Publications by authors named "Shin-ichi Nagaoka"

Japanese black Wagyu cattle are renowned for producing some of the world's most highly valued and recognized beef with exceptional marbling. Therefore, the primary focus of genetic selection for Wagyu cattle has historically been on meat quality, particularly achieving high marbling levels. However, even when the price of the final product is high, production costs also remain high, especially considering that most of the feed has to be imported.

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  • The study measured the radical-scavenging rate constants (k) of various antioxidants, including different forms of Tocopherol (TocH) and ubiquinol-10 (UQH), using a specific solution in a stopped-flow spectrophotometry setup.
  • The results showed that the k values for the TocHs increased when UQH was present, indicating a synergistic effect that enhances their antioxidant activity.
  • Additionally, similar experiments with vegetable oils revealed that the k values also increased when UQH was present, leading to a proposed new mechanism for the enhanced antioxidant effects when these compounds coexist.
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Recently, singlet-oxygen (O) quenching and aroxyl-radical (ArO·) scavenging rates (k and k, respectively) of eight vegetable oils were measured in the ethanol/chloroform/DO solution. Furthermore, the k and k values and concentrations of four tocopherols and four tocotrienols contained in the vegetable oils were measured. In this study, the concentrations of nine fatty acids (including stearic, oleic, linoleic, and linolenic acids) comprising the above-mentioned eight vegetable oils were determined by gas chromatography.

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  • A study investigated how singlet oxygen (O) reacts with eight different vegetable oils that vary in tocopherol and tocotrienol concentrations.
  • The reaction's rate constants (k) were measured in a specific solvent at 35°C using UV-vis spectrophotometry, showing that the oils' fatty acids also significantly influence the reaction rates.
  • The findings contrast with another study that measured the rate constants for aroxyl radicals, where the values were successfully explained by the antioxidants' concentrations alone.
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Recently, a new assay method that can quantify the singlet oxygen-absorption capacity (SOAC) of antioxidants (AO) and food extracts in homogeneous organic solvents has been proposed. In the present study, second-order rate constants (k ) for the reaction of singlet oxygen ( O ) with vitamin E homologs (α-, β-, γ-, and δ-tocopherols [Toc] and α-, β-, γ-, and δ-tocotrienols [Toc-3]) were measured in an aqueous Triton X-100 (5.0 wt%) micellar solution (pH 7.

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  • The study examines the activities of singlet-oxygen quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) in hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones using advanced spectroscopic techniques.
  • It finds that in hydroxyflavones and anthocyanidins, enhanced free-radical scavenging and oxygen quenching activity is linked to the electron transfer from the B-ring due to the presence of an electron-donating OH group.
  • However, in 3-hydroxyflavones, the OH group reduces ESIPT activity, creating an inverse relationship, while in 1-h
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  • A kinetic study examined the reaction between aroxyl radicals and various fatty acid esters, revealing that the reaction rates increased with the number of double bonds in the esters.
  • The second-order rate constants (k values) for these reactions were measured spectrophotometrically in toluene, with the highest k value recorded for ethyl arachidonate.
  • A similar study with carotenoids showed the same trend in reaction rates and also identified the mechanism as allylic hydrogen abstraction, incorporating insights from density functional theory for further analysis.
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Recently, a new assay method for the quantification of the singlet oxygen absorption capacity (SOAC) of antioxidants (AOs) and food extracts in homogeneous organic solvents was proposed. In this study, second-order rate constants (k) for the reaction of singlet oxygen (O) with eight different carotenoids (Cars) and α-tocopherol (α-Toc) were measured in an aqueous Triton X-100 (5.0 wt %) micellar solution (pH 7.

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Site-specific electron relaxations caused by Si:2p core-level photoionizations in FSiCHCHSi(CH) and ClSiCHCHSi(CH) vapors have been studied by means of the photoelectron Auger electron coincidence spectroscopy. FSiCHCHSi(CH) shows almost 100% site-specificity in fragmentation caused by the Si:2p ionization. However, substitution of Cl for F of FSiCHCHSi(CH) considerably reduces the site-specificity at the Si atom bonded to three halogen atoms, with the site-specificity at the Si site bonded to three methyl groups remaining largely unchanged.

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  • Detailed kinetic studies explored how various catecholamines (CAs) and catechins interact with aroxyl and α-tocopheroxyl radicals, focusing on their ability to scavenge free radicals.
  • Rate constants for these reactions showed a hierarchy of effectiveness, with catecholamines like norepinephrine being the least effective and 6-hydroxydopamine and EGCG showing high scavenging activity, comparable to established antioxidants.
  • The findings indicate that CAs can help protect against oxidative damage in the nervous system by neutralizing free radicals and aiding in the regeneration of α-tocopherol from its radical form.
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Measurements of the reaction of sodium salt of pyrroloquinoline quinone (PQQNa2) with vitamin C (Vit C) were performed in phosphate-buffered solution (pH 7.4) at 25 °C under nitrogen atmosphere, using UV-vis spectrophotometry. The absorption spectrum of PQQNa2 decreased in intensity due to the reaction with Vit C and was changed to that of pyrroloquinoline quinol (PQQH2, a reduced form of PQQ).

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Measurements of singlet oxygen ((1)O2) quenching rates (kQ (S)) and the relative singlet oxygen absorption capacity (SOAC) values were performed for seven rice bran extracts 1-7, which contained different concentrations of antioxidants (AOs) (such as α-, β-, γ-, and δ-tocopherols and -tocotrienols, three carotenoids (lutein, β-carotene, and zeaxanthin), and γ-oryzanol), in ethanol at 35 °C using UV-vis spectrophotometry. The concentrations of four tocopherols and four tocotrienols, three carotenoids, and γ-oryzanol contained in the extracts were determined using HPLC-MS/MS, UV-HPLC, and UV-vis absorption spectroscopy, respectively. Furthermore, comparisons of kQ (S) (Obsd.

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  • The study investigates how excited-state intramolecular proton-transfer (ESIPT) and singlet-oxygen quenching activities interact in certain anthraquinones with hydrogen bonds, using static and laser spectroscopies.
  • It finds that the ESIPT activity is influenced by specific substituents, which can be explained through a model related to molecular geometry called the nodal-plane model.
  • A positive linear correlation is observed between ESIPT activity and (1)O2 quenching, attributed to changes in the molecule's shape and interaction with singlet oxygen during the proton transfer process.
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Measurements of the singlet oxygen ((1)O2) quenching rates (kQ (S)) and the relative singlet oxygen absorption capacity (SOAC) values were performed for 11 antioxidants (AOs) (eight vitamin E homologues (α-, β-, γ-, and δ-tocopherols and -tocotrienols (-Tocs and -Toc-3s)), two vitamin E metabolites (α- and γ-carboxyethyl-6-hydroxychroman), and trolox) in ethanol/chloroform/D2O (50:50:1, v/v/v) and ethanol solutions at 35 °C. Similar measurements were performed for five palm oil extracts 1-5 and one soybean extract 6, which included different concentrations of Tocs, Toc-3s, and carotenoids. Furthermore, the concentrations (wt%) of Tocs, Toc-3s, and carotenoids included in extracts 1-6 were determined.

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Measurements of aroxyl radical (ArO•)-scavenging rate constants (k(s)(AOH)) of antioxidants (AOHs) [α-, β-, γ-, and δ-tocopherols (TocHs) and -tocotrienols (Toc-3Hs)] were performed in ethanol solution via stopped-flow spectrophotometry. k(s)(AOH) values of α-, β-, γ-, and δ-Toc-3Hs showed good agreement with those of the corresponding α-, β-, γ-, and δ- TocHs. k(s)(AOH) values were measured not only for each antioxidant but also for mixtures of two antioxidants: (i) α-TocH with β-, γ-, or δ-TocH and (ii) α-TocH with α-, β-, γ-, or δ-Toc-3H.

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Vitamin E is localized in membranes and functions as an efficient inhibitor of lipid peroxidation in biological systems. In this study, we measured the second-order rate constants (ks) for the reaction of tocotrienol homologues (α-, β-, γ-, and δ-Toc-3Hs) with the aroxyl radical (ArO•) used as a model for lipid peroxyl radicals (LOO•) in the membranes of egg yolk phosphatidylcholine (EYPC) vesicles by stopped-flow spectrophotometry, and compared them to those of tocopherol homologues (α-, β-, γ-, and δ-TocHs). The relative rate constants of Toc-3H homologues to α-Toc-3H in membranes (α/β/γ/δ=100/83.

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Spectator resonant Auger electron spectra with the Si 1s photoexcitation of Cl3SiSi(CH3)3 have been measured using an electron spectroscopic technique combined with undulator radiation. The transition with the highest intensity in the total ion yield (TIY) spectrum, coming from excitation of a Si 1s electron on the Cl-side into a vacant valence orbital, generates the resonant Auger decay in which the excited electron remains in this valence orbital. Photoexcitation of 1s electrons into some Rydberg orbitals induces Auger shake-down transitions, because higher-lying Rydberg orbitals in the two Si atoms closely positioned hold spatially overlapping considerably.

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  • - Measurements of the aroxyl radical-scavenging rate constants of various antioxidants (like PQQH2, α-TocH, and UQ10H2) were done in DMSO solution using a specific spectrophotometry technique, revealing that antioxidant mixtures enhance their scavenging efficiency.
  • - A significant synergistic effect was found when combining antioxidants, with increases in scavenging rate constants up to 2.50 times when using pairs of α-TocH with either PQQH2 or UQ10H2.
  • - The study also showed PQQH2 regenerates α-Toc• (an oxidized form of α-TocH) more effectively than UQ10H2, suggesting
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A new free radical absorption capacity assay method is proposed with use of an aroxyl radical (2,6-di-tert-butyl-4-(4'-methoxyphenyl)phenoxyl radical) and stopped-flow spectroscopy and is named the aroxyl radical absorption capacity (ARAC) assay method. The free radical absorption capacity (ARAC value) of each tocopherol was determined through measurement of the radical-scavenging rate constant in ethanol. The ARAC value could also be evaluated through measurement of the half-life of the aroxyl radical during the scavenging reaction.

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Measurements of aroxyl radical (ArO(•))-scavenging rate constants (ks(AOH)) of antioxidants (AOHs) (α-tocopherol (α-TocH), ubiquinol-10 (UQ10H2), and sodium ascorbate (Na(+)AsH(-))) were performed in 2-propanol/water (2-PrOH/H2O, 5/1, v/v) solution using stopped-flow spectrophotometry. ks(AOH) values were measured not only for each AOH but also for the mixtures of two AOHs ((i) α-TocH and UQ10H2 and (ii) α-TocH and Na(+)AsH(-)). A notable synergistic effect that the ks(AOH) values increase 1.

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Time-resolved emission of aloesaponarin I was studied with the fluorescence up-conversion and time-correlated single-photon-counting techniques. The rates of the excited-state intramolecular proton transfer, of the solvent and molecular rearrangements, and of the decay from the excited proton-transferred species were determined and interpreted in the light of time-dependent density functional calculations. These results were discussed in conjunction with UV protection and singlet-oxygen quenching activity of aloe.

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  • The study measured singlet oxygen quenching rates and relative absorption capacities of various phenolic antioxidants and vitamin C in a specific solvent mixture at 35 °C, showing new insights into antioxidant effectiveness.
  • Singlet oxygen absorption capacity (SOAC) was found to correlate with the oxidation potentials of the antioxidants, revealing that those with lower potentials exhibit higher reactivities when quenching singlet oxygen.
  • Measurements indicated that the quenching rates of phenolic antioxidants and carotenoids are consistent across different solvent types, suggesting that the antioxidant performance remains reliable regardless of solvent choice when α-tocopherol serves as a standard.
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The measurements of the UV-vis absorption spectra of α-, β-, γ-, and δ-tocopheroxyl (α-, β-, γ-, and δ-Toc(•)) radicals were performed by reacting aroxyl (ArO(•)) radical with α-, β-, γ-, and δ-tocopherol (α-, β-, γ-, and δ-TocH), respectively, in acetonitrile solution including three kinds of alkali and alkaline earth metal salts (LiClO(4), NaClO(4), and Mg(ClO(4))(2)) (MX or MX(2)), using stopped-flow spectrophotometry. The maximum wavelengths (λ(max)) of the absorption spectra of the α-, β-, γ-, and δ-Toc(•) located at 425-428 nm without metal salts increased with increasing concentrations of metal salts (0-0.500 M) in acetonitrile and approached some constant values, suggesting (Toc(•)···M(+) (or M(2+))) complex formations.

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A kinetic study of regeneration reaction of α-tocopherol (α-TocH) by ubiquinol-10 has been performed in the presence of four kinds of alkali and alkaline earth metal salts (LiClO(4), NaClO(4), NaI, and Mg(ClO(4))(2)) in methanol and acetonitrile solutions, using double-mixing stopped-flow spectrophotometry. The second-order rate constants (k(r)'s) for the reaction of α-tocopheroxyl (α-Toc•) radical with ubiquinol-10 increased and decreased notably with increasing concentrations of metal salts in methanol and acetonitrile, respectively. The k(r) values increased in the order of no metal salt < NaClO(4) ~ NaI < LiClO(4) < Mg(ClO(4))(2) at the same concentration of metal salts in methanol.

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In an aim to create a "sharp" molecular knife, we have studied site-specific fragmentation caused by Si:2p core photoionization of bridged trihalosilyltrimethylsilyl molecules in the vapor phase. Highly site-specific bond dissociation has been found to occur around the core-ionized Si site in some of the molecules studied. The site specificity in fragmentation and the 2p binding energy difference between the two Si sites depend in similar ways on the intersite bridge and the electronegativities of the included halogen atoms.

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