Stability and Phase Transitions of Nontoxic γ-Cyclodextrin-K+ Metal-Organic Framework in Various Solvents

Cyclodextrin (CD) has been used to prepare biocompatible and nontoxic metal-organic frameworks (MOFs) suitable for biomedical applications as drug carriers. In this study, γ-CD/K-based MOF (γ-CD-MOF-1-α) was synthesized and its stability in various solvents was explored by single-crystal X-ray diffractometry (SCXRD) and powder X-ray diffractometry (PXRD). As a result of solvent-induced phase transformations, two novel crystalline phases of γ-CD-MOF-1 were discovered. The newly formed e- and δ-phases crystallize in orthorhombic and tetragonal symmetry, respectively. In e-phase, toluene was determined as a guest molecule by SCXRD. Interactions between γ-cyclodextrin and solvent molecules in e-phase were evaluated using Hirshfeld surface analysis. The thermal stability of the new crystal forms of γ-CD-MOF-1 was analyzed by differential scanning calorimetry and thermogravimetric analysis.