Theoretical studies of inclusion complexes of ?-cyclodextrin with methylated benzoic acids

Abstract

AM1 semiempirical molecular orbital calculations have been performed on the inclusion complexes of β-cyclodextrin (β-CD) with methylated benzoic acids in two orientations, the “head-first” and “tail-first” positions. In the former, the CO2H group points toward the primary hydroxyls of the CD. In the latter, it points away from them. Out of 30 possible inclusion complexes, AM1 results predict only three clearly stable inclusion complexes. These are β-CD with 4-methyl benzoic acid in the head-first position, β-CD with 2,4-dimethyl benzoic acid in the head-first position, and β-CD with 3,5-dimethyl benzoic acid in the tail-first position. The orientations of the stable inclusion complexes correlate with the total number of intramolecular hydrogen bonds and intermolecular hydrogen bonds. The stability of a complex also correlates with the closeness of the host and guest geometries in the complex to their isolated molecule geometries. © 1997 John Wiley & Sons, Inc. Int J Quant Chem 64: 711–719, 1997