No abstract

Nucleobase mimicking small molecules able to reconfigure DNA are a recently discovered strategy that promises to extend the structural and functional diversity of nucleic acids. However, only simple, unfunctionalized molecules such as cyanuric acid and melamine have so far been used in this approach. In this work, we show that the addition of substituted cyanuric acid molecules can successfully program polyadenine strands to assemble into supramolecular fibers. Unlike conventional DNA nanostructure functionalization, which typically end-labels DNA strands, our approach incorporates functional groups into DNA with high density using small molecules and results in new DNA triple helices coated with alkylamine or alcohol units that grow into micrometer-long fibers. We find that small changes in the small molecule functional group can result in large structural and energetic variation in the overall assembly. A combination of circular dichroism, atomic force microscopy, molecular dynamics simulations, and a new thermodynamic method, transient equilibrium mapping, elucidated the molecular factors behind these large changes. In particular, we identify substantial DNA sugar and phosphate group deformations to accommodate a hydrogen bond between the phosphate and the small-molecule functional groups, as well as a critical chain length of the functional group which switches this interaction from intra- to interfiber. These parameters allow the controlled formation of hierarchical, hybrid DNA assemblies simply through the addition and variation of small, functionalized molecules.

The construction of metallic nanostructures with customizable morphologies and complex shapes has been an essential pursuit in nanoscience. DNA nanotechnology has enabled the fabrication of increasingly complex DNA nanostructures with unprecedented specificity, programmability and subnanometer precision, which makes it an ideal approach to rationally organize metallic nanostructures. Here we report an Assemble, Grow and Lift-Off (AGLO) strategy to construct robust standalone gold nanostructures with pre-designed customizable shapes in solution, using only a simple 2D DNA origami sheet as a versatile transient template. Gold nanoparticle (AuNP) seeds were firstly assembled onto the pre-designed binding sites of the DNA origami template and then additional gold was slowly deposited onto the AuNP seeds. The growing seed surfaces eventually merge with adjacent seeds to generate one continuous gold nanostructure in a pre-designed shape, which can then be lifted off the origami template. Diverse customized patterns of templated AuNP seeds were successfully transformed into corresponding gold nanostructures with the target structure transformation percentage over 80%. Moreover, the AGLO strategy can be incorporated with a magnetic bead separation platform to enable the easy recycling of the excess AuNP seeds and DNA components. Electronic supplementary information (ESI) available: Experimental details, DNA sequences and modications, DNA origami design, seed-origami assembly and gold growth optimizations, additional experimental results, additional AFM and TEM images. See

Deoxyribonucleic acid (DNA) hydrogels are a unique class of programmable, biocompatible materials able to respond to complex stimuli, making them valuable in drug delivery, analyte detection, cell growth, and shape-memory materials. However, unmodified DNA hydrogels in the literature are very soft, rarely reaching a storage modulus of 10 3 Pa, and they lack functionality, limiting their applications. Here, a DNA/small-molecule motif to create stiff hydrogels from unmodified DNA, reaching 10 5 Pa in storage modulus is used. The motif consists of an interaction between polyadenine and cyanuric acid-which has 3-thymine like faces-into multimicrometer supramolecular fibers. The mechanical properties of these hydrogels are readily tuned, they are self-healing and thixotropic. They integrate a high density of small, nontoxic molecules, and are functionalized simply by varying the molecule sidechain. They respond to three independent stimuli, including a small molecule stimulus. These stimuli are used to integrate and release DNA wireframe and DNA origami nanostructures within the hydrogel. The hydrogel is applied as an injectable delivery vector, releasing an antisense oligonucleotide in cells, and increasing its gene silencing efficacy. This work provides tunable, stimuli-responsive, exceptionally stiff all-DNA hydrogels from simple sequences, extending these materials' capabilities.

Discrete self-assembly of two Re(I) squares was achieved by a simple and efficient strategy where the complexes, [Re(4-pytpy-κ(2)N)(CO)3Br] and [Re(4-pytpy-κ(3)N)(CO)2Br], act as their own ligands. The photophysical and electrochemical properties of the assemblies and their precursors are described along with solid-state X-ray diffraction studies.