Estudo teórico de compostos de inclusão dos herbicidas 2,4-D e dicamba em β-ciclodextrina

Abstract

The present work comprises a theoretical study on the inclusion process involving the acid 2,4-dichlorophenoxyacetic (2,4-D) in neutral and deprotonated forms, its isomer dicamba (DIC) in deprotonated form and the host molecule β-cyclodextrin (β-CD). In the first part of the work the stability and spatial arrangement of the inclusion complex 2,4D@β-CD were studied. Different spatial arrangements were evaluated in vacuum, gas phase and aqueous solution through the Density Functional Theory (DFT). Continuous models of solvation (PCM and SMD) were applied to evaluate the solvent effect on the stability of complexes. It was possible to distinguish the geometry of the most adequate spatial arrangement with a tendency to include the aromatic portion of the host molecule in the CD cavity via head. Such geometry presents the same spatial orientation found by experimental studies of complexes using modified β-CD. In the second part a theoretical analysis was conducted using the solvation model SMD and distinct functionals of DFT (PBE0, B97-D and M06-2X), as well as simulations of Molecular Dynamics in order to investigate the best approach to study inclusion compounds between the host molecules 2,4-D and DIC, both deprotonated, with β-CD, for which there are experimental data available. The Gibbs free energy in the condensed phase obtained by the functionals B97-D and M06-2X presented better results in accordance with experimental data. The Molecular Dynamics did not produce any trustful information for the investigated inclusion compounds in function of the large variations during simulations.