At high temperatures, the properties of aqueous electrolyte systems differ markedly from those at 25°C. For mixed-electrolyte dilute solutions at high temperatures, the degree of ion-association is sufficiently large that the association equilibrium must be incorporated in any model describing the solutions. These association reactions usually do not occur to a measurable extent at room temperature. Oscarson and co-workers have designed a correlation model based on the excess Gibbs energy which can correlate log K and ∆H values as well as the heats of dilution for aqueous electrolyte systems as a function of temperature (T) and ionic strength (I) from 275 to 350°C. Use of calorimetric data to develop the model has been shown to be more accurate than using ∆dilH values from the variation of log K with temperature because one less differentiation with respect to temperature is required. In this study, the computer program developed by Oscarson and co-workers has been modified by incorporating the IAPWS-95 water equation of state and Archer and Wang's correlation of the dielectric constant of water into the excess Gibbs engergy model. The difference between the present work and prior work is that it uses a more accurate equation of state for water, a more accurate dielectric constant for water and the best equilibrium constants currently available. The properties of water play a very important role in the calculation of ∆dilH values, and the modified program developed here using improved water equations is shown to be superior to the previous one. The results of this modified model were tested by comparing the predicted heats of dilution with experimental measurements from Oscarson's work. These experimental data cover the range from 523.15 K to 623.15 K and 103 bar to 128 bar. The nominal concentrations of the solutions used for the ∆dilH experiments were 0.25, 0.5 and 1.0 m. Equilibrium constants K for Na2SO4 (aq), H2SO4 (aq), NaAc (aq), and HCl (aq) association were taken from conductivity values measured by Wood and co-workers using a flow conductance apparatus. These log K values were used to compare the predicted log K values from Oscarson's model and those from this modified model.

<p> Recent investigations by H. G. Thode, J. Macnamara and C. Collins have shown that the S^32/S^34 ratio in natural sulfur-containing compounds varies by as much as five percent. These wide-spread variations suggest that fractionation of the sulfur isotopes occurs in natural processes due to differences in the chemical properties of isotopic molecules. In order to determine the magnitude of the effects that could be expected, partition function ratios for isotopic molecules containing sulfur and equilibrium constants for many isotopic exchange reactions involving sulfur have been calculated by methods of statistical mechanics. The results of these calculations are discussed. </p> / Thesis / Master of Science (MSc)

We report for the first time a broad equilibrium model describing the complexation of ionic species in non-aqueous media that explicitly includes ion pairing for one of the components and that relies upon activities rather than molar concentrations. This model directly contradicts existing commonplace equilibrium treatments, which were shown to be incomplete, often invalid, and misleading. Experimental validation of our model was achieved through studies of pseudorotaxane formation between dibenzylammonium salts (DBAm-X) and dibenzo-24-crown-8 (DB24C8) in CDCl3:CD3CN (3:2). In that particular case, we showed that fluctuations in the apparent Ka,exp values as usually reported are attributable to ion pairing, with a dissociation constant Kipd, and that the constant Kassoc for pseudorotaxane complexation is independent of the counterion, a result of the complex existing in solution as a free cation. In accord with this model, we further described a straightforward and simple method to increase the extent of complexation by using either a ditopic cation and anion host, or adding to the charged host/guest solution a molecularly separate host capable of complexing the dissociated counterion. Also in accord with this model, we investigated the influence of the solvent¡¯s dielectric constant on Kipd and Kassoc. On the basis of competing condensation reactions between amines and ketones which were shown to occur within the timescale of host/guest recognition, we also challenged the commonly employed use of acetone in similar complexation studies involving 2o ammonium ions. Because a major goal of this work was to ultimately increase binding efficiency and selectivity, we explored new methods to drive complexation in related pseudorotaxane systems. We noted that addition of di- or tri-topic hydrogen bond accepting anions to solutions of bis(5-hydroxymethyl-1,3-phenylene)-32-crown-10 or bis(5-carboxy-1,3-phenylene)-32-crown-10 and paraquat di(hexafluorophosphate) served to significantly enhance host/guest interaction. The addition of Et4N+TFA- to an acetone solution of diacid crown and paraquat 2PF6 effectively boosted Ka,exp 40-fold, as estimated by 1H NMR studies. Similar increases in the apparent Ka,exp were observed upon the addition of n-Bu4N+OTs-. Evidenced by crystal structures, the increase in association resulted from chelation of the OH moieties of the crown by the di- or tri-topic anions, forming supramolecular bicyclic macrocycles (pseudocryptands) and stabilizing the complex in a cooperative manner. Significantly, Ka,exp of one of the pseudocryptands was shown to equal that determined in the corresponding cryptand complex. / Ph. D.

Secretory phospholipase A2 (sPLA2) is an important part of apoptosis and disposal of damaged and dying cells. However, healthy cells are not susceptible to attack by sPLA2. Recent studies have focused on membrane properties necessary to induce susceptibility in both artificial and biological membranes. Hydrolysis of phospholipids by sPLA2 requires at least two preliminary steps: first, adsorption of the enzyme to the cellular membrane, and second, movement of a phospholipid into the active site of the enzyme. We determined the effects of susceptibility on each of the two steps and determined the contributions changing the equilibrium constants have on susceptibility. The equilibrium constant for step one increased by a factor of 2 during susceptibility, while the equilibrium constant for step two increased by a factor of 4. The rise in the second equilibrium constant caused the majority of the change in hydrolysis rate seen during susceptibility; the influence of the first equilibrium constant is minimal. We confirmed these results with adsorption studies (assessment of the first step). We additionally found that sPLA2 has a high affinity for the cellular membrane and that only a small percentage (3-5%) of the membrane is covered when all adsorption sites are filled by the enzyme. We proposed a mathematical model describing the mechanism of action of sPLA2, and we were able to experimentally justify the assumptions made in the model.

Orientador: Yoshitaka Gushikem / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica / Made available in DSpace on 2018-08-09T15:34:14Z (GMT). No. of bitstreams: 1 Pissetti_FabioLuiz_D.pdf: 855103 bytes, checksum: e55ee07323e46240da5c3f9bf26b3491 (MD5) Previous issue date: 2007 / Resumo: Neste trabalho foram preparadas redes poliméricas com propriedades elastoméricas a partir do poli(dimetilsiloxano) (PDMS), modificadas com íon piridínio ou etilenodiamina. Os materiais preparados foram caracterizados por espectroscopia no infravermelho, análise termogravimétrica, calorimetria diferencial de varredura e ressonância magnética nuclear de C e Si. Os resultados destas análises mostraram que ambos os materiais apresentam boa estabilidade térmica e uma temperatura de transição vítrea de ~ 160 K. Os dados de RMN indicaram que rede foi formada pela reticulação das cadeias lineares de PDMS por ¿clusters¿ de siloxanos do tipo T, provenientes da hidrólise/condensação de 3-cloropropiltrimetoxissilano e do 2-aminoetil-3- aminopropiltrimetoxissilano. Além disso, por ensaios de intumescimento foi calculada a massa molecular média entre os nós da rede polimérica e também a densidade de reticulação dos materiais. Os valores encontrados sugerem um alto grau de reticulação para ambos os materiais estudados. A rede modificada com etilenodiamina apresentou a maior densidade de reticulação. Com intuito de avaliar a potencialidade dos materiais como adsorventes de íons metálicos de uma solução etanólica, foram obtidas isotermas de adsorção. Para o material modificado com o íon piridínio os metais estudados foram o Co, Cu e Fe, que foram retirados da solução com boa eficiência, 0,25, 0,29 e 0,45 mmol g, respectivamente. Os haletos metálicos foram adsorvidos pela rede polimérica modificada na forma de complexos aniônicos FeCl4¨, CuCl4 e CoCl4. Os resultados de UV-Vis sugeriram que os complexos formados na interface têm uma simetria tetraédrica ou tetraédrica distorcida. Para a rede modificada com etilenodiamina foram estudados os metais Cu, Ni e Fe. Neste caso o material apresentou uma elevada capacidade de adsorção para os cloretos de Fe (1,35 mmol g) e Cu (1,25 mmol g), enquanto que, para o Ni a capacidade de adsorção foi consideravelmente menor, 0,36 mmol g. Os resultados de espectro eletrônico para este material sugeriram que o cobre é adsorvido pela rede polimérica modificada na forma do complexo, [Cu(en)], com uma estrutura tetraédrica distorcida, enquanto que para o níquel os resultados sugeriram formação de um complexo octaédrico. Os dados obtidos nas isotermas de adsorção foram usados para calcular as constantes de equilíbrio para a adsorção dos íons metálicos. Estes resultados permitiram verificar que no material modificado com o íon piridínio a adsorção de CoCl2 e CuCl2 segue o modelo descrito por Langmuir. Para a adsorção do FeCl3 outro modelo, em que centro adsorvedor é composto por dois grupos ligantes, foi necessário para descrever o processo de adsorção. Neste caso, há um efeito cooperativo entre as espécies formadas na superfície. Para o material modificado com etilenodiamina, os cálculos mostraram que a adsorção dos três íons metálicos pode ser descrito adequadamente pelo modelo de Langmuir / Abstract: In this work elastomeric polymeric networks based on poly(dimethilsiloxane) PDMS, modified with pyridine ion or ethylenediamine, were prepared. These materials were characterized by infrared spectrometry, thermogravimetric analysis, differential scanning calorimetry and nuclear magnetic resonance (NMR) of Si and C. The results showed that both materials presented a good thermal stability and a glass transition temperature at ~ 160 K. The NMR data indicated that the polymeric network was formed by PDMS linear chain crosslinked with siloxane clusters of T Si units formed from hydrolyses/condensation of 3-chloropropyltrimethoxysilane or 2-aminoethyl-3- aminopropyltrimethoxysilane. Using the swelling measurements, the average molecular weight between crosslinking points and the polymeric network crosslinking density were calculated. The results obtained suggested a high degree of crosslinking for the prepared materials, which was higher for the ethylenediamine. To evaluate the potential use of the prepared materials as adsorbents, adsorption isotherms were obtained from an ethanolic solution. For the polymeric network modified with pyridine ion the metallic ions studied were Cu, Co and Fe, which were adsorbed with high efficiency of 0.25, 0.29 e 0.45 mmol g, respectively. Metal halides were adsorbed by the modified polymeric network as an anionic complex, FeCl4¨, CuCl4 and CoCl4. The UV-Vis data suggested that the formed complexes at surface presented a tetrahedral symmetry or distorted tetrahedral symmetry. For The polymeric network modified with ethylenediamine, the metallic ions studied were Cu, Ni and Fe. In this case, the material showed a higher capacity of adsorption for Fe (1.35 mmol g) and Cu (1.25 mmol g), while, to Ni that capacity was significantly lower, 0.36 mmol g. The electronic spectra data suggested that the copper was adsorbed by the modified polymeric network as [Cu(en)], with a distorted tetrahedral symmetry, while the nickel was adsorbed with a octahedral symmetry. From the isotherm data, the equilibrium constants of the metallic ion adsorption were calculated. These results allowed verifying that the adsorptions of CoCl2 e CuCl2 are appropriate described by Langmuir equation. For the FeCl3 another model, which two adsorptions centers are envolved was necessary to describe the adsorption process. In this case, there was a cooperative effect among the adsorbed species. The results for polymeric network modified with ethylenediamine showed an adsorption described by the Langmuir equation for all metallic ions studied / Doutorado / Quimica Inorganica / Doutor em Ciências

In order to meet increasing indium demands, (bio)hydrometallurgical winning of low-grade sources will likely be required. The goal of this work in the scope of the Biohydrometallurgical Centre Freiberg, was to use geochemical modelling to improve indium leaching and extraction efficiency. Indium stability constants and chemical conditions of process relevant solutions were required. Electrochemical methods were used to determine the stability constants of indium complexes with nitrate, chloride, sulfate, and hydroxide ions, as well as with electrowinning additives. High pressure liquid chromatography techniques were adapted to quantify polysulfides (Sx2–) and metal ions in leaching and extraction solutions. This cumulative information was used in geochemical modelling. Predominance, Pourbaix, and speciation diagrams were produced to describe and explain the behaviour of multiple components in various process relevant solutions. / Um den steigenden Bedarf an Indium zu decken, ist eine (bio-)hydrometallurgische Gewinnung von ‚low-grade sources‘ erforderlich. Ziel dieser Arbeit im Rahmen des Biohydrometallurgischen Zentrums Freiberg war es, durch geochemische Modellierung die Indium-Laugungs- und Extraktionseffizienz zu verbessern. Dazu wurden Indium-Stabilitätskonstanten und chemische Bedingungen prozessrelevanter Lösungen benötigt. Mit elektrochemischen Methoden wurden die Stabilitätskonstanten von Indiumkomplexen mit Nitrat-, Chlorid-, Sulfat- und Hydroxidionen sowie mit Elektrogewinnungsadditiven bestimmt. Hochdruck-Flüssigkeitschromatographieverfahren wurden zur Quantifizierung von Polysulfiden (Sx2–) und Metallionen in Laugungs- und Extraktionslösungen angepasst. Alle experimentell bestimmten Parameter wurden in der geochemischen Modellierung verwendet. Prädominanz-, Pourbaix- und Speziationsdiagramme wurden erstellt, um das Verhalten mehrerer Komponenten in verschiedenen prozessrelevanten Lösungen zu beschreiben und zu erklären.

[pt] Um grande número de complexos de cobre(II) tendo como ligantes compostos biológicos têm sido utilizados como modelos para o entendimento das diversas reações que ocorrem in vivo. Diversas desordens neurodegenerativas são caracterizadas pela presença anormal de proteínas no sistema nervoso central que possuem uma alta afinidade pelo íon cobre(II). Essa coordenação do metal à proteínas favorece o processo de deposição e associado ocorre a produção em excesso de espécies reativas de oxigênio (ROS - reactive oxygen species). A metionina é um antioxidante presente no meio biológico que pode se ligar ao cobre e prevenir os danos oxidativos. No presente trabalho, estudamos em solução aquosa, os complexos binários Cu(II):L1 e Cu(II):L2 e o complexo ternário Cu(II):L1:L2 (L1 = GlyGly e L2 = Met) a 25 °C e μ = 0,1 mol L-1. As constantes de formação dos complexos foram calculadas utilizando o programa BEST7. Os modos de coordenação dos ligantes nos complexos de Cu(II) foram investigados por cálculos DFT utilizando o programa TURBOMOLE 6.1. Foi utilizado o funcional PBE empregando a aproximação da resolução da identidade (RI-J) e com o conjunto de bases def2-SVP. Os efeitos do solvente foram incluídos através do modelo de solvatação COSMO. Os resultados DFT mostraram comportamento bidentado da glicilglicina na espécie Cu(H-1GlyGly), sem a participação do oxigênio do grupo carboxílico na esfera de coordenação do metal. O modelo de cluster-contínuo foi utilizado para obter, para os complexos mais estáveis, as energias livres em fase gasosa e em solução aquosa através dos métodos DFT: B3LYP/def2/TZVP e PBE0/def2-TZVP. Para os complexos mais estáveis foi incluída a segunda camada de solvatação (36 moléculas de água) para verificar a interferência de moléculas explícitas do solvente nos cálculos. Os resultados mostraram comportamento monodentado do ligante glicilglicina no complexo [Cu(GlyGly)(H2O)36]+, sem a participação do oxigênio peptídico na esfera de coordenação do centro metálico. Observou-se que os clusters assumem diferentes geometrias: octaédrica ([Cu(Met)(H2O)36]+), pirâmide de base quadrada ([Cu(GlyGly)(H2O)36]+, [Cu(H-1GlyGly)(H2O)36], [Cu(Met)(OH)(H2O)36], [Cu(Met)(OH)2(H2O)36]-, [Cu(HGlyGly)(Met)(H2O)36], [Cu(GlyGly)(Met)(H2O)36]- e [Cu(GlyGly)(Met)(OH)(H2O)35]2-) e quadrado distorcido ([Cu(GlyGly)(OH)(H2O)35]-). Todos os clusters apresentaram uma configuração eletrônica do estado fundamental t6 2g d22 d1 x2-y2 o que concorda com a distorção Jahn-Teller. Nas doenças neurodegenerativas o pH fisiológico é levemente acidificado. Na espécie ternária [Cu(GlyGly)(Met)(H2O)36]-, que é formada em pH 7, o enxofre não faz parte da esfera de coordenação do cobre, indicando que ele pode exercer uma ação antioxidante em sistemas biológicos sob condições de estresse oxidativo. / [en] A great number of copper(II) complexes that have as ligands biological compounds have been used as models for the understanding of several reactions that occur in vivo. Several neurodegenerative disorders are characterized by the abnormal presence of proteins in the central nervous system that have a high affinity for the copper(II) ion. This coordination of metal to proteins favor the deposition process and associated the production in excess of reactive oxygen species (ROS) occurs. The methionine is an antioxidant present in the biological medium that could bind to copper and prevent the oxidative damages. In the present work we studied in aqueous solution the binary complexes Cu(II):L1 and Cu(II):L2 and the ternary complex Cu(II):L1:L2 (L1 = GlyGly and L2 = Met) at 25C and μ = 0.1 mol L-1. The binding constants of the complexes were determined using the BEST7 program. The coordination modes of the ligands in the Cu(II) complexes were investigated by DFT calculation using the TURBOMOLE 6.1 program. The PBE functional was used employing the resolution of identity approximation (RI-J) and with the def2-SVP basis set. The solvent effects were included through the COSMO solvation model. The DFT results showed bidentate behavior of the glycylglycine in the Cu(H-1GlyGly) species without the participation of the oxygen from the carboxylic group in the metal coordination sphere. The cluster-continuum model was used to obtain for the more stable complexes the free energies in gas phase and in the aqueous solution through DFT methods: B3LYP/def2/TZVP and PBE0/def2-TZVP. The second solvation shell (36 water molecules) was included in the more stable complexes to verify the interference of solvent explicit molecules in the calculation. The results showed monodentate behavior of the glycylglycine ligand in the complex [Cu(GlyGly)(H2O)36]+, without the participation of the peptidic oxygen in coordination sphere of metallic centre. It was observed that the clusters assume different geometries: octahedral ([Cu(Met)(H2O)36]+), square pyramid ([Cu(GlyGly)(H2O)36]+, [Cu(H-1GlyGly)(H2O)36], [Cu(Met)(OH)(H2O)36], [Cu(Met)(OH)2(H2O)36]-, [Cu(HGlyGly)(Met)(H2O)36], [Cu(GlyGly)(Met)(H2O)36]- and [Cu(GlyGly)(Met)(OH)(H2O)35]2-) and distorted square ([Cu(GlyGly)(OH)(H2O)35]-). All the clusters presented an electronic configuration of ground state t6 2g d22 d1 x2-y2 that agree with the Jahn-Teller distortion. In the neurodegenerative diseases the physiologic pH is slightly acidified. In the ternary species [Cu(GlyGly)(Met)(H2O)36]-, that is formed in pH 7, the sulfur is not part of the coordination sphere of copper, indicating that it could exert an antioxidant action in biological systems under oxidative stress conditions.