Kouta Sugikawa

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.

Porphyrin-uptake in liposomes and living cells using an exchange method with cyclodextrin

The water-solubilisation of porphyrin derivatives is very important for biological applications. Although liposomal drug carriers for porphyrin derivatives have shown significant promise in the field of medicinal chemistry (e.g., as sensitisers for photodynamic therapy), it is currently not possible to prepare lipid-membrane-incorporated tetraphenylporphyrin (TPP) with a high concentration of TPP using conventional methods. In this study, we have succeeded in preparing lipid-membrane-incorporated TPP and zinc(II) tetraphenylporphyrin (ZnTPP) from the corresponding TPP or ZnTPP·cyclodextrin complex using the exchange method in lipid-membranes composed of liposomes. Furthermore, the exchange method allowed for the incorporation of TPP or ZnTPP into the plasma membranes of HeLa cells. However, it was not possible to prepare lipid-membrane-incorporated porphyrin derivatives with polar and hydrophilic groups in the meso positions using this exchange reaction.

Anisotropic Self-Assembly of Citrate-Coated Gold Nanoparticles on Fluidic Liposomes.

The behavior of self-assembly processes of nanoscale particles on plasma membranes can reveal mechanisms of important biofunctions and/or intractable diseases. Self-assembly of citrate-coated gold nanoparticles (cAuNPs) on liposomes was investigated. The adsorbed cAuNPs were initially fixed on the liposome surfaces and did not self-assemble below the phospholipid phase transition temperature (Tm ). In contrast, anisotropic cAuNP self-assembly was observed upon heating of the composite above the Tm, where the phospholipids became fluid. The number of self-assembled NPs is conveniently controlled by the initial mixing ratio of cAuNPs and liposomes. Gold nanoparticle protecting agents strongly affected the self-assembly process on the fluidic membrane.

Photodynamic Activities of Porphyrin Derivative–Cyclodextrin Complexes by Photoirradiation

Water-soluble cyclodextrin (CyD) complexed with porphyrin derivatives with different substituents in the meso-positions showed different photodynamic activities toward cancer cells under illumination at wavelengths over 600 nm, the most suitable wavelengths for photodynamic therapy (PDT). In particular, aniline- and phenol-substituted derivatives had high photodynamic activity because of the efficient intracellular uptake of the complexes by tumor cells. These complexes showed greater photodynamic activity than photofrin, currently the main drug in clinical use as a photosensitizer. These results represent a significant step toward the optimization of porphyrin derivatives as photosensitizers.

Reversible Vesicle-to-Disk Transitions of Liposomes Induced by the Self-Assembly of Water-Soluble Porphyrins

Structural control of lipid membranes is important for mechanisms underlying biological functions and for creating high-functionality soft materials. We demonstrate the reversible control of vesicle structures (liposomes) using supramolecular assemblies. Specifically, water-soluble anionic porphyrin molecules interact with positively charged lipid membrane surfaces to form one-dimensional self-assembled structures (J-aggregates) under acidic conditions. Cryogenic transmission electron microscopy revealed that porphyrin J-aggregates on the membrane surface induced an extensive structural change from vesicles to layered disks. Neutralization of the solution deformed the porphyrin J-aggregates, thereby reforming nanosized liposomes from the layered disks.

Formation of lipid membrane-incorporated small π-molecules bearing hydrophilic groups

Nineteen poorly water-soluble π-conjugated molecules were evaluated in terms of their ability to be stably incorporated into lipid membranes. The resulting lipid membrane-incorporated π-conjugated guest molecules (LMIGs) were classified into four categories, including (i) those that formed stable LMIGs; (ii) those where some of the guest molecules precipitated; (iii) those that formed small self-aggregates consisting of lipids and/or guest molecules; and (iv) those that leaked some of the guest molecules into the bulk water. Compounds belonging to category (ii) were confirmed by UV-vis absorption analysis. In contrast, compounds belonging to categories (i), (iii) and (iv) were discriminated based on their 1H NMR spectra and the broadening or disappearance of the peaks of the guest molecules and the lipids in LMIGs and large liposomes. Several LMIGs could be converted from one category to another using other lipids. Furthermore, the guest molecules belonging to category (iv) were successfully predicted using the octanol–water partition coefficient, which was calculated by simulation.

Size controlled fullerene nanoparticles prepared by guest exchange of γ-cyclodextrin complexes in water

Fullerene nanoparticles (nCx; x = 60 or 70) with a monodisperse size and morphology are obtained through guest exchange of a γ-cyclodextrin (γ-CD) complex. The size of nCx could be controlled by changing the initial concentration of the Cx–γ-CD complexes.

Liposome collapse resulting from an allosteric interaction between 2,6-dimethyl-β-cyclodextrins and lipids

Although heptakis(2,6-di-O-methyl)-β-cyclodextrin (DMe-β-CDx) has been reported to exhibit higher cytotoxicity than many other cyclodextrins because of the way in which it abstracts cholesterols from liposomes, we have identified another reason for its cytotoxicity based on its interaction with lipids. These interactions exhibited nonlinear sigmoidal responses with Hill coefficient values (n) in the range of 3.0–3.6, which indicated that this phenomenon involves positive allosterism. Furthermore, analysis by mass spectroscopy revealed that the lipid–DMe-β-CDx complexes had stoichiometric ratios in the range of 1 : 1–1 : 4.

Stepwise Growth of Fullerene Nanoparticles through Guest Exchange of γ-Cyclodextrin Complexes in Water

Stepwise growth of fullerene nanoparticles (nCx ; x=60 or 70) was performed through guest exchange of a γ-cyclodextrin (γ-CD) complex. Fullerenes bicapped by γ-CD were mixed with presynthesized nCx in the presence of poly(ethylene glycol) (PEG) in water. Fullerenes expelled from the γ-CD hosts by PEG were piled on the original nCx , resulting in growth of nCx . This process could be repeated and the size of nCx increased according to the number of growth steps. The growth of fullerene nanoparticles was confirmed by UV/Vis absorption spectroscopy, dynamic light scattering measurements, and TEM observations. The stepwise growth method also enabled the preparation of C60 /C70 core/shell fullerene nanoparticles, which had the ability to photogenerate active oxygen, 1 O2 .

Water Solubilization of Fullerene Derivatives by β-(1,3-1,6)-d-Glucan and Their Photodynamic Activities toward Macrophages

Anionic and neutral fullerene derivatives were dissolved in water by using β-(1,3-1,6)-d-glucan (β-1,3-glucan) as a solubilizing agent. In the water-solubilized complexes, the concentrations of fullerene derivatives were ≈0.30 mm and the average particle sizes were ≈90 nm. The β-1,3-glucan-complexed fullerene derivative with a carboxylic acid was found to have higher photodynamic activity toward macrophages under visible-light irradiation (λ>610 nm) than other β-1,3-glucan-complexed fullerene derivatives. This result suggests that carboxylic acid moieties in the complex enhance the binding affinity with β-1,3-glucan receptors on the surface of macrophages when the β-1,3-glucan is recognized. In contrast, all β-1,3-glucan-complexed fullerene derivatives showed no photodynamic activity toward HeLa cells under the same conditions.