The Significance of Multivalent Bonding Motifs and "Bond Order" in DNA-Directed Nanoparticle Crystallization.

Multivalent oligonucleotide-based bonding elements have been synthesized and studied for the assembly and crystallization of gold nanoparticles. Through the use of organic branching points, divalent and trivalent DNA linkers were readily incorporated into the oligonucleotide shells that define DNA-nanoparticles and compared to monovalent linker systems. These multivalent bonding motifs enable the change of "bond strength" between particles and therefore modulate the effective "bond order.

Directed Assembly of Nucleic Acid-Based Polymeric Nanoparticles from Molecular Tetravalent Cores.

Complementary tetrahedral small molecule-DNA hybrid (SMDH) building blocks have been combined to form nucleic acid-based polymeric nanoparticles without the need for an underlying template or scaffold. The sizes of these particles can be tailored in a facile fashion by adjusting assembly conditions such as SMDH concentration, assembly time, and NaCl concentration. Notably, these novel particles can be stabilized and transformed into functionalized spherical nucleic acid (SNA) structures through the incorporation of capping DNA strands conjugated with functional groups.

Hydrophobic organic linkers in the self-assembly of small molecule-DNA hybrid dimers: a computational-experimental study of the role of linkage direction in product distributions and stabilities.

Detailed computational and experimental studies reveal the crucial role that hydrophobic interactions play in the self-assembly of small molecule-DNA hybrids (SMDHs) into cyclic nanostructures. In aqueous environments, the distribution of the cyclic structures (dimers or higher-order structures) greatly depends on how well the hydrophobic surfaces of the organic cores in these nanostructures are minimized. Specifically, when the cores are attached to the 3'-ends of the DNA component strands, they can insert into the minor groove of the duplex that forms upon self-assembly, favoring the formation of cyclic dimers.

Methane storage in metal-organic frameworks: current records, surprise findings, and challenges.

We have examined the methane uptake properties of six of the most promising metal organic framework (MOF) materials: PCN-14, UTSA-20, HKUST-1, Ni-MOF-74 (Ni-CPO-27), NU-111, and NU-125. We discovered that HKUST-1, a material that is commercially available in gram scale, exhibits a room-temperature volumetric methane uptake that exceeds any value reported to date. The total uptake is about 230 cc(STP)/cc at 35 bar and 270 cc(STP)/cc at 65 bar, which meets the new volumetric target recently set by the Department of Energy (DOE) if the packing efficiency loss is ignored.

Simultaneously high gravimetric and volumetric methane uptake characteristics of the metal-organic framework NU-111.

We show that the MOF NU-111 exhibits equally high volumetric and gravimetric methane uptake values, both within ≈75% of the DOE targets at 300 K. Upon reducing the temperature to 270 K, the uptake increases to 0.5 g g(-1) and 284 cc(STP) per cc at 65 bar.

Metal-organic framework materials with ultrahigh surface areas: is the sky the limit?

We have synthesized, characterized, and computationally simulated/validated the behavior of two new metal-organic framework (MOF) materials displaying the highest experimental Brunauer-Emmett-Teller (BET) surface areas of any porous materials reported to date (~7000 m(2)/g). Key to evacuating the initially solvent-filled materials without pore collapse, and thereby accessing the ultrahigh areas, is the use of a supercritical CO(2) activation technique. Additionally, we demonstrate computationally that by shifting from phenyl groups to "space efficient" acetylene moieties as linker expansion units, the hypothetical maximum surface area for a MOF material is substantially greater than previously envisioned (~14600 m(2)/g (or greater) versus ~10500 m(2)/g).

Designing higher surface area metal-organic frameworks: are triple bonds better than phenyls?

We have synthesized, characterized, and computationally validated the high Brunauer-Emmett-Teller surface area and hydrogen uptake of a new, noncatenating metal-organic framework (MOF) material, NU-111. Our results imply that replacing the phenyl spacers of organic linkers with triple-bond spacers is an effective strategy for boosting molecule-accessible gravimetric surface areas of MOFs and related high-porosity materials.

Enhancing the melting properties of small molecule-DNA hybrids through designed hydrophobic interactions: an experimental-computational study.

Detailed experimental and computational studies revealed the important role that hydrophobic interactions play in the aqueous assembly of rigid small molecule-DNA hybrid (rSMDH) building blocks into nanoscale cage and face-to-face (ff) dimeric structures. In aqueous environments, the hydrophobic surfaces of the organic cores in these nanostructures are minimized by interactions with the core in another rSMDHs, with the bases in the attached DNA strands, and/or with the base pairs in the final assembled structures. In the case that the hydrophobic surfaces of the cores could not be properly isolated in the assembly process, an ill-defined network results instead of dimers, even at low concentration of DNA.

Successful stabilization of graphene oxide in electrolyte solutions: enhancement of biofunctionalization and cellular uptake.

Aqueous dispersions of graphene oxide are inherently unstable in the presence of electrolytes, which screen the electrostatic surface charge on these nanosheets and induce irreversible aggregation. Two complementary strategies, utilizing either electrostatic or steric stabilization, have been developed to enhance the stability of graphene oxide in electrolyte solutions, allowing it to stay dispersed in cell culture media and serum. The electrostatic stabilization approach entails further oxidation of graphene oxide to low C/O ratio (~1.

Luminescent infinite coordination polymer materials from metal-terpyridine ligation.

A new class of infinite coordination polymers (CP) was synthesized using a tetrahedral tetrakis[4-(4'-phenyl-2,2':6',2''-terpyridine)phenyl]methane ligand as an organic node to direct the three-dimensional growth of the network and M(II) (M = Zn, Fe, Ni, and Ru) ions as inorganic linkers, an approach that is the opposite of the metal-as-a-node strategy used in the construction of metal-organic frameworks (MOFs). The unusual rod-like morphology of the resulting microporous materials can be tuned via solvents and reaction conditions. The covalent entrapment of a [Ru(tpy)(2)](2+) moiety in the skeleton of the 3D-network enables the Ru-CP to exhibit room-temperature luminescence.

Cooperative melting in caged dimers with only two DNA duplexes.

Small molecule-DNA hybrids with only two parallel DNA duplexes (rSMDH2) displayed sharper melting profiles compared to unmodified DNA duplexes, consistent with predictions from neighboring-duplex theory. Using adjusted thermodynamic parameters obtained from a coarse-grain dynamic simulation, the experimental data fit well to an analytical model.

De novo synthesis of a metal-organic framework material featuring ultrahigh surface area and gas storage capacities.

Metal-organic frameworks--a class of porous hybrid materials built from metal ions and organic bridges--have recently shown great promise for a wide variety of applications. The large choice of building blocks means that the structures and pore characteristics of the metal-organic frameworks can be tuned relatively easily. However, despite much research, it remains challenging to prepare frameworks specifically tailored for particular applications.

DNA melting in small-molecule-DNA-hybrid dimer structures: experimental characterization and coarse-grained molecular dynamics simulations.

When DNA hybridization is used to link together nanoparticles or molecules, the melting transition of the resulting DNA-linked material often is very sharp. In this paper, we study a particularly simple version of this class of material based on a small-molecule-DNA-hybrid (SMDH) structure that has three DNA strands per 1,3,5-tris(phenylethynyl)benzene core. By varying the concentration of the SMDHs, it is possible to produce either SMDH dimers or bulk aggregates, with the former having highly packed duplex DNA while the latter has an extended network.

Design, characterization, and X-ray structure of an interlocked dinuclear chair-like metallomacrocycle: [Fe(II)2(3,5-bis(2,2':6',2''-terpyridin-4'-phen-3-yl)toluene)2][4PF6-].

The self-assembly of 3,5-bis(2,2':6',2''-terpyridin-4'-phen-3-yl)toluene with an equimolar amount of a Fe(II) salt afforded a high yield of an interlocked dinuclear tetracationic "molecular gear" that was confirmed by single crystal X-ray data.

Synthesis and single-crystal X-ray characterization of 4,4"-functionalized 4'-(4-bromophenyl)-2,2':6',2"-terpyridines.

To expand the utility of bis(terpyridine) metal connectivity, the selective symmetrical and unsymmetrical 4,4"-functionalization (-CN, -Me, -CO2Me) of 4'-(4-bromophenyl)-2,2':6',2"-terpyridines was achieved using the Kröhnke synthesis. The final substituted 2,2':6',2"-terpyridines along with their corresponding intermediates, 4a-c, were recrystallized and characterized by 1H NMR and 13C NMR as well as X-ray crystallography; COSY correlations were also conducted to permit definitive proton assignment.