Volume 44 Issue 6, June 2012

DNA nanotechnology has enabled precise bottom-up integration of metal nanoparticles (NPs) on a nanometer scale. The DNA origami technique facilitated still more complicated control of the positioning not only in 2 dimensional (D) but also in 3D structures. We constructed an alternating streptavidin/gold NP heteroarray with 26 nm separation using a nanometer-sized cavity (a DNA well) embedded in a 2-nm-thick DNA origami sheet. The basic idea and other recent examples of such metal NP arrays on DNA nanostructures are reviewed.

Bicontinuous cubic (Q) lyotropic liquid crystal (LLC) phases formed by the self-organization of amphiphiles in water are intriguing structures for transport applications because they possess ordered, 3D-interconnected water nanochannels. Q-phase polymer materials can be formed by templated polymerization of conventional monomers around Q phases or direct polymerization of Q phases formed by reactive amphiphiles. Herein, we provide an overview of work in these areas, with a focus on our group’s work on polymers prepared by the direct cross-linking of reactive Q phases and their development into functional materials.

Application of natural viruses to nanotechnology have attracted much attention due to their fascinating nanostructures. However, chemical strategy to de novo design virus-like nanostructures is still in its infancy. In this review article, we describe novel C₃-symmetric molecular design of peptides and their characteristic self-assembly into virus-like nanostructures. We have developed trigonal conjugates of β-sheet-forming peptides, trigonal conjugates of glutathione and a viral β-annulus peptide fragment.

Hybrid self-assemblers based upon dendritic building blocks such as aliphatic polyether and/or poly(benzyl ether) dendrons can be prepared by a combination of physically different flexible linear and rigid discotic segments. The unconventional self-assemblers organize into various bulk liquid crystalline morphologies, which can be used as a versatile platform for ion-conducting materials.

We present a molecular design of a preprogrammed supermolecule that can stabilize frustrated molecular organization of an isotropic liquid-crystalline phase. The tapered amphiphilic compound exhibited an unusual smectic A to cubic phase transition. The chiral T-shaped compound showed amorphous blue phase III with a temperature range of 25 K. We demonstrate high-transmittance, sub-millisecond response and hysteresis-free switching in room temperature amorphous blue phase stabilized by a designed LC supermolecule.

Macroscopic liquid crystal structures have been developed in hydrogels by self-assembly of a semi-rigid polyion complex. During the polymerization of isotropic precursor solution of a cationic monomer in the presence of a semi-rigid polyanion, the polycation will interact with oppositely charged polyanion to form polyion complexes. These semi-rigid complexes self-assemble further to form macroscopically ordered structure that is frozen in a nanoscale network by the following chemical cross-linking reaction.

Dendrimers have attracting great interests in the design of functional materials. Because the core porphyrin unit in dendrimer porphyrin (DP) is surrounded by large poly(benzyl ether) dendritic wedges with ionic periphery, various functional nano-devices, such as DP-loaded polyion complex micelles, ternary complex system for gene delivery, polymer-metal complex micelle, hollow nanocapsules for combination cancer therapy, DP-immobilized surface for diagnostic tools, have been designed through electrostatic interaction with oppositely charged polymeric materials.

For high-performance boron neutron capture therapy , core-shell-type biodegradable nanoparticle-containing boron cluster is designed in order to improve accumulation tendency to tumor. Copolymerization of styrene carrying carborane with poly(ethylene glycol)-block-poly(lactide) (PEG-b-PLA-MA), possessing a methacryloyl group at the PLA end is performed. The accumulation of the polymerized micelles in tumor is much higher than that of the non-polymerized micelles because of the enhancement of the stability of the micelles. Thermal neutron irradiation exhibits significant suppression of tumor growth in the mice treated with the polymerized micelles.

Various types of dendrimer-based nanomaterials, such as poly(ethylene glycol)-modified dendrimers, functional shell-bearing dendrimers, thermosensitive dendrimers, dendron-based lipid assemblies and dendrimer-gold nanoparticle (NP) hybrids were developed by surface modification, assembling and hybrid formation strategies. These dendrimers and dendrimer-based nanomaterials exhibited various bio-related functions, such as drug encapsulation, stimuli-responsive transition and photo-induced heat generation. Based on these functions, these dendrimers and dendrimer-based nanomaterials have potential usefulness in the biomedical field, such as target-specific drug delivery and non-invasive therapy.

Highly efficient synthesis of heteroarm star-shaped polymers containing independent stimuli-responsive moieties was demonstrated using a one-pot arm-linking method via base-assisting living cationic polymerization. The linking reaction of mixed two or more kinds of living polymers with a divinyl compound successfully yielded heteroarm star polymers with narrow molecular weight distributions. Furthermore, this methodology was expanded to polar functional monomers, producing a heteroarm star-shaped polymer with amino-containing and thermosensitive arms. The obtained heteroarm star-shaped polymers exhibited their unique stimuli-responsive behaviors in water or their film surfaces.

Four-arm star block copolymers comprising poly(N-vinylimidazolium salt) as a poly(ionic liquid) segment and poly(NIPAAm) as a thermoresponsive segment were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Stimuli-responsive properties and temperature-responsive self-assembly process of these star block copolymers were studied in aqueous solution. Chain architectures, the sequence and comonomer composition of the diblock arms, and salt concentration had a significant effect on their thermally induced phase separation behavior and assembled structures.

In this study, the useful information for the design of side-chain liquid crystal polymers was described. Side-chain liquid crystal PEIs with different spacer lengths (n) were newly synthesized. In the case of short spacers, only a smectic A phase with a bilayer structure was formed. The long spacers led to the formation of a smectic A, C and F phases with a monolayer structure.

The orientation of nanoscale double-helical morphologies of SBM triblock terpolymer at various film thicknesses (h) were studied using transmission electron microtomography, following solvent annealing and drying at a controlled solvent evaporation rate (R). The combination of h and R were found to be essential factors to determine orientation of the double-helical microdomains in thin films. Perpendicularly aligned double-helical morphology extending several micrometers from the substrate to the air surface was achieved.

Euler buckling forms surface microwrinkles ranging in size from sub-micrometers to tens of micrometers as a result of the modulus difference between the surface of the material and the material itself. When the buckling occurs in the limited areas smaller than the wrinkle wavelength, the shape of the buckled surface deforms into concave dimples or convex lenses. The shape of the buckled surface can be controlled by changing the modulus of poly(dimethylsiloxane). Hierarchical patterning by using a photomask was also achieved. This process provides a novel way to pattern soft substrates, including elastomers and gels.

Unsymmetrical P-stereogenic tetraphosphine and hexaphosphine were synthesized using optically active bisphosphines as chiral building blocks. The boranes coordinating with phosphorus atoms could be chemoselectively removed by an organic base owing to the different coordination ability of the phosphorus atoms, leading to their successful use for heteromultimetallics.

Size-controlled CaCO₃ composite particles were obtained by a carbonate-controlled addition method with a carboxylate-terminated hyperbranched poly(amidoamine) (HYPAM-ONa). The sizes of the CaCO₃ particles decreased from 1.3±0.2 to 0.36±0.18 μm with increasing the complexation time of HYPAM-ONa-Ca²⁺ from 3 min to 72 h. The surfaces of the CaCO₃ composite particles were coated with gold nanoparticles by addition of the aqueous solution of the gold nanoparticles stabilized with HYPAM-ONa to the aqueous dispersion of the CaCO₃ particles and subsequent addition of HAuCl₄ and formaldehyde as a reducing agent.

Nematic liquid-crystalline (LC) gels showing electrooptical switching have been prepared for the mixtures of a new polymerizable lysine-based gelator and a nematic LC compound, 4-cyano-4′-pentylbiphenyl. Finely dispersed fibrous networks are formed by self-assembly of the gelators through the formation of hydrogen bonds. In-situ photopolymerization of the gelators in the self-assembled state leads to thermal stabilization of the fibrous network structures. The threshold voltage of electrooptical switching for the polymerized LC gel is lower than that for non-polymerized LC gels.

Ditopic hydrogen bonding melamines possessing perylene bisimide chromophores were synthesized and their self-aggregation and coaggregation with complementary guest molecules were investigated. In this system, 2-D lamellar structures of perylene bisimides were constructed through hierarchical organization of hydrogen-bonded tapes, which can gelate aliphatic and aromatic solvents. The resulting gels are highly transparent and exhibit remarkably low critical gelation concentrations of 8.0 × 10⁻⁴ M. The thermal stabilities and the mesoscopic morphologies of these organogels could be reasonably explained by the number of perylene bisimide chromophores introduced in the melamine components.

We have successfully developed a system to perform active self-organization of microtubules (MT) using a streptavidin–biotin interaction in a nitrogen atmosphere (inert chamber). Use of inert chamber dramatically improved the lifetime of assembled microtubules and kept them active for a longer period of time compared to the case without using inert chamber. Longer lifetime of assembled microtubules obtained using the inert chamber would be significantly important in further development of biomolecular motor protein-based organized systems.

The hollow-coned morphologies have been formed on carbonate crystals of calcite, aragonite and vaterite polymorphs through a molecular-control approach by using an acid organic polymer. The oriented nanocrystals with incorporation of organic polymers formed the mesocrystal structures leading to the formation of the macroscopic hollow-coned morphologies.

Crystallization of calcium carbonate (CaCO₃) in the presence of single-walled carbon nanotube (SWCNT)/fullerodendron supramolecular nanocomposites in aqueous environments was carried out with a CO₂ diffusion method to afford monodisperse spherical SWCNT/CaCO₃ hybrids with a core-shell structure. The crystals nucleate at the carboxyl groups on the surface of SWCNT/fullerodendron supramolecular nanocomposites grow around a spherical scaffold made of the SWCNTs, and finally form spherical calcite crystals embedded and covered by the SWCNTs. After removing the SWCNTs by the calcination in an air flow at 800 °C, the morphology of the core-shell microsphere was maintained.

A novel nucleobase-terminated organosilane with both nucleobase and ethoxysilane moieties was synthesized by a simple method that includes only a reaction of bromouracil with amino-terminated organosilane without using solvents. The uracil-terminated organosilane was self-assembled on a hydroxylated surface, followed by chemical modifications to uracil-concentrated surface. Adenine complementary to uracil was effectively adsorbed onto the resultant uracil-concentrated surface by multiple hydrogen bonds. This paper provides with a simple method for synthesizing a nucleobase-terminated organosilane and for modifying a hydroxylated surface to a nucleobase-concentrated surface.

A fluorescent-labeled hyper-branched polymer with mesogenic shell was captured by the disclination lines of a liquid crystal. In a Grandjean–Cano wedge cell, the particles of the hyper-branched polymer migrated toward the periodically aligned defect line and thus formed a two-dimensional lattice array.

A new process to prepare a monolayer level photoreactive surface on a polyimide is proposed. The procedure involves the irradiation with vacuum ultraviolet light (172 nm), which generates oxidized hydroxyl group at the top-most surface without changing the nature of the bulk polymer. The chemically functionalized surface can be utilized to introduce photoreactive units on the surface to provide photoresponsive liquid crystal cells.

A diacetylenic-acid arginine salt gelated water. The properties of the supramolecular hydrogel were examined by optical microscopy, electron microscopy, X-ray diffraction and ultraviolet (UV)-absorption and circular dichroism (CD) spectroscopies. Microscopic images showed that 10, 12-docosadiynedioic acid arginine salt formed a fibrous structure. Upon UV irradiation, the gel polymerized to diacetylene oligomers fibers. After the removal of arginine, CD spectra indicated that the diacetylene oligomers maintained chirality.

Newly designed β-sheet peptides bearing the calcium ion binding Glu residue were self-assembling into self-supporting hydrogels. The hydrogelation from the viscous sol-state solution can be induced by a slower self-assembly process followed by a rapid injection to Ca²⁺ solution. Peptide gel strings can be easily constructed. Cell culture experiments demonstrated low toxicity and high-adhesive abilities of the peptide hydrogels.

We report a rapid and reversible morphology control of a polyhedral oligomeric silsesquioxane (POSS) containing block copolymer (PEO-b-PMAPOSS), which composed of poly(ethylene oxide) (PEO) and POSS-containing poly(methacrylate), (PMAPOSS), between ordered arrays of dots and lines for several tens of seconds by combination of thermal annealing and solvent annealing. The reversible morphology change and ordering of phase morphology in a short time are enabled by a distinctive property of PEO-b-PMAPOSS with highly mobility of the chain at the thermal and the solvent annealing states.

Molecular self-assembly in IL is promoted by controlling cohesive energies of amphiphiles and ILs.

Highly efficient DNA release was achieved by the polyamidoamine-modified superparamagnetic particles (PAMAM–SpMNPs) that were prepared with 10-nm magnetite cores. We optimized the surface amine numbers of the PAMAM–SpMNPs to control the interaction between a DNA molecule and the amine groups on the particle. With this optimization, the PAMAM–SpMNPs maintained a high DNA adsorption capacity and high dispersivity in solution. The DNA-release efficiency using PAMAM–SpMNPs was over 95%. Furthermore, the complete DNA release from PAMAM–SpMNPs was achieved by applying an alternating magnetic field for 10 min.