With respect to the principles of biomineralization, it is of interest to study the crystallization of calcium oxalates under various experimental conditions. Calcium oxalates play decisive roles as biominerals in plants and as pathological “urinary/kidney stones” in vertebrates. Calcium oxalate exists in three different hydration states; calcium oxalate monohydrate (COM, monoclinic, a = 6.290(1)Å, b = 14.583(1)Å, c = 10.116(1)Å, β = 109.46°, P21/c), calcium oxalate dihydrate (COD, tetragonal, a = b = 12.371(3)Å, c = 7.357(2)Å, α = β = γ = 90°, I4/m) and calcium oxalate trihydrate (COT, triclinic, a = 6.11(1)Å, b = 7.167(2)Å, c = 8.457(2)Å, α = 76.5(2)°, β = 70.35(2)°, γ = 70.62(2)°, P ). Monoclinic COM and tetragonal COD are the most common phyto-crystals and the main constituents of kidney and urinary stones. The occurrence of calcium oxalates in plants represents a useful biogenesis (protection against herbivores) unlike the devastating occurrence in renal tubules. Therefore, biomineralization can be physiological or pathological. A systematic investigation of the morphological evolution of calcium oxalates in the presence of organic components is essential for understanding the mechanism of “pathological biomineralization”. In order to understand the pathological biomineralization of uroliths, it is necessary grow calcium oxalates comparable in morphology under similar growth conditions. The formation of calcium oxalate stones within a gelatinous state of proteins, polysaccharides, lipids and other biomacromolecules under a flow of supersaturated urine supports the fact that an “organic” gel model can simulate the process of urinary stone formation under in vitro conditions. Furthermore, synthetic polymers with precisely known functions and solution behaviours are better choices to understand the interaction of acidic proteins with calcium oxalates. Therefore, as a first step to unravel the complex pathology of uro/nephro lithiasis, we started to examine the structure and morphology of calcium oxalates crystallized in the presence of organic additives such as the sodium salt of polyacrylic acid (PAA) as well as agar gel. The influence of initial calcium oxalate concentration, pH and concentration of the additives on the formation of hydration states of calcium oxalates have been investigated along with the stated general methods. Apart from the three hydrated forms, calcium oxalate exists also in the anhydrous form (COA). Although three modifications of COA (α, β and γ) are reported in the literatures, the crystal structures and phase transformations were controversially discussed. We have been able to reveal the crystal structure of the β-modification of the anhydrous calcium oxalate by a combination of atomistic simulations and Rietveld refinements on the basis of powder X-ray diffraction pattern. β-COA belongs to the monoclinic system with unit cell parameters, a = 6.1644(3)Å, b = 7.3623(2)Å, c = 9.5371(5)Å, β = 90.24(2)°, P2/m (No. 10). The dehydration of COM was mimicked in silico to receive an initial model of the crystal structure of anhydrous calcium oxalate. This general approach may also be accessible for other decomposition processes ending up with crystalline powders of unknown crystal structure. No evidence for transformations from or to the α- or γ- modifications was found during our investigations. The growth pattern of COD crystals precipitated from aqueous solutions in the presence of PAA is clearly dependent on the concentration of PAA. By increasing the concentration of PAA, the shape of COD has been found to change from tetragonal bi-pyramids with dominant (101) pyramidal faces to tetragonal prisms with dominant (100) prism faces and finally to dumbbells. At still higher PAA concentrations, the morphology is reverted back to rod-like tetragonal prisms. Apart from these experiments, the interaction of PAA with (100) and (101) crystal faces of COD was explored with the aid of atomistic simulations. The simulation confirmed that during the development of the aggregates, strong interactions of PAA with the (100) faces take over control of morphologies. Our investigations show that the inner architecture of all the morphological varieties of COD was found to be dominated by an inner “core” consisting of thin elongated crystallites together with incorporated PAA and an outer “shell” formed as a consequence of secondary nucleation processes. We propose that for all types of COD aggregates, relative proportion of calcium oxalate and PAA dictates the shape and formation of nanometer sized crystallites which then aggregate and align to form the core. Such cores enriched with PAA may act as the sites for secondary nucleation events of calcium oxalate crystallites which then cover the core like a shell. In vitro experimental models for the growth of calcium oxalates can give valuable information on the growth and aggregation of urinary stones. Therefore, the “double diffusion technique” in agar gel matrix has been used for the biomimetic growth of calcium oxalate (COM) stones. A great variety of morphological forms of COM are produced in agar gel matrices (2 wt.-% agar gel of pH 8.5) ranging from platy crystallites to dumbbells and spherulites. The COM dumbbells and spherulites are assumed to be formed by the aggregation of smaller crystallites as a consequence of increased supersaturation inside the gel. Moreover, an increase of the pH value of the agar gel has been found to suppress the growth of COM and favours the growth of COD. The morphology of COD crystals grown in 2 wt.-% agar gel of pH 11.5 includes tetragonal prisms and dumbbells. The system calcium oxalate/ PAA/ H2O is a suitable model system for the investigation of principles of biomineral growth (shape development) in general. Our results demonstrate that the double diffusion technique in agar gel is a convenient route to grow calcium oxalate aggregates showing close resemblance to biogenic calculi and to study their ontogeny.

O óxido de cério (CeO2), quando dopado com óxidos de terras raras, tem sua condutividade iônica aumentada, possibilitando seu uso como eletrólito de Células a Combustível de Óxido Sólido de Temperatura Intermediária (IT-SOFC), que são operadas entre 500 e 700°C. Os aditivos ou dopantes mais eficientes para o aumento da condutividade iônica são a samária (óxido de samário Sm2O3) e a gadolínia (óxido de gadolínio Gd2O3), com concentrações molares entre 10 e 20%. Neste contexto foram sintetizados, neste trabalho, pós de composição Ce0,8(SmGd)0,2O1,9 pelas rotas de síntese por coprecipitação de hidróxidos, carbonatos e oxalatos. O efeito do tratamento hidrotérmico foi avaliado para pós precipitados com hidróxido de amônio. Utilizou-se, como matériasprimas, concentrados de terras raras contendo 90% em massa de CeO2 e outro contendo 51% de Sm2O3 e 30% de Gd2O3, ambos provenientes do processamento da monazita. Estes concentrados foram utilizados devido ao menor custo em relação às matérias-primas puras adquiridas comercialmente e a semelhança química dos demais elementos de terras raras contidos. Inicialmente, foram definidas as condições das etapas de coprecipitação e a influência da temperatura de calcinação nas características dos pós e produtos sinterizados. Os resultados obtidos mostraram que os pós calcinados na faixa de temperatura entre 450 e 800ºC apresentam elevada área de superfície específica (90-150 m2.g-1) e estrutura cristalina cúbica tipo fluorita da céria, indicando a formação da solução sólida. Observou-se, por microscopia eletrônica de varredura, que a forma das partículas e dos aglomerados é função do tipo de agente precipitante. As análises dilatométricas indicaram maior taxa de retração em temperatura próxima a 1300-1350ºC. Entretanto, valores elevados de densificação (>95% DT) são obtidos em temperaturas superiores a 1400ºC. A síntese por coprecipitação de hidróxidos seguida pelo tratamento hidrotérmico demonstrou ser uma rota promissora para cristalização, em baixas temperaturas (200oC), de nanopós à base de céria, mantendo-se elevados os valores de área de superfície específica (cerca de 100 m2.g-1). Cerâmicas com densificação superior a 95%DT foram obtidas em menores temperaturas de sinterização (1400oC), quando comparadas às provenientes de pós cristalizados por calcinação. / Cerium oxide (CeO2) when doped with rare earth oxides has its ionic conductivity enhanced, enabling its use as electrolyte for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC), which is operated in temperatures between 500 e 700°C. The most effective aditives or dopants for ionic condutivity improvement are (samarium oxide Sm2O3) and gadolinia (gadolinium oxide Gd2O3), fixing the concentration between 10 and 20 molar%. In this work, Ce0,8(SmGd)0,2O1,9 powders have been synthesized by hydroxide, carbonate and oxalate coprecipitation routes. The hydrothermal treatment has been studied for powders precipitated with ammonium hydroxide. A concentrate of rare earths containing 90wt% of CeO2 and other containing 51% of Sm2O3 and 30% of Gd2O3, both prepared from monazite processing, were used as starting materials. These concentrates were used due the lower cost compared to pure commercial materials and the chemical similarity of others rare earth elements. Initially, the coprecipitation and calcination conditions were defined. The process efficiency was verified by ceramic sinterability evaluation. The results showed that powders calcined in the range of 450 and 800°C presented high specific surface area (90 - 150 m2.g-1) and fluorite cubic structure, indicating the solid solution formation. It was observed, by scanning electron microscopy, that morphology of particles and agglomerates is a function of precipitant agent. The dilatometric analysis indicated the higher rate of shrinkage at temperatures around 1300-1350°C. High densification values (>95% TD) was obtained at temperatures above 1400ºC. Synthesis by hydroxides coprecipitation followed by hydrothermal treatment demonstrated to be a promising route for crystallization of ceria nanopowders at low temperatures (200oC). High values of specific surface area were reached with the employment of hydrothermal treatment (about 100 m2.g-1). High density ceramics were obtained at lower temperatures (1400oC), compared to those employed for calcined powders.

O óxido de cério (CeO2), quando dopado com óxidos de terras raras, tem sua condutividade iônica aumentada, possibilitando seu uso como eletrólito de Células a Combustível de Óxido Sólido de Temperatura Intermediária (IT-SOFC), que são operadas entre 500 e 700°C. Os aditivos ou dopantes mais eficientes para o aumento da condutividade iônica são a samária (óxido de samário Sm2O3) e a gadolínia (óxido de gadolínio Gd2O3), com concentrações molares entre 10 e 20%. Neste contexto foram sintetizados, neste trabalho, pós de composição Ce0,8(SmGd)0,2O1,9 pelas rotas de síntese por coprecipitação de hidróxidos, carbonatos e oxalatos. O efeito do tratamento hidrotérmico foi avaliado para pós precipitados com hidróxido de amônio. Utilizou-se, como matériasprimas, concentrados de terras raras contendo 90% em massa de CeO2 e outro contendo 51% de Sm2O3 e 30% de Gd2O3, ambos provenientes do processamento da monazita. Estes concentrados foram utilizados devido ao menor custo em relação às matérias-primas puras adquiridas comercialmente e a semelhança química dos demais elementos de terras raras contidos. Inicialmente, foram definidas as condições das etapas de coprecipitação e a influência da temperatura de calcinação nas características dos pós e produtos sinterizados. Os resultados obtidos mostraram que os pós calcinados na faixa de temperatura entre 450 e 800ºC apresentam elevada área de superfície específica (90-150 m2.g-1) e estrutura cristalina cúbica tipo fluorita da céria, indicando a formação da solução sólida. Observou-se, por microscopia eletrônica de varredura, que a forma das partículas e dos aglomerados é função do tipo de agente precipitante. As análises dilatométricas indicaram maior taxa de retração em temperatura próxima a 1300-1350ºC. Entretanto, valores elevados de densificação (>95% DT) são obtidos em temperaturas superiores a 1400ºC. A síntese por coprecipitação de hidróxidos seguida pelo tratamento hidrotérmico demonstrou ser uma rota promissora para cristalização, em baixas temperaturas (200oC), de nanopós à base de céria, mantendo-se elevados os valores de área de superfície específica (cerca de 100 m2.g-1). Cerâmicas com densificação superior a 95%DT foram obtidas em menores temperaturas de sinterização (1400oC), quando comparadas às provenientes de pós cristalizados por calcinação. / Cerium oxide (CeO2) when doped with rare earth oxides has its ionic conductivity enhanced, enabling its use as electrolyte for Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC), which is operated in temperatures between 500 e 700°C. The most effective aditives or dopants for ionic condutivity improvement are (samarium oxide Sm2O3) and gadolinia (gadolinium oxide Gd2O3), fixing the concentration between 10 and 20 molar%. In this work, Ce0,8(SmGd)0,2O1,9 powders have been synthesized by hydroxide, carbonate and oxalate coprecipitation routes. The hydrothermal treatment has been studied for powders precipitated with ammonium hydroxide. A concentrate of rare earths containing 90wt% of CeO2 and other containing 51% of Sm2O3 and 30% of Gd2O3, both prepared from monazite processing, were used as starting materials. These concentrates were used due the lower cost compared to pure commercial materials and the chemical similarity of others rare earth elements. Initially, the coprecipitation and calcination conditions were defined. The process efficiency was verified by ceramic sinterability evaluation. The results showed that powders calcined in the range of 450 and 800°C presented high specific surface area (90 - 150 m2.g-1) and fluorite cubic structure, indicating the solid solution formation. It was observed, by scanning electron microscopy, that morphology of particles and agglomerates is a function of precipitant agent. The dilatometric analysis indicated the higher rate of shrinkage at temperatures around 1300-1350°C. High densification values (>95% TD) was obtained at temperatures above 1400ºC. Synthesis by hydroxides coprecipitation followed by hydrothermal treatment demonstrated to be a promising route for crystallization of ceria nanopowders at low temperatures (200oC). High values of specific surface area were reached with the employment of hydrothermal treatment (about 100 m2.g-1). High density ceramics were obtained at lower temperatures (1400oC), compared to those employed for calcined powders.

The work deals with evaluation of the incidence of individual types of urinary stones in dogs, and the effect of specialised clinical diets on the treatment of urolithiasis. The evaluted material consists of an aggregate of analytical results from extracted urinary stones from the Veterinary clinic Vltava, in the period from January 30, 2008 to September 12, 2011. The effect of administration of specialised clinical diets for urolithiasis was evaluated on the basis of case histories of sample patients with proven struvite urolithiasis and an occurence of calcium oxalates and urates. The analysed aggregate of laboratory results of tested urinary stones has shown that besides a high incidence of struvite, the frequency of occurence of calcium oxalates increases as well. In this analysis even up to an identical percentage with struvite occurence at 44,44 % (that is, 24) analysed concrements. A link has been established with overal greater proneness of males to the formation of urinary stones. In the patient group with analysed majority percentage of whewellite, only 12,5 % of the analysed aggregate were females. Considering the widely varied pedigrees of analysed patients, incidence of urolithiasis is expected with ever greater frequency even in dogs not predisposed by breed and crossbreeds. Specialised clinical diets are employed in the treatment and prevention of certain types of urinary stons with high success rate, which adjust the urine environment and thus reduce the risk of occurence of urinary stones. Given the possibility of recurrence of urinary stones, i tis necessary to perform regular urine testing, and eventual sonographic examinations of the bladder

Indiana University-Purdue University Indianapolis (IUPUI) / Oxalate decarboxylase (EC 4. 1. 1. 2 OxDC) from Bacillus subtilis is a manganese-dependent enzyme that catalyzes the cleavage of the chemically inactive C-C bond in oxalate to yield formate and carbon dioxide. A mechanism involving Mn(III) has been proposed for OxDC, however no clear spectroscopic evidence to support this mechanism has yet been obtained. In addition, a recent study has shown that N-terminal metal binding site loop variants of OxDC were able to catalyze the oxidation of oxalate to yield hydrogen peroxide and carbon dioxide, which makes OxDc function as another oxalate degradation protein in the cupin superfamily, oxalate oxidase (EC 1.2.3.4 OxOx). In this work, wild-type (WT) Bacillus subtilis OxDC and a series of variants with mutations on conserved residues were characterized to investigate the catalytic mechanism of OxDC. The application of membrane inlet mass spectrometry (MIMS), electronic paramagnetic resonance (EPR) spectroscopy and kinetic isotope effects (KIEs) provided information about the mechanism. The Mn(III) was identified and characterized under acidic conditions in the presence of dioxygen and oxalate. Mutations on the second shell residues in the N-terminal metal binding site affected the enzyme activity properties of the metal. In the N-terminal domain, the functional importance of the residues in the active site loop region, especially Glu162, was confirmed, and evidence for the previously proposed mechanism in which OxDC and the OxDC/OxOx chimeric variant share the initial steps has been found. In addition, the mono-dentate coordination of oxalate in the N-terminal metal binding site was confirmed by X-ray crystallography. A proteinase cleavable OxDC was constructed and characterized, revealing the interaction between the N-terminal and C-terminal domains.