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, H-1-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 N-2 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 A degrees 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 A degrees C. Putting it all together, the results supported that CB7 imparts significant thermal/physical stability on the ABZ drug in the solid state.