Language：Japanese   Publishing type：Research paper (scientific journal)  

To determine the long-term dynamics of mercury discharged from Chisso chemical plant between 1932 and 1968, the vertical variation in mercury concentrations in Yatsushiro Sea sediments was studied from 2013 to 2020 at 31 locations and compared to the mercury concentration distribution obtained in 1996. The results suggest that new sedimentation occurred after 1996, but the mercury concentrations at the surface ranged from 0.2 to 1.9 mg kg-1, which did not decrease significantly over a 20-year period. It was estimated that approximately 17 t of mercury remained in the southern Yatsushiro Sea sediment, which is equivalent to 10-20% of the total mercury discharged between 1932 and 1968. From results of WD-XRF and TOC measurement, it was suggested that mercury in sediment had been transported with suspended particles derived from sludges from the chemical plant and further suggests that the suspended particles derived from the sediment surface layer are still slowly diffusing.

DOI： 10.1007/s11356-023-27505-0

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Sensitive detection methods for nitrite (NO2-) and nitrate (NO3-) ions are essential to understand the nitrogen cycle and for environmental protection and public health. Herein, we report a detection method that combines ion-chromatographic separation of NO2- and NO3-, on-line photochemical conversion of these ions to peroxynitrite (ONOO-) by irradiation with a 222 nm excimer lamp, and chemiluminescence from the reaction between luminol and ONOO-. The detection limits for NO2- and NO3- were 0.01 and 0.03 μM, respectively, with linear ranges of 0.010-2.0 and 0.10-3.0 μM, respectively, at an injection volume of 1 μL. The results obtained by the proposed method for seawater analysis corresponded with those of a reference method (AutoAnalyzer based on the Griess reaction). As luminol chemiluminescence can measure ONOO- at picomolar concentrations, our method is expected to be able to detect NO2- and NO3- at picomolar concentrations owing to the high conversion ratio to ONOO- (>60%), assuming that contamination and background chemiluminescence issues can be resolved. This method has the potential to emerge as an innovative technology for NO2- and NO3- detection in various samples.

DOI： 10.1021/acs.est.3c00273

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Language：Japanese   Publishing type：Research paper (scientific journal)  

To elucidate the dynamics of mercury emitted and released by artisanal and small-scale gold mining (ASGM) activity and to estimate its impact on the ecosystems of the bay, the distribution of mercury in the atmosphere, soil, water, and sediment around Mambulao Bay, Camarines Norte, Philippines, was investigated. The ASGM operations use mercury to extract gold from ore and are located on the east shore side of the bay. Samplings were conducted in August 2017 and September 2018. The samples were used for determination of total mercury (T-Hg) and organic mercury (org-Hg) concentrations, total organic carbon (TOC) content, and chemical composition. The atmospheric mercury concentration on the east shore side, 6.1-25.8 ng m-3, was significantly higher than the value of 1.4-9.9 ng m-3 observed on the west shore side. The average concentrations of T-Hg in the forest soils of the west shore side and those of the east shore side were 0.081 ± 0.028 mg kg-1 and 0.496 ± 0.439 mg kg-1, respectively. In the vertical distribution of T-Hg in the soil of the east shore side, a higher concentration was observed near the surface. For the vertical variations in T-Hg in the marine sediment, higher values were observed near the estuary, and the vertical variations in core samples showed an increase in mercury concentration toward the surface. The highest concentration of T-Hg in sediment, 9.5 mg kg-1, which was 2 orders of magnitude higher than the background levels of this area, was found near the river mouth. The T-Hg, org-Hg, and TOC levels showed a positive correlation, suggesting that the rivers are the main sources of T-Hg and org-Hg in the bay. Although the fish sample containing a mercury content higher than the regulatory level for fish and shellfish of 0.4 mg kg-1 in Japan was only one of 42 samples, the percentage of org-Hg in fish samples was 91 ± 18%. Mercury released into the surroundings by the ASGM activities can be converted into methylmercury and affect the bay's ecosystem.

DOI： 10.1007/s11356-022-23497-5

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Language：Japanese   Publishing type：Research paper (scientific journal)  

N-Nitrosodimethylamine (NDMA) is a carcinogenic constituent commonly found in recycled water and pharmaceuticals. Developing an analytical method to continuously monitor changes in NDMA concentrations during water recycling and pharmaceutical manufacturing can mitigate accidents caused by NDMA formation. However, NDMA analysis in high-matrix water samples, such as beverages, wastewater, and pharmaceutical ingredients, is difficult. In this study, we adapted reverse osmosis (RO) membrane treatment as a pretreatment for NDMA analysis by isolating NDMA from interfering substances in high-matrix water samples. Subsequently, high-performance liquid chromatography-chemiluminescence detection was used for NDMA analysis. In a pure water matrix, 95% of NDMA can pass through at a low permeate flux of 1 L m−2 h−1. The method was then validated using beer, which is known to contain high concentrations of NDMA, as a representative high-matrix water sample. We found that RO pretreatment leads to clean chromatograms in which NDMA peaks are clearly visible while other peaks are mostly absent. Analysis of six different beer samples showed a maximum NDMA concentration of 315 ng L−1, and an average NDMA concentration of 138 ± 83 ng L−1 (n = 6), which fall within the regulation limits for NDMA in beer in the United States of America. The proposed pretreatment method has the potential to provide a platform for developing technologies for continuous monitoring of NDMA in aqueous solutions.

DOI： 10.1039/d3ew00222e

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Wakamiko Proto-Caldera, a submarine volcano, is located at the bottom of the sea in the bay head area of Kagoshima Bay. In Kagoshima Bay, several species of fish with total mercury exceeding the provisional regulation value of 0.40 mg kg−1 were found in the 1970s. The effects of mercury released from submarine volcanoes are suspected. However, the path from volcanic mercury to the broader ecosystem has not yet been clarified. In this study, as the first step to elucidate the impact of volcanic activity on the ecosystems of Kagoshima Bay, seasonal changes in the concentrations of dissolved gaseous mercury (DGM), Hg(II), filtered total mercury (FT-Hg), particulate mercury (P-Hg), and mercury in suspended particulate matter (Hg in SPM) in seawater of Kagoshima Bay were tracked every two months from Feb. 2014 to Dec. 2017. The dissolved total mercury (DT-Hg) concentration was calculated by summing the DGM and FT-Hg concentrations. The DT-Hg at the location in the caldera ranged from 0.09 to 6.83 ng L−1 showing higher values in summer compared to winter, that is, in the stratified period. The P-Hg showed similar periodic variation as DT-Hg, and the highest Hg in SPM was 2.15 mg kg−1, which is one order of magnitude higher than that observed at the reference site. The high mercury concentration in SPM suggests the accumulation of dissolved mercury discharged from volcanic activity on SPM. Since mercury loaded on SPM can be taken up by suspension feeders and enter the food chain, the Hg in SPM may be a key factor affecting Hg in fishes in Kagoshima Bay.

DOI： 10.1016/j.marchem.2022.104133

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Language：Japanese   Publishing type：Research paper (scientific journal)  

The purpose of this study was to investigate the behavior of previously discharged mercury (Hg) released from the Itomuka Hg mine into the surrounding environment, especially into soil. Total-Hg (T-Hg), methylmercury (MeHg), and ethylmercury (EtHg) concentrations in the surface soil at eight sample sites around the mine were 3.8-64.2 mg/kg, 6.0-54.7 μg/kg, and undetected to 4.5 μg/kg, respectively. Core samples collected from seven of the eight sample sites showed that the vertical distribution of T-Hg was the highest in the surface soil layer and decreased rapidly in the lower layers. A strong positive correlation was observed between T-Hg and MeHg concentrations in the core samples; however, the slope of the regression line varied considerably for each core. This suggests that Hg and MeHg were not supplied from the atmosphere simultaneously, but rather that MeHg was produced on-site. Further, the formation of MeHg and EtHg in soil was considered in terms of the total organic carbon/total nitrogen ratio, which is a decomposition index of soil organic matter. The strong positive correlation between T-Hg and MeHg can be attributed to the migration of organic matter containing Hg species to the lower layers. There was no relationship between T-Hg and MeHg at the riverbed sample site because of the high T-Hg in the lower soil layers, suggesting that Hg was supplied by ore at this sample site. These assumptions of the formation change and migration of Hg in soil were supported by the results of the fractionation experiment and the elution test. To understand the current conditions in this area, measurements of Hg in the water, sediment, atmosphere, and plants were also conducted.

DOI： 10.1016/j.scitotenv.2021.152492

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Maghemite nanoparticles coated with polyacrylic acid (pAA) were dispersed in the protic ionic liquid, diethylethanolammonium trifluoromethanesulfonate (DEEAH+⋅TfO−), and the thermodynamics of particle dispersion was studied by means of potentiometric and calorimetric titrations over the entire accessible pH range. As previously reported, the domain of colloidal stability is divided into two pH regions, mildly acidic and basic, separated by a flocculation domain at an intermediate pH. In this study, solvent DEEAH+⋅TfO− was first characterized in terms of the thermodynamic parameters of two reference reactions: autoprotolysis and ionization of acetic acid. A negative autoprotolysis entropy is obtained due to hydrogen-bond formation between the neutralized solvent cation, DEEA, and the neighboring cation DEEAH+. This suggests that the solvent structure is reinforced by the formation of neutral species, being an opposite trend to both ethylammonium nitrate and water. Second, the ionization and flocculation of pAA-coated nanoparticles (CNps) in the ionic liquid were examined. The potentiometric results could be modeled using a simple pAA ionization, independent of the aggregation state over the entire pH range. However, the calorimetric titration detected extra heat generation in an acidic condition prior to flocculation, in addition to an ionization enthalpy of pAA of 30 kJ/mol. This exothermic contribution is attributed to a change in the solvation process of CNps in the ionic liquid. Herein, we propose a model in which different types of solvation in the acidic and basic domains are sufficient to ensure colloidal stability, while aggregation unfolds between the switching pH.

DOI： 10.1016/j.molliq.2021.118146

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.talo.2021.100035

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Language：Japanese   Publishing type：Research paper (scientific journal)  

N-nitrosamines are contaminants of emerging concern, and controlling these chemicals in potable water and recycled water for potable reuse has become important for protecting public health. This study aimed to evaluate the influence of the alkyl chain lengths of N-nitrosamine precursors (secondary and tertiary amines) on the formation of N-nitrosamines via chloramination. The molar conversion efficiency from dimethylamine, an N-nitrosodimethylamine (NDMA) precursor, to NDMA (0.67%) was greater than that from diethylamine, an N-nitrosodiethylamine (NDEA) precursor, to NDEA (0.38%). Similarly, the molar conversion efficiency from trimethylamine to NDMA (0.92%) was greater than from triethylamine to NDEA (0.33%). Interestingly, a considerable difference in molar conversion efficiencies were observed for tertiary amines with the N,N-dialkyl-α-arylamine structure: the molar conversion efficiencies from N,N-dimethylbenzylamine and N,N-diethylbenzylamine to NDMA and NDEA were 50.2% and 1.7%, respectively. These results indicate that amines with ethyl groups have lower potentials for producing the corresponding N-nitrosamines than those with methyl groups. These differences in yields between amines with methyl and ethyl groups can be explained by the difference in electron density in the nitrogen atom of the amine, which influences the protonation of the amine and stabilization of intermediate species. These findings could be useful for enhancing source control of water and wastewater by regulating runoff or industrial wastewater containing high concentrations of specific N-nitrosamine precursors.

DOI： 10.1016/j.eti.2021.101520

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Volcanic activity is one of the primary sources of arsenic in nature, and chemical forms of arsenic discharged by volcanic activity are inorganic. Kagoshima Bay has active submarine volcano located in the 200 m deep basin of its northern part. Since dissolved inorganic arsenic is more toxic than organic arsenic it is important to understand the dispersion of discharged arsenic in seawater. To estimate the influence of arsenic emitted from the bottom vents seasonal changes in As(III) and As(V) concentrations in seawater were studied. There are few studies on the impact of arsenic discharged by submarine volcanos in the inner bay. The total concentrations of As(III) and As(V) (T-As) in seawater at the background site in Kagoshima Bay was 1.71 +/- 0.35 mu g L-1 (av. +/- s.d.), similar to the world average value of 1.7 mu g L-1. The highest T-As value at the nearest point to the submarine volcano, 3.48 mu g L-1, was observed in summer. Since the vertical mixing of seawater cannot occur in summer due to the formation of the thermocline, the deep water is strongly affected by volcanic activity. The increase in T-As was caused by the increase in As(III) concentration suggesting the discharge of As(III) from the vents.

DOI： 10.1007/s12665-021-09619-1

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

An ultra-sensitive analytical system that can determine the concentration of N-nitrosamines at the ng/L level without preconcentration was used to investigate the contamination, decomposition, and formation of N-nitrosodimethylamine (NDMA) and other N-nitrosamines in water samples during general analytical procedures. A preliminary experiment was performed to estimate the NDMA concentrations in ambient air. Since the air samples contained NDMA at concentrations in the range of 2.0 - 10.7 ng/m(3), ambient air was identified as the source of NDMA contamination in water samples. We directly confirmed that the concentration of aqueous 10-ng/L NDMA samples stored in clear glass bottles decreased upon exposure to sunlight. Thus, to maintain the N-nitrosamine concentration, such samples must always be protected from sunlight during sampling. The existence of N-nitrosamines in experimental reagents, such as ranitidine and sodium hypochlorite solutions, was also confirmed, as was the formation of NDMA on an activated carbon solid-phase extraction cartridge.

DOI： 10.2116/analsci.20P162

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER INTERNATIONAL PUBLISHING AG  

This study was conducted to understand the environmental behavior of mercury released by artisanal and small-scale gold mining (ASGM) activities. For this purpose, we attempted to assess the effect of diffused mercury on mercury concentrations in soil, demonstrate the presence of methylmercury in soil affected by the deposited mercury and determine the reactions associated with methylmercury production. The vertical profiles of mercury were obtained from two sites in the forest of the ASGM village in Pongkor (West Java, Indonesia) and from two sites in Mount Halimun-Salak National Park, which is approximately 12 km from the ASGM village. The highest total mercury concentration, 8.9 mg kg(-1), was observed for soil samples collected at the ASGM village. The mercury was concentrated at the surface or in the subsurface layers, and the concentrations were several times to more than ten times higher than the lowest values observed in the deeper layers at each site. Even in the national park, the highest concentration of 1.9 mg kg(-1) was observed in the upper soil layer. These results suggest that the primary source of mercury in the forest soil is atmospheric deposition; fallen plant leaves also deliver accumulated mercury to the soil surface. The organic mercury percentages of the total mercury were 0.2 +/- 0.1% for the national park and 0.3 +/- 0.2% for ASGM sites. The vertical variation in organic mercury concentration did not always match that in total mercury concentration, which suggested that the formation of methylmercury in soil was closely related to the decomposition of organic matter near the surface. The soil surface is an important reaction field for methylmercury production in forested areas.

DOI： 10.1007/s42452-020-3008-5

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Language：Japanese   Publishing type：Research paper (scientific journal)  

© 2020 Elsevier Ltd Total-Hg (T-Hg) and methylmercury (MeHg) concentrations in rice grains were measured to understand the MeHg accumulation process. Rice plants were cultivated in Hg2+-spiked non-contaminated soils in experimental pots at three different places. Although soil MeHg concentrations in the pots changed significantly and individually during the rice-growing season, T-Hg concentration of brown rice grain was high at high soil MeHg concentration. In addition, there was no significant variation in T-Hg concentration in brown rice grains from individual panicles or among panicles obtained from the same pot, although the period of growth for each panicle was different. The highest T-Hg concentration of brown rice grains recorded for a panicle was 1.4 ± 0.1 mg kg−1 (n = 8), and the corresponding MeHg ratio was 76%. In addition, the T-Hg and MeHg concentrations in various parts of the brown rice grain—white rice (endosperm), bran, and embryo—were measured. Among the parts of the brown rice grain, the embryo had the highest Hg concentration. Furthermore, Hg concentration in the grain was constant during grain filling. These findings suggest that MeHg formed in soil accumulates in the rice plant during growth and is supplied to the rice grains continuously for the entire duration of the grain development period.

DOI： 10.1016/j.chemosphere.2020.125827

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1039/c9cp06717e

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Language：Japanese   Publisher：The Japan Society of Calorimetry and Thermal Analysis  

One of the fundamental roles of analytical chemistry is to provide the information of chemical species distributing in solutions, where chemical equilibria of acid dissociation, dissolving of salts, complex formation, electrode reaction, etc., are considered. This extensively owes to chemical thermodynamics, however, the relationship is rarely taught in detail in the class of physical chemistry nor analytical chemistry. It will be a great loss in both fields. In this article, with beginning from the usual equilibria in analytical chemistry, its groundwork of chemical thermodynamics will be explained. First, chemical potential is introduced as the determining factor of equilibrium constant, then Gibbs energy is defined. Although this is inverted from the ordinary way of instruction, possibly more convenient for the field of analytical chemistry. Then, activity coefficient and the standard state are explained, followed by the derivation of chemical potential from the work for changing concentration of solute in solution for clarifying its physical meaning. Turning to the solvent, the solvent transfer is considered by both transfer Gibbs energy and transfer activity coefficient. Finally, electrochemical potential is outlined. They are described within the word of analytical chemistry. Hopefully, this article will help establishing the energy-based perspective on the chemical equilibria in solutions.

DOI： 10.11311/jscta.46.4_195

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/chem.201903485

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Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.66.0_259

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

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DOI： 10.14862/geochemproc.66.0_126

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/acs.jpcb.8b08870

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DOI： 10.1007/s12665-018-7616-y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Academic Press Inc.  

Hypothesis: Ionic liquids (ILs) are extremely concentrated electrolyte solutions. The ubiquitous presence of ions induces specific behaviors for chemical reactions compared to reactions in water solutions. This is also the case for the stability of colloidal dispersions, for which the DLVO model cannot be applied as the ionic strength is out of the model range. In a previous work, in the protic IL ethylammonium nitrate (doi: https://doi.org//10.1016/j.jcis.2015.04.059), we observed an unexpected influence of the pH on the stability of dispersion of maghemite nanoparticles coated with poly(acrylic acid) (pAA). Experiments: To clarify and generalize these observations, we investigated here the pH response of the dispersion in a second protic ionic liquid with a different acid-base nature, diethylethanolammonium trifluoromethanesulfonate. pH titrations of the dispersions were achieved with an IS-FET electrode and the associated thermodynamic constants determined. The colloid structural properties were examined by small angle X-ray scattering. Findings: Under acidic or mildly basic condition, a stable dispersion was obtained, i.e., when the degree of dissociation of pAA, α was α &lt
0.1 or α &gt
0.7. Dispersions form quite dense but reversible aggregates in the intermediate α range. A model for the solvation layer around the particles is proposed and generalizes the former findings.

DOI： 10.1016/j.jcis.2018.01.004

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Metal ions in ionic liquids are laid under an unprecedented reaction field. In order to assess the reaction thermodynamics of metal ions in such a situation, Cu2+-chloro complex formation was examined with spectroscopic and calorimetric titrations in an ionic liquid, 1-buthy1-3-methylimidazolium trifluoromethanesulfonate (C(4)mimTfO). In addition, the effect of the structure of the solvated complexes on the complexation mechanism was investigated with the aid of DFT calculations. Chloro complexation successively proceeded and finally provided a [CuCl4](2-) species, which is also the final product in conventional molecular solvents. Their stability constants were comparable to those in molecular solvents. Interestingly, in spite of the charged solvent in the ionic liquid, the entropy profile of the complexation resembled that in the conventional molecular liquids. This indicates that the entropy gain of the released solvent species from the complexes is the main driving force of the chloro complexation in the ionic liquid. In contrast, unlike the major molecular solvents, the total coordination number of Cu2+ is saturated to 4 in the ionic liquid, and the Cl- complexation tends to be accompanied by a 1:1 exchange of the solvent TfO- from the complex. In addition, this ligand exchange was almost athermal. This possibly indicates that the coordination number is dominated by the electrostatic hindrance among the ligands including the solvent ions in the primary coordination sphere.

DOI： 10.1021/acs.jpcb.7b06287

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The separate influences of drying and storage conditions on methylmercury (MeHg) concentrations in soil and sediment samples were investigated. Concentrations of MeHg and total Hg were determined in various soil and sediment samples that had been stored or dried under differing conditions. The influence of drying conditions (oven-drying (40 degrees C) versus freeze-drying) on MeHg concentrations in marine sediments, river sediments, soils, and paddy field soils was investigated (n = 43). The ratio of the MeHg concentration in oven-dried sub-samples divided by the concentration in freeze-dried sub-samples ranged from 0 to 336%. In order to confirm the production of MeHg during storage in some samples, Hg2+ was added at 15 mg kg(-1) to a paddy soil, and the sample was then stored at 30 degrees C. The concentrations of MeHg at 1-h, 1-day, 4-days and 7-days after Hg2+ spiking were 2.0 +/- 0.1, 13.8 +/- 1.0, 36.0 +/- 5.0, and 24.9 +/- 1.6 mu g kg(-1) (n = 3), respectively. The concentration of MeHg at 4-days after Hg spiking and sterilizing (121 degrees C, 30 min) was 1.8 mu g kg(-1), similar to the original value. These results indicate that bacterial Hg methylation and MeHg demethylation occurred within days in the soil. In addition, tests of the stability of MeHg in wet and dry samples during storage were also performed. Overall, our results indicate that the best way to preserve MeHg in soil and sediment samples is to freeze the samples immediately after collection, followed subsequently by freeze-drying, grinding, homogenization, and storage of the dry material in cool, dark conditions until analysis.

DOI： 10.1016/j.chemosphere.2017.01.053

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

A novel method for the determination of secondary amines at the nanomolar level was developed. The method is based on the nitrosation reaction of secondary amines, with the generated N-nitrosamines being measured using an HPLC separation, photochemical reaction, and chemiluminescence detection system. The efficient nitrosation of secondary amines was performed using sodium nitrite (200 mM) and acetic acid (0.8 M) at 80 degrees C over 60 min. Although compounds bearing OH and SH functional groups also underwent the nitrosation reaction, the sensitivity of these compounds was 1000 times lower than that of the secondary amines. Our method was applied to the determination of low molecular weight secondary amines, including dimethylamine, morpholine, pyrrolidine, diethylamine, and piperidine, giving method detection limits of 0.7 nM, 0.2 nM, 0.4 nM, 0.7 nM, and 1.5 nM, respectively. The calibration curves were linear in the range of 5-100 nM. We then applied this method for the detection and quantification of these secondary amines in samples of tap water, river water, treated wastewater, and sea water. Dimethylamine was detected at concentrations up to 15.4 nM, &lt;0.7 nM, and 48.5 nM in tap water, river water, and treated wastewater samples, respectively, with recoveries ranging from 94 to 103%. Other amines were also detected at nanomolar levels. These results indicate that our proposed method can be applied to the analysis of secondary amines in various environmental water samples. To the best of our knowledge, the proposed method is one of the most sensitive and selective methods for the determination of secondary amines without pre-concentration steps. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.aca.2016.11.045

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

As a contaminant in drinking water, N-nitrosodimethylamine (NDMA) is of great concern because of its carcinogenicity; it has been limited to levels of ng/L by regulatory bodies worldwide. Consequently, a rapid and sensitive method for monitoring NDMA in drinking water is urgently required. In this study, we report an improvement of our previously proposed HPLC-based system for NDMA determination. The approach consists of the HPLC separation of NDMA, followed by NDMA photolysis to form peroxynitrite and detection with a luminol chemiluminescence reaction. The detection limit for the improved HPLC method was 0.2 ng/L, which is 10 times more sensitive than our previously reported system. For tap water measurements, only the addition of an ascorbic acid solution to eliminate residual chlorine and passage through an Oasis MAX solid-phase extraction cartridge are needed. The proposed NDMA determination method requires a sample volume of less than 2 mL and a complete analysis time of less than 15 min per sample. The method was utilized for the long-term monitoring of NDMA in tap water. The NDMA level measured in the municipal water survey was 4.9 ng/L, and a seasonal change of the NDMA concentration in tap water was confirmed. The proposed method should constitute a useful NDMA monitoring method for protecting drinking water quality. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chroma.2016.07.014

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

To quantify the properties of protic ionic liquids (PILs) as acid-base reaction media, potentiometric titrations were carried out in a neat PIL, ethylammonium nitrate (EAN). A linear relationship was found between the 14 pK(a) values of 12 compounds in EAN and in water. In other words, the pK(a) value in EAN was found to be roughly one unit greater than that in water regardless of the charge and hydrophobicity of the compounds. It is possible that this could be explained by the stronger acidity of HNO3 in EAN than that of H3O+ in water and not by the difference in the solvation state of the ions. The pH value in EAN ranges from -1 to 9 on the pH scale based on the pH value in water.

DOI： 10.1002/anie.201511328

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Recently, we revealed N-methylimidazole C(1)Im equimolar mixtures with superacids and strong acids such as trifluoromethanesulfonic acid HTfO (Tf: CF3SO2-), bis-(trifluoromethanesulfonyl)amide acid HTf2N or trifluoroacetic acid CF3COOH are essentially protic ionic liquids by means of potentiometry of direct pH measurement in such liquids. Here, we demonstrated Raman spectroscopic speciation analysis of [C(1)hIm(+)][TfO-] and [C(1)hIm(+)][Tf2N-] (C(1)hIm(+): N-methylimidazolium) to elucidate both liquids are spectroscopically protic ionic liquids; much excess ionic species exist in these liquids and the amount of electrically neutral molecular species are practically negligible. In addition, to further insight into the hydrogen bond in the imidazolium-based protic ionic liquids, liquid structure of [C(1)hIm(+)][TfO-] were studied by high-energy X-ray total scattering HEXTS experiments with the aid of molecular dynamics simulations. Comparing with the hydrogen bond in [C(1)hIm(+)][Tf2N-] previously reported, the hydrogen bond in [C(1)hIm][TfO-] is stronger probably due to the narrower negative charge de-localization.

DOI： 10.1246/bcsj.20160130

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Liquid structure of bis-(trifluoromethanesulfonyl)amide TFSA(-) based protic and aprotic ionic liquids composed of imidazolium [h(2)Im(+)], N-methylimidazolium [C(1)hIm(+)] and N,N'-dimethylimidazolium [C(1)mIm(+)] were investigated by high-energy total scattering (NETS) experiments. The nearest neighboring cation-anon orientation variations by the N-methyl groups substitution to proton were suggested based on the peaks at around 6 and 9 angstrom in the differential radial distribution functions as the form of r(2){G(x-ray)(r)-1) for these ionic liquids. It was supposed that the NH center dot center dot center dot O hydrogen bond causes the cation-anion orientation variations. To obtain further insight into the hydrogen bond in the PIL, MD simulations performed and agreed well with the experiments. According to spatial distribution functions (SDF) for the three ionic liquids, the O atom of TFSA(-) prefers the NH hydrogen of the imidazolium that has the most positive partial atomic charge in the cation, while the F atom locates right above and right below the imidazolium ring plane. In addition, the NH center dot center dot center dot O hydrogen bond has short bond lengths and linear bond angles, while the C2H center dot center dot O interaction is long and bent. The NH center dot center dot center dot O hydrogen bond in the PIL was discussed based on structural aspect accompanied by a thermodynamic viewpoint. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.molliq.2015.08.005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Submarine fumaroles are located in the 200-m deep basin of the northern part of Kagoshima Bay. To estimate the influence of mercury emitted from these fumaroles, the seasonal changes in total mercury (T-Hg), reactive mercury (RM), dissolved gaseous mercury (DGM), and monomethylmercury (MMHg) in water were studied. Seawater samples were collected from five separate locations in the northern part from May, 2011 to May, 2012 using a CTD-Rosette water sampler; the samples were taken every 50 m, starting from the surface. T-Hg, DGM, RM, and MMHg in the seawater columns (n = 132) were in the range of 0.05-3.04 ng L-1, 0.003-1.08 ng L-1, 0.006-1.47 ng L-1, 0.02-0.69 ng L-1 for an entire sample. Although the average T-Hg values at the surface and middle layers (0-100 m) for each sample showed no significant seasonal variation throughout the year, those at the deeper layer (150-200 m) were high from summer to autumn and low in winter. The seasonal changes and vertical distributions of DGM, RM, and MMHg concentrations were similar to those of T-Hg. A thermodine was observed from spring to autumn and ceased in winter. Because the thermocline prohibits vertical circulation of seawater, the fumarole impact may increase during those months. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.marchem.2015.10.009

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

A 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.

DOI： 10.2116/bunsekikagaku.64.189

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

To estimate the current contamination levels in Minamata Bay, the vertical and horizontal distributions of mercury in the sediment were investigated. Sediment core samples were collected in 2002, 2006, 2008, and 2010 at 12 locations by gravity core sampling in Minamata Bay and Fukuro Bay, which is located in the southern part of Minamata Bay. The average total mercury concentrations during each year in the surface sediment were 2.47-3.34 and 3.50-4.66 mg kg(-1) for Minamata Bay and Fukuro Bay, respectively; significant variation in the values was not observed during the study period. The total mercury concentration in Fukuro Bay increased with increasing depth and reached a maximum at 8-14 cm from the surface and decreased with increasing depth in the deeper layer. In Minamata Bay, the total mercury concentration did not change significantly from the surface to a depth of 10 cm and the values were considerably higher than the background level. In the lower layers of the long cores taken from both areas, the total mercury concentration decreased with depth, and the deepest layers exhibited relatively uniform low values. These values can be considered to represent the background concentration in the absence of anthropogenic influence. The depth of the sediment affected by the effluent was estimated to be 20 +/- 7 cm and 33 +/- 4 cm for Minamata Bay and Fukuro Bay, respectively. Furthermore, it was estimated from the average concentration and volume of the contaminated layer that approximately 1 ton of discharged mercury remained in the sediment of the two bays. (C) 2014 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.marchem.2013.12.002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Complexation characteristics of 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6, 18C6) with Li+ and K+ in a hydrophobic ionic liquid of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) amide under dry and humid conditions at 298.2 K were studied by H-1 and C-13 NMR chemical shifts. The comparison of the H-1 and C-13 chemical shifts of 18C6 molecule between the dry and humid IL solutions without the alkali metal ions showed that uncomplexed 18C6 molecules are solvated by water molecules in the humid ionic liquid solution. The changes in the H-1 and C-13 chemical shifts of 18C6 ligand molecule with the increases in the Li+ and K+ concentrations revealed that in both dry and humid ionic liquid solutions 18C6 molecule forms 1:1 complexes with Li+ and K+. The H-1 NMR data of water molecules in the humid ionic liquid solutions demonstrated that water molecules interact with Li+-18C6 complexes and free Li+, but do not with K+-18C6 complexes and free K+. The mechanisms of the formation of the Li+ and K+ complexes in the humid ionic liquid solution are different from each other due to the differences in the complex-water interactions.

DOI： 10.1007/s10847-014-0427-1

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/chem.201302228

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

A sensitive determination method for mercury speciation analysis was developed. Four mercury species, mercury ion, methylmercury, ethylmercury, and phenylmercury, were complexed with emetine-dithiocarbamate (emetine-CS2), and then injected onto a HPLC instrument coupled with a tris(2,2'-bipyridine)ruthenium(III) chemiluminescence detection system. The emetine-CS2 complexing agent was effectively used to measure the concentration in addition to serving as a separation and detection reagent. The calibration curves for these mercury complexes were linear in the range of 0.050 - 10 mu g L-1 (as Hg). The limit of detection for (emetine-CS2)(2)Hg, emetine-CS2-methylmercury, emetine-CS2-ethylmercury, and emetine-CS2-phenylmercury were 30, 17, 21, and 22 ng L-1, respectively. The sensitivity of this method enables the determination of mercury species in water samples at sub-ppb levels. Furthermore, the method was applied to biological samples in combination with acid leaching and liquid-liquid extraction using emetine-CS2 as an extraction reagent. The determination results were in good agreement with the values of the certified reference materials.

DOI： 10.2116/analsci.28.959

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PubMed

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

In order to estimate the dispersion of arsenic released thorough mining activity, a total of 39 soil samples were taken around the Gejiu tin mine, Yunnan, China. The highest total arsenic concentration, 1.1 x 10(4) mg kg(-1), was observed in the tailing. Although the concentration in soil samples was slightly lower than that in the tailings, higher than 5.1 x 10(2) mg kg(-1) of arsenic was still observed. A linear relation was observed between SiO(2) and Fe(2)O(3), which can be used for estimating the dispersion of the tailings. A trend was observed that the higher the chemical index of alteration, the lower the arsenic concentration, which suggests the elution of arsenic from tailings through weathering.

DOI： 10.2116/bunsekikagaku.61.21

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST PHYSICS  

Short- and long-range liquid structures of [C(n)mIm(+)][TFSA(-)] with n = 2, 4, 6, 8, 10, and 12 have been studied by high-energy x-ray diffraction (HEXRD) and small-angle neutron scattering (SANS) experiments with the aid of MD simulations. Observed x-ray structure factor, S(Q), for the ionic liquids with the alkyl-chain length n &gt; 6 exhibited a characteristic peak in the low-Q range of 0.2-0.4 angstrom (-1), indicating the heterogeneity of their ionic liquids. SANS profiles I-H(Q) and I-D(Q) for the normal and the alkyl group deuterated ionic liquids, respectively, showed significant peaks for n = 10 and 12 without no form factor component for large spherical or spheroidal aggregates like micelles in solution. The peaks for n = 10 and 12 evidently disappeared in the difference SANS profiles Delta I(Q) [= I-D(Q) - I-H(Q)], although that for n = 12 slightly remained. This suggests that the long-range correlations originated from the alkyl groups hardly contribute to the low-Q peak intensity in SANS. To reveal molecular origin of the low-Q peak, we introduce here a new function; x-ray structure factor intensity at a given Q as a function of r, S-Qpeak(r). The S-Qpeak(r) function suggests that the observed low-Q peak intensity depending on n is originated from liquid structures at two r-region of 5-8 and 8-15 angstrom for all ionic liquids examined except for n = 12. Atomistic MD simulations are consistent with the HEXRD and SANS experiments, and then we discussed the relationship between both variations of low-Q peak and real-space structure with lengthening the alkyl group of the C(n)mIm. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3672097]

DOI： 10.1063/1.3672097

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS INC  

A sensitive method for simultaneous determination of organic and inorganic mercury species has been developed and is presented in this study. The method is based on complex formation of mercury species with the emetine dithiocarbamate (emetine-CS(2)) ligand, HPLC separation, and tris(2,2'-bipyridine) ruthenium(III) chemiluminescence detection. The complexation reactions of the mercury species and emetine-CS(2) ligand occurred instantaneously upon the addition of emetine-CS(2) solution to the solution containing the mercury species. The complete separation of these complexes was achieved using an ODS column with 20mM NaH(2)PO(4)-acetonitrile (52:48, v/v) containing 30mM NaClO(4) as an ion-pair reagent. The calibration graphs of these complexes were linear in the range from 1-100 mu g/L. The detection limits were 0.27 mu g/L, 0.33 mu g/L, 0.39 mu g/L, and 0.17 mu g/L for methylmercury, ethylmercury, phenylmercury, and the mercury ion, respectively, at a signal-to-noise ratio of 3. The developed technique was validated by analyzing certified reference materials, CRM7402-a (cod fish, NMIJ) and CE464 (tuna fish, ERM), in combination with sonication-assisted acid leaching and liquid-liquid extraction. The emetine-CS2 ligand has been used for extraction, separation, and detection of mercury species. The results determined using the proposed method were in good agreement with the values of the certified reference materials. The MeHg(+) and EtHg(+) recoveries for the spiked samples were found to be almost 100%.

DOI： 10.1080/00032719.2011.565442

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION PURE APPLIED CHEMISTRY  

Ionic liquids (ILs) are expected to have specific properties as solvents for chemical reactions in view of solution chemistry. Among physicochemical properties, liquid structure, acid-base, and electron-pair donating and accepting abilities of solvent play a crucial role in ion-solvation and acid-base, metal-ion complexation, and electrochemical reactions. Various types of ILs have been developed, and among others, the bis(trifluoromethanesulfonyl)amide (TFSA-)-based ILs are extensively used. TFSA- is a flexible molecule to give two stable conformers, cis (C1) and trans (C2), which are present in equilibrium in the liquid state. The conformational equilibrium shifts upon solvation to the metal ion. This is quantitatively studied to obtain thermodynamic parameters of conformational change from C2 to Cl in the bulk and in the solvation sphere of the lithium ion. On the other hand, with ethylammonium nitrate (EAN), a typical protic IL, it is revealed that the ammonium group is hydrogen-bonded with three nitrate ions to form a heterogeneous liquid structure. The solvent acid-base property of EAN and acid dissociation reaction in EAN have been quantitatively revealed, and the results will be discussed in comparison with those in normal molecular solvents.

DOI： 10.1351/PAC-CON-09-10-28

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Electrochemical Society of Japan  

DOI： 10.5796/electrochemistry.78.687

CiNii Books

Other Link： https://jlc.jst.go.jp/DN/JALC/00354999630?from=CiNii

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Ethylammonium nitrate (EAN) is a typical protic ionic liquid (PIL) known for a long time. In order to investigate acid-base reaction mechanisms in PIL, thermodynamic quantities of a reaction, which corresponds to autoprotolysis in amphoteric solvents, has been determined in neat EAN. Unlike H3O+ and OH- in water, proton donor and acceptor species in EAN are both neutral; this makes acid-base reaction mechanisms in EAN distinct from that in water. EAN-water mixtures have also been studied.

DOI： 10.1246/cl.2010.578

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

We investigated the solvation properties of aqueous Solutions of aliphatic alcohols and fluorinated alcohols. These included ethanol (EtOH), 2-propanol (2-PrOH), 2,2,2-trifluoroethanol (TFE), and 1, 1, 1,3,3,3-hexafluoro-2-propanol (HFIP). The amphiphilic diol, 1,4-pentanediol (1,4-PD), was used as the solute to probe solvation properties at the molecular level. Small-angle neutron scattering (SANS) experiments revealed that the inherent microheterogeneity or HFIP-water binary Solutions was significantly enhanced by addition of 1,4-PD. In contrast, the addition of 1,4-PD to EtOH-, 2-PrOH-, and TFE-water solutions hardly changed the mixing state. Molecular dynamics simulations were used to obtain the spatial distribution functions for the oxygen atom of water molecules and the carbon and fluorine atoms of alcohol molecules around 1,4-PD. Of the alcohols studied, these spatial distributions illustrated that HFIP molecules formed the strongest hydrophobic solvation shell around the hydrocarbons of 1,4-PD. This preferential solvation of 1,4-PD by HFIP leads to enhancement of HFIP Clusters ill the Solutions. (13)C NMR and infrared spectroscopic measurements on 1,4-PD ill the different alcohol-water Solutions suggested that the number of water molecules around the hydrocarbons of 1,4-PD decreased in aliphatic alcohol-water solutions. Additionally, HFIP Molecules are thought to strongly interact with the hydrocarbons of 1,4-PD in HFIP-water solutions.

DOI： 10.1021/jp9097414

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Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.2477/jccj.H2013

Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Ethylammonium nitrate (EAN) is composed of C2H5NH3+ and NO3- ions, which behave as an acid and a base, respectively. The ionic liquid thus involves small amounts of C2H5NH2 and HNO3 molecules owing to proton transfer from C2H5NH3+ to NO3-. The equilibrium constant K-s (= [C2H5NH2][HNO3]), which corresponds to the autoprotolysis constant of water, was obtained to be ca. 10(-10) mol(2) dm(-6) by potentiometry using an ion-selective field-effect transistor and hydrogen electrodes at 298 K. The value indicates that C2H5NH2 and HNO3 molecules of ca. 10(-5) mol dm(-3) are involved in neat EAN. On the other hand, in an EAN-water mixture, a water molecule behaves as a base. The apparent pK(s) value was determined in EAN-water mixtures of various solvent compositions. Interestingly, the pK(s) value is remained at 10.5 in mixtures over the range of an EAN mole fraction of 0.05 - 0.9. The value is close to the pKa of C2H5NH2, or the acid-dissociation constant of C2H5NH3+, in aqueous solution. This implies that the reaction C2H5NH3+ + H2O -&gt; C2H5NH2 + H3O+ is responsible for the pK(s) over a wide range of solvent composition. The pK(s) value in neat EAN is thus slightly smaller than that in the mixtures, implying that H3O+ is a stronger acid than HNO3 in an EAN solution, unlike water.

DOI： 10.2116/analsci.24.1347

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Large angle X-ray scattering of the N-butyl-N-methylpyrrolidinium bis-(trifluoromethanesulfony) amide (P-14*TFSA(-)) ionic liquid was measured at 298 K. The total interference function i(LAXS)(s) and the total pair correlation function G(LAXS)(r) were successfully obtained. The i(LAXS)(s) was analyzed in terms of the intramolecular geometries of the conformational isomers of the P-14* and TFSA(-) ions based on the crystal structures, s the inter-molecular correlation function G(inter)(LAXS)(r) and the inter-molecular radial distribution function as the form D-inter(LAXS)(r)-4 pi r(2)rho(0) were evaluated. With G(inter)(LAXS)(r)-4 pi r(2)rho(0). the inter-molecular correlation peaks at 3.5. 4.5 and 5-6 angstrom evidently appeared as the short range interaction, while considerable long range interactions were found as the broad peaks at 10 and 15 angstrom. Molecular dynamics simulations of the ionic liquid based on the effective pairwise potentials were carried out. The X-ray total interference function derived from the MD simulations i(MD)(S) was in agreement with the experimental one. According to the inter-molecular partial atom-atom correlation functions from MD simulations, the observed peaks at 3.5, 4.5 and 5-6 angstrom can be predominantly ascribed to the closest atom-atom correlations between the P-14* and TFSA(-) ions such as C...O and C...F In the inter-molecular partial atom-atom correlation function between terminal methyl carbons of the butyl chain in the P-14* ion. a peak at 4.0 angstrom was found as the inter-molecular correlation, suggesting that the ionic liquid shows an alkyl chain aggregation, which is similar to that observed for 1-alkyl-3-methylmidazolium ionic liquids. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.molliq.2008.02.012

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The liquid structure of 1-ethyl-3-methylimidazolium bis-(trifluoromethanesulfonyl) imide (EMI+TFSI-) has been studied by means of large-angle X-ray scattering (LAXS), H-1, C-13, and F-19 NMR, and molecular dynamics (MD) simulations. LAXS measurements show that the ionic liquid is highly structured with intermolecular interactions at around 6, 9, and 15 angstrom. The intermolecular interactions at around 6, 9, and 15 angstrom are ascribed, on the basis of the MD simulation, to the nearest neighbor EMI+...TFSI- interaction, the EMI+...EMI+ and TFSI-...TFSI- interactions, and the second neighbor EMI+...TFSI- interaction, respectively. The ionic liquid involves two conformers, C-1 (cis) and C-2 (trans), for TFSI-, and two conformers, planar cis and nonplanar staggered, for EMI+, and thus the system involves four types of the EMI+...TFSI- interactions in the liquid state by taking into account the conformers. However, the EMI+...TFSI- interaction is not largely different for all combinations of the conformers. The same applies also to the EMI+...EMI+ and TFSI-...TFSI- interactions. It is suggested from the C-13 NMR that the imidazolium C-2 proton of EMI+ strongly interacts with the O atom of the -SO2(CF3) group of TFSI-. The interaction is not ascribed to hydrogen-bonding, according to the MD simulation. It is shown that the liquid structure is significantly different from the layered crystal structure that involves only the nonplanar staggered EMI+ and C-1 TFSI- conformers.

DOI： 10.1021/jp7105499

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

Anion conformation of a low-viscosity room-temperature ionic liquid 1-ethyl-3-methylimidazolium his(fluorosulfonyl) imide (EMI+FSI-) has been studied by Raman spectra and theoretical DFT calculations. Three strong Raman bands were found at 293, 328, and 360 cm(-1), which are ascribed to the FSI- ion. These Raman bands show significant temperature dependence, implying that two FSI- conformers coexist in equilibrium. This is supported by theoretical calculations that the FSI- ion is present as either C-2 (trans) or C-1 (cis) conformer; the former gives the global minimum, and the latter has a higher SCF energy of about 4 W mol(-1). Full geometry optimizations followed by normal frequency analyses show that the observed bands at 293, 328, and 360 cm(-1) are ascribed to the Q, conformer. The corresponding vibrations at 305, 320, and 353 cm(-1) were extracted according to deconvolution of the observed Raman bands in the range 280-400 cm(-1) and are ascribed to the C-2 conformer. The enthalpy Delta H degrees of conformational change from C-2 to C-1 was experimentally evaluated to be ca. 4.5 W mol(-1), which is in good agreement with the predicted value by theoretical calculations. The bis(ti-ifluoromethanesulfonyl) imide anion (TFSI-) shows a conformational equilibrium between C-1 and C-2 analogues (Delta H degrees = 3.5 kJ mol(-1)). However, the profile of the potential energy surface of the conformational change for FSI- (the F-S-N-S dihedral angle) is significantly different from that for TFSI- (the C-S-N-S dihedral angle).

DOI： 10.1021/jp074325e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Molecular vibrations of N,N-dimethylacrylamide (DMAA) and N,N-dimethylpropionamide (DMPA) in the liquid state were studied by means of Raman and IR spectra over the wide frequency range. It has been established in our previous work that DMPA involves two rotational isomers within its propionyl CH3-CH2-C(=O)- group. In the present work, it is revealed that, like DMPA, DMAA also involves two rotational isomers, the planar cis and nonplanar staggered ones, within its acryl CH2=CH-C(=O)- group. The terminal methylene carbon of the acryl group locates cis to the 0 atom within the amide O=C-N plane (the planar cis conformer) or above the amide plane (the nonplanar staggered conformer). This is well supported by theoretical MO calculations. Torsion potential energy surfaces (PES) for the C-C-C-O dihedral angle 0 of the acryl group show that a global minimum appears at ca. theta=0 degrees (the planar cis conformer) and a local minimum at ca. theta=130 degrees (the nonplanar staggered conformer). The geometry optimization followed by normal frequency analyses showed that theoretical Raman and IR bands for the conformers satisfactorily reproduce the observed ones. The enthalpy for the conformational change from the planar cis conformer to the nonplanar staggered one was experimentally evaluated by analyzing the integrated intensity changes of the bands in the range 700-800 cm(-1). The value thus obtained for the acryl group of DMAA is ca. 9 kJ mol(-1), which is significantly higher than the corresponding value for the propionyl group of DMPA (5 kJ mol(-1)). (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.molliq.2007.02.007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

The solvation structure of the lithium ion in room-temperature ionic liquids 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) imide (EMI+TFSI-) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (BMP+TFSI-) has been studied by Raman spectroscopy and DFT calculations. Raman spectra of EMI+TFSI- and BMP+TFSI- containing Li+TFSI- over the range 0.144-0.589 and 0.076-0.633 mol dm(-3), respectively, were measured at 298 K. A strong 744 cm(-1) band of the free TFSI- ion in the bulk weakens with increasing concentration of the lithium ion, and it revealed by analyzing the intensity decrease that the two TFSI- ions bind to the metal ion. The lithium ion may be four-coordinated through the 0 atoms of two bidentate TFSI- ions. It has been established in our previous work that the TFSI- ion involves two conformers of C-1 (cis) and C-2 (trans) symmetries in equilibrium, and the dipole moment of the C-1 conformer is significantly larger than that of the C-2 conformer. On the basis of these facts, the geometries and SCF energies of possible solvate ion clusters [Li(C-1-TFSI-)(2)](-), [Li(C-1-TFSI-)(C-2-TFSI-)](-))]-, and [Li(C-2-TFS)(-))(2)](-) were examined using the theoretical DFT calculations. It is concluded that the C-1 conformer is more preferred to the C, conformer in the vicinity of the lithium ion.

DOI： 10.1021/jp076869m

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC JAPAN  

5-Azonia-spiro[4.4]nonane tetrafluoroborate [(CH2)(4)N(CH2)(4)](+) BF4- is dissolved in dimethyl carbonate (DMC) to yield two liquid phases, DMC and salt-rich DMC solutions. The molecular structure of the [(CH2)(4)N(CH2)(4)](+) ion in the crystalline state and in the salt-rich DMC solution was studied by means of Raman spectroscopy at 298 K and theoretical DFT calculations. The [(CH2)(4)N(CH2)(4)](+) ion involves two pyrrolidinium (CH2)(4)N rings bridged through the N atom, and each pyrrolidinium ring involves various types of conformation. Theoretical DFT calculations for the [(CH2)(4)N(CH2)(4)](+) ion show that the distorted envelope-envelope conformers of the type E1-E1 and E1-E3 give relatively small energies. Observed Raman spectra of [(CH2)(4)N(CH2)(4)](+) BF4- crystals and the salt-rich DMC solution were satisfactorily explained in terms of the favorable presence of the sole envelope-envelope conformer of the type E1-E1.

DOI： 10.5796/electrochemistry.75.628

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Ethylammonium nitrate (EAN) is a protic room-temperature ionic liquid and classified into an amphoteric solvent. The equilibrium constant K-S = [EtNH2][HNO3] has directly been obtained for the first time by using an ion-selective field effect transistor (ISFET) electrode. The obtained K-S value is of 10(-10.0) mol(2) dm(-6), indicating that the neutral EAN involves HNO3 and EtNH2 molecules as much as 1.0 x 10(-5) mol dm(-3), or the pH (= - log[HNO3]) is 5 at 298 K.

DOI： 10.1246/cl.2007.684

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

The solvation structure of magnesium, zinc(II), and alkaline earth metal ions in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA), and their mixtures has been studied by means of Raman spectroscopy and DFT calculations. The solvation number is revealed to be 6, 7, 8, and 8 for Mg2+, Ca2+, Sr2+, and Ba2+, respectively, in both DMF and DMA. The delta (O-C-N) vibration of DMF shifts to a higher wavenumber upon binding to the metal ions and the shift Delta nu (= nu(bound) - nu(free)) becomes larger, when the ionic radius of the metal ion becomes smaller. The nu (N-CH3) vibration of DMA also shifts to a higher wavenumber upon binding to the metal ions. However, the shift Delta nu saturates for small ions, as well as the transition-metal (II) ions, implying that steric congestion among solvent molecules takes place in the coordination sphere. It is also indicated that, despite the magnesium ion having practically the same ionic radius as the zinc(II) ion of six-coordination, their solvation numbers in DMA are significantly different. DFT calculations for these metalsolvate clusters of varying solvation numbers revealed that not only solvent-solvent interaction through space but also the bonding nature of the metal ion plays an essential role in the steric congestion. The individual solvation number and the Raman shift Delta nu in DMF-DMA mixtures indicate that steric congestion is significant for the magnesium ion, but not appreciable for calcium, strontium, and barium ions, despite the solvation number of these metal ions being large. Copyright (c) 2006 John Wiley & Sons, Ltd.

DOI： 10.1002/jrs.1662

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.11436/mssj1998.9.39_18

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Conformational structure of the N-butyl-N-methyl-pyrrolidinium (P-14(+)) ion within its bis(trifluoromethanesulfonyl) imide (TFSI-) and bromide salts has been studied by means of DFT calculations and Raman spectroscopy. The P-14(+) ion gives various types of conformations with respect to the pyrrolidinium ring and N-butyl group. DFT calculations indicate that, among others, the eq- and ax-envelope conformers with the N-butyl group at equatorial and axial positions, respectively, against planar C-4 atoms of the envelope pyrrolidinium ring (-NCH2CH2CH2CH2-) are relatively stable, and the former gives the global minimum. It revealed by comparing observed and calculated Raman spectra that the P-14(+) ion is present mainly as the ax-envelope conformer in the P14+Br- crystal, whilst the eq- and ax-envelope conformers are present in equilibrium in the P14+TFSI- ionic liquid. The presence of conformational equilibrium is further supported by Raman spectra measured by varying temperature. It is also established that conformation of the N-butyl group is restricted to the trans-TT, in which the butyl group locates trans against its nearest carbon atom in the pyrrolidinium ring, and all carbon atoms in the butyl chain are located trans each other. (C) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.molliq.2006.08.054

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

Metal-ion clusters involving alkaline earth metal and perchlorate ions, and N,N-dimethylformamide (DMF) have been studied by electrospray ionization mass spectrometry (ESI-MS). Three types of metal-ion clusters, [M(DMF)(n)](2+), [M(ClO4)-(DMF)(n)](+), and [M-2(CIO4)(3)(DMF)(n)](+) (M = Mg, Ca, and Sr) are found. It is proposed on the basis of DFT calculations that the metal ion in the [M-2(CIO4)(3)(DMF)(6)](+) clusters is six-coordinated with three mu-CIO4- ions and three DMF molecules.

DOI： 10.1246/cl.2006.1118

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：INT UNION PURE APPLIED CHEMISTRY  

Metal ions are solvated in solution, and, in a sterically congested organic solvent, those solvent molecules that are simultaneously bound to the metal ion will be subject to consequential steric interactions through space. The molecular structure of a solvent, particularly that of any functional groups in the vicinity of the coordinating atom to the metal ion, plays a key role in the solvation steric effect. Weak solvation steric effects lead to a distorted octahedral structure for six-coordinate transition-metal(II) ions, whereas strong steric effects lead to a decreased solvation number. In particular cases, the conformation of a solvent may undergo a change in response to coordination to the metal ion. Solvation steric effects play a decisive role in reaction thermodynamics and kinetics of the metal ion. Here, we show our recent results on solvation steric effects in terms of structure and thermodynamics, particularly, the conformational change of solvent and its effect on the metal-ion complexation.

DOI： 10.1351/pac200678081595

Web of Science

Scopus

Language：Japanese  

The structure of bis(trifluoromethanesulfonyl) imide (TFSI) in the liquid state has been studied by means of Raman spectroscopy and DFT calculations. Raman spectra of 1-ethyl-3-methylimidazolium (EMI + ) TFSI - show relatively strong bands arising from TFSI - at about 398 and 407 cm - . Interestingly, the 407 cm -1 band, relative to the 398 cm -1 one, is appreciably intensified with raising temperature, suggesting that an equilibrium is established between TFSI - conformers in the liquid state. According to DFT calculations followed by normal frequency analyses, two conformers of C 2 and C 1 symmetry, respectively, constitute global and local minima, with an energy difference 2.2-3.3 kJ mol -1 . The wagging ω-SO 2 vibration appears at 396 and 430 cm -1 for the C 1 conformer and at 387 and 402 cm -1 for the C 2 one. Observed Raman spectra over the range 380-440 cm -1 were deconvoluted to extract intrinsic bands of TFSI - conformers, and the enthalpy of conformational change from C 2 to C 1 was evaluated. The enthalpy value is in good agreement with that obtained by theoretical calculations. We thus conclude that a conformational equilibrium is established between the C 1 and C 2 conformers of TFSI - in the liquid EMI + TFSI - , and the C 2 conformer is more favorable than the C 1 one. © 2006 American Chemical Society.

DOI： 10.1021/jp0612477

Scopus

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

Language：Japanese  

Raman spectra of liquid 1-ethyl-3-methylimidazolium (EMI + ) salts, EMI + BF 4 - , EMI + PF 6 , EMI + CF 3 SO 3 - , and EMI + N(CF 3 SO 2 ) 2 - , were measured over the frequency range 200-1600 cm -1 . In the range 200-500 cm -1 , we found five bands originating from the EMI + ion at 241, 297, 387, 430, and 448 cm -1 . However, the 448 cm -1 band could hardly be reproduced by theoretical calculations in terms of a given EMI + conformer, implying that the band originates from another conformer. This is expected because the EMI + involves an ethyl group bound to the N atom of the imidazolium ring, and the ethyl group can rotate along the C-N bond to yield conformers. The torsion energy for the rotation was then theoretically calculated. Two local minima with an energy difference of ca. 2 kJ mol -1 were found, suggesting that two conformers are present in equilibrium. Full geometry optimizations followed by normal frequency analyses indicate that the two conformers are those with planar and nonplanar ethyl groups against the imidazolium ring plane, and the nonplanar conformer is favorable. It elucidates that bands at 241, 297, 387, and 430 cm-1 mainly originate from the nonplanar conformer, whereas the 448 cm-1 band does originate from the planar conformer. Indeed, the enthalpy for conformational change from nonplanar to planar EMI + experimentally obtained by analyzing band intensities of the conformers at varying temperatures is practically the same as that evaluated by theoretical calculations. We thus conclude that the EMI + ion exists as either a nonplanar or planar conformer in equilibrium in its liquid salts. © 2005 American Chemical Society.

DOI： 10.1021/jp053476j

Scopus

Language：Japanese  

Chloride complexation of cobalt(II), nickel(II) and zinc(II) ions has been studied by calorimetry and spectrophotometry in N-methylformamide (NMF) containing 1.0 mol-dm -3 (n-C 4 H 9 ) 4 NClO 4 as an ionic medium at 298 K. A series of mononuclear complexes, MCl n (2 -n)+ (M=Co, Ni and Zn) with n = 1, 3 and 4 for cobalt(II), n = 1 for nickel(II), and n = 1-4 for zinc(II), are formed and their formation constants, enthalpies and entropies were obtained. It revealed that complexation is suppressed significantly in NMF relative to that in N,N-dimethylformamide (DMF) in all metal systems examined. The suppressed complexation in NMF is mainly ascribed to the smaller formation entropies in NMF reflecting that the solvent-solvent interaction or solvent structure in the bulk NMF is much stronger than that in the bulk DMF. Formation entropies, ΔS 1 o , of the monochloro complex in DMF, dimethyl sulfoxide and NMF are well correlated with the Marcus&#039; solvent parameter, ΔΔ v S o /R, according to ΔS 1 o /R = aΔΔ v S o /R+b. The a value is negative and similar in all metal systems examined, whereas the b value depends on the metal system. When a gaseous ion is introduced into a solvent, the ionic process of solvation is divided into two stages: the ion destroys the bulk solvent structure to isolate solvent molecules at the first stage and the ion then coordinates a part of isolated solvent molecules around it at the second stage. We propose that the a and b values may reflect the changes in the freedom of motion of solvent molecules at the first and second stages, respectively, of the ionic process of solvation. © 2005 Springer Science+Business Media, Inc.

DOI： 10.1007/s10953-005-5114-9

Scopus

Language：Japanese   Publisher：Journal of Solution Chemistry  

The distribution of 1,10-phenanthroline (phen) in micellar solutions of the nonionic surfactants Triton X and C 12E n with varying poly (ethylene oxide) chain lengths has been studied by potentiometry, calorimetry, and fluorometry at 298 K. Micelles accommodate 1,10-phenanthroline according to the reaction, phen + Y m = Y m(phen), where Y m denotes a surfactant molecule aggregated in micelles. The constant K m for the reaction of Triton X increases as a linear function of n*, the number of ethylene oxide (EO) groups, as K m = K EOn* + K c. Nonzero K EO and K c values suggest a heterogeneous inner structure of the micelle, i.e., the hydrophobic core surrounded by a hydrophilic poly (ethylene oxide) (PEO) shell. On the basis of molar volumes, the intrinsic thermodynamic parameters of transfer of 1,10-phenantholine were extracted. The enthalpy and entropy of transfer of 1,10-phenanthroline from the PEO shell to the core are found to be small and negative. By using K EO and K c values for C 12E n obtained by fluorometry, individual fluorescence spectra of 1,10-phenanthroline in the PEO shell and core were extracted. The fluorescence intensity of 1,10-phenathroline accommodated in the core, like in organic solvents, is significantly reduced relative to that in water. These facts indicate that the aromatic rings of 1,10-phenanthroline penetrate into the hydrophobic core, while its hydrophilic N site is still hydrated in the PEO shell.

DOI： 10.1023/B:JOSL.0000043634.09653.cb

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：KLUWER ACADEMIC/PLENUM PUBL  

The distribution of 1,10-phenanthroline (phen) in micellar solutions of the nonionic surfactants Triton X and C12En with varying poly (ethylene oxide) chain lengths has been studied by potentiometry, calorimetry, and fluorometry at 298 K. Micelles accommodate 1,10-phenanthroline according to the reaction, phen + Y-m = Y-m(phen), where Ym denotes a surfactant molecule aggregated in micelles. The constant Km for the reaction of Triton X increases as a linear function of n*, the number of ethylene oxide (EO) groups, as K-m = K(EO)n* + K-c. Nonzero K-EO and K-c values suggest a heterogeneous inner structure of the micelle, i.e., the hydrophobic core surrounded by a hydrophilic poly (ethylene oxide) (PEO) shell. On the basis of molar volumes, the intrinsic thermodynamic parameters of transfer of 1,10-phenantholine were extracted. The enthalpy and entropy of transfer of 1,10-phenanthroline from the PEO shell to the core are found to be small and negative. By using KEO and Kc values for C12En obtained by fluorometry, individual fluorescence spectra of 1,10-phenanthroline in the PEO shell and core were extracted. The fluorescence intensity of 1,10-phenathroline accommodated in the core, like in organic solvents, is significantly reduced relative to that in water. These facts indicate that the aromatic rings of 1,10-phenanthroline penetrate into the hydrophobic core, while its hydrophilic N site is still hydrated in the PEO shell.

Web of Science

Language：Japanese   Publisher：Analytical Sciences  

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N′,N′-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(II) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.

DOI： 10.2116/analsci.20.415

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)  

Hysteretic behavior was found on the heat of protonation of diethylenetriamine (dien) in aqueous solution at 298 K. We propose the presence of two conformers for Hdien+, which have significantly different proton affinities. Mutual transformation between the conformers may be practically forbidden, but is strongly accelerated upon their protonation to form H2dien2+.

DOI： 10.1246/cl.2004.186

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Academic Press Inc.  

Formation of cobalt(II)-thiocyanato complexes in nonionic surfactant solutions of poly(ethylene oxide) type with varying poly(ethylene oxide) chain lengths of 7.5 (Triton X-114), 30 (Triton X-305), and 40 (Triton X-405) has been studied by titration spectrophotometry and calorimetry at 298 K. Data were analyzed by assuming formation of a series of ternary complexes Co(NCS)nYm (2-n)+ (Y = surfactant) with an overall formation constant βnm. In all the surfactant systems examined, data obtained can be explained well in terms of formation of Co(NCS)+ and Co(NCS)2 in an aqueous phase (aq), and Co(NCS)4Y2- in micelles, and their formation constants, enthalpies, and entropies have been determined. The β41/β20 ratio increases and the corresponding enthalpy becomes significantly less negative with an increasing number of ethylene oxide groups. This suggests that micelles of these nonionic surfactants have a heterogeneous inner structure consisting of ethylene oxide and octylphenyl moieties. Indeed, on the basis of molar volumes of ethylene oxide and octylphenyl groups, intrinsic thermodynamic parameters have been extracted for the reaction Co(NCS)2(aq) + 2NCS-(aq) = Co(NCS)4Y2- (ΔrG°, ΔrH°, and ΔrS°) at each moiety. The ΔrG°, ΔrH°, and ΔrS° values are -16 kJ mol-1, -15 kJ mol-1, and 3 J K-1 mol-1, respectively, for the ethylene oxide moiety, and -15 kJ mol-1, -70 kJ mol-1, and -183 J K-1 mol-1 for octylphenyl. Significantly less negative ΔrH° and ΔrS° values for ethylene oxide imply that the hydrogen-bonded network structure of water is extensively formed at the ethylene oxide moiety, and the structure is thus broken around the Co(NCS)4 2- complex with weak hydrogen-bonding ability. © 2001 Academic Press.

DOI： 10.1006/jcis.2001.7457

Scopus

Language：Japanese   Publisher：Physical Chemistry Chemical Physics  

The distribution thermodynamics of 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmphen) in micelles of the non-ionic surfactant Triton X-100 were studied by potentiometry and titration calorimetry at 298 K. Both of these ligands form HL+ and HL2+ (L = phen and dmphen) in acidic solution. Their formation constants were determined in aqueous solutions containing various concentrations of Triton X-100, and were found to decrease with increasing concentration of the surfactant. The decrease is explained in terms of accommodation of neutral phenanthrolines in micelles by taking into account the surfactant solution as a heterogeneous solvent mixture. The case in which the surfactant is treated as the third reactant was also examined, and thermodynamic parameters for the interaction between the surfactant and phenanthrolines, i.e. the Gibb's energies, enthalpies and entropies of transfer of phenanthrolines from aqueous solution to a micellar pseudo-phase, were obtained. The Gibb's energies of transfer of the neutral ligand L are -8.2 and -11.7 kJ mol-1 for L = phen and dmphen, respectively. The corresponding enthalpies of transfer are both small and negative, implying that these neutral 1,10-phenanthrolines are still strongly hydrated in micelles, as well as in water, through the hydrophilic nitrogen sites.

DOI： 10.1039/b009132o

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

The distribution thermodynamics of 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (dmphen) in micelles of the non-ionic surfactant Triton X-100 were studied by potentiometry and titration calorimetry at 298 K. Both of these ligands form HL+ and HL2+ (L = phen and dmphen) in acidic solution. Their formation constants were determined in aqueous solutions containing various concentrations of Triton X-100, and were found to decrease with increasing concentration of the surfactant. The decrease is explained in terms of accommodation of neutral phenanthrolines in micelles by taking into account the surfactant solution as a heterogeneous solvent mixture. The case in which the surfactant is treated as the third reactant was also examined, and thermodynamic parameters for the interaction between the surfactant and phenanthrolines, i.e. the Gibb's energies, enthalpies and entropies of transfer of phenanthrolines from aqueous solution to a micellar pseudo-phase, were obtained. The Gibb's energies of transfer of the neutral ligand L are -8.2 and -11.7 kJ mol(-1) for L = phen and dmphen, respectively. The corresponding enthalpies of transfer are both small and negative, implying that these neutral 1,10-phenanthrolines are still strongly hydrated in micelles, as well as in water, through the hydrophilic nitrogen sites.

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Adduct formation of the inert complexes Ru(phen)(3)(2+), Co(phen)(3)(3+) and Si(phen)(3)(4+) with 1,10-phenanthroline (phen) has been studied by potentiometry and calorimetry in aqueous solution containing 0.1 mol dm(-3) NaCl as an ionic medium at 298 K. Formation of a 1:1 adduct, in which planar 1,10-phenanthroline molecules are stacked, has been found for all the inert complexes and their formation constants, enthalpies and entropies were obtained. Adduct formation constants are hardly influenced by the ionic charges of the metal center. The enthalpy values are all negative, indicating that a specific pi-pi interaction operates between stacked 1,10-phenanthroline molecules. The corresponding entropy values are positive for Ru(phen)(3)(2+) and Co(phen)(3)(3+), while it is negative for Si(phen)(3)(4+). The positive entropies indicate that reduction of hydrophobic hydration upon stacking also plays a key role in the adduct formation. Both enthalpy and entropy values significantly decrease with increasing charge, and they strongly compensate to give similar formation constants. This implies that hydrophobic hydration around aromatic rings within the inert complexes is reduced to a greater extent with increasing charge, Ru(phen)(3)(2+)&lt;Co(phen)(3)(3+)&lt;Si(phen)(3)(4+). 1,10-Phenanthroline forms protonated H(phen)(+) and H(phen)(2)(+) species in an acidic solution, and 1,10-phenanthroline molecules are stacked in the latter. The enthalpy and entropy of formation of H(phen)(2)(+) are significantly negative, also indicating that pi-pi interaction play an essential role in the formation of H(phen)(2)(+). On the other hand, both the enthalpy and entropy of solution of 1,10-phenanthroline remain unchanged in solution containing NaCl over the range 0.05-1 mol dm(-3), suggesting that hydrophobic hydration shells are restricted at the vicinity of 1,10-phenanthroline.

DOI： 10.1039/b003854g

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Academic Press Inc.  

Formation of copper(II) thiocyanato and cadminum(II) iodo complexes in micelles of poly(ethylene oxide) (PEO)-type nonionic surfactants with varying PEO chain lengths of 9.5 (Triton X-100), 30 (Triton X-305), and 40 (Triton X- 405) has been studied by titration spectrophotometry and calorimetry at 298 K. In a given surfactant solution, all data obtained were analyzed by assuming formation of ternary complexes MX(n)Y(m)/(2-n)+ (M = Cu(II), Cd(II)
X = SCN-, I-
Y = surfactant), and the complexes thus form in aqueous phase (m = 0) or in micelles (m = 1). In the Cu(II)-SCN- system, spectrophotometric data obtained by varying concentrations of the surfactant can be explained well in terms of formation of Cu(NCS)2Y in micelles and Cu(NCS)+ and Cu(NCS)2 in an aqueous phase, and it turned out that formation constant of Cu(NCS)2Y increases with increasing PEO chain length. In the Cd(II)-I- system, the formation of CdI3Y- and CdI4Y2- is concluded in micelles, and that of CdI+, CdI- 3, and CdI2- 4 in an aqueous phase. Interestingly, formation enthalpies of CdI3Y- and CdI4Y2- become significantly less negative with increasing PEO chain length. This suggests that transfer of the complexes from aqueous solution to a hydrophobic octylphenyl (OP) moiety in micelles is significantly more exothermic than that to a hydrophilic PEO one. Thermodynamic parameters of transfer of CdI- 3 and CdI2- 4 from aqueous solution to the OP and PEO moieties of micelles have been evaluated. (C) 2000 Academic Press.

DOI： 10.1006/jcis.2000.6722

Scopus

Language：Japanese Book type：Scholarly book

Language：Japanese Book type：Scholarly book

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

環境中に放出された水銀は、環境中で特に有毒なメチル水銀に変化し食物連鎖を通じ生体に蓄積することが知られている。しかしながら、環境中に放出された水銀がどこでどのようにメチル水銀化するのかは詳細には明らかになっていない。本研究では、自然水銀が産出することで知られた旧イトムカ水銀鉱山周辺で，水銀の環境挙動とメチル水銀の生成について調査した結果について報告する．

Language：Japanese   Publisher：GEOCHEMICAL SOCIETY OF JAPAN  

海底熱水噴出孔は海水中水銀の主要な起源の一つと考えられ、その周辺環境への影響に関心がもたれている。そこで、活発な熱水活動が行われている伊平屋北海丘と明神礁カルデラで採取された底質及び生体中の総水銀、有機水銀の濃度を測定し、熱水噴出孔から周辺への水銀の拡散や化学形の変化、また周辺に生息する生体への影響について考察した。

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

J-GLOBAL

J-GLOBAL

J-GLOBAL

J-GLOBAL

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

J-GLOBAL

J-GLOBAL

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：English   Publishing type：Book review, literature introduction, etc.   Publisher：JAPAN SOC ANALYTICAL CHEMISTRY  

Titration Raman spectroscopy has been developed for studying the solvation structure of metal ions in solution. The method affords us the solvation number, and the value thus obtained in neat solvents is in good agreement with that determined by EXAFS. The method is then applied to solvent mixtures, and the individual solvation number for each solvent is extracted. In a solvent mixture of N,N-dimethylformamide (DMF) and N,N,N',N'-tetramethylurea (TMU), the metal ion prefers DMF to TMU, which is ascribed to the solvation steric effect. The same applies also for the solvent mixture of N,N-dimethylpropionamide (DMPA) and DMF. However, unlike TMU, DMPA changes its conformation from the planar cis to non-planar staggered upon solvation to the metal ion. The enthalpy for the conformational change of DMPA is positive in the bulk, while it is significantly negative in the coordination sphere of the manganese(II) ion. Here, we briefly describe the procedure of measurements and analyses for the titration Raman spectroscopy, and review the solvation structure of the alkaline earth, first transition metal(H) and lanthanide(III) ions in some solvent mixtures in view of solvation steric effect.

Web of Science

Event date： 2023.11

Event date： 2023.9

Presentation type：Oral presentation (general)  

Event date： 2022.9

Presentation type：Poster presentation  

Event date： 2017.11

Language：English   Presentation type：Oral presentation (keynote)  

Venue：Fukuoka, Japan  

Event date： 2016.7 - 2016.8

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Hawaii, USA  

Event date： 2015.8 - 2015.9

Language：English   Presentation type：Poster presentation  

Venue：Prague, Czech Republic  

Event date： 2013.10

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Yokohama, Japan  

Event date： 2013.7

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Venue：Kyoto, Japan  

Event date： 2013.3

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Venue：仙台  

Event date： 2012.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：東京  

国内学会

Event date： 2012.11

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：佐賀  

国内学会

Event date： 2012.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Osaka, Japan  

国際学会

Event date： 2012.6

Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

Venue：北海道（旭川）  

Event date： 2011.10

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：群馬  

Event date： 2011.8

Language：English  

Venue：Montpelier, France  

国際学会

Event date： 2010.12

Language：English  

Venue：アメリカ合衆国（ハワイ）  

国際学会

Event date： 2010.8

Language：English  

Venue：Tsukuba, Japan  

国際学会

Event date： 2010.8

Language：English  

Venue：Tsukuba, Japan  

国際学会

Event date： 2010.5

Language：Japanese  

Venue：福岡  

研究会

Event date： 2010.3

Language：English  

Venue：Bamberg, Germany  

国際学会

Event date： 2010.3

Language：English  

Venue：Bamberg, Germany  

国際学会

Event date： 2009.8

Language：English  

Venue：Innsbruck, Austria  

国際学会

Event date： 2009.6

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Venue：Cairns, Australia  

国際学会

Event date： 2009.6

Language：English  

Venue：Cairns, Australia  

国際学会

Event date： 2009.3

Language：English  

Venue：Fukuoka, Japan  

国際学会

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (keynote)  

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (general)  

Country：Japan