Chemical ModificationAs a Versatile Tool for TuningStability of Silica Based Mesoporous Carriers in Biologically RelevantConditions.

A comparative study of the degradation in a model phosphatebufferedsaline (PBS) medium of mesoporous mixed silica–zirconia oxidesand hybrid organosilica materials is reported, and their thermodynamicand kinetic stability are discussed. Thin film morphology was usedto monitor the degradation rates of all these materials for the firsttime directly in liquid and undersaturated medium. The introductionof zirconium centers in mesoporous materials strongly inhibits degradationand allowed the self-limitation of soluble silica concentration inthe immediate environment of the vector. This avoids renucleationof potentially toxic silica small nanoparticles with uncontrolledsurface chemistry in the release medium. Chemical modifications (hybridationor zirconia doping) of mesoporous silica allow the fine-tuning ofits degradation from hours to days. Methylated thin films are highlystable when the functionalization ratio is high (50%). The hybridationby mercaptopropyl and aminopropyl moieties can be successfully performedwithout any high thermal treatment, allowing not only slowing downsilica dissolution but also opening the possibility to introduce inone-pot other thermally fragile molecules into the vector. Dissolutionrates K measured for the first time at different biologically relevanttemperatures follows an Arrhenius law: K= KoExp(−Ea/RT). Stabilities of these chemically modified silicas aremainly associated with a strong decrease of the pre-exponential factor K0of modified silicas. Counterintuitively, activationenergies Eadecrease with increasing thehybrid/silica or the zirconia/silica ratios. [ABSTRACT FROM AUTHOR]