Screening of the Relaxivity of Gadolinium-Loaded Periodic Mesoporous Silica Functionalized by Means of Soft Metalorganic Silylamide Grafting



Soft metalorganic grafting of periodic mesoporous silica (PMS) materials is introduced as a method for obtaining nanostructured GdIII-loaded silica particles with relatively high 1H relaxivity. The silylamide complex Gd[N(SiHMe2)2]3(THF)2 was grafted onto MCM-41, SBA-15, and SBA-1, thereby providing PMSs of distinct symmetry as well as pore size and configuration. The materials were characterized by infrared spectroscopy, elemental analysis, powder X-ray diffraction (PXRD), N2 physisorption, and scanning as well as transmission electron microscopy (SEM/TEM). Relaxivities up to 15.8 mM–1 s–1 were determined at high magnetic field strength (400 MHz). The nuclear magnetic resonance dispersion (NMRD) data of a calcined Gd[N(SiHMe2)2]3(THF)2@SBA-1 material had a shape typical for slow-tumbling systems, with a maximum at approximately 50 MHz. Temperature-dependence studies of the relaxivity (r1) indicated that the grafted materials were characterized by an efficient water exchange. To maintain a high relaxivity, a low (1 wt.-%) GdIII loading and a hydrophilic surface had to be provided. Varying the topology of the silica support only resulted in small variations in r1 of the hybrid materials.