Self-Standing Chiral Copper-Coordinated Covalent-Organic Framework Nanochannel Membrane for Enantioselective Sensing of Reducing Amino Acids

Chiral covalent-organic framework (COF) nanochannel membranes with ordered channels and predesigned structures play a pivotal role in enantioselective sensing. However, the enantioselectivity of chiral COFs is still limited due to the lack of chiral environment regulating. Herein, we report a self-standing chiral copper-coordinated COF (COF-Cu(II)) nanochannel membrane for the enantioselective sensing of reducing amino acids based on the synergistic integration of stereochemical recognition and redox-responsive signal amplification. With phenylethylamine as a chiral catalyst, a tris(<i>N</i>-salicylideneamine)-derived β-ketoenamine-COF was prepared via the interfacial polymerization asymmetric catalysis of 1,3,5-triformylphloroglucinol (TP) and 4,4',4″-triaminotriphenylamine (TAPA). Furthermore, the Cu(II)-coordinated chiral COF (chiral COF-Cu(II), (Δ)- and (Λ)-COF-Cu(II)) nanochannel membranes were obtained via postmodification. The chiral COF structure creates spatially confined cavities for stereochemical recognition, while the Cu(II) acts as a redox-responsive switch. Selective binding to reducing amino acid enantiomers resulted in the reduction of the coordinated Cu(II) in COF nanochannel membranes to Cu(I), affecting the wettability and surface charge density for transmembrane ion transport to achieve enantioselective sensing. The as-prepared chiral sensor exhibited excellent enantioselective sensing performance for reducing amino acids such as l/d-cysteine, l/d-arginine, and l/d-proline (limits of detection of 13 - 21 pg L^-1). This study shows the tremendous potential of a chiral metal-coordinated COF nanochannel membrane for enantioselective sensing.