Inclusion complexes of β-cyclodextrin with pyrazinamide and piperazine: Crystallographic and theoretical studies

The inclusion complexes of -cyclodextrin (beta-CD) with pyrazinamide (PYA) and piperazine (PIZ) have been investigated both in the solid phase by single-crystal X-ray diffraction analysis and in the gas phase by semi-empirical PM3 calculation. In the crystalline phase, the disordered PYA and PIZ molecules are entirely embedded in the beta-CD cavity. The PYA pyrazine-centre displaces upwards by 1.15(1) angstrom from the beta-CD plane, whereas the PIZ centre shifts downwards by 0.76(1) angstrom from the beta-CD plane. The inclusion scenario changed in the gas phase. Two inclusion geometries of the PYA molecule are comparatively stable with binding energies of -22.28 and -25.29 kJ mol(-1): the pyrazine centre shifts upwards by 0.5 and downwards by 2.0 from the beta-CD plane. The PIZ molecule positioning at 2.0 below the beta-CD plane gives a more stable inclusion complex than does the PYA molecule by 22-25 kJ mol(-1).