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Volume 64, Issue 3
Chemical Reactions in Solutions for Analytical Chemistry
Displaying 1-8 of 8 articles from this issue
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Accounts
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Masanari NAGASAKA, Takuji OHIGASHI, Nobuhiro KOSUGIArticle type: Accounts
2015 Volume 64 Issue 3 Pages 163-172
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSFor a better understanding of the electrochemical reaction, it is necessary to investigate the local structures of electrolytes, including solid-liquid interfaces at different potentials. X-ray absorption spectroscopy (XAS) is an element-specific method to investigate the local structures of a liquid. Recently, we developed a transmission-type liquid flow cell for XAS in the soft X-ray region below 1 keV, including many chemically important absorption edges, such as C, N, and O K-edges. By using the liquid flow cell with built-in electrodes, we have successfully measured the XAS of electrolytes in electrochemical reactions, and revealed changes in the valence of Fe ions in aqueous iron sulfate solutions at different potentials by Fe L-edge XAS. Electrochemical reactions of iron sulfate solutions have also been observed by in operando XAS with a potential modulation method at the same scan rate as in cyclic voltammetry (typically 100 mV s−1). Finally, we have considered a microscopic XAS analysis of electrolytes in an electrochemical reaction with a spatial resolution of about 30 nm by including the liquid flow cell in a scanning transmission X-ray microscope (STXM).View full abstractDownload PDF (1717K) -
Takeyoshi GOTO, Akifumi IKEHATA, Yusuke MORISAWA, Noboru HIGASHI, Yuki ...Article type: Accounts
2015 Volume 64 Issue 3 Pages 173-184
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSFar-ultraviolet (FUV, <200 nm) absorption spectroscopy provides molecular information about the electronic ground state and the excited state. Because photon energy of FUV light corresponds to various kinds of valence electronic transitions including σ, n, and π electron excitation and charge transfer (CT), almost all chemical compounds show characteristic FUV spectra. However, FUV spectral measurements of liquid samples are highly challenging, because the absorptivity of most liquids is very intense. We have developed an attenuated total reflection FUV spectrophotometer in order to measure the FUV spectra of liquid water and aqueous solutions. This paper introduces the FUV spectra (140–300 nm) of various aqueous solutions to describe (1) how the first electronic transition (Ã←X) bands of water molecules in Group I, II, XIII, and lanthanoid (Ln3+) electrolyte solutions are associated with the hydration states of those metal cations, (2) how the protonation states of amino acids in aqueous solutions affect the electronic transition of the amino acids, and (3) the analysis of O3 photolytic reaction in aqueous solution using a nano-sec pump-probe transient FUV spectrophotometer.View full abstractDownload PDF (2243K) -
Nobuyuki MATUBAYASIArticle type: Accounts
2015 Volume 64 Issue 3 Pages 185-188
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSThe free-energy analysis is essential to understand and control a chemical process in condensed phase. The current status of theoretical/computation chemistry is, however, that the free energy remains a most difficult quantity to compute. For fast and accurate computation of the free energy with its molecular understanding, a new theory of solutions has been combined with molecular simulation. This theory is called the method of energy representation, and constructs the solvation free energy as a functional of distribution functions of the solute-solvent pair interaction energy. The method of energy representation greatly expands the scope of solution theory, and is amenable to such frontline topics of physical chemistry and biophysics as supercritical fluid, flexible molecules with intramolecular degrees of freedom, inhomogeneous system, and quantum-mechanical/molecular-mechanical (QM/MM) system. In fact, the binding of a molecule into such molecular-aggregate systems as solution, lipid membrane, and micelle can be viewed as solvation in an extended sense, and the method of energy representation can provide the free energy of solvation in the extended sense; the strength and site of binding are determined from calculations of the solvation free energy. We present a brief introduction to the free-energy calculation in solution, and introduce an application to a lipid-membrane system. The membrane is treated as an inhomogeneous, mixed solvent system consisting of water and an amphiphilic molecule, and the binding of a hydrophobic solute into it is analyzed with the combination of the molecular simulation and the energy-representation method. The solvation free energy is determined as a function of the binding depth, and the common role of water is pointed out under density-variable conditions such as the membrane/water interface, air/water interface, and supercritical water.View full abstractDownload PDF (578K) -
Ryo KANZAKIArticle type: Accounts
2015 Volume 64 Issue 3 Pages 189-196
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSA certain type of onium salt whose melting point is near an arbitrary temperature is a so-called a protic ionic liquid (PIL). PILs are expected to be the ‘third solvents’ that follow water and organic solvents for many techniques in analytical chemistry, such as separation, purification, and extraction, because of its ability for being an acid-base reaction medium. In this article, some ideas for understanding the acid-base reactions in PILs are briefly introduced with comparing with those in water and conventional non-aqueous solvents (i.e., organic solvents). Then, recent results of the autoprotolysis constants and acid dissociation constants in PILs are summarized to show quantitatively that PILs exhibit their acid-base property, depending on the constituting anion and cation. The relationship between the pH and the reactivity of hydrogen ion in a typical PIL, ethylammonium nitrate, is compared with that in water.View full abstractDownload PDF (818K) -
Yasuhiro UMEBAYASHI, Kenta FUJII, Soshi SAITO, Hikari WATANABE, Hiroyu ...Article type: Accounts
2015 Volume 64 Issue 3 Pages 197-202
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSSpeciation analysis is defined as identifying and/or measuring the quantities of one or more individual chemical species in a sample; it also involves evaluations of the species distribution and molecular structure of the species, and even their conformers. Raman/IR vibration spectroscopy and neutron/X-ray scattering experiments can reveal not only molecular and/or liquid structures, but also species formation equilibria thermodynamically. We propose that such techniques can be called "Spectrothermodynamics". In this contribution, we show this speciation analysis applied to lithium ion solvation in the bis-(trifluoromethanesulfonyl)amide and the bis-(fluromethanesulfonyl)amide based ionic liquids, based on the spectrothermodynamics. We also describe ionic liquids specific central metal ion stabilization by the ionic liquid consisting of cations at the metal ion second sphere and the solvation structure equilibria evaluated thermodynamically.View full abstractDownload PDF (1008K)
Research Papers
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Toshiyuki TAKAMUKU, Oscar F. YAGAFAROV, Yoshinori KATAYAMA, Tatsuya UM ...Article type: Research Papers
2015 Volume 64 Issue 3 Pages 203-210
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSEnergy-dispersive X-ray diffraction measurements have been conducted on aqueous calcium chloride solutions with two different concentrations (CaCl2·RH2O, R = 10 and 25) under high temperatures and high pressures using a press machine installed at BL14B1 in SPring-8. One of the two measurement conditions was the isothermal condition at 300 K with varying pressure from 0.7 to 1.6 GPa, while the other was the constant load condition at 20 t with rising temperature from 373 to 673 K. The hydration distances of Ca–O and Cl–O do not significantly change under both conditions. The hydration numbers of Ca2+ in both solutions fall into the range of 4–5. The values are smaller than those (6–8) under ambient conditions. The hydration numbers of Cl− in the solution at R = 10 are slightly larger than those under ambient conditions, and those in the solution at R = 25 are markedly larger. The hydration numbers of both ions at 300 K are increased by pressurization. Particularly, the increase in the value for Cl− is more significant than that for Ca2+. In contrast, the hydration structure of both ions is disrupted with rising temperature. However, the contact ion pair Ca2+–Cl− is not remarkably stable.View full abstractDownload PDF (776K)
Notes
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Naoki TACHIKAWA, Kazuki YOSHII, Yasushi KATAYAMAArticle type: Notes
2015 Volume 64 Issue 3 Pages 211-217
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSThe formal potentials for Ag(I)/Ag, Pb(II)/Pb, Sn(II)/Sn, Fe(III)/Fe(II) and [Fe(bpy)3]3+/[Fe(bpy)3]2+ (bpy = 2,2’-bipyridine) were investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) ionic liquid at 25°C. The formal potentials and thermodynamic properties of metal redox couples were evaluated on the basis of the potential of ferrocene/ferrocenium couple in various electrolytes including organic solvents and ionic liquids. The formal potentials for Ag(I)/Ag, Pb(II)/Pb and Sn(II)/Sn are more positive in BMPTFSA than in conventional organic solvents, resulting in the positive Gibbs energy of transfer for metal ion from the organic solvents into BMPTFSA. The donor number of BMPTFSA was estimated from the correlation with the formal potentials of metal redox couples. The estimated donor number of BMPTFSA is consistent with the literature values based on other methods, such as the lanthanide redox potentials and the chemical shift of 23Na NMR. The donor ability of TFSA−-type ionic liquids was located between nitromethane and acetonitrile, suggesting that the interaction between metal ion and TFSA− is weak as compared with other media.View full abstractDownload PDF (791K) -
Seiji KATAKURA, Naoya NISHI, Kazuya KOBAYASHI, Ken-ichi AMANO, Tetsuo ...Article type: Notes
2015 Volume 64 Issue 3 Pages 219-224
Published: March 05, 2015
Released on J-STAGE: April 09, 2015
JOURNAL FREE ACCESSThe surface structure of the quaternary ammonium based ionic liquid, tributylmethylammonium bis(trifluoromethanesulfonyl)amide ([TBMA][C1C1N]), has been studied using molecular dynamics simulation. The atomic number density profiles reveal that the ionic multilayering structure is formed at the surface with a layer thickness of the ionic diameter (∼10 Å). At the surface of the ionic liquid, TBMA+ and C1C1N− are oriented with the butyl chains of TBMA+ and the CF3 group of C1C1N− protruding out of the ionic liquid phase, respectively. However, all the three butyl chains are rarely pointed to the vacuum simultaneously. C1C1N− tends to point the CF3 group to the vacuum more strongly than TBMA+ does the butyl chains. The C2 conformation of C1C1N− is more stable than the C1 conformation even in the first ionic layer on average, as in the bulk. However, in the outmost part of the first ionic layer, the stability of C1 exceeds that of C2.View full abstractDownload PDF (970K)
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