Masters Degrees (Chemistry and Polymer Science)

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Chemical characterisation of the uropygial secretion of Rhinopomastus cyanomelas
(Stellenbosch : Stellenbosch University, 2004-03) Ghebrealfa Kahsai, Negassi; Le Roux, M.; Burger, B. V.; Stellenbosch University. Faculty of Science . Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: The uropygial gland of most birds produces a variety of hydrocarbons, lipids, waxes, fatty acids, alcohols and other organic compounds. These compounds have two widely recognized functions, viz. they are considered essential for the maintenance of a good plumage condition, and may be used for fungicidal, bactericidal or other hygienic purposes. Scimitar-billed woodhoopoes, Rhinopomastus cyanomelas, are groupterritorial birds that live in groups comprising between two and twelve individuals. Individuals enter the roost cavities shortly after sunset and exit the following morning soon after sunrise. During the period that the birds are inside the roost, they are vulnerable to a range of vertebrate predators, including snakes, genets and rats. When disturbed while roosting, woodhoopoes immediately face away from the threat hence presenting their uropygial glands in the direction of the threat. Typically, a drop of brown, highly pungent secretion is then formed at the tip of the papilla to the uropygial gland, and kept in place by a few tuft-like feathers. This response pattern has led some observers to believe that the secretion serves an anti-predatory role. It has been found that the synthetic volatile constituents of the uropygial secretion of the green woodhoopoe, P. purpureus, individually or as a mixture, have potent defensive properties against feline and reptilian predators. In addition, the compounds also showed activity against a range of bacteria. The aim of the present study was to determine the chemical composition of the uropygial secretion of the scimitar-billed woodhoopoe, Rhinopomastus cyanomelas, as a first step towards the evaluation of, inter alia, the semiochemical function of the secretion. Using gas chromatography-mass spectrometry, 179 constituents of the uropygial secretion of the scimitar-billed woodhoopoe have been identified. The majority of the constituents of the secretion are branched and unbranched aldehydes (aliphatic and aromatic), acids (aliphatic and aromatic), sulfides and ketones. This group of volatile compounds is responsible for the obnoxious odour of the secretion and possibly also for its defensive action against predators. The secretion also contains a large number of branched and unbranched alkanes and wax esters. The chemical composition of the secretion was compared with the secretion of P. purpureus as well as with that of the hoopoe, Upupa africana. The uropygial gland secretion of the scimitar-billed woodhoopoe is quite similar to that of the green woodhoopoe, although it is much more complex than that of the green woodhoopoe. In contrast to the uropygial secretions of the green and the scimitar-billed woodhoopoes, the secretion of Upupa africana does not have a strongly obnoxious odour and it also does not contain large quantities of alkanes and wax esters.
Chemical communication : chemical characterization of volatile constituents of urine of the southern African cheetah, Acinonyx jubatus jubatus, using headspace sampling and GC-MS
(Stellenbosch : Stellenbosch University, 2002-12) Visser, Runine (Runine Cecile); Burger, B. V.; Le Roux, M.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: The cheetah, Acinonyx jubatus, sometimes referred to as "the greyhound of the cats", is probably the most elegant member of the cat family. Formerly widespread in southern Africa it is now threatened with extinction. It occurs in open savanna and light woodland, but also hilly country on occasion. The cheetah is a predator that can reach speeds of more then 110 km/h in short bursts. With a mass of between only 40 to 60 kg, it is not very powerful and cannot defend itself very effectively against carnivores such as the lion and hyaena, for example. This might be the reason why, in order not to advertise its presence, the urine of this animal is practically odourless. In turn, this might explain why no research has so far been devoted to the urine of this animal. In contrast extensive work has been done on the chemical characterisation of the urine of many other carnivores, notably the lion. Extraction of the urine with dichloromethane gave too little material for GC-MS. SPME sampling of the urine itself gave insufficient sample enrichment. Better results were obtained when an SPME-type of headspace sampling, using a larger mass of polydimethylsiloxane, was employed although many of the constituents of the urine could still barely be detected. The compounds identified include a large number of ketones, aldehydes, cyclic and acyclic ethers, carboxylic acids, amides two sulphur compounds in barely detectable quantities, and elemental sulphur. Perhaps the most remarkable result of this thesis is that it was found that the urine of the cheetah, although it is a carnivore, does not contain several sulphur compounds in relatively high concentrations. However, it does contain elemental sulphur. Perhaps a mechanism exists by which the cheetah can convert strongly odorous sulphur containing compounds into the less strongly smelling sulphur.
Chemiese karakterisering van die aroma van die heuningbosspesie Cyclopia Genistoides
(Stellenbosch : University of Stellenbosch, 2006-03) Cronje, Christel; Le Roux, M.; Burger, B. V.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
Honeybush (Cyclopia spp.) is indigenous to South Africa and consists of more than 20 species of which only a few are used to make a herbal tea with a unique aroma and sweet taste. The aroma of unfermented and fermented honeybush tea differs considerably, indicating that changes take place in the chemical composition of the aroma during the fermentation process. Using a sample enrichment probe (SEP) and gas chromatography-mass spectrometry (GC-MS), the chemical composition of the aroma of unfermented and fermented C. genistoides, was analyzed and the resulting aroma profiles were compared. A total of 74 compounds were identified in the unfermented honeybush aroma, comprising, inter alia, a large number of saturated and unsaturated alcohols, aldehydes and methyl ketones that were found to be either absent, or present in lower relative concentrations, in the aroma of fermented honeybush. Most of these compounds, including 6-methyl-5-hepten-2-one, identified as one of the major constituents of unfermented honeybush, are probably responsible for its grassy, hay-like aroma. In the aroma of fermented honeybush 70 compounds were identified, of which 36 were found to be terpenoids. These compounds are probably responsible for the pleasant sweet aroma of the fermented honeybush. For instance, the major aroma constituent in the fermented honeybush, α-terpineol, is known to have a delicately floral and sweet odour. Other terpenoids occuring in significant quantities in the fermented honeybush, are linalool, cis and trans linalool oxide, nerol, geraniol, 2,6-dimethyl-1,7-octadien-3,6-diol, hexahydrofarnecyl acetone and phytol. These terpenoids are known to have sweet, sweet-woody en floral odours that probably contribute to the overall sweet aroma of the fermented honeybush. In the aroma of the unfermented honeybush a total of 25 terpenoids was identified, of which geranyl acetone, β-ionone, and dihydroactinidiolide are the most significant, since they are present in higher relative concentrations compared to the same terpenoids in the fermented honeybush. These three terpenoids have overall woody and even slightly green odours which contribute to the typical aroma of the unfermented honeybush. The terpenoids present in the aroma of unfermented and fermented honeybush belong to the following compound classes: • Terpenes • Terpene alcohols • Terpene aldehydes • Ketoterpenes • Terpene ethers • Terpene lactones Apart from the terpenoids present in the aroma of unfermented and fermented honeybush, the following classes of compounds are also present: • Aliphatic hydrocarbons (saturated) • Aliphatic alcohols (saturated and unsaturated) • Phenols • Aliphatic aldehydes (saturated and unsaturated) • Aliphatic ketones (saturated and unsaturated) • Aliphatic carboxylic acids (saturated) • Esters (methyl esters, ethyl and higher esters and aromatic esters) • Furane compounds • Lactones The present research was done to compare the chemical composition of the aroma of unfermented and fermented honeybush of one particular species, namely C. genistoides, to obtain an understanding of the evolution and/or disappearance of volatile compounds during fermentation that ultimately could help to identify compounds or compound types and their precursors responsible for its unique sweet aroma.
Chemiese karakterisering van die preorbitale afskeiding van die suni-ooi, Neotragus moschatus
(Stellenbosch : Stellenbosch University, 2001-03) Spies, Anena; Burger, B. V.; Le Roux, M.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: Please refer to fulltext for abstract
Die isolering en identifisering van die hondafwerende faktor in die kutikulêre afskeiding van die geelhondebosluis, Haemaphysalis leachi
(Stellenbosch : Stellenbosch University, 2004-12) Marx, Brenda; Burger, B. V.; Le Roux, M.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: When in close contact with the Yellow Dog Tick, Haemaphysalis leachi, dogs show clear signs of disgust or even nausea. It is accepted that the secretion is produced by the tick in order to prevent the dog from removing the tick from its body with its teeth, thereby increasing the chances for the tick's survival. The composition of this secretion was studied in order to identify the chemical compounds responsible for the repellent action of the secretion. Because of the dog's keen sense of smell, the tick only needs to produce minute quantities of this repellant, which significantly complicated the detection of the different components by conventional GC-methods. Several sampling and sample enrichment methods were explored, including solvent extraction, SPME sample enrichment, adsorption on active charcoal, cryoprecipitation, sorption in a phasecoated open tubular trap, as well as solventless sampling, in order to determine which method would ensure an appropriate amount of sample for gas chromatographic detection. Two of these sampling methods yielded acceptable results: The first method consisted of rinsing irritated female ticks with dichloromethane and, after concentrating the sample by evaporation, GC-MS analysis using normal splitless injection. The second method entailed collecting secretions by wiping irritated ticks with glass micro fibre filter paper after which the paper was inserted directly into the inlet liner of the GCMS system, where thermal desorption of the volatile constituents of the secretion preceded gas chromatographic separation and mass spectral detection. Live dogs were needed for the evaluation of the isolated material to determine whether the samples had an aversive effect on them. The extract was separated into different fractions, which were further separated into subfractions. After each separation process, all the fractions were tested for efficacy in order to determine which fraction contained the active components, narrowing down the number of candidate target compounds. It was concluded that a combination of aldehydes, namely hexanal, heptanal, octanal, nonanal, decanal, undecanal and dodecanal, is responsible for the dog repelling action of the secretion. In most cases the semiochemicals of insects and mammals are secreted in a more complex matrix to ensure prolonged activity. For this reason some of the other compounds in the complex cuticular secretion of this tick species were also identified during the course of this study.
Die karakterisering van die reukmerkvloeistof van die Bengaalse tier, Panthera Tigris Tigris
(Stellenbosch : University of Stellenbosch, 2006-03) Viviers, Marlize Z.; Burger, B. V.; Le Roux, M.; University of Stellenbosch. Faculty of Science. Dept. of Chemistry and Polymer Science.
Although the Bengal tiger, Panthera tigris tigris, appears on the IUCN Red Data List for endangered animals, very little information is available in the literature on the components of this animal's marking fluid. Scent marking is the main form of communication in all cat species. In some species, including the Bengal tiger, the liquid used for spraying is not pure urine, but is mixed with scent gland secretions. The objective of this study was to characterise the volatile components in the marking fluid of the Bengal tiger to achieve a better understanding of the semiochemical communication of this animal. The marking fluid of the tiger was characterised through the use of analytical techniques, such as gaschromatography, low resolution gas chromatography - mass spectrometry and retention time comparison. Homologous series of alkanes, alcohols, aldehydes, methyl ketones, carboxylic acids, γ- and δ-lactones, amides and lactams, as well as esters and nitrogen containing compounds, were identified. Of these identified compounds the unbranched alkanes, saturated alcohols, aldehydes, branched methyl ketones, saturated carboxylic acids and γ- and δ- lactones are commonly found in mammalian secretions. Compounds that aren't as common in their secretions are the methyl ketones, branched carboxylic acids, dimethyl esters of dicarboxylic acids and amides. The marking fluid contains a phthalic acid ester. Phthalic acid esters are used in the polymer industry and are nowadays found almost everywhere in nature. It is known that these pollutants have endocrine disrupting properties. The heat, humidity and wet conditions that are characteristic of the Bengal tiger's natural habitat makes it necessary for the tiger to make use of a fixative to prolong the life of the semiochemical message. The compounds and the concentrations in which these compounds are present in the urine and the lipid fraction of the marking fluid of the tiger was determined and compared to assess the fixative role of the lipids. This study has provided evidence that the lipid material has a greater affinity for the volatile organic constituents of the marking fluid and that it can therefore extend the lifetime of a semiochemical message left by the tiger.
The role of micro-organisms in the production of semiochemicals in the interdigital secretion of the bontebok, Damaliscus pygargus pygargus
(Stellenbosch : Stellenbosch University, 2004-03) Scott, Gary Terri; Le Roux, M.; Burger, B. V.; Stellenbosch University. Faculty of Science. Dept. of Chemistry & Polymer Science.
ENGLISH ABSTRACT: Bontebok, Damaliscus pygargus pygargus, formerly classified as D. dorcas dorcas, are territorial animals with interdigital glands between the toes of the forelegs. Males regularly defecate on dung heaps, on which they often lie, to communicate with other members of their species. They also communicate by means of visual displays, scent marking and occasionally with scraping or pawing of dung heaps. It is assumed that scent marking with the interdigital secretion serves to define territories frequented by these antelope. These glands secrete a complex mixture of volatile and non-volatile compounds and the volatile compounds in the secretion serve as a chemical signal for other bontebok. It has been suggested that the interdigital secretion is not produced in its final composition by the interdigital gland alone, but that microbial activity is responsible for many of the compounds present in the secretion. In general, many compounds can be attributed to the by-products of microbial hydrolysis of triglycerides, a common characteristic of sebum. It is well documented that micro-organisms inhabit the deep recesses of sebaceous glands and the presence of micro-organisms has been found to be consistent in all antelope exocrine glandular areas. This study involved the chemical characterisation of the volatile metabolites produced in vitro by micro-organisms from the interdigital cavity of the bontebok. Various comparative studies were made, one of which was comparison of the metabolites produced by the individual microbial species as well as the total community of bacteria incubated in different media. A comparison of the compounds identified in the interdigital secretion and the metabolites produced by the micro-organisms in the different media was also made. The volatile metabolite extracts of the individual bacterial species and of the total community were chemically characterised by low-resolution gas chromatography-mass spectroscopy. Classes of compounds identified from the volatile metabolite extracts include: • Acids - Aliphatic (saturated and unsaturated) • Alcohols - Aliphatic (saturated and unsaturated) • Aldehydes - Aliphatic (saturated and unsaturated) • Aromatic compounds • Ketones - Aliphatic (saturated and unsaturated) • Pyrazines • Dimethyldisulphide • Squalene and cholesterol Several qualitative differences were found between the compounds identified in the volatile metabolite extracts of the micro-organisms when incubated in tryptic soy broth (TSB) and minimal salt medium (MSM). In particular, when the microbes were incubated in TSB medium a number of pyrazines were found that were not present when utilising MSM as a medium. Additional qualitative differences were found between the compounds identified in the metabolite extracts of the individual bacterial species and the total community of bacteria, when incubated in both TSB and MSM media. A comparison of the interdigital secretion and the metabolite extracts of the microbial communities incubated in TSB and MSM revealed that many compounds produced in MSM corresponded to the compounds identified in the interdigital secretion. These corresponding compounds were found to be saturated and unsaturated acids, aldehydes and squalene. Furthermore, there was only one corresponding compound in the case of TSB as medium.

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

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