Doctoral Degrees (Chemistry and Polymer Science)

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Chemical characterisation of the aroma of honeybush (Cyclopia) species
(Stellenbosch : University of Stellenbosch, 2010-12) Cronje, Joan Christel; Le Roux, Maritha; Burger, B. V.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
ENGLISH ABSTRACT: Honeybush tea, also known as “South Africa’s sweetest tea”, is a herbal tea made from the leaves and twigs of Cyclopia spp., indigenous to the fynbos biome in the Western and Eastern Cape provinces of South Africa. The pleasant sweet aroma and taste of fermented honeybush, its low tannin content and the absence of caffeine have led to widespread interest in the commercial cultivation and processing of honeybush tea since the mid-1990s. Although more than 20 species of honeybush grow in the wild, only a few species are commercially exploited for the manufacture of tea. Currently the more prominent species are C. intermedia, C. subternata, C. genistoides, and C. sessiliflora. The present research contributes to a comprehensive honeybush research programme being conducted at the Agricultural Research Council (ARC) Infruitec-Nietvoorbij in South Africa. The first phase of the present study, using C. genistoides as representative species, was aimed at developing the necessary methodology for the analysis of extremely low concentrations of honeybush volatiles. A high-capacity headspace sample enrichment probe was applied successfully in conjunction with gas chromatography-mass spectrometry (GC-MS) to analyse the volatile organic compounds present in dry or infused unfermented and fermented honeybush. A total number of 255 volatile compounds were identified in unfermented and fermented honeybush, the majority of which are terpenoids (138; 54%) comprising mostly terpenes, terpene ketones, terpene alcohols and terpene ethers. Of the other compound classes, the aldehydes are the largest group, followed by esters, hydrocarbons and ketones. The stereochemistry of the identified compounds was determined whenever possible. This is the most comprehensive chemical characterisation of the volatile compounds in a South African herbal plant reported to date. A comparative study of green and fermented honeybush showed that the same compounds are, to a large extent, present in both, albeit in different relative concentrations. Not all of the identified honeybush volatiles are necessarily odour-active compounds contributing to the overall typical honeybush aroma. An important aspect of this research was thus the identification of the 46 odour-active compounds in fermented honeybush by means of gas chromatography-olfactometry (GC-O), using detection frequency and aroma extract dilution analysis methods. Fifteen of these compounds, mainly terpenoids, were singled out as the most intense individual contributors to the honeybush aroma based on consideration of all the relevant GC-O data. The odours of certain compounds, i.e. (6E,8Z)-megastigma-4,6,8-trien-3-one, (6E,8E)-megastigma- 4,6,8-trien-3-one, (7E)-megastigma-5,7,9-trien-4-one, 10-epi- -eudesmol, epi- -muurolol and epi- - cadinol, were perceived by GC-O assessors as typically honeybush-like. The quantitative GC-MS data of seven different Cyclopia samples (including four different species and variants thereof) were compared with respect to all the volatile components and particularly with respect to the odour-active compounds. Interesting variations were found in the concentrations of certain odour-active compounds in the various samples. The quantitative data obtained for the odour-active honeybush volatiles and data obtained from the sensory analysis of eight Cyclopia samples (including four different species and variants thereof) were subjected to statistical analysis and interesting associations between compounds with certain sensory aroma attributes were established. The present study has made a major contribution to the scientific knowledge regarding one of South Africa’s most popular indigenous herbal teas.
Chemiese kommunikasie van die Suid-Afrikaanse gordelakkedisse
(Stellenbosch : Stellenbosch University, 2003-12) Louw, Stefan; Burger, B. V.; Le Roux, M.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: The sungazer, Cordylus giganteus, is an endangered lizard species belonging to the family Cordylidae. It has been speculated that the function of semiochemical communication is performed by two types of skin glands, the femoral glands and the generation glands, which are also found in this family of lizards. Other skin glands and also the cloacal glands are further possible sources of semiochemicals. The investigation of these potential sources of chemical messages in C. giganteus, served as a starting point towards a better understanding of the chemical communication of lizard species belonging to the family Cordylidae. In continuation of this study the femoral gland secretion of the Cape girdled lizard, C. cordylus, was also investigated. Gas chromatography, low resolution GC-MS, GC-HR-MS, MO-TMS derivatisation and retention time comparison were used as analytical techniques in the chemical characterization of the femoral and generation gland secretions of C. giganteus and the femoral gland secretion of C. cordylus. Some compounds were not identified because of their low concentration in the secretions and/or mass spectra could not be obtained for pure compounds because of co-elution with other compounds. Compounds identified in the femoral gland secretion include the following: Carboxylic acids - saturated and unsaturated Alcohols Ketones Aldehydes - saturated and unsaturated Esters - saturated and unsaturated Hydrocarbons - saturated and unsaturated Nitriles Amides - saturated and unsaturated y-Lactones Squalene u-Tocopherol Steroids Quantitative analysis of the femoral and generation gland secretions of a number of sungazers indicated distinct differences between the secretions of males and females (in the case of the femoral gland secretions), but no apparent trend could be found in the differences between the femoral and generation gland secretions of individual lizards of the same gender. Qualitative seasonal differences were however observed in the femoral gland secretions of all individuals of C giganteus.
Elektrofiele addisiereaksies in die sintese van hormone en feromone
(Stellenbosch: University of Stellenbosch, 1977-03) Visagie, Hester E.; Gerbers, C. F.; Burger, B. V.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
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Identification of the putative urinary intraspecific recognition pheromone of the caracal caracal caracal
(Stellenbosch : Stellenbosch University, 2017-03) Hailemichael Goitom, Aron; Burger, B. V.; De Villiers, Andre J.; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.
ENGLISH ABSTRACT: Sheep husbandry makes a considerable contribution to the economy of South Africa. However, it has been pressure during the last few decades due to the rapidly growing numbers of predators such as the caracal, Caracal caracal, and the red jackal, Canis mesomelas. Currently, sheep farming is hardly viable in the arid southern parts of the country. When experimenting with various methods of controlling caracal numbers, sheep farmers found that this problem animal could be effectively lured into traps using the urine of another male or female caracal. The main disadvantage here is that a sheep farmer could incur serious stock losses before he is able to obtain a starting sample of urine from another source (e.g., another farmer). It was hypothesised that caracal urine contains a volatile organic substance, or substances (VOCs), that are involved in the semiochemical communication between members of this species. The objective of this investigation was to identify these putative attractants in the urine, for the subsequent formulation of a caracal lure composed of synthetic analogues of the natural VOCs. As sheep farmers reported that male and female urine were equally effective attractants, it was considered unlikely that the attracting agent could be a sex pheromone; rather, it could have an intraspecific signalling function. Efforts were made to identify all the VOCs present in caracal urine samples donated by farmers from different sheep farming areas of the country. A total of 191 VOCs, including five steroid hormones, were identified. The identification of 86% of these VOCs was corroborated by gas chromatographic-mass spectrometric (GC-MS) comparison of the natural substances with authentic synthetic analogues. Obligate proteinuria is known in certain animals, in which it is not an indicator of renal abnormality. In the house mouse, Mus domesticus, for example, so-called major urinary proteins (MUPs) bind dehydro-exo-brevicomin and 2-(sec-butyl)-4,5-dihydrothiazole elicit male aggression. The carboxylesterase-like urinary excreted pheromone-binding protein, also known as cauxin, has been identified in the urine of several felids, but was not found in caracal urine. However, the pheromone-binding proteins ‘Transgelin fragment (M3WJ37)’ and ‘Uncharacterized protein (M3XEJ0)’, both previously identified in Felis catus and Felis silvestris catus, were identified in caracal urine. The macrocyclic C15 ketone, cyclopentadecanone, was identified as one of the VOCs present in the headspace gas of caracal urine. The headspace concentration of this ketone increased when the urine was heated at 95 ºC for 10 min. A similar, but more pronounced increase in cyclopentadecanone concentration was observed when urinary protein present in caracal urine was denatured by subjecting it to similar treatment. This was interpreted as an indication that this ketone is a ligand of caracal urinary protein. The C13, C14, C16, and C17 macrocyclic ketones were subsequently also identified as urinary protein ligands. In bioassays, a mixture of synthetic analogues of a large number of the other ketones identified in caracal urine, including cyclopentadecanone, elicited typical feline behaviour in two male caracal in captivity. Similar behavioural patterns were observed when a mixture of the C13, C14, C15, and C16 macrocyclic ketones were tested. It was concluded that these ketones, that are ligands of the caracal’s urinary protein, could play an essential role in the intraspecific communication of the caracal.
Investigation into the semiochemical communication involved in neonatal offspring recognition in sheep
(Stellenbosch : University of Stellenbosch, 2010-03) Viviers, Marlize Zaretha; Burger, B. V.; Le Roux, M.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
ENGLISH ABSTRACT: Sheep husbandry substantially contributes to South Africa’s economy. Lamb mortality is regarded as a major constraint to sustainable sheep production, and an important factor in lamb survival is the strong ewe–lamb bonding. This is a well-known phenomenon in all sheep races and strong evidence exists that the selective ewe–lamb bond formation has a pheromonal basis, in that the ewe can distinguish her lamb by its unique, familiar smell. Sheep farmers and scientists have examined various methods of making alien lambs acceptable to foster ewes. The survival rate of offspring could be substantially increased if a reliable method could be devised to prevent ewes from rejecting their own lambs or if ewes could be induced to accept alien lambs. A better understanding of the semiochemicals involved in this communication between ewe and offspring could facilitate the development of a method by which ewes can be coaxed into adopting foster lambs. This would positively contribute to efficient sheep production in South Africa. The objective of this study was to characterise the volatile constituents present in the wool and the amniotic fluid collected from the Döhne Merino lambs to achieve a better understanding of the ewe–lamb semiochemical communication. The volatile organic constituents associated with the wool and amniotic fluid were characterised and a total of 133 volatile organic compounds were identified. Several compound classes are represented in these samples and the majority of these compounds have previously been identified in the excretions and secretions of numerous mammalian species. A number of different aspects of ewe–lamb kin recognition were investigated. First, the odour profiles of twin lambs were compared to those of other twins. The results of these analyses revealed that the wool volatiles of twin lambs are qualitatively as well as quantitatively practically identical, but different from those of other lambs in the flock. Second, the change in the odour profiles of lambs was studied over a seven-day period. It was found that the odour profiles of lambs are not fixed, and for as long as a ewe makes use of olfactory recognition as the main mode of identification of her lamb she has to continue learning the odour of her lamb. Third, the amniotic fluid was investigated as a possible source of maternal labels, i.e. as chemical codes consisting of mixtures of compounds in specific quantitative ratios that are imprinted on lambs by their mothers at birth. It was found that the amniotic fluids of first- and second-born lambs are qualitatively and quantitatively different. It is possible that the duration of the lambing birth process could contribute to this change in amniotic fluid composition. Fourth, the role of residual proteins in the dissemination of the semiochemicals involved in ewe– lamb communication was investigated and six proteins were identified as amniotic fluid and wool-associated proteins. Bioassays carried out during the lambing season of 2009 confirmed the role of the odour of the lamb in ewe-lamb recognition, but bioassays carried out with synthetic pheromone formulations gave inconclusive results.
Olfactory communicatiaon : chemical characterization of the interdigital secretion of the black wildebeest, Connochaetes gnou
(Stellenbosch : Stellenbosch University, 2000-12) Slade, Desmond; Burger, B. V.; Le Roux, M.; Stellenbosch University. Faculty of Science . Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: The black wildebeest, Connochaetes gnou, is a terriorial animal and although it is not generally accepted, it is believed that it defines its territory by scent marking, using interdigital and preorbital secretions, faeces, and urine. The aim of this study was to characterize the chemical constituents of the interdigital secretion. Due to the complexity of the secretion, only one hundred and ten of the approximately 350 compounds could be determined with known techniques. Gas chromatography, low resolution GC-MS and retention-time comparison were the main analytical techniques used. Classes of compounds identified in the interdigital secretion include the following: • Hydrocarbons - Aliphatic (saturated and unsaturated) and aromatic • Alcohols - Aliphatic (saturated, unsaturated, cyclic and diols) • Phenols and Phenylalkanols • Aldehydes - Aliphatic (saturated and unsaturated) and aromatic • Ketones - Aliphatic (saturated, unsaturated, cyclic and diketones) and aromatic • Hydroxy ketones - Aliphatic and cyclic • Carboxylic acids - Aliphatic (saturated, unsaturated and cyclic) and aromatic • An anhydride • Esters - Methyl esters, ethyl and higher esters, unsaturated esters and aromatic esters • Lactams • A steroid Only small qualitative and quantitative differences were found between the male and female interdigital secretions.
Ontwikkeling van instrumentasie vir omvattende tweedimensionele gaschromatografie
(Stellenbosch : Stellenbosch University, 2001-12) Snyman, Tertia; Burger, B. V.; Le Roux, M.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: Even capillary gas chromatography does not always give complete separation of the components of complex mixtures. During the last few decades several two-dimensional gas chromatographic techniques were developed to circumvent this problem and towards the end of the previous century, a technique that became known as comprehensive twodimensional gas chromatography, was introduced with which the peak capacity of capillary gas chromatography could be increased by at least two orders of magnitude. This technique is based on utilizing different separation mechanisms of two coupled chromatographic columns to get a better separation of complex mixtures than would be possible with the individual columns. To be classified as comprehensive twodimensional gas chromatography, the analytes eluted from the first or primary column must al be transferred to the second column as sharp sample pulses by, for example, focusing of analytes. Focusing of the analytes can be achieved by trapping or immobilizing the analytes in a short capillary tube that serves as a connection between the two columns, after which the trapped material is released as a sharp pulse into the secondary column by rapidly, i.e. within a fraction of a second, heating this capillary which therefore serves to modulate the effluent from the primary column. This ensures optimum separation on the secondary column and the independence of retention times of the analytes on the two columns. A modulator consisting of a capillary (modulator capillary) coated with a thick film of an apolar stationary phase was used in the present project to immobilize or trap the analytes. This capillary was housed in a stainless-steel tube (heater) which was subdivided into a number of segments of equal lengths (maximum of 10). These segments were heated sequentially to desorb the analytes from the inlet end of the modulator to its outlet end at such a rate as to generate and transfer a sharply focused analyte pulse into the secondary column. In a typical analysis each of the 10 segments of a lO-segment heater would, for example, be heated to a temperature 50°C higher than that of the gas chromatograph's oven (50°C temperature increment) within 200 milliseconds, after which each segment would be allowed to immediately cool down to the temperature of the oven. After the last segment had been heated, a pause of, for example, two seconds followed to allow analytes to be trapped in the modulator capillary after which the cycle was repeated until the analysis had been completed. For several reasons, heating the segments resistively by using a current of between 1 and 20 Ampere was preferred to the application of high voltages. A computer controlled power supply was developed with which any combination of duration of the energizing pulses of the segments from 10 to 2500 milliseconds, pause times from 100 milliseconds to 100 seconds and temperature increments of 100°C or higher could be used with acceptable precision and high reproducibility in comprehensive two-dimensional gas chromatographic analyses. The effectivity of the focusing that can be achieved with heaters having different numbers of segments, modulator capillaries with different inside diameters, different heating increments, as well as different rates at which the modulators are heated, were investigated. The best results were obtained with heaters having 8 and 10 segments, a modulator capillary with an inside diameter of 0.2 mm, a heating increment between 50°C and 10Goe, and a heating cycle composed of a total heating time of two seconds followed by a pause time of two to three seconds before the next cycle is started. A light petroleum oil fraction was used in a preliminary evaluation of the comprehensive two-dimensional system that was developed. At this stage of the project the influence of various parameters such as the average carrier gas velocity, the temperature program and the length of the secondary column was investigated. It was found that changing one parameter required the re-optimization of the other parameters. The concentrations of the sample also had a marked influence on the parameters that had to be used to achieve optimum results. A low sample concentration appeared to require a higher carrier gas velocity, a higher temperature-programming rate or considerably longer pause times to achieve satisfactory focusing of analytes, whereas too high a concentration resulted in breakthrough of the analytes from the modulator capillary. The two-dimensional gas chromatographic device was also interfaced to a quadrupole mass spectrometer. A GC-MS analysis of a petroleum oil sample gave mass spectra of surprisingly good quality in spite of the high scanning speed that was required by the sharp constituent peaks produced by the gas chromatographic component of the system. The two-dimensional system that was developed therefore appears to offer a costeffective alternative to other systems that have been developed elsewhere in which other modulation mechanisms are used. One remaining problem that still has to be solved is the unsatisfactory synchronization of the timing device of the power supply with that of the computer on which data are accumulated. Although the difference in timing may seem negligible, the result is that certain software packages cannot be used for the two-dimensional visualization of the data Of several possible solutions to the problem, redesigning the control circuitry of the power supply will be the first option to be explored. An important consideration in the development of the system was to avoid having moving parts so that the modulator could be installed in any gas chromatograph without requiring structural alterations to the instrument. No provision was therefore made to install the two columns and the modulator in separate temperature-programmable compartments in the oven of the gas chromatograph. During the evaluation of the present system it was, however, found that the parameters which gave acceptable results were confined to rather narrow limits. Not being able to cool the modulator to temperatures below that of the oven was found to be the most important limiting factor. A simple solution to this problem is to cool the modulator to a selected suitable temperature below the oven temperature with compressed air, the flow of which is regulated by a computer controlled mass flow regulator to maintain the same increment below the oven temperature right through an analysis. As this development was considered to be outside the scope of the present project, this idea was not implemented and evaluated. However, successful exploratory experiments were done in which the flow was mechanically regulated. A prototype of the component in which the modulator can be cooled was built and the mass flow regulator, control unit and software will be commissioned shortly.
Stir bar sorptive extraction and gas chromatography : mass spectrometry for the analysis of biological matrices
(Stellenbosch : University of Stellenbosch, 2007-12) Stopforth, A.; Sandra, P. J. F.; Crouch, A. M.; Burger, B. V.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
This study describes the development of simplified analytical methods for the analysis of trace quantities of selected naturally occurring target compounds in complex biological matrices by stir bar sorptive extraction (SBSE) and gas chromatography/mass spectrometry (GC/MS). SBSE facilitates the direct extraction of organic compounds from aqueous samples by allowing the solutes to partition between the aqueous phase and a glass stir bar that is coated with a layer of polydimethylsiloxane (PDMS). The partitioning of polar compounds into the PDMS coating was enhanced by using different derivatization techniques in combination with SBSE. The derivatization of polar functional groups was performed with ethyl chloroformate, acetic acid anhydride, and O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine directly in the aqueous samples. Headspace derivatization of compounds containing a secondary alcohol group was performed directly on the stir bar coating in the presence of acetic acid anhydride vapors. The derivatized compounds were thermally desorbed (TD) and analyzed on-line by GC/MS. A number of experimental parameters, including salt addition, temperature and time were optimized to improve the recovery of the derivatized compounds by SBSE. The optimized methods were validated in terms of linearity, precision, and detection and quantitation limits prior to performing the quantification. Trace levels of tuberculostearic acid, a marker of tuberculosis, was detected in sputum samples that were decontaminated and concentrated before being analyzed by SBSE-TD-GC/MS. The method is sufficiently sensitive to detect the marker without the need to culture the organisms, namely M. Tuberculosis. The analysis of 4-hydroxynonenal has also been demonstrated by detecting trace levels of this oxidative stress marker in urine samples obtained from healthy volunteers. Furthermore, abnormally low testosterone/epitestosterone ratios were detected in a group of HIV positive patients by means of SBSE-TD-GC/MS. Further research is required to determine the clinical significance of this finding in the context of HIV infection. Finally, the excessive urinary excretion of estrone and 17β-estradiol following the administration of a high dose of the conjugated equine estrogens to a female volunteer has also been demonstrated.
Synthesis and radiochemical stability evaluation of radiopharmaceutical compounds containing radioiodinated prosthetic groups
(Stellenbosch : Stellenbosch University, 2004-12) Rossouw, Daniel Du Toit; Burger, B. V.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: A study was undertaken to investigate the radiochemical stability of the βiodoethoxyl moiety, a relatively novel prosthetic group employed in radiopharmaceutical chemistry, in which an oxygen atom in a β-position relative to the radioiodine atom has a stabilising effect on the aliphatic carbon-iodine bond. The investigation was started as a pilot study by synthesising various model compounds containing a β-radioiodoethoxyl moiety, as well as two reference compounds lacking such a moiety. The purpose was to determine the influence of various groups in the vicinity of the β-oxygen atom on the stability of the abovementioned moiety. Radiochemical stability tests were carried out in vitro at 37°C in human blood serum. The results confirmed the superior stability of such a moiety compared to that of the reference compounds and also showed that the branching of such an aliphatic unit resulted in a considerable improvement in its stability, especially over a longer period. The investigation was extended to the synthesis of other compounds containing a few selected β-iodoethoxyl moieties that showed improved stability in the pilot study work. Reference compounds containing the classical iodovinyl unit, as well as those lacking a stabilising β- oxygen atom, were also prepared. The carrier molecules used in this part of the work was a benzamide containing a phenolic oxygen atom which acted as the β-oxygen atom, as well as two heterocyclic amines, benzotriazole and 2-methyl-5-nitroimidazole, in which the β- iodoethoxyl moiety was linked to a secondary nitrogen atom. Various suitable alkylating agents were prepared, chemically linked to the carrier molecules, the resulting intermediate compounds converted into tosylate or triflate iodination precursors and labelled with radioiodine by means of iodide-for-tosylate/triflate exchange. In vitro stability tests of these compounds showed similar trends to those obtained with the model compounds. Moreover, the stability of the stabilised β-iodoethoxyl moiety compared favourably with that of the iodovinyl unit, especially when incorporated into a heterocyclic amine. The results of this study have shown that some of the radioiodinated compounds synthesized in this work, especially the nitroimidazole derivatives, have the potential to be considered as novel radiopharmaceuticals.

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Browsing Doctoral Degrees (Chemistry and Polymer Science) by browse.metadata.advisor "Burger, B. V."

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