The crystal and molecular structure of the β-cyclodextrin inclusion complex with aspirin and salicylic acid

The crystal structure of the -cyclodextrin (-CyD) molecular complex with aspirin (acetylsalicylic acid), salicylic acid, and water, (C₄₂H₇₀O₃₅)₂ (C₉H₈O₄)₂ (C₇H₆O₃) 23.3H₂O, was determined by X-ray structure analysis. The crystal data is space group Pl, a=19.777(5), b=15.247(3), c=15.475(4) Å, =102.63(2)°, =116.96(2)°, =104.12(2)°, V=3729(2) ų, D_m=1.409(2) g/cm³, D_X=1.419 g/cm³, and Z=1. The two -CyDs form a dimer unit with hydrogen bond networks among the secondary hydroxyl groups of both -CyDs. This -CyD dimer includes three guest molecules of two different types in its hydrophobic cavity. Two of them are aspirin, which are separately included in each cavity of the -CyD unit, with their hydrophobic benzene rings protruding into the hydrophobic cavities of the host -CyDs. The remaining guest molecule is the hydrolyzed product of an aspirin, that is salicylic acid, which is sandwiched in the space constructed by the -CyD dimer formation, and is statistically disordered at three sites.