Knotting matters: orderly molecular entanglements

• Published in: Chemical Society reviews 2022-09, Vol.51 (18), p.7779-789
• Main Authors: Ashbridge, Zoe, Fielden, Stephen D. P, Leigh, David A, Pirvu, Lucian, Schaufelberger, Fredrik, Zhang, Liang
• Format: Article
• Language: English
• Subjects: Binding; Catalytic activity; Chemistry; Complexity; Knots; Stereochemistry; Topology
• ISSN: 0306-0012; 1460-4744
• DOI: 10.1039/d2cs00323f

Entangling strands in a well-ordered manner can produce useful effects, from shoelaces and fishing nets to brown paper packages tied up with strings. At the nanoscale, non-crystalline polymer chains of sufficient length and flexibility randomly form tangled mixtures containing open knots of different sizes, shapes and complexity. However, discrete molecular knots of precise topology can also be obtained by controlling the number, sequence and stereochemistry of strand crossings: orderly molecular entanglements. During the last decade, substantial progress in the nascent field of molecular nanotopology has been made, with general synthetic strategies and new knotting motifs introduced, along with insights into the properties and functions of ordered tangle sequences. Conformational restrictions imparted by knotting can induce allostery, strong and selective anion binding, catalytic activity, lead to effective chiral expression across length scales, binding modes in conformations efficacious for drug delivery, and facilitate mechanical function at the molecular level. As complex molecular topologies become increasingly synthetically accessible they have the potential to play a significant role in molecular and materials design strategies. We highlight particular examples of molecular knots to illustrate why these are a few of our favourite things. We review recent progress in molecular knotting, the chemistry of orderly molecular entanglements. As complex nanotopologies become increasingly accessible they may play significant roles in molecular design.