Bio‐adhesive Nanoporous Module: Toward Autonomous Gating

Here we report a bio‐adhesive porous organic module (GlueCOF) 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. GlueCOF 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 (CaMCOF⊃SRB). CaM is known to change its conformation on binding with Ca2+ ions. We confirmed that mixing CaMCOF⊃SRB with Ca2+ resulted in the release of SRB from the nanopores, whereas the use of weakly binding Mg2+ ions resulted in a much slower release of SRB. A porous covalent organic framework (GlueCOF) carrying guanidinium ion pendants has been developed that can accommodate guests and bind to biopolymers. The strong bio‐adhesive nature of GlueCOF was used to noncovalently bind to calmodulin (CaM), which acted as a gating component for the guest‐loaded 1D nanopores (CaMCOF⊃guest). The conformational change of the CaM gate upon selective binding with Ca2+ enabled the release of guest molecules.