Assembly of a bifurcated knot via sequence selective imine condensation

Abstract

Knotting and weaving, at both macroscopic and molecular scales, play an essential role in determining the physical properties of materials. While classical crossing points in molecular knots have been extensively studied, synthetic bifurcated knots, containing characteristic junctions where a strand divides into two branches, represent an underexplored class of topologically complex molecular knots. Although reports of such structures are rare due to synthetic challenges, natural bifurcated knots have been identified in proteins and linked to potentially enhancing protein robustness. Here we report the synthesis of a 524-atom bifurcated knot featuring 3 classical crossings and 20 bifurcated junctions via 2 sequential, selective, imine condensations. First, Zn II ions are used to template the subcomponent self-assembly of a Zn II 8 L 6 architecture, with three unreacted aldehyde groups protruding from each of its eight vertices. Second, a geometry-matching tris-aniline condenses with these terminal aldehydes, yielding a covalently linked bifurcated knot with enhanced robustness, as quantified using collision-induced dissociation mass spectrometry. We anticipate that this approach will facilitate the design of new mechanically interlocked molecules and highly entangled molecular materials with increased robustness.