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Biomedical subjects

A Fujishima

Publications and source records attributed to A Fujishima.

At least 37 records · Page 2Linked to original sources
PubMed2001

Pyloricidins, novel anti-Helicobacter pylori antibiotics produced by bacillus sp. II. Isolation and structure elucidation.

Novel anti-Helicobacter pylori antibiotics, pyloricidins A, A1, A2, B, C and D were isolated from Bacillus sp. HC-70 and Bacillus sp. HC-72 by column chromatographies using adsorption and ion exchange resins. Their structures have been elucidated based on spectroscopic and degradation studies and shown to be peptide-like compounds. These compounds contained two unusual amino acids, viz., 5-amino-2,3,4,6-tetrahydroxyhexanoic acid and 3-amino-3-phenylpropionic acid (beta-phenylalanine). The structure-activity relationship studies suggested that 3-(5-amino-2,3,4,6-tetrahydroxyhexanoyl)amino-3-phenylpropionic acid moiety was essential for anti-H. pylori activity.

Amino Acids↗
PubMed2000

Electron transfer from diamond electrodes to heme peptide and peroxidase.

Direct electron transfer from boron-doped diamond electrodes to heme undecapeptide and horseradish peroxidase (HRP) was examined and evaluated for the application to H2O2 biosensors. As-grown and oxygen plasma-treated diamond electrodes on which heme peptide is adsorbed exhibited cathodic current responses to H2O2 on the basis of the direct electron transfer. In a comparative study of carbon electrodes on which heme peptide was adsorbed, an oxygen plasma-treated diamond electrode exhibited responses comparable with those of an edge-oriented pyrolytic graphite (EOPG) electrode, despite much smaller roughness. However, electron transfer to compounds I and II of HRP from the diamond electrodes was much slower than that from EOPG or glassy carbon, suggesting that the pi electrons of an sp2 carbon may play an important role in the direct electron transfer to the heme moiety of HRP. To examine the applicability of heme peptide-modified diamond electrodes to oxidase-based biosensors, anodic current responses of the oxygen plasma-treated diamond electrode to possible interfering agents, ascorbic acid and uric acid, were examined and compared with those of EOPG. Since the diamond electrode exhibited much less sensitivity to those interfering agents, the heme peptide-modified diamond electrode should be a promising H2O2 biosensor for the application to oxidase-based biosensors.

Diamond↗
PubMed2000

Selective voltammetric and amperometric detection of uric acid with oxidized diamond film electrodes.

Electrochemically anodized diamond film electrodes were used for selective detection of uric acid (UA) in the presence of high concentrations of ascorbic acid (AA) by differential pulse voltammetry and chronoamperometry. Because the oxidation peak potential for AA is approximately 450 mV more positive than that for UA at anodized diamond electrodes, UA can be determined with very good selectivity. By use of chronoamperometry, linear calibration curves were obtained for UA over the concentration range up to 1 x 10(-6) M in 0.1 M HClO4 solution, with the lowest experimental value measured being 5 x 10(-8) M. This is consistent with the fact that a statistical analysis of the calibration curve yielded a detection limit of 1.5 x 10(-8) M (S/N = 3). AA in less than 20-fold excess does not interfere. The practical analytical utility of the method is demonstrated by the measurement of UA in human urine and serum without any preliminary treatment.

Diamond↗
PubMed2000

Electrochemical oxidation of histamine and serotonin at highly boron-doped diamond electrodes.

The electrochemistry of histamine and serotonin in neutral aqueous media (pH 7.2) was investigated using polycrystalline, boron-doped diamond thin-film electrodes. Cyclic voltammetry, hydrodynamic voltammetry, and flow injection analysis (FIA) with amperometric detection were used to study the oxidation reactions. Comparison experiments were carried out using polished glassy carbon (GC) electrodes. At diamond electrodes, highly reproducible and well-defined cyclic voltammograms were obtained for histamine with a peak potential at 1.40 V vs SCE. The voltammetric signal-to-background ratios obtained at diamond were 1 order of magnitude higher than those obtained for GC electrodes at and above 100 microM analyte concentrations. A linear dynamic range of 3-4 orders of magnitude and a detection limit of 1 microM were observed in the voltammetric measurements. Well-defined sweep rate-dependent voltammograms were also obtained for 5-hydroxytryptamine (5-HT). The characteristics of the voltammogram indicated lack of adsorption of its oxidation products on the surface. No fouling or deactivation of the electrode was observed within the experimental time of several hours. A detection limit of 0.5 microM (signal-to-noise ratio 13.8) for histamine was obtained by use of the FIA technique with a diamond electrode. A remarkably low detection limit (10 nM) was obtained for 5-HT on diamond by the same method. Diamond electrodes exhibited a linear dynamic range from 10 nM to 100 microM for 5-HT determination and a range of 0.5-100 microM for histamine determination. The FIA response was very reproducible from film to film, and the response variability was below 7% at the actual detection limits.

Boron↗
PubMed1999

Axially chiral 1,7-naphthyridine-6-carboxamide derivatives as orally active tachykinin NK(1) receptor antagonists: synthesis, antagonistic activity, and effects on bladder functions.

Cyclic analogues of N-[3,5-bis(trifluoromethyl)benzyl]-7,8-dihydro-N, 7-dimethyl-5-(4-methylphenyl)-8-oxo-1,7-naphthyridine-6-carboxamide (1) having a 6-9-membered ring (6-9) were synthesized and evaluated for NK(1) antagonistic activities. The 8-membered ring compound with a beta-methyl group at the C((9))-position, (aR,9R)-7-[3, 5-bis(trifluoromethyl)benzyl]-8,9,10, 11-tetrahydro-9-methyl-5-(4-methylphenyl)-7H-[1,4]diazocino[2,1-g] [1, 7]naphthyridine-6,13-dione [(aR,9R)-8b], was atropodiastereoselectively synthesized by cyclization of a chiral intermediate, 10g. On the other hand, the 7-membered ring compound with a beta-methyl group at the C((9))-position [(9S)-7b] was obtained as an equilibrium mixture of atropisomers with a ratio of ca. 3:2 in solution at room temperature (measured by NMR in CDCl(3)). Compounds (9S)-7b and (aR,9R)-8b exhibited excellent antagonistic activities both in vitro [IC(50) (inhibition of [(125)I]BH-SP binding in human IM-9 cells) = 0.28 and 0.45 nM, respectively] and in vivo (iv and po). Significantly, the in vitro activity of (aR, 9R)-8b was ca. 750-fold higher than that of its enantiomer (aS, 9S)-8b, ca. 40-fold higher than its atropisomer (aS,9R)-8b, and ca. 20-fold higher than its diastereomer (aR,9S)-8b. The structure-activity relationships in this series, along with the X-ray analysis of (aR,9R)-8b, indicated that the stereochemistry around the -C((6))(=O)-N((7))-CH(2)Ar moiety is important for NK(1) receptor recognition. The NK(1) antagonists showed effects on bladder functions in guinea pigs upon intravenous injection: i.e., the antagonists increased the shutdown time of distension-induced rhythmic bladder contractions and the bladder volume threshold, and the effects on the shutdown time were found to correlate well with the NK(1) antagonistic activities. Compound (aR,9R)-8b has been identified as a potential clinical candidate for the treatment of bladder function disorders.

Animals↗
PubMed1999

A study on the adsorption structure of an adhesive monomer for precious metals by surface-enhanced Raman scattering spectroscopy.

In order to clarify the role of a primer on the adhesion between dental precious metals and resin, surface-enhanced Raman scattering (SERS) technique has been applied to the structural analysis of the adhesive monomer, 6-(N-(4-vinylbenzyl)propylamino)-1,3,5-triazine-2, 4-dithione (VBATDT) adsorbed on colloidal Au surfaces. VBATDT is one of the major components of commercial primers. A mixture of a methanol solution of VBATDT and aqueous Au colloid was illuminated by the 647.1 nm line from a Kr ion laser to obtain the SERS. The most intense peak at 458 cm-1 due to C = S stretching in the Raman spectrum of solid VBATDT disappears completely in the SERS, while all the other peaks due to vinylbenzyl group vibrations remain unchanged. It suggests that some structural change occurs in VBATDT upon adsorption on Au which involves the C = S bonds and that the molecule undergoes thione-thiol-type tautomerization in the adsorption process. The SERS spectrum of a commercial primer containing VBATDT exhibits a similar spectral pattern. The present results lead us to conclude that some specific interactions exist between the sulfur atoms of VBATDT and Au surface to form chemical bond likes, which are effective to improve the bond strength between dental precious metals and resin. The ambivalent properties of the primer, chemical stability in storage and chemical affinity to Au, are also explained by the thione-thiol-type tautomerization of VBATDT on the basis of the spectroscopic evidence.

Adhesives↗
PubMed1999

Resin content in cement liquids of resin-modified glass ionomers.

Qualitative and quantitative analyses were conducted on four kinds of resin-modified glass ionomer (RMGI) cement liquids, LC, LC II, LC III (hereinafter referred to as LCs) and VM, using HPLC and laser Raman spectroscopic methods. HPLC revealed that among the RMGI liquids LCs contain 31-32% HEMA (2-Hydroxyethyl methacrylate), and VM contains 18% of the same. The composition of RMGI cement liquids varied significantly between manufacturers. In Raman spectroscopic analyses, the spectra of liquids of various ratios of polyacrylic acid and HEMA were measured, and calculations were made on the peak intensity ratios of C=C stretch vibration to C=O stretch vibration, common in both HEMA and polyacrylic acid. The composition ratio of polycarboxylic acid to HEMA of commercial glass ionomer cements was assessed by the regression curve generated by a combination of peak intensity ratios and composition ratios. In addition, Raman spectroscopy was able to identity the differences in form of the methacryloyloxy group.

Carboxylic Acids↗
PubMed1998

Axially chiral N-benzyl-N,7-dimethyl-5-phenyl-1, 7-naphthyridine-6-carboxamide derivatives as tachykinin NK1 receptor antagonists: determination of the absolute stereochemical requirements.

A potent and orally active NK1 antagonist, trans-N-[3, 5-bis(trifluoromethyl)benzyl]-7,8-dihydro-N, 7-dimethyl-5-(4-methylphenyl)-8-oxo-1,7-naphthyridine-6-carboxamide (1t), was shown to exist as a mixture of separable and stable (R)- and (S)-atropisomers (1t-A and 1t-B) originating from the restricted rotation around the -C(6)-C(=O)- bond; the antagonistic activities of 1t-A were ca. 6-13-fold higher than those of 1t-B. Analogues of 1t (3), which have (S)- and (R)-methyl groups at the benzylic methylene portion of 1t, were prepared and separated into the diastereomeric atropisomers, 3a-A, 3a-B and 3b-A, 3b-B, in enantiomerically pure forms. Among the four isomers of 3, the (aR, S)-enantiomer (3a-A) exhibited the most potent antagonistic activities with an IC50 value of 0.80 nM (in vitro inhibition of [125I]BH-SP binding in human IM-9 cells) and ED50 values of 9.3 micrograms/kg (iv) and 67.7 micrograms/kg (po) (in vivo inhibition of capsaicin-induced plasma extravasation in guinea pig trachea), while the activity of the (aS,R)-enantiomer (3b-B) was the weakest with an IC50 value of 620 nM. The structure-activity relationships in this series of antagonists indicate that the (R)-configuration at the axial bond and the stacking (or stacking-like) conformation between the two phenyl rings as shown in 1t-A and 3a-A are essential for high-affinity binding and suggest that the amide moiety functions as a hydrogen bond acceptor in the interaction with the receptor.

Administration, Oral↗
PubMed1997

The crystal structure of human cathepsin L complexed with E-64.

We have determined the three dimensional structure of the complex of human cathepsin L and E-64, an irreversible inhibitor of cysteine proteases, at 2.5 A resolution. The overall structure was similar to that of other known cysteine proteases and apparently identical to the mature region of procathepsin L. The electron density for E-64 is clearly visible except for the guanidinobutane moiety. From comparison of the active sites of cathepsin L and B, we found the following: (1) The S' subsites of cathepsin L and B are totally different because of the 'occluding loop' lying on the end of the S' subsites of cathepsin B. (2) The S2 pocket of cathepsin L is shallow and narrow compared to that of cathepsin B. (3) The S3 subsites of the two enzymes are more similar than the other subsites, but cathepsin L may accommodate a more bulky group at this site. Knowledge of the active site structure of cathepsin L should be helpful for the structure-based design of potent and specific inhibitors which are of therapeutic importance.

Cathepsin L↗
PubMed1997

A study on adsorption structures of methacryloyloxyalkyl dihydrogen phosphates on silver substrates by infrared reflection absorption spectroscopy.

10-Methacryloyloxydecyl dihydrogen phosphate (M10P) for use in dentistry has recently been noted as an adhesive monomer contained in a metal primer. Although the treatment of a metal surface with primer before the application of resin is recognized to improve the adhesion between metal and resin, the role of M10P in the adhesion process has not been clarified. In this study, infrared reflection absorption (IRA) spectroscopy was employed to study the adsorption structures of M10P as well as 2-methacryloyloxyethyl dihydrogen phosphate (M2P) on evaporated silver substrates. The IRA spectra of the self-assembled films of those phosphates verified the adsorption of M10P or M2P on silver substrates from the methyl methacrylate solutions (5 x 10(-5) mol/L). The saturation coverages of M10P and M2P were completed after about 50 and 25 min, respectively. Two characteristic bands around 980 and 1080 cm-1 due to the PO(2-)3 stretching vibrations were observed. These results indicate that the phosphate groups of both monomers are adsorbed to silver surfaces in the dissociated form, -PO(2-)3, and form hydrophobic monolayers. The monolayer of M10P was found to be more durable against thermocycling in water than that of M2P by IRA measurements. The roles of M10P in the metal primer are presumably to form such a monolayer with appreciable durability and to promote polymerization with resin monomers.

Adsorption↗
PubMed1997

In vitro inhibition of caries around a resin composite restoration containing antibacterial filler.

Class V cavities were prepared and restored with resin composite containing antibacterial filler powder (Apacider-AW, Ap-AW) using experimental restorations. The restored teeth were incubated in vitro with the cariogenic bacteria Streptococcus mutans IFO 13955. Ground sections were then prepared and examined using macrophotography. Lesions of the outer and inner wall were noted, and the depths of which the lesions penetrated were measured. We found that, in restorations containing 1-5 wt% Ap-AW, caries penetrated the marginal area, while in restorations containing 10 wt% Ap-AW the margin remained free of caries out to a distance of about 1.1 and 1.8 mm on the occlusal and gingival sides, respectively.

Biocompatible Materials↗
PubMed1996

Characterization and crystallization of recombinant human cathepsin L.

Human procathepsin L (25mg) was highly purified from the culture filtrate (4L) of mouse myeloma cells (Sp-HCL/HE14) transformed with human procathepsin L cDNA. The procathepsin L was almost completely converted to the mature form (18mg) under the acidic condition. Some properties of the mature cathepsin L were found to be different from those of the human liver-derived enzyme. In addition, we first produced crystals of mature human cathepsin L with E-64 using polyethylene glycol 6000 as the precipitant. The crystal was orthorhombic and belonged to the space group P2(1)2(1)2(1). The unit cell dimensions were: a = 49.8 A, b = 103.9 A, c = 47.8 A. The cell volume (2.47 x 10(5) A3) and calculated molecular mass (24.6 kDa) gave a volume/mass ratio of 2.5 A3/Da, which indicates that the asymmetric unit contains one molecule of enzyme.

Animals↗
PubMed1996

Photoinduced Magnetization of a Cobalt-Iron Cyanide

Photoinduced magnetization was observed in a Prussian blue analog, K0.2Co1.4- [Fe(CN)6]·6.9H2O. An increase in the critical temperature from 16 to 19 kelvin was observed as a result of red light illumination. Moreover, the magnetization in the ferrimagnetic region below 16 kelvin was substantially increased after illumination and could be restored almost to its original level by thermal treatment. These effects are thought to be caused by an internal photochemical redox reaction. Furthermore, blue light illumination could be used to partly remove the enhancement of the magnetization. Such control over magnetic properties by optical stimuli may have application in magneto-optical devices.

Journal Article↗
PubMed1996

Comparison of four modes of fracture toughness testing for dental composites.

OBJECTIVES: Investigators have reported on the measurement of fracture toughness (K(lc)) of dental composites using a variety of testing methods. However, fracture toughness has been shown to be dependent upon several variables, including crack-tip sharpness and specimen geometry. This study was designed to compare the fracture toughness values obtained for two experimental and three commercial posterior composites, using four popular testing methods. METHODS: The four methods for testing fracture toughness included single-edge notched, compact tension, short rod with chevron notch and double torsion. The results were compared by ANOVA and Tukey's multiple comparison test (p < or = 0.05). RESULTS: The values obtained from the short rod test were significantly higher than those from the three other tests. Evaluation of the load-deflection curves and fracture surfaces suggested that the data for this test may not have been valid because a stable crack growth region could not be identified. In general, the fracture toughness results obtained from the double torsion test were lower than values obtained from the single-edge notched and compact tension methods. The double torsion test was the most difficult to conduct, resulting in only a 50% success rate. SIGNIFICANCE: The double torsion test, though possibly the most technique-sensitive of the four fracture toughness methods evaluated provides the most information about crack initiation and propagation and may be most indicative of the true fracture toughness of dental composites.

Acrylic Resins↗
PubMed1995

Shear bond strength of four commercial bonding systems to cp Ti.

OBJECTIVES: The purpose of this study was to evaluate the bond strength of veneering composite to commercially pure titanium (cp Ti) using several different bonding systems and a post-cure heat treatment. METHODS: Four commercial bonding systems (Cesead, Kuraray; New Metacolor, Sun Medical; Silicaoater MD, Kulzer; Termoresin LC II, GC) were evaluated. Bonding was attempted with the opaque resin provided by each bonding system as well as with the New Metacolor opaque resin. New Metacolor resin composite was used for the veneering composite. Half of the specimens were subjected to a post-cure heat treatment at 100 degrees C for 30 min. The shear bond strengths were tested after aging the specimens in water at 37 degrees C for 1 d and also after thermocycling for 16.5 d (20,000 cycles). RESULTS: Strong bonds, exceeding 20 MPa, were achieved with all of the bonding systems with the exception of Thermoresin LC II, which is designed for noble metals. Bond strengths were only increased by the post-cure heat treatment for the New Metacolor system. Thermocycling caused a significant reduction in bond strength for the New Metacolor adn the Thermoresin LC II systems. The use of the New Metacolor opaque resin produced increased bonding for the Silicoater MD and the opaque resin produced increased bonding for the Silicoater MD and the Cesead systems, but the effect was eliminated after thermocycling. SIGNIFICANCE: Strong, durable bonds can be achieved between composite and sandblasted cp Ti, thus enhancing the usefulness of this metal for esthetic resin-veneered crowns and other fixed prosthetics.

Acrylic Resins↗
PubMed1994

Intracellular Ca2+ concentration change of T24 cell under irradiation in the presence of TiO2 ultrafine particles.

We reported that malignant cells are inactivated by photo-excited TiO2 particles (Cai, R.-X., et al. (1992) Cancer Res. 52, 2346-2348). In the present study, the process of cell death of a human bladder cell line T24 with the irradiated TiO2 was investigated by monitoring the time course change in intracellular calcium concentration ([Ca2+]i) under UV irradiation using calcium fluorescence indicator, fura-2. In the presence of photo-excited TiO2 particles (100 micrograms/ml), [Ca2+]i showed a rapid two-step increase; while in the absence of TiO2, it exhibited only a slight and monotonous increase or maintained a constant level. The rapid elevation of [Ca2+]i in the presence of photo-excited TiO2 particles was caused by the influx of extracellular Ca2+ through the plasma membrane and cell death occurred only after the second rapid elevation of [Ca2+]i. These results suggested that the cell membrane permeability to Ca2+ was promoted prior to cell death.

Calcium↗
PubMed1994

Preliminary crystallographic study of Escherichia coli RuvC protein. An endonuclease specific for Holliday junctions.

Single crystals of the RuvC protein, an Escherichia coli endonuclease specific for Holliday junctions, were grown by the microdialysis method. The crystals belong to the space group P2(1), with unit cell dimensions a = 72.8 A, b = 139.6 A, c = 32.4 A and beta = 93.0 degrees, and contain four molecules in an asymmetric unit. Diffraction data to a Bragg spacing of 2.5 A resolution has been obtained using a synchrotron X-ray source.

Bacterial Proteins↗