Orientador: Mario Noboru Tamashiro / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-08-15T20:51:05Z (GMT). No. of bitstreams: 1 Constantino_MairaAlves_M.pdf: 3844438 bytes, checksum: af45f6cbe23805204e63a810f7f6de8b (MD5) Previous issue date: 2010 / Resumo: Obtivemos a energia livre eletrostática de íons próximos a uma interface dielétrica planar e esférica entre fluidos imiscíveis utilizando a teoria de dielétrico contínuo. Para a geometria planar, o íon foi modelado como uma esfera dielétrica com densidade de carga superficial uniforme e fixa. Para evitar a polarização de cargas na interface iônica, consideramos não haver contraste dielétrico entre o interior do íon e o meio dielétrico externo em que ele está presente (aproximação de dielétrico misto), permitindo uma solução exata do problema eletrostático utilizando o método de carga imagem. Mostramos que resultados publicados anteriormente na literatura para este modelo subestimam a energia livre eletrostática associada a íons não-polarizáveis por uma ordem de magnitude, especialmente quando há penetração iônica parcial na interface. Para a geometria esférica, o íon é modelado tanto como pontual quanto como uma esfera com densidade de carga superficial uniforme e fixa cujo interior é novamente modelado utilizando a aproximação de dielétrico misto. Mostramos que as energias livres eletrostáticas dos íons pontual e de raio finito para a interface esférica são numericamente idênticas na ausência de penetração na interface e são sempre inferiores à energia livre eletrostática associada com a interface planar / Abstract: We obtain the electrostatic free energy of ions near a planar and spherical dielectric interface between immiscible fluids within the framework of the classical continuum dielectric theory. For the planar geometry, the ion is modeled as a dielectric sphere with a fixed uniform surface charge density. In order to avoid the generation of additional induced charges on the ionic surface, it is assumed there is no dielectric contrast between the ion core and the external dielectric medium where it is embedded (mixed-dielectric model), which allows an exact solution of the electrostatic problem by the image-charge method. It is shown that earlier results reported in the literature, especially when there is partial ionic penetration into the interface, underestimate the electrostatic free energy associated with nonpolarizable ions by an order of magnitude. For the spherical geometry, the ion is modeled as punctual and as a dielectric sphere with a fixed uniform surface charge density whose core is again modeled as a mixed dielectric. It is shown that the electrostatic free energies of the point-like and the finite-sized ions for the spherical interface are numerically the same in the absence of penetration into the interface and that they are always lower than the electrostatic free energy associated with the planar interface / Mestrado / Física Estatistica e Termodinamica / Mestra em Física

Nonheme iron(II) oxygenases within a common 2-His-1-carboxylate binding motif catalyze a wide range of oxidation reactions involved in biological functions like DNA repair and secondary metabolic processes. The mechanism of O2 activation catalyzed by this enzyme family has been examined by spectroscopic, crystallographic, and computational studies, where it is clear the iron(II) center works with substrate, and cosubstrate to activate O2 by forming a highly oxidizing iron species (iron(IV)-oxo). From a thermodynamic perspective, substrate and/or co-substrate binding organizes the active site for O2 activation, and understanding the interactions among metal, substrate, cosubstrate, and enzyme provides insight into the intramolecular contacts that guide the reaction catalyzed by the enzymes. This dissertation is focused on elucidating the interactions between metal, substrate, and co-substrate in a representative enzyme subfamily of nonheme iron(II) oxygenases, namely the 2-oxoglutarate dependent dioxygenases. Specifically, we investigated the thermodynamic properties of divalent metal ions binding to taurine-dependent dioxygenase (TauD), using Mn2+, Fe2+, and Co2+ ions. Additionally, the thermodynamics associated with substrate and co-substrate binding to Fe·TauD and iron(II)-ethylene forming enzyme (Fe·EFE) were explored using calorimetry and other biophysical techniques.