Aplicação de métodos de química teórica computacional: três estudos de casos experimentais

Abstract

Currently, many studies exemplify the advantages of using combined theoretical and experimental methods. However, many researchers assume that the simulations are very superficial, far from the experimental reality, and this generates resistance in the use of these theoretical tools. This thesis exemplifies how Computational Theoretical Chemistry contributes to the understanding of experimental observations, bringing the researcher closer to the atomic and molecular level, which can be associated with statistical thermodynamics (a branch of science that explores the relationships between properties at both levels). For the development of this thesis, three separate and independent case studies were carried out. Methods based on quantum mechanics (AM1, PM3, PM6 and DFT / B3LYP) and molecular mechanics (molecular docking and molecular dynamics) were used. The first case study compared four similar compounds and derivatives, and the results, some already published, confirm the proximity of most properties. With molecular dynamics studies, the possibility of formation of molecular clusters proved to be an interesting approach for investigating biomolecular activities. The second case study reproduced the interactive effects of the polyaniline/silica nano-composite, explaining how the molecular vibrations combine and intensify in order to superimpose and “hide” silica signals. In addition, molecular aspects of polyaniline and interactions with silica allowed a better understanding of the formation of the nano-composite. The third case study validates the possibility of the existence of two conformations for an alkaloid skeleton, in addition to predicting the energy trends in the formation of derivatives and suggesting a way to "follow" the reactions in an energetic and geometric perspective. Adapted optimizations converge reagents for products, validating the description of interactions between nucleophiles and electrophiles in the gas phase.