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Biomedical subjects

Akira Harada

Publications and source records attributed to Akira Harada.

At least 19 recordsLinked to original sources
PubMed2007

Preparation and properties of rotaxanes formed by dimethyl-beta-cyclodextrin and oligo(thiophene)s with beta-cyclodextrin stoppers.

Novel cyclodextrin rotaxanes with oligothiophene as an axis molecule have been prepared by the Suzuki coupling reaction of 6-O-(4-iodophenyl)-beta-CD (6-I-Ph-beta-CD) with di(1,3,2-dioxaborolan-2-yl)-oligothiophene (oligothiophene diboric ethylene glycol esters) in aqueous solutions of dimethyl-beta-cyclodextrin (DM-beta-CD). These reactions gave [2]rotaxanes and [3]rotaxanes, which were isolated by reversed phase chromatography. The fluorescence intensities of rotaxanes are higher than those of dumbbell-shaped molecules (without DM-beta-CD) in aqueous solutions. The inclusion ratio and chain length of rotaxanes have been found to relate to the emission properties and emission intensities of oligothiophene. In aqueous solutions, fluorescence quantum yields of rotaxanes are higher than those of dumbbell-shaped molecules. The increase in the fluorescence efficiency of rotaxane is caused by suppression of intermolecular interactions, indicating the effect of insulated oligothiophene with DM-beta-CD. beta-CD at the both ends of rotaxanes functions not only as bulky stoppers but also as the recognition site for guest molecules, as verified by fluorescence quenching experiments.

Journal Article↗
PubMed2006

Solvation and dynamic behavior of cyclodextrins in dimethyl sulfoxide solution.

High-frequency dielectric relaxation behavior up to 20 GHz was investigated for plain (alpha, beta, gamma) and (62 and 100%) methylated cyclodextrins, CDs, in dimethyl sulfoxide, DMSO, solution. Each hydrogen atom of OH groups of the CDs solvated a DMSO molecule for a residence time of 130-180 ps due to the hydrogen bond formation to an oxygen atom of DMSO, and a few DMSO molecules were included in cavities of the CDs for a while similar to the residence time. The overall rotational relaxation modes of solvated CDs were also observed depending on the effective sizes of the solvated CDs.

Chemistry, Physical↗
PubMed2006

Asymmetric hydrogenation with antibody-achiral rhodium complex.

Monoclonal antibodies have been elicited against an achiral rhodium complex and this complex was used in the presence of a resultant antibody, 1G8, for the catalytic hydrogenation of 2-acetamidoacrylic acid to produce N-acetyl-L-alanine in high (>98%) enantiomeric excess.

Amino Acids↗
PubMed2006

Selection between pinching-type and supramolecular polymer-type complexes by alpha-cyclodextrin-beta-cyclodextrin hetero-dimer and hetero-cinnamamide guest dimers.

Novel supramolecular complexes have been prepared from an alpha-cyclodextrin-beta-cyclodextrin hetero-dimer (alpha-CD-beta-CD hetero-dimer) and hetero-cinnamamide guest dimers, G-t-Boc and G-NH2, having adamantyl groups in aqueous solutions. On addition of the competitive guest, the supramolecular structure formed by a mixture of the alpha-CD-beta-CD hetero-dimer and G-t-Boc was found to be different from that of a mixture of the alpha-CD-beta-CD hetero-dimer and G-NH2 by the 1H NMR spectroscopy, the ROESY NMR spectroscopy, and the circular dichroism spectroscopy. The size of the supramolecular complex from the mixture of the alpha-CD-beta-CD hetero-dimer and G-NH2 is larger than that from the mixture of the alpha-CD-beta-CD hetero-dimer and G-t-Boc, which was proved by the pulse field gradient spin-echo NMR and the atomic force microscopy. These results suggest that the mixture of the alpha-CD-beta-CD hetero-dimer and G-t-Boc formed a pinching-type complex, and the mixture of the alpha-CD-beta-CD hetero-dimer and G-NH2 formed a supramolecular polymer-type complex.

Cinnamates↗
PubMed2006

Contrast viscosity changes upon photoirradiation for mixtures of poly(acrylic acid)-based alpha-cyclodextrin and azobenzene polymers.

Polymer-polymer interactions were investigated for mixtures of a poly(acrylic acid) (pAA) carrying azobenzene (pC12Azo) and two kinds of pAA carrying alpha-cyclodextrin (CD), in which CDs are attached to the main chain through the 3- and 6-positions in CD (p3alphaCD and p6alphaCD, respectively), using several techniques, such as viscosity and NMR measurements. Viscosity data exhibited contrast changes upon UV irradiation: thinning (p3alphaCD/pC12Azo) and thickening (p6alphaCD/pC12Azo). NOESY spectra confirmed that the contrast viscosity changes were ascribable to differences in how CD moieties interact with pC12Azo after photoisomerization of azobenzene moieties from trans to cis: dissociation of inclusion complexes (p3alphaCD/pC12Azo) and formation of interlocked complexes (p6alphaCD/pC12Azo).

Acrylic Resins↗
PubMed2005

Kinetic control of threading of cyclodextrins onto axle molecules.

We report here, for the first time, kinetic control of the face-direction of cyclodextrin (CD) in the construction of a pseudo-rotaxane with an alkyl chain bearing pyridyl end caps. The yields of complexes of CDs with guest alkyl derivatives were controlled by the simple change of the position and the number of methyl groups bound to the pyridyl moiety. Single-substituted pyridyl groups attached to the ends of the alkyl chain regulated the rate for CDs passing them. Two methyl substituents could clearly govern the degree of complex formation of CD with guest molecules and resulted in the distinction of face-direction of CD molecules entering the gates at guest ends.

Journal Article↗
PubMed2005

Chiral supramolecular polymers formed by host-guest interactions.

alpha-Cyclodextrin with a p-t-butoxyaminocinnamoylamino group in the 3-position (3-p-(t)()BocCiNH-alpha-CD) has been found to form a supramolecular polymer in an aqueous solution. The degree of polymerization of the supramolecular polymer is higher than 15 at 20 mM, as proved by VPO (vapor pressure osmometry) measurements and turbo ion spray TOF MS measurements. The existence of substitution/substitution interactions between adjacent monomers of the supramolecular polymer have been confirmed by the observation of positive and negative Cotton bands in circular dichroism spectra. The mechanism for the induction of the chirality was confirmed using model compounds. The substituents were found to exist as a left-handed anti configuration in supramolecular polymers. The supramolecular polymer was found to take a helical structure. The structure of the supramolecular polymer was observed by STM measurements.

Journal Article↗
PubMed2005

A [2]rotaxane capped by a cyclodextrin and a guest: formation of supramolecular [2]rotaxane polymer.

A [2]rotaxane capped by a beta-cyclodextrin and a 2,4,6-trinitrophenyl group has been prepared by dissolving 6-aminocinnamoyl beta-cyclodextrin in water with 1-adamantane carboxylic acid and complexation with alpha-cyclodextrin followed by the reaction with 2,4,6-trinitrobenzene sulfonic acid sodium salt. The [2]rotaxane has been found to form supramolecular polymers by host-guest interactions.

Journal Article↗
PubMed2004

Peroxidase activity of cationic metalloporphyrin-antibody complexes.

Peroxidase activity of a complex of water-soluble cationic metalloporphyrin with anti-cationic porphyrin antibody is reported. Antibody 12E11G, which was prepared by immunization with a conjugate of 5-(4-carboxyphenyl)-10,15,20-tris(4-methylpyridyl)porphine iodide (3MPy1C), bound to tetramethylpyridylporphyrin iron complex (FeIII-TMPyP) with the dissociation constant of 2.6 x 10(-7) M. The complex of antibody 12E11G with FeIII-TMPyP catalyzed oxidation of pyrogallol, catechol, and guaiacol. A Lineweaver-Burk plot for the oxidation of pyrogallol catalyzed by the FeIII-TMPyP-antibody complex showed Km=8.6 mM and kcat=680 min(-1). Under the same conditions, Km and kcat for horseradish peroxidase (HRP) were 0.8 mM and 1750 min(-1), respectively. Although the binding interaction of the antibody to the substrates was one order lower than that of native HRP, the peroxidase activity of this system was in the same order of magnitude as that of HRP.

Antibodies, Monoclonal↗
PubMed2004

Construction of supramolecular polymers with alternating alpha-, beta-cyclodextrin units using conformational change induced by competitive guests.

Supramolecular polymers having alternating alpha- and beta-cyclodextrin (CD) units have been prepared by using conformational change induced by competitive guests. Although each CD unit does not form intermolecular complexes, a mixture of an alpha-CD derivative and a beta-CD derivative formed intermolecular complexes to give supramolecular polymers having alternating CD units. This is the first example of construction of supramolecular polymers with alternating alpha-, beta-cyclodextrin units.

Biomimetic Materials↗
PubMed2003

Formation process of cyclodextrin necklace-analysis of hydrogen bonding on a molecular level.

By means of scanning tunneling microscopy (STM), we succeeded for the first time in the quantitative analysis of the intramolecular conformation of a supramolecule, cyclodextrin (CyD) necklace, driven by hydrogen bonding. Contrary to the current model, based on macroscopic analyses, which indicates that all CyDs are arranged in head-to-head or tail-to-tail (secondary-secondary or primary-primary hydrogen bonding) conformation, about 20% head-to-tail (primary-secondary hydrogen bonding) conformation was found to exist in the molecule. In addition, comparing the STM results with the theoretical model of the necklace formation, the formation ratio of the tail-to-tail and head-to-tail conformations due to the strength difference between primary-primary and primary-secondary hydrogen bonds of CyDs was directly obtained, for the first time, to be 2:1.

Journal Article↗