Construction of Single Molecule Nanostructures by Self-Assembly and Fixation

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The potential for strands of DNA to spontaneously assemble into branched nanostructures was first described in 1982; however, although DNA-based fabrication has seen extraordinary advances over the intervening thirty years, the resultant structures are relatively weak, reducing its versatility as a nanoscale manufacturing approach. Additionally, the construction of highly complex structures requires multiple, sequential fabrication steps, requiring periodic stabilization of the incomplete structure. This award supports an investigation into the fabrication of single molecule nanostructures that are progressively built up from small molecular components to generate complex, multi-dimensional nanostructures with excellent thermal, chemical, and mechanical stability. This project will provide the capability to fabricate self-assembled, nanoscale devices that remain stable under harsh environments where weaker structures would fail. Owing to the multi-disciplinary nature of this project, the student participants will be trained to identify questions in organic and polymer chemistry, and in reaction kinetics and thermodynamics, and design and carry out the experiments necessary to answer those questions. The students will have a broad skill set for tackling emerging research areas and will be effective at communicating with researchers from different disciplines. Additionally, this project will assist the recruitment, education, and development of the next generation of scientists through outreach to under-represented demographics, widening the pool of researcher talent. In this research, reversible, pH- and temperature-sensitive reactions, specifically amine/aldehyde condensation and furan/maleimide Diels-Alder cycloaddition reactions, will be employed as dynamic covalent "base pairs". In an approach mimicking the self-assembly commonly observed in complementary DNA strands, the assembly of complementary strands of peptoid- and hybrid peptoid/peptide-based dynamic covalent oligomers, fabricated using solid phase synthesis, will be performed and the hybridization selectivity of the double-stranded assemblies will be characterized. Fixation reactions, in conjunction with the base pairs that dimerize under orthogonal reaction conditions, will be employed, allowing for multiple assembly steps to be performed without disruption of the emergent nanostructure. Finally, through careful consideration of their residue sequence, the dynamic covalent-mediated assembly of oligomers into branched nanostructures will be demonstrated. The successful completion of this work will yield both the understanding and capability to fabricate arbitrary, robust nanostructures using dynamic covalent-mediated assembly, an important new direction in nanomanufacturing.