Bio-adhesive Nanoporous Module: Toward Autonomous Gating.

Here we report a bio-adhesive porous organic module ( COF) composed of hexagonally packed 1D nanopores based on a covalent organic framework. The nanopores are densely decorated with guanidinium ion (Gu ) pendants capable of forming salt bridges with oxyanionic species. COF strongly adheres to biopolymers through multivalent salt-bridging interactions with their ubiquitous oxyanionic species. By taking advantage of its strong bio-adhesive nature, we succeeded in creating a gate that possibly opens the nanopores through a selective interaction with a reporter chemical and releases guest molecules. We chose calmodulin (CaM) as a gating component that can stably entrap a loaded guest, sulforhodamine B (SRB), within the nanopores ( COF⊃SRB). CaM is known to change its conformation on binding with Ca ions. We confirmed that mixing COF⊃SRB with Ca resulted in the release of SRB from the nanopores, whereas the use of weakly binding Mg ions resulted in a much slower release of SRB.