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Crystallographic,eletronic and molecular dynamics studies of some Calixarene supramolecular compounds and its complexes with heavy atoms


The ability of calyx(n)arenes to act as molecular reservoirs for the recognition and transport of small chemical species makes these versatile molecules potentially useful for environmental purposes (by sequestering aquifer ionic contaminants, such as Hg2+, Pb2+, Cd2+, etc), and in extraction processes of precious metals (such as Ag +) and of compounds strategic and technologically relevant (such as UO2 +2). We shall study several of these compounds and its complexes with metal ions, to contribute to the understanding of their complexation processes, aiming to the design of efficient and selective derivatives that are useful to complex with specific metals. We will employ X-ray crystallographic methods to determine the crystal and molecular structure of supra-molecular and coordination compounds. This structural information will establish the basis to rationalize the physical chemical behavior of the studied system and will provide a reference frame for calculations of theelectronic structure and molecular dynamics simulations. Our team member in guildford will provide experimental determination of fundamental thermodynamic parameters, such as quantitatively assessments of selectively based on the stability constant ratios of the complexes in a given solvent and at a given temperature. Theoretical studies on the molecular electronic structure and the minimum energy conformations will be performed employing molecular mechanics, as an initial step to work out geometrical structures. This information will provide a guide to analyze geometric structural aspects and will serve to initialize other more elaborated procedures, such as molecular orbital and molecular dynamics calculations. Because it does not relay on calculations involving multi-centric bi-electronic integrals, the density functional theory provides a technique which is appropriate to deal with supra-molecular systems. Furthermore, as the electron correlation is built in the method, there is no need to resort to computationally costly post Hartree-Fock calculations, and we shall also make use of this method to obtain better results.The theoretical studies, which shall complement and eventually rationalize and orient the experimental work, could contribute to the knowledge at a microscopic level of the processes of complexation. This provides a valid alternative to postulate mechanisms of encapsulation and also of chemical bonds between the guest and the host. These knowledge and the corresponding experimental validations could afford to predict the formation of new species and their electronic and structural properties. (AU)

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