Quantum-chemical studies on the interactions of β-cyclodextrin and 4-methylpyridine

Semi-empirical PM3 calculations have been performed on the inclusion complexation of beta-cyclodextrin (beta-CD) with 4-methylpyridine for methyl group up and down inclusion orientations, respectively. The single point energy of the resultant complexes are, further computed at the level of B3LYP/3-21G* in vacuo and in water solution. The results obtained show that the complexation orientation in which the methyl group is located near the primary hydroxyl rim of the CD cavity is found to be more favourable energetically arising from the effective hydrophobic interactions. The statistical thermodynamics calculations at 1 atm and 298.15K suggest that the inclusion complexation processes of two different orientations are enthalpy-driven in origin.