Molecularly imprinted cyclodextrins as selective receptors for steroids

beta-Cyclodextrin (beta-CyD) was cross-linked by toluene 2,4-diisocyanate in the presence of various steroids in dimethyl sulfoxide, and the steroids were removed after the polymerization. The molecularly imprinted beta-CyD polymer, obtained by using cholesterol or stigmasterol as the template, efficiently and reversibly bound the steroid in the mixtures of water and tetrahydrofuran. In these polymers, the mutual orientation of beta-CyD molecules is regulated so that they cooperatively bind the target guests which are too large to be included in the cavity of one beta-CyD molecule. When either the alkyl residue at the 17-position or the hydroxyl residue at the 3-position is absent from the template, however, the molecular imprinting is much less efficient. The mechanism for the imprinting and the structure of the guest-binding sites in the imprinted polymers have been proposed.