Made available in DSpace on 2014-11-10T11:09:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-01-14Bitstream added on 2014-11-10T11:57:25Z : No. of bitstreams: 1 000774915_20150228.pdf: 817618 bytes, checksum: 24cc6ba731989fdd1bdd5461735b376a (MD5) Bitstreams deleted on 2015-03-03T12:45:19Z: 000774915_20150228.pdf,Bitstream added on 2015-03-03T12:45:56Z : No. of bitstreams: 1 000774915.pdf: 2837940 bytes, checksum: 3b0281f8b4bc331d209a2b8aad1d6af7 (MD5) / No presente trabalho foi estudada a obtenção de nanopartículas do sistema (98,95)SnO2(1,0)ZnO(0,05)Nb2O5 através do Método Pechini (método dos precursores poliméricos) e a preparação de filmes varistores destas partículas. O pó obtido foi caracterizado por Difração de Raios X, Microscopia eletrônica de Varredura e adsorção de N2. Os filmes das nanopartículas foram obtidos por deposição em substrato de Si (100)/TiO2 (10.000 A°)/Ti (200 A°)/Pt (1500 A°), com espessura 356-406 nm, através da técnica de eletroforese, utilizando suspensão etílica estável deste pó. Os filmes foram sinterizados em forno microondas por temperaturas de até 1000 °C e patamar de até 40 minutos visando à formação e o crescimento dos grãos. Após a sinterização e caracterização por MEV_FEG, foi depositada uma película de íons Cr3+ através da eletroforese na superfície dos filmes e submetidos aos tratamentos térmicos de 900 e 1000 °C por 5, 10 e 15 minutos para fins de difusão dos cátions nos contornos de grãos. O Cr+3 é responsável pelo aumento do coeficiente de não-linearidade no sistema varistor a base de SnO2, característica principal desejada na obtenção de varistores. Esta adição permite controlar, através da difusão por tratamento térmico, a resistividade, a tensão de ruptura e coeficiente de não linearidade em filmes cerâmicos à base de SnO2 visando a aplicação como varistores. Após deposição dos íons de Cr3+ e do tratamento térmico, os filmes foram caracterizados eletricamente através da análise em corrente contínua, para a determinação das curvas V vs I (tensão aplicada em função da corrente elétrica) e das curvas ln(J/T²) vs E1/2, e caracterização em corrente alternada (espectroscopia de impedância). A partir das curvas V vs I foi possível obter valores do coeficiente de não-linearidade, campo elétrico de ruptura e corrente de fuga. Os parâmetros da barreira de potencial formada... / The present work was studied obtaining nanoparticles of the system (98,95)SnO2(1,0)ZnO(0,05)Nb2O5 by Pechini method (polymeric precursor method) and the preparation of varistors films of these particles. The powder obtained was characterized by X-Ray Diffraction, Scanning electron microscopy and N2 adsorption. The films of nanoparticles were obtained by deposition on Si (100)/TiO2 (10.000 A°)/Ti (200 A°)/Pt (1500 A°) substrate with 356-406 of thickness, by electrophoretic technique, using stable suspension of this powder. The films were sintered in the microwave oven for temperatures up to 1000 °C and time up to 40 minutes, in order to form and growth of grains. After sintering and characterization SEM, was deposited a layer of Cr3+ ions by electrophoresis on the surface of the film and submitted to heat treatment of 900 and 1000 ° C for 5, 10 and 15 minutes for purposes of diffusion of cations in the grain boundaries. The Cr+3 is responsible for increasing the coefficient of nonlinearity in varistor system based on SnO2, main characteristic required to obtain varistors. This addition allows to control, through the diffusion by heat treatment, the resistivity, breakdown voltage and nonlinearity coefficient in ceramic films based on SnO2 order to use as varistors. After deposition of ions Cr3+ and heat treatment, the films were electrically characterized by analyzing a direct current to the determination of curves V vs I (voltage applied as a function of electrical current) and curves ln(J/T²) vs E1/2, and characterization alternating current (impedance spectroscopy). From the V vs I curves was possible to obtain the coefficient of nonlinearity, breakdown voltage and leakage current. The parameters of the potential barrier formed at grain boundary region were calculated after analysis of the curves ln(J/T²) vs E1/2 obtained by the V vs I measurements as a function of temperature. The films showed nonlinear coefficient (α)...

Orientador: Maria Aparecida Zaghete Bertochi / Co-orientador: Leinig Antônio Perazolli / Banca: Mario Cilense / Banca: Eder Carlos Ferreira de Souza / Resumo: No presente trabalho foi estudada a obtenção de nanopartículas do sistema (98,95)SnO2(1,0)ZnO(0,05)Nb2O5 através do Método Pechini (método dos precursores poliméricos) e a preparação de filmes varistores destas partículas. O pó obtido foi caracterizado por Difração de Raios X, Microscopia eletrônica de Varredura e adsorção de N2. Os filmes das nanopartículas foram obtidos por deposição em substrato de Si (100)/TiO2 (10.000 A°)/Ti (200 A°)/Pt (1500 A°), com espessura 356-406 nm, através da técnica de eletroforese, utilizando suspensão etílica estável deste pó. Os filmes foram sinterizados em forno microondas por temperaturas de até 1000 °C e patamar de até 40 minutos visando à formação e o crescimento dos grãos. Após a sinterização e caracterização por MEV_FEG, foi depositada uma película de íons Cr3+ através da eletroforese na superfície dos filmes e submetidos aos tratamentos térmicos de 900 e 1000 °C por 5, 10 e 15 minutos para fins de difusão dos cátions nos contornos de grãos. O Cr+3 é responsável pelo aumento do coeficiente de não-linearidade no sistema varistor a base de SnO2, característica principal desejada na obtenção de varistores. Esta adição permite controlar, através da difusão por tratamento térmico, a resistividade, a tensão de ruptura e coeficiente de não linearidade em filmes cerâmicos à base de SnO2 visando a aplicação como varistores. Após deposição dos íons de Cr3+ e do tratamento térmico, os filmes foram caracterizados eletricamente através da análise em corrente contínua, para a determinação das curvas V vs I (tensão aplicada em função da corrente elétrica) e das curvas ln(J/T²) vs E1/2, e caracterização em corrente alternada (espectroscopia de impedância). A partir das curvas V vs I foi possível obter valores do coeficiente de não-linearidade, campo elétrico de ruptura e corrente de fuga. Os parâmetros da barreira de potencial formada... / Abstract: The present work was studied obtaining nanoparticles of the system (98,95)SnO2(1,0)ZnO(0,05)Nb2O5 by Pechini method (polymeric precursor method) and the preparation of varistors films of these particles. The powder obtained was characterized by X-Ray Diffraction, Scanning electron microscopy and N2 adsorption. The films of nanoparticles were obtained by deposition on Si (100)/TiO2 (10.000 A°)/Ti (200 A°)/Pt (1500 A°) substrate with 356-406 of thickness, by electrophoretic technique, using stable suspension of this powder. The films were sintered in the microwave oven for temperatures up to 1000 °C and time up to 40 minutes, in order to form and growth of grains. After sintering and characterization SEM, was deposited a layer of Cr3+ ions by electrophoresis on the surface of the film and submitted to heat treatment of 900 and 1000 ° C for 5, 10 and 15 minutes for purposes of diffusion of cations in the grain boundaries. The Cr+3 is responsible for increasing the coefficient of nonlinearity in varistor system based on SnO2, main characteristic required to obtain varistors. This addition allows to control, through the diffusion by heat treatment, the resistivity, breakdown voltage and nonlinearity coefficient in ceramic films based on SnO2 order to use as varistors. After deposition of ions Cr3+ and heat treatment, the films were electrically characterized by analyzing a direct current to the determination of curves V vs I (voltage applied as a function of electrical current) and curves ln(J/T²) vs E1/2, and characterization alternating current (impedance spectroscopy). From the V vs I curves was possible to obtain the coefficient of nonlinearity, breakdown voltage and leakage current. The parameters of the potential barrier formed at grain boundary region were calculated after analysis of the curves ln(J/T²) vs E1/2 obtained by the V vs I measurements as a function of temperature. The films showed nonlinear coefficient (α)... / Mestre

The aim of this study was to reveal mechanisms of pH change in wood ant nests. Contents of basic cations and glucose brought in ant food, i.e., honeydew and prey, into the nests were measured. Manipulation experiment was carried out to test effects of glucose and Ca2+ cations brought by ants into the nest on increase in pH.

This thesis concerns the thermodynamics of macrocycles and their metal cation complexes in non-aqueous media and these are discussed under two main headings, i) Thermodynamics of Alkali-Metal Cations and Macrocycles in Solution and in the Solid State. Thermodynamic parameters of complexation for alkali-metal cations and macrocycles (18-crown-6 and ethyl p-tert-butylcalix(6)arene hexanoate) in benzo-nitrile at 298.15 K are first reported. These data are compared with those previously reported for cryptand 222 and these cations in this solvent. A 'peak' selectivity for potassium is observed for the complexation of the calix(6)arene ester with alkali metal cations. The process is enthalpy controlled with an exothermic maximum for the potassium cation. Thermodynamic data of complexation are characterised by a lower enthalpic stability and a more favourable entropy (except for K+) than corresponding data involving cryptand 222 or indeed 18-crown-6. Standard enthalpies of solution, DeltasH0, of macrocycles and their sodium and potassium salts in benzonitrile measured calorimetrically are discussed in relation to (i) data for the uncomplexed salts and (ii) previously reported data for sodium and potassium cryptate salts in various solvents. Enthalpies of coordination, DeltacoordH0, for eighteen systems involving sodium and potassium coronates, cryptates and calix(6)arenates are derived and whenever possible these are discussed on the basis of (i) available X-ray crystallographic data and (ii) the anion effect on the coordination process. ii) Thermodynamics of Lower Rim Calix(4)arene Derivatives with the Silver Cation in Different Media at 298.15 K. The DeltasH0 values of p-tert-butyl(bis-diethylamine-bis-methysulphanyl) calix(4)arene (EATCalix4) in various solvents at 298.15 K are reported. Transfer parameters from acetonitrile to other solvents are calculated. The interaction of EATCalix4 and the silver cation was investigated by 1H NMR in deuterated acetonitrile at 298 K showing that the ligand hosts the metal cation through interaction with the different donor atoms (O, N, S). Conductimetric titrations indicate that the stoichiometry of the complex is 1:1. The thermodynamics of complexation of EATCalix4 and silver in six solvents at 298.15 K is reported. The DeltasH0 values of the free and the complex silver perchlorate salts have been also measured in various solvents and these have been combined with DeltacH0 data to derive the DeltacoordH0 of this system. A few representative examples about the use of coordination data are given. The medium effect on the complexation process is assessed in terms of DeltatG0, DeltatH0 and DeltatS0 of the reactants and the product from acetonitrile to the appropriate solvent. The relevance of analysing the solvation changes that these species undergo upon complexation is emphasised.

Please read the abstract in the section 00front of this document. / Dissertation (MSc (Chemistry))--University of Pretoria, 2007. / Chemistry / unrestricted

The aim of the project was to determine whether a by-product of industrial fermentations, Saccharomyces cerevisiae, could be utilized to bioaccumulate heavy metal cations and to partially define the mechanism of accumulation. S. cerevisiae cells were found to be capable of accumulating Cu²⁺in a manner that was proportional to the external Cu²⁺ concentration and inversely proportional to the concentration of biomass. The accumulation process was only minimally affected by temperature variations between 5 and 40°C or high ambient concentrations of sodium chloride. The accumulation process was however considerably affected by variations in pH, bioaccumulation being most efficient at pH 5 - 9 but becoming rapidly less so at either extreme of pH. Selection for copper resistant or tolerant yeast diminished the yeast's capacity for Cu²⁺ accumulation. For this and other reasons the development of heavy metal tolerance in yeasts was deemed to be generally counterproductive to heavy metal bioaccumulation. The yeast biomass was also capable of accumulating other heavy metal cations such as c0²⁺ or Cd²⁺. The yeast biomass could be harvested after bioaccumulation by tangential filtration methods, or alternatively could be packed into hollow fibre microfilter membrane cartridges and used as a fixed-bed bioaccumulator. By immobilizing the yeast in polyacrylamide gel and packing this material into columns, cu²⁺, C0²⁺ or Cd²⁺ could be removed from influent aqueous solutions yielding effluents with no detectable heavy metal, until breakthrough point was reached. This capacity was hypothesized to be a function of numerous "theoretical plates of equilibrium" within the column. The immobilized biomass could be eluted with EDTA and recycled for further bioaccumulation processes with minor loss of bioaccumulation capacity. Yeast cells were fractionated to permit identification of the major cell fractions and molecular components responsible for metal binding. Isolation of the yeast cell walls permitted investigation of their role in heavy metal accumulation. Although the amino groups of chitosan and proteins, the carboxyl groups of proteins, and the phosphate groups of phosphomannans were found to be efficient groups for the accumulation of copper, the less effective hydroxyl groups of the carbohydrate polymers (glucans and mannans) had a similar overall capacity for copper accumulation owing to their predominance in the yeast cell wall. The outer (protein-mannan) layer of the yeast cell wall was found to be a better Cu²⁺ chelator than the inner (chitinglucan) layer. It appeared that the physical condition of the cell wall may be more important than the individual macromolecular components of the cell wall in metal accumulation. It was apparent that the cell wall was the major, if not the sole contributor to heavy metal accumulation at low ambient heavy metal concentrations. At higher ambient metal concentrations the cytosol and vacuole become involved in bioaccumulation. Copper and other metals caused rapid loss of 70% of the intracellular potassium, implying permeation of the plasma membrane. This was followed by a slower "leakage" of magnesium from the vacuole which paralleled Cu²⁺ accumulation, suggesting that it may represent some form of ion-exchange. An intracellular copper chelating agent of approximately 2 kDalton molecular mass was isolated from copper tolerant yeast. This chelator was not a metallothionein and bound relatively low molar equivalents of copper compared to those reported for metallothionein. Treatment of the biomass with hot alkali yielded two biosorbents, one soluble (which could be used as a heavy metal flocculent), and an insoluble biosorbent which could be formed into a granular product to be used in fixed-bed biosorption columns. The granular biosorbent could accumulate a wide range of heavy metal cations in a semispecific manner and could be stored in a dehydrated form indefinitely, and rehydrated when required. Bioaccumulation by live algae was investigated as an alternative to yeast based processes. Various strains of algae, of which Scenedesmus and Selenastrum were the most effective, were found to be capable of accumulating heavy metals such as Cu²⁺, Pb²⁺ and Cr³⁺.

The infection process of intracellular opportunistic microsporidia involves the forcible eversion of a coiled hollow polar filament that pierces the host cell membrane, allowing the passage of infectious sporoplasm into the host cell cytoplasm. Although the exact mechanism of spore activation leading to polar filament discharge is unknown, we have shown that spore adherence to host cells, which is mediated by sulfated glycosaminoglycans, may play a vital role. When adherence is inhibited, host cell infection decreases, indicating a direct link between adherence and infection. The goal of this study was to evaluate the effects of exogenous divalent cations on microsporidia spore adherence and infection. Data generated using an in vitro spore adherence assay show that spore adherence is augmented by manganese (Mn2+) and magnesium (Mg2+), but not by calcium (Ca2+). However, each of the three divalent cations contributed to increased host cell infection when included in the assay. Finally, we show that Mn2+ and Mg2+ may activate a constituent on the microsporidia spore, not on the host cell, leading to higher infection efficiency. This report further supports recent evidence that spore adherence to the host cell surface is an important aspect of the microsporidial infection process.

No description available.

<p> Fluorosulphonic acid has been employed to generate cyclohexadienyl cations by protonation of weak bases in order to study the affect of uv light on such systems which are variably substituted. Differing substitution has been obtained by selecting polymethylbenzenes, cyclohexadienones and polymethylphenols as cation precursors. </p> <p> The photoisomerization of the 1,2,4,5-te-tramethylcyclohexadienyl cation to the 1,2,4,5-tetramethylbicyclo-[3 .1.O.] hexenyl cation has been studied by nmr methods and is discussed mechanistically in terms of competitive electrocyclic and [ δ2a + π2a] mechanisms of ring closure. Investigations of a similar 1,2,3,5-tetrarnethylcyclohexadienyl cation failed to uncover an analogous photoisomerization. This result is briefly discussed in relation to the demonstrated instability of the supposed photo-product which has been produced by a non photo chemical route. </p> <p> Both the 1-hydroxy-6,6-dimethyl- and 1-hydroxy-4 1 4 dimethylcyclohexadienyl cations have been generated from the corresponding cyclohexadienones by low temperature protonation in FS03H. Photoisornerization of these systems produced the same 2-hydroxy-6,6-dimethylbicyclo[3.l.0.] hexenyl cation which underwent further photorearrangement to various protonated phenols, the nature of which depended upon the frequency of irradiation. </p> <p> A number of protonated polymethylphenols have been investigated with respect to their site(s) of protonation in fluorosulphonic acid and their tendency to undergo photochemical reaction. Several members of this series have been shown to rearrange photochemically to isomeric phenols through a bicyclo[3.l.O.] hexenyl cation intermediate. A necessary criterion for this reaction has been established as protonation of a methyl bearing ring carbon. </p> <p> An exceptional example of the phenol photo- isomerization was the photo-conversion of protonated 2,4,6-trimethy·lphenol·to protonated 1,3,5-trimethyl. bicyclo[3.1.o] hex-3-en-2-one. This, as well as additional evidence led to the conclusion that a significant amount of meta protonation occurred with this phenol. </p> / Thesis / Master of Science (MSc)

<p> The behaviour of iodic acid, of mixtures of iodic acid and iodine, and of various other iodine compounds as solutes in sulphuric and fluorosulphuric acids has been studied, using mainly cryoscopic and conductimetric techniques. Evidence has been obtained for the existence of polymeric species containing iodine (V), of the oxy-cation IO+, of the iodine cation, I+, in small concentrations in equilibrium with its disproportionation products, and of the cations I3+, I5+ and I2Cl+. The reaction of iodosyl sulphate with disulphuric acid has been studied. Conductimetric studies have been made of solutions of water, potassium nitrate and potassium perchlorate in fluorosulphuric acid. The results of some spectrophotometric and nuclear magnetic resonance experiments are also reported.</p> / Thesis / Doctor of Philosophy (PhD)