Pillar[5]arene-based dually crosslinked supramolecular gel as a sensor for the detection of adiponitrile

Abstract

Host–guest inclusion complex formation between pillar[5]arene (P5A) and various guest molecules (amine- and heterocycle-substituted N-Boc-aminohexanes) in CDCl₃ was investigated using NMR titration as well as 2D NMR (NOESY and DOSY) techniques. Supramolecular complexes with methylimidazolium (MIHA) and pyridinium substituted guests were demonstrated to have the highest binding affinity towards P5A (log K_a = 3.32 ± 0.10, 3.66 ± 0.09, respectively). Dimethyl acrylamide-2-vinyl-4,4-dimethyl azlactone copolymer was modified with mono-substituted P5A and MIHA as well as a photo-crosslinker based on 3,4-dimethyl maleimide to obtain host and guest polymers, which were combined and spin-coated onto a gold-coated quartz substrate to fabricate a dually crosslinked supramolecular gel (DCSG) containing reversible and irreversible crosslinks in a single network. Such DCSG chip was utilized as a sensor for the detection of adiponitrile (AN) in organic solutions based on a competitive complex formation with P5A. Macroscopic changes in the gel (e.g., in swelling degree or in refractive index) upon presence of AN (1 μM–1 mM) in chloroform were monitored with surface plasmon resonance (SPR) spectroscopy. The limit of detection of AN using our platform was determined to be as low as 25 μM.