In this study, synthetic routes to certain short acyl chain phospholipids were developed. Their inhibitory or substrate properties for phospholipase A₂ were then examined. An improved method for the acylation of glycerophosphocholine is described using a mixed fatty acid - trifluoroacetic acid anhydride. This partial synthetic route is particularly suitable for obtaining short acyl chain phosphatidylcholines. A new pathway for constructing the unnatural sn-1-phosphatidylcholines is also described, starting from L-arabinose. This is converted first to a key intermediate, 2,3-O-isopropylidene-sn-glycerol, which is then phosphorylated and transformed into sn-glycero-1-phosphocholine. This can be acylated as above to give sn-1-phosphatidylcholines. Routes to the short chain phosphatidylethanolamines were investigated and discussed. A procedure, using phospholipase D, was used to convert L-diC₆ PC into L-diC₆ PE in a transphosphatidylation reaction. Failed attempts to obtain shorter chain homologs by this and other methods are also detailed. The kinetics of inhibition of the phospholipase A₂ hydrolysis of L-diC₆ PC by the D-isomer are also reported for the monomeric concentration range. It was found that the D- enantiomer did not behave as a pure competitive inhibitor, and that an enzyme-substrate-inhibitor complex can exist. The implications of these results with regard to PLA₂ hydrolysis of mixed micelles is discussed. The PLA₂ substrate properties of both the anionic and zwitterionic diC₆ PE's were also studied. It was established that the anionic diC₆ PE is either a very poor substrate relative to the zwitterionic diC₆ PE, or acts as a competitive inhibitor towards its hydrolysis. Similarly, the rates of base-catalyzed acyl ester hydrolysis are about 18 times greater for the zwitterionic than for the anionic diC₆ PE. The importance of a protonated amino group in both these hydrolyses studies is noted. In addition, certain physical properties of diC₆ PE, such as its critical micelle concentration and carbon-13 NMR spectrum, are also given.

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The aim of this study is to attain a better understanding of the fate and preservation of organic matter through the high temperature processes associated with intrusions and atmospheric entry. Three high temperature regimes were investigated: Intrusions emplaced into organic-rich sediments with differing organic matter types; The STONE 6 atmospheric entry experiment using a sample of Devonian carbonaceous laminate; experimental pyrolysis of the Murchison carbonaceous chondrite.  A further study was performed on refining the experimental pyrolysis technique. For the intrusion studies, each case exhibited zones of petroleum generation towards the intrusion contacts, along with a significant increase in structural order.  Raman spectroscopy has been used to locate the position of an effective oil window next to one intrusion example.  The STONE 6 atmospheric entry experiment has returned carbon preserved in a disordered form alongside some evidence of interior protection.  The structural order of the organic matter present in the Murchison carbonaceous chondrite has increased significantly through both increasing temperature and duration.  An estimation of the size of meteorite that would be required to provide safe transit of organic materials is present at the end of this study with a detailed discussion on the complexities of interpreting the structural changes that are observed in disordered organic materials.

A thesis submitted to the Faculty of Science, University of the Witwatersrand in fulfilment of the requirements for the degree of Doctor of Philosophy. WITS University, Johannesburg, 2016. / In this work, natural and synthetic sorbents were investigated for the extraction and removal of different organic compounds (nitroaromatic compounds and polycyclic aromatic hydrocarbons) from aqueous samples. Natural sorbents like the raw Moringa oleifera seed powder and the physically modified biochared powder were investigated for their potential in the extraction of nitrobenzene (NB) (paper I). For the raw and biochared Moringa oleifera seed powder, the carbon content as determined by energy dispersive X-ray spectroscopy (EDS) was 80% and 70%, respectively. Though the surface area of the biochared was double that of the raw (12.6 m2 g-1 and 6.3 m2 g-1, respectively), the uptake of nitrobenzene by the later was higher in all optimizations and applications investigated. This implied that the interaction type between the Moringa oleifera seed powder and nitrobenzene was more chemisorption than physiosorption. The presence and absence of the proteneous compounds (bearers of the functional groups) infuenced the performance of the Moringa oleifera seed powder as a sorbent. For the raw and biochared Moringa oleifera seed powder sorbent, the kinetic data was best modelled by the pseudo-second-order and the adsorption capacities were found to be 0.084 and 0.071 mg g-1, respectively. As determination by HPLC-UV method, the LOD and LOQ for NB were found to be 11.5 and 38.5 μg L-1, respectively. In paper II, 2,4-dinitrotoluene was used as an imprint in the synthesis of magnetic molecularly imprinted polymers (MMIPs). These synthetic sorbents were used for the extraction of nitroaromatic compounds (2,4-dinitrotoluene, 2-nitotoluene and nitrobenzene). In all the optimization parameters investigated, the MMIP had a great extraction of 2,4-dinitrotoluene showing the effect of imprinting. For 2,4-dinitrotoluene, nitrobenzene and 2-nitrotoluene HPLC-UV analysis, detection limits of 13.6, 7.7 and 27.2 μg L-1, respectively and good correlations of determination (R2 > 0.993) of all the analytes were obtained. Recoveries of 82.7%, 88.1% and 82.0% were obtained for 2,4-dinitrotoluene, nitrobenzene and 2-nitrotoluene from spiked real water samples, respectively, with %RSD values ranging from 1.4%-11.9%. In paper III, another synthetic sorbent, β-cyclodextrin covalently functionalized to carbon nanofibers (β-CD@CNFs) was prepared and fully characterized. This material was loaded in solid phase extraction catridges, which were then applied for the extraction and pre-concentration of six nitroaromatic compounds. High correlations of determination (R2 > 0.997) for 3-nitrotoluene (3-NT), 1,3-dinitrobenzene (1,3-DNB), 2,6-dinitrotoluene (2,6-DNT), 4-nitrotoluene (4-NT), nitrobenzene (NB) and 2-nitrotoluene (2-NT) were obtained. Low limits of detection of 3.3, 7.1, 8.6, 9.7, 23.1 and 13.0 μg L-1 were found for the respective compounds. The applicability of the developed method using β-CD@CNF as a sorbent was investigated using spiked real water samples collected within the vicinity of an operational gold mine and recoveries of 36.6%-102.2% were obtained. Paper IV dealt with a novel combination of molecularly imprinted polymers (MIPs) dispersed in an organic solvent in membrane assisted solvent extraction (MASE) bags for the extraction of polycyclic aromatic hydrocarbons (PAHs) from sewage wastewater samples from Goudkoppies wastewater treatment plant in Johannesburg, South Africa. Before application to real wastewater, optimization was carried out and toloune was found to be the best acceptor phase, and 80 mg of the MIPs gave optimum extraction of PAHs. 25% N,N-dimethylformamide in aqueous solution as an organic modifier was found to be the best donor composition. An extraction time of 90 min at a stirring rate of 1000 rpm gave the optimum pre-concentration of the PAHs. The optimized parameters where then applied to the sewage wastewater were the effluent was found to be cleaner than the influent. In paper V, nano-sized fibers were synthesized by electrospinning polyacrylonitrile (PAN). Due to the combination of functional groups along the fiber and the increased surface area due to nano-sizing, there was a great extraction of four nitrotoluenes. The approach was loading a small amount of the electrospun polyacrylonitrile nano-fibres in pipette tips in a miniaturized pipette tip solid phase extraction (SPE). The linear dynamic range was 150 - 1000 μg L-1 with coefficients of determination of R2 > 0.99 for all the nitroaromatic compounds. Optimum recoveries were recorded at pH 6, 15 mg of the PAN sorbent. Twenty aspirating/dispensing cycles (at the loadind stage) and 1 mL acetonitrile gave maximum recoveries. Application of the PAN-PT-SPE to real wastewater samples gave recoveries ranging from 70% to 115%. The low values of the relative standard deviations (RSD < 12%) meant the method was suitable for application to real wastewater samples. / LG2017

Thesis (MTech(Chemistry))--Cape Technikon, Cape Town, 2001 / Many naturally occurring antibiotics have been identified and their synthesis successfully carried out in laboratories. It was envisaged by our group that by preparing a variety of, for example, quinoid compounds and then comparing their biological properties and activities, a better insight would be gained into a molecular structure - activity relationship. Chapter 1 deals with the attempted synthesis of 2-(1 '-hydroxyethyl)-3-(prop-2'enyl)- 1,4-benzoquinone (17) which may be converted by known methods into benzopyran derivatives. The second chapter describes a synthetic route to (±)(3R, 4R)-3,4-dihydro-3methyl- 4-hydroxy-l H-benzo[c]pyran-5,8-dione (42) and its (±)(45) diastereomer (43), both of which were found to be active against Gram negative and Gram positive organisms. The trans-l,3-dimethyl-4-hydroxypyranquinones (45) and (46) were also successfully synthesised. A different route of synthesis for the compounds (53), (54), (55) and (56) was also investigated. Several compounds were evaluated for biological activity. It was found that the quinones synthesised during this study were active against Gram negative and Gram positive bacteria, with the exception of compound (25) which had an acetate group in place of a hydroxy group. It was found that this trend was carried through all of the quinone derivatives tested.

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2007 / The inclusion behaviour of the two host compounds, 9-(4-methoxyphenyl)-9Hxanthen- 9-o1 (A1)• and 9-(4-methylphenyl)-9H-xanthen-9-o1 (A10) were investigated. These host compounds are large, bulky, rigid and they contain functionalities that allow them to selectively interact with other molecules, such as the guests in this work. The host molecules form inclusion complexes with small organic guest molecules. The host•••guest interactions are the interesting focus of this study. The host A1 included the guests: cyclohexane, 1,4-dioxane and N,N-dimethylformamide. Kinetics of desolvation were studied for the 1,4-dioxane and N,N-dimethylformamide compounds. Guest-exchange reactions were performed. The hostA1 was also used in the separation of 1, 4-dioxane and benzene. The host A10 included the guests; benzene, 1,4-dioxane, cyclohexane, cyclohexanone, N,N-dimethylacetamide and N,N-dimethylformamide. Kinetics of desolvation were studied for the benzene and cyclohexane compounds. The host A10 was used in the separation of the following pairs of guests: benzene and 1,4-dioxane; N,N-dimethylformamide and N,Ndimethylacetamide. The structures of the compounds were elucidated using single crystal X-ray diffraction. Thermal analysis was performed in order to determine the thermal stabilities of the complexes, including techniques such as thermogravimetry, differential scanning calorimetry and melting point measurement. The reactions in the guest exchange experiments were monitored using differential scanning calorimetry. Competition experiments were performed to determine the selectivity of a host for a series of related guests. These experiments were conducted between pairs of guests.

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2012. / Crystal engineering is the synthesis of new crystalline materials with specific chemical and physical properties which allows the comprehensive understanding of the non covalent interactions that occur between molecules in the crystalline state. This has lead to extensive work being done in terms of host design. The study of non-covalent interactions formed by these materials is crucial to understanding many biological processes. This study focuses on the inclusion compounds of 1, 4-bis (diphenylhydroxymethyl) benzene H, a host compound engineered by EWeber, that conforms to Weber's rules for host design as it is bulky, rigid, and has hydroxyl moieties that act as hydrogen-bonding donors. A Cambridge Structural Database (CSDversion 5.33) search has revealed that no research has been conducted on this host compound. Characterization of the compounds were conducted using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC}, hot stage microscopy (HS), gas chromatography (GC}, powder X-ray diffraction(PXRD} and single X -ray diffraction. Host: guest ratios determined from TG analysis were correlated with structural analysis results.