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Hierarchical aggregation in a complex fluid; The Role of isomeric interconversion

Massey, D.*; Williams, C. D.*; Mu, J.*; Masters, A. J.*; 元川 竜平; 青柳 登; 上田 祐生; Antonio, M. R.*

Journal of Physical Chemistry B, 127(9), p.2052 - 2065, 2023/03

 被引用回数:0 パーセンタイル:0.01(Chemistry, Physical)

There is an ever-increasing body of evidence that metallic complexes, involving amphiphilic ligands, do not form normal solutions in organic solvents. Instead, they form complex fluids with intricate structures. For example, the metallic complexes may aggregate into clusters and these clusters themselves may aggregate into super-clusters. In order to gain a deeper insight into the mechanisms at play, we have used an improved force field to conduct extensive molecular dynamics simulations of a system composed of zirconium nitrate, water, nitric acid, tri-$$n$$-butyl phosphate and $$n$$-octane. The important new finding is that a dynamic equilibrium between the cis and trans isomers of the metal complex is likely to play a key role in the aggregation behavior. The isolated cis and trans isomers have similar energies but simulation indicates that the clusters consist predominantly of cis isomers. With increasing metal concentration, we hypothesize that more clustering occurs and the chemical equilibrium shifts towards the cis isomer. It is possible that such isomeric effects play a role in the liquid-liquid extraction of other species and the inclusion of such effects in flowsheet modelling may lead to a better description of the process.


Stoichiometry of lanthanide-phosphate complexes at the water surface studied using vibrational sum frequency generation spectroscopy and DFT calculations

日下 良二; 渡邉 雅之

Journal of Physical Chemistry B, 125(24), p.6727 - 6731, 2021/06

 被引用回数:6 パーセンタイル:52.93(Chemistry, Physical)

In the solvent extraction of metal ions, the transport mechanism of metal ions through the liquid-liquid organic/aqueous interface remains unclear. In this study, the adsorption process of trivalent lanthanide ions from the aqueous phase to the interface in the solvent extraction of lanthanides with di(2-ethylhexyl)phosphoric acid (HDEHP) extractant is investigated by using a model interface - water surface covered with HDEHP (air/HDEHP/aqueous interface). As a result, symmetric POO$$^{-}$$ stretch signals of HDEHP observed by vibrational sum frequency generation spectroscopy and density functional theory calculations show that the stoichiometric ratio of lanthanide-HDEHP complexes formed at the air/HDEHP/aqueous interface is 1:1. The formation of the interfacial 1:1 lanthanide-HDEHP complex could be an elementary chemical process occurring just before the transfer of lanthanide ions to the side of the organic phase.


Understanding competition of polyalcohol dehydration reactions in hot water

Chang, Y. L.*; 佐々木 岳彦*; Ribas-Ari$~n$o, J.*; 町田 昌彦; 志賀 基之

Journal of Physical Chemistry B, 123(7), p.1662 - 1671, 2019/02

 被引用回数:4 パーセンタイル:14.81(Chemistry, Physical)

バイオマス由来ポリアルコールの脱水は、有機溶媒または金属触媒を使用せずに、高温水または高温炭酸水で制御可能な選択的反応の典型としてグリーンケミストリーにおいて最近注目を集めている。この研究では、酸性の高温水中での1,2,5-ペンタントリオールの競合分子内脱水反応のメカニズムを理解するために、第一原理メタダイナミクスとブルームーンアンサンブルシミュレーションに基づく自由エネルギー解析を行った。その結果、最も支配的なメカニズムは、水によるヒドロキシル基のプロトン化およびC-O結合の切断および形成が同時に起こる、プロトン支援S$$_{rm N}$$2型のプロセスであることがわかった。シミュレーションから見いだされた詳細なメカニズムは、どのようにして反応経路が熱水中で選択的であるか、そしてなぜ反応速度が酸性環境において加速されるかを示し、競合する多価アルコールの脱水プロセスについて実験結果の明確な説明を与える。


A Novel microemulsion phase transition; Toward the elucidation of third-phase formation in spent nuclear fuel reprocessing

Mu, J.*; 元川 竜平; 阿久津 和宏*; 西辻 祥太郎*; Masters, A. J.*

Journal of Physical Chemistry B, 122(4), p.1439 - 1452, 2018/02

 被引用回数:31 パーセンタイル:73.52(Chemistry, Physical)

We present evidence that the transition between organic and third phases, which is an unusual transition between two isotropic, bi-continuous micro-emulsion phases. This system contains quaternary; water, n-dodecane, nitric acid, tributyl phosphate (TBP). This quaternary system has been shown to exhibit, under appropriate conditions, three coexisting phases: a light organic phase, an aqueous phase, and the so-called third phase. In this work, we focused on the coexistence of the light organic phase with the third phase using methods of molecular dynamics (MD) simulation and small-angle X-ray scattering (SAXS). Snapshots from the MD simulations as well as a cluster analysis of the organic and third phases revealed structures akin to bi-continuous micro-emulsion phases, with the polar species residing within a mesh, and with the surface of the mesh formed by amphiphilic TBP molecules. The non-polar n-dodecane molecules were observed in these snapshots to be outside this mesh. The only large-scale structural differences observed between the two phases were the dimensions of the mesh. Evidence for the correctness of these structures was provided by the results of SAXS studies, where the profiles obtained for both the organic and third phases agreed well with those calculated from simulation.


Nanoscopic structural investigation of physically cross-linked nanogels formed from self-associating polymers

関根 由莉奈; 遠藤 仁*; 岩瀬 裕希*; 竹田 茂生*; 向井 貞篤*; 深澤 裕; Littrell, K. C.*; 佐々木 善浩*; 秋吉 一成*

Journal of Physical Chemistry B, 120(46), p.11996 - 12002, 2016/11

 被引用回数:10 パーセンタイル:29.4(Chemistry, Physical)



Reverse stability of oxyluciferin isomers in aqueous solutions

野口 良史*; 樋山 みやび*; 志賀 基之; 杉野 修*; 秋山 英文*

Journal of Physical Chemistry B, 120(34), p.8776 - 8783, 2016/09

 被引用回数:6 パーセンタイル:16.91(Chemistry, Physical)



Comparative molecular dynamics study on tri-$$n$$-butyl phosphate in organic and aqueous environments and its relevance to nuclear extraction processes

Mu, J.*; 元川 竜平; Williams, C. D.*; 阿久津 和宏*; 西辻 祥太郎*; Masters, A. J.*

Journal of Physical Chemistry B, 120(23), p.5183 - 5193, 2016/06

 被引用回数:27 パーセンタイル:63.71(Chemistry, Physical)

A refined model for tri-$$n$$-butyl phosphate (TBP), which uses a new set of partial charges generated from our ab initio density functional theory calculations, has been proposed in this study. Molecular dynamics simulations are conducted to determine the thermodynamic properties, transport properties, and the microscopic structures of liquid TBP, TBP/water mixtures, and TBP/$$n$$-alkane mixtures. These results are compared with those obtained from four other TBP models, previously described in the literature. We conclude that our refined TBP model appears to be the only TBP model from this set that, with reasonable accuracy, can simultaneously predict the properties of TBP in bulk TBP, in organic diluents, and in aqueous solution. This new TBP model is thus appropriate for the simulation of liquid-liquid extraction systems in the nuclear extraction process, where one needs to simultaneously model TBP in both aqueous and organic phases. It is also promising for the investigation of the microscopic structure of the organic phase in these processes and for the characterization of third-phase formation, where TBP again interacts simultaneously with both polar and nonpolar molecules. Because the proposed TBP model uses OPLS-2005 Lennard-Jones parameters, it may be used with confidence to model mixtures of TBP with other species whose parameters are given by the OPLS-2005 force field.


Neutron diffraction of ice in hydrogels

関根 由莉奈; 深澤 倫子*; 相澤 守*; 小林 理気*; Chi, S.*; Fernandez-Baca, J. A.*; 山内 宏樹; 深澤 裕

Journal of Physical Chemistry B, 118(47), p.13453 - 13457, 2014/08

 被引用回数:2 パーセンタイル:4.16(Chemistry, Physical)

ハイドロゲル中に存在する水の構造や性質を明らかにすることを目的として、10-300Kにおける重水を含むポリ$$N$$,$$N$$,-ジメチルアクリルアミドハイドロ(PDMAA)ゲルの中性子回折パターンを測定した。250K以下において観察された回折ピークは、ゲル中に氷が存在することを示した。これらのピーク位置は、通常の六方晶の氷(Ice Ih)よりも低い角度であった。このピーク位置のシフトはゲル中の氷の構造における$$a$$軸, $$c$$軸の格子が通常のIce Ihよりも各々0.29, 0.3%大きいことを示す。この結果は、PDMAAゲル中に低密度の氷が存在することを示す。このような氷構造の歪みは、ゲル中における水分子と高分子鎖の相互作用によるものと考えられる。


Dissociation free-energy profiles of specific and nonspecific DNA-protein complexes

米谷 佳晃; 河野 秀俊

Journal of Physical Chemistry B, 117(25), p.7535 - 7545, 2013/06

 被引用回数:13 パーセンタイル:34.87(Chemistry, Physical)

DNA-binding proteins recognize DNA sequences with at least two different binding modes, specific and nonspecific. Experimental structures of such complexes provide us a static view of the bindings. However, it is difficult to reveal further mechanisms of their target-site search and recognition only from static information because the transition process between the bound and unbound states is not clarified by static information. What is the difference between specific and nonspecific bindings? Here we performed adaptive biasing force molecular dynamics simulations with the specific and nonspecific structures of DNA-Lac repressor complexes to investigate the dissociation process. The resultant free-energy profiles showed that the specific complex has a sharp, deep well consistent with tight binding, whereas the non-specific complex has a broad, shallow well consistent with loose binding. The difference in the well depth, 5 kcal/mol, was in fair agreement with the experimentally obtained value and was found to mainly come from the protein conformational difference, particularly in the C-terminal tail. Comparison of the free-energy barrier for sliding, $$sim$$8.7 kcal/mol, and that for dissociation (at least $$sim$$16 kcal/mol) calculated in this study suggests that sliding is much preferred to dissociation.


Microscopic structures of tri-$$n$$-butyl phosphate/$$n$$-octane mixtures by X-ray and neutron scattering in a wide $$q$$ range

元川 竜平; 鈴木 伸一; 小川 紘樹*; Antonio, M. R.*; 矢板 毅

Journal of Physical Chemistry B, 116(4), p.1319 - 1327, 2012/02

 被引用回数:36 パーセンタイル:67.26(Chemistry, Physical)

Tri-$$n$$-butyl phosphate (TBP) is an important extractant for separating hexavalent uranium and tetravalent plutonium from used nuclear fuel by solvent extraction. In such solvent extractions using TBP, the organic phase occasionally separates into two organic phases, namely, light and heavy organic phases. The latter one in particular is called the third phase. The purpose of this work is to elucidate the mechanism whereby the third phase forms in biphasic liquid-liquid solvent extraction of heavy metal ions. Toward this end, small- and wide-angle X-ray and neutron scattering experiments were conducted to examine the microscopic structures of TBP/octane mixtures. These investigations of solute associations provide insights into system performance. After the extraction of heavy metal ions, for example, the microscopic structures formed in the organic phase are likely to be correlated with the initial microscopic structures, which are revealed here. SWAXS and SWANS, with accurate estimations of incoherent scattering intensities for all solution samples, revealed the following: (1) TBP self-associates in octane, and the average distance between two TBP molecules in the TBP assemblies is evaluated as 0.9-1.0 nm; (2) the shape of the TBP assembly is ellipsoidal; and (3) the attractive interaction among TBP assemblies in octane is miniscule, and thus, they tend to be dispersed homogeneously due to the excluded volume effect.


Self-assembly process of peptide amphiphile worm-like micelles

島田 智子*; 坂本 直紀*; 元川 竜平; 小泉 智*; Tirrell, M.*

Journal of Physical Chemistry B, 116(1), p.240 - 243, 2012/01

 被引用回数:46 パーセンタイル:74.26(Chemistry, Physical)

Peptide amphiphile molecules (PA) are remarkably versatile and useful as building blocks for construction of complex supramolecular structures in a bottom-up fashion. Worm-like micelles of PA have been demonstrated to have successful application to creation of synthetic extracellular matrix materials for tissue engineering and regenerative medicine. However, the pathway of the self-assembly process of the PA worm-like micelle has not been fully characterized or understood. This work analyzes the self-assembly process leading to worm-like micelle formation in our designed PA with small-angle neutron scattering and atomic force microscopy. The experimental results demonstrate the existence of transient spherical micelles in the early stage of the process and subsequent micelle chain elongation by attachment of spherical micelles to the end of growing cylindrical micelles to form worm-like micelles in a process mimicking chain-growth polymerization.


Ion specific effects on the structure of molten AF-ZrF$$_4$$ systems (A$$^+$$ = Li$$^+$$, Na$$^+$$, and K$$^+$$)

Pauvert, O.*; Salanne, M.*; Zanghi, D.*; Simon, C.*; Reguer, S.*; Thiaudi$`e$re, D.*; 岡本 芳浩; 松浦 治明*; Bessada, C.*

Journal of Physical Chemistry B, 115(29), p.9160 - 9167, 2011/07

 被引用回数:60 パーセンタイル:81.43(Chemistry, Physical)

AF-ZrF$$_4$$ system (A$$^+$$=Li$$^+$$, Na$$^+$$, K$$^+$$)混合系融体の構造を、EXAFS分光法と分子動力学(MD)計算法の組合せによって調べた。EXAFSの結果は、MD計算によって良好に再現された。計算では、融体中の7配位や6配位の構造の安定化の促進具合を評価した。Li, Na及びKの間の違いと、組成による違いを、系統的に調べた。MD計算からラマン分光スペクトルの導出も行った。また、配位構造がどの程度の時間保たれるかの評価も実施した。配位構造同士の相関については、Zr$$^{4+}$$-Zr$$^{4+}$$対の部分相関関数から評価した。


Determination of structural parameters of protein-containing reverse micellar solution by near-infrared absorption spectroscopy

村上 洋; 西 孝樹*; 豊田 祐司*

Journal of Physical Chemistry B, 115(19), p.5877 - 5885, 2011/04

 被引用回数:14 パーセンタイル:34.36(Chemistry, Physical)



In situ experimental evidence for a nonmonotonous structural evolution with composition in the molten LiF-ZrF$$_4$$ system

Pauvert, O.*; Zanghi, D.*; Salanne, M.*; Simon, C.*; Rakhamatullin, A.*; 松浦 治明*; 岡本 芳浩; Vivet, F.*; Bessada, C.*

Journal of Physical Chemistry B, 114(19), p.6472 - 6479, 2010/05

 被引用回数:57 パーセンタイル:79.67(Chemistry, Physical)

50モル%ZrF$$_4$$までの組成の溶融LiF-ZrF$$_4$$系の構造を核磁気共鳴分析(NMR)法、広域X線吸収微細構造分析(EXAFS)法、及び分子動力学(MD)計算の組合せによって調べた。$$^{91}$$Zr高温NMR分析の結果から、Zrイオンの周りの配位数はすべて7であることがわかった。MD計算の結果は、EXAFSの結果とよく一致し、融体中に[ZrF$$_6$$]$$^{2-}$$, [ZrF$$_7$$]$$^{3-}$$, and [ZrF$$_8$$]$$^{4-}$$のような錯イオン種があることが判明した。


Anisotropic swelling behavior of the cornea

松浦 豊明*; 池田 仁英*; 井戸田 直和*; 元川 竜平; 原 嘉昭*; 安中 雅彦*

Journal of Physical Chemistry B, 113(51), p.16314 - 16322, 2009/12

 被引用回数:14 パーセンタイル:34.53(Chemistry, Physical)

The phase equilibrium property and structural and dynamical properties of pig cornea were studied by macroscopic observation of swelling behavior, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) under various conditions. The corneal gel collapses uniformly into a compact state at a temperature above 55$$^{circ}$$C because of the denaturation of collagen, whereas it collapses along an axis parallel to the optic axis with increasing NaCl concentration. Anisotropic deswelling was also observed during desiccation. SAXS measurements revealed that the periodicity of the collagen fiber of the cornea does not change even at higher NaCl concentration, which indicates that hydration and dehydration resulting from changes in salt concentration simply cause swelling and deswelling of the glycosaminoglycan (GAG), which is located between the regular two-dimensional lattices of collagen fibers, which obliges the change in thickness. From observations of the dynamics of light scattered by the corneal gel, intensity autocorrelation functions that revealed two independent diffusion coefficients were obtained. Divergent behavior in the measured total scattered light intensities and diffusion coefficients with varying temperature was observed. That is, a slowing of the dynamic modes accompanied by increased static scattered intensities was observed. This is indicative of the occurrence of a phase transition as a function of temperature.


Nucleobase lesions and strand breaks in dry DNA thin film selectively induced by monochromatic soft X-rays

藤井 健太郎; 鹿園 直哉; 横谷 明徳

Journal of Physical Chemistry B, 113(49), p.16007 - 16015, 2009/11

 被引用回数:19 パーセンタイル:44.43(Chemistry, Physical)



Hydration-dependent protein dynamics revealed by molecular dynamics simulation of crystalline Staphylococcal nuclease

城地 保昌*; 中川 洋; 片岡 幹雄; 北尾 彰朗*

Journal of Physical Chemistry B, 112(11), p.3522 - 3528, 2008/03

 被引用回数:10 パーセンタイル:26.14(Chemistry, Physical)



Electron photodetachment from iodide in ionic liquids through charge-transfer-to-solvent band excitation

加藤 隆二*; 吉田 陽一*; 勝村 庸介; 高橋 憲司*

Journal of Physical Chemistry B, 111(18), p.4770 - 4774, 2007/05

 被引用回数:53 パーセンタイル:77.31(Chemistry, Physical)

Solvation of iodide and electrons in an ionic liquid (${it N,N,N}$-trimethyl-$$n$$-propylammonium bis(trifluoromethanesulfonyl) imide; TMPA-TFSI) was studied through the absorption spectra of the charge-transfer-to-solvent(CTTS) state of iodide and of solvated electrons. The interaction between the TMPA cation and iodide was strong, where as electrons were weakly solvated in TMPA-TFSI. We followed electron photodetachment from iodide to the ionic liquid and formation of the solvated electrons by observing absorption in the visible and near-infrared regions using a nanosecond laser flash photolysis method. The quantum yield of the photodetachment in TMPA-TFSI was estimated to be 0.34, which is much higher than that in a high-concentration aqueous salt solution previously reported. We also examined a reaction of the solvated electrons with the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (Bmim-TFSI) as a solute in TMPA-TFSI. The reaction rate was determined to be 5.3$$times$$10$$^{8}$$ M$$^{-1}$$s$$^{-1}$$. The electrons before full solvation (dry electrons) reacted with Bmim cations efficiently. These observations suggest that the electrons in TMPA-TFSI can move easily before solvation.


Reaction between diiodide anion radicals in ionic liquids

高橋 憲司*; 酒井 慎吾*; 手塚 博昭*; 比江嶋 祐介*; 勝村 庸介; 渡邉 正義*

Journal of Physical Chemistry B, 111(18), p.4807 - 4811, 2007/05

 被引用回数:41 パーセンタイル:69.85(Chemistry, Physical)

Photodetachment of electrons from iodide ions produced diiodide anion radicals in ionic liquids containing ammonium, pyrrolidinium, and piperidinium cations. The rates of reaction between diiodide anion radicals in molecular solvents such as H$$_{2}$$O, methanol, and ethanol could be estimated by the Debye-Smoluchowski equation, which accounts for electrostatic interactions using dielectric constants for the molecular solvents. In contrast, the rates of reaction between diiodide anion radicals in the ionic liquids were close to the diffusion limited rates for the neutral molecules, suggesting that electrostatic repulsion between the diiodide anion radicals is weakened by Coulombic shielding in the ionic liquids.


Customized morphologies of self-condensed multisegment polymer nanowires

佃 諭志*; 関 修平*; 杉本 雅樹; 田川 精一*

Journal of Physical Chemistry B, 110(39), p.19319 - 19322, 2006/10

 被引用回数:23 パーセンタイル:51.64(Chemistry, Physical)


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