Annulated Mesoporous Silica as Potent Lanthanide Ion Adsorbents and Magnetic Resonance Contrast Enhancing Agents

We report a series of SBA-15 type mesoporous silica (MS) possessing functional annulated rings of different sizes obtained by post-synthesis grafting with diamines containing backbones and different numbers of carbon atoms as efficient magnetic resonance imaging (MRI) contrasting agents. Interestingly, lanthanide ion adsorption assays in aqueous solutions of pH 7 at room temperature showed that adsorption efficiency was higher for materials with rings than those without rings. Furthermore, annulated MS synthesized with 1,5-diaminopetane exhibited selective chelation with smaller Yb(III) ions owing to the “macrocyclic effect” of the cation cavity that offers a “best fit.” Additionally, Gd(III) ions chelated with the material modified by 1, 5-diaminopetane denoted as Gd@annulated-MS exhibited high r2/r1 relaxivities of 12, 12, and 28 while measured with 7.0 T (300 MHz), 9.4 T (400 MHz), and 11.4 T (500 MHz), respectively. Finally, the nanoscale parent materials for annulated modification were successfully synthesized for further in vivo applications. The MS materials thus obtained open auxiliary avenues for selective lanthanide ion absorption via manipulation of the annular ring size to be potentially applied in new generation MRI contrast agents.