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Biomedical subjects

H Einaga

Publications and source records attributed to H Einaga.

6 recordsLinked to original sources
PubMed2004

Preparation of collagen/calcium phosphate multilayer sheet using enzymatic mineralization.

The multilayer sheets (2-10 layers), which consisted of alternately cumulated collagen and calcium phosphate layers with the thickness of 6-8microm in each layer, were prepared. The inorganic layer was mineralized by means of an alkaline phosphatase-catalyzed hydrolysis of water-soluble phosphate esters in the presence of calcium ions. The calcium phosphate, which was formed on the collagen, was assayed as a mixture of hydroxyapatite (main) and amorphous calcium phosphate. The multilayer sheets were not only strong mechanically but also semitransparent and flexible in a dry state. Furthermore, the collagen/calcium phosphate multilayer sheets did not swell in water to keep the original morphology. As a scaffold, the sheets having the calcium phosphate layer on the top supported the attachment and growth of L929 fibroblast cells. The enzymatic mineralization and the collagen/calcium phosphate composite sheets were discussed in conjunction with physicochemical and biological properties.

Alkaline Phosphatase↗
PubMed2001

Characterization of an NH-pi interaction in Co(III) ternary complexes with aromatic amino acids.

The NH-pi interaction has been detected in the crystal structures of Co(III) ternary complexes with N,N-bis(carboxymethyl)-(S)-phenylalanine (BCMPA) and aromatic amino acids including (S)-phenylalanine ((S)-Phe), (R)-phenylalanine ((R)-Phe), and (S)-tryptophan ((S)-Trp)). Additionally, this interaction has been studied in solution for Co(III) ternary complexes with BCMPA or NTA (NTA = nitrilotriacetic acid) and several amino acids (AA) by means of electronic absorption, circular dichroism (CD), and (1)H NMR spectroscopies. The CD intensities of the Co(III) complexes with aromatic amino acids measured in the d-d region ( approximately 20.5 x 10(3) cm(-)(1)) are significantly decreased in ethanol solutions relative to water. Analogous complexes with aliphatic amino acids do not exhibit this solvent effect. The (1)H NMR spectra of the Co(III) complexes with aromatic amino acids measured in DMSO-d(6) exhibit upfield shifts of the NH peaks compared with those with aliphatic amino acids, which suggest a shielding effect due to the aromaticity. The upshift values coincide with those experimentally evaluated from the crystal structures. The magnitude of the upfield shifts agrees well with Hammett's rule, indicating that the increase of pi-electron densities on the aromatic rings leads attractive NH-pi interaction that exerts a larger shielding effect for the NH protons. In ligand-substitution reactions of the carbonatocobalt(III) complexes with amino acids, the yields of those with aromatic amino acids are higher than the yields obtained for complexes with aliphatic amino acids. This observation is discussed in connection with the important contribution of the NH-pi interaction as one of the promotion factors in the reaction.

Amines↗
PubMed2001

Complete oxidation of benzene in gas phase by platinized titania photocatalysts.

Photocatalytic oxidation of benzene in gas phase was carried out with a flow reactor at room temperature. In a humidified airstream ([H2O] = 2.2%), benzene was quantitatively decomposed to CO2 over UV-irradiated 1.0 wt %-Pt/TiO2 catalyst. When the benzene conversion was decreased, the selectivity to CO2 was decreased, while that to CO was increased. As the amount of Pt loaded on the TiO2 catalyst was increased, the rate of the CO photooxidation was increased, while that of benzene photooxidation was almost unchanged. These findings showed that the photooxidation of benzene to CO2 over Pt/TiO2 catalyst proceeded by the two sequential steps: (i) benzene was decomposed to CO2 and CO with the selectivities of 94% and 6%, respectively, and (ii) CO was subsequently oxidized to CO2. The rate of CO photooxidation over Pt/TiO2 catalyst was greatly decreased by the presence of benzene in the reaction gas stream. The complete oxidation of benzene to CO2 could be also achieved by using the hybrid catalysts comprising pure TiO2 and platinized TiO2.

Benzene↗
PubMed2000

Syntheses, structures, and properties of tetrakis(mu-acetato)dirhodium(II) complexes with axial pyridine nitrogen donor ligands with or without assistance of hydrogen bonds.

Eight adducts of Rh2(O2CCH3)4 with axial pyridine derivatives that contain hydrogen-bonding amino and/or steric methyl substituents in the 2- and 6-positions have been prepared and examined by electronic absorption and 1H NMR spectroscopy in solution and by elemental, IR, thermogravimetric, and X-ray diffraction analyses in the solid state. The results indicated that strong hydrogen bonding interactions between Rh2(O2CCH3)4 and axially coordinated pyridine derivatives with a 2- or 6-amino group occur in both solution and the solid state and contribute to the higher thermal stability of the molecular assembly of dirhodium complexes. It was demonstrated that such a combination of coordinate and hydrogen bonds is useful as a building tool in designing and constructing new organic-inorganic hybridized compounds and supramolecular architectures.

Journal Article↗
PubMed2000

A novel diiron complex as a functional model for hemerythrin.

Diiron(II) complexes with a novel dinucleating polypyridine ligand, N,N,N',N'-tetrakis(6-pivalamido-2-pyridylmethyl)-1,3-diaminopropan-2-ol (HTPPDO), were synthesized as functional models of hemerythrin. Structural characterization of the complexes, [Fe2II(Htppdo)(PhCOO)](ClO4)3 (1), [Fe2II(Htppdo)((p-Cl)PhCOO)](ClO4)3 (2), [Fe2II(Htppdo)((p-Cl)PhCOO)](BF4)3 (2') and [Fe2II(tppdo)((p-Cl)PhCOO)](ClO4)2 (3), were accomplished by electronic absorption, and IR spectroscopic, electrochemical, and X-ray diffraction methods. The crystal structures of 1 and 2' revealed that the two iron atoms are asymmetrically coordinated with HTPPDO and bridging benzoate. One of the iron centers (Fe(1)) has a seven-coordinate capped octahedral geometry comprised of an N3O4 donor set which includes the propanol oxygen of HTPPDO. The other iron center (Fe(2)) forms an octahedron with an N3O3 donor set and one vacant site. The two iron atoms are bridged by benzoate (1) or p-chlorobenzoate (2). On the other hand, both Fe atoms of complex 3 are both symmetrically coordinated with N3O4 donors and two bridging ligands; benzoate and the propanolate of TPPDO. Reactions of these complexes with dioxygen were followed by electronic absorption, resonance Raman and ESR spectroscopies. Reversible dioxygen-binding was demonstrated by observation of an intense LMCT band for O2(2-) to Fe(III) at 610 (1) and 606 nm (2) upon exposure of dioxygen to acetone solutions of 1 and 2 prepared under an anaerobic conditions at -50 degrees C. The resonance Raman spectra of the dioxygen adduct of 1 exhibited two peaks assignable to the nu(O-O) stretching mode at 873 and 887 cm(-1), which shifted to 825 and 839 cm(-1) upon binding of (18)O2. ESR spectra of all dioxygen adducts were silent. These findings suggest that dioxygen coordinates to the diiron atoms as a peroxo anion in a mu-1,2 mode. Complex 3 exhibited irreversible dioxygen binding. These results indicate that the reversible binding of dioxygen is governed by the hydrophobicity of the dioxygen-binding environment rather than the iron redox potentials.

Crystallography, X-Ray↗