3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item The antimicrobial properties and chemical composition of leaf essential oils of indigenous Plectranthus ( Lamiaceae) species(2003-11-10) Maistry, KesheniSpecies of the genus Plectranthus, a member of the mint family ( Lamiaceae ), have been used in alternative medicines in third world countries dating back to the early Chinese empire. Plectranthus species have been used in the past for coughs and colds (P. ambiguus) and as a mouth-wash for loose and bleeding teeth (P. laxiflorus). The crushed leaves of P. madagascariensis are used by Xhosa as an ointment for scabies P. hadiensis is used orally as a cough mixture. Eight species from the genus were chosen to study the essential oil composition and antimicrobial activity.Item Nitrogen-containing derivatives of naphthoquinone and podophyllotoxin(2012-03-05) Jeftic, Tanya DushankaIn the initial, methodological part of this MSc project we intended to expand upon and improve various aspects of the ultrasound accelerated, iodine catalyzed, conjugate addition reaction of amines with 1,4-naphthoquinones first reported by Ji and co-workers in Synthetic Communications (2008, 38, 1201-1211). In recent times, the synthesis of 2-amino-1,4-naphthoquinones has become a heated area of research as a direct consequence of their multitude of diverse pharmaceutical activities; including anticancer, antimalarial, antifungal and trypanocidal properties. Sonochemical transformations, reactions accelerated by ultrasound irradiation, have attracted considerable attention of late due to the shorter reaction durations, higher yields and milder reaction conditions associated with these processes. Additionally, as a result of its unique catalytic properties, iodine has been extensively exploited in diverse, atom-economical and accelerated organic reactions to afford the corresponding products in excellent yields with high selectivity. With these considerations in mind a combinative library of eleven 2-amino-1,4-naphthoquinones with promising anticancer activity were successfully constructed in moderate to exceptional yields, with greatly reduced reaction times, 60 - 90 minutes, using the environmentally friendly, protic solvent ethanol.Item XRF analysis of base metals prepared by fused bead method(2012-02-27) Engelbrecht, ChantelleThe objective of the study was to investigate the preparation of glass beads for base metal analysis of mining samples prior to x-ray fluorescence analysis. The research method used included the investigation of different fluxes, oxidising, non-wetting agents, fusion temperature and time. The experiments were carried out using different fusion instruments: Electrofluxer and Katanax followed by both EDXRF and WDXRF analysis. The x-ray spectrometers were calibrated with standards prepared from pure oxides and the results compared to values determined by alternative techniques. Different statistical methods were used to validate the experiments including factorial designs. Not all the elements and oxides were recovered successfully, however, perfect glass beads were prepared. The two areas of concern were addressed successfully: firstly the loss of copper was overcome by using an alternative heating mechanism of the Katanax and sodium iodide as the non-wetting agent. Secondly, the sulphur was successfully oxidised and retained in the glass beads.Item Crystallographic investigation of n-Aminopyridinium perhalometallates(2012-02-06) Lawrence, EsteeThis dissertation presents the results of a crystallographic investigation into nineteen novel n-aminopyridinium perhalometallates of the general formula (C5H7N2 +)2MX4 2- where n = 2, 3 or 4, M = Zn, Cd or Hg and X = Cl, Br or I. The aim was to identify positional effects of the cation hydrogen bonding donor groups on the structures and to possibly identify robust synthons. Overall structural trends were also studied. The hybrid crystals were synthesized using temperature controlled crystallization methods and were characterized using X- ray diffraction techniques. Eighteen of the nineteen hybrid crystals displayed isolated tetrahedral perhalometallate anions. The results were classified into six different classes of isostructural compounds. Eight of the nineteen hybrid structures (42%) contained water. The 42% include two 3-ammoniopyridinium structures and all cadmium and mercury containing 4-aminopyridinium structures. The effect of a change in metal and/ or halide on the structure was investigated, and the overall structural trends in each n-aminopyridinium family were identified. Four different synthons were observed in the 2-aminopyridinium series while one synthon was observed throughout the 4-aminopyridinium series. A common synthon was observed in both the 3-aminopyridinium and 3-ammoniopyridinium series.Item Chemistry in Sepedi: Translation strategies for success(2007-02-22T11:14:13Z) Maleka, Raisibe GloriaThis dissertation attempts to offer a contribution to the field of translation by applying the practices of descriptive translation studies to a corpus of Chemistry terms in English and translated into Sepedi in order to establish whether the translation strategies opted for prove successful in promoting Sepedi to be a language for special purposes (LSP). The theoretical framework which is used in this project is the model of Baker (1992) of translation strategies of Descriptive Translation Studies (DTS). DTS is one of the three main branches of Translation Theory (Holmes, 1972). It differs from the other approaches in that it does not offer a set of guidelines which dictate how a translation should be done. Attention was also paid to theories of translation, such as those of Lawrence Venuti (2000) and his concepts of domesticating and foreignising translation in order to establish whether the translators have domesticated or foreignised the text and to what extent? Both strategies are evident in the corpus. This project also focused on the issue of the mother tongue education in the South African context with the emphasis on the perceptions and attitudes of learners and educators towards translated materials. Learners and their educators show some resistance to the use of local African languages, specifically Sepedi as medium of instruction in high schools. Reasons for their resistance against mother tongue education are economic and political. African languages are regarded as “low languages”, languages of inferior status as compared to English and Afrikaans.Item Organometallic chemistry of some manganese and zirconium complexes: A green chemistry approach(2006-10-27T07:30:31Z) Stanley, ManziniThe solventless reaction between Mn(CO)4(PPh3)Br and PPh3 as neat reagents using FTIRS was conducted and the activation enthalpy change of formation was found to be 143 ± 19 kJmol-1 while the activation entropy change of formation was 104 ± 7 Jmol-1K-1. The same reaction was also carried out in chloroform and the activation enthalpy change of formation was found to be 146 ± 8 kJmol-1 while the activation entropy change of formation was 114 ± 6 Jmol-1K-1. When the reaction was conducted in TCE solution, the activation enthalpy and entropy changes of formation were 137 ± 6 kJmol-1 and 97 ± 5 Jmol-1K-1 respectively. The solventless reaction of Mn(CO)4(PPh3)Br with PPh3 in KBr matrix using DRIFTS was also conducted and the activation enthalpy change of formation was found to be 169 ± 28 kJ.mol-1 while the activation entropy change of formation was 204 ± 57 J.mol-1.K-1. The sample preparation method, the type of support and the particle size of the support material influenced the reaction rate. The soventless reaction Mn(CO)4LBr + L → Mn(CO)3L2Br + CO [L= P(p-C6H4-R)3, R = Ph, MeO, Cl, F] in KBr using DRIFTS was also studied. It was found that the electronic effects of the ligand already attached on the metal complex influenced the rate of the reaction. An optical microscopy study of the reaction Mn(CO)4LBr + L' → Mn(CO)3LL'Br + CO [L= P(p-C6H4-R)3, R = H, Ph, MeO] was undertaken in an attempt to reconcile the wellbehaved reaction kinetics of the solventless reactions with solventless reactions by observing the microscopic behaviour of the reagents. The reactions were observed to go through a melt phase at temperatures much lower than the lowest melting point of the reagents, provided the reagents were in contact with each other. Isolated reagents neither reacted nor melted. The molten reagent thus served as a medium that allowed the diffusion of the reagents and products to ensure well-behaved kinetics. Investigation using 31P NMR demonstrated that the dissociation of the attached phosphine ligands also iii iv took place. The evidence obtained using the various techniques enabled the elucidation of the reaction mechanism. The solventless reaction, (η5-C5H5)2ZrCl2 + Na+RCOO-, R = C6H5, p-C6H4-NO2, p-C6H4- NH2 → (η5-C5H5)2ZrCl(RCOO) + NaCl did not occur but the reaction was found to take place in the NMR solvent. Single crystal XRD study of (η5-C5H5)2ZrCl(RCOO) R = C6H5, p-C6H4-NO2 revealed that the carboxylato ligand was coordinated in a bidentate fashion. The reaction of chlorobis(η5-cyclopentadienyl)hexylzirconium(IV) with internal hexene isomers failed to yield terminal olefins even under harsh experimental conditions. Isomerisation reactions using substituted zirconium metallocenes also failed to produce the terminal olefin. The reaction of Cp2ZrCl2 / n-BuLi with internal hexenes yielded a stoichiometric amount of 1-hexene. The reaction was found to be catalytic in Cp2ZrCl2 but limited by the amount of n-BuLi.