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 beta-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 Delta G(cond)(0) and the differential molar optical rotations Delta Theta were thoroughly analyzed under the perspective of the enthalpy-entropy compensation effect. Experimental data Suggest all intimate participation ('dynamic co-inclusion') of solvent molecules in the formation and in the conformational dynamics of tile host-guest inclusion complex. (C) 2009 Elsevier Ltd. All rights reserved.