Cooperative binding by cyclodextrin dimers

Abstract

Dimers containing β-cyclodextrin (β-CD) moieties at both ends of dicarboxylic acids were prepared by the reaction of bis(m-nitrophenyl) dicarboxylate with a large excess of β-CD, and were purified by dialysis and gel chromatography. The interaction of the dimers with potassium 2-p-toluidinylnaphthalene-6-sulfonate (TNS) was studied by the fluorescence technique and compared with that of β-CD and poly(acryloyl-β-CD). The dimers were found to bring about a much greater enhancement and blue shift of the TNS fluorescence than β-CD but less than the polymer. The succinate dimer enhanced the TNS fluorescence twofold more than the glutarate dimer. Dissociation constants and stoichiometries were determined by fluorometric titration and continuous variation methods. The dimer complexes showed exclusively 2:1 stoichiometry (CD: TNS), even in the concentration range in which β-CD showed 1:1 stoichiometry. The 2:1 complexes of the dimers were much more stable than the 2:1 complex of β-CD and were comparable to that of the polymer. Thus, two CD units linked by the chain were found to cooperate in binding one TNS molecule. © 1980, The Society of Polymer Science, Japan. All rights reserved.