Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

DOI： 10.1016/j.jphotochem.2021.113189

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.joc.0c02825

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jphotochem.2020.113122

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Copyright © 2018 American Chemical Society. A core-expanded, pyrrole-fused azacoronene analogue containing two unusual N-doped heptagons was obtained from commercially available octafluoronaphthalene and 3,4-diethylpyrrole in two steps as a heteroatom-doped nonplanar nanographene. Full fusion with the formation of the tetraazadipleiadiene framework and the longitudinally twisted structure was unambiguously confirmed by single-crystal X-ray diffraction analysis. The edge-to-edge dihedral angle along the acene moiety was 63°. This electron-rich π-system showed four reversible oxidation peaks. Despite the nonplanar structure, the Hückel aromaticity owing to a peripheral π-conjugation in the dicationic state was concluded from the bond-length alternation and nucleus-independent chemical shift (NICS) and anisotropy of the induced current density (ACID) calculations.

DOI： 10.1021/jacs.8b06079

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Singlet-oxygen (O-1(2)) quenching, free-radical scavenging, and excited-state intramolecular proton-transfer (ESIPT) activities of hydroxyflavones, anthocyanidins, and 1-hydroxyanthraquinones were studied by means of laser, stopped-flow, and steady-state spectroscopies. In hydroxyflavones and anthocyanidins, the O-1(2) quenching activity positively correlates to the free radical scavenging activity. The reason for this correlation can be understood by considering that an early step of each reaction involves electron transfer from the unfused phenyl ring (B-ring), which is singly bonded to the bicyclic chromen or chromenylium moiety (A- and C-rings). Substitution of an electron-donating OH group at B-ring enhances the electron transfer leading to activation of the O-1(2) quenching and free-radical scavenging. In 3-hydroxyflavones, the OH substitution at B-ring reduces the activity of ESIPT within C-ring, which can be explained in terms of the nodal-plane model. As a result, the 102 quenching and free-radical scavenging activities negatively correlate to the ESIPT activity. A catechol structure at B-ring is another factor that enhances the free-radical scavenging in hydroxyflavones. In contrast to these hydroxyflavones, 1-hydroxyanthraquinones having an electron-donating OH substituent adjacent to the O-H-O = C moiety susceptible to ESIPT do not show a simple correlation between their O-1(2) quenching and ESIPT activities, because the OH substitution modulates these reactions.

DOI： 10.1021/acs.jpca.7b07869

Web of Science

researchmap

DOI： 10.3390/magnetochemistry3020020

Web of Science

researchmap

DOI： 10.3390/inorganics4020007

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

An acenaphthylene-fused cyclo[10]pyrrole 1b was selectively synthesized via an oxidative coupling reaction of the corresponding 2,2'-bipyrrole with the appropriate dianion template, croconate anion. The structure of 1b as the isolated largest cyclo[n]pyrrole was elucidated by X-ray crystallographic analysis. The absorption spectrum exhibited a markedly red-shifted, intensified L band at 1982 nm, which was interpreted by application of Michl's perimeter and Gouterman's 4-orbital models, supported by magnetic circular dichroism (MCD) data and theoretical calculations.

DOI： 10.1021/jacs.6b04941

Web of Science

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Excited-state intramolecular proton-transfer (ESIPT) and singlet-oxygen (O-1(2)) quenching activities of intramolecularly hydrogen-bonded 1-(acylamino)anthraquinones have been studied by means of static and laser spectroscopies. The ESIPT shows a substituent effect, which can be explained in terms of the nodal-plane model. The ESIPT activity positively and linearly correlates with their O-1(2) quenching activity. The reason for this correlation can be understood by considering ESIPT-induced distortion of their ground-state potential surface and their encounter complex formation with O-1(2). Intramolecularly hydrogen-bonded hydroxyanthraquinones found in aloe also show a similar positive and linear correlation, which can be understood in the same way.

DOI： 10.1021/jp508355k

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

[Cu(dmit)(2)](2-) formally consists of a magnetic Cu2+ ion (S = 1/2) and closed-shell pi-conjugated dmit(2-) ligands. However, it has been determined by electron spin resonance and molecular orbital calculations that the majority (91-100%) of the spin delocalizes over the ligands in the ground state, while the spin significantly (40-90%) localizes on Cu under UV irradiation. Considering the results of X-ray structural analyses under UV irradiation, the spin distribution varies depending on the wavelengths irradiated and retaining the square-planar coordination geometries.

DOI： 10.1246/cl.140318

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WORLD SCI PUBL CO INC  

A series of O-chelated BODIPYs fused with aromatic rings such as benzene and acenaphthylene at beta,beta-positions was synthesized as a near-infrared dye. The photophysical properties were examined by UV-vis-NIR absorption and fluorescence measurement. Acenaphthylene-fused O-BODIPYs showed a intense absorption at 750-840 nm with the epsilon of 10(5) M-1.cm(-1). and a fluorescene emission at 770-850 nm with the high Phi value of 0.06-0.43.

DOI： 10.1142/S1088424614500503

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

The simple molecular salt NMQ[Ni(dmit)(2)] (NMQ = N-methylquinolinium, dmit = 1,3-dithiol-2-thione-4,5-dithiolate) functions as a diamagnetic insulator with an activation energy E-a(dark) of 0.20 eV. However, at 300 K, it exhibits ca. 40 times higher conductivity (sigma(UV)) under UV irradiation [(375 +/- 5) nm, 15.7 mW cm(-2)] than it does under dark conditions (sigma(dark)). The ratio sigma(UV)/sigma(dark) rapidly increases with decreasing temperature and reaches ca. 880 at 200 K. From the temperature dependence of sigma(UV), the activation energy under irradiation E-a(UV) is 0.12 eV. These observations cannot be explained as the result of sample heating during UV irradiation. Rather, the X-ray photoelectron spectra of the sulfur and nickel atoms, the calculated band structure, and the UV/Vis spectra of the salt can all be explained consistently as follows: charge transfer between the Ni(dmit)(2) moieties upon exposure to 375 nm UV light induces melting of the charge-ordered state and produces the unusually large photoconductivity of NMQ[Ni(dmit)(2)].

DOI： 10.1002/ejic.201402035

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

beta-DiCC[Ni(dmit)(2)] (dmit: 1,3-dithiole-2-thione-4,5-dithiolato and DiCC: 3,3'-dihexyloxacarbocyanine) is a charge-transfer salt with redox activity. When voltages are applied, it brings about a reversible, hysteretic, solid-state-electrolytic reaction exhibiting a capacitor-like electric response. Based on the electron spin resonance spectra, the resistivity behavior, and the tight-binding band calculation, it is indicated that one can finely and reversibly control the redox equilibrium between DiCC(+) and [Ni(dmit)(2)](-) molecules by applying voltages.

DOI： 10.1246/cl.140309

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JOURNAL CLINICAL BIOCHEMISTRY & NUTRITION  

Scavenging rate constants of eight hydrophilic antioxidants, including caffeic acid, chlorogenic acid, genistein, glutathione, N-acetylcysteine, rutin, trolox, and uric acid against multiple ROS, namely superoxide anion, hydroxyl radical, singlet oxygen, and alkoxyl radical were determined with the electron spin resonance method. Direct flash photolysis measurement of the second-order rate constant in the reaction of alkoxyl radical plus the spin trap 5,5-dimethyl-pyrroline N-oxide made it possible to evaluate scavenging rate constants in antioxidants. The magnitudes of scavenging rate constants were notably dependent on the character of each ROS and the overall rate constants were highest in hydroxyl radical scavenging and the lowest in superoxide anion. The highest scavenging rate constant against superoxide anion was obtained by chlorogenic acid (2.9 x 10(5) M-1 s(-1)) and the lowest was by N-acetylcysteine (5.0 x 10(2) M-1 s(-1)) For singlet oxygen, the highest was by glutathione (9.4 x 10(8) M-1 s(-1)) and the lowest was by uric acid (2.3 x 10(6) M-1 s(-1)). All other numbers are listed and illustrated. Redox potential measurements of the antioxidants indicated that the antioxidants are likely to react with superoxide anion and singlet oxygen through electron transfer processes.

DOI： 10.3164/jcbn.13-53

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Mono- and multi-layered films comprised of amphiphilic cationic iridium(III) complexes hybridized with the exfoliated nanosheets of synthetic saponite were prepared by the modified Langmuir-Blodgett method. Three iridium(III) complexes with different emission maxima (lambda(max)) were used as incorporated complexes: [Ir(dfppy)(2)(dc9bpy)](+) (lambda(max) = 500 nm) (dfppyH = 2-(4',6'-difluorophenyOpyridine; dc9bpy = 4,4'-dinonY1-2,2'-bipyridine) [Ir(ppy)(2)(dc9bpy)](+) (lambda(max) = 550 nm) (ppyH = 2-phenylpyridine) and [Ir(piq)(2)(dc9bpy)](+) (lambda(max) = 590 nm) (piqH = 1-phenylisoquinoline) for blue, yellow and red emissions, respectively. Six triple-layered films with different layer sequences were fabricated by layer-by-layer deposition onto quartz substrates. Stationary emission spectra were recorded on the prepared films under vacuum and at various oxygen pressures Notably the change in the spectral shape at surrounding oxygen pressure depended remarkably on the layer sequence. Quenching by oxygen molecules was analyzed by applying a two-site model to the Stern-Volmer plots. The present nanometer-thick films were regarded as a benchmark for an optical device emitting different visible lights in response to oxygen pressure.

DOI： 10.1039/c3nj00879g

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

A series of O-chelated BODIPYs fused with aromatic rings such as benzene and acenaphthylene at β,β-positions was synthesized as a near-infrared dye. The photophysical properties were examined by UV-vis-NIR absorption and fluorescence measurement. Acenaphthylene-fused O-BODIPYs showed a intense absorption at 750–840 nm with the ε of 105 M-1.cm-1. and a fluorescence emission at 770–850 nm with the high Φ value of 0.06–0.43.<br />
<br />
<br />
Read More: http://www.worldscientific.com/doi/abs/10.1142/S1088424614500503

DOI： 10.1142/S1088424614500503

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

An acenaphthylene-fused cyclo[8]pyrrole was synthesized by using an oxidative coupling reaction of the corresponding 2,2-bipyrrole. Two conformational isomers 1a and 1b were isolated, and their molecular structures were elucidated by X-ray crystallographic studies. The less-polar and lower-symmetry 1b isomer can be converted into the 1a isomer through a thermal ring flip. Application of the perimeter model developed by Michl to magnetic circular dichroism spectroscopic data and theoretical calculations demonstrate that there is a marked redshift of the near-IR absorption maxima relative to cyclo[8]isoindole because there is a significant stabilization of the LUMO due to the differing effects of a fused ring expansion with acenaphthylene and benzene moieties on the frontier molecular orbitals.

DOI： 10.1002/chem.201301294

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

An organic insulating crystal reversibly becomes a magnetic conductor under UV irradiation. The rapid and qualitative change in the physical properties is wavelength selective and explained by charge transfer between donor and photochemically active acceptor molecules. The photochemical redox reaction in the crystal produces a partially filled band and localized spins simultaneously.

DOI： 10.1002/adma.201203153

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Langmuir-Blodgett (LB) films were prepared by hybridizing a floating monolayer of an amphiphilic cationic iridium(m) complex with clay particles in a subphase. Two kinds of iridium(III) complexes were used: [Ir(dfppy)(2)(dc9bpy)](+) (denoted by DFPPY: dfppyH = 2-(4',6'-difluoro-phenyl)pyridine; dc9bpy = 4,4'-dinonyl-2,2'-bipyridine) with the maximum emission wavelength (lambda(max)) at 500 nm and [Ir(ppy)(2)(dc9bpy)](+) (denoted by PPY: ppyH = 2-phenylpyridine) with lambda(max) at 550 nm. Stationary emission spectra were recorded on the following films under vacuum: {DFPPY or PPY/clay}(n) (n = 1-3), {DFPPY/clay/PPY/clay} and {PPY/clay/DFPPY/clay}. The intensity of emission from {PPY/clay}(n) or {DFPPY/clay}(n) increased nearly in proportion to the layer number (n). Both DFPPY and PPY emitted simultaneously from {DFPPY/clay/PPY/clay}, indicating the low contribution of energy transfer. Contrarily PPY emitted exclusively from {PPY/clay/DFPPY/clay} as a result of the efficient quenching of excited DFPPY in the lower layer by PPY in the upper layer. The introduction of oxygen gas resulted in the decrease of emission for all films. Notably {DFPPY/clay/PPY/clay} exhibited a dual emitting character under an oxygen atmosphere, that is, the broad emission maximum was observed around 530 nm at lower oxygen pressure (0 &lt; P-O2 &lt; 4 kPa), while the emission peak shifted to 550 nm at higher oxygen pressure (P-O2 &gt; 4 kPa).

DOI： 10.1039/c2nj40351j

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A kinetic study on singlet oxygen (O-1(2)) quenching by 4-hydroxycinnamic acid derivatives (ferulic acid (FA) and caffeic acid (CA)) has been performed by measuring time-evolutions of O-1(2) phosphorescence at 1274 nm in ethanol, in an ethanol/acetone mixed solvent and in an ethanol/H2O mixed solvent under acidic, neutral and basic conditions. In organic solvents, the estimated second-order rate constants of O-1(2) quenching (k(Q)) were distributed between 10(5) and 10(6) M-1 s(-1): for example, in ethanol, 2.2 x 10(5) M-1 s(-1) for FA and 5.2 x 10(5) M-1 s(-1) for CA. On the other hand, the k(Q) values in ethanol/H2O solutions were enlarged from those in organic solvents, and varied largely with pH from 10(6) to over 10(8) M-1 s(-1). In the case of FA, the O-1(2) quenching activity decreased in the order of FA(2-) (at pH &gt; 10)&gt;&gt; FA(-) (pH 5-9) &gt; FA (pH &lt; 4). The result suggests that deprotonation due to the acid-base equilibrium affects the O-1(2) quenching activity. For both of FA and CA, the phenolate anion under basic conditions (pH 10-12) showed the largest activity probably because of occurrence of the favored chemical quenching through the electron transfer from the phenolate anion to O-1(2). These behaviors would affect several antioxidant assays in vivo and in vitro targeting O-1(2). (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2012.08.021

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

UV irradiation reversibly switches a new insulating and nonmagnetic molecular crystal, BPY[Ni(dmit)(2)](2) (BPY = N,N'-ethylene-2,2'-bipyridinium; Ni(dmit)(2) = bis(1,3-dithiole-2-thione-4,5-dithiolato)nickelate(III)), into a magnetic conductor. This is possible because the bipyridyl derivative cations (BPY2+) trigger a photochemical redox reaction in the crystal to produce a change of similar to 10% in the filling of the Ni(dmit)(2) valence band, leaving localized spins on the BPY themselves. In the dark, almost all of the BPY molecules are closed shell cations, and most of the Ni(dmit)(2). radical anions form spin singlet pairs; thus, this material is a diamagnetic semiconductor. Under UV irradiation, a photocurrent is observed, which enhances the conductivity by 1 order of magnitude Electron-spin resonance. measurements indicate that the 'UV:. irradiation reversibly generates. carriers and localized spins on the Ni(dmit)(2). and the BPY, respectively: This high photoconductivity can be explained by charge transfer (CT) transitions between Ni(dmit)(2) and BPY in the UV region. In other words, the photoconduction and "photomagnetism" can be described as reversible optical control of the electronic states between an ionic salt (BPY2+/[Ni(dmit)(2)](-), nonmagnetic insulator) and a CT complex (BPY2(1-delta)+/[Ni(dmit)(2)]((1-delta)-) (delta approximate to 0.1), magnetic conductor) in the solid state.

DOI： 10.1021/ja306260b

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.jphotochem.2012.06.007

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/jp300771q

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The UV protection and singlet-oxygen ((1)O(2)) quenching activity of intramolecularly hydrogen-bonded hydroxyanthraquinone derivatives found in aloe have been studied by means of laser spectroscopy. The UV protective activity provided by excited-state intramolecular proton-transfer (ESIFT) in these molecules correlates with their (1)O(2) quenching activity, and the UV protective molecules have high (1)O(2)-quenching function. The reason for this correlation can be understood by considering ESIPT-induced distortion of ground-state potential surfaces in encounter complexes with (1)O(2). (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2011.10.006

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The quenching kinetics of superoxide (O(2)(-center dot)) in water/oil (w/o) interface region of Aerosol OT reversed micelle has been investigated with a transient absorption method. Photodecomposition of alpha-tocopherol by 266 nm laser light in the presence of O(2) produced O(2)(-center dot) together with the tocopheroxyl radical (Toc(center dot)). The subsequent reaction between Toc(center dot) and O(2)(-center dot) occurred in the time region of 1-150 mu s after the photoexcitation. There. O(2)(-center dot) kinetics could be traced by monitoring the Toc(center dot) absorption. In an Aerosol OT reversed micelle solution containing vitamin C (VC), VC would be located in water droplets inside the reversed micelle and would react with both Toc(center dot) and O(2)(-center dot) at the w/o interface around the reversed micelle. The Toc(center dot) decay in the time region of 1-150 mu s was accelerated by addition of VC, suggesting that the O(2)(-center dot) quenching by VC progressed as well as the Tor quenching by VC. From a numerical simulation with treating the simultaneous rate equations for Toc(center dot) concentration by Runge-Kutta method, the rate constant for the O(2)(-center dot) quenching by VC could be estimated to be 6.9 x 10(7) M(-1) s(-1). This value is much larger than the corresponding value reported in homogeneous water solution, suggesting that the O(2)(-center dot) quenching by VC indeed occurred at the w/o interface of the reversed micelle. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2010.12.008

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The Langmuir-Blodgett films were prepared by hybridizing the clay minerals (synthetic saponite, synthetic hectorite and sodium montmorillonite)with the floating film of a cationic Ir(III) complex, [Ir(ppy)(2)(dc18bpy)](+) (ppy = 2-phenylpyridine; dc18bpy = 4,4'-dioctadecyl-2,2'-bipyridine). When the single-layered hybrid LB film was irradiated at 430 nm, it emitted light in the visible region, whose intensity responded reversibly to the pressure change of oxygen.

DOI： 10.1039/c0nj00534g

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

Retro: Cyclo[8]isoindole, which has a saddle-shaped geometry (see picture, 2), was synthesized by oxidative coupling of a bicyclo[2.2.2]octadiene(BCOD)- fused 2,2′-bipyrrole followed by a retro-Diels-Alder reaction of BCOD-fused cyclo[8]pyrrole (1). Key trends in the optical spectra of ring-annelated cyclo[8]pyrroles are identified based on magnetic circular dichroism spectra and theorectical calculations. Copyright © 2011 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim.

DOI： 10.1002/anie.201007510

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Free base and zinc porphyrins are linked with fullerene (C(60)) through beta,beta`-pyrrolic positions rather than meso-positions by Diels-Alder reaction of monoanthraporphyrins (H(2)P-mA and ZnP-mA) and C(60) to afford a pi-expanded free base porphyrin-fullerene dyad (H(2)P-C(60)) and its zinc porphyrin-fullerene dyad (ZnP-C(60)) in 86 and 51% yield, respectively The X-ray crystallographic analysis of ZnP-C(60) showed two comma-shaped swirls-like structure in a unit cell The intramolecular center-to-center and edge-to-edge distances between the porphyrin and fullerene moieties were 11 5 and 2 5 angstrom, respectively The porphyrins and fullerenes were packed in layer-by-layer structure and the porphyrins lied down in parallel The Intermolecular center-to-center distances between the neighboring fullerenes were 10 252, 10028, and 10 129 angstrom, which were less than typical van der Waals distance and the pi-pi interaction spread two-dimensionally The energy of the charge-separated (CS) state of ZnP-C(60) (1 11 eV) determined by differential-pulse voltammetry measurements in benzonitrile is significantly lower than those of zinc porphyrin-C(60) dyads linked at meso positions because of the low oxidation potential of the a-expanded ZnP moiety The CS energy of ZnP-C(60) in a nonpolar solvent such as toluene (1 40 V) is lower than the triplet excited state of C(60) ((3)C(60)*), enabling us to attain a longed lived triplet CS state (8 1 mu s) in toluene, detected by nanosecond laser flash photolysis experiments The distance between unpaired electrons in the triplet CS state was determined by the EPR spectrum to be 9 1 angstrom, which agreed with the distance between a zinc atom of the porphyrin and a carbon edge of C(60) in the crystal structure of ZnP-C(60) The rate constants of photoinduced electron transfer and back electron transfer of H(2)P-C(60) and ZnP-C(60), which were determined by femtosecond and nanosecond laser flash photolysis measurements, were analyzed in light of the Marcus theory of electron transfer

DOI： 10.1021/jp102966x

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

A synthesized vitamin K model compound, NQ-6 (2-hexyloxy-1,4-naphthoquinone) showed weak fluorescence around 440 nm in ethanol. Addition of antioxidants such as vitamin E to a NQ-6 solution suppressed the NQ-6 emission quantitatively. A kinetic study on the quenching of the NQ-6 emission by hydrogen-donor type antioxidants (three tocopherol analogues, catechin, and 2,6-di-tert-butyl-4-methylphenol) in ethanol was performed. The quenching rate constant obtained from the Stern-Volmer plots for the steady-state fluorescence intensity was consistent with the second-order rate constant of each antioxidant for the free-radical scavenging. The NQ-6 emission is thought to be the delayed fluorescence caused by the thermal population to the excited singlet state from the triplet state. Thus, the fluorescence quenching occurred through a hydrogen atom transfer reaction from an antioxidant to NQ-6 in the excited triplet state ((3)NQ-6*). The second-order rate constant for the reaction between (3)NQ-6* and a-tocopherol was estimated to be 1.2 x 10(10) M(-1) s(-1) from the quenching parameter and the (3)NQ-6* lifetime in ethanol (1.2 mu s) measured with the transient absorption. From the high reactivity of (3)NQ-6* to the antioxidants and the amphiphilic property of NQ-6 as a vitamin K model, NQ-6 is applicable to the quantitative antioxidant assay as a new fluorescence probe. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2010.07.020

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The singlet oxygen (O-1(2)) behavior in emulsions dispersing natural vitamin E (VE) (alpha-, beta-, gamma-, and delta-tocopherols) was investigated by measuring time-profiles of O-1(2) phosphorescence. The O-1(2) rise and decay dynamics noticeably reflected the existence of VE oil-droplets. The decay rate constant (k(d)) in the a-tocopherol emulsion decreased with increase of VE concentration ([VE]), and became roughly constant in [VE] &gt; 5 x 10(-4)M. This k(d) behavior correlated to the oil-droplet diameter measured by dynamic light scattering. The droplet diameter increased rapidly from 270 to 430 nm with increase of [VE], and reached the limit for dispersing in [VE] &gt;= 5 x 10(-4) M. This result means that the O-1(2) surroundings became more hydrophobic with increase of droplet size. On the other hand, in the emulsions dispersing tocopherols other than alpha-tocopherol, the k(d) values were roughly constant, indicating that the oil-droplets did not contribute to O-1(2) quenching. The droplet diameter in the delta-tocopherol emulsion was around 212-243 nm and was much smaller than that in the alpha-tocopherol emulsion. The peculiar results observed in the alpha-tocopherol emulsion should be due to the large hydrophobicity of alpha-tocopherol which has two methyl-groups neighboring the OH group.

DOI： 10.1246/bcsj.20090277

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

In order to investigate effect of the inhomogeneous dispersion system on photogeneration and decay dynamics of the tocopheroxyl radical (Toc(center dot)), transient absorption and steady-state and time-resolved EPR measurements on photolysis of vitamin E (VE) were carried out. Tocopherol (TocH) is photo-decomposed through electron-detachment in the excited state and the subsequent proton releasing, which produce Toc(center dot) and the solvated electron (e(solv)(-)). The decay of Toc(center dot) is explained by (i) a rapid decay within 2 mu s by recombination between Toc(center dot) and e(solv)(-), (ii) a second-order decay observed in the range of 5-150 mu s by reaction between Toc(center dot) and the superoxide anion radical (O(2)(center dot-)), and (iii) a slow decay in &gt;10 ms by bimolecular self-quenching of Toc(center dot). The Toc(center dot) decay in the VE emulsion was very different from that in the homogeneous solution. In the emulsion, the Toc(center dot) yield was small, the contribution of the reaction with O(2)(center dot-) was rather small, and the decay due to the bimolecular reaction of Toc(center dot) was much accelerated. In the emulsion, Toc(center dot) could not be detected by steady-state EPR, although it could in ethanol. These differences should be caused by the oil-droplet formation in the emulsion. From these results, we can expect that the photostability of the VE emulsion is superior to that of the VE homogeneous solutions. (C) 2010 Elsevier By. All rights reserved.

DOI： 10.1016/j.jphotochem.2010.01.001

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Singlet oxygen ((1)O(2)) quenching by trolox C (TC, 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), which is a water-soluble vitamin E analogue, in ethanol-water solutions and in aqueous SDS and CTAC micelles was studied by measuring the time-profiles of (1)O(2) phosphorescence at 1274 nm. The second-order rate-constant for (1)O(2) quenching by TC was determined in the ethanol-water solution to be 1.03 x 10(8), 6.22 x 10(7) and 6.23 x 10(7) M(-1) s(-1) at pH 2.0, 7.0, and 8.4, respectively. These values mean that the non-dissociated form of TC under acidic conditions has superior activity to the mono-anion form. In aqueous micelle systems, the decay rate of (1)O(2) at first decreased and then increased with increase of the concentration of TC. This behavior is explained in terms of the (1)O(2) quenching by TC in the bulk phase and in terms of shifting the environment surrounding (1)O(2) to lipophilic by dissolving TC in the hydrophobic region inside the micelle. The present investigation on (1)O(2) emission dynamics in inhomogeneous solutions made it possible to detect a little change in the solutions, which affects the environment around (1)O(2) , such as the micelle formation and dissolving solute in the micelle. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotobiol.2009.08.010

Web of Science

Scopus

PubMed

researchmap

Language：Japanese   Publisher：The Vitamin Society of Japan  

Recent studies on the kinetics of the regeneration reactions of vitamin E in solutions by means of stopped-flow spectroscopy confirmed that the quantum effect often plays an important role. Vitamin E may inhibit the autooxidation of lipids in cellular membranes by taking advantage of proton tunneling. It is interesting that the microscopic quantum-mechanical tunneling effect manifests itself in a macroscopic vital function. Although this finding is in conflict with our intuition at first glance, living cells might, in reality, know quantum mechanics very well and use them effectively.

DOI： 10.20632/vso.83.9_521

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The second-order rate constants (k(Q)) of singlet-oxygen quenching by caffeic acid and related phenols were measured in ethanol and toluene. Caffeic acid derivatives deactivate singlet-oxygen largely by physical quenching at k(Q) = 10(6) - 10(7) M-1 s(-1) through the charge-transfer transition state.

DOI： 10.1246/bcsj.82.689

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Series of radical salts derived from a 2,4,6-triphenylpyridinium (TPP) carrying TEMPO-substituent and transition metal complexes were prepared by the anion exchange of the TPP-TEMPO tetrafluoroborate with [n-Bu(4)N][Ni(dmit)(2)], [n-Bu(4)N](2)[Pd(dmit)(2)], [n-Bu(4)N(2)][Pt(dmit)(2)], [n-Bu(4)N][Ni(mnt)(2)], or [n-Bu(4)N](2)[Ni(mnt)(2)] to give crystals with different structural features. While weak antiferromagnetic interactions of the Curie-Weiss behavior of S = 1/2 spin are predominantly observed in the salts of Pd(dmit)(2), Pt(dmit)(2) and Ni(mnt)(2), the magnetic behavior of 1:1 Ni(dmit)(2) salt can be explained by the additional contribution from the spins on Ni(dmit)(2) anions (chi - chi(TEMPO)), obeying the 2D Heisenberg model. A couple of the oxidized salts, [TPP][Ni(dmit)(2)] as well as [TPP](2)[Pd(dmit)(2)], exhibit semi-conducting properties with relatively high room temperature conductivities. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.synthmet.2009.01.046

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

In order to understand the dynamics of antioxidant actions of vitamin E (alpha-, beta-, gamma-, and delta-tocopherols, TocH) in biological systems, kinetic study of the formation and decay reactions of vitamin E radicals (alpha-, beta-, gamma-, and delta-tocopheroxyls, Toc center dot) has been performed in organic solvents, using stopped-flow spectrophotometry. By mixing alpha-, beta-, gamma-, and delta-TocH with aryloxyl radical (ArO center dot) in ethanol, the peaks of the UV-vis absorption due to alpha-, beta-, gamma-, and delta-Toc center dot radical appeared rapidly at ca. 430-340 nm, showed maxima, and then decayed gradually. The second-order rate constants (k(f) and 2k(d)) for the formation and decay (that is, bimolecular disproportionation) reactions of alpha-Toc center dot were determined by comparing the observed curves with the simulation ones obtained by the numerical calculation of differential equations related to the above reactions. From the results, the wavelengths of absorption maxima (lambda(i)(max)) and molar extinction coefficients (epsilon(i)) (i = 1-4) of the optical spectra were determined for alpha-Toc center dot radical. Notable solvent effects have been observed for the reaction rates (k(f) and 2k(d)) and absorption spectra (lambda(i)(max) and epsilon(i)) of alpha-Toc center dot radical. The scheme of the formation and decay reactions of alpha-, beta-, gamma-, and delta-Toc center dot radicals has been discussed based on the results obtained.

DOI： 10.1246/bcsj.82.494

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A study of the kinetics of the proton-transfer reaction in flavonoid in ethanol solution by means of stopped-flow spectroscopy indicated that proton tunneling plays an important role in the antioxidant reaction.

DOI： 10.1246/bcsj.82.216

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The photochemical reactions of vitamin K (VK) with antioxidant vitamins (vitamin E (VE) and vitamin C (VC)) in aqueous hexadecyltrimethylammonium chloride (CTAC), sodium dodecyl sulfate (SDS), and Triton X-100 micelle systems, and in an aerosol OT (AOT) reversed micelle system were investigated by a time-resolved EPR (TR-EPR). The photolysis of VK with VE in the aqueous micelle solutions gave the TR-EPR spectra having strong intensity and net emissive polarization, suggesting that the excited triplet state of VK ((3)VK(center dot)) was rapidly quenched by VE coexisting inside the micelle. On the other hand. the photolysis of VK with VC in the aqueous SDS and CTAC micelle systems gave the spectra having weak intensity, showing that the reaction between (3)VK(center dot) and VC was inefficient in these micelle systems, probably because (3)VK(center dot) scarcely diffused Out from the micelle. The photolysis of VK with VC in the AOT reversed micelle solution gave the spin-correlated radical pair CIDEP spectrum. The result suggests that the long-lived radical pair was generated from the reaction between (3)VK(center dot) and VC in the water/oil interface region of the AOT micelle, although one of the reactants dissolved in the oil phase and another did in the separated water phase. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2008.07.011

Web of Science

Scopus

researchmap

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

DOI： 10.1246/bcsj.81.345

Scopus

researchmap

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1002/biof.5520320107

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOS PRESS  

Detailed kinetic studies have been performed for the reaction of aroxyl (ArO center dot) radical with vitamin E (alpha-, beta-, gamma-, delta-tocopherol, TocH), ubiquinol-10, and related antioxidants in micellar solution, using a stopped-flow spectrophotometer. The second-order reaction rates (k(s)) obtained increased in the order of hydroquinone &lt; tocol &lt;delta-T6cH &lt; ubiquinol-0 &lt;gamma-TocH similar to beta-TocH &lt; ubiquinol-10 &lt;alpha-TocH at pH 4 similar to 9. The antioxidants which have lower oxidation potentials (E(p)) showed higher reactivities. The reaction rates obtained in micellar solution were pH dependent because of the dissociation of OH groups in the antioxidants. For instance, by comparing the k(s) values with the mole fraction of each molecular form of ubiquinol-10, the reaction rate k(s1) (1.21 x 10(5) M(-1)s(-1)) for undissociated form, k(s2) (1.04 x 10(6) M(-1) s(-1)) for monoanion and k(s3) (0 M(-1)s(-1)) for dianion, and the pK(a1) and PK(a2) values (11.4 and 12.7) were determined. It was found that the relative ratio of K(s) values (100:21:20:2.9) of alpha-, beta-, gamma-, delta-tocopherols in micellar dispersion has good correlation with the relative biological activities for rat fetal resorption, rat haemolysis, and chicken muscle dystrophy. The relative antioxidant activities of alpha-tocopherol and ubiquinol-10 have been discussed on the basis of the products of the k(s) values and their concentrations in serum and several tissues (heart, muscle, liver, kidney, and brain).

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The UV protection and singlet oxygen quenching of aloesaponarin I have been studied by means of laser spectroscopy. The excited-state intramolecular proton transfer that provides the UV protection takes place along only one of the molecule's two intramolecular hydrogen bonds, and this can be understood by considering the nodal pattern of the wave function. The functional groups participating in the excited-state intramolecular proton transfer also play important roles in the singlet oxygen quenching. Aloesaponarin I has a quenching rate constant larger than that of vitamin E and has a long duration of action due to its resistance to UV degradation and chemical attacks by singlet oxygen and free radicals.

DOI： 10.1021/jp075224j

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER IRELAND LTD  

The rate constant and activation energy of the regeneration reaction of natural vitamin E by vitamin C were determined with a double-mixing stopped-flow spectrophotometer. The formation of vitamin C radical was observed in the absorption spectrum. The kinetic effect of methyl substitution on the aromatic ring of vitamin E radical indicates that partial charge-transfer plays a role in the reaction. Since a substantial deuterium kinetic isotope effect was not found, the tunneling effect may not play an important role under the present experimental conditions. (c) 2007 Elsevier Ireland Ltd. All rights reserved.

DOI： 10.1016/j.chemphyslip.2006.12.001

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The reaction rates (k(s)) of vitamin E (alpha-, beta-, gamma-, delta-tocopherols, TocH), ubiquinol-10, and related antioxidants (tocol, ubiquinol-0, and hydroquinone) with aroxyl (ArO center dot) radical have been measured in micellar solution by stopped-flow spectrophotometer. The k(s) values increased in the order of hydroquinone &lt; tocol &lt; delta-TocH &lt; ubiquinol-0 &lt; gamma-TocH approximate to beta-TocH &lt; ubiquinol-10 &lt; alpha-TocH at pH 4 similar to 8. The antioxidants which have lower oxidation potentials showed higher reactivities. The k(s) values of alpha-, beta-, gamma-, delta-tocopherol, and tocol remained constant between pH 4 and 10, and decreased rapidly at pH 11 similar to 12 by increasing pH value. From the pH dependence of k(s) values, the pK(a) values (= 13.1 similar to 12.6) have been determined for these tocopherols. The k(s) values of ubiquinol-10 also remained constant between pH 4 and 9, and increased rapidly at pH 9.5. Ubiquinol-10 is dibasic acid and can exist in three different molecular forms, depending on the pH value. By comparing the k(s) values with the mole fraction of each molecular form of ubiquinol-10, the reaction rate k(s1) (= 1.21 x 10(5) M(-1)s(-1)) for the undissociated form, k(s2) (= 1.04 x 10(6) M(-1)s(-1)) for monoanion and k(s3) (= 0 M (-1)s (-1)) for dianion, and the pK(a1) and pK(a2) values (= 11.4 and 12.7) were determined. The k(s2) value is 8.6 times as large as the k(s1) value. Similar analyses were performed for ubiquinol-0 and hydroquinone. It was found that the relative ratio of k(s) values (100:21:20:2.9) of alpha-, beta-, gamma-, delta-tocopherols in micellar dispersion has good correlation with the relative biopotency ratios for rat fetal resorption, rat hemeolysis, and chicken muscle dystrophy. The relative antioxidant activities of alpha-tocopherol and ubiquinol-10 have been discussed based on the k(s) values obtained and their concentrations in serum and several tissues (heart, muscle, liver, kidney, and brain).

DOI： 10.1021/jp0650580

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A kinetic study involving 4-hydroxycinnamic acid derivatives (HCAs) was performed in order to clarify the mechanism for free radical-scavenging and vitamin E-regenerating. The second-order rate constants of the radical-scavenging reaction (k(s)) observed for caffeic acid derivatives are larger than those for ferulic acid derivatives. The result may be explained by i) the lower oxidation potential coming from the existence of the more electron-donating hydroxy group comparing with methoxy group, and ii) the stabilization effect of the corresponding radicals produced in the radical-scavenging reaction through intramolecular hydrogen bonding. The radical-scavenging activity of HCAs in ethanol mainly occurs via the hydrogen atom transfer from the phenolic OH-protons. The pH dependence of k(s) for ferulic acid in the aqueous Triton X-100 micelle solutions suggests the importance of the phenolic OH proton on the radical-scavenging reaction. On the other hand, the pH dependence of k(s) for caffeic acid and chlorogenic acid suggests the occurrence of intramolecular hydrogen bonding and an electron-transfer process in the radical-scavenging reaction.

DOI： 10.1246/bcsj.79.1501

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The anomalous net absorptive CIDEP spectra observed in the photoinduced hydrogen abstraction reaction of chromone (CR) and chromone2-carboxylic acid (CRCA) from 2-propanol with addition of hydrochloric acid (HCl) were investigated with FT-EPR. In neat 2-propanol, the spectra of the ketyl and 2-hydroxypropan-2-yl (2-HP) radicals display E-*/A (low-field side emission and high-field side absorption, the asterisk denoting excess net polarization) or E/A type polarization, which is explained by the STO mixing radical pair mechanism and minor contributions of the triplet mechanism (TM). The addition of HCl to these systems gives the net absorptive CIDEP spectra, while the triplet states of CR and CRCA should have emissive polarizations. The analysis of the time developments of the EPR signals indicates that the radical generation rate increases with the increase of the HCl concentration, while the signal intensity of radicals does not increase. The net absorptive polarization might be explained by non-reactive quenching of the triplet by the spin-sublevel dependent back charge-transfer process in the intermediate exciplex. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jphotochem.2005.12.014

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A kinetic study was performed for edaravone (3-methyl-1-phenyl-2-pyrazolin-5-one) in order to clarify the mechanism of its free-radical-scavenging and vitamin E-regenerating actions. The second-order rate constants for the radical-scavenging reaction of edaravone were measured in several organic solvents and in a water/methanol mixed solvent at various pH. The keto-enol tautomerism and the acid-base dissociation equilibrium of edaravone produce keto, enol, and anion forms in solutions, and their contributions and activities varied depending on the properties of the solutions. From the results of NMR and kinetic studies, it has been clarified that the keto-enol tautomerism of edaravone actually exists, and the keto form has larger radical-scavenging activity than the enol form. Furthermore, the pH dependence of the rate constants suggests that the anion form produced by the acid-base dissociation equilibrium of edaravone has the highest radical-scavenging activity in the keto, enol, and anion forms.

DOI： 10.1246/bcsj.79.421

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Four kinds of 1:1 salts of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl = ethyl and methyl) radical cations with the Ni(dmit)(2) anion ([p-EtPyDV](+)[Ni(dmit)(2)](-) (1), [m-EtPyDV](+)[Ni(dmit)(2)](-) (2), [p-MePyDV](+)[Ni(dmit)(2)](-) (3), and [m-MePyDV](+)[Ni(dmit)(2)](-) (4)) have been prepared. The magnetic properties of salts 1-4 were discussed based on the results obtained by magnetic susceptibility and ESR measurements of 1-4 and the crystal structure analysis of 1. The results of the crystal structure analysis of salt 1 indicate the dimer formation in Ni(dmit)(2) anion molecules, and the dimers are sandwiched between two verdazyl cations [p-EtPyDV](+), indicating the formation of a magnetic linear tetramer in 1. The magnetic susceptibility data for salt 1 have been fitted to a four-spin linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -780 K and a central interaction of 2J(2)/k(B) = -200 K. The conductivity (sigma) of salts 1, 2, 3, and 4 at room temperature was sigma = 2.3 x 10(-5), 1.8 X 10(-4), 1.4 x 10(-5), and 5.4 x 10(-6) S cm(-1) with an activation energy of E-A = 0.28, 0.52, 0.21, and 0.33 eV, respectively. The 1: 1 salts 1-4 are new molecular paramagnetic semiconductors.

DOI： 10.1246/bcsj.78.2114

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Five kinds of (1:1) and (1:3) salts of 3-(4- and 3-alkyl-pyridinium)-1,5-diphenylverdazyl (alkyl = ethyl and methyl) radical cations with Ni(dmit)(2) anion ([p-EtPyDV](+)[Ni(dmit)(2)](3)(-) (1), [m-EtPyDV](+)[Ni(dmit)(2)](-) (2), [p-MePyDV](+)[Ni(dmit)(2)](-) (3), [m-MePyDV](+)[Ni(dmit)(2)](-) (4), and [p-MePyDV](+)[Ni(dmit)(2)](3)(-) (5)) (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) have been prepared, and the magnetic susceptibilities (chi(M)&apos;s) have been measured between 1.8 and 300 K. The chi(M) of salt 1 can be well explained by a four-spin linear tetramer model ([p-EtPyDV](+)-[Ni(dmit)(2)](-)-[Ni(dmit)(2)](-)-[p-EtPyDV](+)) with an end exchange interaction 2J(1)/k(B) = -780 K and a central interaction 2J(2)/k(B) = -200 K. The formation or magnetic tetramer in salt 1 has been ascertained by the crystal structure analysis of 1. The chi(M) of salt 2 was explained by the SUM of the contributions from: (i) a dimer system (2J/k(B) = -320 K) due to Ni(dmit)(2) anions and (ii) the one-dimensional (1D) Heisenberg ferromagnetic linear-chain system (2J k(B) = +2.5 K) due to verdazyl cations. The chi(M) of salt 3 is similar to that of salt 1, suggesting a formation of magnetic tetramer in salt 3. The chi(M) of salt 4 shows a broad maximum at T-max = 100 +/- 2 K, and can be explained by a 1D Heisenberg antiferromagnetic alternating-chain model with 2J(1)/k(B) = -165 K (alternation parameter alpha = J(2)/J(1) = 0.6). The conductivity (sigma) of salts 1, 2, 3 and 4 at 293 K was sigma = 2.3 x 10(-5), 1.1 x 10(-3), 1.4 x 10(-5) and 5.4 x 10(-6) S cm(-1) with an activation energy of E-A = 0.28, 0.52, 0.21 and 0.33 eV, respectively. The (1:3) salt 5 (sigma = 1.0 S cm(-1), E-A = 0.048 eV) showed three to five orders of magnitude higher conductivity than those of the (1:1) salts 1-4 at room temperature. All the (1:1) and (1:3) salts 1-5 are new molecular paramagnetic semiconductors. (c) 2005 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.poly.2005.03.073

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

A novel alpha-diketone precursor of pentacene, 6,13-dihydro-6,13-ethanopentacene-15,16-dione, was prepared and converted successfully to pentacene in 74% yield by photolysis of the precursor in toluene: Irradiation of the diketone solution in toluene with light of 460 nm under an Ar atmosphere caused the solution to change from yellow to fluorescent orange-pink within a few minutes, after which, purple precipitates appeared. After 35 min, the solution changed to colorless and the purple precipitates were filtered to give pentacene in 74% yield. By contrast, in the presence of oxygen, the color of the solution changed from yellow to pale yellow., and only 6,13-endoperoxide of pentacene was quantitatively obtained. The rate of the reaction upon photolysis was measured by observing the decay of n-pi* absorption of the precursor at 460 nm, and was found to be similar in both the presence and absence of oxygen. Therefore, the photoreaction of the alpha-diketone precursor seemed to occur via the singlet excited state. Because the T-T absorption of pentacene was observed upon photolysis of the precursor in the nanosecond transient absorption measurement under an Ar atmosphere, the excited triplet state of the pentacene generated singlet oxygen by sensitization, and it reacted with the ground-state pentacene to give the 6,13-endoperoxide. The alpha-diketone deposited on glass was also converted successfully to pentacene film by photoirradiation. In addition, diketone precursors of a mixture of 2,8- and 2,9-di-bromopentacene and 2,6-trianthrylene were also prepared and their photoconversion was performed.

DOI： 10.1002/chem.200500564

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

A kinetic study of the quenching reaction of singlet oxygen (O-1(2)) with catechins (catechin (CA), epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG), epigallocatechin gallate (EGCG)) and related compounds (5-methoxyresorcinol (MR), 4-methylcatechol (MC), and n-propyl gallate (PG)) was performed in ethanol at 35 degrees C. MR, MC, and PG are considered to be a model of resorcinol (A)-, catechol (B)-, and gallate (G)-rings in catechins, respectively. The overall rate constants, k(Q) ( k(q) + k(r) physical quenching + chemical reaction), for the reaction of catechins with 10, increased in the order of PG &lt; MR &lt; MC &lt; CA &lt; EC &lt; EGC &lt; ECG &lt; EGCG. In a comparison of the rate constants, the relationship between quenching rates and chemical structures is discussed. The catechins which have lower peak oxidation potentials, E-P, show higher reactivities. It was observed that the chemical reaction (k(r)) is almost negligible in the quenching reaction Of O-1(2) by catechins. The kQ values of EGCG (1.47 x 10(8) M-1 s(-1)) and ECG (7.81 X 10(7)) were found to be larger than those of lipids (1.3 x 10(5-)1.9 X 10(5) M-1 s(-1)), amino acids (&lt; 3.7 x 10(7)), and DNA (5.1 x 10). Further, these values are similar to those (1.15 x 10(8)-2.06 x 10(8) M-1 s(-1)) of alpha- and gamma-tocopherol, ubiquinol-10, and gamma-tocopherol hydroquitione (plastoquinol model). The result suggests that catechins may contribute to the protection of oxidative damage in biological systems, by quenching O-1(2). (c) 2005 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.freeradbiomed.2005.04.027

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The reaction rates (k(r)) of 5,7-diisopropyl-tocopheroxyl radical (Toc(center dot)) with catechins (epicatechin (EC), epicatechin gallate (ECG), epigallocatechin (EGC), epigoallocatechin gallate (EGCG)) and related compounds (methyl gallate (MG), 4-methyleatechol (MC), and 5-Foethoxyresorcinol (MR)) have been measured by stopped-flow spectrophotorneter. The k(r), values increased in the order of MR &lt;&lt; MG &lt; EC &lt; MC similar to ECG &lt; FGC &lt; EGCG in ethanol and 2-propanol/H2O (5/1, v/v) solutions, indicating that the reactivity of the OH groups in catechins increased in the order of resorcinol A-ring &lt;&lt; gallate G-ring &lt; catechol B-ring &lt; pyrogallol B-ring. The catechins which have lower oxidation potentials show higher reactivities. The rate constants for catechins in micellar solution showed notable pH dependence with one or two peaks around pH 9-11, because of the dissociation of various phenolic hydroxyl protons in catechins. The Structure-activity relationship in the free-radical-scaveril-ing reaction by catechins has been clarified by the detailed analyses of the pH dependence of kr values. The reaction rates increased remarkably with increasing the anionic character of catechins, that is, the electron-donating capacity of catechins. The mono anion form at catechol B-and resorcinol A-rings and dianion form at pyrogallol B-and gallate G-rings show the highest activity for free-radical-scavenging. It was found that catechins (EC, ECG, EGC, and EGCG) have activity similar to or higher than that of vitamin C in vitamin E regeneration at pH 7-12 in micellar solution. (c) 2005 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.freeradbiomed.2005.01.011

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A kinetic Study was performed for the free-radical scavenging actions of curcumin and half-curcumin, which has a half-structure of curcumin, in order to clarify the mechanism of free-radical-scavenging in curcumin. The second-order rate constants for radical-scavenging reactions of curcumin and half-curcumin were measured by a stopped-flow spectrophotometer in several organic solvents (methanol, ethanol, acetonitrile, chloroform, and benzene) and in aqueous Triton X-100 (5.0 wt %) micelle solutions at various pH. The difference in the rate constant and solvent dependence between curcumin and half-curcumin suggests that the enol structure with the intramolecular hydrogen-bond Of Curcumin strongly enhances the radical-scavenging activity. Furthermore, notable pH dependences were observed for the rate constants of curcumin and half-curcumin in micelle solutions, suggesting that the acid-base dissociation equilibrium of phenol-protons in curcumin and half-curcumin affects their radical-scavenging activities.

DOI： 10.1246/bcsj.78.615

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The quenching rate of singlet oxygen (O-1(2)) by seven kinds of flavonoids (flavone, flavonol, chrysin, apigenin, rutin, quercetin, and myricetin) with 2,3-double bonds has been measured spectrophotometrically in ethanol at 35 degreesC. The overall rate constants k(Q) (=k(q) + k(r), physical quenching + chemical reaction) increased as the number of OH groups substituted to the flavone skeleton (that is, the total electron-donating capacity of flavonoids) increases. The existence of catechol or pyrogallol structure in the B-ring is essential for the O-1(2) quenching of flavonoids. Log k(Q) was found to correlate with their peak oxidation potentials, E-P; the flavonoids that have smaller E-P values show higher reactivities. Similarly, log k(Q) values of flavonoids correlate with the energy level of the highest occupied molecular orbital (E-HOMO), calculated by the PM3 MO method, and the longest wavelength pipi* excitation energy (E-ex). The contribution of the chemical reaction (k(r)) was found to be negligible in these flavonoids. The k(Q) values of rutin, quercetin, and myricetin [(1.21similar to5.12) x 10(8) M-1 s(-1)] were found to be larger than those of lipids [(0.9similar to6.4) x 10(4) M-1 s(-1)], amino acids (&lt; 3.7 x 10(7) M-1 s(-1)),and DNA (5.1 x 10(5) M-1 s(-1)). The result suggests that these flavonoids may contribute to the protection of oxidative damage in foods and plants, by quenching O-1(2).

DOI： 10.1021/jp0451389

Web of Science

Scopus

PubMed

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Four kinds of 1:1 and 1:3 salts of 3-[4-(trimethylammonio)phenyl]-1,5-diphenyl-6-oxoverdazyI radical cation ([1](+)) and its mono- and dimethyl derivatives ([2](+) and [3](+)) with Ni(dmit)(2) anions (d(mit) = 1,3-dithiol-2-thione-4,5-dithiolate) ([1](+)[Ni(dmit)(2)](-) (4), [2](+)[Ni(dmit)(2)](-) (5), [3](+)[Ni(dmit)(2)](-) (6), and [1](+)[Ni(dmit)(2)](3)(-) (7)) have been prepared, and the magnetic susceptibilities (chi(M)) have been measured between 1.8 and 300 K. The chi(M) values of salts 5 and 7 can be well reproduced by the sum of the contributions from (i) a Curie-Weiss system with a Curie constant of 0.376 (K emu)/mol and negative Weiss constants (Theta) of -0.4 and -1.7 K and (ii) a dimer system with strong negative exchange interactions of 2J/k(B) = -354 and -258 K, respectively. The dimer formations in Ni(dmit)(2) anions have been ascertained by the crystal structure analyses of salts 4-6. In salts 4 and 6, Ni(dmit)(2) dimer molecules are sandwiched between two verdazyl cations, indicating the formation of a linear tetramer in 4 and 6. The magnetic susceptibility data for salts 4 and 6 have been fitted to a linear tetramer model using an end exchange interaction of 2J(1)/k(B) = -600 K and a central interaction of 2J(2)/k(B) = -280 K for 4 and 2J(1)/k(B) = -30 K and 2J(2)/k(B) = -580 K for 6, respectively. The results of the temperature dependence of the 9(T) value in salts 4-6 obtained by ESR measurement also support the above analyses. The 1:1 salts 4-6 are insulators. On the other hand, the conductivity of the 1:3 salt 7 at 20 degreesC was sigma = 0.10 S cm(-1) with an activation energy E-A = 0.099 eV, showing the semiconductor property. Salt 7 is a new molecular paramagnetic semiconductor.

DOI： 10.1021/ic030068q

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The excited high-spin quartet (S = 3/2) state of the intramolecular triplet-radical pair between the excited triplet state of pyrene and a dangling verdazyl radical was reported. A novel verdazyl radical with the pyrene moiety was designed and synthesized. The time-resolved ESR spectrum and a DFT calculation show the photo-induced ferromagnetic spin alignment between the excited triplet state of the pyrene moiety and the dangling verdazyl radical. This is the first observation of the high-spin (S &gt; 1) excited state of the pi-conjugated pyrene-radical pair.

DOI： 10.1246/bcsj.77.95

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The photoinitiated reaction between vitamin C and xanthone in sodium lauryl sulfate (SDS), hexadecyltrimethylammonium chloride (CTAC), and Triton X-100 micelle solutions at various pH was investigated by time-resolved electron paramagnetic resonance (TR-EPR). The TR-EPR spectra were explained by superimpositions of the xanthone ketyl and the vitamin C radicals, showing that a fast hydrogen abstraction reaction of the excited xanthone from vitamin C progresses around the water-oil interface region of the micelles. The EPR signal intensity of the vitamin C radical showed the notable pH dependence, which seems to be attributable to the acid-base dissociation equilibrium of vitamin C. The results suggested that the present reaction is controlled by the transportation of the excited xanthone and vitamin C to the reaction-progressing region, which is the surface or inside of the micelle, and by the difference of the reactivity between the dissociation forms of vitamin C.

DOI： 10.1021/jp0353486

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

The models of vitamin K and vitamin E linked molecule, (1-(1,4-naphthoquinone-2-oxy)-6-(hydroxy-2,5,7,8-tetramethylchroman-2-carbonylox y)-hexane), was synthesized as a model of vitamin K and vitamin E which coexist in biological membranes. The time-resolved EPR (TR-EPR) spectra of this molecule could be assigned to vitamin K and E radicals and showed that the excited triplet state of thh vitamin K moiety was rapidly quenched by abstraction of hydrogen from the vitamin E moiety. The broad and emissive CIDEP spectra observed in ethanol suggested that the intramolecular interaction between vitamin K and vitamin E radicals was strong there. The relatively resolved spectra observed in a TX-100 micelle system, on the other hand, indicated that the interaction between these radicals was very weak. These results suggest that the vitamin K and E radicals existed around the water-oil interface of the micelle independently. The absence of a deuterium effect in our experiments showed that tunneling does not contribute significantly to the quenching reaction.

DOI： 10.1021/jp004375i

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Three kinds of (1:1) salts of TCNQF(4) anion with 3-(4trimethylaminophenyl)-1,5-diphenyl-6-oxo-verdazyl radical cation [1(+)] and its mono-methyl [2(+)] and di-methyl [3(+)] derivatives have been prepared, and magnetic property and crystal structure of the salts have been studied. The salts were found to be new genuine organic magnetic compounds consisting of open-shell verdazyl radical cation and electron acceptor TCNQF(4) anion.

DOI： 10.1080/10587250210771

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Studies of the kinetics of the proton- or hydrogen-transfer reactions concerning vitamin E in solutions and in micellar dispersions by means of stopped-flow and absorption spectroscopy indicated that proton tunneling plays an important role in the antioxidant and regeneration reactions that are advantageous in vivo but not as a part of the harmful prooxidant action.

DOI： 10.1021/jp9932113

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The addition effect of hydrochloric acid (HCl) on the photoreduction of chromone-2-carboxylic acid (CRCA) is studied by time-resolved EPR, The EPR lines of CRCA ketyl radical show an enhanced absorption in the presence of HCl, while without HCl these show an emissive character. On the other hand, the lines of the CRCA alkyl type radical show an emissive character whether HCl is included or not. The simultaneous reactions of the closely-lying two excited tripler states (T-1 and T-2) of CRCA may induce the above anomalous CIDEP behavior. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(99)01417-7

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The photosensitized reaction of maleimide (MI) with xanthone (Xn) in 2-propanol was investigated by the time-resolved EPR method. The emissive CIDEP spectrum observed in neat 2-propanol is predominantly assigned to two kinds of MI alkyl-type radicals. On the other hand, the absorptive spectrum of the MI anion radical has been newly observed in 2-propanol including hydrochloric acid. The addition effect of hydrochloric acid indicates the existence of two mechanisms for the photosensitization of MI by Xn. One is a typical triplet-triplet energy transfer followed by hydrogen abstraction by the triplet state of MI from the solvent. The other is an electron-transfer process to MI from the Xn ketyl radical produced primarily by a fast reaction of the triplet Xn with HCl. The spin-polarization transfer mechanism based on these photosensitization processes can successfully explain the present CIDEP results. The effect of water and the sensitizer dependence on the above reaction were also investigated.

DOI： 10.1246/bcsj.73.37

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOCIETY JAPAN  

The magnetic susceptiblities, ESR and powder X-ray patterns of verdazyl radical alloy, (p-CDpOV)(1-x)(p-BDpOV)(x) (x = 0-1), were measured to study the doping effects of magnetic impurities for the quasi-1D Heisenberg ferromagnet (p-CDpOV) and antiferromagnet (p-BDpOV) with S = 1/2, which have similar van der Waals radius to each other. The susceptibility curves systematically change with impurity concentration x. The most noticeable point is that the impurity effect is rather mild on the 1D ferromagnetic Heisenberg system. The characteristic feature of 1D ferromagnet still survives even in the heavily doped sample with x = 0.50. The positive Weiss constant (theta) and the ferromagnetic intrachain exchange interaction (2J(intrachain)) remain constant between x = 0 and 0.50. The results indicate that the p-BDpOV radical functions as an ideal dopant for the 1D ferromagnet; p-CDpOV. This is the first report of the effects of magnetic impurities on the quasi-1D ferromagnetic chain system.

DOI： 10.1143/JPSJ.68.3078

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

CIDEP spectra from free radicals produced by the photolysis of xanthone (Xn) in 2-propanol were investigated with FT-EPR. The spectra were assigned to the 2-hydroxypropan-2-yl (2HP) and xanthone ketyl (XnH) radicals. In pure 2-propanol and 2-propanol containing 10% H2O, the spectra display low field emission/ high field absorption with net emission (E*/A) type polarization. The observed CIDEP pattern is mainly due to the S-To radical pair mechanism (RPM) with minor contributions from the triplet mechanism (TM) and radical triplet pair mechanism (RPM). Upon addition of HCl, the polarization changes to net absorption. The rise time of the absorptive signals is determined by the response time of the spectrometer (similar to 3 x 10(-8) s). Transient optical absorption measurements show that the triplet state of xanthone ((3)Xn*) is quenched by HCl, and the change in spin polarization produced by HCl addition is attributed to this quenching process. The dependence of the CIDEP pattern and triplet xanthone lifetime on HCl concentration shows that both involve a diffusion-controlled process. The main 3Xn(*) quenching process was found to be nonreactive, but it is proposed that its spin selectivity produces spin polarization in the products of the hydrogen abstraction reaction that runs in parallel with this quenching process.

DOI： 10.1021/jp973380s

Web of Science

Scopus

researchmap

Language：Japanese   Publisher：The Crystallographic Society of Japan  

Since a vitamin E radical produced by the antioxidant reaction of vitamin E causes damage to vital functions, ubiquinol and vitamin C regenerate a vitamin E molecule from a vitamin E radical &lt;I&gt;in vivo&lt;/I&gt;. The kinetic studies of the regeneration reactions have been carried out in solutions by means of stopped-flow spectroscopy. Substantial deuterium kinetic-isotope-effects on the second-order rate constants have been observed in both the reactions of ubiquinol and vitamin C. Furthermore, a deviation from a linear relationship in the Arrhenius plot has been observed in the reaction of ubiquinol. These results suggest that the tunneling effect plays an important role in the regeneration reactions in various tissues and mitochondria.

DOI： 10.5940/jcrsj.40.119

CiNii Books

researchmap

Language：English   Publishing type：Research paper (scientific journal)  

Magnetic susceptibilities of 8 kinds of 3-(4-R-phenyl)-1,5-diphenyl-6-oxo- and -thioxoverdazyl radical crystals (p-MDpOV (R = OCH3), p-MeDpOV (R = CH3), p-CyDpOV (R = CN), p-NDpOV (R = NO2), p-MDpTV (R = OCH3), p-MeDpTV (R = CH3), p-CyDpTV (R = CN), and p-NDpTV (R = NO2)) were measured between 4.2 and 300 K. The susceptibilities of p-MDpOV, p-CyDpOV, and p-MDpTV can be well explained by a one-dimensional (1D) antiferromagnetic (AFM) Heisenberg linear chain model with exchange interaction of 2 J/k = −27.3, −27.3, and −10.9 K, respectively. The susceptibility of p-MeDpTV can be interpreted in terms of a 1D AFM Heisenberg alternating chain model with 2 J1/k = −92.0 K (alternation parameter α = J2/J1 = 0.7). On the other hand, the susceptibilities of p-MeDpOV, p-NDpOV, and p-CyDpTV follow the Curie−Weiss law with positive Weiss constants of +2.5, +1.5, and +2.9 K, respectively, and the exchange interactions 2 J/k were estimated to be +7.0, +5.0, and +7.0 K, assuming the one-dimensionality for these radical crystals. The susceptibility of p-NDpTV follows the Curie−Weiss law with a negative Weiss constant of −0.9 K. Ab initio molecular orbital (MO) calculation was performed for five kinds of 6-oxoverdazyl radicals to clear the origin of the intermolecular ferromagnetic exchange interaction that is observed with high probability for these verdazyl radicals. A very strong spin polarization effect has been found, which is advantageous to the intermolecular ferromagnetic interaction.

DOI： 10.1021/jp973241a

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The hydrochloric-acid-addition effect on the photochemical reaction of xanthone in alcohol is studied by a time-resolved ESR technique. The CIDEP spectra of the transient radicals peculiarly reveal an enhanced absorption by the addition of hydrochloric acid, while the ordinary triplet mechanism of xanthone is known to be emissive. The spin-polarization inversion phenomenon is explained by the triplet mechanism induced by the excitation of a ground-state weak charge-transfer complex of xanthone and HCl.

DOI： 10.1021/jp971183n

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The magnetic field dependence of the chemically induced dynamic electron polarization (CIDEP) spectra of spin-correlated radical pairs (SCRPs) was studied by time-resolved EPR at three different external magnetic fields, i.e., X band (9.2 GHz, 330 mT), S band (3.0 GHz, 100 mT), and L band (1.5 GHz, 50 mT). The CIDEP spectra were obtained by the photolysis of three systems, xanthone and 2,6-di-tert-butylphenol (2,6-DBP) in a sodium dodecyl sulfate (SDS) micelle solution, zinc tetrakis(4-sulfonatophenyl)porphyrin (ZnTPPS) and p-benzoquinone (p-BQ) in a cetyltrimethylammonium chloride (CTAC) micelle solution, and acetone in 2-propanol, at low temperatures. In the two micelle systems, the SCRP spectra scarcely depend on the external magnetic field, and the decay times do not change much on going from the X band to the L band. These observations are discussed in terms of the cage escape rate and the spin-lattice relaxation rate. The strong magnetic field dependence found for the net emissive polarization in the CIDEP spectra of the xanthone and 2,6-DBP system is ascribed to the magnetic field dependence of the triplet mechanism (TM). On the other hand, the intensity of the SCRP spectrum in the acetone system drastically decreases with decreasing the magnetic field. This observation is rationalized on the basis of the restricted motions of the SCRPs in the 2-propanol solution at low temperatures.

DOI： 10.1021/jp9619752

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

The Chemically Induced Dynamic Electron Polarization (CIDEP) mechanisms in the hydrogen abstraction reactions of excited azaaromatic compounds; quinoxaline, phenazine, and quinoline are investigated in detail. It is shown that several polarization mechanisms are involved and the observed CIDEP spectra vary strongly depending on various factors such as the concentration, the temperature, the delay time, and the excitation light intensity. The net emissive spin polarization is ascribed mainly to the radical-triplet pair mechanism (RTPM), which is strongly dependent on the concentrations of the radical and triplet molecules. It is shown that the triplet molecules are long-lived and the condition to produce the RTPM polarization is satisfied. The observed time evolutions of the transient EPR signals are qualitatively explained on the basis of the rate equations, which include the RTPM polarization and the relaxation.

DOI： 10.1246/bcsj.69.1517

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The secondary quenching reactions of the 2-hydroxypropan-2-yl radical produced by photolysis of pyrazine, quinoxaline, and p-benzoquinone in 2-propanol were investigated with time-resolved EPR. The quenching rate constants are 6.6 x 10(6), 1.2 x 10(8), and similar to 10(8) M(-1) s(-1) for pyrazine, quinoxaline, and p-benzoquinone, respectively. The time profiles of the transient EPR signals of pyrazinyl and 2-hydroxypropan-2-yl radicals were measured by FT-EPR and analyzed in detail in terms of a reaction scheme involving the primary hydrogen abstraction reaction and the subsequent quenching reaction. It is found that half of the signal intensity of the pyrazinyl radical arises from polarization transfer accompanying 2-hydroxypropan-2-yl quenching by pyrazine.

DOI： 10.1021/jp9527362

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A CIDEP study on the triplet mechanism (TM) was carried out on three systems, zinc tetraphenylporphyrin (TPP) and p-benzoquinone (p-BQ) in alcohols, pyrazine/2-propanol, and maleic anhydride/2-propanol, in three different microwave frequency regions, i.e. X-(9.5 GHz), S-(3.0 GHz), and L-(1.5 GHz) bands. The CIDEP spectra involving TM contributions drastically change depending on the microwave (MW) frequency or the magnetic field. Tn the ZnTPP and p-BQ systems the TM contribution increases with a decrease of the MW frequency, whereas in the other two systems the TM contribution increases with an increase of the MW frequency. The results can be explained by the frequency dependence of the initial spin polarization produced by the TM which is strongly influenced by the rotational correlation time, the zero field splitting, and the reaction rate of the triplet molecule. The experimental results are compared with the predictions of the Atkins-Evans theory. Reasonable agreements between the experimental results and the theoretical predictions are obtained.

DOI： 10.1021/j100051a003

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The results of an FT-EPR study of the CIDEP of 2-propanolyl radical produced by the photochemical reaction of acetone with triethylamine are reported. The time profiles of the signals are explained satisfactorily on the basis of a hydrogen abstraction reaction involving the acetone singlet and/or triplet excited states depending upon the amine concentration and CIDEP mechanisms involving singlet and/or triplet geminate pairs and triplet F pairs together with spin-lattice relaxation.

DOI： 10.1016/0009-2614(94)01310-R

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Chemically induced dynamic electron polarization (CIDEP) in an acetone/2-propanol system is investigated in the L band microwave frequency region at various temperatures. The polarization due to the ST- mechanism is analyzed in terms of the mixing of hyperfine-independent (ST-M-i) and hyperfine-dependent (ST-M-d) mechanisms. At higher temperature, ST-M-d dominates over ST-M-i in the ST-M polarization, while the relative contribution of ST-M-i increases with decreasing temperature. A mechanism of ST-M-d is discussed based on the radical diffusion in solution and a possible contribution of the ST+M polarization in the CIDEP spectrum is discussed.

DOI： 10.1016/0009-2614(94)00541-9

Web of Science

Scopus

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

A triplet photosensitization reaction of maleic anhydride with alcohols and the subsequent secondary reaction were studied by a time-resolved ESR method. The hydrogen abstraction reaction of the C=C bond site of maleic anhydride in the excited triplet state was examined and discussed as the primary step. The adduct radical formed in the secondary reaction between maleic anhydride and alcohol radicals showed a characteristic E/A-shaped hyperfine line(s). This phenomenon can be explained by the CIDEP ''memory transfer'' of the multiplet (E/A) spin polarization of the alcohol radicals to the adduct radical. The spin-lattice relaxation times of the excited triplet state of xanthone as the sensitizer in 2-propanol and cyclohexanol were also estimated.

DOI： 10.1246/bcsj.65.1672

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

DOI： 10.1246/cl.1990.1635

Web of Science

researchmap

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

DOI： 10.1246/bcsj.62.2435

Web of Science

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Korean   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：フレグランスジャーナル社  

CiNii Books

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：AMER CHEMICAL SOC  

Web of Science

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：English  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/jp300771q

Web of Science

researchmap

Language：Japanese   Publisher：コスメトロジー研究振興財団  

CiNii Books

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

DOI： 10.11362/cssj2.55.0_276

CiNii Books

J-GLOBAL

researchmap

Language：Japanese  

DOI： 10.11494/kisoyuki.2011.0.374.0

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：日本粘土学会  

DOI： 10.11362/cssj2.55.0_276

CiNii Books

researchmap

Language：Japanese   Publishing type：Research paper, summary (national, other academic conference)   Publisher：The Society of Physical Organic Chemistry, Japan  

In recent years there has been a growing focus on the chemistry of ring-expanded porphyrins such as hexaphyrins and octaphyrins, because their properties differ markedly from those of conventional porphyrins in a manner that makes them potentially suitable for a number of novel practical applications. First cyclo[8]pyrrole ([30]octaphyrin(0.0.0.0.0.0.0.0)) has been reported by Sessler and his co-workers based on an oxidative-coupling of 2,2&#039;-bipyrrole in 2002. Recently, we reported the first successful synthesis of cyclo[8]isoindole based on an oxidative-coupling of bicyclo[2.2.2]octadiene(BCOD)-fused 2,2&#039;-bipyrrole, followed by the retro-Diels-Alder reaction. Herein we report synthesis 9,10-anthracene- and 1,2-acenaphthylene-fused cyclo[8]pyrroles by oxidative-coupling of 2,2&#039;-bipyrrole and their vis-NIR absorptions, fluorescence spectra and molecular structures by X-ray crystal structural analysis.

DOI： 10.11494/kisoyuki.2011.0.374.0

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (trade magazine, newspaper, online media)  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publisher：THE VITAMIN SOCIETY OF JAPAN  

Recent studies on the kinetics of the regeneration reactions of vitamin E in solutions by means of stopped-flow spectroscopy confirmed that the quantum effect often plays an important role. Vitamin E may inhibit the autooxidation of lipids in cellular membranes by taking advantage of proton tunneling. It is interesting that the microscopic quantum-mechanical tunneling effect manifests itself in a macroscopic vital function. Although this finding is in conflict with our intuition at first glance, living cells might, in reality, know quantum mechanics very well and use them effectively.

DOI： 10.20632/vso.83.9_521

CiNii Books

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：THE VITAMIN SOCIETY OF JAPAN  

DOI： 10.20632/vso.83.5-6_288

CiNii Books

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

DOI： 10.5111/bunkou.55.263

CiNii Books

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Internal/External technical report, pre-print, etc.  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：English   Publishing type：Research paper, summary (international conference)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Web of Science

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (bulletin of university, research institution)  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Authorship：Corresponding author   Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

CiNii Books

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publisher：The Crystallographic Society of Japan  

Since a vitamin E radical produced by the antioxidant reaction of vitamin E causes damage to vital functions, ubiquinol and vitamin C regenerate a vitamin E molecule from a vitamin E radical <I>in vivo</I>. The kinetic studies of the regeneration reactions have been carried out in solutions by means of stopped-flow spectroscopy. Substantial deuterium kinetic-isotope-effects on the second-order rate constants have been observed in both the reactions of ubiquinol and vitamin C. Furthermore, a deviation from a linear relationship in the Arrhenius plot has been observed in the reaction of ubiquinol. These results suggest that the tunneling effect plays an important role in the regeneration reactions in various tissues and mitochondria.

DOI： 10.5940/jcrsj.40.119

CiNii Books

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (bulletin of university, research institution)  

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Language：Japanese  

J-GLOBAL

researchmap

Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Event date： 2022.11

Language：Japanese   Presentation type：Poster presentation  

researchmap

Event date： 2021.6

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation (general)  

researchmap

Event date： 2020.6

Language：Japanese  

researchmap