Supramolecular Science最新文献

Small and large unilamellar biotinylated liposomes (SUVs and LUVs) composed of egg phosphatidylcholine and 2 mol% of biotinylated phosphatidylethanolamine were assembled in the presence of avidin at a low concentration (0.05–0.1 mg ml^-1) and simultaneously immobilized in fused-silica capillary tubing. LUV assemblies were immobilized to 21 nmol phospholipid in one capillary, about twice as high as found for the SUV assemblies. Estimated values showed that the capillary inner surface was coated by 4–15 liposome layers. The liposome-coated capillary can be used in capillary electrophoresis for microanalysis of drug-membrane interactions. This avidin–biotin-assembly method may also be applied to immobilize liposomes or proteoliposomes in a high order on a planar solid surface for construction of biomaterials.

A novel C₆₀ pyrrolidine derivative, C₆₀(C₈H₁₅NO₂) (1), has been synthesized and its Langmuir and LB films were investigated. The monolayer of 1 can be transferred on to hydrophilic substrates. Photocurrent generation of the LB film modified ITO electrode has been measured. The anodic photocurrent can be suppressed by oxygen and enhanced by the electron donor Vc (ascorbic acid). The quantum yield is 1.9% with the concentration of Vc at 0.5 mg ml^-1 in the KCl solution.

The effects of macromolecules as soluble additives and solid matrices have been examined for the crystallization of CaCO₃. A vaterite form grows on a glass substrate in the presence of poly(glutamic acid) (PGA) containing a carboxylic acid group as a soluble additive. In contrast, no crystal growth has been observed when poly(acrylic acid) (PAA) exists as an additive though it has the same functional group. The conformation or the backbone structure of the polymers may have an influence on the crystal polymorph of CaCO₃. Thin film states of CaCO₃ crystals have been obtained as organic/inorganic composites with chitosan that acts as a solid matrix in the presence of PAA or PGA as a soluble additive.

Photopolymerizations of intercalated 4-vinylbenzoate (VBA) and p-(or m-) phenylenediacrylates (PDA) were investigated in the presence of an anion exchange clay, hydrotalcite. UV irradiation of clay powder adsorbing VBA and 4-benzoylbenzoate (BBA) ions gave rise to the cyclodimerization of the olefin and a radical polymerization to form polyvinylbenzoate. The degree of the polymerization was 10–10³. The stereoregularity was investigated by NMR analysis and is discussed in relation to the state of molecular aggregation in the clay interlayers. In contrast to VBA, photoreaction of the intercalated PDAs resulted in the formation of oligomers in [2+2] cycloaddition manner, of which the polymerization degrees were rather low (up to ten at most). The stereochemistry of the oligomer was revealed to be of a syn-head-to-head structure by NMR analysis. Dianionic molecules such as PDAs showed an interesting intercalation behavior in contrast to monoanions, i.e. just one double-negatively charged molecule was estimated to occupy three anion exchange sites of the hydrotalcite layer. Also, the relatively low polymerization degrees of the PDAs were found to be due to the above intercalation characteristics. Powder X-ray diffraction analysis showed that the molecular aggregation state was remarkably changed by desiccating the clay composite in vacuum, thus suppressing the efficiency of the photoreaction.

Polymeric receptors for cholesterol were synthesized by crosslinking β-cyclodextrin (β-CyD) with hexamethylene diisocyanate or toluene 2,4-diisocyanate in dimethyl sulfoxide (DMSO) in the presence of cholesterol as the template. Non-imprinted β-CyD polymers were much poorer in the cholesterol adsorption. When β-CyD was cross-linked by epichlorohydrin in aqueous alkaline solutions (even in the presence of cholesterol), the cholesterol adsorbing activity was nil. Use of DMSO as the cross-linking solvent is necessary for the imprinting, since β-CyD molecules form inclusion complexes with cholesterol in this solvent and thus their mutual conformation in the polymer is regulated appropriately for cholesterol binding. The adsorbed cholesterol was completely removed from the polymers by treating the adducts with ethanol, indicating a strong potential for practical applications.

Electron beam lithography was investigated using a cross-linkable polymer Langmuir–Blodgett (LB) film. Cross-linking reaction occurs in the LB film with electron beam irradiation as well as UV light irradiation and the irradiated LB film becomes insoluble in the organic solvents to form a two-dimensional network in the LB film. The sensitivity and contrast of the cross-linkable polymer LB film are 3 μC cm^-2 and 0.64, respectively. The limiting resolution of patterning is 0.2 μm line-and-space. The electron beam lithography using the cross-linkable polymer LB film is applicable to the future nanotechnology.

Magnetotactic bacteria orient and migrate along magnetic field lines. This ability is based on a submicron assembly of single-magnetic domain iron mineral particles that elegantly solves the problem of how to construct a magnetic dipole that is large enough to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized cell. The solution is based on the ability of the bacteria to accumulate high concentrations of iron, and control the deposition, size and orientation of a specific iron mineral at specific locations in the cell.

Organic photochromic units and molecules can be regarded as light-driven nano molecular machines. Once such molecules are aligned at a surface, the supramolecular organization provides an efficient macroscopic mechanical response in a collective way. Amphiphilic polymers having an azobenzene (Az) side chain are the favorable materials for observation of such effects since they show marked photomechanical response with essentially full reversibility. An in situ Brewster angle microscopic observation showed marked morphological and rheological photoinduced changes in the molecular films. Moreover, we have newly found that the identical photosensitive molecular film transferred on to a solid mica surface shows large morphological changes under highly humid conditions as proven by atomic force microscopy (AFM). It is supposed that the molecular film is driven in the same mechanism both on water and water-adsorbed mica surfaces. These microscopic observations provide new insights of the photomechanical response in photochromic monolayers.

This paper reviews our recent progress in synthesis, optical properties and reassembling behaviour of nanosheet-crystallites of quasi-TiO₂. Processing to thin anatase flakes from them is also presented. The colloidal nanosheets were synthesized by soft-chemically exfoliating a layered protonic titanate of $\text{H}{}_{\mathrm{x}}\text{Ti}{}_{\mathrm{2-x/4}}\text{□}{}_{\mathrm{<mtext>x</mtext><mtext>/4</mtext>}}\text{O}{}_4\text{·}\text{H}{}_2\text{O}$ (x∼0.7, □: vacancy). The action of bulky quarternary alkylammonium ion in large excess induced osmotic swelling involving Δd>3 nm. Lowering the dose of the electrolyte promoted further interlayer expansion leading to delamination into elementary host layers. The resulting nanosheets exhibited a sharp UV-visible absorption band which is considerably blue-shifted compared to bulk TiO₂. These distinct features and a well-structured photoluminescence may be interpreted as a reflection of their molecular nature. Slow drying of the colloids brought about spontaneous reassembling of the nanosheets, which was initiated by association of a limited number of the nanosheets with a very large intersheet spacing of >10 nm and finally yielded a well-ordered lamellar structure. Freeze-drying of the suspension produced the lamellar phase in an open microstructure which can be converted into thin flaky particulates of anatase tens nanometers thick. The material, an assembly of the flakes, possessed a high specific surface area (40–110 m² g^-1) associated with mesopores.

Ordered mesoporous silicas with spherical morphology and average particle size in the range between 100 nm and 2 μm were synthesised according to two novel routes. Both synthesis routes used tetraethoxysilane, water, alcohol and aqueous ammonia for producing spherical silica beads. The porosity was created by adding two different kinds of pore structure directing agents to the starting solution: one was an n-alkyltrialkoxysilane which was covalently bonded to the silica framework, the other was an n-alkylamine which acted as a nonionic template. After calcination and post treatment the resulting particles showed a specific surface area up to 1000 m² g^-1, a specific pore volume of up to 0.8 cm³g^-1 and an average pore diameter between 2 and 6 nm.