This thesis is made as it is submitted as a sum of published papers by the candidate. Aluminium hydroxides including gibbsite, boehmite and diaspore, are the major components, while iron hydroxides/oxides and kaolinite are the major impurities in bauxite. The dehydroxylation pathways during thermal activation of bauxite have been debated for decades. Phase transformation during thermal activation or calcination of bauxite to achieve high yields of alumina has been an important goal for the refining industry. This study deals with natural and synthetic aluminium and iron hydroxides using vibrational spectroscopy in conjunction with X-ray diffraction and electron microscopy, followed by the characterisation of the phase transformation in activated bauxite. In the Raman spectra, gibbsite shows four bands at 3617, 3522, 3433 and 3364 cm-1, and bayerite shows seven bands at 3664, 3652, 3552, 3542, 3450, 3438 and 3420 cm-1 in the hydroxyl stretching region. Five bands at 3445, 3363, 3226, 3119 and 2936 cm-1 for diaspore and four at 3371, 3220, 3085 and 2989 cm-1 for boehmite are present. The far infrared spectrum of boehmite resembles that of diaspore in the 300-400 cm-1 region. Boehmite has two characteristic bands at 366 and 323 cm-1 while diaspore has five at 354, 331, 250, 199 and 158 cm-1. The far infrared spectrum of gibbsite resembles that of bayerite in the 230-300 cm-1 region. Gibbsite shows three characteristic bands at 371, 279 and 246 cm-1 whereas bayerite shows six at 383, 345, 326, 296, 252 and 62 cm-1. The far infrared spectra are in-harmony with the FT-Raman spectra, allowing the study and differentiation of the stretching of AlO4 units to characterize these four alumina phases. The surface properties of kaolinite and gibbsite are studied using Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS). The FTIR-PAS spectra of kaolinite are recorded at mirror velocities of 0.05, 0.1, and 0.2 cm s-1, and compared to the gibbsite spectra recorded at mirror velocity of 0.2 cm s-1. It is found that the hydroxyl surface spectra are a function of depth. For the FTIR spectroscopy of thermal dehydroxylation of goethite to form hematite, the intensity of hydroxyl stretching and bending vibrations decreased with the extent of dehydroxylation of goethite. Infrared absorption bands clearly show the phase transformation between goethite and hematite, in particular the migration of excess hydroxyl units from goethite to hematite. Data from the band component analysis of FT-IR spectra indicate that the hydroxyl units mainly affect the a- plane in goethite and the equivalent c- plane in hematite. A larger amount of non-stoichiometric hydroxyl unit is found to be associated with a higher aluminium substitution. A shift to a higher wavenumber of bending and hydroxyl stretching vibrations is attributed to the effects of aluminium substitution associated with non-stoichiometric hydroxyl units on the a-b plane relative to the b-c plane of goethite. The dehydroxylation pathways of both the aluminium hydroxides and the impurities are intensively studied. Gibbsite completely decomposed at 250 °C, followed by boehmite and kaolinite at 500 °C. No phase transformations were observed for hematite, anatase, rutile or quartz up to 800 °C. Small amounts of gibbsite transformed to boehmite but the majority transformed to chi (χ) alumina, a disordered transition alumina phase, after dehydroxylation at 250 °C. The dehydroxylation pathways of crystalline gibbsite follow the orders: (a) gibbsite (&lt250 °C) to boehmite (250-450 °C) to gamma alumina (γ) (500-800 °C); or (b) gibbsite (&lt250 °C) to chi alumina (χ) (250-800 °C) to chi (χ) + kappa alumina (κ) (700-800 °C). Boehmite completely altered to gamma alumina (γ), while kaolinite altered to metakaolinite at 500 °C. The vibrational spectroscopy including FT-IR and FT-Raman, is a rapid, accurate and non-destructive technique in characterising both single and mixed mineral phases. In particular, the vibrational spectroscopy has shown its advantages over other techniques in terms of its sensitivity to hydroxyl groups. Future work on the simulation of bauxite dehydroxylation with emphasis on the studies of transition aluminas is proposed. The application of the advanced technique synchrotron x-ray spectroscopy, in addition to those techniques used in the present study, is recommended.

No description available.

A hemoglobina (Hb) do anelídeo Glossoscolex paulistus é uma Hb extracelular gigante. Esta é constituída por quatro cadeias polipeptídicas a, b, c e d contendo o heme. As cadeias a, b e c formam um trímero mantido por ligações dissulfeto e a cadeia d é um monômero. Neste trabalho, as técnicas espectroscópicas de absorção ótica no UV-Vís, fluorescência e dicroísmo circular foram utilizadas para monitorar as mudanças produzidas na estrutura do monômero d na forma oxi da hemoglobina extracelular gigante de Glossoscolex paulistus (HbGp) em pH 7,0 e 9,0 devido à interação com surfactantes iônicos, dodecil sulfato de sódio (SDS), cloreto de cetiltrimetilamônio (CTAC) e neutro, polioxietileno lauril éter (BRIJ - 35). A interação entre surfactantes e proteínas globulares tem sido estudada através de uma variedade de técnicas espectroscópicas visando à obtenção de informações relevantes com respeito à relação estrutura-atividade das proteínas. Os resultados de fluorescência mostraram que na presença dos surfactantes, há um aumento do rendimento quântico, sendo que o maior aumento é verificado na interação com o surfactante catiônico CTAC, sugerindo que a proteína apresenta uma quantidade maior de sítios específicos carregados negativamente, como os resíduos aniônicos, glutamil e aspartil. Na interação do monômero d da HbGp com CTAC ocorreu a formação de espécie pentacoordenada em ambos os pHs. Para o sistema monômero da HbGp-SDS em pH 7,0 e 9,0, foi observada a oxidação do monômero d, caracterizada pela formação da espécie hemicromo. A interação do monômero d em pH 7,0 e 9,0 com CTAC, analisada pelos espectros de dicroísmo circular, indicaram uma perda não muito significativa da estrutura secundária. No entanto, para os surfactantes SDS e BRIJ-35 foi possível constatar uma perda menos acentuada em relação ao CTAC. / The annelid hemoglobin (Hb) of the Glossoscolex paulistus is a giant extracellular hemoglobin (Hb). It is constituted by four polypeptide a, b, c and d chains containing the heme. The chains a, b and c form a trimer maintained by disulfide bond and the d chain is a monomer. In this work, the spectroscopic techniques of UV-Vís optical absorption, fluorescence and circular dichroism were used to monitor the changes induced by ionic detergents sodium dodecyl sulphate (SDS), cetyltrimethylammonium chloride (CTAC) and neutral, ether lauryl polioxitelene (BRIJ-35) in the structure of the d monomer in the oxi form of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in pH 7.0 and 9.0. The interaction between surfactants and globular proteins has been studied through a range of spectroscopic techniques targeting the obtaining of prominent information with regard to the relation structure-activity of the proteins. The fluorescence results showed that in the presence of the surfactants a quantum yield increases, and the CTAC promoted the more significant effect, suggesting that the protein presents a larger quantity of specific negative sites, as the anionic residues, glutamil and aspartil. In the interaction of d monomer of the HbGp with CTAC occurred the formation of pentacoordinated species in both pHs. For system monomer of HbGp-SDS at pH 7.0 and 9.0, was observed by oxidation of d monomer, characterized by the formation of the species hemichrome. The interaction of d monomer at pH 7.0 and 9.0 with CTAC, analyzed by circular dichroism spectra, indicates the loss of secondary structure. However, for SDS and BRIJ-35 surfactants it is possible to detect the lower loss of secondary structure in relation to CTAC.

A hemoglobina (Hb) do anelídeo Glossoscolex paulistus é uma Hb extracelular gigante. Esta é constituída por quatro cadeias polipeptídicas a, b, c e d contendo o heme. As cadeias a, b e c formam um trímero mantido por ligações dissulfeto e a cadeia d é um monômero. Neste trabalho, as técnicas espectroscópicas de absorção ótica no UV-Vís, fluorescência e dicroísmo circular foram utilizadas para monitorar as mudanças produzidas na estrutura do monômero d na forma oxi da hemoglobina extracelular gigante de Glossoscolex paulistus (HbGp) em pH 7,0 e 9,0 devido à interação com surfactantes iônicos, dodecil sulfato de sódio (SDS), cloreto de cetiltrimetilamônio (CTAC) e neutro, polioxietileno lauril éter (BRIJ - 35). A interação entre surfactantes e proteínas globulares tem sido estudada através de uma variedade de técnicas espectroscópicas visando à obtenção de informações relevantes com respeito à relação estrutura-atividade das proteínas. Os resultados de fluorescência mostraram que na presença dos surfactantes, há um aumento do rendimento quântico, sendo que o maior aumento é verificado na interação com o surfactante catiônico CTAC, sugerindo que a proteína apresenta uma quantidade maior de sítios específicos carregados negativamente, como os resíduos aniônicos, glutamil e aspartil. Na interação do monômero d da HbGp com CTAC ocorreu a formação de espécie pentacoordenada em ambos os pHs. Para o sistema monômero da HbGp-SDS em pH 7,0 e 9,0, foi observada a oxidação do monômero d, caracterizada pela formação da espécie hemicromo. A interação do monômero d em pH 7,0 e 9,0 com CTAC, analisada pelos espectros de dicroísmo circular, indicaram uma perda não muito significativa da estrutura secundária. No entanto, para os surfactantes SDS e BRIJ-35 foi possível constatar uma perda menos acentuada em relação ao CTAC. / The annelid hemoglobin (Hb) of the Glossoscolex paulistus is a giant extracellular hemoglobin (Hb). It is constituted by four polypeptide a, b, c and d chains containing the heme. The chains a, b and c form a trimer maintained by disulfide bond and the d chain is a monomer. In this work, the spectroscopic techniques of UV-Vís optical absorption, fluorescence and circular dichroism were used to monitor the changes induced by ionic detergents sodium dodecyl sulphate (SDS), cetyltrimethylammonium chloride (CTAC) and neutral, ether lauryl polioxitelene (BRIJ-35) in the structure of the d monomer in the oxi form of the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp) in pH 7.0 and 9.0. The interaction between surfactants and globular proteins has been studied through a range of spectroscopic techniques targeting the obtaining of prominent information with regard to the relation structure-activity of the proteins. The fluorescence results showed that in the presence of the surfactants a quantum yield increases, and the CTAC promoted the more significant effect, suggesting that the protein presents a larger quantity of specific negative sites, as the anionic residues, glutamil and aspartil. In the interaction of d monomer of the HbGp with CTAC occurred the formation of pentacoordinated species in both pHs. For system monomer of HbGp-SDS at pH 7.0 and 9.0, was observed by oxidation of d monomer, characterized by the formation of the species hemichrome. The interaction of d monomer at pH 7.0 and 9.0 with CTAC, analyzed by circular dichroism spectra, indicates the loss of secondary structure. However, for SDS and BRIJ-35 surfactants it is possible to detect the lower loss of secondary structure in relation to CTAC.

The technique of Raman spectroscopy was used in a study of shards of known (Ming and Meissen) and unknown (archaeological) origin. A tile shard from the Citadel of Algiers was included in this study as further confirmation of the consistency of the methods that are developed. The Citadel from which the tile shard was obtained was built in 1516 and represents a landmark from pre-colonial Algeria. The results were compared with those obtained from studies on intact museum pieces of known (Ming) origin. A consistent method of studying underglaze pigments on glazed ceramic artifacts by directing the laser beam through the predominantly silicate glaze was developed. The glaze depth profiling method developed proved to be very useful in the analysis and gives not only a detailed composition for the glaze/ceramic interfacial pigment, but also the order in which the various interfacial pigment layers were applied at the time of manufacture. The information acquired leads to an understanding of the level of technological development of the manufacturers. The detailed study and characterisation of the pigments that were analysed in this way gives insight into trade relations among ancient societies of the Mediterranean and will also assist archaeologists in establishing cut-off dates for the archaeological sites from which the artifacts were recovered. All the shards, except one from Meissen (Germany), were provided by the National Cultural History Museum of South Africa and the intact Ming dynasty plates were provided by the J.A. van Tilburg Museum of the University of Pretoria. The tile shard sample from the Citadel of Algiers was donated for the study. The results indicate that none of the archaeological shards could possibly be of Ming dynasty origin based on, firstly, the use of amorphous carbon to darken the cobalt blue (CoAl2O4) used as decoration on the shards, and secondly on the use of white (synthetic) anatase to whiten the ceramic surface before the application of the pigment since this synthetic anatase is known to have been manufactured for the first time around 1920. An ancient rediscovered ternary pigment (Pb2SnSbO6.5) previously found on Italian paintings of the 16th century, for example, “Lot and his daughters” by G.B. Langetti and “Entrance of Christ in Jerusalem” by Luca Giordano, was identified on the Citadel tile and successfully characterised. A Pb-O vibrational Raman band at 127 cm-1 for this pigment was assigned for the first time. Additional pigments identified on the tile include Naples yellow (Pb2Sb2O7), lead (II) stannate (Pb2SnO4), cobalt blue (CoAl2O4) and cassiterite (SnO2). The bulk of the tile body is composed mainly of hematite (á-Fe2O3), maghemite (ã-Fe2O3), magnetite (Fe3O4) and quartz (á-SiO2), with traces of calcite (CaCO3) and amorphous carbon. The unique non destructive depth profiling method that was developed in this study can now be applied to the study of underglaze pigments on intact porcelain artifacts in museums and private collections around the world for authentication purposes and for comparison with archaeological shard samples. / Thesis (PhD)--University of Pretoria, 2010. / Chemistry / unrestricted

No description available.

No description available.

<p> Under 248 nm laser flash photolysis, the photodecomposition of 1,3,4-trimethyl-1-phenyl-1-germacyclopent-3-ene (28) in dry, deoxygenated hexane solution at 23 °C leads to the prompt formation of two transient species: phenylmethylgermylene (29) and its Ge=Ge doubly bonded dimer, 1,2-dimethyl-1 ,2-diphenyldigemene (30). The formation of 29 proceeds in high chemical yield as shown by the results of steady state trapping experiments with methanol and isoprene. The transient assigned to 29 exhibits λmax = 490 nm and decays with second-order kinetics (τ ~ 2 μs). The second transient, which is formed from the latter, is assigned to digermene 30 and exhibits λmax = 420 nm and a lifetime, τ ~ 8 μs. The assignments are based on comparisons to the spectra of other simple germylenes, such as dimethyl-, diphenyl and dimesitylgermylene as well as on the pattern of reactivity with trapping reagents in solution at room temperature.</p> <p> Reactions studied include N-H, O-H and Sn-H insertion reactions, the [1+2] addition to isoprene and t-butylacetylene, and halogen atom abstraction from carbon tetrachloride.</p> <p> Absolute rate constants for quenching of 29 with the above mentioned scavengers were obtained by direct measurement of the germylene decay kinetics, over the concentration range where the formation of the digermene was more than 70% quenched. This ensures that the decay of 29 was dominated by the reaction with the trapping reagent.</p> <p> Absolute rate constants for reaction of the same reagents with 30 have also been determined for most of the scavengers studied. However, the digermene was found to be considerably less reactive than phenylmethylgermylene in all cases.</p> <p> The trends in spectroscopic properties and reactivity of simple germylenes in solution are discussed.</p> / Thesis / Master of Science (MSc)

Peptídeos antimicrobianos são vistos como alternativas promissoras a serem empregadas pela iindústria farmacêutica no controle de infecções causadas por microrganismos, como também na indústria alimentícia, onde podem desempenhar papéis como conservantes naturais de alimentos. Plantaricina149 é um membro deste grupo, sendo composto por 22 resíduos de aminoácidos, com natureza catiônica e atividade inibitória sobre algumas bactérias patogênicas. Neste trabalho, foram sintetizados diferentes peptídeos análogos à Plantaricina149 para investigar suas ações sobre microrganismos (bactérias e fungos), a fim de correlacionar estes estudos com a ação lítica do peptídeo em modelos de membrana diversos (monocamadas e vesículas fosfolipídicas). A interação de Plantaricina149 com estes sistemas foi monitorada pelas espectroscopias de dicroísmo circular e fluorescência, ensaios de tensão superficial, calorimetria e ressonância plasmônica de superfície, e mostrou ser altamente específica para superfícies fosfolipídicas que apresentam densidade de cargas negativas, tais como a membrana celular de bactérias. A interação eletrostática inicial que se estabelece entre o peptídeo e os fosfolipídios é de extrema importância, sendo capaz de induzir uma estruturação helicoidal na região C-terminal do peptídeo, enquanto a região Nterminal contribui com as interações hidrofóbicas necessárias para a penetração do peptídeo nas camadas fosfolipídicas levando a ruptura das mesmas. De forma semelhante, a atividade antimicrobiana de Plantaricina149a (e alguns de seus análogos) também mostrou ser resultado das interações das duas regiões da molécula, e foi afetada com a retirada ou modificação da região N-terminal do peptídeo. Com a deleção desta região, o peptídeo passou a ter somente ação bacteriostática sobre Staphylococcus aureus e Pseudomonas aeruginosa, perdendo a capacidade bactericida. / Antimicrobial peptides are seen as promising alternatives to be employed in pharmaceutical industry for controlling infections caused by microorganisms, and also in food industry, where they can play roles as natural food preservatives. Plantaricina149 is a member of this group, constituted of 22 amino acid residues, cationic in nature and presenting inhibitory activity against some pathogenic bacteria. In this work, different Plantaricina149 analog peptides were synthesized to investigate their action against microorganisms (bacteria and fungi), with the aim of correlating these studies with the lytic action of the peptide on several membrane models (phospholipid monolayers and vesicles). The Plantaricina149 interaction with these systems was monitored by circular dichroism and fluorescence spectroscopies, surface tension assays, calorimetry and surface plasmon resonance, and showed to be highly specific to phospholipid surfaces that present negative charge density, such as the bacteria cell membrane. The initial peptide-phospholipids electrostatic interaction is extremely important, and it is capable of inducing a helical structure in the peptide C-terminal region, while the Nterminal region contributes with the hydrophobic interactions needed to the peptide penetration in the phospholipid layers and to the disruption of them. Similarly, the Plantaricina149 antimicrobial activity has also proved to be a result of the interactions from the two regions of the molecule, and it was strongly affected by the removal or modification of the peptide N-terminal region. Promoting the deletion of this region has left the peptide only with a bacteriostatic action against Staphylococcus aureus and Pseudomonas aeruginosa, removing its bactericide ability.

Peptídeos antimicrobianos são vistos como alternativas promissoras a serem empregadas pela iindústria farmacêutica no controle de infecções causadas por microrganismos, como também na indústria alimentícia, onde podem desempenhar papéis como conservantes naturais de alimentos. Plantaricina149 é um membro deste grupo, sendo composto por 22 resíduos de aminoácidos, com natureza catiônica e atividade inibitória sobre algumas bactérias patogênicas. Neste trabalho, foram sintetizados diferentes peptídeos análogos à Plantaricina149 para investigar suas ações sobre microrganismos (bactérias e fungos), a fim de correlacionar estes estudos com a ação lítica do peptídeo em modelos de membrana diversos (monocamadas e vesículas fosfolipídicas). A interação de Plantaricina149 com estes sistemas foi monitorada pelas espectroscopias de dicroísmo circular e fluorescência, ensaios de tensão superficial, calorimetria e ressonância plasmônica de superfície, e mostrou ser altamente específica para superfícies fosfolipídicas que apresentam densidade de cargas negativas, tais como a membrana celular de bactérias. A interação eletrostática inicial que se estabelece entre o peptídeo e os fosfolipídios é de extrema importância, sendo capaz de induzir uma estruturação helicoidal na região C-terminal do peptídeo, enquanto a região Nterminal contribui com as interações hidrofóbicas necessárias para a penetração do peptídeo nas camadas fosfolipídicas levando a ruptura das mesmas. De forma semelhante, a atividade antimicrobiana de Plantaricina149a (e alguns de seus análogos) também mostrou ser resultado das interações das duas regiões da molécula, e foi afetada com a retirada ou modificação da região N-terminal do peptídeo. Com a deleção desta região, o peptídeo passou a ter somente ação bacteriostática sobre Staphylococcus aureus e Pseudomonas aeruginosa, perdendo a capacidade bactericida. / Antimicrobial peptides are seen as promising alternatives to be employed in pharmaceutical industry for controlling infections caused by microorganisms, and also in food industry, where they can play roles as natural food preservatives. Plantaricina149 is a member of this group, constituted of 22 amino acid residues, cationic in nature and presenting inhibitory activity against some pathogenic bacteria. In this work, different Plantaricina149 analog peptides were synthesized to investigate their action against microorganisms (bacteria and fungi), with the aim of correlating these studies with the lytic action of the peptide on several membrane models (phospholipid monolayers and vesicles). The Plantaricina149 interaction with these systems was monitored by circular dichroism and fluorescence spectroscopies, surface tension assays, calorimetry and surface plasmon resonance, and showed to be highly specific to phospholipid surfaces that present negative charge density, such as the bacteria cell membrane. The initial peptide-phospholipids electrostatic interaction is extremely important, and it is capable of inducing a helical structure in the peptide C-terminal region, while the Nterminal region contributes with the hydrophobic interactions needed to the peptide penetration in the phospholipid layers and to the disruption of them. Similarly, the Plantaricina149 antimicrobial activity has also proved to be a result of the interactions from the two regions of the molecule, and it was strongly affected by the removal or modification of the peptide N-terminal region. Promoting the deletion of this region has left the peptide only with a bacteriostatic action against Staphylococcus aureus and Pseudomonas aeruginosa, removing its bactericide ability.