Determina??o das conforma??es mais est?veis da isomaltose ?-Dglicopiranosil-(1?6)-D-glicose

• Ano de defesa: 2007
• Autor(a) principal: Javaroni, F?bio
• Orientador(a): Silva, Clarissa Oliveira da
• Tipo de documento: Dissertação
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal Rural do Rio de Janeiro
• Programa de Pós-Graduação: Programa de P?s-Gradua??o em Qu?mica
• Departamento: Instituto de Ci?ncias Exatas
• País: Brasil
• Palavras-chave em Português: isomaltose; mapa conformacional; ?ngulo diedro glicos?dico
• Palavras-chave em Inglês: conformational map; glycosidic dihedral angle
• Área do conhecimento CNPq: Qu?mica
• Link de acesso: https://tede.ufrrj.br/jspui/handle/tede/17

Knowing that the conformation of disaccharide molecules is defined by the energy of rotation of the glycosidic linkage defined by dihedral angles ? (phi) and ? (psi) (and ?(omega), when it exists), our work has consisted by the definition of a set of values of angles that allow to the isomaltose molecule to reach stable conformations of low energy, in gas phase and aqueous solution. To reach this objective, we have performed scannings on the dihedral angles ? (phi) and ? (psi) of the molecule, with the aid of an ab initio computational theoretical method, based only on the laws of the quantum mechanics. Although it takes much computational times, this method describes quantitatively properties of the molecule that depend on its electronic distribution, such as the exo-anomeric effect and hydrogen bonds. The available experimental data in the literature for isomaltose are very scarce and the theoretical data are divergent in its results, thus justifying again the choice of this method. From the calculations performed, conformational maps (graphics that represent the energy values as a function of the respective values of each angle ?, ? e ? exactly assumes in one given conformation) were built. From the conformational maps, regions of minimum energy were identified. Solvation does not create new regions of stability. For the final structures, calculations of vibrational frequency were carried out, to properly characterize these structures as energy minimum and to make possible the incorporation of thermal and entropic corrections. All the calculations were carried out at HF level with a 6-31G (d, p) basis set, a description suited for carbohydrates. The calculations in solution were carried out with the Polarizable Continuum Model (PCM). A total of 18 regions of stability were obtained, making of isomaltose the molecule with the highest number of stable conformations of low energy among all the existing disaccharides with two glucose units, proving that the rotation of its glycosidic linkage have a degree of freedom with a low barrier, since this peculiar linkage ?(1,6) allows a larger distance between the two glycosidic units. This higher flexibility does not have a direct association with the high solubility (solvation degree) of the molecule. For a more direct relationship with the solvation degree, other parameters were investigated in this work, as, for example, the dipole moment of the molecule.