Metal-Peptide Torus Knots from Flexible Short Peptides

Entanglements of strings are regularly encountered on the macroscale yet rarely utilized in nanoscale construction. Here, we report highly entangled peptide-mimic structures created through folding and assembly of silver(I) ions and a triglycine ligand (L). The highly flexible triglycine strand assembled into a septafoil knot ([Ag center dot L](7)) and its eight-crossing link analog ([Ag center dot L](8)), both of which were formed for the first time by chemical synthesis. The two structures result from circular oligomerization of the same 1-crossing Ag center dot L motif. We also obtained poly[n]catenane [Ag center dot L](n) from a topologically isomeric 2-crossing motif. Our observations reveal that dynamic linkages of short peptides enable easy access to knotted structures, which are restricted in protein structures because of the entropic (and/or kinetic) disadvantage of self-threading processes in long peptide chains, with remarkable stereoselectivity in the self-assembly process.