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Biomedical subjects

K Umemoto

Publications and source records attributed to K Umemoto.

At least 19 recordsLinked to original sources
PubMed2005

Co1-xFexS2: a tunable source of highly spin-polarized electrons.

In the emerging field of spin-electronics ideal ferromagnetic electron sources would not only possess a high degree of spin polarization, but would also offer control over the magnitude of this polarization. We demonstrate here that a simple scheme can be utilized to control both the magnitude and the sign of the spin polarization of ferromagnetic CoS2, which we probe with a variety of techniques. The position of the Fermi level is fine-tuned by solid solution alloying with the isostructural diamagnetic semiconductor FeS2, leading to tunable spin polarization of up to 85%.

Journal Article↗
PubMed2002

Enhanced hydrolytic stability of dental composites by use of fluoroalkyltrimethoxysilanes.

The hydrolytic stability of a group of experimental composite materials was evaluated. Seven distinct composites were formed by the mixing of a resin monomer mixture with silica filler that had been pre-treated with one of 7 different ethanol solutions. In one case, the filler was treated with an ethanol solution that contained only 3-methacryloyloxypropyltrimethoxysilane. In 5 cases, it was treated with solution containing a mixture of 3-methacryloyloxypropyltrimethoxysilane and one of the following hydrophobic fluoroalkyltrimethoxysilanes: trifluoropropyl-, nonafluorohexyl-, tridecafluorooctyl-, heptadecafluorodecyl-, and henicosafluorododecyl-trimethoxysilane. The tensile strength, after being immersed in water for 1800 days, of 2 of the experimental composites, whose pre-treatment regimen had included a fluoroalkyltrimethoxysilane, was significantly higher than that of the composite whose pre-treatment regimen had not included a fluoroalkyltrimethoxysilane. Moreover, there was no significant difference between the tensile strength of fresh samples of these 2 composites and the tensile strength of identically produced samples that had remained under water for 1800 days or that had been subjected to 30,000 cycles of thermal stress.

Absorption↗
PubMed2001

Distance mapping of protein-binding sites using spin-labeled oligosaccharide ligands.

The binding of a nitroxide spin-labeled analog of N-acetyllactosamine to galectin-3, a mammalian lectin of 26 kD size, is studied to map the binding sites of this small oligosaccharide on the protein surface. Perturbation of intensities of cross-peaks in the (15)N heteronuclear single quantum coherence (HSQC) spectrum of full-length galectin-3 owing to the bound spin label is used qualitatively to identify protein residues proximate to the binding site for N-acetyllactosamine. A protocol for converting intensity measurements to a more quantitative determination of distances between discrete protein amide protons and the bound spin label is then described. This protocol is discussed as part of a drug design strategy in which subsequent perturbation of chemical shifts of distance mapped amide cross-peaks can be used effectively to screen a library of compounds for other ligands that bind to the target protein at distances suitable for chemical linkage to the primary ligand. This approach is novel in that it bypasses the need for structure determination and resonance assignment of the target protein.

Amino Sugars↗
PubMed2001

Compositional analysis of copoly (DL-lactic/glycolic acid) (PLGA) by pyrolysis-gas chromatography/mass spectrometry combined with one-step thermally assisted hydrolysis and methylation in the presence of tetramethylammonium hydroxide.

Rapid and precise compositional analysis of copoly (DL-lactic/glycolic acid) (PLGA) was performed by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) combined with one-step hydrolysis and methylation in the presence of tetramethylammonium hydroxide (TMAH). Pyrolysis of PLGA with TMAH gave two characteristic products, derivatives of DL-lactic acid and glycolic acid, which directly reflect the average molar composition of PLGA. The analytical results for PLGA samples with various compositional ratios were in good agreement with those obtained by 1H-NMR spectrometry, and the precision was satisfactory.

Gas Chromatography-Mass Spectrometry↗
PubMed2000

Tripodal peptide hydroxamates as siderophore models. Iron(III) binding with ligands containing H-(alanyl)n-beta-(N-hydroxy)alanyl strands (n = 1-3) anchored by nitrilotriacetic acid.

Combining three units of one of H-(alanyl)n-beta-(HO)alanyl peptides (n = 1-3) with nitrilotriacetic acid affords tripodal peptide hydroxamate ligands (1L, 1D, 2LL, 2DL, and 3LLL, where each L or D denotes the L- or D-alanyl residue). These ligands form six-coordinate octahedral complexes (Fe-1L, Fe-1D, Fe-2LL, Fe-2DL, and Fe-3LLL) with iron(III) in aqueous near neutral pH solution, and the stability and the chirality of the complexes formed depend on the alanyl residues incorporated. Thus Fe-2LL is the most stable against attack of H+ and OH- ions and the least labile in the iron(III) removal by EDTA. The CD spectra show a predominance of the A configuration for Fe-1D, Fe-2LL, Fe-2DL, and Fe-3LLL, but the opposite delta configuration for Fe-1L. These ligands and their gallium(III) complexes are studied by 1H NMR spectroscopy in DMSO-d6 solution. CD and NMR spectral analysis, aided by molecular model examinations, indicates that critical factors in controlling the configuration and the stability of the complexes are (1) the hydroxamate-carrying alanyl residue, (2) the expanse of an interior space in the ligand, and (3) an interstrand amide NH hydrogen bond; the latter bonding is possible with ligands 2LL and 2DL. A microbial growth promotion activity test shows that ligands 1L, 2LL, and 3LLL all act as iron-transporting agents.

Alanine↗
PubMed2000

Determination of residual solvents in bulk pharmaceuticals by thermal desorption/gas chromatography/mass spectrometry.

Thermal desorption (TD) techniques followed by capillary GC/MS were applied for the analysis of residual solvents in bulk pharmaceuticals. Solvents desorbed from samples by heating were cryofocused at the head of a capillary column prior to GC/MS analysis. This method requires a very small amount of sample and no sample pretreatment. Desorption temperature was set at the point about 20 degrees C higher than the melting point of each sample individually. The relative standard deviations of this method tested by performing six consecutive analyses of 8 different samples were 1.1 to 3.1%, and analytical results of residual solvents were in agreement with those obtained by direct injection of N,N-dimethylformamide solution of the samples into the GC. This novel TD/GC/MS method was demonstrated to be very useful for the identification and quantification of residual solvents in bulk pharmaceuticals.

Chemistry, Pharmaceutical↗
PubMed1999

Synthesis and enzymatic degradation of optically active depsipeptide copolymers.

This paper describes the synthesis and biodegradation of copolymers of cyclic depsipeptide with epsilon-caprolactone (CL) or lactide (LA). Optically active cyclic depsipeptides, 3,6-dimethyl-2,5-morpholinediones (DMOs), were prepared by the reaction of an amino acid (D-, L-, or DL-alanine) with a hydroxy acid derivative (DL-2-bromopropionyl bromide). These isomers are abbreviated as D-DMO, L-DMO and DL-DMO respectively, according to the names of alanine isomers. Then, we have prepared the copolymers of DMO isomers with CL using tin(II) octylate as a catalyst. The NMR spectra and thermal properties of DMO/CL copolymers revealed that these copolymers exist randomly. The enzymatic degradation of the copolymers has been examined using Rhizopus delemar lipase, cholesterol esterase (from Pseudomonas sp.), and Proteinase K (from Tritirachium album). Cholesterol esterase and Proteinase K show high degradability, while the lipase shows little degradation. Among the enzymes used, only Proteinase K could recognize the isomerism of DMO, resulting in the following order of degradability: copoly(L-DMO/CL) > copoly(DL-DMO/CL) > copoly(D-DMO/CL), i.e. this enzyme has the highest substrate specificity for naturally occurring L-alanine. Further, we have prepared the random copolymers of L-DMO with lactide (L-LA or DL-LA), and evaluated the enzymatic degradation of the copolymers by Proteinase K. The introduction of a small amount (up to c. 10 mol%) of L-DMO unit into LA homopolymers brought about greater degradability compared with LA homopolymers. In particular, L-DMO/L-LA copolymers with high degradability have been obtained without significant decrease in the mechanical and thermal properties of L-LA homopolymer.

Endopeptidase K↗
PubMed1997

GC rich DNA oligonucleotides with narrow minor groove width.

Investigation of the width of the minor groove using 500 MHz NMR spectroscopy in three closely related 11-mer B-DNA duplexes shows that the minor groove is narrow in a GC rich oligonucleotide, and that a narrow minor groove is not something endemic to DNAs with persistent repetitions of adenine nucleotides (A-tract DNA). The width of the groove is dictated by local sequence contexts and independent of neighboring A-tract DNA.

Base Composition↗
PubMed1997

Basic study of a new denture base resin applying hydrophobic methacrylate monomer.

To improve the water sorption of poly(methyl methacrylate), new hydrophobic monomers, such as norbonyl and phenyl methacrylate, were studied to determine the resin with lower water sorption with no decrease in mechanical property. Water sorption of the copolymers of the hydrophobic monomers and MMA decreased with the increase in the concentration of the monomers. Compressive and bending strength of the copolymers were higher than that of PMMA, and the elastic modulus in bending was the same as that of PMMA. In addition, the transverse-deflection values satisfied ADA specifications. Dynamic mechanical thermal analysis of the copolymers showed a similar tendency to that of PMMA in spite of the introduction of bulky groups, such as norbonyl and phenyl, in the polymer molecule. The polymerization shrinkage in volume was in the following order: norbonyl < phenyl < methyl methacrylate.

Compressive Strength↗
PubMed1996

Presence of poorly stained myocytes in acute myocarditis predicts improvement in cardiac function.

Histological findings in the acute phase of myocarditis were evaluated as a prediction of hemodynamic state in the chronic phase in 20 patients with clinical and pathological diagnoses of myocarditis who were followed up with echocardiography for at least 1 year. Endomyocardial biopsy samples were obtained from the left ventricle within 1 year of the onset of symptoms. Azan-Mallory staining was performed on the myocytes, which were categorized as either well stained or poorly stained. The point counting method was used to determine the fraction of each type. The improvement in ejection fraction within 1 year correlated significantly with the fraction of poorly stained myocytes (r = 0.46, p < 0.05). The ejection fraction at biopsy was negatively correlated with the volume fraction of well stained myocytes (r = -0.64, p < 0.01). The staining condition of myocytes may be useful in predicting the hemodynamic recovery of patients with myocarditis.

Acute Disease↗
PubMed1995

Structural fluctuation of methyl N,N'-diacetyl-beta-D-chitobioside in vacuo and in aqueous solution: molecular dynamics simulations and proton NMR spectroscopy.

Molecular dynamics (MD) simulations of methyl N,N'-diacetyl-beta-D-chitobioside (GlcNAc beta-(1-->4)GlcNAc beta-OMe) have been performed both in vacuo and in aqueous solution with the explicit inclusion of the solvent water molecules. The beta-(1-->4) glycosidic linkage fluctuates considerably, over a range of +/- 10 degrees, in each of the MD simulations in vacuo and in aqueous solution. The intra- and inter-residue hydrogen bonds in vacuo are replaced by intermolecular hydrogen bonds with the solvent water molecules in aqueous solution. Multiple conformations (gg and gt) exist for the exocyclic hydroxymethyl groups. The results of the MD simulations are compared with those of 1H-1H nuclear Overhauser effect measurements.

Carbohydrate Conformation↗
PubMed1995

Effects of mixed silane coupling agent on porcelain tooth material and various dental alloys.

Mixed salines, 3-methacryloxypropylsilytriisocyanate and 3-mercaptopropyltrimethoxysilane, were used as primers for adhesion of poly(methyl methacrylate) to porcelain teeth, precious alloys and nonprecious alloys. After thermocycle testing, the mean bond strength of the resin to porcelain, silver alloys and stainless steel were excellent. The fracture patterns of porcelain teeth after thermocycling followed by adherent testing were similar to those of specimens subjected to 48-hour water immersion at 37 degrees C. Two specimens failed cohesively in the porcelain and the other specimens failed in the resin. The mixed primer had no effect on cobalt-chromium alloy specimens.

Boron Compounds↗
PubMed1994

Familial occurrence of two patients with malignant rheumatoid arthritis.

In Japan, patients with rheumatoid arthritis associated with severe extra-articular manifestations due to vasculitis are diagnosed as having malignant rheumatoid arthritis. We report the occurrence of two cases of malignant rheumatoid arthritis in a Japanese family. Both patients, a father and son, expressed HLA-DR4 (Dw15), and were infected with Epstein-Barr virus. Moreover, the father developed malignant rheumatoid arthritis during reactivation of the Epstein-Barr virus. An unaffected male family member with the same HLA haplotypes was not infected by the virus. The possible role of the virus infection in the pathogenesis of malignant rheumatoid arthritis in a genetically susceptible family is discussed.

Adult↗
PubMed1993

A basic study of a new adhesive lining cement applied emulsion of hydrophobic polymer.

To diminish the effect of water on the adhesive durability of lining cement, an experimental lining cement using a hydrophobic polymer as the cement liquid was studied. The polymers were styrene-butadien-alkyl acrylate copolymer (SBA copolymer) and carboxylated styrene-butadien-alkyl acrylate copolymer (CSBA copolymer) and were used as aqueous emulsions. The cement powder consisted of alkaline silicate and calcium disilicate. The pH values of the immersion water of the cement prepared from emulsion of SBA copolymer (SBA cement) was almost the same as that of calcium hydroxide cement. The compressive and diametral tensile strengths of SBA cement gradually increased over time in water. The bond strengths of cement prepared from the CSBA copolymer emulsion containing five percent carboxyl groups by weight were superior to those of calcium hydroxide cement.

Acrylic Resins↗
PubMed1992

Analysis of differential accumulation of winged bean Kunitz chymotrypsin inhibitor mRNA species by a sequence-specific termination method.

Winged bean Kunitz chymotrypsin inhibitor (WCI) is encoded by a multigene family and accumulation of its mRNA is restricted in mid-maturation stage seeds and tuberous roots. In this paper, we analyzed the accumulation of mRNA derived from each WCI gene using a novel method: sequence-specific termination analysis. The results demonstrated that the accumulation of each WCI mRNA was differentially regulated in winged bean plants.

Base Sequence↗
PubMed1992

Tetraplex formation of d(GGGGGTTTTT): 1H NMR study in solution.

The oligonucleotide d(G5T5) can in principle form a fully matched duplex with G.T pairing and/or a tetraplex. Non-denaturing gel electrophoresis, circular dichroism and NMR experiments show that the tetraplex is exclusively formed by this oligomer in solution. In the presence of its complementary strand d(A5C5) at low temperature, d(G5T5) forms the tetraplex over the normally expected Watson-Crick duplex. However, when d(G5T5) and d(A5C5) are mixed together in equimolar amounts and heated for several minutes at 85 degrees C, and then allowed to cool, the product was essentially the Watson-Crick duplex. The lack of resolution in the 500 MHz 1H NMR spectra and the presence of extensive spin diffusion do not allow us to derive a quantitative structure for the tetraplex from the NMR data. However, we find good qualitative agreement between the NOESY and MINSY data and a theoretically derived stereochemically sound structure in which the G's and T's are part of a parallel tetraplex.

Base Sequence↗