Oliver Plietzsch

Branched DNA That Forms a Solid at 95 °C

Control over the structure of materials may be achieved by using predictable interactions, such as base pairing. Base pairing between DNA strands is emerging as one of the most versatile design principles of nanoconstruction. A range of hybridization and folding motifs of linear and circular DNA have been reported. The flexibility of the design has been further expanded by linking oligonucleotides to synthetic branching elements or “cores”. 5] The resulting construct can have properties not found in natural DNA. This includes DNA-coated gold nanoparticles that assemble into three-dimensional aggregates, the melting transitions of which are exceptionally sharp. Nanoparticle size and linker structure affect the association behavior, and crystallization may be induced in favorable cases. For DNA hybrids with organic cores, the effect of linking the DNA to a branching element can be more dramatic still. Four-arm hybrid 1 (Scheme 1) with its tetrahedral core was recently shown to assemble into a macroscopic material, even though its oligonucleotide arms are just dimers. The assembly process is sequence specific, as demonstrated by mismatch controls, but the UV-melting transitions are broad, not sharp as in the case of gold nanoparticles. Shortly after the publication of the unusually stable assemblies of 1, the first designed DNA crystals were reported. The fact that the association of the rigid triangle motifs that serve as rigid “cores” in these crystals is also driven by no more than dimer “sticky ends” again suggests that the rules for 3D construction of periodic assemblies are quite different from those of linear DNA.

Two Base Pair Duplexes Suffice to Build a Novel Material

Tetrahedral DNA hybrids with tetrakis(p‐hydroxyphenyl)methane cores hybridize in a sequence‐specific fashion at much higher temperatures than isolated linear duplexes. Dinucleotide DNA arms suffice to induce the formation of a solid at room temperature; this demonstrates the strength of multivalent binding. The graphic shows a view of a modeled assembly.

Click chemistry produces hyper-cross-linked polymers with tetrahedral cores

Methane and adamantane based hyper-cross-linked polymers have been prepared by click chemistry reacting the corresponding tetraalkynes with 1,4-diazidobenzene. The adamantane based HCP proved to be very efficient for CO2 capture at low pressures.