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Volume 64, Issue 4
Chemical Reactions in Solutions for Analytical Chemistry
Displaying 1-6 of 6 articles from this issue
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Accounts
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Takashi TOKUSHIMA, Yuka HORIKAWAArticle type: Accounts
2015 Volume 64 Issue 4 Pages 237-245
Published: April 05, 2015
Released on J-STAGE: April 08, 2015
JOURNAL FREE ACCESSSoft X-ray spectroscopies that utilize the electronic transition of core electrons are known as powerful tools for observing electronic structures, and are extensively applied to solid and gaseous samples in a vacuum. However experimenting on a liquid sample is not easy. While soft X-rays require a vacuum because of low penetration ability, one cannot hold liquid-phase samples in vacuum due to the vaporization of liquids. Recently, extensive developments in experimental techniques have enabled the application of X-ray emission and absorption spectroscopy to liquid and solution samples. We have also developed a liquid flow cell and X-ray emission spectrometers dedicated to the research of liquid and solution samples at BL17SU in the third-generation synchrotron facility, SPring-8. Here, we will present our recent developments and aspects on electronic-state studies of liquids and solutions concerning the liquid structure of water, the molecular interaction of water molecules in solution and electronic state selective observations of solute molecules.View full abstractDownload PDF (1328K) -
Masashi HOJO, Xiaohui CHENArticle type: Accounts
2015 Volume 64 Issue 4 Pages 247-260
Published: April 10, 2015
Released on J-STAGE: April 08, 2015
JOURNAL FREE ACCESSThe specific interactions between alkaline earth metal (Mg2+, Ca2+, or Ba2+) and p-toluenesulfonate (L−), 1,5-naphthalenedisulfonate (L2−), or 1,3,6-naphthalenetrisulfonate (L3−) ions (from the tetraethylammnonium salt of L−, L2−, or L3−) have been examined by means of UV-visible spectroscopy in primary alcohols (from methanol to hexanol) as well as in binary acetonitrile-alcohols (MeCN-MeOH, MeCN-EtOH), ethanol-methanol (EtOH-MeOH) and methanol-water (MeOH-H2O) solvents. The precipitation of non-charged species (e.g. ML0) and the successive re-dissolution of the precipitates, with increasing concentration of M(ClO4)2, have revealed the formation of cationic charged species or "reverse coordinated" species, M2L2+, even in protic media as well as the aprotic solvent MeCN. The solubility products (Ksp) and the "reverse coordination" constants (2M2+ + L2− ↔ M2L2+, K2(−2) = [M2L2+]/[M2+]2 [L2−]) have been evaluated. In ethanol, both phenomena concerning the precipitation of ML0 and the successive re-dissolution to produce M2L2+ are observed for Ca2+ or Ba2+, but not for Mg2+. In butanol, the interaction between Mg2+ and the L2− causes the complete precipitation of MgL0 (pKsp = 10.39) as well as the successive re-dissolution of Mg2L2+ (log K2(−2) = 8.08). Even in methanol, the interaction between Ba2+ and L2− results the precipitation (pKsp = 8.28) and the "reverse coordinated" species, Ba2L2+ (log K2(−2) = 5.58). The interaction of Ba2+ with L− or L3− causes no precipitation in methanol, however, in all the other alcohols, it results in both precipitation (BaL2 or Ba3L2) and "reverse coordinated" species, BaL+ or Ba2L+. The formulation for the formation constants (K2(−3)) for M2+ and L3− is newly presented, and the constants (2Ba2+ + L3− ↔ Ba2L+, K2(−3) = [Ba2L+]/([Ba2+]2 [L3−]) are evaluated in ethanol and propanol as well as the binary EtOH-MeOH solvents, up to 70% (v/v) MeOH. The donicities towards M2+ of the media have been related to the pKsp and "reverse coordination" constants for L−, L2−, and L3−.View full abstractDownload PDF (1617K) -
Takehiko TSUKAHARA, Kyojiro MORIKAWA, Kazuma MAWATARI, Takehiko KITAMO ...Article type: Accounts
2015 Volume 64 Issue 4 Pages 261-271
Published: April 05, 2015
Released on J-STAGE: April 08, 2015
JOURNAL FREE ACCESSAn extended nanospace (10—100 nm scale) makes it possible to induce unique physicochemical properties, because scientific and technological concepts in this region are shifted from the bulk condensed phase to single molecule, and from microfluidic technology to conventional nanotechnology, respectively. In this study, the molecular structure and dynamics of water and nonaqueous solvents confined in extended nanospaces on a fused-silica substrate were examined by using NMR chemical spectra, relaxation times, and so on. The results showed that the collective properties of molecular clusters with a size range from 10 to 100 nm in a liquid phase were characterized due to the effects of charged surface SiOH groups, and that unique properties differing from bulk water and surface-adsorbing water could appear in extended nanospaces. In particular, we found that (1) inhibition of molecular translational motions, (2) localization of proton charge distribution along a linear O···H–O hydrogen bonding chain, and (3) an enhancement of proton transfer of water due to the Grotthuss mechanism; (∫SiO−···H+···H2O) + H2O→∫SiO− + (H3O+ + H2O)→∫SiO− + (H2O + H3O+), were induced in extended nanospaces. Such changes appeared for sizes smaller than 800 nm. These results suggested that a proton transfer phase, in which water molecules are loosely coupled within about 50 nm from the surface, exists in extended nanospaces. This model could be qualitatively supported by a three-phase theory invoking the bulk, proton transfer, and surface-adsorbing phases.View full abstractDownload PDF (1451K) -
Hiroharu YUI, Akira SUZUKI, Toshinori MORISAKUArticle type: Accounts
2015 Volume 64 Issue 4 Pages 273-282
Published: April 05, 2015
Released on J-STAGE: April 08, 2015
JOURNAL FREE ACCESSWater confined in nanospaces with diameters of 1–10 nm is ubiquitous in natural materials, such as intracellular organic space and interlayers in inorganic minerals (e.g., clay and zeolite). The confined water in those nanospaces plays a crucial role in the expression of their structure, properties, and functions. For this reason, the thermodynamic properties of the confined water have been intensively studied, especially in inorganic minerals, due to their easy controllability of the space sizes. On the other hand, few studies have been reported concerning the structure and properties of water confined in organic molecular self-assemblies composed of small organic molecules, especially lipids, in the human body. This is because regulation of the size distribution is generally difficult for such organic self-assemblies. Here, we focus on glycolipid nanotubes and AOT reverse micelles as organic self-assemblies due to good controllability of their sizes. The inner surface of a glycolipid nanotube is covered with hydrophilic hydroxyl groups, while that of an AOT reverse micelle is composed of hydrophilic ionic groups and their corresponding counter ions. Since both inner surfaces have a strongly polarized structure, they strongly interact with water molecules, which have large dipole moments. Our current study using spectroscopic techniques, especially infrared spectroscopy, reveals the anomaly on the structure and phase transition temperature of the water confined in the nanotubes and micelles. We clarified and anomalous structure and thermal properties of the water confined in the nanotubes and micelles, which are crucially different from those of bulk water at the same temperature and under the same pressure.View full abstractDownload PDF (1371K) -
Koji YOSHIDA, Toshio YAMAGUCHIArticle type: Accounts
2015 Volume 64 Issue 4 Pages 283-293
Published: April 05, 2015
Released on J-STAGE: April 08, 2015
JOURNAL FREE ACCESSQuantum beams (e.g. synchrotron X-rays and neutrons) are powerful tools used to investigate the structure and dynamics of hydrated proteins and protein hydration water. Inelastic X-ray scattering can reveal the collective dynamics of hydrated proteins on the sub-femtosecond time scale since X-rays are coherent and their energy exchange with a sample corresponds to the excitation energy of the atomic vibrations of the sample. Incoherent quasi-elastic neutron scattering can be used to investigate the single-particle dynamics of protons, since the incoherent cross section of a proton is larger by ∼40 than that of other atoms. The time scale is in the range from picosecond to nanosecond. Small-angle scattering can characterize the nanoscale structure of protein aggregates (e.g., size, shape, and fractal dimension of the protein aggregate). From this review, IXS revealed the collective dynamics of hydrated β-lactoglobulin (β-LG) and antifreeze proteins. A dispersion relation of collective excitation energy vs. Q was found for the hydrated proteins, but it was not for dry ones. The fast sound velocity obtained from the dispersion relation at 180 K was found to be higher than that at higher temperatures, implying a kind of dynamic transition of the hydrated proteins, as can be seen in the single-particle dynamic observed by incoherent neutron scattering. The structure of the aggregate and dynamic properties of β-LG were revealed as a function of the alcohol concentration in alcohol-water mixtures with small-angle and quasi-elastic neutron scatterings. The β-LG in the alcohol-water solutions undergoes aggregation and gelation at specific alcohol concentrations. With increasing the alcohol concentration, the fraction of mobile protons, accompanied with increasing the sphere radius where hydrogen atoms in hydrophobic residues of the protein move around. A possible mechanism of the protein aggregation process would be as follows: the addition of alcohol makes the embedded amino acid residues be exposed to the solvent. The protein is more molten globule-like, i.e. disordered in the aggregation.View full abstractDownload PDF (1410K)
Research Papers
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Toshio YAMAGUCHI, Kosei LEE, Mikio YAMAUCHI, Nami FUKUYAMA, Koji YOSHI ...Article type: Research Papers
2015 Volume 64 Issue 4 Pages 295-308
Published: April 05, 2015
Released on J-STAGE: April 08, 2015
JOURNAL FREE ACCESSRaman scattering measurements were conducted at 25−350°C and 40 MPa on a 1 mol dm−3 Mg(NO3)2 aqueous solution. Along with elevating temperature, the N–O ν1 band of the nitrate ion at 1050 cm−1 shifts to a lower wave number, whereas the O–D ν1 band of a water molecule does to a higher wave number at 2540 cm−1. For the both bands, an inflection point was observed at around 200°C, suggesting a structure change in the hydration shell of nitrate ion and the solvent water hydrogen network. Energy-dispersive X-ray diffraction measurements were also performed at 25−210°C and 40 MPa on a 1 mol dm−3 Mg(NO3)2 aqueous solution. The experimental structure factors were subjected to empirical potential structure refinement (EPSR) modeling to reveal 3D structures of solvent water, ion hydration and ion-pairs. For solvent water, there was no significant structure change in the first coordination shell of a water molecule, but the number of the second coordination shell decreased from 10.5 at 25°C and 0.1 MPa to 8.5 at 210°C and 40 MPa. A Mg2+ ion is surrounded by six water molecules in an octahedral manner at 25°C and 0.1 MPa. At 210°C and 40 MPa one nitrate ion enters the first coordination shell of Mg2+ to form a contact ion pair in a monodentate fashion with a Mg–ON–N bond angle of about 150°. About 11 water molecules surround a central nitrate ion without specific coordination sites over the measured temperature range, except for a slight decrease in the coordination number of the nitrate ion at 210°C and 40 MPa, probably due to the formation of a Mg2+–NO3− ion pair.View full abstractDownload PDF (5991K)
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