Knots

REFERENCE: Ayme et al. “A synthetic molecular pentafoil knot.” Nature Chemistry (2011) 4 pgs 15 – 20.

                DNA, polymers and some proteins are able to form knots (one macromolecule that crosses itself and wraps into a continuous circle) or catenanes (interlocked circles).  Chemically synthesizing knots without using DNA bases has been unsuccessful.  

                Figure 13.1 shows a table of prime knots ordered from lowest complexity (the unknot) to highest complexity.  To date, the unknot and the trefoil knot (31) have been synthetically prepared and verified.  Chemists have been unable to extend these same strategies to making higher order knots.

 

                The knot labeled as 5₁ goes by many names: pentafoil, Solomon’s seal, and torus knot.  It has five crossing points and such a molecule would be inherently chiral.  Using a combination of new and well-known strategies, Ayme et al describe their preparation of a pentafoil knot using five bis-aldehyde and five bis-amine building blocks surrounding five metal cations and one anion in the November issue of Nature Chemistry.  The complex self-assembles in a one-pot reaction and the authors stress that this is the most complex non-DNA molecule ever prepared.

                The molecule was confirmed by NMR, MS and, most fascinatingly, X-ray crystallography.  Pictures of the gorgeous molecule are below (directly from their paper).

                The authors hope that this chemistry will allow scientists to synthesize more complex and larger molecular species.