(607h) Information-Directed Assembly of Dynamic Covalent Molecular Ladders

Nucleic acids present the most versatile class of materials for producing nanostructures to date and, through careful consideration of their residue sequence, can be designed to self-assemble via the hybridization of complementary strands into arbitrary structures with nanometer precision. Unfortunately, the versatility of nucleic acid assemblies is tempered by their thermal and mechanical instability, attributable to the weakness of the hydrogen bonds that hold the strands together. The substitution of the canonical nucleic acid base pairs with covalent inter-strand interactions precludes this instability and yields a unique and powerful nanofabrication strategy wherein the complex, information-driven assembly of nucleic acids is combined with the strength of covalent bonds. Notably, the creation of exquisite nanostructures by self-assembly and the toughness imparted by covalent bonds are generally perceived as mutually exclusive owing to the prevalent irreversibility of covalent bond-generating reactions. Fortunately, several covalent interactions are known to be reversible under particular reaction conditions, enabling the error correction mechanism that is essential for the selective fabrication of supramolecular structures. As a result of the enormously greater strength and directionality offered by covalent bonds in comparison to the weaker interactions observed in biology, these 'dynamic' covalent chemistries offer an elegant approach to nanostructure assembly that combines complexity AND toughness. Here, we demonstrate the sequence-dependent self-assembly of peptoid-based oligomers to afford molecular ladders with up to sixteen rungs via scandium(III)-­catalyzed imine metathesis. Moreover, we examine the ability of this approach to generate branched ladders that can assemble into larger, robust, multi-dimensional nanostructures.