The crystalline state of ibuprofen (IBU) confined in mesoporous silica was characterized using low-field time-domain nuclear magnetic resonance (TD-NMR). IBU was loaded into ordered (Santa Barbara Amorphous-15 [SBA-15]; SBA) or nonordered mesoporous silica (Sylysia 320; SYL) using a well-known incipient wetness impregnation method. The dissolution profile of IBU from the silica was measured. The IBU-loaded SBA showed a relatively higher drug concentration at 10 and 20 min, which was typical of a supersaturated solution. However, it did not maintain that concentration. By contrast, the IBU-loaded SYL did not show such a dissolution profile in the early stage. To characterize the crystalline state of IBU confined in silica, the T1 relaxation time of IBU-loaded silica powder was measured and analyzed by curve fitting. Monophasic T1 relaxation was observed for IBU-loaded SBA. This may indicate that the amorphous phase, which has various molecular mobilities, was close to within the length of 1H spin diffusion. The TD-NMR technique, even if the sample is powder, can rapidly and easily measure NMR relaxation. Therefore, it can be useful toward fully characterizing the crystalline state of drugs confined in mesopores.
Keywords: NMR relaxation; amorphous; crystalline; mesoporous silica; spin diffusion.