Guided Self-Assembly of Silsesquioxane Nanocubes: Two Lessons From DNA

The most promising approach to molecular assembly consists of manipulating and connecting chemically synthesized nanoscale building blocks, of which the geometrically most favorable are nanocubes. Silsesquioxanes are a promising set of such nanocubes-cubic cages of silica (1 nm) with organic groups on each of the eight corners. Silsesquioxanes could be synthesized into larger, easier-to-manipulate multicage nanocubes (3-10 nm), which have the advantage of presenting additional face-bonding opportunities in a larger, easier-to-manipulate molecule. The highest value products that nanocube assembly will manufacture are fully 3-D electronic circuits with 5 nm features. Such integrated circuits would consist of nanocubes with electron-donating or electron-accepting semiconducting moieties in their intracube and intercube links. The synthesized nanocubes must be positioned with high precision and reliability so that they could be connected into NAND gates, billions at a time. Two different approaches are available: (1) Wang cube self-assembly and (2) pixilated DNA origami templating. Wang nanocubes are complex heterogeneous 3-D nanocubes with precisely controlled anisotropy. Their self-assembly would be similar to the sequential solid-phase synthesis process used to make DNA oligomers, and amino and bis-amino acid polypeptides, except that instead of building 1-D linear chain molecules that need additional weak-force self-folding and/or processing to form 3-D nanostructures, Wang nanocubes could form arbitrary 3-D nanostructures directly. Their existence depends on the synthesis of complex enantioselective multicage nanocubes with six independent face-connection chemistries with controlled orientation. In pixilated DNA origami templating, higher order silsesquioxane nanocubes would be attached (via amines, thiols, etc.) to one of hundreds of custom-sequence helper strands. Then, the molecular recognition of subsequences of a long single-stranded scaffold connect via Watso- - n-Crick binding to the matching helper strand/nanocube complex, thereby making many arbitrary nanostructures possible.