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Journal Articles

Radiation-induced effects on the extraction properties of hexa-$$n$$-octylnitrilo-triacetamide (HONTA) complexes of americium and europium

Toigawa, Tomohiro; Peterman, D. R.*; Meeker, D. S.*; Grimes, T. S.*; Zalupski, P. R.*; Mezyk, S. P.*; Cook, A. R.*; Yamashita, Shinichi*; Kumagai, Yuta; Matsumura, Tatsuro; et al.

Physical Chemistry Chemical Physics, 23(2), p.1343 - 1351, 2021/01

 Times Cited Count:0 Percentile:100(Chemistry, Physical)

The candidate An(III)/Ln(III) separation ligand hexa-$$n$$-octylnitrilo-triacetamide (HONTA) was irradiated under envisioned SELECT (Solvent Extraction from Liquid waste using Extractants of CHON-type for Transmutation) process conditions using a solvent test loop in conjunction with cobalt-60 gamma irradiation. We demonstrate that HONTA undergoes exponential decay with increasing gamma dose to produce a range of degradation products which have been identified and quantified by HPLC-ESI-MS/MS techniques. The combination of HONTA destruction and degradation product ingrowth, particularly dioctylamine, negatively impacts the extraction and back-extraction of both americium and europium ions. The loss of HONTA was attributed to its reaction with the solvent (${it n}$-dodecane) radical cation of ${it k}$(HONTA + R$$^{.+}$$) = (7.61 $$pm$$ 0.82) $$times$$ 10$$^{9}$$ M$$^{-1}$$ s$$^{-1}$$ obtained by pulse radiolysis techniques. However, when this ligand is bound to either americium or europium ions, the observed ${it n}$-dodecane radical cation kinetics increase by over an order of magnitude. This large reactivity increase to additional reaction pathways occurring upon metal-ion binding. Lastly nanosecond time-resolved measurements showed that both direct and indirect HONTA radiolysis yielded the short-lived ($$<$$100 ns) HONTA radical cation as well as a longer-lived ($$mu$$s) HONTA triplet excited state. These HONTA species are important precursors to the suite of HONTA degradation products observed.

Journal Articles

Controlled deuterium labelling of imidazolium ionic liquids to probe the fine structure of the electrical double layer using neutron reflectometry

Akutsu, Kazuhiro*; Cagnes, M.*; Tamura, Kazuhisa; Kanaya, Toshiji*; Darwish, T. A.*

Physical Chemistry Chemical Physics, 21(32), p.17512 - 17516, 2019/08

 Times Cited Count:2 Percentile:70.02(Chemistry, Physical)

We combined the deuterium labeling and neutron reflectivity techniques to determine the fine structure of the electric double layer structure in an imidazolium ionic liquid (IL). For this, a simple and large scale deuteration method for imidazolium ILs was developed, where the deuteration level can be systematically controlled.

Journal Articles

Mechanism of phase transfer of uranyl ions; A Vibrational sum frequency generation spectroscopy study on solvent extraction in nuclear reprocessing

Kusaka, Ryoji; Watanabe, Masayuki

Physical Chemistry Chemical Physics, 20(47), p.29588 - 29590, 2018/12

 Times Cited Count:6 Percentile:46.87(Chemistry, Physical)

Mechanistic understanding of solvent extraction of uranyl ions (UO$$_{2}$$$$^{2+}$$) by tributyl phosphate (TBP) will help improve the technology for the treatment and disposal of spent nuclear fuels. So far, it has been believed that uranyl ions in the aqueous phase are adsorbed to a TBP-enriched organic/aqueous interface, form complexes with TBP at the interface, and are extracted into the organic phase. Here we show that uranyl-TBP complex formation does not take place at the interface using vibrational sum frequency generation (VSFG) spectroscopy and propose an alternative extraction mechanism that uranyl nitrate, UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$, passes through the interface and forms the uranyl-TBP complex, UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$(TBP)$$_{2}$$, in the organic phase.

Journal Articles

Nuclear quantum effects in the direct ionization process of pure helium clusters; Path-integral and ring-polymer molecular dynamics simulations on the diatomics-in-molecule potential energy surfaces

Suzuki, Kento*; Miyazaki, Takaaki*; Takayanagi, Toshiyuki*; Shiga, Motoyuki

Physical Chemistry Chemical Physics, 20(41), p.26489 - 26499, 2018/11

 Times Cited Count:1 Percentile:92.46(Chemistry, Physical)

The direct photoionization of pure helium clusters and its subsequent short-time process have been studied by path integral molecular dynamics (PIMD) and ring-polymer molecular dynamics (RPMD) simulations. The PIMD simulations reproduced the experimental ionization spectra with a broad and asymmetric nature, which can be ascribed to the inhomogeneity of the energy levels of He atoms. From the RPMD simulations, it is found that the ionized helium cluster in the highly excited state brings about fast electronic state relaxation via nonadiabatic charge transfer and subsequently slow structural relaxation.

Journal Articles

Pressure-induced stacking disorder in boehmite

Ishii, Yusuke*; Komatsu, Kazuki*; Nakano, Satoshi*; Machida, Shinichi*; Hattori, Takanori; Sano, Asami; Kagi, Hiroyuki*

Physical Chemistry Chemical Physics, 20(24), p.16650 - 16656, 2018/06

 Times Cited Count:2 Percentile:83(Chemistry, Physical)

The structure of an aluminum layered hydroxide, boehmite ($$gamma$$-AlOOH), as a function of pressure was studied by using ${it in situ}$ synchrotron X-ray and neutron diffraction. Peak broadening and subsequent splitting, which are only found for hkl (h $$neq$$ 0) peaks in the X-ray diffraction patterns above 25 GPa, are explained by stacking disorder accompanied with a continuously increasing displacement of the AlO$$_{6}$$ octahedral layer along a-axis. This finding could be the first experimental result for the pressure-induced stacking disorder driven by the continuous layer displacement. The magnitude of the layer displacement was estimated from the X-ray scattering profile calculation based on the stacking disordered structure model. Hydrogen bond geometries of boehmite, obtained by structure refinements on the observed neutron diffraction patterns for deuterated sample up to 10 GPa, show linearly approaching O-D covalent and D$$cdots$$O hydrogen bond distances and they could merge below 26 GPa. The pressure-induced stacking disorder would make the electrostatic potential of hydrogen bonds asymmetric, yielding less chance for the proton-tunnelling.

Journal Articles

X-ray absorption near edge structure and first-principles spectral investigations of cationic disorder in MgAl$$_{2}$$O$$_{4}$$ induced by swift heavy ions

Yoshioka, Satoru*; Tsuruta, Konosuke*; Yamamoto, Tomokazu*; Yasuda, Kazuhiro*; Matsumura, Sho*; Ishikawa, Norito; Kobayashi, Eiichi*

Physical Chemistry Chemical Physics, 20(7), p.4962 - 4969, 2018/02

 Times Cited Count:3 Percentile:83(Chemistry, Physical)

Cationic disorder in the MgAl$$_{2}$$O$$_{4}$$ spinel induced by swift heavy ions was investigated using the X-ray absorption near edge structure. With changes in the irradiation fluences of 200 MeV Xe ions, the Mg K-edge and Al K-edge spectra were synchronously changed. The calculated spectra based on density function theory indicate that the change in the experimental spectra was due to cationic disorder between Mg in tetrahedral sites and Al in octahedral sites. These results suggest a high inversion degree to an extent that the completely random configuration is achieved in MgAl$$_{2}$$O$$_{4}$$ induced by the high density electronic excitation under swift heavy ion irradiation.

Journal Articles

A Significant role of non-thermal equilibrated electrons in the formation of deleterious complex DNA damage

Kai, Takeshi; Yokoya, Akinari*; Ukai, Masatoshi*; Fujii, Kentaro*; Toigawa, Tomohiro; Watanabe, Ritsuko*

Physical Chemistry Chemical Physics, 20(4), p.2838 - 2844, 2018/01

 Times Cited Count:11 Percentile:23.22(Chemistry, Physical)

It is thought that complex DNA damage which induces in radiation biological effects is formed at radiation track end. Thus, the earliest stage of water radiolysis at the electron track end was studied to predict DNA damage. These results indicate that DNA damage sites comprising multiple nucleobase lesions with a single strand breaks can therefore be formed by multiple collisions of the electrons within three base pairs (3bp) of a DNA strand. This multiple damage site cannot be processed by base excision repair enzymes. However, pre-hydrated electrons can also be produced resulting in an additional base lesion more than 3bp away from the multi-damage site. This clustered damage site may be finally converted into a double strand break (DSB) when base excision enzymes process the additional base lesions. These DSBs include another base lesion(s) at their termini that escape from the base excision process and which may result in biological effects such as mutation in surviving cells.

Journal Articles

The Structure of a lanthanide complex at an extractant/water interface studied using heterodyne-detected vibrational sum frequency generation

Kusaka, Ryoji; Watanabe, Masayuki

Physical Chemistry Chemical Physics, 20(4), p.2809 - 2813, 2018/01

 Times Cited Count:6 Percentile:46.87(Chemistry, Physical)

Solvent extraction plays an integral part in the separation and purification of metals. Because extractants generally used as complexing agents for metal extractions, such as di-(2-ethylhexyl)phosphoric acid (HDEHP) for lanthanide extractions, are amphiphilic, they come to the organic/water interface, and the interface plays a crucial role as the site of the formation of metal complexes and subsequent transfer reaction to an organic phase. Despite the importance of the interface for solvent extractions, however, molecular-level structure of the interface is unclear because of experimental difficulty. Here we studied structure of a trivalent europium (Eu$$^{3+}$$) complex with HDEHP formed at HDEHP monolayer/water interface by heterodyne-detected vibrational sum frequency generation (HD-VSFG) spectroscopy. The study on the HDEHP/water interface enables us to investigate the structure of the interfacial Eu$$^{3+}$$ complex by excluding the migration of Eu$$^{3+}$$ into an organic phase after the complex formation at the interface. The interface-selective vibrational Im$$chi$$$$^{(2)}$$ spectra observed by HD-VSFG of HDEHP/Eu(NO$$_{3}$$)$$_{3}$$ aqueous solution interface in the 2800-3500 cm$$^{-1}$$ region indicate that Eu$$^{3+}$$ at the HDEHP/water interface is bonded by HDEHP from the air side and by water molecules from the water side. To the best of our knowledge, such metal complex structures have not been identified in the organic or water solutions.

Journal Articles

Transmutation effects on long-term Cs retention in phyllosilicate minerals from first principles

Sassi, M.*; Okumura, Masahiko; Machida, Masahiko; Rosso, K. M.*

Physical Chemistry Chemical Physics, 19(39), p.27007 - 27014, 2017/10

 Times Cited Count:4 Percentile:71.66(Chemistry, Physical)

no abstracts in English

Journal Articles

Photoexcited Ag ejection from a low-temperature He cluster; A Simulation study by nonadiabatic Ehrenfest ring-polymer molecular dynamics

Seki, Yusuke*; Takayanagi, Toshiyuki*; Shiga, Motoyuki

Physical Chemistry Chemical Physics, 19(21), p.13798 - 13806, 2017/06

 Times Cited Count:7 Percentile:51.67(Chemistry, Physical)

Ring-polymer molecular dynamics (RPMD) simulations have been performed to understand the photoexcitation dynamics of the Ag atom embedded in a low-temperature cluster consisting of 500 helium atoms, after the electronic excitation of the Ag atom. Along the RPMD trajectory the time evolution of the electronic wavefunction within the spin-orbit $$^{2}$$P manifold is calculated, whereby the time-dependent Schr$"o$dinger equation and the RPMD equation of motion are coupled, $`a$ la Ehrenfest mean field approach. It is found from the simulations that the Ag atom is mostly ejected from the helium cluster with the average time of 100 ps after photoexcitation. The average velocity of the ejected Ag atom is estimated to be 60-70 m/s. These results are qualitatively in line with previous experimental findings.

Journal Articles

The Effect of dynamical fluctuations of hydration structures on the absorption spectra of oxyluciferin anions in an aqueous solution

Hiyama, Miyabi*; Shiga, Motoyuki; Koga, Nobuaki*; Sugino, Osamu*; Akiyama, Hidefumi*; Noguchi, Yoshifumi*

Physical Chemistry Chemical Physics, 19(15), p.10028 - 10035, 2017/04

 Times Cited Count:4 Percentile:71.66(Chemistry, Physical)

In this study, the effect of hydration on the absorption spectra of oxyluciferin anion isomers in an aqueous solution is investigated for elucidating the influence of characteristic hydration structures. Using a canonical ensemble of hydration structures obtained from first-principles molecular dynamics simulations, the instantaneous absorption spectra of keto-, enol-, and enolate-type aqueous oxyluciferin anions at room temperature are computed from a collection of QM/MM calculations using an explicit solvent. It is demonstrated that the calculations reproduce experimental results concerning spectral shifts and broadening, for which traditional methods based on quantum chemistry and the Franck-Condon approximation fail because of the molecular vibrations of oxyluciferin anions and dynamical fluctuations of their hydration structures.

Journal Articles

The Reaction mechanism of polyalcohol dehydration in hot pressurized water

Ruiz-Barragan, S.*; Ribas Ari$~n$o, J.*; Shiga, Motoyuki

Physical Chemistry Chemical Physics, 18(47), p.32438 - 32447, 2016/12

 Times Cited Count:6 Percentile:71.34(Chemistry, Physical)

The use of high-temperature liquid water (HTW) as a reaction medium is a very promising technology in the field of green chemistry. In order to fully exploit this technology, it is crucial to unravel the reaction mechanisms of the processes carried out in HTW. In this work, the reaction mechanism of 2,5-hexanediol dehydration in HTW has been studied by means of three different ab initio simulations: string method, metadynamics and molecular dynamics in real time. It is found that the whole reaction involving the protonation, bond exchange and the deprotonation occurs in a single step without a stable intermediate. The hydrogen bonded network of surrounding water has a vital role in assisting an efficient proton relay at the beginning and at the end of the reaction. It is confirmed that the reaction is energetically most favorable in the SN2 pathway with an estimated barrier of 36 kcal/mol, which explains the high stereo selectivity and the reaction rate observed in experiment.

Journal Articles

Structure determination of the rutile-TiO$$_{2}$$(110)-(1$$times$$2) surface using total-reflection high-energy positron diffraction (TRHEPD)

Mochizuki, Izumi*; Ariga, Hiroko*; Fukaya, Yuki; Wada, Ken*; Maekawa, Masaki; Kawasuso, Atsuo; Shidara, Tetsuo*; Asakura, Kiyotaka*; Hyodo, Toshio*

Physical Chemistry Chemical Physics, 18(10), p.7085 - 7092, 2016/03

 Times Cited Count:13 Percentile:34.61(Chemistry, Physical)

no abstracts in English

Journal Articles

Investigation of the fragmentation of core-ionised deoxyribose; A Study as a function of the tautomeric form

Herv$'e$ du Penhoat, M.-A.*; Kamol Ghose, K.*; Gaigeot, M.-P.*; Vuilleumier, R.*; Fujii, Kentaro; Yokoya, Akinari; Politis, M.-F.*

Physical Chemistry Chemical Physics, 17(48), p.32375 - 32383, 2015/12

 Times Cited Count:8 Percentile:58.87(Chemistry, Physical)

Journal Articles

The Effects of alloying and segregation for the reactivity and diffusion of oxygen on Cu$$_{3}$$Au(111)

Oka, Kohei*; Tsuda, Yasutaka*; Makino, Takamasa*; Okada, Michio*; Hashinokuchi, Michihiro*; Yoshigoe, Akitaka; Teraoka, Yuden; Kasai, Hideaki*

Physical Chemistry Chemical Physics, 16(36), p.19702 - 19711, 2014/08

 Times Cited Count:6 Percentile:71.75(Chemistry, Physical)

Journal Articles

Initial stages of Cu$$_{3}$$Au(111) oxidation; Oxygen induced Cu segregation and the protective Au layer profile

Tsuda, Yasutaka*; Oka, Kohei*; Makino, Takamasa*; Okada, Michio*; Di$~n$o, W. A.*; Hashinokuchi, Michihiro*; Yoshigoe, Akitaka; Teraoka, Yuden; Kasai, Hideaki*

Physical Chemistry Chemical Physics, 16(8), p.3815 - 3822, 2014/02

 Times Cited Count:10 Percentile:54.64(Chemistry, Physical)

Journal Articles

Temperature dependence of the Fricke dosimeter and spur expansion time in the low-LET high-temperature radiolysis of water up to 350$$^{circ}$$C; A Monte-Carlo simulation study

Sanguanmith, S.*; Muroya, Yusa*; Tippayamontri, T.*; Meesungnoen, J.*; Lin, M.; Katsumura, Yosuke*; Jay-Gerin, J.-P.*

Physical Chemistry Chemical Physics, 13(22), p.10690 - 10698, 2011/06

 Times Cited Count:17 Percentile:42.41(Chemistry, Physical)

Monte-Carlo simulations of the radiolysis of the ferrous sulfate (Fricke) dosimeter with low-linear energy transfer (LET) radiation have been performed as a function of temperature from 25 to 350$$^{circ}$$C. The predicted yields of Fe$$^{2+}$$ oxidation are found to increase with increasing temperature up to 100-150$$^{circ}$$C, and then tend to remain essentially constant at higher temperatures, in very good agreement with experiment. Moreover, the observed dependence of G(Fe$$^{3+}$$) on temperature largely reflects the influence of temperature upon the primary free-radical product yields of the radiolysis, especially the yield of H atoms. Above 200-250$$^{circ}$$C, the more and more pronounced intervention of the reaction of H atoms with water also contributes to the variation of G(Fe$$^{3+}$$), which may decrease or increase slightly, depending on the choice made for the rate constant of this reaction.

Journal Articles

Structural changes in surface and bulk LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$ during electrochemical reaction on epitaxial thin-film electrodes characterized by ${it in situ}$ X-ray scattering

Sakamoto, Kazuyuki*; Hirayama, Masaaki*; Konishi, Hiroaki*; Sonoyama, Noriyuki*; Dupr$'e$, N.*; Guyomard, D.*; Tamura, Kazuhisa; Mizuki, Junichiro; Kanno, Ryoji*

Physical Chemistry Chemical Physics, 12(15), p.3815 - 3823, 2010/04

 Times Cited Count:30 Percentile:24.09(Chemistry, Physical)

Surface and bulk structural changes of LiNi$$_{0.5}$$Mn$$_{0.5}$$O$$_{2}$$ were investigated during electrochemical reaction using synchrotron X-ray scattering and a restricted reaction plane consisting of two dimensional epitaxial-film electrodes. The changes in bulk structure confirmed lithium diffusion through the (110) surface, which was perpendicular to the two-dimensional (2D) edges of the layered structure. No (de)intercalation reaction was observed through the (003) surface at voltages of 3.0-5.0 V. However, intercalation did proceed through the (003) plane below 3.0 V, indicating unusual three-dimensional (3D) lithium diffusion in the over-lithiated 2D structure. During the electrochemical process, the surface of the electrode showed different structure changes from those of the bulk structure. The reaction echanism of the intercalation electrodes for lithium batteries is discussed on the basis of surface and bulk structural changes.

Journal Articles

H$$_6$$$$^+$$ in irradiated solid $$para$$-hydrogen and its decay dynamics; Reinvestigation of quartet electron paramagnetic resonance lines assigned to H$$_2$$$$^-$$

Kumada, Takayuki; Tachikawa, Hiroto*; Takayanagi, Toshiyuki*

Physical Chemistry Chemical Physics, 7(5), p.776 - 784, 2005/02

 Times Cited Count:11 Percentile:62.13(Chemistry, Physical)

The quartet ESR lines observed in X-ray irradiated solid parahydrogen, which have previously been assigned to H$$_2$$$$^-$$, are reinvestigated. We have reassigned the quartet lines to H$$_6$$$$^+$$ rather than H$$_2$$$$^-$$. Based on the new assignment, previous data have been reinterpreted as follows. The H$$_6$$$$^+$$ ion is composed of the collinearly aligned H$$_2$$$$^+$$ core at the center and two H$$_2$$ rotors at both ends. The ortho-para conversion of H$$_2$$$$^+$$ core of H$$_6$$$$^+$$ is completed within the time-scale of hours. H$$_6$$$$^+$$ diffuses quantum mechanically by the repetition of H$$_6$$$$^+$$ + H$$_2$$ $$rightarrow$$ H$$_2$$ + H$$_6$$$$^+$$ reaction, and the diffusion terminates by the reaction with a HD impurity as H$$_6$$$$^+$$ + HD $$rightarrow$$ H$$_5$$D$$^+$$ + H$$_2$$. Finally, we will propose a possible reason why H$$_6$$$$^+$$ is produced instead of H$$_3$$$$^+$$ in the irradiated solid H$$_2$$.

Journal Articles

Vibrational dissipation and dephasing of I$$_{2}$$(v = 1-19) in solid Kr

Karavitis, M.*; Kumada, Takayuki; Goldschleger, I. U.*; Apkarian, V. A.*

Physical Chemistry Chemical Physics, 7(5), p.791 - 796, 2005/02

 Times Cited Count:28 Percentile:30.07(Chemistry, Physical)

Energy dissipation and phase relaxation of the vibrational quantum states of iodine molecules in solid krypton have been studied in the temperature range between 7 and 45 K using a technique of time-resolved coherent anti-stokes Raman scattering (CARS) spectroscopy by a femto-second laser. The rate of energy dissipation was independent of tempeature, but proportional to the vibrational quantum number v. The pure dephasing rate exponentially increased with an increase in temperature and was proportional to v$$^{2}$$. The energy relaxation was found to take place by transfering the vibrational energy of iodine to four phonons in the krypton solid. The pure dephasing was induced by elastic scattering with phonon. It was suggested by a computer simulation that the phonon which induced the pure dephasing accompanied libration mode of iodine molecules.

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