Host-guest complexes of cucurbit[7]uril with albendazole in solid state: Thermal and structural properties

The inclusion complex of cucurbit[7]uril (CB7) and albendazole (ABZ) in solid state was prepared by freeze-drying. The formation of a host-guest complex was confirmed by microanalysis, ¹H-nuclear magnetic resonance spectroscopy, and fourier transformed-infrared spectroscopy (FT-IR) techniques. The shifts in the NMR peaks supported the encapsulation from the propylthio and not the carbamate site, in agreement with the previously reported results in solution. The N₂ adsorption-desorption isotherms indicated no change in the calculated surface area or the pore size distribution for the unbound and CB7-bound ABZ solid drugs. Freeze-drying produced a system with a higher degree of amorphisation as confirmed by the X-ray powder diffraction (XRD) technique. Thermal analysis of the drug-loaded CB7 by using differential scanning calorimetry and thermogravimetry demonstrated the possibility of dehydration at temperature 100 C beyond the melting point of unbound ABZ since no melting of the samples was observed until the CB7 itself begins to decompose around 300 C. Putting it all together, the results supported that CB7 imparts significant thermal/physical stability on the ABZ drug in the solid state.