Reversible molecular recognition–removal cycles at a thymine-containing ionically crosslinked polyallylamine film

Abstract

Reversible molecular recognition–removal cycles of 2,4,6-triaminopyrimidine (TAP) based on complementary triple hydrogen bonding were achieved at a cast thin film consisting of a thymine-containing ionically crosslinked polyallylamine (P(TS)C18), based on evidence from FTIR reflection absorption spectroscopy. By immersing the film in a 15 mM TAP aqueous solution at room temperature, approximately 80% of the maximum recognition amount was achieved within 5 min, and the recognition was almost saturated in 1 h. The adsorbed TAP was almost completely removed by immersion of the film in pure water at 60 °C for 30 min. Successive cycles of such recognition–removal behavior were carried out with high reproducibility. Simultaneously with the recognition, the packing structure of the long alkyl chains in the film was also found to change from the orthorhombic to the hexagonal structure, reverting to the orthorhombic structure as the guest molecules were removed from the film. The excellent reversibility of recognition–removal cycles observed for the P(TS)C18 film is thought to be due to the film structure being flexible and stable enough to make spaces for incorporation of the guest molecule in the film matrix.