Using nickel to fold discrete synthetic macromolecules into single-chain nanoparticles

Macromolecules found in Nature display a precise control over the primary as well as higher ordered architectures. To mimic the folding found in Nature, we herein demonstrate the design and characterization of single-chain nanoparticles that are formed by the folding of sequence-defined macromolecules with metal ions. The study showcases the influence of the loop size of such precision macromolecules on their relative hydrodynamic radius. The sequence-defined structures are fabricated using thiolactone chemistry, where two picolyl moieties are installed forming a valuable ligand system for subsequent metal complexation. Next, metal ions such as Ni(ii) and Cu(ii) ions are introduced to fold the unimers into sequence-defined single-chain nanoparticles (SD-SCNPs). After proving the successful complexation using a trimer, a systematic study is conducted altering the distance between the respective ligands by incorporating variable numbers of non-functionalized spacer units. Finally, the loop size formation of the SD-SCNPs is evidenced by DOSY measurements. The result indicates that the positioning of the ligands plays a crucial role on the compaction process and, more specifically, on the final size of the SD-SCNP. In addition, molecular dynamics (MD) simulations show the effects of the sequence and Ni(ii) complexation on the structure and compaction of the SD-SCNPs, and highlight the differences of the nanoparticles' shape when varying the number of spacer units. Finally, the system is further expanded to a dodecamer and even a heptadecamer with drastically decreased hydrodynamic radii after compaction.