This Thesis is focused on the study of Keplerates: a family of sizable polyoxometalates (POM) with icosahedral symmetry. POMs are anionic inorganic clusters composed of MO_n units. M represents a transition metal atom usually in its highest state of oxidation (Mo^VI, W^VI, V^V, etc.). One of the most representative examples of Keplerates is the Mo₁₃₂ capsule, namely [(Mo^VI₅(Mo^VI)O₂₁)₁₂(Mo^V₂O₂(µ-O)₂(L^n-)₃₀]^(12+n)-, where L represents a bidentate ligands that decorates the inner surface of the Keplerate. Throughout this Thesis, the electronic structure of Keplerates has been studied at the Density Functional Theory (DFT) level. Furthermore, the interaction between the Mo₁₃₂ capsule and its corresponding internal ligands has been studied by means of the same methodology. On the other hand, in collaboration with other groups, both theoretical and experimental, a formation mechanism of the Mo₁₃₂ capsule has been proposed. Finally, a force field partially extracted from the previous DFT calculations has been applied to perform classical Molecular Dynamics simulations in order to study the behavior of the Mo₁₃₂ macro-ion in aqueous solution, in the presence of different counter-cations species and at different temperatures. Particularly, the effect that the hydrophobic character of the counter-cations has on the plugging process of the Mo₁₃₂ capsule has been analyzed.