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Takuzo Aida

Publications and source records attributed to Takuzo Aida.

At least 55 records · Page 3Linked to original sources
PubMed2004

Tetrafluoroborate salts as site-selective promoters for sol-gel synthesis of mesoporous silica.

Tetrafluoroborate ion (BF(4)(-)) serves as a powerful and better-behaved promoter than fluoride ion (F(-)) for hydrolytic condensation of alkoxysilanes, such as tetraethoxy orthosilicate, in aqueous media containing amphiphiles with onium ion headgroups as templates, affording thermally and hydrothermally stable mesoporous silica. According to (19)F NMR spectral profiles, BF(4)(-) is localized on a positive-charged micellar surface, thereby allowing a site-selective growth of the silica framework. The resulting porous silica has an ordered hexagonal structure with a well-developed and thick silicate wall. Even without calcination, the condensation with BF(4)(-) as the promoter progresses to a large extent to furnish a [Si(OSi-)(4)]/([HOSi(OSi-)(3)] + [(HO)(2)Si(OSi-)(2)]) ratio of 6.2, which is greater than that of mesoporous silica formed without BF(4)(-) before (1.5) and even after calcination (3.5) to promote thermal condensation in the solid state.

Journal Article↗
PubMed2004

Self-assembled hexa-peri-hexabenzocoronene graphitic nanotube.

An amphiphilic hexa-peri-hexabenzocoronene self-assembles to form a pi-electronic, discrete nanotubular object. The object is characterized by an aspect ratio greater than 1000 and has a uniform, 14-nanometer-wide, open-ended hollow space, which is an order of magnitude larger than those of carbon nanotubes. The wall is 3 nanometers thick and consists of helical arrays of the pi-stacked graphene molecule, whose exterior and interior surfaces are covered by hydrophilic triethylene glycol chains. The graphitic nanotube is redox active, and a single piece of the nanotube across 180-nanometer-gap electrodes shows, upon oxidation, an electrical resistance of 2.5 megohms at 285 kelvin [corrected]. This family of molecularly engineered graphite with a one-dimensional tubular shape and a chemically accessible surface constitutes an important step toward molecular electronics.

Journal Article↗
PubMed2004

Selective extraction of higher fullerenes using cyclic dimers of zinc porphyrins.

Higher fullerenes (>/=C76) were selectively extracted from a fullerene mixture obtained from a combustion-based industrial production source by cyclic dimers of beta-unsubstituted porphyrin zinc complexes 2C5-2C7 with C5-C7 alkylene spacers as host molecules. Results of single extraction of the fullerene mixture with 2C5-2C7 together with a beta-substituted analogue of 2C6 (1C6) and spectroscopic titration of 2C6 and 1C6 with C60, C70, and C96 indicated that the host selectivity toward higher fullerenes is much dependent on the structure of the porphyrin units and the size of the host cavity. Sequential three-stage extraction of the fullerene mixture with the best-behaved 2C6 resulted in considerable enrichment in very rare fullerenes C102-C110 (<0.1 abs %) up to 82 abs % (C76-C114, 99 abs %) (356 nm) of total fullerenes.

Journal Article↗
PubMed2004

A condensable amphiphile with a cleavable tail as a "Lizard" template for the sol-gel synthesis of functionalized mesoporous silica.

Use of a dialkoxysilane-containing, condensable alanine amphiphile with a cleavable hexadecyl ester tail (1) as a "lizard" template for sol-gel synthesis results in the formation of a mesoporous silicate (2) whose channels are filled with an organic group of the template. Treatment of 2 with aqueous HCl allows selective cleavage of the ester moiety to leave nanochannels (3) whose surface is densely covered with alanine-CO2H. According to XRD and TEM, 2, on conversion into 3, can preserve its regular hexagonal structure. 3 displays a clear N2 adsorption/desorption isotherm with a BET surface area of 536 m2 g-1. 3 can also adsorb a basic guest such as NH3 up to 0.7 mmol g-1, which is 7 times greater than that observed for mesoporous silica obtained by calcination of 2.

Journal Article↗
PubMed2004

Chiroptical transcription of helical information through supramolecular harmonization with dynamic helices.

With biologically important "peptide bundling" as the motif, new chromophoric cyclic host 1 was designed, which consists of two zinc porphyrin units that are connected by dynamic peptide helices of nonameric aminoisobutyric acid (Aib) units. Upon inclusion of pyridine-anchored helical peptides between the zinc porphyrin units, 1 displayed an intense exciton-coupled circular dichroism (CD) band at 410-450 nm, whose sign reflected the helical sense of the guest peptides. Studies with conformationally defined dehydrophenylalanine-containing analogues indicated that the dynamic helical chains in the host are stereochemically harmonized with right- or left-handed helices of the guest peptides in a confined nano space, leading to either clockwise- or anticlockwise-twisted geometry (chiroptical output) of the connecting zinc porphyrin chromophores.

Aminoisobutyric Acids↗
PubMed2004

Bioinspired molecular design of light-harvesting multiporphyrin arrays.

Recent progress in fundamental studies on multiporphyrin arrays has provided structural parameters for the molecular design of artificial light-harvesting antennae which mimic the wheel-like antenna complexes of photosynthetic purple bacteria. Covalent and noncovalent approaches have been employed for the construction of artificial light-harvesting multiporphyrin arrays. Such arrays are categorized into ring-shaped, windmill-shaped, star-shaped, and dendritic architectures. In particular, dendritic multiporphyrin arrays have been proven to be promising candidates for both providing a large absorption cross-section and enabling the vectorial transfer of energy over a long distance to a designated point. Such molecular and supramolecular systems are also expected to be potent components for molecular electronics and photonic devices.

Journal Article↗
PubMed2003

A novel supramolecular multicolor thermometer by self-assembly of a pi-extended zinc porphyrin complex.

A zinc complex of (3-pyridyl)porphyrin with an alkynyl sidearm (1) preferentially formed a cyclic tetramer in toluene, which showed supramolecular thermochromism at ambient temperatures of 0-100 degrees C. Because of an appropriate extension of pi-electronic conjugation of the porphyrin chromophore, the thermal-induced self-assembling dynamics of 1 can be detected as a vivid color change from red to yellow to green. In sharp contrast, 2 without any alkynyl group, on heating, developed only a small color change from orange to pink, while 3 bearing two alkynyl groups stayed green and did not display any thermochromism.

Journal Article↗
PubMed2003

Polyion complex micelles entrapping cationic dendrimer porphyrin: effective photosensitizer for photodynamic therapy of cancer.

Photosensitizers play a crucial role in the photodynamic therapy (PDT) of cancer. In this study, a third-generation aryl ether dendrimer porphyrin with 32 primary amine groups on the periphery, [NH2CH2CH2NHCO]32DPZn, and pH-sensitive, polyion complex micelles (PIC) composed of the porphyrin dendrimer and PEG-b-poly(aspartic acid), were evaluated as new photosensitizers (PSs) for PDT in the Lewis Lung Carcinoma (LLC) cell line. The preliminary photophysical characteristics of [NH2CH2CH2NHCO]32DPZn and the corresponding micelles were investigated. Electrostatic assembly resulted in a red-shift of the Soret peak of the porphyrin core and the enhanced fluorescence. Compared to the dendrimer porphyrin [NH2CH2CH2NHCO]32DPZn, relatively low cellular uptake of dendrimer porphyrin [NH2CH2CH2NHCO]32DPZn incorporated in the PIC micelle was observed, yet the latter exhibited enhanced photodynamic efficacy on the LLC cell line. Importantly, the use of PIC micelles as a delivery system reduced the dark toxicity of the cationic dendrimer porphyrin, probably due to the biocompatible PEG shell of the micelles.

Animals↗
PubMed2003

Switching of spin states triggered by a phase transition: spin-crossover properties of self-assembled iron(II) complexes with alkyl-tethered triazole ligands.

Iron(II) complexes of triazole derivatives having two C12 and C16 long alkyl chains, (C12trz)FeII and (C16trz)FeII, serve as novel spin-crossover materials, which display a spin-state transition in response to a phase transition. In contrast, a triazole complex with two C8 alkyl chains ((C8trz)FeII) exhibits only a poor response. EXAFS and XRD analyses of (C16trz)FeII indicate an interdigitating self-assembled structure of polynuclear iron(II) species. According to DSC, VT-IR, and VT-XRD profiles, the spin-state transition is triggered by melting of the interdigitating alkyl chains, which is likely responsible for the "lock-and-release" feature of the spin state. By virtue of the thermoreversibility of the phase transition, the spin crossover could be repeated without deterioration.

Journal Article↗
PubMed2003

Supramolecular peapods composed of a metalloporphyrin nanotube and fullerenes.

An acyclic dimer of a dendritic zinc porphyrin bearing six carboxylic acid functionalities (1acid) interacts with fullerenes, such as C60 and C70, to form "supramolecular peapods", composed of a hydrogen-bonded zinc porphyrin nanotube and fullerenes (3). According to TEM, the peapods are very long (>1 mum) and have a uniform diameter of 15 nm. Without fullerenes, the zinc porphyrin dimer forms only a heavily entangled, irregular assembly. In contrast with 1acid, an ester version of the acyclic dimer without hydrogen-bonding capability (1ester) hardly interacts with fullerenes.

Journal Article↗
PubMed2003

Characteristics of organic transformations in a confined dendritic core: studies on the AIBN-initiated reaction of dendrimer cobalt(II) porphyrins with alkynes.

Cobalt(II) complexes of poly(aryl ester) dendrimer porphyrins [(m-[Gn]TPP)Co(II)] (generation number n=0-4), in the presence of azobisisobutyronitrile (AIBN) at 60 degrees C, underwent alkenylation with several alkynes at the metal center. A complete inhibition of double-bond migration (secondary transformation) was observed for [(m-[Gn]TPP)Co(II)] (n=3 and 4), which gave [(m-[Gn]TPP)Co(III)-C(=CH(2))R] (n=3 and 4) exclusively. Overall reaction rates for [(m-[Gn]TPP)Co(II)] (n=0-3) were hardly dependent on the size of the dendritic substituents, while a notable retardation was observed for the largest dendrimer, [(m-[G4]TPP)Co(II)]. Mechanistic studies on double-bond migration with pure [(m-[Gn]TPP)Co(III)-C(=CH(2))Bu] (n=0-4) demonstrated that the secondary transformation involves participation of [(m-[Gn]TPP)Co(III)H] (n=0-4), derived from [(m-[Gn]TPP)Co(II)] and AIBN, rather than [(m-[Gn]TPP)Co(II)] alone. Crossover experiments using [(m-[Gn]TPP)Co(III)-C(=CH(2))Bu] (n=2-4), in combination with nondendritic [(m-[G0]TPP)Co(II)] and AIBN, indicated a high level of steric protection of the active center by a robust [G4]-dendritic cage, as suggested by a (1)H NMR pulse relaxation time profile of m-[G4]TPPH(2).

Alkynes↗
PubMed2003

Molecular ordering of organic molten salts triggered by single-walled carbon nanotubes.

When mixed with imidazolium ion-based room-temperature ionic liquid, pristine single-walled carbon nanotubes formed gels after being ground. The heavily entangled nanotube bundles were found to untangle within the gel to form much finer bundles. Phase transition and rheological properties suggest that the gels are formed by physical cross-linking of the nanotube bundles, mediated by local molecular ordering of the ionic liquids rather than by entanglement of the nanotubes. The gels were thermally stable and did not shrivel, even under reduced pressure resulting from the nonvolatility of the ionic liquids, but they would readily undergo a gel-to-solid transition on absorbent materials. The use of a polymerizable ionic liquid as the gelling medium allows for the fabrication of a highly electroconductive polymer/nanotube composite material, which showed a substantial enhancement in dynamic hardness.

Journal Article↗
PubMed2003

Chaperonin-mediated stabilization and ATP-triggered release of semiconductor nanoparticles.

Various properties of semiconductor nanoparticles, including photoluminescence and catalytic activity, make these materials attractive for a range of applications. As nanoparticles readily coagulate and so lose their size-dependent properties, shape-persistent three-dimensional stabilizers that enfold nanoparticles have been exploited. However, such wrapping approaches also make the nanoparticles insensitive to external stimuli, and so may limit their application. The chaperonin proteins GroEL (from Escherichia coli) and T.th ('T.th cpn', from Thermus thermophilus HB8) encapsulate denatured proteins inside a cylindrical cavity; after refolding, the encapsulated proteins are released by the action of ATP inducing a conformational change of the cavity. Here we report that GroEL and T.th cpn can also enfold CdS semiconductor nanoparticles, giving them high thermal and chemical stability in aqueous media. Analogous to the biological function of the chaperonins, the nanoparticles can be readily released from the protein cavities by the action of ATP. We expect that integration of such biological mechanisms into materials science will open a door to conceptually new bioresponsive devices.

Adenosine Diphosphate↗