Purpose: In this paper, the nature of ibuprofen incorporated into both mesoporous silicon dioxide and magnesium aluminometasilicate by sublimation and adsorption was investigated using neutron vibrational spectroscopy. Methods: Crystalline ibuprofen was the model drug compound. Neutron vibrational spectra of both neat and nano-confined ibuprofen were compared with the simulated ibuprofen spectra using first-principles phonon calculations. Results: The different character of the neutron vibrational spectra at lower frequencies for the nano-confined ibuprofen, compared to neat crystalline ibuprofen, infers that the overall structural order was markedly reduced once the ibuprofen molecules were in the pores. Furthermore, the dimerization of ibuprofen molecules via hydrogen bonding between carboxylic acid groups was also inhibited, possibly due to spatial constraints or competition with surface hydroxyl groups. Based on the attainable ibuprofen loadings by sublimation, the results suggest that most if not all of the nano-confined ibuprofen molecules were bound to the pore surfaces via hydrogen bonding between the carboxylic acid groups of ibuprofen and surface functional groups of the mesoporous media. Conclusions: The amorphous nature of ibuprofen in mesoporous media was characterized in detail using neutron vibrational spectroscopy. The results of this study are consistent with previous observations, as alluded to by powder X-ray diffraction.
Citation: Pharmaceutical Research
Pub Type: Journals
Neutron vibrational spectroscopy, First-principles calculations, Mesoporous, Amorphous, Ibuprofen