Doubly crossed supercoils built by cooperative anion and metal coordination

Supercoiled structures with multiple, continuous “figure-eight” conformations, such as complex DNA plectonemes, are ubiquitous and play vital roles in biological systems. In comparison, synthetic small-molecule supercoils with two or more crossings are scarce. Herein, we report a supercoiled plectoneme structure with two crossings assembled by synergistic cation and anion coordination to a heterotopic ligand, which contains an oligourea backbone for sulfate anion coordination and two pyridyl ends for platinum(ii) ion coordination. The supercoiled structure is confirmed by single-crystal diffraction to be a racemic mixture with positive and negative crossings. Enantiopure supercoils can be induced by adenosine monophosphate or inosine monophosphate binding inside the apical loops, resembling the polymerase encapsulation in bacterial plectonemes that guides DNA and RNA synthesis.