Multiple-point adsorption of terbium ions by lead ion templated thermosensitive gel: Elucidating recognition of conformation in gel by terbium probe

Lead ion templated thermosensitive heteropolymer gel which has recognition ability of methacrylate pairs has been synthesized and characterized. The gel consists of a main monomer component, N-isopropylacrylamide (NIPA), responsible for volume phase transition, methacrylic acid (MAA) moieties imprinted as pairs to adsorb terbium ions and cross-links. An imprinting technique was applied using lead ion complex with methacrylate ligands in dioxane media. After gel was obtained, lead ions were removed by washing and the imprinted gel showed strong binding ability to terbium ions, comparable with that of the non-imprinted gel prepared without lead ions. It was found that the Tb³⁺ fluorescence intensity was considerably increased upon binding this ion to both imprinted and non-imprinted gels, but the largest enhancement of fluorescence intensity was observed when Tb³⁺ was bound to imprinted gel in shrunken state. This is because of the decrease of coordinated water molecules on Tb³⁺ and the strong binding of this ion to methacrylate pairs which are encoded within the weakly cross-linked network of imprinted gel.