Molecular State of Methyl p-Hydroxybenzoate in the Solid Dispersion Prepared by Grinding with α-Cyclodextrin

The molecular interaction in a ground mixture of α-cyclodextrin (α-CD) and methyl p-hydroxybenzoate (MPHB) has been studied as a function of the mixing molar ratio. The states of MPHB molecules were investigated by means by powder X-ray diffraction, differential scanning calorimetry measurement and the determination of remaining MPHB after sublimation. The results indicated that in the ground mixture the MPHB molecules could exist in a mono-molecular dispersed state in the hydrogen bonding network of α-CD as well as in the α-CD cavity. It was suggested that two types of crystalline MPHB, fine crystals embedded in the α-CD matrix and intact crystals, were also present in the ground mixture of molar ratio 5 (MPHB/α-CD) or above.