Pseudo Polyampholytes with Sensitively Ion-Responsive Conformational Transition Based on Positively Charged Host-Guest Complexes

Biological polyampholytes are ubiquitous in living organisms with primary functions including serving as transporters for moving chemical molecular species across the cell membranes. Synthetic amphoteric macromolecules that can change their phase states depending on the environment to simulate some properties of natural polyampholytes are of great interest. Here, the implementation of synthetic pseudo polymeric ampholytes is explored with ion-recognition-triggered conformational change. The phase transition behaviors of the ion-recognition-creative polyampholytes that contain deprotonated carboxylic acid groups as negative charges and 18-crown-6 units for forming positively charged host-guest complexes are systematically investigated. The ion-recognition-triggered phase transition behaviors of pseudo polyampholytes significantly depend on cation species and concentrations. Only those specific ions such as K+, Ba2+, Sr2+ and Pb2+ ions that can form 1:1 host-guest complexes with 18-crown-6 units in polymers enable control over conformational change like that of traditional pH-dependent polyampholytes. By regulating the content of carboxylic acid groups to match the content of ion-recognized positive charges provided by the host-guest complexes, the pseudo polyampholytes are more sensitive to the recognizable cations. Such ion-recognition-triggered amphoteric characteristics make the pseudo polyampholytes act like biological proteins, nucleic acids, and enzymes as molecular transporters, genetic code storage, and biocatalysts in artificial systems.