Ratio control site selection influenced

The ligands - Cl, OAr, and BINOL - were used to probe the accessibility of the imprinted sites. The recovery ratios of Bu -BINOL on the imprinted Pt sites were 83%, 67%, and 27%, respectively, as shown in Fig. 22.4a. The smallest ligand, a single Cl atom, could not access 17% of the imprinted sites, indicating sites are buried inside the bulk of the polymer (Fig. 22.4b). A surface site is more accessible for reactant molecules, but generally results in low selectivity because the influence of the imprinted cavity is absent. On the other hand, a site located in the bulk of the polymer while still accessible from the surface of the polymer can act as a selective reaction site. A site buried inside the polymer is isolated and catalytically inactive (Fig. 22.4b). It is sometimes difficult to control the bulk structure of the polymers and the location of imprinted sites within the polymer matrix. The probe molecules are smaller than the template Bu -BINOL. Nevertheless, a catalytic activity at imprinted sites was small. These results indicate low accessibilities of the reactants in imprinting matrix. 

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