Single-Molecule Macrocyclic Carrier Overcomes the Direct Transmembrane of Medium-Sized Cargoes

Direct transmembrane transport plays an important role in the biomedical field. Although well-established methods exist for the direct membrane transport of small-sized cargoes (e.g., water and ions) and large-sized cargoes (e.g., proteins, DNAs, polysaccharides), they are challenging to directly apply to medium-sized cargoes (e.g., drugs, probes, oligopeptides, and growth hormones). Here, we present a negatively charged single molecular carrier, carboxyl-modified azocalix[6]arene (CAC6A), as a direct transmembrane tool that facilitates the transport of medium-sized cargoes. The cellular uptake pathway of CAC6A was identified using pharmacological inhibitors, and the direct transmembrane transport was confirmed. Further mechanistic transport investigations reveal that the modification group at the upper rim, the cavity size, and the appropriate amphiphilicity of CAC6A promote direct membrane transport. Combined with the hypoxia-responsive property, CAC6A achieved the targeted release of the payload. The findings in this work may lead to the development of macrocycle-based transmembrane systems with broad applications in biomedicine, diagnostics, and sensing.