Multiply entangled receptors for high-affinity anion recognition in water

Despite recent synthetic advances, creating multiply entangled molecules with defined functions remains a formidable challenge. Here, we describe the rational design and straightforward synthesis of doubly interlocked [2]catenanes (also known as Solomon links) that bind sulfate in water with exceptional affinity (K ≈ 106–107 M−1). In this design, mechanical entanglement is exploited to generate highly preorganized yet adaptable binding sites complementary to sulfate. These entangled receptors display an unusual solvent dependence, binding sulfate most strongly in water. This result is particularly noteworthy given the high hydration energy of sulfate, which typically impedes its aqueous recognition. Moreover, introducing appropriate chromophores into the receptor enables sulfate binding to be monitored through changes in emission. This work demonstrates for the first time that multiply entangled architectures can be engineered to achieve high-affinity anion recognition in competitive, biologically relevant environments.