Guest exchange in anhydrous inclusion compounds of α-cyclodextrin and its amorphization

Abstract

The limited applications of α-cyclodextrin (αCD) require elaboration of effective preparation procedures for inclusion compounds of this native macrocyclic host. The solid-phase guest exchange in anhydrous inclusion compounds with organic guests was used in the present work to activate the inclusion properties of αCD without the presence of water. The initial inclusion compounds and the products of this exchange process were characterized using thermogravimetry combined with mass spectrometry of evolved vapors (TG/MS) and powder X-ray diffraction. Solid-phase guest exchange in inclusion compounds of αCD enables encapsulation of organic guests in the higher amounts than can be achieved with a saturated hydrate of α-cyclodextrin under the same conditions. The developed guest exchange procedure does not demand optimization of components ratio and preparation conditions. The solid-phase guest exchange in one of the studied ternary systems produces an amorphous inclusion compound, which heating gives a true amorphous αCD without any traces of its crystalline phase. This is a first evidence of α-cyclodextrin amorphization without its complete dissolution, that can be used in practical applications where an amorphous state of this host is needed having a higher inclusion capacity than its crystalline forms.