Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds characterized by having two or more condensed aromatic rings. These substances, as well as their nitrated and oxygenated derivatives, can be found widely spread as constituents of complex mixtures in the environment. A variety of PHAs, in many cases showing similar structures, can be found in the environment. The United States Environmental Protection Agency (U.S. EPA) has listed 16 PAHs based on their toxicological profiles, as priority pollutants. In the present study, the performance of the solid substrates Amberlite XAD-2, polyethylene, high-density polyurethane foam, silica gel and quartz fiber were investigated as alternative to XAD-2 to remove HPAs from solutions. The investigation of the adsorption of naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene and chrysene was conducted in aqueous solutions by batch experiments, considering the initial concentrations of substrates and PHAs, time, temperature and influence of cosolvency. Spectrophotometry and liquid chromatography with UV detection were used to assess the removal yield. The results showed that the yields of PAH strongly dependent on the substrate as well as the PHA. The PAHs were most quickly and almost totally (except chrysene and anthracene) removed by polyurethane foam. High density polyethylene behaves similarly to XAD-2. Among the investigated PHAs, chrysene showed a different behavior, since the best adsorbents for this compound were as silica gel and quartz fiber. Thus the personal samplers for PHAs must be prepared as a mix of adsorbents instead of having a unique composition. / Hidrocarbonetos policíclicos aromáticos (HPAs) fazem parte de uma classe de compostos caracterizados por terem dois ou mais anéis aromáticos condensados. Estas substâncias, assim como seus derivados nitrados e oxigenados, podem ser encontradas difundidas como componentes de misturas complexas no ambiente. Uma variedade de HPAs, que em muitos casos, mostram estruturas semelhantes, pode ser encontrada no meio ambiente. A Agência de Proteção Ambiental dos Estados Unidos (U.S EPA) listou 16 HPAs com base em seus perfis toxicológicos, como poluentes prioritários. No presente estudo, o desempenho do substrato de Amberlite XAD-2, polietileno de alta densidade, espuma de poliuretano, sílica gel e fibra de quartzo foram investigados como alternativa ao XAD-2 para remover HPAs a partir de soluções. O estudo da adsorção do naftaleno, acenaftileno, acenafteno, fluoreno, fenantreno, antraceno e criseno foi realizado em soluções aquosas através de experimentos em batelada, avaliando a influência das concentrações iniciais dos HPAs e substratos, tempo, temperatura e efeito do co-solvente. Espectrofotometria e cromatografia líquida com detecção por UV foram utilizados para avaliar o rendimento de remoção. Os resultados mostraram que os rendimentos são fortemente dependentes do substrato, bem como dos HPAs. Os HPAs foram mais rapidamente e quase totalmente removidos por espuma de poliuretano (exceto criseno e antraceno). O polietileno de alta densidade apresenta um comportamento semelhante ao de XAD-2. Entre os HPAs investigados, criseno apresentou um comportamento diferente, uma vez que os melhores adsorventes para este composto foram à sílica gel e a fibra de quartzo. Assim, os amostradores pessoais para HPAs devem ser preparados como uma mistura de adsorventes em vez de ter uma composição única.

Le phénomène d'oxygénation tardive des produits naturels a été investigué sur deux modèles d'études : les chalasines polycycliques et les diterpènes résiniques. Pour les chalasines, les cibles de synthèse envisagées étaient la trichoderone A et la trichodermone, deux chalasines d'origine fongique isolées récemment du champignon endophyte Trichoderma gamsii. En plus de leurs structures fascinantes, ces chalasines ont montré une inhibition modérée contre la lignée cellulaire tumorale humaine HeLa. Les études rétrosynthétiques de la trichoderone A et de la trichodermone, basées sur les hypothèses de biosynthèse des PKS-NRPS, ont dévoilé la possibilité d'un précurseur biomimétique commun par l'intermédiaire d'oxygénations bio-inspirées fréquentes in vivo. Ces travaux de thèse décrivent la synthèse totale de ce précurseur biosynthétique à travers le développement d'une nouvelle méthodologie de métathèse d'ényne cyclisante, suivie d'un réarrangement [3,3] d'Ireland-Claisen. La construction du squelette polycyclique repose sur une stratégie de Diels-Alder intramoléculaire, accédant ainsi au précurseur desiré. Des résultats préliminaires encourageants d'oxygénation bio-inspirées sont également décrits, en vue de l'accès vers les chalasines naturelles trichoderone A et trichodermone. Concernant les acides résiniques, une nouvelle méthodologie de photooxygénation bioinspirée a été développée. A l'aide d'un montage simple et efficace, des réactions de photooxygénations couplées à des réarrangements de Hock et de Kornblum-DeLaMare ont permis la formation de produits naturels ainsi que des molécules originales montrant des des activités antibactériennes prometteuses. / The late-stage oxygenation of natural products has been investigated on two studies templates: the polycyclic chalasans, the main topic of this thesis, and onto resinic diterpenes. Concerning the polycyclic chalasans, the envisaged synthetic targets were trichoderone A and trichodermone, two fungal secondary metabolites recently isolated from the endophytic fungus Trichoderma gamsii. In addition to their fascinating structures, these chalasans showed a moderate inhibition against human tumor HeLa cell line, which makes them very attractive for total synthesis. Based on the biosynthesis of PKS-NRPS compounds, the retrosynthetic studies of trichoderone A and trichodermone suggested the possibility of a common biomimetic precursor through bioinspired oxygenations frequently occurring in vivo. This thesis developed the total synthesis of this biomimetic precursor including the development of a new ring-closing enyne metathesis methodology, followed by a [3,3] Ireland-Claisen rearrangement. The construction of the polycyclic skeleton is based on an intramolecular Diels-Alder strategy, affording the desired precursor. Encouraging preliminary results have also been described towards the access to the natural chalasans trichoderone A and trichodermone, which have never been synthesized so far. On the subject of resinic diterpenes, a new bioinspired photooxygenation methodology has been developed. Thanks to a simple and efficient experimental set-up, photooxygenation reactions coupled with Hock and Kornblum-DeLaMare rearrangements allowed the formation of already isolated natural products, as well as novel molecules exhibiting promising antibacterial activities.

Polycyclic aromatic hydrocarbons (PAH) have been linked to cancer in humans. Subsequently, 16 of them were listed as priority pollutants by the Environmental Protection Agency in the Clean Water Act. The Florida manatee (Trichechus manatus latirostris) is an herbivorous endangered species that could have the potential to accumulate these compounds. The waters they inhabit have been shown to have PAH concentrations in the sediment from 0.035 μg/g w.w. (wet weight) to 0.686 μg/g w.w. PAH bioaccumulate due to their lipophilic nature and the manatee has a thick blubber layer that may allow for the accumulation of these compounds. Forty-eight archived subcutaneous manatee blubber samples were collected from Florida Fish and Wildlife Conservation Commission Marine Mammal Pathobiology lab and analyzed for 16 known priority pollutant PAH. Samples were then compared to a standard using HPLC analysis. Concentrations were found to range from 0.001 μg/g w.w. to 84.84 μg/g w.w. All 16 priority pollutant PAH were found, however not all 16 were found in any one animal. Forty-six of forty-eight manatee samples analyzed were found to have at least one form of PAH. The number of occurrences of each PAH out of 48 samples ranged from 1-19. The highest average PAH concentration was acenaphthylene with 12.60 μg/g w.w. There was no significant difference (p-value >0.10) between total, carcinogenic and noncarcinogenic PAH, with levels of 2.01 μg/g w.w., 2.18 μg/g w.w. and 1.84 μg/g w.w. respectively. No significant difference (p-value >0.10) was found between year or location of carcass recovery as well as sex of manatee. Averages ranged between 0.02 μg/g w.w. and 18.92 μg/g w.w. for year and 0.15 μg/g w.w. and 5.68 μg/g w.w. for location. Male average levels were 5.21 μg/g w.w., while female averages and perinatal averages were 1.51 μg/g w.w. and 1.147 μg/g w.w. respectively.

The synthesis of a novel, cage spiro-oxetane was carried out. Pentacyclo[5.4.0.0^2,6.0^3,10.0^5,9]undecane-8- one (PCUD-8-one) undergoes one-carbon homologation to a mixture of endo- and exo- PCUD-carboxaldehydes which then are converted into 8,8-bis(hydroxymethyl)PCUD. The monotosylate obtained via reaction of 8,8- bis(hydroxymethyl)PCUD with tosyl chloride(1 equivalent) reacts with sodium hydride to afford the corresponding spiro-oxetane via intramolecular Williamson reaction. Six new substituted heptacyclo[6.6.0.0^2,6.0^3,13.0^4,11. 0^5,9.0^10,14]tetradecanes (HCTD) were synthesized. These compounds will be used as substrates in a photoelectron spectroscopic study. The ring-expansion reaction of PCUD-8-one with ethyl diazoacetate in the presence of BF_3:OEt_2 was performed. The major product was converted into an alcohol, and the structure of the 3,5-dinitrobenzoate of this alcohol was elucidated by single crystal x-ray structural analysis.

Contorted polycyclic aromatic hydrocarbons have found increasing utility in the application of molecular electronics due to the surpamolecular properties that result from these non-planar structures. The [n]circulene series of molecules are particularly attractive members of the contorted aromatic family due to the unique structural implications that result from their changing value of n. For example, when n ≤ 5, the structures adopt a bowl-like shape; when n = 6, a planar structure is observed; and when 7 ≤ n ≤ 16, the compounds assume a saddle-like shape. Very few molecules exhibit the structural contortions that these contorted aromatics do – primarily because aromatic molecules desire to adopt highly planar conformations. Following the model of aromaticity developed by Erich Clar, we set our sights on the synthesis of tetrabenzo[8]circulene, the stabilized form of [8]circulene established through the addition of four fused benzenoid rings around the periphery of the molecule. The initial approach towards this structure employs a Diels-Alder [4 + 2] cycloaddition reaction and a palladium catalyzed arylation reaction as the key transformation steps. The results of these studies were promising, establishing the structural characterization of this new molecule and providing access to functionalized derivatives of the saddle-shaped structure. However, access towards these functionalized derivatives proved limiting, compelling us to investigate alternative synthetic methodologies. In the course of our studies, we established a new methodology towards 2,5-diarylthiophene-1-oxides, a key precursor to the Diels-Alder cycloaddition reaction. These reactive dienes are prepared from readily available arylacetylene precursors via zirconacyclopentadiene intermediates. The isolated yields of the desired thiophene-1-oxides are comparable to those obtained from previously established oxidation strategies while avoiding the formation of over-oxidation products. Of significant importance to scope of our work, this newly established methodology offers broader versatility providing products outfitted with electron-donating or electron-withdrawing groups. These new methodologies provided access to functionalized derivatives of the saddle-shaped molecule tetrabenzo[8]circulene in improved yield when coupled with a revised Diels-Alder/oxidative cyclodehydrogenation approach. This methodology affords products containing both electron-rich and electron-poor functional groups in a more efficient manner. The optoelectronic effects that result from the introduction of this functionality and investigations into the development of larger contorted aromatic systems are also discussed.

No description available.

Fossil fuels are currently the primary industrial energy source on Earth. They are principally composed of complex hydrocarbons in either long-chain or cyclic conformation. Industrial use of petroleum, diesel, oil, tar and other coal-derived products inevitably leads to pollution of the environment. The most serious pollution is caused by polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) that are not easily removed from soil after a spill. Long-chain and cyclic conformation makes fossil fuel hydrocarbons difficult to break down. However, certain free-living soil microorganisms have adapted to utilising these PAHs/PCBs as a source of energy. In many cases, their efficacy is greatly enhanced by the presence of plants. By inhabiting the rhizosphere, microbes form a mutualistic relationship with the plant, receiving nutrients from it and in return providing a less polluted environment in which the plant can grow. The purpose of this study was to elucidate some of the microbial population diversity in PAH/PCB-polluted soils in South Africa through the use of denaturing gradient gel electrophoresis (DGGE). In an initial study, DGGE was employed to separate soil communities in polluted and unpolluted soils into a genetic fingerprint, the main bands of which were sequenced and subjected to a BLAST analysis through a database for possible identification of species present. Phylogenetic and distance studies indicated that unpolluted soils have a far greater species diversity. It thus was evident that PAH/PCB pollution of soil leads to a decrease in microbial diversity by selecting for microorganisms with the ability to activate metabolic pathways allowing them to utilise the pollutants as an alternative source of carbon. Population diversity of pro- and eukaryotes found within polluted and non-polluted soils was compared. DGGE was employed to determine the genetic fingerprint of each population. Following this, dendogram analyses based on Shannon indices were done to determine PAH breakdown potential of prokaryotic vs. eukaryotic communities. A higher diversity and better adaptation potential were evident within prokaryotic than eukaryotic communities in pollution-stressed environments, indicating that the prokaryotic component of these samples had the greatest PAH-metabolism potential. To determine the capacity for PAH/PCB metabolism by the organisms within the soil samples being studied, the presence of xylE and ndoB genes, responsible for toluene/xylene and naphthalene biodegradation, respectively, was determined. DGGE was performed to analyse genetic diversity between these two genes, based on community fingerprints. Polluted soil communities tended to have comparable community diversity within their functional genes, depending on their physical situation, plant species proximity and soil conditions. In general, soil contained indigenous microbes with a high natural potential for biodegradation of PAHs/PCBs. A portion of the 16S gene of eight bacterial isolates representing the most dominant culturable taxa in the polluted soils was sequenced and analysed for identification purposes. These identifications were conducted in conjunction with the use of the catabolic gene probes xylE and ndoB to establish the hydrocarbon degrading capacity of the isolates. Pseudomonas, from the rhizosphere of Cyperus esculentus, was the most common PAH-degrading genus found in this study. Considering the well-established rhizosphere competence and PAH-degrading capacity of Pseudomonas, this genus seems to be the best suited for bioaugmentation purposes in South Africa. The presence of the nifH gene, the general marker gene of nitrogen-fixing bacteria in communities from unpolluted and polluted soils, was determined. It was hypothesised that bioremediation could be enhanced by nitrogen addition to polluted environments. Nested-PCR of the nifH gene was conducted on a diagnostic basis and was followed by DGGE of the product to determine the functional gene diversity within pollution-dwelling, nitrogen-fixing bacterial communities. Nitrogen-fixing microorganisms were present in all the soils sampled but, in only 80% of the pure cultures isolated from polluted and unpolluted soils and rhizospheres. Although different rhizospheres and pollutants were examined, it was found that of the polluted soils studied, most nifH gene diversity of polluted soils existed within machinery oil polluted, wood chip mulched, non-rhizosphere soil. Thus, it would appear that the more polluted the soil the higher the free microbe nitrogen fixation diversity possibly due to environmental stress. / Thesis (PhD (Microbiology))--University of Pretoria, 2007. / Microbiology and Plant Pathology / unrestricted

Please read the abstract in the section 00front of this document / Thesis (PhD (Applied Science: Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

This thesis discusses methods for the comparatively mild covalent functionalization of graphene. Several graphene models were investigated: polycyclic aromatic hydrocarbons (PAHs), chemical vapor deposition (CVD)-graphene on SiO2/Si substrate, graphite foil, graphite flakes, kish graphite and highly oriented pyrolytic graphite. The PAHs were viewed as graphene edge analogs with the following molecules representing different edge motifs: pyrene, perylene, benzo[a]pyrene, benzo[e]pyrene, triphenylene, acenapthylene, and anthracene. Ozone was used in combination with different solvents to functionalize PAHs, graphite, and CVD-graphene on SiO2/Si. Ozonation in water or methanol resulted in trapping of the carbonyl oxide intermediate that was formed in the reaction, producing a variety of functional groups. Ozonation in hydrogen peroxide solution with sonication promoted radical formation, possibly resulting in edge-oxidation of graphite. The regioselectivity for addition reactions (ozonolysis) and electrophilic aromatic substitution reactions with graphene edges is discussed. To achieve functionalization of the basal plane of graphite or graphene, white light irradiation was used in combination with several transfer hydrogenation reagents. Formic acid treatment under irradiation resulted in the expected hydrogenation, whereas iso-propanol treatment resulted in iso-propanol attachment to the graphene. The developed methods provide opportunities for graphene functionalization without the need for metal based reagents or harsh conditions.

The gas-phase ion chemistry of hydroxyl- and amino-substituted polycyclic aromatic hydrocarbons (PAHs) and their protonated counterparts were studied using mass spectrometry. Ions were generated using an electron ionization (EI) source and the unimolecular chemistry of metastable ions was studied by performing mass-analysed ion kinetic energy spectrometry (MIKES) experiments with a magnetic sector tandem mass spectrometer. Collision-induced dissociation (CID) experiments were used in conjunction with MIKES experiments to determine ion structure. The ten molecules studied were: 1-naphthol, 2-naphthol, 1-naphthylamine, 2-naphthylamine, 1-aminoanthracene, 2-aminoanthracene, 1-phenanthrol, 9-phenanthrol, 1-hydroxypyrene and 1-aminopyrene. Since it is believed that larger PAHs, on the order of more than 50 carbon atoms, populate the interstellar medium, the goal of this study was to attempt to extrapolate the results from smaller systems to larger ones. The trends found include: hydroxy-substituted PAH radical cations lose carbon monoxide spontaneously and amino-substituted PAH radical cations lose HCN. Mechanisms for both processes are proposed, and it appears from the present results that this process should extrapolate to larger PAHs. Another trend found was that all the remaining fragment ions were always a closed ring. Protonated amino-substituted PAHs were generated by electrospray ionization using a quadruple time-of-flight mass spectrometer. By protonating 1-naphthol and 2-naphthol using methane in the high-pressure EI source, it was found that they lost exclusively H2O. As for 2-naphthylamine, 1-aminoanthracene and 2-aminoanthracene, it was found that 2-naphthylamine lost NH3 and a hydrogen atom, NH3being the dominant channel. However, as the ion size 3 increases, the hydrogen-loss channel became the dominant channel. This means that larger PAHs will likely lose exclusively a hydrogen atom to reform the parent radical cation.