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

Abstract

<p>The knotting of biomolecules impacts their function, and enables them to carry out new tasks. Likewise, complex topologies underpin the operation of many synthetic molecular machines. The ability to generate and control more complex knotted architectures is essential to endow these machines with more advanced functions. Here we report the synthesis of a molecular knot with eight crossing points, consisting of a single organic loop woven about six templating metal centres, <i>via</i> one-pot self-assembly from a simple pair of dialdehyde and diamine subcomponents and a single metal salt. The structure and topology of the knot were established by NMR spectroscopy, mass spectrometry and X-ray crystallography. Upon demetallation, the purely organic strand relaxes into a symmetric conformation, whilst retaining the topology of the original knot. This knot is topologically chiral, and may be synthesised diastereoselectively through the use of an enantiopure diamine building block.<b></b></p>

Mechanically axially chiral catenanes and noncanonical mechanically axially chiral rotaxanes

“…Our analysis also led to the surprising conclusion that catenanes based on two rings each containing a single stereogenic center can be described as either mechanically topologically or axially chiral but that only one mechanical stereodescriptor is required to specify their structure, an observation with implications for future studies. Given the increasing interest in applications of chiral interlocked molecules 44,45,46,47,48,33 including examples based on mechanical and coconformationally chiral systems 49,50,51 , as well as other exotic or hard to access mechanical stereogenic units 52,53,54,55,56,57 , we anticipate these results will spur progress in the development of functional chiral interlocked systems 58 . Finally, it should be noted that dynamic stereochemistry related to that of mechanically axially chiral catenanes and rotaxanes can also arise due to conformational and coconformational processes 59,60 , both of which have been observed but are poorly understood (Supplementary section 15).…”

Cyclohexane and Beyond: Tangled Hexagons and Octahedra

“…The assembly is a tensegrity‐type structure if the thicker bronze edges are considered linked rods and the thin black lines as cables. The rods form a piecewise linear representation of the 8‐crossing knot with symbol 8 19 – the torus knot T (4,3), a knot nicely realized in a molecule [14] …”

A topologically chiral catenane that is not topologically chiral

“…1d) 8 . Such catenanes have since been referred to simply as "topologically chiral", alongside Mobius ladders and some knots, 14,15 which display topological enantiomerism independent of their constitution. Although it is clearly correct to discuss catenanes in terms of their topology, perhaps for this reason, no one has to our knowledge challenged the idea that the stereochemistry of catenanes containing two oriented rings is inherently topological in nature.…”