A multitechnique approach was conducted to investigate the confinement of caffeine in a series of UiO-66(Zr)-type MOFs, functionalized with −H, −NH2, −Br, and −2OH groups. DFT calculations were first undertaken to elucidate the preferential geometries of the drug within the pores and the resulting drug/host framework interactions. It was shown that the caffeine molecules are preferentially located in the smaller cages, giving rise to only weak interactions with the function groups grafted on the organic linker. These host/guest interactions were concomitantly probed by advanced 1D and 2D high-field/ultrafast MAS NMR and FTIR spectroscopies, which allowed us to not only validate the DFT predictions but also to bring complementary insight into the nature of the interacting sites of both the caffeine and the MOFs. Dielectric relaxation measurements further revealed significant modifications of the ligand dynamics upon the drug encapsulation for all UiO-66(Zr) solids. It was demonstrated that the perturbation of the ligand flip strongly depends on the nature of the grafted function. While the dynamics of the ligand is slightly enhanced in the case of the −NH2 form, it is significantly slower for the −Br analogue. Such specific behaviors were then interpreted in light of the conclusions drawn from the DFT calculations and NMR observations.

209241-BioMOFs ERC and the Region Languedoc Roussillon for its financial support through the award "Chercheur d'Avenir" 2009 (G.M.). G.M. and S.D.V. acknowledge the Scientific Council of UniversitéMontpellier 2 and S. El Ghazi for her participation to the dielectric relaxation measurements. G.M. thanks the Institut Universitaire de France for its support.

The mobility of the Na+cations localized at the inner surface of the studied mordenite zeolite depends on the material surface properties. In this work, we show that the activation energy,ΔEhop, relating to the Na+cation hopping displacement is associated to the surface potential and therefore can be used to get a better insight into the zeolite surface properties. Indeed, when molecules as water are adsorbed at the surface, they modify the surface potential energy and hence influence the value ofΔEhop. If the adsorbed molecules are polar they directly interact with the cations which become more mobile. The more theΔEhopvalue is, the less the amount of adsorbed water molecules is. Alterations of theΔEhopvalue with respect to the amount of adsorbed water molecules are interpreted using the Dubinin model which is based on simple adsorption principle.