Self-association of a naphthalene-capped-β-cyclodextrin through cooperative strong hydrophobic interactions

NMR, circular dichroism and fluorescence techniques were used to study the structure in solution of a new β-cyclodextrin derivate in which naphthalene chromophore group is bridged to O(2) and O(3) secondary positions of the same glucopyranose unit through a bidentate hinge. The results point to the formation of a very stable dimer in aqueous solution which dissociates in non-polar solvents. Dimerization was enthalpy and entropy favoured. The hydrophobic character of the naphthyl moiety plays a very important role in the entropy change sign. Molecular mechanics as well as molecular dynamics calculations indicated that the most stable dimers are head-to-head oriented. For these dimer structures the naphthyl moieties, relatively shielded from the solvent, are sufficiently close to each other to couple their transition moments, but without forming excimers.

Figure optionsDownload as PowerPoint slideHighlights
► Dimerization processes, structure and conformational behavior of a new naphthalene-β-cyclodextrin derivate.
► A wide variety of experimental techniques (NMR, UV-absorption, steady-state and lifetime fluorescence and circular dichroism) was used.
► CD derivative self-assemble by strong hydrophobic interactions without the need for inclusion in the neighbor CD.
► Dimerization was enthalpy and entropy favoured.
► Molecular modelling indicated dimers are head-to-head oriented.