Design of Artificial Cell Membrane Interface and Development of Evaluation System for Biorecognition Function

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To develop an anion sensing system in water based on a chromoionophore/artificial cell membrane conjugate, novel thiourea-based chromoionophores having various lengths of alkyl chains (Cn-TU) were designed and their anion recognition function in aqueous vesicle solutions were evaluated. This study revealed that the positioning of chromophore binding sites inside the didodecyldimethylammonium bromide (DDAB) vesicle was successfully controlled by the alkyl chain length of Cn-TU. The cationic vesicle interface was found to exhibit a filter function for the less hydrophobic anions, and highly selective anion recognition via hydrogen bonding was achieved by C1-TU located deep inside the DDAB vesicle. Function of crown ether chromoionophores for alkali metal ion recognition in micellar system were also examined. The surface charge of the micelle was found to strongly influence the ion selectivity and sensitivity, and selective Na^+ recognition was only performed by anionic micellar system. To evaluate ion recognition at these membrane interfaces, a resonant second harmonic generation (SHG) analysis system was developed by using 15-crown-5 azophenol as a model probe. Selective sorption of alkali metal complexes with the azoprobe at heptane/water interface was confirmed by SHG spectra, and their conformation changes upon metal recognition at the interface were successfully evaluated by SHG analysis.