Binding properties of heptakis-(2,6-di-O-methyl)-β-cyclodextrin and mono-(3,6-anhydro)-β-cyclodextrin: a polarimetric study

The binding constants for the inclusion complexes formed between heptakis-(2,6-di-O-methyl)-beta-cyclodextrin (M beta CD) and mono-(3,6-anhydro)-beta-cyclodextrin (A beta CD) with a set of suitably selected organic guests, were measured by means of polarimetry. Measurements were carried out at various pH values in order to ensure the correct protonation state for ionizable guests. Experimental data suggest that the binding properties of M beta CD may be rationalized considering the less polar and more hydrophobic character of the cavity, although similar variations in conformational/dynamic behaviour occur as for native beta CD. On the other hand, A beta CD shows some similarities with alpha CD, due to the significant distortion in the shape and reduction in size of the macro cycle, as confirmed also by simple computational models.