INTERACTIONS OF PYRENE WITH CYCLODEXTRINS AND POLYMERIC CYCLODEXTRINS

Interactions of alpha- and beta-cyclodextrin (CD) and polymerically linked beta-CDs with pyrene were studied using luminescence intensity and lifetime measurements. For the monomeric CDs, both single and double capping of the pyrene were unambiguously observed. The hydrophobicity of the binding environments was quite different for the two monomeric CDs as judged by luminescence spectra. The binding constants, as well as the hydrophobicity of the binding environment, were rationalized on the basis of the differing structures of the inclusion complexes. The polymeric systems exhibited large differences as a function of the average spacer polymer length. In particular, they can have much higher formation constants than the monomeric CDs. Binding was much tighter for the longer spacers, and the environment was much more hydrophilic. A model involving sequential 1:1 and 1:2 clam shell binding with a second CD on the same polymer chain was developed that successfully accounted for these effects. A minimum spacer length is required to permit intramolecular clam shell binding. Molecular modeling supports our interpretation of the monomeric and polymeric CD results. The properties of the polymeric CD suggest their use in catalysis and drug delivery systems. They have very high water solubility, and their very efficient formation of clam shell binding can be used to solubilize otherwise hydrophobic molecules.