Physicochemical Characterization of Cyclodextrin-Drug Interactions in the Solid State and the Effect of Water on These Interactions

The characterization of cyclodextrin (CD)-drug interactions has encountered difficulties in the solid state, especially of amorphous state. However, recent advances in experimental techniques, such as X-ray diffraction, spectroscopy, thermal analysis, and solid-state nuclear magnetic resonance, as well as computational chemistry have provided new insights in this area. Furthermore, inclusion complexes have been found to originate from noncovalent interactions, such as van der Waals and hydrogen bonding. The formation of CD hydrates and inclusion complexes in the solid state is considered to only rely on intermolecular interactions, without any covalent bond rupture and formation in host and guest molecules. The presence of water molecules as special guests impacts on the solid-state arrangement of CD molecules, which makes this influence important to consider. Accordingly, this review presents an overview of recent work about the physicochemical characterization of CD-drug interactions in the solid state with a focus on the effect of water molecules on these interactions.