Correlating Surface-Functionalization of Mesoporous Silica with Adsorption and Release of Pharmaceutical Guest Species

We present here a detailed molecular-level understanding of the interactions among surface-functionalized mesoporous SBA-15 silica and pharmaceutical guests that influence macroscopic adsorption and release behaviors. A model drug species, methylprednisolone sodium succinate, was adsorbed on the surfaces of functionalized mesoporous SBA-15 silica materials with different aminoalkyl species and without or with C<sub>60</sub> fullerene moieties. Zeta potential measurements show that the electrostatic interactions among methylprednisolone species and modified silica surfaces are important for the adsorption and release of the methylprednisolone molecules. Complementary one and two-dimensional (2D) solid-state <sup>13</sup>C­{<sup>1</sup>H} NMR measurements provide evidence for specific intermolecular interactions between adsorbed methylprednisolone species and different types of functionalized silica surfaces. In particular, correlated <sup>13</sup>C and <sup>1</sup>H signal intensities from the methylprednisolone alkyl moieties and the aminoalkyl groups of the functionalized silica surfaces unambiguously establish their close (<1 nm) molecular proximities and strong interactions. The molecular-level insights are correlated with macroscopic adsorption and release behaviors of methylprednisolone, providing detailed new understanding of the interactions responsible for the high loadings and slow release of this important pharmaceutical agent from surface-functionalized mesoporous materials.