Conformationally Regulated Molecular Binding and Release of Molecularly Imprinted Polypeptide Hydrogels That Undergo Helix–Coil Transition

Abstract

Polypeptides have inherent secondary structures, such as α-helix, β-sheet, and random coil structures, depending on their amino acid sequence. β-Cyclodextrins (CDs) as ligands of molecular recognition sites were introduced into poly(l-lysine) (PLL), which undergoes a structural transition in response to a pH change. CD-introduced PLL (CD-PLL) hydrogels with dynamic molecular recognition sites for bisphenol A (BPA) were strategically designed by molecular imprinting, where BPA was used as a template molecule with a minute amount of cross-linkers. The resulting BPA-imprinted CD-PLL hydrogels with a random coil structure underwent a change in volume in response to the target BPA because the ligand CDs formed a complex with BPA. Additionally, a change in pH induced a structural transition of the CD-PLL chains from the random coil to an α-helix, followed by a conformational change of the molecular recognition sites within the BPA-imprinted CD-PLL hydrogels. As a result, BPA adsorption into the BPA-imprinted CD...