Rationalization of the entrapping of bioactive molecules into a series of functionalized porous zirconium terephthalate MOFs

The encapsulation of two different bioactive molecules, the cosmetic caffeine and the analgesic and anti-inflammatory ibuprofen, has been evaluated by combining impregnation and advanced characterization experimental tools in a series of microporous rigid zirconium(IV) terephthalates UiO-66 bearing different polar or apolar functional groups (-H, -Br, -NH2, -2OH, -NO2, -Cl, -2CF(3), -CH3, -2CH(3)). It has been first evidenced that these hybrid solids exhibit drug payloads that significantly outperform those obtained using current drug formulations or other conventional porous solids. A quantitative structure-activity relationship strategy has been further conducted with the aim of rationalizing the experimental drug uptakes and further emphasizing the most relevant chemical and structural features that significantly impact their encapsulation performances. Indeed, it appears that the caffeine loading is optimized when the functionalized organic linker both shows a large octanol-water partition coefficient and contains grafted functions with low hydrogen bond acceptor abilities, whereas the ibuprofen entrapping is enhanced when the organic linker contains functional groups with a large solvent surface area and free volume, and to a lesser extent low hydrogen bond acceptor abilities. Moreover, it has been shown that the solvent used as media for the biomolecule impregnation plays a crucial role in the encapsulation performance due to the formation of a competitive adsorption process between the solvent and the active molecule.