SOLUTE-SOLVATED CYCLODEXTRIN-BONDED PHASE INTERACTIONS AS STUDIED BY THE SPIN PROBE TECHNIQUE

The interaction of a series of spin probes with two solvated silica-bound cyclodextrin phases involving alpha and beta-cyclodextrins (Cyclobond III and I) have been investigated using electron paramagnetic resonance techniques. The results show that the interactions of the spin probes with the alpha-cyclodextrin surface (Cyclobond III) do not involve insertion into the cyclodextrin cavity but rather result from polar/nonpolar interactions with the solvated surface. With surface-immobilized beta-cyclodextrins (Cyclobond I), there is a bimodal behavior depending on the polar nature of the solute molecule. For probes with a nonpolar character, at least partial insertion into the cyclodextrin cavity is the major means of solute-surface interaction. However, when the probes become polar in nature, the probe-surface interaction centers on the interactions between the solute molecule and the hydroxyl region surrounding the rims of the bound cyclodextrin. In all cases, the evidence supports the view that surface immobilized cyclodextrins are not simply a tethered version of free cyclodextrin molecules.