Metal–peptide rings form highly entangled topologically inequivalent frameworks with the same ring- and crossing-numbers

Abstract

With increasing ring-crossing number (c), knot theory predicts an exponential increase in the number of topologically different links of these interlocking structures, even for structures with the same ring number (n) and c. Here, we report the selective construction of two topologies of 12-crossing peptide [4]catenanes (n = 4, c = 12) from metal ions and pyridine-appended tripeptide ligands. Two of the 100 possible topologies for this structure are selectively created from related ligands in which only the tripeptide sequence is changed: one catenane has a T2-tetrahedral link and the other a three-crossed tetrahedral link. Crystallographic studies illustrate that a conformational difference in only one of the three peptide residues in the ligand causes the change in the structure of the final tetrahedral link. Our results thus reveal that peptide-based folding and assembly can be used for the facile bottom-up construction of 3D molecular objects containing polyhedral links.

A metal–peptide capsule by multiple ring threading

“…A thin capsular shell provides the superstructure with mechanical stability and encloses its huge inner cavity. In this virus capsid, the essence of the shell formation process can be described as concomitant intra-strand (folding) and inter-strand (entwining) self-assembly processes, and this has inspired us to demonstrate the same using chemistry 2–7 . Previously, the self-assembly of Ag + and ditopic oligopeptide 1 has resulted in peptide [2]catenane 2 (Fig.…”

“…The Pro-Gly-Pro-x-Gly-Pro-Pro sequence (Pro: l -proline, Gly: glycine, and x: imino-(1,3-phenylene)carbonyl spacer) of 1 adopted a loop conformation on coordination to Ag + and assembled to form a simple link of two Ag 1 ( 1 ) 1 macrocycles. In contrast, shorter peptide ligand 3 afforded peptide [4]catenane 4 , which is formed of four tetrahedrally linked macrocycles with 12 strand-crossing points 3 ; this structure is described as the T 2 -tetrahedral link topology 7 by the practical topological description method developed for DNA polyhedral catenanes 8 in knot theory 9 (Fig. 1b).…”

Isogonal weavings on the sphere: knots, links, polycatenanes

“…We note a recent report of molecular assemblies with the rkh structure, wherein it is identified as the 'three-crossed tetrahedral link' (Sawada, Saito et al, 2019). Data for the regular, stick-transitive, structures…”

“…Weavings, knots, links and related geometrical structures are currently of considerable interest in materials chemistry and biochemistry, as testified in recent reviews (Lim & Jackson, 2015;Flapan, 2015;Bruns & Stoddart, 2016;Pieters et al, 2016;Horner et al, 2016;Fielden et al, 2017) and in other recent reports (Danon et al, 2017;Wu et al, 2017;Kim et al, 2018;Zhang et al, 2018;Leigh et al, 2019;Sawada, Saito et al, 2019;Sawada, Inomata et al, 2019;Inomata et al, 2020). Suggested knots most suitable for self-assembly have recently been identified (Marenda et al, 2018).…”

Controlling the Shape and Chirality of an Eight-crossing Molecular Knot

“…7 Knotting at the molecular level thus has major effects upon material properties. 8,9 Since Sauvage's first full characterisation of synthetic knotted molecules three decades ago, 10 the beauty of these woven architectures has attracted chemists, 11 leading to recent breakthroughs in the synthesis of complex, highly symmetric, knots, 12,13,14,15,16,17,18 and to investigations of their functions. 19,20 To date, synthetic routes to molecular knots and links have focussed on the preparation of highly symmetric knots with few crossing points, such as the threecrossing trefoil knot.…”