Artificial receptor for peptide recognition in protic media: The role of metal ion coordination

The production of molecularly imprinted polymers (MIPs) for the recognition of C-terminal cholecystokinin pentapeptide (CCK-5) in the presence of metal ion is reported. The MIPs were produced under the same molar ratio of template to monomers (acrylamide, N,N′-methylene bisacrylamide) in the presence or absence of nitrilotriacetic acid–nickel (Ni–NTA) complex. Scanning electron microscopy images of MIPs were obtained in an attempt to correlate the adsorption characteristics with polymer's morphology. Subsequently Ni2+ was removed and substituted by other divalent ions such as Mg2+, Fe2+, Zn2+, Co2+ and Cu2+. It was found that polymers containing the metal ion complex with the order Fe–NTA, Ni–NTA and Cu–NTA presented lower dissociation constant values than the rest thus exhibiting stronger guest binding activity. The percentage of theoretical maximum binding sites Bmax was almost the same for these ions, indicating that the ion-template coordination is responsible only for their binding strength and not for the number of active sites. The data showed that the proper ion or the ion exchange in the produced MIPs could lead to materials with interesting recognition abilities regarding CCK-5 or/and other isoforms of CCK hormone.