Crystallization of the Ground Mixtures of α-, β-Cyclodextrins by Water Vapor Adsorption

Abstract

Crystallizing behavior of the ground cyclodextrins and the ground mixtures of cyclodextrins with medicinals were investigated at various relative humidities (RH) by powder X-ray diffraction and thermal method. The ground .alpha.-cyclodextrin, being in amorphous state at 68% RH, turned into crystals at 84% RH. The ground mixtures of cinnamic acid with .alpha.-cyclodextrin (molar ratio 1:2) crystallized at 84% RH. From the X-ray diffraction patterns the crystals were identified as an inclusion compound. On the other hand, the ground mixtures of diazepam with .alpha.-cyclodextrin (weight ratio 1:9) transformed not into inclusion compound crystals but into diazepam and .alpha.-cyclodextrin crystals at 84% RH. For all combinations of cyclodextrins with medicinals used in this experiment, the crystallization of the ground mixtures did not occur at 68% RH while it occurred at 84% RH in two ways along including behaviors in solution, that is the ground mixtures of host-guest combinations which produced the inclusion compound in solution turned into inclusion compound crystals by adsorbing water vapor, and those of producing no inclusion compound crystallized into respective component crystals separately.