Influence of ligand structure and water interactions on the physical properties of β-cyclodextrins complexes

The water sorption and physical properties of freeze-dried beta-cyclodextrin (BCD) and 2-hydroxypropyl-beta-cyclodextrin (HBCD) were studied. The stability of the inclusion complexes of these cyclodextrins with different hydrophobic ingredients, such as myristic acid and alpha-terpineol, was investigated as a function of the storage time and water content of the systems. Besides increasing its solubility, BCD ring modification with hydroxypropyl groups conferred amorficity to the dehydrated matrices, and modified the sorption properties and their ability to form hydrates. Both ligands decreased BCD and HBCD water adsorption, in comparison with the pure cyclodextrins. The water adsorption data and glass transition values obtained are consistent with the displacement of water molecules from the inner cavity of the CDs when the ligand is included. Encapsulation of non-polar ligands of linear hydrocarbon chain, like myristic acid, was initially incomplete, depending on the ligand/CD ratio, and increased with the time of storage and water content. (C) 2011 Elsevier Ltd. All rights reserved.