Binding equilibria between β-cyclodextrin and p-nitro-aniline derivatives: the first systematic study in mixed water–methanol solvent systems

Complexation equilibria, in mixed water–methanol solvent media, between native β-cyclodextrin and a set of suitably selected p-nitro-aniline derivatives were studied by means of polarimetry. The effects exerted by the organic co-solvent on the conditional inclusion free energies ΔGcond0 and the differential molar optical rotations ΔΘ were thoroughly analyzed under the perspective of the enthalpy–entropy compensation effect. Experimental data suggest an intimate participation (‘dynamic co-inclusion’) of solvent molecules in the formation and in the conformational dynamics of the host–guest inclusion complex.