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Mehran Mostafavi - One of the best experts on this subject based on the ideXlab platform.
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time dependent yield of the hydrated electron and the hydroxyl radical in d2o a picosecond Pulse Radiolysis study
Physical Chemistry Chemical Physics, 2018Co-Authors: Furong Wang, Uli Schmidhammer, J.-p. Larbre, Jeanlouis Marignier, Zizhao Zong, Mehran MostafaviAbstract:Picosecond Pulse Radiolysis measurements were performed in neat D2O and H2O in order to study the isotopic effect on the time-resolved yield of the hydrated electron and hydroxyl radical. First, the absorption band of the hydrated electron in D2O, eD2O−, is measured between 250 and 1500 nm. The molar absorption coefficient of the solvated electron spectrum in D2O was determined using the isosbestic point method by scavenging the solvated electron using methyl viologen. The amplitude and shape of the absorption spectrum of the hydrated electron in D2O are different from those previously reported in the literature. The maximum of the hydrated electron in the D2O absorption band is ca. 704 nm with a molar absorption coefficient of (22 900 ± 500) L mol−1 cm−1. Based on this extinction coefficient, the radiolytic yield of eD2O− just after the 7 ps electron Pulse was determined to be (4.4 ± 0.2) × 10−7 mol J−1, which coincides with the one for eH2O− in H2O. The time-dependent radiolytic yield of eD2O− was determined from a few ps to 8 ns. To determine the OD˙ radical yield, the contribution of the solvated electron and of the transient species produced by the electron Pulse in the windows of the fused silica optical cell was taken into account for the analysis of the transient absorption measurements at 260 nm. Therefore, an appropriate experimental methodology is used for measuring low absorbance at two different wavelengths in ps Pulse Radiolysis. The yield of the OD˙ radical just after the 7 ps electron Pulse was found to be (5.0 ± 0.2) × 10−7 mol J−1. In the spurs of ionization, the decay rate of eD2O− is slower than eH2O−, whereas the decay rate of OD˙ is similar to the one of OH˙. Here, the established time-dependent yield of the solvated electron and the hydroxyl radical provide the foundation for improving the models used for spur reaction simulations in heavy water mainly for the chemistry of CANDU reactors.
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radiation induced chemical reactions in hydrogel of hydroxypropyl cellulose hpc a Pulse Radiolysis study
Radiation Research, 2016Co-Authors: Shinichi Yamashita, Mehran Mostafavi, Jeanlouis Marignier, Akihiro Hiroki, Mitsumasa Taguchi, Yosuke KatsumuraAbstract:We performed studies on Pulse Radiolysis of highly transparent and shape-stable hydrogels of hydroxypropyl cellulose (HPC) that were prepared using a radiation-crosslinking technique. Several fundamental aspects of radiation-induced chemical reactions in the hydrogels were investigated. With radiation doses less than 1 kGy, degradation of the HPC matrix was not observed. The rate constants of the HPC composing the matrix, with two water decomposition radicals [hydroxyl radical (•OH) and hydrated electron ()] in the gels, were determined to be 4.5 × 109 and 1.8 × 107 M−1 s−1, respectively. Direct ionization of HPC in the matrix slightly increased the initial yield of , but the additionally produced amount of disappeared immediately within 200 ps, indicating fast recombination of with hole radicals on HPC or on surrounding hydration water molecules. Reactions of with nitrous oxide (N2O) and nitromethane (CH3NO2) were also examined. Decay of due to scavenging by N2O and CH3NO2 were both slower in hydrogels t...
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picosecond Pulse Radiolysis of highly concentrated phosphoric acid solutions mechanism of phosphate radical formation
Journal of Physical Chemistry B, 2015Co-Authors: Uli Schmidhammer, Mehran MostafaviAbstract:Eight solutions containing phosphoric acid with concentrations ranging from 2 mol L–1 to neat acid have been studied by picosecond Pulse Radiolysis. The absorbance of the secondary radical H2PO4• f...
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direct evidence for transient pair formation between a solvated electron and h3o observed by picosecond Pulse Radiolysis
Journal of Physical Chemistry Letters, 2014Co-Authors: Uli Schmidhammer, Mehran MostafaviAbstract:The reaction between the solvated electron and hydronium cation H3O+ in water constitutes a fundamental reaction in chemistry. Due to significant rearrangement of solvent molecules around both the electron and H3O+, the reaction rate of this process is not controlled by diffusion. The presence of a reaction barrier suggests the formation of an intermediate that has so far not been observed. Here, the time-resolved visible absorption spectra in three concentrated acid solutions, perchloric, sulfuric, and phosphoric, at various concentrations are recorded by the picosecond Pulse Radiolysis method. In contrast to previous reports, a strong blue shift of the absorption band of the solvated electron in acidic solutions compared to neat water is clearly observed, consistent with formation of a pair between the solvated electron and hydronium cation.
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spur reactions observed by picosecond Pulse Radiolysis in highly concentrated bromide aqueous solutions
Journal of Physical Chemistry A, 2013Co-Authors: Abdel Karim El Omar, Uli Schmidhammer, Anna Balcerzyk, Jay A Laverne, Mehran MostafaviAbstract:The formation of the well-known product Br3–, observed in the steady-state Radiolysis of highly concentrated Br– aqueous solutions, has now been directly observed at ultrashort times corresponding to the relaxation of the spur. The transient absorption induced by picosecond Pulse Radiolysis of 6 M Br– aqueous solution was probed simultaneously at 260 nm with the third harmonic laser wave and from 350 to 750 nm with a supercontinuum generated by the fundamental laser wave. This approach allows several transient radiolytic species to be followed in parallel, particularly the solvated electron, BrOH–•, Br2–•, and Br3–. The kinetics measured within 4 ns at 260 and 370 nm clearly exhibit that the decay of Br2•– is correlated with the formation of Br3–. In highly concentrated Br– solutions, the OH• radical is fully replaced by Br2•–, and the spur kinetics of OH• radical in pure water is comparable with that of Br2–•. Model calculations indicate that the main OH• radical combination product H2O2 in pure water ha...
Tetsuro Majima - One of the best experts on this subject based on the ideXlab platform.
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proton transfer of guanine radical cations studied by time resolved resonance raman spectroscopy combined with Pulse Radiolysis
Journal of Physical Chemistry Letters, 2015Co-Authors: Jungkweon Choi, Mamoru Fujitsuka, Sachiko Tojo, Cheolhee Yang, Hyotcherl Ihee, Tetsuro MajimaAbstract:The oxidation of guanine (G) is studied by using transient absorption and time-resolved resonance Raman spectroscopies combined with Pulse Radiolysis. The transient absorption spectral change demonstrates that the neutral radical of G (G•(−H+)), generated by the deprotonation of G radical cation (G•+), is rapidly converted to other G radical species. The formation of this species shows the pH dependence, suggesting that it is the G radical cation (G•+)′ formed from the protonation at the N7 of G•(−H+). On one hand, most Raman bands of (G•+)′ are up-shifted relative to those of G, indicating the increase in the bonding order of pyrimidine (Pyr) and imidazole rings. The (G•+)′ exhibits the characteristic CO stretching mode at ∼1266 cm–1 corresponding to a C–O single bond, indicating that the unpaired electron in (G•+)′ is localized on the oxygen of the Pyr ring.
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photodissociation of pyrene dimer radical cation during the Pulse Radiolysis laser flash photolysis combined method
Research on Chemical Intermediates, 2013Co-Authors: Shingo Samori, Mamoru Fujitsuka, Tetsuro MajimaAbstract:Photodissociation of pyrene (Py) dimer radical cation (Py2∙+) giving pyrene radical cation (Py∙+) and Py and subsequent regeneration of Py2∙+ by association of Py∙+ and Py were directly observed during the Pulse Radiolysis–laser flash photolysis combined method at room temperature. When Py2∙+ was excited at the local excitation band with the 532-nm laser flash, the rapid growth and decay of monomeric Py∙+ were observed at 460 nm. The dissociation of Py2∙+ proceeded via a one-photon process to give the ground-state Py∙+(D0) and Py in the quantum yield (Φdiss) of (2.9 ± 0.9) × 10−3. It was shown that Py∙+ decayed with a time constant of several tens of nanoseconds, indicating that the association of Py∙+ with Py regenerating Py2∙+ proceeds at a diffusion-controlled rate. The photodissociation proceeded from the lowest excited state of Py2∙+, even when Py2∙+ was excited to the higher excited state. The difference between the Φdiss value of Py2∙+ and that previously reported for naphthalene dimer radical cation (Np2∙+) is discussed.
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Folding dynamics of cytochrome c using Pulse Radiolysis.
Journal of the American Chemical Society, 2012Co-Authors: Jungkweon Choi, Mamoru Fujitsuka, Sachiko Tojo, Tetsuro MajimaAbstract:Pulse Radiolysis is a powerful method to realize real-time observation of various redox processes, which induces various structural and functional changes occurring in biological systems. However, its application has been mainly limited to studies of the redox reactions of rather smaller biological systems such as DNA because of an undesired reaction due to various free radicals generated by Pulse Radiolysis. For application of Pulse Radiolysis to generate plenty of redox reactions of biological systems, selective redox reactions induced by electron Pulses have to be developed. In this study, we report that in the presence of the high concentration of the denaturant, guanidine HCl (GdHCl), the selective reduction of the oxidized cytochrome c (Cyt c) takes place in time scales of a few microseconds by the electron transfer from the guanidine radical that is formed by the fast reaction of eaq– with GdHCl, consequently leading to folding kinetics of Cyt c. By providing insight into the folding dynamics of Cy...
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donor acceptor substituted tetrakis phenylethynyl benzenes as emissive molecules during Pulse Radiolysis in benzene
Journal of Organic Chemistry, 2007Co-Authors: Shingo Samori, Mamoru Fujitsuka, Sachiko Tojo, Eric L Spitler, Michael M Haley, Tetsuro MajimaAbstract:Emission from charge recombination between radical cations and anions of various tetrakis(phenylethynyl)benzenes (TPEBs) was measured during Pulse Radiolysis in benzene (Bz). The formation of TPEB in the singlet excited state (1TPEB*) can be attributed to the charge recombination between TPEB*+ and TPEB*-, which are initially generated from the radiolytic reaction in Bz. This mechanism is reasonably explained by the relationship between the annihilation enthalpy change (-DeltaH degrees) for the charge recombination of TPEB*+ and TPEB*- and excitation energy of 1TPEB*. It was found that the charge recombination between TPEB*+ and TPEB*- occurred to give 1TPEB* as the emissive species, but not the excimers because of the large repulsion between substituents caused by the rotation around C-C single bonds of TPEBs. Since donor-acceptor-substituted TPEBs possess three types of charge-transfer pathways (linear-conjugated, cross-conjugated, and "bent" conjugated pathways between the donor and acceptor substituents through the ethynyl linkage), the emission spectra of 1TPEBs* with intramolecular charge transfer (ICT) character depend on the substitution pattern and the various kinds of donor and acceptor groups during Pulse Radiolysis in Bz.
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photophysical and photochemical properties of corannulenes studied by emission and optoacoustic measurements laser flash photolysis and Pulse Radiolysis
Chemical Physics Letters, 2006Co-Authors: Minoru Yamaji, Mamoru Fujitsuka, Sachiko Tojo, Tetsuro Majima, Kazuyuki Takehira, Takaaki Mikoshiba, Yukihiro Okada, Seiji Tobita, Jun NishimuraAbstract:Abstract Photophysical and photochemical properties of corannulene (CA) and tetrabromocorannulene (TBCA) in solution were investigated as follows. Spectra, quantum yields and lifetimes of fluorescence in solution at 295 K, and spectra and lifetimes of phosphorescence in a rigid matrix at 77 K were determined. Phosphorescence at 295 K was observed from TBCA. Intersystem crossing yields were determined to be as large as 0.9 by optoacoustic techniques. Triplet–triplet absorption spectra were obtained by laser flash photolysis. Absorption spectra of the radical cation and anion of CA were obtained by Pulse Radiolysis techniques.
Seiichi Tagawa - One of the best experts on this subject based on the ideXlab platform.
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femtosecond Pulse Radiolysis study of geminate ion recombination in biphenyl dodecane solution
Radiation Physics and Chemistry, 2013Co-Authors: Takafumi Kondoh, Jinfeng Yang, Seiichi Tagawa, Koichi Kan, Takahiro Kozawa, K Norizawa, Atsushi Ogata, Yoichi YoshidaAbstract:The kinetics of geminate ion recombination was studied by the femtosecond Pulse Radiolysis of n-dodecane with biphenyl solution. The complicated biphenyl concentration-dependence behaviors of the transient absorptions at 800 nm are observed and elucidated with a Monte Carlo simulation of geminate recombination and charge transfer processes in the biphenyl-dodecane solution. The experimental data suggested the existence of n-dodecane excited radical cation in the Radiolysis. It plays very important roles especially in the high-concentration solution. The reaction rate constant of the excited radical cation with biphenyl molecule was 3.5 � 10 11 dm 3 mol � 1 s � 1 , which is comparable with the reaction rate constant of the electron with biphenyl molecule. The contributions of the geminate ion recombination, the charge transfer reaction and the relaxation of the excited radical cation were obtained as a function of the biphenyl concentration.
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subpicosecond Pulse Radiolysis in liquid methyl substituted benzene derivatives
Radiation Physics and Chemistry, 2007Co-Authors: Kazumasa Okamoto, Yoichi Yoshida, Takahiro Kozawa, Akinori Saeki, Seiichi TagawaAbstract:Abstract The early processes of radiation chemistry in the picosecond time region in methyl-substituted benzene derivatives have been investigated using subpicosecond Pulse Radiolysis. In o -xylene, a fairly slow geminate ion recombination was observed within 50 ps after the electron beam irradiation; this is due to the smaller electron mobility. The kinetic traces were analyzed using the Smoluchowski equation with exponential and modified-Gaussian (YGP) functions as the distribution of thermalized electrons. Only exponential functions well reproduced the experimental data within 50 ps after the electron Pulse.
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Pulse Radiolysis based on a femtosecond electron beam and a femtosecond laser light with double Pulse injection technique
Radiation Physics and Chemistry, 2006Co-Authors: Jinfeng Yang, Takafumi Kondoh, Y Yoshida, Takahiro Kozawa, Seiichi TagawaAbstract:Abstract A new Pulse Radiolysis system based on a femtosecond electron beam and a femtosecond laser light with oblique double-Pulse injection was developed for studying ultrafast chemical kinetics and primary processes of radiation chemistry. The time resolution of 5.2 ps was obtained by measuring transient absorption kinetics of hydrated electrons in water. The optical density of hydrated electrons was measured as a function of the electron charge. The data indicate that the double-laser-Pulse injection technique was a powerful tool for observing the transient absorptions with a good signal to noise ratio in Pulse Radiolysis.
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Pulse Radiolysis study on proton and charge transfer reactions in solid poly methyl methacrylate
Japanese Journal of Applied Physics, 2004Co-Authors: Atsuro Nakano, Kazumasa Okamoto, Takahiro Kozawa, Seiichi TagawaAbstract:Poly(methyl methacrylate) (PMMA) is a good matrix for a case study aimed at understanding reaction mechanisms of electron beam, X-ray and EUV resists. Radiation-induced reactions and proton dynamics of solid PMMA were studied under room temperature by Pulse Radiolysis. PMMA samples were doped with pyrene (Py), crystal violet lactone (CVL) or an anion scavenger to observe charge and proton transfer reactions in the solid matrix. The time-dependent behavior of ionic radicals was observed with the time resolution of 10 ns. The electron transfer from PMMA anion radicals to the anion scavenger or Py was observed in the time range of several hundred nanoseconds. The dynamics of protons generated in irradiated PMMA was traced using CVL. The growth of optical absorbance attributed to proton adducts of CVL was observed in the time range of several hundreds minutes. Protons derived from PMMA cation radicals have a long lifetime and migrated in the solid PMMA matrix.
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direct observation of guanine radical cation deprotonation in duplex dna using Pulse Radiolysis
Journal of the American Chemical Society, 2003Co-Authors: Kazuo Kobayashi, Seiichi TagawaAbstract:The dynamics of one-electron oxidation of guanine (G) base mononucleotide and that in DNA have been investigated by Pulse Radiolysis. The radical cation (G+.) of deoxyguanosine (dG), produced by oxidation with SO4-., rapidly deprotonates to form the neutral G radical (G(−H).) with a rate constant of 1.8 × 107 s-1 at pH 7.0, as judged from transient spectroscopy. With experiments using different double-stranded oligonucleotides containing G, GG, and GGG sequences, the absorbance increases at 625 nm, characteristic of formation of the G(−H)., were found to consist of two phases. The rate constants of the faster (∼1.3 × 107 s-1) and slower phases (∼3.0 × 106 s-1) were similar for the different oligonucleotides. On the other hand, in the oligonucleotide containing G located at the 5‘- and 3‘-terminal positions, only the faster phase was seen. These results suggest that the lifetime of the radical cation of the G:C base pair (GC+.), depending on its location in the DNA chain, is longer than that of free dG. In...
Uli Schmidhammer - One of the best experts on this subject based on the ideXlab platform.
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time dependent yield of the hydrated electron and the hydroxyl radical in d2o a picosecond Pulse Radiolysis study
Physical Chemistry Chemical Physics, 2018Co-Authors: Furong Wang, Uli Schmidhammer, J.-p. Larbre, Jeanlouis Marignier, Zizhao Zong, Mehran MostafaviAbstract:Picosecond Pulse Radiolysis measurements were performed in neat D2O and H2O in order to study the isotopic effect on the time-resolved yield of the hydrated electron and hydroxyl radical. First, the absorption band of the hydrated electron in D2O, eD2O−, is measured between 250 and 1500 nm. The molar absorption coefficient of the solvated electron spectrum in D2O was determined using the isosbestic point method by scavenging the solvated electron using methyl viologen. The amplitude and shape of the absorption spectrum of the hydrated electron in D2O are different from those previously reported in the literature. The maximum of the hydrated electron in the D2O absorption band is ca. 704 nm with a molar absorption coefficient of (22 900 ± 500) L mol−1 cm−1. Based on this extinction coefficient, the radiolytic yield of eD2O− just after the 7 ps electron Pulse was determined to be (4.4 ± 0.2) × 10−7 mol J−1, which coincides with the one for eH2O− in H2O. The time-dependent radiolytic yield of eD2O− was determined from a few ps to 8 ns. To determine the OD˙ radical yield, the contribution of the solvated electron and of the transient species produced by the electron Pulse in the windows of the fused silica optical cell was taken into account for the analysis of the transient absorption measurements at 260 nm. Therefore, an appropriate experimental methodology is used for measuring low absorbance at two different wavelengths in ps Pulse Radiolysis. The yield of the OD˙ radical just after the 7 ps electron Pulse was found to be (5.0 ± 0.2) × 10−7 mol J−1. In the spurs of ionization, the decay rate of eD2O− is slower than eH2O−, whereas the decay rate of OD˙ is similar to the one of OH˙. Here, the established time-dependent yield of the solvated electron and the hydroxyl radical provide the foundation for improving the models used for spur reaction simulations in heavy water mainly for the chemistry of CANDU reactors.
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picosecond Pulse Radiolysis of highly concentrated phosphoric acid solutions mechanism of phosphate radical formation
Journal of Physical Chemistry B, 2015Co-Authors: Uli Schmidhammer, Mehran MostafaviAbstract:Eight solutions containing phosphoric acid with concentrations ranging from 2 mol L–1 to neat acid have been studied by picosecond Pulse Radiolysis. The absorbance of the secondary radical H2PO4• f...
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direct evidence for transient pair formation between a solvated electron and h3o observed by picosecond Pulse Radiolysis
Journal of Physical Chemistry Letters, 2014Co-Authors: Uli Schmidhammer, Mehran MostafaviAbstract:The reaction between the solvated electron and hydronium cation H3O+ in water constitutes a fundamental reaction in chemistry. Due to significant rearrangement of solvent molecules around both the electron and H3O+, the reaction rate of this process is not controlled by diffusion. The presence of a reaction barrier suggests the formation of an intermediate that has so far not been observed. Here, the time-resolved visible absorption spectra in three concentrated acid solutions, perchloric, sulfuric, and phosphoric, at various concentrations are recorded by the picosecond Pulse Radiolysis method. In contrast to previous reports, a strong blue shift of the absorption band of the solvated electron in acidic solutions compared to neat water is clearly observed, consistent with formation of a pair between the solvated electron and hydronium cation.
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spur reactions observed by picosecond Pulse Radiolysis in highly concentrated bromide aqueous solutions
Journal of Physical Chemistry A, 2013Co-Authors: Abdel Karim El Omar, Uli Schmidhammer, Anna Balcerzyk, Jay A Laverne, Mehran MostafaviAbstract:The formation of the well-known product Br3–, observed in the steady-state Radiolysis of highly concentrated Br– aqueous solutions, has now been directly observed at ultrashort times corresponding to the relaxation of the spur. The transient absorption induced by picosecond Pulse Radiolysis of 6 M Br– aqueous solution was probed simultaneously at 260 nm with the third harmonic laser wave and from 350 to 750 nm with a supercontinuum generated by the fundamental laser wave. This approach allows several transient radiolytic species to be followed in parallel, particularly the solvated electron, BrOH–•, Br2–•, and Br3–. The kinetics measured within 4 ns at 260 and 370 nm clearly exhibit that the decay of Br2•– is correlated with the formation of Br3–. In highly concentrated Br– solutions, the OH• radical is fully replaced by Br2•–, and the spur kinetics of OH• radical in pure water is comparable with that of Br2–•. Model calculations indicate that the main OH• radical combination product H2O2 in pure water ha...
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competition reactions of h2o radical in concentrated cl aqueous solutions picosecond Pulse Radiolysis study
Journal of Physical Chemistry A, 2012Co-Authors: Abdel Karim El Omar, Uli Schmidhammer, Jay A Laverne, Bernard Rousseau, Mehran MostafaviAbstract:Picosecond Pulse–probe Radiolysis measurements of highly concentrated Cl– aqueous solutions are used to probe the oxidation mechanism of the Cl–. The transient absorption spectra are measured from 340 to 710 nm in the picosecond range for the ultrafast electron Pulse Radiolysis of halide solutions at different concentrations up to 8 M. The amount of Cl2•– formation within the electron Pulse increases notably with increasing Cl– concentration. Kinetic measurements reveal that the direct ionization of Cl– cannot solely explain the significant amount of fast Cl2•– formation within the electron Pulse. The results suggest that Cl– reacts with the precursor of the OH• radical, i.e., H2O•+ radical, to form Cl• atom within the electron Pulse and the Cl• atom reacts subsequently with Cl– to form Cl2•– on very short time scales. The proton transfer reaction between H2O•+ and the water molecule competes with the electron transfer reaction between Cl– and H2O•+. Molecular dynamics simulations show that number of wate...
Mamoru Fujitsuka - One of the best experts on this subject based on the ideXlab platform.
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proton transfer of guanine radical cations studied by time resolved resonance raman spectroscopy combined with Pulse Radiolysis
Journal of Physical Chemistry Letters, 2015Co-Authors: Jungkweon Choi, Mamoru Fujitsuka, Sachiko Tojo, Cheolhee Yang, Hyotcherl Ihee, Tetsuro MajimaAbstract:The oxidation of guanine (G) is studied by using transient absorption and time-resolved resonance Raman spectroscopies combined with Pulse Radiolysis. The transient absorption spectral change demonstrates that the neutral radical of G (G•(−H+)), generated by the deprotonation of G radical cation (G•+), is rapidly converted to other G radical species. The formation of this species shows the pH dependence, suggesting that it is the G radical cation (G•+)′ formed from the protonation at the N7 of G•(−H+). On one hand, most Raman bands of (G•+)′ are up-shifted relative to those of G, indicating the increase in the bonding order of pyrimidine (Pyr) and imidazole rings. The (G•+)′ exhibits the characteristic CO stretching mode at ∼1266 cm–1 corresponding to a C–O single bond, indicating that the unpaired electron in (G•+)′ is localized on the oxygen of the Pyr ring.
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photodissociation of pyrene dimer radical cation during the Pulse Radiolysis laser flash photolysis combined method
Research on Chemical Intermediates, 2013Co-Authors: Shingo Samori, Mamoru Fujitsuka, Tetsuro MajimaAbstract:Photodissociation of pyrene (Py) dimer radical cation (Py2∙+) giving pyrene radical cation (Py∙+) and Py and subsequent regeneration of Py2∙+ by association of Py∙+ and Py were directly observed during the Pulse Radiolysis–laser flash photolysis combined method at room temperature. When Py2∙+ was excited at the local excitation band with the 532-nm laser flash, the rapid growth and decay of monomeric Py∙+ were observed at 460 nm. The dissociation of Py2∙+ proceeded via a one-photon process to give the ground-state Py∙+(D0) and Py in the quantum yield (Φdiss) of (2.9 ± 0.9) × 10−3. It was shown that Py∙+ decayed with a time constant of several tens of nanoseconds, indicating that the association of Py∙+ with Py regenerating Py2∙+ proceeds at a diffusion-controlled rate. The photodissociation proceeded from the lowest excited state of Py2∙+, even when Py2∙+ was excited to the higher excited state. The difference between the Φdiss value of Py2∙+ and that previously reported for naphthalene dimer radical cation (Np2∙+) is discussed.
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Folding dynamics of cytochrome c using Pulse Radiolysis.
Journal of the American Chemical Society, 2012Co-Authors: Jungkweon Choi, Mamoru Fujitsuka, Sachiko Tojo, Tetsuro MajimaAbstract:Pulse Radiolysis is a powerful method to realize real-time observation of various redox processes, which induces various structural and functional changes occurring in biological systems. However, its application has been mainly limited to studies of the redox reactions of rather smaller biological systems such as DNA because of an undesired reaction due to various free radicals generated by Pulse Radiolysis. For application of Pulse Radiolysis to generate plenty of redox reactions of biological systems, selective redox reactions induced by electron Pulses have to be developed. In this study, we report that in the presence of the high concentration of the denaturant, guanidine HCl (GdHCl), the selective reduction of the oxidized cytochrome c (Cyt c) takes place in time scales of a few microseconds by the electron transfer from the guanidine radical that is formed by the fast reaction of eaq– with GdHCl, consequently leading to folding kinetics of Cyt c. By providing insight into the folding dynamics of Cy...
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donor acceptor substituted tetrakis phenylethynyl benzenes as emissive molecules during Pulse Radiolysis in benzene
Journal of Organic Chemistry, 2007Co-Authors: Shingo Samori, Mamoru Fujitsuka, Sachiko Tojo, Eric L Spitler, Michael M Haley, Tetsuro MajimaAbstract:Emission from charge recombination between radical cations and anions of various tetrakis(phenylethynyl)benzenes (TPEBs) was measured during Pulse Radiolysis in benzene (Bz). The formation of TPEB in the singlet excited state (1TPEB*) can be attributed to the charge recombination between TPEB*+ and TPEB*-, which are initially generated from the radiolytic reaction in Bz. This mechanism is reasonably explained by the relationship between the annihilation enthalpy change (-DeltaH degrees) for the charge recombination of TPEB*+ and TPEB*- and excitation energy of 1TPEB*. It was found that the charge recombination between TPEB*+ and TPEB*- occurred to give 1TPEB* as the emissive species, but not the excimers because of the large repulsion between substituents caused by the rotation around C-C single bonds of TPEBs. Since donor-acceptor-substituted TPEBs possess three types of charge-transfer pathways (linear-conjugated, cross-conjugated, and "bent" conjugated pathways between the donor and acceptor substituents through the ethynyl linkage), the emission spectra of 1TPEBs* with intramolecular charge transfer (ICT) character depend on the substitution pattern and the various kinds of donor and acceptor groups during Pulse Radiolysis in Bz.
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photophysical and photochemical properties of corannulenes studied by emission and optoacoustic measurements laser flash photolysis and Pulse Radiolysis
Chemical Physics Letters, 2006Co-Authors: Minoru Yamaji, Mamoru Fujitsuka, Sachiko Tojo, Tetsuro Majima, Kazuyuki Takehira, Takaaki Mikoshiba, Yukihiro Okada, Seiji Tobita, Jun NishimuraAbstract:Abstract Photophysical and photochemical properties of corannulene (CA) and tetrabromocorannulene (TBCA) in solution were investigated as follows. Spectra, quantum yields and lifetimes of fluorescence in solution at 295 K, and spectra and lifetimes of phosphorescence in a rigid matrix at 77 K were determined. Phosphorescence at 295 K was observed from TBCA. Intersystem crossing yields were determined to be as large as 0.9 by optoacoustic techniques. Triplet–triplet absorption spectra were obtained by laser flash photolysis. Absorption spectra of the radical cation and anion of CA were obtained by Pulse Radiolysis techniques.
