Development of Supramolecular Complex Sensor Possessing Biological Recognition Function

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In this study, novel supramolecular complex sensors for ion and molecule recognition in water have been designed. The boronic acid flouoroionophore/β-CyD complex binds sugars and produces increased fluorescence emission in Water. To evaluate the structural effect, three different boronic acid fluoroionophores in which the boronic acid recognition site and the pyrene fluorophore are conjugated with different length of ester spacer (Cn-PB) or amide spacer (Cn-APB) are designed. Based on the fluorescence emission mechanism (the suppression of PET from pyrene donor to trigonal phenylboronic acid acceptor), the highest response efficiency and selectivity obtained for C1-APB. For selective Pb^<2+> recognition, a podand structure possessing pseudo-18-crown-6 structure that can stabilize Pb^<2+> chelate complexes while reducing the interaction with alkali metal cations is utilized. Thus the podand fluoroionophore (PD-1)/γ-Cyclodextrin (γ-CyD) complex sensor exhibits markedly high selectivity for Pb^<2+> ion in water. The response mechanism is based upon the dimerization of the fluoroionophore inside the γ-CyD, thereby resulting in a Pb^<2+>-selective pyrene dimer emission. The micellar solution is expected to provide a hydrophobic microenvironment that solubilizes the lipophilic fluoroionophore in water and enhances the ionophore/metal interaction. However below the critical micelle concentration (CMC) of Triton X-100, the podand fluoroionophore (DAC-1)/Triton X-100 complex is found to exhibit sit amplified fluorescence response for Pb^<2+> in water. Dynamic light scattering and dark-field microscope analyses reveal that the DAC-1/Triton X-100 complex forms micron-size aggregates triggered by selective Pb^<2+> binding, resulting in the enhancement of fluorescence intensity with a distinct blue shift of the fluorescence emission. This is a novel supramolecular function of the DAC-1/Triton X-100 complex sensor for selective Pb^<2+> recognition in water.