Urinary catheters are indispensable in healthcare and, with an ageing population, their use will continue to increase. However, they are commonly associated with colonisation and urinary tract infections (UTIs) caused by the attachment of bacteria to the catheter surface. Application of a novel cationic compound as a catheter coating may have a significant impact on the costs associated with treatment of UTIs and reduce the need for catheter replacement, as well as decreasing the number of UTI associated morbidity and mortality. Cationic compounds in particular are known to interact with the negatively charged outer membrane of bacteria, therefore have a broad spectrum of activity. The purpose of this study was to source and evaluate a novel cationic antimicrobial for use as a potential coating to impede biofilm formation on urinary catheters, and to investigate the cellular response to the selected lead compound. This research has demonstrated that the antimicrobial activity of commercially available Byotrol™ was superior to that of polyamines and quaternary ammonium compounds that were screened. Using high-throughput antimicrobial assays, such as the minimum inhibitory concentration and microtitre plate biofilm forming assays, the inhibitory concentrations of Byotrol™ were found to range from 3 µg/mL to 15 µg/mL for planktonic cultures, and 3 µg/mL to 20 µg/mL for the biofilm growth of uropathogenic bacteria. Furthermore, the minimum biofilm eradication concentration assay demonstrated that 200-1000 µg/mL Byotrol™ was able to eradicate an established biofilm. Byotrol™ may also have significant potential as a device coating, as pre-coating data on glass slides and microtitre plates with the compound inhibited bacterial growth on the surface at concentrations of 400 µg/mL for E. coli, and 1000 µg/mL K. pneumoniae. Atomic force microscopy validated the expectation that higher concentrations of Byotrol™ coated a surface more evenly than lower concentrations. Using two-dimensional gel electrophoresis, the metabolic protein tryptophanase was seen to be significantly over-expressed when E. coli K12 was treated with sub-inhibitory concentrations of Byotrol™. A transcriptomic approach using RNA-Seq demonstrated that a majority of the differentially expressed genes were identified in cells that were challenged with 4 times the minimum inhibitory concentration of Byotrol™. Genes associated with protein synthesis and stress response were significantly up-regulated. Interestingly, the global gene regulators AI-2 and indole were significantly up-regulated, which may have an influence on the expression of genes related to motility, biofilm formation and acid-resistance. Genes associated with chemotaxis and motility, acid-resistance and iron transport were significantly down-regulated, particularly in cells challenged with Byotrol™.Byotrol™ displayed antimicrobial activity both in suspension and as a coating. Identification of differentially expressed genes and proteins, when the bacteria were treated and challenged with Byotrol™, has, for the first time, revealed the bacterial cell’s response to this biocide. The findings may enable the development of strategies to prevent or better manage catheter associated urinary tract infection (CAUTI).

South Africa is the second largest producer of zircon (ZrSiO4) in the world, Australia being the largest. Zircon is notorious for its chemical inertness. Extreme processing conditions such as alkaline fusion (NaOH at 600 °C or Na2CO3 at 1200 °C) are used to extract the zirconium values from the mineral. The purpose of this study was to investigate the use of microwave digestion as an alternative process, and to determine the parameters for this technique for the digestion of zircon with ammonium acid fluoride (AAF) under various conditions. Ammonium acid fluoride is more convenient and safer to use than conventional fluorination methods such as HF and F2. In this study zircon was treated with ammonium acid fluoride (NH4F∙1.5HF) by means of microwave assisted digestion. Reaction times ranged from 10 to 330 minutes at temperatures between 100 °C and 240 °C. Successive microwave digestion steps, interrupted by an aqueous wash procedure, resulted in a >99 % conversion of zircon to the water soluble intermediates (NH4.)3ZrF7 and (NH4)2SiF6. XRD and Raman spectroscopy confirm that zircon was the major phase present in the insoluble fraction of the product after washing. Arrhenius rate laws are derived for both reaction control (progressively shrinking particle) and diffusion control by the product layer. Both models show reasonably good agreement with the experimental data, but diffusion control was accepted as the most probable. The derived diffusion coefficient corresponds to a solid-liquid case. Copyright / Dissertation (MSc)--University of Pretoria, 2013. / Chemical Engineering / unrestricted

Ammonium nitrate (AN) is commonly used as an explosive and as a fertilizer. In both roles it is provided as prills or pellets, approximately spherical and a few millimetres in diameter. The microstructures of several commercially-available AN compositions were investigated usingenvironmental scanning electron microscopy (ESEM) and X-ray microtomography. Those intended for explosive use were found to bemore porous than those intended for fertilizer use. The pores in explosiveprills were also found to form a connected network. The elemental composition of pellets of mixed AN and dolomite was investigated using energy-dispersive X-ray spectroscopy (EDX); the dolomite additivewas found to take the form of grains roughly 50 μm in size. The compaction behaviour of confined cylindrical beds of these prillsand pellets was studied at strain rates between 4 x 10-4 s-1 and 200 s-1. Quasi-static experiments were performed using a screw-driven instrumented press, while higher-rate experiments used a drop weight,instrumented with a line laser and load cell. The resistance of a bed to compaction was found to depend on the microstructure of its prills in most cases. Denser prills offered greater resistance to compaction. The exception to this rule was a pellet, rather than prill, formulation. Beds were also found to offer more resistance to compaction at higher strain rates. The Kawakita compaction model was found to agree well with the experimental data. A commercial fertilizer, not containing any AN, was assessed for use as an inert mock for AN prills and pellets. Prills of a suitable size for this purpose were found using EDX to consist of P2O5, with a coatingof unknown composition. They were supplied mixed with smaller K2CO3 and urea prills. The mixture was found to have comparablecompaction behaviour to AN compositions, indicating that it was useful as a mock for those compositions. In a plate impact experiment on a single layer of P2O5 prills, very little light was observed. Thisindicated that these prills were sufficiently inert for these purposes. The light produced by shocked granular ammonium nitrate beds and single prill layers was investigated using high-speed framing photography, photodiodes and gated visible-light spectroscopy. Framing photography of prill layers suggested that reaction in prill beds was dominatedby effects internal to prills. This was further supported by the similarity between photodiode recordings of prill beds and beds of inert prills containing a single reactive prills. Framing photography of drop weight experiments searching for a mechanism for initiation of reaction by interaction between prills found nothing. Decay of the light output of the beds suggested that in both granularand prill beds this light output was due to small regions heated to thousands of kelvin, which then cooled. Spectroscopic study confirmed this. These regions were found to reach a peak temperature of 6660 ± 20 K, well in excess of the approximately 2000 K predicted by a simple chemical model. Investigation of spectral lines observedduring this study indicated that the exothermic reaction that led to heating of these emitting regions involved NO.

O etanol é o combustível que mais se destaca como alternativa à gasolina no setor do transporte. No entanto, a melhoria da eficiência da fermentação, aprimorando o processo de conversão de biomassa em etanol combustível e reduzindo o custo de produção são desafios ainda pertinentes. Neste cenário, as fermentações com alta concentração de açúcar ou VHG (very high gravity) estão sendo cada vez mais estudadas. A adição de compostos como fonte de nitrogênio pode gerar benefícios para a produção de etanol, entretanto, a maioria dos estudos com suplementação de fontes nitrogenadas é realizada em sistema descontínuo simples e em escala laboratorial, embora os processos fermentativos industriais sejam conduzidos em sistema descontínuo alimentado. Neste contexto, este trabalho visou avaliar o perfil fermentativo da linhagem CAT-1 em mosto contendo alta concentração de açúcar fermentescível e suplementado com as fontes nitrogenadas peptona e sulfato de amônio, nas concentrações 5 e 10 g/L, em sistema de descontínuo simples e descontínuo alimentado com reciclo de células, utilizando diferentes escalas produtivas. Nos experimentos em sistema descontínuo simples, os tratamentos controle e peptona (5 g/L) apresentaram uma melhor produção de etanol, maior rendimento e produtividade em comparação com os demais tratamentos. Nos experimentos em sistema descontínuo alimentado não houve diferença significativa entre os tratamentos controle e peptona 5 e 10g/L, porém, o tratamento com sulfato de amônio (10 g/L) apresentou parâmetros fermentativos de produção de etanol e produtividade superiores ao tratamento controle, o oposto do descontínuo simples. Os resultados mostraram que quando as células de levedura foram submetidas a concentrações crescentes de açúcar, como é o caso do sistema descontínuo alimentado, ocorre uma adaptação das mesmas, proporcionando melhores resultados, com uma redução no tempo de fermentação para 16h. Além disso, a alta concentração de etanol no meio fermentativo causa um efeito prejudicial às células, já que nos tratamentos onde houve teores mais elevados de etanol ocorreu menor viabilidade e maior quantidade de açúcar residual. / Ethanol is the fuel that stands out as an alternative to gasoline in the transportation sector. However, improving the efficiency of fermentation, improving the process of converting biomass to fuel ethanol and reducing the cost of production are still relevant challenges. In this scenario, fermentations with high sugar concentration or very high gravity (VHG) are being studied more and more. The addition of compounds as a source of nitrogen can generate benefits for ethanol production, however, most of the studies with nitrogen supplementation are carried out in a simple discontinuous system and in laboratory scale, although the industrial fermentation processes are conducted in a fed batch system . In this context, the objective of this work was to evaluate the fermentation profile of the CAT-1 strain in must containing high fermentable sugar concentration and supplemented with nitrogen peptone and ammonium sulfate at 5 and 10 g / L in a simple discontinuous system and fed batch system, fed with recycle of cells, using different productive scales. In the simple discontinuous system experiments, the control and peptone treatments (5 g / L) presented better ethanol production, higher yield and productivity in comparison to the other treatments. However, the treatment with ammonium sulfate (10 g / L) showed fermentative parameters of ethanol production and productivity higher than the control treatment, the opposite of simple discontinuity. The results showed that when the yeast cells were submitted to increasing concentrations of sugar, as is the case of the fed batch system, an adaptation occurs, providing better results, with a reduction in the fermentation time to 16h. In addition, the high concentration of ethanol in the fermentation medium causes a detrimental effect on the cells, since in the treatments with higher levels of ethanol; less viability and more residual sugar were observed.

Orientador: Gisela Ferreira / Resumo: Para o nitrogênio (N) ser utilizado pela planta para síntese de metabólitos vegetais ele deve estar disponível nas fontes nitrato (NO3-) ou amônio (NH4+). O NO3- demanda mais energia do que o NH4+ para ser assimilado e incorporado em esqueletos carbônicos por necessitar de agentes redutores. O metabolismo do N está relacionado ao metabolismo do carbono (C), pois o N necessita de esqueletos carbônicos para sua incorporação e a assimilação de CO2 depende de um adequado suprimento de N para formação do aparato fotossintético. Além da relação entre N e C com o metabolismo primário, há relação também com o metabolismo especializado, envolvendo a síntese de compostos voláteis foliares formados por unidades de C e a síntese de alcaloides, que são compostos nitrogenados. Deste modo, o objetivo do presente trabalho foi analisar como o NO3- e NH4+ influenciam na fotossíntese e se há alteração na produção de alcaloides e voláteis foliares em Annona sylvatica em função das diferentes fontes de N. Para tanto, foi realizado experimento em esquema fatorial 4x3, sendo 4 tratamentos [NH4+, NO3-, NO3-:NH4+ e sem o fornecimento de N (S/ N)] e 3 épocas de coleta [30, 60 e 90 dias após o início do experimento (DAT)]. Foi observado que aos 90 DAT, as plantas que receberam NH4+ apresentaram maior taxa de assimilação líquida de CO2 (Anet) que as plantas que receberam NO3- e que não receberam N; a eficiência de carboxilação da enzima rubisco (Anet/Ci) foi... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: For nitrogen (N) to be used by the plant for synthesis of plant metabolites it must be available through the sources nitrate (NO3-) or ammonium (NH4+). NO3- requires more energy than NH4+ to be assimilated and incorporated into carbon skeletons because it requires reducing agents. N metabolism is related to carbon (C) metabolism, since N requires carbonic skeletons for its incorporation and CO2 assimilation depends on an adequate N supply for photosynthetic apparatus formation. In addition to the relationship between N and C with primary metabolism, there is also a relationship with secondary metabolism, involving the synthesis of leaf volatiles compounds formed by units of C and the synthesis of alkaloids, which are nitrogen compounds. Thus, the objective of the present studie was to analyze how NO3- and NH4+ influence gas exchange, and if there is alteration in the production of alkaloids and leaf volatiles in Annona sylvatica, due to the supply of different N sources. 90 days after the beginning of the treatments (DAT), the plants that received NH4+ presented higher rate of net CO2 assimilation (Anet) than the plants that received NO3- and that did not receive N; the carboxylation efficiency of the rubisco enzyme (Anet/Ci) was higher in NH4+ plants; internal CO2 concentration in the substomatic chamber (Ci) was lower in NH4+ plants compared to NO3-:NH4+ plants and without N (S/N); NH4+ treatment showed higher effective quantum yield of photosystem II (ΦFSII) than S/N treat... (Complete abstract click electronic access below) / Mestre

Pelchem NF3 plant produces an ammonium acid fluoride waste stream. The material of construction for the piping and stirrer fabrication in the plant is Monel. As a predominantly nickel-copper alloy, with minute quantities of carbon, manganese, silicon, sulfur and iron, these may leach into process fluids involved. The two biggest constituents of Monel contaminate the ammonium acid fluoride waste stream. Despite being the lesser of the two in terms of the composition of the Monel, copper is higher in concentration than nickel in the waste stream: the solubility of copper (II) cation in ammonium fluoride is higher than that of nickel (II) cation. Additionally, the ammonium acid fluoride is stored in steel barrels because of the relatively high process temperature that preclude the use of polymeric drums. This results in the leaching of iron from the steel drum to the solution. Pelchem expressed an interest in a suitable method of purification of ammonium fluoride, with specific interest of removing nickel (II) cation, copper (II) cation as well as iron (II) cation. The constraints to consider when selecting the appropriate methods are operating costs as well as the capital costs, but the most important factor to consider is the effectiveness of the method in removing the contaminant. In this regard, cationic exchange resins are very suitable, and they are very practical for industrial applications. In its simplest form, ammonium fluoride solutions are prepared by bubbling ammonia gas through solutions of hydrofluoric acid. Quite a few interesting uses of ammonium fluoride are available, these include as a chemical modifier in lead analysis, synthesis of beta zeolites, etc. The most prominent use is as a technical grade etchant in the electronics industry. The main aim of this research was to investigate ion exchange as a method of removing contaminants from Pelchem ammonium acid fluoride. Static equilibrium/selectivity experiments reveal that Purolite S930 Plus and Lewatit TP207 show a great affinity for the copper cation. For the limiting step of the reaction, the analysis includes apparent kinetics modelling contrasted with mass transfer modelling. In the case of reaction kinetics, Arrhenius and Van’t hoff equations were used to determine reaction parameters: the activation energies are 14 368 J∙mol-1 and 24 116 J∙mol-1, for Purolite and Lewatit respectively. The pre-exponential constants are 2 213 and 269 682 L2∙min-1∙mol-2 for Purolite and Lewatit in that order. The heats of reaction are -26 555 and -4 696 J∙mol-1 for Purolite and Lewatit respectively. Whilst the equilibrium pre-exponential constants are 75 057and 150 for Purolite and Lewatit respectively. Diffusivities for the two resins were found to be in reasonable agreement with those recorded in literature. They follow a temperature dependency trajectory. Weisz-Prater analysis of the observed reaction rate and the diffusion rate, in the two resins, reveals that intraparticle diffusion is the limiting step in the reaction. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted

Philosophiae Doctor - PhD / Background: Oropharyngeal candidiasis, caused by the fungus Candida, is the most common opportunistic infection affecting the quality of life of immunocompromised patients. Fluconazole is widely used as the first line of treatment for fungal infections. However, the inappropriate and misguided use of the drug has led to the evolvement of fluconazole-resistant Candida organisms. This arising resistance resulted in the urgent need for the development of new antimicrobial drugs. The aim of the present study was to investigate the antifungal action of K21, a novel antimicrobial quarternary ammonium compound, on fluconazole-resistant Candida species.

No description available.

Polymer composites are used in a varying extent and are challenging the use of traditional materials due to the push towards sustainable development. They have replaced steels and aluminum alloys in applications. Polymer composites are used in load-bearing and semi-load bearing applications in automotive, transport and aerospace industry due to their good characteristics. Polymer poses beneficial characteristics such as chemical stability, corrosion resistance, attractive strength-to-weight ratio, and be processed with ease. However, many polymers are highly flammable, making them a fire hazard. The fact that polymer composite is highly flammable, they need to undergo fire safety treatment that are sustainable towards the environment and humans. In this study biochar and ammonium polyphosphate (APP) were added in different combinations to epoxy resin. The purpose was to evaluate the synergistic effects that biochar and APP has on epoxy composite and how it will affect the fire- and mechanical properties. Additionally, developing a composite that retains a high compressive strength while increasing its thermal stability. Lastly, evaluate if the best performing composite could be recommended for load/semi-load‑bearing applications along with being sustainable towards the environment and humans. This thesis was conducted through literature study and laboratory work where three different tests were done such as cone calorimeter (CC), thermogravimetric analysis (TGA) and compressive test. The CC and TGA test were done to analyze the synergistic effect APP and biochar had on epoxy composites fire properties, but also determine which composition obtained the best fire properties. The compressive test was done to analyze the synergistic effect APP and biochar had on the epoxy composites mechanical properties. From the CC- and TGA tests it was observed that biochar and APP individually improved the fire properties of the epoxy where a decrease in peak heat release rate per unit area (PHRRPUA) and a decrease in mass loss was obtained. Additionally, it was noticed that the addition of only APP had a greater impact in improving the fire properties compared to only biochar. However, a combination of 15 wt.% biochar and 20 wt.% APP improved the fire properties the most. The compression tests indicated that biochar reduced the compressive strength drastically compared to the neat epoxy, since the biochar-based samples exhibited a porous structure. The addition of only APP in the epoxy showed a minimal reduction in compressive strength compared to neat epoxy. In conclusion, biochar and APP were improving the fire properties of epoxy composite whereas the compressive strength decreased. Overall, by an addition of only APP to the epoxy, the fire properties were enhanced where the compressive strength was conserved compared to neat epoxy. Since the composition with only APP performed the best overall, this composition can thereby be recommended for development in load/semi-load-bearing applications.

No description available.