnadiene sterols (180-185) and the known metabolite (169). Compounds 180-185 are the first pregnadienes obtained from the marine environment containing a C-7 substituent. An alternative procedure for the quick assignment of the absolute configuration at C-3 in this series of compounds was proposed. A companson of the pyrroloiminoquinone alkaloids of three undescribed l'}trunculid sponges resulted in the isolation of 3-dih¥drodiscorhabdin C (243), 3-dihydrodiscorhabdin B (244), discorhabdin H (197) and the previously reported alkaloids discorhabdin A (189) and discorhabdin D (192). While all three sponges were found to be morphologically different they all contained discorhabdin A as the major metabolite and discorhabdin H as one of their minor metabolites. It was found that a feature common to most of the South African latrunculid sponges is the reduction of the C-3 carbonyl gr,o up in some of the minor metabolites. The indole alkaloids, dilemmaones A-C (261-263), containing an unusual cyc1opentanone-indole skeleton, were isolated in trace amounts by bioassay guided fractionation of an extract obtained from a mixed collection of sponges collected near Cape Town. In an attempt to acquire more of these novel compounds for further investigation of their biological activity, several synthetic strategies towards their total synthesis were explored. A key feature of these approaches was the exploitation of the regioselective Gassman's artha-alkylation procedure for the introduction of an aromatic methyl substituent.
  • Full Text:
  • Date Issued: 2000

Studies of the population structure and generic diversity of domesticated and "wild" ostriches (Struthio camelus)

  • Authors: Bezuidenhout, Cornelius Carlos
  • Date: 2000
  • Subjects: Ostriches Ostriches -- Genetics Ostriches -- South Africa
  • Language: English
  • Type: Thesis , Doctoral , PhD
  • Identifier: vital:3907 , http://hdl.handle.net/10962/d1003966
  • Description: DNA sequencing and restriction fragment length polymorphism analysis (RFLP) of polymerase chain reaction (PCR) amplified mitochondrial DNA fragments, and random amplified polymorphic DNA sequence (RAPD) analysis were techniques evaluated in this study for applicability in the investigation various aspects of genetic diversity within the ostrich (Struthio camelus). The genetic aspects that were investigated were (i) relationships between ostrich subspecies, (ii) genetic variability between and within domesticated populations of southern African ostriches (Struthio camelus australis), (iii) linking egg production in domesticated ostriches to RAPD profiles, and (iv) determining the zygosity of twin ostriches. In the first part of this study DNA sequencing and the polymerase chain reaction - restriction fragment length polymorphism (PCR-RFLP) methods were evaluated for resolving genetic differences in the small mtDNA fragments ofthe ostrich. DNA sequencing ofPCR amplified 450 bp 12S rRNA gene fragments of representatives from the southern African population ostrich (S.c. australis) did not reveal any differences between the populatiohs from different geographical areas, representing ostrich lineages with different breeding histories. The PCRRFLP analysis ofmtDNA fragments (450 bp 12S rRNA gene fragment and 550 bp D-loop region) also did not reveal any genetic variability between the domesticated s.,c. australis populations included in this study. PCR-RFLP analysis of a 450 bp 12S rRNA gene fragment, however, showed differences between the subspecies s.c. australis and s.c. molybdophanes. The proportion of shared fragments (F) between these two subspecies was 0.286 and nucleotide sequence divergence estimated at 8.9 %. Divergence time between these two subspecies was estimated at 4.5 million years ago. The data presented from this study are comparable to the data from a previous study in which the entire mitochondrial genome and a larger number of restriction enzymes were used. The PCR-RFLP method thus demonstrated its usefulness for genetic studies of ostriches at thesubspecies level. The sequences used in this study could not reveal any markers that were useful for genetic studies of ostriches at the population level. In the second part of the study the RAPD method was evaluated for application in the genetic studies of ostriches. RAPD profiles, based on three RAPD primers, revealed differences between three subspecies of ostriches and indicated relationships between these subspecies that are consistent with observations from other studies. The numerical analysis of pooled and individual primer data demonstrated that the subspecies s.c. australis is more closely related to s.c. massaicus than to s.c. molybdophanes. RAPD marker differences between s.c. molybdophanes on the one hand, and s.c. massaicus and s.c. australis on the other is also consistent with observations from studies that proposed separate specie~ status for s.c. molybdophanes. RAPD analysis by five primers revealed geographic variation between s.c. australis populations. The clustering patterns observed in the dendrograms and Neighbour Joining Trees generated by computer programs showed trends of separating ostric1;t populations into geographical groups, possibly reflecting their different breeding histories. In the RAPD profiles of the inbred population, band-sharing was generally greater than in the outbreeding group. RAPD analysis thus showed that it may be a useful method in the population studies of domesticated S. c. australis. RAPDs also generated data that grouped ostriches according to trends in egg production capabilities. Analysis ofRAPD profiles by computer software showed a Neighbour Joining Tree and a dendrogram that predominantly grouped ostriches into clusters associated with either good or poor egg production. Evidence supporting the suitability of RAPDs as a tool in breeding programmes of ostriches was thus provided by this study. RAPDs also provided data, demonstrating that two sets of ostrich twins were non-identical twins. It was demonstrated by this study that RAPDs analysis may be a useful technique for applying to (1) systematic (2) population (3) breeding and (4) twin studies of ostriches (Struthio camelus).
  • Full Text:
  • Date Issued: 2000

Assessment of the potential contribution of the Coega industrial development initiative to the Eastern Cape Economy

  • Authors: Bibby, Ray Russ
  • Date: 2000
  • Subjects: Harbors -- Environmental aspects -- South Africa -- Port Elizabeth , Industrial development projects -- South Africa -- Port Elizabeth
  • Language: English
  • Type: Thesis , Masters , MTech
  • Identifier: vital:10830 , http://hdl.handle.net/10948/20 , Harbors -- Environmental aspects -- South Africa -- Port Elizabeth , Industrial development projects -- South Africa -- Port Elizabeth
  • Description: The research problem addressed in this study was to analyse and report on the development of the Coega Industrial Development Zone as an infrastructure for renewed entrepreneurial activity and profitable management of existing firms in the Eastern Cape. To achieve this objective, a literature study was undertaken to assess the potential benefits achieved at similar industrial development zones around the world and what could be learnt from these developments which will make the Coega Industrial Development Zone workable. The Empirical results obtained, indicate that most local companies are confident that the Coega industrial Development Zone will be beneficial to the region. In conclusion, various recommendations have been made with regard to the findings ascertained in the Empirical Study.
  • Full Text:
  • Date Issued: 2000

An evaluation of recirculating artificial stream designs for acute toxicity testing using two South African Ephemeroptera species exposed to sodium sulphate

  • Authors: Binder, Markus
  • Date: 2000
  • Subjects: Water -- Pollution -- Toxicology , Toxicology -- Research , Aquatic organisms -- Effect of water pollution on , Sodium sulfate , Mayflies
  • Language: English
  • Type: Thesis , Masters , MSc
  • Identifier: vital:5690 , http://hdl.handle.net/10962/d1005376 , Water -- Pollution -- Toxicology , Toxicology -- Research , Aquatic organisms -- Effect of water pollution on , Sodium sulfate , Mayflies
  • Description: Three artificial stream designs, termed Large Artificial Stream Units (LASUs), Raceways, and Channels, at two major scales (1700 L, 12.5 L and 20 L recirculated volume) were developed at the Institute for Water Research, Rhodes University, Grahamstown, in order to explore the possibilities of using indigenous rheophilic macroinvertebrates in routine toxicity tests. This study compared these systems, using 96h-EC50 values from sodium sulphate toxicity tests as the experimental response. Two local Ephemeroptera (Leptophlebiidae: Adenophlebia auriculata Eaton, and Baetidae: Afroptilum sudafricanum Lestage) were evaluated for their suitability in routine toxicity tests; and the possible effects of elevated salinity levels in South African rivers on the test species were assessed. Two sets of experiments with each mayfly species were conducted, following an unreplicated regression design. Dechlorinated tap water was used as the water source. Experiments in the Channels were repeated to determine experimental variability. Results were compared statistically by testing for overlap of 95% confidence limits (95%Cls) of EC50 values. The differences between A. auriculata EC50 values in the different systems were statistically significant (no overlap of 95%CLs), but they were not more variable than has been considered normal for biological systems (Coefficient of variation 20.1 %; ratio of greatest EC50 / smallest EC50 1.63). The differences were not related to the scale or the average current velocity characteristic of each stream design (average current velocity LASUs - Raceways - Channels 0.090 - 0.083 - 0.038 m/s). The Channels proved to be most efficient with regard to practical performance as they are portable and easily transportable, user-friendly, reliable, splash-free, cost effective to construct, and can easily be adapted to specific requirements. These systems are therefore recommended for regular use. The suitability of the two mayfly species for routine toxicity testing was evaluated. A. auriculata EC50 values showed a significant negative correlation with the corresponding average body-size (range 1476 - 1610 μm, mean 1555 μm). The different average body-sizes probably reflected the abundance of a certain size range present in the Palmiet River at the time of collection. Both species reacted similarly to Na₂S0₄ (similar slopes of the toxicity curves), identifying this salt as a slow acting toxicant. A. sudafricanum populations were more sensitive to Na₂S0₄ (EC50 3.404 g/L) than A. auriculata (EC50 8.090 g/L), probably because of its smaller body-size (mean 709 μm) and a lack of extremely tolerant individuals. In comparison to other freshwater macro invertebrates, including the standard toxicity test organism Daphnia spp., both mayfly species seemed to be moderately tolerant of Na₂S0₄; therefore there was no particular advantage to using these indigenous taxa rather than Daphnia spp. An assessment of the effects of elevated salinity/TDS levels on the test taxa yielded preliminary insights. A NaCI-EC50 for A. sudafricanum could be extrapolated and suggested a higher sensitivity to Na₂S0₄ than to NaCl. When Na₂S0₄ EC50 values of both species were compared to selected TDS levels of South African rivers, 4. auriculata would mostly not be affected, but A. sudafricanum might occasionally suffer from sub-lethal effects, depending on the sulphate proportion of the TDS. The South African guideline for TDS seemed to protect both species sufficiently.
  • Full Text:
  • Date Issued: 2000
  • Disclaimer
  • Privacy
  • Copyright
  • Contact