Munenori Numata

Post-polymerization of preorganized assemblies for creating shape-controlled functional materials.

Combination of supramolecular chemistry with molecular recognition has been successfully applied to creating large superstructures with a wide variety of morphologies. Control of shapes and patterns of ordered molecular assemblies in nano and micro scales has attracted considerable interest as promising bottom-up technology. It is known, however, that these molecular assembling superstructures are fragile, reflecting the characteristic of the non-covalent interaction, a driving force operating in these molecular systems. In fact, they easily collapse or change by small perturbation in the environmental conditions. Thus, over the last decade, researchers have been seeking possible methods for the immobilization these superstructures. This critical review focuses on recent advances in in situ post-modification under the influence of the molecular assemblies as templates and polymerization of ordered molecular assemblies such as organogel fibers and crystals to preserve their original superstructures and intensify their mechanical strength.

‘Supramolecular wrapping chemistry’ by helix-forming polysaccharides: a powerful strategy for generating diverse polymeric nano-architectures

We have exploited novel supramolecular wrapping techniques by helix-forming polysaccharides, β-1,3-glucans, which have strong tendency to form regular helical structures on versatile nanomaterials in an induced-fit manner. This approach is totally different from that using the conventional interpolymer interactions seen in both natural and synthetic polymeric architectures, and therefore has potential to create novel polymeric architectures with diverse and unexpected functionalities. The wrapping by β-1,3-glucans enforces the entrapped guest polymer to adopt helical or twisted conformations through the convergent interpolymer interactions. On the contrary, the wrapping by chemically modified semi-artificial β-1,3-glucans can bestow the divergent self-assembling abilities on the entrapped guest polymer to create hierarchical polymeric architectures, where the polymer/β-1,3-glucan composite acts as a huge one-dimensional building block. Based on the established wrapping strategy, we have further extended the wrapping techniques toward the creation of three-dimensional polymeric architectures, in which the polymer/β-1,3-glucan composite behaves as a sort of amphiphilic block copolymers. The present wrapping system would open several paths to accelerate the development of the polymeric supramolecular assembly systems, giving the strong stimuli to the frontier of polysaccharide-based functional chemistry.

Carbohydrate-appended curdlans as a new family of glycoclusters with binding properties both for a polynucleotide and lectins

Beta-1,3-glucans having carbohydrate-appendages (alpha-D-mannoside, N-acetyl-beta-D-glucosaminide and beta-lactoside) at the C6-position of every repeating unit can be readily prepared from curdlan (a linear beta-1,3-glucan) through regioselective bromination/azidation to afford 6-azido-6-deoxycurdlan followed by chemo-selective Cu(i)-catalyzed [3 + 2]-cycloaddition with various carbohydrate modules having a terminal alkyne. The resultant carbohydrate-appended curdlans can interact with polycytosine to form stable macromolecular complexes consistent with two polysaccharide strands and one polycytosine strand. Furthermore, these macromolecular complexes show strong and specific affinity toward carbohydrate-binding proteins (lectins). Therefore, one can utilize these carbohydrate-appended curdlans as a new family of glycoclusters.

Polybenzyl ether dendrimers for the complexation of [60]fullerenes

The formation of host-guest complexes between C60 and polybenzyl ether dendrimers with different central cores (phloroglucinol, meso-tetraphenylporphyrin, cyclotriveratrylene) has been investigated in organic solvents by means of 13C-NMR and UV-Vis spectroscopy. The interior of the dendrimers with a phloroglucinol core provides the correctly sized space for the inclusion of [60]fullerene and 13C-NMR studies suggest that the guest resides near the central core. In the dendrimers containing a meso-tetraphenylporphyrin (TPP) core, the absorbance of the porphyrin Soret band is substantially reduced in the presence of [60]fullerene, thus providing evidence for close vicinity of the fullerene guest to the central core. In solution, the cyclotriveratrylene (CTV) unit alone is a poor receptor for fullerene, but its functionalization with polybenzyl ether dendrons affords an internal cavity with a more appropriate shape and dimension, thus allowing complexation. Indeed, the Ka values (order of magnitude 101–102 L mol−1) increase significantly with the generation number of the surrounding dendritic substituents.

β-1,3-Glucan polysaccharides as novel one-dimensional hosts for DNA/RNA, conjugated polymers and nanoparticles

Beta-1,3-glucan polysaccharides have triple-stranded helical structures whose sense and pitch are comparable to those of polynucleotides. We recently revealed that the beta-1,3-glucans could interact with certain polynucleotides to form triple-stranded and helical macromolecular complexes consisting of two polysaccharide-strands and one polynucleotide-strand. This unique property of the beta-1,3-glucans has made it possible to utilize these polysaccharides as potential carriers for various functional polynucleotides. In particular, cell-uptake efficiency of the resultant polysaccharide/polynucleotide complexes was remarkably enhanced when functional groups recognized in a biological system were introduced as pendent groups. The beta-1,3-glucans can also interact with various one-dimensional architectures, such as single-walled carbon nanotubes, to produce unique nanocomposites, in which the single-walled carbon nanotubes are entrapped within the helical superstructure of beta-1,3-glucans. Various conductive polymers and gold nanoparticles are also entrapped within the helical superstructure in a similar manner. In addition, diacetylene monomers entrapped within the helical superstructure can be photo-polymerized to afford the corresponding poly(diacetylene)-nanofibers with a uniform diameter. These findings indicate that the beta-1,3-glucans are very attractive and useful materials not only in biotechnology but also in nanotechnology. These unique properties of the beta-1,3-glucans undoubtedly originate from their inherent, very strong helix-forming character which has never been observed for other polysaccharides.

A new synthetic method for rotaxanes via tandem claisen rearrangement, diesterification, and aminolysis

A novel methodology to make rotaxanes via covalent bond formation has been developed. Rotaxanes composed of crownophanes having two phenolic hydroxy groups as a molecular rotor and an axle having diamide moieties were synthesized in moderate yields via three step processes: tandem Claisen rearrangement, intramolecular diesterification, and aminolysis.

Alternate Layer-by-Layer Adsorption of Single- and Double-Walled Carbon Nanotubes Wrapped by Functionalized β-1,3-Glucan Polysaccharides

A great deal of attention has been focused on exploiting novel methods to fabricate thin carbonaceous capsules from multiple components for advanced materials. A layer-by-layer (LbL) method is therefore being introduced to synthesize thin and multi-carbon nanotube (CNT)-based hollow capsules from CNT complexes with cationic or anionic complementarily functionalized beta-1,3-glucans as building-blocks. These ionic beta-1,3-glucans wrap around single-walled carbon nanotubes (SWNTs) and double-walled carbon nanotubes (DWNTs) to form water-soluble complexes with ionic groups on their exterior surface. Alternate self-assembly of these CNT complexes on the silica particles is demonstrated in solution by electrostatic interactions. The LbL adsorption processes were carefully monitored by zeta-potential measurements, frequency shifts of a quartz crystal microbalance (QCM), and electron micrographs. Silica particles were then dissolved away by HF acid to obtain CNT-based hollow capsules composed of SWNTs and DWNTs. We believe that these novel surface adsorption methods are useful for potential design of CNT-based advanced functional materials.

Single-walled carbon nanotubes acquire a specific lectin-affinity through supramolecular wrapping with lactose-appended schizophyllan.

Single-walled carbon nanotubes can be entrapped within a helical superstructure composed of schizophyllan bearing lactoside-appendages to show an excellent water-solubility as well as a specific lectin-affinity.

β-1,3-Glucan (Schyzophyllan) Can Act as a One-Dimensional Host for Creating Chirally Twisted Poly(p-phenylene Ethynylene)

It has been demonstrated that a chiral, insulated poly(p-phenylene ethynylene) (PPE) nano-wire can be created by a polymer wrapping method utilizing natural β-1,3-glucan polysaccharide schizophyllan (SPG). Spectroscopic and microscopic measurements have revealed that PPE adopts a rigid conformation and exists as one piece in the helical hollow constructed by two SPG chains. Moreover, the inherent helical structure of SPG can induce the chiral twisting of the insulated PPE backbone. It is believed that the present system is really applicable for designing novel chiral sensors based on PPE.

Self-Assembled Polysaccharide Nanotubes Generated from β-1,3-Glucan Polysaccharides

β-1,3-Glucans act as unique natural nanotubes, the featuresof which are greatly different from other natural or synthetic helical polymers. The origin mostly stemsfrom their strong helix-forming nature and reversible interconversion between single-strand random coiland triple-strand helix. During this interconversion process, they can accept functional polymers, molecularassemblies and nanoparticles in an induced-fit manner to create water-soluble one-dimensional nanocomposites,where individual conjugated polymers or molecular assemblies can be incorporated into the one-dimensionalhollow constructed by the helical superstructure of β-1,3-glucans.The advantageous point of the β-1,3-glucan hosting system is thatthe selective modification of β-1,3-glucans leads to the creationof various functional one-dimensional nanocomposites in a supramolecular manner, being applicable towardfundamental nanomaterials such as sensors or circuits. Furthermore, the composites with functional surfacescan act as one-dimensional building blocks toward further hierarchical self-assemblies, leading to the creationof two- or three-dimensional nanoarchitectures.