Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains vii, 65 p. : ill. Includes abstract. Includes bibliographical references (p. 33-36).

The existence of the reactive intermediate trans-10b,10c-dimethyl-10b,10c-dihydropyr-1-yne, 57, generated via dehydrobromination, was proved by trapping with N,N-diethyl-1,3-butadienylamine, furan and a series of isoannelated furans. Comparison of 57 with benzyne, 1, was implemented using the results of MMX/PCMODEL calculations. A fast route to annelated dihydropyrenes was developed via the reactive intermediate 57. Through this route, five annelated dihydropyrenes, namely, trans-14b,14c-dimethyl-14b,14c-dihydronaphtho (2,1,8-gra) naphthacene, 204, trans-16b,16c-dimethyl-16b,16c-dihydrobenzo (a) naphtho (2,1,8-fgh) naphthacene, 206a, trans-16b,16c-dimethyl-16b,16c-dihydrobenzo (a) naphtho (2,1,8-hij) naphthacene, 206b, trans-14b,14c,18b,18c-tetramethyl-14b,14c,18b, 18c-tetrahydrodinaphtho (2,1,8-uva; 2,1,8-jkl) pentacene, 224a, and trans-15b,15c,18b,18c-tetramethyl-15b,15c,18b, 18c-tetrahydrodinaphtho (2,1,8-uva; 2,1,8-pon) pentacene, 224b, and one bridged oxa (17) annulene, namely, trans-11b,11c-dimethyl-11b,11c-dihydropyreno (1,2-c) furan, 222, were synthesized. Metal complexation of the benzo (a) dihydropyrene 95 was investigated. This led to the first two metal dihydropyrene complexes, namely, (7,8,9,10,10a,10b-η6)-trans-12b,12c-dimethyl-12b,12c-dihydrobenzo (a) pyrenechromium(0)-tricarbonyl, 239, and (1,2,3,3a-η4) -trans-12b,12c-dimethyl-12b,12c-dihydrobenzo (a) pyreneiron(0)tricarbonyl, 209. The delocalization effects due to complexation were studied. Combining the results of the newly synthesized annelated dihydropyrenes with previously obtained ones, a series of correlations between theoretical calculations and experimental results, such as bond order vs. chemical shift, bond order vs. coupling constant, and ring current vs. chemical shift were devised. The ortho-metalation of dihydropyrene derivatives and synthesis of 1-bromo-2-fluoro-dihydropyrene were attempted. This led to two new dihydropyrene derivatives, namely, trimethylacetamino-trans-10b,10c-dimethyl-10b,10c-dihydropyrene, 99, and 2-diethylcarbamyl-trans-10b,10c-dimethyl-10b,10c-dihydropyrene, 109, and two new cyclophane derivatives, namely, syn-5-bromo-6-fluoro-9,18-dimethyl-2,11-dithia (3.3) metacyclophane, 131a, and anti-5-bromo-6-fluoro-9,18-dimethyl-2,11-dithia (3.3) metacyclophane, 131b. / Graduate

Liquid Chromatography/ Mass Spectrometry (LC/MS) is used to interface the separating power of LC with the sensitivity and specificity of MS for the determination of trace levels of organic compounds in a variety of matrices. The technique is finding increasing application in the field of environmental and pharmaceutical analysis. Particle Beam LC/MS (PB/LC/MS) uses a particle beam interface to connect the LC to the MS. This interface design has the advantage of being able to produce "classical" electron impact (El) spectra which can then be searched against commercial MS libraries. The aim of this work was to apply PB/LC/MS to a range of new problems in environmental analysis and evaluate the usefulness of this technique. PB/LC/MS was used to determine compounds that cannot easily be analysed by more conventional techniques such as gas chromatography with mass spectrometry (GC/MS) or liquid chromatography with UV/vis detection (LC/UV). For example, some polycyclic aromatic hydrocarbons (PAH) are too involatile to analyse by GC/MS, some commonly prepared isocyanate derivatives cannot be accurately identified by LC/UV and some classes of pesticides are thermally labile and so cannot be determined by GC/MS.The work presented in this thesis examines the factors affecting the sensitivity and performance of PB/LC/MS and comparisons are made with other analytical methods. Compound classes examined are polycyclic aromatic hydrocarbons (PAH), pesticides and isocyanate derivatives in a variety of environmental matrices. Methods for improving the sensitivity of PB/LC/MS are investigated and the results of these experiments used to compare the different models are used to explain PB/MS behaviour. Conclusions regarding the accuracy of these models are then made. The ability of PB/MS to provide useful El MS for identification purposes in complex environmental matrices is also investigated.

M.Sc. (Chemistry) / The aim of this study was to investigate the oxidation of aromatic compounds and benzylidene acetals with dimethyldioxinne. Dimethyldioxirane, either by Insitu preparation or in the isolated form, has shown remarkable reactivity. This oxidant is effective in oxygen transfer, readily prepared from commercial materials and reacts under mild conditions. Quinones are natural materials with biological activity and some are key intermediates in the synthesis of medicines. A well-known method for the preparation of quinones, is the oxidation of phenols and aromatic ethers. The oxidation of simple phenol and anisole derivatives by dimethyldioxirane yielded complex mixtures. More hindered aromatic compounds were investigated, since the oxidation of these compounds proceeded in a more controlled manner. In this study the phenols were found to be more reactive than the corresponding aromatic ethers. para-Quinones were formed preferentially, whereas ortho-quinones were observed in one or two cases. Products formed in these oxidations depend on the substitution pattern of the substrate. The oxidation of phenols and aromatic compounds formed complex mixtures and does not have many synthetic applications. Mechanisms are proposed for the formation of the different products. Benzylidene acetals are important protecting groups in the chemistry of carbohydrates. Cleavage of these benzylidene acetals gave either the free diol or benzyl ether or benzoyl ester, depending on the reagent used. The reaction of dimethyldioxirane with benzylidene acetals gave the benzoylesters. With dioxanes, e.g. 4,6-O-benzylidene sugar derivatives, there are no difference in stereoelectronic effects in the cleavage of C-4 and C-6. The major product has a 6-benzoate group, probably due to the greater stability of the primary benzoate. In dioxolanes both reactivity and regioselectivity of the reactions are influenced by stereoeleetronic effects. It has been found that the cleavage of dioxolanes took place preferably in a conformation where the oxygen is antiperiplanar towards the leaving group. It has been shown that dimethyldioxinme can be used with success in the deprotection of benzylidene acetals in the chemistry of carbohydrates.

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In Part I, the C.D. spectra of a number of 3-keto and 20-keto steroids are reported. The 3-keto steroids were comprised of two series of compounds. For one series, the conformationally transmitted effects of olefinic centers located in, or exocyclic to, rings B and C were investigated. It was found that these effects were reflected in the C.D. spectra when the double bond was located in ring B, but not when the double bond was located in ring C. Further, no correlation could be made between the relative rates of alkali-catalyzed benzaldehyde condensation and the C.D. data. For the other series, the conformations of ring A in a number of steroids substituted at the 2- and 4- positions are discussed. The C.D. results are in agreement with other evidence on this subject, and suggest that a 1,3-diaxial methyl interaction leads to flattening of ring A. For the Δ⁵- 4,4-dimethyl-3-keto steroids, a non-chair conformation is indicated, but a distinction between a boat and a flat chair conformation cannot be made . For 2 α -bromo-4,4-dimethylcholest-5-en-3-one, a conformational equilibrium is suggested. The 20-keto steroids were comprised of a large number of 16-substituted pregnanone and 17 α -pregna-none derivatives. The C.D. spectra of the 16,17 trans compounds and the 16α , 17α -cis-compounds were similar to those of the 16-unsubstituted parent compounds. Modifications in rings A and B had little effect upon the dichroism of the 20-keto group. The C.D. spectra of the 16β, 17β-compounds were very sensitive to the nature of the 16β -substituent, These results are interpreted in terms of the preferred conformation of the 17β -acetyl group. Finally, the C.D. spectra of a number of 16, 17-epoxy-20-keto steroids are reported and discussed with reference to the "reversed octant rule". In Part II, the structural determination of the mould metabolite, hirsutic acid C, is reported. The functional groups were established from chemical information; however the X-ray analysis of the p-bromo-phenacyl ester was required to reveal the novel ring system. During the X-ray irradiation an unusual solid-phase rearrangement occurred, transforming the α-epoxy hydroxyl system of p-bromophenacyl hirsutate to a β -hydroxy ketone system without disrupting the crystal structure. The X-ray analysis revealed a 50:50 mixture of starting material and rearrangement product. A combination of the X-ray and the chemical data was required to complete the structural determinations of both products. The generality of the rearrangement process was investigated. It occurred with methyl hirsutate and dihydromethylhirsutate, but not with hirsutic acid. It could not be induced thermally. It did not occur with the steroids 3 α - and 3 β -hydroxy-4 β, 5-epoxy-5β-cholestane. The rearrangement process is probably controlled by the nature of the molecular packing and hydrogen-bond formation. In Part III, the biogenetic-type syntheses of a number of acetate-derived aromatic compounds are reported. A discussion of the preparation of the condensed polypyrone intermediates is given, and in particular the synthesis of the tetrapyrone, 4-hydroxy-9-methyl-2,5,7,12-tetraketo 1,6,8,11-tetra-oxachrysene from the condensation of bis (2,4-dichlorophenyl) malonate and the tripyrone, 7-methyl-1-hydroxy-3,5,10-triketo 4,6,9-trioxaphenanthrene is reported. Treatment of the tripyrone with methanolic potassium hydroxide solution resulted in ring opening to form a poly- β-keto chain, and subsequent aldol-type condensation to give aromatic compounds representative of the naturally-occurring 6,8 dihydroxy-isocoumarins and C-acetylorsellinic acid. Treatment with methanolic magnesium methoxide solution gave aromatic compounds derivable from different cyclization modes of the poly- β-keto chain. Among the compounds isolated were two representative of the naturally-occurring curvulinic acid and the 5,7-dihydroxychromones respectively. Structural assignments were made largely on the basis of the characteristic spectral properties of the compounds. / Science, Faculty of / Chemistry, Department of / Graduate

Eskom has embarked on the development of the Pebble Bed Modular Reactor to generate electricity at low cost compared to that of coal with no greenhouse gas emissions. The proposed PBMR requires about 600 tons of nuclear-grade graphite blocks in its construction. A considerable amount of pitch is required as impregnants for the manufacture of this graphite. Anthracene oil is a high-boiling coal-tar distillate fraction consisting of a complex mixture of mainly unsubstituted polyaromatic hydrocarbons, with some methyl substitution. Conversion to pitch may be effected by dehydrogenation, i.e. volatile oil molecules condensing together to yield material of high molecular mass. Two dehydrogenation reagents, elemental sulfur and a novel reagent, hexachlorocyclohexane (HCH), an industrial waste product, were used to give three series of pitches with differing softening points. These products were characterised by standard pitch analyses, elemental analyses, thermogravimetric analysis (TGA), proton nuclear magnetic resonance spectroscopy (1HNMR), gas chromatography (GC), gas chromatography–mass spectrometry (GC-MS), Maldi-TOF mass and mass probe spectrometry and then compared with commercial pitch grades from Mittal Coke and Chemicals. The results obtained showed that the reaction products reacted with 15 and 20 wt % of sulfur, with the softening points of 61.3 and 91.4 °C, would be suitable as commercial products. All pitches showed very little, if any, ash, making them suitable for use in the manufacture of high-purity graphite. Pitches prepared with 15-20 wt % of sulfur and HCH pitches may have more applications in impregnation because of their low QI content. Total sulfur content detected by elemental analysis is high. This is undesirable because sulfur may cause puffing which will result in poor quality of graphite. All pitches show very little, if any, ash, making them suitable for use in the manufacture of high-purity graphite. TGA results showed that pitches prepared with higher concentrations of sulfur can be suitably used as impregnants because of their high coking yields. The coking yields of HCH-derived pitches are lower than those of Mittal Coke and Chemicals commercial pitches. Results from the (1HNMR showed that cross-linking on reaction with sulfur is through aliphatic carbon atoms; the percentages of aliphatic protons decrease with the increase in the sulfur concentration, and aromatic percentages increase. There is a slight increase in the proportion of aromatic protons of the HCH pitches; therefore cross linking is through aromatic-aromatic carbon atoms. Model reactions were prepared by reacting pure aromatic hydrocarbons with HCH, demonstrating the incorporation of the dehydrogenation reagent. These reactions were used to determine the reactivity of the main components of anthracene oil. The reaction products were characterised by Maldi-TOF and GC-MS. The results obtained from HCH pitches showed the formation of chlorobenzenes. This is undesirable because chlorine may cause corrosion of the equipment during coking. / Dissertation (MSc (Chemistry))--University of Pretoria, 2008. / Chemistry / unrestricted

Although environmental monitoring of polycyclic aromatic hydrocarbons (PAH) is an essential step to prevent human exposure to contaminated sites, it provides little information on the actual human uptake and subsequent risks. To this end, urine analysis of short-term biomarkers such as PAH metabolites fill an important niche. The general approach follows the sequence of urine hydrolysis, sample clean-up and pre-concentration, chromatographic separation and determination. Whereas chromatographic methods are based on well established laboratory techniques, the development of easy-to-use, cost-effective and large sample throughput techniques is becoming increasingly relevant to investigate adverse PAH effects on large human populations. This thesis compares the room-temperature, 77K and 4.2K fluorescence properties of 1-naphthol, 2-naphthol, 1-hydroxypyrene, 2-hydroxyfluorene, 3-hydroxybenzopyrene and 9-hydroxyphenanthrene. These metabolites are used as model biomarkers to investigate the analytical potential of a simple method of analysis based on Solid-Phase Extraction and Room-Temperature Fluorimetry. Metabolites are directly determined in the eluting solvent (methanol) without the need of previous separation via multidimensional formats. Metabolite recoveries varied between 87 ± 1.51% (9-hydroxyphenanthrene) and 99 ± 1.05% (3-hydroxybenzopyrene). For 10mL of urine samples, limits of detection varied between 0.01ng.mL-1 (3-hydroxybenzopyrene) and 0.6ng.mL-1 (2-hydroxynaphthalene). These figures of merit demonstrate the potential of this approach for screening purposes

<p>This thesis details a study of saprophytic competence in the Gram-negative bacterium Sinorhizobium meliloti, and comprises three main areas of research. The B-ketoadipate pathway is required for the catabolism of a wide range of aromatic compounds that are released into soil through the degradation of lignin. We demonstrate that S. meliloti encodes enzymes associated with the protocatechuate branch of the B-ketoadipate pathway within two operons (pcaDCHGB and pcaIJF) whose expression is regulated by the LysR-protein PcaQ and the IclR-type regulator PcaR, respectively. We show that purified PcaQ recognizes a motif with partial dyad symmetry (5' ATAACCN4-GGTTAA 3') positioned upstream of the pcaD promoter, and that this site is required for the regulated expression of pcaD in vivo. We report that PcaQ also regulates the expression of a protocatechuate-inducible ABC-type transport system that we infer is involved in the uptake of this aromatic acid, and we extend this analysis to identify PcaQbinding motifs in the genomes of a-,B-, and y-proteobacteria. </p> <p>In addition to protocatechuate, S. meliloti may utilize hydroxyproline as an energy source, as this amino acid is released into soil during the natural decay of plant tissue. We demonstrate that S. meliloti encodes a hydroxyproline-inducible ABC-type transport system that mediates the uptake of trans-4-hydrox-L-proline, as determined via growth and transport assays. </p> <p>As a more comprehensive method of examining saprophytic competence, we assayed the growth of S. meliloti upon inoculation into sterile bulk soil. We screened 40 S. meliloti strains carrying deletions within the pSymA or pSymB megaplasmids for growth in soil, and report that the majority of strains establish a stable population (greater than or equal to 10^8 cells g^(-1) soil) that persists for several weeks. In contrast, two S. meliloti strains exhibited a decreased ability to colonize soil, indicating that loci within the deleted regions play a role in saprophytic competence. </p> / Thesis / Doctor of Philosophy (PhD)