Evaluation of the binding specificity of electrosynthesized poly-ortho-phenylenediamine molecularly imprinted with metal chelates

We have examined the specificity of electrosynthesized poly- o -phenylenediamine as a kind of material molecularly imprinted with metal chelates. Molecularly imprinted polymers (MIPs) were prepared in situ by an electrochemical method. The EDTA chelate complexes of Cu(II), Zn(II), Fe(III) and Cd(II) ions were used as templates of the MIPs deposited on a gold electrode of a quartz crystal microbalance (QCM). The binding ability and specificity of the MIPs were investigated via the frequency response of the QCM to the adsorption of the template chelates and their analogs. Linear relationships are observed between the frequency shift and the concentration of the template chelates over a typical range of ~10 −6 to ~10 −4  mol·L −1 . The results reveal good binding specificity of such MIPs for their templates over structurally related analogs, but the selectivity coefficients are less significant than that for enantiomers. The results also suggest no significant correlation between binding specificity and the ionic (or atomic) radius of the investigated metal ions. The observed specificity is qualitatively attributed to the overall conformational difference of the metal-EDTA complexes resulting from their difference in both ionic radius and electronic structures. Schematic Representation of the Molecular Imprinting Procedures. The metal ions chelate with EDTA to form metal-EDTA chelates as the template, then polymerization is initiated by an electrochemical method. After the polymerization, the templates are removed to create cavities in the polymer film which have binding ability and specificity to the templates.