Cooperative oxygen binding by vertebrate tetrameric hemoglobins (Hbs) has been extensively studied and is relatively well understood. Nonetheless, Hill coefficients greater than four have been reported for adult avian, amphibian, and reptilian red blood cells. Such reports also exist for embryonic red cells from various animals. These results are controversial and not yet convincingly established. Oxygen binding studies on avian Hb D, which is known to undergo deoxygenation-dependent self-association, were carried out to answer this question. The goal was to determine unequivocally whether Hill coefficients greater than four occur. Such high Hill coefficients were observed but only at very high Hb D concentrations. Moreover, the early model of avian deoxy Hb D self-association was found to be incomplete. The model has now been expanded to describe better the observed sedimentation data at high Hb concentrations. The possibility that embryonic deoxy Hbs self-associate was also assessed by sedimentation studies of deoxygenated Hb solutions from a marsupial, the tammar wallaby. The results obtained show unambiguously that these embryonic Hbs self-associate upon deoxygenation. Recent phylogenetic analyses suggest that the avian [alpha superscript D]-globin originated from embryonic [alpha]-globins. This finding suggests that the propensity to self-associate upon deoxygenation is an intrinsic property of tetrameric Hbs with embryonic [alpha]-globins. Furthermore the residues mediating the inter-tetramer interactions in adult avian deoxy Hb D and embryonic deoxy Hbs are likely to be the same. Recombinant globins were expressed in bacteria and protocols for the assembly of avian recombinant tetrameric Hb D developed. Initial measurements by sedimentation were carried out to verify the role of a conserved glutamate residue previously speculated to be involved in inter-tetramer interactions. The present studies provide a framework for future investigations of deoxygenation-dependent Hb self-association. In particular the need to carry out oxygen equilibrium measurements at high Hb concentrations as well as sedimentation studies of the deoxygenated Hb solutions is stressed. / text

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The settling vessels are equipment destined to solid-liquid separation; usually have continuous operation, with a circular section, presenting one conic and one cylindrical part. The solid particle splitting with small granular becomes difficult through the operation of conventional sedimentation. An expedient very used in the industry is the flocculant substance addition, whose objective is to promote the precipitation of particles, in which decantation speed is upper than the single one. The present work aim the study of the burst operational conditions that influence the formation and the stability of these aggregates, the flake and the effect of pH and the concentration of flocculant in the capacity of conventional settling vessel, which area of the transversal remains constant, considering this operational conditions. The experiments were made using a kaolin suspension, with pH adjustment and iron sulfate as flocculant. It was made batch sedimentation tests to find great points of pH and flocculant concentration on sedimentation and calculate the maxim rate of sedimentation by Kynch (1952) method. The experimental design results in a great pH of 7,5 and flocculant concentration of 0,0031mL/g of kaulim; using the flocculation process the diameter particle raised of 5,06 to 311_m; the batch sedimentation experiments were very efficient in spite of simplicity, obtaining a good adjustment of experimental data by constitutive equations of TILLER e LEU (1980) for pression and permeability; the area of transversal section had an influence in sedimentation velocity, the biggest one provide a bigger velocity, indicating a wall effect in the process; calculating the settling vessel capacity by Kynch (1952) method, a great performance was showed up with flocculation process, showing its importance in sedimentation of very small particles, and this study ended in a suggestion of a procedure to a continuous operation of a conventional settling vessel with suspensions previously flocculated. / A sedimentação é uma das operações unitárias mais utilizadas na indústria química. Nela, as fases sólida e líquida são separadas devido à diferença de peso. Para o caso de partículas sólidas muito pequenas, a eficiência de separação diminui drasticamente, inviabilizando a separação com padrões aceitáveis, tornando-se então necessária a pesquisa de métodos para otimização da eficiência de separação. Uma maneira de contornar tal situação consiste na adição de agentes floculantes, cuja ação consiste em produzir estruturas complexas (flocos) com os quais as partículas sólidas interagem e podem ser adsorvidas. Tais estruturas possuem peso suficientemente alto para promover a separação de forma adequada. Os objetivos desse trabalho foram estudar as variáveis que afetam o desempenho de sedimentadores convencionais operando com suspensões previamente floculadas, tais como o pH e a massa de material floculante e apresentar um procedimento para sedimentação contínua com floculação utilizando o sedimentador convencional. Os experimentos foram conduzidos utilizando-se suspensões aquosas de caulim, com ajuste de pH, floculada com sulfato férrico. Foram feitos experimentos em batelada em proveta para encontrar os pontos ótimos de pH e concentração de floculante na sedimentação; experimentos em batelada em proveta e no sedimentador para determinação da taxa máxima de sedimentação pelos métodos de Kynch (1952) e Tiller e Chen (1988). O planejamento experimental resultou em um pH ótimo de operação de 7,5 e concentração ótima de floculante de 0,0031mL/g de caulim; utilizando o processo de floculação conseguiu-se um aumento do diâmetro médio da partícula de 2,9 para 311_m; os ensaios de proveta se mostraram muito eficientes apesar da simplicidade, pois obteve-se um bom ajuste dos resultados experimentais pelas equações constitutivas de TILLER e LEU (1980) para pressão e permeabilidade; houve uma influência da área da seção transversal na velocidade de sedimentação, as provetas de maiores diâmetros proporcionaram as maiores velocidades, indicando que o efeito de parede interfere no processo; o calculo da capacidade do sedimentador pelos métodos de Kynch e Tiller e Chen forneceram um melhor desempenho utilizando-se o processo de floculação, mostrando assim a importância de se utilizar este processo nos casos de sedimentação de partículas muito finas.O estudo da sedimentação com floculação proporcionou a sugestão de um procedimento para a operação contínua do sedimentador convencional operando com suspensões previamente floculadas. / Mestre em Engenharia Química